Half-Bridge Inverter

HALF-BRIDGE INVERTER

The figure given below shows the circuit representation of a single-phase half- bridge inverter:

The circuit consists of SCR's and diodes along with the dc input source. Here an initial assumption is made that the SCR connected in the circuit conducts only up to the time of gate pulse is present across it and as soon as the gate pulse is removed it gets off. For this circuit, considered that at time instant T/2 the gate pulse from one SCR is removed and immediately provided to another SCR in the given configuration.

Thus, this makes the two SCR's conduct one after the other and not simultaneously.

Thus, the whole circuit operation is divided into two periods:

Period I: 0 d" te" T/2; T₁ is conducting

Period II: T/2 d" te" T; T₂ is conducting

At instant T/2, a gate pulse is removed from T₁ and applied to T₂. The figure given below represents the waveform representation of single-phase half-bridge inverter:

The circuit operation is such that for a time duration between 0 to T/2, T₁ is in conducting state due to the supply input V/2. This allows current I_g1 to flow through the load for this particular condition. Thus, in the above-given waveform representation, a square wave is shown for the period between 0 to T/2.

when at T/2 instant gate pulse is removed from T₁ and applied to T₂, the T₂ begins to conduct. But this time, the voltage across the load will be -V/2 due to the lower potential of voltage V/2. In this case, current I_g2 will flow through the load. Thus, for the time duration between T/2 to T, square wave representation is shown above. For T₂ the waveform is in opposite direction to that of T₁ and the reason for this is the opposite direction of flow of current. Square wave ac output voltage is obtained. And by varying the time instant for application and removal of gate pulse the frequency of this ac signal can be varied.

The operation of a half-bridge inverter makes use of 3 wire dc supply which was a major drawback hence to overcome this full-bridge inverter was considered.