Applying high-frequency power devices, such as gallium nitride (GaN) semiconductor devices, to the motor drive can significantly reduce system volume, losses, audible noise and increase system power density. In this paper, an LC filter designed as a sine wave filter is introduced into the servo drive system based on the GaN power device. An undamped method with variable delay time is proposed to solve the electrical resonance issue caused by LC filter and stator inductor. Detailed stability analysis is conducted, and rules on parameter tuning are provided. With additional proper time delay, the system can be stable without any extra sensors or power losses. Besides, this method is suitable for resonance suppression at variable switching frequency. Moreover, a wait-free and phase-continuous spread spectrum frequency modulation is applied to solve the issue of electromagnetic interference (EMI). The field-programmable gate array (FPGA) is used to achieve high control bandwidth when implementing the control algorithm. Finally, the ideal sinusoidal drive and low conducted EMI of permanent magnet synchronous motor (PMSM) is realized. Experiments on a 100 kHz GaN inverter with LC filter verify the validity of the proposed design and method.

The thyristor level is the basic unit of ultra-high-voltage and extra-high-voltage direct current (DC) converter valves, and its main-circuit parameters are important indicators for characterizing the health status of converter valves. To meet the demand for efficient detection of converter valve thyristor levels, this paper proposes a parameter inversion method for converter valve thyristor levels by combining the time-frequency-domain features of valve voltage and current, temporal characteristics of feedback signals from the thyristor-level monitoring unit, and a Grey Wolf Optimizer–Backpropagation Neural Network (GWO-BPNN). First, a six-pulse converter valve circuit simulation model is established. Based on this model, the original dataset is generated using the Latin hypercube sampling (LHS) method. Wavelet packet decomposition is then used to extract time-frequency-domain features, and dimensionality reduction is carried out by comparing the coefficient of variation and explained variance ratio so as to obtain input data suitable for neural network training. A BP neural network is then trained, and the network parameters are optimized using the Grey Wolf Optimizer to improve the accuracy and convergence speed of parameter inversion. Simulation comparison results show that the GWO-BP method is more efficient than the state equation method and is suitable for efficient inversion of damping parameters in multi-level thyristor systems. After GWO optimization, the maximum inversion errors of both parameters are reduced to below 5%. Compared with BP, GA-BP, and PSO-BP, the proposed GWO-BP model provides the best overall balance between resistance-inversion accuracy and training efficiency. By further incorporating feedback feature signals, the inversion error can be reduced to 1%. The proposed method provides a new technical route for efficient detection of thyristor converter valves and has broad application prospects.

To address the issues of temperature rise accumulation, structural vibration, and air gap degradation that occur during the long-term operation of Anode Saturable Reactors used in high-voltage direct-current (HVDC) converter valves, electromagnetic-structural and electromagnetic-thermal multi-physics coupling analysis models were established using COMSOL Multiphysics software. The monitorable quantities capable of characterizing defects in Anode Saturable Reactors were systematically investigated from three aspects: vibration signals, thermal signals, and electrical signals. First, a one-way electromagnetic-structural coupling vibration model was established to analyze the vibration characteristics under normal operation, loose core conditions, and polyurethane hardening conditions. Second, an electromagnetic-thermal coupling model was established to compare the core loss and temperature rise distribution between the defect-free condition and the condition with reduced air gap defects. Finally, the effects of air gap reduction on electrical parameters such as unsaturated inductance and frequency sweep impedance were analyzed. The results indicate that the dual-peak characteristics and residual vibration of vibration signals can reflect the looseness of the iron core, while thermal aging of the polyurethane filling material further weakens the system’s damping capacity, intensifying vibration impact on the core and structural components. A reduction in air gap leads to an increase in local core loss of approximately 47.9%, giving rise to local hot spots. For the shell-type ASR investigated in this study, the temperature rise of the reactor casing remains almost unchanged. The unsaturated inductance and the impedance value near 10 kHz are highly sensitive to air gap variations and can serve as effective feature quantities for online monitoring.

The reliability of the characteristics of high-voltage (HV) thyristors is related to the operational safety of the entire HVDC project. In order to investigate the degradation mode of thyristors in HVDC projects more realistically, aging experiments were conducted on HV thyristors under the combined action of sinusoidal half-wave voltage and current in a simulated operating environment. Experimental results show that the on-state voltage, reverse recovery characteristics, and reverse leakage current of thyristors have all degraded to varying degrees during the aging process. The main failure mode of thyristors can be summarized as the failure of the reverse blocking characteristic. Microstructural characterization of failed HV thyristors is conducted to explain the degradation mechanisms, including device surface morphology and elemental composition analysis. Observations have shown that the failed thyristor silicon wafer has been burned and hollowed out, accompanied by copper impurities, and significant thermal breakdown has occurred at the edge of the anode surface of the chip. Defects in chip structure and the invasion of impurities can lead to a decrease in the minority carrier lifetime of materials, which is an important factor in the characteristics of semiconductor devices. On this basis, further simulation research is carried out to conclude that the shortening of the minority carrier lifetime of the thyristor will distort the carrier space distribution, resulting in the rise in the on-state voltage. Meanwhile, the carrier transport capability decreases, leading to a decrease in the reverse recovery speed. The energy released during the rapid generation and recombination of carriers is one of the main reasons for the failure of blocking characteristics. This work provides comprehensive insights into the failure modes and mechanisms of HV thyristors.