Stability Analysis of Cyber-physical Fusion in Cyber-energy Systems

Although the cyber-physical system stability has been widely studied, most scholars pay more attention on system stability with communication time delay or attack. It is urgent for numerous scholars to provide one guide regarding cyber-physical system without communication network. Therein, the system regarding grid-connected inverters with the digital control system is regarded as one simplest and typical cyber-physical energy system. Meanwhile, the switching/sampling frequency of the inverter is always selected as low as possible from an efficiency viewpoint, resulting in unavoidable delay time (time delay in control theory). This delay time is always apt to cause the system low frequency/sub-synchronous oscillation, which is more prone to severity under weak grid. To this end, this paper provides one stability-oriented analysis approach of cyber-physical fusion in cyber-energy systems, which is suitable for grid-connected inverters under weak grid. Firstly, the system impedance model with equivalent delay time is constructed, which is based on the Pade approximate approach. This equivalent delay time consists of three parts, i.e., sampling delay time in cyber/physical level, calculation delay time in cyber level and pulse-width modulation delay time in physical level, which reflects the cyber-physical interaction impact. Furthermore, the stability forbidden criterion is applied to make the switching/sampling frequency solving process become a Hurwitz matrix identification problem through space mappings. Based on these space mappings, the adaptive step collection algorithm is adopted to obtain the minimum switching/sampling frequency. Finally, the simulation and experiment results illustrate the effectiveness of the proposed approach. © 2023 Science Press. All rights reserved.