harmonic cancellation pwm

[401608]

Hi,
my company plans to use an ABB HVDC light converter system. In the technical description the keyword "harmonic cancellation PWM" is lined out. What I understood so far is that this feature was developed to reduce harmonic distortion of converters since avoiding harmonics is the best filter technology you could imagine.... Does anybody know more about how this works?

Best regards, Patrick

 

[MikiBg]

Is that attached paper all u have? It's only harmonic spectrum of PWM voltage, without THD (although it can be calculated from diagram). The idea is to kill most severe components with tuned passive harmonic filter, and then prevent zero sequence components with delta wired transformer to flow into AC network. Since there is a "filter bus" and registered name for filter, I suppose that filter isn't integral part of converter, or at least not by default, but I'm not sure. Same question for transformer. Think that "HVDC Light scheme" would help.

 

[401608]

Hello MikiBg,
first thanks for the rapid answer.
Unfortunately there is not much more precise information than that I cutted out of the ABB brochure. What I also read is that the showed general AC filter is always used and tuned to the specific HVDC variant. However I am more curious how the switching is performed / controlled.

Regards, Patrick

 

[MikiBg]

Looks like free frequency switching to me, the same PWM type that modern double conversion UPS use (attached), but can't say for sure. As far as I know, manufacturers aren't willing to provide internal schemes/circuits/logic, unless you are their tech. support/reseller or similar. If you intend to supply your grid/load with this inverter, maybe output characteristic (voltage THD, voltage regulation, overload capacity, step load response...) should be more important to you.