Compensation of Parameter Variation Effects in Sensorless Indirect Vector Controlled Induction Machines Using Model-Based Approach

The majority of speed estimation schemes for sensorless vector control of induction machines use a mathematical model of the machine in the estimation process. These schemes are therefore inherently sensitive to parameter variation effects in the machine. The variety of speed estimation methods makes any attempt to develop a universal approach to compensation of parameter variation effects impossible. This paper concentrates on one of the most frequently used schemes, in which speed is estimated using model reference adaptive control approach (MRAC) on the basis of two estimated values of the rotor flux space vector. The estimator is analyzed in conjunction with indirect feed-forward rotor flux-oriented induction machine. An attempt is made to improve the accuracy of the speed estimation by appropriate modification of the speed estimator and the indirect vector controller structures using modified induction motor models that account for one or more of the phenomena that are neglected in development of the basic constant parameter scheme. In particular, compensation of main flux saturation, compensation of iron loss, and simultaneous compensation of both the iron loss and main flux saturation are elaborated. Novel structures of the speed estimator are developed for each of the three cases and are applied in conjunction with the appropriate modified form of the indirect rotor flux-oriented controller. Excellent compensation capability is demonstrated in all the cases by performing extensive simulation studies.     

考虑铁耗的感应电机模型及对矢量控制的影响

为了探讨感应电机铁耗所造成矢量控制器控制性能下降的主要因素,从感应电机的定、转子铁耗出发,得到d-q同步旋转坐标系下,考虑铁耗的感应电机串联等效电路,并建立了考虑铁耗的感应电机状态模型.在电机参数辨识准确的情况下,借助电机状态模型,分析得到铁耗对感应电机矢量控制的磁场定向角产生偏差,电机实际输出转矩减小,电机转速的动态响应变慢.通过Matlab/Simulink仿真,验证了分析的正确性,体现了铁耗补偿对提高感应电机矢量控制性能的必要性,并为感应电机矢量控制器的铁耗补偿算法设计提供了理论参考.     

ROTOR FLUX COMPUTATION IN SATURATED FIELD-ORIENTED INDUCTION MACHINES

ABSTRACT

The paper discusses effects of main flux saturation in field–oriented induction machines and proposes improved schemes for rotor flux space vector calculation. Field–oriented control with rotor flux computation out of the measured quantities is elaborated. Two rotor flux computer structures are analyzed. The first one is based on stator voltages and currents as measured variables, while the second scheme carries out calculations on the basis of sensed stator currents and rotor speed (position). The sensitivity of the constant parameter rotor flux computers to saturation degree variation is investigated in detail. Modified structures of the computing schemes are then proposed, which account for change in saturation level in the machine. The modified rotor flux calculators are derived from flux state–space model of a saturated induction machine. Accurate computation of rotor flux space vector is enabled in this way, irrespective of the actual saturation level in the machine. Verification of the developed modified rotor flux computers, which account for main flux saturation, is provided by the aid of digital simulation.     

Increasing the dynamic torque per ampere capability of inductionmachines

The objective of this paper is to present a novel means of increasing the dynamic torque per ampere capability of induction machines. The method developed is based on use of an indirect field oriented controller (IFOC) for the induction machine. It is well known that IFOC allows the rotor flux amplitude to be controlled by the d-axis component of stator current. It is also well established that the flux-producing component of the stator current may be controlled independent of the torque-producing component of the stator current. The principal constraint, however, is that the amplitude of the peak current (the vector amplitude) is limited by the power electronic switch ratings. This constraint implies that optimal partitioning of the current components should be possible. Previously used methods have optimized steady state efficiency or steady state torque per ampere. This paper identifies a dynamic method which achieves transient torques over 35% greater than the prior methods. The limitations of the method and its sensitivity to detuning is also examined     

MRAS-based sensorless control of a vector controlled five-phase induction motor drive

Multi-phase ac motor drives are nowadays considered for various applications, due to numerous advantages that they offer when compared to their three-phase counterparts. In principle, control methods for multi-phase machines are the same as for three-phase machines. Variable speed induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the sensor, information of the rotor speed is extracted from measured stator currents and voltages at motor terminals. Vector controlled drives require estimating the magnitude and spatial orientation of the fundamental magnetic flux waves in the stator or in the rotor. Open-loop estimators and closed-loop observers are used for this purpose. They differ with respect to accuracy, robustness, and sensitivity against model parameter variations. This paper analyses operation of an open-loop and model reference adaptive system (MRAS)-based sensorless control of vector controlled five-phase induction machine with current control in the stationary reference frame. The MRAS-based sensorless operation of a three-phase induction machine is well established and the same principle is extended in this paper for an IRFOC five-phase induction machine. Performance, obtainable with hysteresis current control, is illustrated for a number of operating conditions on the basis of simulation results. Full decoupling of rotor flux control and torque control is realised. Dynamics, achievable with a five-phase vector controlled induction machine, are shown to be essentially identical to those obtainable with a three-phase induction machine. Experimental verification is also provided.     

