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A unified power quality conditioner (UPQC) for simultaneous voltage and current compensation
Abstract
The paper discusses the topology and control of a unified power quality conditioner (UPQC) that can be used simultaneously in voltage or current control mode in a power distribution system. In the voltage control mode, the UPQC can force the voltage of a distribution bus to be balanced sinusoids. At the same time it can also perform load compensation resulting in the drawing of balanced sinusoidal currents from the distribution system bus in the current control mode. Both these objectives are achieved irrespective of unbalance and harmonic distortions in load currents or source voltages. We shall discuss a suitable UPQC structure that allows the tracking of reference current and voltage generated to meet the objective stated above. The reference generation scheme along with the switching control scheme is presented in detail. Extensive results of digital computer simulation studies are presented to validate the proposed structure and control.
... It is customary to mitigate the voltage unbalance by using custom power devices in the power grid. The mitigation process starts with unbalance extraction/tracking and then a control signal is generated to operate these custom power devices such as a dynamic voltage restorer (DVR) [13], distribution static compensator (DSTATCOM) [14], and unified power quality conditioner (UPQC) [15]. These publications focus on the mitigation of the negative-sequence components using these custom power devices. ...
... The magnitude and angle of any-sequence voltage are calculated as, (15) Eventually, the formulas in (14) and (15) are used to estimate the positive-sequence and negativesequence voltages at the loads side (PCC) to complete the operation of the control scheme in Fig. 2. ...
... The loads in the microgrid are a parallel combination for two balanced loads of , which are estimated using the developed formulation in (12)(13)(14)(15). The positive-sequence factor is displayed in Fig. 3, where it shows almost 100% and the negative-sequence factor is almost 1%. ...
... Some devices, such as passive, active, or hybrid power filters and operation strategies, have been developed for the local correction of power-quality problems [40][41][42][43]. Since the performance of SAPFs is more dependent on the current control method, many currentcontrol schemes have been proposed in the research [44][45][46]. ...
... Some devices, such as passive, active, or hybrid power filters and operation strategies, have been developed for the local correction of power-quality problems [40][41][42][43]. Since the performance of SAPFs is more dependent on the current control method, many current-control schemes have been proposed in the research [44][45][46]. ...
Active power filters (APFs) are used to mitigate the harmonics generated by nonlinear loads in distribution networks. Therefore, due to the increase of nonlinear loads in power systems, it is necessary to reduce current harmonics. One typical method is utilizing Shunt Active Power Filters (SAPFs). This paper proposes an outstanding controller to improve the performance of the three-phase 25-kVA SAPF. This controller can reduce the current total harmonic distortion (THD), and is called fractional order PI-fractional order PD (FOPI-FOPD) cascade controller. In this study, another qualified controller was applied, called multistage fractional order PID controller, to show the superiority of the FOPI-FOPD cascade controller to the multistage FOPID controller. Both controllers were designed based on a non-dominated sorting genetic algorithm (NSGA-II). The obtained results demonstrate that the steady-state response and transient characteristics achieved by the FO (PI + PD) cascade controller are superior to the ones obtained by the multistage FOPID controller. The proposed controller was able to significantly reduce the source current THD to less than 2%, which is about a 52% reduction compared to the previous work in the introduction. Finally, the studied SAPF system with the proposed cascade controller was developed in the hardware-In-the Loop (HiL) simulation for real-time examinations.
... The main function of the electric power distribution is to provide power to individual consumer's premises which is done with much low voltage level. Distribution of electrical power is usually done by distribution network such as distribution substation, primary distribution feeder, distribution transformer, distributor and service mains [17]. Distribution system can be classified in terms of voltage of primary distribution voltage (11kv), secondary distribution (33kv) and tertiary distribution voltages (415v) between phase or 220/240 between phases and neutral. ...
... 17 shows an unequal distribution of power-line with respect to voltage drop with capacity combination of 500KVA, 400KW and 300KVAR respectively. ...
... There exists a common DC link capacitor between the series and shunt filters. At PCC, whenever there is fault, a series VSI can able to control and maintain the voltage harmonics with in the limits [5][6][7][8][9][10]. ...
