Basic Direct Torque Control Research Articles

Analysis of fuzzy and neural controllers in direct torque controlled synchronous motors

<p><span>In this study, multiple intelligent control systems for direct torque-controlled Synchronous motors are implemented and compared. Using a lookup table to pick a vector through the inverter voltage space, the direct torque control (DTC) system can be obtained. To replicate the state selector in relation to the look-up table, intelligent controllers are deployed. Intelligent logic controllers like fuzzy and neural are used to regulate the performance of permanent magnet synchronous motors (PMSM). In steady-state applications, neural and fuzzy controllers reduce the torque ripple and stator current harmonic distortion. These outcomes are compared with those obtained when the synchronous motor was put under the basic direct torque control method using a proportional integral (PI) controller. The accuracy and effectiveness of the suggested control topologies have been verified using computer simulation software like MATLAB/Simulink.</span></p>

Five‐level torque controller‐based DTC method for a cascaded three‐level inverter fed induction motor drive

Two cascaded two-level inverters can synthesise three-level voltage space vector. For the cascaded three-level inverter controlled induction motor, this study proposes a five-level torque controller (FLTC)-based direct torque control (DTC) method especially for improving steady-state motor torque performance and retaining the high dynamic performance. The proposed FLTC method employs hysteresis controllers, uses look-up tables and ends up with variable switching frequency of the cascaded three-level inverter. Computationally, the envisaged FLTC method is quite comparable to that of the basic DTC method. The FLTC method ensures reduced switching commutations in the inverter switching devices during low speeds of operation and simultaneously achieves reduced d v /d t switching stresses. An inherent drawback of FLTC method at higher speeds of operation is identified, theoretically analysed and a pseudo error-based correction is also suggested in this study to overcome the drawback. The steady-state and transient motor torque performance of the induction motor with the use of the envisaged FLTC-based DTC method is thoroughly analysed, simulated using Matlab/Simulink and then experimentally validated on a laboratory prototype for starting, speed reversal and load change conditions with the use of the cascaded three-level inverter.

Feed-Forward Approach in Stator-Flux-Oriented Direct Torque Control of Induction Motor with Space Vector Pulse-Width Modulation

Two major obstacles in the utilization of electrical vehicles are their price and range. The collaboration of direct torque control (DTC) with induction motor (IM) is preferred for its low cost, easy implementation, and parameter independency. However, in terms of edges, the method has drawbacks, such as variable switching frequency and undesired current harmonic distortion. These drawbacks result in acoustic noise, reduced efficiency, and electromagnetic interference. A feed-forward approach for stator-flux-oriented DTC with space vector pulse-width modulation is presented in in this paper. The outcome of the proposed method is low current harmonic distortion with fixed switching frequency while preserving the torque performance and simple application feature of basic DTC. The method is applicable to existing and forthcoming IM drive systems via software adaptation. The validity of the proposed method is confirmed by simulation and experimental results.

Modeling and Experimental Validation of 5-level Hybrid H-bridge Multilevel Inverter Fed DTC-IM Drive

This paper aims to improve the performance of conventional direct torque control (DTC) drives proposed by Takahashi by extending the idea for 5-level inverter. Hybrid cascaded H-bridge topology is used to achieve inverter voltage vector composed of 5-level of voltage. Although DTC is very popular for its simplicity but it suffers from some disadvantages like- high torque ripple and uncontrollable switching frequency. To compensate these shortcomings conventional DTC strategy is modified for five levels voltage source inverter (VSI). Multilevel hysteresis controller for both flux and torque is used. Optimal voltage vector selection from precise lookup table utilizing 12 sector, 9 torque level and 4 flux level is proposed to improve DTC performance. These voltage references are produced utilizing a hybrid cascaded H-bridge multilevel inverter, where inverter each phase can be realized using multiple dc source. Fuel cells, car batteries or ultra-capacitor are normally the choice of required dc source. Simulation results shows that the DTC drive performance is considerably improved in terms of lower torque and flux ripple and less THD. These have been experimentally evaluated and compared with the basic DTC developed by Takahashi.

