Voltage Harmonic Compensation Research Articles

Virtual Admittance Loop for Voltage Harmonic Compensation in Microgrids

The use of the virtual admittance concept for harmonic and/or unbalance compensation in microgrids when multiple inverters operate in parallel is proposed in this paper. The virtual impedance concept has been traditionally used for these purposes. However, one drawback of the virtual impedance is that it can only be applied to distributed generation (DG) units operating in voltage control mode (VSI-VCM), but is not applicable to DG units working in current control mode (e.g., current-regulated voltage-source inverters, VSI-CCM). Contrary to this, the proposed method can be used in any converter topology and control mode, including VSI-CCM and VSI-VCM.

Voltage Regulation and Harmonic Current Compensation in ThreePhase Distribution System using DSTATCOM

Voltage Regulation and Harmonic Current Compensation in ThreePhase Distribution System using DSTATCOM

영구자석 동기 전동기의 고속운전 시 토크리플 저감 알고리즘

Torque ripples generate mechanical vibration at low speed and acoustic noise at high speed. The back emf harmonics of a PM synchronous motor is one of the main sources of torque ripples. To reduce torque ripples resulting from back emf harmonics, dq-axis harmonic currents that reduce the torque ripples are generally compensated to the current controller. Harmonic current compensation is effective at low speed, but it is not applicable at high speed because of the limited bandwidth of the current controller. In this study, dq-axis harmonic voltage compensation that can reduce torque ripples at high speed is proposed. The dq-axis harmonic voltages are calculated from the motor speed and the dq-axis harmonic currents. The effectiveness of the proposed method in reducing torque ripple is verified by a simulation and experiments.

Harmonic current and voltage compensation using HSAPF based on hybrid control approach for synchronous reference frame method

Abstract This paper presents a Hybrid Series Active Power Filter (HSAPF) for compensation of source current and load voltage harmonics. The HSAPF combination consists of a small rated series active power filter and a shunt connected passive power filter. This combination is suitable for compensation of voltage-type as well as current-type harmonic producing load. The HSAPF uses the synchronous rotating reference frame method that based on hybrid control approach, which eliminate both source current as well as load voltage harmonics and also tests the performance of HSAPF for ideal voltage, non-ideal voltage and also at different loading conditions, etc.

A Novel Design of UPQC with Kalman Filter for Mitigation of Voltage and Current Disturbances

In this project proposed a new concept of optimal utilization of a unified power quality conditioner. The series inverter of the UPQC is controlled to perform simultaneous voltage sag/swell compensation and load reactive power sharing with the shunt inverter. Kalman filter is designed to remove the harmonic components of the supply voltage and load current. The proposed method operates both in the time and frequency domains allowing the selective compensation of voltage and current harmonics with fast dynamical responses. The simulation is conducted by using MATLAB/SIMULINK. The simulation result shows the proposed UPQC has a good effect in the mitigation of the voltage sag.

Grid to Standalone Transition Motion-Sensorless Dual-Inverter Control of PMSG With Asymmetrical Grid Voltage Sags and Harmonics Filtering

This paper describes a variable-speed motion-sensorless control system for permanent-magnet synchronous generator (PMSG) connected to grid via back-to-back inverters for wind energy generation. The grid-side inverter control system employs proportional-integral (PI) current controllers with cross-coupling decoupling and line-voltage feedforward disturbance compensation. Also, a D-module filter is used to robustly extract the line voltage positive sequence followed by a phase-locked-loop (PLL) based observer to estimate the positive-sequence angle for control, including the case of asymmetric voltages and automatic seamless transfer method from grid connected to stand alone and vice versa. In stand-alone mode, a voltage control scheme with selective harmonic compensation is employed. The PMSG motion-sensorless control system uses an active power controller and a PLL-based observer to estimate the rotor position and speed without using the electromotive force (EMF) integration and initial rotor position. The paper investigates and validates the ride-through performance of this proposed system during asymmetric power grid-voltage sags, transition from grid connected to stand alone and vice versa and voltage harmonics compensation. While some of the aforementioned issues have been treated rather individually in previous conference publications of the authors, the present paper integrates them into a comprehensive control system of PMSG.

