Wednesday, December 17, 2014

The Realist

"The Pessimist complains about the wind; The Optimist expects it to change; The Realist adjusts the sails."
- William A. Ward
I have been raised to be a firm believer in attitude affects everything. Life is %10 what happens to you and %90 how you decide to handle it. There is obviously a wide gambit of ways to handle any single unfortunate situation. However Mr. Ward broke those infinite ways down into the three most categorically common viewpoints on a problem.

Tuesday, December 9, 2014

PWM control and Dead Time Insertion

So as is often the case I vastly overestimated my knowledge on a few subjects. In my last post on this project I had successfully designed and put together my physical motor driver. This meant that all I really needed to do to get the motor spinning was fire up some pwm signals on my micro and done, right!? Well I was wrong. There were two fundamental gaps in my knowledge on BLDC control that I did not know I was lacking in until I attempted to start writing the code to control a motor. The first of the two being the PWM control scheme. There are 4 main variants of PWM control schemes for a 3 phase BLDC controller. I originally was just under the naive impression that there was one standard way to perform the functionality, and was no so surprised to find that "there is more than one way to skin a cat." The second area of knowledge that I did not know too much about, and was only vaguely aware of, is the practice of dead-time insertion (DTI). The main goal of DTI is to avoid a short circuit from the high side of the DC Bus to ground through the two transistors that control a single phase. This can happen because switching on and off transistors just like anything else is not instantaneous and some overlap may occur. DTI is guaranteed off time to ensure that no overlap happens. I knew that DTI was necessary I just had no idea how much was needed or how to go about implementing it. I had to do a bit of research before being able to answer either of those questions.

Trying to avoid this....

Blown Transistor

This post will hopefully allow me to re-enforce what I learned and maybe teach others about these two subjects as well.