Modular Multilevel Converter with Wireless Magnetic Power Decoupling for Three-phase MV Adjustable-speed Drives

Abstract

In this paper, we propose a modular multilevel converter (MMC) with a wireless magnetic power decoupling approach suitable for medium-voltage high-power variable-speed machine drives. Our proposed power decoupling approach is independent of the operating frequency, which solves the issue of wide fluctuations of low-frequency voltage ripple components in submodule (SM) capacitors, especially at low-speed operations without using any ripple power capacitor. Employing wireless magnetic elements reduces the amount of high-voltage insulation between the transformer windings, resulting in a significant reduction in the overall size of the system. The basic idea of our proposed approach is to magnetically couple the instantaneous three-phase ripple power of each of the three adjacent-arm SMs. The proposed MMC is free from low-frequency capacitors, resulting in enhanced system reliability, volume, and lifetime. The operation principles of the proposed MMC are explained, and a control design is introduced. The performance of the proposed scheme was verified via simulation and experimental tests.