Improved Four-Level Neutral Point Clamped Converter

As a trade-off solution for medium-voltage (>1.5kV) and large-scale photovoltaic generation application, the four-level converters show less components than five-level converters and lower blocking voltages than three-level converters. However, the existing voltage balancing methods for the four-level converters, such as 4L-NPC converter, usually leads to increased voltage stresses across some inner power devices. To improve this problem, one improved 4L-NPC converter is proposed based on the existing 4L-NPC converter. With the adoption of voltage balancing control, the proposed improved 4L-NPC converter is featured with: (a) no flying capacitors; (b) uniform and small voltage stress that is 1/3 of the total input voltage. Simulation studies have been presented to verify the proposed topology.