# Ultra-Fast Bidirectional SiC Solid-State Circuit Breaker for 800V / 400A Aircraft Applications

Christopher Dahmen, Florian Kapaun, Gerhard Steiner, Hubert Rauh, Florian Bayer

► To cite this version:

Christopher Dahmen, Florian Kapaun, Gerhard Steiner, Hubert Rauh, Florian Bayer. Ultra-Fast Bidirectional SiC Solid-State Circuit Breaker for 800V / 400A Aircraft Applications. The 26th European Conference on Power Electronics and Applications, GDR SEEDS France & EPE Association, Mar 2025, Paris, France. 10.34746/epe2025-0241. hal-05088437

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# Ultra-Fast Bidirectional SiC Solid-State Circuit Breaker for 800V/400A Aircraft Applications

Christopher Dahmen

Central Research & Technology
Airbus

Taufkirchen, Germany
christopher.dahmen@airbus.com

Florian Kapaun

Central Research & Technology
Airbus

Taufkirchen, Germany
florian.kapaun@airbus.com

Gerhard Steiner

Central Research & Technology
Airbus

Taufkirchen, Germany
gerhard.steiner@airbus.com

Hubert Rauh

Fraunhofer IISB

Erlangen, Germany

hubert.rauh@iisb.fraunhofer.de

Florian Bayer

Fraunhofer IISB

Erlangen, Germany

florian.bayer@iisb.fraunhofer.de

**Abstract**—The shift toward electric propulsion in aircraft brings unique challenges to power distribution and protection systems, requiring the advancement of technologies like solid-state circuit breakers (SSCBs). This paper explores the pivotal role of SSCBs in electric aircraft, highlighting their potential to improve safety, reliability, and efficiency in 800V high-power environments. However, their integration in aviation also presents challenges, such as ultra-fast fault isolation within complex electrical architectures, efficient thermal management, enhanced reliability and safety, and the demand for lightweight, compact designs. This paper addresses these challenges by analyzing current technological limitations, exploring potential solutions, and presenting experimental results from a bidirectional silicon carbide (SiC) SSCB that successfully detects a 1kA fault current with a response time of less than 1µs. The results emphasize the need for continued innovation in SSCB technology to meet the stringent demands of next-generation electric aircraft.

***Index Terms***—Solid-state circuit breaker, SiC-MOSFET, Ultra-fast fault detection, Reliability and safety, Electric aircraft

## I. INTRODUCTION

The adoption of DC power distribution systems (DCPDSs) as part of a DC-grid architecture is set to become crucial for future electric aircraft systems (EASs). A key function of DCPDSs is the rapid detection and isolation of faults in network nodes that connect propulsion systems, sub-networks, sources, or loads, particularly in cases of component failures or overloads. This is essential to protect critical components and reduce the risk of electrical fires [1]. Given the low-impedance nature of these grid structures, the protective switchgear must be capable of handling high current slopes in the event of failures like short circuits – a task that mechanical switches are generally incapable of performing effectively [2]. Therefore fuses and pyrofuses are usually chosen for clearing high current short circuits. Fuses have generally disadvantages such as dependencies of trigger value, timing, degrading etc. Pyrofuses are flexible controllable by electronics for current sensing and triggering, but unfortunately both of these components are not resettable. A careful design to prevent false triggering is

mandatory, and in case of utilizing pyrofuses a proper selection of the confirmation time is crucial [3], [4].

Solid-state circuit breakers (SSCBs) represent a major advancement in DCPDS technology, providing faster response times, improved reliability, and enhanced control compared to traditional mechanical circuit breakers. By utilizing semiconductor technologies such as transistors and thyristors, SSCBs can swiftly interrupt electrical currents during faults, minimizing damage to critical components and improving overall system safety. Their precise current monitoring and control capabilities make SSCBs particularly well-suited for future EAS, where traditional circuit breakers may not meet the rigorous demands.

