PI and fuzzy estimators for tuning the stator resistance in directtorque control of induction machines

Direct torque control (DTC) of induction machines uses the stator resistance of the machine for estimation of the stator flux. Variations of stator resistance due to changes in temperature or frequency make the operation of DTC difficult at low speeds. A method for the estimation of changes in stator resistance during the operation of the machine is presented. The estimation method is implemented using proportional-integral (PI) control and fuzzy logic control schemes. The estimators observe the machine stator current vector to detect the changes in stator resistance. The performance of the two methods are compared using simulation and experimental results. Results obtained have shown improvement in DTC at low speeds     

Total Airgap Flux Minimization in Dual Stator Winding Induction Machines

Multiphase machines are gaining attention in specific applications due to their increased reliability and the possibility to split the power between more than one inverter. Dual stator winding machines can be seen under certain conditions as two independent induction machines coupled by the rotor. To ensure control independence of both windings, airgap flux saturation must be avoided. Proper flux synchronization of both windings is required to achieve this goal while maximizing the torque per ampere ratio of the machine. The conditions to obtain proper orientation of the fluxes are discussed in this paper, and the inverter control scheme to perform such orientation is developed.     

Stator resistance tuning in a stator-flux field-oriented driveusing an instantaneous hybrid flux estimator

A self-tuning control scheme for stator-flux field-oriented induction machine drives in electric vehicles operating over a wide speed range is discussed in this paper. The stator flux can be determined accurately from the terminal voltage when the machine is operating at high speed. However, at low speed, the stator resistance must be known to calculate the stator flux. The problem of calculating the stator flux accurately over the entire speed range is addressed. The rotor flux can be found from the machine speed and rotor time constant. The stator flux, at low speed, is then calculated directly from the rotor flux. By alternating between these two methods of determining the stator flux, a self-tuning operation is achieved, wherein the stator and rotor resistances are periodically updated. Since both methods of determining the stator flux are forced to track one another, a smooth transition between flux estimators is obtained. The torque and flux are then controlled in a deadbeat fashion. Good torque control over a wide speed range can therefore be obtained. With the proposed scheme, the advantages of direct torque control are obtained over the entire speed range with the addition of a speed sensor     

Transient simulation of lamination material properties inelectrical machines

All zero-speed-sensorless control schemes of electrical drives use a high-frequency excitation of the machine to determine local differences of the leakage inductances and to estimate the flux or the rotor position. One of these methods detects the local differences by evaluating the change of the stator current space phasor due to stator voltage test phasors. To get a deeper insight into the transient electric behavior of the machine, it is necessary to take into account also dynamic processes in the lamination material. To achieve this, a model has been developed to simulate the magnetization process in an induction motor fed by a voltage-source inverter. The proposed model calculates the current change due to voltage pulses taking into account the hysteresis as well as eddy currents. In order to limit the computation time, the model has to be kept simple. Measurements on an inverter-fed induction machine as well as on a stator lamination are presented. to verify the applicability of the model     

Online identification of induction machine electrical parameters for vector control loop tuning

In a vector-controlled induction machine drive, accurate knowledge of the machine electrical parameters is required to ensure correct alignment of the stator current vector relative to the rotor flux vector, to decouple the fluxand torque-producing currents and to tune the current control loops. This paper presents a new method for online identification of the induction machine parameters required to tune a rotor-flux-oriented (RFO) vector control scheme. Accuracy of the slip frequency estimation required for RFO vector control is achieved by utilizing the parameter independent "flux pulse" rotor time constant estimation scheme, which utilizes short-duration pulses injected into the flux-producing current. The parameters required to tune the synchronous frame current control loops with a decoupling circuit are estimated using a recursive estimation scheme derived from the synchronous frame voltage equations. As the "flux pulse" scheme requires signal injection into the flux-producing current a new rotor time constant estimation scheme is presented, based on the sensitivity analysis of the recursive parameter estimation scheme. Simulation and experimental results are presented which demonstrate the effectiveness of the online parameter identification and control loop tuning technique.     