... The voltage sections in the direct and quadrature rotating axis are given in Eqs. (4) and (5). ...
A unified power quality conditioner (UPQC) is a combination of shunt and series converter used to mitigate various power quality issues. In this work the shunt and series converters are designed with reduced number of switches. The new UPQC with reduced switches is controlled using SRF based Carrier Double Zero Sequence Signal Modulation (CDZSSM) technique to mitigate the various power quality issues like voltage sag, current ripples and Total Harmonic Distortion in voltage and current waveforms. This reduced switch UPQC with CDZSSM control inherits all the merits of the conventional UPQC system, but the proposed UPQC system has better utilization of DC link voltage and moreover the voltage stresses across the switches are reduced. The results obtained from simulation and hardware of the reduced switch UPQC are compared and presented.
... Inverter placed in series monitors and try to compensate sag and/or swell in voltage at the point of common coupling. Current harmonics are controlled by shunt active filter [12] [13]. The general block diagram for operation of power quality conditioner with shunt and series filters is shown in figure 1: ...
... Many techniques are used for controller reference generation such as: synchronous reference frame theory, instantaneous power theory, Fourier Transformation, PI Controller and many more. Here, we are using digital PI Controller with Park's transformation (dq0 transformation) [8], [10], [13], [14]. Low pass filter, filters out the higher harmonics components and extracts the fundamental DC component of the input signal to generate reference signal. ...
... power flows through the series inverter is:(11) The expressions for the active and reactive power flow through the series inverter are as:= sin ( 1 2 ) = cos ( 1 3 ) The magnitude of is specified and the and are to be obtained from Eq. (10) and(11), respectively. The battery rating, in this case, is equal to the value of . ...
... power flows through the series inverter is:(11) The expressions for the active and reactive power flow through the series inverter are as:= sin ( 1 2 ) = cos ( 1 3 ) The magnitude of is specified and the and are to be obtained from Eq. (10) and(11), respectively. The battery rating, in this case, is equal to the value of . ...
... Both UPFC and UPQC consist of shunt and series inverters. There is a considerably large volume of literature on UPQC [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and a state-of-art review can be obtained in [2]. ...
... There are different research directions on UPQC. These are: (i) development of different types of series compensation techniques, for example UPQC-P [2,4], UPQC-Q [4], UPQC-S [5], UPQC-VAmin etc., (ii) development of topological configuration for UPQC, for example, 3-phase 4 wire structure [7], interline UPQC [8] in which the two inverters are placed in different feeders of a network, UPQC without the common DC link or OPEN UPQC [9] etc. (iii) development of new control strategy for UPQC, for example phase angle control [10], simultaneous voltage and current compensation scheme [11], particle swarm optimization based feedback controller [12] etc., (iv) minimization of the cost/VA rating for UPQC [6,13], and (v) investigation on the combined operation with distributed generation units [14,15] etc. ...
... A promising solution (Hossain et al. 2018) for mitigating power quality disturbances such as sag, swell, and flicker (Zhao 2016;Edomah 2009;Chen et al. 2013) can be a unified power quality conditioner (Honrubia-Escribano et al. 2015;Khadkikar 2011;Kesler and Ozdemir 2010;Ghosh and Ledwich 2001;Graovac et al. 2007;Khadkikar et al. 2006). A unified power quality conditioner is a complete configuration of hybrid filters, which is identified as a multifunctional power conditioner utilized to compensate for different voltage disturbances ). ...
... Table 1 shows the yearly financial loss due to power interruption and different power quality issues for various locations of USA [23]. The causes of power quality issues are categorized in different segments as shown in Fig. 2. The classification of various power quality problems as per IEEE-1159 standard is given in Fig. 3 [24][25][26]. Electricity discharge lamp, arc welding, arc furnace, integrated circuit, large induction motor and electronics devices are the sources of problems associated with power quality. ...
... All VSCs consist of a three-phase converter (Ghosh et al.,2001) with a commutation reactor and high-pass output filter as shown in Fig. 3. To avert the flow of switching harmonics into the power supply the commutation reactor (L f ) and high pass output filter (R f , C f ) is connected. ...
