Control method for reducing impact on LCL-type grid-connected inverter from digital control time delay

Abstract

The invention discloses a control method for reducing the impact on an LCL-type grid-connected inverter from digital control time delay, and the method comprises the steps: 1, carrying out PWM instant loading modulation; 2, connecting a first-order high-pass link (HPF) in a capacitor current negative feedback loop in a series manner, wherein the output of the first-order high-pass link to be overlapped with the output of a controller Gc(s). The PWM loading half-beat time delay in the digital control is eliminated at step 1, and the zero-order holder half-beat time delay of a capacitor current negative feedback inner loop at a resonant frequency band is compensated at step 2. The compatibility of the resonant frequency of the LCL-type grid-connected inverter with the control frequency is improved through steps 1 and 2. The invention proposes the scheme: PWM instant loading + HPF compensation control, thereby eliminating the PWM loading half-beat time delay, achieving the compensating for the time delay of an active damping inner loop at the resonant frequency band, and improving the compatibility of the switching frequency with the resonant frequency of the LCL-type grid-connected inverter and the system stability margin.

Description

technical field [0001] The invention relates to the field of control methods of LCL type grid-connected inverters, in particular to a control method for reducing the influence of digital control delay on LCL type grid-connected inverters. Background technique [0002] Under the background of the gradual shortage of traditional fossil energy and the increasingly serious pollution, the application of grid-connected power generation of new energy such as photovoltaic and wind energy has made great progress. With the continuous improvement of the penetration rate of new energy sources such as photovoltaic and wind energy, grid-connected inverters pose great challenges to the stability and power quality of distribution networks. The LCL type grid-connected inverter is a third-order missing system. Considering the existence of the LCL resonance peak, the open-loop system is unstable. There are many control schemes for the suppression of resonance peaks. Among them, the active dam...

AI Technical Summary

Problems solved by technology

Considering the introduction of digital control delay, on the one hand, it reduces the phase angle margin of the open-loop transfer function of the system and affects the dynamic characteristics; in addition, the delay seriously affects the impedance characteristics of the active damping LCL filter, and the system resonance frequency drops In different frequency bands, LCL impedance characteristics are quite different

As a result, the design of the resonant frequency of the LCL filter and the selection of the switching frequency are no longer independent, and the two are coupled to each other. Once the selection is mismatched, the minimum phase property of the system is difficult to guarantee, and the stability of the grid current is challenged.

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