A new stator resistance tuning method for stator-flux-orientedvector-controlled induction motor drive

Field-oriented-controlled induction motor drives have been widely used over the last several years. Conventional direct stator-flux-oriented control schemes have the disadvantage of poor performance in the low-speed operating area when the stator flux is calculated using the voltage model, due to the stator resistance uncertainties and variations. In this paper, a new closed-loop stator-flux estimation method for a stator-flux-oriented vector-controlled induction motor drive is presented in which the stator resistance value is updated during operation. This method is based on a simple algorithm capable of running in a low-cost microcontroller, which is derived from the dynamic model of the induction machine. The effects of stator resistance detuning, especially in the low-speed operating region, are investigated and simulation results are shown. The motor drive system as well as the control logic and the resistance estimator are simulated and characteristic simulation results are derived. In addition, the proposed control scheme is experimentally implemented and some characteristic experimental results are shown. The simulation as well as the experimental results reveal that the proposed method is able to obtain precise flux and torque control, even for very low operating frequencies     

Microprocessor-Based Field-Oriented Control of A CSI-Fed Induction Motor Drive

This paper describes the method of field orientation of the stator current vector with respect to the stator, mutual, and rotor flux vectors, for the control of an induction motor fed from a current source inverter (CSI). A control scheme using this principle is described for orienting the stator current with respect to the rotor flux, as this gives natural decoupling between the current coordinates. A dedicated micro-computer system developed for implementing this scheme has been described. The experimental results are also presented.     

Self-tuning of tapped stator winding induction motor servo drivesusing the universal field-oriented controller

The universal field-oriented controller is used to control induction motor torque and airgap flux independently of each other. The decoupling equations of the universal field-oriented (UFO) controller are identical for both direct and indirect field orientation. In this paper, a UFO controller is described that can operate both in a direct or indirect field orientation mode, allowing transitions from one mode to another. The proposed field-oriented controller can be realized at minimal cost in AC servomotor drives requiring motion control or accurate speed control     

Field-oriented control of induction motors using neural-networkdecouplers

This paper presents a novel approach to the field-oriented control (FOC) of induction motor drives. It discusses the introduction of artificial neural networks (ANNs) for decoupling control of induction motors using FOC principles. Two ANNs are presented for direct and indirect FOC applications. The first performs an estimation of the stator flux for direct field orientation, and the second is trained to map the nonlinear behavior of a rotor-flux decoupling controller. A decoupling controller and flux estimator were implemented upon these ANNs using the MATLAB/SIMULINK neural-network toolbox. The data for training are obtained from a computer simulation of the system and experimental measurements. The methodology used to train the networks with the backpropagation learning process is presented. Simulation results reveal some very interesting features and show that the networks have good potential for use as an alternative to the conventional field-oriented decoupling control of induction motors     

Speed-sensorless sliding-mode torque control of an induction motor

Novel induction motor control optimizing both torque response and efficiency is proposed in the paper. The main contribution of the paper is a new structure of rotor flux observer aimed at the speed-sensorless operation of an induction machine servo drive at both low and high speed, where rapid speed changes can occur. The control differs from the conventional field-oriented control. Stator and rotor flux in stator fixed coordinates are controlled instead of the stator current components in rotor field coordinates i_sd and i_sq. In principle, the proposed method is based on driving the stator flux toward the reference stator flux vector defined by the input command, which are the reference torque and the reference rotor flux. The magnitude and orientation angle of the rotor flux of the induction motor are determined by the output of the closed-loop rotor flux observer based on sliding-mode control and Lyapunov theory. Simulations and experimental tests are provided to evaluate the consistency and performance of the proposed control technique     

Effekte zeitdiskreter Ansteuerung von Asynchronmaschinen bei hohen Drehzahlen

When controlling an induction machine, the stator voltage vector is discretized temporally. This leads to cross-coupling in the rotor flux frame as well as to current ripples, deteriorating flux control and estimation performance. This article presents both input and output compensation methods for this effect.     

基于垂直轴双馈风力发电系统的仿真研究

以垂直轴风轮（VAWT）和双馈感应发电机（DFIG）为研究对象,建立了包括风力机模型、传动系统模型和双馈电机模型的垂直轴双馈风力发电系统的数学模型及结构,采用双馈电机定子磁链定向前馈解耦控制,使得电机的有功分量和无功分量可以分别得到控制。运用Matlab/Simulink建立了系统仿真模型,对定子磁链定向前馈解耦控制策...     

