Predictive Direct Control of Nine-Switch Converter Unified Power Quality Conditioner Based on Time-Sharing Cooperative Control

In order to solve problems present in traditional indirect control in the nine-switch converter unified power quality conditioner (NSC-UPQC), such as response delay caused by harmonic detection and phase-locked loop (PLL), system coupling caused by coordinate transformations as well as difficulties in tuning proportional-integral (PI) controller parameters. A predictive direct control strategy based on time-sharing cooperative control (TSCC) was hereby proposed for NSC-UPQC. The strategy integrated the NSC topology working principle, and the cooperative control concept was introduced. In the first place, a mathematical model was established for the UPQC predictive direct control system in the αβ coordinate system. This model was formulated based on an analysis of the configuration and operational principles of the NSC-UPQC system, incorporating principles of direct control and finite set model predictive control. Besides, the power balance principle and dead-beat control principle were employed to construct the mechanisms for generating reference currents on the series and parallel sides. This method avoided the complexities associated with coordinate transformations and PLL detection, eliminating the need for harmonic detection and PI controller parameter tuning. As a result, it effectively simplified the control system structure and enhanced the dynamic response capability of the system. On such a basis, the concept of cooperative control was introduced, leveraging the redundancy of the NSC-UPQC topology switches. Additionally, the principles for vector selection and control mechanisms under TSCC were presented, and coordinated control on the series and parallel sides of NSC-UPQC was achieved, considerably enhancing the precision of system control. Finally, detailed simulation and hardware-in-loop test analyses of the proposed strategy were conducted, further validating its feasibility and effectiveness.