# A Secondary Reconfigurable Inverter and Its Control Strategy
## 2 Materials and Methods  
### The Topology Structure of the Secondary Reconfigurable Inverter  
The topology structure of the proposed secondary reconfigurable inverter is shown in Figure 1. The inverter DC side voltage is provided by battery storage, which can ideally be considered as two DC sources with equal voltage value. V\({}_{1}\)-V\({}_{6}\) are the power semiconductor devices IGBT, which constitute the three-phase inverter circuit. TR\({}_{13}\), TR\({}_{35}\), TR\({}_{\rm b}\) and TR\({}_{\rm w}\) are the TRIACS, which consist of the secondary reconfigurable circuit. A series of LC filters are used to inhibit higher harmonics and excessive short-circuit current. When the secondary reconfigurable inverter is operating normally, it is a TPSS inverter circuit. The usual faults for the inverter are the short circuit and the open circuit of the power semiconductor devices. When the power semiconductor devices in the inverter encounter a short-circuit fault, the corresponding fast fuses will be fused, and the short-circuit fault is transformed into the open-circuit fault. The secondary reconfigurable inverter circuit is formed by cutting off the fault switches and connecting with the corresponding Triacs. When one or two of the power switch is faulty, the relationship among the corresponding Triacs and power switches are shown in Table 1.  
In Table 1, consider cases 1 and 2 as examples. When the power switch \(\rm V_{1}\) in the TPSS inverter circuit is faulty, turn on the Triacs \(\rm TR_{w}andTR_{13}\). Sending the pulse of \(\rm V_{1}\) to be the pulse of \(\rm V_{3}\) means that \(\rm T_{v3}=T_{v1}\). The DC side voltage source can be considered as the b-phase bridge of the inverter, which constitutes the TPSS inverter circuit. \(\rm V_{4}\) stops working. The reconstructed phases are \(\rm S_{a}(V_{3}\), \(\rm V_{2})\) and \(\rm S_{b}(C_{1},C_{2})\). The reconstructing process is shown in Figure 2a, which is the first fault tolerance. Now the  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Case** & **First Fault** & **On** & **Reconfigured Phases** & **Second** & **Reconfigured Phases** & **Switch Pulse** \\ \hline
0 & / & \(\rm TR_{b}\) & / & / & / & / \\
1 & \(\rm V_{1}\) & \(\rm TR_{w}\) and \(\rm TR_{13}\) & \(\rm S_{a}\left(V_{3},V_{2}\right)S_{b}\left(C_{1},C_{2  
inverter is running in a fault-tolerant state. If V\({}_{2}\) is also faulty, V\({}_{3}\) and V\({}_{4}\) construct phase S\({}_{\text{a}}\)(V\({}_{3}\), V\({}_{4}\)), sending the pulse of V\({}_{2}\) to be the pulse of V\({}_{4}\), T\({}_{\text{v}4}\) = T\({}_{\text{v}2}\), which is the secondary reconfiguration as shown in Figure 2b. Other cases have a similar switch process. The traditional reconfigurable fault-tolerant inverter is shown in Figure 3.  
From Figure 3, it can be seen that if one or two of the power switches in the traditional fault-tolerant inverter are faulty, the whole bridge needs to be removed. The relationship between the corresponding Triacs and power switches are shown in Table 2.  
According to Table 2, the fault-tolerant space is small with just nine cases. The topology of the secondary reconfigurable inverter proposed in this paper greatly improves the fault-tolerant space. According to Table 1, the proposed secondary reconfigurable inverter has 21 fault-tolerant cases.