Inverter For Grid-connected Photovoltaic System Research Articles

Adaptive Backstepping-Based H${_{\infty}}$ Robust Controller for Photovoltaic Grid- Connected Inverter

To improve the robustness and stability of the photovoltaic grid-connected inverter system, a nonlinear backstepping-based H ∞ controller is proposed. A generic dynamical model of grid-connected inverters is built with the consideration of uncertain parameters and external disturbances that cannot be accurately measured. According to this, the backstepping H ∞ controller is designed by combining techniques of adaptive backstepping control and L2-gain robust control. The Lyapunov function is used to design the backstepping controller, and the dissipative inequality is recursively designed. The storage functions of the DC capacitor voltage and grid current are constructed, respectively, and the nonlinear H ∞ controller and the parameter update law are obtained. Experimental results show that the proposed controller has the advantage of strong robustness to parameter variations and external disturbances. The proposed controller can also accurately track the references to meet the requirements of high-performance control of grid-connected inverters.

A Feedback-Based Passive Islanding Detection Technique for One-Cycle-Controlled Single-Phase Inverter Used in Photovoltaic Systems

Single-stage, single-phase photovoltaic (PV) distributed generation (DG) systems rated below 5 kW are becoming popular because of the reduction in the cost of PV panels and also due to various policy initiatives. One cycle control (OCC) based inverters are ideally suitable for such DG systems because of its cost-effectiveness, simple structure, and phase-locked loop free implementation. These inverter-based DG systems should have a robust islanding detection method (IDM) incorporated into it and should fulfill the recent standard requirements. This article proposes a novel feedback-based passive IDM, which is suitable for OCC-based grid-connected PV inverter system. The proposed method relies on the inbuilt feedback nature of OCC-based system, which drives the voltage at the point of common coupling outside the normal range of operation during an islanding condition. The proposed IDM works effectively under the new standard requirements with negligible nondetection zone. The IDM does not rely on additional computational effort or injection of external disturbance into the grid. Simulation studies are performed to verify the effectiveness of the proposed IDM. A laboratory prototype has been developed, and experimental studies are conducted to ascertain the viability of the proposed method.

A Model Predictive Power Control Method for PV and Energy Storage Systems With Voltage Support Capability

The cascaded control method with an outer voltage loop and an inner current loop has been traditionally employed for the voltage and power control of photovoltaic (PV) inverters. This method, however, has very limited power regulation capability. With the fast increasing penetration of PV power generation systems in the distribution network, the voltage rise/drop has become a serious problem impacting negatively on the power quality and grid stability. Therefore, flexible power regulation is highly desired for PV inverters to provide ancillary services. This paper proposes a novel model predictive power control (MPPC) scheme to control and coordinate the dc–dc converter and inverter for grid-connected PV systems with energy storage systems (ESS). By regulating the dc-bus voltage and controlling the active and reactive power flows, MPPC can support the power grid to maintain stable voltage and frequency and improve the power factor. Numerical simulation and controller hardware-in-the-loop (CHIL) testing have been conducted on a PV-ESS system to verify the capability and effectiveness of the proposed control strategy.

Dual-mode operation based second-order sliding mode control for grid-connected solar photovoltaic energy system

This paper proposes a second-order sliding mode control technique for the grid-connected solar photovoltaic system. The proposed technique is tested under grid faults to meet the requirements of low-voltage ride through capability. A dual-mode control technique of the converter and inverter is designed to maintain the required dc-link voltage regulation and the active-reactive power during grid fault. The sliding mode control technique is developed from the model of the grid connected to the converter and the dc-link. The proposed dual-mode control technique is validated using real-time simulator OPAL-RT and experimental three-phase grid-connected photovoltaic inverter system. Simulation and experimental results show that the control technique is quite effective in maintaining the dc-link voltage regulation and the power control. As it shows smooth transitions between the two modes of operation (normal and grid fault). Moreover, the sliding mode control approach is robust against unknown disturbances and uncertainties in the system.

A novel hybrid Phase Shifted-Modified Synchronous Optimal Pulse Width Modulation based 27-level inverter for grid-connected PV system

In grid connected Photovoltaic (PV) systems, Multilevel Inverters (MLI) are commonly employed for providing better reliability and getting minimal harmonics. Most of the MLIs function with Phase-Shifted Pulse Width Modulation (PSPWM) techniques for achieving high level performance. However, in the in existing PSPWM techniques, the harmonic voltage profiles are not efficient. This paper aims to improve the harmonic voltage profile of the 4 KW grid-connected PV system using a novel hybrid PSPWM-Modified Synchronous Optimal PWM (PS-MSOPWM) technique for a 27-level inverter. With the combination of these hybrid PSPWM-Modified SOPWM techniques, optimum switching angles are computed to match the switching frequency with the fundamental frequency. From the results, it is identified that the proposed hybrid modulation method effectively reduces the Total Harmonic Distortion (THD) and exhibits improved reliability of the grid-connected solar system.

