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Sensored BLDC motor issue

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RenesasT

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Hello All,

Again, I need one more help on the sensored BLDC motor.

I am developing a driver which is having max current protection 20A. The motor is driven on 12V and 24V.

The motor is 3 phase BLDC motor.

My driver gives motor speed as 1800 RPM at 24V ,1.3A without load and 900 RPM at 12V,0.9A without load.

I have checked other 2 and 3 drivers which has dedicated IC in the circuitry for BLDC motors. They are giving following speeds,

2000 RPM at 24V , 1.5A current
1100 RPM at 12V, 1.1A current

My project is to change those dedicated IC's with micro controller. I have implemented and its working fine. All functionalities are working fine.

The project is not acceptable because of speed characteristics are not matching. Other functions are OK. Just speed characters are not fine,

It would be 1000000000 times helpful for me if you all guys will help me in this issue, So that I can submit my project.

Awaiting for your reply.
 

Hi,

It´s not clear to me what you need.
There is no question.

If you are just worried about the voltage-to-speed relationship...
* then you should give a valid specification ... with tolarance.

No_load_RPM of a motor will depend on:
* aging
* temperature
* type of motor
* production tolerance

A loaded motor RPM will be less than unloaded RPM.
But usually a motor is meant to drive a load ... so - in my eyes - it is more important to specify a loaded_RPM than an unloaded_RPM.

Klaus
 

Hello KlausT,

The loaded speeds are also less.

My driver is giving 100 RMP less than others.

I need your help to check what could be the issue. Please tell me which information you will need.

Please let me know, if you will need test report for the same.
 

Hello All,

If speed issue gets resolved then I would be able to submit my project.

Please help me with this. If you need any other information please let me know.
 

I am getting 100 RPM lesser than other drivers. I need to match the speed.
 

Hi,

If you loose RPM, then the cause may be:
* too much voltage drop in the driver (measure the voltage drop with a scope)
* wrong operation mode of the driving circuit (fast decay mode) (measure voltage waveform with a scope)
* too much delay between hall signals to driver signals (measure delay time with a scope)

We don't know which one is the case. Maybe a combination.

****
Btw: how did you test it? With exactely same supply? With exactely same motor? With exactely same RPM measurement tool?

Klaus
 

Hello KlausST,

I had test it on dynamo meter.
The supply was same for both the drivers i.e 24V. and form same source.

The motor is not changed. Motor is also same.
The RPM measurement tool is also same.

What can be done to increase the speed.

I had calculated efficiency of both the drivers.
The driver with is giving proper speed has max efficiency of 82%. My driver is giving max efficiency of 80-80.5%.

please suggest.
 

Hi,

What can be done to increase the speed.
Click to expand...
1) you can do with "trial and error". For this you don´t need us

2) or you can do it straight forward: First find the cause, then correct the issue.
--> for this you need to follow my recommendations of post#6

Klaus
 

Hello KlausST,

I had tested it again. What I found is,

I am controlling signals from MCU. There are total 6 signals required from MCU.

From those 6 sigals Upper MOSFETS, I have configured as high and low logics.
Downer MOSFETS, I have configured as PWM signals.

Shall I reverse this thing to get more speed.

Like downer MOSFETS to be used as high and low logics and upper MOSFETS as PWM.

Does this will increase the speed?. If any way is to increase the speed, please let me know.
 

Hi,

Sorry for saying this, but you are really lazy with giving informations.

Here an example:
From those 6 sigals Upper MOSFETS, I have configured as high and low logics.
Downer MOSFETS, I have configured as PWM signals.
Click to expand...
We need to assume that you use a driver fir high side mosfet gates.
These are usually supplied with a bootstrap circuit.
But bootstrap circuit needs a minimum PWM duty cycle to operate well.
So driving HIGH or LOW is no good idea.

But it's just guessing without schemati , without code, without scope picures.

Those scope pictures I requested a couple times already.

Don't get me wrong, it's my spare time here...
And always requesting the same informations is a waste of time for me...

Klaus
 

Hello KlausST,

Please find the schematic of my driver.

View attachment AP3.pdfView attachment AP3.pdf

Please find the commutation code of my drive. The code also consist of code of ADC for Throttle which is used to change the RPM.

Code: 
ak=P6;     
 if(state==0)danticlock(&ak);



void danticlock(unsigned char *seq)
{
 switch(*seq)
 {
  case 3:
  U1=0;U2=1;U3=1;
  B1=prd;B2=ducycle;B3=prd;
  break;
  case 2:
  U1=0;U2=1;U3=1;
  B1=prd;B2=prd;B3=ducycle;
  break;
  case 6:
  U1=1;U2=0;U3=1;
  B1=prd;B2=prd;B3=ducycle;
  break;
  case 4:
  U1=1;U2=0;U3=1;
  B1=ducycle;B2=prd;B3=prd;
  break;
  case 5:
  U1=1;U2=1;U3=0;
  B1=ducycle;B2=prd;B3=prd;
  break;
  case 1:
  U1=1;U2=1;U3=0;
  B1=prd;B2=ducycle;B3=prd;
  break;
 }
}

Please let me know, what you will need apart from this..
 

Hi,

The schematic without values is about useless.

But what can be seen so far:
You never tested the voltage drop of your motor driver as I recommended in post#6.
This is 3 days ago. You are stealing your own (and my) time.
Without values it's just guessing, but with 24V input...I assume your motor never sees more than 20V.
The difference voltage decreases the motor speed, decreases motor torque, decreases efficiency = increases heating of your Mosfets.
--> use a proper Mosfet high side driver

I wonder: did you never look at other schematics and application notes on how to drive high side N-ch Mosfets?
Did you never wonder why they use dedicated circuits with bootstrap supply?

My recommendation for your next project:
* read through application notes
* read how other designs are made and about their benefits and drawbacks
* at least: do a simple measurement (especially when you are told to do)

Don't get me wrong. What I want is, that with your next application you are faster and the same time you get a better result.

Klaus
 

Hello KlausST,

Please let me know, how to measure the voltage drope using scope.

I will tell you the answer. Please suggest.
 

Hi,

You never used a scope?

The best way is to measure one motor line (= power bridge outptu) referenced to your system GND.
If you have a second channel, then measure power bus voltage with it.

Timing: one screen should contain 1-2 PWM cycles.
Upload the scope picture. And give additional description, like scope setup, channel name...

The low side dropout: lower horizontal line voltage of motor signal
High side dropout: power_bus_voltage - higher horizontal line of motor signal

Klaus
 

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