Dynamic Behavior of a 21-Level (Line-to-Line) BTB System Based on Series Connection of Sixteen Converter-Cells under a Single-Line-to-Ground Fault Condition: Experimental Verification by a 200-V, 20-kW Laboratory System

Abstract

This paper deals with the dynamic behavior of a 21-level (line-to-line) BTB system based on series connection of sixteen converter-cells under a single-line-to-ground fault condition. A laboratory system rated at 200V and 20 kW was designed and built up to confirm the validity of the system. Experimental results obtained from the system lead to the following conclusions: i) The BTB system has a capability of reducing both negative-sequence voltage and current appearing during the fault. ii) A dc-capacitor voltage regulator that has been already developed by the authors makes it possible to suppress the dc-voltage fluctuation sufficiently. iii) Flux fluctuations in transformers used for the system strongly depend on a voltage depth during the fault. These would make a significant contribution to putting the BTB system into practical use.