Instantaneous Power Theory and Applications to Power Conditioning
Abstract
This book presents a deep review of various power theories and shows how the instantaneous active and reactive power theory provides an important basic knowledge for understanding and designing active filters for power conditioning. The only book of its kind, it also demonstrates how the instantaneous active and reactive power theory can be used for combined shunt-series filters and in Flexible AC Transmission Systems (FACTS). © 2007 the Institute of Electrical and Electronics Engineers, Inc.
... This mode can be applied in grid-forming or gridfollowing. In this case, the power electronic converter is also used for improving the power quality in the following cases: (i) harmonic content mitigation from non-linear loads (Akagi et al., 2017); (ii) reactive power compensation (Duarte et al., 2020); (iii) uninterruptible power supply for enhancing the security of supply (Serban & Marinescu, 2014); (iv) compensate a voltage sag and swell in critical loads (Silva et al., 2017); (v) an energy manager by a battery system for peak clipping, valley filling, load shifting or peak shaving (Hossain et al., 2019). ...
... The active filter controller can determine in real-time the compensating currents references and force a power converter to synthesize it accurately (Akagi et al., 2017). The active filter extracts the oscillating power of the nonlinear load, and then it obtains the reference current. ...
... The active filter extracts the oscillating power of the nonlinear load, and then it obtains the reference current. There are some techniques that have been developed for extracting the current reference, such as the Instantaneous p-q Theory technique (Akagi et al., 2017). The p-q theory uses the Clarke Transform to map instantaneous values of voltages and currents from the natural a − b − c system coordinates into an orthogonal alpha − beta − 0 reference frame coordinate. ...
In this article, a smart inverter model that executes ancillary services with automated decisions is presented, such as power sharing and voltage and frequency stabilization, compensation of unbalance voltage, mitigation of harmonic content, and the balance of generation and demand. The droop control was utilized for power-sharing between the distributed generations; the mitigation of negative-sequence voltage is used for unbalanced voltage compensation, and finally, a feed-forward current is adopted for harmonic compensation. Therefore, the smart inverter was controlled through a supervisory system, identifying which ancillary function to activate at certain times. Results show the successful operation of the system and can be used as validation of the proposed control strategies, including the automated decisions in the microgrid.
... In [27], a fuzzy-based modified real-reactive power strategy for inverter control has been presented for achieving better control over the current and voltage overshoot during FRT mode by increasing the reactive power injection and minimizing the active power transfer. A brief concept, detailed mathematical explanation of instantaneous power theory (IPT), and its application for designing the shunt active filter (SAF) has been discussed in [28]. A current control algorithm is proposed in [29] to calculate dq-axis current references during voltage sag. ...
... By keeping in mind the necessary requirements, the controller has been designed based on IPT. The application of the theory proposed in [28] to design the proposed controller, initially, the grid side three-phase instantaneous voltage (V inst_grid ) and current (I inst_grid ) have been tracked from the point of common coupling (PCC) and transformed to α-β coordinate by Clark transformation and it is shown in Eqs. (10) and (11). ...
The paper proposes an instantaneous power theory (IPT) based an improved low voltage ride-through (LVRT) strategy for photovoltaic-proton exchange membrane fuel cell (PV-PEMFC) based grid following hybrid microgrid architecture. The concept of the instantaneous power theory-based proportional-integral control (IPT-PIC) mechanism has been introduced to enhance the dynamic response of the grid-tied power electronic medium. Based on the direct quantities measured, the processed IPT-PIC output has been used to regulate the active and reactive current injection during the grid side contingencies. Besides, the instantaneous power theory-based fuzzy current control (IPT-FCC) mechanism has also been proposed and compared with the conventional instantaneous power theory-based approaches and found to be suitable for real field applications, particularly in the hybrid microgrid architecture. The percentage improvement of the LVRT capability has been found in the detailed simulated platform using MATLAB/Simulink 2021a. Furthermore, the response time, computational burden and real-time applicability have been evaluated in the dSPACE DS1103PPC controller board.
... As a direct consequence of this fact, there is an observed increase in harmonic contamination of the current demanded by these loads. The presence of such harmonic currents, when the point of common coupling (PCC) does not have the same harmonic voltage components, results in the existence of a portion of non-active power, defined by Budeanu as 'distortion power' [3], which affects the power factor (PF) of the load. Furthermore, the power factor is also affected by the use of predominantly capacitive and inductive loads, with the latter being quite common nowadays. ...
... The boost PFC converter is composed by a full-wave diode rectifier connected to a conventional boost converter, as shown in Fig. 1. As commonly observed with electronic loads, the boost converter requires a current profile that often leads to high non-active power, as defined in Budeanu's power theory [3]. However, in addition to its ability to function as a stepup converter, the boost PFC converter is also known for its capability to improve the power factor of the system to bring it closer to unity. ...
... Akagi was the first person to put forward this concept [60]. This theory suggests that in order to calculate active and reactive power in this frame, three-phase instantaneous values must initially be converted into two-phase values in a stationary reference frame using the Clark transformation [60]. ...
... Akagi was the first person to put forward this concept [60]. This theory suggests that in order to calculate active and reactive power in this frame, three-phase instantaneous values must initially be converted into two-phase values in a stationary reference frame using the Clark transformation [60]. The block diagram for this theory is given in Figure 2. Grid voltages U a , U b , U c and load currents i La , i Lb , i Lc are sensed and fed to the controller for processing and generating the reference currents i a * , i b * , i c * . ...
Photovoltaic (PV) inverters are now supposed to provide additional supporting services with more reliability and efficiency. This paper presents three different control methods for generating reference current in a multifunctional, multilevel grid-tied PV inverter for harmonic, reactive, and unbalance compensation. These methods are the synchronous reference frame (SRF) theory (d-q), the instantaneous reactive power (IRP) theory (p-q), and the conservative power theory (CPT). As a result, the primary goal is to propose a low-cost multifunctional solar invert for distributed generation, with an appropriate prototype developed in the laboratory for experimental validation of various modes of operation. Demonstrated results show that the presented inverter is capable of providing various ancillary services with all three types of control.
