Direct Torque Control Of Induction Machines Research Articles

Exponential Reaching Law and Sensorless DTC IM Control with Neural Network Online Parameters Estimation based on MRAS

The most important problem in the control of induction machine (IM) is the change of its parameters, especially the stator resistance and rotor-time constant. The objective of<em> </em>this paper is to implement a new strategy in sensorless direct torque control (DTC) of an IM drive. The rotor flux based model reference adaptive system (MRAS) is used<em> </em>to estimate conjointly<em> </em>the rotor<em> </em>speed, the stator resistance and the inverse rotor time constant, the process of the estimation is performed on-line by a new MRAS-based artificial neural network (ANN) technique. Furthermore, the drive is complemented with a new exponential reaching law (ERL), based on the sliding mode control (SMC) to significantly improve the performances of the system control compared to the conventional SMC which is known to be susceptible to the annoying chattering phenomenon. An experimental investigation was carried out via the Matlab/Simulink with real time interface (RTI) and dSPACE (DS1104) board where the behavior of the proposed method was tested at different points of IM operation.

Modified Look-Up Table for Enhancement of Torque Response in Direct Torque Controlled Induction Machine

Basically, the direct torque control (DTC) drive system is operated at light load. At light load, supplying the drive system with rated flux will decrease the efficiency of the system. To maximize the efficiency of drive system, an optimal flux has been applied during steady-state but when a torque is suddenly needed, for example during acceleration, the dynamic of the torque response would be degraded. Therefore, a modification to the voltage vector as well as look-up table has been proposed for the torque response improvement. The proposed voltage vector is generated by adding two adjacent conventional voltage vectors and implemented by using duty ratio. The duty ratio is used to estimate the activation time of each conventional voltage vector in order to produce the proposed voltage vector.

Lookup-Table-Based DTC of Induction Machines With Improved Flux Regulation and Extended Kalman Filter State Estimator at Low-Speed Operation

Direct torque control (DTC) based on lookup table is known to have poor flux regulation at low speed that can cause a significant deterioration in the speed estimation of a sensorless drive. In this paper, stator flux regulation at low speed is improved under no load by replacing the hysteresis torque comparator with constant switching frequency controller, without any changes to the conventional lookup table; hence, the simple structure of DTC is maintained. In order to reduce the sampling time and hence improve the estimation process at very low speed, a simple fifth-order extended Kalman filter (EKF) is used in this paper. The fast execution time helps the linearization process of the EKF; hence, results in an improvement in its performance. Simulations and experimental results of the proposed sensorless drive system with the EKF estimator proves excellent flux regulation, and good speed robustness and stability at very low speed.

Classification of Faults in DTC Induction Machine using Wavelet Decomposition Method

Background: Fault detection is essential problem in machinery. The different type faults can occur in induction machine due to stator short circuits and rotor failures. Direct Torque Control (DTC) is a well known control design for induction motor drive in high power applications. Methods: Generally, the classification of faults is done by Principal Component Analysis (PCA) and Support Vector Machine (SVM) techniques. In this paper Discrete Wavelet Decomposition (DWD) technique is used to categorize the stator and rotor faults of DTC induction machine. Using the DTC Simulink model a variety of faults are generated and tested. Finding: By using wavelet decomposition, the information on the health and fault of a system can be extracted from signal over wide a range of frequencies. The extracted features are used to classify the healthy machine from faulty machine. Application: This method can be applicable in windmill, lathe and drilling industries to increase the efficiency of machines.

Direct Torque Control of Sensorless Induction Machine Drives: A Two-Stage Kalman Filter Approach

Extended Kalman filter (EKF) has been widely applied for sensorless direct torque control (DTC) in induction machines (IMs). One key problem associated with EKF is that the estimator suffers from computational burden and numerical problems resulting from high order mathematical models. To reduce the computational cost, a two-stage extended Kalman filter (TEKF) based solution is presented for closed-loop stator flux, speed, and torque estimation of IM to achieve sensorless DTC-SVM operations in this paper. The novel observer can be similarly derived as the optimal two-stage Kalman filter (TKF) which has been proposed by several researchers. Compared to a straightforward implementation of a conventional EKF, the TEKF estimator can reduce the number of arithmetic operations. Simulation and experimental results verify the performance of the proposed TEKF estimator for DTC of IMs.

Solar Direct Torque Controlled Induction Motor Drive for Industrial Applications

With the continuous decrease of the cost of solar cells, there is an increasing interest in photovoltaic (PV) system applications. Electric motors powered by solar energy are one of the most important applications now-a-days, such as in water pumping systems, electric vehicles etc. This paper investigates a photovoltaic-electro mechanic chain, composed of a PV generator, an impedance adapter DC–DC converter, inverter and a direct torque controlled induction machine. The PV generator is forced to operate at its maximum power point (MPP) by using a fuzzy based maximum power point tracking algorithm. Induction motor performance is obtained at different irradiation and temperature conditions. Simulation results show the effectiveness and feasibility of such an approach.

