The so-called frequency converter is the electrical conversion of DC (DC) to AC (AC) device, the common power supply (AC220V/440V) power input into the frequency converter, change the voltage and frequency, and then supply to the Motor (Motor), control the speed of the motor. As the speed control device of 3-phase induction motor, frequency converter can be regarded as the core product of factory automation. Now many frequency converters are used in all kinds of PLANT equipment and air conditioning equipment. In addition, frequency converter is also used in the field of energy saving.