Single Phase Half Bridge Cycloconverter in Circulating Current Mode
Working of Single Phase Half Bridge Cycloconverter in Circulating Current Mode
- In the circulating current mode both the bridges conduct simultaneously. In order to avoid short circuit on the ac supply the reactor L is placed between them as shown in Figure.
- It is not possible to connect a freewheeling diode across the load as it will not allow one cycle of the ac output to appear across the load and we want ac output voltage.
- Semiconverter cannot be used in the bridge configuration as they do not allow the load voltage to become negative due to internal freewheeling action
- Therefore inverting mode is not possible obtain to which is actually essential while feeding the inductive loads.
- One converter will work in the rectification mode while another works in the inversion mode. The values of firing angles of positive and negative converters (Op and respectively) are set in such a a way that αP + αN = 180°
- The dynamic response of cycloconverters operating in the circulating current mode is faster than that in the noncirculating mode because SCRs in both the bridges (P and N converter) are simultaneously conducting.
- In the circulating mode, the circulating current flows between the two converters (and through reactor L) which does not flow through the load. Some energy is lost in the reactor L due to which the efficiency of cycloconverter is low in the circulating current mode.
- This mode is more complex than the non circulating current mode.
Features of Circulating Current Mode in Single Phase Half Bridge Cycloconverter :
- Both converters conduct simultaneously.
- One converter acts as rectifier and the other as inverter.
- αP + αN = 180°
- Better dynamic response.
- Interconverter circulating current is present.
- Higher power dissipation in the reactor L.
- Lower efficiency.
- Higher complexity.
Circuit Diagram of Single Phase Half Bridge Cycloconverter :
