Jin Zhu’s research while affiliated with China Academy of Chinese Medical Sciences and other places

Thyristor-based dc solid-state circuit breakers (T-SSCBs) have been widely investigated due to their low losses and low cost. However, the current solutions are not cost-effective in dc microgrid because the number of auxiliary devices [e.g., auxiliary thyristors, capacitors and metal oxide varistors (MOVs)] will significantly increase in multiport scenario. In this article, a novel T-SSCB topology with the ability to expand the number of ports arbitrarily is proposed. Due to the adoption of integrated auxiliary branch structure, active turn- off and soft reclosing of all ports are achieved by only one capacitor and one MOV. The concept of multiport T-SSCB (MT-SSCB) is proposed for the first time, the number of devices is significantly reduced compared to traditional T-SSCBs in multiport scenario. Moreover, the proposed MT-SSCB can eliminate MOV leakage current during off -state. As a result, the MT-SSCB presents advantages in low cost, small volume and high reliability. The operation principles and parameters designing are presented in detail. Experiment and comparative analysis verify the feasibility and effectiveness of the proposed MT-SSCB.

Conventional power supply for micropower devices typically includes batteries, energy harvesting devices, or AC-DC converters with magnetic components (e.g., inductors or transformers), which results in bulky volume and high cost. This article proposes a novel non-isolated 110/220 V input AC-DC converter without magnetic components, high voltage filter capacitors or rectifier circuits. The proposed converter has advantages of small volume, low cost and high reliability. The converter can interface the mains voltage (110/220 V AC) directly and convert it to a regulated DC voltage of 3.3/5 V for micropower devices. The working principles and theoretical analyses are presented in detail. Experimental results and comparative analysis verify the effectiveness of the proposed converter. The power supply solution achieves a maximum output power of 416 mW, resulting in a power density of 792 mW/cm3 based on PCB prototype, and the solution takes approximately one-third of commercial non-isolated product cost.

Solid state circuit breakers (SSCBs) based on full-controlled devices such as IGBT and based on half-controlled devices such as thyristor have their respective advantages. The mixture device solid state circuit breaker (M-SSCB) combines the advantages together and can achieve lower loss, high efficiency, active and reliable blocking at the same time. However, the conduction loss will increase significantly when the topology expanding to a bidirectional topology because the bidirectional line commutation switch (LCS) structure composed of two groups of IGBTs in reverse series. In this paper, a novel discrete branch mixture SSCB (DBM-SSCB) is proposed, bidirectional current only flows through one IGBT that has the obvious conduction losses advantage at the same voltage and current level. Only one energy-absorbing component is shared by two discrete branches can guarantee optimal costs and volume. By calculation, the proposed DBM-SSCB can reduce the conduction loss about 30.4% in 10 kV MVDC system, while retaining other advantages of the mixture device SSCB, such as without introducing additional thyristors, charging power supply and the ability to actively interrupt bidirectional fault currents. The blocking principles and designing guidelines are presented in detail, the feasibility is verified by 500 V-18 A simulation results and scale-down experiment, the engineering calculation and simulation of 10 kV-1 kA prototype is completed and compared with other DCCBs. Experimental results and comparative analysis show that the proposed DBM-SSCB has both lower losses and significant performance advantages thus has a good engineering application prospect.

Solid-state circuit breakers (SSCBs) have been widely used to achieve actively and high-efficiency turn off . However, the conduction losses and costs may significantly increase when the SSCBs are used in multiport system. In this article, a new multiport SSCB (M-SSCB) concept is proposed for direct current (dc) microgrids. The energy absorbing branches (EABs) are integrated into one, thus the required number of devices can be reduced by at least half compared with typical separate bidirectional SSCB topologies in the same voltage and current level applications. Moreover, by introducing the grounded EAB based on a thyristor, the leakage current is eliminated from the system and the fault current is bypassed. This further increases the allowable dc voltage and safety of the breaker. As a result, the M-SSCB has a more economic design, smaller volume and higher safety. The operation principles and designing guidelines are presented in detail. The feasibility and effectiveness are verified based on experimental results and comparative analysis.

Direct ac–ac converters work without dc links. They have the advantages of small volume and high reliability. However, direct ac–ac converters cannot realize simultaneous decoupling control of the output voltage amplitude and phase. In this article, we present a four-leg direct ac–ac converter and a corresponding modulation strategy suitable for flexible ac-link (FACL) devices, enabling the decoupling control between three-phase ac–ac input and output with fewer devices and a simpler structure. Each FACL consists of three proposed four-leg direct ac–ac converters, and each output of the proposed converter has two operations of inverse and noninverse; this topology can reduce up to 50% of FACL switching devices. The two outputs share the same ground with the input. Antiseries switches are not required. Comparative analysis and experiments demonstrate the effectiveness and feasibility of the proposed four-leg converter.

Dynamically reconfigurable battery (DRB) technology can effectively address the imbalance problem in traditional energy storage systems. However, the additional switches required for each battery in this technology can introduce significant losses. To further reduce this portion of the losses, this letter proposes a DRB topology suitable for DC microgrid applications. This topology uses the same number of switches as the half-bridge topology but reduces the number of switches that current flows through during operation. Moreover, it allows for hybrid series-parallel connections between batteries, whereas the half-bridge topology only permits series connections. Comparative analysis shows that the proposed topology reduces losses from the additional switches by approximately 33% compared to the half-bridge topology in applications of a similar scale. Simulation and experimental results validate the performance of this topology in controllable input/output and self-balancing. Compared to existing topologies, this solution reduces losses while maintaining reconfiguration capability, making it well-suited for scenarios where high reliability and efficiency are critical. This advancement in DRB technology offers a new approach to energy storage system topology selection.