Single-phase Grid-connected Photovoltaic System Research Articles

Modelling Analysis and Characteristics of Multi-Level Inverter for Integrating Solar PV System to Grid

This paper investigates the implementation of a cascaded H-bridge multi-level inverter in a single-phase grid-connected solar photovoltaic (PV) system to address harmonic distortion challenges in DC-to-AC power conversion. The primary objective is to enhance power quality and system efficiency by leveraging the inverter's ability to reduce harmonics through power sharing and a lower switching frequency. A Simulink model is developed to evaluate the proposed system's performance, incorporating a unipolar Pulse Width Modulation (PWM) control strategy and an LCL filter for effective harmonic mitigation. The system employs Maximum Power Point Tracking (MPPT) based on the Perturb and Observe (P&O) algorithm, combined with Synchronous Reference Frame Theory-Phase Disposition PWM (SRFT-PDPWM) for optimal control. The proposed inverter ensures precise synchronization between the grid and inverter frequencies, achieving a Total Harmonic Distortion (THD) below 5%. Simulation results demonstrate the system's robust responsiveness to variations in solar irradiance, with increased irradiance leading to further reductions in THD and improved power quality. These findings validate the proposed inverter's capability to deliver high-quality, efficient power under varying environmental conditions, aligning with global objectives for integrating clean and sustainable energy into utility networks.

Adaptive nonlinear control of the Single-Phase Grid-Connected Photovoltaic System

This paper addresses the problem of controlling the single-phase grid connected to the photovoltaic (PV) system through a three-level boost converter (TLBC) and half-bridge inverter (HBI) with LCL-filter. This study aims to achieve four main objectives: (i) ensure that the output voltage of PV panel track a reference given by the MPPT block based on the perturb and observe (P&O) algorithm; (ii) regulate DC bus voltage to ensure injection of photovoltaic power into the grid; (iii) guarantee power factor correction (PFC); (iv) ensure a balance between TLBC output voltages. The problem is dealt with using a nonlinear controller based on the backstepping and lyapunov approaches, a filtered-PI regulator to ensure the power balance between the grid and the PV panel. An adaptive observer is designed in order to estimate the voltage and the impedance parameters of power grid, by measuring only the grid current. The proposed controller and observer performances are confirmed by simulation in MATLAB\\Simulink.

Fault Ride Through approach for Grid-Connected Photovoltaic System

This paper presents a fault ride-through approach for grid-connected photovoltaic (PV) systems, aimed at improving the system's response during voltage sags and limiting the maximum inverter current during symmetrical faults. A constant active current reactive power injection approach was developed for low-voltage ride-through (LVRT) operation of grid-connected solar PV inverters in low voltage grids. The method manages the active and reactive power references and satisfies grid code requirements while also addressing tripping problems caused by overcurrent. The approach improves the speed response of the power converters during voltage sags, resulting in better dynamic grid support. The authors evaluated the approach using a 2-kW single-phase grid-connected PV system and demonstrated its ability to inject the required reactive power during a fault to improve the voltage profile and achieve dynamic grid support requirements. The accuracy of the proposed methodology is identified to be 98.3%, and the detection time is reduced by a reasonable margin in accordance with the grid standards. Overall, the fault ride-through approach can enhance the performance and reliability of grid-connected PV systems, particularly in low voltage grids.

Design and experimental validation of an efficient control based on variable step size P&O MPPT technique and predictive current controller for a single-phase grid-connected photovoltaic system

Design and experimental validation of an efficient control based on variable step size P&O MPPT technique and predictive current controller for a single-phase grid-connected photovoltaic system

Experimental Investigation of Modern Control Algorithms for Power Quality Improvement for Single-Phase Grid-Connected Photo-Voltaic System

Experimental Investigation of Modern Control Algorithms for Power Quality Improvement for Single-Phase Grid-Connected Photo-Voltaic System

Design and implementation of a new adaptive energy management algorithm capable of active and reactive power control for grid-connected PV systems

This paper presents a new adaptive energy management algorithm (AEMA) integrated active and reactive power control (PQ) for single-phase grid-connected photovoltaic (PV) system. Four possible operating cases of the proposed grid-connected PV system were identified in the study. The AEMA detects possible operating cases of the system. The proposed control algorithm also detects the active and reactive power of the load and the inverter in the PV system operates in filter mode. The proposed control algorithm allows the PV system to generate active and reactive power and provides reactive power support to the grid. The AEMA with PQ algorithm detects that the load demands reactive power and generates reference current signals for the inverter. This study combines the benefits of clean energy generation from PV systems and efforts to improve the quality of power in the grid. A single-phase grid-connected 2.1 kW PV array experimental setup was developed to demonstrate the performance of the proposed control algorithm, and the results were verified with a power quality and energy analyzer.

