Frequency and voltage are the most significant indicators in AC microgrids (MGs). To maintain the stability of grid frequency and bus voltage, this paper proposes a distributed secondary control scheme based on bi-limit homogeneity for frequency restoration, average voltage recovery, active and reactive power sharing among DGs in AC MGs subjected to non-uniform communication delays and actuator saturations. First, a state-transformation-based strategy by virtue of the past information of the control input is designed to deal with non-uniform delays, which can fully alleviate the adverse effects of communication delays. Additionally, the hyperbolic tangent function is introduced to approximate the non-smooth saturation function and to design anti-saturation fixed-time controller, which can mitigate the impact caused by actuator saturations. Then, by constructing an auxiliary bi-limit homogeneous system, the fixed-time stability of the close-loop control system with the constraint of actuator saturation can be demonstrated. Finally, several simulation cases are conducted to evaluate the performance of the proposed strategy on a test MG system, and the results are compared with other existing methods. Simulation and comparison results reveal the proposed method's validity, robustness and flexibility in restoring the MG's frequency/average bus voltage and achieving accurate active/reactive power sharing.

With the increase of extreme natural disasters and the frequent occurrence of man-made attacks, resilience studies of power grids have attracted much attention, among which resilience assessment reflects the resistance and resilience of power systems to cope with extreme disasters. To improve the resilience of distribution grids under extreme weather conditions, this paper proposes a resilience assessment framework for distribution grids under typhoon disasters. First, a probabilistic generation model of typhoon is established. Second, a spatiotemporal vulnerability model of the distribution grid lines to quantify the spatiotemporal impacts of typhoon. Third, a breadth-first search algorithm is used to island the distribution grid, and the amount of load shedding of the islanded microgrid is calculated. Meanwhile, the resilience of the distribution grid was quantitatively assessed according to the proposed new resilience index. Finally, the feasibility of the proposed resilience assessment method is verified in the IEEE 33-bus test system, and the results show that the proposed method can accurately account for the impact of typhoon on the distribution grid and provides a quantitative reference basis for later power system planning and scheduling.

A fast state of charge (SOC) estimation method is proposed based on simplified electrochemical model in this paper. Firstly, the solution-phase and solid-phase lithium-ion diffusion models are stripped from the simplified electrochemical model to characterize the lithium-ion concentration. Then, based on the correlation analysis between the solution-phase lithium-ion concentration, the solid-phase surface lithium-ion stoichiometry and the obtained electrochemical impedance spectroscopy (EIS) data, key frequency features for SOC estimation are extracted through the established five feature extraction principles. Finally, the proposed SOC estimation method is expanded to consider the influences of ambient temperature. Experimental study indicates that the integration of lithium-ion diffusion process can significantly improve the accuracy of SOC estimation and reduce the computational time compared with the traditional broadband domain method and the fractional-order equivalent circuit model (FOECM).

Power systems are required to show certain resilience against natural disaster induced contingencies. The advent of major contingencies in the power system will significantly change the network topology, thereby leading to unpredictable system dynamics that cannot be easily depicted by existing models and coped with traditional control schemes. Therefore, in this article, we proposed a novel robust control scheme based on hidden Markov jump system (HMJS) to stabilize the power system for temporary service provision under major contingencies, where the HMJS model is utilized to depict the stochastic switching of the system topology and its dynamics. In this process, the non-synchronization between the system’s state and the controller’s states are coped with an asynchronous sliding mode observer (ASMO). Subsequently, an observer based sliding mode controller (OSMC) is proposed for the short term service provision and stabilization of the power system. Experiments are performed to validate the performance and superiorities of the HMJS-OSMC in addressing three typical grid contingencies. The importance of the proposed method lies in that it solves the problems of post-contingency dynamic behavior depiction and temporary service provision for renewables-penetrated power systems that cannot be dealt with conventional approaches.

In the all-electric ships (AESs), the uncertain navigation conditions bring the drastic propulsion power fluctuations and the uncertain power control characteristics of large-scale shipboard hybrid energy storage systems (HESSs). A dynamic power management method of shipboard HESS is therefore proposed in this paper; First, a novel multi-scenario propulsion power model is employed to models the impacts of deterministic navigation conditions separately from other uncertain factors; Then, a dynamic battery model considering the internal states coupling is employed to accurately estimates the available power range of battery in harsh marine environments; Finally, a dynamic power allocation strategy is proposed to coordinate the HESS power to smooth the resulting direct current (DC) voltage sags while ensuring that the battery output safely. The proposed method is proven with three case studies, including a hardware-in-the-loop (HIL) simulation, and the results show the following: 1) The proposed power model can quantify the propulsion power fluctuations, and the maximum test accuracy of the model is 98.7%; 2) the proposed battery model can reduce the average estimation error of 1.622% at most; 3) the proposed power allocation strategy can improve the mean DC voltage by 17.39%, and the power fluctuations of the battery is reduced by 18.4%.

Cascading trip faults in large-scale wind power centralized integration areas bring new challenges to the secure operation of power systems. In order to deal with the complexity of voltage security regions and the computation difficulty, this paper proposes an autonomous voltage security region (AVSR) for each wind farm and the point of common coupling (PCC) substation, whose voltage can be controlled in a decoupled way. The computation of the AVSR can be completed using a stepwise search method exchanging voltage and power information between the control center and the wind farms. At each wind farm, an AVSR is determined to guarantee the normal operation of each wind turbine generator (WTG), while in the control center, each region is designed in order to guarantee secure operation both under normal conditions and after an N-1 contingency. A real system in Northern China was used to carry out case studies to verify the effectiveness of the AVSRs proposed, and good performance was demonstrated using the Monte Carlo method.