Research And Design Of The Interleaved Flyback Micro-inverter

Since we human being entered into industrial age, the more rapid development of global economy, the more serious energy crisis it caused. To solve the energy crisis, we had begun studying solar energy for years. Photovoltaic(PV) generation is a typical way of utiling solar energy, in the traditional centralized PV grid-connected system, many PV modules were connected in series or parallel to obtain sufficient energy, however, this structure had power loss because of mismatch between single PV module and inverter. To solve this problem, a micro-inverter, which consists of a single PV module and a single-phase inverter is being studied. Micro-inverter can achieve maximum power point tracking for single PV module, and can produce more electrical energy, so it become a hot research direction of photovoltaic generation.Micro-inverter is a connection with PV module and power grid, it must not only ensure the maximum power output of PV module, but alse ensure that the inverter transports high quality energy to the power grid, at the same time, the power factor and current harmonics of grid current need meet the standards of the State or of the power industry. So efficient topology structure and control system are very important. Flyback inverter is an attractive solution because of its advantages of simple structure, lower cost, and electrical isolation between the PV modules and the grid. Also, by using the interleaved technique in the flyback inverter, the power level can be improved and the current ripple and power loss can be reduced.This paper firstly analyzed the working principle of the interleaved flyback micro-inverter in the DCM mode, then designed the main power circuit and non-complementary active clamp circuit, and then completed the design of circuit parameters and selection of components. Secondly, the control system was designed based on the functional requirements and topology structure, and the control system mainly included the control process of the system, grid current control algorithm and share load control algorithm, etc, alse the feasibility of the control algorithms were verified by simulation. Finally, a 250 W micro-inverter prototype was designed, and completed the experimental verification.To further reduce the power loss and improve the efficiency of the micro-inverter, three optimized control strategies were proposed. In order to reduce the power loss of the active clamp circuit, an optimized control strategy based on the voltage of the flyback MOSFET is proposed. In order to reduce the power loss with light load and half load, an optimized control strategy based on the active output power of the micro-inverter is proposed. In order to reduce the power loss in the full load range, an optimized control strategy based on the instantaneous output power of the micro-inverter is proposed. The feasibility of all the proposed optimized control strategies is verified by simulation.