Cascaded Control System of the Modular Multilevel Converter for Feeding Variable Speed Drives

Abstract

The design process of a holistic control system for a MMC to feed variable-speed drives is proposed in this paper. The performance of the control system is finally validated by measurements on a lowvoltage MMC prototype, which feeds a field-oriented controlled induction machine For high-power drive applications the modular multilevel converter (MMC) is an upcoming topology especially in the medium voltage range. First, from the analysis of the equivalent circuits the design of the current control for the independent adjustment of several current components is derived. Second, the current and voltage components by the investigation of the transformed arm power components for balancing the energies in the arms of the MMC are identified systematically. At minimum necessary internal currents over the complete frequency range The control system ensures a dynamic balancing of the energies in the cells of the MMC. Simultaneously, all other circulating current components are avoided to minimize current stress and additional voltage pulsations. . Here we are using the fuzzy controller compared to other controllers i.e. The fuzzy controller is the most suitable for the human decision-making mechanism, providing the operation of an electronic system with decisions of experts. In addition, using the fuzzy controller for a nonlinear system allows for a reduction of uncertain effects in the system control and improve the efficiency. A cascaded structure with subordinated current control loops and filter-based energy control loops is proposed in this paper. Simulation results are shown below