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Driving of 3 phase motor

electronicsLearner77

Jul 2, 2015
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Two questions i have regarding this.
a. When driving a 3 phase magnet using hall sensor, we use 6 pwm legs, 3 for and 3 for low side. When ever i have seen commutation diagram three voltages are mentioned like high, float and negative. I am able to understand positive that will be Batter+ and negative will be Battery-. Then what exactly is float. I am asking this because with pwm you can provide either high or low, floating is not possible. Can someone please explain me.
B. Next is hall signals will be going from high to low or vice versa. What high actually represents a North or South pole. When exactly this transition will happen? At the middle?
 

Minder

Apr 24, 2015
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Apr 24, 2015
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3,478
It sounds like you are describing a BLDC motor as these are generally the ones that use Hall effect sensors for commutation.
In a BLDC motor only two coils are powered at any one time.
There is generally three possible conditions, driving = wingdings powered, all off, and three bottom devices on.
It sounds to me as though you are describing situation where no output device, Mosfet etc is conducting?
Here is a PDF example of the relationship between the halls and the three windings, they show a 3 ph sine wave due to back feed rotation of the rotor.
The other condition is the three lower Mosfet can be all turned on for braking effect.
http://www.masinaelectrica.com/simple-brushless-controller-explained/
M.
 

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electronicsLearner77

Jul 2, 2015
306
Joined
Jul 2, 2015
Messages
306
Yes I am at it again. One further doubt i have is at any one point of time let us say i am driving one high side leg and one low side leg. For example i take H1L2. Now my doubt is I have done the following two methods of driving
a. Both H1 and L2 driving with 50% duty cycle.
b. I am driving H1 with PWM of 50% duty cycle and keeping the L2 permanently ON.
Which is efficient method and what differences I can observe in terms of performance. I know it is a kind of decay of current. But what exactly is this? Will the current delivered to the motor will be less? How the torque will vary? Please help.
 
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