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To improve the robustness and dynamic tracking performance of the stator current control for the long stator linear synchronous motor (LSLSM) used in high-speed maglev train traction system, a composite current control strategy combining a sliding mode current controller (SMCC) and a sliding mode disturbance observer (SMDO) is proposed in this article. First, the LSLSM mathematical model in double feed mode is optimized. Then, an SMCC is designed based on the model. An improved stability criterion is proposed and the SMCC switching gain is obtained quantitatively to meet the current following speed required for the stator changeover process. As disturbance factors, parameter perturbation of the LSLSM and the stator changeover will bring about transient current fluctuations and chattering. Therefore, an SMDO is designed to estimate the disturbances and perform feed-forward compensation for the SMCC, thereby improving the robustness and suppressing the current chattering. Finally, the hardware-in-the-loop experiments verify the effectiveness of this strategy and compare it with the traditional current control strategy. [ABSTRACT FROM AUTHOR]

This paper compares the machine learning algorithm‐based prediction methods for the traction characteristics in linear traction induction motors operating at common working conditions, i.e. different slip and running velocity, with a symmetric or asymmetric secondary. These models provide a method for obtaining the dynamic characteristics in the motor that considers nonlinear effects. First, some analytical results for the prototype machine under different working conditions is calculated. Second, classification and feature extraction of traction characteristics results including thrust, transversal and vertical forces is made according to the different slip, running speed and lateral secondary displacement, and the results set is divided into training sets and test sets. Third, the prediction model established by different machine learning algorithms are analyzed and compared in principle. These algorithms in this paper mainly contain: artificial neural networks (ANNs), linear regression (LR), symbolic regression using GP, k‐Nearest Neighbour (kNN), random forests (RFRs). The machine learning algorithm‐based prediction methods are trained with the training set, and then the verified with the test set. Finally, this paper discusses the most optimal model for predicting traction characteristics. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The traction characteristics of a linear induction motor (LIM) are quite different from those of a rotary induction motor (RIM) due to the parameters variations caused by longitudinal end effect, transversal edge effect, and so on. The conventional indirect field-oriented control (IFOC) scheme of the LIM based on flux attenuation compensation is not suitable for high-power traction drives due to the deviation of current and thrust characteristics. In this paper, the traction characteristics of the LIM and RIM are compared from different perspectives. The performance of different control schemes of the LIM is discussed with consideration of the output limitations of the inverter. The IFOC scheme based on optimized slip frequency for the LIM is proposed. By dynamically adjusting the d- and q-axis reference currents and corresponding closed-loop control, the output thrust of the LIM is shifted close to the peak operation point. The average output thrust of the LIM can be increased without increasing the primary current, which can reduce the influence of end and edge effects on thrust performance. The effectiveness of the proposed scheme is verified by both simulation and experiments on an LIM metro vehicle. [ABSTRACT FROM AUTHOR]

For railway traction drives, the active front end usually adopts a single-phase rectifier. However, the dc-link voltage of this single-phase rectifier contains a second-order fluctuating component due to the fluctuation of the instantaneous power at both the ac and dc sides. Fed by the fluctuating dc-link voltage, the traction motor suffers from severe torque and current pulsation. The hardware solution with an additional LC resonant filter is simple, but it will reduce the power density of the system. An alternative solution is to eliminate the beat component in the stator voltage/current through modulation ratio or frequency compensation. However, it is difficult to achieve high performance for the conventional feedforward method. In this paper, an improved closed-loop torque and current pulsation suppression method is proposed, which can eliminate the q-axis current pulsation component in the field-oriented control system through frequency compensation. The torque pulsation suppression is also achieved automatically. Simulation and experimental results show that the proposed scheme can effectively reduce the torque and current pulsation in various operation modes compared with the conventional feedforward method. [ABSTRACT FROM AUTHOR]

Traditional seven-level active neutral-point-clamped (ANPC-7L) converters suffer from the problems of dynamic voltage balancing in series switches and multilevel voltage jumping of phase output voltage during switching states transition. This paper presents a novel ANPC-7L topology with auxiliary commutating branches and elaborates on its commutating strategies. The presented topology and its commutating strategies completely resolve the two problems mentioned above. The validity of the presented topology and its commutating strategies are verified by experimental results from a 380 V/5 kW ANPC-7L converter. [ABSTRACT FROM AUTHOR]

Voltage balance control of dc capacitors is the key problem of multilevel diode-clamped converters (DCCs). In this paper, a novel hybrid voltage balance method is proposed for five-level DCCs. First, to balance the upper or lower two capacitors, a novel flying-capacitor-based voltage balance circuit (VBC) is proposed, and the time-domain average model of the VBC is established. Then a state-machine-based control strategy is developed to balance capacitor voltages as well as to limit overcurrent of inductors in a transition process. To keep the midpoint voltage stable, a zero-sequence injection method is proposed, which inherently ensures the improved modulation signals locate within the linear modulation ranges. With the flying capacitor transferring energy between dc capacitors, the device voltage stresses of the VBC are equalized, and the steady-state current ripples of the inductors are much smaller than those of the conventional chopper-based VBCs, which can reduce the volume and weight of the inductor. Simulation and experimental results for both inverter and rectifier operations prove that the proposed hybrid voltage balance method can balance dc capacitors of five-level DCCs in both steady states and transition states, and the inductor currents of VBCs can also be restricted within safe ranges. [ABSTRACT FROM PUBLISHER]