A new method of rotor resistance estimation for vector-controlledinduction machines

The estimation of rotor time constant, or rotor resistance, in a vector-controlled induction machine is necessary to achieve high-performance torque control. A new method of estimating the rotor resistance online, for use in a vector-controlled induction machine, is presented. It uses short duration pulses added to the constant flux reference current i_dse* and based on the resultant torque command current produced by a proportional-integral controller i_qse * adjusts the rotor resistance estimate. This method of self-tuning the vector controller to the rotor time constant, when operating in a closed-loop speed control loop, does not produce torque pulsations when correctly tuned. In comparison to other online methods such as the extended Kalman filter and the extended Luenberger observer, this method does not require voltage sensors and is computationally simpler. The rotor resistance estimation technique is illustrated through simulation and practical implementation of a vector-controlled induction machine     

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     

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     

Estimation of induction machine inverse rotor time constant using torque angle tangent calculation

A new inverse rotor time constant estimation scheme for an induction machine is presented. For high performance induction machine control, indirect rotor flux oriented vector control is the most commonly applied control technique. It requires that an accurate estimate of the inverse rotor time constant is obtained to ensure correct orientation of the current vector with the rotor flux vector. An incorrect estimate will result in an incorrect flux level, reduced dynamic torque performance and reduced maximum available torque. A novel parameter estimation scheme is presented, based on the calculation of the tangent of the torque angle. The effectiveness of the technique is demonstrated through simulation and practical results.     

On-line rotor cage monitoring of inverter-fed induction machines bymeans of an improved method

This paper suggests a fault-detection technique to monitor defects such as cracked rotor bars in induction machines. It has been introduced as the Vienna monitoring method. Rotor bar faults cause an asymmetric magnetic flux pattern in the air gap. Thus, the current phasor (or voltage phasor at current-controlled machines), flux phasor and air-gap torque differ from those of an ideal symmetric machine. The Vienna monitoring method compares the outputs of a reference model, which represents an ideal machine, to a measurement model. Observing the deviations of these two models makes it possible to detect and even locate rotor faults. It can be applied to inverter-fed machines as no frequency analysis is used. The method is verified by online experimental results from a DSP-controlled IGBT inverter drive. The findings match the outcomes of a detailed machine simulation. Air-gap flux density evaluation by a measurement coil system proves both the excellent sensitivity and fault location ability of the proposed scheme     

Independent field-oriented control of two split-phase induction motors from a single six-phase inverter

Split-phase (six-phase) induction motor stator windings consist of two sets of three phase windings, which are spatially phase separated by 30 electrical degrees. Due to mutual cancellation of the air gap flux for all the 6n/spl plusmn/1 (n=1,3,5...) order harmonic voltages, called zero sequence components, large harmonic currents are generated in the stator phases. Only the 12n/spl plusmn/1 (n=0,1,2,3...)-order harmonic voltage components contribute toward the air gap flux and electromagnetic torque production in the machine. In this paper, a novel scheme is proposed where two six-phase induction motors are connected in series with proper phase sequence so that the zero sequence component voltages of one machine act as torque and flux producing components for the other. Thus, the two six-phase motors can be independently controlled from a single six-phase inverter. A vector control scheme for the dual motor drive is developed and experimentally verified in this paper.     

A vector control scheme for EV induction motors with a series ironloss model

Electric vehicle (EV) motors are characterized by their low inductance and high current density, so that they run at high speed and produce a high starting torque. Due to the low inductance coil design, the current ripple caused by pulsewidth modulation (PWM) switching makes a significant amount of eddy-current loss and hysteresis loss, especially in high-speed operation. If one simply neglects the iron loss, the overall vector controller is detuned, resulting in an error in the torque control. The iron loss is modeled, in general, by a parallel resistor R_M to the magnetizing inductor L_M. The authors propose a series R-L model that accounts for the effects of the iron loss. A major advantage of the series model is that it does not increase the number of state variables in developing a vector control. In this paper, they derive a rotor-flux-oriented flux error, orientation angle error, and torque error caused by iron loss. Finally, they demonstrate the effectiveness of the proposed control method through computer simulation and experimental results     

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     

Online rotor resistance estimation using the transient state underthe speed sensorless control of induction motor

In the speed sensorless control of the induction motor, the machine parameters (especially rotor resistance R₂) have a strong influence on the speed estimation. It is known that the simultaneous estimation of the rotor speed and R₂ is impossible in the slip frequency type vector control, because the rotor flux is constant. But the rotor flux is not always constant in the speed transient state. In this paper, the R₂ estimation in the transient state without signal injection to the stator current is proposed. This algorithm uses the least mean square algorithm and the adaptive algorithm, and it is possible to estimate R₂ exactly. This algorithm is verified by the digital simulations and experiments     

Predictive Torque Control of Induction Machines Using Immediate Flux Control

This paper proposes a new concept for the control of voltage-source inverter (VSI)-fed induction machines. The method uses a predictive algorithm and can be split into two parts. The purpose of the first part, i.e., predictive torque control (PTC), is to predict the stator reference flux vector corresponding to the reference torque at the end of the sampling interval. The second part of the method provides accurate tracing of the stator reference flux by selecting either an active or a zero voltage vector. This approach is called immediate flux control (IFC), where two possible variants are suggested. In the first variant, a simple and fast algorithm obtains minimal stator flux error by impressing either an active or a zero voltage vector throughout the entire sampling interval. Consequently, the switching frequency becomes very low, but current and torque ripple are considerable. The second IFC variant generates the stator flux more accurately by applying an active voltage vector only throughout a calculated time slot within a sampling interval, whereas, during the remaining time of the sampling interval, a zero voltage vector is impressed. As a result, higher switching frequency arises, but it is still lower than that with space vector modulation. Both IFC variants, together with PTC, require minimal processing time and were efficiently implemented in a digital signal processor, which controlled a 3-kW induction machine drive. The obtained experimental results confirm the validity of the proposed approach.     

