# Sinusoidal control of BLDC motor

#### electronicsLearner77

Joined May 26, 2012
125
I am referring to the following application note AN1017. I find so many calculations going on very confused. So many questions but if some one can help to understand the first basic thing then i can go advance a little.

The TImer1 input Clock converts what? Why should i take Timer1? In the sense let us take some 20MHz as the clock. The motor is running at let us say 6000 rpm (rotations per minute) => (6000 / 60) rps (rotations per second) => 100 rps. For 10 pole motor it is 100 * 10 rps. How to proceed to the next step is it something like
1000 rotations ---> 1 second
(?) rotations ---> (1/20MHz)

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Joined Jul 18, 2013
19,163
Timer 1 clock is the frequency of the clock running the picmicro timer timer 1 , and using the 1:64 prescale ratio (timer/64) in this case.
Max.

#### electronicsLearner77

Joined May 26, 2012
125
There is one more statement as shown

There is a statement "Rotating electric field in the stator that is 90 degrees ahead of rotor field". Does it mean that the sine wave driving produces maximum torque at all times compared to trapezoidal driving? Is this configuration same as FOC since here also we try to achieve max torque? Please advise.

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#### electronicsLearner77

Joined May 26, 2012
125
Thank you very much for the link. So, it is confirmed that i need to implement FOC. But currently i have one limitation i do not have any position detection sensors except the hall sensors. I want to predict the rotor position using Hall sensors. Can I proceed to do it? Please advise.

#### electronicsLearner77

Joined May 26, 2012
125
Just one clarification the algorithm on page 14 or the document itself refers to the sinusoidal control so i can do with sinusoidal control for maximum torque and not required to go for FOC. Am i correct or again in wrong direction.

Joined Jul 18, 2013
19,163
It is a general rule that BLDC control over sinusoidal produces more torque in a P.M. 3 winding motor, just that in open loop velocity control, the BLDC motor produces 'cogging' effect at low RPM, the way around this is to control with a PID loop which can eliminate it.
I have mainly experimented with BLDC, although I do have the MC-LV development board.
Max.

#### electronicsLearner77

Joined May 26, 2012
125
One more doubt is how to confirm that I am actually generating the sinusoidal voltage? I checked the phase to phase voltage they are a kind of pwm signals with varying duty cycle. Is it possible that can i see a continuous wave form in the form of sine wave. Does the phase currents will be like a sine wave? Please advise.

#### tsan

Joined Sep 6, 2014
92
One more doubt is how to confirm that I am actually generating the sinusoidal voltage?
You can connect RC filter to pwm pin (PWM pin to ground). Select resistor and capacitor values so that PWM frequency is filtered but fundamental frequency is not too much attenuated. You can see waveform of the generated voltage by measuring the voltage across the capacitor.

#### electronicsLearner77

Joined May 26, 2012
125
Thank you for the reply. In the document attached in post 1 in one of the pages the following diagram is shown

This the phase to phase voltage. So with a differential probe can't I see this waveform? Please advise.

#### tsan

Joined Sep 6, 2014
92
If PWM is filtered on both phases, you should see sinusoidal waveform like in figure 16, when measuring between the two phases. Without filtering you see PWM pulses like you wrote earlier.