Voltage Harmonic Compensation Research Articles

Impedance Emulation for Voltage Harmonic Compensation in PWM Stand-Alone Inverters

This paper proposes a selective voltage harmonic compensation strategy for stand-alone inverters. The use of LC output filters makes it possible to reduce switching harmonics at the output terminals of the inverter; however, it also produces voltage distortion when feeding nonlinear loads due to the harmonic voltage drop across the filter inductances. To compensate the voltage harmonic distortion and produce sinusoidal voltage, it is proposed to add virtual impedances to the fundamental voltage control. The whole process and considerations for the impedance design are described and a stability analysis of the system is presented. Finally, simulations and experimental results are shown to confirm the good performance of the proposed strategy under both steady state and load steps.

Coordinated control of multifunctional inverters for voltage support and harmonic compensation in a grid-connected microgrid

In this paper, a coordinated harmonic compensation and voltage support scheme is presented for distributed generations’ (DGs’) interface inverters in a resistive grid-connected microgrid. Voltage support is performed by reactive power compensation which can mitigate the over/under voltage problem; furthermore, the active power curtailment is proposed in order to mitigate the overvoltage problem when the reactive power compensation is not sufficient. Harmonic compensation is achieved by using virtual admittances in selected harmonic frequencies. Reactive power and harmonic compensation currents are injected with regards to the limited capacity of the interface inverter. If necessary, the reference powers of the grid-tied inverters are changed. Voltage support and harmonic compensation can be achieved based on local or central (communication-based) measurement schemes. The effect of communication delay is also investigated in this study. Experimental and simulation results are obtained in order to demonstrate the effectiveness of the proposed method.

A power sharing scheme for voltage unbalance and harmonics compensation in an islanded microgrid

In this paper, a hierarchical control structure with voltage unbalanced compensation scheme in ac islanded microgrid is proposed to improve Critical Load Bus (CLB) voltage quality and address inaccurate power sharing problems. The hierarchical scheme includes primary and secondary control levels. The primary control mainly contains the power droop controllers, voltage and current controllers, selective virtual impedance loop, and voltage unbalanced compensation. The virtual impedance loop includes virtual positive- and negative-sequence impedance loops at fundamental frequency and virtual variable harmonic impedance loop at harmonic frequencies. The secondary control is designed to restore frequency and amplitude of the CLB voltage. In order to compensate the CLB voltage, an unbalanced compensation is proposed to change the voltage reference of the distributed generation (DG) units. This strategy also employs the low bandwidth communication (LBC) technique to send the proper signals of the secondary control from the microgrid control center (MGCC) to the primary control. To evaluate the performance of the proposed control strategy, simulations are conducted on two islanded microgrid prototype. The results demonstrate the effectiveness of the proposed control structure in the unbalance and harmonic compensation of the CLB voltage and proper power sharing of reactive, unbalanced and harmonic powers among the DG units.

Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids

In recent years, the harmonics and unbalance problems endanger the voltage and current quality of power systems, due to increasing usage of nonlinear and unbalanced loads. Use of Distributed Generation (DG)-interfacing inverters is proposed for voltage or current compensation. In this paper, a flexible control method is proposed to compensate voltage and current unbalance and harmonics using the distributed generation (DG)-interfacing inverters. This method is applicable to both grid-connected and islanded Microgrids (MGs). In the proposed method, not only the proper control of active and reactive powers can be achieved, but also there is flexibility in compensating the voltage or current quality problems at DG terminals or Points of Common Coupling (PCCs). This control strategy consists of active and reactive power controllers and a voltage/current quality-improvement block. The controller is designed in a stationary (αβ) frame. An extensive simulation study has been performed and the results demonstrate the effectiveness of the proposed control scheme. Depending on the compensation modes, the harmonics and unbalance compensation of DG output current, MG-injected current to the grid, as well as PCC and DG voltages, can be achieved in grid-connected operation of MG while in the islanded operation, and the PCC and DG voltages compensation can be obtained through the proposed control scheme.

