How to control the 3-phase brushless dc motor?

[tcad]

Hello,

I have some questions about the 3-phase brushless dc motor. Could you give me some help? Thank you very much.

I know there are two different control method for the 3-phase brushless dc motor, one is the sensorless DSP control and one is to use the hall position sensor. I'd like to know which is better and common in the industral? what's the different?

The power wave for the 3-phase brushless dc motor is trapezoidal wave and some is sinusoidal wave? The six-step control with switches 120 degree on can produce the trapezoidal wave? How to produce the sinusoidal wave for the brushless dc motor? 180 degree on?

Where do the neutral point of the 3-phase brushless connect to in the reality? When I do the simulation the results are very different if I connected it to ground or just let it float.

Thanks again.

tcad

 

[kirkpong]

1. For the control methods of this motor, they depend on user environment. If it is very critical (high temp or etc), sensorless is needed because hall effect sensor (for sensor control) is very sensitive for high temperature).
2. For sine or trapezoidal, it depend on wiring on stator(distribute as sine or salient pole, respectivelty) not switching method. For 120 and 180 degree, we applied them to trapezoidal, only.
3. For neutral point of the motor, as I have seen, it was not connected in any point of circuit
Bye

 

Hi kirkponq,

Thank you very much.

I have another question about the bldc motor control. I find it is difficult to use six-step(trapezoidal) method for the position control. because the the BLDC changes rotating direction frequently. and always has some error in the position. but it is more easy to use the sinusoidal waveform for the position control. I wonder if the BLDC with six-step comutation scheme is often used for the position control?

Thanks again.

Min

 

[cbarn24050]

Hi, the usuall method with these motors is to use an ac resolver on the motor shaft.

 

[DeanBanks]

When using BLDC motors in position control applications, adding a dedicated encoder or resolver to the motor output shaft allows you to close the loop around position at whatever resolution you require.

-Dean