Research on discrete double vector controller of series-connected voltage sag compensator

Series power quality conditioner is the most cost-effective solutions for voltage sags. In this paper the continuous and discrete state space models of the series connected sag compensator in dq synchronous reference frame are established. Then the discrete double vector control algorithm which incorporates both current controller and voltage controller with inner current loop and outer voltage loop is derived on the basis of the state space model employing the forward Euler method and deadbeat control principle. By the combination of system model and controller equations, as well as the proper selection of controlled and inputs variables, the closed-loop model of the discrete control system is derived. An integration term is introduced to the proportional controller in order to compensate the static error caused by one sample delay due to analog to digital conversion and computer calculation time. A realistic simulation model is built using PSCAD/EMTDC to test the discrete dual vector controller. Simulation results show that controller possesses good dynamic and static performances when the fault is three-phase balanced and the load voltage can be compensated to the reference level within 2 ms. When it comes to the unbalanced fault, the proposed approach still respond fast, although the compensated load voltage is somewhat unbalanced.