A single phase induction motor such as a Capacitor-run Motor used usually in the home appliance has some problems when it is operated on unbalanced condition and difficulties in controlling the speed of the motor in a wide range. To avoid these problems, it needs to operate on balanced condition using a 2-phase system concept. For the method of controlling the speed of a 2-phase induction motor, generally, the stator voltage control or the phase control is used. The stator voltage control scheme in low speed range gives rise to increase the stator current so that the copper losses increase, thereby causing a severe machine heating problem. The pulsating torque is generated when only the one of two-phase stator voltage is controlled. Hence, it is required for this machine to operate with nearly constant air gap flux to solve these problems. To satisfy this requirement, a two-phase induction motor should be operated with variable voltage and variable frequency so that the motor speed can be controlled in a wide range and the pulsating torque caused by unbalanced operation can be reduced.
