Reseach Of The Three-Port DC-DC Converter Based On The Photovoltaic System

With the aggravation of environmental pollution and energy crisis,renewable power systems such as solar and wind power has been rapidly developed recently.Because of the intermittent nature,the PV source cannot provide sufficient power when the load or irradiation varies rapidly.Therefore,energy storage elements,such as batteries,are used to smoothly supply energy to load in stand-alone PV power system applications.A three-port converter is a good candidate for such a stand-alone PV power system.At present,the non-isolated three port converter has some disadvantages,such as low voltage gain,energy storage port unable to realize bidirectional energy flow and complex system control.A non-isolate three port converter system for photovoltaic power generation system is proposed in this paper.The steady-state of the proposed topology has been analysis in detail.The non-isolated three-port converter has the characteristics of three ports common ground,high voltage gain and bidirectional energy flow of the battery port.According to the characteristics of demand,the corresponding control strategy is proposed according to the proposed three-port converter.The control strategy is divided into three parts: maximum power point tracking of photovoltaic cells,output voltage control and battery protection.The three-port converter can rapidly transform the operation modes under various operating conditions,and can achieve MPPT and output voltage constant simultaneously.The parameters of the three-port converter are designed under the condition of continuous current mode.The simulation model of the converter is built by MATLAB/Simulink software,and the control strategy is simulated and verified.Finally,an experimental prototype with a working frequency of 20 kHz,400V output voltage and 300 W output power is built in the laboratory.The correctness and feasibility of the proposed three-port converter system are verified by experimental results.