Compensation Of Nonlinear Loads Research Articles

A Novel Algorithm for Optimal Harmonic Load Flow including Harmonic Compensation

Load flow analysis is widely used for finding voltage at various parts of a large, interconnected power system. The exponential increase in the use of power electronic devices and the noticeable percentage of integration of renewable energy sources in modern power systems result in the occurrence of non-sinusoidal voltages at various parts of the power system. By reformation of the Newton-Raphson load flow method, a few harmonic load flow algorithms have been developed for modern transmission systems. However, for larger transmission systems, complexity and heavy computational burden are often encountered in the load flow solution process due to the increased size of the Jacobean matrix that further increases with multiple non-linear load buses and compensation requirements. This leads to convergence problems and increased execution time. In this paper, an optimal harmonic load flow algorithm is proposed, that employs a modified PSO technique to select control variables and the harmonic load flow method to find solutions for load flow analysis with a reduced size of the Jacobean matrix. The formulated method uses a simple technique to take into account nonlinear loads and results in faster convergence. The novelty of the algorithm is that an optimal load flow solution with the desired amount of reactive and harmonic compensation currents is obtained. The algorithm can help in getting load flow solutions in future power systems with distorted voltage and currents with compensation. The performance of the proposed algorithm is tested on a modified IEEE 30-bus system with multiple non-linear load buses and is validated with the Simulink model of the system.

Performance Analysis of Universal Power Quality Conditioner Systems Based on Seven-level NPC Inverter Using PD-SPWM with Fuzzy Control Scheme

This paper presents novel Unified Power Quality Conditioner (UPQC) system based on seven-level Neutral Point Clamped (NPC) inverter using combined PD-SPWM and fuzzy control scheme. The proposed UPQC is adopted to mitigate source current harmonics and compensate all voltage disturbances simultaneously. It is designed by the combination of series and shunt Active Filters (AFs) connected by a common DC link capacitor. The DC voltage at common DC bus is maintained constant using proportional integral voltage controller. The Synchronous Reference Frame (SRF) method is used to get the shunt APF reference signals and the power reactive theory (P-Q theory) for the series APF. Conventional control schemes require complex calculations, the use of intelligent systems help to reduce the control system size and the operation complexity. The shunt and series Active Power Filter (APF) reference signals derived from the control algorithm are injected in Fuzzy intelligent controllers to generate switching signals. The functionality of proposed UPQC system and its control system is evaluated using Matlab-Simulink software and SimPowerSystem Toolbox under various operation conditions in cases of most common power quality problems such as voltage sag, voltage swell, current harmonic compensation of nonlinear loads and unbalanced load. The simulation results show UPQC performances to improve the power quality in steady and transient conditions operation at the point of common coupling on power distribution under unbalanced and distorted voltage conditions.

Global identification and compensation of nonlinear variable load for an electrohydraulic system

In an electrohydraulic system, the load is an external factor that cannot obtain similar results by repetitive experiments compared with other internal factors. It can work a great change in an extremely short time determined by the characteristics of the loaded object, which is more difficult to be identified timely and compensated precisely. This paper first built the mathematic model of the electrohydraulic system containing load characteristics and illustrated most kinds of basic loads that possibly occur in it. Then, a practice nonlinear variable load composed of these basic loads is presented, and the corresponding effect to the electrohydraulic system is analyzed. Based on the summary of load, a nonlinear variable load compensation controller (NVLCC) with neural networks is proposed to identify the mathematic model of the electrohydraulic system. The nonlinear variable load is considered as a part of the model to be globally identified, and an adaptive sliding mode control method is combined to quickly converge the errors of system state variables. The compensation effectiveness is demonstrated by both rigid step response and dynamic sine response in the simulations, and the actual improvements are verified with the experiments using three different typical linear loaded objects and a representative nonlinear loaded object.