However, implementing SSCBs in aircraft systems poses unique challenges, largely due to the harsh operational environments and specific aviation requirements, particularly at high altitudes. These challenges include:

* Ultra-fast fault isolation in complex electrical architectures

* High power density

* Effective thermal management

* High functional flexibility

* Enhanced reliability and safety

* Electromagnetic compatibility

* The need for lightweight, compact designs

This paper presents the design, implementation, and measurement validation of a bidirectional silicon carbide (SiC) SSCB for 800 V / 400 A aircraft applications, with a fault detection time of less than 1 µs.

## II. SOLID-STATE CIRCUIT BREAKERS

### A. General structure of Solid-state circuit breakers

A SSCB (see Fig. 1) is composed of several fundamental functional blocks, each playing a critical role in providing fast and reliable protection in electrical systems. These blocks work together to ensure the system's safety and efficiency.
<figure><img src="image_2.png" /><figcaption>Fig. 1. Function blocks of a common solid-state circuit breaker</figcaption></figure>

The central element of the SSCB is the **power semiconductor**, such as a MOSFET, IGBT, or wide-bandgap (WBG) devices like SiC or GaN. This component manages the switching and current interruption, allowing for precise control during fault events.

The **gate drive unit (GDU)** is responsible for controlling the power semiconductor. It converts control signals into the appropriate gate commands, enabling the semiconductor to switch rapidly between states, ensuring quick fault response.

To protect the system from potential overvoltage during faults, a **voltage clamping circuit** is included. This block safeguards the power semiconductor and other key components from damage caused by voltage spikes.

The **sense and trip electronics** continuously monitor the system for irregularities, such as overcurrent or short circuits. Once a fault is detected, it signals the gate drive unit to open the breaker, quickly isolating the fault to prevent further damage.

Finally, the **auxiliary power** ensures that the gate driver, sensing circuits, and control electronics have a stable low-voltage power supply. This guarantees that the SSCB remains operational and responsive under various operating conditions.

## B. State of the art in solid-state circuit breakers

Solid-state circuit breakers are leading a shift in how electrical systems in aircraft are protected, offering much faster response times, higher protection levels and – for the main switchgear components – higher reliability than traditional electromechanical circuit breakers (EMCBs) [5]–[7]. By utilizing semiconductor devices, SSCBs can isolate electrical faults almost instantaneously – crucial in aircraft systems where quick fault clearance is vital to safety. Advances in semiconductor technologies and hybrid designs are paving the way for more widespread use of SSCBs in aerospace.

1) *Semiconductor Technologies:* SSCBs rely on advanced power semiconductor devices such as MOSFETs, IGBTs, and thyristors. These components switch rapidly between conductive and non-conductive states, enabling SSCBs to interrupt currents within microseconds, significantly faster than EMCBs, which typically take milliseconds to respond [8], [9].

Recent developments in WBG semiconductors, particularly silicon carbide (SiC) and gallium nitride (GaN), have significantly enhanced SSCB performance. SiC devices are capable of operating at higher voltages and temperatures, while offering lower switching losses, making them ideal for high-power aircraft electrical systems [10]. GaN-based switches, on the other hand, are noted for their superior efficiency at lower voltages and faster switching speeds, making them well-suited for compact, high-frequency applications typical of aircraft power systems [11].

2) *Advanced Protection Mechanisms:* A key focus in SSCB development is the integration of advanced digital control systems. These systems continuously monitor current and voltage to detect and respond to electrical faults. Modern SSCBs leverage real-time monitoring, combining techniques such as model predictive control (MPC) and adaptive protection systems to optimize fault response. This allows the SSCB to adapt dynamically to different types of faults and operating conditions, ensuring minimal system disruption [12].

3) *Hybrid Circuit Breaker Designs:* While fully solid-state designs offer clear advantages in terms of speed and reliability, they also face challenges in high-power applications, such as increased conduction losses and the need for efficient thermal management. To address this, hybrid circuit breakers (HCBs) have been developed, combining the strengths of both solid-state and mechanical technologies. In these designs, the solid-state component is responsible for fault isolation, while the mechanical switch manages current during normal operation, reducing energy losses and improving efficiency [13], [14].

