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High Performance Power Converter Systems for Nonlinear and Unbalanced Load/Source
Abstract
Author's abstract: This dissertation covers three levels of issues and solutions dealing with unbalanced and/or nonlinear situations in power electronic systems, namely power converter level, power converter system level, and large-scale power electronics system level. At power converter level, after review of traditional PWM methods, especially two-dimensional space vector modulation schemes, three-dimensional space vector modulation schemes are proposed for four-legged voltage source converters, including inverters and rectifiers. The four-legged power converters with three-dimensional space vector modulation schemes have a better DC link voltage utilization and result in a low distortion. It is an effective solution to provide the neutral point for a three-phase four-wire system and to handle the neutral current due to unbalanced load or source and nonlinear loads. Comprehensive design guidelines for a four-legged inverter are presented. The four-legged rectifier is also presented which allows not only fault tolerant operation, but also provides the flexibility of equal resistance, equal current, or equal power operation under unbalanced source. Average large-signal models of four-legged power converters in both the a-b-c and d-q-o coordinates are derived. Small signal models are obtained in the d-q-o rotating coordinates. Voltage control loops are designed in the d-q-o coordinates for a high power utility power supply. Performance is studied under various load conditions. At the power converter system level, the load conditioner concept is proposed for high power applications. A power converter system structure is proposed which consists of a high-power low-switching frequency main inverter and a low-power high-switching frequency load conditioner. The load conditioner performs multiple functions, such as active filtering, active damping, and active decoupling with a high current control bandwidth. This hybrid approach allows the overall system to achieve high performance with high power and highly nonlinear loads. At the large-scale power electronics system level, the nonlinear loading effect of load converters is analyzed for a DC distribution system. Two solutions to the nonlinear loading effect are presented. One is to confine the nonlinear load effect with the sub-converter system, the other is to use a DC bus conditioner. The DC bus conditioner is the extension of the load conditioner concept. System requirements: PC, World Wide Web browser and PDF reader. Available electronically via Internet. Title from electronic submission form. Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1998. Vita. Abstract. Includes bibliographical references.
... No obstante, la medición de la corriente de los capacitores no permite implementar un esquema de protección por sobrecorriente, requiriéndose de sensores adicionales [10]. En [11] se propone utilizar un acondicionador de carga, que consiste en un segundo inversor conectado en paralelo, el cual permite reducir el acoplamiento de los canales, justificándose su uso cuando se requieren alimentar cargas no lineales de alta potencia [12]. ...
... Asumiendo que la frecuencia de conmutación es significativamente superior a la frecuencia fundamental, puede demostrarse que el circuito equivalente del convertidor puede representarse como se indica en la Fig. 2 [11], dónde ̅ , ̅ ̅ son las tensiones de fase promediadas en un período de conmutación, mientras que ̅ representa la corriente de la barra de CC. Estas variables pueden expresarse como, ...
... Estas soluciones pueden representarse por un vector que rota a velocidad en el referencial estacionario . Para una carga lineal balanceada, este vector será visto inmóvil desde un referencial sincrónico dq0 que rota también a velocidad , este referencial 0 permitirá entonces obtener un punto continuo de operación [11]. Para transformar el modelo al referencial dq0 se aplicará las transformaciones de Clarke y de Park, la combinación de ambas puede expresarse por medio de la siguiente matriz de transformación ...
... In the available literature, voltage control of three-phase inverters is mainly performed in a-b-c or d-q-o coordinate systems [4]. References [5,6] have utilized d-q-o rotating coordinate system, also called as synchronous reference frame control for achieving output voltage control. Independent per-phase control, also known as natural reference frame control, is introduced in Refs. ...
... Independent per-phase control, also known as natural reference frame control, is introduced in Refs. [6,7]. The authors in Ref. [6] have stated that incase of unbalance and nonlinearity in the system, the best strategy is to use the actual AC voltage and current for controller design. ...
... [6,7]. The authors in Ref. [6] have stated that incase of unbalance and nonlinearity in the system, the best strategy is to use the actual AC voltage and current for controller design. But the limitation of stationary reference frame comes from the fact that PI controller cannot remove the steady-state error since the steady-state variables in a-b-c coordinate are sinusoidal and the absence of the DC operating point makes it difficult for the controller to track the reference signal due to the time varying characteristics of the reference signal [6]. ...
Solar photovoltaics (PV) is one of the popular renewable energy sources in tropical countries like India which can help in supplementing the rising demand of electrical energy. DC input from solar PV strings needs to be converted into AC component both for ON and for OFF grid applications. Three-phase inverters are used for the above inversion when power levels are high. In OFF grid applications, task of maintaining stable terminal voltage across the loads lies with the inverter in the absence of utility grid. It also has to supply variety of balanced and unbalanced loads. In this paper, cascaded voltage control scheme, for a three-phase four-leg inverter, is developed. Parameters of the proportional resonant controllers (PR) are tuned using bode plot techniques. Simulations results are presented for operation under different loading conditions.
... This approach needs a smaller DC-link capacitance for the same voltage ripple. However, it still suffers from insufficient use of the DC-link voltage as the first topology [10]. Considering the merits and demerits of topologies for the 3-phase VSIs, in this study the four-leg VSI is considered for their advantages to high-performance applications, where a good power quality might be required, or when sensitive electronics equipment are used as four-leg VSI loads [10]. ...
... However, it still suffers from insufficient use of the DC-link voltage as the first topology [10]. Considering the merits and demerits of topologies for the 3-phase VSIs, in this study the four-leg VSI is considered for their advantages to high-performance applications, where a good power quality might be required, or when sensitive electronics equipment are used as four-leg VSI loads [10]. ...
... The CVC control strategy is described by (11). The selection of the αβγ voltage vector is obtained by the needed αβγ current time derivatives, according to (10). Table 1 presents the voltage vector selection, based on the analysis of the current errors. ...
This paper presents the design and experimental voltage quality evaluation of controllers for the output voltages of 3-phase four-leg voltage source inverters. These inverters are needed in stand-Alone power systems to supply linear and non-linear, balanced or unbalanced loads with constant RMS value voltages at fixed frequency. Comparisons include closed loop outer voltage controllers based on predictive, sliding mode and decoupled proportional-integral controllers in dqo synchronous space, fitted with an inner hysteretic current loop vector controller in abg space. The 3-phase four-leg VSI output voltages waveform quality is analysed under unbalanced and non-linear loads.
... Assuming a balanced three phase three-wire system, following equation holds [2]: ...
... 1.1.11 does not necessarily hold [2]. ...
... In a system, during steady state, the vector representations above would both be rotating in their αβ or αβγ -coordinate systems. The controllers for such a system would have constantly oscillating reference signals even at steady state, which would lead to stationary errors in the output signals [2]. ...
... Some solutions for Power Quality issues demand that the inverter should be able to deal with a neutral connection from the load. The use of a neutral connection in a Three-Phase Voltage Source Inverter (VSI) may be performed in two ways [1], [2]: ...
... Although four-leg inverters are less common than three-leg inverters, this topology presents a robust solution for handling load imbalances and the need of the neutral current. Also, a smaller DC capacitance is required [2], and a simpler control (e.g. PI scheme) for the DC voltage may be used, comparing with a split-capacitor topology [3]; these features are useful when high power systems applications are considered [2]. ...
