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.

This letter proposes an improved scheme for torque ripple reduction of permanent-magnet synchronous machines (PMSMs) considering dc-link voltage utilization. Different from the previous methods, both q -axis and d -axis harmonic currents are optimized and injected. Specifically, the appropriate q -axis harmonic current reference is obtained through harmonic analysis of PMSM. Furthermore, the harmonic voltage control loop is included to generate the d -axis harmonic current reference, which can ensure that the magnitude of the voltage vector satisfies the maximum output voltage circle under the voltage constraint. The virtual signal and multiple reference frame-based proportional-integral controllers are employed to regulate the harmonic components. The effectiveness of the proposed method is validated by experimental results.

Low-altitude aviation is rapidly emerging as a transformative solution for next-generation transportation, driving significant advancements in electric propulsion systems. As a core subsystem in electric aircraft, electric propulsion systems require comprehensive evaluation of their technological progress, ongoing challenges, and future opportunities to support the development of low-altitude aviation. Unlike land vehicle applications, aircraft propulsion systems demand safety-critical designs governed by stringent operational constraints. This review identifies three critical metrics for such systems: power density, operational reliability and fault tolerance, and thermal management efficiency. While existing studies often address these metrics individually, their interdependencies are not well explored. To bridge this gap, this review systematically investigates state-of-the-art solutions, benchmarks their limitations under flight-critical conditions, and establishes correlations between technological advancements and operational requirements. Furthermore, it highlights future research directions by identifying emerging methodologies. As low-altitude aviation approaches scalable deployment, this paper aims to serve as a technical reference to support the safe and effective development of aerial propulsion technologies.

Torque ripple reduction based on harmonic current injection has been widely applied to surface-mounted permanent-magnet synchronous machine (SPMSM) drive systems. However, additional voltages are typically required for harmonic injection, and the dc-link voltage limit should be considered in practical drive systems. This article proposes a novel harmonic control for SPMSMs in which the torque ripple reduction and high dc-link voltage utilization can be achieved simultaneously. The influence of harmonic injection on voltage utilization is investigated in detail. In addition to injecting the appropriate q -axis harmonic currents to suppress torque ripple, the d -axis harmonics are also optimized and injected. The geometric principle is applied to obtain the analytical expression for the optimal d -axis harmonic voltage, which can minimize the maximum magnitude of the stator voltage vector. Since the reference harmonic voltage is directly calculated in accordance with the analytical solution, the implementation complexity of harmonic voltage regulation is relatively low. Moreover, a virtual dual three-phase system with auxiliary currents is developed to decompose the fundamental and harmonic currents without low-pass filters, thus avoiding additional delay in the control loop. Finally, the experimental results are provided to verify the validity of the proposed method.

In the permanent-magnet synchronous machine (PMSM) drive system, the adoption of silicon carbide (SiC) devices brings up new challenges, such as overvoltage, electromagnetic interference emission, and bearing current. To surmount these barriers, the LC filter designed as the sine wave filter can be introduced into the machine drive system. However, filter and stator inductance can create unwanted electrical resonance issues. For the LC -equipped PMSM drive system, there are two main factors that cause the drift of resonant frequency and change of stable region: (1) synchronous coordinate transformation with variable fundamental frequency, (2) parameter variations due to the magnetic saturation effect. In this paper, the deviation of resonant frequency caused by coordinate transformation is discussed. Then, the inherent damping effects and stability range in the rotating reference frame are derived in detail. Furthermore, considering the parameter mismatch disturbances, an active damping method based on the enhanced notch filter is presented, of which notch frequency is designed lag behind the nominal resonant frequency. The accurate discretization method and theoretical stability analysis in discrete z -domain are conducted. The experimental results are presented to verify the effectiveness and robustness of the proposed analysis and method.

Permanent-magnet synchronous machine drive with sine wave filter has features of low insulation stress and current harmonics. However, the filter can affect the current control of machine. Specifically, the increased axes cross-coupling degrades the response performance in the transient state, and the introduced resonant frequency oscillations can make the system unstable. To solve the issues, a complex vector frequency-domain model of LC -equipped permanent-magnet synchronous machine drive is established in this article. Moreover, a quantitative index related to the symmetrical extent of double-sided frequency responses is introduced to evaluate the performance. A decoupling strategy based on the modified complex vector controller is proposed and compared against conventional methods in terms of decoupling performance and parameter robustness based on the aforementioned evaluation index. Further, an active damping method based on virtual impedance in parallel with the stator inductance is proposed to suppress the resonance. The quantified double-sided frequency-domain analysis is performed to illustrate the relationship between cross-coupling and system stability. Then, the systematic co-design procedure of decoupling controller and active damping link in the z-domain is proposed. Finally, the experimental results show that the proposed scheme can improve the overall control performance in both transient and steady states.