... All electrical power is distributed as sinusoidal voltage. When we look at the basics of how the generator works, we will understand the electrical power distributed as a sinusoidal wave [2]. ...
... Since the harmonic current is the source of an active state, only the primary stream is extracted from the display. In practice, the current harmonic sizes are reduced by 90%, and because the source impedance at the harmonic frequencies of the voltage distortion is reduced [2]. ...
This paper discussed the method of filtering technology by using an active power filter. Sometimes studying the problem is more important than starting to solve it. Firstly, the paper started by studying the importance of power quality and how to improve it, and naturally, the power factor as well. Recently, wide applications of non-linear devices in an electrical grid, which they use, have become urgent. The elimination of harmonics and solving this problem are not new. Since more methods are planned to decrease harmonics, improve power quality, and reduce reactive power losses, One of the best methods of filtering is the active filter. Presently, many countries use this type of filtering, depending on its capacity to eliminate harmonics up to the 25th level. The MATLAB/SIMULINK power system toolbox is used to simulate the planned system.
... The first group of adaptive systems which often needs change in its electrical characteristics are systems for improving the quality of electricity [1][2][3][4]. A further possible area of usage of the TI solutions is in static power electronics devices, formally known as flexible AC transmission systems (FACTS) [1,5,6], installed in AC grids. ...
... As a result of the compensation process the current, flowing from the power line node to these loads, should have both a suitable shape and a correct phase relationship with the voltage waveform in the node. The details of the compensation process depend on the chosen compensator operation strategy, that can be related to a reactive power alone or to both a reactive and a distortion power [2,[15][16][17]. However, presented in this work, the operation of an adaptive passive compensator, as a whole, is not related to any given power theory. ...
This work is devoted to possible implementation of tunable magnetic devices in electrical systems with adaptive properties. The basic idea, underlying operation of the presented magnetic device, depends on interaction of two (or more) magnetic fluxes in a quasi-linear range of ferromagnetic core characteristics. This is a new approach to the design of such magnetic elements; typically, saturation phenomenon of the ferromagnetic core of an inductor is used to change a value of its inductance. The good examples of adaptive electrical power systems can be devices for improving a quality of electrical energy. When used in compensators of reactive and a distortion power (or a reactive power only), tunable magnetic devices clearly offer wider possibilities for the compensation, compared to solutions, using compensators based on fixed magnetic elements. However, the application of the proposed tunable device in an adaptive compensator is only one example of its possible use in an electrical power area. In this work, the following issues are presented: exemplary solution of the adaptive passive compensator, basics of operation of tunable magnetic device, and test results of the experimental model of an electrical system with such a device.
... In order to address and alleviate power quality concerns, the implementation of specialized power devices is employed. The active management of bespoke power devices necessitates the continuous monitoring of several AC grid parameters, such as frequency, phase, and basic voltage magnitude [4]. The topology of VSC which is a shunt connected active filter known as DSTAT-COM is used as a custom power device is incorporated for addressing the current related power quality issues due to current harmonics [5]. ...
An adaptive observer with a decreased order is proposed in this study for use in the hardware implementation of a 3-p, 3-w distribution static compensator (DSTATCOM), which extracts grid parameters. The DSTATCOM is inculcated for attaining various functions like reactive power compensation, mitigation of current source related harmonics accompanied by the self-sufficient DC bus. A reduced order-based adaptive observer is incorporated to determine grid parameters which work under the polluted condition and does not depend on the linearization of PD output using PLL. A Lyapunov function is incorporated for ensuring the proper tracking of grid parameters under the distorted conditions which makes the system adaptive. In order to achieve the fine tuning of proportional integral gains which preserves the DC bus voltage to its craved value, Gray Wolf Optimizer is employed which utilizes very less memory and requires very less parameters reducing the computation time offering faster response in achieving the values with lower settling and rise time in comparison with manual method. Simulation in MATLAB and hardware prototyping in the laboratory with the aid of a digital signal processor are used to evaluate the control algorithm's performance, with the findings validating the control algorithm's performance.
... Active Power Filters (APF) are a well-known tool for suppressing higher harmonics in current and voltage waveforms [1][2][3][4][5]. For practical reasons industry usually uses Parallel Active Power Filters (PAPF), i.e., those in which the converter is connected in parallel to the load. ...
The article presents selected static characteristics of a parallel active filter with voltage control in the supply line (VPAPF – Voltage-controlled Active Power Filter) as a function of parameters of the supply network. The tests were done on the basis of a simulation model of the supply network and an appropriate compensator. The test results showed that VPAPFs are most suitable for operation in weak networks, maintaining an almost constant level of voltage distortion, regardless of the value of the network impedance. In addition, the influence of the parameter G corresponding to the conductance value suppressing higher harmonics of the network voltage on the operation of the active power filter was determined.
... The negative impact of nonlinear loads on the operation of the power grid is widely known and is a well-analysed problem (see e.g. [3][4][5][6][7]). For example, solutions with diode and thyristor rectifiers and simple power electronics converters draw a distorted current and this is the main reason for their negative impact on the operation of the power grid. ...
... From Akagi et al. (2017) the current reference vector can be obtained by ...
Two Grid-Forming (GFM) control strategies based on emulation of Synchronous Machine (SM) behavior, namely Droop Control and Synchronverter, and two Andronov-Hopf Dispatchable Virtual Oscillator Control (dVOC)-based techniques are unified into a compact yet generalized control framework for GFM inverters. In the light of the proposed framework, we reassess the control laws of the studied GFM analytically, and further validate these analyzes in silico for steady-state power sharing and transient responses. We show how the mathematical structures of the studied GFM methods differ and resemble, which has an impact on the underlying grid forming performance. These differences are attributed to intrinsic nonlinearities, which can be translated as operating point parameter dependence for each GFM technique being recast for the suggested framework. Furthermore, we show that, to a certain extent, the techniques can be parameterized to have similar steady-state and dynamic responses. This work succeed in developing a technology-agnostic metrics for steady-state power sharing and dynamic behaviors of GFM methods, an important requisite for the interoperability of grid-connected inverter units.