4) *Challenges and Future Directions:* Despite recent advancements, SSCBs still face several challenges when it comes to aircraft applications. One major challenge is thermal management, particularly in high power density systems like electric aircraft, where space and weight constraints limit cooling options [15]. Another challenge is the relatively high cost of WBG materials such as SiC and GaN, though efforts are being made to reduce production costs. Finally, electromagnetic interference (EMI) caused by the fast switching speeds of SSCBs can be problematic in sensitive environments like aircraft, and ongoing research aims to mitigate these effects through improved packaging and circuit design [16].

SSCBs hold significant potential for improving the safety and efficiency of aircraft electrical systems. Their fast response times, compact size, enhanced flexibility including resetability and controllability make them well-suited for aviation applications, though challenges such as heat management, cost, and EMI need to be addressed. Continued advancements in semiconductor technology and hybrid circuit breaker designs are likely to push SSCBs toward greater adoption in the aerospace industry.

## III. DESIGN OF AN ULTRA-FAST SiC SOLID-STATE CIRCUIT BREAKER

Designing ultra-fast SSCB involves several key challenges that affect both performance and reliability. The key challenges
are fault detection speed and current measurement accuracy, where the breaker needs to quickly identify faults and distinguish them from normal electrical fluctuations. Accurate current sensing is crucial to avoid unnecessary trips. Generally, SSCBs must manage two types of failure scenarios, which influence the required switching energy and current slope:

* When a failure occurs far from the power source in an electrical network, high impedances contain significant amounts of energy, which must be absorbed by the SSCB.

* When a failure occurs close to the power source in an electrical network, low impedances create steep current slopes (di/dt), requiring extremely fast response times to trip the switch and contain the current spike.

The switching speed is equally important, as the SSCB must cut off the current flow rapidly, demanding advanced semiconductor technologies. Another challenge is thermal management, as the heat generated during an SSCB current-clearing event must be efficiently dissipated to maintain system stability. Finally, overvoltage protection is essential to handle voltage spikes that occur during fault isolation, ensuring the system remains safe from damage. The overvoltage protection using a clamping circuit was implemented as part of the ultra-fast SiC SSCB, but its design and experimental verification are presented in a separate publication [17].

The general electrical and thermal requirements for the investigated aircraft application can be seen in the following table (see Tab. I).

<table><caption>TABLE I
ELECTRICAL AND THERMAL REQUIREMENTS FOR THE INVESTIGATED AIRCRAFT APPLICATION</caption><thead><tr><th colspan="3">Electrical properties</th></tr><tr><th>Parameter</th><th>Value</th><th>Description</th></tr></thead><tbody><tr><td>V<sub>DC</sub></td><td>800 V</td><td>Nominal DC-link voltage</td></tr><tr><td>I<sub>DC</sub></td><td>400 A</td><td>Nominal line current</td></tr><tr><td>I<sub>inrush</sub> = 2 I<sub>DC</sub></td><td>800 A</td><td>Inrush current (max. 0.5 s)</td></tr><tr><td>I<sub>SC</sub></td><td>1000 A</td><td>Short circuit (failure) current</td></tr><tr><td>L</td><td>150 μH</td><td>Max. line inductance</td></tr><tr><th colspan="3">Thermal properties</th></tr><tr><th>Parameter</th><th>Value</th><th>Description</th></tr><tr><td>ϑ<sub>J</sub></td><td>135 °C</td><td>Max. junction temperature</td></tr><tr><td>ϑ<sub>A</sub></td><td>80 °C</td><td>Ambient (coolant inlet) temperature</td></tr></tbody></table>

According to common norms in the aircraft industry, the electrical system has to account for an inrush current – occurring at start-up or at potential load changes – which can be significantly higher than the nominal line current. Hence the SSCB was designed to withstand an inrush current $I_{inrush}$ of at least twice the nominal current for a period of up to half a second. In this time frame, the SSCB must not isolate the circuit. At a value of $I_{SC} = 1$ kA, the desired trigger level of the SSCB is reached – at this current threshold the SSCB has to turn off and isolate connected grid components from a possible short circuit. The energy occurring at a SSCB turn-off can be divided into two components:

1) $E_L$: caused by the max. line inductance $L$:

$$E_L = \frac{1}{2} \cdot L \cdot I_{SC}^2 \quad (1)$$

2) $E_S$: caused by the energy source:

$$E_S = V_{DC} \cdot \int_{0}^{t_{clear}} i_{SSCB}(t) \, dt = \frac{1}{2} \cdot V_{DC} \cdot I_{SC} \cdot t_{clear} \quad (2)$$

The sum of these energies:

$$E = E_L + E_S = \frac{1}{2} \cdot I_{SC} \cdot (L \cdot I_{SC} + V_{DC} \cdot t_{clear}) \quad (3)$$

has to be absorbed by the SSCB and is dissipated in the voltage clamping circuit [17]. The total energy $E$ is an essential design parameter for SSCB.