... The significance of the power quality issues in the distribution system is the uncharacteristic behaviour of end equipment's, upsurge of loss, reduced efficacy, electromagnetic nosiness with the neighbouring, and abbreviate the lifetime of the organization [4,5]. Subsequently, that to overcome these PQ (power quality) issues modern power systems implement some compensation devices like dynamic voltage restorer (DVR) [6], distribution static synchronous compensator (D-STATCOM) [7], unified power flow controller (UPFC) [8] and unified power quality conditioner (UPQC) [9]. Yahiya et al. discussed the power quality enhancement with the aid of various methods, which reveals the enriched performance of UPQC [10]. ...
A unified power quality conditioner (UPQC) plays a crucial role in the Power quality improvement of a power system. In this paper, a reduced switch multilevel inverter is with artificial neural network, soft computing technique control is proposed for UPQC. This proposed topology is employed for the mitigation of various power quality issues such as voltage sag, voltage swell, power factor, harmonics, and restoration time of voltage compensation. To show the enriched performance of the proposed topology comparative analysis is made with other two topologies of UPQC such as Conventional UPQC and UPQC using cascaded H bridge (CHB) five-level Inverter. All configurations are analysed using Matlab with variable nonlinear loads to analyse the performance during the conditions mentioned above.
... UPQC open-loop operation does not assure internal stability and suitable performance. Therefore, the UPQC model uses linear averaged approximations to obtain a closed loop based on two decoupled control systems, as shown in [6]. However, there are coupling effects between the power converters and the grid [7] that must be considered in the system model to prevent undesired behavior in transient events such as sags, swells, and load changes. ...
Performance degradation is, in general, regarded as a power quality problem. One solution to recover grid performance is through the application of a unified power quality conditioner (UPQC). Although these devices are multi-input/multi-output (MIMO) systems, the most common control strategies consist of two decoupled controllers, which neglect the coupling effects and add uncertainty to the system. For this reason, this paper proposes a multivariable resonant observer-based control strategy of a UPQC system. This method includes all significant coupling effects between this system and the grid. This strategy results in a stability-based compensator, which differs from recently proposed strategies that are based on signal calculation and cannot assure closed-loop stability. In addition, this paper introduces a simplified controller tuning strategy based on optimal conventional methods without losing closed-loop performance. It implies that the controller can be easily tuned, despite the complexity of the MIMO dynamic model. The UPQC with the resonant observer is verified on an experimental setup for a single-phase system, obtaining three relevant results for power quality improvement: (1) harmonics compensation tested with a total harmonic distortion limit of 5%; (2) sags and swells mitigation; and (3) power factor correction, achieving a unitary value on the grid side.
... 23 Instantaneous power angle (δ) determination[136].A. Ghosh and G. Ledwich have discussed the operation and control of a UPQC that can be used simultaneously in voltage or current control mode in a power distribution system[137]. The series component of the UPQC called DVR forces the voltage of a distribution bus to be balanced sinusoids and free of distortion in the voltage control mode. ...
... Tolbert et al. [14] proposed a multilevel diode clamped controller-based universal power conditioner, wherein the authors use multilevel PWM to increase switch utilisation. Ghosh et al. [15] presented the simultaneous voltage and current control of UPQC. In the voltage control mode, the voltage of a distribution bus is balanced. ...
Integrated photovoltaic (PV) distribution systems voltage stability is of great significance in supporting all connected equipment smooth functioning in the distribution network. Voltage profile maintenance is one of the challenging tasks in PV integration. To maintain a constant voltage profile to a sensitive load of 22 kVA is the main idea of this study. A single‐phase PV‐integrated distribution system is selected for the study. The novelty is that differential inverters are used for dynamic voltage restorer and distribution static synchronous compensator of the unified power quality conditioner (UPQC). Active power decoupling facility is the main advantage using the differential inverter. The research work objective is to synchronise a 10 kW solar PV system to the distribution system using this new UPQC. The research work discusses and derives the most suitable control strategy for the UPQC with battery energy storage system. A 20 kVA UPQC is designed for the PV integration and to increase voltage stability of the distribution system. The frequency, voltage and reactance/resistance ratio of the distribution system is assumed to be constant. A prototype model of differential UPQC is developed. Experimental and simulation results validate the main objective.
