Measurement Technology And Equipment For Impedance Characteristics Of New Generation Power Generation

In order to cope with increasingly severe environmental pollution,new energy power generation technology has started being applied to real life.As a clean,environmental friendly and sustainable energy source,new energy power generation can reduce environmental disruption while meeting demands for energies.Mutual coupling between new energy grid-connecting equipments and non-ideal power grid to be connected will give rise to resonance or instability of grid-connected system and seriously affect quality of electric energy.As for this type of system stability problem caused by system interconnection,analysis method of impedance stability can be used to rapidly and accurately figure out causes for system instability and frequency range in which resonance may happen.In order to analyze stability of new energy power generation and grid-connected system and provide effective solutions,a design method of measurement equipment for impedance characteristics in new energy power generation is proposed in this paper.This measurement equipment can be directly connected to new energy power generation and grid-connected system to be tested,and measured bandwidth is lOHz-1kHz.(1)First of all,stability analysis method of new energy power generation and impedance modeling situation are introduced.Influences of different state-space model analysis methods on impedance calculation results are compared,and state-space frequency-domain impedance modeling method is selected to analyze stability of the grid-connected system.This method can simply and rapidly calculate system impedance and improve impedance calculation efficiency,and moreover,it is applicable to impedance model analysis within various frequency domains.In consideration of influence of current control and phase-locked loop structure on new energy power generation system,impedance model of new energy power generation equipment under dq domain is established and impedance characteristics are analyzed;based on stability criteria for impedance ratio,the relationship between stability of new energy power generation and impedance parameter is analyzed.Broadband impedance measurement method of new energy power generation equipment under dq domain is studied;influences of two different disturbance injection modes——parallel disturbance current and series disturbance voltage injection-on impedance measurement are investigated,and finally series disturbance voltage injection mode is selected to measure impedance.(2)Overall design scheme of impedance measurement device is proposed,and the emphasis is laid on analyzing design method of various parts of voltage disturbance injection unit,including power submodule design,LC output filter design and coupling transformer design;voltage disturbance injection unit is of multi-power submodule cascaded structure,and each power submodule consists of three-phase uncontrollable rectifier module,high-frequency isolated DC/DC converter and single-phase H-bridge module which are in series connection;according to requirements of impedance measurement device for high voltage,large capacity and broadband output,a control method for voltage disturbance injection unit is proposed,which controls output voltage amplitude of disturbance injection unit through real-time adjustment of output voltage of high-frequency isolated DC/DC converter while modulation ratio of cascaded H bridge module is fixed.This design scheme can measure impedance characteristics with a wide frequency band under broadband during new energy power generation process.Based on comparison of matching level between ideal impedance curve and measured impedance curve,influences of impedance factors on new energy power generation can be figured out.(3)An experimental platform of low-voltage impedance measurement is built.Main circuit hardware design,selection of main electronic components and functions of main circuit modules on the experimental platform for low-voltage impedance measurement are described in details;a control method for broadband voltage disturbance injection unit in this platform is designed;impedance calculation procedures are designed based on Labview software.Experimental results have verified correctness of impedance measurement and analysis method proposed in this paper.