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SPICE model for brushed DC motor -- some questions

Discussion in 'Electronic Design' started by [email protected], Dec 1, 2012.

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  1. Guest

    Could some electronics guru please shed
    some light on this ? I created a SPICE
    model for a simple brushed DC motor. It
    is complete as it includes the models
    for torque and inertia. When excited with
    a SPICE pulse or piece-wise linear model,
    the armature current, when plotted shows
    the upward and downward spikes, of the
    correct amplitude, as expected. Now when
    I replace the SPICE pulse or piece-wise
    linear sources with a DC source and a power
    MOSFET that is pulsed (switched-on/off)
    with at the same frequency as for the
    pure SPICE case, the armature current
    looks very different. Namely, there are
    no downward going spikes, and the
    amplitude of the positive spikes is smaller
    than when the excitation is made with
    the SPICE pulse or piece-wise linear. I
    have used a SPICE 'switch' but that has
    not helped either. I use HSpice or NgSpice
    alternatively, and the results are consistent.
    Any hints/suggestions would be of immense
    help. Thanks in advance.
     
  2. Robert Macy

    Robert Macy Guest

    help to post your model.
     
  3. Guest

    I had already checked the voltage at the output
    node of the MOSFET/switch -- that is, the input
    node of the motor, and it is much lower than the
    case when the motor is excited with SPICE PULSE
    or PWL. So, clearly the impedance is driving
    the voltage down.
     
  4. Guest

    The following is the bare-bones brushed DC motor with
    a piece-wise linear excitation. I use HSpice/NGSpice.

    *SIMPLE BRUSHED DC MOTOR

    V_AMP 1 0 DC 0.0 AC 1 PWL(0MS 0V 5MS 5V 10MS 10V 1000MS 10V 1010MS 5V 1020MS 0V 1050MS 0V 1060MS 5V 1070MS 10V 2000MS 10V 2010MS 5V 2020MS 0V 2050MS0V 2060MS 5V 2070MS 10V 3050MS 10V 3060MS 5V 3070MS 0V)

    * MOTOR VOLTAGE
    RA 1 2 0.5
    LA 2 3 0.0015
    H_EMF 3 4 VSENSE2 0.05
    VSENSE1 4 0 DC 0V

    * MOTOR TORQUE BASED ON INERTIA AND FRICTION
    H_TORQ 6 0 VSENSE1 0.05
    LJ 6 7 0.00025
    RB 7 8 0.0001
    VSENSE2 8 0 DC 0V

    * MOTOR POSITION
    FPOS 0 11 VSENSE2 1
    CPOS 11 0 1
    RPOS 11 0 1MEG


    * ANALYSIS
    ..OPTIONS NOPAGE METHOD=GEAR
    ..IC V(2)=0.0 V(3)=0.0 V(4)=0.0 V(6)=0.0 V(7)=0.0 V(8)=0.0 V(11)=0.0
    ..PROBE V(*)
    ..TRAN 100ms 3100ms 50ms UIC
    ..PRINT TRAN V(1,4) I(VSENSE1) I(VSENSE2)
    ..END
     
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