Stability-Oriented Minimum Switching/Sampling Frequency for Cyber-Physical Systems: Grid-Connected Inverters Under Weak Grid

Abstract

Although the cyber-physical system stability is widely studied, scholars focus more on system stability with communication time delay. Therein, grid-connected inverters with the digital control system are regarded as one simplest and typical cyber-physical 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. This delay time is apt to cause the system instability, which is more prone to severity under weak grid. To this end, this paper provides a minimum switching/sampling frequency for grid-connected inverters. Firstly, the system impedance model with equivalent delay time is constructed, which is based on padé 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 pulsewidth 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 Hurwitz matrix identification problem through space mappings. Based on these space mappings, an adaptive step search approach is adopted to obtain the minimum switching/sampling frequency. Finally, the proposed approach can well evaluate the system stability under different frequencies through simulation and experiment.

Distributed cooperative control for power sharing of DC distribution network with event‐triggered communication mechanism

“…Lemma By Reference 5, if the undirected graph G of the DDN system is connected, it's sure that the origin of the active DDN system can be asymptotically stable, which also holds for the whole system .…”

“…The control method proposed in References 15 and 13 can improve the power quality of the DDN system and realize power sharing among distributed power sources. In recent years, previous studies have been conducted on the distributed control of PV power generation units in DC MG. 14,16,17 Meanwhile, distributed control methods involving consensus theory have been applied to load control, 5 economic scheduling problem, 18,19 voltage and frequency adjustment and other fields in power system.…”

“…By promoting the distributed new energy and energy storage systems, the consumption of distributed new energy can be achieved while improving the utilization rate of renewable energy. With the development of distributed renewable energy generation in active DC distribution network, distributed power generation presents the characteristics of large‐scale, distributed, large scale and random connection, which brings a series of operation problems such as terminal voltage rise, power fluctuation, and so forth, to the power grid 4,5 . However, for the new power system, how to allow flexible and random access to new energy without affecting the safe and reliable operation of the grid is one of the challenges.…”

“…In recent years, previous studies have been conducted on the distributed control of PV power generation units in DC MG 14,16,17 . Meanwhile, distributed control methods involving consensus theory have been applied to load control, 5 economic scheduling problem, 18,19 voltage and frequency adjustment and other fields in power system.…”

A Transformer-Based Multi-Entity Load Forecasting Method for Integrated Energy Systems

“…A comprehensively optimized IES is capable of delivering considerable energy savings, pollution reduction advantages, better system stability, etc. (Zhang et al, 2020;Wang et al, 2022). One key specification of IES is the demand pattern of the energy end-users.…”