The Research On Two-Stage Converter And Control Method For Photovoltaic Systems

Nowadays, on account of the problems of exhaustion of fossil energy and environmental pollution becoming worse and worse, people around the world pay a high attention to exploring and using of new energy. Especially in recent years, when the manufacturing process of solar cell and power electronic technology improved, the photovoltaic technology is developing rapidly and with the trend of low cost, high efficiency and high power density, which aroused strong interest of engineers and researcher. As the core aspects of PV system, the most optimized implementation of power conversion will improve the entire system’s performance and investment expectation. In this case, a two-stage converter for photovoltaic systems is study in this paper, with emphasis on its control methodThe high frequency link technology was introduced to meet the trend of photovoltaic conversion system. Pull-push forward (PPF) circuit was isolated by high frequency transformer, on which subsequent research have revealed several properties. For instance, switching loss and stress in the switches are significantly reduced by floating capacitors, and the bias magnet of transformer core is inhibited. From the application standpoint, the PPF circuit appears to be suitable for low voltage and high current situation. Full bridge topology was employed in inverter stage, because its wide range of applications. Reasonable control method can guarantee the output quality and improve the efficiency of the converter. The traditional analog chip technology is mature, inexpensive, while the sliding mode control of modern control theory has better robustness, based on the variable structure. A power compensator design and PI controller were designed and analyzed using analog PWM chip, including their correctness, feasibility and effectiveness of the control method. Then the sliding mode variable structure control technology was analyzed deeply, and applied to DC/AC full-bridge inverter. The basic model of dynamic control was established and computer simulation verified the superiority of the control method.In experimental part, a two stage converter was designed in detail and simulated by PSIM software. It also describes the calculation of main circuit parameters, device selection and program design. And then, an experimental prototype with analog chip and digital control system was established. The experiment results verify the feasibility and validity of the theoretical analysis.