Study On Operation Characteristics Of HVDC System With Controlled Series Capacitor Converters

Controlled series capacitor commutation technology (CSCC) is the combination of capacitor commutation technology (CCC) and power electronic technology, which applied to the high voltage direct current transmission system. Firstly, based on the topology of controlled series capacitor commuted convertor, comparative analysis of the differences and similarities between CSCC and CCC. Then, based on the converter valve’s commutation process in a complete power cycle of CSCC, the paper establishes the CSCC’s state mathematical model; Secondly, reserch on the control strategy of the high voltage direct current transmission system which based on controlled series capacitor commuted convertor(CSCC-HVDC), including conventional high voltage direct current transmission’s control strategies and the controlled series capacitor’s control strategies.Based on the parameters of the Qinghai-Tibet HVDC project, on the electromagnetic transient simulation software PSCAD/EMTDC, the simulation model of HVDC with controlled series capacitor commuted convertor (CSCC-HVDC) is built. Then through the simulation of model which with CSCC’s reactive power and harmonic characteristics, and comparing with the Qinghai-Tibet HVDC project. The results show that the reactive power consumed by CSCC is just sixty percent to eighty percent compared with the conventional convertor, but the injected harmonics in AC and DC system produced by CSCC is much larger than it produced by the conventional inverter, so it should be installed more efficient AC and DC filter equipments for CSCC.The most difference between CSCC-HVDC and the Qinghai-Tibet HVDC project is there are series capacitors between the inverter bus and the converter transformer, on both ends of the series capacitor have anti parallel thyristors, by changing the thyristors trigger angle can change the series capacitor’s equivalent capacitive reactance, which changes the reactive power produced by series capacitor. Then it can reach the purpose of stable system voltage voltage and improve the transmission capacity. The results shows that, the CSCC-HVDC can effectively restrain the commutation failure occurs, and have a better operation and recovery characteristics in the transient process.