Shiqi Ji

Nowadays, distribution transformers require more flexible voltage regulation capabilities to cope with voltage fluctuations caused by dynamic sources and loads. Power electronic transformers (PETs) can offer advanced voltage regulation performance but the cost is high. The hybrid solution that integrates fractionally rated power electronic converters with conventional distribution transformers, which is called the magneto-controlled transformer (MCT), provides a cost-effective alternative. This paper proposes a novel flux-shunt DC-saturated MCT with a five-leg magnetic core and very small portion of converters. The topology and basic principle are introduced in details. Then, the magnetic equivalent circuit (MEC) of the proposed MCT is derived, and its parameters are designed accordingly. Finally, a 10 kVA prototype is implemented, and the voltage regulation performance of the proposed MCT and the accuracy of MEC modeling are validated.

The high-frequency and high-power operation of power converters has imposed stringent requirements on the switching loss and electromagnetic interference performance of power devices, particularly for the increasingly popular high-speed insulated-gate bipolar transistors (IGBTs). Conventional soft-switching techniques with snubbers encounter significant challenges in high-frequency and high-power scenarios due to their inherent complexity and the substantial influence of parasitic parameters. This article presents an easy-to-implement flexible commutation design aimed at reducing switching losses, $di/dt$ and $dv/dt$ simultaneously in high-speed power IGBTs for high-frequency and high-power applications. The proposed design includes a snubber capacitor and two printed-circuit-board-based coupled inductors as the busbar, facilitating soft-switching conditions for the IGBTs, along with a lossless energy recovery circuit to achieve lossless operations. Importantly, the design incorporates only passive components and specially utilizes distributed parasitic parameters, ensuring both ease of implementation and high performance. The proposed design is experimentally validated through double-pulse tests using a high-power and high-speed IGBT rated at 1.2 kV/140 A, with the switching performance analyzed comprehensively in comparison to a conventional hard-switching design.

The stray inductance of the commutation circuit significantly impacts power semiconductor device switching. This article presents a comprehensive investigation on stray inductance extraction in half-bridge power modules. After reviewing existing methods including electromagnetic simulation, switching transient extraction, and static measurement, we propose a novel perspective that identifies six distinct commutation paths from the distinct positioning of diodes and active switches. Our findings reveal 9%–17% differences in stray inductance across these paths, highlighting the importance of path-specific analysis for precise extraction. We further supplement direct impedance measurement approaches to vector network analyzer-based measurements, and analyze the limitations of fixture compensation. These perspectives provide new insights and guidance into high-precision stray inductance characterization for power electronics applications.

The accurate current measurement is critical for power semiconductor characterization. Considering the switching speed of power semiconductors has become much faster in recent years, it is difficult to measure the current effectively using existing current probes due to their limited bandwidth. Also, in many cases, it is necessary to directly characterize power semiconductors in real power converters in long-term operations, requiring some other key specifications on current probes including dc accuracy, galvanic isolation, easy installation, etc. This article proposes a novel hybrid current measurement method, including the tunnel-magnetoresistance-based low frequency measurement section, Rogowski coil-based high-frequency measurement section, and signal conditioning circuits for seamless frequency combination. Accordingly, a current probe based on the proposed method is developed, achieving high bandwidth, galvanic isolation, and compact size. The performance is experimentally validated with a double pulse test and long-term continuous pulse test in a 1.2 kV/120 A SiC mosfet power module-based converter platform. Eventually, the proposed probe is comprehensively compared with the commercial shunt and Rogowski coil.

This paper discusses the design, development, and testing of a flexible combined heat and power (F-CHP) system. It includes two parts: the power conditioning system (PCS) converter, which connects the system to the grid and is the key component to provide grid support services, and the F-CHP central controller, which accommodates the control of local sources, local loads, and the PCS converter. The functions and structures of the central controller are discussed. The central controller’s system-level performances are verified with hardware-in-the-loop (HIL) tests, and the mode transition and grid transient performances are validated with power electronic converter-based hardware testbed (HTB) tests. The PCS converter is designed with 10 kV SiC MOSFETs. The grid requirements are considered in the 13.8 kV/1 MW PCS converter design, and the impact of different requirements on the converter design is identified. Also, converter scalability is studied with the paralleling operation. Two 13.8 kV/100 kW converter prototypes are developed to verify the converter design and scalability. The second prototype is an improved design of the first one; the volume is reduced by 49% and the efficiency at the rated output power is increased from 96.4% to 98.4%. The test results of the converter performances, grid support functions, and parallel operation are also discussed.

