June-Seok Lee and Kyo-Beum Lee, “New Modulation Techniques for a Leakage Current Reduction and a Neutral-Point Voltage Balance in Transformerless Photovoltaic Systems Using a Three-Level Inverter,” IEEE Transactions on Power Electronics, vol. 29, no. 4, p > Paper

Transformerless topologies of many topologies are widely used in photovoltaic (PV) systems because these topologies have many

advantages in terms of the weight, size, and efficiency. A three-level inverter has an outstanding performance and is advantageous

in the switching device selection than a two-level inverter. In the transformerless PV systems using the three-level inverter, the PV

systems should suffer from the leakage current and generate the neutral-point voltage unbalance. To solve two problems, this paper

proposes modulation techniques to reduce the leakage current and balance the dc-link voltages. The cause of the leakage current

in the three-level inverter is analyzed. The proposed technique LMZVM using the large, medium, and zero vectors reduces the

common mode voltage that causes the leakage current than that of the conventional PWM. Moreover, the proposed technique

LMSVM using the large, medium, and small vectors balances the dc-link voltages with reduced CMV as the same in LMZVM. The

effectiveness of the proposed techniques is verified by comparing its results with those of the convectional PWM. The results are

obtained through simulations and experiments.