Nonlinear optimal control of a multi-rotor wind power unit with PMSGs and AC/DC converters)

Abstract

AbstractA nonlinear optimal (H-infinity) control method is developed for a wind power unit that comprises twin turbines, permanent magnet synchronous generators (PMSGs) and AC/DC converters. By proving differential flatness properties for this system the associated setpoints definition problem is solved. The dynamic model of the wind power unit being initially expressed in a nonlinear and multivariable state-space form, undergoes approximate linearisation around a temporary operating point that is recomputed at each time-step of the control method. The linearisation relies on first-order Taylor series expansion and on the computation of the associated Jacobian matrices. For the linearised state-space model of the wind power unit, a stabilising optimal (H-infinity) feedback controller is designed. This controller stands for the solution to the nonlinear optimal control problem of the wind power unit under model uncertainty and external perturbations. To compute the controller's feedback gains an algebraic Riccati equation is repetitively solved at each iteration of the control algorithm. The global stability properties of the control method are proven through Lyapunov analysis. Finally, to implement state estimation-based control of the wind power unit, without the need to measure its entire state vector, the H-infinity Kalman Filter is used as a robust state estimator.Keywords: Multi-rotor wind power systempermanent magnet synchronous generatorAC/DC converterVSC-HVDC converterMMC convertersdifferential flatness propertiesnonlinear H-infinity controlTaylor series expansionJacobian matricesRiccati equationglobal stability Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationNotes on contributorsGerasimos RigatosDr. Gerasimos Rigatos (Senior Member, IEEE) received a Diploma (1995) and a PhD Degree (2000) both from the Department of Electrical and Computer Engineering of the National Technical University of Athens (NTUA), Greece. He is Research Director at the Industrial Systems Institute, Greece. He has led research cooperation projects in the areas of nonlinear control, nonlinear filtering and control of distributed parameter systems. His results have appeared in nine research monographs. Since 2007, he has been awarded visiting professor positions at several academic institutes (Université Paris XI France; Harper-Adams University College, UK; University of Northumbria, UK; University of Salerno, Italy; Ecole Centrale de Nantes France). He is a Senior Member of IEEE and a Member and CEng of the IET. He holds an Editor's position for the Journal of Advanced Robotic Systems and for the SAE Journal of Electrified Vehicles.Pierluigi SianoDr. Pierluigi Siano (Senior Member, IEEE) Pierluigi Siano (M'09–SM'14) received the M.Sc. degree in electronic engineering and the Ph.D. degree in information and electrical engineering from the University of Salerno, Salerno, Italy, in 2001 and 2006, respectively. He is a Professor and Scientific Director of the Smart Grids and Smart Cities Laboratory with the Department of Management & Innovation Systems, University of Salerno. Since 2021 he has been a Distinguished Visiting Professor in the Department of Electrical & Electronic Engineering Science, University of Johannesburg. His research activities are centred on demand response, energy management, the integration of distributed energy resources in smart grids, electricity markets, and planning and management of power systems. In these research fields, he has co-authored more than 700 articles including more than 410 international journals that received in Scopus more than 18000 citations with an H-index equal to 65. In the period 2019–2022 he has been awarded as a Highly Cited Researcher in Engineering by Web of Science Group. He has been the Chair of the IES TC on Smart Grids. He is Editor for the Power & Energy Society Section of IEEE Access, IEEE Transactions on Power Systems, IEEE Transac