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