Chapter 13 - High-power current source converters

Abstract

Current source converters (CSCs) have been widely adopted in high-power applications such as high-voltage direct current and high-power medium-voltage (MV) drives. The pulse width modulated (PWM) CSCs enjoy superior performance with specific PWM strategy and have received increased attention in recent years. To increase the system power capacity and reduce the output harmonics, parallel connection of modular CSCs with multilevel current output is becoming a more popular option. The parallel CSC topologies can be divided into two categories: independent DC link and shared DC link. For CSC-fed high-power MV drives without transformers (or transformerless), one of the major considerations is to contain the common-mode voltage (CMV), which can potentially cause motor winding isolation failure if not suppressed. Moreover, for parallel CSC drives, an essential issue is the circulating current (CC) flowing through the parallel modules. As a result, the DC current balance will be a priority task especially in shared DC-link parallel structure. This chapter mainly introduces the CSC applications in MV drives and presents the study of transformerless parallel CSC system including technical issues such as CMV, CC, and DC current balance. Several modulation strategies such as interleaved space vector modulation (SVM), multilevel SVM, and phase-shifted sinusoidal PWM that can deal with those challenges are presented.