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As one of popular high-power power interface topologies between the energy storage devices and the dc link, the three-phase dual-active-bridge (3$\Phi$-DAB) dc–dc converter has received increasing attention. However, due to high number of semiconductor devices and multiple possible operation modes in the 3$\Phi$-DAB converters, the reliability and healthy operation become increasingly challenging compared with traditional single-phase DAB converters. This study presents detailed waveform analyses for 3$\Phi$-DAB converters under the normal and open-circuit faulty mode operation. Based on the analysis, a fast, cost-effective, reliable and sensor-less fault detection (FD) and fault isolation (FI) mechanism based on finite state machines for 3$\Phi$-DAB converters is presented in this article. Specifically, switch node voltages between the primary and secondary bridges of 3$\Phi$-DAB converters are adopted as the open-circuit fault (OCF) diagnostic signature and a low-cost OCF diagnostic circuit is utilized to perform the required signal processing. Using this technique, the open-circuit FD was achieved within 1/25th of the switching frequency and the open-circuit FI was performed within 1/6th of the switching frequency, which is the fastest FD and FI time for 3$\Phi$-DAB converters reported so far. Experimental results were acquired from a built prototype under various OCF scenarios to validate the effectiveness of the proposed technique.

The control coupling and stability of three-phase photovoltaic systems with constant power loads (CPLs) are two key technical issues that urgently need to be addressed. However, current methods are difficult to solve both technical challenges simultaneously. To address these issues, this article proposes a novel decoupled continuous control set model predictive control (CCS-MPC) strategy for LC-filter T-type three-phase four-leg three-level voltage source inverters (3P4L-3L-VSIs) driving CPLs. The control strategy is developed in αβγ frame. The model of 3P4L-3L-VSIs is first transformed from abc frame to the αβγ frame to remove the coupling effects in the abc frame. Then based on the decoupled model in the αβγ frame, a novel CCS-MPC strategy is proposed to provide balanced sinusoidal voltages. The α and β components are regulated by the A, B, and C legs, while the zero-sequence component is regulated by the N leg. To confirm the effectiveness of the proposed strategy, both simulation and experimental results are presented to verify the proposed decoupled CCS-MPC strategy. The results show that the proposed control achieves low computational burden and total harmonic distortion and can increase the stability margin especially for CPLs compared with the commonly used PI-based control, PR-based control, and deadbeat control.

Voltage equalizers (VEs) are essential for partially shaded photovoltaic (PV) modules by equalizing the voltage of PV modules and preventing anti-paralleled diodes from bypassing the shaded PV modules, resulting in improved power yield under partial shading conditions (PSCs). Recently, different topologies for VEs have been discussed based on the distributed maximum power point tracking (DMPPT) principle at the module level. Considering that the power flow distribution, operation modes, and actual performance of these VEs show distinct differences, it becomes increasingly important for the performance quantification and comparative assessment of various topologies both theoretically and experimentally. Here, three typical differential-power-processing-based VEs are selected, including series-resonant-voltage-multiplier (SRVM), flyback-based PV-to-IP (Flyback-PV-IP), and flyback-based PV-to-Bus (Flyback-PV-Bus). Key performance indexes for VEs have been defined, including the processed power, power losses, and overall system efficiency. To quantify the performance of different topologies of VEs, an algorithm is developed in MATLAB with daily irradiation and temperature under various PSCs. Moreover, three experimental prototypes for the selected topologies have been built and main tests under different mismatching conditions have been conducted. With a systematic performance quantification and a fair comparison of typical VEs, this article will propose a systematic evaluation method for VE schemes. Meanwhile, the optimal VE topology with its control for typical PSC cases will be identified.