Study of Parameter Sensitivity in High-Performance Inverter-Fed Induction Motor Drive Systems

Vector control schemes are used in inverter-fed induction motor drives to obtain high performance. Crucial to the success of the vector control scheme is the knowledge of the instantaneous position of the rotor flux. The position of the rotor flux is measured in the direct scheme and estimated in the indirect schemes. Since the estimation of the flux position requires a priori knowledge of the induction motor parameters, the indirect schemes are all machine-parameter dependent. Changes in temperature and saturation levels of the machine vary the machine parameters and, hence, indirectly influence both the steady state and the dynamic operation of the drive system. Analytic expressions are derived to evaluate the effects due to parameter sensitivity. The simulation is experimentally verified on a drive system.     

基于多模糊控制器的感应电动机矢量控制系统实验研究

给出了一个完全基于模糊控制器的感应电动机间接转子磁场定向矢量控制系统.在控制系统中,三个精心设计的模糊控制器分别用于控制电机的转速、励磁电流分量和转矩电流分量,实现转速精确控制和感应电动机的励磁和转矩之间的解耦控制.最后,本文对该感应电动机矢量控制系统进行实验研究,验证其可行性.     

基于多模糊控制器的感应电动机矢量控制系统

介绍了一个完全基于模糊控制器的感应电动机间接矢量控制系统.一个模糊控制器用于控制电动机的转速,实现转速精确控制.在同步坐标轴系下,另外两个模糊控制器用于控制电动机的励磁电流分量和转矩电流分量,实现励磁和转矩之间的完全解耦控制.最后给出了控制系统的仿真和实验结果.     

The universal field oriented controller

This paper synthesizes and develops a universal field oriented (UFO) controller for induction machines. The UFO controller decouples flux and torque in an arbitrary flux reference frame. Due to its high degree of generality the UFO controller lends itself to be fully compatible with all existing field oriented controllers, indirect as well as direct field orientation. As a consequence, the digital implementation of the UFO scheme is identical for all induction motor drives enabling the usage of identical hardware and software. Examples of UFO control block diagrams for different field oriented controllers are presented. The execution time of the UFO algorithm is compared with the classical rotor flux field orientation method when using a high speed digital signal processor. Further, this paper indicates that the flexibility of changing the flux reference frame can extend the stability region of the drive especially at high speed during flux weakening. Detuning problems in field orientation are handled in an optimal manner for each field oriented controller by proper selection of the model of the induction machine and its reference frame     

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     

Evaluation of Steady-State and Transient Behavior of a MRAS Based Sensorless Rotor Flux Oriented Induction Machine in the Presence of Parameter Detuning

One of the most frequently applied methods of speed-sensorless rotor flux-oriented control of induction machines relies on utilization of model reference adaptive system (MRAS)-based speed estimation. Accuracy of this method heavily depends on correct setting of the machine parameters within the estimator and the controller. The paper discusses sensorless indirect feed-forward current-fed rotor flux-orientedinduction motor drive in whichspeed estimation is performed utilizing rotor flux-based MRAS scheme. A study is conducted in order to evaluate speed estimation error and other detuning effects in both steady-state and transient operation of the drive caused by incorrect setting and/or variation of parameters. Theoretical principles behind the steady-state analysis are at first developed, and steady-state detuning effects are then evaluated. Incorrect setting of magnetizing inductance, stator resistance variation, rotor resistance variation, and leakage inductance variation are encompassed by steady-state analysis. Next, simulation of the complete drive is performed in order to examine impact of parameter detuning on transient behavior of the drive. Results obtained by simulation, using dynamic model, for any steady-state operating point are found to be in excellent agreement with results obtained by steady-state analysis, so that developed theoretical concepts are fully verified. It is shown that rotor resistance variation leads to the largest speed estimation error, whereas stator resistance variation at low speeds significantly affects accuracy of field orientation and hence dynamics of the drive.     

Lower speed range drive for sensorless vector controlled induction machines with stator voltage offset compensation method

The vector control method is widely used for induction machine drives. Recently, sensorless vector control for induction machines has been investigated and proposed. The speed range for the drives is limited to about 1:100 in industry. The main reason for this limitation is the inaccuracy of stator voltage measurement. The lower the rotor speed is, the lower the stator voltage. Therefore, it is difficult to detect the stator voltage accurately in the lower speed region, and difficult to control motor speed and motor torque precisely. This paper presents a method of improving the lower speed performance of sensorless vector controlled induction machine drives using offset compensation of stator voltage. The offset is compensated by using the fluctuation of the estimated rotor flux. The validity of the proposed method is verified by experimentation. © 2000 Scripta Technica, Electr Eng Jpn, 133(1): 79–86, 2000     

