A new control scheme for an HVDC transmission link with capacitor-commutated converters having the inverter operating with constant alternating voltage
2012 (English)In: 44th International Conference on Large High Voltage Electric Systems 2012, 2012, 1-11 p.Conference paper (Refereed)
Experience and theoretical analysis show that the voltage and power stability becomes an important issue when high-voltage direct current (HVDC) systems using line-commutated converters (LCC) are connected to AC systems with low short-circuit capacity and that these problems become more pronounced the lower the short-circuit capacity of the connected AC system is, as compared with the rating of the HVDC converter station. Normally some additional equipment, like static or synchronous compensators, will be installed in order to improve the performance of the HVDC transmission system, when it is connected to a weak AC system. The cost of the substation thereby will be increased. The Capacitor-Commutated Converter (CCC), which has been developed by ABB, offers an alternative to the LCC in this kind of application. It reduces the reactive power interaction between the converter and the connected AC system. The CCC is, in principle, a classical converter provided with a series capacitor placed between the converter valves and the converter transformer. In this paper a new control strategy that can be used together with such a CCC is presented. In the new control system the inverter emulates the operation of a Voltage Source Converter, in the sense that, beside the control of the active power flow through the converter, the reactive power exchange with the AC network can also be managed in order to adjust the alternating voltage of the converter bus. Studies have shown that the interaction between the inverter and the connected AC system is significantly reduced, when the CCC is used together with this new control strategy. Keeping the alternating voltage constant makes it possible to control the DC-side voltage of the HVDC transmission system, allowing the rectifier converter to control the active power by means of controlling the direct current. This combination allows stable operation of the HVDC transmission system even under severe network conditions associated with low short-circuit power in the connected AC network at the inverter side. In the paper it is shown that, with the new control scheme, it is possible to operate the inverter into an almost passive AC network (a network with very few rotating generators, resulting in almost no short circuit power). Simulation results have indicated satisfactory operation of the HVDC transmission with the inverter operating into a network having a Short-Circuit Ratio as low as 0.2 (SCR ≈ 0.2). To the knowledge of the authors, operation of a line-commutated converter at such low SCR values has never been reported previously. A description of the new control scheme will be presented. The calculated performance in a practically implemented installation, the Rio Madeira Back-to-Back system, will be illustrated.
Place, publisher, year, edition, pages
2012. 1-11 p.
CCC-capacitor commutated converter, Control principles, HVDC, LCC-Line commutated converter, Rio Madeira, Weak system
Other Electrical Engineering, Electronic Engineering, Information Engineering
IdentifiersURN: urn:nbn:se:kth:diva-116822ScopusID: 2-s2.0-84872119905OAI: oai:DiVA.org:kth-116822DiVA: diva2:601647
44th International Conference on Large High Voltage Electric Systems 2012, 26 August 2012 through 31 August 2012, Paris
QC 201301302013-01-302013-01-282013-01-30Bibliographically approved