... Trata-se de uma fonte com injeção controlada de corrente, projetada para sintetizar potências reais (pc) e imaginárias (qc) no nó 23 da microrrede. Esta representaçãoé baseada na teoria pq, presente em Akagi et al. (2017), e no referencial síncrono para definição das correntes a serem injetadas na rede elétrica. Este tipo de geração normalmente fornece somente potência ativa (ou seja, potência real) para a rede elétrica, no entanto esse modelo representará o bloco GMU em questão, queé o conjunto da carga e geração FV. ...
Microgrids are basically composed of dispatchable and distributed generation, storage system and loads. They must be able to guarantee a stable supply of energy to the loads, being able to operate in connected or islanded mode in relation to the energy utility. Studies to evaluate the Electric Power Quality indices must be carried out for different operating conditions. In this paper, a modeling of the distribution grid of the CAMPUSGRID microgrid using PSCAD/EMTDC software are presented. Simulation results of diferent load profiles, load connection/disconnection scenarios and intermittent generation integration are presented.
... It employs a manipulated feedback "PID control" to push the ER error quickly towards and then onto its sliding surface. In the end, it depicts the PEMFC stack's ideal nonlinear dynamic, which quickly approaches a stable situation [93]. The feed forward controller and SMC collaborate as illustrated in Fig. 11(b), which resulted in an improvement in the recovery of oxygen stoichiometry towards the intended reference under sudden demand variations from 500 ms to 30 ms. ...
... Therefore, it is important to generate reference current in order to compensate the harmonics producing non linear load. The active power filter is made up of Voltage Source Inverter (VSI), Inductive Capacitive element as (LC) filter and a DC link capacitor is used as a supply for three phase inverter [4]- [7]. The corresponding gate pulses are generated by using synchronized six pulse generator. ...
Power system harmonics are a menace to electric power system with disastrous consequence. Due to the presence of non linear load, power quality of the system gets affected. To overcome this, shunt active power filter have been used near harmonic producing loads or at the point of common coupling to block current harmonics. The shunt active power filter is designed to minimize harmonics in source current and reactive power in the non linear power supplies which are creating harmonics. In this paper,
Instantaneous power of p-q theory is employed to generate the reference
currents and PI controller is used to control the dc link voltage. In addition to this, Artificial Intelligence (AI) technique is used to minimize the harmonics produced by nonlinear load. The main objective of this paper is to analyze and compare THD of the source current with PI controller and by artificial neural network based back propagation algorithm. The proposed system is
designed with MATLAB/SIMULINK environment.
... where A ∈ R 6×9 is the incidence matrix of the directed graph. By applying the standard (amplitude-invariant) Clarke transformation [21], namely T αβ0 , the input and output currents can be mapped to the αβ0 space as: ...
This paper presents a circulating current reference generator based on a constrained model predictive control approach to perform the inter-cluster capacitor voltage balancing in Modular Multilevel Matrix Converters (M3C). The proposed reference generator incorporates nominal current limits as bound constraints into the optimal control problem. This approach enables the reference generator to efficiently provide the necessary circulating current in each cluster, thereby balancing the energies of the converter's clusters. As a result, the M3C can operate even during critical frequency points, significant power steps, and severe imbalance levels while ensuring that every cluster current remains within its feasible limits. Experimental results on a M3C prototype of 36 submodules are provided to validate the effectiveness and high-quality performance of the proposed strategy.
... De acordo com a teoria pq (Akagi et. al, 2007), a potência real através do elo CC do MD 2 VC, pode ser expressa por: A sobretensão ocasionada pela injeção de potência por parte da GD, que neste caso é da ordem de 0,6 MW, altera o perfil de tensão no PCC, fazendo com que as magnitudes dessas tensões estejam fora dos limites adequados estabelecidos pelo módulo número 8 da norma PRODIS ...
This paper proposes a modified structure for the Dynamic Direct Voltage Controller (D2VC), here defined as Modified Dynamic Direct Voltage Controller (MD2VC) for application in distribution grids. An advantage of this controller structure is the online voltage compensation in distribution systems using a three-phase Voltage Source Converter (VSC) for the shunt side of the controller instead of three single- phase VSCs as in the case of the original proposed configuration of D2VC. In this case, the series VSCs are connected to the shunt VSC by only a single dc link, unlike the original configuration where, for each of phase, the series VSC is connected to the respective shunt VSC by the respective dc link. In this work, a control algorithm for dc-link voltage based on pq theory is proposed, dismissing the use of the adaptive hysteresis band current single-phase control strategy. This configuration of D2VC has the number of switches for shunt converters and dc links reduced. Simulation results carried out in time domain using PSCAD/EMTDC are presented to show the effectiveness of the proposed control.
Modular multilevel converters with non-sinusoidal ac voltage output can reduce cost and volume in medium-voltage-connected electric vehicle battery charging applications. The use of full-bridge submodules in such converters enables single-stage ac/ac voltage conversion, allowing a medium-voltage grid to be directly connected to a medium-frequency isolation transformer. The application of a square wave voltage at the medium-frequency transformer's single-phase port enhances the converter's efficiency and power density in comparison to a sinusoidal voltage. This paper presents the analysis and modelling of a modular multilevel converter, comparing its operation with sinusoidal and square wave output voltages. A single control scheme for both output voltage waveforms is proposed for the three-phase and single-phase ac currents, circulating currents, and the energy stored in the submodule capacitors. The control strategy of the three-phase and single-phase port currents is verified through simulation and experiments using a scaled-down prototype, thereby validating its suitability for high-power bidirectional battery chargers.
