Pulsed-Power-Loads (PPLs) are becoming more common in medium-voltage naval DC micro-grids. To reduce their impact on the electrical system, energy storage elements can be installed. For optimal performance the interface converters need to have fast dynamics and excellent disturbance rejection capabilities. Moreover, these converters often need to have a voltage transformation capability and galvanic isolation since common energy storage technologies like batteries and super capacitors typically operate at relatively low voltages. In order to address these issues a Dual-Active-Bridge converter with a Moving Discretized Control Set Model Predictive Control (MDCS-MPC) is proposed in this paper. The controller has a fixed switching frequency, which allows straightforward filter design. The operating principles of the MDCS-MPC are introduced in this paper with the development of a cost function that provides stiff voltage regulation. Resonance damping and sampling noise resistance have been achieved by an adding additional term in the cost function. This paper presents an assessment of the performance of the proposed MDCS-MPC and comparisons with other control methods. Experimental validation from a 300V/300V 20kHz 1kW Dual-Active-Bridge converter are also presented to verify the theoretical claims.

Modular multilevel converters (MMCs) have attracted extensive research interests in various ac and dc conversion applications due to their modular structure and excellent harmonic performance. However, the large number of power switches increases the potential risk of submodule (SM) failure, which greatly challenges the safe and reliable operation of the MMC. This article presents a detailed review of fault diagnosis and fault-tolerant control methods of the MMC under SM failures. On this basis, comprehensive comparisons are conducted among different fault diagnosis methods, and verification results are provided to analyze the advantages and disadvantages of the popular fault-tolerant control methods. Finally, the review is concluded, and future trends and research opportunities are discussed.

Pulsed-Power-Loads (PPLs) are commonly incorporated in medium-voltage navy DC microgrids. To mitigate their detrimental effects, energy storage systems (ESSs) can be installed and their converters need to have excellent disturbance rejection capability. To facilitate this objective, a Moving-Discretized-Control-Set Model-Predictive-Control (MDCS-MPC) is proposed in this paper and applied on a Dual-Active-Bridge converter. Fixed switching frequency is maintained, enabling easy passive components design. The proposed MDCS-MPC has a small number of calculating points in each switching period, which enables the implementation in standard commercial control platforms. The operating principle of the MDCS-MPC is introduced in development of a cost function that, on one hand, provides stiff voltage regulation; on the other hand, minimizes current stress. Theoretical claims are verified on a 300V/300V 20kHz 1kW Dual-Active-Bridge.

The open-circuit fault detection and localization (FDL) technique can improve the reliability of the modular multilevel converter (MMC). However, the conventional software-based FDL methods usually have a heavy computation burden or a limited localization speed. This article proposes a simplified and fast software-based FDL approach for the grid-connected MMC. First, the errors between the measured state variables (the output current and the circulating current) and their estimated values are calculated. By comparing these errors with their threshold values, the switch fault can not only be detected but also be localized to the specific arm. Then, the capacitor voltages in this faulty arm are collected, and the submodule (SM) with the highest capacitor voltage is selected. To confirm the switch fault in this SM, a modified Pauta criterion is presented to check the abnormal voltage data. As a result, the computation burden of the proposed software-based FDL approach is significantly reduced, and the faulty SM can be localized in a short period. Simulation and experimental results verify that the proposed approach can effectively detect and localize different open-circuit faults, and it is immune to the step of power references.

Fault-tolerant operation ability is of great importance for stable operation of cascaded H-bridge (CHB) converters, under open-circuit (OC) or short-circuit (SC) switch failures in submodule (SM). In this paper, an improved fault-tolerant control strategy is proposed for CHB based static synchronous compensator (STATCOM) under SM faults. First of all, compared with the conventional fault-tolerant method of directly bypassing the faulty SMs, the proposed fault-tolerant method takes advantage of the healthy switches of the faulty SMs, where they are still able to generate either positive or negative voltage level. As a result, more output voltage levels can be generated, and it raises the attainable balanced line-to-line voltage, especially when different fault types exist at the same time. Then, based on the specific condition of OC fault or SC fault, when the output voltage reference of the faulty phase reaches its limit, the references of the other two healthy phases are redistributed to generate the desired line-to-line voltage. With the reconfiguration of modulation waves, the attainable balanced line-to-line voltage can be further improved. In addition, the proposed fault-tolerant method possesses the ability of cluster voltage balancing, which is an important issue for the STATCOM application. Simulation and experimental results validate the effectiveness of the proposed fault-tolerant method.