Operation Limits of Grid-Tied Photovoltaic Inverters With Harmonic Current Compensation Based on Capability Curves

Generally, due to variations in solar irradiance, photovoltaic (PV) inverters operate below their rated current. Therefore, the available current margin can be used to perform ancillary services, such as reactive power control and harmonic current compensation (HC) of nonlinear loads. An important component of the PV system is the passive filter, which attenuates the harmonic generated by inverter switching. The filter may reduce the inverter ability to compensate the harmonic currents. This work presents an investigation of inverter capability to provide HC of nonlinear loads. An algorithm is proposed to determine the capability curves of a multifunctional inverter during harmonic current compensation. The proposed methodology is validated in an experimental setup. The obtained results show that the proposed modeling can estimate with accuracy the minimum required dc-link voltage, when harmonic current compensation is performed by the PV inverter. Also, a sensitivity parameter analysis is carried out. Thus, the main system parameters that affect the inverter capability to provide harmonic current compensation are identified. Furthermore, simulation and experimental results validate the proposed approach.

Multimode Operation of Solar PV Array, Grid, Battery and Diesel Generator Set Based EV Charging Station

This article deals with the multimode operation of a photovoltaic (PV) array, a battery, the grid and the diesel generator (DG) set-based charging station (CS) for providing the continuous charging and uninterruptible supply to the household loads. In this CS, a single voltage source converter operates the CS in an islanded mode, the grid connected mode and the DG set connected mode (DGM) and performs various tasks, such as power management among different energy sources and charging the electric vehicles (EVs), extraction of maximum power from the PV array, the regulation of voltage and frequency of the generator, harmonics current compensation of nonlinear loads and intentional reactive power compensation. The control of charging station (CS) is designed such that it primarily takes power from the PV array and a storage battery. In the absence of these two sources, the charging station takes power from the grid, and at last, it utilizes a squirrel cage induction generator-based DG set. However, the DG set is operated such that it generates up to 33% more power than its rated capacity without exceeding the rated current in windings, therefore, the size of the DG is reduced. Moreover, the voltage and frequency of the generator are regulated at its rated values without a mechanical speed governor. In all operating modes, the CS complies with the IEEE 1547 standard and the total harmonic distortion of voltage and current, is achieved less than 5%.

To study unplanned islanding transient response of microgrid by implementing MSOG and SRF‐PLL based hierarchical control in the presence of non‐linear loads

This study considers the hierarchical control of microgrid and harmonic compensation of non-linear load specially in transition from grid-connected to unplanned islanding. The proposed controllers are based on the stationary reference frame with hierarchical control levels (inner, primary, and secondary). In the inner control loop, proportional and multi-resonant voltage and current controllers for three-phase voltage source inverters are proposed. Moreover, a droop control is used to share active and reactive power in the primary control loop. To achieve decoupled active and reactive power sharing, virtual impedance loop is implemented, too. The mentioned procedure increases the total impedance and consequently reduces the initial current and subsequently facilitates the continuous connection of DGs to the MG. To attain smoother transition, selective harmonic virtual impedance is applied by multiple second-order generalised integrator module to extract the fundamental positive sequence and harmonic components of the output current of the DGs. In secondary control level, synchronisation procedure is considered to make connection and restoration by the advanced three-phase synchronous reference frame PLL with in-loop moving average filter which significantly enhances its disturbance rejection capability. The results are shown smoother transition, robustness, and high performance of the proposed hierarchical control VSIs during variation of system configuration.

Frequency Adaptive Multistage Harmonic Oscillator for Renewable-Based Microgrid Under Nonideal Grid Conditions

Diurnal and seasonal variability associated with the renewable power generation is disinterested by grid integration. However, for the cases of developing and underdeveloped countries, the utility grids are relatively weak and exacerbate the issues related to power quality, frequency jumps, grid voltage distortion, sag, and swell. To deal with these issues of weak grid-integrated hybrid-renewable-power-generation-based microgrid and to ensure reliable and effective operation, the frequency adaptive multistage harmonic oscillator (MSHO) control is used in this article. This control comprises of multistage filter with dc bias rejection loop and frequency-locked loop. The multistage filter is tuned to dominant lower order harmonic and allows the selective elimination of the harmonics. An MSHO is used for assessing the fundamental constituent from harmonics and dc-bias-infected grid voltage. It also extracts the positive-sequence constituent from distorted/unbalanced grid voltages while maintaining the balanced grid currents. It effectively overcomes the frequency perturbations and nonlinear load compensation and significantly increases the overall reliability and quality of power. A set of back-to-back associated power converters provide a flexible speed operation of the wind power generation system. Different functionality modes are incorporated in order to address round the clock operation of the microgrid, enabling the reactive power compensation capability and mitigation of the harmonics demanded by the nonlinear load connected at the distribution side. The maximum power operating point for both wind and solar photovoltaic arrays is acquired by the individual implementation of the perturb and observe technique. The performance investigation of the system is carried out on a developed laboratory prototype. The aptness and the functionality of the control algorithms are noticeable from the experimental results. The issues of loss of supply, estimation of grid voltage signal, effects of weak grid, variability of renewables with curtailable load are addressed, and the power quality standard IEEE-519-2014 is satisfied.

