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 load side voltage disturbances can be effectively mitigated by connecting a dynamic voltage restorer (DVR), a series compensating device. A DVR is realised by a voltage source inverter with DC storage device and a series injection transformer. Rating and design issues of an injection transformer are of prime concern for the proper voltage compensation using DVR. Voltage underrating of the transformer may lead to its saturation, whereas, overrating increases the cost and size of the DVR. The voltage applied to the primary winding of the transformer is a combination of several components of different frequencies. Considering above aspects, rating and design issues are presented in this paper. A novel method is proposed to find the voltage rating of the transformer as a function of the fundamental frequency. Furthermore, the inrush current due to saturation is avoided during transient period. K factor method is used to account for the effects of current harmonics in the transformer. A PSCAD model is used...

Rating and design issues of DVR injection transformer

Dynamic Voltage Restorer (DVR) restores the distribution system load voltage to a nominal balanced sinusoidal voltage, when the source voltage has distortions, sag/swell and unbalances. DVR has to inject required amount of Volt-Amperes (VA) into the system in order to maintain a nominal balanced sinusoidal voltage at the load. A new control technique is applied to compensate the sag and harmonics with phase jumps in the source voltages. Keeping the cost effectiveness of DVR, it is desirable to have a minimum VA rating of the DVR, for a given system without compromising compensation capability. Hence, a methodology has been proposed in this work to minimize VA rating of DVR. The optimal angle at which DVR voltage has to be injected in series to the line impedance so as to have minimum VA rating of DVR as well as the removal of phase jumps in the three-phases is computed by Particle Swarm Optimization (PSO) technique. The present method was able to compensate voltage harmonics and sags with phase jumps by keeping the DVR voltage and power ratings minimum, effectively. The proposed method has been validated through detailed simulation studies.

Compensation of voltage sags and harmonics with phase-jumps through DVR with minimum VA rating using Particle Swarm Optimization

In this paper, a new methodology is proposed to mitigate the unbalanced voltage sag with phase jumps by Unified Power Quality Conditioner (UPQC). UPQC is used to mitigate both voltage and current power quality (PQ) problems. During the process of mitigation, UPQC is supposed to inject real and reactive power into the system to mitigate current (shunt) and voltage (series) power quality (PQ) problems. As per the sensitive load concerns, deep and long duration sags are more vulnerable than shallow and short duration sags. To resolve these issues a new methodology is proposed with optimal Volt-Ampere (VA) loading on UPQC to mitigate deep and long duration unbalanced sag with phase jumps. Particle Swarm Optimization (PSO) is utilized as a tool for evaluating the optimal VA loading of UPQC with constraints like magnitude of injected voltage from Series active power filter, Total Harmonic Distortion (THD) of source current and terminal voltage. The proposed methodology ensures optimal VA loading on UPQC without compromising mitigation capability of the UPQC. The proposed method has been validated through detailed simulation studies.

Optimal VA loading of UPQC during mitigation of unbalanced voltage sags with phase jumps in three-phase four-wire distribution system

This paper discusses the power quality survey conducted in the distribution system of Indian Institute of Technology Madras, Chennai, India. Individual power quality parameters measured from the survey are analyzed and presented in detail. To assess the power quality, measured data are compared with various power quality standards including IEEE 519-1992 standard for the measured voltage and current harmonics. The information obtained from this survey will be useful in improving the quality of power in the Institute.

Power quality survey in a technological institute

Inter-area oscillations in power systems needs to be monitored and accurate estimation of frequency and damping of the oscillations in real time is vital as they provide considerable insight into system stability. Zolotarev polynomial based filter bank (ZPBFB) is proposed for decomposing the PMU signals into monocomponents. Modal frequency and damping are obtained from the decomposed monocomponent signals through eigen realization algorithm (ERA). The salient property of ZPBFB lies in signal decomposition with sum of decomposed signals produced by filter bank, without oversampling, is an exact replica of input signal with delay. A narrow bandwidth of 0.1 Hz is achieved in the frequency range of 0 to 1 Hz with ZPBFB. The robustness of the proposed method to noise is demonstrated using Monte Carlo simulations. The proposed ZPBFB and cosine modulated filter bank (CMFB) are implemented on two-area test system and 16-machine, 68-bus system and the performances are compared. The efficacy of the proposed method is also demonstrated on three real time signals recorded by wide area frequency measurement system (WAFMS) at 3 locations in India on November 30, 2011.

B. Kalyan Kumar

Papers

Rating and design issues of DVR injection transformer

Compensation of voltage sags and harmonics with phase-jumps through DVR with minimum VA rating using Particle Swarm Optimization

Optimal VA loading of UPQC during mitigation of unbalanced voltage sags with phase jumps in three-phase four-wire distribution system

Power quality survey in a technological institute

Identification of Inter-Area Oscillations Using Zolotarev Polynomial Based Filter Bank With Eigen Realization Algorithm