Model Predictive Control of Modular Multilevel Converter with Enhanced Harmonic Performance

Modular multilevel converters (MMCs) have been increasingly adopted in medium/high-voltage high-power systems. However, the control of MMC is not a trivial task considering its multi-objective feature. This paper proposes a model predictive control (MPC) method for MMC which regulates the phase currents, circulating currents and arm energies (and thus capacitor voltages) simultaneously. The cost function is directly optimized through quadratic programming technique, and the optimal solutions are sent to an independent modulator as arm voltage references, avoiding the high calculation cost for enumerating a large number of control actions as conventional MPC methods. Furthermore, a level-shifted pulse-width modulation (LS-PWM) scheme is employed in the modulation stage, which greatly improves the harmonic performance compared with previous MPC alternatives. The effectiveness of the proposed strategy is verified through extensive simulation tests.