GATE EE 2014 Set 3 — Question 65
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Power Electronics → Inverters → VSI (1φ, 3φ)
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Question
A single-phase voltage source inverter shown in figure is feeding power to a load. The triggering pulses of the devices are also shown in the figure. 
If the load current is sinusoidal and is zero at , the node voltage has the waveform
Correct answer
(D) [figure]
Solution
In a single-phase full-bridge voltage source inverter (VSI), the node voltage (voltage of node A with respect to the DC link midpoint O) is determined by the state of the switches and and the direction of the load current during dead-bands.
1.Switching States:
- When is ON, node A is connected to the positive rail, so .
- When is ON, node A is connected to the negative rail, so .
- is triggered from to . Thus, in this interval.
- is triggered from to . Thus, in this interval.
- During the intervals where both and are OFF (, , etc.), the voltage is determined by the conduction of the anti-parallel diodes or , which depends on the load current .
- Given is sinusoidal and zero at , it is positive () for and negative () for .
- For , (flowing out of node A). When and are OFF, the current must flow from the negative rail through to node A. This clamps to .
- For , (flowing into node A). When and are OFF, the current must flow from node A through to the positive rail. This clamps to .
- : (diode conducts)
- : ( conducts)
- : (diode conducts)
- : (diode conducts)
- : ( conducts)
- : (diode conducts)
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