As an effective approach of implementing power load shifting, fostering the accommodation of renewable energy, such as the wind and solar generation, energy storage technique is playing an important role in the smart grid and energy internet. Compressed air energy storage (CAES) is a promising energy storage technology due to its cleanness, high efficiency, low cost, and long service life. This paper surveys state-of-the-art technologies of CAES, and makes endeavors to demonstrate the fundamental principles, classifications and operation modes of CAES. Critical subsystems of CAES are elaborated exhaustively. The application prospects and further research directions are summarized to promote the popularization of CAES in smart grid and energy internet.

The virtual synchronous generator (VSG) is emerging as an effective approach for controlling converter to mimic the traditional synchronous generator (SG). VSG can provide virtual inertia, handle both reactive and active power, which is grid‐friendly for integrating distributed generations. Generally, when grid voltage is unbalanced, the negative sequence voltage components will appear. Due to traditional VSG control strategy does not consider the negative sequence components and cannot eliminate them, thus it will lead to current unbalance and power oscillations. To address these problems, a comprehensive control strategy of VSG under unbalanced voltage conditions is proposed. Herein, the basic principle of VSG and inherent reasons for VSG current unbalance and power fluctuation are demonstrated with quantitative analysis. The cascaded control framework and design process of the comprehensive control strategy are presented, integrating the traditional VSG control algorithm, novel current reference generator and typical current regulator. Additionally, related critical issues such as sequence components extraction and control parameter design are discussed. The proposed control strategy can flexibly meet different operation demands, including current balancing and suppression of active power or reactive power oscillations. The validity and effectiveness of the proposed control strategy are verified with simulation and experimental results.

Virtual synchronous generator (VSG) is grid-friendly for integrating distributed generations (DGs) since it can emulate the operation mechanism of traditional synchronous generator (SG). However, the traditional VSG control strategy, which is mainly suitable for balanced voltage conditions, may lead to power oscillations, current unbalance and even overcurrent under unbalanced voltage sags. To overcome this difficulty, a flexible unbalanced control with peak current limitation for VSG under unbalanced operating conditions is proposed. Based on the basic VSG control algorithm, the control strategy integrates two novel control modules, which are current reference generator (CRG) and power reference generator (PRG). The proposed control strategy can flexibly meet different operation demands, which includes current balancing, constant active or reactive power. And the injected currents are kept within safety values for a better utilization of the VSG power capacity. Furthermore, the experimental platform is built. Experimental results demonstrate the validness and effectiveness of the proposed control strategy.

Consensus-based control has been widely applied in the frequency/voltage restoration and power sharing of microgrids. Considering the existence of plug-and-play devices and accidental communication failures in microgrids, the physical and cyber structure of a microgrid may be time-varying, where the performance of traditional consensus-based control methods under ideal cases may not be guaranteed. This article proposed a novel finite-time consensus-based secondary frequency control strategy, i.e., a control strategy with finite-time convergence performance. The convergence time of the proposed control strategy is independent of both the structure and operation states of the microgrid, which guarantees the effectiveness of the control strategy under flexible operating conditions. Moreover, a detailed performance analysis of the finite-time control strategy is presented, and an optimal design method of the control parameters is developed, which significantly improves the performance of the finite-time control strategy. The flexibility of the proposed control strategy, as well as the effectiveness of the optimal design method, is verified by both simulation and experimental results.

Active dampers and other damping approaches are commonly applied to mitigate high-frequency resonance of AC microgrids with multiple parallel interface converters. The parameter mismatch of control diagram and passive components in active dampers and other parallel converters will influence the effectiveness of resonance damping. Traditional stability analysis of multiple parallel converters mainly utilizes root loci of system eigen-function with single parameter changing. In this paper, to achieve a reasonable selection of parameters and characterizing the variation of multiple parameters simultaneously and intuitively, a region-based stability analysis approach is proposed. To enhance the computational efficiency of obtaining the intuitive stability region, a Kernel Ridge Regression (KRR) approach is applied to derive an approximate analytical expression for the stability region. The stability region established with multiple dominant control parameters of active dampers and other converters can provide reference for control parameter design, guaranteeing the effectiveness of active resonance damping. Moreover, the effects of circuit parameter mismatch in the region-based stability analysis are also taken into consideration to increase the robustness of the stability region and providing guidelines for the selection of passive components (i.e., filter inductance and capacitance). Compared to traditional analysis approach, the proposed region-based stability analysis can depict the stability region when multiple dominant parameters vary with an error band indicating the impacts of parameter mismatch. Simulation and experimental results verify the effectiveness of the proposed region-based stability analysis.