A Direct-Flux-Vector-Controlled Induction Generator With Space-Vector Modulation for Integrated Starter Alternator

A direct-flux-vector-controlled scheme of induction generator has been proposed in this paper for future 42-V automobile application. The fundamental relationship between the rotating speed of the stator flux vector and torque is analyzed. A simple structure with only one proportional-integral (PI) controller is shown to implement the torque and flux controls adequately. By controlling the electromagnetic torque of the induction machine, the required dc-bus voltage can be well regulated within the 42-V PowerNet specifications. Fixed switching frequency and low torque ripple are obtained with space-vector modulation technique. Simulation and experimental results indicate that the proposed scheme provides a practical solution for an integrated starter alternator other than the widely applied field-oriented- control scheme.     

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。     

基于模糊控制的感应电机直接转矩控制仿真研究

电机控制的关键是控制电机的转矩。继矢量控制后提出的直接转矩控制,直接着眼于对感应电动机瞬时力矩的控制,避免了矢量控制中转子磁链难于准确观测、系统特性受电动机参数的影响较大,使得实际的控制效果难于达到理论分析的结果。在通常的直接转矩控制系统中,磁链误差和转矩误差被直接用于开关状态选择,而引入模糊逻辑后,通过区分磁链误差和...     

Variable flux control of permanent magnet synchronous motor drivesfor constant torque operation

In this paper, a small signal model of permanent magnet synchronous machines is developed which includes both components of torque, i.e., magnet torque and reluctance torque. The effects of flux variations on the torque are analyzed by the use of the developed model. The off-line torque compensation method proposed for induction machines is then adapted to permanent magnet motor drives to achieve a constant torque, variable flux operation of the drives. A sensitivity analysis is performed to show that the off-line method is influenced considerably by machine parameter variations. Therefore the concept of forced compensation is introduced and an on-line torque compensation controller is proposed. Simulation results are presented to show the effectiveness of the proposed controller. An experimental vector controlled permanent magnet motor drive including the on-line torque compensation controller is implemented based on a TMS320C31 DSP to evaluate the method. The experimental results also confirm a desirable variable flux control of the motor drive under constant torque operation     

交流电动机矢量控制变压变频调速系统（七） 第七讲 异步电动机矢量控制系统

异步电动机矢量控制系统可以分为直接矢量控制系统和间接矢量控制系统。首先对具有转矩内环和磁链闭环的商接矢量控制系统进行了介绍，给出了其动态解耦结构图，然后介绍了电压源型和电流源型两种间接矢量控制系统，最后，对无速度传感器异步电动机矢量控制系统进行了简要的介绍。     

Low-frequency signal-demodulation-based sensorless technique for induction motor drives at low speed

The paper presents a method to compute the air-gap flux position in induction motors at very low including zero-stator frequency. A low-frequency (50 /spl divide/ 100 Hz) sinusoidal stationary signal is added to the normal stator variables to provide the machine with a suitable permanent excitation. Such an additional excitation modulates the saturation level of the magnetic core of the machine according to the angular position of the air-gap flux. As a result, a new zero-sequence stator-voltage component is generated that contains useful information about the position of the air-gap flux unaffected by load variation. Such a zero-sequence voltage can be easily employed to provide a wide bandwidth measurement of the air-gap flux position. A key feature of the proposed approach is that a low-frequency (0 /spl divide/ 5 Hz) signal is demodulated, thus avoiding any drawback featured by previous sensorless techniques operating with high-frequency signal injection.     

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.     

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     

Sequences of field-oriented control for the detection of faultyrotor bars in induction machines-the Vienna Monitoring Method

Rotor cage asymmetries of induction machines cause disturbances of the air-gap flux pattern. These deviations affect torque and speed as well as stator terminal voltages and currents. The proposed fault detection technique senses the actual machine state with the help of real-time space-phasor models. The Vienna Monitoring Method compares online a voltage model output with a current model and observes the deviations in a rotor fixed reference frame. High accuracy and robustness allow the detection of a faulty rotor bar out of the switched voltage and current signals of an inverter-fed machine in an early state. The focus of this paper is the detection of a single rotor bar increase under transient speed conditions without the necessity of a clutched load. During an inverter-controlled acceleration, lasting only 200 ms, the Vienna Monitoring Method evaluates currents, voltages, and rotor position for the calculation of an indication quantity that allows for reliable detection. As only one acceleration task does not excite every rotor cage bar sufficiently, a set of acceleration and deceleration cycles has to be driven