The increasingly extensive use of non-linear loads, mostly including static power converters, in large industry, commercial, and domestic applications, as well as the spread of renewable energy sources in distribution-generated units, make the use of the most efficient power quality improvement systems a current concern. The use of active power filters proved to be the most advanced solution with the best compensation performance for harmonics, reactive power, and load unbalance. Thus, issues related to improving the power quality through active power filters are very topical and addressed by many researchers. This paper presents a topical review on the shunt active power filters in three-phase, three-wire systems. The power circuit and configurations of shunt active filtering systems are considered, including the multilevel topologies and use of advanced power semiconductor devices with lower switching losses and higher switching frequencies. Several compensation strategies, reference current generation methods, current control techniques, and DC-voltage control are pointed out and discussed. The direct power control method is also discussed. New advanced control methods that have better performance than conventional ones and gained attention in the recent literature are highlighted. The current state of renewable energy sources integration with shunt active power filters is analyzed. Concerns regarding the optimum placement and sizing of the active power filters in a given power network to reduce the investment costs are also presented. Trends and future developments are discussed at the end of this paper. For a rigorous substantiation, more than 250 publications on this topic, most of them very recent, constitute the basis of bibliographic references and can assist readers who are interested to explore the subject in greater detail.
The proposed control scheme is based on the least mean square (LMS) algorithm. The LMS algorithm is employed to estimate the necessary reference tracking current for the active power filter (APF). The proposed control scheme aims to enhance the dynamic response of the APF and minimize steady-state error. The weights of the LMS technique are calculated based on the estimated current of the APF. This algorithm is employed to minimize the error difference between the desired system output and its actual output, known as the mean square error (MSE). The estimated weights are utilized to modify the reference current weights, enabling them to follow the intended current of the APF. The online adaption of the LMS method involves the real-time adjustment of the weights. The performance of the LMS-based APF control is evaluated through a simulation study in MATLAB/Simulink, where it is compared with the conventional control method.
Power quality (PQ) problems such as voltage sags, swells, harmonics, and transient disturbances pose significant challenges to modern electrical distribution systems. In response, distribution static synchronous compensators (DSTATCOMs) have emerged as effective solutions to mitigate these PQ problems. This paper provides a comprehensive review of DSTATCOM applications in PQ improvement. Beginning with an explanation of the fundamental principle of DSTATCOM operation, it highlights their capability for harmonics, reactive power, and nonlinear load compensation. The review extensively discusses various DSTATCOM topologies and control strategies aimed at enhancing PQ. Additionally, the paper offers valuable insights into the efficacy of DSTATCOMs in enhancing PQ within electrical distribution networks, supported by real-time simulation results.
This work represents a renewable wind turbine-based energy system using a self-excited induction generator (SEIG) for electromechanical energy conversion. The system employs a robust variable step-size fractional least mean square (RVSS-FLMS) control technique to control the amplitude of the frequency and voltage at the common coupling point (PCC) and improve power quality, while a battery energy storage system (BESS) maintains power balance during wind fluctuations. The RVSS-FLMS approach outperforms the conventional least mean square (LMS) algorithm, showcasing a superior combination of reduced overshoot percentage and faster settling time. Additionally, the proposed control scheme demonstrates exceptional performance in both steady-state and dynamics when compared to existing methods. The proportional–integral (PI) gains have been optimized by the system using the whale optimization algorithm (WOA), which allows for adaptation to changing system parameters. The performance of WOA is compared with particle swarm optimization algorithm (PSO). The recommended work is evaluated with statistical tools like rise time, settling time, and percentage overshoot under dynamics. The simulation framework of the entire structure is developed in MATLAB software, and observations from simulation indicate the efficiency of the suggested control method for compensating the reactive power, neutral current, and harmonic current within the IEEE 519-2014 standard.
In response to the high performance requirements of pulse width modulation (PWM) converters in grid-connected power systems, H-Infinity (H∞) control has attracted significant research interest due to its robustness against parameter variations and external disturbances. In this work, an advanced robust H∞ control is proposed for a grid-connected three-phase PWM rectifier. A two-level control strategy is adopted, where cascaded H∞ controllers are designed to simultaneously regulate the DC bus voltage and input currents even under load disturbances and non-ideal grid conditions. As a result, unit power factor, stable DC bus voltage, and sinusoidal input currents with lower harmonics can be accurately achieved. The design methodology and stability of the proposed controller are verified through a comprehensive analysis. Simulation tests and experimental implementation on a dSPACE 1103 board demonstrate that the proposed control scheme can effectively enhance disturbance rejection performance under various operating conditions.
The paper describes a new version of the integral power theory in the α-β reference frame, which combines the advantages of the well-known instantaneous and integral power theories, and a shunt active filtering strategy based on it. From
p-q
power theory, it takes the α-β reference frame and separation of instantaneous powers on average and oscillating components. The three-phase current decomposition of integral Currents’ Physical Components power theory in the frequency domain was improved by dividing the unbalance power component into two orthogonal components with separate integral unbalance powers. The method is proposed for determining these two integral unbalance power components using double fundamental frequency functions. This method was practically implemented by performing real-time algebraic operations with the instantaneous power oscillating components and α-β voltage coordinates synchronized with a three-phase network. Based on this current decomposition in α-β reference frame, the compensation three-component signal for shunt active filtering is proposed, each component of which is proportional to a separate integral inactive power. However, to save voltage and current sensors and avoid the need for a voltage reference point, the input and output information for the shunt active filter control system is set in the two-wattmeter reference frame. The proposed control system successfully passed the verification by computer simulation with selective compensation of the inactive power components. The suggested compensation algorithm has shown its effectiveness and reliability for a linear and even a non-linear load.
