Scalable Control Allocation: Real-time Optimized Current Control in the Modular Multilevel Converter for Polyphase Systems

Abstract

The main novelty of this paper is to introduce a new real-time optimized control allocation (CA) method of the currents scalable to any modular multilevel converter (MMC). It can be adapted to an MMC of any number of phases and submodules (SM) without having to undergo changes in the control algorithm. First the scalable state-space model of the MMC currents is presented end than, this minimal order model is used to develop the scalable current control allocation method. The control allocation is computed by fast real-time optimization using linear programming and quadratic programming algorithms. Three control allocation methods are Hardware-Inthe-Loop tested for polyphase AC systems from 3 up to 101 phases, showing their ability to guarantee the current reference tracking as well as the scalability of the tracking performance. A comparison between the resolution methods highlights the benefits and pitfalls of each.