June-Seok Lee and Kyo-Beum Lee, "A Carrier-Based PWM Method for Neutral-Point Ripple Reduction of a 3-Level Inverter," in Proc. ECCE Conf., Sep. 2014, pp. 2095–2100. > Paper

The purpose of neutral-point voltage balancing algorithms in a 3L-NPC topology is to eliminate the DC and AC voltage unbalance

of top- and bottom-side dc-link voltages. The DC unbalance problem can cause the output current distortion; therefore, this problem

has to be solved. The AC unbalance problem means the ripple component of top- and bottom-side dc-link voltages exists. In

applications using the NPC topology, a large dc-link capacitor value is required to mitigate the AC unbalance. As a result, the size

and cost of applications become large and expensive. Therefore, this paper focuses on the compensation to mitigate the AC 

unbalance of the neutral-point voltage when a carrier based PWM method is applied. In this paper, the process of the ​

optimal compensation value calculation is discussed and the effectiveness of the proposed compensation method is verified by

using the simulation.