Resourance Analysis Of DC Microgrid And Its Suppression Method Research

DC microgrid has the advantages of high energy conversion effic iency and strong compatibility and can make full use of various types of distributed power sources while meeting the power requirements of different DC loads.In the existing DC microgrid structure,many controlled converters are present in the form of a constant power load(CPL),and the negative impedance effect of CPL reduces the damping of the DC microgrid.Without the traditional synchronous generator,the power system also exhibits low inertia operating characteristics,leading to voltage resonance and power oscillation frequently.In view of this,a resonance mechanism analysis method is proposed,and resonance suppression strategies are designed.Firstly,the current stability criterions are reviewed in this paper.In the small signal stability analysis method,the stability criterion based on impedance ratio is given priority.The disadvantage of this type of criterion is the assumed direction of the power flow.This assumption may not match the actual.In addition,different definitions of subsystems can lead to different analysis results.Thus,the passivitybased stability criterion has been developed by domestic and foreign scholars.This method evaluates the stability of the DC microgrid based on the passivity of the oneport network impedance.By comparing the principles of different stability criteria,their conservative characteristics are analyzed in detail.Then,based on the impedance model and the node impedance matrix of the system,a single bus and multi-bus resonance analysis method for DC microgrid under distributed control is proposed respectively and is verified by the small-signal state-space model.Small signal impedance models considering the influence of controllers is established for each subsystem according to the respective control structure and system parameters.Based on this model,the equivalent circuit of DC microgrid is established,and the stability of the system is determined by the proposed method.At the same time,the main factors affecting the resonance stability of the system are studied.The simulation model of DC microgrid is built based on PSCAD,and the simulation results verify the correctness of the proposed.Finally,in order to improve the resonance stability of the system,this paper proposes active damping control and virtual dc machine control to enhance system damping and inertia.drawing on the principle of active damping,this paper introduces a damping signal into the control loop.The purpose of resonance suppression and improvement of system resonance stability is achieved by simulating the damping characteristics of the resistor or reshaping the converter impedance.In addition,inspired by the virtual synchronous generator control in the AC microgrid,the virtual dc machine control is introduced into the DC microgrid.The disturbance rejection ability of the voltage is improved by simulating machine inertia and capacitor port voltage characteristics.The simulation platform of active damping control and virtual dc machine control is built based on PSCAD and MATLAB.The simulation results verify the effectiveness of the proposed resonance suppression strategies.