Power quality investigation of a solar PV transformer-less grid-connected system fed DVR

This paper presents a single stage transformer-less grid-connected solar photovoltaic (PV) system with an active and reactive power control. In the absence of active input power, the grid-tied voltage source converter (VSC) is operated in a reactive power generation mode, which powers the control circuitry, and maintains a regulated DC voltage to the VSC. A data-based maximum power point tracking (MPPT) control scheme which performs power quality control at a maximum power by reducing the total harmonic distortion (THD) in grid injected current as per IEEE-519/1547 standards is implemented. A proportional-integral (PI) controller based dynamic voltage restorer (DVR) control scheme is implemented which controls the grid side converter during single-phase to ground fault. The analysis includes the grid current THD along with the corresponding variation of the active and reactive power during the fault condition. The MPPT tracks the actual variable DC link voltage while deriving the maximum power from the solar PV array, and maintains the DC link voltage constant by changing the modulation index of the VSC. Simulation results using Matlab/Simulink are presented to demonstrate the feasibility and validations of the proposed novel MPPT and DVR control systems under different environmental conditions.     

THD reduction with reactive power compensation for fuzzy logic DVR based solar PV grid connected system

Dynamic voltage restorer (DVR) is used to protect sensitive loads from voltage disturbances of the distribution generation (DG) system. In this paper, a new control approach for the 200 kW solar photovoltaic grid connected system with perturb and observe maximum power point tracking (MPPT) technique is implemented. Power quality improvement with comparison is conducted during fault with proportional integral (PI) and artificial intelligence-based fuzzy logic controlled DVR. MPPT tracks the actual variable DC link voltage while deriving the maximum power from a photovoltaic array and maintains DC link voltage constant by changing modulation index of the converter. Simulation results during fault show that the fuzzy logic based DVR scheme demonstrates simultaneous exchange of active and reactive power with less total harmonic distortion (THD) present in voltage source converter (VSC) current and grid current with fast tracking of optimum operating point at unity power factor. Standards (IEEE-519/1547), stipulates that the current with THD greater than 5% cannot be injected into the grid by any distributed generation source. Simulation results and validations of MPPT technique and operation of fuzzy logic controlled DVR demonstrate the effectiveness of the proposed control schemes.     

Modeling and simulation of three phase multilevel inverter for grid connected photovoltaic systems

This paper presents a control for a three phase five-level neutral clamped inverter (NPC) for grid connected PV system. The maximum power point tracking (MPPT) is capable of extracting maximum power from the PV array connected to each DC link voltage level. The MPPT algorithm is solved by fuzzy logic controller. The fuzzy MPPT is integrated with the inverter so that a DC–DC converter is not needed and the output shows accurate and fast response. A digital PI current control algorithm is used to remain the current injected into the grid sinusoidal and to achieve high dynamic performance with low total harmonic distortion (THD). The validity of the system is verified through MATLAB/Simulink and the results are compared with three phase three-level grid connected NPC inverter in terms of THD.     

Adaptive fuzzy control with an optimization by using genetic algorithms for grid connected a hybrid photovoltaic–hydrogen generation system

The integration of significant amounts of renewable-storage hybrid power generation systems to the electric grid poses a unique set of challenges to utilities and system operators. This article deals with the designing methodology of an intelligent control based grid-connected a hybrid system composed of renewable energy source (RES) and storage system (SS). RES is a photovoltaic (PV) source and SS is a process of hydrogen transformation system (H₂TS) which composed of alkaline water electrolysis (AWE) for decomposition water by using the PV power, a tank used for gas storage and a proton exchange membrane (PEM) fuel cell (FC) to transform the H₂ to the electrical energy. The interconnection of the grid with the power generation system (PGS) is ensured through using a DC/AC hysteresis converter and it can synchronize current with the grid voltage among an independent control of active (P) and reactive (Q) power through a possibility of the Q compensation. In the proposed system, three algorithms are applied; two used inside generation and the third is used inside the grid. Perturb and observe (P&O) maximum power point tracking (MPPT) control algorithm always finds optimal power in the PV generator. A simple cascade controls loop of DC-DC boost converter and operate the FC generator to ensure maximum power and to regulate the DC Bus voltage. In addition, adaptive fuzzy logic control (FLC) unit is developed to control the DC/AC inverter, with adopting an off-line optimization based on genetic algorithms (GAs) applauded for tune different issues as scaling factors of the FLC and PIDs gains of the PV and the H₂TS control loops. Simulated results prove a big success of the proposed controls of the grid connected the hybrid PV-H₂TS with good performance.     

