Three-phase Grid-connected Photovoltaic System Research Articles

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.

Dynamic Performance Improvement of a Grid-Tied PV System Using a Feed-Forward Control Loop Acting on the NPC Inverter Currents

This paper presents a three-phase grid-connected photovoltaic (PV) system, which is implemented using the neutral-point-clamped (NPC) inverter. A current feed-forward control loop (FFCL) is proposed to improve the PV system dynamic behavior, due to the PV array being constantly subjected to sudden solar irradiance change, which causes voltage oscillations in the dc bus and, hence, interferes in proper PV system operation. As the current FFCL acts to speed up the calculation of the inverter current references, the dynamic response of the currents injected into the grid is improved. As a consequence, the dynamic behavior of the dc-bus voltage is also enhanced, reducing both settling time and overshoot. Besides the injection of active power into the grid, the PV system is also controlled to perform active power-line conditioning, so that load harmonic currents are suppressed, as well as load reactive power is compensated. However, the NPC inverter must be properly designed to guarantee that its power rating will not be exceeded, since both fundamental and nonfundamental current components flow through the grid-tied inverter. Extensive experimental results based on a digital signal processor are presented in order to evaluate the effectiveness, as well as the static and dynamic performance of the PV system.

Recurrent Fuzzy Cerebellar Model Articulation Neural Network Based Power Control of a Single-Stage Three-Phase Grid-Connected Photovoltaic System During Grid Faults

A recurrent fuzzy cerebellar model articulation neural network (RFCMANN)-based controller to regulate the active and reactive power of a single-stage three-phase grid-connected photovoltaic (PV) system during grid faults is proposed in this study. Since the rapid growth of the amount of the PV systems in recent year has greatly affected the stability of the power system, the grid codes demand the grid-connected PV systems to have the low-voltage ride through (LVRT) capability to help sustaining the stability of power system especially during the grid faults. To satisfy the LVRT requirements and ensure the injected current within the safety value, the active and reactive power commands are calculated by using the current profile of the LVRT grid requirements and the current limit of the inverter. Moreover, the proposed RFCMANN controller uses the signed distance and input space repartition mechanisms to convert the dual-input variables to sole-input variable and repartition the input space to an appropriate quantity. Therefore, the structure and computation complexities of the proposed RFCMANN controller are effectively reduced and make it more practical. Furthermore, varied learning-rate coefficients are designed to guarantee the convergence of the tracking error for the proposed RFCMANN controller.

A NOVEL FLC FOR PV ARRAYS CONNECTED TO THE UTILITY GRID

This paper provides a suitable fuzzy logic control (FLC) system for three-phase grid-connected photovoltaic (PV) system which aims to work at unity power factor and constant output voltage suitable with the grid for any PV side or grid side disturbances. Also by the control system, the (PV-common DC link) interface transfers the energy drawn from the PV array by keeping dc voltage constant. Also, FLC results are compared with conventional (PI) control at the same disturbances. The model contains a detailed representation of the main components of the system that are the PV arrays, the booster converter and the grid side inverter. A novel method for Maximum Power Point Tracking (MPPT) technique through fuzzy logic system is implemented and compared with INC MPPT technique. MPPT techniques are obtained under different temperature values and irradiation levels. Modeling and control is carried out using MATLAB-SIMULINK. The simulation results showed the control performance and dynamic behavior of the system at various disturbances such as three-phase short circuit at connection point, one line outage and irradiation variations

A new backstepping finite time sliding mode control of grid connected PV system using multivariable dynamic VSC model

