Seem OK. Tweak: For light load high efficiency decrease on-period; for high torque= increase on-period. =20 Sine driving do not need freewheeling since the voltages are following the= EMF I believe it=B4s possible to approach sine using PWM, and make sure not= driving all three phases at the same time. Hmmm also depends on Y or D= winding... Hmmm >By the way, you are exactly right about using the back EMF to provide= feedback rather than the hall effect sensors. Many controllers do that. Must be complicated if using PWM at the same time. Current sensing each= phase too? Think Variable Frequency drives do so. /Morgan >Hej Sean H. Breheny. Tack f=F6r ditt meddelande 14:55 2002-08-06 enligt= nedan: >Hi Morgan, > >I will have to think about this more when I get a chance, but essentially= this is what I am thinking: > >You could drive one of these motors with three phase AC and it would work= well (as far as I know). So, therefore, our job is essentially to= approximate three sinusoidal signals, each 120 deg later in phase than the= last, with our three half H-bridges. A sine wave has no freewheeling= period, it always presents a rather low (zero, ideally) impedance to each= motor winding, but with a variable voltage. However, there comes a point in= the cycle (actually twice per cycle per phase) where the voltage of the= sine wave matches the back EMF plus inductive voltage of each phase and no= current flows in that phase. At this point in the cycle, it would not= matter if you disconnected that phase for a few degrees. Since our half= H-bridges can only produce high, low, or tristate output, we can= approximate a sine wave with just a square wave (high for 180 deg, low for= 180 deg) but we can do it a lot better with a three state wave (high for= 120 deg, tristate for 60 deg, low for 120 deg, tristate for another 60= deg). > >Is this wrong somehow? -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics