Do you really mean "multiple", or did you intend to say "modified"?
(Modified sine wave inverters generate a step wave which is basically two rectangular waves added together to produce a shape which is a very rough approximation of the sine wave's shape. This reduces the high harmonic components of the wave, and produces output which many devices are MUCH happier with than they would be with the simple square-wave inverters.)
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(Modified sine wave inverters generate a step wave which is basically two rectangular waves added together to produce a shape which is a very rough approximation of the sine wave's shape. This reduces the high harmonic components of the wave, and produces output which many devices are MUCH happier with than they would be with the simple square-wave inverters.)
It might be just what you are looking for.