Design of Two Feeder Three Phase Four Wire Distribution System Utilizing Multi Converter UPQC with Fuzzy Logic Controller

This paper proposes the instantaneous p-q theory based fuzzy logic controller (FLC) for multi converter unified power quality conditioner (MC-UPQC) to mitigate power quality issues in two feeders three-phase four-wire distribution systems. The proposed system is extended system of the existing one feeder three-phase four-wire distribution system, which is operated with UPQC. This system is employed with three voltage source converters, which are connected commonly to two feeder distribution systems. The performance of this proposed system used to compensate voltage sag, neutral current mitigation and compensation of voltage and current harmonics under linear and nonlinear load conditions. The neutral current flowing in series transformers is zero in the implementation of the proposed system. The simulation performance analysis is carried out using MATLAB.

Voltage unbalance and harmonics compensation for islanded microgrid inverters

Voltage source inverters (VSIs) are usually used for all kinds of distributed generation interfaces in a microgrid. It is the microgrid's superiority to power the local loads continuously when the utility fails. When in islanded mode, the voltage and frequency of the microgrid are determined by the VSIs; therefore the power quality can be deteriorated under unbalanced and non-linear loads. A voltage unbalance and harmonics compensation strategy for the VSIs in islanded microgrid is proposed in this study. This method is implemented in a single synchronous reference frame (SRF) and is responsible for both the voltage unbalance and harmonic compensation. Furthermore, the virtual impedance loop is modified to improve the compensation effect. The impedance model of the VSI is built to explain the compensation ability of the proposed strategy. The whole control system mainly includes power droop controllers, a modified virtual impedance loop and inner SRF-based voltage unbalance and harmonics compensators. The proposed strategy is demonstrated in detail and validated with simulations and experiments.

Improving voltage harmonic compensation of a single phase inverted-based PEM fuel cell for stand-alone applications

Fuel cell (FC) is an efficient energy conversion technology that is growing rapidly and will have a significant role to play in a number of energy end-use sectors, from small-scale applications to large-scale power plants. In this paper, two new methods for voltage harmonic compensation of a stand-alone single phase inverted-based FC are presented and evaluated. The stand-alone power system under study consists of: 1) Proton-Exchange-Membrane (PEM) FC with unidirectional DC/DC converter, which converts the DC voltage delivered by the FC to the DC bus voltage; 2) single-phase pulse width modulated (PWM) inverter; 3) transformer; 4) passive filter; and 5) linear and non-linear loads. The dynamic model of this system and the non-sinusoidal output-based controls applied to the PWM inverter for voltage regulation and harmonic compensation are detailed in this paper, and evaluated by simulation under different linear and non-linear loads. Simulation results show the effectiveness of the two purposed methods for voltage harmonic compensation to acceptable levels defined in grid codes.

Medium-Voltage 12-Pulse Converter: Output Voltage Harmonic Compensation Using a Series APF

In this paper, compensation of the dc-side voltage harmonics of a medium-voltage (MV) 12-pulse ac/dc converter is achieved using a series active power filter (APF). The output voltage harmonics are dependent on the converter firing delay angles and, consequently, on the specific power locus followed by the ac/dc converter. This power locus ensures minimum fifth and seventh harmonics (total rms) in the input current which provides minimum input current total harmonic distortion when the reactive power is less than 0.5 p.u. The series APF is connected between the load and the converter output via a magnetic amplifier to eliminate the dc current from the APF inverter, thus reducing inverter losses. Voltage harmonic compensation using a series APF, with and without a magnetic amplifier, is examined with both resistive and inductive loads. The simulation results for compensating a 3.3-kV MV 12-pulse converter system are experimentally verified using a scaled prototype 12-pulse converter with a series APF.

Harmonic Suppression Method Based on Immune Particle Swarm Optimization Algorithm in Micro-Grid

Distributed generation has attracted great attention in recent years, thanks to the progress in new-generation technologies and advanced power electronics. And micro-grid can make full use of distributed generation, so it has been widespread concern. On the other hand due to the extensive use of power electronic devices and many of the loads within micro-grid are nonlinear in nature, Micro-grid generate a large number of harmonics, so harmonics pollution needs to be addressed. Usually we use passive filter to filter out harmonic, in this paper, we propose a new method to optimize the filter parameters, so passive filter can filter out harmonic better. This method utilizes immune particle swarm optimization algorithm to optimize filter parameters. It can be shown from the simulation results that the proposed method is effective for micro-grid voltage harmonics compensation.

