In SX Microcontrollers, SX/B Compiler and SX-Key Tool, PJMonty wrote:

Beau,

You're correct about the area involving figure 4 not being simply about 3 phase motors.  However, my reading of the article section you pointed out leads me to believe they are doing a vaguely similar thing with a very different idea in mind.  In Bean's case, he specifically wants to reduce the interrupt rate while retaining full 8 bit resolution.  In the AC motor case, it appears they simply want to have some crazy high power/high voltage motors controlled by [b]independent[/b] PWMs that are added together to create the illusion (to the motor) of a single monster PWM.  In the article it says:

[i]For example, the three-level inverter in Figure 4 has two independent 2-level inverters arranged so that the output voltages add. [/i]

They are talking about motors running at 2400 and 4160 volts.  Yikes!

The article doesn't clearly point out why they want to use multiple independent PWM sub-systems.  I'm not sure if it's a problem to create a single high power PWM at those voltages.  However, they aren't talking in the article about faking a high resolution ADC and lowering the interrupt time for the CPU.  Perhaps they want a lower interrupt frequency to better deliver power to the motor?  I know that tailoring PWM frequency to the load can help make for a more efficient transfer of power.

Thanks,
PeterM

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