局部阴影条件下基于改进电导增量法的光伏系统最大功率跟踪方法

在局部阴影的情况下,由于串联式光伏组件的输出特性不同而产生多个极值点,使得传统的最大功率追踪（maximum power point tracking, MPPT）方法陷入局部极值点而失效。文中提出一种针对两级并网光伏系统的改进电导增量法以适应光伏阵列在局部阴影下的多峰值最大功率跟踪,通过分析最大功率点电压的变化范围,设定最大功率电压搜索范围以提高搜索效率,并通过DC/DC Boost变换器占空比实现输入电压控制,保证算法不陷入局部极值点。最后利用仿真实验验证了该算法在有、无阴影情况下均能准确地跟踪光伏方阵最大功率,有效提高了光伏阵列输出效率。     

SMC-DPC based active and reactive power control of grid-tied three phase inverter for PV systems

In this paper, sliding mode control (SMC) – direct power controller (DPC) based active and reactive power controller for three-phase grid-tied photovoltaic (PV) system is proposed. The proposed system consists of two main controllers: the DC/DC boost converter to track the possible maximum power from the PV panels and the grid-tied three-phase inverter. The Perturb and Observe (P&O) algorithm is used to transfer the maximum power from the PV panels. Control of the active and reactive powers is performed using the SMC-DPC strategy without any rotating coordinate transformations or phase angle tracking of the grid voltage. In addition, extra current control cycles are not used to simplify the system design and to increase transient performance. The fixed switching frequency is obtained by using space vector modulation (SVM). The proposed system provides very good results both in transient and steady states with the simple algorithms of P&O and SMC-DPC methods. Moreover, the results are evaluated by comparing the SMC-DPC method developed for MPPT and the traditional PI control method. The proposed controller method is achieved with TMS320F28335 DSP processor and the system is experimentally tested for 12 kW PV generation systems.     

Resiliency oriented control of a smart microgrid with photovoltaic modules

The resiliency of a standalone microgrid is of considerable issue because the available regulation measures and capabilities are limited. Given this background, this paper presented a new mathematical model for a detailed photovoltaic (PV) module and the application of new control techniques for efficient energy extraction. The PV module employs a single-stage conversion method to integrate it with the utility grid. For extraction the maximum power from PV and integrate it to power grid, a three-phase voltage source converter is used. For obtaining the maximum power at a particular irradiance a maximum power point tracking (MPPT) scheme is used. The fuzzy logic control and adaptive network-based fuzzy inference system are proposed for direct current (DC) link voltage control. The proposed model and control scheme are validated through a comparison with the standard power-voltage and current–voltage charts for a PV module. Simulation results demonstrate that the system stability can be maintained with the power grid and in the island mode, in contrast with the MPPT.     

Fuzzy logic-based MPPT controllers for three-phase grid-connected inverters

In photovoltaic (PV) applications, a maximum power point tracking (MPPT) module is necessary to extract the whole energy that the PV module can generate depending on the instantaneous conditions of the PV system. A PV module is obtained by connecting a number of solar cells in series and parallel, which causes voltage and current to increase at module terminations. The present work is based on a three-phase grid-connected inverter designed for a 100 kW PV power plant that uses an MPPT scheme based on fuzzy logic controllers. The whole system presented is simulated in MATLAB. The fuzzy logic-based MPPT controllers show accurate and fast responses and are integrated into the inverter, so that the there is no requirement for a dc–dc converter. The inverter allows full control of reactive power.     

Direct power control of grid connected PV systems with three level NPC inverter

This paper presents the control of a three-level Neutral Point Clamped (NPC) voltage source inverter for grid connected photovoltaic (PV) systems. The control method used is the Extended Direct Power Control (EDPC), which is a generic approach for Direct Power Control (DPC) of multilevel inverters based on geometrical considerations. Maximum Power Point Tracking (MPPT) algorithms, that allow maximal power conversion into the grid, have been included. These methods are capable of extracting maximum power from each of the independent PV arrays connected to each DC link voltage level. The first one is a conventional MPPT which outputs DC link voltage references to EDPC. The second one is based on DPC concept. This new MPPT outputs power increment references to EDPC, thus avoiding the use of a DC link voltage regulator. The whole control system has been tested on a three-level NPC voltage source inverter connected to the grid and results confirm the validity of the method.     

