Frequency locked loop method based on double self-tuning second-order generalized integrators

Abstract

The invention discloses a frequency locked loop method based on double self-tuning second-order generalized integrators. A self-tuning filter is cascaded with the second-order generalized integrator to obtain a third-order structure of the self-tuning second-order generalized integrator, so that the self-tuning second-order generalized integrator has good filtering property in the case of serious distortion of a power grid; a differencing node and a first-order high-pass filter is imported in the structure of the self-tuning second-order generalized integrator, so that the self-tuning second-order generalized integrator has the ability of eliminating DC component disturbance; and the adaptive control of nonlinear closed loop of frequency is converted into a linear design effect by using an amplitude normalization algorithm, and the programming implementation of DSP is facilitated. The frequency locked loop method disclosed by the invention is not only suitable for normal working conditions of the power grid, and is still suitable for the faulty power grid, the structure is simple, and the method is easy to implement, thereby having a wide application prospect in new energy grid connection and other fields.

Description

technical field [0001] The invention relates to the control field of new energy grid-connected access technology, in particular to a method for synchronous operation and control of a grid-connected converter and a power grid when harmonic pollution occurs in the power grid and a DC component is contained in an input signal. Background technique [0002] In recent years, problems such as energy depletion and environmental pollution have become increasingly serious, while renewable energy represented by solar energy and wind energy has developed rapidly. At the same time, with the large-scale grid integration of new energy power generation systems and electrical equipment based on power electronic devices, the stability of the power grid is facing huge challenges. Since the actual power grid is not absolutely stable, and when abnormal conditions such as three-phase voltage imbalance, frequency jump, and voltage distortion occur in the power grid, the grid-connected equipment m...

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Problems solved by technology

[0003] At present, the research on the synchronization method of grid-connected converters connected to the grid mainly includes the following two aspects: ① PLL as a traditional grid synchronization technology has been widely used, and the phase-locked loop in the single synchronous rotating coordinate system The loop is a typical representative. Under the normal working condition of the power grid, the estimated phase information is used to transform the three-phase grid voltage through the coordinate transformation of the synchronous coordinate system to obtain the reactive component. After adjustment by the PI regulator, a phase closed-loop system is formed, so that The estimated value of the phase is the same as the actual phase, so as to realize the locking of the actual phase. However, when the grid voltage is unbalanced, the double frequency fluctuation generated by the negative sequence component on the dq axis seriously affects the detection and synchronization of the synchronization information by this method. extract

② As another power grid synchronization technology, the frequency-locked loop has a simpler frequency-locked structure and better dynamic performance than the double-loop structure of the phase-locked loop. Among them, the frequency-locked loop based on the second-order generalized integrator is a typical representative , this method uses the product of the steady-state error signal obtained by making a difference between the input signal and an output signal that is equal in size and phase to the input signal and another output signal that is equal in size to the input signal and lags behind the phase by 90° as the input of the frequency-locked loop , after the input signal passes through the frequency-locked loop, it forms a closed-loop system of angular frequency, so that the estimated value of the angular frequency is the same as the actual angular frequency, so as to realize the tracking of the actual angular frequency. However, when the grid is polluted by harmonics and the input signal When the contained DC component is disturbed, there will be serious fluctuations in the angular frequency, which directly reduces the accuracy of grid synchronization information detection such as diagonal frequency

[0004] Although the above-mentioned phase-locked loop and frequency-locked loop synchronization technologies can accurately detect and extract synchronization information under normal grid conditions, the actual grid is not absolutely stable, especially when new energy is connected to the grid on a large scale. A series of faults such as harmonic pollution and DC component disturbance are more likely to occur, which directly leads to the inability of the grid-connected converter and the grid to operate normally synchronously

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