Research On Control Strategy Applied To Switch On/off AC Filters In Converter Stations

When HVDC system operates，it will consume the reactive power．For the AC system, theinverter is a reactive load．As important equipment, the AC filter is configured in theconverter stations usually to compensate the reactive power．The paper makes a research ofthe AC filter’s control strategy, analyses the problem of operation, and thus to be a guide forthe operation and maintenance．Firstly, the principle and the classification of the AC filter are described in the paper．Thepaper focuses attention on equivalent circuit and impedance frequency characteristics of thefilter of single-tuned filter, high-pass filter, multiple-tuned filter, and outlines the mainprinciple of filter configuration．The article also introduces types, electric wiring and elementsof the AC filter．It also puts forward some indexes for evaluating the performance of the filter．Secondly, with four HVDC projects in CSG, it contrasts the reactive power mode and ACbus voltage mode in the paper．On this basis, it points out that the AC bus voltage controlmode isn’t precision enough in the some state．It will cause the reactive power flow in thepower system．Therefore, the reactive power control mode is used often in practice．Finally, it makes a study of the reactive power control program in Bao-An convertorstation．It concludes the strategy table which shows the AC filter control logic under thevarious conditions of HVDC system．Accordingly, the paper sums up the principles of ACfilter’s control strategy:(1) to keep the AC bus voltage within the specified range;(2) to keepthe optimum assembly of harmonic filter group;(3) to maintain reactive power of convertorstation within the specified range．It shows right after verifying the other HVDC project．Andthe paper analyses the problem such as bus over-voltage and filters switching on/offfrequently．...