Grid-connected Voltage Source Inverter Research Articles

Direct Power Regulation of Grid-Connected Voltage-Source Inverters Based on Bang-Bang Funnel Control

Direct Power Regulation of Grid-Connected Voltage-Source Inverters Based on Bang-Bang Funnel Control

Power management and optimized control of hybrid PV-BESS-grid integrated fast EV charging stations

The rapid growth of on-road electric vehicles (EVs) empowered the increasing demand for charging stations, hindering widespread EV adoption due to factors like limited range and insufficient charging infrastructure. To address these concerns, the implementation of DC fast charging stations (FCSs) has emerged as a solution to reduce charging time and promote industry adoption. However, the integration of such FCSs poses challenges in terms of power management, power quality and charging service stability, especially in weak grid infrastructures. This paper proposes a power management strategy for a DC-FCS located near highways, aiming to provide stable, fast, and reliable charging services to EVs while minimizing grid dependency. The proposed strategy incorporates various energy sources and operation modes to ensure charging service stability. Additionally, an optimized tuning control based on an improved Snake optimization (ISO) algorithm is introduced to enhance the performance of the grid-connected voltage source inverters (VSIs) in the DC-FCS. The optimized tuning method using the proposed algorithm shows superior performance compared to other methods. Simulation and experimental tests validate the effectiveness of the proposed system, showcasing its potential for efficient management, stable charging service, and improved power quality in the DC-FCS.

Modelling and design of grid voltage oriented vector control scheme for DC railway recuperating system

The braking energy harvested by a railway vehicle can be restored to the utility grid with a power recuperating system. A grid connected voltage source inverter (VSI) is commonly used as a grid-feeding converter in the recuperating system. This paper proposes to integrate grid voltage oriented vector control (GVOVC) and third harmonic voltage injection pulse width modulation (THVI-PWM) technique for the VSI to ensure grid voltage and frequency synchronization. A simulation study is carried out to evaluate the feasibility of the proposed control and modulation schemes using MATLAB/Simulink. The results show that the proposed controller may reach steady-state operating mode within 7 ms by producing good quality AC voltages and currents waveforms. With the independent control of voltage quantities in dq reference frame, the regulation of active and reactive power could be realized.

Resonance suppression and quality improvement control strategy for a three-phase grid-connected voltage-source inverter under weak grid conditions

The three-phase voltage-source grid-connected inverters suffer from grid-connected current quality problems due to system resonance caused by the under-damping characteristics of the filter and grid impedance, on the one hand, and the grid-connected current distortion caused by the high content of low harmonics in the grid voltage, on the other hand. To resolve this problem, a current quality improvement control strategy, combining capacitor-current feedforward active damping and harmonic virtual impedance reshaping, is proposed by analyzing the mechanisms of system resonance and grid-connected current distortion. In addition, the proposed control strategy allows determining the virtual impedance parameters by using the root locus method, so as to achieve the purpose of improving the output grid-connected current quality of the three-phase voltage-source grid-connected inverter under weak grid conditions. Finally, the correctness and effectiveness of the proposed control strategy are verified by simulation and experiment.

An Evolutionary Annealing–Simplex Method for Inductance Value Selection for LCL Filters

Grid-connected voltage-source inverters (VSIs) have evolved over the past years for the interconnection of renewable energy sources with the grid to satisfy the increased electrical load demand and utilize clean carbon-free energy. However, VSIs suffer a significant drawback of switching harmonics caused by the inverter switches. To reduce the amount of current distortion injected into the utility grid and meet harmonic constraints as defined by power quality standards, an LCL filter is often used. Although extensive literature describes assorted design procedures for an LCL filter, all these methods cannot guarantee an optimal solution, because no direct mathematical function between the LCL filter parameters and the total harmonic distortion (THD) exists. Presented in this paper is the application of an evolutionary annealing–simplex method to select the inductance values in the LCL filter. This method is compared to other methods previously presented in the literature: a systematic method and an inductance grid-search method based on a calculated distribution of total harmonic distortion for various inductance values. The goal is to select the smallest overall inductance values to ensure lower manufacturing costs while maintaining the filter performance. Simulation and experimental results verify that at least a 40% reduction in overall inductance can be achieved with the proposed method while simultaneously guaranteeing the filtering performance.