Nowadays energy storage systems (ESS) are becoming an integral part of modern power systems (PES) and are used to solve a wide range of tasks. However, as the penetration level and power of ESS grows, their impact on the processes and operation modes of EPS is also increasing. Therefore, there is a need for using mathematical models of ESS, taking into account the specifics, various distinctive properties of each type and class of EPS, as part of the models of large-scale EPS. However, in foreign and national literature there are no review papers about detailed mathematical models of commonly use types and classes of SNE and simplifications used for them, which can be used to adequately simulate the large-scale EPS depending on the research tasks. Therefore, the first part of this paper considers the most promising types and classes of SNE used in the EPS, as well as the a-reas and tasks of their use. The principles of implementation of detailed mathematical models and structures of automatic control systems are described for the considered types and classes of SNE. In the second part of the paper the modern approaches of simplification of mathematical models of SNE, and analysis of consequences of such simplifications and areas of their application are given. Thus, the review paper consists of two parts and can help in choosing a mathematical model of the SNE for solving specific research tasks of analysis of their operation as a part of real EPS.
In this work, a novel SRF-PLL and DSOGI-PLL with the JAYA based optimization approach is presented herein for the control of a unified power quality conditioner (UPQC) system. The proposed UPQC system is linked to a three-phase distribution system that has nonlinear loads. Increased use of non-linear loads has contributed to harmonic effluence in power distribution systems and thus power quality issues have been elevated which is essential to be efficiently addressed. Since, the UPQC consists of a shunt and a series filters therefore, it is a most promising custom power device to mitigate power quality issues of instance voltage swell, sag, phase unbalance, current and voltage harmonics, DC-link voltage regulation, reactive power compensation etc. SRF-PLL and DSOGI-PLL perform grid synchronization and reference signal generation simultaneously in a single platform. Additionally, JAYA based optimization has been employed for determination of PI controller gains of both the controller. To validate the performance of UPQC and its controller, the complete UPQC system has been developed and fabricated in MATLAB/ Simulink as well as in hardware platform. The accuracy of simulation as well as hardware outcomes and their comparative power quality investigation is found to be satisfactory.
Today voltage source inverters (VSIs) operate with high switching frequencies (let us assume higher than 50 kHz) owing to the fast Si (Silicon) or SiC (Silicon Carbide) switching transistors. However, there are some applications, e.g., with slower switches (e.g., IGBT—Isolated Gate Bipolar Transistor) or when lower dynamic power losses are required when the switching frequency is low (let us assume about 10 kHz). The resonant frequency of the output filter is usually below 1 kHz. The measurements of Bode plots of the measurement traces of various microprocessor-controlled VSIs show that in this frequency range, the characteristics of these channels can be simply approximated through two or three switching periods delay. For the high switching frequency, it is not noticeable, but for the low frequency it can cause some oscillations in the output voltage. One of the solutions can be to use the predictor of the measured state variables based on the full-state Luenberger observer or the linear Kalman filter. Both solutions will be simulated in MATLAB/Simulink and the chosen one will be tested in the experimental VSI. The research aims to omit delays in the measurement channels for the low switching frequency by using the predictions for the measured state variables and finally increasing the gains of the controller to decrease the output voltage distortions.
Grid-connected converter should transmit power from distributed generation to the grid as much as possible, even under unbalanced conditions. However, under the necessary constraints of the point of common coupling (PCC) voltage support and current limitation, it is difficult for the converter to transmit more power to the grid. To fill this gap, this paper provides a mechanism analysis of the power transfer considering the zero-sequence voltage influence. Moreover, a new control strategy is proposed to improve the power transfer capability under unbalanced conditions. It is found that the phase difference between the PCC voltage and the grid voltage in the positive- and negative-sequence network is a key factor affecting power transfer capability, while playing an important role in the accurate calculation of the PCC voltage amplitude. Based on the key factor, we propose a new control strategy to improve the power transfer capability of the grid-connected converter. The proposed strategy can flexibly control the phase difference and transfer more power to the grid under the premise of current limiting and voltage support. Finally, the proposed voltage support strategy is validated with an experimental study.
A R T I C L E I N F O Keywords: Grid-forming inverter Droop control Electrical inertia Voltage-controlled inverter Voltage-forming inverter A B S T R A C T Currently, the transient stability of the grid is mainly ensured by the inertial behavior of its synchronous generators. The increase of renewable energy sources connected to the grid through grid following (GFL) inverters is severely affecting the inertia of the grid and its stability is beginning to be compromised. Moreover, in case of a large disturbance, these renewable energy sources disconnect from the grid by design, thus exacerbating the problem. The idea of mimicking the behavior of synchronous generators in an inverter and participating in the grid stability gave birth to the so-called grid forming (GFM) inverters. This implies a change in paradigm from current controlled sources (GFL) to voltage-controlled sources (GFM). Despite known stability issues in current controlled converters, a typical approach to GFM converters with LCL output filters is based on cascaded current and voltage control loops. An internal current loop controls the inverter's output currents and an external voltage loop controls the filter capacitors' voltages. The problem is that this solution is complex and is also marginally stable. Alternatively, in this paper we explore a direct voltage control, which is based on droop control. The proposed control's output is used for the direct control of the inverter's output voltage in amplitude and phase. A complete analysis is performed, and a method is proposed to determine the appropriate control parameters as well as the sizing of the inverter components. Finally, an experimental setup is presented and the effectiveness of the proposed method is shown in simulations as well as in real-life experiments.
Hysteresis current controllers (HCCs) are extensively used in low-frequency power inverters and active power filters. Very little is known about their strengths and weaknesses when applied at supraharmonic frequencies. The major concern regarding the use of HCCs is their variable and uncontrollable switching frequencies. This results in difficulties in filter design, high switching losses, and the possibility of resonance conditions with power system elements. In this article, investigations are conducted on the application of HCCs in a hybrid filter for a 6 kHz matrix converter (MC)-coupled supraharmonic load. The effects of the MC-coupled load and VSC switches on the HCC’s switching frequency are analyzed. A novel mathematical model for obtaining a fixed-frequency HCC is presented. The model is verified in open- and closed-loop HCC control configurations for a three-phase hybrid active power filter (HAPF). Fast Fourier transform (FFT) analysis of the supply current after the implementation of the novel HCC-HAPF showed 2.31% of the 50 Hz fundamental. The analysis is verified in a MATLAB/Simulink environment.
