Tingna Shi

New Sliding-Mode Observer for Position Sensorless Control of Permanent-Magnet Synchronous Motor

This paper proposes a novel sliding-mode observer (SMO) to achieve the sensorless control of permanent-magnet synchronous motor (PMSM). An observer is built according to the back electromotive force (EMF) model after the back EMF equivalent signal is obtained. In this way, not only are low-pass filter and phase compensation module eliminated, but also estimation accuracy is improved. Numerical simulations and experiments with an 11-kW low-speed PMSM are carried out. The results demonstrate that the novel SMO can effectively estimate rotor position and speed and achieve good static and dynamic performance.

A New Approach of Minimizing Commutation Torque Ripple for Brushless DC Motor Based on DC–DC Converter

Brushless dc motor still suffers from commutation torque ripple, which mainly depends on speed and transient line current in the commutation interval. This paper presents a novel circuit topology and a dc link voltage control strategy to keep incoming and outgoing phase currents changing at the same rate during commutation. A dc-dc single-ended primary inductor converter (SEPIC) and a switch selection circuit are employed in front of the inverter. The desired commutation voltage is accomplished by the SEPIC converter. The dc link voltage control strategy is carried out by the switch selection circuit to separate two procedures, adjusting the SEPIC converter and regulating speed. The cause of commutation ripple is analyzed, and the way to obtain the desired dc link voltage is introduced in detail. Finally, simulation and experimental results show that, compared with the dc-dc converter, the proposed method can obtain the desired voltage much faster and minimize commutation torque ripple more efficiently at both high and low speeds.

A Novel Direct Torque Control of Matrix Converter-Fed PMSM Drives Using Duty Cycle Control for Torque Ripple Reduction

A novel direct torque control (DTC) strategy using duty cycle optimization is proposed for matrix converter (MC)-based permanent-magnet synchronous motor (PMSM) drive system, which is characterized by low torque ripples, no need for rotational coordinate transformation, and fixed switching frequency. Analytical expressions of change rates of torque and flux of PMSM as a function of MC voltage vectors are derived. An enhanced switching table is established by means of discretization and averaging, in which changes of torque and flux caused by voltage vectors are shown explicitly. Then, the proposed MC-fed DTC algorithm is implemented based on the table. Numerical simulation and experiments with a prototype are carried out. Both simulation and experimental results demonstrate that remarkable torque ripple reduction, more than 30%, has been achieved. As a result, the proposed strategy is proved to be effective in reducing torque ripples for MC-based PMSM drives.

A Simplified Finite-Control-Set Model-Predictive Control for Power Converters

Finite-control-set model-predictive control (FCS-MPC) requires a large amount of calculation, which is an obstacle for its application. However, compared with the classical linear control algorithm, FCS-MPC requires a shorter control loop cycle time to reach the same control performance. To resolve this contradiction, this paper presents an effective method to simplify the conventional FCS-MPC. With equivalent transformation and specialized sector distribution method, the computation load of FCS-MPC is greatly reduced while the control performance is not affected. The proposed method can be used in various circuit topologies and cases with multiple constraints. Experiments on two-level converter and three-level NPC converter verify the good performance and application value of the proposed method.

Implementation of Finite-State Model Predictive Control for Commutation Torque Ripple Minimization of Permanent-Magnet Brushless DC Motor

A strategy based on finite-state model predictive control is proposed for permanent-magnet brushless dc motors (BLDCMs) to reduce commutation torque ripple. The main contribution is a detailed description of the algorithm design process applied to BLDCM for commutation torque ripple minimization, which points out that the optimal conduction status is directly selected and the exact duration of each conduction status is not required in control process. This method proposes a unified approach for suppressing commutation torque ripple over the entire speed range without distinguishing high speed and low speed and overcomes the difficulties of commutated-phase-current control, avoiding complex current controllers or modulation models. A discrete-time noncommutated-phase-current predictive model of BLDCM during commutation is established. According to the predefined cost function, the optimal switching state is directly selected and applied during the next sampling period so as to make the slope rates of incoming and outgoing phase currents match in the course of commutation, thus ensuring the minimization of commutation torque ripple. The simulation and experiment results show that the proposed method can effectively reduce commutation torque ripple within the whole speed range and achieve good performance in minimizing commutation torque ripple in both dynamic and steady states.

Torque Ripple Reduction in Brushless DC Drives Based on Reference Current Optimization Using Integral Variable Structure Control

In this paper, a current optimization control method for reducing torque ripple in brushless dc drives using integral variable structure control (IVSC) is proposed. The conventional current control method will result in torque ripple if the back electromotive force (EMF) is a nonideal trapezoidal waveform. Based on back-EMF waveforms, the proposed method can optimize the reference currents in both two-phase conduction mode and commutation mode. A Luenberger full-order estimator is designed in order to estimate back-EMF waveforms. During commutation, commutation control with two-phase or three-phase switching mode is employed to reduce torque ripple by controlling the currents of noncommutated windings to trace the optimized reference current, and a three-phase inverter is switched between the two switching modes according to the current rate of change and the difference between the reference current and the actual current. Current controllers using IVSC, which exhibits broadband noise-suppressing capacity and strong robustness against external disturbances, are designed to obtain optimal phase currents, and the experimental results validate the effectiveness of the proposed method.

Voltage Disturbance Rejection for Matrix Converter-Based PMSM Drive System Using Internal Model Control

A strategy based on internal model control (IMC) is proposed for a matrix converter-based permanent magnet synchronous machine (PMSM) drive system to reduce the adverse impact on drive performance caused by nonlinear output characteristics of matrix converter in the case of input voltage disturbance. Based on the duty-cycle space vectors and small-signal model, the relationship between output and input disturbances is obtained in the synchronous reference frame. Output characteristics of matrix converter are analyzed, and practical considerations are discussed for the purpose of controller design. A general design procedure of the robust IMC controller is described, and parameters of the controller are determined. Numerical simulations and experiments with a 10-kW prototype are carried out. The results show that good dynamic and steady-state performance on PMSM speed regulation is achieved under the unbalanced and distorted input voltage conditions, and the immunity of the drive system is verified to be improved.

Research on Torque Calculation Method of Permanent-Magnet Spherical Motor Based on the Finite-Element Method

In this paper, the finite-element method (FEM) is used to calculate the spinning torque of the permanent-magnet (PM) spherical motor. Three-dimensional (3-D) FE model of the PM spherical motor is established. Spinning torque distribution on the spherical surface and its variation curve on the equator are obtained respectively. In order to avoid the complicated torque calculation process under 3-D magnetic field and thus reduce the computational burden, the torque calculation method based on the 2-D conversion model is proposed. This method equivalently simplifies the magnetic field of the spherical PMs and the shape of cylindrical stator windings to be simulation parameters of the 2-D conversion model. With these parameters, 2-D conversion model of the PM spherical motor is established. Spinning torque variation curves obtained by the 3-D model and the 2-D conversion model respectively are compared and the results agree extremely well. By comparing the maximum static torque (MST) obtained under different configuration parameters of the PM spherical motor, it is found that the errors are within the allowable range. Therefore, the reliability of the proposed torque calculation method in the paper is verified. Finally, based on the 2-D conversion model, variation curves of the MST with the length of the air gap, the ampere turns, the length of stator windings and the outer radius of stator windings are obtained, and they are validated by those based on the 3-D model. These results can provide the basis for the optimization of the PM spherical motor.

Input–Output Feedback Linearization and Speed Control of a Surface Permanent-Magnet Synchronous Wind Generator With the Boost-Chopper Converter

A diode bridge rectifier followed by a boost-chopper circuit is a common topology of the generator-side converter for the direct-drive surface-permanent-magnet-synchronous-generator-based wind energy conversion system. Owing to its nonlinearity, it is difficult for the system to maintain good performance within normal operating range under the ordinary proportional-integral control. In this paper, a piecewise nonlinear mathematical model for the whole system, including both generator and converter, is proposed based on the commutation points of the diode bridge rectifier for more accurate controller design. The input-output feedback-linearization-based nonlinear transform for the mathematical model of the system is piecewise made. Then, a speed controller is designed according to the converted linear model, considering the integral of time multiplied by the absolute error. The proposed strategy has the advantages of relatively simple transform of state variables for linearization and developed parameter tuning method. The parameters of the linearized controller for different model intervals are the same. Finally, simulation results indicate that the proposed nonlinear controller is able to reject parameter perturbation to some extent, and experimental results are presented with a 3-kVA prototype, demonstrating that the dynamic performance of the system is improved effectively.

An Improved Control Strategy of Triple Line-Voltage Cascaded Voltage Source Converter Based on Proportional–Resonant Controller

In this paper, the operation principle of a multiple converter, which is composed of the traditional two-level six-switch voltage source converter and constructed in line-voltage cascaded mode, is analyzed. The equivalent switching circuit model of the multiple converter is built based on its operation characteristic. By analyzing the feature of the multiple converter control, an improved voltage-current double-loop control strategy based on the proportional-resonant (PR) controller is proposed. The control strategy, which has the merit of the integrated control, can also realize the independent control of the transmission power of each unit of the multiple converter by adding the voltage-sharing compensation control. Meanwhile, a PR controller is adopted in the current loop. By giving a suitable current reference value for the controller, the problem of ac-side line-current asymmetry can be solved, and the effect of unbalanced grid voltages on the system can be avoided as well. The availability of the proposed control strategy is verified by the experimental results.