On-line single-phase grid-connected inverter weak grid impedance measurement method based on rpwm

Abstract

The invention discloses an RPWM-based online single-phase grid-connected inverter weak grid impedance measurement method, which is characterized in that: active measurement and passive measurement are combined, passive measurement is performed in real time, and when the disturbance condition is met, the disturbance is applied Active measurement is carried out; the 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 met; the disturbance condition is based on the degree of current distortion; the active measurement is to change the PWM modulation mode from SPWM modulation timing Switch to RPWM modulation, so as to achieve the purpose of disturbing and dispersing the harmonic spectrum before calculation. The invention realizes more time-sensitive THD measurement, and accurately measures inductive reactance in real time. The invention does not need to add additional equipment, and the frequency spectrum after the disturbance is scattered, and the electromagnetic interference is small; the variable carrier frequency RPWM modulation mode is selected to effectively stimulate the disturbance, and the inductive reactance can be accurately measured 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] Larger impedances cause impedance mismatches, which in turn generate harmonic currents. The method of adjusting the controller parameters to adapt to different grid conditions by detecting the impedance can effectively suppress the impact of grid impedance, which requires accurate online detection of parameters, such as exciting filter ...

AI Technical Summary

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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