You will be able to find BLDC motors or brushless DC motors in industrial equipment, appliances and medical instruments as they provide various advantages as compared to others like it.
However, before usingthese motors particularly for blade pitch control, you must first have a complete understanding of its mechanism which consequently results to a fast review of the construction of a DC motor.
A BLDC motor is particular type of servo motors which basically relies on wire coils on rotors and frames of rigid motors which on the other hand places permanent magnets all over the rotor.
Electric current passing through the windings make some magnetic field which either repels it from the magnet or attracts a winding to the magnet. Brushes placed on stators and contacts placed on rotors choose various windings as power while the rotors turn.
In BLDC motors, the coils make up the motors’ outsides and the rotors provide permanent magnets. Once again, the repulsions and attractions of the coils and the permanent magnets make the rotors spin. However, in BLDC motors, commutations do no occur on spinning shafts.
Even though these motors are more expensive than other brush-DC motors, they provide benefits. Their exterior coils dissipate heat better than those on rotors. BLDC motors do not have commutators or brushes to tire out or need maintenance regularly, thus they can function unattended for a very long period of time. Lastly, these motors don’t produce electromagnetic interference or EMI from machine-driven commutators.
Rather than utilizing mechanical commutators, servo motors like BLDC use automated commutation in switching the coils to on or to off. This kind of commutation is classified into two – the sensorless or the sensor-based.
The sensor-based motors, Hall-effect sensors are placed inside the coils of the motor to sense the position of the permanent magnets of the rotors. Microcontrollers or MCU read the states of the sensors and utilize a particular algorithm to know which of the coils to power as well as when.
On the other hand, sensorless motors require MCUs to measure the back electromotive force orr EMF produced across coils by spinning rotors’ magnets. The back EMF or BEMF defines the magnets’ positions.
However, the sensorless method is faced with a challenge because controller as well should power coils consequently to make the motors turn. Thus, how can one separate pulse-width signals of modulation which drive coils BEMF signals?
The answer is quite simple. Program MCUs to filter high-frequency PWM signals out as well as measure BEMF near the time when PWM signals pass through zero Voltage. The BEMF depends on various factors like coil resistance, number of coil windings, rotor magnets strengths and many others.
No comments:
Post a Comment