Frame-Angle Controlled Wavelet Modulated Inverter and Self-Recurrent Wavelet Neural Network-Based Maximum Power Point Tracking for Wind Energy Conversion System

In this work, a new control methodology is proposed for Type -IV wind energy conversion system (WECS) using a self-recurrent wavelet neural network (SRWNN) control with a Vienna rectifier as the machine side converter (MSC). A SRWNN combines excellent dynamic properties of recurrent neural networks and the fast convergence speed of wavelet neural network. Hidden neurons of SRWNN contains local self-feedback loops, which provide the memory feature and the necessary information of past values of the signals, allowing it to track maximum power from WECS under varying wind speeds. The Vienna rectifier allows unity power factor operation to increase electrical efficiency. Frame angle-controlled wavelet modulation is proposed for the grid side converter (GSC). Wavelet modulated inverter produces output voltage fundamental components with higher magnitudes than those obtained from the pulse width modulated inverters. The non-linear load compensation and power quality enhancement are achieved by executing frame angle control for WM inverter. The overall system is modeled, and performance is verified in MATLAB Simulink. The hardware prototype is developed, and the switching pulses for the rectifier and inverter are generated using dSPACE1104 controller. The results prove that the system provides low harmonic content and high magnitude of the fundamental current component at the machine and grid sides and ensures maximum power operation at various wind speeds.

Partial Harmonic Current Compensation for Multifunctional Photovoltaic Inverters

Recent works have addressed the ancillary services provided by multifunctional photovoltaic inverters. This concept is based on the addition of extra functions to the conventional photovoltaic systems, such as harmonic current compensation of nonlinear loads and reactive power support. However, it is important to ensure that photovoltaic inverters work below the rated current peak. Therefore, this paper proposes two current dynamic saturation techniques to limit the current peak of multifunctional photovoltaic inverters during harmonic current compensation of nonlinear loads. One technique is based on a closed loop and other on an open loop. With this approach, the photovoltaic inverters are able to perform partial harmonic current compensation, i.e., it will only be allowed to compensate harmonic currents within their maximum current capacity. Mathematical models are developed to determine the parameters of the techniques. Comparisons in simulation and experimental environments show that both techniques provide improvements in the grid power quality at the same time as the inverter rated current capacity is respected.

Development of Wind and Solar Based AC Microgrid With Power Quality Improvement for Local Nonlinear Load Using MLMS

This work proposes a microgrid ( μ -grid) integrating wind and solar photovoltaic (PV) resources, along with the battery energy storage (BES) to the three-phase grid feeding the nonlinear load. The μ -grid disconcerted by probabilistic nonlinear time dependent parameters and their effects are compensated by cohesive controllers used for utility grid side voltage source converter (GVSC) and machine side voltage source converter (MVSC). The switching controls and the reconfigurability of the μ -grid are addressed on imperative aspects of improving power quality (PQ), power reliability, nonlinear load compensation, and economic utilization of resources. The nonlinear load compensation and PQ enhancement are achieved by executing modified version of the adaptive filtering technique including “momentum”-based least mean square (MLMS) control technique, utilized for providing the switching control signals to the GVSC. It utilizes two preceding gradient weights for obtaining updated weight thereby improving the convergence rate and overcoming the limitation of conventional control of the same family. The MVSC acquires its switching signals from conventional vector control scheme and the encoderless estimation of speed and rotor position of the synchronous generator driven by wind turbine through back electromotive force control technique. The external environmental disturbances are overcome by utilizing perturb and observe (P&O) maximum power point (MPP) for wind optimal power extraction and adaptive P&O with variable perturbation step size for solar MPP estimation. Test results are obtained from the laboratory prototype under steady-state and dynamic conditions, including altering wind speed, intermittent solar insolation, and variable load conditions. The PQ issues are addressed and investigated successfully.

