Hi All,
I'm working with a 3phase BLDC motor (High torque/current capable) and custom driver board. It has a current shunt on the phase returns(for measuring total current). A PWM High side/Low side On scheme is being used as well as halls for commutation, pwm frequency around 20KHz. A lab supply is being used to power the BLDC motor and controller.
When looking at the instantaneous shunt voltage and converting to current at a particular duty cycle(say 30%), the current is considerably higher than my supply voltage.
That is, if the motor is running steady, my supply is set to 12V, lab supply shows 2.4A, then for one pwm cycle, the current is 8A for the 30% period, then 0 for the remainder. If I multiply the instantaneous phase current by the duty cycle percent, it is the same as the supply voltage ( 8A * 30% ~ 2.4A).
So, the question is why is the instantaneous phase currents SO MUCH HIGHER than the supply current? Is this an effect of the motor, back emf, inductance, etc?
Any explanation, theory or links appreciated!