Review, analysis, and performance evaluation of the most common four active methods for islanding detection in grid-connected photovoltaic systems

• The AFD, SFS, SMS, and SVS active islanding detection methods. • The studied methods provide good detection times within the new grid standards. • The methods have good detection times under different parameters and scenarios. • The active methods are studied and compared for the first time in a detailed study. This paper systematically analyzes the islanding performance under different case studies and scenarios of the most well-known active islanding detection methods (IDMs) for single-phase grid-connected photovoltaic (PV) systems. They are named as follows: Active Frequency Drift (AFD), Sandia Frequency Shift (SFS), Slip Mode frequency Shift (SMS), and Sandia Voltage Shift (SVS) anti-islanding detection strategies. The performance of these four active anti-islanding methods has been examined in detail using Matlab/Simulink. Moreover, the quality factor and non-detection zone (NDZ) influence on islanding detection is also analyzed. According to the new grid codes and standards, the studied active IDMs provide good detection times. Furthermore, the case studies illustrate that these active detection techniques can successfully detect the islanding operation mode under different quality factors, types of loads, solar irradiance changes, and fault-ride through (FRT) operation mode.

Power Flow Management With Q-Learning for a Grid Integrated Photovoltaic and Energy Storage System

This article develops a fuzzy Q-learning (FQL) approach-based power flow management algorithm for a single-phase grid-connected (GC) photovoltaic (PV) system with an energy storage unit (ESU). The FQL coordinates the PV power generation, which is based on the mission profile, the state of charge (SOC) of ESU, and the load profile such that a power balance is achieved in the network. Furthermore, the transition between standalone (SA) and GC modes during the power flow management is achieved using a proportional capacitor current feedback. While operating in the SA mode, the control action for the load voltage is achieved by an outer current loop. This combination of coordinated and transition control achieves power balance and smooth transition between the SA and GC modes. To verify the effectiveness of the proposed control strategy, a 4 – kWp PV system is operated along with an ESU in both SA and GC modes for a varying mission and load profile. The simulation and experimental results validated the multifunctional features of the proposed method.

Modeling and simulation of novel dynamic control strategy for grid-connected photovoltaic systems under real outdoor weather conditions using Fuzzy–PI MPPT controller

ABSTRACT This paper proposes the modeling and simulation of a novel dynamic control strategy for 2.4 kWp single-phase grid-connected photovoltaic systems under real outdoor weather conditions using an intelligent Fuzzy–PI MPPT controller. The PV array in the first case is fixed and tilted at a 32° angle, whereas the PV array in the second is equipped with dual-axis sun tracking. The objective is to deliver the maximum power from the PV array and to improve the drawbacks of the classical MPPT control. The optimization is performed using a real-time daily profile of Ghardaia, Algeria (32.24°N – 3.24°W). The proposed MPPT controller (Fuzzy PI MPPT) is optimized under different climatic scenarios based on four selected typical days: the first two days in winter and the second two days in summer. An analysis of the performance and simulation of a photovoltaic conversion system associated with a solar tracker, comparing it from an energy point of view with a fixed photovoltaic converter, has been carried out in Matlab/Simulink software. The results show that grid-connected PV with dual solar tracking enhances the PV array output power efficiency by about 25% compared to a similar fixed PV system. The results show that higher injected power quality is achieved and the overall system has higher efficiency.

A hybrid random parameters modification to MPPT algorithm to mitigate interharmonics from single-phase grid-connected PV systems

As the on-grid photovoltaic (PV) system’s penetration level increases, the utility grid power quality (PQ) becomes a vital emerging issue to spot the lights on. The recent studies confirmed that one source of interharmonics emission from PV inverters is the maximum power point tracking (MPPT) algorithms. Following this issue, a strong relationship has been found between the interharmonics generating characteristics and the MPPT parameters, such as the sampling rate and perturbation step size. Utilizing a big step size and fast sampling rate will enhance the tracking performance but will raise the level of interharmonics injected into the grid and lower the overall efficiency. Therefore, there is a trade-off between MPPT parameters, efficiency, and interharmonics characteristics in PV systems. To alleviate mentioned issue, this paper investigates the mechanism of interharmonics generation and emission under different power operating conditions. Accordingly, a new mitigation technique is presented for interharmonics generation in grid-connected PV systems. The proposed method is based on modifying the MPPT algorithm in a way that maintains its performance characteristic while effectively minimizing the generated interharmonics by a random selection of big or small perturbation step sizes and fast or slow sampling rate, respectively. Thereby, the frequency spectrum distribution is modified, and interharmonics peaks are reduced in the output injected current to the grid by 27 % compared to the other conventional and modified perturb and observe (P&O) MPPT algorithms found in the literature. The effectiveness of the proposed method is verified by simulation studies on a single-phase grid-connected PV system.

