Abstract
This paper proposes a new dual modular multilevel converter (MMC) topology as a medium-voltage drive for adjustable-speed applications incorporating open-end stator winding machines. A novel concept of sharing one capacitor between each two adjacent-arm sub-modules (SMs) of MMC phase-legs, operating with out-of-phase modulation, is realised through new SM arrangement. This concept allows the MMC to utilise half the number of the SM capacitors, compared to a traditional MMC topology. Additionally, the sizing requirement of the shared capacitor is diminished, which significantly reduces the volume of the drive system and its stored energy. The switching scheme of the shared capacitor between two oppositely modulated SMs eliminates the problem of capacitor wide-voltage fluctuations, independent of the operating frequency. Further, the proposed MMC can efficiently operate at near zero frequency; therefore, a machine speed-range from zero speed to the rated speed is possible under rated torque operating condition. The proposed MMC topology is elucidated in detail, and its effective performance is verified through simulation.
Highlights
With its superior performance in medium- to high-voltage high-power applications, the modular multilevel converter (MMC) has been adopted in industry, serving as a standard converter interface in the high-voltage direct-current (HVDC) transmission systems [1]
This paper proposes a new MMC topology that applies a novel concept of sharing capacitors between adjacent-arm SMs that operate with out-of-phase modulation
This paper presented a new dual MMC topology for MV motor drives incorporating open-end stator winding machines
Summary
With its superior performance in medium- to high-voltage high-power applications, the modular multilevel converter (MMC) has been adopted in industry, serving as a standard converter interface in the high-voltage direct-current (HVDC) transmission systems [1]. With the need of driving highpower machines at the medium-voltage (MV) level over a wide speed range, while Volt/Hertz control is applied, the MMC experiences large voltage fluctuations that extremely increase at reduced operating frequencies. This threatens the safety of the MMC switching devices and adversely affects the MMC normal operation. The proposed topology is fundamentally a dual converter configuration, that is, suitable for machines with open-end stator windings It operates at half the dc-link input voltage, compared to a single-sided MMC topology, for the same output voltage and power level. Employing half the number of the SM capacitors, compared to conventional MMC topologies
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