A Wide-Speed High Torque Capability Utilizing Overmodulation Strategy in DTC of Induction Machines With Constant Switching Frequency Controller

This paper presents a simple overmodulation method employed in direct torque control (DTC) constant switching frequency (CSF) controller of induction machines. The proposed overmodulation method is utilized to extend a constant torque region and hence produce high torque capability in field-weakening region with six-step operation. It will be shown that the overmodulation operation using the DTC-CSF scheme can be established by controlling the stator flux locus from circular to the hexagonal shape. This is achieved by modifying the flux error status produced from the flux hysteresis controller before it is fed to the lookup table. The main benefit of the proposed method is its simplicity since it requires only a minor modification to the conventional DTC hysteresis-based structure and does not require a space-vector modulator.

Simple Dynamic Overmodulation Strategy for Fast Torque Control in DTC of Induction Machines With Constant-Switching-Frequency Controller

This paper presents a simple dynamic overmodulation method to obtain a fast dynamic torque response in direct torque control (DTC) of induction machines with constant-switching-frequency controller. A fast dynamic torque response can be obtained by switching only the most optimized voltage vector during torque dynamic condition. The optimized voltage vector can be identified by comparing the rate of change of torque produced between applications of two possible active voltage vectors, according to the flux position. The selection of the optimized voltage vector can be simply implemented by modifying the flux error status before it is being fed to the lookup table. It will be shown that the proposed switching strategy facilitates the DTC to perform under six-step mode to achieve the fastest dynamic torque response. The effectiveness of the proposed dynamic overmodulation to obtain the fast torque response is verified with some experimental results.

Improvement of direct torque control in high power induction motors

Matrix converter rather than voltage source inverter can be used as high-performance technique supplying electric motor in direct torque control (DTC). DTC’s most significant deficiency in induction motor, magnetic torque ripple, can be markedly reduced by appropriate space voltage-vectors whose influence on stator flux and electromagnetic torque in DTC of induction machine that uses “matrix converter” the subject of this work. DTC degrees of freedom were shown seriously limited by 60° flux sectors, thus division to twelve 30° sectors of flux-space vector hexagon is proposed. The increased “matrix converter” degrees of freedom were then extracted for DTC implementation. Key words: Induction motor, direct torque control, matrix converter.

Spoiler effects reduction with using active power filter on a direct torque controlled induction machine

Harmonics, which may be placed in electrical systems, have important effects on performance parameters of electrical motors. In this paper, effects of electrical power system voltage harmonics on torque position of induction motors are dealt with. System modeling with Pulse Width Modulation (PWM) type Active Power Filter (APF) is used for reducing these effects. APF, as a subsystem, is placed into torque control system entrance to save the control system and induction motor output torque. Motor outputs, that are before-after APF connections, are handed for understanding effects of voltage harmonics. Since APF design was based on voltage harmonics, Electromagnetic Interference (EMI) has not changed. Main goal of the filter is zero effect of voltage harmonics on motor torque. A new place is selected for APF and the filter control system is designed with using Lyapunov function at the same time. Classical PI controlled APF is used like as a reference filter system and final result is that motor and system elements are defended by nonlinear controlled APF.

Adaptive hysteresis band control for constant switching frequency in DTC induction machine drives

It is fairly well known that direct torque control (DTC) exhibits fast dynamic torque response, a property that originates in the fact that torque and flux is directly controlled by instantaneous space voltage vector, unlike field-oriented control. For this reason direct torque control gradually has been used in the field, eliciting quick response and high efficiency since its introduction in the mid-1980s. Conventional fixed band hysteresis control has several problems. One of these is variable switching frequency, which causes serious problems in DTC. In this paper, an adaptive hysteresis band control strategy is proposed, where the hysteresis band is controlled in real time as variation of applied voltage vectors, thereby reducing the torque ripple whilst maintaining a constant torque switching frequency. The proposed adaptive hysteresis band control technique is verified by simulations. The system is first simulated by using the program Matlab and tested by hardware in the loop. Then, it is implemented in hardware based on a TMS320C6711, 32-bit fixed-point digital signal processor. Experimental results prove the feasibility of the proposed strategy compared with conventional method.