### A. Power module

The power module in the developed SiC SSCB (see Fig. 2) has been designed with a focus on performance and efficient heat management – optimized for fast switching and high power demands in an 800 V DCPDS. As shown in the picture, a common-source configuration was implemented to enable bidirectional operation.

<figure><img src="image_3.png" /><figcaption>Fig. 2. Bare SiC solid-state circuit breaker power module</figcaption></figure>

Since the main cause of losses in steady-state conduction of the SSCB is its serial on-resistance ($R_{DSon}$), only a moderate increase in its value – compared to common mechanical contactors – is tolerable. Analyzing costs, benefits and feasibility, an $R_{DSon}$ ratio of 3 to 5 times that of mechanical contactors can therefore be considered acceptable for the design [5]–[7]. Additional series resistances according to SSCB terminals, internal bus bars and shunt measurement are estimated to be lower than 500 μΩ. Considering the availability of 1.2 kV-SiC-chips, CPM3-1200-0016A dies from WOLFSPEED were chosen [18]. Having a typical $R_{DSon}$ of 16 mΩ at room temperature, the amount $x$ of paralleled chips can finally be found as:

$$x = 2 \cdot \frac{R_{DSon,chip}}{R_{DSon,module}} = 2 \cdot \frac{16 \text{ mΩ}}{1.5 \text{ mΩ}} = 21.3 \quad (4)$$

As mentioned above, a bidirectional switch in a common-source configuration was implemented. The pre-factor in (4) is taking the anti-serial connection of two chips per path into account. According to manufacturing limitations, a high number
of parallel chips on a single substrate can cause mechanical tension, potentially leading to cracks in the structure. As a result, the module is divided into sub-modules. The amount of sub-modules is – due to the common denominator of $x$ – three.

The sensing is performed using two 500 μΩ shunt resistors per module, connected in parallel. Accounting for the remaining components, such as SSCB terminals, internal bus bars, and shunt measurement, a total SSCB on-resistance $R_{SSCB}$ of less than 2 mΩ was achieved (see Tab. II).

Additionally, a temperature sensor is integrated in each sub-module to measure the absolute temperature under steady-state conditions.

Table II is summarizing the key features of the developed SiC-SSCB. One highlight is the high power density of the SSCB, making it particularly suitable for applications such as electric aircraft.

<table><caption>TABLE II
KEY FEATURES OF THE DEVELOPED SiC SOLID-STATE CIRCUIT BREAKER</caption><thead><tr><th colspan="3">General and steady state properties (V<sub>DC</sub> = 800 V)</th></tr><tr><th>Parameter</th><th>Value</th><th>Description</th></tr></thead><tbody><tr><td>m</td><td>0.6 kg</td><td>Weight of the SSCB (incl. power supply)</td></tr><tr><td>V</td><td>1 L</td><td>Volume of the SSCB (incl. power supply)</td></tr><tr><td>R<sub>DSon</sub></td><td>1.52 mΩ</td><td>SSCB MOSFET on-resist. @ ϑ<sub>J</sub> = 25 °C</td></tr><tr><td>R<sub>SSCB</sub></td><td>1.92 mΩ</td><td>SSCB total on-resistance @ ϑ<sub>J</sub> = 25 °C</td></tr><tr><td>P<sub>sw</sub></td><td>800 kW</td><td>Max. SSCB switching power</td></tr><tr><td>dP<sub>sw</sub>/dV</td><td>1.33 MW/kg</td><td>SSCB Switching power density (mass)</td></tr><tr><td>dP<sub>sw</sub>/dV</td><td>800 kW/L</td><td>SSCB Switching power density (volume)</td></tr><tr><th colspan="3">Dynamic properties at high energy (L = 150 μH; V<sub>DC</sub> = 800 V)</th></tr><tr><th>Parameter</th><th>Value</th><th>Description</th></tr><tr><td>E<sub>L</sub></td><td>75 J</td><td>Energy stored in the line inductance</td></tr><tr><td>E<sub>S</sub></td><td>125 J</td><td>Energy stored in the grid-node source</td></tr><tr><td>E</td><td>200 J</td><td>Total energy absorbed by the SSCB</td></tr><tr><td>t<sub>clear</sub></td><td>310 μs</td><td>Fault clearing time of the SSCB @ 1 kA</td></tr><tr><th colspan="3">Dynamic properties at high di/dt (L = 2.6 μH; V<sub>DC</sub> = 800 V)</th></tr><tr><th>Parameter</th><th>Value</th><th>Description</th></tr><tr><td>t<sub>react</sub></td><td>700 ns</td><td>Reaction time of the SSCB</td></tr><tr><td>di/dt</td><td>300 μs</td><td>Current slope handling capability @ 1 kA</td></tr></tbody></table>

