soft starter for single phase induction motor using pic microcontroller

Soft starter for single phase induction motor using pic microcontroller is a power electronics device. Soft starter project is used to smoothly start single phase and three phase induction motor. But this project is for single phase induction motor only. I will also post a project on soft starter for three phase induction motor in next article. In this soft starter project, PIC16F877A microcontroller is used  to provide firing angle control signals to thyristor. Soft starter is a technique which is used for the protection of induction motor. You may also like to check our other induction motor related projects:

• Speed control of three phase induction motor using pic microcontroller
• Variable frequency drive for three phase induction motor
• thyristor controlled power for single phase induction motor

Why we need soft starter for induction motor?

When we supply power to induction motor, initially it takes more than the rated current of induction motor. This initial current is also know as inrush current.  So we need a device which can control this inrush current. Inrush current is very dangerous for induction motors. Because it can damage induction motor winding and also it is wastage of resources. So to limit the starting current of induction motor, soft starter is used. Inrush current required only at the starting of motor. After motor reaches its full speed speed, motor also start to draw steady state current. But the chances for the motor to get damaged during starting is very high. Therefore soft starter is used to start induction motor smoothly.  So Now lets see how soft starter works.

What is soft starter for single phase induction motor?

As I mentioned earlier, soft starter is a device which is used to run or start induction motor smoothly. Bu now the question is. How the soft starter makes the induction motor to start smoothly. Soft starter applies controlled voltage to induction motor. By applying gradually increasing voltage from low to high. As I mentioned earlier motor draws high current at the start than its rated capacity. So the voltage applied to the induction motor increases gradually from low to high value so that motor can draw small current at the start according to applied voltage. Because at low voltage motor will draw low current and at higher voltage motor draws high current.  So this gradual increase in voltage stops the motor to withdraw inrush current and helps the induction motor to start smoothly. This is also known as smooth start of induction motor.

Soft starter for single phase induction motor using pic microcontroller

Software starter for single phase induction motor consists of following main components.

• Zero crossing detector circuit : This circuit is used to detect zero crossing signal of ac power supply.  Because firing angle which is used to control thyristor operating angle is triggered at every zero crossing.
• PIC16F877A microcontroller: PIC16F877A microcontroller senses zero crossing and generates triggering pulse at specified firing angle.In soft starter, Firing  angle will be maximum at the start, because we want minimum voltage at the start. After that firing angle will be decreased gradually, so that voltage also increase gradually.
• Thyristor or Two back to back Silicon controlled rectifiers : Thyristor is used as a switch.
• Optoisolator : It is used to provide isolation between pic microcontroller and high side voltage operating circuit.

Circuit diagram of soft starter for single phase induction motor

Circuit diagram of soft starter for single phase induction motor using pic microcontroller is given. I have already explained the all the components of this circuit diagram above. 

In above circuit diagram, lamp is used as load instead of induction motor. Because induction motor is not available in Proteus. Because we just want to check the functionality of voltage change gradually at the start from low to high value. So AC voltmeter is also connected parallel to lamp to check change in voltage. Oscilloscope shows the operating range of firing angle from maximum to minimum.  For more details about the working of this soft starter project using pic microcontroller , check the simulation given below:

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