**Abstract**

The asynchronous or Induction Motor (IM) is one of the most widely used electrical machines in the world, due to the three following advantages namely 1. Their construction is simple and rugged 2.The absence of slip rings, commutators and brushes make it cheaper, and 3.It is also maintenance free compared to DC motors and Synchronous motor due to wear and tear of brushes, slip rings and commutators respectively. The Section 1 deals with the introduction of induction motor and Direct Torque Control scheme. Section 2 briefly discusses the types of Induction motor. Section 3 tells about the control strategies of Induction motor respectively scalar control and vector control, and also briefly explains about Direct Torque Control (DTC) method. The Section 4 discuss about the Types of Control Strategies for Torque ripple Reductions in DTC as well as the two proposed schemes namely 1.Fuzzy Logic Controller (FLC) for DTC-SVM and 2.Artificial Neural Network (ANN) controller for DTC-SVM respectively for IM and its results, The two proposed schemes uses Hybrid Asymmetric Space Vector Pulse Width Modulation (HASVPWM) for switching the inverter. The Section 5 revels about the modern advanced techniques such as ANN and FLC based DTC.

**Keywords:** types of IM, control techniques of IM, direct torque and flux control (DTC), torque ripple reductions in DTC, modern strategies of DTC, fuzzy logic controller (FLC) for DTC-SVM, artificial neural network (ANN) controller for DTC-SVM, hybrid asymmetric space vector pulse width modulation (HASVPWM)

### **1. Introduction**

The electric motors are electromechanical machines, which are used for the conversion of electrical energy into mechanical energy. The foremost categories of AC motors are asynchronous and synchronous motors. The asynchronous motors are called singly excited machines, that is, the stator windings are connected to AC supply whereas the rotor has no connection from the stator or to any other source of supply. The power is transferred from the stator to the rotor only by mutual induction, owing to which the asynchronous motors are called as induction machines. The induction motor is used widely in several industrial applications because of the following advantages 1. Ruggedness 2. Good efficiency 3. Simple and easy control. When the induction motor is compared to separately excited DC drives it is inferior because of coupled torque and flux. To bring high performance in induction motor drive the advanced control techniques of induction motor uses independent control of torque and flux, like in separately excited DC drives.

The advanced control techniques such as field oriented control and direct torque control play vital role in today's high performance AC drives. Later in the 1980s, the direct torque control (DTC) method was proposed by Takahashi and Depenbrock [1, 2]. The direct torque control is a robust method compared to other methods. In this method by selecting optimum inverter switching modes the motor torque and flux are controlled independently and also direct. The primary input of the motor is stator voltage and stator current. From this the stator flux and electromagnetic torques are calculated. The torque errors and flux errors are limited within the hysteresis band. The Direct torque control of induction motors based on discrete space vector modulation using adaptive sliding mode control was proposed by Ben Salem and Derbel [3], the results shows the effectiveness and the robustness of the DTC- discrete SVM adaptive sliding mode control of induction motors. The variations of induction motor parameters is shown by Ben Salem and Derbel in their subsequent two publications namely Performance Analysis of DTC-SVM Sliding Mode Controllers-Based on Estimator of Electric Motor Speed Drive [4], and DTC-SVM Based Sliding Mode Controllers with Load Torque Estimators for Induction Motor Drives [5] respectively. The advantages of this direct torque control method is improved efficiency and fast response of torque in dynamic conditions [6, 7].

#### **2. Types of induction motor**

A typical three phase Induction motor consists of two parts namely stator and rotor, the outer part is called stator having coils supplied with three phase AC current to produce a rotating magnetic field. The inside rotating part is called rotor attached to the output shaft that is gives the useful torque produced by the rotating magnetic field. The stator is made up of stack of steel laminations of 0.35-o.5 mm thick with slots similar to a stator of a synchronous machine. The Coils are placed in the slots to form a three or single phase winding. **Figure 1A** shows the stator stampings with slots of induction motor **Figure 1B** shows the stator of induction motor [6].

The rotors of induction motors are of two types namely squirrel cage rotor and slip ring rotor. The squirrel cage rotor is made up of punched laminations with (0.35 to 0.5) mm thick steel core with rotor slots. Aluminum bars are molded in the slots instead of winding. End rings short circuit the aluminum bars at each side [6]. **Figure 2** shows the squirrel cage rotor.

three brushes through which three resistances can be connected in three phase star configuration for reducing starting current and speed control as well as increasing

The various IM control techniques are classified in to scalar and vector control methods. The general classification of IM control strategies [8, 9] which are based

The various scalar control methods are as follows 1. Stator voltage control 2. frequency control 3. Voltz/Hertz (V/F) control 4. Rotor Voltage control 5. Changing the number of poles. Out of these scalar methods, V/F control method is the best scalar control method. It can able to adjust the speed of the Induction motor by controlling the amplitude and frequency of the stator voltage of induction motor, the ratio of stator voltage to frequency should be kept constant so that, it is called as V/F control of induction motor drive. The vector control is preferred over scalar control methods due to the following disadvantages of scalar methods 1. Control of

the torque [6]. **Figure 3** shows the slip ring rotor.

*Torque Ripple Reduction in DTC Induction Motor Drive*

*DOI: http://dx.doi.org/10.5772/intechopen.94225*

**3. Classification of IM control strategies**

**3.1 Scalar control**

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**Figure 2.** *Squirrel cage rotor.*

**Figure 3.** *Slip ring rotor.*

on the variable frequency control is shown in **Figure 4**.

The slip ring rotor or wound rotor has windings like the stator and at the end of each phase the winding is connected to a slip ring. There are three slip rings and

**Figure 1.** *(A) Stator stamping with slots of induction motor. (B) Stator of Induction Motor.*

*Torque Ripple Reduction in DTC Induction Motor Drive DOI: http://dx.doi.org/10.5772/intechopen.94225*

**Figure 2.** *Squirrel cage rotor.*

**Figure 3.** *Slip ring rotor.*

three brushes through which three resistances can be connected in three phase star configuration for reducing starting current and speed control as well as increasing the torque [6]. **Figure 3** shows the slip ring rotor.