A Single-Stage Three-Phase Grid-Connected Photovoltaic System With Modified MPPT Method and Reactive Power Compensation

Single-stage grid-connected photovoltaic (PV) systems have advantages such as simple topology, high efficiency, etc. However, since all the control objectives such as the maximum power point tracking (MPPT), synchronization with the utility voltage, and harmonics reduction for output current need to be considered simultaneously, the complexity of the control scheme is much increased. This paper presents the implementation of a single-stage three-phase grid-connected PV system. In addition to realize the aforementioned control objectives, the proposed control can also remarkably improve the stability of the MPPT method with a modified incremental conductance MPPT method. The reactive power compensation for local load is also realized, so as to alleviate grid burden. A DSP is employed to implement the proposed MPPT controller and reactive power compensation unit. Simulation and experimental results show the high stability and high efficiency of this single-stage three-phase grid-connected PV system.     

New control strategy for 2-stage grid-connected photovoltaic power system

This work deals with the performances and responses of a grid-connected photovoltaic (PV) plant in normal and disturbed modes. The system is composed of a solar array, a dc–dc converter and a three-phase inverter connected to the utility grid. On the one hand a suitable control of the dc–dc converter is developed in order to extract the maximum amount of power from the PV generator. On the other hand an active and reactive power control approach (PQ) has been presented for the inverter. This method can provide a current with sinusoidal waveform and ensure a high power factor. Therefore, the grid interface inverter transfers the energy drawn from the PV into the grid by ensuring constant dc link voltage. Modeling and controlling were carried out using the informational graph of causality and the macroscopic energy representation methods. The simulation under MATLAB/SIMULINK and the experimental results show the control performance and dynamic behavior of grid-connected PV system in normal and disturbances modes.     

Implementation of photovoltaic water pumping system with MPPT controls

To increase the output efficiency of a photovoltaic (PV) system, it is important to apply an efficient maximum power point tracking (MPPT) technique. This paper describes the analysis, the design and the experimental implementation of the tracking methods for a stand-alone PV system, using two approaches. The first one is the constant voltage (CV) MPPT method based on the optimum voltage, which was deduced experimentally, and considered as a reference value to extract the optimum power. The second one is the increment conductance (Inc-Cond) MPPT method based on the calculation of the power derivative extracted by the installation. The output controller can adjust the duty ratio to the optimum value. This optimum duty ratio is the input of a DC/DC boost converter which feeds a set of Moto-pump via a DC/AC inverter. This paper presents the details of the two approaches implemented, based on the system performance characteristics. Contributions are made in several aspects of the system, including converter design, system simulation, controller programming, and experimental setup. The MPPT control algorithms implemented extract the maximum power point (MPP), with satisfactory performance and without steady-state oscillation. MATLAB/Simulink and dSpace DS1104 are used to conduct studies and implement algorithms. The two proposed methods have been validated by implementing the performance of the PV pumping systems installed on the roof of the research laboratory in INSAT Tunisia. Experimental results verify the feasibility and the improved functionality of the system.     

Highly efficient maximum power point tracking using DC–DC coupled inductor single-ended primary inductance converter for photovoltaic power systems

Solar photovoltaics (PVs) have nonlinear voltage–current characteristics, with a distinct maximum power point (MPP) depending on factors such as solar irradiance and operating temperature. To extract maximum power from the PV array at any environmental condition, DC–DC converters are usually used as MPP trackers. This paper presents the performance analysis of a coupled inductor single-ended primary inductance converter for maximum power point tracking (MPPT) in a PV system. A detailed model of the system has been designed and developed in MATLAB/Simulink. The performance evaluation has been conducted on the basis of stability, current ripple reduction and efficiency at different operating conditions. Simulation results show considerable ripple reduction in the input and output currents of the converter. Both the MPPT and converter efficiencies are significantly improved. The obtained simulation results validate the effectiveness and suitability of the converter model in MPPT and show reasonable agreement with the theoretical analysis.     

Optimization of a fuzzy logic controller for PV grid inverter control using S-function based PSO

This paper presents implementation of particle swarm optimization (PSO) algorithm as a C-Mex S-function. The algorithm is used to optimize a 9-rule fuzzy logic controller (FLC) for maximum power point tracking (MPPT) in a grid-connected photovoltaic (PV) inverter. The FLC generates DC bus voltage reference for MPPT. A digital PI current control scheme in rotating dq-reference frame is used to regulate the DC bus voltage and reactive power. The proposed technique simplifies optimal controller design and ensures fast simulation speeds due to seamless integration with the simulation platform. Validity of the proposed method was verified using co-simulation in PSIM and MATLAB/Simulink. Simulation results show that the optimized FLC gives a better performance compared to fixed-step MPPT.     

