Research And Design The Photovoltaic Grid-connected Inverter With SVPWM Control Method Based On FPGA

With the rapid development of social economy, the traditional non renewable energy continuous depletion and hazards to the environment deepening, thus people are paying more and more attention exploitation of new green energy. Solar energy as a clean, non-polluting and renewable source of energy to be more and more used widely, and the grid connected photovoltaic power generation as an important form of solar energy development and utilization, also obtained the fast development. With the analysis of main circuit topology of photovoltaic grid-connected inverter in this paper, three-phase photovoltaic grid-connected inverter system will be mainly studied with the modulation method of SVPWM. Firstly, the soft core of SVPWM was designed. Secondly, the strategy of combining repetitive and PI controls based on the traditional PI control was introduced to the paper, ensure the same frequency and phase of the output current of the inverter and grid voltage with less total harmonic distortion. Main contents of this paper are following:First of all, the topologies of grid connected photovoltaic system have been analyzed in this paper. Introduced the isolated grid connected photovoltaic inverter and non isolated grid connected photovoltaic inverter, analyzed several kinds of main circuit topology of three phase photovoltaic grid connected inverter. The principle of the three-phase full bridge inverter circuit and the synthesis method of the space vector were studied in detail.Secondly, the unipolar SPWM control technology and the bipolar SPWM control technology have been analyzed. The principle of SVPWM modulation technology was introduced in the paper, and engineering algorithm for SVPWM modulation is derived. Through comparing and analying the SPWM and SVPWM modulation methods, choosing SVPWM modulation as the modulation technology of three-phase full bridge photovoltaic grid-connected inverter.Thirdly, in order to ensure the grid-connected photovoltaic inverter system operate efficient and stably. The output current of three-phase grid connected photovoltaic inverter through the synchronous rotating coordinate transforms to two-phase stationary coordinate, then photovoltaic grid-connected inverter system was designed by using the strategy of feed forward decoupling PI control, and the PI control system was simulated by SIMULINK software, the results show that the output current can track command current with no static error. Adopting the strategy of combining repetitive and PI controls, the effect of dead zone in periodic interference signals has been decreased efficiently and the waveform quality of output current from the inverter has been improved.Finally, according to the principle of SVPWM modulation technology, the SVPWM soft core is designed by using EP2C8Q208C8N FPGA chip. SVPWM soft core system mainly includes the DDS sinusoidal signal generator module, sector identify module, triangle wave comparator module, PWM generation module and dead zone delay module. The validity of system design is verified by simulation for analyzing each sub module and the whole system.