Robust phase-locked system and method for grid-connected converter

Abstract

The invention discloses a robust phase-locked system for a grid-connected converter. The robust phase-locked system comprises a current feed-forward module, a first subtractor, a second subtractor, aphase compensation module and a phase-locked ring module. The invention also discloses a robust phase-locked method for a grid-connected converter. The robust phase-locked method comprises the steps of 1, subtracting a grid voltage sample signal by an output signal of grid current subjected to first-order differentiation element so as to obtain a voltage corrected signal; 2, subjecting a fundamental frequency grid current amplitude reference signal to phase compensation element to generate a phase compensation angle signal, and acquiring a difference between an expected power factor angle signal and the phase compensation angle signal to generate a power factor angle corrected signal; feeding the voltage corrected signal, the power factor angle corrected signal and the fundamental frequency grid current amplitude reference signal to the phase-locked ring module so as to generate an output signal synchronous to grid voltage. The robust phase-locked system and method have the advantagesof great applicability to large-range grid impedance changes, good grid current quality, simple structure and good design convenience.

Description

technical field [0001] The invention belongs to the field of current control of grid-connected converters (including inverters, rectifiers, reactive power compensators, etc.), and particularly relates to a strong robust phase-locked grid-connected converter, that is, a grid voltage synchronization method. Background technique [0002] With the vigorous development of new energy distributed grid-connected power generation, grid-connected converters, as a key part of them, have gained widespread attention. However, converters using pulse width modulation technology generate a large number of switching frequency sub-harmonics. Inserting a filter between the converter and the grid can effectively suppress harmonics. Commonly used filters include L and LCL filters. In order to achieve higher grid-connected power factor and lower grid-side current harmonic distortion, scholars have proposed a large number of grid-connected converter control methods. However, the existing relati...

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Problems solved by technology

However, if the grid impedance further increases, the converter system may experience harmonic amplification or even resonance near a lower frequency (close to 100Hz or even down to the fundamental frequency)

In the vicinity of this frequency, the influence of the phase-locked link in the control system of the grid-connected converter is more significant, and an improper phase-locked link is one of the reasons for the low-frequency oscillation of the converter

However, so far, there are still few phase-locked methods for grid-connected converters with strong robustness under weak grid conditions.

[0004] Therefore, in the field of current control of grid-connected converters, in order to solve the problem of poor system stability under large-scale changes in grid impedance, it is necessary to study a grid-connected converter that takes into account stability and current quality, has a simple structure and is easy to implement. Phase-locked grid voltage synchronization method

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