Abstract
This paper investigates the stability of the Francis hydro-turbine governing system with complex penstocks in the grid-connected mode. Firstly, a novel fractional-order nonlinear mathematical model of a Francis hydro-turbine governing system with complex penstocks is built from an engineering application perspective. This model is described by state-space equations and is composed of the Francis hydro-turbine model, the fractional-order complex penstocks model, the third-order generator model, and the hydraulic speed governing system model. Based on stability theory for a fractional-order nonlinear system, this study discovers a basic law of the bifurcation points of the above system with a change in the fractional-order α. Secondly, the stable region of the governing system is investigated in detail, and nonlinear dynamical behaviors of the system are identified and studied exhaustively via bifurcation diagrams, time waveforms, phase orbits, Poincare maps, power spectrums and spectrograms. Results of these numerical experiments provide a theoretical reference for further studies of the stability of hydropower stations.
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Abbreviations
- M t :
-
Mechanical torque of hydro-turbine, N. m
- Q :
-
Discharge of hydro-turbine, m3/s
- H :
-
Head of hydro-turbine, m
- n :
-
Hydro-turbine/rotor speed, rad/s
- a :
-
Guide vane opening, p.u
- m t :
-
Relative deviation of mechanical torque, p.u
- q :
-
Relative deviation of discharge, p.u
- h :
-
Relative deviation of hydro-turbine head, p.u
- x :
-
Relative deviation of rotor speed, p.u
- y :
-
Relative deviation of guide vane opening, p.u
- e x , e y , e h :
-
Partial derivatives of mechanical torque of hydro-turbine with respect to hydro-turbine speed, guide vane opening, and hydro-turbine head, p.u
- e qx , e qy , e qh :
-
Partial derivatives of hydro-turbine discharge with respect to hydro-turbine speed, guide vane opening, and hydro-turbine head, p.u
- T wR , T w1 :
-
Water inertia time constants of main penstock and first bifurcation penstock, s
- h w1 :
-
Characteristic coefficient of first bifurcation penstock, p.u
- δ :
-
Rotor angle, rad
- ω :
-
Relative deviation of rotor speed, p.u
- ω 0 :
-
Base angular speed, rad/s
- T ab :
-
Mechanical starting time, s
- m e :
-
Electromagnetic torque of generator, N. m
- P e :
-
Electromagnetic power of generator, N. m
- D :
-
Damping coefficient, p.u
- E ′ q :
-
Transient electric potential of q-axis, p.u
- E ″ q :
-
Subtransient electric potential of q-axis, p.u
- T ′ do :
-
Transient open circuit time constant of d-axis, s
- E f :
-
Hypothetical no-load electric potential, which depends on field voltage, p.u
- x d :
-
Synchronous reactance of d-axis, p.u
- x ′ d :
-
Transient reactance of d-axis, p.u
- i d :
-
Stator current of d-axis, p.u
- V s :
-
Infinite bus voltage, p.u
- x q :
-
Synchronous reactance of q-axis, p.u
- x L :
-
Reactance of electric transmission line, p.u
- x T :
-
Short-circuit reactance of transformer, p.u
- T y :
-
Engager relay time constant, s
- u :
-
Output signal of the governor, p.u
- r :
-
Reference input of generator speed, p.u
- k p :
-
Adjustment coefficient of proportion, p.u
- k i :
-
Adjustment coefficient of integral, s−1
- k d :
-
Adjustment coefficient of differential, s
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Acknowledgements
This study was supported by the Scientific Research Foundation of the National Natural Science Foundation–Outstanding Youth Foundation (No. 51622906); National Natural Science Foundation of China (No. 51479173); Fundamental Research Funds for the Central Universities (201304030577); Scientific Research Funds of Northwest A&F University (2013BSJJ095); the Scientific Research Foundation for Water Engineering in Shaanxi Province (2013slkj-12); the Science Fund for Excellent Young Scholars from Northwest A&F University (Z109021515); and the Shaanxi Nova Program (2016KJXX-55).
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Wang, F., Chen, D., Xu, B. et al. Fractional-Order Modeling and Dynamical Analysis of a Francis Hydro-Turbine Governing System with Complex Penstocks. Trans. Tianjin Univ. 24, 32–44 (2018). https://doi.org/10.1007/s12209-017-0093-7
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DOI: https://doi.org/10.1007/s12209-017-0093-7