Renewable generation is mainly connected through converters. Even if they provide more and more ancillary services to the grid, these may not be sufficient for extremely high penetrations. As the share of such generating units is growing rapidly, some synchronous areas could in the future occasionally be operated without synchronous machines. In such conditions, system behaviour will dramatically change, but stability will still have to be ensured with the same level of reliability as today. To reach this ambitious goal, the control of inverters will have to be changed radically. Inverters will need to move from following the grid to leading the grid behaviour, both in steady state and during transients. This new type of control brings additional issues on converters that are addressed in this study. A solution is proposed to allow a stable operation of the system together with a limited solicitation of inverters during transients.
Eigencalculation is a challenging task in large-scale power systems with high power electronics penetration for at least two reasons. First, the well-known inter-area modes are no longer the only coupling modes as such couplings may involve also power converters. Next, it is difficult to find all coupling modes without a priori knowledge about them (frequency or path of oscillation). In this paper we propose a new method to overcome these difficulties. It is fully analytic, i.e., does not need operator manipulations like dynamic simulations, and it is exhaustive in the sense that makes a full scan of the system for coupling modes. The approach involves concepts from matrix computation and dynamic systems analysis which hold in largescale and need no hypothesis (like the one about large inertia generators usually associated to inter-area modes) or knowledge about the structure of the power system. Validations on several models are presented, including realistic large-scale model (more than 1000 generators/dynamic devices) of the European power system.
This paper addresses the problem of damping interarea oscillations via power modulation of a VSC-HVDC link integrated in a power AC grid. Motivated by the fact that interarea modes may be at higher frequencies, close to other modes of the system, and classic tuning methods of standard (IEEE) power oscillations damping controller structures may not give satisfactory results. A reduced order model of a meshed AC grid with a HVDC link is proposed for control design. Based on this model which carefully integrates the dynamics of interest, a robust controller for the HVDC link is designed to damp interarea oscillations and enhance the damping of the other modes. Investigations with both linearized and nonlinear model of the system are carried out to settle and validate the approach. The efficiency and robustness of the proposed controller are tested and compared with standard controller structures.
This paper is focused on interaction between two closed-connected high-voltage DC (HVDC) lines. This interaction is studied by employing electromagnetic transients (EMT)-based nonlinear modeling in MATLAB R /Simulink R software environment. In order to describe the mechanism behind the HVDCs interaction, both nonlinear time-domain simulations and modal analysis of the coupled HVDC links, using linearized version of the system, have been performed. System stability has been assessed and the path of interactions has been identified by computing the participations of various states in the oscillatory modes.
This paper proposes a static decentralized controller design method for an HVDC link embedded in a large-scale AC grid based on the Linear Matrix Inequalities (LMIs) technique. The considered studied system is treated as composed by two overlapping subsystems. The interconnection between the two subsystems is nonlinear and is treated by increasing disturbance rejection and robustness against norm-bounded parametric uncertainties of the closed-loop. Indeed, the overall robustness and tracking ability of the entire closed-loop is significantly improved with the proposed controller. This is both analytically ensured in the synthesis of the gains of the regulators and, next proven by validation simulations. The overall robustness and tracking ability of the entire closed loop system can be significantly improved. It is shown that this control can deal with HVDC link with different lengths, including the short ones for each the coupling between the two converters is strong.Another advantage of the proposed decoupling control is the resilience: as no communication is used between the two stations, in case of failure of one converter or loss of measures as control, the control of the other converter is not affected. Moreover, it guarantees the stability of the overall system. Finally, the efficiency and robustness of the proposed controllers are tested and compared with each others, to illustrate the control synthesis and its effectiveness.
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