| In contrast of the current AC distribution network,the DC distribution network has smaller supply radius,high reliability,better power quality,Low line loss rate,freedom from reactive compensation.DC distribution network is becoming an inevitable procedure for the existing AC distribution to move towards AC/DC hybrid power grid.Because of these characteristics,it will be a new direction for power distribution system.This paper has a review on the research of DC power distribution system in developed countries and regions where the study is on laboratory stage according to chronological and geographical order.Surrounding the operation control and the static stability analysis of islanding DC distribution network,the main jobs of the thesis are as the following.In the first place,because of the DC distribution relied on DC micro-grid,so a summary of control strategies and control modes of micro-grids are given.The control strategies of the distributed generations can be summarized as follow,P control,V control and droop control.Besides the above,based on the energy management system(EMS)of the DC micro-grid,three control modes also summarized as follows,master slave control,peer-to-peer control and multi-larger agent control.Secondly,a control strategy of islanding DC distribution network applied to laboratory condition is designed and implemented.This model simplifies the step by collecting information on current rather than power,it considers the impact of the line parameter on control mode and makes improvement.A DC distribution network system has been modeled and simulated using the Simulink in the MATLAB.The simulation results show that this control mode can maintain power quality of system,Reduce the impact of the distributed power grid current,minimized circulating current among distributed generations and assure share load according to their rated load.Again,consider joining after rectifying link,the impact on the AC power line parameters put forward the AC power line parameters which not affect the normal operation.Again,a DC/DC controller of DC distribution network based islanding operation mode is designed by the dSPACE1104 controller development system.Such as hardware circuit project and components selection,including main circuit,drive circuit and sample circuit.An experimental platform of DC distribution network is set up.Control system software has been developed,including the collection section and the signal processing section,main control section,software protection section and PWM control signal generating section.The quality of the controller mode is verified by experiments under the circumstance of low voltage.Results show that the main circuit and proposed controller of the system can maintain stable operation under the proposed control schemes and satisfy system control requirements of islanding operation mode.Finally,for DC distribution network,through the establishment of its node voltage equation,a small-signal state-space model of DC distribution network is built considering the dynamic characteristics of the sources,loads and cables.The model can obtain the eigenvalues calculated at steady-state operation points are used to analyze the stability.Through changing the parameters of cables to get the stability margin of the dc distribution network and the results of matlab verify the correctness of the proposed method.The simulation results show that the droop coefficient should be less than the reciprocal value of conductance coefficient of load model.Considering stability margin,the inductance is small enough and distributed source installation should be as close as possible.At the same time,in order to assure to larger steady-state stability margin,design of DC distribution network should minimize the length of the line. |
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