Frequency observation method for droop control of grid-connected inverter

Abstract

The invention discloses a frequency observation method for droop control of a grid-connected inverter, and belongs to the technical field of distributed power generating / micro power grids. The method includes the steps of carrying out Clarke transformation for the three-phase grid voltage, obtaining the voltage value on a two-phase static coordinate system, conducting quadratic differential operation on the value to construct a linear equation group, eliminating negative sequence and second harmonic components by solving the equation, extracting positive sequence components in cooperation with low-pass filtering under a rotating coordinate system calculating real-time grid phase angle accordingly, selecting a shorter calculation window, and fitting the frequency value according to the angle and time sequence in the window by using an improved least squares method. Modified LSM is used to calculate the low-frequency component frequency value in the rotating coordinate system, so as to compensate the phase angle lagging caused by low-pass filtering, and to accurately observe the grid phase angle.

Description

technical field [0001] The invention relates to a frequency observation method for grid-connected control of distributed power sources, which can quickly and accurately observe the phase and frequency of a power grid, and belongs to the technical field of distributed power sources / micro-grids. Background technique [0002] At present, more and more new energy sources are connected to the grid in the form of distributed generation (DG). In order to overcome the impact of DG fluctuations on the grid, multiple DGs, energy storage devices and loads are usually formed into a microgrid, which is then connected to the main grid. Power electronic inverter is the main interface between DG and microgrid, and its grid-connected control technology is a research hotspot in recent years. For the grid-connected inverter of the interface in the microgrid, constant power control (PQ control) and droop (Droop) control are often used. Among them, droop control is more and more widely used in...

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Problems solved by technology

[0004] The first type is to construct a linear equation system for phase sequence separation, the literature "SVENSSON J, BONGIORNO M, SANNINO A. Practical implementation of delayed signal cancellation method forphase-sequence separation [J]. IEEE Trans on Power Delivery, 2007, 22(1 ): 18-26." It is constructed by T / 4 (T is the power frequency period) delay method, but this causes a lag to the frequency observation; the literature "Zhou Peng, He Yikang. The power grid voltage is asymmetrical and the harmonic distortion is synchronous with the fundamental voltage Signal detection [J]. Journal of Instrumentation, 2010, 31(1): 78-84." Introduce differential operation to ensure real-time performance, but high-order differential will accumulate and amplify errors

[0005] The second category is to design filters to filter non-positive sequence components. The literature "Wu Xiaobo, Zhao Rende, Hu Chaoran, etc. Phase-locking method based on improved adaptive notch filter [J]. Power System Automation, 2014,38(5 ):103-108.", Literature "Zeng Zheng, Yang Jiaqiang. A power grid synchronization method with frequency adaptive moving average filter [J]. Journal of Zhejiang University: Engineering Edition, 2014, 48(9):1696-1703. " and "Shen Kaikui, Li Yanlong, Zhao Yuan, et al. Design of power grid instantaneous frequency tracking algorithm [J]. Power System Protection and Control, 2015,43(5):75-80." respectively designed adaptive notch filters , moving average filter, and finite impulse response filter for phase locking, but the parameter design is complex, and when the grid frequency shifts, the parameters need to be readjusted

[0006] The third category is to design new control algorithms, such as generalized second-order integral method and model reference adaptive algorithm, but the algorithm is complex and has certain difficulties in engineering applications

The traditional zero-crossing detection method, Fourier transform method and three-point method can no longer take into account the rapidity and accuracy of frequency detection. By introducing methods such as least squares method (LSM) and wavelet analysis, the detection performance is improved to a certain extent. improved, but in practical applications will also be limited due to the large amount of calculation

Therefore, so far, there is still a lack of a phase-locked and frequency observation method suitable for grid-connected inverter droop control, which limits its application in grid-connected control

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