Project

Speed Control of an Induction Motor

The speed control of induction motor is constant and can be made variable by various methods. But we have to find the most reliable and cheap method for regulate the speed of an induction motor. There are methods like pole changing, voltage control but in each and every case there is some or minor causes which make them difficult and expensive. But in this project we are using Bridge type cyclo-converter which controls the speed of an induction motor. In this we are firstly giving the 230V supply and there is step-down transformer is used, which converts 230V to 5V. In next step we are using the voltage regulator which regulates as well as avoid the harmonics in the power output of 5V. Then we are controlling the bridge type cyclo-converter by using the ATMEL series 8051 microcontroller. This works at 5V that’s why we are using the step-down transformer. By varying the number of poles and varying the frequency (in proportion to voltage) are two methods to change the speed of induction motor. But, we can also employ the method which control the time delay of cyclo-converter. The speed control through the first method is uneconomic and the number of poles cannot be changed under running conditions and the size of the machine also converts large. It is also very hard to control the voltage by varying frequency. So, in this method we control the speed of an induction motor by controlling time delay. In this method, we programmed the microcontroller with time delay code which regulate the bridge cyclo-converter with fixed time delay of 20ms and 30ms for the f/2 and f/3 frequency respectively. 8051 Series microcontroller is used with a twosome of slide switch to choose the required speed of range of the operation of an induction motor. These controls switch interfaced with the microcontroller. The status of the switches enables the microcontroller to deliver the pulses to trigger the SCR’s in a dual bridge. By that we can control the speed of an induction motor.