Online single-phase grid-connected inverter weak network impedance measurement method based on RPWM

Abstract

The invention discloses an online single-phase grid-connected inverter weak network impedance measurement method based on RPWM. The method is characterized in that active measurement and passive measurement are combined, the passive measurement is performed in real time, and the active measurement is performed by applying disturbance when a disturbance condition is satisfied; a weak network impedance is taken as the active measurement value after the disturbance is applied, and the passive measurement value when the disturbance condition is not satisfied; the disturbance condition is based onthe degree of current distortion; and in the active measurement, a PWM modulation mode is regularly switched from SPWM modulation to RPWM modulation so as to achieve purposes of disturbing and dispersing a harmonic spectrum, and then calculation is performed. THD measurement with timeliness is realized and an inductive reactance is accurately measured in time. There is no need to add additional equipment and a spectrum is dispersed after the disturbance, and an electromagnetic interference is small. A variable carrier frequency RPWM modulation method is used to effectively provoke the disturbance and accurately measure the inductive reactance in real time.

Description

technical field [0001] The invention belongs to the technical field of grid-connected inverter control, and in particular relates to an online weak grid harmonic impedance measurement method. Background technique [0002] With the increase of distributed power grid-connected power and the wide distribution of grid-connected locations, considering factors such as longer transmission and distribution lines, more isolation transformers, and a large number of distributed power generation equipment connected to grid-connected points, the power grid More and more showing the characteristics of weak grid, grid impedance can not be ignored. [0003] Large inductive reactance will cause impedance mismatch, which in turn will generate harmonic currents. The method of detecting the inductive reactance and then adjusting the controller parameters to adapt to different power grid conditions can effectively suppress the influence of the grid inductive reactance, which requires accurate o...

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Problems solved by technology

However, the traditional THD measurement method always needs to analyze the waveform with an integer multiple of the cycle, that is, the measured THD value always contains the harmonic information of at least one cycle in the past, which cannot meet the timeliness requirements for THD when judging the duration of the disturbance.

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