Baodong Bai

Novel Direct Torque Control Based on Space Vector Modulation With Adaptive Stator Flux Observer for Induction Motors

This paper describes a combination of direct torque control (DTC) and space vector modulation (SVM) for an adjustable speed sensorless induction motor (IM) drive. The motor drive is supplied by a two-level SVPWM inverter. The inverter reference voltage is obtained based on input-output feedback linearization control, using the IM model in the stator D-Q axes reference frame with stator current and flux vectors components as state variables. Moreover, a robust full-order adaptive stator flux observer is designed for a speed sensorless DTC-SVM system and a new speed-adaptive law is given. By designing the observer gain matrix based on state feedback H∞ control theory, the stability and robustness of the observer systems is ensured. Finally, the effectiveness and validity of the proposed control approach is verified by simulation results.

Multiobjective Optimization Based on Response Surface Model and Its Application to Engineering Shape Design

A combined method is presented to deal with the practical engineering problems of multiobjective optimization. The nondominated sorting genetic algorithm II (NSGA-II) is adopted as a searching tool for the Pareto-optimal solutions, which is improved by using a new crossover operator. The response surface model (RSM) based on the radial basis function is used to reduce the computational effort. The application of the method to the shape optimization process of a permanent magnet assembly for magnetic resonance imaging devices is described, and the numerical results show that the method is feasible and efficient for the engineering shape optimization.

A Novel Optimal Design Method of Passive Shimming for Permanent MRI Magnet

In magnetic resonance imaging (MRI) magnets, field shimming technique is, in general, necessary to increase the field homogeneity in imaging region to an acceptable level after manufacturing. This paper presents a novel passive shimming method using permanently magnetized shimming pieces. In the method, the shimming design is modeled as an integer programming problem, and the distribution of shimming pieces is optimized. Through an application to a 0.3-T permanent magnet MRI system, the optimally designed shimming pieces are proven to improve the field homogeneity from 1456 to 784 ppm after just one iteration of shimming courses is carried out.

Identification of the Jiles-Atherton model parameters using simulated annealing method

This paper presents a method and the experimental measurement system for the determination of Jiles-Atherton model parameters of the 30ZH120 electrical steel sheet. The paper utilities Epstein Square devices to proceed the experiment and measurement on a group of hysteresis loops of some certain transformer which use the 30ZH120 electrical steel sheet under two different lap ways. The approach relies on simulated annealing optimization method in order to minimize the error between the measured and modeled hysteresis curves and yield the best five Jiles-Atherton model parameters. A convenient program based on the Simulink platform is developed that can identifies the J-A model parameters automatically from experimental saturated hysteresis loop which is used to model the nonlinear characteristics of the electrical steel sheet. Research shows that Simulated annealing Optimization method get satisfactory results.

Suppression for Discharging Bearing Current in Variable-Frequency Motors Based on Electromagnetic Shielding Slot Wedge

High-frequency current in the bearings of variable-frequency motors coupled with their shafts is a common issue that will shorten the bearings lifetime ultimately. A new method, which could be used to suppress high-frequency discharge bearing current, was proposed in this paper. In this method, an electromagnetic shielding slot wedge (ESLW) was used to reduce the capacitive coupling between the stator windings and the rotor. The electromagnetic coupling resulted from the common-mode voltage could be blocked by this electromagnetic shield layer. In addition, the mathematical model of the suppression method was given and the high-frequency electromagnetism performance of the motor was analyzed. Finally, an experimental platform was setup and a motor was modified to evaluate the suppressing effectiveness. The shaft voltage, bearing currents, and the general features of the modified motors, with and without ESLW, were measured and compared.

A Complex-Valued Rotating Magnetic Property Model and Its Application to Iron Core Loss Calculation

This paper presents a complex-valued model when considering rotational magnetic properties of an electrical steel sheet from the viewpoint of improving the computation efficiency. The effective magnetic reluctivity and magnetic hysteresis coefficients in this model were interpolated from measured data based on a 2-D rotational magnetic property measurement system, in which the effect of higher harmonic terms of magnetic field intensity after saturation was considered. To reduce the computation error to some extent resulted from complex approximation of magnetic field quantities, the effective magnetic coefficients were expressed as the function of magnitude and direction of magnetic flux density. Considering transformer and three-phase induction motor core models as examples, the magnetic field distribution and core loss were calculated and the effectiveness of the proposed model was verified with the experimental results.

Second Order Sliding Mode Control of Flux and Torque for Induction Motor

A second order sliding mode controller is employed to realize the dynamic robust decoupling between stator flux and electromagnetic torque for induction motor in this paper. In order to guarantee electromagnetic torque and stator flux to track its reference signal strictly, the electromagnetic torque sliding mode variable and stator flux sliding mode variable were selected separately. Control law was achieved by twisting algorithm of the second order sliding mode. The discontinuous control effects on the higher differential, and eliminate the chattering phenomenon of conventional sliding mode control theoretically. Simulations results are presented to illustrate the second order sliding mode control has very strong robustness against parameters variations, simultaneously attenuates chattering effectively.

Study on the improved control strategy for PWM rectifier

This paper uses the improved feed forward control strategy to design a PWM rectifier control system. It overcomes the power network fluctuation and the effect of load disturbance. The simulink model of the system is built and compared to the traditional PWM rectifier. The result shows that the improved PWM rectifier can get a steady DC-Bus output voltage rapidly and a good robustness.

3-D FEM Analysis in Electromagnetic System Considering Vector Hysteresis and Anisotropy

This paper presents a new 3-D finite-element method for taking account of vector hysteresis and anisotropy. The proposed method combines the improved scalar Preisach model with the lagging angle between magnetic flux density and magnetic field intensity to solve vector hysteresis problem. Magnetic materials curves with any other directions to rolling direction are obtained by interpolating the measured curves to solve anisotropy problem. The method enables us to solve vector hysteresis and anisotropy problem simply. In order to validate the algorithm presented, TEAM problem32 has been analyzed using 3-D FEM as an example.

3-D Thermal Analysis and Computation of Flameproof Induction Motor

The 3-D temperature rise of flameproof induction motor are analyzed and computed by using finite element method. The heat resource of the motor, the equivalent coefficient of heat conductivity for the stator coil, and the coefficient of heat convection in the air-gap are analyzed. The complex heat exchanges between the stator and air-gap and that between the rotor and air-gap by convection are specially dealt with. The problem of the heat exchange between the stator and rotor is resolved appropriately. The temperature distribution of the motor is simulated and the result is analyzed in this paper. It is the foundation of flameproof induction motor for optimal design.