Investigation of resonance phenomena in a DVR protecting a load with PF correction capacitor

The source impedance of the supply voltage of a dynamic voltage restorer (DVR) may change due to the change of power system grid configuration. Hence the resonance frequency of the DVR system will change and that results in harmonic resonance in the DVR. This paper presents a detailed study on possible resonance phenomena in a DVR protecting a load with power factor correction capacitor. The study reveals that the harmonic resonance cannot be reliably prevented with the existing open-loop control of the DVR due to the lack of damping and stability margin. It is proved that the closed-loop controller consisting inner current loop and outer voltage loop can dampen out possible harmonic resonance in the DVR system by properly selecting the gain parameters of the controller.