Speed control of Three phase induction motor
Speed control of three-phase induction motor using pic18 microcontroller article will help you to design your project. Three phase induction motors are very popular in industrial, appliances and heavy industry applications. Three phase induction motors are mostly used in motion based applications. Three phase induction motors are robust and reliable in motion based applications. Induction motors runs at specific speed when power is supplied to induction motor. But main problem is control the speed of induction motor. This technical article help you to design variable speed driver for induction motor using pic microcontroller.
Recent development in power electronics made speed control of induction motor very easy. Power electronics made improvement in dynamic and steady state characteristics of induction motor. For example in home washing machine speed need to be control at different steps of washing. This is also a domestic application of induction motor.
Methods for speed control of induction motor
Speed control of induction motor is very complex due to its non linear characteristics. Mainly three methods are used for speed control of induction motor:
- Voltage control method
- Variable voltage and variable frequency method ( VVVF) ( This method is used in open loop applications ) . It can be implemented by low power pic microcontrollers
By reading rated voltage and rated frequency of induction motor from its name plate, you can get the idea of induction motor speed at rate RPM.
Types of induction motors
According to construction of rotor, induction motors are of two types, squirrel cage induction motor and slip ring motors. Stator is almost same in both motors.
- Squirrel cage motor : Mostly induction motors used in industry and domestic applications are squirrel cage type. This because they are simple rugged in construction.
- Slip ring induction motors : Slip rings mounted on the shaft of the motor is basic difference between slip ring and squirrel cage motors.
How to control speed of induction motor
Speed control of induction motor is implemented by two methods as I mentioned earlier in this article. But the most popular method is variable voltage and vaiable frequency (VVVF). In this method Three phase AC voltage is converter into DC using Three phase diode bridge rectifier circuit. A capacitors bank is used to filter AC ripples for DC voltage. This DC voltage is converted back into variable voltage and variable frequency three-phase AC supply using H bridge as Shown in figure below:
Speed control of induction motor using pic microcontroller block diagram
Block diagram for three phase induction motor speed control is given below. Potentiometer connected to ADC of PIC microcontroller is used to adjust the speed of induction motor. PIC microcontroller read value of potentiometer and set new speed of induction motor by changing reference frequency of induction motor.
Three phase diode bridge rectifier converts AC into DC. Three phase voltage inverter converts DC into AC based on PWM controller signal from PIC microcontroller. IGBT or MOSFET driver circuits is used to driver MOSFETS with minimum time from on to off state or off to on state. So to control speed of induction motor using pic microcontroller, you should know that how to design three phase bridge rectifier circuit? How to design three-phase voltage source inverter? How to use Gate driver circuits? and how to use PIC microcontroller to generate PWM signals for H bridge. For complete working check this video
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