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Fault current limiters (FCLs) have high impedance during fault conditions. However, it is inevitable to introduce additional impedance to the system, which may increase power losses, cause overvoltage, and degrade system dynamic performance. A voltage-clamping type dc FCL (VC-FCL) with low power losses is proposed in this article. This topology has nearly no on-state loss. Under the demagnetization effect of the coupled inductor, this topology presents a very small inductance during normal operation, which is beneficial to the dynamic response of the system. Therefore, VC-FCL can be installed directly into the system without replacing the dc reactor. In addition, the number of power electronic devices and costs are reduced by using a metal oxide varistor (MOV) for voltage clamping. The parameter design of the coupled inductor and MOV is produced out to ensure both the current limiting capability and low power losses of VC-FCL. The simulation case study and experiment test are implemented to further verify the good performance of the proposed topology.

In the future, electric vehicle (EV) charging dc–dc converter systems are usually required for realizing bidirectional operation, electric isolation, and large voltage range, which can be realized at the dc stage. However, because of unavoidable reactive power, the typical bidirectional and isolated dc–dc converters, such as dual-active-bridge (DAB) dc–dc converters and LC-based resonant dc–dc converters, usually generate large current stress at wide-range voltage. Thus, the design cost for high-power applications will inevitably be expensive. Consequently, this article, combining a three-level buck–boost stage, adopts a DAB-based two-stage dc–dc converter with a low current stress. Then, the simple control schemes, including the soft start-up method, the linear current-control-based inner loop technique, and the soft shutdown method, are proposed for the charging of EV. Especially, based on the naturally transient behavior, the linear current-control-based inner loop technique is presented with low computational burden and without instability concern. The proposed linear technique can easily and steadily realize the charging requirements such as constant current, power, and voltage charging. Besides, the presented method has no current and voltage shoots during transient process, which can significantly enhance charging reliability. Moreover, the changing rate of a charging current can be consistent and controllable to fulfill batteries’ charging requirement. Finally, experiment results are provided to verify the effectiveness of the proposed techniques.

Compared to the traditional modular multilevel converter and alternative arm converter, the hybrid multilevel converter (HMC) exhibits superiority in terms of cost and volume. In the HMC, the pulse width of the direction switch (DS) is conventionally utilized to maintain capacitor voltage balancing (CVB). However, this method has certain limitations, including a restricted range of modulation indices and the inability to support pure reactive power operation. To address these drawbacks, a new CVB method based on the phase angle of the DS is proposed in this article. Compared to the traditional method, the proposed method enables the HMC to achieve a full range of modulation index and four-quadrant operation. Additionally, it demonstrates improved performance in terms of SM capacitance and capacitor voltage ripple, especially under severe grid voltage sags and low power factors. A comparative analysis is conducted between two CVB methods, focusing on the SM number, switch number, and SM capacitance. Furthermore, a unified control strategy considering asymmetrical and symmetrical grid voltage sags is proposed for these two CVB methods. Finally, the effectiveness and superiority of the proposed CVB methods are verified by simulation and experimental testing.

Cascaded H-bridge converters (CHBCs) are widely utilized in medium- and high-voltage systems. However, they present challenges such as large submodule (SM) capacitance and complex capacitor voltage balancing strategy. To improve converter power density and reduce hardware consumption, this letter proposes a new topology for CHBC, which features centralized active power decoupling (APD) capability. The periodic parallel connection and energy interaction between the SMs allows for double-line frequency power fluctuation suppression of all SMs through only one APD branch, leading to reduced components and simplified control. This letter provides a detailed analysis on the operating, modulation, and control strategies of the proposed topology. Experimental results are also presented to demonstrate the feasibility of this new circuit.