... Also, a smaller DC capacitance is required [2], and a simpler control (e.g. PI scheme) for the DC voltage may be used, comparing with a split-capacitor topology [3]; these features are useful when high power systems applications are considered [2]. Lately technological development and cost reduction of power electronics equipments are overcoming the issues regarding costs due to the inverter extra leg. ...
The Space Vector PWM implementation and opera-tion for a Four-leg Voltage Source Inverter (VSI) is detailed and discussed in this paper. Although less common, four-leg VSIs are a viable solution for situations where neutral connection is necessary, including Active Power Filter applications. This topology presents advantages regarding the VSI DC link and capacitance, which make it useful for high power devices. Theory, implementation and simulations are also discussed in this paper.
... Sin embargo, dimensionando esta inductancia con un valor adecuado, puede disminuirse el rizado de la corriente de neutro originado por la modulación del inversor [9]. Por otra parte, un incremento del valor de L n , reducirá la frecuencia de resonancia que se produce en el eje 0, lo cual no es deseable desde el punto de vista del control [25]. A partir de esta relación de compromiso, en este trabajo se dimensionó esta inductancia para que su frecuencia de resonancia resulte una década superior a la frecuencia f 1 . ...
... Las representaciones en espacio de estados de R Tvy (z) se obtienen a partir de (11) y (12), siendo el orden de los controladores n=2 para los ejes α y β y n=8 para el eje 0. En la Fig. 10 se muestra el diagrama de bloques resultante del lazo externo, a partir del cual se obtiene la ecuación en espacio de estados (30). Aplicando transformada z a (30), para la condición v * y (kT)=0, se obtiene la impedancia de salida, Z oTy (z) (31). 1) Diseño de los aportes de fase θ hv0 Para el diseño de los aportes fase, se resuelve (18) con h=3, 15, 21, y=0, x=v, y se evalúa la función de transferencia M 1vy (z) indicada en (25), para ambas condiciones de carga. Los aportes de fase resultantes se indican en la Tabla III. ...
This paper presents a new control strategy for three-phase four-leg inverters, to meet the requirements of total and individual harmonic content imposed by IEC 61000-2-2 when the inverter feeds a non-linear reference load defined by IEC 62040-3. The analysis and design of the controllers are based on a discrete-time model, developed in the 0 reference frame. The proposed control strategy consists of an inner current control loop and an outer loop to control the phase voltages, using Proportional-Resonant controllers. The concept of harmonic impedance, proposed initially for single-phase inverters, is used to tune the controllers. Simulation and experimental results are presented to validate the harmonic impedance obtained and the design of the proposed control strategy when the inverter feeds non-linear loads
... Now, the sequencing of the switching vectors has a great impact on power losses and harmonic content. Particularly, the use of both zero vectors within one switching period with symmetrical vector sequencing yields the lowest output distortion and harmonic spectrum [15]. Such switching sequence is also referred to as sevensegment switching or high-quality sequence, and is shown in Fig. 6 again applied to sector Iin the reminder of the paper this will be identified as SVPWM. ...
... Multiple discontinuous modulation strategies may be envisioned: -Switching losses may be minimized by not switching the phase carrying the highest current in any switching interval [15]. This is identified as DMOPT in this paper; -120° discontinuous modulation, where each phase is locked to either +DC or -DC for 120°. ...
Space Vector Modulation is a popular technique for driving power converters. Alternative switching sequences may optimize power losses, as well as affecting harmonic content. When SVM is used in UPS applications, power losses are of particular interest. In fact, most UPS applications are energy-intensive, requiring maximization of UPS efficiency. This paper reviews alternative switching strategies, evaluating their power losses and side effects, considering the peculiarities of UPS applications. The analysis is supported by experimental measurements on high power double-conversion transformer-based UPS.
... The equation of straight line after substituting is shown as (6) 0 Finally, the switching function is obtained as (7) 3. (8) Where V M represents the amplitude of control signal Substitute (8) into (7) the switching function can be obtained by (9) Where i = a,b,or c , Assume the initial phase angle Then , , and ...
... power circuit exact model in Matlab/Simulink 2.3.2 Average model The average model of the exact electrical system is the mathematical model which is based on representing each component of the electric system as mathematical equations [5][6] Fig. 9 shows the mathematical model of the exact model in previous figure Fig. 8. open loop average model in Matlab/simulinkDecoupling methodThe dq0 system has mutual coupling between the d component and q component, so the decoupling method is used to eliminate the effect of mutual coupling between them.[6][7]. ...
The mathematical model aims to establish a linear system that allows the model to deal with linear controllers using Matlab/Simulink. In order to gain more ability to control either transient or steady state response and the ability to study and change the performance of the overall system under different loads.
... If isolation is necessary for the interface inverter, then, adding a transformer with the star or zig-zag secondary connection, at the output of a conventional three phase threeleg voltage source inverter (VSI) is the simplest way to provide the neutral path [4]. On the other hand, in three phase transformerless applications, the load neutral point can be simply connected to the midpoint of the DC-link [5]. ...
... On the other hand, in three phase transformerless applications, the load neutral point can be simply connected to the midpoint of the DC-link [5]. This topology needs a very high capacitance in the DC-link to limit the DC voltage fluctuations due to the load neutral current flowing through the DC-link capacitors [4][5]. ...
Distributed generation (DG) has been considered as an alternative source of power generation, especially in stand-alone applications, where both single and three phase loads must be supplied with fixed amplitude and frequency sinusoidal voltages. Therefore, the presence of the neutral wire is inevitable. A four-leg inverter is a common solution to connect DGs to stand-alone loads as well as providing the neutral wire. In this paper, by considering a filter inductor in the fourth (neutral) leg of the four-leg inverter, a detailed model is presented, which illustrates a strong coupling among different phases. In order to remove this coupling effect, it is proposed to transform the quantities from the abc to the αβγ reference frame. Furthermore, based on the proposed decoupled model, a new deadbeat (DB) control scheme is proposed to provide balanced sinusoidal voltages at the output of the inverter. To confirm the effectiveness of the proposed modeling and control technique, experimental results on a 3kW setup with the DSP-based digital controller are provided under various loading conditions, such as linear/non-linear, balanced/unbalanced and single/three phase loads.
... The 4Leg-IMC is usually controlled and modulated using a carrierbased pulse-width modulation (PWM) or three-dimensional space vector modulation (3D-SVM) techniques [14]- [21]. Compared to the carrier-based PWM technique, the 3D-SVM offers many advantages such as good dc-link utilization and minimum output distortion [4], [22]; but, they do so at the expense of higher computational requeriments [23]. ...
... The cost function given in eq. (22) is considered in the first half of this simulation where the weighting factor is considered equal to = 15. The observed maximum value of CMV is = 368[ ] while maintaining a good behavior of the load and source currents. ...
