ESjaavik, thanks for the comments! As I'm sure you have seen elsewhere in life, people (like me) become attached to their own ideas and will resist change unless the reasons are compelling (like: it won't work). I do appreciate the comments and will try to answer all points, but sometimes people just disagree about stuff.
Regarding the "soft turn on", I believe that is a reference to the way the chip allows different size gate resistors for turn on and turn off. I don't think it helps the issue I'm concerned about. And regarding the reliance on perfect PWM, I don't think it's really an issue because the pulses are done by the hardware and there is no real "programming" involved (that is, set one register to X and another to X+1 and you're done with what is required here). Even if there was a problem it would not blow up the power stage because the IR2137 is protected against turning both transistors on at the same time (it won't let you).
Regarding the LS7183, I will stick with it for two reasons: 1) although your coding idea is a clever one that should work, I am worried about implementing it perfectly and testing it adequately in the border cases. 2) I have 20 of the LS7183 that I don't have another use for :-) If the chip gets discontinued, that can be dealt with (just as if the other single source components -- the AVR and the IR2137 disappear that would be necessary as well).
Regarding the high speed version of the IGBT, thanks that's a good find. They are more difficult to obtain and it appears like using them would add about $1 per IGBT, but it might be worth looking into. As long as the somewhat anemic gate drive current from the IR2137 is adequate, any IGBT should really be usable. The idea of using two PWM channels per half bridge is I think not unusual... it's just a pity since the deadtime thing is a feature of the gate driver chip anyway.
Regarding higher voltage, all of these parts are designed to deal with 350v bus voltages. I can only see two changes to the thing I am actually building: 1) the board has a rather sizable capacitor across the input high voltage supply. That goes up in price with voltage so I'm using a 250v part, but putting in a higher voltage part instead should not be a problem. 2) there's a voltage divider to monitor bus voltage; a minor component change would make it able to handle a higher range (one resistor value changed).
Thanks again for the comments!
Xerxes:
I will eventually release the source code to the PC side of the application, but that will only happen after the rest of it settles down, either into a successful stable design that I'm not changing any more or into something that died out for lack of interest or success. The big advantage of making the actual hardware and firmware open to inspection is that people can detect flaws in the design, and manufacture it (or variants of it) as they wish. Those things are not as important for the PC software side.
My experience with internet collaborations on such things is that it rarely works and is almost always more frustrating than helpful. However, it's not a very complicated application and any software coder could build a similar program with little effort.
In your poll thread you said that your design did not require tuning; I thought that was an extremely cool feature, have you changed that in the last couple days?  |