We consider drives built around single phase induction and single phase synchronous motors in this section.
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 phase rectifiers) on the utility AC system.
Note: There is a reason for using diode rectifiers on the AC utility as the first stage of a power electronic converter.
1. To minimize supply side distortions and disturbances
2. To make the subsequent conversions easier
Power Circuit of 1 Phase Drive
Q1, Q2, Q3, Q4 - Power switches
D1, D2, D3, D4 - Fast recovery diodes (freewheeling diodes)
C1 - DC-link capacitor
S1, S2, S3, S4 - Switching signals (Binary signals)
Switching signal S1, S2, S3, and S4 are generated by the control unit according to the mode of control used.