Design and Testing of a 13.8 kV/1.1MVA 3-Phase 5-Level Flying Capacitor Converter with 10 kV SiC MOSFETs

The flying capacitor converter receives increasing attention recently for high power density converter design with the emerging SiC and GaN devices. This paper demonstrates a 13.8 kV / 1.1MVA 3-phase 5-level (5L) flying capacitor (FC) converter design with emerging 10 kV SiC MOSFET for medium voltage applications. This paper first focuses on the FC value selection method with the analysis of the relation between capacitor ripples and device blocking voltage operation. The three FCs in 5L FC converter are designed to reduce the total volume of flying capacitors. After the FC values are selected., this paper presents the design of different components including the converter layout arrangement, gate driver design and auxiliary power system design. In this paper, one AC-DC single phase leg is built and tested for verification. The testing of different components is first conducted. The testing result of the phase leg is also shown in this paper.

I. Introduction

Multi-level converter is widely adopted in converter design when the required voltage is higher than the single device blocking voltage. Diode-clamped converter and flying capacitor (FC) converter are two typical multi-level converter structures. However, with Si device, FC converter receives limited interest compared to the diode-clamped converter in the industrial product design. That is mainly because the low switching frequency of Si device requires a large FC to limit the voltage ripple. In recent years, SiC and GaN devices receive increasing attention because of their benefit in high-efficiency high power density converter design. [1]–[6] With the new SiC and GaN devices, FC converter receives increasing attention recently because the high switching frequency can significantly reduce the volume and value of the flying capacitor. In the literature, a few FC converters [7]–[8] have been demonstrated for low-voltage applications .