| The full use of renewable energy sources and the strong sense of environmental protection contribute to the application of the bidirectional high voltage conversion ratio converters in the DC micro-grid, fuel cell vehicles, DC distribution systems, energy storage systems etc.Firstly, in allusion to the high voltage conversion ratio feature of the bidirectional high voltage conversion ratio converters, the means to accomplish a high voltage gain of the unidirectional converters, which are proposed in recent years and some of them are also applied in the bidirectional high voltage conversion ratio converters, are summarized in the dissertation. Then, a bidirectional high voltage conversion ratio converter is proposed based on a pre-existing unidirectional converter. The rectifier diodes of the pre-existing converter in high voltage side are replaced by a couple of switch devices, therefore, the converter has a potential for bidirectional energy flow in respect of circuit topology. In addition, different control methods are proposed in the dissertation, so that the converter can operate not only in boost mode in forward direction, but also in buck mode in reverse direction.When the proposed converter operates in boost mode in forward direction, a fixed switching frequency plus pulse width modulation(PWM) method is used to regulate the voltage gain of the converter. To ensure the high voltage side switches working in synchronous rectification state, the corresponding drive signal s of the switches are designed. The stages of the converter working in different duty cycles are analyzed in detail. The voltage gain expression of the converter in boost mode is deduced, and the soft switch switching is analyzed. Moreover, the influence on the low voltage side current ripple when the inductors are interleaved is analyzed in detail.When the proposed converter operates in buck mode in reverse direction, the variable switching frequency pulse PWM control technology is proposed. Varying the switching frequency is to achieve zero current switching(ZCS) of the high voltage side switches and changing the duty cycle is to regulate the voltage conversion ratio of the converter in buck mode. The stages of the converter working in different duty cycles are analyzed in detail. The voltage conversion ratio of the converter in buck mode is deduced, and the soft switch switching is analyzed.Finally, an experimental prototype is built and tested in order to verify the validity of the theoretical analysis. The processes of the power devices selection, the magnetic elements design, and the control system design of the converter are introduced. The experiments in the boost mode and buck mode under different duty cycles are carried out. Furthermore, the efficiency comparsion between the proposed converter and the pre-existing unidirectional converter is showed. |
