IMA Motor Voltage

3435 Views 6 Replies 4 Participants Last post by Insight Driver, May 27, 2003

jkennedy

Discussion Starter · May 20, 2003

I am somewhat confused as I try to figure out the battery Module/Motor Drive Module/ IMA Motor relationship. Obviously the battery is DC but according to the literature the MDM converts the DC to AC for the IMA motor. But the IMA motor literature says it is a DC motor. This just does'nt seem to work. Can anyone clarify this for me?

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Armin

· #2 · May 20, 2003

brushless DC

jkennedy,

The Insights motor is a "permanent magnet brushless DC motor". That's functionally identical to a synchronous AC motor. The only difference is in the drive. An AC motor is driven with a sinewave, usually straight from an AC distribution mains. A brushless DC is driven with a squarewave voltage(usually pulse-width modulated to approximate a sinewave in the resulting current waveform). This can easily be generated in an inverter. The MDM contains the inverter that drives the three coils of the motor.

The DC in the name of this type motor is a relic of it's ancestry more than a description of how it works. Traditional DC motors have a commutator built-in that chops the applied DC voltage and creates the appropriate waveform to run the motor. One key component of the commutator were carbon brushes (that used to wear out a lot). The lack of the commutator and it's infamous brushes gives our type of DC motor it's name. But since there is no commutator, we need to drive it with AC (essentially).

The bottom line: all motors need some form of AC to run. DC just won't create rotating motion.

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Armin

· #4 · May 21, 2003

current control

Don't worry about inrush current. I think what you are referring to is what happens when an AC asynchronoys motor (like in a fan) is connected to an AC mains with a switch (the brutal way). You are connecting full voltage at 60Hz across a stationary motor winding. The currents in that condition are huge. Only after the motor spins up and it's frequency gets closer to that of the supply does the current drop.

In the Insight, the inverter controls the motor current directly (through PWM). It also drives the motor at exactly the frequency it needs, depending on it's rpm. So there never is a mismatch that would cause excessive current.

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Armin

· #6 · May 21, 2003

stepper motor

Will M said:
I'm beginning to think of the electric motor less as a spinning motor and more as an armature that can be told to move to any of three positions. The electronic controls then tell it to turn one position farther than it already is, controlling the force with which it is shoved toward that position.

Will, this is a pretty accurate description of a stepper motor. Again, motor-wise a very close relative to the brushless DC or synchronous AC but different in it's drive. Steppers are usually used for positioning things (like in robots: move this far and stop).

Our motor is always rotating, so it's fed continous waveforms. It is dynamic, i.e. it rotates smoothly where a stepper would "jerk" from step to step, unless you do fancy tricks like microstepping it.

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