This paper presents a comprehensive review on the unified power quality conditioner (UPQC) to enhance the electric power quality at distribution levels. This is intended to present a broad overview on the different possible UPQC system configurations for single-phase (two-wire) and three-phase (three-wire and four-wire) networks, different compensation approaches, and recent developments in the field. It is noticed that several researchers have used different names for the UPQC based on the unique function, task, application, or topology under consideration. Therefore, an acronymic list is developed and presented to highlight the distinguishing feature offered by a particular UPQC. In all 12 acronyms are listed, namely, UPQC-D, UPQC-DG, UPQC-I, UPQC-L, UPQC-MC, UPQC-MD, UPQC-ML, UPQC-P, UPQC-Q, UPQC-R, UPQC-S, and UPQC-VA. More than 150 papers on the topic are rigorously studied and meticulously classified to form these acronyms and are discussed in the paper.

Enhancing Electric Power Quality Using UPQC: A Comprehensive Overview

This paper introduces a new concept of optimal utilization of a unified power quality conditioner (UPQC). The series inverter of UPQC is controlled to perform simultaneous 1) voltage sag/swell compensation and 2) load reactive power sharing with the shunt inverter. The active power control approach is used to compensate voltage sag/swell and is integrated with theory of power angle control (PAC) of UPQC to coordinate the load reactive power between the two inverters. Since the series inverter simultaneously delivers active and reactive powers, this concept is named as UPQC-S (S for complex power). A detailed mathematical analysis, to extend the PAC approach for UPQC-S, is presented in this paper. MATLAB/SIMULINK-based simulation results are discussed to support the developed concept. Finally, the proposed concept is validated with a digital signal processor-based experimental study.

UPQC-S: A Novel Concept of Simultaneous Voltage Sag/Swell and Load Reactive Power Compensations Utilizing Series Inverter of UPQC

This paper presents a novel philosophy to compensate the load-reactive power demand through a three-phase unified power quality conditioner (UPQC). Most of the UPQC-based applications show the dependency on shunt inverter for load-reactive power compensation, whereas the series inverter is always looked as controlled voltage source to handle all voltage-related problems. This paper proposes a new functionality of UPQC in which both the shunt and series APFs supply the load-reactive power demand. This feature not only helps to share the load-reactive power demand, but also helps to reduce the shunt APF rating, and hence, the overall cost of UPQC. This results in better utilization of the existing series inverter. The theory and complete mathematical analysis termed as ldquopower angle control (PAC)rdquo is presented. The simulation results based on MATLAB/Simulink are discussed in detail to support the concept developed in the paper. The proposed approach is also validated through experimental study.

A New Control Philosophy for a Unified Power Quality Conditioner (UPQC) to Coordinate Load-Reactive Power Demand Between Shunt and Series Inverters

The paper discusses load compensation using a distribution static compensator (DSTATCOM). It is assumed that the DSTATCOM is associated with a load that is remote from the supply. It is shown that the operation of a DSTATCOM assuming that it is connected to a stiff source in such situations will result in distortions in source current and voltage at the point of common coupling. To avoid this, the DSTATCOM is connected in parallel with a filter capacitor that allows the high frequency component of the current to pass. However, this generates control issues in tracking, as standard controls such as a hysteresis control are not suitable in these circumstances. This paper proposes a new switching control scheme and demonstrates its suitability for this problem. It also proposes a scheme in which the fundamental sequence components of a three-phase signal can be computed from its samples. The overall performance of the proposed scheme is verified using digital computer simulation studies.

Load compensating DSTATCOM in weak AC systems

Generation of electricity using wind power has received considerable attention worldwide in recent years. In order to investigate the impacts of the integration of wind farm into utilities' network various windmill models have been developed. One such impact is related to the critical clearing time (CCT) of the wind power based embedded generators (WPBEG). The work in this paper has shown that oversimplification of the modeling of windmill mechanical drive train could introduce significant error in the value of the CCT that defines the stability limit of an integrated wind farm. This paper also reports investigation into the factors that influence the dynamic behavior of the WPBEGs following network fault conditions. It is shown that wind farm CCT can be affected by various factors contributed by the host network. Results obtained from several case studies are presented and discussed. This investigation is conducted on a simulated grid-connected wind farm using EMTP.

