Question

A single-phase voltage controller, using one SCR in anti parallel with a diode, feeds a load R and Vs = 230 V. For a firing angel of 90° for the SCR, the PMMC voltage connected across R would read

(a) 0

(b) 51.8 V

(c) –51.8 V

(d) –36.82 V

The question was posed to me by my school teacher while I was bunking the class.

My doubt stems from AC Voltage Controllers-3 topic in section Voltage Controllers of Power Electronics

Answer 1

The correct option is (c) –51.8 V

Easy explanation: As firing angle is 90, there is ideally be no conduction in the positive half. Hence, the average value will be zero.

Vo = (√2 Vs)/2π x (cos90 – 1) = – 51.8 V.