IntroductionThe basic principle behind the functioning of an induction motor is electromagnetic induction; which results in the production of a voltage in a conductor primarily due to the effect of the magnetic field (August and Hand 25). Different approaches can be implemented in order to control the induction motors, such as the use of voltage to frequency control and vector control. The simplest approach to controlling an induction motor can be based on the alteration of the orientation of the stator design and winding structure which ensures that the starting current is reduced to desired levels.
Another basic way of controlling induction motors is through the use of pole changing technique, whereby the numbers of magnetic poles in the stator are changed to desired levels (August and Hand 36). In the design of modern induction motors, the stator voltages and respective currents are subject to be under control in order to ensure that the induction motor functions optimally. In the steady state conditions, these parameters are defined by magnitude and frequency. A control technique that basically involves the adjustment of magnitude and frequency are typically referred to as scalar control techniques.
The use of scalar methods in the control of induction motors is generally known to produce transient effects that may turn out to be undesirable due to rapid changes in the magnitude and frequency can result to a disturbance in the torque of the induction motor. Vector control methods usually involve the changes in torque variables (Emadi 56). Vector control is effective in high performance drive systems. The vector control methods primarily rely on the concept of the space vectors for induction motors which employs the use of instantaneous values that are obtained in the respective three phase variables of the induction motors.
Under the vector control technique, the vector variables are manipulated according to the desired control algorithm and the technique is primarily tailored to maintain a constant value of the induction motors torque during the rapid changes in the magnitude and frequency. Vector control methods are generally complex in implementation compared to scalar control methods; current and voltage sensors always play a vital part in the control of induction motors (Emadi 60). Controlling Induction motors using the vector control methodThe controlling of an induction motor is more difficult in cases where the LC filter is deployed.
Such contexts do not warrant the use of a complex vector control. Vector control is used in cases whereby high control performance is required (Gottlieb 58). The inductor current and the capacitor voltage in most cases is controlled by deadbeat controller, the correct voltage reference is obtained by use of a high pass filter stator voltage and also employs the use of the multi-loop feedback controller.
A key challenge in the use of the vector control method in inductor controlling is to maintain the required variables low in order to facilitate control reliability (Gottlieb 65). This control technique makes use of the vector concept. Conventionally, there are three alternating currents in an AC induction motors that are normally displaced by 1200 at the stator coils within the motor (Gottlieb 90). The resultant flux that is evident in the stator winding causes a current to be induced in the coils of the rotor; as a result the rotor generates a field in order to counteract the alternating current induced by the stator which results in a balancing of the torque.
In a DC induction motor, the control of the currents in the can be initiated by an external source, this therefore implies that the currents are controlled by the interaction between the stator fields and the resulting currents that have been induced in the rotors of the induction motor. The limitations of using vector control is that optimal torque cannot be produced since the physical design implementation of the AC induction motors comprises of separate rotor and stator in the design (Hambley 102).