Windmill Modeling Consideration and Factors Influencing the Stability of a Grid-Connected Wind Power Based Embedded Generator

The unified power quality conditioner (UPQC) is a custom power device, which mitigates voltage and current-related PQ issues in the power distribution systems. In this paper, a UPQC topology for applications with non-stiff source is proposed. The proposed topology enables UPQC to have a reduced dc-link voltage without compromising its compensation capability. This proposed topology also helps to match the dc-link voltage requirement of the shunt and series active filters of the UPQC. The topology uses a capacitor in series with the interfacing inductor of the shunt active filter, and the system neutral is connected to the negative terminal of the dc-link voltage to avoid the requirement of the fourth leg in the voltage source inverter (VSI) of the shunt active filter. The average switching frequency of the switches in the VSI also reduces, consequently the switching losses in the inverters reduce. Detailed design aspects of the series capacitor and VSI parameters have been discussed in the paper. A simulation study of the proposed topology has been carried out using PSCAD simulator, and the results are presented. Experimental studies are carried out on three-phase UPQC prototype to verify the proposed topology.

A Modified Three-Phase Four-Wire UPQC Topology With Reduced DC-Link Voltage Rating

The unified power-quality conditioner (UPQC) is used to provide balanced and sinusoidal source currents and load voltages under unbalanced and distorted three-phase supply voltages and load currents in a power distribution network. In this paper, a particle swarm optimization-based feedback controller is designed for UPQC. This feedback controller has optimal performance in various operating conditions and is robust to parametric uncertainties when compared to the conventional feedback controllers, such as the linear quadratic regulator. The proposed method is implemented on a distribution system and detailed simulation and experimental results are presented.

Particle Swarm Optimization-Based Feedback Controller for Unified Power-Quality Conditioner

The Unified Power Quality Conditioner (UPQC) is a versatile device which could function as series active filter and shunt active filter. UPQC can simultaneously fulfill different objectives like, maintaining a balanced sinusoidal (harmonic free) nominal voltage at the load bus, eliminating harmonics in the source currents, load balancing and power factor correction. Keeping the cost effectiveness of UPQC, it is desirable to have a minimum VA loading of the UPQC, for a given system without compromising compensation capability. Hence, a methodology has been proposed in this work to minimize VA loading of UPQC considering the effects of source voltage and load current distortion. The series active filter of UPQC can be made to inject voltages in such a way that a minimum VA loading of UPQC is possible. The optimal angle at which series voltage has to be injected so as to have minimum VA loading of UPQC is computed by Particle Swarm Optimization (PSO) technique. The proposed method has been validated through detailed simulation studies. The VA loading without optimization and with optimization has been compared.

Minimization of VA loading of Unified Power Quality Conditioner (UPQC)

This paper proposes a modified four leg Distribution Static Compensator (DSTATCOM) topology for compensation of unbalanced and nonlinear loads in three phase four wire system. This proposed modified topology uses a capacitor connected in series with the interface inductor at the point of common coupling (PCC). This Modified topology requires a lower value of dc link voltage (V dcref ) across the dc storage capacitor of voltage source inverter (VSI) for compensation of source currents, when compared with the basic four leg DSTATCOM topology. The reference filter currents are generated using instantaneous symmetrical component theory and are tracked using hysteresis current control technique. A detailed simulation study to compare the performances of basic and modified topologies are carried out using PSCAD 4.2.1.

B. Kalyan Kumar

Papers

A Modified Three-Phase Four-Wire UPQC Topology With Reduced DC-Link Voltage Rating

Particle Swarm Optimization-Based Feedback Controller for Unified Power-Quality Conditioner

Minimization of VA loading of Unified Power Quality Conditioner (UPQC)

Modified four leg DSTATCOM topology for compensation of unbalanced and nonlinear loads in three phase four wire system

Improving fault ride-through capability of wind generation system using DVR