[Joshua Bretz]

I recently attended the 2008 Applied Power Electronics Conference. Steven Schultz gave a nice presentation that included some details about the Chevy Volt.

http://www.apec-conf.org/images/PDF/2008/Plenary/schulz_presentation.pdf

Here's a bio of Mr. Schultz:
http://www.apec-conf.org/images/PDF/2008/Plenary/schulz.pdf

 

[KariK]

An excellent presentation, thanks for the link.

Several things there that are worthy of comment:
1. 135 kW electric drive. This is presumably peak power, but is higher than the 115 kW motor quoted earlier. This is exciting, if true, as it will give the car a bit more acceleration.
2. 300 mile total range. This is down considerably from the 640 mile figure quoted earlier. I wonder if GM is concerned with the weight, and is making the gas tank smaller?
3. 110V, 15 Amp recharging. So no 220 V one, and time for a typical 12 kWh recharge: 7.3 hours, a bit more than the 6.5 hours I have read earlier, but no big deal.
4. DC to DC converter with 12 V, 100 - 200 Amp output (so max 2.4 kW), as well as 42 V output (hmm, for AC?).
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?

 

[Joshua Bretz]

Questions 5 & 6

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?

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.

 

[calgaryvolt]

I took a look at the presentation today and noticed the comment about a 300 mile total range. I'm concerned about that number. As a urban commuter that's fine, it will run mostly on electricity but say I want to take it to the cabin or out on a little road trip 300 miles is not nearly adequate. That will make for a lot of pit stops and the potential for an out of fuel situation. There are stretchs of highway that I travel on camping trips that don't have a gas station for about 250 miles or so, that's really getting to an uncomfortable level.

Like Karik, I was expecting higher (500-600 miles)

 

[Joshua Bretz]

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]

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".

 

[Joshua Bretz]

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".

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)

 

[Cybereye]

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.

 

[G35X]

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

 

[Lentz]

Thanks for posting this!

Thanks for posting this! Tried to put no message in the title and the board wouldn't let me.

My sports board has better features than this.

 

[Cybereye]

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

 

[G35X]

Cybereye,
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. Its rotational direction can be reversed by simply switching the stator coil terminals (a nice feature for automotive use). You control its speed and torque by changing the voltage. 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. Speed of induction AC motor is frequency-dependant. Varying voltage does not change its speed (to a point). This is the reason why you need a variable frequency generator for automotive use. You use PWM to control torque (therefore, speed) of DC motor rather than rheostat because a resistor in series means waste of energy. PWM for AC motor controls the torque while the frequency determines the speed.

 

[Cybereye]

Cybereye,

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.

 

[G35X]

Cybereye,
Since nobody has responded to your post yet, let me try to explain...

The direct-wound motor can be use AC or DC, but not in the same fashion...
It rotates by exactly the same principle.

In a DC motor brushes, you can't control rotational direction by switching the stator coil terminals...
Yes, you can. Take apart an electric screwdriver and look inside. If a motor has a permanent magnet stator you cannot change its rotational direction unless you use DC and switch its polarity.

In some AC motor, current is Torque, not speed... In any motor the amount of current is directly related to torque simply because the strength of magnetism is directly related to the amount of current.

...It can be on AC or DC motor, but it does not appy all motor...
Yes, it does. You can fry any motor by supplying too much current especially when it is not rotating.

...You never loses electron...
Yes, electron never loses. But, you loose energy as heat (current*current*resistance). Therefore, to control torque you change the duty time of the on/off pulse rather than putting a resistor in series.

...In AC motor, it a huge waste when it get a high speed...
No, an AC motor does not waste energy as it increases speed. Speed of AC synchronous motor (the kind used for EV's) is determined by the number of poles and the frequency of power supply. To increase its speed you increase the frequency. Its torque (power) is still controlled by the integrated amount of current that is controlled by PWM. In the VVVF design a complex combination of current (voltage) and frequency is needed.

 

[Cybereye]

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.

 

[BillR]

Possible Drive System

I don't pretend to be an authority on electric drive, but it is used in locomotives and on some fairly large ships.

I believe the drive for the Volt will use a synchronous permanent magnet motor with a variable speed drive. See this link for more info:

http://www.freescale.com/webapp/sps/...02nQXGrrlPZL8l

Note the speed range for the motor can be 0 to 20,000 rpm. With this design, the speed of the motor is controlled by the input frequency of the power. And I believe the specifications for the Volt call for a 3 phase AC motor. I also remember that this type of drive was used for the EV-1, because synchronous motors are very efficient.

I had originally posted this under "Suggestions for GM" in regards to the need for a 5 speed transmission.

 

[BillR]

Updated Link

Apparently the link above doesn't work.

Let's me try again.

http://www.freescale.com/webapp/sps/site/overview.jsp?nodeId=02nQXGrrlPZL8l

 

[Eric E]

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?

 

[Cybereye]

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.

 

[Engineer_101]

Cybereye,

There is something wrong with the previous explanation on the way that a 3-phase induction PWM drive operates.

DC does not come directly from the stator of the electric machine. The flux in the air gap ( I will withhold information on the source ) couples with the windings in the stator. Faraday's Law applies here - a magnetic flux induces a current in a conductor that cuts across that flux. This current flows through the inverter bridge of the PWM drive electronics according to the ON or OFF state of the semiconductors (most likely power-type MOSFETs, or other transistors working in a switched mode) Regeneration (braking) is a function of adjusting the conduction trigger angle with respect to the sinusoidal current coming from the traction motor, which is functioning as a generator. The permanant magnet in the rotor provides a source of the time-varying magnetic flux that is being cut by the stator windings.

For ICE gearheads, a good example of the conduction trigger angle function in the motor drive is similar to the advance/retard of a spark ignition system. The power developed from an ICE engine is dependent on the timing of the spark with respect to Top Dead Center (TDC). Too much spark advance and the power impulse trys to run the engine backwards.

In the electric drive, too much advance is going to reverse the power flow back through the inverter bridge and will recharge the battery. This is a good thing.

Braking effort of the electric motor can only be sustained to a point that the drive is capable of transferring power back to the battery (receptivity) or dumped as heat in a breaking resistor. The Volt must still have a service brake for the final stop. (rolling stops - a.k.a. California Stops, will get you a ticket)

Hope that this clears some of the fog.