motor/generator

[bradysplace]

from time to time the mfd indicates that mg2 is acting like a generator and a motor at the same time. Is that possible?

[jamesbalch]

<div class='quotetop'>QUOTE(bradysplace @ Mar 25 2007, 11:07 PM) [snapback]412099[/snapback]</div>

from time to time the mfd indicates that mg2 is acting like a generator and a motor at the same time. Is that possible?
[/b]

What the heck are you sitting in in your picture? An MD-80?

[qbee42]

The MFD status is slow compared to what's actually happening; it's best to think of it as the average over the last bit of time. Since the display takes MG1 and MG2 and simplifies them into one MG, you can't really see any detail.

Tom

[DFWPrius]

It may be possible, the gearbox has both a Gen and Motor in it. That is how it can switch from one to the other and never be out of phase. The control relays for each could be exticing the fields of both at the same
time and it would show Gen output and drive power from the motor at the same time.

Just like a engine at idle and the prop in low pitch, the engine is driving the prop some, but also the windmilling prop is driving the engine some.

It should be just in a narrow power band.

[donee]

<div class='quotetop'>QUOTE(DFWPrius @ Mar 26 2007, 01:08 AM) [snapback]412132[/snapback]</div>

It may be possible, the gearbox has both a Gen and Motor in it. That is how it can switch from one to the other and never be out of phase. The control relays for each could be exticing the fields of both at the same
time and it would show Gen output and drive power from the motor at the same time.

Just like a engine at idle and the prop in low pitch, the engine is driving the prop some, but also the windmilling prop is driving the engine some.

It should be just in a narrow power band.
[/b]

Hi DFW,

The transmission has two electrical machines and either can act as motors or generators depending on the duty. Usually, MG1 is acting like a generator, and MG2 like the motor. But there is a mode dubed "heretical" mode during highway cruising when MG1 acts as the motor. MG1 is also the motor that starts the engine.

Relays would be too slow for the switching, and prone to burn out, as they cannot be synchronized with the fields in the motors.

Most likely an H configured (comonly called a "bridge circuit") semiconductor switch is used for each electric machine. Specifically, Insulated Gate Bipolar Transistors made from Silicon Carbide (SiC) semiconductor material. This material has the advantage of higher operating temperature.

As to bradyplace's question. MG1 is the generator for the mode you are seeing. And MG2 is the motor. A brief description goes something like this. When the engine is reving high, and the wheels are slow, the engine overspeed goes into MG1. MG1 generates electricity that goes through the inverter box into MG2. The semiconductor switches convert the multi-phase MG1 signals into pulsing DC, which is filtered by a capacitor. That current into the capacitor comes out into the inverter for the MG2 , which switches it at the proper rate for the wheel speed. This is how the electrical CVT works. That is, something like an electric Torque Converter. The extra engine RPM is turned into extra torque at MG2. And as the MG1 generated electric power signal is switched back into DC, it does not matter what speed MG1 or MG2 are going for the energy to flow to MG2.