... Power Quality problem are majorly classified as harmonics generation, reactive power usage in line increasing, poor power factor, distortions in voltage waveform. [3], [4]. ...
... The two-phase instantaneous currents i α , i β and i p , i q can be obtained as below [21,22]. ...
The significant increase in electronic devices has resulted in serious harmonic pollutions in electricity grids. In addition, due to the resonance of the system capacitance and inductance, the harmonic current may be amplified dramatically when it goes through the transmission line which is harmful to the normal operation of electrical equipment. To suppress the voltage and current harmonics resonance, many control strategies of active power filter (APF) are proposed. Nevertheless, these strategies cannot attenuate the amplified harmonic voltage and current due to resonance. In this paper, the harmonic propagation characteristics are investigated on a long transmission line and a new control strategy called VI-APF based on current-controlled and voltage-controlled current sources connected in parallel is presented. According to the simulation results, the proposed control strategy can suppress the total harmonic distortion to a low level. Finally, the effectiveness of VI-APF is demonstrated through the simulation on the IEEE 33-bus distribution system.
... The unified power quality conditioner (UPQC) is one of the effective CPD and its topology consists of the integration of two active power filters connected in a back-to-back configuration to a common DC-link bus [4]. The UPQC combines both the operations of load current and supply voltage imperfections with quick response and high reliability at the same time [5][6][7][8]. The fuel cell integrated UPQC (FCI-UPQC) is the combination of series and shunt connected active power filters with a fuel cell. ...
Electrical and electronic devices, when exposed to one or more power quality problems, are prone to failure. This study aims to enhance the quality of power in three-phase four-wire distribution grid using fuel cell integrated unified power quality conditioner (FCI-UPQC). The proposed FCI-UPQC has a four-leg converter on the shunt side and three-leg converter on the series side. A combination of a synchronous reference frame and instantaneous reactive power theories is utilised to generate reference signals of the FCI-UPQC. Also, this study proposes an adaptive neuro-fuzzy inference system (ANFIS) controller to maintain the DC-link voltage in the FCI-UPQC. The ANFIS controller is designed like a Sugeno fuzzy architecture and trained offline using data from the proportional–integral controller. The obtained results proved that the proposed FCI-UPQC compensated power quality problems such as voltage sag, swell, harmonics, neutral current, source current imbalance in the three-phase four-wire distribution grid. The presence of fuel cell in this work makes more effectiveness of the proposed system by providing real power support during supply interruption on the grid side.
... In Ref. [10], a new topology of UPQC based on current sourced converters is developed, in which shunt inverter is placed on the left side of series inverter and these two inverters share a common DC reactor for the power exchange. In some of these works, different control schemes for UPQC are developed, for example phase angle control (PAC) [11], simultaneous voltage and current compensation scheme [12], design of a feedback controller using particle swarm optimization (PSO) [13] etc. In Ref. [14], the impact of fixed and variable PAC approaches on the VA loadings of series and shunt inverters of UPQC are studied under voltage sag and swell conditions. ...
This paper presents a comparative study among different models of unified power quality conditioner (UPQC) designed to improve the energy efficiency of the radial distribution networks. An UPQC consists of two voltage-sourced inverters, i.e., series and shunt inverters. In connected UPQC topology, these two are connected with a DC link. In open UPQC (UPQC-O), these two are not physically connected. But, they share a common communication link. Four models are formulated. They are: (1) UPQC without real power injection, (2) UPQC with real power injection, (3) UPQC-O without real power injection, and (4) UPQC-O with real power injection. A planning optimization model is formulated to determine the optimal locations for the series and shunt inverters for these four models. The objective function consists of the investment and maintenance cost of the inverters and battery, and the cost of energy loss. The energy loss comprises of line losses, inverter losses, and transformer loss. The planning optimization is constrained to ensure a desired power quality level of the network. Particle swarm optimization is chosen as the solution tool. The results show that the placement of UPQC-O provides higher energy efficiency as compared to the connected UPQC topology.