Multi-resonant Controller Design for a PV-Fed Multifunctional Grid-Connected Inverter in Presence of Unbalanced and Nonlinear Load

The use of Active Power Filters (APFs) in future power grids with high penetration of nonlinear loads is unavoidable. Voltage Source Inverters (VSIs) interfacing Photovoltaic (PV) generator could play the APF role in addition to power supply. In this paper, the control of a PV-fed multifunctional grid-connected three-phase VSI is addressed with nonlinear and unbalanced load. The control objective is threefold. The first one is to deliver the maximum available power from the PV source to the grid satisfying power quality standards. The second one is the Voltage Balancing Control for DC-link capacitors to guarantee correct operation of the VSI. The last one is shunt APF control to compensate for nonlinear and unbalanced load harmonics, reactive power, and unbalanced sequences. A quasi-Proportional-Resonant (PR) controller with harmonic compensators is proposed for the current control loop. The quasi-PR controller parameters are determined through optimization algorithms such as Particle Swarm Optimization (PSO), Genetic Algorithm (GA), and a combination of both PSO and GA. The aim of the objective function is to improve static and dynamic behavior. The different gains at the fundamental resonant frequency and the selected odd harmonics are obtained for the proposed quasi-PR controller. The dynamic characteristics of the optimized quasi-PR controllers show superiority against conventional ones in terms of gain margin, phase margin, overshoot, and robustness. With the proposed control scheme, the harmonics, reactive power, and unbalanced sequences are appropriately compensated. The performance of the PV-fed VSI shunt APF under irradiance change, load change, and distorted grid voltage conditions is validated through numerical simulations performed on hbox {PSIM}^{copyright } software. The results show that the grid currents Total Harmonic Distortion for irradiance change case study are 4.57%, 4.57%, and 3.22% in phase a, b, and c with the proposed control method, while they are 9.25%, 5.65%, and 10.12% with conventional instantaneous p-q theory.

2DOF-based current controller for single-phase grid-connected voltage source inverter applications

This paper presents the design of a discrete-time control scheme for the current injected into the grid by a single-phase voltage source inverter (VSI). The VSI is connected to the grid by means of an LCL filter that attenuates the switching harmonics present in the output waveform of the inverter. The current control is based on a resonant regulator implemented in a Two-Degrees-Of-Freedom (2DOF) scheme that allows the location of all the poles to be defined in the closed loop of the system without the need for observers and measuring only the current injected into the grid. This control scheme, therefore, allows the attenuation of the resonance frequency of the LCL filter and requires no additional damping methods with which to mitigate the resonance phenomenon. The design parameters can be obtained using a fairly straightforward mathematical approach that involves only operations with real numbers. The simulation and experimental results obtained show that the control scheme performs correctly even considering changes in the grid inductance.

Power Decoupling Method for Voltage Source Inverters Using Grid Voltage Modulated Direct Power Control in Unbalanced System

The grid voltage modulated direct power control (GVM-DPC) is a novel power regulation method for grid-connected voltage source inverters (VSI). However, interactions between real and reactive powers still exist in GVM-DPC under unbalanced grid voltage condition, which may deteriorate its transient performance. This article proposes a power decoupling method for GVM-DPC-based VSI in unbalanced systems based on the dynamic feedforward power compensation strategy, which can reduce the coupling magnitudes of real and reactive powers in the transient stages. First, the power coupling mechanism of positive and negative sequence real and reactive powers of VSI under the unbalanced voltage condition is analyzed. Then, the power coupling magnitudes (PCM) are derived according to relationships among the positive sequence components of real power, reactive power and point of common coupling (PCC) voltages. Next, the PCM are compensated into the GVM-DPC for the better decoupling performance. Furthermore, a stability analysis of the proposed control system is studied based on the impedance model, and a comparison with the traditional power decoupling method based on virtual impedance is conducted to show the superiority of the proposed method. Finally, simulations, hardware-in-loop test and experiment are conducted to validate the effectiveness of the proposed method.

