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

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

Power system reconfiguration in a radial distribution network for reducing losses and to improve voltage profile using modified plant growth simulation algorithm with Distributed Generation (DG)

Grid integrated renewable DG systems: A review of power quality challenges and state-of-the-art mitigation techniques

This paper reports the development of a laboratory prototype of a fully digital DSP-controlled 12-kVA unified power quality conditioner (UPQC), capable of compensating for both the supply voltage and the load current imperfections. A fully digital controller based on the TMS320F2812 DSP platform is implemented for the reference generation as well as control purposes. The delay problem in the digital controller is overcome by application of a fast DSP, a compact control technique and proper flow of control steps in the DSP software. A phase-locked loop-less software grid synchronization method has been implemented for the effective operation of the UPQC under conditions of grid frequency variation. A sequence-based compensation strategy has been developed to compensate for balanced and unbalanced sags while accommodating the fact that the voltage injection capability of the UPQC is limited. The prototype UPQC power circuit, control features, and control algorithm along with experimental results are presented in this paper.

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A 12-kVA DSP-Controlled Laboratory Prototype UPQC Capable of Mitigating Unbalance in Source Voltage and Load Current

This paper presents a novel optimal utilization of photovoltaic solar system as STATCOM for voltage regulation and power factor correction during both nighttime and daytime. The PV solar system conventionally generates real power during the day but the entire asset remains idle at night. This novel PV solar system operated as STATCOM is termed PV-STATCOM which utilizes the entire inverter capacity in the night and that remaining after real power generation during the day for accomplishing various STATCOM functionalities. Bluewater Power Corporation in Sarnia, Canada, is going to showcase this new concept of optimal utilization of PV solar system on a 10kW PV system in its network. The controller for the PV-STATCOM is being developed in the university lab and will be installed in the distribution utility network. A simulation model for the 10kW PV-STATCOM and the Bluewater Power distribution system network is developed in PSCAD software. This paper presents the steady state and transient performance of the PV-STATCOM controller for voltage regulation and power factor control both during nighttime and daytime. This proposed PV-STATCOM if connected at the terminals of an industrial customer having induction motor loads can help improve power factor and avoid potential penal tariffs over a 24-hour period, in addition to generating revenues due to sale of real power during the day.

Optimal 24-hr utilization of a PV solar system as STATCOM (PV-STATCOM) in a distribution network

PV solar farms produce power during the day and are completely idle in the nights. This paper presents a novel utilization of a PV solar plant as STATCOM in the night for load reactive power compensation and voltage control. This STATCOM functionality will also be available to a substantial degree during the daytime with the inverter capacity remaining after real power production. The local distribution company London Hydro is implementing this new technology, for the first time in Canada, on a 10 kW solar system to be installed on the rooftop of their headquarters building. The PV solar plant inverter controller will be designed, developed and tested in the university Lab and will then be installed in field by Spring 2011. This paper presents the EMTDC/PSCAD simulation studies of the performance of the 10 kW PV solar plant as a STATCOM. The benefits of employing such a new control of the PV solar system as a Flexible AC Transmission System (FACTS) device are presented.

Novel application of a PV solar plant as STATCOM during night and day in a distribution utility network

dc link voltage control of UPQC for better dynamic performance

This study presents a protection scheme for protecting the series inverter of a unified power quality conditioner (UPQC). The proposed scheme protects the series inverter from overcurrents and overvoltages, which appear during short-circuit faults on the load side of the UPQC. The main protection element is a crowbar connected across the secondary of the series transformer and consists of a pair of antiparallel connected thyristors, which is governed by a simple Zener diode-based control circuit. In the case of an overvoltage, the crowbar short circuits the secondary of the transformer, thus removing the overvoltage and diverting the fault current from the series inverter. An additional circuit is used to disable the inverters in overcurrent conditions. The effectiveness of the proposed protection scheme is demonstrated both through simulation and experimentation.

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Iurie Axente

Papers

A 12-kVA DSP-Controlled Laboratory Prototype UPQC Capable of Mitigating Unbalance in Source Voltage and Load Current

Optimal 24-hr utilization of a PV solar system as STATCOM (PV-STATCOM) in a distribution network

Novel application of a PV solar plant as STATCOM during night and day in a distribution utility network

dc link voltage control of UPQC for better dynamic performance

Protection of unified power quality conditioner against the load side short circuits