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Generator

Morikeh Daramy
Intellectual 480 points
Other Parts Discussed in Thread: MOTORWARE

Hi;

I am using;

tms320f28027f, c2000 launchpad with a maxon bldc motor and drv8301 motor drive.

I am confused as to which method is the best method to produce an electric generator!

Using the InstaSPIN Universal GUI, I am able to vary the Iq_Ref.

By setting this to a negative value, I can demand an arbitrary negative value of current, which- according to a 4-quadrants of operation- should generate electricity via the back EMF.

Indeed this is true, I have coupled the two motors I am using, and can confirm that the generator device (hardware stated above) is generating electricity. The amount of back EMF is also increased by increasing the magnitude of the negative current, although I am not aware of the equation that would define this relationship, can I have the direction to such resource please?

This generator will be used in a dynamic system, I am not sure if the Iq_Ref should vary (inverse) proportionally with the speed of the driving motor?

I know that this can be configured in CCS however, after speaking with some colleagues, they have suggested trying to altering the PWM output, directly in the project (project11)!

My main question is;

Which method is the best/correct in order to produce a generator (not a regenerative braking system);

through the current controller?

or

by modifying the PWM structure (using the example given in the "HAL Module of MotorWare" document)?

Kind Regards

Morikeh

  • 0
    TI__Guru** 119670 points
    back emf voltage is created from the interaction of the spinning rotor with the stator.
    the voltage is given by the Flux_VpHz * Frequency_Hz

    if you are driving a motor (regardless of if the IqRef is + or -) you aren't generating net energy. It is only when coasting or when the rotor is being driven by an external force (like a turbine blade) that net electrical energy can be created.

    yes, you can use an FOC controller to maximize the generation of your motor through control of the inverter. controlling Iq_Ref will limit the peak phase current. you may want to monitor and control the Vbus voltage as well.
  • 0 in reply to ChrisClearman
    Intellectual 480 points
    Chris;

    I am driving the motor stated above with another motor, I think this second motor is provide the external force needed.

    My confusion lies in the fact, that when I drive the motor in question, I am able to generate electricity without changing anything - which is correct for a DC motor, however I am using a BLDC.
    my understand is that; although there is a back EMF generated due to being driven, this current from this has no where to go because the gates are closed? is this understanding correct?

    "yes, you can use an FOC controller to maximize the generation of your motor through control of the inverter. controlling Iq_Ref will limit the peak phase current. you may want to monitor and control the Vbus voltage as well."

    Limiting the peak phase current reduces the torque produced in the motor in question and, if negative, it reverses the direction of the current and the torque, therefore running as a generator.

    through control of the inverter? I think this is where I am confused. when you say "control the inverter", you mean the PWM right, not just setting a value for Iq_Ref in the project.c file?

    Thank you for your time
  • 0 in reply to Morikeh Daramy
    TI__Guru** 119670 points
    "although there is a back EMF generated due to being driven, this current from this has no where to go because the gates are closed? is this understanding correct?"

    assuming the phases are hooked up to 3-ph inverter, yes, you understand it correctly.

    " through control of the inverter? I think this is where I am confused. when you say "control the inverter", you mean the PWM right, not just setting a value for Iq_Ref in the project.c file?"

    controlling the inverter means controlled switching of the 3 phases (through use of PWM signals) to allow current flow. the FOC system is already set-up to do this. You control a torque element (Iq) and a field element (Id, normally set to 0) to allow for a maximum amount of peak current (torque) oriented (Id) with respect to the rotor flux to make the torque necessary with minimal current (efficiency).

    in a motoring application you either control torque or use torque to control a velocity.
    in a generating application you use torque to control a voltage or overall power.
  • 0 in reply to ChrisClearman
    Intellectual 480 points

    Chris;

    The frequency you gave in your earlier post, it refers to which frequency parameter, full scale frequemcy or the speed?

    Thank you once again, very helpful

    Kind Regards

  • 0 in reply to Morikeh Daramy
    TI__Guru** 119670 points

    the rotor electrical frequency