Mitigation of Power Quality Problems Using Custom Power Devices: A Review

Electrical power quality (EPQ) in distribution systems is a critical issue for commercial, industrial and residential applications. The new concept of advanced power electronic based Custom Power Devices (CPDs) mainly distributed static synchronous compensator (D-STATCOM), dynamic voltage restorer (DVR) and unified power quality conditioner (UPQC) have been developed due to lacking the performance of traditional compensating devices to minimize power quality disturbances. This paper presents a comprehensive review on D-STATCOM, DVR and UPQC to solve the electrical power quality problems of the distribution networks. This is intended to present a broad overview of the various possible DSTATCOM, DVR and UPQC configurations for single-phase (two wire) and three-phase (three-wire and four-wire) networks and control strategies for the compensation of various power quality disturbances. Apart from this, comprehensive explanation, comparison, and discussion on D-STATCOM, DVR, and UPQC are presented. This paper is aimed to explore a broad prospective on the status of D-STATCOMs, DVRs, and UPQCs to researchers, engineers and the community dealing with the power quality enhancement. A classified list of some latest research publications on the topic is also appended for a quick reference

Performances of Six-leg DSTATCOM Topology under Various SRF Algorithms

Six-leg DSTATCOM can be employed for improving the superiority of power in a distribution system. DSTATCOM is the most valuable current harmonic reduction device because of its excellent compliance in active situations. The DSTATCOM has a shunt voltage source inverter (VSI) attached to the common coupling point of power system via the interfacing inductor. In its controllers, the various SRF algorithms such as Conventional SRF, DCC based SRF and ICC based SRF have been adopted due to its easy execution aspects. These algorithms create balanced and sinusoidal supply current, compensate the reactive power, improving the power factor near unity on common coupling point and mitigate harmonic in the supply current. The reference signal for PWM generator is generated using SRF algorithms. A 3-phase 4-wire power system with rectified RC/RL load has been taken for the detailed simulation study. The performances of DSTATCOM topology have been compared under conventional SRF, DCC based SRF and ICC based SRF control strategies in terms of power quality improvement.&nbsp

Power quality improvement based on hybrid coordinated design of renewable energy sources for DC link channel DSTATCOM

This paper presents a comprehensive analysis of power quality for static synchronous compensator on the distribution power system (DSTATCOM) when a different types of energy sources are used to supply the dc link channel of DSTATCOM. These types of power supplies have a different effect on the compensation of DSTATCOM due to operation nature of these sources. The dynamic response of the DSTATCOM has been investigated that produced by individual and hybrid energy sources to evaluate the influence of these sources in terms of time response, compensation process and reduce the harmonics of current for source. Three cases have been considered in this study. First the photovoltaic (PV) cells alone second the battery storage alone and third a hybrid coordinated design between (PV cells with battery storage) is used. A boost Dc-Dc circuit has been connected to a photovoltaic cell with Maximum Power Point Tracking (MPPT) while a Dc-Dc buck-boost circuit is used with a battery. High coordination between PV and battery circuits in the hybrid system is used in order to improve the performance. A synchronous reference frame (SRF) with unit vector has been used to control the STATCOM circuit. The simulation results show that the hybrid design has the superiority response compared to the individual sources

Performance Analysis of Photovoltaic Fed Distributed Static Compensator for Power Quality Improvement

