Power Quality Compensator Research Articles

D-STATCOM for harmonic mitigation in low voltage distribution network with high penetration of nonlinear loads

With the increased use of power electronic for ac-to-dc converters, electrical distributions systems are experiencing an increased in non-linear loads. These non-linear loads, such as the classical rectifier, draw non-sinusoidal currents which tend to have a deleterious impact on the power quality of the modern AC distribution systems. The interaction of non-sinusoidal currents with the grid impedance leads to distorted system voltage which can adversely impact other devices connected to the grid. The integration of distributed energy resources (DERs) with the distribution power grid can further exacerbate the harmonic power issues. The traditional methods of compensation are no longer adequate and hence it is necessary to develop a means to provide local reactive and harmonic compensation at the source of the power quality problem within the low-voltage distribution network. This article investigates the use of a capacitor-less distribution static synchronous compensator (D-STATCOM) for power quality compensation in modern distribution systems. The proposed topology is based on a matrix converter (MC), controlled by finite control set model predictive control (FCS-MPC) which makes possible the use of inductive energy storage rather than electrolytic capacitors, which have been proven to be the most failure-prone components in a power electronic circuit. Simulation and experimental results are presented to validate the effectiveness of the approach.

YN/VD connected balance transformer-based hybrid power quality compensator for harmonic suppression and reactive power compensation of electrical railway power systems

In this study, YN/VD connected balance transformer-based hybrid power quality compensator (HPQC) is proposed for harmonic suppression and reactive power compensation in electrified railways. The HPQC is composed of a balance transformer in YN/VD connection, a controllable three-phase voltage source inverter (VSI), as well as fully-tuned passive power filters (PPFs). It is able to integrate the active compensation device with the main transformer, without using auxiliary step-down transformer. This circuit configuration enables one to adopt VSI with low power rating, so that merits such as easy for system integration and low operation losses can be achieved. In this paper, the equivalent circuit model and the corresponding mathematical model of the HPQC in the harmonic domain are established to reveal its mechanism on harmonic suppression. And then, the working principle and control strategy of such a new topology are elaborated in detail. Finally, simulation and experimental results are provided to verify the feasibility and effectiveness of the above-mentioned structure and control strategy.

Experimental Evaluation of a Control System Based on a Dual-DSP Architecture for a Unified Power Quality Conditioner

An experimental evaluation of a digital control system based on a dual Digital Signal Processor (DSP) architecture is proposed for a three phase Unified Power Quality Conditioner (UPQC). A classical UQPC is constituted by two power conditioners, connected in series and shunted with the power grid, and sharing a common DC-link. In a smart grid scenario of operation, a UPQC will be fundamental for compensating power quality problems, also contributing to improving the efficiency of the electrical grids from a global perspective. The UPQC operation requires a bidirectional energy transfer between the two power conditioners, however, respecting some constraints, they can be controlled independently. In order to take advantage of this characteristic, the control algorithms can be executed on two independent DSPs, without any communication between them and maintaining the operational characteristics of the UPQC. Comparing with the classical control architecture based on a single DSP, with the proposed dual DSP architecture, the computational effort of each DSP is decreased of about 35%, allowing to increase the sampling rate. Therefore, the main advantages of the proposed approach are the minimization of delays caused by the processing time, which are very common in digital control systems, as well as the increment of the UPQC performance. Along the paper, detailed analysis of the processing speed and memory requirements to implement the UPQC control algorithms in both DSPs is presented. The paper also presents a set of detailed experimental results, obtained with a developed 5 kVA laboratory prototype of UPQC, which was used to evaluate the performance of the proposed dual DSP architecture.

