Modified direct torque control method for induction motor drives based on amplitude and angle control of stator flux

This paper proposes design and implementation of a direct torque controlled induction motor drive system. The method is based on control of separation between amplitude and angle of reference stator flux for determining reference stator voltage vector in generating PWM output voltage for induction motors. The objective is to reduce electromagnetic torque ripple and stator flux droop which result in a decrease in current distortion in steady-state condition. In addition, the proposed technique provides simplicity of a control system. The direct torque control is based on the relationship between instantaneous slip angular frequency and rotor angular frequency in adjustment of the reference stator flux angle. The amplitude of the reference stator flux is always kept constant at rated value. The system has been implemented to verify its capability such as torque and stator flux responses, stator phase current distortion both during dynamic and steady state with load variation, and low speed operation.     

Performance analysis of a speed-sensorless induction motor drive based on a constant-switching-frequency DTC scheme

A control technique, which utilizes the stator flux components as control variables, has been applied to a speed-sensorless induction motor drive. The scheme may be regarded as a development of a direct torque control scheme, aimed at achieving a constant-switching-frequency operation. At each sampling period the required voltage vector is calculated on the basis of the error between the reference and the estimated stator flux vector. The problems related to the voltage-source inverter dead time and the stator flux estimation at low speed have been analyzed, and an efficient solution has been proposed. The performance of the drive system has been verified by experimental tests, and good results have been achieved in both steady-state and transient operating conditions.     

凸极式永磁无刷直流电机直接转矩控制研究

提出并分析研究了一种凸极式永磁无刷直流电机定子磁链幅值不控型直接转矩控制策略。结合凸极式永磁无刷直流电机及其两相导通工作特点,全面建立起两相导通时电压矢量对电磁转矩控制理论。采用转矩单环控制,根据转矩滞环比较输出和定子磁链位置给出所施加的电压矢量,实现转矩的快速控制。推导出两相静止坐标系下电磁转矩计算模型,并针对实际无刷电机转子反电势既非理想梯形波,又非正弦波的情况,提出采用查表方式获得转矩观测所必需的转子反电势和转子磁链方法。实验结果表明,所提控制方案具有快速的动态响应和良好的稳态性能。     

Nonlinear adaptive state-feedback speed control of a voltage-fed induction motor with varying parameters

An adaptive nonlinear-state-feedback speed control scheme of a voltage-fed induction motor has been developed in which the control of torque and flux is decoupled. The inputs to the control algorithm are the reference speed, the reference flux, the measured stator currents, the measured rotor speed, the estimated rotor flux, and estimates of the rotor resistance, stator resistance, and load torque, which may vary during operation. The controller outputs are the reference stator voltages in rotor-flux rotating reference frame. An accurate knowledge of the rotor flux and machine parameters is the key factor in obtaining a high-performance and high-efficiency induction-motor drive. The rotor flux is estimated using the induction-motor rotor-circuit model. Although the estimated rotor flux is insensitive to the stator-resistance variation, it does depend on the rotor resistance. A stable model reference adaptive system (MRAS) rotor-resistance estimator insensitive to stator-resistance variation has been designed. Stable stator-resistance and load-torque MRAS estimators have also been developed. These estimators have been developed to constitute a multi-input-multi-output (MIMO) decoupled-cascade structure control system. This simplifies the design problem of the estimators for a stable operation from a MIMO design problem to a single-input-single-output (SISO) design problem. The continuous adaptive update of the machine parameters and load torque ensures accurate flux estimation and high-performance operation. Simulation and experimental results are presented to verify the stability of the induction-motor drive in various operating modes.     

Speed sensorless torque control of an IPMSM drive with online stator resistance estimation using reduced order EKF

Speed sensorless control of an interior permanent magnet synchronous motor (IPMSM) based on direct torque control (DTC) is proposed in this paper. The rotor speed and position of the IPMSM are estimated based on an active flux concept, where, the active flux vector position is identical to the rotor position. The proposed algorithm does not require neither high frequency injection signal nor complicated schemes even at vary low speed operation. Torque/ flux sliding mode controller (SMC) combined with space vector modulation is proposed to improve the performance of the classical DTC. Stator resistance value is required for a stator flux and electromagnetic torque estimation. Its variation due to temperature or frequency degrades the scheme performance, especially, at low speed operation. To overcome this problem, a reduced order extended Kalman filter (EKF) is proposed to update online the stator resistance. The advantages of the direct torque control, sliding mode controller, and speed sensorless control are incorporated in the proposed scheme. Simulation works are carried out to show the ability of the proposed scheme at different operating conditions. The results demonstrate the activity of the scheme at wide range speed operation with load disturbance and parameters variation.     

