An inverter without a transformer?
So-called modified sine wave inverters use a DC rail that is approximately \$\sqrt{2}\$ times the RMS voltage of the sine that is being simulated, so about 170V for 120VAC, and a duty cycle that causes the RMS output to match the sine wave (image from here):

Duty cycle should be 50%, so the RMS value and the peak value match that of a sine wave of 120V RMS.