... Similarly, 3P3W filters are divided into passive-passive [72], passive-active [73], and active-active systems [67]. Finally, 3P4W filters are further classified as passive-passive, passive-active, and active-active systems [67,112]. Operating a three-phase power supply in a single-phase load system results in imbalanced neutral current and reactive power load problems. ...
This study summarizes an analytical review on the comparison of three-phase static compensator (STATCOM) and active power filter (APF) inverter topologies and their control schemes using industrial standards and advanced high-power configurations. Transformerless and reduced switch count topologies are the leading technologies in power electronics that aim to reduce system cost and offer the additional benefits of small volumetric size, lightweight and compact structure, and high reliability. A detailed comparison of the topologies, control strategies and implementation structures of grid-connected high-power converters is presented. However, reducing the number of power semiconductor devices, sensors, and control circuits requires complex control strategies. This study focuses on different topological devices, namely, passive filters, shunt and hybrid filters, and STATCOMs, which are typically used for power quality improvement. Additionally, appropriate control schemes, such as sinusoidal pulse width modulation (SPWM) and space vector PWM techniques, are selected. According to recent developments in shunt APF/STATCOM inverters, simulation and experimental results prove the effectiveness of APF/STATCOM systems for harmonic mitigation based on the defined limit in IEEE-519.
Voltage stability in integrated photovoltaic (PV) distribution systems is crucial for enabling the efficient operation of all linked equipment in the distribution network. One of the most challenging aspects of PV integration is keeping voltage profiles stable. The primary focus is maintaining a constant 22 kVA load voltage profile. In the end, we settled on a PV integrated distribution system with a single phase. Combining a differential inverter with a dynamic voltage restorer (DVR) and a distribution static synchronous compensator (D-Statcom) is a first for the power conditioning sector (UPQC). The purpose of this innovative UPQC system is to employ a fuzzy controller to successfully connect a 10 kW solar PV system to the grid. Based on these results, the optimal battery-powered UPQC control strategy may be selected. As a means of increasing PV integration and ensuring voltage stability in the distribution network, a 20 kVA UPQC was constructed. Total harmonic dispersion may be minimised by maintaining a steady distribution system frequency, voltage, and reactance/resistance ratio.
While the unified power quality conditioner based on modular multilevel converter (MMC-UPQC) can be used for recovering power quality of voltage and current in high voltage grids, it is difficult to manage the power quality when the grid voltage imbalance is large. In this paper, a passivity based control (PBC) combined with sliding mode control (SMC) is proposed for MMC-UPQC to improve the power quality under the unbalance of grid voltage in power systems. First, according to the structure of MMC-UPQC, the equivalent mathematical model is presented for unbalanced power grids. Second, the detection quantity is separated without phase-locked loop using a method of positive and negative sequence separation. Furthermore, a passive sliding mode control (PSMC) strategy is designed and applied to a multi-level and high voltage power quality compensation system. The proposed controller can improve the control accuracy of system parameters, response speed, and compensation effectiveness. Finally, the MATLAB/Simulink simulation and the real time laboratory (RT-LAB) based hardware-in-the-loop (HIL) experimental results show that the proposed PSMC strategy can compensate voltage and current rapidly and accurately, and the controller has strong robustness against system parameter changes.
The development of a Solid State Transformer that incorporates a DC-DC multiport
converter to integrate both photovoltaic power generation and battery energy storage is
presented in this dissertation. The concept of a Solid-State Transformer (SST) is a subject of
vivid attention and extensive research in the recent decade, motivated by their potential impact
extending well beyond 50 Hz transformers for power distributions. The solid-state
transformers result in a significant reduction in size and weight due to the use of a
high-frequency transformer. With the controllable SST architecture, it is possible to provide
additional functions such as grid integration of DC microgrids and maintaining the power
quality of the distribution network. The AC-DC stage is implemented with a
pulse-width-modulated single-phase rectifier. A unified gyrator-based average model is
developed for a general multi-active-bridge converter controlled through phase-shift
modulation. An SST uses power electronic devices and a high-frequency transformer to
achieve isolation and voltage conversion from one level to another. Several SST topologies
have been proposed by different researchers. This paper also presents an overview of SST
topologies enabling features that provide desired additional functionalities for future energy
systems.
