# Hardware Design for Cascade-Structure, Dual-Stage, Current-Limiting, Solid-State DC Circuit Breaker
## 5 Simulation and Experimental Results
### Experimental Verification  
The experimental result waveforms for this experiment are shown in Figure 13a-d. Due to limited experimental conditions, the AD module was not designed, and the STM32 microcontroller controls the semiconductor devices in the prototype based on the conduction and turn-off times of each branch obtained from the simulation results. After the mechanical switch of the capacitor power supply is turned on, the capacitor power supply switch is activated, conducting the steady-state branch and turning off the power electronic branch. After 600 \(\upmu\)s, at time \(t_{0}\), the microcontroller realizes a short-circuit to the load, during which the steady-state branch current \(i_{s}\) gradually rises to the rated current of 0.6 A, as shown in Figure 13a. Another 100 \(\upmu\)s later, at time \(t_{1}\), the power electronics branch is conducted and the steady-state branch is turned off; the steady-state branch current rises to 1.2 A before being turned off, while the power electronic branch is conducted and inherits the transferred current from the steady-state branch, which continues to rise as shown in Figure 13b at \(i_{z}\). After 400 \(\upmu\)s, at time \(t_{2}\), the power electronics branch is turned off; during this period, the current in the power electronics branch rises to the threshold of 3.5 A and then rapidly flows into the buffer capacitor, with the peak current in the buffer capacitor reaching 3.3 A, as shown in Figure 13c at \(i_{c}\). Subsequently, the varistor is engaged to dissipate the residual energy in the system, as illustrated in Figure 13d at \(i_{mov}\), completing the dissipation after 300 \(\upmu\)s, with the peak current carried by the varistor reaching 2.9 A. Figure 13e shows the waveform of the system short-circuit current \(i_{dc}\) and the voltage \(U_{mov}\) across the varistor, indicating that at time \(t_{3}\), when the system current rapidly decreases, the varistor clamps the system overvoltage to 68 V, successfully isolating the fault.  
After fault isolation and a 2 ms deionization time, the microcontroller performs a reclosing operation, as shown in Figure 14a. First, the power electronic branch is conducted. After a 200 \(\upmu\)s fault detection time, if the current \(i_{z}\) in the power electronic branch is 0.5 A, which is less than the system's rated current of 0.6 A, then the fault is identified as a transient fault. The steady-state branch is then conducted, and the power electronic branch is turned off. The system current is established and stabilizes at 0.6 A in the steady-state branch, indicating a successful reclosing. Conversely, as shown in Figure 14b, if the current \(i_{z}\) in the power electronic branch is 1.1 A after a 200 \(\upmu\)s delay, which is significantly higher than the system's rated current of 0.6 A, then the fault is identified as a permanent fault. The power electronic branch is immediately turned off, successfully isolating the fault for the second time.  
Figure 12: **(a)** Clearance and reclosing waveform; **(b)** fault not cleared and reclosing waveform.