Head of EEE Department Sarada Institute of Technology & Science, Khammam, AP, India.
Dr. B V Sanker Ram
Prof. EEE Department JNT University, Hyderabad, AP, India
Dr K.Raghu Ram
Laqshya Institute of Technology & Science, Khammam, A.P, India
- I. INTRODUCTION
This thesis proposes a speed control for induction motors without and with multi-level inverter. In this proposed method, V/F based speed control of Induction Motor drive have been simulated using MATLAB. The simulated results have shown improved performance over without Multi-level inverter & PI controller. It has been seen that SVPWM technique generate lesser Harmonic distortion in the output voltage and current applied to the phases of an induction motor. Owing to its simplicity this strategy can be used as backup control strategy in the event of sensor failure.
- II. LITERATURE SURVEY
Induction machines (IM) have been widely used in a variety of industrial and residential applications. Right from its inception its ease of manufacture and its robustness have made it a very strong candidate for electromechanical energy conversion device. Induction motor is existing from fractional horsepower ratings to megawatt levels. To control the induction machine there are different types of control strategies are used.
The most commonly used control strategies are constant V/f control and vector control. In constant V/f control the working principle is based on the constant relation between voltage and frequency. By applying a specific phase voltage and frequency to induction machine, it can settle down at a desired speed. However, the speed control of conventional constant V/f controls lacks
accuracy due to the existence of the rotor slip. This results in the increase of error between reference speed and actual speed. This method requires additional voltage and current sensors, so the complexity of the system has been increased.
To overcome this problem vector control method is preferred. The vector control algorithm is based on two currents. An induction motor can be modeled most simply using two quadrature currents rather than the familiar three phase currents actually applied to the motor. These two currents called direct (Id) and quadrature (Iq) are responsible for producing flux and torque respectively in the motor. In addition, at least two current sensors and one position sensor is necessary to meet the minimum feedback requirements of vector control. As a result, the failure of the sensor or even the drift of system parameters could potentially result in system malfunction.
This Thesis has simple, cost-effective and reliable control strategy as a backup control strategy to continue operate the system in case of failure of current and voltage feedback sensors. In this method the space vector modulation technique has been used because it generates less harmonic distortion in the output voltages and or currents applied to the phases of an AC motor and to provide more efficient use of supply voltage compared with sinusoidal modulation technique. The fuzzy logic bases intelligent controller is used instead of the PI controller, excellent control performance can be achieved even in the presence of parameter variation and drive non-linearity.
III. INDUCTION MOTOR
- Basic Construction and Operating Principle:
Like most motors, an AC Induction Motor has a fixed outer portion, called the stator and a rotor that spins inside with a carefully engineered air gap between the two. Virtually all electrical motors use magnetic field rotation to spin their rotors.
In an AC Induction Motor, one set of electromagnets is formed in the stator because of the AC supply connected to the stator windings. The alternating nature of the supply voltage induces an Electromagnetic Force (EMF) in the rotor (just like the voltage is induced in the transformer secondary) as per Lenz’s law, thus generating another set of electromagnets; hence the name – Induction Motor. Interaction between the magnetic field of these electromagnets generates twisting force, or torque. As a result, the motor rotates in the direction of the resultant torque.
The stator is made up of several thin laminations of aluminum or cast iron. They are punched and clamped together to form a hollow cylinder (stator core)