The **direct** **torque** **control** (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 [1]-[3]. In nature the DTC is the hysteresis **control**. **Voltage** **vector** **selection** **strategy** as the hysteresis **control** principle determines the system’s performance. Normally switching table is used as **voltage** **vector** **selection** **strategy** to **control** the amplitude of stator flux and **torque**. But switching table can’t always satisfy the **control** of **torque** [4], [5]. Thus to study **voltage** **vector** **selection** **strategy** is critical to improve the PMSM DTC system’s performance [6]- [8].

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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, [53] used Field Oriented **Control**-Space **Vector** Modulation (FOC- SVM) while [63] used **Direct** **Torque** **Control**-Space **Vector** Modulation (DTC- SVM), and they consider **voltage** and current limit conditions to compute the

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Abstract — **Direct** **torque** **control** (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**-**torque** **control** (DTFC) with space **vector** modulation (SVM) is made. The principle and a tuning procedure of the fuzzy **direct** **torque** **control** 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.

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From the simulation results in this paper, we can see that in the traditional DTC **control** **strategy**, the current, **torque** and flux ripple are large, and the static dynamic performance is not particularly stable. But the space **voltage** **vector** modulation technology, which takes advantage of SVM, use **voltage** **vector** 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**

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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 **direct** **torque** **control**-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 **direct** **torque** **control**-space **vector** modulation are developed. Finally, section V presents the simulation and results obtained with the proposed techniques.

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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 **voltage** **vector**, 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.

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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 **voltage** **vector** 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.

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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 **direct** **torque** **control** drives are simu lated in all the four quadrant of operation) and the results areanalyzed [8].A LNASIR Z. A. presents the design of a **direct** **torque** **control** model and tested using MATLAB/SIMULINK package.Simulation results illustrate the validity & h igh accuracy of the proposed model [9]. A new **torque** ripple reduction schemeis proposed with a modified look up table. This table including a large no. of synthesized non- zero active **voltage** **vector** toovercome the limitation of the conventional **strategy** and duty ratio **control** switching **strategy** [10]. The DT C principle isbased upon the decoupling of **torque** and stator flu x. **Direct** **torque** **control** 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 [11] [12].

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In conventional **direct** **torque** **control** (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 **direct** **torque** **control** for induction motor drives. However, the **direct** **torque** **control** 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.

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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 **voltage** **vector** 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 **voltage** **selection** algorithm.

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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 [6]. S. A. Zaid [7] 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 **direct** **torque** **control** drives are simulated in all the four quadrant of operation) and the results are analyzed [8].A LNASIR Z. A. presents the design of a **direct** **torque** **control** model and tested using MATLAB/SIMULINK package. Simulation results illustrate the validity & high accuracy of the proposed model [9]. 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 **voltage** **vector** to overcome the limitation of the conventional **strategy** and duty ratio **control** switching **strategy** [10]. The DT C principle is based upon the decoupling of **torque** and stator flu x. **direct** **torque** **control** 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 [11] [12].

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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 **voltage** **vector** 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 **voltage** **selection** algorithm.

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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 [6].

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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-**voltage** **vector** 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

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Singh et. al. [4] 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 **voltage** **control** 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 [5] 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. [6] presented a **direct** **torque** **control** 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 **direct** **torque** **control** and **vector** **control** **strategy** along with their respective comparative study through simulink models.

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ABSTRACT: This paper presents improved performance of **Direct** **Torque** **Control** (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 **voltage** **vector** **selection** 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.

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ALNASIR Z. A. presents the design of a **direct** **torque** **control** model and tested using MATLAB/SIMULINK package. Simulation results illustrate the validity & high accuracy of the proposed model [9]. 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 **voltage** **vector** to overcome the limitation of the conventional **strategy** and duty ratio **control** switching **strategy** [10]. The DTC principle is based upon the decoupling of **torque** and stator flux. **Direct** **torque** **control** 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 [11] [12].

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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 **voltage** **vector** 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 [18], 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

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