Research And Design Of20KW Off-grid Potovoltaic Inverter And MPPT Technology Based On STM32

With the rapid development of the society and economy, the energy crisis and environmental pollutinon problems have become more and more serious caused by the large-scale conventional energy consumption, the human pay more attention to the development and use of new green energy. In the new green energys, because of its clean, eco-frendly, inexhaustible, solar ennergy is accepted commonly. The photovoltaic power generation, which is an important way to use solar energy, also got a rapid development, and become the focus of the application research subject of new energy. Off-grid photovoltaic(PV) inverter as the core equipment of off-grid photovoltaic power system, which converting electrical energy, playing a crucial role in overall system’s efficiency, stability and cost. Thereforc, in order to improve the generating efficiency and control ability of off-grid PV power system, researching a high-performance off-grid PV inverter has an important significance. The high-efficiency photovoltaic power generation technology and inverter control technology of off-grid PV power system is researched in this paper. The main research work are as follows:Firstly, the main circuit-topology-structure of the single-phase full-bridge photovoltaic (PV) off-grid inverter is studied, and the operating principle of the single-phase full-bridge photovoltaic (PV) off-grid inverter is analysed. Then the center of an area equivalent to the SPWM control algorithm and voltage and current double closed-loop feedback control algorithm based on PI controller are studied in this paper. On the basis of the above research, the process of voltage stability control is achieved.Secondly, the output characteristic of the PV array, Maximum power point tracking(MPPT) control algorithm and charging characteristics of battery is analyzed in the paper. On the basis of analyzing and comparing several commonly used MPPT control algorithms, a modified variable step size perturbation and observation (P&O) MPPT control method is proposed in this paper. and the algorithm is also simulated. Simulation results show that the control algorithm can track the solar photovoltaic cell maximum power point effectively. Meanwhile, several common DC/DC conversion circuits are introduced, and the operating principle of the Boost conversion circuit is analyzed, and the Matlab/Simulink simulation model of MPPT control method has been established based on Boost circuit. And the simulation results show that the modified variable step size P&O MPPT control method can track the photovoltaic array maximum power point (MPP) effectively and improve the system dynamic and static performance. Then a solar charge controller with Maximum power point tracking(MPPT) function and constant voltage charging function which improves the utilization of PV array and achieves a optimized management for charging of battery is designed.Thirdly, the design of the main circuit components parameters and part of hardware circuit of20KW off-grid photovoltaic inverter is provided.Fourthly, the detailed design for system software and the software flow pattern each function module of the system are introduced, the DSPWM control signal with dead zone compensation, voltage stability control and signal sample are in detail discussed.Fourthly, detailed design for system software and function module are introduced, the DSPWM control signal with dead zone compensation, voltage stability control and signal sample are in detail discussed.Finally, according to the above theoretical analysis and simulation studies, the20KW off-grid photovoltaic inverter based on STM32is designed. And then its performance has been tested. IGBT driving waveform and the output voltage waveform in the case of no-load and load are analysed, and the feasibility of the20KW off-grid photovoltaic inverter in the paper is verified.