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

Review on power quality solution technology

This paper presents a comprehensive study of various possible solutions for power quality improvement in common applications and supply system. This includes improved power quality converters (IPQC), multi-pulse converters, active compensation, passive compensation and their hybrid configurations. Various configurations and topologies of custom power devices such as DSTATCOM (Distribution Static Compensator), DVR (Dynamic Voltage Restorer) and UPQC (Unified Power Quality Compensator) are also described in detail. Main applications of these devices are for reactive power compensation, harmonic elimination, voltage sag/swell mitigation, voltage regulation, load balancing, neutral current reduction etc. Many such cases of power quality problems have been taken up and suitable solutions have been identified for those cases. As an example, a model of DSTATCOM is developed and its performance is presented for a distribution system feeding nonlinear loads

Power Angle Control Scheme for Integration of UPQC in Grid Connected PV System

The quality of electric power is greatly affected by the proliferation of non-linear loads in electrical energy processing applications like switched mode power supplies, electric motor drives, battery chargers, etc., The custom power devices like UPQC has gained more importance in power quality arena as it gives the best solution for all power quality issues. UPQC is the combination of both shunt and series active power filters connected through a common DC link capacitor. The shunt active power filter is the most corrective measure to remove the current related problems, power factor improvement by supplying reactive power and regulates DC link voltage. The series APF acts as controlled voltage source and corrects voltage related problems, like sag or swell, flickering, harmonics, etc.,. As a combination of both of these, UPQC improves service reliability. In the present work, shunt inverter control is based on modified active- reactive (p-q) power theory, uses High selectivity filter (HSF) for reference current generation. The series APF uses Power Angle Control (PAC) scheme for compensating sag/swell, interruption and voltage related problems along with sharing a part of load reactive power demand with shunt APF and thus ease its loading and makes the utilization of UPQC to be optimal. The topology uses three phase three leg inverters for both shunt APF and series APF. The gating signals were generated using Hysteresis controller. The output of High step-Up DC-DC Converter is used to work as DC voltage source for both APFs. The input voltage for the converter is provided by Photo Voltaic array incorporated with P&O MPPT technique. The use of high step-up DC-DC converter is for high voltage gain with better efficiency. The present topology avoids the PLL in shunt active power filter. The simulation results are presented to show the effectiveness of the three phase, three-wire PV-UPQC and here obtained an acceptable THD for source current and kept load voltag

Control strategy for selective compensation of power quality problems through three-phase four-wire UPQC

This paper presents a novel control strategy for selective compensation of power quality (PQ) problems, depending upon the limited rating of voltage source inverters (VSIs), through a unified power quality conditioner (UPQC) in a three-phase four-wire distribution system. The UPQC is realized by the integration of series and shunt active power filters (APFs) sharing a common dc bus capacitor. The shunt APF is realized using a three-phase, four-leg voltage source inverter (VSI), while a three-leg VSI is employed for the series APF of the three-phase four-wire UPQC. The proposed control scheme for the shunt APF, decomposes the load current into harmonic components generated by consumer and distorted utility. In addition to this, the positive and negative sequence fundamental frequency active components, the reactive components and harmonic components of load currents are decomposed in synchronous reference frame (SRF). The control scheme of the shunt APF performs with priority based schemes, which respects the limited rating of the VSI. For voltage harmonic mitigation, a control scheme based on SRF theory is employed for the series APF of the UPQC. The performance of the proposed control scheme of the UPQC is validated through simulations using MATLAB software with its Simulink and Power System Block set toolboxes

Power quality enhancement in secondary electric power distr[i]bution networks using dynamic voltage restorer.

Doctoral Degree. University of KwaZulu-Natal, Durban.This research study investigates and proposes an effective and efficient method for improving voltage profile and mitigating unbalance voltage, voltage variation disturbances in rural and urban secondary distribution networks. It also proffers solutions for improving the performance of future distribution networks in order to increase the optimum functioning, security and quality of electricity supply to end users, thus making the power grid smarter. This study involves the compensation of power quality disturbance in balanced and unbalanced, short and long distribution networks. The mitigation of result of this voltage variation, poor voltage profile and voltage unbalance with an effective power electronics based custom power controller known as Dynamic Voltage Restorer (DVR) conceived. DVR is usually connected between the source voltage and customer load. An innovative new design-model of the DVR has been proposed and developed using a dq0 controller and proportional integral (PI) controller method. Model simulation was carried out using MATLAB/Simulink in Sim Power System tool box. An analysis of the results obtained when the new DVR is not connected to and tested on LV networks shows that the voltage profile, percentage voltage deviation and percentage voltage unbalance for 0.5 km for balanced and unbalanced distribution networks are within standards and acceptable limits, hence, the voltages are admissible for customers’ use. It was further established that the voltage profile, percentage voltage unbalance, voltage drop and percentage voltage deviation for distribution networks of 0.8 km to 5 km range from the beginning to the end of the feeder are less than the statutory voltage limits of -5%, 2 %, 5 % and ± 5 % respectively, hence, voltages are inadmissible for customers’ use. Others results obtained when DVR was connected recognized that for distribution feeder lengths of 0.5 km to 5 km range for balanced and unbalanced, short and long distribution networks the voltage profile, voltage variation, voltage drop and percentage voltage unbalance are within statutory voltage limits of 0.95 p.u and 1.05 p.u, -5 %, and less than 2 % respectively. Based on this investigation, and in order to achieve efficient, reliable and cost-effective techniques for improving voltage profiles, decreasing voltage variations and reducing voltage unbalances, the new DVR model is recommended for enhancing optimal performances of secondary distribution networks