Power Quality Enhancement in Power Distribution system using Artificial intelligence based Dynamic Voltage Restorer

The power quality enhancement is very mandatory with the newer generation load equipments, whose performance is very sensitive to power quality disturbances especially with voltage sag, Harmonics and Interruption. The power electronic based power conditioning devices can be the effective solution to enhance the quality of the power supplied to the power distribution system. The series connected Dynamic Voltage Restorer (DVR) is one of the effective solution to mitigate power quality problems in the distribution system. In this paper, the Artificial Neural Network (ANN) controlled DVR is designed and the performance of the rectifier load connected system is investigated with conventional Proportional-Integral (PI) controller. The Levenberg- Marquardt (LV) Back propagation algorithm is used to implement the control scheme of the Voltage Source Inverter (VSI). The ANN is trained offline using data from PI controller. In addition to the compensation of voltage sag and harmonics, the DVR is also used to protect a linear load from various disturbances in the source voltage. Three different types of faults with two level of voltage sag are analyzed and the performance of DVR with these disturbances is modeled using MATLAB/SIMULINK. The comprehensive result of the PI and ANN controllers are also presented.

An Enhanced Harmonic Voltage Compensator for General Loads in Stand-alone Distributed Generation Systems

This paper develops an enhanced harmonic voltage compensator which is implemented with the aid of two repetitive controllers (RCs) in order to improve the output voltage performance of stand-alone distributed generation (DG) systems. The proposed harmonic voltage compensator is able to maintain the DG output voltage sinusoidal regardless of the use of nonlinear and/or unbalanced loads in the load side. In addition, it can offer good steady-state performance under various types of loads and a very fast dynamic response under load variations to overcome the slow dynamic response issue of the traditional RC. The feasibility of the proposed control strategy is verified through simulations and experiments.

An Islanding Microgrid Power Sharing Approach Using Enhanced Virtual Impedance Control Scheme

In order to address the load sharing problem in islanding microgrids, this paper proposes an enhanced distributed generation (DG) unit virtual impedance control approach. The proposed method can realize accurate regulation of DG unit equivalent impedance at both fundamental and selected harmonic frequencies. In contrast to conventional virtual impedance control methods, where only a line current feed-forward term is added to the DG voltage reference, the proposed virtual impedance at fundamental and harmonic frequencies is regulated using DG line current and point of common coupling (PCC) voltage feed-forward terms, respectively. With this modification, the impacts of mismatched physical feeder impedances are compensated. Thus, better reactive and harmonic power sharing can be realized. Additionally, this paper also demonstrates that PCC harmonic voltages can be mitigated by reducing the magnitude of DG unit equivalent harmonic impedance. Finally, in order to alleviate the computing load at DG unit local controller, this paper further exploits the band-pass capability of conventionally resonant controllers. With the implementation of proposed resonant controller, accurate power sharing and PCC harmonic voltage compensation are achieved without using any fundamental and harmonic components extractions. Experimental results from a scaled single-phase microgrid prototype are provided to validate the feasibility of the proposed virtual impedance control approach.

Dynamic properties of system «rectifier with buck converter - load»

The introduction of high-speed rolling stock, the growth of passenger and freight transportation are placing ever greater demands for power supply devices and electric energy quality in a contact network. The application of direct current at traction substation along with uncontrolled diode rectifier of a controlled buck converter allows adjusting the average value of rectified voltage in the contact system. In addition, using the buck converter in a closed structure allows compensating the unwanted harmonic components of the load voltage. The need for investigating the dynamic properties of the “rectifier buck converters - load” system is specified by the possibility of realizing the finite duration processes in the voltage regulation channel, allowing the load voltage harmonic compensation on the feedback circle. The buck converter, operating in the pulse width modulation mode, allows using it as a wideband active filter. All the above requires a mathematical description of dynamic processes in the described system for the task solution. The obtained system of equations allows describing the dynamic processes in rectifying installation with width-controlled BC.

Hybrid Cascaded H-bridge Converter for Harmonic Current Compensation

This paper describes a three-phase trasformerless active filter system based on hybrid cascaded H-bridge converters with delta configuration. It is intended for dynamically compensating harmonic current of three-phase nonlinear load. This active filter is characterized by per-phase series connection of a high-voltage converter operating at 50 Hz and a low-voltage converter operating at 7.5 kHz. DC-link voltages of all converters are regulated purely by control algorithm without any auxiliary circuit. The dc voltage ratio of 2:1 is realized for the series-connected converters by injecting zero-sequence current with fundamental, third-harmonic, and fifth-harmonic components to the three clusters. An experimental prototype rated at 100 V and 1 kVA is built up in authors' lab. Experiment results confirm the validity of this dc voltage control method and harmonic current compensation capability.

