# Three phase brushless motor controllers with back EMF suggestions

#### jlawley97

Joined Oct 5, 2019
25
[unsure if this is correct forum, but Ive used it to talk about inverters in the past]
Hello, I am working with a co worker on making essentially a electronic centrifugal pump. We are currently at the stage where the cheap motor driver we purchased is limiting the speed of the rotor as it is reaching a fault mode if the duty cycle is too high which equates to only about 500rpm. The driver is also outputting at 20kHz, and it our belief that this frequency is too low and limiting the speed. Looking a motor drivers such as https://makermotor.com/pn00110-24c-brushless-bldc-24v-motor-driver-speed-controller-17a/. They list the input PWM frequency but not explicitly what the output frequency would be and assuming the input PWM to be the output PWM would make it a lower top frequency.

this is an ongoing research project and obviously a proprietary driver circuit will be produced but at this point the goal is to get flow data so we just need a sufficient driver.

Joined Jul 18, 2013
26,291
Strange that they do not show any commutation inputs, for a BLDC motor there is usually 3 sensor outputs for each phase.
I wonder if it is actually a 3ph motor driver? The motors are identical except for commutation.
.

#### Alec_t

Joined Sep 17, 2013
13,232
assuming the input PWM to be the output PWM
If I understand the usual function of such a driver correctly (I could be wrong), the input PWM frequency has no direct relation to the output frequency. The input PWM is likely averaged to provide a DC signal proportional to the duty cycle. That signal is used by a microcontroller as a 'target speed demand'. The 3-phase output frequency (non-PWM) will be ramped up from stationary and will depend on the number of poles the motor has and the actual rotational speed.
How high is your target rpm?

Joined Jul 18, 2013
26,291
The 3-phase output frequency (non-PWM) will be ramped up from stationary and will depend on the number of poles the motor has and the actual rotational speed.
If so then it is not BLDC as described!

#### shortbus

Joined Sep 30, 2009
9,762

#### jlawley97

Joined Oct 5, 2019
25