Online Control of Modular Active Power Line Conditioner to Improve Performance of Smart Grid

This thesis is explored the detrimental effects of nonlinear loads in distribution systems and investigated the performances of shunt FACTS devices to overcome these problems with the following main contribution: APLC is an advanced shunt active filter which can mitigate the fundamental voltage harmonic of entire network and limit the THDv and individual harmonic distortion of the entire network below 5% and 3%, respectively, as recommended by most standards such as the IEEE-519

Control System Design, Analysis, and Simulation of a Photovoltaic Inverter for Unbalanced Load Compensation in a Microgrid

This thesis presents a control scheme for a single-stage three-phase Photovoltaic (PV) converter with negative sequence load current compensation. In this thesis a dual virtual impedance active damping technique for an LCL filter is proposed to address the issue of LCL filter resonance. Both inverter-side current and the capacitor current are used in the feedback loop. Using both signals provides higher DC rejection than using capacitor current alone. The proposed active damping scheme results in a faster transient response and higher damping ratio than can be obtained using inverter-side current alone. The feedback gains can be calculated to achieve a specified damping level. A method of determining the gains of the Proportional and Resonant current controller based on frequency response characteristics is presented. For a specified set of gain and phase margins, the controller gains can be calculated explicitly. Furthermore, a modification is proposed to prevent windup in the resonator. A numerically compensated Half-Cycle Discrete Fourier Transform (HCDFT) method is developed to calculate the negative sequence component of the load current. The numerical compensation allows the HCDFT to accurately estimate the fundamental component of the load current under off-nominal frequency conditions. The proposed HCDFT method is shown to have a quick settling time that is comparable to that obtained with conventional sequence compensation techniques as well as immunity to harmonics in the input signal. The effect of unbalance compensation on the PV power output depending on the irradiance and the operational region on the power-voltage curve is examined. Analysis of the DC link voltage ripple shows the region of operation on the P-V curve affects the amplitude of the DC link voltage ripple during negative sequence compensation. The proposed control scheme is validated by simulation in the Matlab/Simulink® environment. The proposed control scheme is tested in the presence of excessive current imbalance, unbalanced feeder impedances, and non-linear loads. The results have shown that the proposed control scheme can improve power quality in a hybrid PV-diesel microgrid by reducing both voltage and current imbalance while simultaneously converting real power from a PV array

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

A Grid Connected Wind Energy System’s Power Quality Improvement By Using D-Statcom

Now a day’s one of the Main issue is Power Quality. The modern device performance is very sensitive with the power supply quality and makes it’s an important aspect. Power Quality problem occurs when the voltage, current and frequency become nonstandard and end use equipment gets damage. The harmonics, compensation of reactive power and power factor is a main problem dealt here. According to the guideline specified in International Electro-technical Commission standard, IEC-61400, by the measurements and norms specified can determine the performance there by power quality of a wind turbine. The active power, reactive power, voltage changes, flicker, harmonics, electrical behavior of switching operation are the concerning power quality measurements by the effect of the wind turbine in the grid system. These quantities are measured based on national/international guidelines. The power electronic switching devices such as Flexible AC Transmission System (FACTS) have been developed; introduction of customs power devices and the technology of emerging branch provide a modern control capability of power system. The paper study describes how the wind turbine installation creates power quality problem in grid system. In the proposed system in order to solve the power quality issues a battery energy storage system (BESS) connected by STATIC COMPENSATOR (STATCOM) at a common point coupling. The real power source under fluctuating wind power is sustained by the integrated   battery energy storage. For the power quality improvement of a grid connected wind energy generation system a STATCOM control scheme is simulated using MATLAB /SIMULINK in power system block set. Finally the proposed scheme is applied to a balanced linear load, unbalanced liner load, balanced non linear load and unbalanced non linear load