Single-stage Grid-connected Photovoltaic System Research Articles

High-Voltage Ride-Through Method for Single-Stage Grid-connected Photovoltaic System Based on Model Predictive Control

High-Voltage Ride-Through Method for Single-Stage Grid-connected Photovoltaic System Based on Model Predictive Control

Enhancing of single-stage grid-connected photovoltaic system using fuzzy logic controller

The power generated by photovoltaic (PV) systems is influenced by environmental factors. This variability hampers the control and utilization of solar cells' peak output. In this study, a single-stage grid-connected PV system is designed to enhance power quality. Our approach employs fuzzy logic in the direct power control (DPC) of a three-phase voltage source inverter (VSI), enabling seamless integration of the PV connected to the grid. Additionally, a fuzzy logic-based maximum power point tracking (MPPT) controller is adopted, which outperforms traditional methods like incremental conductance (INC) in enhancing solar cell efficiency and minimizing the response time. Moreover, the inverter's real-time active and reactive power is directly managed to achieve a unity power factor (UPF). The system's performance is assessed through MATLAB/Simulink implementation, showing marked improvement over conventional methods, particularly in steady-state and varying weather conditions. For solar irradiances of 500 and 1,000 W/m<sup>2</sup>, the results show that the proposed method reduces the total harmonic distortion (THD) of the injected current to the grid by approximately 46% and 38% compared to conventional methods, respectively. Furthermore, we compare the simulation results with IEEE standards to evaluate the system's grid compatibility.

Assessment of a single-phase single-stage grid-connected photovoltaic system

A grid-connected photovoltaic (GCPV) system plays an important role in the development of green technology. However, generated photovoltaic (PV) power that is injected into the grid causes instability in the grid system. Previous studies have shown that power quality for a three-phase system is thoroughly being discussed, but not for a single-phase system. Single-phase system also contribute to instability in low-voltage grid networks during high power penetration as majority of the single-phase GCPV nowadays are installed on rooftops. Thus, in this study, the power quality of a single-phase single-stage GCPV system is investigated based on the total harmonic distortion (THD), power factor (PF), and the generated active (P) and reactive (Q) power during different solar irradiance and varying loads conditions. A model of the GCPV system was developed in MATLAB/Simulink, so that certain variables can be varied to observe their effect towards the power quality. The results show that the current and voltage of generated PV power are synchronized and having low current THD which is less than 1% for all cases. PF values are also in the acceptable range in compliance to IEC 61727 standard which is 0.9971, and the generated PQ is in accordance to the connected load.

Comparative assessment of swarm-based MPPT techniques in MPC-based single-stage grid-connected PV system

The predominant topology to connect the Photovoltaic (PV) system to the grid is the two-stage conversion process integrated with PI-based controllers. In the last decade, single-stage conversion has drawn significant attention due to relatively low conversion losses and installation costs. Operating a single stage grid connected PV system using the model predictive control (MPC) method is introduced in the literature very recently. Under such a scheme, the behaviours of the different maximum power point algorithms are still unknown. This paper investigates the performance of swarm-based Maximum Power Point Tracking (MPPT) techniques in MPC controlled single-stage grid-connected PV systems. For comparison, three algorithms namely particle swarm optimization, grey wolf optimization and artificial bee colony are chosen. All MPPT algorithms are cascaded with a continuous control set-based model predictive controller for inverter control. MPPT schemes are tested under uniform irradiance variation and partial shading conditions. It is observed that in a 12S30P PV configuration, an artificial bee colony performs slower tracking compared to the other two. Nevertheless, all three algorithms track the global MPP under all conditions successfully. The swarm-based MPPT techniques perform well with the MPC controller and a smooth AC signal is generated for grid integration. The total harmonic distortion (THD) is recorded as 3.05% in the steady state.

