Analysis Method of Frequency Nonlinear Characteristics of Hydropower System Based on Improved Nonlinear Transformation

Abstract

The invention discloses an improved nonlinear transformation-based frequency nonlinear characteristic analysis method of a hydropower system. The method comprises the following steps of firstly building a hydropower system model including an elastic water hammer; calculating a characteristic value and left and right characteristic vectors to obtain a Taylor series expansion; obtaining a Z1 space expression according to linear transformation, carrying out a series of improved nonlinear transformation and reserving secondary nonlinear terms related to oscillation modes each time; finally obtaining a transformed Z space equation, carrying out decoupling in a space oscillation mode and reserving second-order nonlinearity; transforming the Z space equation in a plural form into a real number equation; and adding disturbance in the space, thereby obtaining nonlinear characteristics of the corresponding oscillation frequency. The method disclosed by the invention has greater concept advantages than direct generalization of a linearization method; more nonlinear characteristics are reserved than those of normal and modal series methods; decoupling of multiple oscillation modes is achieved in the transformation space; the characteristic information of a system is provided; and analysis of the nonlinear characteristics of the system in various oscillation frequencies is facilitated.

Description

technical field [0001] The invention belongs to the technical field of electric power information, and relates to a method for analyzing the frequency nonlinear characteristics of a hydroelectric system based on improved nonlinear transformation. Background technique [0002] Large-scale hydropower stations are generally built in remote places, and are powered by two or three long-distance transmission lines with the large power grid. Therefore, in many cases, these hydropower stations and the power grid belong to weakly interconnected power grids [1]. Under the strong power grid connection, the dynamics of hydropower stations are slow dynamic behaviors, which have little influence on the dynamic oscillation of the system, but have a great influence on the medium and long-term stability of the system. However, under weak grid conditions, even under small disturbances, the system will show strong nonlinear characteristics, and the nonlinear interaction of oscillation modes be...

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Problems solved by technology

[0005] However, the above transformation methods discard the nonlinear characteristics in the transformed space in order to obtain a closed-form analytical solution. Therefore, the nonlinearity can only be studied in the original space, and the oscillation frequencies of the original space are coupled together, so it is difficult to study the non-linearity of a single frequency. Linearity

[0006] There is a literature [10] that studies the nonlinear characteristics of the electromechanical oscillation frequency of the power system in the case of large disturbances in the weak grid, but the nonlinear characteristics related to mechanical power have not been studied.

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