Direct current microgrid line impedance detection method and device based on low-frequency current injection

Abstract

The invention discloses a direct current microgrid line impedance detection method and device based on low-frequency current injection, and belongs to the technical field of direct current microgrid operation control. According to the method, an alternating-current current signal of specific frequency is chosen, and the current signal is injected into an inductor current of an energy storage converter; after a current disturbance signal is injected, the input voltage and the input current of an energy storage unit converter are measured; according to the relationship between the voltage and the current in a circuit principle, the line impedance between a direct current bus voltage and an energy storage unit is calculated; the device comprises a disturbance current injection unit, a voltagecurrent measurement unit and a line impedance calculation unit; according to the method, the injection alternating current frequency is selected based on the impedance frequency characteristic, so that the method has relatively low influence on system stability, can improve the load sharing effect when the direct current converter is in parallel current sharing, is beneficial to stable operationof the system, takes into account the line impedance of each energy storage unit, and can be applied to the direct current microgrids of various structures; and the device is simple in structure, highin economical efficiency and high in line impedance detection efficiency.

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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