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The advent of novel power systems has given rise to a multitude of safety and stability concerns associated with the integration of emerging energy sources and power electronic equipment. The active support of the grid-forming control strategy represents an effective solution to the voltage and frequency stability issues associated with the weak damping and low inertia inherent to high-ratio new energy systems. Firstly, a static voltage stability index based on critical impedance is proposed for assessment of the static stability margin of a new energy grid-connected system, based on the static voltage stability theory of a traditional single-unit single-load system. Secondly, an analysis is conducted of the control principle of the grid-forming control converter and its impedance characteristics. In conclusion, a method for enhancing the static voltage stability margin of grid-connected new energy stations through parameter control of grid-forming converters is presented. The simulation verification of the single-feed and multi-feed systems demonstrates the efficacy and accuracy of the methodology presented in this study.

With the increasing penetration of distributed energy in the distribution network, it is urgent to study how to ensure the stable and reliable operation of the power grid under fault conditions. To solve this problem, this study proposes a method for partitioning distribution network islands and reconstructing faults considering the Conditional Value at Risk (CVaR). This method aims to enhance the resilience of the distribution network and the recovery capability of critical loads. Initially, a partitioning model for distribution network islands based on depth-first and breadth-first search algorithms was constructed. Building upon this partitioning, a fault reconstruction method for distribution networks that considers CVaR was developed. This method utilizes CVaR theory to transform costs and quantifies the risk that the uncertainty of distributed energy resources poses to distribution network reconstruction strategies. Finally, the effectiveness of the proposed method is demonstrated using an improved IEEE 33-node system, generating typical fault scenarios. [ABSTRACT FROM AUTHOR]

This paper proposes a design method for an additional damping reduced-order controller based on the projective control theorem. Improvements are made to the projective theorem to achieve additional damping control through Controllable-Line-Commutated Converter (CLCC)-based High Voltage Direct Current (HVDC), which suppresses low-frequency oscillations. Using small disturbance identification techniques, the system's linear model is first identified, and the state feedback control law of the system is then determined using the state-space pole assignment control method. Then, by retaining the dominant oscillation modes of the closed-loop system through the improved projective theorem, the state feedback is converted into output feedback. Ultimately, the sixth-order state feedback controller is reduced to a second-order one and applied in the CLCC HVDC additional damping strategy to suppress low-frequency oscillations. Simulation results based on the electromagnetic transient simulation software PSCAD demonstrate that the designed CLCC HVDC additional damping reduced-order projective control exhibits good suppression performance, strong robustness, and low order, which are of significant importance for engineering practice. [ABSTRACT FROM AUTHOR]

Deploying high penetration of variable renewables represents a critical pathway for deep decarbonizing the power sector. The conflict between their temporal variability and limited system flexibility has been largely ignored currently at planning stage. Here, we present a novel capacity expansion model optimizing investment decisions and full-year, hourly power balances simultaneously, with considerations of storage technologies and policy constraints, such as carbon tax and renewable portfolio standards (RPS). Based on a computational efficient modeling formulation, all flexibility constrains (ramping, reserve, minimum output, minimal online/offline time) for the 8760-h duration are incorporated. The proposed model is applied to the northwestern grid of China to examine the optimal composition and distribution of power investments with a wide range of renewable targets. Results indicate that the cost can increase moderately toward 45% of RPS, when properly designing the generation portfolio: prioritizing wind investments, distributing renewable investments more evenly, and deploying more flexible midsize coal and gas units. Reaching higher penetrations of renewables is expensive and the reductions of storage costs are critically important for an affordable low-carbon future. RPS or carbon taxes to reach a same target of emission reduction in China will result in similar overall costs but different generation mixes. [ABSTRACT FROM AUTHOR]

• Twenty-one steel angle members were locally corroded using the mechanical drilling method. • The failure mechanism of the corroded steel angles was observed and analysed by tests and simulations. • The effect of corrosion length, corrosion width, and slenderness ratio on the residual bearing capacity was investigated. • A simplified method was proposed to calculate the residual bearing capacity of the corroded steel angles. To investigate the effect of local corrosion damage on the bearing performance of steel angle members, a total of 21 specimens, with various slenderness ratios and corrosion levels, were prepared and subjected to axial compression. During the test, the load–displacement curves, load–strain histories, failure modes, and residual bearing capacity of the steel angles were experimentally obtained and analysed. After that, the finite element analysis (FEA) model, calibrated by the test results, was established to further reveal the failure mechanism of the corroded steel angles under axial compression. It was found that all the corroded steel angles finally failed under global buckling around the weak axis induced by local buckling, and their residual bearing capacities were negatively correlated with the widths and lengths of the local corrosion zones. However, for the angles with a large slenderness ratio or with a local corrosion length larger than 20% of the whole length, the effect of local corrosion on the residual bearing capacity gradually diminished. By using the equivalent cross-sectional area, a simplified design method was also proposed to evaluate the residual bearing capacity of the corroded steel angles, and the predictions agreed well with both the test and simulation results. [ABSTRACT FROM AUTHOR]