## 3 DC Circuit Breakers
### Solid-State Circuit Breakers
#### 3.3.3 Z-Source: The New Generation of SSCBs  
Z-source circuit breakers (ZSCBs) constitute one of the most recent lines of research and development of circuit breakers for over-current faults in DCMGs. ZSCBs feature \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Material** & **Bandgap** & **Electron** & **Hole Mobility** & **Electric Breakdown** \\  & **Energy (eV)** & **Mobility (ye)** & **(\(\upmu\))** & **Field (Ec)** \\ \hline Germanium & 0.7 & 3900 & 1900 & \(1.0\times 10^{5}\) \\ Silicon & \(1.1\) & 1500 & 450 & \(3.0\times 10^{5}\) \\ Gallium Arsenide & \(1.4\) & 8500 & 400 & \(4.0\times 10^{5}\) \\ Arsenide Silicon & 3.3 & 1000 & 120 & \(2.8\times 10^{6}\) \\ Gallium Nitrite & 3.4 & 900 & 150 & \(3.3\times 10^{6}\) \\ Gallium Oxide & 4.85 & 200 & 20 & \(5.2\times 10^{6}\) \\ Diamond & 5.5 & 2200 & 1600 & \(1.0\times 10^{7}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Properties of different semiconductors [84]. \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Switch Type** & **Sic MOSFET IMW120R0,60M1H** & **IGBT 1 KW25N120T2** & **SCR TN4050-12 PI** & **CS-MCT** \\ \hline Rated Current & 26 A@100 \({}^{\circ}\)C & 25 A@110 \({}^{\circ}\)C & 25 [EMAIL_ADDRESS] \({}^{\circ}\)C & 25 A@110 \({}^{\circ}\)C \\ BV & 1200 V & 1200 V & 1200 V & 1348 V \\ Von (25 A/25 \({}^{\circ}\)C) & 1.5 V & 1.7 V & 1.3 V & 1.1 V \\ Conduction Loss & 37.5 W & 42.5 W & 32.5 W & 27.5 W \\ Maximum di/dt (A/\(\upmu\)s) & - & - & Hundreds & Ten of thousand \\ Control-Type & Voltage & Voltage & Current & Voltage \\ Driver & Simple & Simple & Complex & Simple \\ Technology & Imature & Mature & Mature & Mature \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristics of different switches [35]. natural switching, automatic disconnection of the fault load, simple control circuit, isolation of the fault source, and inherent coordination capacity. Furthermore, the ZSCBs' impedance fault limits the fault current and can operate in bidirectional mode. The ZSCBs can take the transient current that occurs at the fault and pass it through the ZSCB capacitor so that the semiconductor-controlled rectifier (SCR) is disconnected. Figure 7 illustrates the states through which the ZSCB switch passes in the event of a fault [58]. The operating states are described as follows: In the steady state, the current passes through the inductor to the load, since the inductor behaves as a short circuit, and the capacitors as an open circuit (Figure 7a). Once the fault occurs, the current passes through the capacitors of the ZSCB to disconnect the SCR naturally. In this state, the capacitor currents increase and cause the SCR to switch, disconnecting the fault source, and a control circuit removes the SCR gate voltage before the SCR voltage becomes negative (Figure 7b). In the next state, two series LC circuits are connected to the fault and the load, initiating a resonance until the inductor voltage becomes negative (Figure 7c). Then, the third state begins, in which the diodes and resistors conduct until the current decays to zero (Figure 7d) [58]. In the Ref. [58], some features of ZSCBs are described, where the most relevant are: (1) Fast operation, since the ZSCB breaker operates with natural commutation; (2) instead of requiring a circuit to detect a fault, the control circuit only needs to detect that the SCR has commutated off, or that the current has dropped below a certain level; (3) the source and SCR do not experience the fault path current; (4) cascaded breaker coordination is inherently automatic; (5) the fault current may be limited by the impedance of the z-source breaker, making the system more fault-tolerant; and (6) the z-source circuit can be modified with bi-directional devices. In the Ref. [58], the authors reported a ZSCB that operates in a system with a source voltage of 120 V and a current of 10 A.