Quasi two-level PWM operation of a nine-arm modular multilevel converter for six-phase medium-voltage motor drives

Abstract

Abstract-This paper proposes a hybrid converter for mediumvoltage six-phase machine drive systems that mixes the operation of a traditional two-level voltage-source inverter and the modular multilevel converter (MMC) to enable operation over a wide frequency range. Topologically, the proposed converter consists of nine arms resembling two sets of three-phase MMCs with three common arms, yielding a nine-arm MMC with a 25% reduction in the number of employed arms compared to a traditional dual three-phase MMC. The multilevel property of a standard MMC is emulated in the proposed converter, however on a two-level basis, resulting in a stepped two-level output voltage waveform. The proposed converter has a reduced footprint with advantages of small voltage steps, modular structure, and ease of scalability. Further, it is able to drive high-power six-phase machines within low operating frequencies at the rated torque. The operating principle of the converter is elaborated, and its modulation scheme is discussed. The features of the proposed converter are verified through simulations and experimentally.Index Terms-Medium-voltage drives, modular multilevel converter (MMC), nine-arm MMC, six-phase machines, submodule (SM) capacitor voltage ripple, quasi two-level PWM.

Multilevel Inverter: A Survey on Classical and Advanced Topologies, Control Schemes, Applications to Power System and Future Prospects

“…Over recent years, MMC has been successfully operated as an efficient power converter in numerous power system applications such as HVDC system [101][102][103][104], FACTS devices [105][106][107], energy storage devices [108][109][110], electric vehicles [111,112], motor drives [113][114][115], active power filters [116,117] and renewable energy [118][119][120][121]. Presently, the primary vital concerns of MMC include capacitor voltage balancing (CVB) and circulating current suppression (CCS).…”

Modular multilevel DC–DC converter with arm interchange concept

“…To generate a two‐level output voltage from the conventional multilevel HBSMs‐based MMC, while keeping the capacitor voltages balanced with the existence of any possible mismatches, at least one extra SM per arm should be employed. Similar to the quasi two‐level operation of MMC [23–25], the two‐level operation (modulation) of the involved HBSMs‐based MMC results in employing small SMs capacitances and small arm inductors.…”

Designing a Passively Damped Quasi-Two-Level-Operated Modular Multilevel Converter for Drive Applications

“…In other research groups, Diab et al proposed quasi-twolevel operation for a special six-phase MMC topology in [15] and recently, a quasi-three-level operation for a modified MMC was proposed by Wei et al [16]. Furthermore, Wang et al propose a control approach in [17] that aims to simplify the control approaches from [12], [13].…”

“…1) approaches that do not control internal (leg) currents of the converter nor the capacitor energies [8]- [10], [15], [16], [19], [20], 2) approaches that control both the leg currents and the capacitor energies [1]- [3], [12], [13], and…”