Analysis And Suppression For Resonance Of Active Distributeion Network

With the development of distributed energy generation and micro-grid, a large number of grid converters are connected to the active distribution network. At the same time, the rapid development of power electronics technology makes more and more non-linear load to be connected to the distribution network. Because of the impedance characteristics of the converter and the nonlinear load, the external characteristics are very complex. With the change process of increasing frequency, the characteristic of the system is difficult to be determined, which means that the active distribution network resonance phenomenon is more complex, making the distribution network system resonance analysis more difficult.Treating the active distribution network as the research object, a regional impedance model of tree topology system is established in this paper, and the resonance characteristics of the system are also analyzed. Firstly, the active distribution network is divided into four parts, including the grid impedance model based on the transformer model, the transmission line model, the load model and the grid inverter model. To establish the inverter model, the αβ stationary reference frame is utilized in this paper, using the grid-side current, capacitive current double closed loop feedback to establish a three-phase grid-connected inverter output impedance model by quasi-resonant control strategy(QPR). Based on the above, a tree topology of three-node and four-node impedance model for active distribution network is established.According to the three-node and the four-node active distribution network models, we use the loop impedance matrix as the core of modal analysis to analysis the series resonant phenomenon of system. And then we use the node admittance matrix as the core of the modal method to analyze the parallel resonance of the system. Through the eigenvalue decomposition of the loop impedance matrix an d the node admittance matrix, we obtain the frequency distribution of the mode admittance of series resonant and mode impedance of parallel resonant. Also, according to the maximum value with modal admittance and modal impedance, the resonant frequency can be determined. Then based on the modal value of the resonance frequency, it is easy to know the easy excitation and observation position of the resonant. Finally, by analyzing the four-node simulation, the relationship between series and parallel resonant can be obtained.After obtaining the resonance frequency of the system based on the the modal analysis method with the matrix analysis, we analyzing the series and parallel resonance sensitivity at the four-node active distribution network system model based on sensitivity analysis theory, obtaining the resonance element sensitivity value. To validate the proposed element sensitivity analysis method, a simulation accomplished in Simulink is utilized in this paper, getting the resonance center of the system.To solve the resonance suppression problem of the active distribution network system, the R-APF active damped harmonic suppression unit is proposed in this paper. The analysis of the parallel resonance suppression on method on the four-node model is studied, which is validated by the modal method. By comparing the inhibitory effects of adding resonance suppression unit on non-actuated position and energized position, we validate the modal analysis method. Finally, an three-node active distribution network experimental platform including two inverters is established. The modal analysis method is validated by the experimental results.