Leakage Current Minimization Using NPC DC Decoupling Method for Three-Phase Cascaded Multilevel PV Inverter

This brief presents a new neutral point clamped (NPC) DC decoupling method based three-phase three-level cascaded multi-level inverter (CMLI) for the minimization of leakage current in PV systems. The proposed CMLI reduces the transitions in the terminal and common-mode voltage during common zero state. Therefore, a common zero state in all the three phases is identified and the value of terminal or common mode voltage is retained to its previous active state value using the clamping circuitry. This action results in reducing the number of transitions in the terminal voltage, which further helps in the minimization of leakage current. As a result, the size of EMI filters and common mode chokes required for the proposed CMLI are also reduced. Further, the mathematical analysis of terminal voltage using the switching function concept is also discussed in this brief. From the mathematical expression of terminal voltage, the analytical waveforms of terminal voltage for both conventional and proposed CMLIs are also shown in this brief. The presented switching function analysis is also supported using the simulation and experimental results presented in this brief. Complete details with respect to the operation, simulation and experimental results of the proposed CMLI are presented in this brief.