Hi Everybody,

I am implementing field oriented control (FOC) of a PMSM motor on TMS320LF2407A DSP processor using Space Vector Modulation. For this purpose I am trying out TI's reference design -
http://focus.ti.com/docs/toolsw/folders/print/sprc107.html.

I would like to limit the phase currents supplied to the motor to a maximum value and similarly also the duty cycle of the PWM waveforms given to the 3-phase inverter.

Could anyone please tell about the methods for implementing the same?

Thanking in advance,

George

 

The key thing to remember here is that current is an INPUT to your algorithm, not an OUTPUT. You command phase voltages (encoded as PWM duty cycle values) to try to get the current you want. So you cannot control or limit the current directly; you can only use your voltage outputs to control current indirectly as best you can, limit your commanded current values to a threshold, and shut things down if the current starts to get out of hand.

You can always limit your voltage outputs with a numerical clamp on your PWM output values.

Curt Wilson
Delta Tau Data Systems

 

One way is to use the "hysteretic" or like "chopping" where you detect current threshold and shut off your power stage momentarily and restart it as the current decays to within a limit. Of course, you still need to keep track of your commutation sequence. The current would flatten out at the peaks and looks like a saw tooth.

oj