A phase-locked loop control method for grid-connected converter and grid signal synchronization

Abstract

The invention discloses a phase-locked loop control method for synchronizing a grid-connected converter with a grid signal, specifically: sampling the three-phase voltage of the grid and performing coordinate transformation to obtain a synchronous rotating coordinate system voltage V gd and V gq , then for V gd and V gq Perform average value filtering, and then divide the quadrant into linear adjustment area and nonlinear adjustment area by judging the quadrant where the initial phase θ of the power grid is located, and use different methods to lock the phase according to different areas; after phase locking, observe the locked phase If the phase sequence is correct, it proves that the phase lock is successful. If the phase lock is not correct, the phase sequence can be corrected by exchanging any two phases of the three-phase electricity obtained by sampling. The implementation method of the invention is simple. The initial phase of the power grid is divided into four quadrants according to the situation, and each quadrant is processed separately according to the situation of each quadrant, so that fast phase locking can be realized, and the phase sequence can be distinguished by judging the positive and negative sequences after phase locking.

Description

technical field [0001] The invention belongs to the technical field of grid-connected power generation, and relates to a phase-locked loop control method for synchronizing a grid-connected converter with a grid signal. Background technique [0002] As more and more photovoltaic grid-connected power generation systems are connected to the grid, the power quality of the grid has attracted more and more attention. In order to achieve a reliable power grid without current impact in the photovoltaic grid-connected power generation system, the filtered inverter output voltage must be consistent with the amplitude, phase and frequency of the grid voltage, otherwise it will increase the harmonic grid, degrade the power quality, and generate Grid-connected commutation may even cause damage to the photovoltaic power generation system. Therefore, phase-locked loop control must be carried out in the grid-connected process to meet the requirements of grid-connected. [0003] A typical ...

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Problems solved by technology

[0004] At present, among the popular methods of researching digital phase-locked loops, the digital phase-locked loop algorithms with greater influence can be divided into three categories: PLL algorithms based on zero-crossing detection, PLL algorithms based on coordinate transformation, and PLL algorithms based on instantaneous power theory. PLL algorithm; the advantage of the PLL algorithm based on zero-crossing detection is that the algorithm is extremely simple; the disadvantage is that when there are harmonics or sampling noise in the grid voltage, multiple zero points may appear, and the phase of the grid voltage cannot be tracked correctly at this time. The phase can only be processed in half a cycle or one cycle, so the system response is relatively slow; the PLL algorithm based on coordinate transformation usually uses the dq synchronous rotating coordinate system to realize digital phase locking (the dq synchronous rotating coordinate system is obtained through the formula (1) The three-phase stationary coordinate system is transformed), and some use the αβ two-phase stationary coordinate system to realize digital phase locking (the αβ synchronous rotating coordinate system is transformed from the three-phase stationary coordinate system by formula (1)) , through this method, in the ideal grid, the two technologies can achieve better results, but in actual engineering, the control method under ideal conditions may not get good results; based on the instantaneous power theory The advantages of the PLL algorithm are short response time, better anti-interference ability to harmonics, and better phase-locking effect, but the disadvantages are that the program is cumbersome, the algorithm is more complicated, and the performance is relatively poor when the grid frequency jumps.

[0005] Although the above methods can achieve better results, if you want to achieve better results, the algorithm programming is more complicated. If the algorithm is simple, then the phase-locking effect is not very good, and the general phase-locking algorithm only locks Phase, does not distinguish phase sequence

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