human: Given a node-centered hypergraph: <hypergraph>, where nodes represent papers and hyperedges represent sets of papers co-cited by a source paper.

Details of the hypergraph:
Center node: "modeling and control of hvdc transmission systems from theory to practice and back"
  Abstract: The problem of modeling and control of multi-terminal high-voltage direct-current transmission systems is addressed in this paper, which contains five main contributions. First, to propose a unified, physically motivated, modeling framework — based on port-Hamiltonian representations — of the various network topologies used in this application. Second, to prove that the system can be globally asymptotically stabilized with a decentralized PI control that exploits its passivity properties. Close connections between the proposed PI and the popular Akagi's PQ instantaneous power method are also established. Third, to reveal the transient performance limitations of the proposed controller that, interestingly, is shown to be intrinsic to PI passivity-based control. Fourth, motivated by the latter, an outer-loop that overcomes the aforementioned limitations is proposed. The performance limitation of the PI, and its drastic improvement using outer-loop controls, is verified via simulations on a three-terminal benchmark example. A final contribution is a novel formulation of the power flow equations for the centralized references calculation.

Connected through hyperedge HE-1 (induced by source paper "permanent magnet synchronous motors are globally asymptotically stabilizable with pi current control"):
  with members:
    - "robust pi passivity based control of nonlinear systems application to port hamiltonian systems and temperature regulation"

Connected through hyperedge HE-2 (induced by source paper "optimal regulation of flow networks with transient constraints"):
  with members:
    - "on resilient control of dynamical flow networks"
    - "a compartmental model for traffic networks and its dynamical behavior"
    - "zero forcing sets and controllability of dynamical systems defined on graphs"
    - "zero forcing number constrained matchings and strong structural controllability"
    - "an internal model approach to optimal frequency regulation in power grids with time varying voltages"
    - "dynamic coupling design for nonlinear output agreement and time varying flow control"

Connected through hyperedge HE-3 (induced by source paper "a tool for stability and power sharing analysis of a generalized class of droop controllers for high voltage direct current transmission systems"):
  with members:
    - "a survey on modeling of microgrids from fundamental physics to phasors and voltage sources"

Question: Please tell me which class the center node belongs to. The 40 classes are: cs.NA(Numerical Analysis), cs.MM(Multimedia), cs.LO(Logic in Computer Science), cs.CY(Computers and Society), cs.CR(Cryptography and Security), cs.DC(Distributed, Parallel, and Cluster Computing), cs.HC(Human-Computer Interaction), cs.CE(Computational Engineering, Finance, and Science), cs.NI(Networking and Internet Architecture), cs.CC(Computational Complexity), cs.AI(Artificial Intelligence), cs.MA(Multiagent Systems), cs.GL(General Literature), cs.NE(Neural and Evolutionary Computing), cs.SC(Symbolic Computation), cs.AR(Hardware Architecture), cs.CV(Computer Vision and Pattern Recognition), cs.GR(Graphics), cs.ET(Emerging Technologies), cs.SY(Systems and Control), cs.CG(Computational Geometry), cs.OH(Other Computer Science), cs.PL(Programming Languages), cs.SE(Software Engineering), cs.LG(Machine Learning), cs.SD(Sound), cs.SI(Social and Information Networks), cs.RO(Robotics), cs.IT(Information Theory), cs.PF(Performance), cs.CL(Computation and Language), cs.IR(Information Retrieval), cs.MS(Mathematical Software), cs.FL(Formal Languages and Automata Theory), cs.DS(Data Structures and Algorithms), cs.OS(Operating Systems), cs.GT(Computer Science and Game Theory), cs.DB(Databases), cs.DL(Digital Libraries), cs.DM(Discrete Mathematics). Directly output the class name.

gpt: cs.SY(Systems and Control)