This article proposes a two-stage power converter with novel control methods for pulsed load applications. The first stage is an isolated converter that transfers only average power to the second stage, which dramatically reduces the input filter size and components’ current rating. The second stage is a buck converter designed for a fast response during pulsed load transients. A flexible intermediate voltage is implemented to reduce the size of the midpoint energy storage capacitor that is responsible for compensating the instantaneous power difference between the two stages. A novel digital input feed-forward controller is proposed for the second stage to eliminate the poor line regulation issue caused by the flexible intermediate voltage. To verify the effectiveness of the two-stage power supply and the control methods, a full-scale 800 W (average)/4 kW (peak) converter prototype is built and tested. The results prove the feasibility of the proposed topology as well as control methods and demonstrate the advantages over traditional concepts.

This paper presents a hybrid Energy Storage System (ESS) for DC microgrids, highlighting its potential for supporting future grid functions with high Renewable Energy Sources (RESs) penetration. While hydrogen ESS provides long-term energy stability, it typically has slower response times than batteries. Integrating hydrogen and battery storage can deliver sustained energy and effectively manage microgrid demand and surplus. Key challenges include integrating power electronics with fuel cell technology for efficient renewable energy conversion. This paper presents a hybrid ESS with 1 kV DC bus voltage. The hydrogen and battery ESSs, along with their converters and control are modeled using MATLAB Simulink. The optimization technique using Mixed Integer Linear Programming (MILP) in CVX-MATLAB aims to minimize operational and maintenance costs while maximizing profit from energy sales during periods of low generation and high demand. The system is validated through Typhoon Hardware-In-the-Loop (HiL) testing, showing high converter efficiencies of > 95%. Analyses with RESs and the grid (including Monte Carlo sensitivity analysis), using commercial and community scale load profiles, demonstrate annual returns of 17.72% and 16.54% for hydrogen ESS, and 17.13% and 18.54% for the hybrid system, including battery ESS, with full recovery of initial investment costs within 6 years.

The increasing demand for the development and utilization of renewable energy resources has lead to a growing interest in the development of LVDC systems. The dc grid provides more flexibility in integrating different forms of renewable energy sources effectively. However, the lack of a reliable protection mechanism remains the main drawback in the growth of dc distribution systems. Unlike ac systems, the absence of a natural zero crossing in dc systems for arc extinction makes the use of a conventional mechanical circuit breaker (MCB) a less reliable solution. The use of a solid-state circuit breaker (SSCB) results in fast fault interruption but reduces the overall efficiency of the system due to the on-state voltage drop of the semiconductor devices. A hybrid circuit breaker (HCB) combining MCB and SSCB yields better static and dynamic performances but the main challenges remains in the demagnetization of the transmission line inductance after a fault interruption and an arc formation between the MCB contacts. This paper proposes a hybrid circuit breaker (HCB) which is suitable for fast fault interruption in low voltage dc (LVDC) systems while alleviating the above issues. Proposed topology employs a semiconductor switch as well as an actively switched capacitor branch in parallel with the main mechanical breaker to facilitate fast current commutation during a fault. The mechanical breaker forming the main branch is turned off at zero voltage. This eliminates the arc formation across the moving contacts of the breaker. Moreover, the fault interruption process does not require a varistor for network demagnetization following the fault current commutation. This paper also presents a discharging mechanism for the capacitor in a practical implementation. Operation of the proposed dc circuit breaker is evaluated through a prototype tested in the laboratory.

In order to supply reliable power to the subsea loads at high system efficiency and low emissions, there is a growing interest in employing offshore renewable resources close to the point of use. However, such system has predominantly stayed in the conceptual stage so far. Hence, there is a need to develop methodologies for interconnecting multiple renewable sources with offshore loads. This paper proposes a Multiport Energy Router (MER) based on a Medium Frequency (MF) Solid-State Transformer (SST) that integrates renewable energy sources (RES) and Energy Storage Systems (ESS) to supply clean energy for subsea loads. The MER forms a three-port network, where HVDC Wind Turbine Generator (WTG) power system and MVDC ESS are interfaced with subsea loads. The MER is realized by series-parallel combination of Triple Active Bridge (TAB) converters. The TAB modules are critical to enhance the power density, fault-tolerance, and efficiency of the proposed system. In this paper, a novel simple algorithm for extending soft-switching region of TAB by selecting optimal control variables is proposed. Moreover, this paper presents a control strategy for the MER, which addresses the DC-link voltage imbalance issue for each of the cascaded TAB converters. The simulation and the Hardware-in-the-Loop (HIL) results based on Typhoon-HIL system are presented to verify the proposed converter operation and the control strategy.

This paper proposes a medium frequency solid state transformer (SST) based grid interface for high power multi-pulse rectifiers. In the proposed approach, the low frequency AC (grid) voltage is transformed to medium frequency (MF) voltage via front-end converters. The three single-phase MF outputs from these converters are fed to the primary side of a 3-phase, 5-limb multi-winding isolation transformer (or alternately three 1-phase transformers). The secondary side windings from the transformer are configured in a certain ‘zig-zag’ arrangement, which are connected to the inputs of 3-phase diode rectifier modules as in a typical multi-pulse system. The proposed topology can better than double the power density by reducing volume (or weight) of the required front-end isolation transformer while maintaining the same input current quality as a conventional low frequency transformer based approach. Usage of an open-loop square wave pulse-width modulation (PWM) for the front-end converters makes this approach simple to implement. This paper explains the proposed concept taking an ASD application's perspective using modeling, simulation, and experimental results from a scaled down laboratory prototype.

In this paper, 650 V / 7.5 A rated enhancement-mode (E-mode) Gallium Nitride (GaN) high-electron-mobility-transistors (HEMTs) with integrated gate drivers are characterized under thousands of accelerated thermal cycles (ATC) at different junction temperature stresses. This research helps in developing fundamental insights into GaN HEMTs' aging characteristics through the degradation of ten devices under ATC tests. For over 20,000 thermal cycles, the forward and reverse conduction losses, I GSS, C oss, and the RDS on are experimentally measured to identify the parameter shifts and the corresponding precursors. Results indicate that both IGSS and C oss do not deviate much, but the values of RDS on, the forward and reverse conduction losses vary considerably with device aging. This paper also presents an empirical method to estimate the correlation between the acceleration factors of the GaN FETs' degradation process and the thermal cycling conditions. The value of the activation energy of the tested GaN HEMT devices is also derived using the empirical equations to be about 1.13 eV under the applied stress factors. This study finds that the degradation process of GaN HEMTs with age facilitates a reasonable correlation with different failure mechanisms, which further helps in reliability improvement.