Yongdong Li

A direct torque control of induction motor based on three-level NPC inverter

The multilevel inverter has attracted great interest in the high-voltage high-power field because of its less distorted output. In this paper, a direct torque control (DTC) technique based on a three-level neutral-point-clamped (NPC) inverter is presented. In order to solve the intrinsic neutral-point voltage-balancing problem and to obtain a high performance DTC, a special vector selection method is introduced and the concept of virtual vector is developed. By using the proposed control strategy, a quick and robust response AC drive can be achieved without sensing the neutral-point voltage. The strategy can be verified by simulation and experimental results.

Application of sliding observer to sensorless permanent magnet synchronous motor drive system

This paper proposes a new control method for shaft sensorless permanent magnet synchronous motor drive systems. The rotor position and speed are estimated by using a sliding observer with only stator voltage and current measurements. The observer structure and its design method are discussed. The simulation results of the overall system are presented to demonstrate the effectiveness of the approach.<<ETX>>

Predictive direct torque control strategies of induction motor based on area voltage vectors table

In this paper, the torque ripples in low speed range of conventional direct torque control are discussed in detail, and a new vector selection table based on area voltage is proposed to control the torque and flux. In this case, two predictive control schemes of torque and flux are presented to reduce torque ripples and improve the steady and dynamic performance. Finally, simulations and experiment results are given to show the validity and the advantages of the proposed predictive schemes based on area voltage vector table.

Speed sensor-less direct torque control of an induction machine in low speed region

This paper presents a practical improvement to the conventional stator flux estimator for digital direct torque control of an induction motor, in which the predictive torque control is adapted to decrease the torque ripple. In addition, the slip frequency estimation method of speed is proposed to get a fast and rather precise speed control, leading to a high performance direct torque control of an induction motor in low speed region. Finally the experimental results show the validity of the proposed method.

Applications of induction motor drive based on DTC in railway traction

In this paper, schemes of direct torque control (DTC) for railway traction over the whole speed range are proposed. In order to observe the phase angle and amplitude of stator flux accurately, a flux observer based on a U-N model is presented. In the low-speed range, the locus of stator flux is controlled to be a circle to reduce torque ripples, and the schemes of start-up and the selection method of voltage vectors are proposed in this paper. In medium-speed and high-speed range, the locus of stator flux is controlled to be hexagonal to reduce switching frequency. In order to obtain good steady state and dynamic performance, a DTC scheme under square wave conditions in the high-speed range is proposed. All of the methods and schemes are implemented on a 500 kW converter and a 190 kW induction motor, and are proved to be effective by experiment results.