Announcements

# Calculation method for Flux estimator time constant

## Calculation method for Flux estimator time constant

Level 5
Level 5

Hi,

I don't understand how to calculate this part. Reading the datasheet doesn't make sense.

1. Can you explain what Tpwm means?
2. Can you explain what Flxtau means?

I need a calculation for Flux estimator time constant.
Can anyone explain this part easily and briefly?

I don't understand even if I read the datasheet.
Even if I calculate based on the expression in the Data Sheet, I keep getting strange values.

Please share the easy calculation method so that I can understand it.

Regards.

1 Solution

## Re: Calculation method for Flux estimator time constant

Moderator
Moderator

Hello

The Flux Estimator Time constant mentioned in the Figure of the original post has typical range of 0.01 to 0.025. From the equation, we can see that the Flux Estimator Time Constant depends on two parameters: 1. Flxtau and 2. TPWM.

The user can choose a value of TPWM based on several factors like power dissipation and thermal considerations. The choice of TPWM may not be decided by Flux Estimator Time Constant. Therefore, FlxTau may be selected such that the value of Flux Estimator Time Constant may be within the range of 0.01 to 0.025. A thumb rule is that the FlxTau may be selected as 4 to 5 times the value of L/R. However, certain applications may need much higher values of FlxTau.

What we enter in the MCEWizard is FlxTau.

I hope this clears the doubt regarding Flux Estimator Time Constant.

RupakC
6 Replies

## Re: Calculation method for Flux estimator time constant

Level 5
Level 5
Hi,
I understand that you are having trouble understanding Tpwm and Flxtau, as well as calculating the Flux estimator time constant. Let me explain these terms and provide a simple calculation method.
1. Tpwm: This term represents the PWM (Pulse Width Modulation) period. It is the time duration between the start of one PWM cycle and the start of the next PWM cycle. The PWM period is the inverse of the PWM frequency (Fpwm). So, Tpwm = 1/Fpwm.
2. Flxtau: This term represents the Flux estimator time constant. It is a parameter that determines the speed of the flux estimator in the motor control algorithm. A smaller Flxtau value results in a faster flux estimator, while a larger Flxtau value results in a slower flux estimator.
To calculate the Flux estimator time constant, you can use the following formula:
Flxtau = Tpwm / (2 * PI * Fc)
Where: - Tpwm is the PWM period (as explained above) - Fc is the desired cutoff frequency for the flux estimator
Assuming you have the values for Tpwm and Fc, you can plug them into the formula to calculate Flxtau.
Please note that the choice of Fc depends on your specific motor control application and requirements. You may need to experiment with different Fc values to find the optimal performance for your system.
I hope this explanation helps you understand these terms and calculate the Flux estimator time constant. If you have any further questions or need more clarification, please feel free to ask.
Regards.https://www.infineon.com/cms/en/product/sensor/current-sensors/tle4971-a120n5-u-e0001/?redirId=20506...
https://www.infineon.com/cms/en/product/sensor/current-sensors/tle4971-a075n5-e0001/?redirId=205087
https://www.infineon.com/cms/en/product/sensor/current-sensors/tli4971-a075t5-e0001/
https://www.infineon.com/cms/en/product/evaluation-boards/eval-m3-im564/
https://www.infineon.com/cms/en/product/evaluation-boards/tli4971-eval-120a/?redirId=199127

## Re: Calculation method for Flux estimator time constant

Moderator
Moderator

Hello @JasonLEE

For speed control, please use a value of 4-5 times that of (L/R) for Flux estimator Time constant (Q60 of MCEWizard).

However, for current control, the default value is set up at 15 ms. For a correct startup with high inertia loads, it is not unusual to see an increase of 5 times this value for obtaining a better low-frequency signal reading. Thus, for high inertia loads, this parameter needs to be tuned by trial.

Tpwm is the Time period of the PWM. For example, if PWM frequency is 10Khz, then Tpwm = 1/fpwm = 100 microseconds.

Regards

RupakC

## Re: Calculation method for Flux estimator time constant

Level 5
Level 5

Hello, @RupakC

I calculated the calculation based on 0.02 seconds.
I think there was a problem with this part.
I will calculation to as you guided me.

If your explanation is correct, is 8khz=80microsseconds correct?

I'm using speed mode and I've rotated the motor with the value of calculating it the way you told me to, and the motor stops with a ton of noise.

Thanks

## Re: Calculation method for Flux estimator time constant

Moderator
Moderator

Hii @JasonLEE

I did not understand your last comment about paying of bills. I never asked you for any bill payment. Infineon does not ask its customers to pay any kind of bills for using Infineon community.

A PWM frequency of 8KHz would mean that the Tpwm would be 1/8000 = 125microseconds.

Regards

RupakC

## Re: Calculation method for Flux estimator time constant

Level 5
Level 5

Hi, @RupakC

Fpwm=8khz
Tpwm=125
Flxtau=0.02
Flux Estimator time constant = 13.1msec

## Re: Calculation method for Flux estimator time constant

Moderator
Moderator

Hello

The Flux Estimator Time constant mentioned in the Figure of the original post has typical range of 0.01 to 0.025. From the equation, we can see that the Flux Estimator Time Constant depends on two parameters: 1. Flxtau and 2. TPWM.

The user can choose a value of TPWM based on several factors like power dissipation and thermal considerations. The choice of TPWM may not be decided by Flux Estimator Time Constant. Therefore, FlxTau may be selected such that the value of Flux Estimator Time Constant may be within the range of 0.01 to 0.025. A thumb rule is that the FlxTau may be selected as 4 to 5 times the value of L/R. However, certain applications may need much higher values of FlxTau.

What we enter in the MCEWizard is FlxTau.

I hope this clears the doubt regarding Flux Estimator Time Constant.

RupakC