how to reduce current and align the waveform

[Sudhakar R]

hi,
i am working in sensor-less bldc motor control using bemf zero crossing detection . my problem was

• dc_current is 10.9amp
• rms ac current is 17.1
• peak to peak AC current is 67.2
• motor rpm is 2000

i got the uneven current and trapezoidal voltage waveform. i have attached the BEMF circuit , OP-Amp output and phase to ground and current waveform.

image-1 back emf circuit

image - 2 op-amp output

channel 1 is op-amp outA, channel 2 is op-amp outB and channel 3 is op-amp outC

image - 3 phase to ground and current waveform

channel 1 is phase to ground waveform and channel 2 is phase current wavefrom. i got the uneven voltage and current waveform. how to solve this problem.

 

[crutschow]

i got the uneven voltage and current waveform. how to solve this problem

Why is that a problem?

 

[D.A.(Tony)Stewart]

Do you need a tracking filter for V and a bipolar limiter for I??

 

[Sudhakar R]

Why is that a problem?

yes, that is my problem

 

[D.A.(Tony)Stewart]

The problem is you must define what you need then apply common methods to achieve it.

Can you draw what you expected?
Or draw an average over each small interval.

I see 3 intervals.
-PWM,
- open decay
- DC pulse with some RL + BEMF response.

Why did you use this circuit to compare sum of ABC to each? What is the attenuation expected of PWM?

Where do you expect BEMF Zero Crossing?
What do you need?

 

[crutschow]

yes, that is my problem

Again, what is the problem?
What do you want to see that would not be a problem?

 

[D.A.(Tony)Stewart]

(hint @crutschow wants you to articulate with a better question with specific details).