10-MHz GaN Class-Φ₂ DC Transformer

The development of the power electronics requires the converters to achieve smaller size, lighter weight and faster dynamics response. Increasing the switching frequency is an effective way to reduce the energy storage requirements of the passive components, such as inductors and capacitors, improve the transient response, shrink the size and weight of the converter. This thesis carries out a research on the high frequency power modules based on the isolated Class-Φ₂ resonate converter.Firstly, the operating principle of the isolated Class-Φ₂ resonate converter is introduced. In addition, the design of the converter, the resonate drive and the hysteresis control are introduced respectively. The simulation results of the converter, the choice of the power FETs and the loss analysis are also given in this paper. In order to verify the operating principle and the design method of the converter, an 18-36 V input 5V/2A output 10 MHz prototype based on the Si MOSFET and the schottky diodes is built. From the loss analysis and the experiment results, it is found that the conduction loss of the diodes is large.In order to increase the efficiency of the isolated Class-Φ₂ resonate converter, the GaN FETs are used and the synchronous rectification of is achieved. The voltage following control is proposed to solve the problem that with the increase of the input voltage ZVS of the SR FET cannot be achieved and the reverse conduction mechanism of the power FETs is triggered. With the proposed voltage following control, the reference voltage of the hysteresis control follows the input voltage proportionally. Then, the output voltage follows the input voltage proportionally and this converter can be used as a DCX. The drive voltage can match well with the drain voltage of the power FETs over a wide input voltage range which reduces the switching loss of the SR FET and the reverse conduction loss of the power FETs. The mathematical model of the converter is built and numerical analysis of this conclusion is also given. In order to verify the proposed voltage following control, an 18-24 V input 18 W output 10 MHz prototype based on the GaN FETs is built. Compared to the hysteresis control, when the voltage following control is used the efficiency of the converter increases by 5.6% at 24 V input and 18 W output.