If "true ac" means sinusoidal, well, it's probably not sinusoidal. But the current certainly alternates direction, so by the definition of ac it's ac.Kobushi said:from : http://www.insightcentral.net/encyclopedia/enmdm.html
"... The current isn't true AC, but IGBT's (Insulated Gate Bi-polar Transistors) in the Motor Power Inverter Module (part of the MDM) are switched in such a way as to simulate AC current."
From the pictures it looks like an 18-pole machine. The frequency should be P/2*rpm/60 (i.e. P/2*rps), where P is the number of poles, if I've got my factors of two sorted out correctly. So that would be 150 to 300 Hz for the typical 1000 to 2000 rpm range. Having that frequency higher than the 50 or 60 Hz line frequency is part of how the power density and efficiency can be better than in a standard line-frequency motor.Kobushi said:If that is correct, does anyone know what the frequency range is?
Great, thanks.Mike Dabrowski 2000 said:While I am out there I will put the scope across the motor windings with it in assist and regen, and post the waveforms.
In this configuration, the current, rather than the voltage, is what gets smoothed. So you won't see that unless you have a current probe you can connect to the scope (e.g., if you have one of those clamp-on current probes that plugs into a regular meter, you can put a ~10 ohm resistor across the output of it and look at that voltage with a scope).Mike Dabrowski 2000 said:I suspect that with the inductive smoothing of the square wave drive, it will look like a sine wave more than a square wave?
Typically for a motor design like this, square waves are ideal, so there's not reason to try to synthesize a sine wave.Mike Dabrowski 2000 said:I know that some of the sine wave inverters that convert DC to AC, use PWM switching drivers to generate a real sine wave by changing dutycycles for the different parts of the wave, but for a motor driver, that level of complexity is probably over kill, and it is also a more lossy conversion.
That would be a nice neat way to classify things, and it would arguably make sense to use that terminology. However, most things you can buy that are called "brushless dc motors" actually require, or sometimes come with, a separate box that houses the circuitry that converts the dc input to the three-phase ac power that goes to the motor windings. Brushless dc motors with the circuitry built in exist, but they are new, novel devices.John Wayland..From an _OLD_ yahoo Insight group post: said:So now.....back to the original question,"Is the Insight's motor a BDC type or is it an AC type?"
Answer...the Insight has an AC motor, more specifically, a PM rotor AC motor. It has no internal circuitry that converts DC to AC, though it does have commutation sensors inside. It has three wires that feed 3 phase AC power into the motor. If you took the motor inverter from the IMA box and built it into the motor, so that there were two wires that brought in DC, then it would be a brushless DC type.