Modeling and Control of Bi-directional Converter based on Battery Management in Photovoltaic System

The schedulable photovoltaic grid connected power generation system has many components, complex structure and changeable operating environment. Photovoltaic power generation has volatility and randomness, so the research on energy management and converter control methods of photovoltaic grid connected system is of great significance to the application and research of photovoltaic power generation. The dc/dc converters involved in the schedulable photovoltaic grid connected power generation system mainly include photovoltaic cell output boost converter and battery management bidirectional buck boost converter. Since the battery plays the role of energy storage and power supply in the system, it is necessary to use bi-directional DC-DC converter (BDC) to control and manage the charging and discharging process of the battery. This paper studies the modeling and control of dc/dc converter in grid connected system. The mathematical models of battery management bidirectional conversion circuit in photovoltaic system under buck charging mode and boost discharge mode are established, and the small signal analysis is carried out. For the charging mode, a two-stage charging method is adopted, in which constant current charging is used to achieve a certain amount of electricity, and then constant voltage charging is used. For the discharge mode, the current and voltage double loop control is adopted. The simulation results show that in buck mode, the bi-directional converter can switch smoothly between the two charging modes and suppress the over-current, and in boost mode, the battery can output power smoothly.