Analysis of total harmonic distortion in single-phase single-stage grid-connected photovoltaic system

<p>This study presents the power quality issue mainly focus the effect of total harmonic distortion (THD) on a grid-connected PV system. Firstly, a grid-connected PV system with a single-phase single-stage has been developed to monitor the output values of voltage and current and also its harmonic distortion behaviours. Maximum power point tracking (MPPT) was implemented since it is proven as the first step for THD reduction because MPPT will extract maximum output power, voltage, and current of the PV system without fluctuation which leads to a low THD level. Furthermore, the employment of a good filter also reduces the THD level in a PV system. Thus, this study will focus on the THD analysis to resolve the power quality problems in the grid-connected PV system. The result shows that the THD value for current, <em>I<sub>THD</sub></em> analysis is more significant than the THD value for voltage, <em>V<sub>THD</sub></em> analysis in the case of grid-connected PV systems operating under different solar irradiances. In a conclusion, the increase in solar irradiance will increase the rated values of generated power and current thus, increasing the performance of THD values.</p>

Optimizing Step-Size of Perturb & Observe and Incremental Conductance MPPT Techniques Using PSO for Grid-Tied PV System

A maximum power point tracking (MPPT) technique plays an important role to ensure maximum photovoltaic (PV) output power is extracted under stochastic weather conditions. The research to date tends to focus on developing a standalone optimization MPPT algorithm rather than looking into a hybrid MPPT algorithm. This paper introduces particle swarm optimization (PSO) to optimize the maximum PV output power and to determine the best design variable for penalising the step size of the conventional methods namely the perturb and observe (PO) and the incremental conductance (IC). With the help of the hybrid MPPT algorithm (PSO+IC and PSO+PO), the step size is no longer fixed, and it is changing according to the solar irradiance. To evaluate the proposed hybrid algorithm, a single-stage grid connected PV system is designed for several different scenarios with various weather conditions. The performance of the hybrid MPPT algorithm and the conventional methods is compared. The results demonstrate that the hybrid MPPT algorithm is remarkably better than the conventional methods in terms of the output power ripple and the settling time.

Single-Stage Grid-Connected PV System With Finite Control Set Model Predictive Control and an Improved Maximum Power Point Tracking

The single-stage grid-connected photovoltaic (PV) topology has recently drawn attention as it can reduce overall losses and installation costs. This paper presents a new control approach for single-stage grid-connected PV systems. The proposed controller is a combination of a finite control set model predictive control (FCS-MPC) and a maximum power point tracking (MPPT) algorithm, which ensures the extraction of maximum power from the PV panels and good transient performance for the output voltage and current. The disadvantages of classical MPPT algorithms in tracking the global maximum power point under fluctuating environmental conditions are avoided by including additional constraints in the cost function of the FCS-MPC. Further, the controller is tested for partial shading in PV. The performance of the proposed controller is compared with the two-stage and single-stage PV configuration with different controls and MPPT algorithms. The simulation results show that the single-stage PV system with the proposed control can effectively extract the maximum power from the PV system and maintain a stable output signal for the transient condition. Finally, experimental results according to a control hardware-in-the-loop (C-HIL) approach are presented to validate the effectiveness of the proposed algorithm.

Assessment and Mitigation of Dynamic Instabilities in Single-Stage Grid-Connected Photovoltaic Systems With Reduced DC-Link Capacitance

Single-stage utility-scale photovoltaic (PV) systems are usually interfaced with the host grid via a centralized voltage-source converter (VSC). Recently, and due to their reliability, the dc-link film capacitors are favored over electrolytic types in grid-connected applications. However, the capacitance per unit volume of film capacitors is significantly smaller than electrolytic capacitors. The overall system stability might be compromised by the reduction of the dc-link capacitance, particularly in PV systems that have a dynamic resistance that varies with operating conditions. Using a detailed small-signal model of the grid-connected PV system, it is shown in this paper that the reduction of the dc-link capacitance interferes with the dynamic resistance of the PV array, which eventually leads to instabilities. The minimum dc-link capacitance that preserves the overall system stability is determined. A simple and effective active compensator is developed to mitigate the instabilities with the reduced dc-link capacitance. Detailed time-domain simulations are presented to validate the analytical results and show the proposed compensator’s effectiveness in preserving the system stability.

Frequency- adaptive control of a three-phase single-stage grid-connected photovoltaic system under grid voltage sags