This article describes a control method called "direct power control" designed specifically for parallel active power filters. The purpose of this method is to attenuate harmonics in the supply current and offset reactive power problems. The main goal is to bring the active power and reactive power back to the reference values through hysteresis control. The output of the hysteresis controller is combined with the switching table to regulate active and reactive power in real time by determining the optimal switching configuration of the inverter. This study proposes a novel switching table design based on analyzing the impact of the inverter switching vector on the instantaneous reactive and active power derivatives. The goal is to reduce the number of commutations by eliminating zero vectors while maintaining the required DC bus voltage using anti-windup techniques based on PI controllers.
The composition and control of a new type of hybrid voltage-source converters are proposed based on diode rectifier units (DRUs) and full-bridge modular multilevel converter (FBMMC) to reduce the topside volume and weight of offshore wind farm (OWF) converter stations. The relationship between FBMMC DC voltage ratio and its modulation index is presented to obtain the FB-MMC active power capacity. The equilibrium point is analyzed using numerical calculations. Then, a controller derived from proportional-integral controller is adopted to control FB-MMC DC voltage and a reactive power controller is added to balance the reactive power of OWF, FB-MMC and DRU, by which the PCC voltage is established for wind turbine converters (WTCs) grid access. In addition, the DC short circuit fault and offshore short circuit fault recovery strategy is also presented. Finally, two specific case parameters are calculated and a simulation model in RSCAD is developed to validate the effectiveness and feasibility of the topology as well as the proposed control strategy of the hybrid voltage-source converter.
This paper presents a case study in which the influence of the 6-pulse thyristor-bridge input reactor size on the shunt active power filter (SAPF)’s work performance is investigated. The purpose of using an SAPF in the power system is in most cases for fundamental harmonic reactive power compensation, harmonics and asymmetry mitigation. The work efficiency of such a filter depends not only on the designed control system, interface filter and dc-link capacitor parameters, but also on the parameters of the electrical system in which it is connected. Therefore, it is necessary to study and know the power system (supplier and consumer sides) before its installation. For instance, in the electrical system with diode or thyristor-bridge as loads, the SAPF performance efficiency may not be satisfied due to the high rate of current change (di/dt) at the points of commutation notches. In this paper, the performed simulation and laboratory experiments show that for a better operating efficiency of the SAPF, the input reactor parameters should be selected based not only on the effective reduction in the inverter switching ripple or the control system demand, but also on the parameters of the load, such as the parameters of the diode or thyristor-bridge input reactor. Apart from the experimental demonstrations on how the input reactor size influences the SAPF work efficiency, the novelties in this paper are: the formulated recommendations on how to choose the SAPF input reactor parameters (the SAPF is more efficient in terms of harmonics, asymmetry and reactive power mitigation when the inductance of its input reactor (L-filter) is smaller than the one of the diode or thyristor-bridge input reactor); the proposed SAPF control system; the proposed expressions to compute the SAPF input reactor inductance, DC voltage and capacitor.
The increasing penetration of power electronics loads in smart grids inherently leads to severe concerns about power quality (PQ) disturbances. This chapter presents the principles of synthesizing control references for an active power filter (APF), which is placed in a smart grid comprising distortion loads, aiming at achieving PQ enhancement and compliance with standardized indexes. In addition, it is argued that the APF control system requires harmonic content identification to generate the targeted compensating currents. Thus, to achieve the disturbance recognition expected for synthesizing control references, harmonic analysis methods can be devised by automation tools and artificial intelligence (AI). For instance, it is demonstrated here that deep neural networks (DNN) can be used in the main pattern recognition stage, simplifying the harmonic content estimation process. The DNN-estimated harmonics are then directly used within the APF control system to compensate disturbances aiming at reducing the total harmonic distortion in a smart grid. Finally, this chapter also presents case studies using experimental load currents to depict the feasibility of the DNN-based method.
Since the future grid needs to provide sufficient electrical energy with high quality, it is envisaged that most of the used energy will be supplied by grid-connected voltage source converters (VSCs). The VSCs are used for connecting renewable energy source to the grid, e.g., wind and solar power. The grid-connected VSC considered in this paper is a three-phase three-wire full-bridge converter in which a capacitor is connected to its dc side, while its ac-side is connected to the grid with current control. When operating under unbalanced voltages at the point of common coupling, either due to the presence of unbalanced loads or due to a grid fault condition, a voltage ripple appears at the dc side. The interaction between the VSC dc- side voltage ripple and the VSC ac-side currents is the main focus of this study. In this paper, we analyze the interaction between the VSC dc-side voltage ripple and the VSC ac-side currents under unbalanced voltages. Furthermore, the proposed model is used to determine in which conditions the stability of the VSC ac-side currents can be guaranteed even in the presence of the dc-side voltage ripple. Experimental results confirm that the system remains stable, although with distorted currents due to the dc voltage ripple. Furthermore, it is also shown that the injection of negative sequence currents can decrease the current distortion.
In this chapter, a current control scheme for grid-connected voltage source converters during unsymmetrical faults is presented. The method that is being given is based on a modification of direct power control with space vector modulation (DPC-SVM), which makes it ideal for controlling the converter during asymmetrical failures. The presented results show that the control scheme can maintain the magnitude of the current within its rated value and keep the distortion in the current minimal; as well as minimize the oscillations in the power caused by the negative-sequence components of voltage and current.
