Robust Tracking Control of UPQC with Integrated Harmonic Estimation and Compensation: An Iterative Observer Approach

Due to the widespread use of renewable energy sources and non-linear loads in power electronics, the level of harmonic injection throughout the power system is showing a significant increase. In this context, the unified power quality conditioner (UPQC) has attracted much attention due to its excellent dynamic voltage restorer and active power filter functions. The UPQC is capable of effectively coping with a wide range of power quality problems including supply voltage dips, voltage fluctuations and flickers, voltage imbalances, harmonic currents and reactive currents. However, it is noted that most of the existing harmonic estimation methods for grid systems embedded with UPQC adopt the idea of multi-observer parallel estimation, which poses a challenge to the limited hardware computational and storage resources of the controller. For this reason, this study gives an efficient iterative observer method, which determines the harmonic order one by one in an iterative manner at each moment and gradually accumulates the estimators of the corresponding order. Based on this disposition, this paper designs a robust tracking controller with integrated harmonic estimation and compensation. Finally, simulation studies demonstrate that the propose method can accurately estimate the harmonics of the UPQC system and can significantly improve the efficiency of the harmonic estimation and compensation process.