Repetitive dual-closed-loop control method for LCL type grid-connected inverter

Abstract

Disclosed is a repetitive dual-closed-loop control method for an LCL type grid-connected inverter. According to the method, the difference value between a given grid-connected current and an actual grid-connected current is used as input of a repetitive controller; the sum of the output of the repetitive controller and the given grid-connected current is used as a given value of an internal loop; the difference value between the given value of an internal loop controller and the actual grid-connected current is used as the input of an internal loop PI controller; the output of a power grid voltage which passes through a feedforward transfer function is used as the output of a power grid voltage feedforward link; and the output of the internal loop PI controller and the output of the feedforward link are added together to be used as a control signal for switching on and switching off an inverter bridge switching tube in an inversion link. According to the repetitive dual-closed-loop control method, the single grid-side current feedback is adopted, so that the dual-loop control is realized, and the cost is lowered; meanwhile, due to the PI controller and the repetitive controller which are connected in series, the decoupling of the controllers is realized; and the grid-connected system has higher steady-state control precision, higher dynamic response speed and higher robustness.

Description

technical field [0001] The invention relates to a control method for a grid-connected inverter, in particular to a repetitive control method for an LCL type grid-connected inverter. Background technique [0002] With the continuous development of new energy sources, grid-connected inverters have been extensively studied as an interface device for grid-connected distributed generation systems. [0003] Commonly used grid-connected inverter control methods include hysteresis control, proportional integral (PI) control, proportional resonance (PR) control, error beat control, and sliding mode control. These methods have their own advantages and disadvantages, and they cannot have the advantages of high steady-state accuracy, fast dynamic response and strong robustness at the same time. The repetitive control method based on the internal model principle has extremely high gain and can track AC signals without static error, so it is widely used in inverters, active power filters...

AI Technical Summary

Problems solved by technology

However, the dynamic response of the control system is slow due to the inherent one-period delay of the fundamental wave in the repetitive control method

For example, the invention patent "Adaptive repetitive control method for active power filter" (publication number: 201210389971.0) discloses an adaptive repetitive control method for active power filter, which can solve the problem caused by grid frequency disturbance. However, when the system setting changes, the one-period lagging system of repeated control is equivalent to an open-loop system, and the dynamic response speed is slow

In order to solve the problem of slow dynamic response of the system, most of the public literature adopts the hybrid control method of PI and repetitive control in parallel, but for the third-order characteristics of the LCL type grid-connected inverter, it is difficult to achieve good results for the parallel structure of PI and repetitive control. control effect, and there is still a coupling problem between the two controllers

For example, the invention patent "A Composite Control Method and System Based on Plug-in Rapid Repetitive Controller" (publication number: 201510549172.9) discloses a composite control method and system based on plug-in fast repetitive controller. However, due to the serious phase lag of the LCL type grid-connected inverter, this method cannot achieve a good correction effect

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