Design and Control of a STATCOM for Non-Linear Load Compensation: A Simple Approach

Abstract This paper presents a systematic procedure to design a simple control for a three-phase VSC-based static synchronous compensator (STATCOM) in order to overcome the problems caused by the presence of the non-linear load at the point of common coupling (PCC). The proposed control method regulates the STATCOM in such a way that the source quadrature current component is forced to be zero so that only the active current component is drawn from the source and the harmonic and reactive current demands of the non-linear load are met by the STATCOM. The tuning of the inner and outer loop PI controllers is carried out with the help of the modulus optimum and symmetric optimum criteria, respectively. At last, a few case studies are presented using MATLAB simulation to exemplify the success of the proposed control method.

Proactive operation of electric vehicles in harmonic polluted smart distribution networks

This study proposes combined framework for proactive operation, i.e. bidirectional active and reactive power management, of the smart distribution network as well as harmonic compensation of non-linear loads using electric vehicles (EVs) equipped with bidirectional chargers. The problem is in the form of non-linear programming (NLP) where the objective function is to minimise the voltage deviation at the fundamental frequency and the total harmonic distortion. The harmonic load flow equations, EVs constraints, system operation and harmonic indexes limits are formulated as problem constraints. The proposed NLP problem is converted to an equivalent mixed integer linear programming (MILP) model using Taylor series and linearisation techniques for AC power flow formulation. Also, the Benders decomposition (BD) algorithm is used to solve the proposed MILP problem that is tested on different distribution test networks to demonstrate its efficiency and performance. The results show that the NLP model can be substituted with the high-speed linear programming model. Moreover, the computation speed is improved by using the BD method. Finally, the network and harmonic indexes improved and charging cost reduced using the proposed idea.

Two alternative robust optimization models for flexible power management of electric vehicles in distribution networks

This paper presents a robust optimization problem of the flexible bidirectional power management of a smart distribution network and harmonic compensation of nonlinear loads using electric vehicles (EVs) equipped with bidirectional chargers. The base deterministic model of the proposed problem is as mixed-integer nonlinear programming (MINLP), having the objective function to minimize the economic and technical indices subject to harmonic load flow equations, EVs constraints, system operation and harmonic indices limits. This model is converted to a mixed-integer linear programming (MILP) model in the next step. In the proposed MILP model, the active, reactive and apparent loads, electrical energy, reactive power and harmonic current prices, as well as EVs characteristics, are considered uncertain parameters. Accordingly, two alternative robust optimization approaches have been implemented for the conditions of having both the probability distribution function or the bounded uncertainty in the proposed MILP problem model. The proposed model is tested on distribution networks to demonstrate its efficiency and performance. The results show that the MINLP model can be substituted by the proposed high-speed MILP model. In addition, the capacity of the injecting power of EVs is reduced in the worst-case scenario with respect to the scenario that is used in the deterministic model, while the consumed power of loads and EVs and energy price increases in this scenario. Finally, the payment of EV owners is reduced by considering EVs power and harmonic control.

A new proposal for the design of hybrid AC/DC microgrids toward high power quality

