Lin, JiangAlabdullatif, Mohammed2025-07-212024-11-29https://hdl.handle.net/20.500.14154/75925This thesis investigates the control of three-phase Voltage Source Inverters (VSIs), which play a central role in integrating Inverter-Based Resources (IBRs) such as solar and wind energy into modern power systems. As the penetration of renewable energy increases, ensuring stable and reliable VSI operation becomes critical. The research focuses on developing and evaluating control strategies for VSIs in both grid-connected and Uninterruptible Power Supply (UPS) applications, with particular attention to system nonlinearities, parameter uncertainties, and external disturbances. A Nonlinear Adaptive Control (NAC) strategy is proposed to enhance inner-loop current control performance in grid-connected VSIs with L filter. The approach incorporates perturbation observers to estimate and compensate for total disturbances, enabling robust performance without requiring exact system models. The method is validated through simulation and experimental testing, demonstrating improved performance over conventional Vector Control (VC) and Feedback Linearisation Control (FLC), particularly under challenging conditions such as voltage fluctuations and parameter variations. The NAC approach is further applied to voltage control in three-phase UPS inverters, where the control structure is simplified by removing current sensors. This sensorless architecture relies solely on voltage feedback and disturbance estimation to maintain output stability across varying load conditions such as: linear, nonlinear, and unbalanced load. Simulation and experimental results show improved voltage regulation and reduced Total Harmonic Distortion (THD) compared to standard PI and FLC methods. In addition, the control of grid-connected VSIs with LCL filters is addressed. A refined NAC strategy incorporating high-order state and disturbance observers is introduced to mitigate resonance effects without requiring active damping. The method is evaluated through simulation and hardware experiments under challenging conditions, including parameter mismatches and fault conditions, demonstrating reliable performance in suppressing oscillations and maintaining control accuracy. A fully developed experimental setup, including power hardware, sensing and protection circuits, and real-time DSP-based control implementation, is designed and utilised to validate the proposed methods. The results confirm the practical applicability and robustness of the NAC strategy under representative nonlinear and uncertain conditions, highlighting its potential for advanced power electronic applications.178enThree Phase InvertersUPS inverterpower electronicsgrid integrationThesis