Abstract
The stabilization problem of multi-terminal high-voltage direct current (MT-HVDC) systems feeding constant power loads is addressed in this paper using an inverse optimal control (IOC). A hierarchical control structure using a convex optimization model in the secondary control stage and the IOC in the primary control stage is proposed to determine the set of references that allows the stabilization of the network under load variations. The main advantage of the IOC is that this control method ensures the closed-loop stability of the whole MT-HVDC system using a control Lyapunov function to determine the optimal control law. Numerical results in a reduced version of the CIGRE MT-HVDC system show the effectiveness of the IOC to stabilize the system under large disturbance scenarios, such as short-circuit events and topology changes. All the simulations are carried out in the MATLAB/Simulink environment.
Highlights
It is possible to observe that: (i) Constant power terminals n and t are non-controlled constant power consumptions which are associated with the variable Psd in the optimization model (22). These values are forecasted from an economic dispatch analysis; (ii) constant power terminals l, k, m and t are controlled generators that provide electrical power to the grid as a function of the energy availability in the case of renewable energy or the economic dispatch in the case of thermal power plants; and (iii) the proposed stabilization scheme is a primary-secondary control scheme based on the hierarchical control design using a centralized controller, where the primary control is entrusted with the grid stabilization, and the secondary controller is entrusted with the grid optimization (i.e., optimal power flow (OPF) solution), i.e., of providing the references for the proposed controller
The problem of the global stabilization on multi-terminal high-voltage direct current (MT-HVDC) systems was addressed in this paper from the inverse optimal control (IOC) method, which allowed dealing with the nonlinearities of the MT-HVDC dynamical model to propose an optimal control law that ensures asymptotic convergence of the state variables to the desired references by adding an integral action to eliminate the steady-state error caused by unmodeled dynamics
Numerical results demonstrate that the IOC design presents a better dynamic performance when compared with the passivity-based control (PBC) approach since the overshoots that occur when the references’ changes were smaller than the obtained with the PBC approach
Summary
HVDC systems have gained much attention in recent decades due to the advantage over power transmission capabilities with low power losses instead of HVAC because there is no radiation, induction, and dielectric losses. To ensure a satisfactory operation of an electrical network, even with AC or DC technologies, it is mandatory to use different levels of control that are entrusted with the stabilization of the grid and the possibility of recovering the secure operation after large disturbance events; as well as the possibility to maintain the grid in an optimal operation point under steady-state conditions. Each one of these levels of control can be condensed with hierarchical operation strategies divided from tertiary to primary levels [6,7]. The main challenge with the design of the hierarchical controller corresponds to the possibility of ensuring global optimization properties in the tertiary control stage and asymptotic stability in the primary and secondary control layers [10]
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