Power circuit for single phase drive - low speed control mode
At low speeds, motor voltage V should not have lower-order harmonics. An ideal would be a pure sinusoidal voltage but a compromise is acceptable.
The square wave voltage used in the high speed mode contains lower order harmonics of order 3,5,7,9...etc. So we con not use it for low speed operations. If attempted we will get some wobbling speed perturbations at low speeds.
We use switching strategy known as PWM (Pulse Width Modulation) to deliver near sinusoidal voltage for the motor. We have two operations of PWM.
(a). Bipolar PWM
(b). Unipolar PWM
