Modular Multilevel Cascade Converter As Active Power Filter - Hardware and Control Reduction

Abstract

This paper analyses the use of a simplified ac-side current control algorithm strategy, independent of the number of submodules, applied to a Modular Multilevel Cascade Converter acting as an Active Power Filter (MMCC-APF) with a reduced hardware structure. This approach reduces not only volume, but also computational effort and overall costs, and thus resulting in an optimized MMCC for APF applications. Here, Model Predictive Control (MPC) with a reduced number of states is used for both ac-side current control and submodules’ capacitor voltage balancing algorithm. For the calculation of APF compensating currents, two main strategies are addressed, in order to assess ac-side currents control limitations: (i) total and (ii) specific frequencies harmonic compensation. The system analyzed in this paper consists of a nine-level MMCC connected to a medium voltage distribution grid, compensating the harmonics drained by a diode rectifier. All the analyses are conducted in an environment of circuit simulation.