A 15-level multilevel inverter circuit includes an outer circuit, an inner circuit, a polarity changing circuit and a computing device. The outer circuit and the inner circuit include a plurality of DC voltage supplies. Each DC voltage supply has a positive and a negative terminal. The outer circuit, the inner circuit and the polarity changing circuit include a plurality of unidirectional power switches. Each unidirectional power switch is a transistor with a diode connected in parallel to the transistor. The computing device is configured to provide control signals to the gates of the plurality of the unidirectional power switches of the outer circuit and the inner circuit to add or subtract the voltage of each of inner DC voltage supplies to form square waveforms approximating sinusoidal waveforms, and to the gates of the plurality of the unidirectional power switches of the polarity changing circuit to switch the polarity of the voltage.