Speed Control Methods in Various Types of Motors

In this blog, we will discuss what speed control is, and the relationship between motors and speed control. By the end of this blog, you will be able to figure out the different speed control methods in various types of motors.

What is Speed Control in Motors?

Speed control is the ability to adjust the speed of a motor according to the requirements of the applications. It plays a vital role in determining the efficiency, performance, and longevity of the motor. The speed control of motors is achieved by controlling the voltage, current, or frequency of the power supply to the motor.

What is Speed Control of a DC Motor?

A direct current motor, termed a DC motor is an electrical machine that transforms direct current electrical energy into mechanical energy.

They are the most common type of motor used in industrial and commercial applications.

It comprises a fixed part known as the stator and a rotating portion called the rotor.

The rotor comprises a coil of wire that interacts with a magnetic field generated by the stator to produce rotational motion. The DC motor’s speed is directly proportional to the applied voltage.  It is inversely proportional to the motor’s resistance. Therefore, to control the speed of a DC motor, we need to vary the voltage or the resistance.

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How can Speed Control of a DC Motor be achieved?

There are several methods of speed control for DC motors. The most commonly used ones are:

• Armature Voltage Control
  • In this method, the voltage supplied to the motor’s armature is varied to control the motor’s speed
  • The speed of the motor can be controlled by increasing or decreasing the voltage supplied to the motor

• Field Current Control
  • The current supplied to the motor’s field winding is varied to control the motor’s speed
  • By increasing or decreasing the current supplied to the field winding, the motor’s speed can be controlled

• Pulse Width Modulation (PWM) Control
  • This method is used for the electronic speed control of DC motors
  • In this method, the voltage supplied to the motor is varied by using a Pulse-width modulation (PWM) signal
  • The average voltage supplied to the motor is varied by changing the duty cycle of the PWM signal.
  • The speed is directly proportional to the average voltage supplied to the motor

Speed Control Method of a DC Shunt Motor

A DC shunt motor is a type of DC motor that has a field winding and an armature winding connected in parallel. These motors are commonly used in industrial and commercial applications requiring constant speed. The speed of a DC shunt motor can be controlled by varying the armature voltage or field current.

The speed control method for DC shunt motors is similar to that of DC motors. The most commonly used methods are armature voltage control and field current control.

Armature Resistance Control

This method involves adding resistance in series with the motor’s armature. By varying the resistance, the voltage drop across the armature can be controlled, which in turn controls the motor’s speed.

Field Control

This method involves varying the amount of current flowing through the motor’s field winding to control its speed. By decreasing the field current, the motor speed can be increased, while increasing the field current will decrease the motor speed.

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What is Speed Control of an Induction Motor?

An induction motor is a type of motor that works on the principle of electromagnetic induction. It also consists of a stator and a rotor. When an AC voltage is applied to the stator, it creates a rotating magnetic field that induces a current in the rotor, causing it to rotate. Induction motors are widely used in industrial applications due to their simplicity, reliability, and low cost. The speed of an induction motor is dependent on the frequency of the power supply to the motor.

Therefore, to control the speed of an induction motor, we need to vary the frequency of the power supply.

AC Motor Speed Control Methods

An AC motor is similar to an induction motor and works on the same principle. The internals are also nearly identical and the working principle is also almost the same

It consists of a stator and a rotor. The stator generates a rotating magnetic field, which induces a current in the rotor, causing it to rotate.

AC motors are used in a wide range of industrial and domestic applications.

The speed control of AC motors is achieved by varying the frequency of the power supply to the motor.

The most commonly used methods of speed control for AC motors are:

• Variable Frequency Drive (VFD)

A variable frequency drive is an electronic device that is used to control the speed of an AC motor. It works by varying the frequency of the power supply to the motor.

The speed of the motor is directly proportional to the frequency of the power supply.

• Voltage Control

In this method, the voltage supplied to the motor is varied to control the motor’s speed. By increasing or decreasing the voltage supplied to the motor, the motor’s speed can be controlled.