This paper presents a new control strategy for a four-leg indirect matrix converter that effectively mitigates common-mode voltages and gives optimal control of source and load currents. This method uses the commutation state of the converter in the subsequent sampling time according to an optimization algorithm given by a simple cost function and a discrete system model. The control goals are the regulation of the output current according to an arbitrary reference and tracking of the source current reference, which is imposed in order to obtain sinusoidal waveforms with low distortion. The technique is enhanced by a reduction of the common-mode voltage using an extra term in the cost function to reduce early motor winding failure and bearing deterioration. Simulation results are presented to support the theoretical development.
... The transformerless neutral connection can be accomplished by connecting the neutral-point of the load to the mid-point of spilt DC-link capacitors of three-leg VSI or to the mid-point of the additional fourth (neutral) leg. With the practice of split DC-link capacitors, the three-leg VSI acts as three single-phase half-bridge inverters and causes poor utilization of the DC-link [2]. Since the unbalanced neutral current ows through the capacitors, a bigger capacitor is also required to maintain an acceptable voltage ripple. ...
... The carrier-based pulse width modulation (PWM) [12], [13] and three-dimensional space vector modulation (3D-SVM) [14] schemes are also being investigated for four-leg VSI. Compared to the carrier-based PWM, 3D-SVM offers many advantages: good DC-link utilization, lower switching frequency and minimum output distortion [2]. Despite its bene ts, the 3D-SVM is very complicated, time consuming and non-intuitive for software and hardware implementation because it requires extensive computational capacity for the 3D transformations, reference vector calculations, duty ratio and switching time calculations during each sampling time, and selection of adjacent switching vectors projected to 24 tetrahedrons from the 6 prisms [13]. ...
In this paper, a simple model predictive current control strategy is proposed for four-leg inverters to deliver power to (un)balanced/(non)linear loads, which can also be delivered to the grid. The classical control requirements for current PI controllers, three-dimensional transformations, and complex modulation stages are eliminated in this scheme. The discrete-time model of the inverter, filter, and load are used to predict the future behavior of the load currents for each of the sixteen possible switching states. The control method chooses a switching state that minimizes the error between the output currents and their references. The feasibility of the proposed method is verified through simulation and experimental results, showing good performance and tracking of the load currents to their respective references.
... This complexity contributes to a range of nonlinear behaviors and challenges, thus amplifying the intricacy and difficulty of system parameter design. Some investigations have resorted to approximating memristive loads as linear loads for the sake of simplicity [29]. Such oversimplified approaches inevitably overlook the intricate and unique characteristics inherent in inverters with memristive loads, thereby hindering their ability to provide comprehensive guidance for the precise design and optimization of these specialized systems. ...
Addressing the issue of system stability is a crucial step towards the successful integration of memristive devices in power electronics applications. This paper focuses on fluorescent lamps possessing memristive characteristics and investigates the instability phenomena and mechanisms within a full-bridge inverter with a fluorescent lamp load. Based on the memristive characteristics of fluorescent lamps, this paper establishes the averaged model of the system, whose coefficient matrix is nonlinear, periodic, and time-varying. This study identifies the occurrence of low-frequency oscillations within the system and elucidates the fundamental mechanism underlying the emergence of low-frequency oscillations. Furthermore, this paper establishes the stability boundaries of the system across different parameter planes. The research findings indicate that the low-frequency oscillations within the system are attributed to the occurrence of Hopf bifurcations in a frequency range higher than line frequency but significantly lower than switching frequency. Lastly, the PSpice circuit of the system is designed, and simulation results are provided for validation. This study can offer guidance on parameters and control strategies for ensuring the stable operation of a full-bridge inverter with fluorescent lamps. Moreover, it can facilitate the comprehension of instability mechanisms in systems incorporating memristive devices, thereby offering a foundation for the expansion of memristor applications.
... The conventional three-leg inverter followed by Δ/Y transformer can be considered as a way to supply unbalanced loads. 3 However, this solution is not feasible in transformerless applications. Another solution is the split-Link four-wire inverter in which the fourth wire is connected to the midpoint of the DC-Link. ...
A favorable option to supply unbalanced loads and provide the neutral wire is the four‐leg inverter. Controllers with high robustness and dynamic response should be used to adjust the inverter load voltages for unknown, unbalanced, and nonlinear loads. Sliding mode controls (SMCs) have a simple structure, good robustness against model parameter uncertainties, and desirable transient response. However, chattering phenomena, variable switching frequency, and error convergence to the operating point on infinite time are the main weaknesses of the conventional SMC method. In this paper, to restrict the conversion time to a finite and controllable value, terminal sliding mode control (TSMC) and fast terminal sliding mode control (FTSMC) procedures are proposed to regulate the load voltages of the four‐leg inverter. In these methods, a continuous control output is suggested to fix the switching frequency and reduce chattering phenomena significantly. Furthermore, the proposed methods are highly robust against model parameter uncertainties. Different simulation and experimental results on a 3‐kW test bench under different loading conditions are done to validate the significant performance of the proposed methods.
... Among both schemes, 3D-SVM is advantageous in terms of better dc link utilization and least output distortion. However, for both techniques, the opportunity cost is paid in terms of complex modeling and higher computational burden [21,22]. ...
This article proposes current control strategy for four-leg two-level voltage source inverters (VSI). This strategy is based on model predictive control (MPC) approach and presents its comparison with finite control set (FCS) model technique. Besides providing a fast dynamic response, proposed technique replaces complex modulation stage and PI controller being used in earlier classical control techniques. Moreover, the proposed methodology selects the switching sequence which reduces tracking error between output and applied reference currents using cost function optimization. This shows the improvement of system response like FCS model technique. However, FCS model technique results in calculation stress and computation burden; resulting computational delay and extra power consumption by the processor. This problem is solved with the help of proposed single predictive technique which makes the inverter more suitable for large time horizon operations and small sampling time instants. The computational delay is reduced up to 6% compared to the case of FCS-MPC controlled inverter. Performance of proposed simplified technique is analyzed and compared with FCS-MPC controlled system with the help of different types of reference signals. This work will boost the industrial application of four-leg two-level VSI by increasing dynamic response and removing complex modulation stage.
... As a result, the inverter must feed unbalanced loads in which the fourth wire must be provided. To realize it, several configurations have been proposed such as connecting a zigzag or Δ/Y transformer at three-leg inverter outputs 5 and connecting the fourth wire to midpoint of the DC link. 6 However, because of several advantages offered by the fourleg inverter like lower voltage ripple of DC-link, better DC-link utilization, and lower cost and size, it may be considered as the preferred solution in most applications. ...
Nowadays, stand‐alone dispersed generation (DG) supplied from renewable energies is rapidly growing. In such a condition, four‐leg inverter can be considered as a successful option to supply unbalanced loads, especially in transformerless systems. In this paper, four‐leg inverter is modeled considering the fourth line inductor. The neutral (fourth) line inductor causes a high coupling through control variables in the natural reference frame. To avoid several transformations among reference frames, a new digital controller based on deadbeat (DB) theory is proposed in the natural reference frame to regulate the load voltages under coupled model. The proposed method offers simplicity, ease of digital implementation, and a fast dynamic response. Furthermore, a delay compensation procedure is also proposed to make the overall performance of the proposed DB controller better. Experimental tests based on a 3kW prototype are implemented to support the analytical analysis. Different tests under various single/three‐phase, nonlinear/linear, and unbalanced/balanced load conditions were performed, which confirm the excellent performance of the proposed control system.
