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# Unable to reach full speed

Level 3
Level 3

Hello,

I am having a strange problem, I cannot push the motor over a certain speed.
I have a 7200rpm motor, but I am able to make it spin only up to nearly 4000rpm.
The strange part is that it is not giving errors, the drive accepts the target speed (say, 6500 rpm) but is not able to push the motor over 4000 rpm.

I have tried to change parameters like Field Weakening and back-EMF, and I could reach up to 5000rpm, but never full scale.

I have noticed that when it is unable to accelerate the current current looks like this

Instead, when it running normally it looks like this

I am a bit confused, what other parameters should I check?

Kind regards to anyone who takes the time to answer,

Marco Negrini

1 Solution

# Re: Unable to reach full speed

Moderator
Moderator

Hi @mngr05,

The parameter Ques 60: Flux Estimator Time Constant (FlxTau) must be calculated from the below points:

• 4 to 5 times of L/R
• Must be chosen such that Flxtm is 0.01 to 0.025 Seconds

So let us consider the example of your setup:

FlxTau = 5*(L/R) = 5* ( 20.4/1500) = 0.068  but this is out of range value and the minimum value that can be chosen based on the configuration file shared is 4 msec.

Yes, Ques 8 - Motor max RPM is not the rated RPM and it is the maximum RPM at which the motor is intended to operate.

Please let us know if any further details are required.

Thanks,

Krupashankar

16 Replies

# Re: Unable to reach full speed

Level 5
Level 5

Hello Marco,

It seems like you are experiencing an issue with your motor not reaching its full speed. Based on the information provided, I would recommend checking the following parameters:

1. Motor Voltage: Ensure that the motor is receiving the correct voltage as per its specifications. If the voltage is too low, the motor may not be able to reach its full speed.
2. Load on the Motor: Check if there is any excessive load on the motor that might be preventing it from reaching its full speed. If possible, try running the motor without any load and see if it can reach the desired speed.
3. Motor Control Algorithm: Verify that the motor control algorithm is properly implemented and tuned. You may need to adjust the control loop gains or other parameters to achieve the desired performance. For example, if you are using an iMOTION™ Integrated Motor Control Solution like the IMD111T-6F040, ensure that the sensorless field-oriented control (FOC) is properly configured.
4. Motor Parameters: Double-check the motor parameters such as resistance, inductance, and back-EMF constant. Incorrect motor parameters can lead to poor performance and limit the motor speed.
5. Protection Features: Ensure that the protection features like overcurrent, overvoltage, and under voltage lockout are not being triggered, causing the motor to operate at a reduced speed. For example, if you are using a MOTIX™ Integrated Full-Bridge IC like the TLE9201SG, check the diagnostic and protection settings.

By checking and adjusting these parameters, you should be able to identify the cause of the issue and resolve it. If you still face difficulties, please provide more details about your motor, motor driver, and control algorithm so that we can further assist you.

Best regards,

# Re: Unable to reach full speed

Moderator
Moderator

Hi

1) Can you please check if the power source is able to supply the required current?t

2) Did the motor reach the maximum current commanded value?

3) Please specify the Back-EMF constant and DC-Bus voltage.

4) In-case the probelm is not resolved, please share the motor datasheet and the parameter file.

Best Regards,

# Re: Unable to reach full speed

Level 3
Level 3

Hello, I have doubled checked the motor data, and the backEMF might be the problem.

The motor datasheet reports a Line-to-Line BackEMF of 65, which divided by square root of 2 is (nearly) 46 Line-to-Neutral RMS.

I have a DCBUS of 330VDC.

Moreover, the motor is in a compressor, so I cannot make it spin without load.

I think I need to turn on the PFC and boost the voltage. (Is this a valid solution?)

Regarding Ld and Lq I have tried with values given by the manufacturer at 7.5A, and I have also tried with values measured at 1kHz as indicated here ( https://www.infineon.com/dgdl/Infineon-How-to-Measure-Motor-Parameters-ApplicationPresentation-v01_0... )
And the result is near what the manufacturer gives for 2.5A

Kind regards for the help,

Marco Negrini

# Re: Unable to reach full speed

Moderator
Moderator

Hi @mngr05,

From the motor datasheet, we can see that line-to-line back EMF is 65V/KRPM. For the line to neutral voltage, it must be divided by a Square root of 3.

Can you please modify the below parameters and share the test results:

• Ques 7 Motor Back EMF Constant Ke -  line-neutral back-EMF = 65 / (root 3) 1.732 = 37.52 V(ln-RMS)/KRPM
• Please try increasing the Ques 52- Motoring Current Limit to 110-130% based on the safer operating limit ( Note: Please make sure if the power board and motor is within safer current limits) Higher current can result in overheating and damage of components.

Thanks,

Krupashankar

# Re: Unable to reach full speed

Level 3
Level 3

Hello, and thank again for the replies.

I have tried with the right backEMF parameter, but the result didn't change. At ~4500RPM it stops accelerating.

I have tested with a EVAL-M1-IR2214, wich has a three phase power supply, and a DCBUS of 580VDC.

At 5600RPM there are oscillations, but it would be able to accelerate more.

In the following graph there is MotorVoltage (Green), it says it is in degree, what does it mean?

What can be the cause?
Maybe a Field Weakening at 10% is too low?
Maybe something like Speed Regulator Gain or Flux Estimaotr Time Constant?

Kind regards,

Marco Negrini

# Re: Unable to reach full speed

Moderator
Moderator

Hi @mngr05,

Yes, all the motor parameters need to be configured correctly.

