Research On Impedance Detection Technology Of DC Distribution System

As a large number of DC loads and distributed modules are connected to the power grid,the interaction between multiple modules and devices can easily lead to a reduction in the stability and dynamic performance of the power system,and even cause system instability.The resonance and instability problems of the DC grid can be summarized as:the impedance parameters of the power supply system and the grid load do not match.The traditional impedance frequency sweeping device has a narrow measurement range and can only meet the detection requirements in a certain range of low and medium frequencies,and has certain limitations in the actual detection of high-frequency signals.Based on this,this thesis designed a high-precision,multi-mode,wide-range impedance sweep device to meet the actual needs of impedance detection.This thesis mainly completed the overall design of the impedance sweeping equipment prototype,device production and verification experiments of related functions,including the following:First,in view of the characteristics of the existing disturbance-type impedance detection device,three major components of the disturbance injection unit,the measurement control unit and the data acquisition and analysis unit are proposed,and corresponding requirements are put forward for the specific functions of the different units.When the load or the parameters of the system under test change,the disturbance injection unit can maintain high low ripple accuracy,repeatability and reliability,the output frequency accuracy should be better than ±0.2%,and the minimum step size should not be greater than 0.5Hz.The measurement control unit shall be able to complete the operation control of measurement channel construction,parameter setting,device start and stop and fault alarm,and assist in the completion of data measurement.The data acquisition and analysis unit should achieve the functions of data collection,extraction,processing,and analysis at different frequency points,not only to meet the measurement requirements at a single frequency point,but also to meet the information detection requirements at multiple frequency points in the set frequency band.In order to realize the different functions of the above-mentioned modules,the hardware components and software design content of the impedance sweep device are designed.The hardware design is the bottom part of the overall impedance detection system,which provides an operable and substantive structure and platform for the realization of the overall function;the software design is the upper module of the detection system to ensure the completion of the main content and functions.The disturbance injection unit mainly relies on high-performance wave generation equipment,combined with the corresponding conversion and power amplifier circuit to realize the generation of disturbance signals;the measurement control unit mainly uses the overall software module constructed by DSP and Labview,and provides basic pre-charging circuits and multi-channel switching circuits.Fault protection circuit,etc.to achieve specific control;the data acquisition and analysis unit mainly uses the content of the Labview module to realize the voltage and current acquisition and analysis,and realizes the coordinated control of the hardware through the communication and transmission with the main control chip such as DSP.Based on the realization of basic detection functions and accuracy,in order to further improve the impedance detection performance,corresponding corrections and experimental verifications are made for the errors introduced in different links of the hardware acquisition.Aiming at the impedance ranges of different sizes to be measured,corresponding adaptive detection algorithms are proposed to improve the acquisition accuracy by matching the appropriate measurement channels.In terms of software,in order to reduce the influence of the background harmonics in the actual power grid,the corresponding algorithm is used to realize the second calculation of the background harmonics.At the same time,in order to balance the speed and accuracy of the measuring device,based on single-point measurement and equal-step measurement,a corresponding variable-step-length algorithm is proposed for selection and switching.