The Study Of Grid-connected Photovoltaic Micro-Inverter Related Technologies And Efficiency

In recent years, with the development of economy, the energy crisis has become a major problem that the human urgently need to solve at present. Therefore, the development and utilization of renewable energy is becoming more and more important. Solar energy has been widely used for its cleanness, sufficiency and safety. Photovoltaic inverter is an important part of photovoltaic generation technology, and has different types according to different functions and uses. The grid-connected micro-inverter has become a hot spot in research for its advantage in power density, efficiency, reliability and so on.The major task of this thesis is to analyze the theory and algorithm of main related technologies involved in the design of grid-connected micro-inverter, write software and hardware implementation, research the efficiency. In order to implement the algorithms on the hardware, we design and build the hardware circuits. The circuit uses DC/DC-DC/AC two stage energy conversion structure with high frequency transformer isolated. This structure has higher isolation performance, smaller volume and easier operation compared with the others. For the control part, double DSC control strategy was creatively adopted, not only simplifies the complex control strategy and improves the control accuracy and reliability, but also realize the electrical isolation in the true sense.The main related technologies realized in this thesis are as follows:(1) Soft-switching control algorithm. Adopting the soft-switching controls the main power transistor whether shut off or not, realizing main power transistor turn on at the zero voltage, reducing the switching loss of power transistor.(2) Grid-connected technology and PLL algorithm. The pure software phase lock algorithm was used based on the d-q synchronous reference frame. In the process of phase locking and tracking, a variable step length control strategy is adopted, realizing the fast phase locking, the accurate and stable phase locking and anti-interference ability.(3) Voltage clamping control. Traditional digital incremental PI control algorithm was ad opted to achieve drain-source voltage clamping of the main power transistor, not only prevent ing damage caused by the instantaneous high voltage when the main power transistor shut off, but also obtaining feedback to the leakage inductance energy.(4)Maximum Power Point Tracking. A maximum power point tracking algorithm withou t current detection was adopted which adopt admittance increment method.