This project is about variable frequency drive for three phase induction motor using pic microcontroller. In this project voltage frequency control ( V/F ) method is used to control the speed of three phase induction motor. Induction motors has many industrial and domestic applications. . Induction motors are widely used in compressors, washing machines. All induction motors which you buy from market have rated power and rated speed. When you power the induction motor, it will start running at its rated speed. But there are many applications where we need variable speed induction motors. So we need a controller which can make induction motor speed controllable. There are many method to design variable speed drive for induction motor for both single phase and three phase. But in this project, we have designed variable frequency drive by voltage frequency control or V/F method. So now lets start with a introduction of V/F control method for variable frequency drive. You may also like to check my other induction motor related projects:
- Bidirectional rotation of induction motor by Remote control device
- ACPWM control for induction motor using pic microcontroller
- Thyristor controlled power for single phase induction motor
- Soft starter for three phase induction motor using Arduino
What is Voltage frequency control method ( V/F)
V/F method is also known as variable voltage and variable frequency. It is a most popular method for speed control of three phase induction motor. It is used in many variable frequency drive applications. We can control the speed of induction motor by applying a variable frequency supply to induction motor. But if we change the frequency only, it will change the motor flux also. Motor flux is directly proportional to motor torque. So only changing the frequency effects the motor torque also. So we need to keep the flux constant. To keep flux constant, we need to change voltage applied to motor also. Because the voltage applied to induction motor is directly proportional to flux and angular speed of motor. So we need to keep the ratio of V/F constant to maintain flux of motor. Only changing the voltage or current may also saturate the core of induction motor. So V/F ratio should be constant in operating range of induction motor. In this variable frequency drive project, we have used V/F method to control the speed of induction motor.
Implementation of variable frequency drive using pic microcontroller
To implement variable frequency drive for three phase induction motor, we first converted single phase supply into dc voltage using rectifier circuit. This dc voltage is used to generate variable voltage and frequency using pic microcontroller. This dc voltage is given to a input of three phase H bridge. Software for this project is implemented using pic18f452 microcontroller and spwm signals are given to three phase H bridge. induction motor is connected at the output of three phase H bridge.
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