Power Quality Control of Smart Hybrid AC/DC Microgrids: An Overview

Today, conventional power systems are evolving to smart grids, which encompass clusters of AC/DC microgrids, interfaced through power electronics converters. In such systems, increasing penetration of the power electronics-based distributed generations, energy storages, and modern loads provide a great opportunity for power quality control. In this paper, an overview of the power quality control of smart hybrid AC/DC microgrids is presented. Different types of power quality issues are studied first, with consideration of real-world hybrid microgrid examples, including data centers, electric railway systems, and electric vehicles charging stations. It shows that compared to traditional centralized power quality compensations, smart interfacing power converters from distributed generations, energy storages, and loads, and the AC and DC subgrids interfacing converters are promising candidates for power quality control. To realize the smart interfacing converters' power quality control, both primary converters control and secondary system coordination are required. In this paper, a thorough review of the primary control of interfacing converters to integrate the power quality compensation are presented, with a focus on the hybrid AC/DC microgrid harmonics compensation and unbalance compensation. For multiple interfacing converters, the secondary control with system-level coordination and optimization for harmonics and unbalance compensation (considering both unbalance and harmonics in single-phase and three-phase systems) are also presented. Challenges like low switching frequency of interfacing converters, parallel interfacing converters operation, and interfacing converters communications are discussed, and typical solutions for primary and secondary controls to deal with them are presented. The paper also includes rich case study results.

Subjective–objective methodology on selection of power quality compensation technology in AC–DC network with electrified railways

Electrified railways contain DC devices and cause power quality (PQ) issues such as harmonics, unbalance, and low-power factor, which should be solved by the most effective compensation technology to reduce the cost. In addition, it is common that more than one issue is caused at a supply bus, with either some issue affecting more than the others or all issues equally affecting, depending on different buses. Different PQ compensation technologies are used in the past work for the improvement of PQ at the network bus side. However, few of them have provided theoretical justification on which technologies should be selected for different network buses with different issues. This study investigates a subjective–objective methodology to provide suggestions on which compensation technologies should be selected for network buses, why and how. The importance of different PQ issues will be obtained and shown as overall weighting factors. The overall weighting factors are derived from the subjective weighting factor, obtained from existing industry standards, and the objective weighting factor, obtained from the entropy of information. The methodology will be applied to a real 124-bus AC–DC network with electrified railways. Based on the overall weighting factor obtained, the most effective compensation technology can be determined.

Enhanced Instantaneous Power Theory Decomposition for Power Quality Smart Converter Applications

Power theories are advancing signal decomposition approaches used for electrical power signal analysis. Currently, they are key tools for designing reliable and efficient power electronic interface controllers. Due to the inherent uncertainty in the power generation within new technology of distributed generation units (such as renewable-based microgrids), most of these theories are not directly applicable in the era of new power engineering systems. Furthermore, the traditional formulations are not appropriate once we face the nonlinearity in the consumption along a weak grid that may not maintain steady voltage or frequency. Therefore, a new signal decomposition method with a higher level of selectivity must be developed to modify the traditional power theories and improve the control strategies from a design viewpoint. This paper describes a novel formulation of an instantaneous power theory, enhanced instantaneous power theory (EIPT), for unbalanced and nonlinear three-phase power systems. EIPT establishes a proper decomposition of current components for cases of balanced, unbalanced, and distorted voltage sources. In addition to mathematical analysis, this research provides comprehensive simulations under different loads and source conditions, which supports the performance of the EIPT in the active filtering methods. Moreover, the performance of the proposed method is compared with the state-of-the-art approach widely known as the conservative power theory. Our results indicate that this new comprehensive approach is helpful in optimizing control strategies for power electronic interfaces and power quality compensators.

A Reconfigurable and Extendable Digital Architecture for Mixed Signal Power Electronics Controller

This brief presents the design of a reconfigurable and extendable digital architecture for an integrated mixed signal power electronics (PE) controller as it could achieve better performances than the purely digital or analog PE controller. A computer-based configuration software interface for the controller is developed. This brief aims to develop a user-interface design platform that can easily guide the controller function in feature-shared PE applications. Here, we simplify not only the design at the software level allowing controller hardware’s swift reconfigurability to save development time, but also allow parallel processing and programmable on-the-fly ability. The proposed digital controller architecture is also easily extendable by adding more building blocks to realize additional PE applications and we designed and fabricated it in 65-nm CMOS. Finally, we tested experimentally the proposed digital controller in power quality compensators to verify its reconfigurability and effectiveness. This digital architecture is fundamental for future mixed signal PE controller integration.

