Phase-locked loop and phase locking method

Abstract

The invention discloses a phase-locked loop and a phase locking method. The phase-locked loop comprises a Clark transformation module, a QSG module, a PNSC module, a synchronous rotating coordinate system PLL module, an HE module and an AFRC module. The novel PLL can accurately operate under the situations of unbalanced voltage and serious voltage harmonic and frequency variation. The provided QSG and AFRC can accurately detect the positive-sequence power grid voltage sequence, the HE can well eliminate harmonic waves under the condition of serious power grid pollution, the AFRC make the frequency self-adapt quickly and be smooth, and the PLL can be achieved in the case that the power grid voltage has frequency fluctuation, imbalance and harmonic waves at the same time; the digital implementation of the improved digital PLL is performed through a method using a Tustin predeformation and increment algorithm to discretize, and the accuracy of the harmonic broadband of the power grid voltage can be ensured.

Description

technical field [0001] The invention belongs to the field of power grid control, in particular to a phase-locked loop and a phase-locked method. Background technique [0002] With the rapid development of power electronic devices, they play an increasingly important role in power systems. In power transmission, power conversion and power quality improvement, various types of power electronic equipment are used, such as flexible AC transmission system (FACTS), uninterruptible power supply (UPS), active power filter (APF) and so on. One of the most important aspects of controlling these grid-connected power converters is proper synchronization with the grid voltage, which requires the use of a phase-locked loop (PLL). [0003] Under normal grid voltage conditions, the synchronization of grid-connected inverters can be achieved by using the traditional PLL algorithm in the synchronous rotating coordinate system or the stationary coordinate system. If the grid voltage fails, t...

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Problems solved by technology

[0005] The present invention provides a phase-locked loop and a phase-locked method, the purpose of which is to overcome the existing in the prior art biquad generalized PLL in the case of frequency fluctuations, imbalances and harmonics in the grid voltage, which cannot be realized phase lock problem

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