Research On Bi-directional DC/DC Converter And Its Application In Power Storage Device Contained Grid-connected PV System

Today the world is facing severe energy shortages and environmental pollution arisingfrom energy production issues, and seeking to develop non-pollution renewable energy isan effective means to solve this problem. PV as a renewable energy has been developedrapidly for its small size, light weight, long life, reliable operation, extensive resources et al.In order to improve the utilization, safety and reliability of photovoltaic power generation,it is extremely important to study electrical equipment and system of grid-connectedphotovoltaic system containing energy storage device. This paper conduct a research onbidirectional DC/DC converter application technology in energy storage device containedgrid-connected photovoltaic power system, in order to explore the organic combinationamong energy storage unit, grid and photovoltaic power to provide theoretical support forthe efficient utilization of solar energy.The current bi-directional DC/DC converters applied in high-voltage and high-powerapplications have such disadvantages as large voltage stress of switches, complex structure,low efficiency. Hence a new isolated three-level bi-directional DC/DC converter isproposed in this paper. The proposed converter, which is of simple structure and lowvoltage stress of switches, has a three-level half bridge circuit in high voltage side and apush-pull circuit in low voltage side. In this paper, the converter’s working principle isdetailed; equivalent circuits of the converter in one switching period and the voltage andcurrent expressions are given; the relationship of input and output voltage is derived, what’smore, the switch voltage stress as well as the opening ZVS condition is elaborated.The parameters of the three-level bi-directional DC/DC converter are studied,including the high-frequency transformer turns ratio, value of filter inductor, filter capacitorand resonant inductor, and the power devices are selected.The simulation model of the researched converter is built and simulation work isconducted. The correctness and feasibility of the converter is verified.Apply the researched bi-directional DC/DC converter to the energy storage devicecontained grid-connected photovoltaic system.9different working modes of the system areanalyzed on the basis of different states of photovoltaic array and battery. And the controlstrategy is given, focusing on the implementation circuit of the energy management controlcircuit, dual-loop control circuit and the flying capacitor voltage balancing circuit.