A small signal stability model is developed based on the small-signal stability and dynamic interaction problems caused by operation mode-switching of unified power quality conditioners（UPQCs）.The small-signal model also includes series and parallel converter controls.The stability and dynamic characteristics between independent converter operating mode and combined series and/or parallel converter operation mode are analyzed.Eigenvalue sensitivity analysis with respect to factors such as control-parameters and load-factors are also studied.This study can provide some theoretical guide for parametric design.A coordinated control strategy is also presented based on the new power flow compensation.Case studies are given to validate the effectiveness of the small signal stability model and feasibility of the proposed control strategy.