基于扩展卡尔曼滤波器的永磁同步电机转速和磁链观测器

为了取消永磁同步电机控制中的机械传感器，获得直接转矩控制中需要的电机磁链信息，设计了一种基于扩展卡尔曼滤波器的永磁同步电机转速和磁链估算方法。选取定子固定坐标系下定子磁链、电机转速和转子位置为状态变量，电压和电流作为输入、输出量，建立估算定子磁链、电机转速和转子位置的EKF滤波器系统。采用空间矢量调制的直接转矩控制策略，有效减小了直接转矩控制方法的转矩脉动，并保持了功率器件恒定的开关频率。实验结果表明EKF准确地观测了电机转速和磁链，所构建的无速度传感器DTC控制系统具有良好的转速和转矩控制性能。     

Hardware Implementation of Direct Load Angle Controlled Induction Motor Drive

In this article, a direct load angle (DLA) control method for induction motor drive is proposed to reduce the torque and flux ripple. It is based on control of incremental change in load angle. The torque control is achieved without losing the benefits of conventional direct torque control (DTC) by reference stator flux angle, which is the sum of load angle and rotor flux angle. In this proposed DTC scheme, coordinate transformation is not required in torque control unit and reference voltage sector number and angle are not required in PWM unit, which reduces the control complexity. Proposed DTC control method is applied to two level voltage source inverter fed induction motor drive and hardware results are presented. From the hardware results, it is found that the proposed DTC control scheme impressively reduces the torque and flux ripples when compared with conventional space vector modulation (SVM) DTC.     

Development of torque and flux ripple minimization algorithm for direct torque control of induction motor drive

Direct torque control (DTC) is known to produce quick and robust response in AC drives. However, during steady state, notable torque and flux ripple occur. They are reflected in speed estimation, speed response and also in increased noise. This paper proposes a new control algorithm, which provides decoupled control of the torque, and flux with constant inverter switching frequency and a minimum torque and flux ripple. Compared to the other DTC methods, this algorithm is much simpler and has less mathematical operations, and can be implemented on most existing digital drive controllers. Algorithm is based on imposing the flux vector spatial orientation and rotation speed, which defines the unique solution for reference stator voltage. This paper contributes (a) Calculation of stator flux vector, torque and flux increments (b) The position of new stator flux vector determination (c) Calculation of the stator reference voltage (d) comparison of errors of different control strategies. In this paper, computer simulations and experimental results have been discussed for the proposed algorithm.     

考虑三次谐波转矩的双五相永磁同步电机串联系统直接转矩控制研究

针对反电动势非正弦的2台五相永磁同步电机串联驱动系统提出一种3次谐波转矩补偿型直接转矩控制策略。首先通过坐标变换建立了考虑3谐波转矩的双五相PMSM串联系统的数学模型,基于电压矢量对转矩的控制关系,分别在2个子空间计算定子磁链增量的期望值;然后根据2台电机定子电压方程,计算出2个平面内电压矢量参考值,并提出一种占空比调制型空间矢量调制算法;最后,通过仿真与实验验证了所提控制算法的可行性。     

内置式永磁同步电机的效率最优直接转矩控制

为提高内置式永磁同步电机驱动系统的运行效率,提出了一种内置式永磁同步电机的效率最优直接转矩控制方法。在建立计及定子铁心损耗的内置式永磁同步电机模型的基础上,分析了电机损耗与转矩、转速和定子磁链的关系,导出了不同运行工况条件下效率最优定子磁链幅值的计算式。通过动态调节定子磁链给定值,实现了内置式永磁同步电机直接转矩控制系统的效率最优控制。实验结果表明,给出的优化控制策略在保持直接转矩控制快速动态响应特性的同时,可有效提高电机的运行效率。     

