I am trying to achieve speed control of a sensorless Brushless dc motor (Back Emf method). Initially its speed is zero so Back emf is zero, so there will be no feedback, in that case what do i do? In my current implementation I can only hear a high pitch noise but no rotation. please help. I Hope this helps. As for the code, Im not sure. Could anybody help me out?
you could use open-loop to start up, so you would linearly increase the pwm duty-cycle and commutation frequency until you reach some speed at which you can get meaningful signals... or just use 2 pots and see what works.
you also need to do something about driving the high side transistors... their source is floating so you have to drive the gate higher than that value. you'd need some sort of bootstrap for n-channels or like a push-pull type thing if you use p's.
also i would recommend testing it on a resistor bridge before connecting it to a motor, just my $.02.