Abstract:
In recent years, the topic of Model Predictive Control (MPC) has received significant attention from the power electronics community as a promising alternative to the established control strategies. Model Predictive Direct Control (MPDxC) has emerged as one of the most promising MPC-based approaches in the field of Medium-Voltage (MV) machine drives. However, MPDxC has not been investigated for other applications. This thesis focuses on the development of MPDxC-based con- trollers for high-power grid-connected Neutral-Point-Clamped (NPC) converters. The first contribution of the thesis is a benchmarking exercise, where Model Predictive Direct Torque Control (MPDTC) and Model Predictive Direct Current Control (MPDCC) are evaluated against an early family of predictive controllers. Using an MV machine drive as a case study, it is shown that MPDxC offers a superior level of performance to the earlier controllers, providing lower switching frequencies and/or output distortion. This justifies the further development of MPDxC for grid-connected converters. Subsequently, MPDCC is presented in the context of a NPC converter with an L-filter-based connection to the grid. Next, a new control strategy, Model Predictive Direct Power Control (MPDPC), is proposed. Both controllers are validated through simulation and experimental results, and are shown to offer a level of steady-state performance that is capable of improving upon voltage- oriented control with space vector modulation, and of responding well to reference steps. The context of the thesis is subsequently shifted to a NPC converter with an LCL-filter-based connection to the grid. Although they offer higher levels of harmonic attenuation, LCL-filters pose several additional challenges, and as such modified MPDCC and MPDPC strategies are pro- posed. Through the inclusion of resonance and harmonic damping techniques, both of the proposed strategies are shown to improve upon the respective L-filter-based approaches, with the LCL-filter facilitating significantly lower switching frequencies. Throughout the thesis, the performance of the proposed strategies is investigated within practical operating limits. Although the controllers that are presented represent promising alternatives to the established control strategies, there remains scope for future work in terms of applications, operational issues and implementation strategies.