Fast Model-based Predictive Control (FMPC) for grid connected Modular Multilevel Converters (MMC)

Abstract

Model-based predictive control, or MPC, is a popular technique widely used in three-phase two-level power converters (VSC), in applications such as motor and generator control. One of the main drawbacks of implementing MPC is the high computation time requirements while evaluating the effects of the six available vectors on the cost function. The computing time becomes unacceptable when the number of vectors is very high, as in modular multilevel converters (MMC), making it impossible to run the MPC algorithm in microcontrollers (MCUs) within reasonable cycle times. This paper proposes a fast method capable of finding the reference voltage vector among a large number of available multilevel voltage vectors, in a single step, which greatly reduces the computation time and makes it possible to use MPC in regular MCUs. Unlike other MPCs, after calculating the reference vector, the proposed method discards the duration times obtained by the MPC and the reference vector is modulated using an SVM.MPC has been little developed for MMC and is normally intended to improve the internal operation of the converter. In contrast, this paper presents a fast MPC, designed to control the active and reactive powers exchanged by a grid-connected MMC, providing a fast dynamic response, low current THD and constant switching frequency. In addition, the implementation is compatible with other known MMC vector control algorithms and can even be used with other multilevel converters.