Modern Power Electronics and Drivers

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

We consider drives built around single phase induction and single phase synchronous motors in this section. Motor Diagram Use of a variable speed drive instead of a fixed speed motor plus external mechanical control yields many advantages. It saves energy significantly and enhances the performance of the drive system (i.e. the load). Energy saving can add up to some MW (Mega watt) level savings in a country due to heavy proliferation of single phase motors in any country. (Note: The largest share of power consumption in most countries attributed to single phase motor). Motor control requires its input voltage V and frequency f be adjustable with appropriate resolutions. There are 3 alternative control modes. 1. High speed control mode 2. Low speed control mode 3. Serve control mode The drive system take power from an unregulated DC input. This is the norm for all drive systems, not only for 1 phase drives. This unregulated DC in obtained using a diode rectifier (1 phase or 3 pha...