High performance of three-level T-type grid-connected photovoltaic inverter system with three-level boost maximum power point tracking converter

A three-phase three-level transformerless T-type grid-connected inverter system with three-level boost maximum power point tracking converter is introduced in this article for high-voltage high-pow...

Research on grid-connected photovoltaic inverter based on quasi-PR controller adjusting by dynamic diagonal recurrent neural network

The single-phase grid-connected photovoltaic inverter system is studied in this paper. In view of the non-linear and time-varying characteristics of this system, the three-closed-loop control strategy consisting of DC voltage outer loop, grid-connected current inner loop and capacitive current inner loop based on quasi-PR control is proposed. Since the quasi-PR controller of fixed parameters is unable to adapt to changes of parameters in power network, a quasi-PR control method of dynamic self-tuning based on a dynamic Diagonal Recurrent Neural Network (DRNN) is presented. DRNN is based on the Recursive Prediction Error (RPE) algorithm with second-order gradient, which has a faster convergence rate than the BP algorithm. The simulation and experiment results prove that the grid-connected photovoltaic inverter with the above control algorithm has a good quality of the output current and fast performance in dynamic response.

Research on the strategy of cooperative control between photovoltaic grid‐connected and reactive power compensation technology

When connecting a large number of generating sets into power grid, there will be the harmonic wave generated in power grid causing voltage and current distortion, which affects power quality seriously. Based on the instantaneous reactive power theory, the active current, reactive current and harmonic current can be real-time monitored. The P–Q method can be adopted to control reactive power compensation. By building the converter control model, the variation of reactive power of power grid between photovoltaic grid-connected inverter working under stand-alone mode and grid-connected mode can be analysed via a simulation system. The experimental analysis of reactive power compensation and harmonic suppression, the availability of the control strategy of the photovoltaic grid-connected inverter system can be proved. Using this novel strategy, the photovoltaic grid-connected power system can not only provide active power but also compensate reactive power and suppress harmonic, which will improve power quality.

Realization of a Single-Phase Multilevel Inverter for Grid-Connected Photovoltaic System

This paper introduces the implementation of a single-phase multilevel inverter for a grid-connected photovoltaic system. The considered topology contains a full bridge converter tied to an auxiliary circuit made of two power switches. A proportional integral (PI) current controller is established with this inverter to inject a sinusoidal current into the grid with a power factor near to unity. The studied system is tested on Matlab/Simulink and verified by experiment through a test bench comprising of a fabricated prototype and a DSP TMS320F28379D. The obtained results prove the efficiency of the inverter to maintain a direct power flow from DC sources, such as solar panels, to the grid by respecting some normalized criteria for this operation.

Realization of a Single-Phase Multilevel Inverter for Grid-Connected Photovoltaic System

Realization of a Single-Phase Multilevel Inverter for Grid-Connected Photovoltaic System

Modified Seven-Level Pack U-Cell Inverter for Photovoltaic Applications

This paper proposes a modified conation of single-phase pack U-cell (PUC) multilevel inverter in which the output voltage has higher amplitude than the maximum dc link value used in the topology as a boost operation. The introduced inverter generates seven-level ac voltage at the output using two dc links and six semiconductor switches. Comparing to cascaded H-bridge and neutral point clamp multilevel inverters, the introduced multilevel inverter produces more voltage levels using less components. The proposed inverter is used in photovoltaic (PV) system where the green power comes from two separate PV panels connected to the dc links through dc–dc converters to draw the maximum power. Due to boost operation of this inverter, two different PV panels can combine and send their powers to the grid. Simulations and experimental tests are conducted to investigate the good dynamic performance of the inverter in grid-connected PV system.

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.

A Robust Continuous-Time MPC of a DC–DC Boost Converter Interfaced With a Grid-Connected Photovoltaic System

The main function of the DC-DC converter in a grid-connected photovoltaic (PV) system is to regulate the terminal voltage of the PV arrays to ensure delivering the maximum power to the grid. The purpose of this paper is to design and practically implement a robust continuous-time model predictive control (CTMPC) for a dc-dc boost converter, feeding a three-phase inverter of a grid-connected PV system to regulate the PV output voltage. In CTMPC, the system behavior is predicted based on Taylor series expansion, raising concerns about the prediction accuracy in the presence of parametric uncertainty and unknown external disturbances. To overcome this drawback, a disturbance observer is designed and combined with CTMPC to enhance the steady-state performance in the presence of model uncertainty and unknown disturbance such as the PV current, which varies nonlinearly with the operating point. An interesting feature is that the composite controller reduces to a conventional PI controller plus a predictive term that allows further improvement of the dynamic performance over the whole operating range. The effectiveness of the proposed controller was tested numerically and validated experimentally with the consideration of the grid-connected PV inverter system and its controller.