基于转子电流的双馈感应电机无速度传感器控制

提出一种基于转子电流的模型参考自适应系统(MRAS)的双馈感应电机(DFIM)无速度传感器控制方法.首先建立了基于定子磁链定向的DFIM矢量控制模型,实现了电机转速/转矩控制和有功/无功功率解耦控制,然后采用基于MRAS的转速辨识方法,将测量得到的转子电流作为参考模型,通过定子电压和电流估测得到的转子电流作为自适应模型,用PI闭环控制构造转子位置和转速信息.为验证理论分析的正确性,以50 kW的DFIM为例设计了一套控制系统.通过电动机运行工况下的空载变速实验和发电机运行工况下的功率控制实验,估测转子位置和转速在不同转速和功率工况下都能准确跟踪实际值.仿真和实验结果表明系统能实现对DFIM无速度传感器控制,证明了所提出的方案的可行性.     

Robust direct torque and flux control of adjustable speed sensorless induction machine drive based on space vector modulation using a PI predictive controller

A Direct torque and flux control design for a sensorless induction motor, following a Lyapunov-based stator flux observer is presented. In this control scheme, the torque error signal and the amplitude of the stator flux reference vector are delivered to a PI predictive controller. The predictive controller also uses information on the amplitude and position of the actual stator flux vector and measured stator currents to determine the voltage command vector for space vector modulation inverter. In addition, a conventional PI speed controller is used to generate the torque reference signal. Using the fifth order model of the three-phase induction machines in a stationary two axes reference frame, a nonlinear stator flux observer is developed in order to estimate the rotor speed, rotor and stator resistances simultaneously. The stability of this observer is proved by Lyapunov theory. It is shown that if the persistancy of excitation condition is satisfied, the estimated quantities converge to their real values. The effectiveness of the proposed control scheme is verified by computer simulation and experimental results.     

考虑磁饱和的感应电机MTPA转矩控制

感应电机的最大转矩电流比(MTPA)控制算法根据需求转矩调节磁链幅值,以达到转矩与定子电流比值的最大化。因磁链随转矩的变化而变化,不再像传统控制算法保持磁场幅值恒定,磁场非线性饱和效应会对控制系统产生影响。针对此问题,该文提出考虑磁饱和特性的MTPA转矩控制系统。根据需求转矩以及饱和模型,通过线性搜索寻找最优磁链目标值,并在计算励磁电流时考虑d轴转子电流的动态特性,用降阶观测器观测转子磁链,并在设计滑模磁链控制器以及反步法设计转矩控制器时考虑观测误差,以确保控制器参数的设置能达到全局稳定。仿真和实验结果证明了所设计控制器的有效性。     

Robust sliding mode control and flux observer for induction motor using singular perturbation

This paper proposes a sequential methodology for designing a robust adaptive sliding mode observer for an induction motor drive using a two-time-scale approach. This approach is based on the singular perturbation theory. The two-time-scale decomposition of the original system of the observer error dynamics into separate slow and fast subsystems permits a simple design and sequential determination of the observer gains. In the proposed method, the stator currents and rotor flux are observed on the stationary reference frame using the sliding mode concept. The control algorithm is based on the indirect field oriented sliding mode control with an on-line adaptation of the rotor resistance to keep the machine field oriented. The control–observer scheme seeks to provide an asymptotic tracking of speed and rotor flux in spite of the presence of an uncertain load torque and an unknown value of rotor resistance. The validity for practical implementation has been verified through computer simulations.     

Vector Control Specialized for Switched Reluctance Motor Drives

This paper proposes vector control specialized for a switched reluctance motor (SRM) drive. Because it is a unipolar drive, a sinusoidal current with a dc offset is applied to each circuit instead of the conventional trapezoidal current. The current consists of dc and ac components which can be identified by their generation of a (virtual) rotor flux and rotating stator magnetic field, respectively. Thus, the vector control system can be developed in the same way as conventional ac machines. The proposed technique provides new mathematical models of SRMs on a rotating reference frame and achieves precise and fast torque response and advanced operations such as linear torque‐current control and maximum‐torque‐per‐ampere control. The vector control theory was verified through simulations and experiments.     