Hybrid harmonic compensation device adapted for variable speed drive system

The structure of the hybrid harmonic compensation device adapted for variable speed drive system is proposed in the paper. The main feature of the proposed device is the usage of common direct current link both for inverter of power frequency converter and for inverter of active part of the hybrid device. This decision allows to decrease the cost of active part of the proposed hybrid device. The proposed hybrid device is firstly intended for voltage and current harmonic determination and elimination. A mathematical model of generalized industrial power supply system with nonlinear load and the proposed hybrid device was developed by means of Matlab Simulink software. During simulation the proper efficiency of the proposed hybrid device is shown in different modes of voltage and current harmonic compensation.

Extensive Application of UPQC-L for a Dual Point of Common Coupling System with Multiple Loads under Unbalanced Source Condition

—This paper presents a synchronous reference frame (SRF)-based power angle control (PAC) approach for a specific unified power quality conditioner (UPQC) arrangement, termed as UPQC-L for dual point of common coupling system under unbalanced source voltage condition. In contrast to a conventional configuration of UPQC, the static compensator (STATCOM) part is on left side of UPQC-L, while dynamic voltage restorer (DVR) is on the right side. The UPQC-L configuration is specifically adapted for protection of sensitive and critical load types from voltage disturbances. Along with its basic compensation capability of current harmonic compensation and voltage compensation, it efficiently handles reactive power demand from sensitive load. This is achieved with the introduction of PAC concept for effective sharing of reactive power between STATCOM and DVR. The extraction of instantaneous power angle faces difficulty with unbalanced voltage and UPQC-L configuration. Thus, the control algorithm for UPQC-L is designed based on SRF and numerical analysis approach with equal reactive power sharing phenomena by STATCOM and DVR of UPQC-L. UPQC-L with the proposed control approach is successfully implemented in MATLAB/SIMULINK (The Mathworks, Inc. USA) and verified experimentally for mitigation of voltage disturbances (such as sag/swell, unbalancing, and harmonics), current harmonics, and high-reactive power demand.

A Novel Control Strategy Based Dynamic Voltage Restorer for Compensation of Voltage Harmonics in Distribution System

Power quality is one of the areas that the power sector is worried about. Power quality is the measure of practical system resemblance to ideal system. Voltage quality can be defined as the maintenance of voltage waveform shape close to ideal shape with proper magnitude and frequency. Even a slight change in voltage of the system can cause serious damage to the power system. Sensitive loads cannot adjust for small change in voltage. This paper presents Dynamic Voltage Restorer (DVR) for voltage harmonic suppression along with sag/swell compensation in distribution system. DVR is a voltage source converter which sends compensating signals when operated through switches of voltage source converter. This paper presents a novel control strategy to control DVR to block out the voltage harmonics in distribution system. The models and results are developed using MATLAB/SIMULINK software and comparative analysis of source voltage harmonics and load voltage harmonics during sag/swell compensation was tabulated.

Admittance based algorithm of dynamic voltage restorer for improved power quality

This study deals with the admittance estimation algorithm for DVR for improvement of PQ in PDS (Power Distribution System). This admittance estimation algorithm based DVR is simple and easy to implement in simulation/hardware. In this admittance estimation algorithm, the estimation of active/reactive power components of load voltages are based on unit vectors in time domain and Low-Pass Filter (LPF). The mathematical analysis is easy, accurate and is used for fast estimation of reference load voltages using proposed algorithm. A three phase DVR using admittance estimation algorithm is modeled and implemented on real time hardware under balanced/unbalanced voltage sag, balanced/unbalanced voltage swell and harmonics compensation using Real Time Hardware Simulation and MATLAB under Simulink. Performance of admittance estimation algorithm for DVR in PDS shows quite satisfactory results using RT-LAB and MATLAB for the above power quality problems as per IEC and IEEE standards.