Can you please share the following:

• Control and Power board schematic
• MCE Wizard Configuration file(.mc2)
• Motor Datasheet

This will help us to understand the issue better.

• Source is able to provide enough power for the given voltage and current to drive the motor at 6500 RPM with load.
• Current sensing parameters are calculated and configured correctly.
• Ques-60 Flux estimator Time constant must be 4-5 times of L/R.

Thanks,

Krupashankar

Attachments are accessible only for community members.

# Re: Unable to reach full speed

Level 3
Level 3

Hello Krupashankar,

Thank you again for the reply 🙂

I made some test with the EVAL-M1-IR2214 evaluation board
https://www.infineon.com/cms/en/product/evaluation-boards/eval-m1-ir2214/
I have copied the configuration as indicated in page 15-16 of the user manual.
(I had to edit the max DCBUS because the three phase around here gives a DCBUS of 600VDC.)

> Ques-60 Flux estimator Time constant must be 4-5 times of L/R.

Based on the motor datasheet I have Ld=18 and Lq=24, and Line-resistance of 1.5 ohm.

21mH / 1.5 ohm x 4 = 56 ms

I configured a Flux estimator Time constant = 60

I am trying to attach the motor datasheet and wizard configuration, it is giving me errors, right now...

# Re: Unable to reach full speed

Level 3
Level 3

It was giving me errors, but the files appearead once I replied... It must have been an issue with firefox,

anyway, thank again Krupashankar

# Re: Unable to reach full speed

Level 3
Level 3

I forgot to add, in the compressor datasheet there are the working-curves at page 19, I am making it work at 10°C evaporation temperature (X axis) and 40°C condensation temperature (Y axis), so it should be 1.6kW input power and 7A working current.

Which is well under the limits of 50A of the FP50R12KT4G available on the eval board

# Re: Unable to reach full speed

Moderator
Moderator

Hi @mngr05

Thanks for providing the motor datasheet, we have the following observations

• Update Motor Resistance value  --> 1.54
• Update Flux estimator time constant value --> 4
• Speed in the datasheet is mentioned as 3600 RPM, the value in MCEwizard is 7200, may we know the rationale behind this
• If it is intended to operate at 7200 rpm double the rated speed, please increase the motoring current limit to 140%. Observe the voltage and current waveform at this motoring current limit value.

Best Regards

# Re: Unable to reach full speed

Level 3
Level 3

Thanks @Viswa for giving a look into this.

I will soon test with the changes, meanwhile about the 7200rpm:

The motor is rated for 15-120Hz, where 1Hz=60rpm, 120x60=7200.

Kind regards,

Marco Negrini

# Re: Unable to reach full speed

Level 3
Level 3

Hello,

Updating the Flux estimator time constant value to 4 made the work, I could see it spinning to 7200RPM!

Now, I don't understand the calculation for Question 60.

Krupashankar says that it should be between 4 and 5 time the motor winding time constant(L/R).
But I calculated a winding time constant of 13 (20mH/1.5ohm), and I thought the Flux estimator time constant should have been between 13*4 and 13*5, which is very far from the 4 that works.

Here ( https://community.infineon.com/t5/Motor-Control-ICs/Calculation-method-for-Flux-estimator-time-con... ) is said that I sould use this formula to calculate value for Question 60:

Tpwm is 1/Fpwm, and Fpwm is this value here, right?

I would have a Tpwm=1/8000 = 0,125ms

Fc is said to be the desired cutoff frequency, what values should I use for this?

If I try to do the calculations and I get Flxtau = 0,125/(2* 3.14 * Fc) , and I hardly see what Fc value can give a 4 out of this equation.

Can you show the calculation you did in order to reach a value of 4 for question 60?

Marco Negrini

# Re: Unable to reach full speed

Level 3
Level 3

another note I would like to add on the rated speed.

The motor datasheet gives a speed range of 15-120Hz, which means 900-7200rpm.

The wizards asks for "Motor Max RPM" (not Motor rated speed), hence I gave 7200 as value, which is doule the rated speed.

# Re: Unable to reach full speed

Moderator
Moderator

Hi @mngr05,

The parameter Ques 60: Flux Estimator Time Constant (FlxTau) must be calculated from the below points:

• 4 to 5 times of L/R
• Must be chosen such that Flxtm is 0.01 to 0.025 Seconds

So let us consider the example of your setup:

FlxTau = 5*(L/R) = 5* ( 20.4/1500) = 0.068  but this is out of range value and the minimum value that can be chosen based on the configuration file shared is 4 msec.

Yes, Ques 8 - Motor max RPM is not the rated RPM and it is the maximum RPM at which the motor is intended to operate.

Please let us know if any further details are required.

Thanks,

Krupashankar

# Re: Unable to reach full speed

Level 3
Level 3

Now I get it, the results of L/R should be considered in milli seconds and not in seconds.
Thank you for clarification 🙂

One more question: I have seen the motor work with an evaluation board with three phase power supply (DCBUS at 600VDC) but not with the evaluation board(EVAL M3 IM564) with a single phase input (DCBUS at 330VDC) I am still stuck at ~5000 RPM.

May I assume that it is due to DCBUS being too low?
May I assume that a possible solution is using the PFC to boost it high enough?

Kind regards,

Marco Negrini

# Re: Unable to reach full speed

Moderator
Moderator

Hi @mngr05,

The reason may be due to low DC-bus voltage as you have mentioned.

The DC-Bus voltage must be higher than the corresponding back-emf voltage for the given RPM.

Thanks,

Krupashankar