Owing to rising demand for electricity, shortage of fossil fuels, reliability issues, high transmission and distribution losses, presently many countries are looking forward to integrate the renewable energy sources into existing electricity grid. This kind of distributed generation provides power at a location close to the residential or commercial consumers with low transmission and distribution costs. Among other micro sources, solar photovoltaic (PV) systems are penetrating rapidly due to its ability to provide necessary dc voltage and decreasing capital cost. On the other hand, the distribution systems are confronting serious power quality issues because of various nonlinear loads and impromptu expansion. The power quality issues incorporate harmonic currents, high reactive power burden, and load unbalance and so on. The custom power device widely used to improve these power quality issues is the distributed static compensator (DSTATCOM). For continuous and effective compensation of power quality issues in a grid connected solar photovoltaic distribution system, the solar inverters are designed to operate as a DSTATCOM thus by increasing the efficiency and reducing the cost of the system. The solar inverters are interfaced with grid through an L-type or LCL-type ac passive filters. Due to the voltage drop across these passive filters a high amount of voltage is maintained across the dc-link of the solar inverter so that the power can flow from PV source to grid and an effective compensation can be achieved. So in the thesis a new topology has been proposed for PV-DSTATCOM to reduce the dc-link voltage which inherently reduces the cost and rating of the solar inverter. The new LCLC-type PV-DSTATCOM is implemented both in simulation and hardware for extensive study. From the obtained results, the LCLC-type PV-DSTATCOM found to be more effective than L-type and LCL-type PV-DSTATCOM. Selection of proper reference compensation current extraction scheme plays the most crucial role in DSTATCOM performance. This thesis describes three time-domain schemes viz. Instantaneous active and reactive power (p-q), modified p-q, and IcosΦ schemes. The objective is to bring down the source current THD below 5%, to satisfy the IEEE-519 Standard recommendations on harmonic limits. Comparative evaluation shows that, IcosΦ scheme is the best PV-DSTATCOM control scheme irrespective of supply and load conditions. In the view of the fact that the filtering parameters of the PV-DSTATCOM and gains of the PI controller are designed using a linearized mathematical model of the system. Such a design may not yield satisfactory results under changing operating conditions due to the complex, nonlinear and time-varying nature of power system networks. To overcome this, evolutionary algorithms have been adopted and an algorithm-specific control parameter independent optimization tool (JAYA) is proposed. The JAYA optimization algorithm overcomes the drawbacks of both grenade explosion method (GEM) and teaching learning based optimization (TLBO), and accelerate the convergence of optimization problem. Extensive simulation studies and real-time investigations are performed for comparative assessment of proposed implementation of GEM, TLBO and JAYA optimization on PV-DSTATCOM. This validates that, the PV-DSTATCOM employing JAYA offers superior harmonic compensation compared to other alternatives, by lowering down the source current THD to drastically small values. Another indispensable aspect of PV-DSTATCOM is that due to parameter variation and nonlinearity present in the system, the reference current generated by the reference compensation current extraction scheme get altered for a changing operating conditions. So a sliding mode controller (SMC) based p-q theory is proposed in the dissertation to reduce these effects. To validate the efficacy of the implemented sliding mode controller for the power quality improvement, the performance of the proposed system with both linear and non-linear controller are observed and compared by taking total harmonic distortion as performance index. From the obtained simulation and experimentation results it is concluded that the SMC based LCLC-type PV-DSTATCOM performs better in all critical operating conditions

Design Simulation of Improved Power Quality Conditioner System for Enhancement of Power Quality

The increased usage of power-sensitive electronic devices has prompted interest in power conditioning solutions, which is no surprise. As a result, some type of compensation must be supplied if power output remains below the standards' prescribed limitations. The UPQC (Unified Power Quality Controller) is one of numerous AC Transmission System families that can control voltage, impedance, and phase angle among other factors (FACTS). This study focuses on modern UPFC systems that have increased power quality efficiency to help utilities reduce voltage concerns. One of the FACTS controls for lowering stress sales effects is a unified power quality conditioner (UPQC). The quadrature voltage is specified using the UPQC series compensator. As a result, the compensator series never utilizes active power in a continuous scenario. As mentioned in the approach, a low power rating compensator injects voltage to remedy the system's power quality problem. The voltage is decreased and the power factor is raised when the fluid logic controller is used in conjunction with traditional UPQC. Furthermore, the load factor has been improved. The circuit is then imitated in MATLAB / SIMULINK using a fluctuating logo controller

Application of DSTATCOM for surplus power circulation in MV and LV distribution networks with single-phase distributed energy resources