Considering the advantages of DC microgrids, the extension of the conventional AC distribution grid can be implemented using a DC microgrid. This justifies the realization of a hybrid AC/DC microgrid. In the present study, a new global solution is presented to improve the power quality and to fully compensate the reactive power of an AC microgrid using DC bus capacity while introducing a new design for a hybrid AC/DC microgrid. In the new design, back-to-back connections of two series and parallel converters, as well as the presentation of new controllers and simultaneous utilization of an earthing switch, are proposed. The proposed method guarantees the quality of the delivered voltage to consumers and the drawn current from the network according to the IEEE-519 and IEEE-1159 standards under different power quality problems (e.g., interruptions, sags, harmonics, and any variation in voltage/current signals from pure sinusoidal). Through the proposed design of the new hybrid AC/DC microgrid, as a new feature, the operation of the network in islanded mode can be achieved in accordance with power quality standards even in the worst load quality conditions. It should be noted that in common hybrid microgrids in islanded mode, the delivered voltage quality is proportional to the quality of the consumer's load current. Another possibility of the proposed design is the instantaneous VAR compensation of nonlinear and induction loads of consumers to keep the power factor of the distribution transformer close to unit value. Simulation results indicate that there are acceptable levels of compensation for different types of power quality problems. Total harmonic distortions and total demand distortions are below 3% in both the grid-connected and isolated modes of the hybrid AC/DC microgrid.

Novel Three-phase Four-wire UPQC Topology Using Adaptive-network-based Fuzzy Inference System for Voltage Sag Compensation

This Study Proposes the novel four wire UPQC topology for Non-linear load and three-phase fault compensation. The electrical power quality is affected by many factors like harmonic pollution due to non-linear loads such as large thyristor power converters, rectifiers and the voltage/current flickering due to arc furnaces and also the sag and swell creation due to the switching of the loads. To overcome the above mentioned problems use of a combined system of shunt and active series filters like Unified Power Quality Conditioner (UPQC) topology. This device contains the integration of a shunt active filter together with a series active filter in a back to back configuration to simultaneously compensate the supply voltage and the load current. Also, it is used to mitigate any type of voltage and current fluctuations and power factor correction in a power distribution network. In this study a novel design of UPQC proposed for voltage sag compensation by using Adaptive Network based fuzzy inference system (ANFIS). This proposed controller has been provided the dynamic control of shunt and series converter operation. It has the combined operations of FL and Artificial Neural Network (ANN) relative advantages and also a powerful processing tool with both advantages can be obtained by combining them together. The simulation results have verified by using MATLAB/SIMULINK environment.

Real-Time Implementation of Multi Level Inverter for 3P4W Distribution Network using ANFIS Control

Power electronics assumes an essential part in controlling the system joined renewable energy sources. This paper presents a novel changeable or inconstant neuro-fuzzy control approach for the renewable interfacing inverter. The principle target is to complete successfully smooth reactive, functioning or allowing movement in two usually opposite directions power flow and nonlinear unbalanced load compensation all the while, where the conventional proportional-integral controller may end weakly because of the quick change in the motion to a great psychological depth of nonlinear framework. The joined ability of neuro-fuzzy controller in taking care of the instabilities also, derive a benefit from the procedures is ended up being sufficiently valuable to justify the investment of time or interest while controlling the inverter under having unpredictable ups and downs working conditions. The inverter in an effective manner controlled to make payment to compensate the harmonics, reactive power, and the current imbalance of a Three-Phase Four-Wire (3P4W) nonlinear load with created renewable power injection into the grid at the same time. This give qualities or abilities to the network to continuously supply/take up mentally an adjusted arrangement of fundamental currents at unity Power factor calculate even the surrounding or near by region of the 3P4W nonlinear unbalanced load at the point of common coupling. The proposed framework is created and reenacted in MATLAB/Sim Power System environment under distinctive working conditions. The computerized sign handling and control building based lab exploratory results are additionally given to approve the proposed control approach.

LCL filter with passive damping for DSTATCOM using PI and HC regulators indq0current controller for load compensation

