变频调速是改变电动机定子电源的频率，从而改变其同步转速的调速方法。变频调速系统主要设备是提供变频电源的变频器，变频器可分成交流-直流-交流变频器和交流-交流变频器两大类，目前国内大都使用交-直-交变频器。(Variable frequency speed regulation is the frequency of changing the stator power supply of the motor, thus changing the speed regulation method of the synchronous speed.Variable frequency speed regulation system is the main equipment to provide frequency conversion power of inverter, the inverter can be divided into ac - dc - ac frequency converter and ac - ac frequency converter two kinds big, cross - straight - to pay inverter are mostly used in China at present.)