... The power stage of a three-phase four-leg VSC with a neutral inductor ( ) is shown in Figure 1. The LC filter parameter design and related calculations are given in [30]. The modeling of the four-leg inverter has been discussed widely in the literature [31]. ...
This paper suggests an enhanced control scheme for a four-leg battery energy storage systems (BESS) under unbalanced and nonlinear load conditions operating in the isolated microgrid. Simplicity, tiny steady-state error, fast transient response, and low total harmonic distortion (THD) are the main advantages of the method. Firstly, a new decoupled per-phase model for the three-phase four-leg inverter is presented. It can eliminate the effect of power stage coupling on control design; thus, the three-phase four-leg power inverter can be viewed as three single input single output (SISO) control systems. Then, using an improved orthogonal signal generation method, the per-phase model of the four-leg inverter in the stationary and synchronous frame is derived. As the second step, a per-phase multi-loop control scheme for the four-leg inverter under unbalanced load conditions is suggested. The proposed control strategy has the ability to provide balanced output voltages under unbalanced load conditions by avoiding the need to deal with the symmetrical components. Finally, a multi-resonant harmonic compensator is used to actively prevent low-order harmonic currents to distort the output voltages of the three-phase four-leg grid-forming power converter. Simulations results are also presented to verify the performance of the suggested control strategy
... Durante a operação do inversor 4-L mostrado na Figura 2, as tensões 8: , 9: e 7: variam entre zero, + 77 e − , de acordo com as respectivas razões cíclicas fase-neutro K 8: , K 9: , K 7: . Assim, as tensões médias L , L e L podem ser calculadas pela equação (5) de acordo com (ZHANG, 1998). ...
This work proposes a selective strategy for generation of the harmonic current references, which are used in the active power filter (APF) control loops. Applying the aforementioned selective strategy, it is possible to select what of the harmonic components, that compose the load currents, could be suppressed by means of the filter. The strategy comprises an algorithm which is based on the synchronous reference frame (SRF). In addition, it uses adaptive filters in order to carry out the harmonic components selection. The APF topology is implemented by using a four-legs inverter, which is mathematically modelled in the 0 two-phase stationary reference frame. Due to the inherent decoupling in the αβ0 model, proportional and integrative (PI) controllers are used in each one of the referred coordinates, allowing the individual control of the compensation currents. The space vector modulation technique is used for switching the four-legs inverter. The SRF-based algorithm is mathematically analyzed, as well as the simulation results are presented in order to validate the theoretical development. Keywords Shunt active power filter, synchronous reference frame, harmonics, power quality, adaptive filter. Resumo Este trabalho propõe uma estratégia seletiva para a geração das correntes harmônicas de referência, as quais são utilizadas nas malhas de controle do filtro ativo de potência paralelo (FAPP). Com a estratégia seletiva é possível selecionar quais das componentes harmônicas presentes nas correntes da carga poderão ser suprimidas por meio do filtro. A estratégia con-siste em um algoritmo baseado no sistema de eixos de referência síncrona (SRF), o qual utiliza filtros adaptativos para a seleção das componentes harmônicas. A topologia de FAPP é formada pelo inversor de quatro braços, também chamado de four-legs, a partir do qual é obtido seu modelo matemático no sistema de eixos de referência estacionária 0. Devido ao inerente desaco-plamento existente no modelo representado nas coordenadas , e 0, controladores proporcional-integral (PI) são utilizados em cada uma das referidas coordenadas, de forma a permitir o controle individual das correntes de supressão harmônicas. A técnica de modulação espacial vetorial é utilizada para o acionamento das chaves de potência do inversor four-legs. A análise matemática do algoritmo SRF é realizada, bem como resultados de simulações são apresentados para validar o desenvolvimento teórico. Palavras-chave Filtro ativo de potência paralelo, harmônicos, qualidade de energia, filtro adaptativo.
... Using the traditional stability analysis method based on the Routh-Hurwitz stability criterion, we need to approximate the nonlinear loads as fixed loads and then deduce the characteristic equation of the inverter. A technique is developed in [4] where the nonlinear load is decomposed into several linear loads. Hence, these stability analysis methods cannot be used to fully describe the characteristics of the inverter with nonlinear loads. ...
... La quantification du phénomène fait appel à la décomposition de la composante fondamentale selon les composantes symétriques de Fortescue. La norme EN50160 [36] condensateurs [88]. Cette variation est causée non seulement par les oscillations à la pulsation ω introduites par la séquence homopolaire, mais aussi par les oscillations à la fréquence 2ω introduites par la séquence inverse. ...
In many of the remote areas, the diesel generator is the main source of power supply. The cost of grid extension is, and will probably continue to be, prohibitive and the fuel cost increases severely with the remoteness of the location. The combination of several energy sources (wind turbines, photovoltaic panels, small hydroelectric power plants etc.) in a Hybrid Power System (HPS) can be very attractive for most of the remote areas, in terms of cost and availability.
However, improvements of the design and operation of the HPS are still needed to make this technology more competitive in remote areas. In this context, the work presented in this thesis is a contribution to the behaviour analysis and the performances control of an HPS constituted by two renewable energy sources, a diesel generator and storage batteries. This kind of system is studied according to three aspects: sizing, maximizing the use of the renewable resources and power quality.
To maximize the use of renewable resources, the size and operation of the HPS components are matched to the load and the available renewable resources. Then, simulation models for all components of the HPS are developed and brought together in a parametric library under MATLAB/Simulink environment. The simulation models, sufficiently precise, are used in a modular manner for a higher flexibility of the HPS dynamic behaviour investigation and to test different control strategies. Each source of the system includes a control strategy either to satisfy an energy criterion or to reproduce a realist dynamic behaviour.
In order to be able to analyze and to improve the voltage quality, simulation models capable of treating unbalances were developed. A four-leg bi-directional converter is the proposed solution to mitigate the voltage unbalance. Special control strategies associated to this topology have been proposed to improve the quality of the output voltage under unbalanced load conditions.
The simulations results show that using power electronics and the suitable control strategies, it is possible to have a high level integration of renewable energy sources and to improve the power quality of an HPS.
... These low-frequency effects make measurement more difficult, as they are not caused by the injected perturbation. While attempts have been made to mitigate these effects [50], they still prevail in many systems. ...
... SVPWM refers to a special way of determining the switching sequence of the upper three power transistors of a 3-<1> VST. It generates less harmonic in the output voltages and or currents in the windings of the motor load, possibility to optimize for lower switching losses, provides more efficient use of DC supply voltage as compared to direct sinusoidal modulation technique (voltage utilization of SVPWM is 2/..J3 times the sine wave) and compatible with the digital controller [19]. The circuit model of typical SVPWM modulated 3-<1> VST is shown in Fig. 4. Switches S I to S6 are six power switches controlled by switching variables SWI, SW2, SW3, SW4, SW5, SW6 that shapes the 3-<1> output voltage. ...