## B. Gate drive unit

The GDU is a crucial component in a SSCB that controls the fast switching operation of the SiC-MOSFET even under tough conditions like high $\frac{di}{dt}$ and $\frac{dv}{dt}$ as well as high thermal stress. As can be seen in Fig. 3, the GDU was developed with a dedicated PCB to drive the MOSFETs of every sub-module separately. The common-source configuration opens up a new degree of freedom to control different failure scenarios in a DCPDS. Turning off one of the two common-source MOSFETs in a path individually, an unidirectional blocking can be initiated. As a future upgrade of the developed SSCB, an individual driver was implemented to increase its flexibility and failure handling capability. Additionally, the separation of those driver circuits relaxes the individual requirements for necessary gate peak currents as well as miller currents to maintain the power MOSFETs off-state.

<figure><img src="image_4.png" /><figcaption>Fig. 3. SiC solid-state circuit breaker power module including gate drive units</figcaption></figure>

## C. Sense and trip electronics

The sense and trip electronics play a key role in SSCB by monitoring key system parameters such as current and temperature. When a fault condition, such as an overcurrent (in case of a short circuit) is identified, this circuit promptly activates the GDU to disconnect the current by turning off the power MOSFET module. Depending on the short circuit location inside the grid, the two aforementioned types of failure scenarios have to be managed by the SSCB:

* **High line impedances causing high amounts of energy:** The voltage clamping circuit of the SSCB must absorb the amount of energy which contains the components according to (3).

* **Low line impedances causing steep current slopes:** The sense and trip electronics has to rapidly detect the current rise and cut it off.

The sense and trip electronics as well as its power supply can be seen in Fig. 4. The general function blocks of the circuitry of the sense and trip electronics can be categorized as follows:

* **Analog amplifier:** A highly precise high bandwidth analog amplifier is sensing the voltage drop across the shunt resistor network. Depending on the current direction, its output varies around an offset of 2 V.

* **Comparator:** The high-speed comparators are triggering (and latching) their output if the amplifier output voltage level (as an equivalent to the SSCB-current) is exceeding or undercutting a reference voltage level, depending on the current direction.

* **Logic unit:** The logic unit combines the signals for each current direction of the comparators as well as error signals sent by the GDUs.

* **External interface:** The time-uncritical functions of the sense and trip electronics are externally controlled by a microcontroller. The electrical isolation barrier is realized by a fiber optics interface.

* **Auxiliary power:** The auxiliary power supply is providing different isolated voltage rails to utilize analog and digital voltage levels to the measurement electronics as well as supplying the three GDUs and its signal electronics.
<figure><img src="image_5.png" /><figcaption>Fig. 4. SiC solid-state circuit breaker sense and trip electronics (top) and its power supply (bottom)</figcaption></figure>

To ensure rapid SSCB failure handling capability in case of a DCPDS overcurrent, the implementation of the time-critical functions are realized solely in hardware components.

