Variable-speed control of brushless half-speed synchronous motor by voltage source inverter

The variable-speed control of a voltage source inverter-fed cylindrical rotor type of brushless half-speed synchronous motor with feedback of the rotor position is described. On the basis of an approximate analysis of the steady state, an expression for torque is derived, and two methods of speed control are discussed. The step response of speed in the drive system is almost the same as that in a speed control method based on a slip frequency control in an induction motor drive, and a relatively high torque is obtained even in a low speed region. The motor has the capability of line start and change over from an induction motor (Gorges phenomenon) to a self-controlled half-speed synchronous motor by using a simple position sensor