Abstract: Back-to-back three-level neutral-point clamped (NPC) converters are widely used in four-quadrant AC-DC-AC frequency conversion occasions. However, the common-mode voltage (CMV) and neutral-point potential (NPP) balance problems of back-to-back three-level converter affect the safe and stable operation of the system. A CMV elimination method based on the decomposition of the modulation signal was proposed for the back-to-back three-level converter. Each original reference modulation signal was divided into two virtual reference modulation signals. And the real PWM signals for each phase were obtained by the difference of two virtual PWM signals generated by comparing the virtual reference modulation signal with the triangle carriers. Then, the CMV was eliminated to zero by using this modulation method. On this basis, an optimized zero-sequence voltage injection method was adopted to control the NPP balance of the back-to-back three-level converter. Finally, experiments were carried out to verify the effectiveness of the proposed unified control method of CMV elimination and NPP balance.