Comparative Study on Direct Torque Control of Interior Permanent Magnet Synchronous Motor for Electric Vehicle

Comparative studies on several direct torque control (DTC) strategies of interior permanent magnet synchronous motor (IPMSM) for electric vehicles (EVs) are discussed in details, namely basic DTC, DTC combined with space vector modulation (DTC-SVM), and deadbeat DTC (DB-DTC). These DTC strategies are reviewed, meanwhile dynamics and steady-state performance are analyzed and compared. Simulations of a 20kW IPMSM for EVs are carried out for comparison studies including: ripple of torque and stator flux, sensitivity to machine's parameter, computational complexity, and total harmonic distortion of stator current. The results can be used as guidance for application of IPMSM to EVs and others.

DTC-SVM-based position regulation of an induction motor: a comparison between different strategies

This work is aimed at looking into potential advantages of direct torque control (DTC) strategies for position regulation applications. Of particular interest is the capability exhibited by DTC strategies to develop the maximum torque at standstill. Within this background, the paper is devoted to the presentation of a comparison study between three DTC strategies dedicated to position control of an induction motor, such that: 1) the basic DTC strategy; 2) the DTC strategy with a look-up table including only active voltage vectors; 3) the DTC-SVM strategy with hysteresis controllers and imposed commutation frequency. Following simulation works, it has been found that the third strategy offers the lower torque ripples. Furthermore, it exhibits a high capability to reject the demagnetisation problem which penalises the stator flux regulation at low speeds in the Takahashi basic strategy. However, the DTC-SVM requires a control system with higher CPU frequencies in such a way its implementation scheme is more complex than the basic DTC strategy.

DTC Based Induction Motor Speed Control Using 10-Sector Methodology for Torque Ripple Reduction

A direct torque control (DTC) drive allows direct and independent control of flux linkage and electromagnetic torque by the selection of optimum inverter switching modes. It is a simple method of signal processing which gives excellent dynamic performance. Also transformation of coordinates and voltage decoupling are not required. However, the possible discrete inverter switching vectors cannot always generate exact stator voltage required, to obtain the demanded electromagnetic torque and flux linkages. This results in the production of ripples in the torque as well as flux waveforms. In the present paper a torque ripple reduction methodology is proposed. In this method the circular locus of flux phasor is divided into 10 sector as compared to six sector divisions in conventional DTC method. The basic DTC scheme and the 10-sector method are simulated and compared for their performance. An analysis is done with sector increment so that finally the torque ripple varies slightly as the sector is increased.

A review of direct torque control of induction motors for sustainable reliability and energy efficient drives

The first and the most important step in solving the environmental problems created by cars with internal combustion engines is research and development of electric vehicles. Selection of a proper drive and optimal control strategy of electric vehicles are the major factors to obtain optimal energy management in order to extend the running distance per battery charge. This paper presents a brief review of direct torque control (DTC) of induction motors (IM) as well as its implementation for electric vehicle (EV) applications. First, the basic DTC technique based on hysteresis controllers will be introduced, and then an overview of the major problems in a basic DTC scheme will be presented and explained, as well as some efforts for improving the technique. The main section presents a critical review of DTC for EV applications, taking into consideration the vehicle mechanics and aerodynamics of electric vehicles. The review is very important to provide guidelines and insights for future research and development on the DTC of IM drives for sustainable reliability and energy efficient EV applications.

Reduction of torque ripple in DTC induction motor drive with discrete voltage vectors

This paper presents ? practical implementation of direct torque control (DTC) of an induction machine on MSK2812 DSP platform, and the analysis of possibilities for reduction of torque ripple. Basic theoretical background relating the DTC was primarily set and the obtained experimental results have been given. It is shown that the torque ripple can be reduced by adjusting the intensity of voltage vectors and by modification of hysteresis comparator, while the simplicity of the basic DTC algorithm has been maintained.

DTC Scheme for a Four-Switch Inverter-Fed Induction Motor Emulating the Six-Switch Inverter Operation

This paper proposes a novel direct torque control (DTC) strategy for induction motor (IM) drives fed by a four-switch three-phase inverter (FSTPI). The introduced strategy is based on the emulation of the operation of the conventional six-switch three-phase inverter (SSTPI). This has been achieved thanks to a suitable combination of the four unbalanced voltage vectors intrinsically generated by the FSTPI, leading to the synthesis of the six balanced voltage vectors of the SSTPI. This approach has been adopted in the design of the vector selection table of the proposed DTC strategy which considers a subdivision of the Clarke plane into six sectors. Simulation results have revealed that, thanks to the proposed DTC strategy, FSTPI-fed IM drives exhibit interesting performance. These have been experimentally validated and compared to the ones yielded by the Takahashi and the basic DTC strategies dedicated to the SSTPI and to the FSTPI, respectively.

