Motor/driver for smoothest and most constant speed

brushless-dc-motordriverencodermotorpwm

Which type of motor/controller can maintain the smoothest and most constant speed in the range 300 – 1000 rpm with minimal vibration? ie: low cogging torque, etc.

I have an application in mind which requires spinning a 100mm diameter 0.5kg static load.

I have been advised to consider the following options, most of which I know nothing about and need help deciphering them:

sensorless low kV BLDC motor with FOC control
PMSM with space vector modulation
high current control bandwidth
HAL sensored brushed DC motor with many (odd numbered) commutators
encoder with high current control bandwidth
rhombic winding

One example development guide can be found in microchip website and video demonstrations of similar setups here and here

Best Answer

Without more info it's hard to do other than generalize, but for low torque ripple a permanent magnet sinusoidally wound BLDC (synchronous motor) with position feedback from a resolver or high resolution encoder and a driver that creates true sinusoidal excitation (via conventional/FO control using SVM or 2 phase current feedback PWM) will give smooth torque and low torque ripple.

Avoid trapezoidally wound BLDC motors, hall sensor feedback, switched reluctance motors, and sensorless commutation schemes (unless you know they perform very well with your particular motor in your speed range of interest.)

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Yes, it turned out that that crossover was significant. I have now manually tuned things so there is no overlap, but now too much dead time is preventing me from going to higher frequencies.

Please feel free to comment on the circuit diagram if there are things that you see I might be able to improve.

Electronic – arduino – Motor speed control using arduino and quadrature encoders

It looks to me that your control loop is essentially:

if speed is too slow:
    increase PWM duty cycle one unit
if speed is too fast:
    descreate PWM duty cycle one unit

As you have observed, this doesn't work so well. Your control loop cyclically overshoots the target speed.

The canonical solution to this sort of problem is a PID controller. The concept is essentially the same, measure a thing and compare it to a target to calculate an error. Then adjust something (in your case, PWM duty cycle) based on the error.

However, a PID controller has three error terms:

P: the current error
I: the integral of the error
D: the derivative of the error

For each of these terms, the controller has programmed some gain. It then multiplies each term by the respective gain to calculate how much the control input (PWM duty cycle) should be changed. Properly tuned, this allows you to get a feedback loop that at first ramps up the duty cycle, then as your vehicle approaches the target speed, backs off smoothly so you get a minimum of overshoot.

Best Answer

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