Development Of High Power Density Flexible Energy Converter

With the increasing depletion of traditional energy and various climate problems caused by destruction of ecological environment,more and more attention has been paid to renewable energy power generation(especially wind power and photovoltaic power).As one of the most important devices serving for renewable energy generation,the efficiency,power density and reliability of power electronic converter have been highly regarded.However,after nearly 60 years of development,performance of power devices based on silicon(Si)material has been reaching its body diode limit.No matte device principle innovation,structure improvement or technological progress,they are all difficult to significantly improve the overall performance,thus restrict the further development of power electronic technology.At this time,silicon carbide(SiC),after more than 20 years of research and development,has gradually entered the market and achieved recognition.Compared with Si devices,SiC has many advantages such as low switching and conduction loss,fast switching frequency,high blocking voltage and high temperature resistance,which makes it better to meet the needs of future power electronics.The utilization of SiC devices can improve the performance of power electronic converters in hardware.However,with the large number of renewable energy generation,the influence of power electronic control technology on power grid has become one of the most popular research directions in power system.Traditional energy power converters use current source to get grid-connection,which neither provide voltage support to power grid nor accept the dispatching instructions,just like the traditional synchronous generators,thus causes security threat to power grid stability.Therefore,improving the control strategy of power electronic converters becomes one of the key technologies to improve the stability of power grid.This paper designs a high power density three-phase inverter with SiC MOSFET:using SiC to reduce switching loss so as to reduce the volume of the radiator;increasing switching frequency to achieve size reduction of the filter;calculating DC voltage ripple to minimize DC side capacitor value;through the reasonable layout of devices and minimizing devices to increase power density.At the same time,in terms of large number of renewable energy connected to grid,the concept of a flexible energy converter is put forward based on the flexibility of power electronic converter control,which can be similar to the traditional synchronous generator to provide grid voltage support and follow the dispatch instruction;unify control equations before and after grid-connnected,realize real seamless switching on voltage source;when the deviation in the power grid frequency turns up,output voltage is still able to follow automatically;ensure grid frequency stable through output power mutation and quickly reach the steady state again.