Research And Design On Power Balance Device For The Photovoltaic Power Generation System

With the energy crisis and environmental pollution becoming more and more prominent,searching for clean and renewable energy to replace the traditional fossil energy is very important for the development of human society.Solar energy as a clean and pollution-free new energy is abundant in the earth.With the rapid development of power electronics technology,photovoltaic power generation technology has become the most important way to use solar energy.With the continuous maturity of photovoltaic power generation technology and the continuous decline in the cost of photovoltaic cells,enterprises and communities have a chance to own the self-contained photovoltaic power generation system.But it changes a lot in the factors of the temperature,light,load disturbance and so on.Therefore,a kind of self-contained power-balanced photovoltaic power generation system is proposed,which is supplemented by the city power grid.A power balance device capable of realizing the two way flow of energy between the city power grid and the AC bus of the system is designed,mainly including the followings:(1)This paper presents a self-contained power-balanced photovoltaic power generation system,which uses the city power supply as the auxiliary power supply.When the output power of the photovoltaic power generation is not enough to keep the load stable,the power is transferred to the AC bus of system for the load.When the output power of the photovoltaic power generation is sufficient to maintain the load stable and much energy is left,the surplus energy is delivered to the grid.The two-way flow of energy between the city power grid and the AC bus of system can be realized.(2)The topology of the power balance device is studied.By analyzing and comparing the different topologies of AC / AC conversion,a single-phase voltage-type dual PWM converter is chosen as the main circuit topology of the power balance device.Based on theanalysis of the four quadrant operation principle of the PWM rectifier,the feasibility of realizing the two-way flow of energy with the dual PWM converter is expounded.(3)The MPPT control technology of PV panel is analyzed,and a two stage MPPT control method is proposed.The mathematical model of voltage-type PWM converter is established,and its current control mode is analyzed.The PI controller is designed according to the double closed loop control of inner current loop and outer voltage loop.The coordinated control strategy of the power balance device is proposed and verified by simulation.(4)According to the actual demands,the hardware circuit of the system is designed,including the main circuit and control circuit.The control circuit is mainly composed of DSP and its peripheral circuit,switch driver circuit,voltage and current sampling circuit and so on.At the same time,the control software of the system is designed,including the main control program and the interrupt program with its subprogram design.(5)The experimental prototype of the power balance device for photovoltaic power generation system is built.Experimental results show that the proposed control strategy is correct and the design of hardware and software is reasonable.The design of power balance device has the advantages of high safety,small volume,realizing two-way flow of energy between the city power and the AC bus of photovoltaic power generation system.It ensures the stable operation of the load and has certain reference value.