Modeling a Simple Single-phase Grid-connected Photovoltaic System Using Negative Conductance of Solar Cells

This paper presents the simulation of a simple single-phase grid-connected photovoltaic (PV) system using the PSPICE model. The modeling system consists of a PV string, a single-phase current source inverter (CSI), load, and a grid voltage source. The system uses the PV string as the current source. The single-phase CSI was controlled by the grid AC voltage. The operation of the system employs the negative conductance characteristics of the PV string. We studied the voltage and current waveform at the inverter output terminal, the current waveform at the load, the AC power with various open-circuit voltages and temperatures of the PV string. The result showed the current waveform at the inverter output terminal follows the I-V characteristics of the PV string. The current waveform at the load depends on its impedance characteristics. The AC power increased with the open circuit voltage. We found that the maximum efficiency of the AC power conversion system was 63.3% at the peak of the AC voltage source, which was equal to the maximum power voltage of the PV string. In addition, the prototype was built for testing and testing verified the simulation results. The experimental results showed the current waveform at the inverter terminal and load were similar to the simulation results.

Sensorless DC-link voltage regulation strategy for single-phase grid-connected solar photovoltaic systems

A sensorless DC-link voltage control technique is proposed for a two stage, single-phase grid-connected solar photovoltaic (PV) system. The developed control strategy is predicated on the fact that if PV power is directly fed into the grid, the DC link voltage would stabilise. However, losses must be properly compensated to maintain a flat DC-link voltage profile. To account for the system losses, teaching-learning-based optimisation (TLBO) is used offline. After the offline implementation, a regression model based on maximum power is built to estimate system losses. The regression model is applied to the system to predictively compensate for system losses. As a result, the DC link control loop is avoided, and sensorless control is achieved. A unit-template-based control is used to synchronise the PV system with the grid. Simulation experiments using MATLAB/Simulink are used to verify the superiority of the proposed scheme over the conventional sensor-based technique.

Sensorless DC-link voltage regulation strategy for single-phase grid-connected solar photovoltaic systems

Sensorless DC-link voltage regulation strategy for single-phase grid-connected solar photovoltaic systems

BACKSTEPPING CONTROL AND ADAPTIVE OBSERVER DESIGN FOR A SINGLE-PHASE GRID-CONNECTED PHOTOVOLTAIC SYSTEM

In this paper, we consider the problem of controlling a single-phase grid-connected photovoltaic system using the backstepping technique and an adaptive observer. The conversion system includes a PV panel, a DC-DC Boost converter, a DC-AC half bridge inverter connected to the grid via an LCL filter. This work aims at achieving threefold control objectives: i) extracting the maximum available power ii) guaranteeing a unitary power factor (UPF) by forcing the grid current to be sinusoidal and in phase with the electric network voltage, iii) regulating the DC link voltage to a desired references value. The performance of the proposed regulator is evaluated through numerical simulation using MATLAB/SIMULINK environment.

Single-phase grid-connected PV system with golden section search-based MPPT algorithm

Maximum power point tracking (MPPT) is a technique employed for with variable-power sources, such as solar, wind, and ocean, to maximize energy extraction under all conditions. The commonly used perturb and observe (P&O) and incremental conductance (INC) methods have advantages such as ease of implementation, but they also have the challenge of selecting the most optimized perturbation step or increment size while considering the trade-off between convergence time and oscillation. To address these issues, an MPPT solution for grid-connected photovoltaic (PV) systems is proposed that combines the golden section search (GSS), P&O, and INC methods to simultaneously achieve faster convergence and smaller oscillation, converging to the MPP by repeatedly narrowing the width of the interval at the rate of the golden ratio. The proposed MPPT technique was applied to a PV system consisting of a PV array, boost chopper, and inverter. Simulation and experimental results verify the feasibility and effectiveness of the proposed MPPT technique, by which the system is able to locate the MPP in 36 ms and regain a drifting MPP in approximately 30 ms under transient performance. The overall MPPT efficiency is 98.99%.

