Presentation at APEC 2008 by Steven Schultz

Questions 5 & 6

KariK said:

An excellent presentation, thanks for the link.
5. Industry trend is favoring IPM motors, rather than induction motors. Is that for propulsion or for accessories? Can anyone explain the difference to a layman? What is a position sensor?
6. Bus Capacitor is 14% of the inverter cost. Would that be a supercapacitor?

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5. This is for the main propulsion drive. IPM is "Interior Permanent Magnet" - as opposed to "AC Induction". I think that the Telsa Roadster uses the latter. An IPM motor is also commonly known as "DC Brushless". An AC Induction motor has no permanent magnets on the rotor (the part that spins), instead using laminate iron & copper, in which magnetic fields are established. The tradeoffs between the two designs are shown in the presentation on page 21.

A position sensor is something that tells the motor controller the position of the rotor. The timing of the switched current in the stator windings must be coordinated with the position of the permanent magnets on the rotor.

6. I think that the "Bus Capacitors" are ceramic, used for ripple reduction on the main bus. These are for high frequency energy storage only - not supercapacitors.

Range

640 miles is what has been quoted by GM in their marketing info. Maybe GM was originally thinking about a 300 mile EV range with no ICE...

Cybereye said:

I believe you misunderstood what IPM is. I know GM have said it an AC motor. What you took IPM is a very good guess. I would not blame on that for a DC motor term. What you were thinking of is "IPMS" (interior permanent magnet synchronous) that use in DC motor. I know GM have said it an AC motor. There is different type of AC motor. My guess of the IPM term is "Induction Pulse Modulation". GM never had said what type of AC motor it using. I'm just taking a clue base on different type of AC motor. I would blame on the people who made the presentation for adding a confuse term. Maybe it just to confuse for Toyota. I'm somewhat trying to find out what the truth about the "300 mile total range".

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The discussion on page 21 of the presentation lists "Costly magnets and position sensor" as a characteristic of "IPM motors". I think this fits best with "Interior Permanent Magnet". I seem to remember that during the presentation, Mr. Schultz inferred that GM was not using an AC induction motor to drive the wheels, but perhaps was using one for lower power applications. (i.e. air conditioning)