| With the deepening of the energy structure transformation policy,the number of distributed new energy power plants such as wind energy and solar energy has increased rapidly,and a high proportion of connected power electronic devices and long-distance transmission lines have built a new power system.In recent years,due to the mismatch of impedance between new energy power stations and weak power grids,the power grid sub/super-synchronous oscillation problem occurs frequently,threatening the safe operation of the power system.However,there are relatively few researches on impedance measurement technology and equipment for new energy power generation stations at home and abroad.This paper relies on the national key research and development plan "Renewable Energy Power Generation Base DC Outbound System Stability Control Technology" and other projects,first from the current control Based on the type of grid-connected inverter,a sequence admittance model considering frequency coupling was established,and then an admittance measurement method suitable for new energy power generation grid-connected systems was proposed,and a 35 k V/1MVA high-voltage megawatt was developed.Class admittance measurement equipment,and completed the online admittance measurement work for a permanent magnet direct-drive fan in the35 k V system.The main contents and innovations of this paper can be summarized as follows:1)A sequence admittance model of a current-controlled grid-connected inverter considering frequency coupling is established,and its admitta nce characteristics are analyzed.Firstly,the reason of frequency coupling phenomenon is analyzed that the controller dq axis is asymmetric.Then,the method of harmonic linearization is used to establish the frequency domain sequence admittance model of the grid-connected inverter considering the frequency coupling,and based on the admittance model of the grid-connected inverter,the admittance characteristics are analyzed.The coupling characteristics mainly exist in the middle and low frequency bands and the increase of the phase-locked loop bandwidth will make the stability of the gridconnected system worse.2)An admittance measurement method suitable for new energy power generation devices in practical engineering is proposed.The basic principles o f admittance measurement are introduced.A method of adding an anti-aliasing filter to the sampling system to filter out power grid noise is proposed,and a data processing method is proposed to add windows to the voltage and current data in the time domain and then perform FFT and interpolation,which improves the accuracy of the admittance calculation results.precision.A control method for safe input and cut-out of admittance measurement equipment is proposed.Finally,the established inverter model is verified by frequency sweep through simulation.The simulation results prove the correctness of the modeling and the accuracy of the proposed measurement method.3)A high-voltage megawatt-level admittance measurement equipment considering frequency coupling is developed,and the details of the research and development are introduced in detail through hardware and software.In terms of hardware,a perturbed voltage output topology with 8 power sub-modules in series per phase is proposed,and an open-loop control method of rectification/feedback and carrier shifting is applied to reduce the output voltage distortion rate.In terms of software,based on the Lab VIEW platform,the host computer software for admittance measurement considering frequency coupling is developed.The software has a rich human-computer interaction interface,and has functions such as two-way communication,data processing,admittance calculation,host computer protection,and data storage.4)At the end of the article,the admittance measurement experiment of passive load is designed first,which verifies that the admittance measurement equipment developed in this paper has good disturbance voltage output performance,and the measurement results prove the correctness of the disturbance signal injection logic;The online measurement experiment of the magnetic direct-drive wind turbine admittance proves that the switching method designed in this paper can effectively protect the equipment.Practicality of grade admittance measurement equipment. |
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