Research On High Power Density DC/DC Converter

With the development of the aircraft power supply technology, further improvingthe power density, efficiency, dynamic performance of the aviation static inverter is needed now. The paper mainly focuses on the first stage DC/DC converter of the aviation static inverter, studies and designs high efficiency and high power density DC/DC converter from the angles of topology and power device.There are many DC/DC topologies now, and they all have advantages and disadvantages. Because the LLC resonant converter can not only realize the ZVS of the primary side switch, but also realize the ZCS of the second side diode. So it’s an ideal topology for realizing the high efficiency and high power density and has become a research hotspot in recent years. Then, the power device is always developing too.After more than 30 years of development the silicon power MOSFET device has reached the limit of the silicon material and itis difficult to further realize the high efficiency and high power density request of switch power supply. And the third generation of power semiconductor device Ga N makes it possible to combine high efficiency and high power density in the converter because of its fast switching speed, small turn-on resistance, and small volume. Firstly, the paper analyses the working principle and gain characteristic of the resonant converter, designs and builds the prototype system based on the design method of the LLC converter. For the short circuit current limit need, the paper comes up with a new idea which combines the high transient current limit and current loop current limit. The paper also studies the five elements resonant method, and verifies the analysis with simulations and experiments. Secondly, the paper analyses the influence of the parasitic capacitance of the second side diode and the transformer to the LLC converter under high frequency conditions. Theresults ofsimulation and experiment prove that the parasitic capacitance may make the resonant current change to influence the ZVS of the switch. Then the paper promotes the methods to decrease the parasitic capacitance and verifies the theory by experiments.The paper summarizes how to design the driver circuit, solder, and verifies the failure condition for deeply understanding the GaN device. Finally, the paper makes efficiency comparison between the Si and GaN board. Both the calculation and test data proves the GaN LLC resonant converter is a good solution to achieve the high efficiency and high power density.