Active grounding device (AGD) is an effective device to eliminate grounding arcs and prevent disasters caused by ground faults in distribution networks. However, due to the uncertainty of the ground fault resistance, the traditional arc suppression control cannot guarantee the suppression effect and the control stability simultaneously under the fixed control parameters. In this article, an arc suppression control method based on adaptive parameters is proposed. According to the dual-loop control model of the AGD connected to the fault distribution network, the relationship between the model input and the fault voltage is derived. Then in two extreme cases of the ground fault resistance, the suppression effect and the system stability are analyzed using the amplitude-frequency curve and the root locus, respectively. Further, a control method is proposed to make control parameters self-adaptive through the feedback information of the residual fault voltage. Finally, the effectiveness of the proposed control method is verified by the simulation model of MATLAB/Simulink and the low-voltage experiment of the prototype, which can realize arc suppression with high, low or dynamic resistance ground fault.

In a 35kV medium voltage system, closing the parallel capacitor will generate high inrush currents, which will shorten the service life of electrical equipment such as capacitor banks and series reactors. This paper analyzes the transient process of closing capacitors theoretically and proposes a split-phase control strategy for vacuum circuit breakers. With the help of MATLAB/Simulink simulation software, by comparing and analyzing the closing inrush current and reactor transient overvoltage data of the proposed strategy and the traditional method of closing the capacitor bank, the selected closing strategy can limit the closing inrush current to 1.5p.u., the transient voltage of series reactor is limited to 2p.u. Further considering the dispersion characteristics of the vacuum circuit breakers, through comparative analysis, the selected closing strategy can still significantly reduce the inrush current and overvoltage during the capacitor closing process, and improve the closing safety of the reactive power compensation device.

The increasing penetration of renewable generations (RGs) poses significant challenges to the operation of transmission power systems, especially for not only steady-stage uncertainties but also dynamic-state stability. Hence, the symmetry of RGs and synchronous generations (SGs) should be improved by a proper planning strategy. For this purpose, a multi-stage stochastic planning method is proposed for transmission power systems (TPSs) considering dynamic frequency stability. Specifically, the progressive uncertainties of RGs over stages are addressed with a multi-stage stochastic method with nonanticipativity constraints. In this scheme, the uncertainty is represented by probability-weighted scenarios, and the planning decisions are only dependent on current realizations of RG uncertainties according to nonanticipativity constraints to improve planning efficiency. Moreover, the dynamic frequency stability constraints are derived considering the frequency regulation strategy of RGs, and these nonconvex constraints are further linearized with high accuracy by a maximal affine function-based method to improve the compatibility with the planning model. Subsequently, a progressive hedging algorithm (PHA) is designed to reduce the computational burden by decomposing the multi-scenario high-dimensional model into multiple small-scale models. Finally, the effectiveness of the proposed method, as well as its superiority over existing approaches, are validated through numerical experiments.

Grid-forming (GFM) control is an important technical solution for addressing the declining voltage-support capability and inertia level of modern power systems. By integrating a high-voltage directly connected grid-side converter with supercapacitors, the grid-forming static power generator (GFM-SPG) can provide active- and reactive-power support to high-voltage power grids. This paper investigates a GFM-SPG with a two-stage converter topology and proposes a coordinated control strategy for the two-stage converters. The transient response characteristics of the GFM-SPG are classified into three operating regions, and the effects of key control parameters are analyzed to establish basic parameter design guidelines. To simultaneously enhance grid inertial support and transient voltage-support capability, a variable inertia time-constant control strategy is further proposed. Under normal operating conditions, a relatively large inertia time constant is adopted to provide inertial support, whereas a small inertia time constant is employed during voltage ride-through to enable rapid phase synchronization and prioritize reactive-power support. The proposed control strategy is validated through electromagnetic transient simulations and hardware-in-the-loop (HIL) experiments. The results demonstrate that the two-stage GFM-SPG can achieve stable DC-bus voltage regulation and provide effective inertia and transient voltage support under different grid operating conditions.