Research On Active Damper For High Frequency Harmonic Suppression Of Wind Power Gridconnected System

Most of the grid-side converters of doubly-fed induction generator(DFIG)based generation system use LC-type filters.Interaction of the grid-side converters with the inductive grid impedance will cause resonance peaks in high frequency bands.The background voltage harmonics with similar frequencies in the power grid will cause the voltage harmonics amplification at the point of the converter’s connection,affecting the stable operation of the wind power system.In this dissertation,the background voltage harmonic amplification phenomenon is studied,the harmonic voltage amplification factor is put forward for quantitative measurement,and the parallel adaptation resistor is quantitatively designed with the voltage amplification factor as an index.Limited by the large capacity of the device,the control bandwidth of the wind power converter is relatively low,and it is difficult to achieve its suppression of highfrequency harmonics through the control algorithm.Therefore,it is proposed to use an additional high-frequency power electronic device—active damper to simulate a resistance in high frequency band,which is connected in parallel with the grid-side converter to increase the impedance of the wind power system,so as to achieve the suppression of the background noise amplification phenomenon of the power grid.The main research contents of this dissertation are as follows:1)Considering the phase-locked loop,time delay,and grid voltage feed-forward to the sequence impedance model of the grid-side converter is established,and further the sequence impedance model of the whole DFIG wind power grid-connected system is established.Impedance frequency-sweeping measurement is performed through the simulation for the modeling verification.2)Considering that in real practice,the controller parameters of the wind power system are difficult to obtain due to confidentiality.This dissertation uses the real controller of the wind power converters to build a real-time simulation platform of control hardware-in-the-loop based on RT-LAB.The output impedance curve of the DFIG grid-connected system is obtained by the frequency-sweeping method.Targeting on the high frequency resonance peak in the impedance curve,the RLC resonant circuit is used for equivalent fitting.Based on the equivalent RLC circuit,the harmonic voltage amplification coefficient is proposed to quantitatively evaluate the background voltage harmonic amplification phenomenon.In order to suppress the harmonic amplification,a quantitative design of the parallel adaptation resistor is carried out by combining the equivalent circuit and the amplification factor.3)In order to ensure the active damper’s capability of simulating a virtual resistor in the high frequency band,considering the constraint relationship between the active damper’s software and hardware parameters,design of the active damper is carried out by taking the active damper’s control bandwidth and the final output impedance characteristics as the goal.And finally the active damper presents the desired adaptive resistance characteristics.4)In view of the above analysis and design,the Simulink model is established for verification.Further,a control hardware-in-the-loop real-time simulation platform based on the wind power converter controller and active damper controller is built.The background voltage harmonic amplification is reproduced through RT-LAB and the effectiveness of the voltage amplification factor is verified.Through frequencysweeping,the active damper’s output impedance is verified to present the desired impedance characteristics.After the active damper is put into operation,the background voltage amplification is suppressed,and the suppressed voltage amplification factor is consistent with the theoretical analysis.