## 4 Simulation Analysis
Figure 10 shows the motor winding currents which resulted from this simulation test, where the motor was initially operated with the drive in normal condition and an open-circuit failure was introduced at \(t=1\) s in power device \(S_{1B}\). Due to the motor speed, the motor winding currents present a different shape. However, as can be seen in Figure 11, the diagnostic variables present a similar behavior to the previous simulation test. The diagnostic variable associated with the leg under fault (\(B\) in this case) will still maintain the value of one in normal condition, changing to zero after the failure. The other diagnostic variables will change from 1 to a higher value, more specifically to 1.3. Finally, a test at nominal speed (2850 rpm) for an open switch fault was also realized. The power device under fault is now the one associated with phase \(C\) (\(S_{1C}\)). The result of the motor winding currents for this test can be seen in Figure 12. The waveform is similar than the previous cases, although in this case, the currents frequency is much higher. Regarding the diagnostic variables, the obtained result can be seen in Figure 13. Analyzing this last figure, it is possible to verify that the behavior is similar than the previous ones, although in this case the variable that shows higher variation is the one associated with phase \(C\). It should be noticed that the change of the speed did not influence the diagnostic variables, since they presented always a similar behavior. In this way, the method is not affected by the speed of the machine. Another aspect that was possible to confirm is that a clear change of the diagnostic variable associated with the leg under fault was verified, allowing in this way to easily define a threshold value. Another easy way that allows one to identify the fault is that the  
Figure 8: Motor winding currents of the _SRM_ at 600 rpm in normal condition and open-circuit failure of power device \(S_{1A}\) (simulation result). Figure 9: Diagnostic variables associated with the motor winding currents of the _SRM_ at 600 rpm in normal condition and open-circuit failure of power device \(S_{1A}\) (simulation result). variable under fault reduces their value (from one to zero) and the other ones will increase their value (becomes higher than one), clearly showing in this way which is the variable associated with the fault. Figure 11: Diagnostic variables associated with the motor winding currents of the \(SRM\) at 1200 rpm in normal condition and open-circuit failure of power device \(S_{1B}\) (simulation result). Figure 7.0 Motor winding currents of the \(SRM\) at 2850 rpm in normal condition and open-circuit failure of power device \(S_{1C}\) (simulation result). Figure 7.1 Motor winding currents of the \(SRM\) at 1200 rpm in normal condition and open-circuit failure of power device \(S_{1B}\) (simulation result). Simulation tests for a different fault, more specifically for short-circuit failure, were also performed. The first tests, considering this failure mode, were performed for low speed, more specifically at 60 rpm and 600 rpm. Thus, for both tests, initially, the motor was operated at normal condition and a short-circuit failure was introduced at \(t=1\) s in the power semiconductors \(S_{1A}\) and \(S_{1C}\) (for the 60 rpm and 600 rpm respectively). The obtained winding currents for both tests can be seen in Figure 7.2 As expected, in normal operation the winding currents are controlled and balanced. However, after the fault, the current in the winding connected to the faulty bridge leg will increase to very high values. The behavior of the correspondent diagnostic variables, considering this failure mode, can be seen in Figure 7.3 Through these results, it is possible to verify that in normal condition all the variables are stable at the value of one. However, after this failure mode the variable associated with the faulty leg changes, increasing for higher values (2 and 2.9 for 60 rpm and 600 rpm).