This paper presents a Distribution Static Compensator (DSTATCOM) with interface inductor–capacitor–inductor (LCL) filter controlled using dq0 current controller and Sinusoidal Pulse Width Modulation (SPWM) switching for compensation of unbalanced nonlinear load. Voltage Source Inverter (VSI) of DSTATCOM, connected at the point of common coupling (PCC) through interface filter, injects currents corresponding to load reactive and harmonic powers. These currents consist of switching frequency ripples. LCL filter has superior switching ripple attenuation capability compared to L filter. Moreover, this can be achieved with small value of overall LCL filter inductance than L filter. However, one major concern with LCL filter is its resonating frequency (determined from its L, C, L values), which can create resonance currents and results in improper load compensation. Therefore, in the present study, a proper design of LCL filter for high switching ripple attenuation along with passive damping and proper dq0 current controller are presented. The dq0 current controller is implemented in Synchronous Reference Frame (SRF) rotating at fundamental frequency and consists of Harmonic Compensation (HC) regulator (realized by sum of Sinusoidal Signal Integrators (SSI)) in parallel to Proportional Integrator (PI) regulator. SSI provides high gain to specified tuned harmonic frequency and helps in minimizing filter current tracking error for harmonic load current compensation. Neutral current compensation, which is required for compensating unbalance in load, is carried out through 0-axis controller. SPWM strategy generates constant frequency gating pulses for VSI switches. This will simplify the design of interface LCL filter, reduces stress on switches and switching noise. A Matlab/Simulink model of LCL filter DSTATCOM is developed and detailed simulation results of load compensation are presented. Experimental validation of proposed scheme is done on a three phase DSTATCOM prototype using dSPACE 1104 with Matlab Real Time Interface (RTI).

Optimal Control of Shunt Active Power Filter to Meet IEEE Std. 519 Current Harmonic Constraints Under Nonideal Supply Condition

A shunt active power filter (APF) is a well-mature technology for the compensation of nonlinear and/or reactive loads. Normally, the shunt APF is controlled such that it eliminates the load current harmonics and supplies load reactive power to achieve harmonic-free source currents at unity power factor. However, these control objectives cannot be achieved simultaneously when the supply voltages are distorted and unbalanced (nonideal). Hence, under such situation, the shunt APF should be controlled optimally to achieve a maximum possible power factor without violating the current harmonic constraints recommended by IEEE Std. 519. This paper presents an optimal algorithm to control a three-phase four-wire shunt APF under nonideal supply conditions. The optimization problem aiming at maximizing the power factor subject to current harmonic constraints as per IEEE Std. 519 has been formulated and solved mathematically using the Lagrangian formulation. The proposed algorithm avoids the use of complex iterative optimization techniques and thus is simple to implement and has fast dynamic response. The effectiveness of the proposed method is evaluated through a detailed experimental investigation using a digital signal processor controlled shunt APF prototype developed in the laboratory.

Design and tests of a new promising ac electric-power generation system for aircraft

This paper deals with the design and tests of an aircraft ac power-supply converter control system. Possible topologies of power converters are shown, and an appropriate topology with three independent half-bridge inverters is justified. A control scheme with inverter nonidealities and nonlinear load compensation for the selected topology is presented. Practical aspects of the designing software for the control system, are shown and a low-level code optimization to decrease the computing time of the control algorithm is presented. Test results with and without compensation for selected harmonics are shown. The form of the voltage and its spectrum are given for full and nonlinear load.

SRF based current controller using PI and HC regulators for DSTATCOM with SPWM switching

This paper presents Distribution Static Compensator (DSTATCOM) for compensation of unbalanced nonlinear load with dq0 current controller (using proportional integrator and harmonic compensation regulators) and Sinusoidal Pulse Width Modulation (SPWM) switching. The dq0 current controller is implemented in Synchronous Reference Frame (SRF) rotating at fundamental frequency and consists of Harmonic Compensation (HC) regulator (realized by sum of Sinusoidal Signal Integrators (SSI)) in parallel to Proportional Integrator (PI) regulator. The SSI provides high gain to specified tuned harmonic frequency and helps in improving filter current tracking performance for harmonic load current compensation. Each SSI in fundamental rotating dq0 reference frame can simultaneously compensate for two load current harmonics and thereby reducing the computational effort compared to SSI in stationary reference frame. Neutral current compensation, which is required for compensating unbalance in load, is carried out through 0-axis controller. SPWM switching strategy results in switching of inverter switches at constant frequency. This will simplify the design of inverter output filter (L/LC), reduces stress on switches and switching noise. Simulation studies of DSTATCOM load compensation using dq0 current controller with interface L and LC filters is carried out in Matlab/Simulink and the corresponding results are presented. Experimental studies are carried out on three phase DSTATCOM prototype using dSPACE 1104 with Matlab Real Time Interface (RTI).