Multivariable control with grid objectives of an HVDC link embedded in a large-scale AC grid

International audienceThe HVDC links are increasingly used not only to interconnect asynchronous AC systems but are also embedded into a same meshed AC power system. Thanks to its speed and flexibility, the HVDC technology is able to provide transmission system advantages as transfer capacity enhancement and power flow control. In addition, studies have shown that the way of controlling the HVDC converters impacts the stability of the AC system. This can be particularly exploited to enhance the dynamic power system performances during transients. In this paper a robust multivariable control design for HVDC link converters is proposed. It is based on the coordination of the control actions of the HVDC converters and the use of a control model which takes into account the dynamics that mostly impact stability of the neighbor zone of the HVDC link. This new methodology was used to synthesize the controller for an actual grid 1000 MW HVDC link reinforcement project called ''Midi-Provence'' in the southern part of the French grid. The synthesis , implementation and validation processes are presented in detail. The new controller is tested in comparison with the standard vector control. A large-scale dynamic model of the whole European power system, currently used and updated by the European TSO's for the interconnection studies has been used with Eurostag simulation software. Ó 2015 Elsevier Ltd. All rights reserved. Introduction The HVDC link is a mean of transmission of electric power based on high power electronics. Thanks to its speed and flexibility, the HVDC technology is able to provide the transmission system advantages as transfer capacity enhancement and power flow control [1]. Initially, it was used in power systems to interconnect asyn-chronous AC systems. The ends of the HVDC link are electrically independent one from each other and this reduces significantly the propagation of perturbations between the two AC grids as it is the case of the England–France interconnection [2]. Nowadays, HVDC links are increasingly embedded into a same meshed AC system in order to enhance the grid's transmission capability and flexibility of the power system. In this context, the HVDC link co-exists with other AC system elements as for instance AC lines and generators. Several projects of insertion of this type of device in a meshed AC system are underway in Europe, as for instance France–Spain HVDC project [3], France–Italy interconnection and Midi-Provence HVDC project [4]. This latter is our case of study. In fact, a 1000 MW HVDC link will be inserted in France between the two areas Fos and Gaudière, in order to enhance capacity of power transmission and the stability of the Midi-Provence region. The need of such HVDC link is due to the fact that only one single 400 kV AC line interconnects the two areas (see Fig. 1). It was shown that the strategy used to control the HVDC converters can impact the stability of the system in which the link is embedded [5–12]. This conducted us develop a methodology which takes into account, in a control model, the neighbor zone of the HVDC link and the dynamics that most impact transient stability. This control model captures the dynamics that are relevant for the transient stability of the power system. The controller synthesis is done on the base of this control model. As a consequence, power system performances are enhanced in addition to local performances. Preliminary results have been presented in [13]. This approach is fully developed here in order to take into account some key critical fault situations at the synthesis stage using the robust H 1 theory. Also the methodology is adapted to handle realistic large-scale cases as the European power system. As a matter of fact, in other papers [14,15], the transient stability is considered as an a priori objective for the synthesis of coordinated controllers for HVDC. However, the effectiveness of these methods had not been proved in the case http://dx