Single-stage Grid-connected Photovoltaic Research Articles

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.

Smart Control Solution for Single-Stage Solar PV Systems

Solar photovoltaic (PV) systems unpredictable characteristics and tight grid-codes demand power electronic-based energy conversion devices. Hence, as the power levels generated by the solar PV systems rise, multi-level voltage source converters (VSC) and their control mechanisms become more necessary for effective energy conversion. Continuous control set model predictive control (CCS-MPC) is a class of predictive control approach that has emerged recently for the applications of power converters and energy conversion systems. In this paper, an artificial neural network (ANN) based controller for single-stage grid-connected PV is implemented. The CCS-MPC is used as an expert / a teacher to generate the data required for off-line training of the neural network controller. After the off-line training, the trained ANN can fully control the inverter’s output voltage and track the maximum power point (MPP) without the need for MPC during testing. The proposed control technique is assessed under various operating conditions. Based on the results obtained, it is observed that the proposed techniques offer improved objective tracking and comparative dynamic response with respect to the classical approaches.

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.

A Normalized Least Means Absolute Third-Based Adaptive Control Algorithm Design for Grid-Connected PV System

This article presents design and real-time control of a single-stage grid-connected photovoltaic (SSGCPV) system. A normalized least means absolute third (NLMAT) algorithm has been employed to design an adaptive controller to achieve effective grid synchronization. The objective is to mitigate harmonics generated by nonlinear load and inject active power to the utility grid with unity power factor (PF). A 20-kW PV system with the above controller has been simulated using MATLAB/Simulink and then verified with a 1.4-kW prototype. A comparison of the proposed controller with least means fourth, variable step size least means square (VSS-LMS), variable leaky least mean square(VLLMS), and NLMAT algorithms has been made. It is found out that although the total harmonic distortion (THD) of the grid current remains within the prescribed limit of the IEEE-519 standard for all the three algorithms, the proposed controller outperforms among all. It provides reduced THD even with unbalanced loading and change in irradiance conditions.

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.

Battery Current-Sharing Power Decoupling Method for Realizing a Single-Stage Hybrid PV System

Conventionally, the single-stage grid-connected PV inverter needs a large PV-side electrolytic capacitor to suppress the double-line frequency current ripple to keep the PV operating at maximum power point (MPP). However, the short lifetime electrolytic capacitor will reduce the PV inverter’s reliability dramatically. In order to overcome the above problem, a novel battery current-sharing power decoupling (BCSPD) method for hybrid photovoltaic (PV) power systems is proposed in this paper. The proposed BCSPD circuit is parallel-connected with the string PV module to achieve as a single-stage topology. Thus, a high power conversation efficiency can be obtained. The current-injection method is adapted to solve the current ripple problem. Therefore, the required capacitance in PV side can be greatly reduced, so long-life film capacitors can be used instead of electrolytic capacitors. In addition, the battery storage system with the droop control is also used to realize the power regulation function to meet the requirements of actual applications. A 1200 W prototype was designed and implemented to assess the system performance. Experimental results show that the proposed system can track MPP, regulate the load power condition, and reduce current ripple.

Configurations and Control Strategy of a Single Stage Grid Connected PV System

In the grid-connected photovoltaic (PV) system, the array forms DC power. This generated power, a two-way grid process is called DC – DC – AC as a two-stage power conversion and, secondly, a DC-AC with a reduced circuit is called a single Stage Grid – Connected PV (SSGCPV) system. SSGCPV is more advantageous for reduced complexity, reliability and efficiency, in order to reduce the number of step-up transformer power with conventional inverter (or transformer) with less high PV voltage. This paper proposes a detailed review of the few configurations of the SSGCPV inverter system and also discusses its control strategy for tracking maximum power and generating pulses to obtain the required output power.

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.