Cascaded H-Bridge Five-Level Inverter for Grid-Connected Photovoltaic System Using Proportional–Integral Controller

Photovoltaic power generation is a promising alternative source of energy and has many advantages than the other alternative energy sources like wind, solar, ocean, biomass, geothermal, and so on. In photovoltaic power generation, multilevel inverters play a vital role in power conversion. The three different topologies, diode-clamped (neutral-point clamped) inverter, capacitor-clamped (flying capacitor) inverter, and cascaded H-bridge multilevel inverter, are widely used in these multilevel inverters. Among the three topologies, cascaded H-bridge multilevel inverter is more suitable for photovoltaic applications since each photovoltaic array can act as a separate direct current source for each H-bridge module. In this paper, a single-phase cascaded H-bridge five-level inverter for grid-connected photovoltaic system using proportional–integral controller is presented. Sinusoidal pulse width modulation technique was used for eliminating the harmonic distortion. The cascaded control strategy enables tracking of the maximum power point of distinct photovoltaic strings and allows independent control of the direct current-link voltages. The performance of single-phase cascaded H-bridge five-level inverter with respect to harmonic content and number of switches is simulated using MATLAB/Simulink. A hardware prototype is developed to verify the performance of the developed system. The results of hardware are compared with the simulation results. The proposed system offers improved performance over conventional two-level inverters.

Direct Power Control and Fault Diagnosis of Photovoltaic Grid Connected Inverter System

Direct Power Control and Fault Diagnosis of Photovoltaic Grid Connected Inverter System

Design of Single-Phase Seven-Level Grid-Connected Inverter using Solar System

This paper proposes a single phase seven-level inverter for grid-connected photovoltaic system, with a novel pulse width-regulated (PWM) control plan. Three reference signals that are indistinguishable to one another with a balance that is proportionate to the abundancy of the triangular bearer sign were utilized to produce the PWM signals. The inverter is fit for delivering seven levels of output voltage levels (Vdc, 2Vdc/3, Vdc/3, 0, −Vdc, −2Vdc/3, −Vdc/3) from the dc supply voltage. A computerized proportional-integral current-control calculation was executed in a TMS320F2812 DSP to keep the current infused into the grid sinusoidal. The proposed system was confirmed through simulation and implemented in a prototype.

Real-Time Testing of a Fuzzy-Logic-Controller-Based Grid-Connected Photovoltaic Inverter System

This paper presents a novel fuzzy-logic-based high-performance control of a three-phase photovoltaic grid-connected inverter. With the aid of the inverter model and fuzzy-logic-based voltage and current-control schemes, a digital signal processor controller board DS1104 generates the sinusoidal pulsewidth modulated signals for the inverter operation in both stand-alone and grid-connected modes. An inverter prototype was built to verify the effectiveness of the control algorithm. The system demonstrates stable ac output voltage satisfactorily during both transient and steady state with grid and load disturbances. The control system generates 2.48% and 4.64% voltage and current total harmonic distortions, respectively. The output waveforms such as output voltage, injected current, and the system power flow are presented to validate the effectiveness of the control strategy.

Adaptive Neuro-Fuzzy Model for Grid-Connected Photovoltaic System

This paper proposed an adaptive neuro-fuzzy inference system (ANFIS) model to multilevel inverter for grid-connected photovoltaic (PV) system. The purpose of the proposed controller is to avoid the requirement of any optimal PWM (pulse width-modulated) switching-angle generator and proportional–integral controller. The proposed method strictly prevents the variations present in the output voltage of the cascaded H-bridge multilevel inverter. Here, the ANFIS models have the inputs which are the grid voltage and the difference voltage, and the output target is the control voltage. By means of these parameters, the ANFIS makes the rules and can be tuned perfectly. During the testing time, the ANFIS provides the control voltage according to the different inputs. Then, the ANFIS-based algorithm for multilevel inverter for grid-connected PV system is implemented in the MATLAB/simulink platform, and the effectiveness of the proposed control technique is analyzed by comparing the model’s performances with the neural network, fuzzy logic control, etc.

English

3 ABSTRACT: This paper proposes a single-phase two stage inverter for grid-connected photovoltaic systems for residential applications. This system consists of a switch mode DC-DC boost converter and a H-bridge inverter. The switching strategy of proposed inverter consists with a combination of sinusoidal pulse width modulation (SPWM) and square wave along with grid synchronization condition. The performance of the proposed inverter is simulated under grid-connected scenario using MATLAB. Furthermore, the intelligent PV module system is implemented using a simple maximum power point tracking (MPPT) method utilizing power balance is also employed in order to increase the systems efficiency.

Modeling and simulation of grid inverter in grid-connected photovoltaic system

This paper presents the development of inverter simulation model in Grid-Connected Photovoltaic System (GCPV) in Matlab/Simulink software. This work is a part of the development of a complete GCPV system simulation model. The inverter simulation model accepts solar irradiance and temperature parameters as inputs (at PV array) and outputs AC power. A phase-shift control method is used to ensure that the inverter output is synchronized with unity power factor to the utility grid. The developed model is validated against data obtained from an actual installed GCPV system at Malaysia Green Technology Corporation (MGTC) in Bangi, Malaysia with system capacity of 45.35 kWp. The validation of model is through Root Mean Square Error (RMSE) and Mean Absolute Percentage Error (MAPE). Results showed that inverter output power from simulation is acceptable with small deviation from the actual data. This is due to inaccuracies of predicting de-rating factors listed in this work.