### D. Thermal management

Effective thermal management is critical in SSCBs used in electric aircraft according to the demanding requirements. The design of the water-cooling system is especially challenging, since the resulting temperature difference of the entire cooling chain is generally very low. In the presented application, it can be assumed that $\Delta\vartheta_{JA} = 55$ K. Due to space restrictions in aircraft applications, a very high coolant temperature of $\vartheta_A = 80$ °C has to be accepted (see Tab. I). Consequently, the heatsink is directly integrated into the module to address the thermal challenges associated with high-speed, high-energy switching. The water channels are placed directly beneath the SiC chips, ensuring effective cooling during operation, which keeps the system stable even under high-power conditions.

To investigate the steady-state thermal behavior of the SSCB-module, a CFD simulation was carried out at different power losses (see Fig. 5). On the left-hand side (Fig. 5(a)), the power loss of 10 W/chip represents the nominal line current $I_{DC}$ of the SSCB. Estimating the temperature-dependent multiplication factor $k$ of the on-resistance from the datasheet as $k = 1.3$, the SSCB current can be calculated at a junction temperature of $\vartheta_J = 94$ °C by applying the result of (4) [18]:

$$I = x \cdot \sqrt{\frac{P_{chip}}{k \cdot R_{Dson,chip}}} = 21 \cdot \sqrt{\frac{10 \text{ W}}{1.3 \cdot 16 \text{ m}\Omega}} = 460 \text{ A} \quad (5)$$

On the right-hand side (Fig. 5(b)), the power loss of 40 W/chip represents the inrush current $I_{inrush}$ of the SSCB. Estimating a value of $k = 1.5$, the SSCB current can be calculated at a junction temperature of 135 °C using (5) and yields 857 A.

The results for the two main operating points show that the doubling of the current is causing a quadruplication of the temperature difference $\Delta\vartheta_{JA}$. Theoretically, this result was expected. However, in practical terms, this achievement must

<figure><img src="image_6.png" /><figcaption>Fig. 5. Thermal simulation of the SSCB and the integrated water-cooled heatsink for different chip power losses (a) 10 W/chip; b) 40 W/chip)</figcaption></figure>

be emphasized, as only well-established heat spreading of the SiC chips can maintain the same thermal resistance of the module at higher temperatures. This means that, on the one side, a safe operation of the SSCB can be ensured even if the inrush current of more than 800 A is conducted continuously. On the other side, there is remaining thermal capacity to absorb switching energy during the transient switching state. The design approach ensures high reliability and ruggedness and allows a short time breakdown of the cooling system assuming a sufficiently high cooling fluid mass. This consideration is especially pertinent in aviation, where maintaining optimized low loss, low weight performance and safety is paramount.

## IV. EXPERIMENTAL VALIDATION OF THE ULTRA-FAST SiC SOLID-STATE CIRCUIT BREAKER

The final chapter is presenting the experimental validation of the ultra-fast SiC-SSCB. In the shown oscillograms in Fig. 6 to Fig. 9, the following 8 key quantities are measured:

* **CH1:** DC-line current (through the SSCB: $i_{SSCB}$) (see Fig. 1)

* **CH2:** Error comparator level detecting the exceeding or undercutting of a reference voltage level, depending on the current direction. The reference voltages for the detection level are 3.6 V for the positive current direction and 0.4 V for the negative current direction.

* **CH3:** Equivalent voltage measurement of the SSCB current. This voltage is proportional to the current $i_{SSCB}$ and offset by 2 V. The AC-transfer ratio of the current measurement is set to 1.6 $mV/A$. It can be observed in the oscillograms that its displayed reference value of 2 V is set to the 0 V-level of all remaining channels.

* **CH4:** DC-link system voltage (at the SSCB: $v_{SSCB}$) (see Fig. 1)
* CH5: The experimental setup includes an additional IGBT in series as a secondary failure protection device. The measured curve indicates the gate-source voltage of the IGBT.

* CH6, CH7, CH8: Gate-source voltages $v_{GS,Mi}$ of the three GDUs. For each sub-module, only one value is shown. It should be noted that the signals were measured on the GDU PCBs and not directly at the MOSFET gates.

