Significance of a Back EMF in DC Motors!

 

The brushless DC motor is getting popular because, as its name suggests, it has several advantages compared to the brushed dc motor with wear-prone brushes. BLDC hub motor controller increases the device's durability. A BLDC motor may also be made lighter and smaller than a brush type while producing the same amount of power, making it appropriate for situations where space is limited.

Alternative arrangements are needed to signal the relative positions of the component elements to ease motor control because the stator and rotor of the BLDC motor have no mechanical or electrical contact. BLDC motors accomplish this in one of two ways: by using Hall sensors or detecting back EMF.



                                                  

Take Advantage of Back EMF

Electric motor windings cut through magnetic field lines, acting as a generator. The windings produce a voltage measured in Volts and known as an electromotive force (EMF). This EMF creates a secondary magnetic field that, by Lenz's law, opposes the original change in magnetic flux that propels the motor's revolution. 

In plainer terms, the EMF is a "back" EMF since it opposes the motor's normal motion. The size of the electromagnetic field (EMF) is inversely proportional to the rotor's angular velocity for a particular motor with fixed magnetic flux and windings.

Driving the motor faster than its rated speed significantly reduces the potential difference across the windings, lowering current and torque. The current and torque will equal zero if the motor is pushed further until the back EMF equals the supply voltage. Back EMF is sometimes viewed as a drawback because it reduces the motor's torque, but in the case of BLDC motors, developers have taken advantage of the phenomena.

 

Ways to Detect Back EMF

The back EMF can be measured using a variety of approaches. The simplest is to use a comparator to compare the back EMF to half the DC bus voltage. The three windings may not all have the same properties, which could cause a positive or negative phase shift from the actual zero crossing point. This is the fundamental disadvantage of the straightforward comparator approach. The motor is still probably running, but it might use too much current.

The solution is to use three resistor networks coupled with the motor windings to create a virtual neutral point. And then, the back EMF is contrasted with the fictitious neutral point.

 

So, in the above sections, we have mentioned the importance of back EMF in brushless DC motors and brushed DC motors. This demonstrates how important the back EMF is in the case of DC motors.

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