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This article presents two simple strategies for output dv/dt reduction in modular multilevel converters through coordination of the switching transients of the submodules. The first method is achieved by adding a delay time between the switching transients of two submodules, which would be switched simultaneously in regular switching strategies of modular multilevel converters. The second method is to inject a reverse dv/dt to the converter's output by switching redundant submodules. Both methods do not affect the switching speeds of the semiconductor devices and require no additional hardware components. They can be applied with different modular multilevel converters modulation strategies. Circuit analysis of the proposed methods and their effects on the converter operation are presented. Simulation and test results of a 1.7-kV SiC-device-based modular multilevel converter are provided to validate the circuit analysis. It is shown that the proposed methods can reduce the converter's output dv/dt to half of a single switching device's dv/dt.

Electrical faults cause fire or shock hazards in homes and offices. Flexible power cords are particularly susceptible to metal or insulation degradation that may lead to a variety of electrical faults. This article introduces a new Smart Plug 2.0 device which offers all-in-one protection against short-circuit, overload, arc, and ground faults in addition to the wireless power control and monitor function of conventional smart plug devices. It offers microsecond-scale time resolution to detect and respond to a fault condition, and significantly reduces the electrothermal stress on household electrical wires and loads. A new arc fault detection method is developed using machine learning models based on load current di/dt events. Comparing to other solid-state circuit breaker designs which typically respond to overcurrent conditions only, Smart Plug 2.0 integrates additional protective functions into the same hardware structure with minimal cost penalty. A 120 V/10 A solid-state Smart Plug 2.0 prototype using power mosefts is designed and tested. It has experimentally demonstrated the comprehensive protection features against all types of electrical faults.

Protection against circuit faults represents a major technical challenge in the emerging dc transmission and distribution power networks. A popular prior-art dc hybrid circuit breaker (HCB) using a series load commutation switch (LCS) offers an excellent solution with arcless operation but suffers from a high conduction power loss associated with the LCS. This article proposes a new HCB architecture that relies on a switching-mode transient commutation current injector (TCCI) circuit instead of the LCS. The TCCI in the electronic path remains in a standby mode with near-zero power loss under normal conditions, but can rapidly generate a pulse current matching the fault current, and therefore facilitate current commutation from the mechanical to the electronic path. It completely eliminates the conduction power loss associated with the LCS, and delivers ultrahigh transmission efficiency. The TCCI circuit provides a near-zero voltage and a small high-frequency ac ripple current condition for the mechanical contacts to separate arclessly. A 600-V/20-A HCB prototype based on a two-phase current source buck converter topology and a high-voltage vacuum relay has experimentally validated the HCB concept, and demonstrated a mechanical to electronic commutation time of $7.2~\mu \text{s}$ , a total active response time of $310~\mu \text{s}$ , and a peak interrupted fault current of 89 A at a dc bus voltage of 400 V. The new HCB architecture can be applicable in medium voltage direct current (MVDC) (>5 kV) and high voltage direct current (HVDC) (>100 kV) applications as well.

This paper presents a self-sustained circuit building block (CBB) that utilizes 10-kV silicon carbide (SiC) devices as the main switches. The CBB achieves a self-sustained operation by powering the gate drives of its main switches with the energy from its dc bus capacitor. The CBB can serve as one of the submodules in a multilevel converter for high-voltage applications. This paper focuses on the design of the 10-kV SiC device’s gate drive and its associated auxiliary power supply (APS). The gate drive and its APS are the major technical challenges in the CBB development. The gate drive in the CBB features a common mode transient immunity (CMTI) over 200 kV/ $\mu \text{s}$ and fast protection functions. Its APS is based on an active voltage divider concept and achieves 7-kV input voltage with a simple circuit structure and control scheme. The operational principles and design guidelines of the gate drive and its APS are presented in detail. Test results of the CBB in a double-pulse test setup with a 7-kV dc bus voltage are presented to validate the design. Reliable operation of the CBB is demonstrated under dv/dt up to 100 kV/ $\mu \text{s}$ .

In order to control simply and reduce harmonic content, high-power DC switch power supply often uses sequential control. As the depth control has low power factor, we use sequential control in order to improve the power factor, but the network side current harmonic content is big in shallow control and will contribute much harmonic pollution to power grid. In this paper, by comparison and analysis of fundamental wave, harmonic wave, THD and power factor for input current from sequential control and synchronous control respectively, an optimum control theory which will decrease the harmonic and maintain the power factor is proposed. Tests proved that the optimum control strategy for multiple thyristor rectifiers will conduct sequential control when in depth control and conduct parallel control in shallow control and will achieve a lower harmonic content than complete order control with relatively the same power factor.