Explanation for Three Phase PWM for the Uno?

Hello! I successfully made a three phase inverter for an AC induction motor, and my simulation testing seems promising. However, I do not really understand the program that I am using to generate the duty cycle output in pins 9, 10, and 11. I found this incredible program from GitHub user cmasenas but could not find his/her email, and I have attached the code here.

I understand the basics of timer interrupts and, of course, the theory behind PWM, but this program is much too complicated for a beginner like me. How would I edit it to make the frequency variable? I want to insert analogRead(Potentiometer_Value_Conversion) somewhere but I don’t understand the code well enough yet.

Thanks in advance for your help!

Three_Phase_Test_v2.ino (4.78 KB)