Develop Of Three-phase PV Grid Inverter And Research Of Grid Control Strategy

With the problem of energy and environment becoming looming large, the research and application of the solar, one kind of renewable energy, has aroused widespread concern. To give full play to the unique advantages of photovoltaic power generation and improve its efficiency, large scale photovoltaic grid power generation become the trend. This paper mainly studies grid-connected control of photovoltaic grid voltage source PWM inverter. Photovoltaic grid-connected system is featured by sinusoidal current output, adjusted power factor, Elimination of grid side harmonic component and the function of anti-islanding detection. The quality of power output is in compliance with standard of distributed grid-connected power generation.This paper is based on actual project in which low power three-phase voltage type PWM inverter which based on DSP is designed and developed. The paper focuses on the following contents:At the beginning, topology structure of Three-phase grid voltage type PWM inverter’s main circuit and working principles are analyzed in detail and then, mathematical models of invert under both the static and rotating coordinate system are established which lay the foundation for design of grid-connected control.Secondly, on the basis of the mathematical model, grid control strategy of three-phase grid inverter is deeply researched, including theoretical analysis of direct voltage control method, basic principle and process of SVPWM, principle analysis of three phases software phase-locked loop. Combined with the actual system parameters, grid-connected control method is stimulation verified by Matlab/simulink simulation software, to improve the realizability of the above theory.Thirdly, this thesis described the mechanism of islanding phenomenon, the model and main research methods of anti-islanding protection. Classifying the popular anti-islanding techniques into two major categories:the passive and the active methods, advantage and restriction are presented respectively. Popular islanding detectiong methods are described in detail. Based on the MATLAB simulation envoronment, a number of issues about islanding protection are studid. This paper raised a new active islanding detection whichi combined active frequency drift and active current disturbance. This method has the following characteristics of short detection time, small NDZ, low impact on power quality verified by MATLAB based simulation and experiment.Fourthly, the hardware design including the core control circuit, IGBT driver circuit, detection circuit, protection circuit, buffer circuit was elaborated. The range of AC reactor and capacitor were determined by the method of main circuit parameters design according to requirements of the control system.Fifthly, the software design of three-phase voltage source PWM inverter which includes voltage and current A/D sampling procedures, SVPWM program, protection algorithm and double closed-loop PI control strategy was carried out based on CCS3.3.Finally, a3kW three-phase voltage source PWM inverter prototype was accomplished. The effectiveness of the control theory was verified by hardware and software debugging and got better experimental results.