Most of the researchers have investigated the behavior of the Unified Power-Quality Conditioner (UPQC) that is present in a secondary power distribution system. Generally, there exist no investigations of UPQC in a sub-transmission system for enhancing the power quality in the primary power distribution substations. The sub-transmission system is identical to the primary power distribution system. It helps a vast geographical area and huge energy is distributed at high voltage levels. This paper intends to improvise the power quality in distribution system using a novel controller-based Multi-Converter Unified Power-Quality Conditioner (MC-UPQC). The fuzzy theory with SRF is used for implementing the control strategies of MC-UPQC. The main objective of the fuzzy controlled-MC-UPQC is to minimize the total harmonic distortion. The efficiency of the suggested fuzzy controlled-MC-UPQC is estimated by comparing over the conventional models.KeywordsFuzzy controllerMulti-converter-UPQCPower quality improvementDistribution systemTotal harmonic distortion
Harmonics pollution is very dangerous in medium power applications. Generally, they are produced in the system due to the presence of nonlinear loads. This article presents a novel load voltage and current harmonic compensation approach using hybrid UPQC. The simulations are carried on MATLAB/ Simulink platform. The output results present the proposed hybrid UPQC compensates for the load current harmonics effectively. The load voltage harmonics are reduced from 11.65% to 1.53% and the current harmonics are reduced from 30.97% to 2.24%, respectively.KeywordsInductive UPQCShunt active power filterInductive transformerHarmonic compensationSeries active filter
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This article has been withdrawn as part of the withdrawal of the Proceedings of the International Conference on Emerging Trends in Materials Science, Technology and Engineering (ICMSTE2K21). Subsequent to acceptance of these Proceedings papers by the responsible Guest Editors, Dr S. Sakthivel, Dr S. Karthikeyan and Dr I. A. Palani, several serious concerns arose regarding the integrity and veracity of the conference organisation and peer-review process. After a thorough investigation, the peer-review process was confirmed to fall beneath the high standards expected by Materials Today: Proceedings.
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This paper discusses the power quality issues for distributed generation systems based on renewable energy sources, such as solar and wind energy. A thorough discussion about the power quality issues is conducted here. This paper starts with the power quality issues, followed by discussions of basic standards. A comprehensive study of power quality in power systems, including the systems with dc and renewable sources is done in this paper. Power quality monitoring techniques and possible solutions of the power quality issues for the power systems are elaborately studied. Then, we analyze the methods of mitigation of these problems using custom power devices, such as D-STATCOM, UPQC, UPS, TVSS, DVR, etc., for micro grid systems. For renewable energy systems, STATCOM can be a potential choice due to its several advantages, whereas spinning reserve can enhance the power quality in traditional systems. At Last, we study the power quality in dc systems. Simpler arrangement and higher reliability are two main advantages of the dc systems though it faces other power quality issues, such as instability and poor detection of faults.
Among the issues of accurate power distribution, stability improvement, and harmonic suppression in micro-grid, each has been well studied as an individual, and most of the strategies about these issues aim at one inverter-based micro-grid, hence there is a need to establish a model to achieve these functions as a whole, aiming at a multi-inverter-based micro-grid. This paper proposes a comprehensive strategy which achieves this goal successfully; since the output voltage and frequency of micro-grid all consist of fundamental and harmonic components, the strategy contains two parts accordingly. On one hand, a fundamental control strategy is proposed upon the conventional droop control. The virtual impedance is introduced to solve the problem of accurate allocation of reactive power between inverters. Meanwhile, a secondary power balance controller is added to improve the stability of voltage and frequency while considering the aggravating problem of stability because of introducing virtual impedance. On the other hand, the fractional frequency harmonic control strategy is proposed. It can solve the influence of nonlinear loads, micro-grid inverters, and the distribution network on output voltage of inverters, which is focused on eliminating specific harmonics caused by the nonlinear loads, micro-grid converters, and the distribution network so that the power quality of micro-grid can be improved effectively. Finally, small signal analysis is used to analyze the stability of the multi-converter parallel system after introducing the whole control strategy. The simulation results show that the strategy proposed in this paper has a great performance on distributing reactive power, regulating and stabilizing output voltage of inverters and frequency, eliminating harmonic components, and improving the power quality of multi-inverter-based micro-grid.