Improved particle swarm optimization for photovoltaic system connected to the grid with low voltage ride through capability

Grid connected photovoltaic (PV) system encounters different types of abnormalities during grid faults; the grid side inverter is subjected to three serious problems which are excessive DC link voltage, high AC currents and loss of grid-voltage synchronization. This high DC link voltage may damage the inverter. Also, the voltage sags will force the PV system to be disconnected from the grid according to grid code. This paper presents a novel control strategy of the two-stage three-phase PV system to improve the Low-Voltage Ride-Through (LVRT) capability according to the grid connection requirement. The non-linear control technique using Improved Particle Swarm Optimization (IPSO) of a PV system connected to the grid through an isolated high frequency DC–DC full bridge converter and a three-phase three level neutral point clamped DC-AC converter (3LNPC²) with output power control under severe faults of grid voltage. The paper, also discusses the transient behavior and the performance limit for LVRT by using a DC-Chopper circuit. The model has been implemented in MATLAB/SIMULINK. The proposed control succeeded to track MPP, achieved LVRT requirements and improving the quality of DC link voltage. The paper shows superiority of IPSO than Incremental Conductance (IC) method during MPPT mode of PV system.     

具有无功功率补偿和谐波抑制的光伏并网功率调节器控制研究

提出一种将有源滤波和无功功率补偿与光伏并网发电相结合的新型光伏并网功率调节系统。利用瞬态无功功率理论中的瞬时无功和谐波电流检测原理,采用电流矢量控制技术,以DSP数字信号处理器为基础,在30KVA光伏并网功率调节器样机中成功地实现了有源滤波、无功功率补偿和光伏并网发电三者的统一控制,使光伏并网功率调节器在向电网提供有功能量的同时也提供无功负载所需的无功能量,从而节省了设备投资,同时也改善了电网的供电质量。     

A maximum power point tracking for photovoltaic-SPE system using a maximum current controller

Processes to produce hydrogen from solar photovoltaic (PV)-powered water electrolysis using solid polymer electrolysis (SPE) are reported. An alternative control of maximum power point tracking (MPPT) in the PV-SPE system based on the maximum current searching methods has been designed and implemented.Based on the characteristics of voltage–current and theoretical analysis of SPE, it can be shown that the tracking of the maximum current output of DC–DC converter in SPE side will track the MPPT of photovoltaic panel simultaneously.This method uses a proportional integrator controller to control the duty factor of DC–DC converter with pulse-width modulator (PWM).The MPPT performance and hydrogen production performance of this method have been evaluated and discussed based on the results of the experiment.     

Analysis of the maximum power point tracking in the photovoltaic grid inverters of 5 kW

The aim of this article is to describe how closely PV grid-connected inverters (of around 5 kW) operate at the actual maximum power point. These inverters could be installed at any low voltage, PV grid-connected systems. To carry this study out, twelve 50 Hz single-phase inverters were selected from the European market. Each one of them was put into an outdoor grid-connected system installed in Spain. PV power generation with respect to irradiance, ambient temperature and local time was measured under different meteorological conditions. DC voltage and maximum power point tracking efficiency were analyzed. From the results obtained it has been possible to see that the MPPT algorithms used in some inverters do not bring the optimum utilisation of the PV array.     

A new RBFN based MPPT controller for grid-connected PEMFC system with high step-up three-phase IBC

Extraction of maximum power from a proton exchange membrane fuel cell (PEMFC) power source is necessary for its economical and optimal utilization. In this paper, a neural network based maximum power point tracking (MPPT) controller is proposed for the grid-connected PEMFC system. Radial basis function network (RBFN) algorithm is implemented in the neural network controller to extract the maximum power from PEMFC. A high step-up three-phase interleaved boost converter (IBC) is also designed in order to reduce the current ripples coming out from the PEMFC. Interleaving technique provides high power capability and reduces the voltage stress on the power semiconductor devices. The performance analysis of the proposed RBFN MPPT controller is analyzed in MATLAB/Simulink platform for both standalone as well as for the grid-connected PEMFC system.     

不平衡电网电压下T型三电平光伏并网逆变器的有限集模型预测控制

为实现电网电压不平衡时对T型三电平光伏并网系统输出功率和电流质量的控制,以达到入网功率平稳或电流正弦为控制目标,结合光伏阵列输出功率前馈,在两相静止坐标系下提出一种直流母线电压外环PI控制、并网电流内环有限集模型预测控制的控制策略,并在电压外环中引入2倍频陷波器以获得平滑的入网功率参考值。仿真结果表明:当电网电压不对称时,采用所提控制策略能够实现对入网有功、无功功率2倍频脉动及负序电流的分别抑制或协调控制,且并网电流谐波畸变小、入网电能质量高,同时实现T型三电平逆变器的中点电位平衡。