This paper presents the short-circuit behavior and degradation of 650-V/60-A E-mode GaN HEMTs under various test conditions. First, the paper introduces the basic information of device, test method, and platform. Subsequently, single pulse, 10 $\mu$ s short-circuit tests are performed from 50 V to 400 V to extract the typical behavior of devices. Both short-circuit current self-regulation phenomenon and quick failure have been observed. Simultaneously, the device short-circuit behavior at various gate drive voltages and temperatures have been explored to identify the protection condition. Then, repetitive short-circuit tests have been performed to reveal device degradation trends. As a result, their output current reduction and gate-to-source threshold voltage shift have occurred. This work shows the critical need to improve the robustness of this type of GaN HEMT from the device and circuit perspectives.

When a 4-Level hybrid clamped converter operates at low frequencies, the high load current causes significant voltage fluctuations among the capacitors in the DC link. A mathematical model is developed to clarify the mechanism of excessive capacitor voltage fluctuations. An improved common mode voltage injection algorithm is proposed and integrated to the overall control method. With the algorithm applied, the voltage fluctuation minimization of the DC-link capacitors and the dynamic voltage balancing capability are investigated. Both simulation and experimental results show the effectiveness of the proposed algorithm, with a voltage fluctuation reduction over 50%.

Wireless power transfer (WPT) holds great potential to achieve strong galvanic isolation, compact size, and low parasitic capacitance in the power supply of gate driver. In this paper, a wireless power supply is designed and analyzed for high voltage gate driver application. The performance of the power supply in terms of power delivery, parasitic capacitance, and driver output is explored in the functional test. Meanwhile, electromagnetic interference (EMI) is investigated in both frequency and space distribution based on measurement and simulation. The experimental results demonstrate that the prototype successfully delivers power for gate driver board with an 80 mm air gap while the maximum transfer efficiency is kept around 90%. The parasitic capacitance brought by the air gap is only 1.72 pF, which significantly increases common mode impedance. Radiated EMI affects the frequency span around the resonant frequency, and its distribution regularity in space is clearly displayed by field curves in horizontal axis and vertical axis.

A procedure to calculate the maximum torque to current ratio operating conditions for the inverter-fed induction machine is proposed. The proposed procedure minimizes the finite element analysis computation load by identifying the variation range of stator current and slip frequency for the entire torque-speed map. Thus, the total calculation time for machine steady state performance estimation can be significantly reduced. The effectiveness of the proposed procedure is validated by experiment.

The permanent magnet vernier machine (PMVM) is featured with high-torque density due to the magnetic field modulation effect. At present, the analysis of the magnetic field characteristics and harmonic torque of PMVM is mainly derived from the perspective of permanent magnet (PM) field modulation. The research on armature magnetic field modulation is very limited. Therefore, this article studies the magnetic field modulation from the perspective of armature magnetic field, revealing the relationship between armature magnetic field and output torque. The process of armature magnetic field modulation and PM magnetic field modulation is compared and analyzed. It was found that in PM field modulation, the fundamental wave of PM magnetomotive force is modulated into different spatial harmonics with the same frequency; whereas in armature magnetic field modulation, the harmonics of different armature magnetomotive force are converted into temporal harmonics with identical frequency. Then, based on the perspective of armature magnetic field modulation, a new PMVM is proposed to improve torque. Compared with the existing uniform split teeth topology, the torque of the new PMVM is increased by 32%. Finally, a prototype of the machine has been manufactured and tested to verify its effectiveness.