Three-phase Grid-connected Inverter System Research Articles

Performance enhancement of a three-phase grid-connected PV inverter system using fractional-order integral sliding mode controls

Grid-integrated photovoltaic (PV) systems hold significant promise for sustainable energy production. However, these systems often struggle with maintaining energy quality and stability in the face of fluctuating conditions. To address these challenges, this study proposes the use of fractional-order integral sliding mode control (FO-ISMC) for grid-connected PV systems. The system comprises solar panel arrays, a DC/DC boost converter with its controller, and a three-phase inverter integrated into the utility grid. The primary goals of this study are to maximize power extraction from the PV system and to regulate system currents, thereby improving effectiveness and power quality. The proposed method is further refined using the particle swarm optimization (PSO) algorithm to fine-tune parameter settings. By optimizing the command gains of the FOI-SMC, the PSO algorithm enhances system performance and stability. Leveraging fractional-order and integral terms provides the control signal with additional degrees of freedom, enhancing system performance in the presence of internal and external disturbances. Simulation results demonstrate the effectiveness of the proposed controller compared to the classical controller, where in the case of Irradiation taking the value of 500 W/m2, the proposed strategy reduced the values of constant voltage, active power, and reactive power by percentages estimated at 88.18%, 90%, and 70%, respectively, compared to the traditional strategy. Also, the overshoot value of active power was reduced in all completed cases compared to the traditional strategy by percentages estimated at 53.57%, 66.66%, and 65%, respectively. The proposed strategy reduced the response time of reactive power in all cases compared to the traditional strategy by percentages estimated at 58.59%, 28.80%, and 75%, respectively. These ratios show the high performance of the proposed control in improving the characteristics of the studied system compared to traditional control based on PI control.

Power Quality Improvement using Solar Fed Multilevel Inverter Based STATCOM

The major goal about suggested technique is to use a PSO-based proportional-integral (PI) controller towards enhance power quality performance about three-phase grid-connected inverter system. An approach like aforementioned tries to stabilize output current & voltage, lower harmonics, & lessen DC link input voltage fluctuation. Through reducing error about voltage regulator & current controller schemes in inverter system, particle swarm optimization (PSO) technique was used towards adjust PI controller settings. When compared to conventional approach, simulation results show certain optimal parameters PI controller created among PSO produces better performance index results. According towards various research, reactive power supply can only modestly reduce voltage sags while totally mitigating harmonics using specialized power devices. Effective & dependable use about PV solar farm inverters as STATCOMs is required towards guarantee certain generating units stay connected towards grid during voltage sags & towards enhance system performance during abnormal circumstances.

Optimization of Grid-Connected Photovoltaic Power Generation Technology Based on Nonlinear Back-Stepping Controller

To address the issue of energy scarcity and to use solar photovoltaic energy as a renewable source, a three-phase grid-connected photovoltaic inverter system with uncertain system model parameters is investigated, which converts DC power into AC power, feeds it into the grid, and maintains the grid-connected part’s quality. An enhanced back-stepping approach is proposed to explore the control strategy of three-phase solar grid-connected inverter, which includes adaptive control, dissipative theory, sliding mode control, and rapid terminal sliding mode control, respectively. It is verified that the system is subjected to external interference F = 5 during 0.5 s–0.8 s. As per the simulation results, the improved adaptive terminal sliding mode control method can suppress the interference to a certain extent and has strong robustness to the external interference. When compared with the adaptive sliding mode control approach, the anti-interference ability is better, and the system stability is improved. Then, to improve the above approach, a high speed terminal sliding mode control method is proposed, which can swiftly converge in finite time and the estimated value of uncertain parameters is closer to the actual value, thereby boosting the system’s robustness.

