**3.3 Three-phase single-switch ZCT SMRs**

The soft-switching SMRs using auxiliary switching circuit can be generally classified into zero-voltage-transition (ZVT) and zero-current-transition (ZCT). The choice depends on the semiconductor devices to be used. The ZVS approaches are generally recommended for MOSFET. On the other hand, ZCS approaches are effective for IGBT. Some existing softswitching SMRs are introduced as follows:

### **3.3.1 Classical three-phase single-switch ZCT SMR**

The classical 3P1SW ZCT SMR (Wang et al, 1994) is simple in structure and easy to realize. However, the auxiliary switch is not operated on ZCS at turn-off. The efficiency is limited.
