Synchronous grid-connection method for micro-inverters based on Kalman filter algorithm

Abstract

The invention relates to a synchronous grid-connected method of a miniature inverter. The synchronous grid-connected method comprises the steps of detecting a three-phase voltage of a power grid side and a three-phase voltage of a miniature inverter side of a grid-connection point in real time; acquiring a symmetric power grid three-phase voltage and a symmetric miniature inverter three-phase voltage after the detected voltages are processed by an LC filter and a signal regulator; calculating a D-axis component and a Q-axis component of the symmetric three-phase voltage by DQ coordinate transformation calculation; calculating voltage difference, phase difference and frequency difference between a power grid and the miniature inverter; and forecasting voltage difference, phase difference and frequency difference of next moment by a Kalman filtering algorithm, judging whether the grid-connected requirement is met or not, if yes, performing grid-connected running by the miniature inverter, otherwise regulating and repeating the abovementioned steps by a diesel engine until the power grid is connected. By the synchronous grid-connected method, rapid and smooth grid connection can be achieved in grid connection of the miniature inverter, and harmonic interference can be suppressed very well.

Description

technical field [0001] The invention relates to photovoltaic power generation technology in the field of electrical engineering, in particular to a micro-inverter synchronous grid-connection method based on a Kalman filter algorithm. Background technique [0002] As a renewable and clean energy, solar energy has become a hotspot of human research and utilization. Micro inverters can make good use of renewable energy solar energy and convert solar energy into electrical energy, with high energy utilization and low environmental pollution. Usually, in order to utilize solar energy efficiently, the micro-inverter can be connected to the large power grid. When the large power grid fails, the micro-inverter needs to be disconnected and switched to island operation. When the large power grid fails, it will return to normal. After running, the micro-inverter needs to re-synchronize and connect to the grid. Therefore, how to coordinate the control of micro-inverters and how to ach...

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Problems solved by technology

[0003] Traditionally, the grid-connected micro-inverter adopts the PI control method to control the grid-connected current, which easily causes high harmonic content in the grid-connected current, and also causes harmonic pollution to the grid, and poor anti-interference ability

[0004] Liu Weiliang and others proposed a support vector machine (SVM) inverse control method in "Flyback Photovoltaic Micro-inverter Grid-connected Current Inverse Control Method" (Acta Solar Energy Sinica, 2016, Vol, 37(7): 1780-2787,) Control the grid-connected method, although this method effectively reduces the harmonic content of the grid-connected current, but the support vector machine (SVM) is a machine learning method that needs to learn from small sample data in order to get a good control method, so this makes the grid connection time longer, unable to meet the requirements of fast grid connection

[0005] In the article "Microgrid Control Strategy Including Synchronous Generator and Voltage Source Inverter Interface" (Grid Technology, 2011, (3): 170-176), Zhang Li et al. The micro-inverter control strategy of the inverter interface adopts the droop control method without tie line, which can realize the smooth transition of the micro-inverter from the network mode to the island mode, and configure the power system stabilizer to improve the stability, but there is no Considering the change time of the operating mode of the micro-inverter from island to grid-connected, the delay of the circuit breaker is longer, and due to the use of high-precision adaptive controllers, the overall control structure of the micro-inverter is more complicated and difficult to implement

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