Modular multi-active bridge (MMAB) converter with inherent advantages of galvanic isolation, modularity and power density, can provide multiple dc ports for multifarious power conversion through high-frequency links (HFL). However, the traditional single phase-shift control, which is widely applied in the converter due to the complex coupling among ports, leads to unfavorable efficiency performance. To independently handle each port with optimal capabilities, a dual-loop optimal control is proposed for MMAB converters to achieve the decoupling of active and reactive powers. Conditioning circuits are designed to extract power-related information that can be used to eliminate the fundamental reactive power, thus optimizing conducting and switching characteristics. The proposed control method regards each port as a subsystem regardless of the coupling through the HFL, which can be easily extended to multi-port systems which have HFL. Finally, the effectiveness of the proposed reactive-power optimal control strategy is validated on a hardware-in-the-loop-based 4-port MMAB converter.

Phase-shift modulation has been widely adopted in dual active bridge (DAB) converters due to its simple implementation and great system performance. However, modular multiactive bridge (MMAB) converter, a multiport version of DAB, has poor efficiency performance under traditional single phase-shift control and lacks a comprehensive analysis of multiphase-shift modulation. In order to improve the efficiency under unfavorable working conditions, this article proposes a universal phase-shift (UPS) modulation scheme for MMAB as well as multiactive bridge converters where the port numbers can be flexibly scaled. A time-domain mathematical model under the UPS scheme is obtained by a decomposition-and-superposition modeling method. Based on the model, an optimization strategy, aiming at full zero-voltage-switching turn- on actions and minimized root-mean-square inductance currents, is proposed to reduce the overall power loss. The proposed optimization strategy takes simplicity, scalability, and optimization performance into consideration, and its optimization effects can be regarded as a global optimum. Finally, a four-port laboratory prototype of MMAB converters has been constructed. The effectiveness and superiority of the proposed UPS control strategy within the full working range have been verified by experimental results.

In modular multi active bridge (MMAB) converters which are inherently coupled among dc ports, single phase-shift (SPS) control has been widely adopted due to its simplicity in implementation and neglect of coupling characteristics in control algorithms. However, under SPS control, the converter may have unfavorable system efficiency performance, especially when voltage conversion ratios of ports mismatch. To improve the efficiency, this paper proposes a common phase-shift (CPS) control method for a generalized MMAB or multi active bridge converter. A comprehensive operation analysis of MMAB converters under CPS control with switching characterization of power semiconductors has been carried out. Besides, an overall power loss model is derived, with main electrical components and their power-loss behaviors taken into consideration. Moreover, an optimal strategy aimed at power loss optimization is proposed to improve the efficiency of the converter. Finally, a four-port experimental MMAB converter prototype has been constructed. The experimental results and tested efficiency curves have verified the feasibility and effectiveness of the proposed CPS control.

Operation condition monitoring of power electronics’ systems can improve analysis visibility for device administrators and researchers. However, the current sensor-based monitoring methods have limitations in accurately monitoring variables at multitimescales. This article presents a real-time digital mapped (RTDM) method for the sensorless multitimescale operation condition monitoring in power electronics’ systems using field-programmable gate array simulators. The mathematical models of power converters are deployed in the simulator considering multitimescale characteristics. Both the digital simulator and the physical power converter are controlled by the same control signals, allowing the simulator to map the accurate operation conditions of the power converters without additional physical sensors. The RTDM method can monitor variables on the switching period timescale to the system transient timescale due to the consideration for the ideal switch modeling of the semiconductor switch. The effectiveness of the proposed method is demonstrated using a 30 kW dual active bridge converter as an example, through the integration of an experimental prototype and a simulator to create an RTDM platform. This method offers an easy and sensorless way to monitor multitimescale variables in power electronics’ systems, providing a more comprehensive and visual analysis of their operation.