Control method of LCL grid-connected inverter based on PI and repetitive control strategy

Abstract

The invention provides a control method of an LCL grid-connected inverter based on a PI and repetitive control strategy. The control method comprises the step of adjusting output of the LCL grid-connected inverter by applying a composite controller connected in parallel by PI control and repetitive control in a two-phase rest coordinate system. The dynamic performance of a system can be met; a steady state performance requirement of the system can be met; coordinate transformation and decouple calculation are simplified; the inhibiting capacity of a photovoltaic inverter for harmonic output isimproved; and a total harmonic distortion rate of grid-connected current of the inverter is reduced.

Description

technical field [0001] The present invention relates to the technical field of photovoltaic grid-connected inverter control, and more specifically, to a control method for an LCL type grid-connected inverter based on a PI+repetitive control strategy. Background technique [0002] Photovoltaic power generation has become one of the new energy sources that people pay close attention to and apply widely. The current is seriously distorted. The traditional method is to choose the PI and repetitive control strategy in the rotating coordinate system of the LCL three-phase photovoltaic inverter to suppress the harmonic current. However, it is difficult for a single PI and repetitive control strategy to meet the requirements of dynamic performance and stability performance of the system at the same time, and the coordinate transformation and decoupling calculation in the rotating coordinate system are more complicated. Therefore, how to suppress the harmonics while improving the qu...

AI Technical Summary

Problems solved by technology

[0003] At present, the research on repetitive control theory based on the internal model principle is relatively mature, and the controllers developed are also widely used in the field of power grid harmonic control: "Composite control technology in independent photovoltaic parallel connection" in "Power System Protection and Control" Issue 7, 2012 Application Research in Power Generation System "In order to suppress grid-connected current harmonics, a compound control strategy of repeated PI control and grid voltage feed-forward control is used to suppress grid-connected current harmonics, but the dynamic performance of the system needs to be improved; 2016 No. 9 "Repetitive Control Strategy of Grid-Connected Inverter in Two-phase Static Coordinate System" in "Journal of Electrotechnical Society" adopts the scheme of PI plus repetitive control in the synchronous coordinate system, which simplifies the process of coordinate transformation and decoupling, and effectively suppresses the grid-connected current harmonics. wave, but the ability to suppress harmonics of grid-connected current needs to be improved; "Grid-connected photovoltaic system using compound current control of the novel repetitive and PI" in the 6th issue of "IEEE International Conference on Applied Superconductivity and Electro-magnetic Devices" in 2015 has limited adoption The impulse response digital filter replaces the traditional combined compensator as a repetitive controller, combined with the traditional PI control technology, effectively suppresses the current harmonics, but there will be distortion at high frequencies; 2013 No. 8 "IEEE Transactions on Power Electronics "A general parallel structure repetitive control scheme for multi-phase DC-ACPWM converters" adopts a compound control scheme combining PI and other control methods with repetitive control, which improves the dynamic response speed of repetitive control and makes the system have good dynamic response and Steady-state characteristics, but the strategy is more complicated and the system stability is poor; "Research on a Weighted Parallel Repetitive Control" in the 8th issue of "Journal of Electrotechnical Society" in 2015 uses the weighting idea to achieve the expected enhanced control link control function, and bring better load shedding dynamic performance to the system, but the design of the compensator is complicated

[0004] The above methods are all implemented under ideal power grid conditions. In practical applications, when the voltage imbalance and low-order harmonics exist in some remote areas or mountainous areas, it will still cause slight or serious current distortion problems, resulting in poor output current quality.

Images