I'm currently working on a simple ESC design to drive a small BLDC motor (6A continuous max). I'm at a stage where I can start the motor reliably, but haven't yet achieved closed-loop control using zero-crossing. I have done some experiments where I keep increasing the commutation frequency, but at some point the motor stalls. The PWM duty cycle doesn't change as I increase commutation frequency.
My question is, does BLDC motors require higher current (increase in PWM duty cycle) at higher rotation rates? This is my intuition as higher current results in stronger magnetic field, which results in "faster" rate of change in angular velocity.
I want to spin the motor at higher frequencies reliably, that's all.
To clarify some of the terms,
Commutation Frequency - how fast the commutation steps change (1->6). This leads to changing speed in BLDC motors
PWM frequency - PWM signals are given during each commutation. Varying duty cycle here simulates varying supplied voltage to motor (and hence current)