Flicker Response And Transfer Calculation Of Distribution Network With Distributed Generators Integrated

This thesis is supported by National Natural Science Foundation of China(51277184).The fluctuant loads and sources can lead to voltage fluctuations and flicker in distribution network which tend to propagate to other parts of the network with some level of attenuation. With the development and application of the renewable energy technologies, different forms of distributed generator begin to be embedded in utility grid, in which wind and photovoltaic power generations are widely used in distribution grid. Induction generator for wind power is the typical rotation interfaced distributed generator and photovoltaic power genenration is the typical inverter interfaced distributed generator. When the voltage at the point of common coupling of induction generator or inverter interfaced distributed generator is fluctuant, the impedance characteristics of distributed generators will perform dynamic changes with different fluctuation frequencies, which determine the flicker transfer in grid directly. Therefore, this thesis studies the dynamic impedance characteristics and the response characteristics of flicker of different distributed generators, and on the bases, analyticly calculates the dynamic impedances for induction generator and inverter interfaced distributed generator and the flicker attenuation factor of the commom coupling point as well as the flicker transfer factor of the arbitrary two points of the gird. The main content of this paper is as follows:① The equivalent model of simple radiation distribution grid when distributed generator integrated is established in this paper, the frequency responses of dynamic impedances of synchronous generator, induction generator and inverter interfaced distributed generator three different types of distributed generators are analyzed, then the method of calculating the flicker attenuation factor and the flicker transfer factor of grid using dynamic impedance and RMS voltage fluctuation is proposed. The flicker transfer factors from commom coupling point to the load point when three different distributed generators integrated into grid are analyzed and compared.② As for induction generator, the impact of the different types of drive train on the dynamic impedance is analyzed, the speed fluctuation, current fluctuation and the frequency response of dynamic impedance are compared when induction generator using different drive train models by Matlab/Simulink. And on the basis, the 7 order linear model of the induction generator taking two-mass drive train model into consideration is bulit. The linear model is used for the analytic calculation of the frequency characteristic of the dynamic impedance and the flicker attenuation factor, and the sensitivities of drive train and impedance parameters are analyzed. The correctness of the proposed method is verified by the dynamic simulation using the detailed model of induction generator set in Matlab/Simulink software.③ As for inverter interfaced distributed generator, the impact of the phase locked loop on dynamic impedance is considered to built the inner-loop current control linear model. As for out-loop, three control modes of constant active and reactive powers, max active powr and constant power factor as well as constant active power and voltage control are taked respectively. And conbined with the inner-loop current control, the linear models of inverter interfaced distributed generator under different control modes are built. The linear models are used to analyticly calculate the frequency responses of the dynamic impedance and the flicker transfer factor, and the sensitivity of control parameters is analyzed. The comparison result of the proposed method and the simulation in Matlab shows the correction of the proposed method.④ The universal analytic calculation method of distribution grid with multi distributed generators integrated using the node impedance matrix taking dynamic impedances of distributed generators into consideration is proposed. An analysis example of a 10 k V grid with 6 buses integrating an induction generator and an inverter interfaced distributed generator at the same time is used to verify the correctness of the proposed method.