Modelling, control and stability analysis of inverter penetrated power system

This century, power industry has been undergoing the revolution transitioning from coal-fired synchronous generators to renewable based generation which typically converts energy by voltage-source converters (VSCs). To address the emerging challenges due to significant integration of VSCs, the primary aim of this research is to model and design advanced control strategy for VSCs and understand and investigate the underlying principles of the interactions between the grid and power electronic inverters. The first part of this research elaborates on the design of control strategies for inverter-based microgrid and multi-microgrid cluster (MMC). As a basis of the control structure in this research, Chapter 2 proposes an autonomous and robust inverter control strategy to facilitate microgrid stable and secure operation, with the emphasis on alleviating fluctuations during microgrid state transitions. Furthermore, Chapter 3 presents a phase reformulation-based sliding framework to decouple inherent control interactions for inverter-based microgrid, and an improved frequency and phase synchronisation scheme to attenuate the interaction between the inverter and the weak grid. In Chapter 4, distributed consensus controllers with event-triggered mechanism are considered for MMC, which achieves reasonable power sharing and remarkably relieves communication and computation burdens. The second part of this research mainly analyses static voltage stability and small-signal stability of the inverter penetrated future power system. From the perspective of static voltage stability in Chapter 5, a systematic index is deduced to assess system loading status, with the impacts of inverter-based distributed generators (DGs) under various control modes rigorously discussed. From the perspective of small-signal stability in Chapter 6, the explicit state-space model for a multi-inverter system including different types of inverter-based DGs is developed by two-level component connection method (CCM), which modularised inverter control blocks at the primary level and inverter-based DGs at the secondary level. Through the analysis on eigenvalues of the partitioned subsystems, adverse impacts of generic inverter control prototypes on the power system stability are revealed. Case studies regarding the proposed methodologies have been undertaken on the benchmarking systems and compared to the existing literature where applicable to demonstrate the effectiveness and superiority