REALIZING A SINGLE-STAGE HYBRID PV SYSTEM USING BATTERY CURRENTSHARING POWER DECOUPLING METHOD

Conventionally, the single-stage grid-connected PV inverter needs a large PV-side electrolytic capacitor to suppress the doubleline frequency current ripple to keep the PV operating at maximum power point (MPP). However, the short lifetime electrolytic capacitor will reduce the PV inverter’s reliability dramatically. In order to overcome the above problem, a novel battery currentsharing power decoupling (BCSPD) method for hybrid photovoltaic (PV) power systems is proposed in this paper. The proposed BCSPD circuit is parallel-connected with the string PV module to achieve as a single-stage topology. Thus, a high power conversation efficiency can be obtained. The current-injection method is adapted to solve the current ripple problem. Therefore, the required capacitance in PV side can be greatly reduced, so long-life film capacitors can be used instead of electrolytic capacitors. In addition, the battery storage system with the droop control is also used to realize the power regulation function to meet the requirements of actual applications. A 1200 W prototype was designed and implemented to assess the system performance. Experimental results show that the proposed system can track MPP, regulate the load power condition, and reduce current ripple.

Power Synchronization Control for Grid-Connected Current-Source Inverter-Based Photovoltaic Systems

Current-source converters (CSCs) have a promising potential to interface the large-scale photovoltaic (PV) generators to electric grids. In order to overcome several drawbacks associated with the conventional vector-controlled CSC-based PV systems, this paper presents for the first time, the power synchronization control (PSC) scheme for the single-stage grid-connected CSC-based PV generator. A detailed small-signal model for the complete CSC-based PV system with the PSC strategy is developed to investigate the system stability, characterize the converter interactions with the electric grid, and design the controller parameters. The PSC of the CSC-based PV system reflects a stable performance under different operating conditions and following sudden variations in the insolation level. Due to the inherent synchronizing feature of the PSC, the phase-locked loop is eliminated and, hence, the integration to the very weak grids is seamlessly achieved. Although there is no direct control on the injected ac current to the grid, the inherent self-current-limiting feature of the CSC through the modulation of the regulated dc-choke current offers an overcurrent protection. Detailed nonlinear time-domain simulations results validate the theoretical analysis and show the effectiveness of the PSC strategy.

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.

Power Loss Comparison of Single- and Two-Stage Grid-Connected Photovoltaic Systems

This paper presents power loss comparison of single- and two-stage grid-connected photovoltaic (PV) systems based on the loss factors of double line-frequency voltage ripple (DLFVR), fast irradiance variation + DLFVR, fast dc load variation + DLFVR, limited operating voltage range + DLFVR, and overall loss factor combination. These loss factors will result in power deviation from the maximum power points. In this paper, both single-stage and two-stage grid-connected PV systems are considered. All of the effects on a two-stage system are insignificant due to an additional maximum power point tracker, but the tracker will reduce the system efficiency typically about 2.5%. The power loss caused by these loss factors in a single-stage grid-connected PV system is also around 2.5%; that is, a single-stage system has the merits of saving components and reducing cost, and does not penalize overall system efficiency under certain operating voltage ranges. Simulation results with the MATLAB software package and experimental results have confirmed the analysis.

Novel Maximum-Power-Point Tracking Algorithm For Grid-Connected Photovoltaic System

This paper presents a novel maximum-power-point (MPP) tracking algorithm for photovoltaic (PV) energy conversion systems. The algorithm is based on utilizing the relation between the PV array MPP current and the solar insolation level at different atmospheric conditions. Also, a single-stage grid-connected PV system is proposed to track the MPP of the PV array, using the new algorithm, and to produce a sinusoidal output current in phase with the utility voltage (i.e., to obtain a unity power factor). The power stage of the proposed system includes, mainly, a direct current–alternate current inverter, whereas the control stage is based on utilizing both the Proportional Integral (PI) and the P resonant controllers. The obtained results satisfy the desired performance for the proposed system.

Comparison of the performance of maximum power point tracking schemes applied to single-stage grid-connected photovoltaic systems

This work presents a comparison of various maximum power point tracking (MPPT) techniques applied to 1-phis, single-stage, grid-connected photovoltaic (PV) systems. A representative single-stage grid-connected PV system, based on buck-boost converter topology operating in discontinuous current mode (DCM) with sine-triangle pulse width modulation (SPWM) and feeding sinusoidal power into the grid, is considered for this study. MPPT techniques are compared on the basis of the time taken to reach (track) the MPP, operating point oscillations in the vicinity of MPP and the dependence of the algorithms, if any, on array configuration and parameters. Comparison is also made on the basis of the energy extracted from the PV source during the transient tracking phase. In this context, an energy tracking factor term (ETF) is introduced and defined. It is observed that all the MPPT schemes studied have their own merits and demerits. The ripple correlation and β methods offer an overall good combination of desirable features. All the results of this study are presented.