Generation of new harmonics caused by the processing of DQ transformation in power quality compensators

Generation of new harmonics caused by the processing of DQ transformation in power quality compensators

Management of Power Quality Issues from an Economic Point of View

In a context with an increased level of competitiveness, companies are more and more interested in aspects concerning sustainable development. The implications of inadequate power quality (PQ) can determine important financial losses and influence companies’ sustainable development through the generated effects. This article aims to facilitate the management of PQ by proposing a method for estimating the economic consequences of a poor PQ, with priority for the disturbances with significant economic effects. To determine the total cost for each type of PQ perturbation that may occur a classification of cost categories was made such as interruptions, process slowdowns, equipment failure, equipment downtime, reduced energy efficiency, lower product quality, lower labor productivity, and other indirect costs. Each PQ disturbance affects the final end-user differently. For calculating the total value for each type of PQ issues, different calculation formulas have been proposed so that each perturbation includes only those components associated with that perturbation. A case study was used to validate the proposed method. Also, the paper includes a technical and economic analysis of the possible compensation solutions for PQ disturbances that may affect the studied company. In conclusion, an understanding of PQ issues’ consequences and an appropriate approach to PQ compensation solutions can be beneficial to any electrical power end-user.

Energy Storage Characteristic Analysis of Voltage Sags Compensation for UPQC Based on MMC for Medium Voltage Distribution System

The modular multilevel converter (MMC), as a new type of voltage source converter, is increasingly used because it is a distributed storage system. There are many advantages of using the topological structure of the MMC on a unified power quality controller (UPQC), and voltage sag mitigation is an important use of the MMC energy storage system for the power quality compensation process. In this paper, based on the analysis of the topology of the MMC, the essence of energy conversion in a UPQC of voltage sag compensation is analyzed; then, the energy storage characteristics are calculated and analyzed to determine the performance index of voltage sag compensation; in addition, the simulation method is used to verify the voltage sag compensation characteristics of the UPQC; finally, an industrial prototype of the UPQC based on an MMC for 10 kV of medium voltage distribution network has been developed, and the basic functions of UPQC have been tested.

A Fuzzy adaptive hysteresis band controller for three phase four wire UPQC

Unified Power Quality Compensator (UPQC) is used to protect the sensitive loads in the distribution system from voltage and current disturbances. The compensation capability of UPQC depends on the control strategies used for shunt and series converters. Conventional adaptive hysteresis controller pulse width modulation technique had failed to track exactly during transient conditions and disturbances at load and source side. In paper fuzzy adaptive hysteresis controller is proposed for three phase four wire UPQC for compensating voltage sag/swell, current harmonics, voltage harmonics and neutral current compensation. Fuzzy adaptive hysteresis controller can effectively compensate the power quality problems during the transient conditions. A comparative simulation analysis of proposed and conventional methods are presented in this paper using MATLAB/SIMULINK tool.

Real-Time Implementation of a Three-Phase THSeAF Based on a VSC and a P+R Controller to Improve the Power Quality of Weak Distribution Systems

This paper proposes a novel three-phase transformerless hybrid series active filter (THSeAF) based on voltage-fed type of converters (VSCs) to address major power quality issues related to residential and commercial buildings. This power quality compensator presents an affordable solution to overcome current-related issues as well as integrating renewables to ensure a sustainable supply to the loads. The controller is based on a novel combination of the synchronous reference frame and pq theory to extract voltage and current harmonics as well as voltage unbalances. A proportional resonant (P+R) regulator is producing gate switching signals for the three-phase THSeAF. The generated duty-cycle waveforms will produce compensating voltage to rectify harmonic currents initiated from typical nonlinear loads. The device ensures a reliable and dynamically restored power supply on the load's point of common coupling by means of three auxiliary dc supplies. This paper describes mitigation of power-quality-related issues of a microgrid systems and smart distribution grids along with the proposed solution to enhance the power system performances. A combination of simulations and experimental laboratory results are carried out to validate the study.

