A method and device for detecting impedance of DC microgrid line based on low-frequency current injection

Abstract

The invention discloses a DC micro-grid line impedance detection method and device based on low-frequency current injection, which belongs to the technical field of DC micro-grid operation control. The method injects the current signal into the energy storage by selecting an AC current signal of a specific frequency In the inductor current of the converter; after injecting the current disturbance signal, measure the input voltage and input current of the energy storage unit converter; according to the relationship between voltage and current in the circuit principle, calculate the line between the DC bus voltage and the energy storage unit Impedance; the device includes: a disturbance current injection unit, a voltage and current measurement unit, and a line impedance calculation unit. This method selects the injected AC current frequency based on the impedance frequency characteristic, which has little influence on system stability and can also improve the parallel connection of DC converters. The load sharing effect during current sharing is conducive to the stable operation of the system. The device considers the line impedance of each energy storage unit and can be applied to DC microgrids with various structures. The device is simple in structure and high in economy. Impedance detection efficiency is high.

Description

technical field [0001] The invention relates to the technical field of DC microgrid operation control, in particular to a DC microgrid line impedance detection method and device based on low-frequency current injection. Background technique [0002] In recent years, microgrid technology has become an important direction of smart grid research. As an emerging branch of microgrid research, DC networking technology has the advantages of less energy conversion times, simple structure, and no need to consider frequency stability and reactive power fluctuations. Compared with other technologies, DC networking technology can more efficiently accept renewable energy, and has received extensive attention in the fields of aircraft and ships. [0003] The stable operation of the DC microgrid itself needs to meet two important indicators: (1) to maintain the stability of the DC bus voltage; (2) to realize the reasonable distribution of distributed power and the dynamic stability of the ...

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Problems solved by technology

Existing peer-to-peer control strategies mostly use droop control. The document "An improved droop control method for DC microgrids based on lowbandwidth communication with DC bus voltage estimation and enhanced currentsharing accuracy" uses the method of increasing the initial voltage value of the converter to adjust the droop coefficient, which can Realize DC bus voltage adjustment, but the effect of load current sharing is poor

In order to solve the problem of low accuracy of current sharing caused by inconsistent line impedance, droop control methods based on virtual impedance are mostly used at present. The difficulty is that the droop coefficient is not easy to determine; "An Improved Current Load Distribution Control Strategy for DC Microgrid In ", the auxiliary controller shares the current current of each micro-source through communication, calculates the current that each micro-source needs to provide, and uses this information to adjust the droop coefficient in the controller, so that the micro-source DC converter has the same output impedance, realizing The load current is evenly shared, but this method requires mutual communication between the micro-sources, which reduces the reliability of the system; the document "DC Microgrid Line Impedance Detection Based on Single Pulse Injection" uses the AC small signal injection method to obtain the current load sharing of the converter , so as to adjust the output voltage value of each distributed micro-source. This method is more complicated in practical application and has higher hardware requirements; the document "A Decentralized Control Method for a Low-Voltage DCMicrogrid" predicts the line impedance value in the grid-connected mode. Use the compensated virtual impedance to offset the influence of the line impedance, but the microgrid cannot work in the off-grid mode during the initial operation, and the working mode is limited

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