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Control of a three-phase inverter with neutral-line voltage injection is proposed to improve the output voltage waveform. This inverter consists of a main three-phase inverter and an auxiliary single-phase inverter; the main inverter acts in the 120-degree conduction mode and the auxiliary inverter behaves as a wave shaper with three times frequency of the main frequency. The main inverter converts almost all the input dc power to ac power in discontinuous rectangular waveform. The auxiliary inverter is applied to lower the output voltage total-harmonic-distortion (THD). Design of the proposed inverter is presented in the paper. Performance of the total inverter is investigated in theory and experiment. The output three-phase voltages had a THD of about 4.5% in experiment. The practicability of the control method is confirmed.