This letter presents a new low-voltage direct-current fault current bypass-based solid-state circuit breaker (SSCB) using silicon-carbide mosfet s. The proposed SSCB provides the possibility to select the clamping voltage of metal–oxide varistors (MOVs) close to the nominal voltage of the dc system. This reduces voltage overshoots across the main switch and snubber components and extends the maximum allowable dc bus voltage on the SSCB. The MOVs are removed from the power line, and their leakage currents are completely eliminated. The clamping voltage of the MOV and its surge energy rating is considered to optimize the MOV. The dv/dt across the main switchis controlled by an auxiliary capacitor, where a design procedure is presented to optimize its value. Also, the stored inductive energy of the line inductor in dc systems is bypassed using an auxiliary branch and prevented from flowing through the faulty section to enhance the safety. LTspice simulations are presented to show the significance of the proposed SSCB. The experiments of 375 V/170 A/2.4 μs and 600 V/163 A/2.4 μs verify the effectiveness of the proposed design in practice.

This article deals with metal-oxide varistor (MOV) and resistor–capacitor–diode (RCD) snubber-based solid-state circuit breakers (SSCBs). There are two main contributions. First, a design methodology of MOV-RCD snubber parameters is proposed by considering thermal dissipation and snubber charging time for the first time. The thermal profile of the main conduction switches determines nominal current under passive cooling. Based on the nominal current, the fault current magnitude is derived, and a design method of key parameters of an MOV-RCD snubber is proposed. Four snubbers are designed with different fault currents and dc voltages. Second, symmetrical layouts with distributed parallel cells are proposed for high current capability, which enables scalability. Q3D simulations facilitate the evenly distributed stray inductances among paralleled branches. Both low- and medium-voltage SSCBs are implemented, ranging from 500 V/300 A to 2 kV/1 kA. The power density achieves 37.8 kW/L at 500 V/1 kA. Experiments demonstrate that the reverse voltage reaches 4.88 kV with an ultrafast interruption speed of 24 μs for 2 kV/1.144 kA fault current including the MOV conduction time interval.

This article proposes a new dc solid-state circuit breaker (SSCB) based on silicon carbide (SiC) MOSFETs. There are two main contributions. First, a transient current commutation (TCC) is obtained in the main switch during current interruption. To achieve this, a compact and fast active injection circuit (AIC) is employed. TCC brings two main benefits: 1) it eliminates the effects of parasitic inductances in circuit connections and removes voltage oscillations on the gate of the main switch, which prevents spurious turn-on and 2) it eliminates the transient power shock on the switch during turn-off, which extends the lifetime of SSCB and increases its reliability. Second, the voltage on the employed metal oxide varistor (MOV) is reduced to zero during the OFF-state. This extends the maximum allowable dc bus voltage on the SSCB and solves the MOV reliability issue in the SSCBs. The presented SSCB employs a time-sequence control and needs no real-time detections of the dc current, which simplify the design. LTspice simulations of 380 V/80 A and 600 V/80 A are presented, and the results are compared with MOV- and MOV resistor–capacitor–diode (MOV-RCD)-based SSCBs. Also, experiments of a 380 V/80 A prototype validate the effectiveness of the proposed SSCB in practice where the voltage on the SSCB is clamped to 721 V with a fixed response time of 9.4 $\mu \text{s}$ .

This article proposes a comprehensive method for optimal coordination of ultrafast solid-state circuit breakers (SSCBs) in radial dc microgrids. The proposed method consists of two consecutive steps. In the first step, SSCBs are optimally coordinated for overload, short circuit, and instantaneous protections. Inverse time-current characteristics (ITCC) curves are formulated to systematically coordinate SSCBs. The trip curve of each SSCB includes overload, short-circuit, and instantaneous profiles. In determining overload protection, the thermal capability of SSCBs is considered; while the short-circuit and instantaneous tripping profiles are realized based on short circuit thermal capability and ultrafast response time of SSCBs. Coordination time interval (CTI) is included between upstream and downstream SSCBs to achieve selectivity. To avoid miscoordination in practice, CTI is chosen by incorporating the SSCBs’ metal-oxide varistor (MOV) conduction time interval during turn-off process and dc current measurement error. In the second step, the operating speed of the protective scheme is optimized by applying distance-based secondary protection (DBSP). The DBSP is used to minimize the tripping time when short circuit faults occur close to upstream SSCBs. This significantly reduces the consumed energy by faults, prevents damage, reduces absorbed energy by SSCBs, and enhances the safety of operators. The proposed coordination removes the need for communication links between SSCBs and presents high reliability. A 400-V dc microgrid benchmark with photovoltaic (PV) and energy storage systems (ESSs) is examined as a case study in simulation. Besides, experiments are conducted in a 400-V dc system to evaluate the effectiveness and accuracy of the DBSP.

This paper investigates limitations of passive voltage clamping based dc solid-state circuit breakers (SSCBs). There are two major contributions of this paper. First, it presents a unique quantifying study of limitations in metal oxide varistor (MOV) clamping based SSCBs in terms of gate voltage distortions and power shock. Second, it provides a comprehensive quantifying investigation of limitations in MOV and resistor-capacitor-diode (MOV-RCD) clamping based SSCBs regarding the power shock and response speed. For MOV based SSCBs, both gate voltage distortions and power shock during turn-off are extremely high, causing switch degradation/failure. For MOV-RCD clamping based SSCBs, a snubber capacitor is added to reduce d v /d t and power shock. However, this capacitor brings two main limitations: a) inevitable high transient power/energy shock at high-current interruption and b) low turn-off speed caused by high-inertia capacitor charging at low-current interruption. Two prototypes are implemented to illustrate limitations: a discrete SiC MOSFET-based 500 V/20 A SSCB, and a SiC MOSFET module-based 800V/100A SSCB. Experiments validate that the transient power shock can reach 256 kW at a 1.2 kA fault current interruption, which affects system reliability. Moreover, the response speed at a 100 A case (7.8 μs) can be 14 times slower than the 1 kA case (0.56 μs) due to the snubber capacitor charging process, which leads to inconsistent control and coordination of SSCBs.

This article introduces a 4 kV/120 A solid-state dc circuit breaker (DCCB) based on discrete SiC mosfets. The DCCB is designed in a five-layer tower structure. Each layer consists of a circular main conduction branch and an attached gate driver. There are two primary benefits of the proposed DCCB. First, it reduces conduction loss with multiple devices in parallel. Second, it achieves an ultrafast response speed with SiC mosfets. Moreover, the gate drivers of the DCCB are powered by a domino inductive power transfer (IPT) system. It achieves the load-independent constant-voltage output characteristics, which means the outputs are immune to load variations. An IPT system prototype is implemented to test the power transfer performance. At 500-kHz frequency, the total output power reaches 15.73 W, which is sufficient to power on five gate drivers, with a peak transfer efficiency of 75.4%. The IPT system is tested to power a 4 kV/120 A DCCB prototype. It validates that the DCCB is effective to turn off 120 A current within 3.5 μs.