Test: Three Phase Bridge Inverter

It is a three-phase bridge type inverter. As SCRs are used as the switching device, it is called as a thyristor inverter.

The three-phase bridge type is a 6-step inverter. That means, the firing changes from one SCR to another 6 times per cycle.

A large C connected across the input terminal keep the supply voltage from altering.

T1-T4 form the first pair. T3-T6 form the second pair, and like-wise. For the 180° mode, each SCR conducts for 180°, but the groups of SCRs lag the prior group by an angle of 120°. e.g. If T1 is fired at 0 then T3 must be fired at an angle of 0 + 120° and T5 at 120 + 120 = 240°.

Each step consists of 60°. 300° to 360° will be step VI.

It requires a min. 6 devices, 2 in each leg. Switching devices could be anything BJT, MOSFET or an IGBT. SCRs are used when very high power ratings are required.

It is a 6 step inverter. Hence, 360/6 = 60°. This means that the SCRs are gated every 60° in proper sequence.

Three devices conduct at a time. One from the upper pair and two from the lower pair or vice-versa.

Each step consists of 60°. 120° to 180° will be step III.

This will depend on the nature on the load, which is not mentioned in the above problem.