The output voltage of inverters is influenced by nonlinear factors such as dead time and voltage drops, injecting low-order harmonics. This results in fifth and seventh harmonic distortions in the stator current, causing periodic torque ripples and significantly affecting the control precision of Permanent Magnet Synchronous Motors (PMSMs). To address this issue, this paper proposes a control strategy named quasi-proportional-resonant sliding mode control (QPR-SMC). Initially, sliding mode control is employed as the current controller to enhance disturbance rejection capability and provide a rapid dynamic response. Subsequently, a quasi-proportional-resonant controller is introduced to extract the sixth harmonic component from the current, which is then used as a compensation term for the sliding mode control surface. Finally, the current tracking error and the compensation term are combined as inputs to the sliding mode control law, forming a current error-proportional resonant-sliding mode control surface. This approach enhances the harmonic suppression capability of the system. The results demonstrate that the proposed method effectively reduces the fifth and seventh harmonic components in the three-phase current and mitigates motor jitter by suppressing the sixth harmonic in the d–q coordinate system.

To address the issue of mechanical resonance frequency detection in dual-inertia servo systems, this paper proposes an online identification method for mechanical resonance frequency using a low-pass filter and cascaded second-order generalized integrator—frequency-locked loop (LPF-CSOGI-FLL). Initially, the cascaded second-order generalized integrator—frequency-locked loop (CSOGI-FLL) is employed to eliminate the interference of direct current (DC) bias in resonance frequency identification. From a dual-stage structural perspective, the first second-order generalized integrator (SOGI-FLL) acts as a band-pass pre-filter to extract the mechanical resonance signal from the signal to be tested. The second SOGI-FLL generates a signal with equal amplitude and frequency to the mechanical resonance and obtains the frequency of the resonance signal through the frequency-locked loop. Subsequently, a low-pass filter (LPF) is applied to the frequency feedback loop of the second-stage SOGI-FLL, effectively reducing the oscillation of the estimated frequency. Finally, combining the CSOGI-FLL with an LPF forms a novel structure, namely, LPF-CSOGI-FLL. The results demonstrate that the proposed method significantly improves the detection accuracy of mechanical resonance frequency under various conditions. Compared to traditional offline techniques, this method overcomes the impact of resonance frequency drift and enhances system stability.

To improve the synchronization accuracy of dual motors under external disturbances, this paper proposes a cross-coupling control strategy based on an improved global fast terminal sliding mode control (GFTSMC) and disturbance observer (DOB). In practical applications, dual-motor systems are often affected by external disturbances, leading to synchronization errors between the motors, which in turn affect the system’s stability and accuracy. First, for single-motor control, this paper uses the improved GFTSMC method to design a speed loop, enhancing the tracking accuracy and dynamic response of the individual motor by optimizing the sliding surface. Then, the improved GFTSMC is combined with a cross-coupling strategy to effectively solve the synchronization problem of dual motors. The cross-coupling strategy coordinates the operation of the two motors, reducing the speed deviation between them, thus improving synchronization accuracy and enhancing the system’s disturbance rejection capability. Moreover, the DOB is used to precisely estimate the frictional torque, and compensating for these disturbances improves the system’s robustness and stability. The results show that the proposed control method significantly improves the speed synchronization of the dual motors and exhibits excellent dynamic performance, effectively coping with complex external disturbances.