Single-phase distributed energy resources (DERs), such as rooftop photovoltaic arrays, are usually installed based on the need and affordability of clients without any regard to the power demand of the connected phase of a three-phase system. It might so happen that the power generation in a particular phase is more than its load demand. This may cause a reverse power flow in a particular phase, especially in a three-phase, four-wire distribution system. If now the load demand in the other two phases is more than their respective generations, then these two phases will see a forward power flow, while there will be a reverse power flow in the third phase. This will create severe unbalance in the upstream network. In this paper, a distribution static compensator (DSTATCOM) is used to circulate the excess generation from one phase to the others such that a set of balanced currents flow from or into the upstream network. Two different topologies of DSTATCOM are proposed in this paper for the low and medium voltage feeders. Two different power circulation strategies are developed for this purpose. Furthermore, a suitable feedback scheme is developed for each topology for power converter control. The performance of the proposed topologies and the control schemes for the DSTATCOM is evaluated through computer simulation studies using PSCAD/EMTDC

Unbalanced Variable Nonlinear Load Compensation Using Multiple Shunt Active Filters

The proposed scheme has considered a three-phase four-wire system, which experienced sag and swell in source voltage for a certain period while feeding an unbalanced and variable non-linear load. The load has unequal resistive and reactive elements in the three phases, forming the unbalanced component. A three-phase silicon controlled rectifier converter with adjustable firing angle connected to the load has formed the variable non-linear component. This has been considered, so as to simulate the unbalanced and variable non-linear  nature of loads in real-time power system. The trends in the total harmonic distortion variation were obtained for the proposed system under power factor correction and voltage regulation mode operation when the load-side converter firing angles of 30°, 60° and 90° were considered using MATLAB/SIMULINK software. Three pulse-width-modulation methods, namely, sinusoidal pulse-width-modulation, space vector modulation and hysteresis pulse-width-modulation have been used to generate pulses for the voltage source converter of the shunt active filter based on the reference currents generated using synchronous reference frame theory.  It has been demonstrated in the proposed paper that power factor correction, voltage regulation, better harmonic reduction and hence load compensation are obtained simultaneously by using two SAFs

Mitigation of power quality issues due to high penetration of renewable energy sources in electric grid systems using three-phase APF/STATCOM technologies: a review.

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

Power quality improvement in low voltage distribution network utilizing improved unified power quality conditioner.

Doctoral Degree. University of KwaZulu-Natal, Durban.The upgrade of the power system, network, and as it attained some complexity level, the voltage related problems and power loss has become frequently pronounced. The power quality challenges load at extreme end of the feeder like voltage sag and swell, and power loss at load centre due to peak load as not received adequate attention. Therefore, this research proposes a Power Angle Control PAC approach for enhancing voltage profile and mitigating voltage sag, voltage swell, and reduced power loss in low voltage radial distribution system (RDS). The amelioration of voltage sag, voltage swell, weak voltage profile, and power loss with a capable power electronics-based power controller device known as Improve Unified Power Quality Conditioner I-UPQC was conceived. Also, the same controller was optimally implemented using hybrid of genetic algorithm and improved particle swarm optimization GA-IPSO in RDS to mitigate the voltage issues, and power loss experienced at peak loading. A new control design-model of Power Angle Control (PAC) of the UPQC has been designed and established using direct, quadrature, and zero components dq0 and proportional integral (PI) controller method. The simulation was implemented in MATLAB/Simulink environment. The results obtained at steady-state condition and when the new I-UPQC was connected show that series inverter can participate actively in ameliorating in the process of mitigating sag and swell by maintaining a PAC of 25% improvement. It was observed that power loss reduced from 1.7% to 1.5% and the feeder is within the standard limit of ±5%. Furthermore, the interconnection of I-UPQC with photovoltaic solar power through the DC link shows a better voltage profile while the load voltage within the allowable range of ±5% all through the disturbance and power loss reduction is 1.3%. Lastly, results obtained by optimal allocation of I-UPQC in RDS using analytical and GA-IPSO show that reactive power injection improved the voltage related issues from 0.952 to 0.9989 p.u., and power loss was further reduced to 1.2% from 3.4%. Also, the minimum bus voltage profile, voltage sag, and power loss are within statutory limits of ±5 % and less than 2 %, respectively. The major contributions of this research are the reduction of sag impact and power loss on the sensitive load in RDS feeder.Publications on page iii