The Research And Design Of The DC-DC Converter Of The Grid-Connected And Off-Grid Dual Mode Inverter

The soaring development of social economy and technology in contemporary society has brought us many benefits, but meanwhile caused lots of pollutions. The ozone hole, greenhouse effect, acid rain and especially the haze weather in the central and eastern regions resent years are threatening our physical and mental health. Seeking for non-pollution is severely urgent. Solar energy, for its special advantages of non-pollution, abundant resources and easy-exploitation, achieved great development recently.Bidirectional smart inverter of string has two types of working model as off-grid and grid-connection, each of which can switch seamlessly. The application of photovoltaic power generation system can ensure stable power supply for users. The existence of storage battery can make peak load shaving for the generating capacity of photovoltaic elements and steady power grid.This text mainly research on the former stage DC-DC shifting, including the unidirectional DC-DC shifting from photovoltaic battery to bus of direct current and the bi-directional DC-DC shifting from bus of direct current to photovoltaic battery. The first section introduces the background, significance and researching content of this text. The second section introduces the working principle of photovoltaic battery and the control of MPPT, and provides the control method of MPPT of variable step size setting threshold level. The method has solved the contradiction of tracing time and accuracy, traced rapidly to the maximum power point when the outside circumstances suddenly changes, and established photovoltaic battery and the modal of MPPT to verify it. The third section introduces and analyzes the convertor of BOOST ZVT-PWM using in this text, and makes simulation and verification for it, which reduces the switching loss and increase the efficiency of the whole system. The forth section designs the battery charge and discharge circuit-the bidirectional DC-DC circuit, by using the non-isolated bidirectional BUCK/BOOST circuit. This circuit has simple construction and high efficiency. The three-stop charging method is used to charge the battery, through testing the terminal voltage of battery for the basis of shifting charging method. The method of control the maximum discharging current by steady direct current bus voltage is used to discharge the battery. Finally test the possibility of this project by simulation. The fifth section mainly design the hardware circuit and the software circuit which control the system. The hardware includes the chip-power-supply circuit, sampling circuit and protecting circuit. The software provides the program flow chart for main program and interrupt program.Finally, I summarize the disadvantages of this text and make an outlook for the later work.