Simultaneous Microgrid Voltage and Current Harmonics Compensation Using Coordinated Control of Dual-Interfacing Converters

The growing installation of distributed generation (DG) units in low-voltage distribution systems has popularized the concept of nonlinear load harmonic current compensation using multifunctional DG interfacing converters. It is analyzed in this paper that the compensation of local load harmonic current using a single DG interfacing converter may cause the amplification of supply voltage harmonics to sensitive loads, particularly when the main grid voltage is highly distorted. To address this limitation, unlike the operation of conventional unified power quality conditioners with series converter, a new simultaneous supply voltage and grid current harmonic compensation strategy is proposed using coordinated control of two shunt interfacing converters. Specifically, the first converter is responsible for local load supply voltage harmonic suppression. The second converter is used to mitigate the harmonic current produced by the interaction between the first interfacing converter and the local nonlinear load. To realize a simple control of parallel converters, a modified hybrid voltage and current controller is also developed in the paper. By using this proposed controller, the grid voltage phase-locked loop and the detection of the load current and the supply voltage harmonics are unnecessary for both interfacing converters. Thus, the computational load of interfacing converters can be significantly reduced. Simulated and experimental results are captured to validate the performance of the proposed topology and the control strategy.

Output Voltage Regulation for Harmonic Compensation under Islanded Mode of Microgrid

This study examines a P+multi resonant-based voltage control for voltage harmonics compensation under the islanded mode of a microgrid. In islanded mode, the inverter is defined as a voltage source to supply the full local load demand without the connection to the grid. On the other hand, the output voltage waveform is distorted by the negative and zero sequence components and current harmonics due to the unbalanced and nonlinear loads. In this paper, the P+multi resonant controller is used to compensate for the voltage harmonics. The gain tuning method is assessed by the tendency analysis of the controller as the variation of gain. In addition, this study analyzes the slight voltage magnitude drop due to the practical form of the P+multi resonant and proposes a counter method to solve this problem by adding the PI-based voltage restoration method. The proposed P+multi resonant controller to compensate for the voltage harmonics is verified through the PSIM simulation and experimental results.

КОНТРОЛЬ КАЧЕСТВА ЭЛЕКТРИЧЕСКОЙ ЭНЕРГИИ НА ПОДСТАНЦИЯХ МОРСКОГО ПОРТА

The need to solve the problem of power quality assessment in distribution networks, to identify the harmonic structure and to develop the methods of voltage harmonic compensation was justified. Quality control of electric power at substations of commercial port was made in the process of port cranes’ work at the coal loading. The points of connection were racks of typical substations supplying the equipment of cranes. The tests of electrical networks, converters, rack equipment of transformer substations with 0.4 kV feeding port cranes of "Sokol-54" and "Aist-21" types, with relay converters and frequency control converters of the powerful electric drive are of particular interest. During the tests, evaluation of the quality of electric energy in the limited time intervals was carried out, as well as short-term (instantaneous) electric network parameters were recorded. It was found that the work of high-power converters has a direct impact on the quality of electric power of typical substation. On the basis of obtained data a number of recommendations to improve the quality of electricity in the distribution network of port cranes were proposed. In order to evaluate the quality of electric power in the distribution network of the fleet infrastructure facilities the use of modern devices that can detect the cause and location of devices that violate the quality of electromagnetic compatibility is provided.

Proportional‐resonant control applied on voltage regulation of standalone SEIG for micro‐hydro power generation

This study deals with the development of a proportional-resonant (PR) control applied on voltage regulation and harmonics compensation of a standalone self-excited induction generator (SEIG) for micro-hydro power generation system. The generation system considers: (i) a three-phase induction generator (IG) as SEIG, (ii) which is driven by an unregulated micro-hydro turbine, (iii) a three-phase three-legs distribution static synchronous compensator (DSTATCOM) and (iv) linear and non-linear loads connected to the AC bus. The voltage regulation is performed through the injection of reactive power to the AC bus through the DSTATCOM, providing excitation current to the IG. It is considered the employment of PR control techniques, which offers suitable voltage regulation through voltage harmonics compensation in the point of common coupling. Furthermore, frequency regulation is performed on the demand side by an electronic load control connected to the DC bus of the DSTATCOM. Experimental results were obtained to demonstrate the good performance of the voltage and frequency regulation, provided by the control system during transients of linear and non-linear loads.