Sliding Mode Control for Single-Phase Grid-Connected Voltage Source Inverter with L and LCL Filters

This paper presents an analysis of the sliding mode control (SMC) method applied to a single-phase grid-connected voltage source inverter (VSI) with L and LCL filters. First, simulation results were presented for the L filter, and then, after some adjustments, the same theory was applied to the LCL VSI with active damping. To improve the obtained results for the SMC control, we adopted the hyperbolic tangent function and the explicit establishment of the modulation index m in the mathematical procedure to help reduce the chattering phenomena; later on, the same function was replaced by the usage of a proportional plus resonant controller to continuously improve the control system responses.

An FPGA Hardware-in-the-Loop Approach for Comprehensive Analysis and Development of Grid-Connected VSI System

Power electronic converters are used for an efficient and controlled conversion of power generated from renewable energy sources and can interface generated power to the grid. Among available power converters, voltage source inverters (VSIs) have been widely employed for grid-connected applications due to better controllability with higher efficiency. Although various conventional, as well as modern control techniques, have been developed for grid connected VSI system, there is a need to select suitable control technique based on application and control requirements. Hardware-in-the-loop (HIL) is considered as a realistic approach for the development of system and control due to the inclusion of an actual hardware system. In this paper, a HIL approach is adopted for the comprehensive analysis and development of a grid connected VSI system using a field programmable gate array (FPGA). The control techniques must deal with trade-off, based on the features and limitations. Therefore, a grid-connected VSI system is developed considering employment of two different conventional control techniques: hysteresis current control (HCC) and PI-based space vector modulation (PI-SVM), as well as finite state model predictive control (FS-MPC) as a modern control technique for investigation considering different parameters. All three control systems are developed through a digital simulator of Xilinx that is integrated with MATLAB-Simulink, while considering an FPGA based system development and testing through FPGA HIL co-simulation methodology.

A New Type of Three-Phase Asymmetric-LCL Power Filter for Grid-Tied Voltage Source Inverter With Step-Up Transformer

Power filters have been widely used to suppress switching harmonics caused by the modulation of grid-connected inverters. In order to save the total inductance and cost and reduce the volume, different power filters were proposed for the three-phase three-wire grid-connected voltage source inverter. However, in industrial applications, due to the consideration of production cost, the difficulties caused by the deviation of actual parameters have to be addressed. In this article, we propose a new three-phase three-wire power filter with a simple structure, almost the smallest total inductance, and strong resistance to the adverse effects of parameter shifts. The parameters of the proposed filter and the design of the grid-connected system controller are introduced in detail. When studying the influence of parameter offset, a comparison between different types of notch power filters is also given. Simulation and experimental results on a 380 V/50 Hz/6 kW three-phase inverter prototype verify the performance of the proposed power filter.

An Adaptive DC-Link Voltage Control of a Multifunctional SPV Grid-Connected VSI for Switching Loss Reduction

In the proposed method in this article, to minimize the burden on the switches of the multifunctional grid-connected voltage-source inverter (MFGCVSI), the voltages of dc-link split capacitors are adjusted according to power injection from the MFGCVSI. The MFGCVSI is used to control the active power injection from solar photovoltaic (SPV) power generation to the main grid and loads, load reactive power compensation, harmonic mitigation, and main grid current total harmonic distortion within 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> . In such a case, the voltages of split capacitors depend on the rated power injection from the MFGCVSI. The power generated from the SPV system and the loads that are connected at the point of common coupling vary with respect to time. It is observed that the selection of rated dc-link voltages during low power injection from the MFGCVSI leads to additional switching stress and higher switching losses. Therefore, to reduce the burden on inverter switches and switching losses, the reference dc voltage is reduced under low power injection from the MFGCVSI. A model predictive controller with a multiconstraint technique is used in the proposed method for balancing the dc-link capacitor voltages and average switching frequency reduction. The proposed method is validated through simulation and hardware setup.