Processor in the Loop Verification of Fault Tolerant Control for a Three Phase Inverter in Grid Connected PV System

ABSTRACT The techno-economic feasibility of photovoltaic (PV) solar generation systems is greatly dependent on its operating conditions. However, significant penetration of PV sources into alternating current (AC) grids may cause lower system inertia, decreased system damping, and higher frequency fluctuations when grids are subjected to fault conditions. In this paper, a two-stage three-phase grid-connected PV-based inverter system is analyzed under grid fault conditions using a robust fault-tolerant super twisting sliding mode control scheme. Moreover, closed control system is formulated using Lyapunov theorem and its global stability is ensured. The proposed controller is tested in processor in the loop experimentation using a Texas Instrument (TI) Launchpad (TMS 320F28379D). The control performance and resilience of the proposed control system is tested under three-phase faults introduced between the inverter–grid interface buses. Under the above test conditions, a comparative analysis is performed for the proposed adaptive super twisting sliding mode control (ASTSMC) and fixed gain sliding mode control (SMC) control method. Under fault conditions, the inverter power has a settling time of 50 m-s with ASTMC control while with fixed gain STSMC, the settling time is longer and the observed settling time is 115 m-s. Moreover under faulty conditions, a voltage dip of 400 V is recorded with ASTSMC while with fixed gain STSMC controller the observed dip is 600 V. With the proposed ASTSMC controller, THD settles down to under 3% in 50 m-s while the fixed gain STSMC takes 115 m-s.

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.

Particle swarm optimization algorithm-based PI inverter controller for a grid-connected PV system.

The lack of control in voltage overshoot, transient response, and steady state error are major issues that are frequently encountered in a grid-connected photovoltaic (PV) system, resulting in poor power quality performance and damages to the overall power system. This paper presents the performance of a control strategy for an inverter in a three-phase grid-connected PV system. The system consists of a PV panel, a boost converter, a DC link, an inverter, and a resistor-inductor (RL) filter and is connected to the utility grid through a voltage source inverter. The main objective of the proposed strategy is to improve the power quality performance of the three-phase grid-connected inverter system by optimising the proportional-integral (PI) controller. Such a strategy aims to reduce the DC link input voltage fluctuation, decrease the harmonics, and stabilise the output current, voltage, frequency, and power flow. The particle swarm optimisation (PSO) technique was implemented to tune the PI controller parameters by minimising the error of the voltage regulator and current controller schemes in the inverter system. The system model and control strategies were implemented using MATLAB/Simulink environment (Version 2020A) Simscape-Power system toolbox. Results show that the proposed strategy outperformed other reported research works with total harmonic distortion (THD) at a grid voltage and current of 0.29% and 2.72%, respectively, and a transient response time of 0.1853s. Compared to conventional systems, the PI controller with PSO-based optimization provides less voltage overshoot by 11.1% while reducing the time to reach equilibrium state by 32.6%. The consideration of additional input parameters and the optimization of input parameters were identified to be the two main factors that contribute to the significant improvements in power quality control. Therefore, the proposed strategy effectively enhances the power quality of the utility grid, and such an enhancement contributes to the efficient and smooth integration of the PV system.

Stability Analysis and Key Parameters Design for Grid-Connected Current-Source Inverter With Capacitor-Voltage Feedback Active Damping

In a three-phase grid-connected current-source inverter system with the capacitor-voltage feedback (CVF)-based active damping method, a high-pass filter is usually employed in the CVF loop to mitigate its impact on system dynamics. Meanwhile, the inherent delays in a digital control system brought by pulsewidth modulation (PWM) and the digital control will make stability analysis and parameters design of the control system more complicated. In this article, the impacts of the high-pass filter and the inherent delays are considered for stability analysis and parameters design. The impacts of the cutoff frequency of the high-pass filter and the CVF damping coefficient on the system stability are analyzed in the discrete domain, and an optimal CVF damping coefficient is obtained. Moreover, a key parameters design method for the control system is proposed. The method simplifies the procedure of key parameters designing, which can mitigate the resonance of the system caused by the CL filter effectively with better dynamics and steady state performance. Finally, simulation and experimental results are provided to verify the effectiveness of the proposed method in this article.