This paper presents independent active and reactive power management of a three-phase grid-connected photovoltaic (PV) generation system using a new nonlinear control approach for the voltage source converter (VSC). Instead of controlling the direct and quadrature-axis currents of the VSC, the instantaneous active and reactive powers are used as error estimation parameters. This mode of control dispenses the unmodelled dynamics of the VSC phase-locked loop system and produces a robust control for the active–reactive power, and dc voltage excursions. This approach reduces computational time as well as complexity by avoiding unnecessary PLL phase calculation in the beginning. However, the PLL is used only to obtain the frequency component needed to generate the PWM signal. Further to improve the stability and robust tracking of the grid connected PV array, backstepping finite time fast sliding mode (BFTSM) control strategy is presented in this paper. The proposed controller offers invariant stability to modeling uncertainties due to converter parameter changes, changes in system frequency and exogenous inputs. Also the finite time sliding mode control offers an important tool for designing continuous finite time control laws. Comprehensive computer simulations are carried out in MATLAB/Simulink to verify the proposed control scheme under several system disturbances like changes in solar insolation, changes in local load, converter parametric changes, and faults on the converter and inverter buses, and partial shading condition of PV array. EMTDC/PSCAD model is established as confirmative study.

Fuzzy logic controller vs. PI controller for MPPT of three-phase grid-connected PV system considering different irradiation conditions

In this paper, a comparison between fuzzy logic controller (FLC) and conventional proportional-integral controller (PIC) is presented for a connected PV array system to utility grid via a three-phase line-commutated inverter. The main objective of the controller is providing maximum power for utility grid in different solar radiation conditions. The simulink model of the studied schemes is built using MATLAB/PSB for generating firing pulses of the thyristors in the inverter by applying PIC and FLC methods separately. Three different radiation conditions are examined on both controller which are constant solar radiation, step solar radiation and a combination of step and ramp scheme. According to simulations, FLC dominates PIC for all radiation types and in many important aspects. Some of these aspects could be named as, extracting power from PV array, providing active power for grid, shape of output current of inverter, shape of grid current waveform and total harmonic distortion (THD) of these currents.

Fault Analysis of Grid Connected Photovoltaic System

A new method of current control strategy for grid connected photovoltaic (PV) system is presented in this paper. The connection of photovoltaic system with the grid is a difficult task as the solar irradiation is a nonlinear quantity. The objective of this work is to develop a model of the photovoltaic system with maximum power point tracking (MPPT) system connected to 11 KV grid by implementing new control technique so that maximum active power transfer from PV to grid can be taken place without injection of harmonics. The considered system consists of a PV system, MPPT controller, boost converter, voltage source inverter (VSI), 3-Φ filter, a control system, a distribution network, load and grid. In the beginning, a model of a photovoltaic array was developed and then a MPPT controller and a direct current to direct current (DC-DC) converter are designed. To connect PV system to grid, a power electronics converter is needed which can convert DC voltage into three- phase AC voltage. Three-phase VSI using insulated gate bipolar transistors (IGBTs) is used. By means of a step-up transformer and filter, this three-phase VSI is connected to the distribution network. The proposed control of the three-phase grid-connected solar PV system is designed in the synchronously-rotating d-q reference frame. Here, Vdc is measured, then compared with Vdcref and accordingly the error is fed to proportional-integral (PI) controller from which Idref is generated. As PV system should inject only active power, so reactive power injected to grid is made zero by making Iqref zero. There after the final model is simulated by using MATLAB/SIMULINK and different output waveforms are analyzed for different conditions. Finally the fault analysis is carried out to observe the behavior of the system.

A Control Strategy based on Fuzzy Logic for Three-phase Grid-connected Photovoltaic System with Supporting Grid-frequency Regulation

A Control Strategy based on Fuzzy Logic for Three-phase Grid-connected Photovoltaic System with Supporting Grid-frequency Regulation

Protection of Three-Phase VSI Grid-Connected PV System During Transient Conditions Using Fuzzy Logic

This paper presents 100 KW three-phase photovoltaic (PV) systems connected to the grid. The system utilizes a two-stage energy conversion power conditioning unit topology composed of a DC–DC boost converter and three-phase voltage source inverter (VSI). The main commonly problem is the capacitor damage of the PV array system during transient conditions due to high impulse voltage when connected to the grid. The problem of VSI capacitor failure during transient conditions is solved in this paper by using fuzzy logic pulse control technique. The fuzzy logic controller is implemented on the three-phase VSI of the PV system. The $$V_{\mathrm{dc}}$$ applied on the capacitor for the above system is tested during transient conditions using two-level and three-level inverters using MATLAB/Simulink.

