Low Frequency Modular Multilevel Converter Topology for Improved Dynamic Performance of Variable-Speed AC Drives

Abstract

This paper presents a control arrangement for the modular multilevel converter (MMC) to drive a variable-speed alternating current machine, mainly concentrating on upgrading dynamic fruition. In a manner, the energy balance in the MMC cell capacitors is prone to be unstable at start-up and low-frequency operations. Moreover, the MMC topology fundamentally requires advanced control methodology to modify imperativeness and smother the voltage pulsation of each cell capacitor. This paper proposes a control system for the healthy dynamic response of MMC even at zero frequency using leg offset voltage injection. The leg offset voltage for changing the arm energy is made by direct calculation but not the circulating current control controller. With the help of the exceedingly capable leg offset voltage from facilitate calculation the dynamic performance of a MMC at low speeds has clearly made progress. The ac machine has been driven from zero to maximum speed without enormous cell capacitor voltage ripples with help of this strategy. The proliferation and trial verify that relentless operation is guaranteed down to <2% of the rated speed under disturbance of 40% step load torque.