Modulation strategies suitable for a large power voltage source converter combining 3-level neutral point clamped power electronic building blocks

This paper presents a review of modulation strategies that can be applied to a novel large power voltage source converter arrangement. This arrangement has been used in a 47 MVAR SSSC demonstrator connected to the 220 kV Spanish transmission network, for power flow control purposes. It employs four standard 3-Level Neutral-Point Clamped (3L-NPC) Power Electronic Building Blocks (PEBB), of well-proven reliability and share a common dc-bus. The 12 resulting inverter poles, are combined by means of a low VA-rating magnetic arrangement to provide open-end output terminals. In this paper four out of all possible modulation strategies are shown. These obtain a clean output waveform that is unlikely to require any filter to meet power quality regulations The converter components and its operation are explained, and experimental results are provided.