Sensor-less operation of hybrid boost modular multilevel converter for subsea multiphase medium voltage drives

Abstract

This paper introduces Hybrid Boost Modular Multilevel Converter (Hybrid Boost MMC) as a suitable candidate for subsea drive systems. The investigated drive system is based on a five-phase Induction Machine (IM) in order to enhance system's reliability and to gain other several merits of multiphase machines compared with conventional three-phase IMs. Each arm in the employed Hybrid Boost combines Half-Bridge (HB) and Full-Bridge (FB) Submodules (SMs) with ratio 2:1 respectively. The suggested Hybrid Boost MMC provides boosting capability with a reduced number of switches, which can be employed effectively instead of employing conventional voltage source converter followed by bulky step-up transformer. In addition, voltage balancing of the capacitors in any MMC is crucial in order to ensure proper operation of the converter. A sensor-less capacitor voltage balancing technique is proposed in this paper, employing five-level five-phase MMC with two HB-SMs and single FB-SM per MMC's arm. A simulation case study for the proposed system is investigated using a 1000 Hp five-phase Induction Machine (IM). - 2017 IEEE.