Bi-directional three-phase three-level Neutral Point Clamped converter with capacitor voltage balancing scheme for unity power factor and low % THD

This paper presents the simulation analysis of three-Ievel Neutral Point Clamped (NPC) converter with bidirectional power flow capacity. Neutral point fluctuation is the major limitation of NPC converter, which is analyzed and minimized in the proposed work. An otTset voltage injected in level-shifted PWM estimated online in a switching period is investigated. A control technique is proposed to minimize the neutral point fluctuation by maintaining the capacitor voltage balance for a three-phase three-Ievel NPC converter. This control technique is designed to achieve constant dc-link voltage and unity power factor by generating reference currents in various steady state and dynamic conditions. The results verify the performance of the controller for unity power factor and low % THD at input current under variable load and reverse power flow conditions, which demonstrates the robustness of the proposed controller.