The low-voltage ride-through service is carried out in this paper according to the voltage profile described by the IEC 61400-21 European normative when short-duration voltage sags happen, and some instantaneous reactive power is delivered to the grid in accordance with the Spanish grid code; the mandatory limitation of the amplitude of the three-phase inverter currents to its nominal value is carried out with a novel control strategy, in which a certain amount of instantaneous constant active power can also be delivered to the grid when small or moderate voltage sags happen. A Multiple second order generalized integrator frequency-locked loop synchronization algorithm is employed in order to estimate the system frequency without harmonic distortions, as well as to output the positive- and the negative- sequence of the αβ quantities of the three-phase grid voltages when balanced and unbalanced voltage sags happen in a frequency- adaptive scheme. The current control is carried out in the stationary reference frame, which guarantees the cancellation of the harmonic distortions in the utility grid currents using a Harmonic compensation structure, and the implementation of a constant active power control in order to protect the DC link capacitor from thermal stresses avoiding the appearance of large harmonic distortions at twice the fundamental frequency in the DC link voltage. A case study of a three-phase single-stage grid-connected PV system with a maximum apparent power about 500 kVA is tested with several simulations using MATLAB/SIMULINK firstly, and secondly, with some experiments using the Controller hardware-in-the-loop (CHIL) simulation technique for several types of voltage sags in order to do the final validation of the control algorithms.

A novel nonlinear sliding mode controller for a single stage grid-connected photovoltaic system

A nonlinear sliding mode controller is proposed for a single stage grid-connected photovoltaic system with a novel nonlinear sliding surface. The proposed controller is designed to ensure maximum power extraction with unity power factor. There are two main advantages of the proposed sliding surface. The new surface will results in a first order sliding mode controller. The second advantage is that maximum power extraction is achieved by tracking DC-link voltage (Vdc) of the PV system. The proposed controller is also compared with the existing sliding mode controller in terms of both numerical simulation and experimental results. It is found that, the proposed controller’s performance is better than the existing controller in terms of power extraction and more robust when there are uncertainties and disturbance in PV system.

Capability Enhancement of DC-Link Voltage in a Single-Stage Grid-Connected Photovoltaic Power System

This article introduces a new approach for the grid-connected single-stage three-phase photovoltaic (PV) inverter in distribution network. This approach aims at improving the voltage profile at point of common coupling (PCC) between the PV power system and the grid. This improvement is achieved by regulating the dc-link voltage based maximum power point tracking (MPPT). The MPPT is fully utilized for updating the dc-link voltage reference (DLVR) according to environmental conditions. The updated DLVR is compared to the actual dc-link voltage through adaptive reference integral-proportional (ARPI) controller to develop reference direct current axis and to generate inverter pulses under normal and abnormal conditions. To verify the validity of the proposed approach, simulation results for multiple scenarios such as various environmental conditions alone, various environmental conditions with simultaneous three-phase faults and various environmental conditions with simultaneous voltage dips on 250-kW single-stage grid-connected PV system show the effectiveness of the ARPI controller compared with the grey wolf-based PI controller.

An Improved P&O Algorithm for Single-Stage Grid-Connected Photovoltaic System under Rapidly Changing Environment Conditions

In producing its power, Photovoltaic (PV) performance is influenced by environmental factors, such as solar irradiance and temperature. System stability is needed to maintain safe operation of the system. This paper presents a Maximum Power Point Tracking (MPPT) control model of PV array to improve system reliability and the performance of MPPT. The main parameters in Matlab/Simulink simulation that become the highlight influences are the changes in solar irradiance from 500W/m2 to 1000W/m2 and ambient temperatures from 25°C to 50°C. With the control algorithm that has been made in the Perturb and Observe (P&O) method, it obtains the optimal voltage control point in each PV conditions in a power system. System simulation shows that the voltage stability was maintained above 510 Volt in various conditions of solar irradiance and temperature. The results of the control scheme show the stability of the system and the optimal performance of PV.

Nonlinear control and stability analysis of single stage grid-connected photovoltaic systems

This work presents the control development of a single stage grid-connected photovoltaic (PV) system. The topology used by the PV system consists of two PV panels, a single-phase half-bridge inverter using two DC link capacitors, and an LCL filter in the grid side. The aim is to design a nonlinear controller to ensure simultaneously the following three objectives: (i) PV panels to provide their maximum power, (ii) balanced power exchange by regulating the DC link voltage, and (iii) power factor correction, i.e. grid current in phase with grid voltage. In order to fulfill these objectives, a multi-loop controller is designed by using back-stepping and Lyapunov approaches for the power factor correction objective and a filtered PI regulator to ensure the power balance between the grid and the PV panels. The controller performances are formally analyzed using an average large signal model. The performance of the proposed controller is shown by means of simulation results in MATLAB/SimPowerSystems environment.