DC-Link voltage control of a multifunctional PV-GCVSI to reduce VSI switching losses

ABSTRACT The reference input dc voltage of grid connected voltage source inverter (GCVSI) is altered in this article based on power (both active and reactive) injection from GCVSI for minimising inverter switching losses, and total harmonic distortion (THD) of grid current. If the GCVSI is exclusively used for actual power injection from the photo-voltaic (PV) system to the utility grid, the needed input dc voltage of GCVSI is twice the utility grid phase peak voltage. According to the literature, GCVSI is also used to compensate for power quality issues, and in these circumstances, the dc-link voltage value is determined by the maximum power injection of GCVSI. Under reduced load, and reduced power generation from the PV system, keeping maximum GCVSI input dc voltage reference causes extra voltage stress at GCVSI switches, and the grid current THD is worse due to high ripple current in filter inductance. Therefore, to reduce the inverter switching losses and to improve the grid current THD, the relationship between the GCVSI input dc voltage reference and the power flow from GCVSI has been formulated. The proposed work is verified using simulation studies, as well as hardware studies, and the results are compared with existing methods for validation.

Adaptive finite-time parameter estimation for grid-connected converter with LCL filter

This study proposes an online finite-time adaptive parameter estimation method for grid-connected voltage source inverter (VSI) with LCL filter. In this framework, a time-continuous state-space system model is first developed, which is different from the nonparametric frequency-response-based method. Then, the parameter estimation error information is extracted by introducing a series of filter operations. Moreover, a sliding mode term is studied and cooperated with the obtained parameter estimation error to design the parameter estimation error-based finite-time adaptive parameter estimation algorithm. With the help of this novel adaptive law, the physical parameters of electrical components can be driven to their true values accurately and fast. Theoretical analysis is conducted in terms of the Lyapunov theory to demonstrate the convergence of the parameter estimation error. Finally, numerical simulation results are provided to illustrate the superiority of the proposed method over the conventional method.

A Three-Phase Grid Connected Photovoltaic System with Modified MPPT Method

In this study, a three-phase grid-connected Photovoltaic system is demonstrated. A photovoltaic (PV) system that is connected to the grid, provides several benefits, including a topology that is simple, high efficiency and so on. Considering control scheme difficulty greatly enhanced because of all the regulatory requirements, which are maximum power point tracking (MPPT), coordinated with the supply voltage, harmonic drop as a current output, must be addressed at the same time. The DC/DC converter, solar panels, DC-link, three-phase voltage source inverter (VSI) on the grid, as well as output filters are all detailed representations of the essential components of the system in this model. Line current harmonic distortion should be reduced. A sophisticated control strategy with two PI controllers and MPPT is purposed in this paper to stabilize DC voltage. A robust phase- locked loop (PLL) synchronizes a grid-connected voltage source inverter with three phases. The simulation and practical findings reveal that the stability as well as efficiency of a three-phase grid connected PV system are high. Keywords- solar energy, grid-connected inverters, photovoltaic (PV), maximum power point tracking (MPPT).

Adaptive Virtual Resistance for Postfault Oscillation Damping in Grid-Forming Inverters

Postfault oscillations in active power and voltage responses of grid-connected voltage source inverters (VSIs) have been reported in the literature. They are caused by nonideally tuned controllers and the implemented current limitations used for protecting the VSIs from overcurrents. These oscillations become even more significant when the VSI is connected to a weak grid, deteriorating the recovery process of the VSI. This article presents a method for damping the postfault oscillations by using an adaptive virtual resistor (VR). Even though these oscillations are observed with both grid-following and grid-forming inverters, this article focuses on droop-based grid-forming inverters. The proposed method dynamically integrates a VR into the VSI control and removes it in the normal operation mode of the VSI. This method is implemented in the synchronous reference frame, which is commonly used due to its decoupled active and reactive power control. The amount of virtual resistance used for oscillation damping is adaptive to the recovery rate of the VSI. Hence, the proposed method is robust against changes in grid strength. Finally, the performance of the method is evaluated in PSCAD/EMTDC and also experimentally validated.