We present a simple and rapid prototyping technique for Field Programmable Gate Array (FPGAs)-based digital controllers for power electronics and motor drives using MATLAB's Simulink and HDL Coder design software. The MATLAB/Simulink models are optimized and converted to target independent, specific and traceable Very High Speed Integrated Circuit Hardware Description Language (VHDL) code for FPGA programming. An example implementation of the space vector pulse width modulation (SVPWM) technique is presented, illustrating the design of a generic 3-phase voltage source inverter (VSI). Simulation and co-simulation, system level design, and verification for rapid prototyping of FPGA-based digital controllers will assist power electronics engineers and researchers to develop and prototypes in a relatively short time by eliminating tedious and time-consuming manual coding. This enables increased productivity and facilitates the development of power electronic controllers with more complex control algorithms.
... Once the value of the DC voltage is determined one may proceed to the determination of the bus capacitance C. In this case, (5) may be used as a rule for choosing an appropriate capacitance (Zhang, 1998): ...
Considering three-phase four-wire systems, this paper leads to practical rules for designing the main components of shunt active power filters which should be able to compensate the undesired effects of non-linear and unbalanced loads. On the whole, the design procedures are based on the analysis of the active filter circuit by means of the Kirchhoff's laws. The filter output current and DC voltage regulators are also discussed. In the case of the current regulator, a dynamic anti-windup algorithm is proposed in order to improve the transient response of the active filter. Simulation and experimental results are shown in order to validate the proposed design rules. The suggested compensation strategy is based on a selective harmonic elimination algorithm which uses adaptive linear elements. Keywords⎯ active filter, unbalanced load, design rules, current controller, voltage regulator. Resumo⎯ Considerando sistemas elétricos trifásicos com condutor de retorno (quatro fios), este artigo apresenta algumas regras de projeto para a escolha dos principais componentes de um filtro ativo de potência paralelo, o qual deve ser capaz de compensar os distúrbios provocados por cargas não-lineares ou cargas desbalanceadas. Os procedimentos e as regras de projeto são baseados na análise do circuito do filtro ativo paralelo através da lei das tensões de Kirchhoff. O projeto dos controladores da tensão CC e da corrente de saída do filtro ativo também serão discutidos. Nos controladores de corrente um algoritmo de saturação dinâmica foi proposto para melhorar a resposta transitória do filtro ativo. Resultados simulados e experimentais são mostrados para validar as regras de projeto propostas. A estratégia de compensação sugerida é baseada em um algoritmo de identificação seletiva de harmônicos que utiliza elementos lineares adaptativos. Palavras-chave⎯ filtro ativo, carga desequilibrada, regras de projeto, controlador de corrente, regulador de tensão.
... In [27], [28] to simply the controller design, a circuit-level decoupling concept was proposed for a three-phase two-level voltage-source inverter, and the corresponding PWM strategy is basically similar to the Class II SVM reviewed in [29]. With the circuit-level decoupling concept [30], a new modulation strategy for the three-level NPC inverters is introduced in this paper. ...
A new pulse width modulation (PWM) strategy which is an alternative approach of the discontinuous PWM (DPWM) for a three-level neutral-point-clamped (NPC) inverter is developed and presented in this paper. The proposed PWM scheme not only takes advantage of the special properties available in NPC inverters, but also reduces the switching loss of the inverter along with an inherent neutral point (NP) voltage control. Based on a circuit-level decoupling concept, the NPC inverter can be decoupled into two three-level Buck converters in every defined operating section, and thereby the controller design can be simplified. The salient features of the proposed scheme, as compared with the existing carrier-based DPWM strategies, are: 1) its reduced computational processing time, 2) its capability to balance the dc-link voltage without any additional control, and 3) its reduced complexity, e.g., only one carrier wave needed for pulse width modulating. Same as a space-vector modulation, the maximum modulation index, 1.1547, can be attainable by the proposed scheme. Moreover, compared to conventional continuous sinusoidal PWM, using this technique proposed here, the switching losses of the devices can be reduced by one third. In order to explain the operation of this topology properly, the decoupling principle including the driving signal synthesis and the NP potential variation are analyzed in detail in this paper. Finally, the viability and performance of the proposed modulation scheme are shown through simulation and experimental results in a laboratory prototype.
This paper discusses the indirect space vector modulation for four-leg matrix converter. Four-leg matrix converter has been proven to be a reliable, cost-effective, and compact power electronic interface to supply unbalanced or nonlinear loads. However, the added fourth leg has shifted the inverter side modulation from simple two-dimension SVM into complex three-dimension. This paper employs a new technique to implement indirect 3D SVM in digital controllers with further simplification in the modulation process. Moreover, Simulink simulation using repetitive controller has been performed to regulate the output voltage for 400 Hz Power supplies.
Este trabajo presenta una estrategia de control digital para inversores trifásicos de cuatro piernas, para cumplir con el requerimiento de normas internacionales de calidad de energía para UPS cuando se alimentan cargas equilibradas y desequilibradas. La estrategia de control propuesta se desarrolla en el marco de referencia dq 0 en tiempo discreto, posee un lazo interno para controlar la corriente de los inductores y un lazo externo para controlar la tensión de salida. Se demuestra que utilizando controladores convencionales pueden desacoplarse las variables de los ejes d y q , lo que permite diseñar los controladores del lazo externo de control de tensión como sistemas SISO independientes, cumpliéndose los requerimientos de régimen transitorio y de régimen permanente impuestos por norma. Para mejorar el desempeño del inversor cuando se alimentan cargas desequilibradas, se propone utilizar un controlador Proporcional-Resonante únicamente en el lazo interno del eje 0, lográndose una estrategia de control simple y de bajo costo computacional. Se presentan resultados de simulación y experimentales que permiten validar la estrategia de control propuesta.
In this paper, the design of voltage regulation controller for 400 Hz four-leg matrix converter has addressed for varying load conditions. 400 Hz frequency converters are frequently in use across naval, aerospace, and military applications, those applications are regularly requiring a precise output voltage regulation with a strict performance specification. Four-leg matrix converter has introduced as an electronic interface between 50/60 Hz power sources and 400 Hz loads, with added the attractive feature of working under sever unbalanced and non- linear loads. However, the voltage regulation of 400 Hz is challenging due to limited control bandwidth, and traditional controllers have failed alone to achieve a proper voltage regulation, so repetitive controller proposed as a critical solution to the control problem. The repetitive controller has achieved a precise voltage regulation, steady-state errors reduction with higher stability. Simulink simulation represented as well to validate the repetitive controller effectiveness.
This paper presents an optimal selection of linear controllers for the three-phase four-leg inverter operating in island-mode. The inverter uses dual-loop linear control strategy to control the output AC voltage. For each loop following linear controller combinations are tested: proportional (P), proportional-integral (PI), proportional-resonant (PR), and proportional-integral-resonant (PIR). Elimination of steady-state error under DC and AC waveforms, output impedance value, system stability and execution time are compared. Results show that only an outer loop PIR controller is able to eliminate steady-state error in the case of both symmetrical and non-symmetrical load regardless of the inner loop controller type. For the inner controller, both PI and PIR controllers show superior characteristic for tested criteria. Finally, the control system is implemented in TI DSP ControlCARD and tested using hardware-in-the-loop setup under symmetrical and non-symmetrical loads.