Modelling and Simulation of Direct Torque Controlled Induction Motor Drive using Slip Speed Control

In this paper an effective control strategy to reduce the torque and flux ripple in direct torque control (DTC) of induction motor drive based on a slip speed control of stator flux is presented. This control strategy is applied to three-level inverter configuration using cascaded two two-level inverters for improving the performance of the system. Torque control is achieved by reference stator flux angle which is generated from the sum of incremental change in stator flux angle and actual stator flux angle. Modelling and simulation of proposed DTC is presented and results of the simulation are compared with basic DTC. From the simulation results it is observed that the torque and flux ripple are less with proposed DTC and also an improvement in the steady-state performance of the drive system at high and low speed operation.

Investigation and improvement of torque response of control system based on direct torque control in interior permanent magnet synchronous motors

AbstractIn this study, we investigate the torque response of a control system that is based on the direct torque control (DTC) principle for an interior permanent magnet synchronous motor (IPMSM). We also propose a gain‐scheduling method for improving the torque response. Reference flux vector calculation (RFVC) DTC is used in this study. In RFVC DTC, a PI controller is used for torque control; this is in contrast to the use of the hysteresis comparator and switching table in basic DTC. In this paper, we present the relationship between the torque response and the gain of the PI controller. This relationship is derived by using the transfer function of the torque control loop. We also examine the difference between the torque responses of two motors that have different machine parameters. The proposed method can be used to realize a torque response that is independent of the operating torque. The simulation results and experimental results presented in this paper show the validity of the derived relationship as well as the effectiveness of the proposed method. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(2): 55–65, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21198

An Optimized Switching Strategy for Quick Dynamic Torque Control in DTC-Hysteresis-Based Induction Machines

A dynamic overmodulation strategy for fast dynamic torque control in direct torque control (DTC)-hysteresis-based induction machine is proposed. The fastest dynamic torque response with a six-step mode can be achieved in the proposed method by switching only the most optimized voltage vector that produces the largest tangential component to the circular flux locus. This paper also discusses the performance of dynamic torque control in basic DTC in order to justify on how the proposed selected voltage vector results in excellent dynamic torque performance. The main benefit of the proposed method is its simplicity, since it only requires a minor modification to the conventional DTC-hysteresis-based structure and does not require a space vector modulator. To verify the feasibility of the proposed dynamic overmodulation strategy, simulation and experimentation, as well as comparison with the conventional DTC scheme, are carried out. Results showed a significant improvement in the dynamic torque response when compared to the conventional DTC-hysteresis-based method.

Eighteen-sector switching strategy for torque ripple reduction of direct torque controlled induction motor drive

Direct torque control (DTC) is an emerging technique for controlling the PWM inverter-fed induction motor drives (IMDs). The low number of voltage vectors, which can be applied to the machine using the basic DTC scheme, may cause undesired torque and current ripple. This paper proposes DTC 18-sector switching strategy, where the d-q flux locus plane is divided into 18 equal sectors, which lead to an increase in the number of voltage vector. Here a modified switching table has been derived on the basis of the optimised state selection of voltage vector. The proposed scheme is simple as it does not increase the complexity in the vector selection process and is less parameters sensitive. The performance of the proposed and conventional DTC schemes has been checked at low speed in order to demonstrate the torque ripple reduction. To verify the feasibility of the proposed scheme, computer simulations and an experimental test has been carried out to validate the results of the proposed method.

Investigation and Improvement of Torque Response of Control System Based on Direct Torque Control in Interior Permanent Magnet Synchronous Motors

In this study, we investigate the torque response of a control system that is based on the direct torque control (DTC) principle for an interior permanent magnet synchronous motor (IPMSM). We also propose a gain-scheduling method for improving the torque response. Reference flux vector calculation (RFVC) DTC is used in this study. In RFVC DTC, a PI controller is used for torque control; this is in contrast to the use of the hysteresis comparator and switching table in basic DTC. In this paper, we present the relationship between the torque response and the gain of the PI controller. This relationship is derived by using the transfer function of the torque control loop. In this study, we also examine the difference between the torque responses of two motors that have different machine parameters. The proposed method can be used to realize a torque response that is independent of the operating torque. The simulation results and experimental results presented in this paper show the validity of the derived relationship as well as the effectiveness of the proposed method.