Fuzzy tuned real and reactive power regulation in GC-VSI for PV systems

ABSTRACT Operating solar Photovoltaic (PV) under fluctuating irradiation and load with variable profiles is a challenging job. Besides, reactive power demand in grid-connected solar PV system makes it more challenging because of its limitations in reactive power capability. As per Indian electricity grid codes, reactive power compensation comes under ancillary services and it is mandatory nowadays. On PV source side, DC/DC boost converter, and on grid side, traditional three-phase Grid-Connected-Voltage Source Inverter (GC-VSI) are taken for research study. If real power delivered to the grid by GC-VSI is less than the capacity, the surplus capacity is used to provide reactive power. Normally, shunt capacitors or Flexible Alternating Current Transmission System (FACTS) devices are used at Point of Common Coupling (PCC) as compensation devices. In this work, the DC-link capacitor employed in front end of GC-VSI is utilised to serve reactive power control to the grid. An effective fuzzy-tuned direct current vector control is implemented to enrich reactive power control. Simulation studies carried with extensive MATLAB/Simulink platform illustrate the efficacy of suggested system and reveal that proposed approach is capable of effective reactive power support by the DC-link capacitor and extraction of maximum possible power from PV arrays.

Switching Frequency Formulation for Predictive Current Control in Grid-Connected VSI

In this paper, a switching frequency has been formulated for grid-connected voltage source inverter (VSI) operated using the Continuous Control Set-Predictive Current Control (CCS-PCC) technique. An instantaneous expression of switching frequency has been derived for the VSI operated using the predictive current control technique. The effect of sampling frequency has been analyzed on the switching frequency of the converter operation. The effect of sampling time has a direct impact on the switching frequency as the cost function of the PCC depends on the sampling frequency. The analysis provides a generalized mathematical expression of switching frequency for the VSI operating in current control mode using the predictive current control method. With the help of this generalized expression, the maximum switching frequency and minimum load current error have been obtained. Simulation has been performed for verification of the analytical results through a Typhoon HIL-402 kit for real-time simulation and experimental validation.

Integration of Photovoltaic to the Grid Using Hysteresis Current Control

This research paper deals with the increasingly urgent energy issues; the world attaches great importance to begin the development of new energy and related technology. At present, large-scale photovoltaic power generation and scale of renewable energy have become parts of development strategy, meanwhile, it is the way to guide the development of the photovoltaic industry. However, because of its own characteristics different from conventional power generation grid-connected PV power station and its security, stability, reliable operation become new challenges that power grid and PV power plant need to face. Grid-connected voltage source inverters are essential for the integration of the distributed energy resources. However, due to the small capacity and intermittent nature of renewable sources, it is extremely difficult to integrate them into the existing grid system. This project has taken an attempt to design a control method for a three-phase grid-connected inverter system for distributed generation applications. The method is hysteresis current control along with PI control. Hysteresis current control is a commonly employed method for power control of VSI. The control procedure is implemented in an analog circuit using Op-amps and other ICs. This controller will generate pulses to fire the inverter in order to control the current output of the inverter. The control method along with the PI controller provides robust current regulation and achieves unity power factor. In addition, in this project development of a controller in D Space is attempted. Simulation and experimental results are provided to demonstrate the effectiveness of the design.

Optimal design of proportional‐resonant controller and its harmonic compensators for grid‐integrated renewable energy sources based three‐phase voltage source inverters

This paper proposes new analytical and optimal design procedures of the proportional-resonant (PR) controller and its harmonic compensators (HCs) for three-phase grid-connected voltage source inverters (VSIs) powered by renewable energy resources. The modeling and analysis based on stationary reference frame are performed for VSIs collaborated with an L-type filter. The theoretical verification and simulation validation of the proposed design guidelines are done to approve its effectiveness and robustness. Particle swarm, grey wolf and Harris hawks' optimization techniques are applied and compared for a proper selection of the parameters of the proposed PR controller and its HCs. To accomplish this study, multi-objective error functions are employed and compared to minimize the total harmonic distortion of the grid output current. The proposed PR controller and its HCs are tested, using MATLAB/Simulink, along with the allowable changes of inverter output active and reactive powers, and also under the grid voltage distortion. Moreover, their performance is evaluated according to IEEE and IEC harmonics standards, and compared with the conventional PI controller based on reference frame. Furthermore, the experimental validation for the proposed controllers is done based on the hardware-in-the-loop real-time simulator using C2000TM-microcontroller-LaunchPadXL-TMS320F28377S kit.