The directtorquecontrol (DTC) for permanent magnet synchronous motor (PMSM) possesses have many advantages: simple control configuration, low parameter dependency, fast dynamic response, lack of coordinate transformation and rotor position except for the initial position. But it also suffers from some disadvantages, especially high torque ripple and variable switching frequency -. In nature the DTC is the hysteresis control. Voltagevectorselectionstrategy as the hysteresis control principle determines the system’s performance. Normally switching table is used as voltagevectorselectionstrategy to control the amplitude of stator flux and torque. But switching table can’t always satisfy the control of torque , . Thus to study voltagevectorselectionstrategy is critical to improve the PMSM DTC system’s performance - .
In practice, a flux weakening strategy is normally used to extend the motor speed operations beyond the base speed and to enhance the capability of torque. Several papers were published [42, 50-63] proposing the solution of achieving maximum torque capability in field weakening region. The common approach adopted is to estimate the optimal flux level of the motor based on the maximum values of inverter voltage and inverter current. Typically, the algorithms require frame transformer, knowledge of machine parameters and space-vector modulator. For examples,  used Field Oriented Control-Space Vector Modulation (FOC- SVM) while  used DirectTorqueControl-Space Vector Modulation (DTC- SVM), and they consider voltage and current limit conditions to compute the
Abstract — Directtorquecontrol (DTC) is a new method of induction motor control. The key issue of the DTC is the strategy of selecting proper stator voltage vectors to force stator flux and developed torque within a prescribed band. Due to the nature of hysteresis control adopted in DTC, there is no difference in control action between a larger torque error and a small one. It is better to divide the torque error into different intervals and give different control voltages for each of them. To deal with this issue a fuzzy controller has been introduced. But, because the number of rules is too high some problems arise and the speed of fuzzy reasoning will be affected. In this paper, a comparison between a new fuzzy direct-torquecontrol (DTFC) with space vector modulation (SVM) is made. The principle and a tuning procedure of the fuzzy directtorquecontrol scheme are discussed. The simulation results, which illustrate the performance of the proposed control scheme in comparison with the fuzzy hysteresis connected of DTC scheme are given.
From the simulation results in this paper, we can see that in the traditional DTC controlstrategy, the current, torque and flux ripple are large, and the static dynamic performance is not particularly stable. But the space voltagevector modulation technology, which takes advantage of SVM, use voltagevector to completely compensate the stator flux error, and make use of the PI regulator to replace the traditional hysteresis comparator in order to achieve steady-state flux-free no-static control. Thus it can reduce the flux ripple and torque ripple of the motor, which is able to make the flux locus smoother and the electromagnetic torque tracking faster. Also, the advantage of fast response in the traditional DTC control
In this work, the speed control of permanent magnet synchronous motor (PMSM) is considered in the aim to achieve high accuracy and a fast dynamic response. In this way, the directtorquecontrol-space vector modulation (DTC-SVM) technic is used for to optimize the switching selection table and offer more voltage space vector than traditional DTC [8, 9].The paper is organized as follows: in section II the proposed and study system is presented. Section III we illustrate the design of fuzzy logic methodology. In section IV the speed control and the directtorquecontrol-space vector modulation are developed. Finally, section V presents the simulation and results obtained with the proposed techniques.
Fig 1 shows a diagram in which three level voltage source inverter feed induction motor drive, which involves two hysteresis band controller. DTC is a scheme that deals so much on stator flux whose principle is characterized by limiting the cycle of both rotor and stator flux. Stator flux controller determines the time duration of the active voltage vectors, which moves the stator flux along the point of reference. Zero voltagevector, which relates to torque controller which ensures that motor torque is sustained within the specific hysteresis band. The inverter switching state is chosen by the selection block at every sampling time to reduce instantaneous flux and torque error.
In order to maximize the amplitude of (α,β) voltage vectors and to minimize (o1-o2) and (o3-o4) voltage vectors we choose the switching modes for the SPIM . Thats why we choose this com- bination 49,56,28,14,7 and 35. Clearly these switching modes generate zero voltage vectors on (o1,o2) subspace (Fig.3) and non zero voltage vectors on (o3,o4) subspace (Fig.4) . To main- tain the torque and the stator flux within the limits of flux and torque hysteresis bands the selection of voltagevector is made ( according to the principal of DTC ) . The voltage vectors are selected according to the errors of stator flux, torque and θ the angular position of the stator vector flux.
DirectTorqueControl (DTC) is a method that has emerged to become one possible alternative to the well- known VectorControl of Induction Motors. This method provides a good performance with a simpler structure and control diagram. In DTC it is possible to control directly the stator flux and the torque by selecting the appropriate VSI state. A variety of techniques have been proposed to overcome some of the drawbacks present in DTC [2, 8]. Some solutions proposed are: DTC with Space Vector Modulation (SVM); the use of a duty-- ratio controller to introduce a modulation between active vectors chosen from the look-up table and the zero vectors; use of artificial intelligence techniques. A different approach to improve DTC features is to employ different converter topologies from the standard two-level VSI. The major advantage of the three-level VSI topology when applied to DTC is the increase in the number of voltage vectors available. This means the number of possibilities in the vectorselection process is greatly increased and may lead to a more accurate control system, which may result in a reduction in the torque and flux ripples.
responses. Variations of motor parameter do not affectthe optimization in the new method. M. satheesh Kumar presents the comparative evaluation of the two popular controlstrategies for induction motor drive. These strategies are classical DTC and DTC-SVM. The Simulin k model of bothclassical and SVPWM directtorquecontrol drives are simu lated in all the four quadrant of operation) and the results areanalyzed .A LNASIR Z. A. presents the design of a directtorquecontrol model and tested using MATLAB/SIMULINK package.Simulation results illustrate the validity & h igh accuracy of the proposed model . A new torque ripple reduction schemeis proposed with a modified look up table. This table including a large no. of synthesized non- zero active voltagevector toovercome the limitation of the conventional strategy and duty ratio control switching strategy . The DT C principle isbased upon the decoupling of torque and stator flu x. Directtorquecontrol method emp loyees hysteresis comparator wh ichproduces high ripples in torque and switching frequency is variab le. The proposed DTC- SVM scheme reduces torqueripples and preserves the DTC transient merits. The SVM technique is utilized to obtain the required voltage space vectorwhich compensates the flu x and torque errors, at each cycle period  .
In conventional directtorquecontrol (DTC), the selection of flux linkage and electromagnetic torque errors are made within the respective flux and torque hysteresis bands, in order to obtain fast torque response, low inverter switching frequency and low harmonic losses. However, DTC drive utilizing hysteresis comparator suffers from high torque ripple and variable switching frequency. Space vector modulation is the strategy to minimize the torque ripple of induction motor in which, the stator flux level is selected in accordance with the efficiency optimized motor performance. In this work space vector modulation method is incorporated with directtorquecontrol for induction motor drives. However, the directtorquecontrol space vector modulation strategy is the calculation of the required voltage space vector to compensate the flux and torque errors exactly by using a predictive technique and then its generation using the space vector modulation at each sample period.
Figure.3.5 shows the voltage vectors which are usually employed in DTC scheme when the stator flux vector is lying sector I is shown in fig 3.8. The selection of a voltagevector at each cycle period is made in order to maintain the torque and the stator flux within the limits of two hysteresis bands. This simple approach allows a quick torque response to be achieved, but the steady state performance is characterized by undesirable ripple in current, flux and torque. This behaviour is mainly due to the absence of information about torque and rotor speed values in the voltageselection algorithm.
By using an input-output feedback linearization control, the inverter reference voltage is obtained. Also a full-order adaptive stator flu x observer is designed and a new speed adaptive law is given. Thus the stability of the observer system is ensured . S. A. Zaid  suggested a decoupled control of amplitude and stator flux angle to generate the pulses of voltage source inverter. MATLAB/SIMULINK software simulates the suggested and conventional DTC. The use of SVM enables fast speed and torque responses. Variations of motor parameter do not affect the optimization in the new method. M. sathish Kumar presents the comparative evaluation of the two popular control strategies for induction motor drive. These strategies are classical DTC and DTC-SVM. The Simu-link mode l of both classical and SVPWM directtorquecontrol drives are simulated in all the four quadrant of operation) and the results are analyzed .A LNASIR Z. A. presents the design of a directtorquecontrol model and tested using MATLAB/SIMULINK package. Simulation results illustrate the validity & high accuracy of the proposed model . A new torque ripple reduction scheme is proposed with a modified look up table. This table including a large no. of synthesized non - zero active voltagevector to overcome the limitation of the conventional strategy and duty ratio control switching strategy . The DT C principle is based upon the decoupling of torque and stator flu x. directtorquecontrol method employees hysteresis comparator which produces high ripples in torque and switching frequency is variable. The proposed DTC- SVM scheme reduces torque ripples and preserves the DTC transient merits. The SVM technique is utilized to obtain the required voltage space vector which compensates the flu x and torque errors, at each cycle period  .
Directtorquecontrol "DTC" technique is one of a high performance control system of an AC motor drive, which was proposed after the vector oriented control scheme during the resent 25 years. It has been developed rapidly for its concise system scheme, transient and dynamic performance. The DTC mechanism consists of voltagevectorselection table, two hysteresis comparators and two estimator’s one for stator flux and another for electromagnetic torque. DTC is directly controltorque and flux by using Voltage Source Inverter VSI, space vector and stator flux orientation and indirect speed regulated. A several control techniques can be used for improving the torque and flux performance. In this paper, the DTC with Proportional-Integral-Derivative (PID) controller used to improve the starting and dynamic performance of asynchronous motor AM, which gives good torque and flux response, best speed control and also minimize the unacceptable torque ripple. The mathematical model of DTC with PID controller of 3-phase induction motor IM are simulated under Matlab- Simulink. Therefore, the DTC based on PID controller has good performance of IM compared to classical DTC for starting, running state and also during change in load.