In this contribution a new decomposition of sinusoidal three-phase currents is proposed. The main feature is that it leads to the compensation of non-active currents partly by elements without energy storage and partly by means of linear elements with energy storage (inductors and capacitors). The proposed decomposition is compared with existing procedures, such as those developed by Akagi-Nabae and by Czarnecki. The possible generalization of this concept to distorted voltages and currents is discussed.
San Diego Gas & Electric (SDG&E) initiated a major transmission system enhancement project involving a key 230/138 kV substation and the installation of a STATCOM-based dynamic reactive compensation system. This project is currently scheduled by SDG&E for an in-service date in October 2002. This paper gives an overview of the SDG&E transmission system project with emphasis on the STATCOM-based dynamic reactive compensation system. The major items with respect to the STATCOM system addressed in this paper include: power system requirements; STATCOM system description; STATCOM system layout; STATCOM construction and installation.
The possible calculation methodologies when designing a selective shunt active filter are presented. To accomplish selective extraction of harmonic sequences, the modulation-filter-demodulation technique is used. The fundamental equations of this method are based on pq theory. Its equivalence with the SRF (synchronous reference frame) method is shown. In order to validate the proposed calculation methods, measured currents from an arc furnace, showing high harmonic distortion, are used. The obtained results show the effectiveness of the proposed method for selective filtering of the undesired current harmonics in a controlled way.
This paper presents the calculation methods for the optimization of the different filtering blocks of a selective active filter in order to minimize the active filter inverter size, keeping the harmonic emissions at the limits stated by the applicable regulations. Since it may be necessary to comply with the regulations at a different (remote) place with respect to the active filter location, the optimization method has been extended to this case. In order to validate the simulations, measurements which were made at a real application-an arc furnace-were used. Finally, the simulated results obtained with a optimized remote hybrid selective filter were compared with those obtained when a shunt active filter is installed directly at the place where the harmonic emission regulations must be met. The comparison shows that optimized remote compensation is an alternative to be seriously considered because it allows the installation of the active filter at the source of harmonic injection (distorting load).
With the introduction and wide acceptance of gate-turn-off power devices (bipolars, power FETS, GTOs, etc. ), the switching behavior of converters has reached the point where further improvements in firing and switching networks bring only marginal benefits. Consequently, the research in the area of static converters has been shifting toward improving the process of power conversion through a combination of new circuit topologies and improved voltage and harmonic control PWM techniques. Although several recently proposed techniques are superior to the original sine PWM technique, little or conflicting data are available about their relative merits. A critical evaluation of these PWM techniques is presented, to provide a framework and guidelines for the selection of the best technique for a given application.
This paper presents a general control method that fully utilizes the inherent capability of AC-fed PWM converters to compensate for reactive and harmonic currents absorbed by other loads. For this purpose, suitable definitions of instantaneous active and reactive current and power terms are introduced. Simulated results demonstrate the capabilities of the proposed compensation method, which can also be implemented in existing systems, as only modifications of the control section are needed.
Different power theories are examined, with regard to their applicability in controlling dynamic filters for non-active power. Frequency-domain approaches and a range of time-domain approaches are considered, the latter being inherently more suitable for real-time control of dynamic filters. Finally, some detailed attention is devoted to a combination of the approaches by Fryze, Buchholz and Depenbrock. This FBD-approach leads to a general time-domain resolution of power components in a generalized m-wire system that can be used effectively in deriving control algorithms for dynamic filters of non-active power.
This work analyzes the resolution of the apparent power in three-phase systems defined by means of symmetrical components and using the product between an equivalent voltage [(V+)2+(V-)2+(V0)2]1/2 and an equivalent current [(I+)2 + (I-)2 + (I0)2]1/2. It was found that each component of such a defined apparent power S has a definite physical meaning. The results emphasize the need to separate the negative and zero sequence active power from the positive sequence power.
The classical definitions for the energetical determining factors in power systems are reviewed and a new model for the apparent power is suggested. — Based on the volt-ampere characteristic of the nonlinear load, an equivalent circuit, containing linear elements, can be determined. In this way, load-flow and harmonic compensation studies can be simplified.In der Arbeit werden zunchst die klassischen Definitionen errtert; darauf basierend wird ein neues Modell fr die Scheinleistung vorgeschlagen, das zu einer Ersatzschaltung mit linearen Elementen fhrt. Damit lassen sich z. B. Lastfluberechnungen und Kompensationsstudien vereinfachen.
The paper presents the generalized theory of electric power, which makes it possible to estimate the operation of complex electric circuits. Use has been made of the correlation analysis and new definitions have been found for various kinds of power occurring in such systems. It has been shown that both the active and the reactive power depend on the voltage-current correlation of the system. A new definition has been found for the distortion power, together with the condition which leads to its minimization.Der vorliegende Aufsatz befat sich mit der allgemeinen Theorie der elektrischen Leistung, die es ermglicht, die Arbeit komplexer elektrischer Stromkreise schtzungsweise zu ermitteln. Zu diesem Zweck hat man sich der Korrelationsanalyse bedient, und es konnten neue Definitionen fr verschiedenartige Leistungen, die in einem solchen System auftreten, gefunden werden. Es wurde nachgewiesen, da sowohl die Wirk- als auch die Blindleistung von der Korrelation zwischen Spannung und Stromstrke des gegebenen Systems abhngig ist. Fr die infolge von Verzerrungen auftretende Leistung ist einen neue Definition aufgestellt worden, und auch die Bedingungen ihrer Verminderung konnten ermittelt werden.
A closed-loop control system to reduce the reactive power required by electronic converters is proposed. The instantaneous reactive power which consists of both displacement of fundamental current and harmonic distortion current is measured and compensated by a reactive power source connected parallel between the power lines and the converter. A combination of a dc choke and a forced-commutated inverter is used for the reactive power source.
A robust control algorithm for the control of a static phase shifting or quadrature boost transformer has been developed and tested. This algorithm utilizes the inherent stabilizing ability of a phase shifter to rapidly return the power system to a stable operating point following severe transients. Under normal operating conditions, the controller minimizes power flow deviations and slip fluctuations due to random power demand changes. The control commands are generated using only local measurements (voltage and complex power at the transformer), specified power flow, and imprecise values of equivalent impedances of the power system.
