Control and nonlinear stability analysis of the electromechanical system of electric vehicles

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Μακρυγιώργου, Δήμητρα
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Abstract
The present PhD dissertation is addressed in the research field of control and analysis of motion systems in vehicular industry and more precisely in providing a systematic procedure for the control design applied on electrified vehicles with respect to the system stability. In particular, taking into account the nonlinear representations of all components involved in an electrified vehicle, namely the energy storage, both electric and internal combustion motors, and power converters, an accurate model is developed that sets the basis for control design and analysis purposes. System performance is examined in a first place via the proposal of a novel open-loop stability analysis. The latter is conducted by applying Lyapunov based nonlinear techniques that actually prove system convergence to its desired equilibrium for any feasible bounded control input signals. Those theoretical results set the cornerstone towards adopting intelligent control techniques, fuzzy and neurofuzzy, due to the bounded control signals they produce and their efficiency in copying with system nonlinearities and uncertainties. In a similar manner, a combination of sliding mode and field oriented techniques are applied and provide an improved system dynamic behavior endowing it with characteristics of robustness with the system stability again to be proven based on the novel open-loop analysis. Towards extending the aforementioned effort, a general systematic procedure for control design based on simple cascaded PI controllers that can ensure stability for a wide category of Euler-Lagrange systems is developed. In this framework, asymptotic stability is proven for the electrified vehicle system by keeping in mind its desired equilibrium and applying proper cascaded PI controllers with their gains to be tuned based on the adopted systematic analysis. In addition, a vehicle to grid system is also considered and analysed based on the proposed method and its accurate dynamic representation. Specifically, in a first stage the mathematical representation of a vehicle to grid system combined with multiple connected vehicles is deployed and its stability is proven by applying trivial PI controllers and adopting the proposed open-loop analysis. Afterwards, a unified vehicle to grid - plug-in electric vehicle system is developed and controlled based on the proposed systematic passivity based procedure that ensures global asymptotic stability of the entire system around its desired equilibrium. In all cases, the extracted theoretical results are verified by conducting extensive simulations that indicate a satisfactory system response with smooth transients and a successful driving of the entire system to its desired equilibrium.
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Electric vehicles, Vehicle to grid system, Stability analysis, Cascaded control, Euler-Lagrange systems, Intelligent control, Nonlinear systems
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