Research On Unified Active Damper For New Energy Grid-connected System

With the urgent demand for clean and renewable energy in modern society,new energy systems represented by wind power and photovoltaics are connected to the power grid on a large scale.Grid-connected power generation systems consisted of power electronic devices are widely located at the end of the grid.The internal parts of the system are coupled with each other,forming a complex multi-scale high-order nonlinear electrical network.It poses new challenges to the stability and power quality of modern power grids and raises more complex problems.Researchers have conducted in-depth and extensive researches on modeling and analysis of new energy grid-connected systems,system stability methods and technical solutions to improve power quality.The research content and the scheme proposed in this paper are supplements and extensions based on the previous studies on the stability and anti-interference content of the new energy grid-connected system.1)In order to enhance the stability of the new energy grid-connected system and improve the anti-interference performance of the system,former solutions can be divided into inverter-level solutions and system-level solutions.Inverter-level solutions are not suitable for stability and interference problems in new energy grid-connected systems.The current optimal system-level solution to the instability of the new energy grid-connected system is the active damper.The traditional active damper can not effectively solve the resonance and harmonics problems of the system in the same time.2)For stability analysis of new energy grid-connected systems,this paper uses the impedance model analysis method.The system impedance model is established according to the system’s Thevenin-Norton equivalent circuit.And the mathematical model of the system is also derived.The resonance of the system due to underdamped characteristic and the interference of the grid background noise are systematically and quantitatively analyzed.Three-dimensional diagrams describing the effect of grid background noise on the PCC voltage and system current command value on the PCC current are depicted.And impedance ratio criterion and the Nyquist graph are used to analyze the influence on the system stability performance in terms of the variable parameters.3)Through the analysis of the resonance mechanism of the electrical network coupled system,the source of the system resonance is clarified by the background noise of the power grid and the damping characteristics of the system.This paper proposes aunified active damper scheme composed of a series and a parallel active damper.The impedance virtualized by the series-connected active damper is to suppress the interference caused by the background noise of the power grid.And the impedance virtualized by the parallel structure provides damping to the system to suppress the system resonance caused by lack of damping.4)In order to verify the validity and correctness of the above theoretical analysis,this thesis firstly conducts the simulation experiment in Matlab/Simulink.Then establishes the RT-lab semi-physical simulation platform to verify the relevant schemes and conclusions.The experimental results show that the unified active damper proposed in this paper can effectively suppress the resonance noise caused by grid background noise and underdamped system,enhance the stability and anti-interference performance of the new energy grid-connected system.