Research On Bidirectional Multiport LLC Resonant DC-DC Converter

With the rapid development of the renewable energy industry,distributed power generation has received extensive attention from the society,and it is used in various places.There have been two constraints in the continuous development of distributed power generation.The first one,portable solar power sources have the problem of difficulty in energy deployment.The Second one,how to raise the efficiency and reliability of the conversion circuit is also an imperative problem to be solved.Based on these problems,a three-port LLC resonant DC-DC converter for portable solar power is studied.It can not only realize the distribution of power,but also enhance the efficiency and stability of the electric source.Firstly,the topology of the three-port LLC converter is designed for the power distribution problem.This topology can realize energy allocation among photovoltaic,energy storage,and loads through the switching of three modes.The voltage gain model of LLC type structure is solved by the fundamental harmonic approximation method(FHA).Based on this,the interaction among the quality factor,scale factor and voltage gain is discussed,and the parameters of key parts in the circuit are solved by the model.Secondly,a small-signal model is established to improve the dynamic and steadystate characteristic of the converter.According to the model,the transfer function is obtained and the bode diagram is drawn.The transfer function are analyzed with the help of the bode diagram,and the compensator is designed to raise the stability and response speed of the system.It is verified by experiments that the amplitude and phase margins of the system after adding the compensator reach 64.5d B and 70.1° respectively.Then,with the increase of the operating frequency of the converter,the problems of increasing energy loss,narrow voltage regulation range,and complicated control strategies gradually emerge.To improve these conditions,the fitting algorithm in numerical analysis is introduced to design the PFM controller,and a new co-modulation method of PWM and PFM is proposed based on this.In this way,the complexity of the system is reduced,and the wide-range soft-switching performance and voltage regulation performance of the converter are guaranteed.A simulation experiment under the simulink environment is designed to verify the feasibility of the control strategy.Finally,according to the research results,a hardware circuits with an input voltage(part1)of 330 V～400 V,an output voltage(part2/part3)of 48 V,and an output current of6 A was built.It is verified by experiments that the converter has a wide range of ZVS performance and it has synchronous rectification capability at the output side.The efficiency and applicability of the converter are enhanced.And it has constant voltage regulation competence during the switching between light load and full load.Figure 47;Table 4;Reference 61...