Research On Key Techniques Of High Efficiency & High Power Density Bridge Power Converter

Since the allowed space and the heat dissipation are limited, power density and convension efficiency become the most important indexes in the applications such as communication base stations, servers, data centers and radars. Also, high power density has always been a goal in the field of power electronics, and the goal is meaningful and valuable. Nowadays, since the 3rd wide bandgap semiconductor power devices such as GaN HEMTs are more and more widely applied, the efficiency uner MHz level switching frequency can be maintained to be high, size of the passive components and the heat sinks can be reduced, thus, improving the power density becomes possible.However, several critical issues limit the power density to be improved furthermore. For instance,the voltage drop of the GaN HEMT during the reverse conduction is higher than the silicon based devices, this disadvantage leads to exta loss while GaN HEMT is applied in bridge circuits or as synchronous rectifications (SRs); the poor dynamic performance of the two-stage structure consists of a nonisolated Buck converter with separately controlled regulation ability and an isolated LLC resonant converter without regulation ability; the efficiency over the entire load range with multi control variables is difficult to optimize.The issues mentioned above are researched in this dissertation. The relationship between turning off transition and the parasitic delay is analyzed, and a SR detecting method based on dual-judgement is proposed. Based on the method, a digital resonant frequency tracking technique is proposed to achieve the maximum efficiency. The integrated control method of two-stage power converter is studied, a fast LUT-PID control algorithm is proposed. Also, a multi-objective optimization method based on genetic algorithm (GA) is proposed to optimize the efficiency of the converter. The research works achieve the innovations such as:(1) The relationship between turning off transition and the parasitic delay is analyzed, and a SR detecting method based on dual-judgement is proposed. Thus, and the SR can be turned off with the minimum body diode condution in the steay-state, thus, the efficiency of the LLC resonant converter is optimized. The test results show that the reverse current from the load to the converter of 100mA level is eliminated, thus, the reliability of the converter is ensured. Also, the proposed SR detecting method optimizes the efficiency LLC resonant converter up to 94.5%;(2) A digital resonant frequency tracking technique is proposed based on the dual-judgement mechanism, the switching frequency of the LLC resonant converter can track the resonant frequency,thus, the efficiency of the LLC resonant converter achieves the maximum. The test results show that the peak efficiency under 1MHz achieves 96%, the efficiency at 20% load current is 92%;(3) The integrated control method of two-stage power converter is studied, a fast LUT-PID control algorithm is proposed. By reducing the complexity of the PID table, the looking-up time and calculating time are both reduced, the multi period control can be eliminated, thus, the steady-state error of the converter is reduced, also, the dynamic performance is optimized. The test results show that under 1MHz switching frequency, the LUT-PID control method optimize the build-up time by 60% during the transient procedure, the steady-state error of the output voltage and current are around 0.1V and 0.5A, respectively;(4) The influences on the efficiency of the control variables are studied, an online multi-objective optimization technique based on GA is proposed, the efficiency of the converter is fitness function,the limitations of the parameters of the individuals are built based on the reliability of the power devices and the magnetic components. Thus, the efficiency of the entire converter is optimized. The peak efficiency of the converter is over 90%, and the efficiency at 20% load current is over 85%.In the end, a prototype is built to verify the proposed techniques, methods and algorithms, the efficiency ove r the entire load range is 85%, the peak efficiency achieves 90%, the power density of the converter can achieve 160W/m3. The experimental results prove that the proposed control techniques improve the efficiency, dynamic performance and power density.