FOC SDK: maximum rotation speed limited

[christianwaldmann9]

Posted on July 03, 2014 at 08:16

We are using the FOC SDK 4.0, the eval board STEVAL-IHM039V1 (STM32F415ZG) and a 400 V, 1kV motor driver STEVAL-IHM025V1.

The motor is working with no mechanical load and a quadrature encoder as position feedback. Controlling the rotation speed works fine from STMCWB.

But when requesting more the 2500 rpm, the requested speed goes up in the speed monitoring graph, but the reel rotation of the motor stays a approximately 2500 rpm. 

Is this a limit of the software?

What parameters ( speed controller, torque controller, field weakening, )  have we to tune, to get to a higher rotation speed?

#stm32100-pmsm-foc-sdk-speed-rpm

[Gigi]

Posted on July 03, 2014 at 08:46

Ciao Christian

First of all we need to be sure that the motor has really reached it's limit because some time a little issue in the WB create confusion. Indeed if the monitor->register->measured speed max value is set to 2500 the WB saturate the measurement but it is just problem of visualization. So please check with the LCD that the motor is realy limited to 2500 rpm.

After that, if the motor reach the maximum speed is possible that one of the two limit has been reached:

- Maximum current

- Maximum modulation index

In your case I suspect that the first can't be the issue because you are testing with no load so maybe you reach the limitation in the modulation index. This mean that you are suppling 100% of the available BUS to the motor and it can't be further accelerated. To verify it you can simply change the input voltage and verify if the reached limit is proportional with the DC voltage value.

This means that you reach the phisycal nominal speed of the motor for that DC bus voltage. In this case the only way to go above this speed is with flux weakening.

Ciao

Gigi

[christianwaldmann9]

Posted on July 03, 2014 at 11:59

Hello Gigi

Thanks for your hints. 

The limiting factor is indeed the bus voltage. The motor is rated for a bus voltage of 400 Vdc, and the eval kit operates with 300V.

And reducing the max. allowed voltage at field weakeing results in higher speed.

We go on learning about the control of PMSM

Christian

[Manoj.M]

Hi,

Have you achieved your desired RPM using flux weakening or did it in any other way?

[Laurent Ca...]

The question has been moved from the "Motor Control Hardware" section to the "STM32 Motor Control" section (the question is about the STM32 MC SDK). 

Best regards