Question

What are the phase voltages when T1, T2 and T3 are conducting? Consider a star connected R load.

(a) VYN = VBN =  VRN = 0

(b) VYN = VRN = Vs/3, VBN = – 2Vs/3

(c) VRN = VBN = – Vs/3, VYN = 2Vs/3

(d) VYN = VBN =  Vs/3, VRN = – 2Vs/3

I have been asked this question in unit test.

I would like to ask this question from 3-Phase Bridge Inverters-2 topic in section Inverters of Power Electronics

Answer 1

Right option is (b) VYN = VRN = Vs/3, VBN = – 2Vs/3

Best explanation: When 6, 1 and 2 are conducting and the others are off. They conducting SCRs can be represented as closed switches. The load terminals R and Y are connected to the positive bus and the terminal B is connected to the nrgative bus. Supply voltage is Vs.

VRN = VYN = Vs/3.

VBN = -2Vs/3.

It should be noted that at any time, the summation of these phase voltages must be zero.