Research On Impedance Modeling And Stability Of Inverter-diesel Generator Distributed Network System

With the tremendous progress of society and the rapid development of the economy,the issues of environment and energy have been widely concerned,and the concept of power electronic power system has become the main direction of the future development of microgrid.In the remote areas where large power grids are difficult to access,new energy accounts for a large proportion of the micro-grid in the whole region and has a high penetration rate,therefore,the coordinated operation between power electronic converters and synchronous generators has become a problem that cannot be ignored.Due to the large differences in the electromechanical inertia of the two types of power generation systems,the scale of integration of PV inverters and external disturbances may have a greater impact on the electromechanical networking system.Therefore,the research of the model of such systems and its related stability mechanism is of great significance.The node voltage and frequency disturbance supported by the diesel generator with drooping characteristics can't be ignored in the modeling process.Firstly,a more reasonable variable frequency impedance model under dq coordinate system is established for the current control mode photovoltaic grid-connected inverter.The influence of external frequency disturbance on the inverter impedance and its related simulation measurements are researched.Based on the steady-state operation principle of synchronous generator and its control mechanism,the synchronous generator and inverter are approximated,and the open-loop impedance model of synchronous generator is established.Then,according to the output power relationship of synchronous generator and the speed excitation control scheme of the diesel generator,established the port impedance model of the diesel generator.Finally,the simulation verification of its transient,steady state and its impedance characteristics is completed.A single-node parallel system impedance network model and a low-voltage Benchmark radiation-type impedance network model are established for the existing impedance models.The complex-domain impedance model is used to lock the frequency point and oscillation source of the system oscillation.Combined with the norm criterion,the generalized Nyquist criterion and MATLAB/Simulink simulation verified the influence of large-scale photovoltaic access on the damping and immunity of the system and the impedance variation of the inverter parallel system under the external frequency disturbance of the system.The island network experimental platform of inverter prototype based on TMS320F28335 and diesel generator simulator and the hardware-in-the-loop test platform based on RTDS-TMS320F28377 S were built respectively to verify the potential stability of large-scale electromechanical networking system and verified the correctness of the relevant conclusions presented in this paper.