Research on Control Strategy of a Unified Power Quality Conditioner Based on a Nine-Switch Converter

To enhance the operational characteristics of systems like new energy generation under non-ideal conditions, this study proposes employing a nine-switch converter (NSC) instead of the traditional back-to-back (BTB) converter for unified power quality conditioning (UPQC). This paper first analyzes the fundamental principles, mathematical model, and modulation techniques of the NSC. Subsequently, it presents a control strategy for the NSC system with power quality conditioning capabilities. The paper also designs simulations and experimental studies to investigate the operational characteristics of the proposed NSC under non-ideal conditions, including grid voltage sags and nonlinear loads. The results demonstrate that the NSC—with fewer switching devices and a simple structure—not only achieves grid-connected power generation and harmonic/reactive power compensation but also operates flexibly under symmetric and asymmetric grid voltage faults.