The utility model provides an auxiliary converter, it keeps apart DCDC converter, three -phase inverter unit, exports filtering unit and external output the control unit to step up unit, intermediatefrequency including input switch and battery charging unit, input filter unit, preceding stage in advance, the input switch and in advance battery charging unit contain two precharging resistor, two precharging resistor establish ties or are parallelly connected, the preceding stage is stepped up the unit and is included two way boost boost module, two way boost boost module establish ties or areparallelly connected, the intermediate frequency is kept apart the DCDC converter and is two, connects respectively two way boost boost module, it is right respectively to be used for the DC voltage of two way boost boost module output carries out the intermediate frequency contravariant, generates the square wave voltage of intermediate frequency, and right the square wave voltage of intermediatefrequency keeps apart after the vary voltage rectification for intermediate dc voltage, two intermediate dc voltage parallelly connected back inputs that DCDC converter output are kept apart to the intermediate frequency three -phase inverter unit.