inverterModulationpwmthree phase
I'm implementing PWM for a three-phase inverter.
The documentation on the subject, especially the technical implementations, is very good but as far as I am able to understand none of the one I read talks about why the reference signal is a triangle or a sawtooth. In one document I found that this type of modulation is the oldest in the game (PWM concerned) so maybe is a thing of old technology that becomes standard?
Yes. The difference is that the PWM pulse will be centered within the train rather than against either edge (type 1).
Start with, say, a guide to the protocol.
Given that you've decided to use an Arduino, you can just speak MIDI more or less directly. There's even a handy tutorial on the Arduino website for MIDI out! MIDI input is slightly more electrically complex as you're supposed to have an optoisolator in there to avoid ground loops.
It's almost entirely a software project, but if you're willing to pick up code from the internet should be reasonably straightforward.
Edit: a bit more googling has found someone who's actually done this, in 40xx CMOS rather than 74: http://www.pykett.org.uk/a_midi_pedalboard_encoder.htm
That's MIDI output rather than input. I still maintain there's no point doing it by halves: if you're going to do MIDI decode in hardware, do all the audio in hardware too, don't just put an Arduino in there as a PWM generator. And if you do have the Arduino, let it do the protocol bit and consider moving the audio side to analog.
Best Answer
The "triangle reference" method that has some history as a standard or popular method was more formally known as the "triangle interception method." It was based on generating switching commands based on the interception of a triangle wave with a sine wave as shown below. It was not too difficult to implement and it provided reasonably good results for variable frequency drives (VFDs). Results were improved by changing the ratio of the triangle wave frequency to the sine wave frequency over the range of the operating frequencies.
After the invention of large scale integrated circuits and microprocessors, more sophisticated PWM strategies became preferred.
Image from Zubek, Abbondanti & Nordby “Pulsewidth Modulated Inverter Motor Drives with Improved Modulation” IEEE Trans. Ind. Appl., Nov./Dec. 1975