the function of a converter, as its name implies, is to convert the electric waveform of the power source to a waveform that the motor can use.For example,if the power source is an ac type and the motor is a dc machine, the converter transforms the ac waveform to dc. In addition, the converter adjusts the voltage (or current) to desired values. The controller can also be designed to perform a wide range of functions to improve system stability,efficiency,and performance.In addition, it can be protect the converter,the motor,or both against excessive current or voltage.