A master thesis from Aalborg University
Performance of a combined LCC and VSC based Bipole HVDC link
Author(s)
Term
4. term
Education
Publication year
2010
Submitted on
2010-06-02
Pages
132 pages
Abstract
This paper presents a performance of a bipole HVDC link based on line commutated converter (LCC) with a Voltage Source Converter (VSC). Connecting a VSC based link in a bipole fashion with an LCC based link has never been practically implemented yet. In implementing such a system, as the commutation process is different for the two. Therefore, study of issues such as the control of the links, commutation failures and harmonics are important for the proper operation of the system. The control strategy for both the LCC and VSC links has been presented. The VSC control is based on PWM techniques which enables it to have full control of the active and reactive power exchanged with the ac grid. However the LCC is controlled by adjusting the firing angle of the converter and can only control the active power exchanged with the ac grid. The LCC link has a higher probability to commutation failures than the VSC. Hence, the performance of the bipole link has been studied during normal operation and faulty conditions. The faults which have been simulated deal with both ac and dc side faults. For ac side faults, single phase to ground, reduction in the amplitude and distortion of the voltages and three phase to ground have been simulated. For dc side, line to ground and sudden rapid increase in the dc current have been simulated. The results obtained by using the simulation program, PSCAD are presented at the end. The results show that the link operates satisfactorily during normal operation. During faulty conditions, depending on the type of fault, the results show that the link either operates through one line or is com- IVpletely down in worst fault case, three phase to ground.
Documents
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