Abstract
Hybrid energy storage system has been widely studied as an important technology for electric vehicles. Since the hybrid energy storage system is a nonlinear and complex system, the modeling of the system and the high-precision nonlinear control strategy are technical difficulties for research. The establishment of a high-precision mathematical model of the hybrid energy storage system is the basis for the study of high-quality nonlinear control algorithms. Fortunately, the theory of fractional calculus can help build accurate mathematical models of hybrid energy storage systems. In order to obtain the high-quality nonlinear control strategy of this complex system, this paper, respectively, carried out fractional-order modeling and analysis on the three basic equivalent working states of the hybrid energy storage system of electric vehicles. Among them, the fractional-order average state space model is carried out for the equivalent Buck and Boost mode. Also, the steady-state analysis of the equivalent Dual-Boost mode is carried out by combining the fractional-order calculus theory with the equivalent small parameter variable method. Finally, the effectiveness and precision of the fractional-order model are proved by simulation and experiment.
Highlights
An accurate mathematical model for the equivalent DCDC converter system corresponding to each working state is the basis for applying the variable structure HESS use in electric vehicles
Some research results prove that the fractional-order model has higher precision than the integer-order model in mathematical modeling of nonlinear circuit systems, and the integer-order model is a special case of the fractional-order model [10]. erefore, this article focuses on the fractional-order modeling research on the three working states of the variable structure HESS
Where α is the order of the fractional inductor L1, β is the order of the fractional inductor L2, and c is the order of the fractional capacitor C, respectively [11]
Summary
Equivalent to the voltage of the motor inverter, the load is the internal resistance of the SC, and the capacitance is the equivalent capacitance of the SC. A fractional-order average state space model can be established for equivalent Buck converter. When t ∈ [dT, T], the equation of state for the equivalent Boost converter is e transfer function of the output voltage to the input voltage is obtained by equation (8) as GV(s) vvion((ss))|d(s) 0 sαρ +. Introducing the duty cycle function in equations (13) and (14), the fractional-order average state model of the equivalent Buck circuit is obtained, as. 4. Fractional-Order Modeling and Steady-State Analysis for Dual-Boost Output Mode. State variable x and δ(t) pulse function are, respectively, expanded into a series form of a sum of a main component and a small component, that is,. B1VC22 + b2VC11 + b3VC00 − 1 − (j3ω)αL1 d(1)VC23, b1VC22 + b2VC11 + b3VC00 − 1 − d(2)VC23. (j3ω)βL2
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