Parameter sensitivity of indirect universal field-orientedcontrollers

The universal field-oriented (UFO) controller was developed to decouple flux and torque in an arbitrary synchronous flux reference frame, realizing a high degree of generality, which makes the UFO controller compatible with all existing field-oriented controllers, including indirect and direct field orientation. This compatibility is useful to realize drives over a wide speed range using both direct UFO (DUFO) control and indirect UFO (IUFO). In this paper, generalized steady-state torque and flux expressions are derived analytically for detuned operation of the IUFO controller in an arbitrary reference frame. For a given machine (determined by its leakage factor), the expressions can be graphically represented (using only three parameters) as a function of the input command ratios. With these graphs, the steady-state performance of all indirect field-oriented controllers (controlling rotor flux, airgap flux, or stator flux) can be readily evaluated     

变速恒频双馈风力发电系统仿真研究

阐述变速恒频双馈风力发电系统工作原理,在分析双馈异步发电机的动态数学模型的基础上,介绍了一种基于定子磁链定向的矢量控制方法,实现对电机的有功功率和无功功率的解耦控制,进而实现最大风能追踪。在DFIG转子励磁电源的研究中,重点讨论基于电网电压定向矢量控制技术的网侧变换器的控制方法,以实现网侧变换器交流侧单位功率因数控制和直流环节电压控制。Matlab仿真结果证明了控制策略的正确性和有效性。     

Five-phase induction motor drives with DSP-based control system

This paper introduces two kinds of control schemes: vector control and direct torque control (DTC). These control schemes can be extensively applied to the operation of a five-phase induction motor using a fully digital implementation. Vector control of the five-phase induction motor not only achieves high drive performance, but also generates the desired nearly rectangular current waveforms and flux profile in the air-gap resulting in an improvement in air gap flux density and an increase of 10% in output torque. The DTC method has additional advantages when applied to multiphase, in this case a five-phase, induction motor. The five-phase inverter provides 32 space voltage vectors in comparison to 8 space voltage vectors provided by the three-phase inverter. Therefore, a more elaborate flux and torque control algorithm for the five-phase induction motor can be employed. Direct torque control of the five-phase induction motor reduces the amplitude of the ripples of both the stator flux and the torque, resulting in a more precise flux and torque control. A 32-b floating-point TMS320C32 digital signal processor (DSP) enables these two sophisticated control techniques to be conveniently implemented with high control precision. Experimental results show that an ideal control capability is obtained for both control methods when applied to the five-phase induction motor and further validates theoretical analysis     

An innovative direct self-control scheme for induction motor drives

The paper presents a new direct self-control (DSC) scheme for induction motor drives using the stator voltage third harmonic component in order to estimate the air-gap flux and the torque as well as to synchronize the supply voltage vector. Compared to previous DSC schemes the new one is independent from any motor parameter variation, specifically on stator resistance thus showing better performances at low speeds. The paper starts with a quick review on standard DSC main features pointing out the influence of stator resistance variations on the flux and torque control. The new DSC scheme is then introduced and evaluated by simulations and experimental tests on a 1.5 kW induction motor drive     

Control of induction motors for both high dynamic performance andhigh power efficiency

The authors attempt to control induction motors with maximum power efficiency as well as high dynamic performance by means of decoupling of motor speed (or motor torque) and rotor flux. For maximum power efficiency, the squared rotor flux is adjusted according to a minimum power search algorithm until the measured power input reaches the minimum. Since the motor speed is dynamically decoupled from the rotor flux, this can be done successfully without any degradation of motor speed responses. The controller depends on rotor resistance but not on stator resistance. However, the performance of the control scheme is robust with respect to variations in rotor resistance because an identification algorithm for rotor resistance is employed. The identification algorithm for rotor resistance has some advantages over the previous methods. To demonstrate the practical significance of the results, some experimental results are presented     

感应电动机转差型矢量控制系统的设计

本文分析了感应电动机矢量控制原理,通过矢量坐标变换和转子磁场定向实现磁通与转矩的解耦控制。在对系统进行仿真研究的基础上,以TMS320LF2407为控制核心进行软、硬件的设计,构建了一个感应电动机转差型矢量控制系统。     

Dual Direct Torque Control of Doubly Fed Induction Machine

The main idea developed in this paper is a novel biconverter structure to supply a doubly fed induction machine (DFIM). Two voltage source inverters (VSIs) feed the stator and rotor windings. The outputs of the two VSIs are combined electromechanically in the machine, and as a result, novel features can be obtained. For example, for high power drive applications, this configuration uses two inverters dimensioned for a half of the DFIM power. A new dual direct torque control is developed with flux model of DFIM. Two switching tables linked to VSI are defined for stator and rotor flux vector control. The satisfactory experimental and simulation results are shown, and they confirm good dynamic behavior in four quadrants of the speed-torque plane. Moreover, experimental results show the correct flux vector control behavior and speed tracking performances.