ABSTRACT
Due to a combination of environmental factors, security, limited fossil resources and increasing demand, the energy sector faces major changes. In the future, any sustainable energy system will be based on the increased use of renewable energy. Naturally decentralized, the renewable energy sources allow the exploitation of local resources close to the final user. Their interconnection in low voltage enables a new paradigm for the electrical power distribution system able of operating autonomously or in interconnection with a main grid, the µGrid. This kind of grid is a promising solution to face the problems of distributed generation integration with high penetration levels of renewable energy. However, technical limitations, mainly related to grid stability and power quality, raise difficult issues about the reliability of such a system.
The research work presented in this thesis proposes new solutions from electrical engineering to enable the integration of distributed generation and improve the µGrids power quality and weak grids stability. A special effort was made on the modelling of the different elements of a µGrid to analyse its dynamic behaviour and to anticipate problems that may occur during islanding operation mode or in interconnection with a main grid. This approach has led to innovative solutions in terms of power electronics interfaces and associated control strategies for the integration of distributed generation and storage, while contributing to the improvement of the power quality in a weak grid context. In the same context, new control laws have been designed to alleviate the fatigue loads of the major mechanical components of the wind turbines and simultaneously involve them in the primary frequency control. A special attention was paid to the validation phase through prototypes and an experimental µGrid platform.
RESUME
En raison d’une combinaison de facteurs environnementaux, sécurité, ressources fossiles limitées et augmentation de la demande, le secteur de l’énergie est confronté à des changements majeurs. A l’avenir, tout système énergétique durable sera basé sur un recours accru aux énergies renouvelables. Naturellement décentralisées, les sources d’énergie renouvelable permettent l’exploitation des ressources locales proches des lieux de consommation. Leur interconnexion en basse tension permet un nouveau paradigme pour le réseau de distribution capable de fonctionner indépendamment ou en interconnexion avec un réseau principal, le µréseau. Ce type de réseau est une solution prometteuse pour répondre aux problèmes d’intégration de la production décentralisée avec un taux élevé d’énergie renouvelable. Toutefois, des contraintes techniques principalement liées à la stabilité du réseau et à la qualité de l’énergie soulèvent des questions difficiles sur la fiabilité d'un tel système.
Les travaux présentés dans ce mémoire consistent ainsi à proposer de nouvelles solutions issues du génie électrique pour faciliter l’intégration de la production décentralisée et améliorer la qualité de l’énergie dans les µréseaux et la stabilité des réseaux faibles. Un effort particulier a été fait sur la modélisation des différentes composantes d’un µréseau afin d’analyser son comportement dynamique et d’anticiper les problèmes qui peuvent apparaitre pendant le fonctionnement en ilotage ou en interconnexion avec un réseau principal. Cette approche a permis d’aboutir à des solutions originales en termes d’interfaces d’électronique de puissance et de commande associée pour l’intégration de la production décentralisée et du stockage, tout en participant à l’amélioration de la qualité de l’énergie dans un contexte de réseau faible. Dans le même contexte, de nouvelles lois de commande ont été conçues pour réduire la fatigue des principales composantes mécaniques des éoliennes et simultanément, les faire participer au réglage primaire de fréquence. Une attention toute particulière a été portée à la phase de validation à travers des prototypes et une plateforme expérimentale µréseau.
As the amount of decentralized generation is continuously increasing the control and maintaining of the grid stability becomes more complex. This is caused by the change of production capacities from the high voltage area into the distribution network. In order to ensure the stability of future smart grids a new 4-leg 4-wire inverter as a part of a power electronic regulator is introduced. The features of the 4-leg 4-wire topology in comparison to the 3-leg 4-wire topology and advantages of a multilevel inverter for harmonic compensation are shown. In combination with a powerful FPGA based controller complex algorithms for Space Vector Modulation and for control can be implemented. Finally the actual status of the hardware development including the technical data of the inverter is shown.
This chapter presents a minimum inverter capacity design for three-phase four-wire center-split hybrid active power filter (HAPF) in dynamic reactive power and current harmonics compensation. Based on HAPF equivalent circuit models in d-q-0 coordinate, the coupling part filtering characteristics of the HAPF without or with neutral inductor can be illustrated. According to the current quality data, the minimum dc-link voltage expressions for the HAPF without and with neutral inductor are deduced and compared. Conventionally, the coupling inductor and capacitor (LC) is usually tuned at a higher fifth or seventh order harmonic frequency to reduce its cost and size compared with the third order case. When triplen harmonic currents exist significantly, the HAPF with a small tuned neutral inductor can further reduce its minimum dc-link voltage requirement. Thus, the initial cost, switching loss and switching noise of the HAPF can be lowered. Representative simulation and experimental results of the three-phase four-wire HAPF with neutral inductor are presented to verify the filtering characteristics analysis and minimum dc-link voltage expressions, to show the effectiveness of reducing its inverter capacity, switching loss and switching noise in dynamic reactive power and current harmonics compensation compared with the conventional HAPF without neutral inductor.
The technology of direct AC/AC power conversion (Matrix Converters) is gaining increasing interest in the scientific community, particularly for aerospace applications.
The aim of this research project is to investigate the use of direct AC/AC three phase four-leg Matrix Converter as ground power unit to supply aircraft with power during stopover or maintenance in airports. The converter fourth leg is used to provide a path for the zero sequence components when feeding unbalanced or non-linear loads. A high bandwidth controller is required to regulate the output voltage of Matrix Converter with a 400Hz output frequency. However, the controller bandwidth is limited due to the reduced ratio between the converter switching frequency and the fundamental frequency. In this case undesirable, periodic errors and distortion will exist in the output voltage above all in the presence of a non-linear or unbalanced load.
Digital repetitive control system is proposed to regulate the output voltage of a four-leg Matrix Converter in an ABC reference frame. The proposed control structure introduces a high gain at the fundamental and its integer multiple frequencies. Using the proposed repetitive controller will reduce the tracking error between the output and the reference voltage, as well as increasing the stability of the converter under balanced and unbalanced load conditions.
Simulation studies using SABER and MATLAB software packages show that the proposed controller is able to regulate the output voltage during balanced and unbalanced load conditions and during the presence of non-linear load. In order to validate the effectiveness of the proposed controller, an experimental prototype of a 7.5KW has been implemented in PEMC laboratory using DSP/FPGA platform to control the converter prototype. The steady state and the dynamic performance of the proposed control strategy are investigated in details, and extensive experimental tests have showed that the proposed controller was able to offer high tracking accuracy, fast transient response and able to regulate the output voltage during balanced, unbalanced and non-linear loading.
This paper suggests the use of synchronous frame harmonic elimination technique in distributed power systems consisting of inverters with nonlinear loads. Inverters of the distributed system are controlled to share the active power. Power sharing is achieved without any communication between the units. To eliminate the harmonics caused by nonlinear loads, synchronous frame controller is used. The technique is explained in detail and simulation results for a system consisting of two inverters are given. The results show that the technique can be successful to eliminate the harmonics caused by nonlinear load while the active power sharing is achieved.
