Liming Shi

Harmonic-Based Phase-Shifted Control of Inductively Coupled Power Transfer

It is a key issue for inductively coupled power transfer system that the output power is regulated with high efficiency especially over a wide load range. In this paper, a novel harmonic-based phase-shifted control method is proposed. With this method, the harmonic component other than the fundamental component of the resonant inverter output voltage is employed to regulate the transferred power. The output power is controlled by changing the phase-shifted angle of the inverter. Different from the conventional approaches, the switching frequency in this method is much lower than the resonant frequency, meaning much reduced switching losses. The operation principle, switching strategy, and dead-time effect have all been presented. Experimental results demonstrate that the proposed power control method can achieve significant performance improvement at the light-load condition.

The Weighted Vector Control of Speed-Irrelevant Dual Induction Motors Fed by the Single Inverter

To improve the control performance of unbalanced load of parallel-connected dual induction motors fed by a single inverter, a novel control strategy based on the weighted vector control is proposed. In this paper, a weighted flux linkage vector model of dual induction motors is developed, and then the control expressions of weighted rotor flux linkage and summation torque of dual speed-irrelevant motors are derived. The weight value of vector control for dual induction motors in unbalanced load is distributed automatically according to the torques and motor speeds. The experimental results in multiple induction motor platforms prove that the proposed method can start in a wide load range, especially at heavy unbalanced load and improves the performance of dynamic response with a sudden change of unbalanced load.

Stability Analysis for Direct Torque Control of Permanent Magnet Synchronous Motors

Direct torque control (DTC) is an effective control strategy for permanent magnet synchronous motor (PMSM). However, the asynchronization between stator flux linkage vector and rotor flux linkage vector may happen and this may result in unstable operation or serious vibration. This paper describes several principles that should be taken into account when we design the DTC system for PMSM. For instance, the choice of stator flux linkage, the effect of zero-voltage vector, the limitation for torque reference, and so on. The simulation results confirm the correctness of the stability analysis

Levitation control scheme for the hybrid Maglev system based on neuron-PID control

The Maglev train can reach the speed of 500 km per hour, and it is one of the most promising conveyance tools, which has the advantages of high speed, low noise, high security and so on. The levitation control scheme is the key problem of the Maglev system, and the propulsion system has to be designed on the base of stable levitation. To lower the suspension power, permanent magnets are added into the levitation system to assistant the magnetic coil. Its air gap is enlarged and the energy consumed by the levitation subsystem is significantly reduced due to the permanent magnets. Novel scheme combined neuron control and the conventional PID control is proposed, which has good online learning ability. The adaptive neuron is used to regulate the parameters of the PID controller by self-learning and associative searching method according to the dynamic characteristics of the control plant. The suggested strategy is verified by experiments, which is model-free, and can realize fast, precise and flexible suspension. Its performance is better than that of state controller.

A novel control method of resonant inverter for movable contactless power supply system of maglev

Movable contactless power supply (MCPS) is superior to traditional contacting power rails for the high-speed maglev trains. The resonant converter is normally preferred so as to improve the power efficiency of MCPS. But this MCPS is characterized with variable load parameters. This paper analyzes the characteristics of resonant converter with frequency and system delay. A direct resonant frequency tracking algorithm is developed to get the resonant current frequency and compensate the system delay, which could minimize switching losses and device stress. The validity of algorithm is verified by simulation results used to MCPS of high-speed maglev trains.

Unbalanced thrust control of multiple induction motors for traction system

Multiple induction motors (IM) fed by a single inverter are generally applied in traction system, such as rail transportation. The characteristics of the thrust difference are theoretically analyzed firstly. A novel control strategy based on weighted voltage vector is proposed to relieve the thrust difference in each wheel with induction motor. The essence of weighted voltage vector is to select suitable slip for the rotor flux oriented vector control. The weights of each voltage vector are calculated by the thrust regulator to obtain new voltage vectors. Results show that unbalanced thrust can be reduced more than 50% comparing proposed method to conventional method. This strategy can be applied in practical traction system driven by multiple induction motors.

A novel field oriented control for parallel-connected double-sided LIM

The long primary double-sided linear induction motor (LIM) has been used in industry. To improve the system efficiency and reduce the drive inverter capacity, the primary parallel connection with segment powered drive has been adopted in the drives consist of long primary double-sided LIMs. But, the LIMs parameters may vary with the position of the secondary, and it results in the thrust ripple. In this paper, a deduced voltage-current model is derived by simplifying the multi-motor stator flux into an average one and then the equivalent circuit with average parameter is obtained. Besides, this paper proposes a novel direct thrust control (DTC) based thrust feedback control method with thrust observer to eliminate the effects from motor parameters changes and to obtain a stable output thrust during acceleration. The control results verify the effectiveness of the method during the load acceleration.

Characteristics analysis of single-sided ironless linear synchronous motor based on permanent magnet Halbach array

This paper presents power angle characteristics of single-sided ironless linear synchronous motor (LSM) based on permanent magnet Halbach array. Sinusoidal magnetic field of air gap is established by magnet Halbach array and normal attraction can be decreased by ironless coil. The problem is pole pitches of primary and secondary are different, that effects power angle characteristics. Besides, normal attraction is produced when magnet Halbach array above the steel sleepers. So linear analytic method and finite element method is adopted to analysis these complications, a method of static scanning point is presented to calculate power angle characteristics when pole pitches are unequal, some important conclusions of this type motor are obtained. Experimental results on a 200KW type motor verify the conclusions and accuracy of calculation.

Comparison analysis of loss calculation methods and measurement techniques in power electronics and motor systems

Analyzing and measuring power losses of power electronics and motor system are of great importance. This paper compares several methods for power loss calculation and measurement. A general scheme for modeling losses of power semiconductors is given. As for the harmonic losses of converter-fed motors, an effective FEM process is described. The constraint of conventional calorimeter is discussed and a simplified calorimetric method is introduced.

Characteristics analysis of multiple in-wheel-induction-motors drive system

High speed maglev maintenance vehicle (MMV) is propelled by multiple in-wheel-induction-motors drive system (IWIM). This paper analyses the characteristics of multiple IWIM drive system for MMV. An electromechanical simulation platform is developed in our Lab. Adaptive flux observer is applied to provide speed sensor-less vector control for multiple IWIM drive system. The influences of different wheel radius, motor parameters and control schemes are simulated by setting different coefficient of radius and motor parameters. It shows that radius difference may seriously cause speed and traction force difference, and motor parameter difference may deteriorate dynamical performance. The coordinating motor control can improve the performance of multi-motors with less hard and software increase.