Power Quality Compensation in Distribution System based on Instantaneous Power Theory and Recursive Fuzzy Proportional-Integral Controller

In this paper, the power quality compensation problems such as current harmonics and system load's reactive power are considered. In this context, we use static distribution synchronous compensator to inject compensation current into the system, which its reference current signals have been derived from the instantaneous power theory. To improve the current control operation and fast tracking of reference signals, a PI recursive controller has been used which is able to reduce to zero tracking error compared to its conventional type. The performance of the controller is delayed for a period; to overcome this problem, the phase rules have been used to adjust the controller parameters to increase the control performance speed. Finally, in simulation we used Matlab / Simulink software, which has been proven to be better than conventional PI controller-based compensation for power quality.

Analysis of the Effects of Operation Voltage Range in Flexible DC Control on Railway HPQC Compensation Capability in High-Speed Co-phase Railway Power

Railway hybrid power quality conditioner (HPQC) is advantageous over conventional railway power quality conditioner (RPC) for its reduction in operation voltage and device ratings in co-phase traction power compensation. In order to further reduce the power loss during operation, flexible dc control has been proposed. However, the operation voltage range for railway HPQC has not yet been discussed. This is important since in contrast to traditional power quality compensation devices, active power compensation is involved in co-phase traction power. Compensation capability in co-phase traction power thus does refer not only to reactive power compensation but also to active power compensation ability. Satisfactory compensation performance can be provided only when railway HPQC can provide enough active and reactive compensation power output at the same time. In this paper, the effects of operation range in flexible dc voltage control on railway HPQC compensation capability is briefly discussed and analyzed. The analysis is verified via PSCAD simulations. A laboratory-scaled hardware prototype is also constructed to obtain experimental results for further verifications.

Enhancement of Power Quality in Multi Feeder Three Phase System with Photovoltaic fed ANFIS-Unified Multi Converter Controller

Substantial growth in modern innovations demands more power from utility. To cope with drastic power demand on grid renewable sources have been integrated. This makes more complex power system as these integrated sources more dynamic in nature. Intelligent usage of renewable sources leads to optimal and reliable power structure. This paper provides an optimal usage of renewable source for unified controlling action to compensate power quality issues on multi distribution feeders. Proposed Unified Multi Converter Controller (UMCC) effectively alleviates power quality issues like harmonics, imperfections in current and voltage on multi feeder. ANFIS based harmonics alleviation is studied and compared with traditional control error tuning. Here, Photovoltaic source is considered. Proposed three phase system is analyzed in MATLAB\SIMULINK platform with variable load and supply voltage conditions.

Analysis of Energy Storage Characteristics of Power Quality Integrated Control System based on MMC

MMC as a new type of voltage source converter is used more and more widely, its essence is a distributed storage system, there are many advantages by using the topological structure of MMC on power quality integrated control system, the power quality control system of voltage sag mitigation is the important use of MMC energy storage system for power quality compensation process. In this paper, based on the analysis of the topology of MMC, firstly analyzes the essence of energy conversion power quality integrated control system of voltage sag compensation, then the energy storage characteristics were calculated and analyzed, the performance index of voltage sag compensation, finally, the simulation method is used to verify the voltage sag compensation characteristics of power quality integrated control system.

A 3D-Space Vector Modulation Algorithm for Three Phase Four Wire Neutral Point Clamped Inverter Systems as Power Quality Compensator

A Unified Power Quality Conditioner (UPQC) is designed using a Neutral Point Clamped (NPC) multilevel inverter to improve the power quality. When designed for high/medium voltage and power applications, the voltage stress across the switches and harmonic content in the output voltage are increased. A 3-phase 4-wire NPC inverter system is developed as Power Quality Conditioner using an effectual three dimensional Space Vector Modulation (3D-SVM) technique. The proposed system behaves like a UPQC with shunt and series active filter under balanced and unbalanced loading conditions. In addition to the improvement of the power quality issues, it also balances the neutral point voltage and voltage balancing across the capacitors under unbalanced condition. The hardware and simulation results of proposed system are compared with 2D-SVM and 3D-SVM. The proposed system is stimulated using MATLAB and the hardware is designed using FPGA. From the results it is evident that effectual 3D-SVM technique gives better performance compared to other control methods.