A thyristor controlled quadrature voltage injection transformer is used to improve the transient stability performance of a generator connected, through a transmission circuit, to a power-system. The paper discusses the effect of alternative control strategies and shows that not only can first swing maximum angle be reduced, but the subsequent transients can be damped.
Definitions of power components are reviewed, and their
disadvantages are analysed. New definitions of active, reactive,
distortion and apparent power are discussed. It is attempted to find a
clear physical interpretation, and to formulate this for each power
component in systems with sinusoidal and/or nonsinusoidal voltage and
current. Formulas for the straightforward calculation of each power
component are obtained. It is shown that distortion power, consist of
both active and reactive terms, and apparent power in a nonsinusoidal
system must be represented as a many-dimensional vector. Examples are
given to illustrate the application of the developed theory
This paper presents the characteristics of two gate turn-off (GTO)
thyristor voltage-sourced inverter-based series power flow control
devices, namely the series power flow controller (SPFC) and the unified
power flow controller (UPFC). These devices represent series extensions
of the STATCON, an inverter-based shunt device developed under a
tailored collaboration by EPRI, TVA and the Westinghouse Science and
Technology Center, which will soon be placed in service on the TVA 161
kV transmission system for transmission voltage control. Operation of
the SPFC and UPFC is illustrated through the use of easily-constructed
circle diagrams on the P-Q plane. The circle diagrams provide the
transmission planning engineer with a simple means to assess the
performance of these devices on the transmission system. A concluding
example illustrates that the UPFC provides a level of power flow control
which is unattainable with more conventional devices
It might be expected that the meaning of the apparent power S, a
quantity of innumerable everyday applications for almost a century, is
well understood. It occurs, however, that this meaning is still a matter
of discussion and some interpretations hard to accept are published.
Also it is suggested in some papers published recently that only
oscillations of the instantaneous power may cause an increase of the
apparent power S, which is not true. Misinterpretations that refer to
fundamental notions such as powers could be particularly harmful for
electrical engineering and should be eliminated as much as possible.
Therefore, this paper shows that the apparent power does not have the
physical meaning suggested recently. Also it shows that load unbalance
in three-phase power systems does not cause any oscillation of the
instantaneous power. The conclusion that load unbalance causes
oscillations of the instantaneous power is a consequence of a
substantial misinterpretation of this quantity in three-phase power
systems
Damping power system resonances by passive filters can introduce
additional unwanted resonances which, under difficult circumstances, can
even lead to switching off of these filters. Active damping using modern
power electronics and controls is presented in this paper as a solution
so as to improve network operation efficiently. Theoretically obtained
results are verified by a lab model
A solid-state, pulse-width-modulated (PWM) phase shifter, based on
gate-turn-off )GTO) thyristors or other valves with force commutation
capabilities, is described. Besides serving the phase-shifter function,
it offers regulated control over three independent quantities: the real
power passing through it and the VAR (volt-ampere reactive) on both
sides to which it is connected. The power transferred can be
bidirectional, and the VArs can be leading or lagging. Digital
simulations show that the PWM phase-shifter reported here is capable of
regulated control of bidirectional real power flow and independent
regulated control of positive or negative VArs on both sides of the
phase shifter
The influence of harmonics on commonly used three-phase watthour
and kVA demand meters was studied using a computer-controlled
three-phase test system capable of generating nonsinusoidal voltages and
currents. A description of the three-phase test system and results of
preliminary tests of several revenue meters are presented. The
performance of the tested meters is compared with the response of
time-division and thermal reference meters for different harmonic
conditions, primarily field-recorded data. Errors up to 2% were observed
during the testing of energy meters and up to 35% for kVA demand meters
The authors present a fictitious power theory derived specifically
for real time fictitious power compensator control. Fictitious power is
defined as that component of apparent (loading) power which does not
contribute to active power. The original instantaneous power theory is
reviewed and evaluated against the original classic theory of active
power and active current. The two theories are integrated. The revised
instantaneous power theory is illustrated with simulated and
experimental waveforms and the advantages over previous theories are
pointed out
Recent advances in power electronics have meant that many loads
now draw a distorted current from the power supply. For the same real
power consumed, the apparent power for the distorted load is greater
than the equivalent sinusoidal load. A real-time active filter
optimization algorithm has been implemented in a TMS320C30 DSP, with the
aim of maximizing the monetary saving from active filtering by reducing
the apparent power consumed at the point of supply. As the basis for
this optimization a savings function which takes into account active
filter efficiency, the cost of energy, and the supply and load current
distortion before and after filtering, has been derived. A simplex
optimization technique, which is able to find the optimum operating
point even under varying load conditions, is used to maximize these
energy savings
This paper describes a control method with a combined filter
system which senses load current, source current, and line voltage to
create reference signals for an active filter. The transfer function of
the active filter is identified and is used for the control system
design. It is shown that the source current feedback is most effective
in suppressing the harmonic-enlarging effects due to parallel resonance
and the harmonic current generated by source harmonic voltages. A small
setup controlled by a DSP was built, and the validity of the proposed
method was demonstrated by experimental results
The definitions of power are reviewed to establish a method for
fictitious power measurement and to derive fictitious power compensation
criteria in power systems with nonsinusoidal currents and voltages. A
time-domain definition of power, using correlation techniques, is
proposed. This leads to the proposal of a network parameter. A
combination of digital and analog signal-processing techniques is
proposed in the measurement and analysis of the components of power. The
results of simulated and practical power measurements, the latter on an
experimental electronic pulsewidth-modulated power converter, used for
fictitious power compensation are given
A New Control Strategy for a Unified Power Flow Controller
- Yu Q.
- Round S.D.
- Norum L.E.
- Undeland T.M.