I'm working on a project that is clearly showing me that power electronics is a completely different beast.
We have a 5HP motor running on a 120Vdc battery. The motor is installed about 100ft (30m), away with big cables. At the moment the motor turns on it peaks at about 180A, then is rests at about 44A. I'm looking for a way to limit the startup peak at about 70A.
Following my first idea, I've chosen a 150A IGBT and a magnetic loop current sensor, like this:
Close to the motor, I have a high current freewheeling diode, and on the IGBT I have a RCD snubber with 1uF capacitance (seems small to me but here, I see that the rule of thumb is 1uF per 100A...).
My control is simply to turn on until the current sensor rises to a top limit then turn it off for a fixed amount of time and repeat... At some point it will work on forever without tripping the top limit. The motor should remain on for only a few seconds and then go off, so things should not get too hot, hopefully.
While projecting and layout-ing the board for this "simple" project I've realized that a lot of things can go wrong.
Does someone see something I'm missing? I do not have boards yet, so never tested the circuit, but, after seeing a lot of people having problems with IGBT dealing with much smaller currents I am already thinking that I should stop and study more before going ahead with this approach.
Another new idea is to turn on the motor with a high power resistor in series to limit the current for a few mili-seconds and then short the resistor with an SCR. But I feel I'm simply changing monster's name (is an SCR simpler to tame than an IGBT? I don't know...)
Also found the CS8312, IC. Maybe replace its serie resistor current sensor by my loop current sensor?
And, no! I'm not asking for a ready solution, just like to hear a more experienced opinion on what I should study to have a reliable solution.