A repetitive-based control for a single-phase shunt active power filter for harmonic voltage compensation

A repetitive-based control for a single-phase shunt active power filter for harmonic voltage compensation

Review of Dynamic Voltage Restorer Application for Compensation of Voltage Harmonics in Power Systems

<p>Power distribution networks are considered the main link between power industry and consumers and they are exposed to public judgment and evaluation more than any other section. Thus, it is essential to study power quality in distribution section. On the other hand, power distribution networks have always been exposed to traditional factors such as voltage sag, voltage swell, harmonics and capacitor switching which destruct sinusoidal waveforms and decrease power quality as well as network reliability. One of the methods by which power quality problems might be addressed is to apply power electronic devices in the form of custom power devices. One of such devices is Dynamic Voltage Restorer (DVR) which is connected in series to distribution networks. At the same time, through injection of voltage to the network it is able to control voltage amplitude and phase. It is adopted lend to compensate for voltage sags through injecting series and synchronous three phase voltage. This paper reviews on the application of DVR for Voltage Compensation in recent years and gives sets of information for each control of the DVR in distribution networks.</p>

THD Reduction of Distribution System Based on ASRFC and HVC Method for SVC under EV Charger Condition for Power Factor Improvement

Electric vehicles (EVs) have been gaining popularity in recent years due to growing concerns about fuel depletion and increasing petrol prices. Random uncoordinated charging of multiple EVs at residential distribution feeders with moderate penetration levels is expected in the near future. This paper describes a high performance voltage controller for the EVs charging system, and proposes a scheme of asymmetric synchronous reference frame controller (ASRFC) in order to compensate for the voltage distortions and unbalance distribution system due to EVs charger. This paper explores the power factor of distribution and residential network under random EVs charger on the bus load. ASRFC and harmonic voltage compensator (HVC) are employed for static VAR compensator (SVC) in this paper. The proposed scheme can improve the power factor and total harmonic distortion (THD) of the smart grid due to the EVs charger in grid. The effectiveness of the scheme was investigated and verified through computer simulations of a 22.9-kV grid.

Improved control strategy for PI-R current of DFIG considering voltage and current harmonics compensation

With the rapid development of wind power generation, the related research of wind power control and integration issues has attracted much attention, and the focus of the research are shifting away from the ideal power grid environment to the actual power grid environment. As the main stream wind turbine generator, a doubly-fed induction generator (DFIG) is connected to the power grid directly by its stator, so it is particularly sensitive to the power grid. This paper studies the improvement of DFIG control technology in the power grid harmonic environment. Based on the DFIG dynamic model considering the power grid harmonic environment, this paper introduces the shortcomings of the common control strategy of DFIG, and puts forward the enhanced method. The decoupling control of the system is realized by compensating the coupling between the rotor harmonic voltage and harmonic current, improving the control performance. In addition, the simulation experiments on PSCAD/EMTDC are carried out to verify the correctness and effectiveness of the improved scheme.

Non-linear load sharing and voltage harmonics compensation in islanded microgrids with converter interfaced units

Summary If sensitive loads are connected to the point of common coupling (PCC), compensation should be carried out in order to reduce PCC voltage harmonics. In this case, compensation is performed by the interface converters of distributed generation (DG) units. In this paper, a novel method is proposed for voltage harmonics compensation in islanded microgrids. The proposed method is capable of adjusting compensation percentage in proportion to the existing level of distortion at PCC. Also, this controller provides a proper sharing of compensation workload, considering the nominal capacity of DGs, which will improve the sharing of nonlinear load. Also, to decrease the asymmetry among phase impedances of microgrid, a novel structure is proposed to generate virtual impedance. At fundamental frequency, the proposed structure for the virtual impedance improves the control of the fundamental component of the power, and at harmonic frequencies, it acts to adaptively improve nonlinear load sharing among DG units. In the structures of the proposed harmonics compensator and the proposed virtual impedance, a self-tuning filter is used for separating the fundamental component from the harmonic components. This self-tuning filter decreases the number of the phase-locked loops. The simulation results in MATLAB/SIMULINK environment show the efficiency of the proposed approach in improving load sharing and decreasing voltage harmonics. Copyright © 2016 John Wiley & Sons, Ltd.