THE PRELIMINARY RESEARCH FOR IMPLEMENTATION OF IMPROVED DTC SCHEME OF HIGH PERFORMANCE PMSM DRIVES BASED ON FPGA

The direct torque control (DTC) is one of control approache that is used commonly in PMSM control system. This method supports a very quick and precise torque response. However, the DTC method is not perfect and has some disadvantages. Many researchers have been proposed to modify the basic DTC scheme for PMSM drive. All this contributions allow performance to be improved, but at the same time they lead to more complex schemes. Furthermore, the PMSM drive control systems are usually based on microcontroller and DSP. Some researchers also have been used DSP and FPGA together to develop DTC for AC drives. These allow improving the performance, but they will increase cost. For the reason above, this paper proposed a new DTC scheme to apply only based on FPGA. The preliminary research showed that the proposed DTC sheme can reduce torque and flux ripples significantly. Therefore, this paper also recomend to realize proposed DTC scheme based on FPGA in order to support to execute very fast computation.The implementation is hoped that it will very potential to replace not only the induction motor but also the DC servo motor in a number of industrial process, commercial, domestic and modern military applications of high-performance drive.

An Improved DTC-SVM Method for Sensorless Matrix Converter Drives Using an Overmodulation Strategy and a Simple Nonlinearity Compensation

In this paper, an improved direct torque control (DTC) method for sensorless matrix converter drives is proposed, which is characterized by minimal torque ripple, unity input power factor, and good sensorless speed-control performance in the low-speed operation, while maintaining constant switching frequency and fast torque dynamics. It is possible to combine the advantages of matrix converters with the advantages of the DTC strategy using space-vector modulation and two PI controllers. To overcome the degrading of dynamic torque response compared with the basic DTC method and the phase-current distortion due to the nonlinearity of the matrix converter, an overmodulation strategy and a simple nonlinearity-compensation method using transformation are also presented. Experimental results are shown to illustrate the feasibility of the proposed strategy.

Research on a direct torque control for an electrically excited synchronous motor drive with low ripple in flux and torque

The electrically excited synchronous motor (ESM) has typically small synchronous inductance values and quite low transient values because of the damper windings mounted on the rotor. Therefore, the torque and stator flux linkage ripples are high in the direct torque control (DTC) drive of the ESM with a torque and flux linkage hysteresis controller (basic DTC). A DTC scheme with space vector modulation (SVM) for the ESM was investigated in this paper. It is based on the compensation of the stator flux linkage vector error using the space vector modulation in order to decrease the torque and flux linkage ripples and produce fixed switching frequency under the principle that the torque is controlled by the torque angle in the ESM. Compared with the basic DTC, the results of the simulation and experiment show that the torque and flux linkage ripples are reduced, the maximum current value is decreased during the startup, and the current distortion is much smaller in the steady-state under the SVM-DTC. The field-weakening control is incorporated with the SVM-DTC successfully.

Limitation of the Load Angle in a Direct-Torque-Controlled Synchronous Machine Drive

The basic direct torque control (DTC) principle is to rotate the flux linkage forward, if the torque must be increased, and reverse, if the torque must be decreased. The torque is, however, increased only up to a maximum torque of the machine, which corresponds to a load angle of about 90/spl deg/ in a synchronous machine. This paper presents a method to overcome the possible loss of synchronism when using DTC. This requires either that the rotor angle is measured or estimated. Both of these cases are considered. Simulation and laboratory results are presented to show the effectiveness of the presented method.

A Novel Direct Torque Controlled Interior Permanent Magnet Synchronous Machine Drive With Low Ripple in Flux and Torque and Fixed Switching Frequency

A modified direct torque control (DTC) scheme for interior permanent magnet synchronous machine (IPMSM) is investigated in this paper, which features in very low flux and torque ripple and almost fixed switching frequency. It is based on the compensation of the error flux linkage vector by means of space vector modulation. Modeling and experimental results show that the flux and torque ripples are greatly reduced when compared with those of the basic DTC. With the new scheme, very short sampling time is not essential. All the advantages of the basic DTC are still retained. In addition, fixed switching frequency at different operating conditions becomes possible. The field-weakening control of this drive is also studied; an IPM DTC drive with a wider operation range and lower flux and torque ripple has been achieved experimentally.