J
Joel Kolstad
I was wondering if anyone could tell me why 12V DC to 120V AC (or 240V AC in
many parts of the world) inverters often output 'modified' square waves,
that is, some negative voltage, 0 volts, some positive voltage... and
repeat, rather than just a square wave? The only reason I could come up
with was so that both the RMS value of the waveform would be correct _as
well as_ the peak value (sqrt(2)*120).
Clearly the harmonic content of such an output is different than that of a
square wave, but that begs the question: What kind of loads care about
harmonics? Transformers and motors presumably will tend to low pass filter
their inputs owing to their magnetiziation inductance, so in such cases
using a modified square wave inverter rather than a sine wave inverter seems
questionable (at least at higher power levels) anyway, no? On the other
hand, if you know your load is going to be, e.g., a switching power supply
(such as a computer, TV, etc.), you could get away with a much smaller
transformer in the inverter and use a considerably higher frequency instead,
correct (while still maintaining the same RMS and peak voltage -- just move
the fundamental and all the harmonics to higher frequencies)?
Thanks,
---Joel Kolstad
many parts of the world) inverters often output 'modified' square waves,
that is, some negative voltage, 0 volts, some positive voltage... and
repeat, rather than just a square wave? The only reason I could come up
with was so that both the RMS value of the waveform would be correct _as
well as_ the peak value (sqrt(2)*120).
Clearly the harmonic content of such an output is different than that of a
square wave, but that begs the question: What kind of loads care about
harmonics? Transformers and motors presumably will tend to low pass filter
their inputs owing to their magnetiziation inductance, so in such cases
using a modified square wave inverter rather than a sine wave inverter seems
questionable (at least at higher power levels) anyway, no? On the other
hand, if you know your load is going to be, e.g., a switching power supply
(such as a computer, TV, etc.), you could get away with a much smaller
transformer in the inverter and use a considerably higher frequency instead,
correct (while still maintaining the same RMS and peak voltage -- just move
the fundamental and all the harmonics to higher frequencies)?
Thanks,
---Joel Kolstad