Motor electrical parameters

mikemike9141 · ‎2014-10-24

Posted on October 24, 2014 at 14:53

Hi,

I am not entierly sure how to correctly enter my motor parameters, and which effect they have, can anyone check if I am doing this correctly (sensorless operation with cordic startup, no extra features like flux weakening, bus voltage sensing):

- max rated speed: used for fault detection only, correct?

- nominal current: used for torque limitation, correct?

- nominal dc voltage: what is this value used for?

- Rs: this is meant per leg, so I measure the DC resistance between two phases and divide this by two

- Ls: same as Rs, measured at 100Hz

- demagnetizing current: what is this value used for?

- B-EmfConstant: I drive the motor externally, measure the AC voltage between two legs, calculate the RMS from that, divide this by used RPM, multiply with 1000

Any help is appreciated.

Regards

Frank

Gigi · ‎2014-10-27

Posted on October 27, 2014 at 09:43

Ciao Frank

- max rated speed is used to set the limit of target speeds (target greater are skipped), is used to scale the internal BEMF measurement, to calculate the PI parameters of the PLL (not for your case)

- nominal current is used for current limitation (yes)

- nominal DC voltage is used to caluclate the PI parameters of the current regulators, the parameters for the State Observer, very important for your case whit bus voltage measurement disabled

- Rs, Ls, B-EmfConstant (seems correct) phase to phase divided by 2 for Rs, Ls not for Bemf ((Peak to zero / 1.414)/(RPM/1000))

- Demagnetizing current is used by the Flux Weakening algorithm (usually can set the same value of nominal current)

Ciao

Gigi

mikemike9141 · ‎2014-10-27

Posted on October 27, 2014 at 09:58

Hi Gigi,

thanks for your fast reply. In my initial post, I wrote in a misleading way. In fact, my board has indeed bus voltage sensing. So I assume that with bus voltage sensing enabled, the feedback gains (current, observer) are adjusted online with varying bus voltage, and that the nominal DC voltage parameter is then irrelevant, corrent? If not, then I assume that I have to enter maximum possible DC voltage here, because bus voltage is an amplification term in the current regulation loop, and this way I can guarantee stability (with the drawback of slower regulation at low bus voltages). Understanding this is especially important for me, because the inverter has a usable operating voltage range of 16 to 100V DC.

Kind Regards

Frank

Gigi · ‎2014-10-27

Posted on October 27, 2014 at 10:16

Ciao Frank

Parameters of current regularors are not adjusted online according of the measured bus voltage. The intended use of the FW is with a bus voltage constant or with a limited ripple let say +- 20%. For an application with a wide range of bus voltages I think is better to set the middle value or think to calculate different parameters and change it on-the-fly (SetKi and Kp of current controller for instance).

Ciao

Gigi

mikemike9141 · ‎2014-10-27

Posted on October 27, 2014 at 11:15

Hi Gigi,

thanks for clarifying this.

Kind Regards

Frank