**3.1. Switching device faults and phase winding open-circuit faults**

Switching device faults and phase winding open-circuit faults are common fault phenomena. In the traditional asymmetrical half-bridge converter, there are two switching devices for each phase; and each phase has four windings for a 12/8 SRM. When there is no current in the excitation region in phase *La*, it means that the open-circuit occurs. The diagnosis needs to locate which part is under fault condition by replacing *S0* by *SA1*, and giving the turn-off single to *S0*. In the right part of the converter, *SA1*, *SA2*, *D1*, *S1*, and *La34* compose a new asymmetrical half-bridge. In the right part asymmetrical half-bridge, if the faulty phase can work, it proves that the left part of converter is under fault condition. By the same method, replacing *S1* by *SA2*, and giving the turn-off single to *S1*; in left part of converter, *S0*, *SA1*, *SA2*, *D0,* and *La12* compose a new asymmetrical half-bridge. In the left part asymmetrical half-bridge, if the faulty phase can work, it proves that the right part of the converter is under fault condition. The diagnosis flowchart of the open-circuit fault is shown in Figure 16.