A low-voltage direct current (LVDC) distribution system comprises a rectifier, a DC network, and customer-end inverters (CEI) responsible for the AC supply to the electricity end-users. The CEIs can be implemented as single-phase or three-phase ones; in this paper, feasible single-and three-phase topologies are introduced and their losses are calculated using nine different power switches. Three commercially available IGBT, MOSFET, and SiC MOSFET power switches are selected for comparison. In this application, a galvanic isolation between the DC network and the customer is required. The isolation is implemented by using an isolating DC/DC converter at the CEI supply, and therefore, the input voltage of the CEI can be different from the DC network voltage. In this paper, the effect of the supply voltage level on the losses of the CEI is calculated for the nine power transistors in single-and three-phase topologies.
Due to a combination of environmental factors, security, limited fossil resources and increasing demand, the energy sector faces major changes. In the future, any sustainable energy system will be based on the increased use of renewable energy. Naturally decentralized, the renewable energy sources allow the exploitation of local resources close to the final user. Their interconnection in low voltage enables a new paradigm for the electrical power distribution system able of operating autonomously or in interconnection with a main grid, the µGrid. This kind of grid is a promising solution to face the problems of distributed generation integration with high penetration levels of renewable energy. However, technical limitations, mainly related to grid stability and power quality, raise difficult issues about the reliability of such a system.
The research work presented in this paper proposes new solutions from electrical engineering to enable the integration of distributed generation and improve the µGrids power quality and weak grids stability. A special effort was made on the modelling of the different elements of a µGrid to analyse its dynamic behaviour and to anticipate problems that may occur during islanding operation mode or in interconnection with a main grid. This approach has led to innovative solutions in terms of power electronics interfaces and associated control strategies for the integration of distributed generation and storage, while contributing to the improvement of the power quality in a weak grid context. In the same context, new control laws have been designed to alleviate the fatigue loads of the major mechanical components of the wind turbines and simultaneously involve them in the primary frequency control. A special attention was paid to the validation phase through prototypes and an experimental µGrid platform.
Non linear loads create harmonics in the system and consequently pollute grid in distributed power generation system. Grid pollution due to harmonics is highly undesirable. This paper presents synchronous reference frame (SRF) based control scheme which can be used to regulate harmonic flow in the system. Load current sharing is achieved between grid and a distributed generation (DG). Real, reactive, negative sequence and harmonic current components of load current are decomposed separately using SRF theory. Results are obtained for two different configurations of non-linear loads. The control algorithm is developed to regulate the flow of harmonic currents in desired manner between the utility grid and DG. The control is developed such that even with nonlinear loads, the grid currents are sinusoidal and linear. The current controller helps to improve power quality of the system.
A novel dual-output four-leg inverter topology is proposed in this paper. The proposed inverter which is able to provide two three-phase voltage sets of independent magnitudes and frequencies is operationally equivalent to two four-leg inverters working independently though with a reduced number of semiconductor switches and hence gate drive and control circuits. The structure of the new topology is developed and the carrier based PWM scheme is elaborated for its two subsequently defined different frequency and equal frequency operation modes. The proposed converter is compared with conventional topology in terms of characteristics of output waveforms, rating of devices and power loss. A prototype of the system is built and tested. The simulation and experimental results confirmed the validity of operation of the proposed topology.
This paper proposes the use of a three-phase four-leg (3P4L) converter in combination with an LCL filter for the inverter stage of a solid state transformer (SST). This configuration gives full control over the line-to-line, as well as the line-to-neutral voltage and currents, while providing exceptional harmonics mitigation. A procedure to calculate the passive components for the LCL filter is presented, as well as a method to reduce resonance caused by the filter. Furthermore, two feedback control schemes are derived and are enhanced with a feedforward control scheme.
In this paper a novel control strategy for four-leg three-phase voltage source inverters (VSI) supplying time variant loads is proposed. Designed control scheme is composed of three parts: A feed-forward current compensator; Inverter main Proportional-Resonant (PR) voltage controller; and inverter output current controller. The PR controller is employed for regulating the output voltage of inverter to produce a symmetrical balanced three-phase voltage under different loading conditions such as balanced, unbalanced, linear, non-linear variant loads. The inverter current control loop designed with state feed-back methods improves the system response. The performance of proposed control strategy is studied under different loading conditions. Simulation results depict marvelous performance of the proposed controller in dynamic and steady states.
The paper has researched on the control of three-phase inverter with unbalanced load. Based on the analysis output characteristic of inverter with unbalanced loads, the method of restrain the unbalance output voltage was researched, and then the models of inverter respectively in dq-frame and αβ-frame were established. According to the models and the characteristics of traditional dual-loop control and repetitive control, a new control strategy in which the dual-loop control in dq-frame was in parallel with repetitive control in αβ-frame was proposed. Based on the model in dq-frame, the dual-loop control of inverter was designed; and based on the model in αβ-frame, the repetitive controller of inverter was designed. The results of simulation in MATLAB and the experiment based on DSP - TMS320F28335 have compared the control effects of dual-loop control, repetitive control and the compound control proposed in this paper. And it has proved to be a correct and available control strategy.
In this paper, a novel control strategy for the load converter supplying the unbalanced AC load in the renewable energy resources system is presented. This novel control strategy is implemented in the a-b-c coordinate, so reference-frame transformation from a-b-c coordinate to d-q-0 rotating coordinate and inverse transformation from d-q-0 rotating coordinate to a-b-c coordinate are not required which decreases the controller operation time comparing with conventional d-q-0 controller. The control algorithm results in balanced and sinusoidal load voltages under unbalanced AC loading. The unbalanced load is characterized in both the a-b-c and d-q-0 coordinates. Also, the mathematical model of the load converter in both a-b-c and d-q-0 coordinates is derived by using the average large signal model. Then, two control strategies for the load converter are presented. The first one uses the conventional d-q-0 controller to ensure the voltage and current regulation. The second one is this novel proposed control strategy based on the power conservation theory. The two control strategies have been applied to the reference voltages generation of the load converter. The performance of the load converter with these two control strategies is compared with each other. Simulation and experimental results show the validity and capability of the novel proposed control strategy.
A new switching scheme, which combines conventional space vector modulation (SVM) and carrier-based pulse width modulation (CBPWM), is proposed for a three-phase four-leg voltage source inverter (VSI). The proposed algorithm is simpler than conventional three-dimensional space vector modulation (3-D SVM) and easy in implementation in a real-time DSP system, it avoids the selection of a prism and tetrahedron in a 3-D SVM, therefore alleviates the computation burden of the DSP. Also, the concept of near-state pulse width modulation (NSPWM) method, which is used in a three-phase three-leg inverter to reduce the common mode voltage (CMV) noises, can be adopted in this algorithm so as to reduce the common mode voltage for a three-phase four-leg VSI. The feasibility of the proposed modulation technique is verified by both computer simulation and experimental results.
