Method and device for obtaining power grid synchronic benchmark sine based on absence of phase lock loop

Abstract

The invention discloses a method and a device for obtaining power grid synchronic benchmark sine based on the absence of a phase lock loop. The method includes the following steps: firstly, a power grid voltage es of a single-phase power grid or one phase of a three-phase power grid is adopted, the power grid voltage es and reference sin(omega 0t +theta ) and cos (omega 0t +theta) with preset frequencies are processed in a second-order active low-pass filtering mode, and low-frequency signals are extracted to obtain Udcos and Udsin. Secondly, a fundamental wave es1 of the power grid voltage and a power grid voltage fundamental wave orthogonal signal e's 1are obtained. Thirdly, mathematical models of single-phase power grid synchronic sine and cosine are obtained through the power grid voltage fundamental wave es1 and the orthogonal signal e's 1. And lastly, the power grid synchronic sine and the cosine obtained from the third step are introduced to a controller of a grid-connected inverter, so that the current introduced into the power grid and the power gird voltage are guaranteed to be in the same frequency and in the same phase. The method and the device are capable of automatically obtaining the power grid synchronic benchmark sine under the conditions of power grid voltage distortion, multiple times of zero passage of voltage waveform and voltage fluctuation.

Description

technical field [0001] The present invention relates to the technical field of photovoltaic grid-connected power generation, and more specifically, to a method and a device thereof for realizing synchronous reference sinusoids of a power grid based on a non-phase-locked loop. Background technique [0002] With its inexhaustible and inexhaustible advantages, solar energy has become one of the new energy sources with the most development potential. Distributed power sources represented by new energy sources such as photovoltaic power generation are gradually developing from independent systems to large-scale grid connection. Grid-connected inverters are mostly used as new energy grid-connected power generation or reactive power compensation devices. The key step is to obtain the grid synchronization reference sine and cosine. At present, the method of obtaining the grid synchronization reference sine or cosine mostly adopts a phase-locked loop (PLL) or a software phase-locked ...

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Problems solved by technology

At present, the method of obtaining the grid synchronization reference sine or cosine mostly adopts a phase-locked loop (PLL) or a software phase-locked loop (SPLL). The phase-locked loop is used to obtain the grid synchronization reference sine error when the grid voltage is distorted or the voltage waveform has multiple zero crossings. Very large, even loss of lock phenomenon, can not get a satisfactory reference sine

For example, in the research on the realization of the reference sine wave of the photovoltaic grid-connected power generation system, a single-chip microcomputer is used to realize "The reference sine circuit of the photovoltaic grid-connected system based on software phase-locking technology" (Zheng Xiangji, Chen Daolian. The reference sine circuit of photovoltaic grid-connected system based on software phase-locking technology Circuit [J]. Electric Power Automation Equipment, 2009, 29(6): 102-105.) is a method, but requires a lot of hardware and complex design

Some scholars have successively studied the single synchronous coordinate system software phase-locked loop (SSRF-SPLL) and the double synchronous coordinate system software phase-locked loop (DDSRF-SPLL). The single synchronous coordinate system software phase-locked loop is more suitable for the ideal power grid , if the three-phase power grid is seriously unbalanced, the error will be large, and the dual-synchronous coordinate system software phase-locked loop needs to undergo multiple d-q transformations and needs to be decoupled, which increases the difficulty of phase-locked loop design

In the harmonic current detection method of the active power filter, scholars at home and abroad have also proposed a detection strategy without a phase-locked loop, which mainly adopts the idea of ​​preset frequency. However, its application field is used for the detection of harmonics and reactive current, and the corresponding method can only be applied to single-phase or three-phase systems alone, and cannot be applied to single-phase and three-phase systems together

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