Reactive Power Control of Three-Phase Grid-Connected PV System During Grid Faults Using Takagi–Sugeno–Kang Probabilistic Fuzzy Neural Network Control

An intelligent controller based on the Takagi–Sugeno–Kang-type probabilistic fuzzy neural network with an asymmetric membership function (TSKPFNN-AMF) is developed in this paper for the reactive and active power control of a three-phase grid-connected photovoltaic (PV) system during grid faults. The inverter of the three-phase grid-connected PV system should provide a proper ratio of reactive power to meet the low-voltage ride through (LVRT) regulations and control the output current without exceeding the maximum current limit simultaneously during grid faults. Therefore, the proposed intelligent controller regulates the value of reactive power to a new reference value, which complies with the regulations of LVRT under grid faults. Moreover, a dual-mode operation control method of the converter and inverter of the three-phase grid-connected PV system is designed to eliminate the fluctuation of dc-link bus voltage under grid faults. Furthermore, the network structure, the online learning algorithm, and the convergence analysis of the TSKPFNN-AMF are described in detail. Finally, some experimental results are illustrated to show the effectiveness of the proposed control for the three-phase grid-connected PV system.

Design, Digital Control, and Simulation of a Grid- Connected Photovoltaic Generation System

This paper presents simulation and digital control of a three-phase grid-connected photovoltaic (PV) generation system. The technique used for maximum power point tracking (MPPT) of photovoltaic power is sliding mode (SM) control. Control of power extraction from DC link capacitor is presented. Space vector pulse width modulation (SVPWM) inverter is utilized to deliver power to utility grid. Simulation is performed using PLECS standalone software package and simulation results are shown. Complete theoretical foundation needed for system simulation is presented.

Robust Nonlinear Controller Design for Three-Phase Grid-Connected Photovoltaic Systems Under Structured Uncertainties

This paper presents a robust nonlinear controller design for a three-phase grid-connected photovoltaic (PV) system to control the current injected into the grid and the dc-link voltage for extracting maximum power from PV units. The controller is designed based on the partial feedback linearization approach, and the robustness of the proposed control scheme is ensured by considering structured uncertainties within the PV system model. An approach for modeling the uncertainties through the satisfaction of matching conditions is provided. The superiority of the proposed robust controller is demonstrated on a test system through simulation results under different system contingencies along with changes in atmospheric conditions. From the simulation results, it is evident that the robust controller provides excellent performance under various operating conditions.

독일 계통 연계 규정에 기반 된 대용량 태양광 발전 시스템의 계통 안정화를 위한 제어 전략

The rising penetration of renewable energy resulted in the development of grid-connected large-scale power plants. Therefore, grid stabilization, which depends on the system-type or grid of each country, plays an important role and has been strengthened by different grid codes. With this background, VDE-AR-N 4105 for photovoltaic (PV) systems connected to the low-voltage grid and the German Association of Energy and Water Industries (BDEW) introduced the medium-voltage grid code for connecting power plants to the grid and they are the most stringent certifications. In this paper, an optimal control strategy scheme for three-phase grid-connected PV system is enhanced with VDE-AR-N 4105 and BDEW grid code, where both active/reactive powers are controlled. Simulation and experimental results of 100kW PV inverter are shown to verify the effectiveness of the proposed implemental control 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.

