Quote:
Originally Posted by BogdanT
On my particular application, I have some questions for the experts. I have some IGBT's lying around which I want to use for the P&S AC board running the AC35 at 144V.
1. How much current can I actually push through them for ~10 seconds? Should I aim 75% of the 400A or 800A peak ratings?
2. How fast/slow are they for the EV application?
They are 600V 400A Powerex CM400DY12NF and have these ratings:
Collector Current*** (DC, TC' = 92°C) IC 400A
Peak Collector Current ICM 800A
Emitter Current** (TC = 25°C) IE 400A
Peak Emitter Current** IEM 800A
Inductive Turn-on Delay Time td(on) — — 300 ns
Load Rise Time tr VCC = 300V, IC = 400A, — — 200 ns
Switch Turn-off Delay Time td(off) VGE1 = VGE2 = 15V, RG = 3.1Ω, — — 450 ns
Time Fall Time tf Inductive Load — — 300 ns
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I certainly don't qualify as an expert.
For question 1
From experience, anything around double the voltage works. IE your 600V IGBTs could drive up to 300V peak to peak. 144V pack is fine.
As for the current, I'm not a heat flow guy. I understand that heat flows from high temp to low temp, and that there is resistance to the flow of heat like there is to the flow of electricity. As for the equations, and the integrals ... sorry! Not my area. I would start with 50% max (ie 400A) and do an acceleration test for 5 seconds, or whatever you can reliably and repeatably do. The difference in temperature is what you are looking for.
If the temp rises from say 20C to 70C then you are done. The temperature inside the IGBT is higher than what you can measure at the heat sink. How much higher depends on that math I talked about earlier.
The heat can't get out of the IGBT very fast compared to how fast you can generate it. But it's tough to put a load on an AC motor in the 100's of amps for very long without a dynamometer. I used a DC motor coupled to an AC motor, and ran the DC motor as the 'motor' and the AC motor as the regenerative brake. If the AC and DC controllers are connected to the same battery pack, you only 'discharge' the difference between motoring and braking ... which is what the IGBT's are putting out for heat. You can do some rough calculations with that and figure out how much heat you are dumping.
For the heating up of the IGBT ... I think this is what was posted the last time someone asked ... but of course I can't find that!
- you have a turn-on time, where the transistor is sort of like a resistor. It has to do with time constants, capacitance, and drive current.
- you have a turn-off time, where the transistor is sort of like a resistor It has to do with time constants, capacitance, and drive current.
- you have a pulse width time, where the transistor is a resistor .. RGon I think?
The turn on and turn off times are multiplied by your switching frequency, or carrier frequency.
The RGon is multiplied by the duty cycle of ON and the switching frequency
That whole mess is divided by 6, since you have 3 IGBTs switching high side and 3 IGBTs switching low side.
I think Paul's board has a max output of 90% duty cycle ... but I can't find any doc to support that number.
For question 2 - yes, they are a bit slow. A lower carrier frequency will help reduce your switching power loss. I think Paul uses a random number between 3KHz and 8KHz to make a white noise 'Shh' instead of a hum. We have industrial controllers running at 0.5 Khz and the motors work fine ... but they are a bit noisier.