Research On Bi-directional Dc-dc Converters For Hybrid Electric Vehicle

With the development of the Automobile Industry in China, Internal-combustion engine faced the unprecedented challenge of environmental pollution, energy shortage and global warming. In this case, HEV(hybrid electric vehicle)are the key to solve these problems at the moment. It has many advantages in many fields, such as technology, economy and environment. To improve the control system, especially the circuit system of HEV, strategy design of HEV is an important way to enhance fuel efficiency and reduce pollution emission. The bi-directional DC/DC converter is the important parts of HEV.Firstly, the paper introduces the working principle of bi-directional DC/DC converter, and through detailed analysis and compare of the features with full bridge and half bridge, a new type half bridge bi-directional converter is selected as the topology of bi-directional DC/DC converter for hybrid electrical vehicle, then PWM plus phase shift control bi-directional DC/DC converter is analyzed in this paper. Compared with phase shift control, PWM plus phase shift control can reduce the current and voltage stresses and RMS currents of the converter. The lose of the converter can also decrease, and all the switches in the converter can achieve ZVS in a wide range of load variation while input or output voltage varies, has the advantages of soft-switching implementation without additional devices, high efficiency.Secondly, through the analysis of the working mode with this bi-directional converter in one cycle, a model construction method based on state space average which is using the PWM plus phase shift control is proposed. Then, the paper gives the method of calculation process with the transformer leakage inductance, this simulationg models of the converter are established using the software SIMetrix, and the results of the simulation testify the analysis dand computation.Lastly, the selection principle and calculation method of these element in the converter are given in this paper, furthermore, the control circuit which is using PWM plus phase shift control and the driving circuit are designed in the thesis at the same time. In boost mode constant voltage cntrol is needed and in buck mode, constant current control is needed, a good control feature is achieved. A prototype, ration power 100w, is made. The experimental results shows the model, analysis and design of this bi-directional DC/DC converter is correct.