Can a Single Phase Motor be Speed Controlled by VFD?

What are the speed regulation methods of single phase motor?

Mechanical speed regulation
Mechanical speed regulation method is suitable for magnetic clutch, hydrodynamic coupling and hydro-viscous clutch. Hydrodynamic coupling is the most widely used, namely connecting a hydraulic-mechanical coupling device in series between the motor and load to adjust the coupling force between motor and load by the level of liquid, thus realizing the speed regulation of load. In 1990s, hydrodynamic coupling was widely used in the fans and pumps driven by high-voltage large-capacity cage motor. Due to its disadvantages of limited speed regulation range (99%-30%), insufficient speed regulation accuracy, low efficiency, single machine only, shutdown for repair, it has a narrow application range and limited application amount.

Cascade speed regulation
Cascade speed regulation must use the winding asynchronous motor to rectify, convert partial energy of the winding, and then return the energy back to the power grid. By this means, it’s equal to adjust the internal resistance of the rotor, thus changing the slippage of motor. Voltage of the rotor is generally not equal to that of the power grid, so a voltage transformer is needed. In order to eliminate this voltage transformer, internal-feedback motor is widely used in application at present, namely adding a three-phase auxiliary winding on the stator to receive the feedback energy of rotor. The auxiliary winding also participates in the work, thus main winding would absorb fewer energy from the power grid, achieving the goal of speed regulation and energy-saving. Winding motor is not widely used in the industrial production, so cascade speed regulation is also used in a limited applications.

VFD speed regulation
Change the power supply frequency through single-phase variable frequency drive, so as to regulate the speed of single-phase motor and improve the operating efficiency of electric drive system. According to the way of current change, VFD can be divided into two kinds of AC-DC-AC VFD and AC-AC VFD. From the perspective of speed regulation effect, variable frequency speed regulation is the best speed regulation technology which has a wide range of speed regulation (from 100%～5%) and highest speed regulation accuracy (±0.5%). As it belongs to stepless speed regulation, it can achieve the soft-start of motor and automatic control of the whole production system.

As an important product used in many fields, single-phase VFD not only has special and key performance parameters, but also has advantages of many aspects. For professionals, single-phase VFD can play a role of protection and achieve an outstanding effect on controlling voltage. It’s widely used in low power fans, water pumps, axial flow fans and single-phase capacitance start-up asynchronous motor. There are also civil VFD for families (available only for single-phase power supply). The products are easy to operation with compact structure, low failure rate, so they are well received by customers.