Improved Active Harmonic Current Elimination Based on Voltage Detection.

With the increasing penetration of power electronic equipment in modern residential distribution systems, harmonics mitigation through the distributed generation (DG) interfacing converters has received significant attention. Among recently proposed methods, the so-called active resonance damper (ARD) and harmonic voltage compensator (HVC) based on voltage detection can effectively reduce the harmonic distortions in selected areas of distribution systems. However, it is found out that when traditional ARD algorithm is used to eliminate harmonic current injected by non-linear loads, its performance is constrained by stability problems and can at most eliminate half of the load harmonic currents. Thus, inspired by the duality between ARD and HVC, this paper presents a novel improved resistive active power filter (R-APF) algorithm based on integral-decoupling control. The design guideline for its parameters is then investigated through carefully analyzing the closed-loop poles’ trajectory. Computer studies demonstrate that the proposed algorithm can effectively mitigate the load harmonic currents and its performance is much better than traditional ARD based on proportional control.

Three Phase Grid Connected PV System for Mitigation of Voltage and Current Harmonics Compensation Using SRF Method

Power quality is an all-encompassing concept for a multitude of individual types of power system disturbances. The presence of harmonics in power supply network poses a severe power quality problem that results in greater power losses in the distribution system, interference problems in communication systems and, sometimes, in operation failures of electronic equipment. This paper presents a three -phase active power filter for harmonic compensation which is consists of a series active power filter and a shunt active filter. The active filter connected in series to a source acts as a harmonic isolator between the sources and loads whereas the shunt active filter is connected in parallel with a load and suppresses the harmonic current produced by the load and. reduce the total harmonic distortion (THD). The voltage source inverter (VSI) is the core of an active power filter. The hysteresis current control is a method of controlling the VSI. Hysteresis control can be either of fixed band type or adaptive band type. In this paper, Synchronous Reference Frame (SRF) theory is implemented for the generation of reference current signals for the controller. Mat lab /Simulink and are used for simulation. From the simulation results it is confirmed that the filter topology is capable of compensating the load current and voltage harmonic distortion within the stipulated limits laid down by the IEEE 519 standard.

An Enhanced Power Sharing Scheme for Voltage Unbalance and Harmonics Compensation in an Islanded AC Microgrid

In this paper, an enhanced hierarchical control structure with multiple current loop damping schemes for voltage unbalance and harmonics compensation (UHC) in ac islanded microgrid is proposed to address unequal power sharing problems. The distributed generation (DG) is properly controlled to autonomously compensate voltage unbalance and harmonics while sharing the compensation effort for the real power, reactive power, and unbalance and harmonic powers. The proposed control system of the microgrid mainly consists of the positive sequence real and reactive power droop controllers, voltage and current controllers, the selective virtual impedance loop, the unbalance and harmonics compensators, the secondary control for voltage amplitude and frequency restoration, and the auxiliary control to achieve a high-voltage quality at the point of common coupling. By using the proposed unbalance and harmonics compensation, the auxiliary control, and the virtual positive/negative-sequence impedance loops at fundamental frequency, and the virtual variable harmonic impedance loop at harmonic frequencies, an accurate power sharing is achieved. Moreover, the low bandwidth communication (LBC) technique is adopted to send the compensation command of the secondary control and auxiliary control from the microgrid control center to the local controllers of DG unit. Finally, the hardware-in-the-loop results using dSPACE 1006 platform are presented to demonstrate the effectiveness of the proposed approach.