This paper presents a novel way of generating the reference currents for an active filter and/or a static compensator. A compensator structure is proposed which is capable of balancing an unbalanced delta-connected load that may also draw harmonic currents. In addition to balancing the load, the supply side power factor is also made unity. The theory of instantaneous symmetrical components is used here to obtain three phase reference currents that are to be tracked by the compensator in a hysteresis band control scheme. The paper demonstrates the feasibility of such as scheme through simulation studies.
This paper deals with unified power quality conditioners (UPQCs), which aim at the integration of series-active and shunt-active power filters. The main purpose of a UPQC is to compensate for voltage flicker/imbalance, reactive power, negative-sequence current and harmonics. In other words, the UPQC has the capability of improving power quality at the point of installation on power distribution systems or industrial power systems. This paper discusses the control strategy of the UPQC, with a focus on the how of instantaneous active and reactive powers inside the UPQC. Experimental results obtained from a laboratory model of 20 kVA, along with a theoretical analysis, are shown to verify the viability and effectiveness of the UPQC
This paper deals with “unified power quality
conditioners” (UPQCs) which aim to integrate series active and
shunt active filters. The main purpose of a UPQC is to compensate for
voltage flicker/imbalance, reactive power, negative sequence current and
harmonics. In other words, the UPQC has the capability of improving
power quality at the point of installation on power distribution systems
or industrial power systems. This paper discusses the control strategy
of the UPQC, with the focus on the flow of instantaneous active and
reactive power inside the UPQC. Some interesting experimental results
obtained from a laboratory model of 20 kVA, along with theoretical
analyses, are shown to verify the viability and effectiveness of the
UPQC
The author outlines the technical and economic factors which
characterise the uniform, all solid-state power-flow controller approach
for real-time controlled, flexible AC transmission systems. The unified
power-flow controller in its general form can provide simultaneous,
real-time control of all basic power system parameters (transmission
voltage, impedance, and phase angle), or any combinations thereof,
determining the transmitted power. The parameters selected for control
can be changed without hardware alterations, e.g. the function of the
controller can be changed from that of a phase-shifter to that of a
series line compensator, or vice versa, with or without additional
terminal voltage regulation and shunt VAr compensation, to adapt to
particular short term contingencies or future system modifications
Time-optimal control laws are known to be bang-bang, and well
suited to relay or power electronic controllers. Closed-form solutions
for the time-optimal control switching are obtained only for a limited
set of low-order systems. The control approach in the paper is to
determine the control value for a linear quadratic regulator, and then
project this value onto the closest available switching control vector.
The paper uses Lyapunov functions to show convergence of this projection
approach, provided that the requested LQR control signal is limited in
magnitude. A sequence of LQR solutions is used to cover the full-state
space, and is found to give a control performance close to time optimal.
When the system is open-loop unstable, convergence regions are
determined from these Lyapunov functions. The region of guaranteed
convergence is shown, in the limit, to be close to the full region of
possible controllability. The sequence of LQR solutions with control
projections is found to be a well defined control design for arbitrary
order linear multi-input multi-output systems, leading to good switching
control performance
Transient Analysis of Alternating-Current Machin-ery
- W A Lyon
W.A. Lyon, Transient Analysis of Alternating-Current Machin-ery, Wiley, New York, 1954 Chapter 2..
A new STATCOM topology to compensate loads containing a.c. and d.c. components, Pro-ceedings of IEEE-PES Winter Meeting
- M K Mishra
- A Ghosh
- A Joshi
M.K. Mishra, A. Ghosh, A. Joshi, A new STATCOM topology to compensate loads containing a.c. and d.c. components, Pro-ceedings of IEEE-PES Winter Meeting, Singapore, 2000.