Question

What is the voltage between the B phase and the neutral, when T2, T3 and T4 are conducting?

(a) -2Vs/3

(b) Vs/3

(c) 2Vs/3

(d) -Vs/3

The question was posed to me in an internship interview.

My question comes from 3-Phase Bridge Inverters-2 in section Inverters of Power Electronics

Answer 1

Correct answer is (d) -Vs/3

To explain: Construct the equivalent circuit, considering the conducting devices as S.C and the non-conducting devices as open circuit.

When 2, 3 and 4 are conducting and the others are off. They conducting SCRs can be represented as closed switches. The load terminals R and B are connected to the negative bus but the terminal Y is connected to the positive bus. Supply voltage is Vs.

VRN = VBN = -Vs/3.

VYN = 2Vs/3.