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How to control speed of DC motor?
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How to control speed of DC motor?

Views:0     Author:Site Editor     Publish Time: 2021-09-22      Origin:Site

The speed control mechanism is suitable for many situations, such as controlling the movement of robotic vehicles, the movement of electric motors in paper mills, and the movement of electric motors in elevators that use different types of DC motors. The speed control of a DC motor is one of the most useful functions of the motor. People may wonder what the function of a DC motor is. It is important to understand the speed control of a DC motor.


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How to control speed of DC motor

Flux control method and armature control method

Voltage control method

 

(1) How to control speed of DC motor

Usually, we want to control the speed of a DC motor as needed. This intentional change in the drive speed is called the speed control of the DC motor.

We can control the speed of DC motors manually or through automatic control equipment. This is different from speed adjustment-speed adjustment can resist natural speed changes caused by changes in the load on the shaft.

The speed of the DC motor (N) is equal to

N = K (V-IaRa)/ø where K is a constant.

This means three things:

The speed of the motor is proportional to the power supply voltage.

The speed of the motor is inversely proportional to the armature voltage drop.

As found on site, the motor speed is inversely proportional to the magnetic flux.

Therefore, the speed of the DC motor can be controlled in three ways:

By changing the magnetic flux and the current through the field winding

By changing the armature voltage and armature resistance

Through the supply voltage

 

(2) Flux control method and armature control method

Due to the field winding, the magnetic flux changes to change the speed of the motor. Since the magnetic flux depends on the current flowing through the field winding, it changes by changing the current flowing through the field winding. This can be achieved by using a variable resistor in series with the field winding resistance.

Initially, when the variable resistor is kept at its minimum position, the rated current flows through the field winding due to the rated power supply voltage, so the speed remains normal. When the resistance gradually increases, the current through the field winding will decrease. This in turn reduces the magnetic flux generated. Therefore, the speed of the motor increases beyond its normal value.

The control of the armature resistance can control the voltage drop across the armature. In this way, the speed of the DC motor can be controlled. This method also uses a variable resistor in series with the armature.

When the variable resistor reaches the minimum value, the armature resistance is the normal value. Therefore, the armature voltage drops. When the resistance value gradually increases, the voltage across the armature will decrease. This in turn causes the motor speed to decrease. In this way, the method can make the speed of the motor lower than its normal range.

 

(3) Voltage control method

Neither of the above methods provide speed control within the desired range. Moreover, the magnetic flux control method will affect the commutation. The armature control method causes huge power loss due to the use of resistors in series with the armature. Therefore, a different method is usually required-a method of controlling the power supply voltage to control the motor speed.


In this method, the field winding receives a fixed voltage and the armature obtains a variable voltage. One such voltage control method technique involves the use of a switch gear mechanism to provide a variable voltage to the armature. Another generator driven by an AC motor provides a variable voltage to the armature (called the Ward-Leonard system).

In addition to these two technologies, the most widely used technology is the use of pulse width modulation to achieve speed control of DC motors. PWM involves applying a varying pulse width to the motor driver to control the voltage applied to the motor. This method has proven to be very effective because the power loss is kept to a minimum and does not involve the use of any complicated equipment.


PWM is realized by changing the pulse applied to the enable pin of the motor driver IC to control the applied voltage of the motor. The pulse change is completed by the input signal of the micro-controller through the button.

Hope we have covered all the detailed information and related descriptions of DC motor speed control.

 


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