GM Volt Forum banner

Presentation at APEC 2008 by Steven Schultz

9911 Views 21 Replies 10 Participants Last post by  tdjvolt
I recently attended the 2008 Applied Power Electronics Conference. Steven Schultz gave a nice presentation that included some details about the Chevy Volt.

Here's a bio of Mr. Schultz:
1 - 7 of 22 Posts
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 magents on the rotor.
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".
Ahhhh, That explain it better. I'll take my word back. I stick with the Interior Permanent Magnet now. It sure raise more question under the hood.
The easiest choice of driving electric motor is direct-would AC/DC motor such as the one found in KitchenAid mixer. It is easy to control its speed and torque simply by varying supply voltage (AC or DC). Also, it is easy to switch its rotational direction. However, since it has coil windings in its rotor it requires commutator and brushes, which are subject to wear and need periodical servicing. "Brushless" motors for automotive propulsion purpose use a permanently magnetized rotor and a stator, which generates moving magnetic field around the rotor. By changing the strength of the magnetic field and its moving speed you can control the speed and torque of the motor. For this purpose you need an electronic circuit to control the energy and frequency going into the stator coils. To control the energy efficiently I think automakers are using PWM or Pulse Width Modulation, which controls duty time of the electrical pulse. To control the frequency you need a variable frequency oscillator. This electronic control system is called VVVF (Variable Voltage, Variable Frequency). The permanent magnet rotor also allows the motor to be short, flat and high-torque.

There is one potential future problem casting a shadow on this "brushless" motor...
China is the major supplier of permanent magnet and also is the major producer or importer of rare metals (such as cobalt) needed to produce strong permanent magnet. It even discourages export of rare metals it produces by imposing export duty on them. China
The direct-wound motor is the kind you make at elementary school science class. Because of the rotor commutator it runs on AC or DC in the same fashion.
The direct-wound motor can be use AC or DC, but not in the same fashion.

Its rotational direction can be reversed by simply switching the stator coil terminals (a nice feature for automotive use).
In a DC motor brushes, you can't control rotational direction by switching the stator coil terminals with two brush on equal side. Think about it as water falling to a wheel to turn it. The higher the water pressure (voltage) the faster it goes. The water volume (current) is pipe size of drinking straw. The wheel is spinning faster cause of the pressure (volage). I could stop the wheel cause the water volume is so small. If you change the water volume of a oil pipe line. I would unable to stop the wheel cause of heavy weight of that water.
If you look at the watermill near the river. The wheel is slowly turning casue little water pressure is pushng the wheel. I sure can't stop the wheel cause of trying to stop large volume of water going thru the wheel. To control rotational direction on the DC motor would be an a third brush near one of the two brush that created more current on one side or a gear the force one way to turn. In AC motor is very different cause frequency is now play with voltage and current as well. There is too many things happen in electrons effect.

You control its speed and torque by changing the voltage.
In a DC motor, control speed is votlage. In AC motor is somwhat fix. In DC motor, control torque is to change amount of current. In some AC motor, current is Torque, not speed.

Speed actually is load-dependant. On a very light load, the power/load equilibrium may make the speed so high that motor destructs itself. Torque (current flow) is highest when the motor is not running, which could cause the motor to fry.
yes, I agree. It can be on AC or DC motor, but it does not appy all motor.

Speed of induction AC motor is frequency-dependant. Varying voltage does not change its speed (to a point).
I agree with that.

You use PWM to control torque (therefore, speed) of DC motor rather than rheostat because a resistor in series means waste of energy.
Wrong, In DC motor in current would control the torque, not speed. When electric go thur a resistor that opposes an electric current by producing a voltage drop between its terminals. When voltage drop it lose it energy. If there is no votage then there is no energy. You never loses electron.
So if you add, Pulse-width modulation (PWM) of a signal or power source involves the modulation of its duty cycle, to control the amount of power sent to a load. It would add current to the DC motor as an on/off switch. It would add more current to the motor give a heavy push when it needed.

PWM for AC motor controls the torque while the frequency determines the speed.
Yeah, I agree. In AC motor, it a huge waste when it get a high speed. The current doesn't drop as much like a DC motor. It doesn't need that much current. So it send a short amount of time in burst of current for a same load as when a motor just started. The frequency of AC is controlling the speed. I add with the PWM as an on and off switch to the AC motor. The AC motor is going on and off so fast that it all most like the AC motor is always on. Like I said, it fool the AC motor like it getting a full load on.
The more I look at the 2008 Applied Power Electronics Conference presentation that included some details about the Chevy Volt. I'm starting to see it only a one page of the GM volt. The rest is about the "Hybrid 2 Mode". I would not look at as it "The Volt" car at all.
So then when the motor is working as a generator is its output also three phase?

And how do you change three phase AC to DC?
The motor does not change three phase AC to DC. When you apply the break, the motor is turn off. There is no AC current going to the motor. Inside the motor, there is a permanent magnet on the rotor. The rotor is spinning from the tire. The wire coil where the AC current normal pass thru when the motor is on. The permanent magnet is passing the coil created DC current. The DC current go back to the battery.

When the motor is on. It become a AC motor. When the motor is off. It become a DC generator.

That the simple as I can put it.
I know it not perfect what I was trying to say. I'm not a good writer. So I try to keep it short and simple. I understaind better what you had said now. I wonder if Eric E understaind what you had said.:) Thanks for correct me.
1 - 7 of 22 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.