A three-phase frequency-locked loop based on l-m algorithm and its realization method
A realization method and technology of frequency-locked loop, applied in automatic control of power, electrical components, etc., can solve problems such as complex parameter setting, phase lag, and poor suppression effect
Active Publication Date: 2021-04-23
CENT SOUTH UNIV
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Problems solved by technology
The improved types are usually divided into two categories: one is to add filter operators inside the phase-locked loop controller, such as dq-MAF-PLL, Adative-Notch-PLL, Type-1-PLL, etc. Although these phase-locked loops It can effectively suppress unbalance and harmonics, but adding filter operators inside the control system will cause a large phase lag, making their dynamic response worse
Therefore, another type of pre-filter operator outside the control system is more popular. In order to effectively deal with problems such as unbalance, harmonics and DC bias, a large number of pre-filter operators have been proposed, which are mainly divided into IIR filter and FIR filter, IIR filter such as second-order generalized integral operator SOGI and complex coefficient operator CCF, they have been improved to varying degrees in previous literature, although they can effectively separate positive and negative sequence component, but the attenuation gain for DC bias and harmonics is insufficient in a highly distorted grid environment
The most typical representative of the FIR filter is the delayed signal elimination operator DSC, which is a simple and efficient filter operator that can flexibly respond to different power grid environments. However, the disadvantage is that the suppression effect becomes worse when the frequency shifts. And this defect can be improved by cascading the same DSC operator
Although the phase-locked loop studied above has shown good detection performance in various complex power grid environments, the dynamic performance is still slow, and the parameter tuning is complicated, especially depending on the accurate establishment of the small-signal model
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Embodiment 1
[0064] 1. Establishment of the mathematical model of the frequency-locked loop:
[0065] First of all, the three-phase voltage in the case of no harmonic grid can be expressed as the following formula:
[0066] v a (k)=V a (k)cos(ωkΔT+φ)
[0067] v b (k)=V b (k)cos(ωkΔT+φ-2π / 3)
[0068] v c (k)=V c (k)cos(ωkΔT+φ+2π / 3)
[0069] V a (k), V b (k), V c (k) is the peak value of the three-phase voltage, ΔT is the sampling interval period, Ф is the initial phase of the fundamental frequency signal, ω=2πf is the angular frequency of the voltage signal, and f is the frequency of the voltage signal.
[0070] It is transformed into a two-phase quadrature signal by Clark:
[0071]
[0072] Using the Clark transformation, the horizontal and vertical axis components v can be obtained α1 (k) and v β1 (k), for a balanced three-phase system, V a (k)=V b (k)=V c (k)=A, at the same time there is v α1 (k) and v β1 (k) Satisfy the following relationship:
[0073]
[0074]...
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The invention discloses a three-phase frequency-locked loop based on the L-M algorithm and its implementation method. The steps of the implementation method are as follows: Step 1: Perform Clark transformation on the input three-phase voltage signal to obtain a two-phase quadrature signal; step 2: Pre-filtering based on DSC operator; Step 3: Amplitude normalization processing; Step 4: Calculation step size d k ; Step 5: Calculating estimated values of frequency, phase angle and amplitude; Step 6: Offset compensation step. The method of the invention has small overshoot, fast response speed, small amount of calculation and easy implementation.
Description
technical field [0001] The invention relates to a three-phase frequency-locked loop based on L-M algorithm and its realization method. Background technique [0002] With the popularization and application of technologies related to renewable energy power generation such as photovoltaics, wind power and energy storage, grid-connected inverters, as a link between distributed power sources and power grids, have become a research hotspot in technologies related to renewable energy power generation. With the large number of applications of distributed generation and nonlinear loads, the grid environment becomes more and more complex. These complex situations usually include unbalanced three-phase voltages, harmonics, frequency offsets, sudden changes in phase angle and amplitude, and DC bias. How to ensure the stable and reliable operation of grid-connected inverters in these complex grid environments is the focus of current research. [0003] Grid synchronization technology is...
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IPC IPC(8): H03L7/087H03L7/091H03L7/081H03L7/093H03L7/095
CPCH03L7/0818H03L7/087H03L7/091H03L7/093H03L7/095
Inventor于晶荣石文帅陈壮深邹勇军徐凯
OwnerCENT SOUTH UNIV