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Research On Dynamic Modeling Of DC Inverter-Interface Distributed Generation And Its Impact On The Small Signal Stability Of Power System

Posted on:2017-04-18Degree:MasterType:Thesis
Country:ChinaCandidate:Z HuFull Text:PDF
GTID:2322330488475993Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
Inverter-interfaced distributed generation has been widely used in the microgrid and large-scale new energy power station. It contains the DC inverter-interfaced distributed generation represent by fuel cell power generation and photovoltaic power generation. Although the inverter-interface makes the DG operating and controlling more flexible, the system is more likely to be oscillatory instable when it is disturbed, because of the small rotaion inertia, strong dynamic and nonlinear of the inverter and the control system.So the small-signal modeling and steability analysis of microgrid with inverter-interfaced resoures has been widely concernd.Besides, different from hydropower, thermal power and wind power these rotating power supply, the DC inverter-interfaced distributed power generations don't have the dynamic stability problem with electromagnetic and mechanical quantity unbalanced,but its large-scale access to the system changed the system power flow, line transmission power and the system equivalent inertia, the influence on damping characteristics of the system also cannot be ignored.Firstly, this paper have analyzed the working characteristics, running mechanism of the solid oxide fuel cell (SOFC) and dynamic characteristics of grid-conected system,builded the full-order state-space model of the power generation adequately considering features of all modular. And then ignored the high dynamic of grid-conected control system and the slow dynamics of SOFC based on the analysis of system characteristic pattern and time scales to point out that the SOFC battery can be repalced by a equivalent voltage source in the process of small disturbance. Put forward a reduced order model of solid oxide fuel cell power generation system suitable for small signal modeling and analysis of micro-grid, described in a first order dynamic mode. At last,proved the correctness and the validity of the theoretical analysis by small disturbance steability simulation of the SOFC power generation system in Matlab/simulink platform.Builded the small signal model of the photovoltaic power (PV) generation system, considering the U-I external characteristic of the photovoltaic cells, dynamic characteristics of the DC line capacitor, inverter and its control system. Based on the model, conventional damping torque analysis is carried out to study the mechanism of how the damping generate, the judging criteria for the nature of the reactive current inner loop pattern is derived and how the system characteristic patterns vary with parameters is analyzed with the eigenvalue trajectory; At last, system parameters are designed according to the above analysis and its correctness is verified through nonlinear time domain simulation. Research shows that the electric damping of the PV generation similar to the dynamic damping of synchronous generator led to the system damping, the equivalent damping coefficient, equivalent synchronous coefficient and the coupling relationship between the state variables determine the nature of the pattern. The transient performance of the system will be improved with the parameters selecting by DTA.The power system analysis software package (PSASP) was used for studying the impact on system damping characteristics with large-scale grid-connected photovoltaic power generation.The electromechanical transient model of PV power generation was established in the PSASP/UDM mode and the EPRI-36 nodes testing system was chosen to study how the damping characteristics and characteristic pattern of the system change when large-scale grid-connected photovoltaic power generation accsed in different place, different capacity and working in different mode. Research shows that the damping photovoltaic power generations do not take part in the system low frequency oscillations.It impact the system damping characteristics by changing the system equilibrium point. When the output increases, the damping characteristics vary, and characteristics strongly related to the conventional unit will show a tendency to increase.
Keywords/Search Tags:Photovoltaic power generation, Solid oxide fuel cell, Inverter-interfaced, Reduced-order model, Small signal modeling, Characteristic pattern, Damping torque analysis, Damping characteristics, Small disturbance steability
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