NDLI: Stability analysis of digitally controlled LCL-type grid-connected inverter considering the delay effect

Content Provider	IET Digital Library
Author	Lyu, Yongcan Lin, Hua Cui, Yesheng
Abstract	Owing to LCL-filter resonance, a single loop may not be adequate to stabilise the digitally controlled LCL-type grid-connected inverter, thus the capacitor-current-feedback active damping is usually introduced. However, the computation and pulse-width modulation delays of the digitally controlled system significantly affect system stability and damping performance. Moreover, the delay varies when the duty-ratio update instant and sampling instant are changed. In this study, the Nyquist diagram is used to investigate the system stability taking into consideration the delay effect in the continuous domain. Then, the general conclusions and formulas can be drawn: if the LCL-filter resonance is above the critical frequency, the Nyquist diagram of single loop may not encircle the critical point, and therefore stabilise the system; and if it is below, a damping strategy is required. However, given the delay effect, the active damping loop may be unstable, and two unstable open-loop poles will be generated in the grid current loop under certain conditions. Then its Nyquist diagram should encircle the critical point to ensure the system is stable. Furthermore, the restriction of the cross-over frequency discussed. Experimental results based on a 5 kW prototype have been provided to verify the theoretical analysis.
Starting Page	1651
Ending Page	1660
Page Count	10
ISSN	17554535
Volume Number	8
e-ISSN	17554543
Issue Number	Issue 9, Sep (2015)
Alternate Webpage(s)	https://digital-library.theiet.org/content/journals/iet-pel/8/9
Alternate Webpage(s)	https://digital-library.theiet.org/content/journals/10.1049/iet-pel.2014.0623
Journal	IET Power Electronics
Publisher Date	2015-04-28
Access Restriction	Open
Rights Holder	© The Institution of Engineering and Technology
Subject Keyword	Active Damping Loop Capacitor Capacitor-current-feedback Active Damping Damping Delay Delay Effect Digitally Controlled LCL-type Grid-connected Inverter Duty-ratio Update Instant Grid Current Loop LC Circuit LCL-filter Resonance Nyquist Diagram Nyquist Diagrams Power 5 KW Power Grid Power System Control Power System Stability Pulse Width Modulation PWM Invertors Sampling Instant Stability Analysis Unstable Open-loop Pole
Content Type	Text
Resource Type	Article
Subject	Electrical and Electronic Engineering

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