[continued from previous message]   
      
   >      Gives torque more like a square wave, but quieter.   
      
   That's just weird.  I think what you are seeing is something similar to   
   the shape you get from vector control.   
      
   >      Trapezoid waves are similar to this, but more noise.   
   >   
   > Seemingly, one "better" option might be to mutate the wave-shape between   
   > Square-Root-Sine and sawtooth depending on the target RPM. Also dropping   
   > the wave amplitude at lower RPMs (at low RPMs motors pull more amperage   
   > and thus generate a lot of heat otherwise).   
   >   
      
   Of course you have lower average voltage at lower speeds and torques -   
   that's why you use PWM to control your wave amplitudes.   
      
   >   
   >   
   >> And whenever you have a frequency inverter, the input to the frequency   
   >> is first rectified to DC, then new AC waveforms are generated using   
   >> PWM controlled semiconductor switches.   
   >>   
   >   
   > Yes:   
   >    Dual-phase: may use a "Dual H-Bridge" configuration   
   >      Where, the H-bridge is built using power transistors;   
   >    Three-phase: "Triple Half-Bridge"   
   >      Needs fewer transistors than dual phase.   
   >   
   > It is slightly easier to build these drivers with BJTs or Darlington   
   > transistors, but these tend to handle less power and generate more heat,   
   > but are more fault tolerant.   
   >   
   >   
   > MOSFETs can handle more power, but one needs to be very careful not to   
   > exceed the Gain-Source voltage limit, otherwise they are insta-dead (and   
   > will behave as if they are shorted).   
   >   
      
   FETs are always used (until voltage or current requirements force you to   
   use IGBTs) - no one uses BJTs or Darlingtons in real motor control.  You   
   need an appropriate gate driver for the FETs, but those are common and   
   cheap, and usually combined with deadtime control to avoid accidental   
   shoot-thrown when you enable the high side and low side together.   
   Modules that combine all this with three half-bridges are also small and   
   cheap.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)