基于定子磁链电压模型的感应电动机新型控制策略

针对感应电动机调速系统,基于定子磁链的电压模型提出了一种新型控制策略,实现了对电磁转矩和定子磁链模值的动态控制,调速系统的控制部分主要由转速调节器、转矩调节器、磁链调节器和定子电压计算模块等组成。根据转矩调节器和磁链调节器的输出值,定子电压计算模块计算出定子电压矢量,使电磁转矩和定子磁链模值跟踪各自给定值的变化。这种控制策略的特点是结构简单,计算量小。仿真结果验证了这种新型控制策略的有效性。     

Sensorless field-orientation control of an induction machine byhigh-frequency signal injection

This paper describes a new scheme to find the rotor flux angle from stator voltages and currents by injecting high-frequency signal. The signal is not a rotating one, but a fluctuating one at a synchronous rotating reference frame with the fundamental stator frequency. When the estimated rotor flux angle coincides with the actual angle, the proposed method makes virtually no ripple torque, no vibration and less audible noise caused by the injected signal. The difference of impedances between the flux axis and the quadrature axis at high-frequency signal injection on the rotor flux angle is explained by the equivalent circuit equation of the induction machine. The difference is verified by experiments on the test motors at various testing conditions. The sensorless field-orientation algorithm is proposed, and the experimental results clarify the satisfactory operation of the algorithm with 150% load torque at zero stator frequency     

基于参考磁链电压空间矢量调制策略的永磁同步电机直接转矩控制研究

设计了基于参考磁链电压空间矢量调制策略的永磁同步电动机直接转矩控制,用H调节器取代了常规直接转矩控制系统中的开关表和滞环控制器,在每一控制周期计算出参考磁链和估计磁链的偏差,选择相邻非零矢量和零矢量并精确计算出其作用时间.仿真结果表明,与常规永磁同步电机直接转矩控制相比,基于参考磁链电压空间矢量调制策略永磁同步电机直接转矩控制转矩脉动显著减小;转矩和转速动态响应更快;具有更好的动、静态性能.     

Online tuning method of stator and rotor resistances in both motoring and regenerating operations for vector‐controlled induction machines

The vector control of induction motors is widely used. This method needs accurate motor parameter but the stator and rotor resistance vary due to motor temperature variation. If the value of resistance in the controller can be set up accurately at first, there must be a difference between the reference and real value of torque because of drift of the resistance. It is necessary to adapt the resistance value. The indirect field‐oriented control of an induction motor requires the value of rotor resistance only, but the direct field‐oriented control method with rotor flux observer requires the value of not only rotor resistance but also stator resistance in the controller. Consequently, it is necessary to adapt both stator resistance and rotor resistance. A parameter adaptation scheme has previously been proposed for the direct field‐oriented control method with rotor flux observer, but this method cannot be used when the motor is in regenerating operation. In this paper, a new stator and rotor resistance adaptation scheme is proposed, which can be applied when the motor is in regenerating operation. The usefulness of the proposed adaptation scheme is confirmed by simulation. © 2001 Scripta Technica, Electr Eng Jpn, 135(1): 56–64, 2001     

An Effective Four-Level Voltage Switching State Algorithm for Direct Torque Controlled Open End Winding Induction Motor Drive by Using Two Two-Level Inverters

This paper introduces an effective four-level voltage switching state algorithm for direct torque controlled open end winding induction motor drive with two-two level inverters in dual mode. In the recent days, direct torque control of open end winding induction motor drive became an interesting area for researchers because it provides high dynamic performance and instantaneous control of stator flux and torque. It is more important especially in applications like propulsion and hybrid electric vehicles they require ripple free torque. The direct torque control provides high flux, torque ripple, and variable switching frequency. This paper introduces an effective voltage switching state algorithm for an open end winding induction motor drive to reduce torque and flux ripple at different frequencies of operation. The experimental results show that the proposed algorithm reduces torque and flux ripples without losing features of conventional direct torque control (DTC) algorithm and in addition it provides multi-level operation.