Figure.3 shows the voltage vectors which are usually employed in DTC scheme when the stator flux vector is lying sector I is shown in fig 3. The selection of a voltagevector at each cycle period is made in order to maintain the torque and the stator flux within the limits of two hysteresis bands. This simple approach allows a quick torque response to be achieved, but the steady state performance is characterized by undesirable ripple in current, flux and torque. This behaviour is mainly due to the absence of information about torque and rotor speed values in the voltageselection algorithm.
In this technique two proportional integral (PI) type con- trollers are used instead of hysteresis band regulating the torque and the magnitude of flux as it shown in Figure 2, by generating the voltage command for inverter control. Noting that no decoupling mechanism is required as the flux magnitude and the torque can be regulated easily by the PI controllers. Due to the structure of the inverter, the DC bus voltage is fixed, therefore the speed of voltage space vectors are not controllable, but we can adjust the speed by means of inserting the zero voltage vectors to control the electromagnetic torque generated by the in- duction motor. The selection of vectors is also changed. It is not based on the region of the flux linkage, but on the error vector between the expected and the estimated flux linkage .
In a DTC drive, flux linkage and electromagnetic torque are controlled directly independently by the selection of optimum inverter switching modes. The selection is made to restrict the flux linkages and electromagnetic torque errors within the respective flux and torque hysteresis bands. The required optimal switching vectors can be selected by using so-called optimum switching-voltagevector look-up table. This can be obtained by simple physical considerations involving the position of the stator-flux linkage space vector, the available switching vectors, and the required torque flux linkage
Singh et. al.  analyzed the performance of the Field Oriented Control (FOC) of Permanent Magnet Synchronous Motor (PMSM) drive with a PID (Proportional Integral Derivative) in dc link voltagecontrol and Fuzzy PID for speed control in closed loop operation thus inferring that the fuzzy controller provides a better response to the drive system especially in the steady state condition. Alexander Verl and Marc Bodson  discussed the problem of maximizing the torque of permanent magnet synchronous motors in the presence of voltage and current constraints. They have given the formulae suitable for the operation with voltage and current source inverters and for real-time computation. Zhong L.Rahman et. al.  presented a directtorquecontrol scheme for permanent magnet synchronous motor drives, where current controllers followed by PWM or hysteresis comparator are not used. The characteristics of a permanent-magnet synchronous motor are influenced greatly by the back-electromotive force waveforms in the motor, which are directly related its magnet shape. Therefore attempts are made by researchers to optimize the radius of the magnet with respect to number of poles, rotor size, and magnet thickness for the best results regarding the total harmonic distortion. Further several designs are tried and being developed for the control of PMSM in the field weakening (constant power) region without any danger of permanent loss of magnetisation employing techniques like Finite Element Modelling (FEM). The paper basically analyses the performance of PMSM under directtorquecontrol and vectorcontrolstrategy along with their respective comparative study through simulink models.
ABSTRACT: This paper presents improved performance of DirectTorqueControl (DTC) of induction motor drives . At the time of switching DTC drive gives the high torque ripple. In DTC induction motor drive there are torque and flux ripples because of incorrect voltagevectorselection by VSI states is unable to generate the exact voltage value required to make zero both the torque electromagnetic error and the stator flux error. To overcome this problem a Fuzzy Logic Controller is proposed. The fuzzy logic controller is used to reducing the torque and flux ripples and it improve performance DTC especially at low speed.
ALNASIR Z. A. presents the design of a directtorquecontrol model and tested using MATLAB/SIMULINK package. Simulation results illustrate the validity & high accuracy of the proposed model . A new torque ripple reduction scheme is proposed with a modified look up table. This table including a large no. of synthesized non-zero active voltagevector to overcome the limitation of the conventional strategy and duty ratio control switching strategy . The DTC principle is based upon the decoupling of torque and stator flux. Directtorquecontrol method employees hysteresis comparator which produces high ripples in torque and switching frequency is variable. The proposed DTC-SVM scheme reduces torque ripples and preserves the DTC transient merits. The SVM technique is utilized to obtain the required voltage space vector which compensates the flux and torque errors, at each cycle period  .
Furthermore, the parameters estimation (stator flux and torque) technique of DTC is much simpler and straightforward than that of FOC. Generally, the estimation is based on manipulation of the stator voltages and currents, expressed in a stationary reference frame, as well as the stator’s resistance only. Nevertheless, the accuracy of parameters’ estimation is of significant importance as it may lead to selection of an improper voltagevector and hence highly degrades the control performance of DTC. The stator flux and torque can be estimated using voltage-, current- based estimators or combination of both. The conventional DTC scheme, proposed in , was based on a combination (voltage and current) estimator. On the one hand, the current-based estimator requires the knowledge of rotor speed. Sequentially, a further speed sensor is mandatory which, in turn, increases system’s complexity. On the other hand, a