35kV/1MVA Wide-band Impedance Characteristic Measurement Technology And Equipment Design And Demonstration

As the proportion of renewable energy sources increases year by year,the proportion of new energy power generation equipment used in power grids is also increasing.Most new energy power generation equipment is connected to the grid through grid-connected inverters.The large number of new energy grid-connected inverters reduces the inertia and damping of the power grid,resulting in stable broadband oscillations between the new energy power generation equipment,which is not conducive to the large-scale consumption of new energy.The frequency domain impedance analysis method is an important way to study the i nstability mechanism of new energy grid-connected systems.It can solve the "black box" or "gray box" problem of existing new energy power generation equipment and directly obtain the impedance characteristic data of the equipment.Therefore,the developme nt of highvoltage broadband impedance measurement technology and equipment,through the impedance online measurement method to obtain the impedance output characteristics of the equipment,can lay a refined model foundation for solving the stability problem of new energy grid connection.At present,the development of impedance measurement equipment at home and abroad mainly focuses on low-voltage or medium-voltage levels.The development of high-voltage broadband impedance measurement equipment is blank at home and abroad.For this,this paper has developed 35 kV/1MVA broadband impedance characteristic measu rement technology and equipment,the measurement frequency range is 1Hz-2000 Hz,the main research content and innovations are as follows:1.Taking new energy power generation equipment as the research object,a grid-connected inverter admittance model considering the effects of phase-locked loop,step-up transformer,delay,etc.is established under polar coordinates,and in-depth study of the effects of phase-locked loop,current loop,and delay on the output admittance characteristics of grid-connected inverter.The generalized Nyquist stability criterion is used to analyze the influence of the phase-locked loop,current loop,step-up transformer and grid strength on the stability of the new energy grid-connected system.2.Aiming at the application difficulties of the existing impedance measurement equipment in high-voltage and megawatt scenarios,an overall topology design and control method for 35 kV/1MVA high-voltage impedance measurement equipment is proposed.The input of the disturbance injection unit adopts a multi-winding phaseshifting transformer,which improves the reliability of the equipment.The power sub-module of the disturbance injection unit adopts the topology of the three-phase PWM rectification of the previous stage and the single-phase H-bridge cascade of the subsequent stage to meet the requirements of impedance measurement equipment to output a wide-band disturbance voltage.The three-phase PWM rectifier adopts the current control method based on feedforward decoupling,which ensures the stability of the DC side voltage and the good dynamic response performance of the system.A simulation model of high-voltage impedance measurement equipment was built on the Matlab simulation platform,and the correctness and effectiveness of the admittance modeling method in polar coordinates and the design scheme of impedance measurement equipment were verified through simulation.3.According to the overall design scheme of 35 kV/1MVA high-voltage impedance measurement equipment,the main circuit hardware parameters,control system hardware circuit and software program design methods of the equipment are analyzed in detail,and the admittance measure ment program in polar coordinates is designed based on Lab VIEW software.A 10 kV/500 kVA high-voltage impedance measurement experimental platform was built and the feasibility of the equipment was verified.On the basis of the experimental platform,the onli ne measurement of the admittance model of the passive load was carried out,and the admittance modeling method under polar coordinates was verified through experiments.Effectiveness of equipment design plan.