Frequency-free static error control method for isolated island microgrid without interconnection lines based on harmonic injection

Abstract

Provided is an interconnection-line-free island micro-grid frequency static-error-free control method based on harmonic injection. A two-inverter parallel system which is controlled by the adoption of a P-f / Q-v droop control algorithm is established; the two-inverter parallel system runs under the traditional P-f / Q-v droop control algorithm, and the output-voltage amplitude value and frequency of the inverter are obtained; the difference value between a standard power frequency of 50 Hz and the output voltage frequency is calculated to obtain a frequency error value, and after the frequency error value is input into a PI adjuster, the output of the PI adjuster serves as a frequency compensation value and is added to a frequency set value in the droop control of a first inverter; by a harmonic injection module, the harmonic voltage of which the frequency is constant and the amplitude value is related to the compensation amount is added to the parallel system; by the amplitude value of a harmonic current extracted by a harmonic extraction module of a second inverter, the frequency compensation amount is reversely calculated; the calculated frequency compensation amount is added to a frequency set value in the droop control of the second inverter, and the frequency error-free control of the two-inverter parallel system is achieved. The method can achieve the frequency error-free control, has no influence on active power distribution, simplifies the system and improves the flexibility of the system.

Description

technical field [0001] The invention relates to the field of micro-grids, in particular to a method for controlling the frequency of isolated island micro-grids without interconnection lines. Background technique [0002] With the increasingly serious energy and environmental problems in recent years, the microgrid technology has been developed on a large scale. Since the inverters in the microgrid mostly use droop control, when they operate in the island mode, the inherent characteristics of droop control will lead to When the load is not at the rated value, the system voltage amplitude and frequency deviate from the given static difference, which is a major difficulty in microgrid control. Most of the existing frequency control methods are for the operation of a single inverter, and a few control methods that consider the parallel connection of multiple inverters also need to introduce additional interconnection lines, which increases the cost and affects the system flexib...

AI Technical Summary

Problems solved by technology

Most of the existing frequency control methods are aimed at the operation of a single inverter, and a few control methods that consider the parallel connection of multiple inverters also need to introduce additional interconnection lines, which increases costs and affects system flexibility.

[0003] In order to achieve high-quality operation of the island microgrid, the frequency must be controlled, but the existing control methods have the problems of increasing cost and affecting flexibility

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