Brushless Direct Current motor run without PWM and without variable resistance

[Madbunny1]

Hi,

Can the BLDC Motor run without PWM techniques? As of I know the answer is no.
Cn anyone clarify?

Thanks

 

[FvM]

A brushless DC can run by just switching an unipolar or bipolar voltage to the stator windings. Most simple BLDC motors, e.g. DC fans are working this way.

 

[c_mitra]

Can the BLDC Motor run without PWM techniques? ...

Of course yes! PWM is only a modulation tool to control average power.

You need three phase power (because BLDC motors are mostly PM rotor and the three phase stator) to run. The three phase power can be produced electronically or a by a motor generator set. Many industrial motor-generator sets produce 400Hz.

You can make three phase power with a very simple circuit: produce a series of pulses and (i) phase I: remove every 2nd and 3rd pulse (ii) phase II: remove every 3rd and 1st pulse (iii) and phase III: remove every 1st and 2nd pulse. Use a big filter to round off the pulses. The scheme does not have the negative part of the sine wave but the point is that it is easy to make pulses 120deg apart.

 

[bala0x07]

Hi Madbunny,

The pwm is no where directly related to drive a BLDC motor. Many people confuse with this because mostly all ESCs (Electronic Speed Controller) takes a pwm input to drive BLDC.

So first get some hints regarding bldc
Actually BLDC motor is not just like a normal brushed DC motor which runs simply by connecting a power supply.

BLDC motors need to change phase in order to run, simply different coil has to be excited in a cyclic manner.
Actually normal motors also need to change phase, but this work is automatically done using the mechanical brushed setup.
But for BLDC u have to control this, how fast you are changing the phase will be the speed if the motor.
If is just connect power supply to any two of it's wire, it will just produce a turn with heavy torque and remain in the same position, then you have to change the power supply in another combination of the wires. Then the other two. Hence finally it will produce one complete rotation.


So finally it's not mandatory to use pwm for its control.
It's all about shifting phases.

Be careful while using them, they are high power. Their current can reach to several amperes. Don't connect any propellers while testing.

Also coils are not rotors in bldc, they are actually the magnets, hence the exterior rotates.

All the best!!!!