Micro-grid harmonic impedance measuring method based on three-phase symmetrical square wave current injection

Abstract

The invention discloses a micro-grid harmonic impedance measuring method based on three-phase symmetrical square wave current injection. The method comprises the following steps: injecting three-phase symmetrical square wave current ih into a certain node of a micro-grid and measuring the voltage disturbance caused by injection; sampling the square wave current ih and the voltage disturbance delta uh, wherein the sampling ratio and the sampling point number meet the requirement of a base-2FFT algorithm; and performing quick Fourier transformation on the sampled square wave current ih and the voltage disturbance delta uh. The harmonic impedance of the micro-grid is measured by injecting the three-phase square wave current into the certain node of the micro-grid. In a micro-grid simulation model based on PSCAD, the harmonic impedance of the system under a droop control mode is measured by the method; and according to the simulation result, the measuring value basically coincides with the theoretical calculation value, so that the method is correct and practical.

Description

technical field [0001] The invention belongs to the field of micro-grid technology, and relates to a method for measuring the harmonic impedance of a micro-grid, in particular to a method for measuring the harmonic impedance of a micro-grid with three-phase symmetrical square wave current injection. Harmonic current of a certain frequency and amplitude, and through correlation analysis and calculation, get the harmonic impedance of the system. Background technique [0002] With the global energy shortage and increasingly serious environmental pollution, countries all over the world are trying to find an efficient way to use energy. Now 90% of the world's electric load is powered by a centralized single power supply system characterized by large units, large power grids, and high voltage. However, due to its own defects, the single power supply of the large power grid can no longer meet the increasingly stringent power requirements of the society. . The combination of large...

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Problems solved by technology

The switching capacitor method saves investment, but the harmonics generated by this method are uncontrollable, which may lead to the loss of some harmonic currents, and the amplitude is too small, and the high-frequency components are greatly attenuated; the thyristor branch switching method can control the injection of harmonics The magnitude of the current, but the harmonic frequency injected into the system cannot be accurately controlled, and the high frequency part of the signal is missing; the above two methods cannot accurately measure the harmonic impedance of the microgrid

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