In order to well solve the problem of the output voltage unbalance, which is caused by unbalanced load of high frequency link matrix converter(MC), a kind of high frequency link three-phase four-leg MC has been proposed. Firstly, the root cause of the output voltage unbalance is analyzed. Then through building up the mathematical model of high frequency link three-phase four-leg MC, it is verified in theory that the de-re-couple control strategy is suitable for three-phase four-leg MC. Finally, closed-loop system suiting for a variety of unbalanced loads is simulated by MATLAB software based on the symmetrical component. The simulation results show that the high frequency link three-phase four-leg MC is a good solution to imbalanced output voltage.
Present paper deals with the implementation of parallel three-phase active power filter used to compensate current harmonics, to correct the displacement between voltage and current generated for capacitive or inductive loads and, by the implementation of the control strategy here described, to perform the current balancing for the three phases, minimizing the neutral current. The reasons for the choice of this topology and the adopted control strategy are presented as well as the mathematical analysis, design procedures, simulation and laboratory results. As final stage of the developing a prototype with 10 kW was built.
Static power conversion systems based on a resonant high frequency (HF) link offers a significant reduction in the size and weight of the equipment over that achieved with conventional approaches, especially when multiple sources and loads are to be integrated. A faster system response and absence of audible noise are the other principal characteristics of such systems. A conversion configuration based on a HF link which is suitable for applications requiring distributed power is proposed.
The paper presents a systematic approach to small-signal modeling,
and control design of three-phase PWM converters. The well established
design procedures used in DC-DC converter control design, are adapted
for the three-phase converter control based on the similarity in the
small-signal dynamics of the three-phase converters and their DC-DC
counterparts. The approach is especially beneficial in three-phase
rectifier control, which is reduced to a single-input single-output
system after closing the current loops. The modeling approach is
verified on a 10 kW three-phase boost rectifier switching at 15.6 kHz
with DSP control. A wide-bandwidth output voltage control loop is then
designed based on the verified small-signal transfer functions
A three-phase harmonic current cancellation scheme based on
optimal pulse width modulation (PWM) current injection using a novel
time sharing technique (TST) is presented. A novel three-phase current
source inverter topology is described, which is simpler and requires
components of lower power rating than conventional circuits. The
performance of the active filter is investigated by simulation and
experiment. Experimental results indicate that the system performs as
expected and give good agreement with theory and simulation studies. The
active power filter is especially suited to cancel harmonics generated
by rectifier and thyristor loads
Uninterruptable power supply (UPS) systems have been developed for those electronic installations, especially computers and communication systems, which require a power supply unaffected by mains degradation or failure. This article describes a laboratory prototype UPS which has been designed to demonstrate the application of PWM techniques to UPS systems. The UPS is based on our Pulse Width Modulation (PWM) speed control system for a.c. motors (see Refs. 1 to 6), and is notable for its simple filter requirements and high efficiency. It has been designed in modular form using two modules: a PWM waveform generation module, type VM5000*, and a power supply and current sensing module, type VM5001*. The power ratings are 3 kVA (three-phase output) and 2 kVA (single-phase output), but the basic design can readily be extended to higher powers.
The authors present calculation approaches for obtaining
compensating components for a reactive and harmonic current compensator
in unbalanced three-phase power systems. The synchronous detection
method is applied to calculate proper compensating components by
monitoring the line currents and voltages. The per-phase calculation
algorithm is implemented to share and distribute the compensating power
using approaches of equal power, equal current, and equal resistance.
The proposed algorithm and the implementation circuit are presented with
their test results. The merits of the proposed methods are the
capabilities to operate under an unbalanced three-phase system by
per-phase calculation, to avoid conversion error by force waveform
calculation, and to implement the hardware in a simple manner. it can be
widely used in active filter designs for current compensation and load
balancing
The parallel operation of static inverters is, in a large amount
of cases, the appropriate solution to achieve the high power required by
some applications or to improve power system reliability. The limited
inverter capacity obliges to parallel the individual units to obtain the
nominal load power. In UPS systems, there are situations where a high
reliability/availability is required by critical loads. Parallel
redundancy appears an immediate solution to satisfy this requirement.
This paper presents a control system for parallel operation of
nonredundant UPSs based on current control. The relative phase between
the inverters is constant. Simulation results as well as experimental
studies are presented. The overall control system is implemented on a
simple and low cost platform
The modeling and control of a PWM rectifier in the case of network
variations are studied. The aim is to limit and stabilize stable
variation of DC output voltage and line currents in such circumstances.
A line current compensation loop method coupled with identification of
network parameters is compared to another approach using a robust DC
voltage regulator
A three-phase multi-functional battery energy storage system
(BESS) is designed and implemented in this paper. When the utility power
is in normal condition, the proposed BESS can be arranged to shave the
peak load or charge the battery bank. In either case, since the load is
unbalanced, harmonic and reactive powers can be compensated through the
proposed active power filtering control, the power factor is maintained
near to unity and the line currents drawn from the utility are balanced
and sinusoidal with very low distortion. As a utility power failure
occurs, the proposed BESS can immediately supply uninterruptible power
to the loads. In this case, an instantaneous control technique is
developed to yield good three-phase voltage waveforms. The determination
of reactive components, the dynamic modeling and the design of
controllers for the proposed BESS are made. Some experimental results
are provided to demonstrate the effectiveness of the proposed BESS
The authors investigate electrical, mechanical, and thermal
limitations of device application and resonant circuit design as higher
output power and higher switching frequencies are simultaneously pursued
in passive clamp resonant DC link (RDCL) converters. The impact of these
limitations on resonant component selection, resonant inductor design,
clamp transformer design, and resonant bus power distribution at these
higher power levels and frequencies is discussed. Resonant circuit
design methodology to select the resonant components is formulated,
based primarily on device electrical and thermal constraints. A clamp
transformer designed for ultra-low leakage reactance to control the peak
resonant bus voltage magnitude and minimize clamp voltage oscillations
is discussed. It utilizes a distributed coaxial winding in an integrated
magnetic assembly that combines the resonant inductor and clamp
transformer functions into one common core. A total mechanical package
assembly that integrated the distributed electrical, mechanical, and
thermal models was implemented for a 600 VDC 200 kW RDCL prototype
operating GTO (gate turn-off thyristor) devices at 20 kHz
A novel method for microprocessor control of three-phase
sinusoidal-voltage pulse-width-modulated (PWM) inverters is proposed.
First, the discretized state equations of the inverter main circuit on
the d - q frame are derived. An algorithm for dead beat
control with a current minor loop that constrains the inverter current
within the safety limit is subsequently developed. To compensate the
computing time delay, a second-order prediction method and a novel
discretization method using twice the time of the sampling period have
been adopted. This method is especially suitable for inverters using
high-speed switching devices and digital signal processors. The validity
of the control system has been demonstrated by precise simulation using
a hybrid computer
A novel approach to realizing efficient high-performance power
converters is presented. The concept of a resonant DC link inverter has
been proposed and realized with the addition of only one small inductor
and capacitor to a conventional voltage source inverter circuit. The
proposed technology is capable of switching almost an order of magnitude
faster than state-of-the-art voltage source inverters at significantly
improved efficiencies using the same family of devices. The topology is
especially suitable for high-power applications using gate turn-off
devices. A 4.5 kW inverter has been fabricated and tested extensively in
the laboratory, and the superior characteristics of the resonant DC link
topology have been verified