A Direct Torque-Controlled Induction Machine Bidirectional Power Architecture for More Electric Aircraft

A Direct Torque-Controlled Induction Machine Bidirectional Power Architecture for More Electric Aircraft

A High Performance Space Vector Modulation - Direct Torque Controlled Induction Machine Drive based on Stator Flux Orientation Technique

A High Performance Space Vector Modulation - Direct Torque Controlled Induction Machine Drive based on Stator Flux Orientation Technique

Adaptive Direct Torque Control of Induction Motors

In direct torque control (DTC), many induction motor parameters are needed, especially those that affect the values of current and flux required in the control algorithm. DTC of induction machines presents an acceptable tracking scheme for both electromagnetic torque and stator flux. This control scheme depends only on stator measurements. The measurement of the stator flux is very difficult to achieve and can be estimated by an observer. The electromagnetic torque and the stator flux (magnitude and angle) can be determined despite their direct dependence on the knowledge of the stator resistance. This resistance can change up to 180% of its nominal value. The resistance changes with the operational conditions of the motor, such as temperature and frequency. Under these circumstances, a parameter identifier is developed to account for the resistance variations, hence establishing adaptive DTC (ADTC). Moreover, load torque represents the changing tasks required from the motor. In this article, the load torque variations are coupled with stator resistance changes, and the effectiveness of ADTC is investigated. More stable motor operations of polyphase induction motors are obtained under these uncertainties using ADTC.

Minimization of torque ripple of direct-torque controlled induction machines by improved discrete space vector modulation

In this paper, discrete space vector modulation (DSVM) technique for induction machine drives is developed, and then a fuzzy logic direct torque control (DTC) scheme based on the proposed DSVM technique is presented. In DSVM technique, new voltage vectors are synthesized by applying three standard voltage space vectors for three equal time intervals at each sampling period. Rearranging the sequence of the three voltage space vectors does not change final synthesized voltage vectors, but has an influence on torque ripple. By comparing torque waveforms in one sampling period, an analysis is carried out to determine the influence. Based on the analysis, new switching tables used in DSVM-DTC are defined. In the switching tables, the three components of each synthesized voltage vector are arranged in optimized sequence. Finally, a fuzzy logic controller is designed to select synthesized voltage vectors. Its control rules are established based on the proposed switching tables. The proposed scheme is verified by simulations. Simulation results show that a reduction of torque ripples is achieved in a whole speed range.

DTC of Induction Machines Considering the Iron Loss

The existence of iron loss is normally neglected in derivation of induction machine models. Consequently, all the model-based high-performance control schemes are characterized with a certain amount of iron loss-induced detuning. Consequences of iron loss on operation of vector-controlled induction machines have been examined in detail recently, and numerous methods of iron loss compensation have been suggested. In contrast to such a situation with regard to vector control, it appears that a corresponding study has never been done in conjunction with direct torque control (DTC) of induction machines. The purpose of this paper is twofold. A detailed simulation study is at first performed so that the impact of iron loss on accuracy of the control is examined in detail. Torque mode of operation in the base speed region is considered. It is shown that the net consequence of the iron loss is a substantial difference between the torque reference and the average motor output torque. In contrast to such a situation with regard to motor torque, stator flux estimation is not affected by the iron loss existence. On the basis of the results of detuning investigation, a simple iron loss compensation method is developed. Its accuracy is verified by simulation. Further simplifications of the iron loss compensation scheme are investigated, and it is shown that, for certain machines, iron loss can be effectively compensated by simple deduction of a constant, iron loss-related torque component from the initial torque estimate.

A speed estimator for high performance sensorless control of induction motors in the field weakening region

The paper proposes a modified version of the model reference adaptive system (MRAS) based speed estimator, whose outputs of the reference and the adjustable model are rotor flux space vectors. The estimator is modified in such a way that the variation in the instantaneous level of the main flux saturation during operation in the field weakening is recognized and properly compensated at all times. The speed estimation scheme is equally applicable to both vector controlled and direct torque controlled induction machines, since it operates in the stationary reference frame and requires measurement of only stator voltages and currents. Verification of the proposed scheme is provided by simulation and by experimentation on an indirect feedforward rotor flux oriented induction machine for speed references of up to twice the base speed.

A Reduced Torque Ripple Controller for Direct Torque Control of Induction Machines

Direct Torque Control (DTC) of induction machines (IM), based on hysteresis comparators and selection table, suffers from variable switching frequency and large torque ripple, especially at low speed. This is because the rate of change of torque and flux and hence the time taken for the torque and flux to reach their upper and lower bands, varies with operating conditions. In this paper a new torque controller with fixed switching frequency is proposed. The structure of the new controller is very simple, with its output similar to that of the conventional three-level hysteresis comparator. The approximate frequency domain analysis of the proposed controller is presented, which served as a guide for the controller's parameters selection. The simulation of the DTC of IM with the proposed torque controller is presented, which is verified by experimental results. The results indicate that the proposed controller is capable of maintaining the torque switching frequency constant and reducing the torque ripple, particularly at low speed.