Abstract
In the paper, the H∞ repetitive current control scheme based on active damping along with the design method is proposed for three-phase grid-connected inverters with inductor-capacitor-inductor (LCL) filters. The control scheme aims to reduce the harmonic distortion of the output currents and achieve better efficiency. The design method introduces capacitor-current-feedback active damping into the H∞ controller design process by proposing an equivalent controlled plant. Additionally, based on the discrete model of the controlled plant with variable computation delay, the algebraic expression of the stable region for the feedback coefficient and the computation delay is obtained to avoid system instability caused by the digital control delay. Finally, the stability criterion is proposed to evaluate the stability of the discrete control system with the H∞ repetitive current control scheme. The theoretical analysis and experimental results prove that the control scheme presented in this paper not only can reject the harmonics of output currents, but is robust under the variation of the grid-impedance.
Highlights
As the application of distributed generation is rapidly growing, the voltage-source-inverter (VSI)is commonly used as the interface between a distributed generator and the grid
A modified method is proposed in this paper to design an H∞ repetitive controller by considering
A modified method is proposed in this paper to design an H∞ repetitive controller by the adoption of capacitor-current-feedback active damping and the delay of digital implementation
Summary
As the application of distributed generation is rapidly growing, the voltage-source-inverter (VSI). Compared with other methods which introduce software filters [4,7,8] or other control algorithms [6] to realize the active damping, the adoption of proportional capacitor-current-feedback can reduce the complexity of the control system design and analysis. The design procedure presented in references [23,24] for the RC did not consider the computation delay of the digital control, which can destabilize the current control system especially when active damping is adopted. The proportional capacitor-current-feedback active damping was adopted to avoid the extra controllers of other active damping methods which could introduce additional poles and increasing the order of the controlled plant. Based on the discrete model, the stable region for the proportional coefficient of the capacitor-current-feedback was proposed under variable computation delay.
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