DC-Link Capacitor Voltage Imbalance Compensation Method Based Injecting Harmonic Voltage for Cascaded Multi-Module Neutral Point Clamped Inverter

In a three-level (NPC) converter, the voltage imbalance problem in the DC-link capacitors is major issue. This paper proposes the DC-link capacitor voltage imbalance compensation method, where a common offset voltage is injected for a multi-module NPC inverter. The offset voltage consists of a harmonic voltage and a voltage difference between the upper and lower capacitors. The proposed method does not require any hardware modification, so that it is easily implemented. In order to show the effectiveness of the proposed balancing method, theoretical analysis is provided to balance the voltages, and both the simulations and the experiments were carried out to show that the voltage difference of the DC-link was decreased by the proposed method.