Unbalance and harmonic voltage compensation for a stand‐alone variable speed constant frequency double‐output induction generator supplying non‐linear and unbalanced loads

This study presents an improved control algorithm for a stand-alone double-output induction machine-based variable speed constant frequency generator. The algorithm ensures sinusoidal load voltage and machine stator current for all types of loads such as balanced, unbalanced, linear and non-linear in any arbitrary combination. This is achieved by incorporating harmonic and unbalanced load compensation function to the stator side converter. Unlike other control strategies reported in the literature for this purpose, the proposed algorithm does not require extraction or compensation of individual harmonic/unbalance components of the load voltage/stator current. Harmonic compensation performance of the algorithm is thoroughly analysed theoretically and design guidelines provided. The experimental results obtained from a laboratory prototype demonstrate excellent load voltage regulation property during severe transient operating conditions. Total harmonic distortion and unbalance of the load voltage and stator current even with large unbalanced non-linear loads are also found to be much smaller compared with similar systems reported earlier in the literature.

Secondary Control for Voltage Quality Enhancement in Microgrids

In this paper, a hierarchical control scheme is proposed for enhancement of sensitive load bus (SLB) voltage quality in microgrids. The control structure consists of primary and secondary levels. The primary control level comprises distributed generators (DGs) local controllers. Each of these controllers includes a selective virtual impedance loop which is considered to improve sharing of fundamental and harmonic components of load current among the DG units. The sharing improvement is provided at the expense of increasing voltage unbalance and harmonic distortion. Thus, the secondary control level is applied to manage the compensation of SLB voltage unbalance and harmonics by sending proper control signals to the primary level. DGs compensation efforts are controlled locally at the primary level. The system design procedure for selecting proper control parameters is discussed. Simulation results are provided in order to demonstrate the effectiveness of the proposed control scheme.

Selective compensation of voltage harmonics in grid-connected microgrids

In this paper, a novel approach is proposed for selective compensation of main voltage harmonics in a grid-connected microgrid. The aim of compensation is to provide a high voltage quality at the point of common coupling (PCC). PCC voltage quality is of great importance due to sensitive loads that may be connected. It is assumed that the voltage harmonics are originated from distortion in grid voltage as well as the harmonic current of the nonlinear loads. Harmonic compensation is achieved through proper control of distributed generators (DGs) interface converters. The compensation effort of each harmonic is shared considering the respective current harmonic supplied by the DGs. The control system of each DG comprises harmonic compensator, fundamental power controllers, voltage and current proportional-resonant controller and virtual impedance loop. Virtual impedance is considered at fundamental frequency to enhance power control and also at harmonic frequencies to improve the nonlinear load sharing among DGs. The control system design is discussed in detail. The presented simulation results demonstrate the effectiveness of the proposed method in compensation of the voltage harmonics to an acceptable level.

Grid-Interfacing Converter Systems With Enhanced Voltage Quality for Microgrid Application—Concept and Implementation

Grid-interfacing converter systems with enhanced voltage quality are proposed for microgrid applications in this paper. By adapting the conventional series-parallel structure, a group of grid-interfacing system topologies are proposed for the purpose of interfacing local generation/microgrid to the grid, or interconnecting microgrids. The functionality of the proposed systems is also reconfigured in order to ease the control design and to improve overall system performance, differing from existing series-parallel structure-based systems. Experiments with a concrete laboratory system are given to detail the proposed concepts and to demonstrate the practical implementations. Two three-phase four-leg inverters, together with dc microsources and nonlinear loads, are employed to construct a general series-parallel grid-interfacing system. Through the introduction of multilevel control objectives, it is illustrated that the proposed system could ride through voltage disturbances and continue the power transfer between the local generation and the grid, while a high-quality voltage is maintained for the local loads. The system also shows the possibility to achieve auxiliary functions such as voltage unbalance correction and harmonic current compensation. The main design aspects of the controllers are specified, and the entire system is effectively validated on a laboratory setup.