EVAL-M1-CTE610N3 Help Driving an Air Compressor

[dservansky]

Hi, I am working on a project where I have a BLDC motor that is rated for 270-360VDC and 400W at 2200RPM.

My initial testing was using an off-the-shelf industrial trap drive rated for 400W. I was able to run my compressor through all the different test scenarios without any issues; however, I wanted to improve efficiency and ability to run at low speed. The trap drive shuts down at a pretty low back pressure at 500 RPM and I need to be able to drive to a higher pressure at this speed.

My current setup is using the EVAL-M1-101TF and EVAL-M1-CTE610N3. I got the motor up and running with the wizard and designer and did some preliminary testing. The only parameter I changed from default was the gatekill threshold which I set to 5A and 10us. Because the compressor has two heads the torque is a sawtooth pattern which peaks every 180 degrees so there are sharp current peaks instead of a relatively flat current like in a fan or washer application. 

The issues I am having are 1) The FOC drive is less efficient at lower speeds and back pressures than the trap drive, and 2) the FOC drive faults out for overcurrent at a much lower back pressure than the off the shelf trap drive.

Does anyone has any thoughts on how I can improve these two aspects? The parameters are attached.

The BLDC motor is wye wound with a line resistance of 3.3ohm, an inductance of 11.4-12.8mH, and a BEMF constant of 20.7.

[psb]

Hello @dservansky ,

Please share the corresponding .mc2 file, the MCE Wizard configuration file. This will help us in viewing the entered values easily, and directly use them for further analysis. 

[dservansky]

Hello Sai,

Attached is the .mc2 file for the application.

Kind regards,

Daniel

[Ramakrishnan_MK]

Hi @dservansky ,

We received the mc2 file. We quickly went through some key parameters and found one or two of them that are not configured properly. For example, the '60-Flux estimator time constant' needs to be 5 times L/R, but is not really configured that way. 

The default configuration file is given to you for probably a specific motor. However, you need to look at all the parameters in mce wizard, there is a detailed explanation given to calculate every parameter. Please follow that and configure all the parameters and try. If you are still not able to get the motor working as per your expectation, please reach out to us.

Regards,

Ram

[psb · Accepted solution]

1.  While doing speed control, the stable equilibrium point at a given speed remains the same for any type of closed loop control. It depends on the load torque, and other ambient conditions only. 
   
   
2. The sensorless Flux Estimation is not very accurate at lower speeds due to reasons like low back emf, etc. Incorrect entering of motor parameters makes it even more incorrect. This value can be seen in the MCE Designer as Flx_M, expressed as a percentage of the value 2048, which corresponds to the actual rotor permanent magnet flux. The value of Flx_M can also be adjusted by adjusting the Pllkp and Pllki values. 
   
   
3. Tuning a speed loop can be seen in the document on Driving high inertia loads with iMOTION™ 2.0  and information on the flux estimators and control loops are available in the iMOTION™ Software Reference Manual.