Compared to a long-stator linear synchronous motor (LLSM), a long-stator doubly-fed linear motor (DFLM) exhibits two distinct advantages for high-speed maglev application: 1) It has two additional degrees of freedom with both the frequency and the phase angle of the mover to improve its control accuracy and dynamic responses; 2) It can use the slip power to feed the mover contactlessly and directly. In order to achieve the propulsion, the levitation, and the contactless power transfer through the common air-gap magnetic field, the “quasi-synchronous operation (QSO)” principle of the DFLM is proposed for high-speed maglev train. Based on the DFLM modeling and distinctive constraint analysis for high-speed maglev application, the performance evaluation of the DFLM is further investigated. To validate the feasibility of the DFLM application for high-speed maglev train, a unit DFLM prototype is designed and tested, and the corresponding simulation studies of the QSO control structure are provided with the comparison to the LLSM system.

Torque ripple suppression plays a crucial role in the electric drive systems of electric vehicles. This article proposes a torque ripple suppression method for interior permanent magnet synchronous machine drive systems based on synchronous optimal pulsewidth modulation (SOPWM). First, the relationship between current harmonics vectors and switching angles of SOPWM is derived in a multisynchronous reference frame. Then, the torque and current harmonics balance equation is introduced, revealing current harmonics on the d-axis have a smaller effect on torque ripple. A weighting coefficient ${\bm{\mu }}$ is designed and incorporated in the optimization function to acquire the inverter switching angles. The method shifts the current harmonics on the q-axis to the d-axis, effectively suppressing torque ripple. The effectiveness of the proposed SOPWM method is validated through both simulation and experimental results.

Within variable air-gap linear motors, such as those used in maglev trains, levitation and thrust forces are both realized through the common air-gap magnetic field, and thus they are intrinsically coupled. Additionally, nonidealities such as cogging, end effect, and saturation influence the thrust and levitation performance and result in force fluctuation. In this article, an accurate modeling method for a variable air-gap linear doubly-fed induction motor based on the magnetic coenergy reconstruction is proposed, where the effects of magnetic saturation, variable air-gap, and spatial harmonics are taken into consideration. This method uses a unified dataset to describe thrust, levitation, and their fluctuations. Furthermore, an adjustable air-gap linear motor prototype is designed and constructed. Bench tests are conducted to verify the proposed model.

In this article, a quasi-synchronous operation (QSO) of a doubly fed linear motor (DFLM) is proposed to achieve accurate regulation of both the propulsion and the contactless power transfer. A new control structure is proposed to achieve the loose coupling control between the stator side and the mover side, where the scalar control is used for the stator side controller (SSC), and the field-oriented control (FOC) is adopted for the mover side controller (MSC). The SSC and the MSC are with “frequency coupling,” which enhances the reliability of the whole control system with less information exchange between the SSC and the MSC. The effectiveness of the proposed design is validated through both simulation and experimental studies.