Dual-mode operation based second-order sliding mode control for grid-connected solar photovoltaic energy system

This paper proposes a second-order sliding mode control technique for the grid-connected solar photovoltaic system. The proposed technique is tested under grid faults to meet the requirements of low-voltage ride through capability. A dual-mode control technique of the converter and inverter is designed to maintain the required dc-link voltage regulation and the active-reactive power during grid fault. The sliding mode control technique is developed from the model of the grid connected to the converter and the dc-link. The proposed dual-mode control technique is validated using real-time simulator OPAL-RT and experimental three-phase grid-connected photovoltaic inverter system. Simulation and experimental results show that the control technique is quite effective in maintaining the dc-link voltage regulation and the power control. As it shows smooth transitions between the two modes of operation (normal and grid fault). Moreover, the sliding mode control approach is robust against unknown disturbances and uncertainties in the system.

Highly efficient three-phase grid-connected parallel inverter system

In this paper, a new three-phase grid-connected inverter system is proposed. The proposed system includes two inverters. The main inverter, which operates at a low switching frequency, transfers active power to the grid. The auxiliary inverter processes a very low power to compensate for the grid current ripple. Thus, no active power is processed by the auxiliary inverter. The goal is to produce a grid current with a low total harmonic distortion (THD) and to obtain the highest efficiency from the inverter system. The main inverter is controlled via a space-vector pulse-width modulation owing to its optimum switching pattern, and the auxiliary inverter is controlled via a hysteresis current-control technique owing to the technique’s fast dynamic response. The proposed system is analyzed in terms of different DC-link voltage, switching frequency, and filter inductance values. The optimum system parameters are selected that provide a THD value of less than 5%. A prototype inverter system at a 10-kW output power has been implemented. The main inverter operates at a 3-kHz switching frequency, and the auxiliary inverter compensates for the grid-current ripple. In total, a THD of 4.33% and an efficiency of 97.86% are obtained using the proposed inverter system prototype.

Robust Feedback Linearizing Control With Sliding Mode Compensation for a Grid-Connected Photovoltaic Inverter System Under Unbalanced Grid Voltages

A robust feedback linearizing control strategy, based on sliding mode compensation, is proposed for the operation of a grid-connected photovoltaic inverter system under grid faults, characterized by unbalanced voltages, to meet low-voltage ride through requirements. Under normal grid condition, the control system is developed for maximum power transfer from the photovoltaic source to the grid by maximum power point tracking operation of the dc–dc converter, and regulation of the dc-link voltage and the current at the inverter-grid side. Under grid fault, which is unbalanced grid voltage due to voltage dips, the active power is regulated to reduce the current excess and the reactive power is injected to avoid the inverter damage or disconnection, while the dc-link voltage is controlled via the dc–dc converter. A sliding mode compensator is injected into the control system to enhance its robustness to uncertainties. The feedback linearizing control schemes are developed from the grid model at the inverter side and the dc-link model at the dc–dc converter side. The proposed control strategies are experimentally validated on a three-phase grid-connected photovoltaic inverter system and experimental results show that the control system is effective in terms of voltage and power control with smooth transitions between the modes.

An Improved Current Control Strategy for a Grid-Connected Inverter under Distorted Grid Conditions

This paper presents an improved current control strategy for a three-phase grid-connected inverter under distorted grid conditions. The main challenge associated with the grid-connected inverter in distributed generation (DG) systems is to maintain the harmonic contents in output current below the specified values even when the grid is subject to uncertain disturbances such as harmonic distortion. To overcome such a challenge, an improved current control scheme is proposed for a grid-connected inverter, in which the fundamental and harmonic currents are independently controlled by a proportional-integral (PI) decoupling controller and a predictive basis controller, respectively. The controller design approach is based on the model decomposition method, where the measured inverter currents and grid voltages are divided into the fundamental and harmonic components by means of moving average filters (MAFs). Moreover, to detect the angular displacement and angular frequency with better accuracy, even in the presence of the grid disturbance, the MAF is also introduced to implement an enhanced phase-lock loop (PLL) structure. Theoretical analyses as well as comparative simulation results demonstrate that the proposed control scheme can effectively compensate the uncertainties caused by the grid voltages with fast transient response. To validate the feasibility of the proposed scheme, the whole control algorithms are implemented on 2 kVA three-phase grid-connected inverter system using 32-bit floating-point DSP TMS320F28335. As a result, the proposed scheme is an attractive way to control a grid-connected inverter under adverse grid conditions.