Implementation of MPPT Algorithm for Single-Stage Grid-Connected Photovoltaic system by using incremental conductance method

This paper presents simulation and implementation of maximum power point tracking algorithm for single stage three-phase grid-connected PV system by using incremental conductance method. The maximum efficiency is realized when PV works at its maximum power point, which is contingent on irradiation and temperature. Since the irradiation and temperature always change with time, a PV system which able to track the maximum power point needs to be established to produce more energy. the IC method shows a superior performance, lower oscillation and it took 3second to match MPP that abest time to give stability to the system. the control strategy is supported out using MATLAB/Simulink and experimentally validated with a dSPACE MicroLabBox controller.

Microinverter Topology based Single-stage Grid-connected Photovoltaic System: A Review

This paper discussed the topology development of a single-stage microinverter in grid-connected PV system. In general, the microinverter topologies can be categorized into four type of topologies: 1) Flyback inverter, 2) Double-boost inverter, 3) Derived zeta-cuk configuration and 4) Buck-boost inverter. Flyback configuration is widely used for single-stage microinverter which offers protection between solar panel and utility grid. However due to the bulkiness of the transformer, new arrangement circuit employ the Half-Bridge topology with film capacitor and microcontroller provide a good room for research and future developments to obtain greater efficiency and compact design of single-stage microinverter grid-connected PV system. Plus, there are several characteristics need to be taken care for future development of the microinverter technology.

Stability and performance analysis of a single-stage grid-connected photovoltaic system using describing function theory

Stability and performance analysis of a single-stage grid-connected photovoltaic system using describing function theory

Modelling and simulation-based performance study of a transformerless single-stage grid-connected photovoltaic system in Indian ambient conditions

This paper presents a transformerless single-stage full-bridge inverter for a grid-connected photovoltaic system (GCPVS) and its performances based on power loss, efficiency, and total harmonic distortion for the conditions: (a) seasonal variations of inputs in the photovoltaic (PV) system, (b) variation of grid voltage, and (c) variation of carrier frequency and Modulation Index of sinusoidal pulse-width modulation of the inverter. A typical 2.8 kWp, 368 V nominal PV array-based GCPVS is modelled and simulated to evaluate proper load matching in Indian ambient and grid conditions prior to practical implementation. Detailed analyses on system powers, power losses, efficiency, and harmonic distortions as well as selection of parameters for the simulation model are presented. The impacts of penetrating PV power into electric grid are investigated in order to predict the possible unwanted consequences.

Design of single-stage three-phase grid-connected photovoltaic system with MPPT and reactive power compensation control

This paper proposes a single stage three-phase grid-connected photovoltaic (PV) system topology, it being simpler and more efficient. This includes the modelling of PV module and the power conditioning unit interfacing the PV to the utility grid with proper power flow control. The output of the PV panel is connected to the DC-side of the voltage source inverter for interfacing to the grid. The maximum power point tracking, grid synchronisation, reactive power compensation, output current harmonic reduction is included simultaneously in the control. The entire system is modelled in MATLAB/Simulink environment and simulations carried out to verify the operation and the control principle. Various simulation results are presented for the proposed PV grid-interfaced system. The results confirm high stability and efficiency of the single-stage grid-connected PV system.

The Modified Control Method for the Single-Stage Three-Phase GridConnected Photovoltaic System

Single-stage topology and the maximum power point tracking (MPPT) algorithm have advantages such as simple configuration and high efficiency in grid-connected photovoltaic (PV) systems. In conventional systems, current and voltage sensors of PV system are normally used for MPPT. This paper presents a modified control algorithm for the single-stage three-phase grid-connected PV system without PV current sensor with a variable step MPP-tracker. This algorithm is not derived from complex state equations and is not dependent on any circuit parameters. It simply calculates the output power of the inverter to replace the input power of the PV systems in the MPPT algorithm. The modified algorithm is simulated by using Matlab/Simulink software and implemented in the experimental prototype. With the single-stage configuration and PV current sensorless method, the prototype is suitable for lowcost high efficient implementation in the practice.

Single-Stage Grid-Connected Photovoltaic System Based on Sliding Mode and PI Control

Single-state grid-connected photovoltaic (PV) system has only one stage of power conversion and the control objectives needed to be considered simultaneously include synchronization with the utility voltage, harmonics reduction for grid-connected current and etc. Then the complexity of control strategy is increased. To deal with the characteristics, sliding mode controller is used to achieve the synchronization between grid-connected current and grid voltage and to control the waveform of grid-connected current, and the slide surface is designed based on PI method. Σ−Δ modulator is proposed to achieve the fixed switching frequency. Simulation results show that the system has good performance and the system is feasible.