Single‐phase ac–dc–ac topology for grid overvoltage and voltage harmonic mitigation

A single-phase ac–dc–ac topology to improve power quality is proposed in this study. This configuration is obtained from the addition of a floating capacitor H-bridge converter on the grid side of the conventional ac–dc–ac three-leg topology. The role of the structure is not only to ensure regulated load voltage with fixed amplitude and frequency, grid current with low harmonic content and unitary power factor, but also to mitigate fundamental overvoltage and voltage harmonics at the grid. As a consequence, the proposed topology is suitable to operate as unified power quality compensator or uninterrupted power supply. It does not use isolation transformer and is capable of generating multilevel input voltages due to the cascaded H-bridge. The operation with asymmetrical dc-link voltages is considered to increase the number of voltage levels and reduce the harmonic content of the generated input voltages. Two pulse-width modulation techniques and a control system are developed to regulate the dc-link voltages and to decrease the harmonic distortion (HD), lowering the switching stress and also the power losses. The proposed configuration is compared with the conventional one with respect to HD and semiconductor losses. Simulated and experimental results are presented for validation purposes.

Neural Network Based ILST Control Strategy for a DSTATCOM with Solar Photovoltaic System for Power Quality Improvement

The power quality compensator chosen in this paper is a DSTATCOM which integrates a three phase four leg Voltage Source Converter (VSC) with a DC capacitor (Cdc). A single stage Solar Photovoltaic (SPV) system is implemented for maintaining the DC link voltage (Vdc) of the Shunt Active Power Filter (SAPF). The system proposed, improves the Power Quality (PQ) of the utility system as well as feeds the solar energy extracted into the system. Maximum Power Point Tracking (MPPT) is implemented to excerpt solar energy. The purpose of the proposed system is to mitigate harmonics and neutral current (Isn),to compensate reactive power and to maintain power factor near unity. The SAPF improves the PQ of the proposed system. The control algorithm proposed for SAPF is Neural Network (NN) based Improved Linear Sinusoidal Tracer (ILST) algorithm. An instantaneous compensation technique controls the variations in PV power of the SPV system with fast dynamic response. The proposed system is also compared with battery operated Boost Converter (BC) SPV fed SAPF system. The battery operated SPV system boost the DC link voltage and thus improves PQ throughout the day. The NN based control strategy and the SPV system are modeled, developed and validated in MATLAB SIMULINK. The simulation results justify the effectiveness of the propounded system.

Operation of a Photovoltaic Microinverter as Active Power Filter using the single phase P-Q Theory and Sliding Mode Control

Context: Microinverters are widely used in modular photovoltaic installations but its operation with reduced power is limited to inject real power into the grid. One way to optimize the use of microinverters consist of providing them the Active Power Filtering (APF) capability, which allows its use as both distributed generation and compensation unit even under unfavorable conditions of insolation. With this approach, the output stage of the microinverter can provide reactive and distortive components of power in order to compensate power quality defects of a localized load.Method: This paper proposes a non-linear control strategy to integrate the APF function in a single-phase two-stage photovoltaic microinverter. The proposal involves the use of the single-phase P-Q theory to generate the current reference, sliding mode control to achieve a robust tracking of that reference and linear robust control to maintain the power balance regulating the DC-link voltage of the microinverter. The proposed control does not require the use of low-pass filters and in turn uses a recursive average computation improving the general performance of the system.Results: The theoretical approach is validated by means of simulation results in which appropriate levels of harmonic distortion are obtained in the grid-side current for different load types and power levels. The robustness of the control system is tested by applying disturbances in the harmonic content of the load current and its power level obtaining an appropriate dynamic performance adapted to the demands of the application.Conclusions: The main advantage of this proposal is the possibility to add the active filter function to coventional microinverters extending its capability to power conditioning only integrating some algorithms. A simple design method to ensure reliability, robustness and high power quality is detailed.Language: English