How to use VFD for single phase motor?


Courtesy of ATO Inc

Using VFD for motor speed regulating has many advantages. Many small power motors adopt single phase power supply. How to use VFD to regulate speed for single phase motors? ATO will provide the following methods.

VFD for 2 phase motor wiring diagram

The mechanical equipment with single phase power supply usually adopts AC motor below 1.5kW. In addition, most of them employ the single phase starting capacitance motor while the other few amount equipments adopt the single phase running capacitance motor. When the single phase starting capacitance motor is used, in starting, the centrifugal switch is closed and then the starting capacitance will be connected. When the motor speed reaches about 75% of the rated speed, the centrifugal switch separates. The starting torque is about 2.4 times of the rated torque. The impulse current is about 7 times of the rated current. With such method, the impulse current is big, mechanical shock is big, starting torque is big and the speed is unable to be regulated. When the single phase running capacitance motor is used, there is no centrifugal switch. The operating capacitance is connected for a long period. This motor has small starting torque, which is usually 3/5 of the rated torque. Therefore, it is only suitable for the loads with soft characteristics, such as the blower and water pump and so on. There are also some other single phase running capacitance motors, for which, increasing the running capacitance can increase the starting torque. However, the starting current is about 6 times of the rated current, and it has mechanical shock. The single phase running capacitance motor employs the voltage regulation method to change the slip ratio of the motor. It can also realize stepless speed regulating. However, such method has a bad effect. The speed can't be controlled stabilized. Its torque characteristic is also bad. Using VFD can make the single phase equipment possess good performance in stepless speed regulating.

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