Analysis of thyristor switch in power conditioning system with SMES

Abstract

Ensuring high level of power quality (PQ) is one of most important issues in supplying in industry loads. There exist some critical types of loads that should be protected from any voltage disturbance. If any voltage disturbance (like voltage sag or dip) occurs an alternative energy source is used to ensure constant voltage amplitude across protected load. In described power conditioning system (PCS), power electronic system is connected in parallel to group of protected loads. The PCS together with protected loads have to be disconnecting from the mains in the case of voltage sag or dip occurs. Disconnection is necessary, if any voltage disturbance occurs, to prevent from delivering energy to low impedance part of power system (the mains in such case) from energy storage that is contained in the PCS (in this situation high temperature superconducting magnetic energy storage (SMES)). In described system breaking the connection between the mains and the load takes place thanks to the thyristor switch (TS). Disconnection and reconnection modes of operation of the PCS are particularly described and analysed in the paper. To obtain relatively low turn off time of thyristor switch a new method of controlling the PCS has been proposed that can assist turning off process of the TS and decreasing turn off time. The resynchronisation of the load voltage and the mains voltage of the PCS is also presented in the paper. It is used to limit the amplitude of the mains current after reconnection process. Influences of resynchronisation and reconnection processes on load voltage are also analysed. To proof correctness of designed controller the simulation and experimental results have been presented and discussed in the paper