牵引电机矢量控制转子磁场准确定向实时校正策略

磁场准确定向是异步电机间接磁场定向控制技术实现转矩和励磁独立解耦控制的关键,磁场准确定向对电机转子时间常数具有很强的敏感性。文中对转子磁场定向不准引起的电机励磁和定子电压控制问题进行了推导和讨论,分析了改进型带幅值相位补偿的电压模型转子磁链观测器实现机理。本文将其他影响磁场准确定向的因素都归结到转子时间常数中予以考虑,提出了基于观测转子q轴磁链误差的实用化转子磁链准确定向实时校正策略,仿真和实验结果验证了理论分析的正确性和磁场准确定向校正策略的有效性。     

Design and performance of field regulated reluctance machine

A unique topological configuration for rotating electromagnetic machines that can produce significantly higher force density than an induction machine is investigated. The stator is constructed using full pitch concentrated windings embedded in conventional slots. Rotor saliency is produced using poles constructed of axially oriented laminations. Operation is such that all of the conductors are actively taking part in torque production all of the time. The means for exciting the stator windings allows for independent control of torque and regulation of the rotor flux. A force density comparison is made based on operation with equal surface current density, conduction losses, and peak air-gap flux density. Construction and testing of a prototype 500 RPM, 28 kW laboratory machine, power converter, and controller are described     

Modeling of iron losses of permanent-magnet synchronous motors

Permanent-magnet (PM) motors offer potential energy savings as compared with induction motors because of the virtual elimination of rotor loss and the reduction of stator loss from operation near unity power factor. In PM machines, iron losses form a significant fraction of the total loss partly due to the nonsinusoidal flux density distribution. Design optimization therefore requires good means of predicting these iron losses. Finite-element analysis can be employed but this approach is cumbersome and costly when used in the many iterations needed in optimizing the design. This paper presents a set of improved approximate models for the prediction of iron loss. They can be used in design optimization programs and, since they are directly related to machine dimensions and material properties, they also provide quick insight into the effects of design changes. A time-stepped finite-element method is employed to evaluate the iron losses in a range of typical PM machines and the results are used to evaluate the adequacy of the models. The predictions of overall iron losses are then compared with measurements made on two PM motors.     

基于DSP＆IPM的矢量控制系统优化控制

对考虑铁损时感应电机在同步旋转坐标系统下的数学模型进行了分析。在分析基础上，通过研究不同运行条件下电机损耗与转子磁通的关系，实现了矢量控制变频调速感应电机（IM）的优化控制。为了进一步提高电机的调速性能，根据电机矢量控制的基本原理，利用数字信号处理器（DSP）和智能功率模块（IPM），给出了矢量控制硬件的实现；阐述了系统的软件实现方法。实验表明，矢量控制变频调速系统能平稳运行，具有较好的静、动态特性，可以广泛用于以IM为驱动装置的电气传动系统中。     

Adaptive sliding mode observer for induction motor using two-time-scale approach

This paper presents an original method for the design of a robust adaptive sliding mode current and flux observer for induction motor drive using two-time-scale approach. This approach, based on the singular perturbation theory, decomposes the original system of the observer error dynamics into separate slow and fast subsystems of lower dimensions and permits a simple design and sequential determination of the observer gains. For the proposed observer, the rotor speed signal is assumed to be available. The stator currents and rotor flux are observed on the stationary reference frame using sliding mode concept, and the adaptive rotor time-constant is derived from Lyapunov stability theory using measured and estimated currents and estimated rotor flux. The control algorithm is based on the indirect field-oriented sliding mode control to keep the machine field oriented. The control-observer scheme seeks to provide asymptotic tracking of speed and rotor flux in spite of the presence of an uncertain load torque and unknown value of the rotor resistance. The effectiveness of this control algorithm has been successfully verified through computer simulations.     

零序分量注入型三电平感应电动机矢量控制系统

提出一种基于三电平中点箝位(NPC)逆变器的零序分量注入型感应电动机矢量控制方案。系统中使用快速电流控制的直接转子磁链定向矢量控制模式,由于定子电流是由快速电流环控制,因此系统中不用使用定子电压方程,并且不需要解耦电路。转子磁链位置角由磁通模型计算得到。感应电动机由三电平NPC逆变器供电,三电平NPC逆变器由于开关器件的电压应力是传统两电平逆变器开关器件上电压应力的一半,所以适合用于中压调速系统。逆变器控制采用开关优化PWM算法,通过注入零序分量,不但优化功率器件的开关频率,而且可以稳定中点电位。仿真结果表明,该方法在三电平逆变器供电的感应电动机上有效地实现了矢量控制,并且具有很好的性能。     

双馈电机功率因数控制技术研究

根据定子磁场定向控制矢量原理建立了双馈电动机功率因数控制模型,对双馈电机功率因数控制技术进行了理论分析,推导出功率因数与转子电压和电机参数之间的关系式以及功率因数控制特性.并以DSP为控制核心研制了双馈电动机闭环控制实验系统.理论分析和实验表明,所提出的双馈电动机功牢因数控制技术是可性的,当双馈电动机的输出功率或转速发生变化时,通过调节转子励磁电压的幅值或相位可以控制双馈电动机的功率因数,从而提高系统运行效率和稳定性,节约电能.     

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.