## Impact and Mitigation of a Power Semiconductor Failure in the Switched Reluctance Motor Drive  
For the switched reluctance motor, the power electronic converter is considered an essential device for its correct operation. In fact, a failure in one of the power semiconductors is able to produce high torque and speed variations and may lead to motor damages. Several topologies can be adopted for the power electronic converter in the \(SRM\) drive, but in all of them, a failure in a power semiconductor will give rise to the problems already referred. In this work, it will be used a topology based on the asymmetrical half-bridge converter (\(AHB\)) but with fault-tolerant capability. Figure 1 shows the power circuit of a classic \(AHB\) topology applied to the \(8\,/\,6\)\(SRM\). In this topology, associated with each phase bridge leg there are two fully controlled power semiconductors and two freewheeling diodes. As mentioned before, a failure in one power device will affect the \(SRM\) drive operation. Usually, in each phase there are different possible failure modes associated with transistors. They are associated with open transistor failure, and to short-circuit transistor failure. These kinds of faults (open or short-circuit) could happen in the upper or lower transistor. After an open-circuit failure in a power device, it will no longer be possible to excite the phase connected to the faulty leg. Figure 2 shows an example of the possible current paths in case of an open-circuit failure in the power devices \(S_{2A}\) or \(S_{1A}\). In Figure 3 it is possible to see the winding currents of the \(8\,/\,6\)\(SRM\) when the converter operates with an open-circuit failure. These waveforms were obtained through the use of a current chopping control. In this figure is possible to see the absence of current in one of the phases caused by open-circuit failure. This failure has impacted on the average electromagnetic torque causing a significant reduction [36]. Figure 1: Electronic power converter used to supply the \(8\,/\,6\) switched reluctance motor. The occurrence of a short-circuit failure in a power device will also affect the phase connected to the faulty leg. Considering this failure mode, it will no longer be possible to reverse the voltage at the winding terminals of the faulty phase, as shown in Figure 4. This figure shows an example of the possible current paths in case of a short-circuit failure in the power devices \(S_{2A}\) or \(S_{1A}\). Considering this failure mode, a large current may appear in the motor winding connected to the faulty bridge leg. Figure 5 presents the motor winding currents of the 8/6 \(SRM\) after a short-circuit failure using the current chopping control. Through this figure is possible to see how large can be the current in the winding associated with the faulty bridge leg. This large amount of current depends on several factors, such as the turn-on and turn-off angles of the healthy devices and the machine speed. So, due to this fault, it will not be possible to apply a negative voltage to the winding connected to the switch under fault, not being possible a quick demagnetization of the winding, as required. Depending on the current amount and the faulty time duration, this can be a dangerous situation for the machine and power converter, putting under stresses its materials and components. To mitigate the impact of power devices failure modes in the drive and \(SRM\), a fault-tolerant power converter is required. Thus, it is proposed in this paper a fault-tolerant circuit that can handle with open or short-circuit failures in power devices. This fault-tolerant topology can be seen in Figure 4. This topology does not require extra power semiconductors and only uses solid state relays (\(SSRs\)) to connect the faulty legs to other healthy phase in order to replace and isolate the faulty devices. It should be noted that the use of mechanical relays is possible, but they are usually not compatible with the operation of the \(SRM\) drives, especially for high-speed operation.