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In the high-speed maglev system, high-power multiple three-level active neutral point clamped rectifiers are connected in parallel to the grid via phase-shifting transformers. Due to the low switching frequency and long dead time, the rectifiers produce rich low-order harmonics, which will deteriorate the power quality. In this article, harmonic current suppression strategies based on improved carrier phase-shifted (CPS) PWM and the extended state observer (ESO) are proposed. Aiming at the minimum total harmonic distortion of the grid-side current, the universal guidelines for the optimal CPS angle with the number of rectifiers are proposed. To suppress the low-order harmonics, multiresonance controllers are introduced into the disturbance estimation loop of the ESO, whose output is used for feed-forward compensation. The effectiveness of the strategies is verified by hardware-in-the-loop simulation and experiments.

The excitation pole of the long stator linear synchronous motor (LSLSM) used to drive the high-speed maglev train is also used as the suspension electromagnet, which makes the adjustment of the suspension system affect the excitation flux linkage of the motor when the train is running at high speed, resulting in significant nonperiodic traction force fluctuations. This article proposes a traction force fluctuation suppression strategy based on the flux linkage observation. First, based on the mathematical model of the LSLSM in double feed mode, the voltage equation based on the new extended back electromotive force is derived, which is less sensitive to the changes of parameters, load current, and speed, so that the flux linkage can be estimated more accurately. Then, to meet the high dynamic requirements of flux linkage observation at high speed, a sliding mode flux linkage observer is designed and a design method of the adaptive sliding mode gain is proposed to achieve fast convergence of the system. Finally, the stator reference current required to suppress the traction force fluctuation is calculated. Hardware-in-the-loop experiments verify the effectiveness of the strategy.