The measurement results from the high-energy switching event utilizing a line inductance of 150 µH and a positive line current are shown in Fig. 6. During the experiment, the SSCB interrupted a fault current exceeding 1 kA, showcasing the SSCBs energy handling capability of 200 J (see Tab. II). The analysis reveals minimal voltage overshoot and efficient thermal management, indicating the device's ability to maintain stability under severe operating conditions [17].

The measurement results from the high current slope event – at a line inductance of 2.6 µH – and a positive line current are shown in Fig. 7. The ultra-low reaction time $t_{react}$ of 700 ns allows the developed SSCB to limit the short circuit current to an overshot of only 20%. This means that the DCPDS current retracts, reaching a value of +1.2 kA. This is achieved by applying the nominal DC-link voltage of 800 V, ensuring SSCB failure handling at a current slope of 300 A/µs. It should be emphasized that accurate current measurement, as well as high EMI rejection capability, ensures excellent reliability of the SSCB. Even under high oscillation potential during the switching event, the operation of the SSCB remains stable. It can be noted that the measured oscillations may not appear as drastic inside the circuit as they do in the oscillogram. A minimal-impact measuring setup is challenging to implement while keeping high $\frac{di}{dt}$ and $\frac{dv}{dt}$ and therefore inductive and capacitive coupling at a low EMI level.

The oscillograms in Fig. 8 and Fig. 9 illustrate the measurements of the high-energy switching event as well as the high current slope event at negative SSCB current direction. It can be observed that the SSCB operates with the same reliability as in the positive current direction.

The results emphasize the robustness and reliability of the SSCB, providing essential insights into its performance and suitability for high-power applications. Such findings are crucial for validating the SSCB's role in enhancing the safety and efficiency of advanced electrical systems, particularly in demanding environments like electric aircraft. A detailed investigation of the voltage clamping circuit can be found in a related publication [17].

## V. CONCLUSION

The newly developed SiC SSCB offers a notable improvement in protection for DCPDS. Its enhanced design ensures rapid fault detection, high efficiency, and compactness, making it particularly suited for demanding applications like electric aircraft.

In this paper the performance of the SSCB was experimentally proven and it was shown that the breaker is able to successfully handle the two essential failure scenarios. On the one hand, by utilizing a high line impedance of 150 µH, short circuit turn-off and isolation were achieved at 1 kA. A high energy amount of 200 J was dissipated by the voltage clamping circuit [17]. On the other hand, by utilizing a low line impedance of 2.6 µH, short circuit turn-off and isolation were achieved at high current slopes of up to 300 A/µs, limiting the overcurrent to 1.2 kA. This was achieved due to the very low reaction time of the SSCB's sense and trip electronics, which is 700 ns.

The experimental results confirm the SSCB's robust performance and reliability in safeguarding critical systems under extreme fault conditions, enabling high-speed operation and stability in harsh environments.

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<figure><img src="image_7.png" /><figcaption>Fig. 6. Measurements of the high energy switching event of the ultra-fast SiC solid-state circuit breaker at positive breaker current ($L = 150~\mu H$; $I_{SSCB} = +1~kA$; $E_L = 75~J$; $E_S = 125~J$; $E = 200~J$)</figcaption></figure>

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<figure><img src="image_8.png" /><figcaption>Fig. 7. Measurements of the high $\frac{di}{dt}$ switching event of the ultra-fast SiC solid-state circuit breaker at positive breaker current ($L = 2.6~\mu H$; $I_{SSCB} = +1.2~kA$; $\frac{di}{dt} = 300~A/\mu s$)</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>Fig. 8. Measurements of the high energy switching event of the ultra-fast SiC solid-state circuit breaker at negative breaker current ($L = 150~\mu H$; $I_{SSCB} = -1~kA$; $E_L = 75~J$; $E_S = 125~J$; $E = 200~J$)</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>Fig. 9. Measurements of the high $\frac{di}{dt}$ switching event of the ultra-fast SiC solid-state circuit breaker at negative breaker current ($L = 2.6~\mu H$; $I_{SSCB} = -1.2~kA$; $\frac{di}{dt} = -300~A/\mu s$)</figcaption></figure>