Resource management with kernel-based approaches for grid-connected solar photovoltaic systems

The increasing penetration of photovoltaic (PV) power generation into the distribution grids has resulted in frequent reverse active power flows, rapid fluctuations in voltage magnitudes, and power loss. To overcome these challenges, this paper identifies the resource management of grid-connected PV systems with active and reactive power injection capabilities using smart inverters. This approach is aimed to minimize the voltage deviations and power losses in the grid-connected systems to accommodate the high penetration of PV systems. A kernel-based approach is proposed to learn policies and evaluate the reactive power injections with smart inverters for improving grid profile, minimizing power losses, and maintaining safe operating voltage limits. The proposed approach performs inverter coordination through nonlinear control policies using anticipated scenarios for load and generation. To assess the performance of the proposed approach, numerical simulations are performed with a single-phase grid-connected PV system connected to an IEEE bus system. The results show the effectiveness of the proposed approach in minimizing power losses and achieving a good voltage regulation.

Dynamic Voltage Support for Low-Voltage Ride-Through Operation in Single-Phase Grid-Connected Photovoltaic Systems

This article presents a dynamic voltage support (DVS) scheme for achieving low-voltage ride-through (LVRT) with a grid-connected photovoltaic (PV) inverter during the voltage sag fault. The DVS scheme is achieved by formulating an additional reactive active current control mode which is developed from a conventional reactive current control approach. This provides stable operation of the system and achieves higher effectiveness due to the lower <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> ratio at the point of common coupling in low-voltage networks. Further, the performance of the proposed controller is assessed by simulating a 4 kW system for voltage sag faults. Further, the proposed controller tested with the real-time simulations and experimental setup for voltage sag conditions. The results presented demonstrate that the active and reactive power is regulated in concordance with grid code requirements. The controller achieves LVRT within the time limits of grid standard during symmetrical faults, which makes it appropriate for fast transient events. This operates the PV system under its nominal capacity, avoiding unwanted grid disconnection events.

Multicarrier PWM Based Control of Modular Multilevel Inverter with Grid Connected Solar PV System

In this work, a new modular multilevel inverter topology is introduced for a single phase grid connected Photovoltaic system. This multilevel inverter use less number of switches to generate seven levels compared to other conventional multilevel inverters. This requires only one isolated dc source to operate. So it is suitable for renewable energy application. This inverter is designed by submodule configuration; each sub module contains two switches and one DC link capacitor. The sub modules will be added to the inverter depending on number of levels. The voltage balancing of DC link capacitor is carried out by Y matrix PWM technique. Because of Y matrix PWM technique, the inverter gets a self capacitor voltage balancing ability. So there is no need of external devices required for balancing the voltage of capacitor. A PLL for grid integration and LCL filter are designed and integrated with this inverter. The simulation of proposed system is carried out by MATLAB/SIMULINK and performance of THD is monitored as per standards

Direct control of active and reactive power for a grid-connected single-phase photovoltaic inverter

This paper presents a single-phase grid-connected photovoltaic system with direct control of active and reactive power through a power management system of a Photovoltaic inverter. The proposed control algorithm is designed to allow maximum utilization of the inverter’s available KVA capacity while maintaining grid power factor and current total harmonic distortion (THD) requirements within the grid standards. To reduce the complexity and improve the efficiency of the system, two independent PI controllers are implemented to control single-phase unipolar PWM voltage source inverter. One controller is used to control the power angle, and hence the active power flow, while the other controller is used to control the reactive power, and consequently the power factor by adjusting the voltage modulation index of the inverter. The proposed system is modelled and simulated using MATLAB/Simulink. The PV inverter has been examined while being simultaneously connected to grid and local load. Results obtained showed the ability of the PV inverter to manage the active and reactive power flow at, and below rated levels of solar irradiances; resulting in an increased inverter utilization factor, and enhanced power quality. The proposed system, was capable of operating at power factors in the range of 0.9 lead or lag for reactive power compensation purposes and delivered its power at a wide range of solar irradiance variations.

PV Systems Control Using Fuzzy Logic Controller Employing Dynamic Safety Margin under Normal and Partial Shading Conditions

Because of the unpredictable activity of solar energy sources, photovoltaic (PV) maximum power point tracking (MPPT) is essential to guarantee the continuous operation of electrical energy generation at optimal power levels. Several works have extensively examined the generation of the maximum power from the PV systems under normal and shading conditions. The fuzzy logic control (FLC) method is one of the effective MPPT techniques, but it needs to be adapted to work in partial shading conditions. The current paper presents the FLC-based on dynamic safety margin (DSM) as an MPPT technique for a PV system to overcome the limitations of FLC in shading conditions. The DSM is a performance index that measures the system state deviation from the normal situation. As a performance index, DSM is used to adapt the FLC controller output to rapidly reach the global maxima of the PV system. The ability of the proposed algorithm and its performance are evaluated using simulation and practical implementation results for single phase grid-connected PV system under normal and partial shading operating conditions.