Robust Partial Feedback Linearizing Stabilization Scheme for Three-Phase Grid-Connected Photovoltaic Systems

This paper presents a robust stabilization scheme for a three-phase grid-connected photovoltaic system to control the current injected into the grid and dc-link voltage to extract maximum power from photovoltaic (PV) units. The scheme is mainly based on the design of a robust controller using a partial feedback linearizing approach of feedback linearization, where the robustness of the proposed scheme is ensured by considering uncertainties within the PV system model. In this paper, the uncertainties are modeled as structured uncertainties based on the satisfaction of matching conditions. The performance of the proposed stabilization scheme is evaluated on a three-phase grid-connected PV system in terms of delivering maximum power under changes in atmospheric conditions.

Reactive Power Control of Single-Stage Three-Phase Photovoltaic System during Grid Faults Using Recurrent Fuzzy Cerebellar Model Articulation Neural Network

This study presents a new active and reactive power control scheme for a single-stage three-phase grid-connected photovoltaic (PV) system during grid faults. The presented PV system utilizes a single-stage three-phase current-controlled voltage-source inverter to achieve the maximum power point tracking (MPPT) control of the PV panel with the function of low voltage ride through (LVRT). Moreover, a formula based on positive sequence voltage for evaluating the percentage of voltage sag is derived to determine the ratio of the injected reactive current to satisfy the LVRT regulations. To reduce the risk of overcurrent during LVRT operation, a current limit is predefined for the injection of reactive current. Furthermore, the control of active and reactive power is designed using a two-dimensional recurrent fuzzy cerebellar model articulation neural network (2D-RFCMANN). In addition, the online learning laws of 2D-RFCMANN are derived according to gradient descent method with varied learning-rate coefficients for network parameters to assure the convergence of the tracking error. Finally, some experimental tests are realized to validate the effectiveness of the proposed control scheme.

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.

Application of DE Algorithm over Control of Grid-Connected PV Inverter

A novel method for optimum vector PWM (OVPWM) control of three-phase grid-connected photovoltaic inverter was described. The control vector and its corresponding action duration composed of the PWM sequences generated by optimum vector PWM strategy. A Differential Evolution (DE) algorithm was applied to determine the action duration of the output voltage vector based on conventional vector PWM (CVPWM). The Matlab-based model of three-phase grid-connected photovoltaic generation system was established. Comparative analysis proving superiority of the OVPWM technique over the CVPWM, and the results of the simulation confirmed the feasibility and advantage of proposed OVPWM strategy.

The Simulative Research of Three-Phase PV Grid-Connected Control System Based on SVPWM Inverter

The PV grid-connected control system is mainly related to a few key issues that are characteristics of photovoltaic cells, maximum power point tracking and grid-connected control of three-phase inverter. In this paper, simulation analysis and study of the three-phase grid-connected PV system control strategy. The control strategy of the three-phase PV grid-connected system is analyzed and studied by simulative experiment in this paper. First, a mathematical model of solar cells is established, then the algorithms based on perturb & observe to track maximum power point is used; Secondly, the structure of three-phase PV grid-connected system is introduced, and the space vector SVPWM controller is used to control the grid-connected inverter; Finally, the simulative results on Matlab/Simulink software show that SVPWM inverter control strategy is superior to the traditional hysteresis current inverter control strategy, which illustrates the reliability and superiority of SVPWM control strategy.

Modeling and Simulation of Three-Phase Two-Level Grid-Connected Photovoltaic System

The model and simulation of three-phase Two-level Grid-connected Photovoltaic System are established. According to the equivalent circuit and mathematical model of the PV cell, the general simulation model of photovoltaic array is established. Regulating duty ratio in Boost circuit to realize the maximum power point tracing with method of high-precision incremental conductance. Model of photovoltaic inverter is established based on power decoupling vector control strategy. SVPWM modulation improves the utilization ratio of voltage in DC side. Finally, the simulation of three-phase two-level grid-connected photovoltaic system is conducted in MATLAB. The result shows that the system can rapidly and accurately track maximum power point and the output of current keep in the same frequency and phase, which can be connected to power grid flexibly.