The increasing growth in the installation of natural-gas fired units has raised necessitates on synergy between the electricity and natural gas networks. This paper discusses how synergistic operation of electricity and natural gas networks can be achieved in a distributed fashion using alternating direction method of multipliers (ADMM). A standard ADMM approach and a consensus-based ADMM approach are developed, respectively, to solve the gas-electric integrated optimal power flow problem with and without a coordination operator. In both cases, the optimization formulation for each operator is modeled, and the solution procedure as well as data exchange among multiple decision-makers are explained. Case studies on both small and large gas-electric integrated systems show that the two ADMM-based distributed approaches have significant efficiencies over the traditional Lagrange relaxation (LR) and augmented LR-based methods.

Cyber-attack is recognized as an emerging risk in smart grids. In this paper, we reveal a potential link between data attack and physical consequences and analyze how the attacker can launch a malicious data attack to trigger sequential outages and thus impose large damages to the grid. In this attack mechanism, the attacker constructs an optimal false data injection (FDI) attack to intentionally trigger a targeted branch outage sequence that trips multiple branches and then leads to subsequent failures. The studied attack mechanism integrates constructing an optimal data attack and identifying critical lines, and imposes a substantial security impact with a high chance of occurring. Simulations on the IEEE 118-bus system verify the introduced attack mechanism and highlight the risk of such attacks in today's smart grids.

Today's smart power networks are exposed to an increasing number of cyber-attack events due to the highly integration of information techniques. It was revealed that an attacker can significantly increase the operation cost of a power system by launching undetectable false data injection attacks. However, the attack vector is determined by solving a bi-level linear programing (LP) problem, which is intractable for large systems. In this letter, we present a simple approach to determine an effective attack vector that can cause a significant increase in the operation cost. This is achieved by solving one LP. The simulation results on the IEEE testing systems verify the effectiveness of the proposed model and reveal that large-scale power systems are under high risk of cyber-attacks.

Frequency stability management of asynchronously interconnected grids is becoming a great challenge. This paper investigates how asynchronous sending- and receiving-end grids can be operated in a synergistic and interactive manner to guarantee frequency stability following the worst case HVDC bipole block while still ensuring operational economy. A novel enhanced frequency stability constrained multiperiod optimal power flow model (EFOPF) with flexible fast-acting HVDC corrective control is proposed. EFOPF dynamically schedules the distribution of primary reserves and HVDC corrective actions to simultaneously handle postcontingency over- and under-frequency disturbances occurring in the sending- and receiving-end grids, respectively. An alternating direction method of multipliers based distributed algorithm was developed to solve this problem. A case study of a modified two-area RTS-96 system demonstrates the effectiveness of the proposed EFOPF.

This letter describes an enhanced multi-period dispatch model for microgrids, in which frequency-aware islanding constraints are established to ensure microgrids with the capability to ride through unplanned islanding events. Rather than specifying the upward/downward primary reserve requirements as fixed amounts, the proposed dispatch scheme determines the primary reserve requirements by explicitly simulating under- or over-frequency dynamics caused by potential islanding events. To remove the nonlinearity, a two-stage solution strategy is proposed. Case studies demonstrate the effectiveness of the proposed microgrid dispatch scheme.

With the increasing integration of renewable energy resources into power grids, system inertia is decreasing considerably. This trend poses major challenges to transmission system operators and requires a comprehensive understanding of inertia-related information to formulate effective strategies that ensure power system frequency stability. In this study, an inertia security evaluation methodology is proposed from a frequency stability perspective, including its definition, quantitative assessment, and application. First, the definition and mathematical underpinnings of the inertia security region (ISR) are introduced. Then an evaluation method for the ISR is established, considering various frequency stability control strategies based on the size of the disturbance. Two quantitative indices, the inertia security ratio and inertia adjustable capability, are introduced to assist grid operators in determining the system inertia security status and assessing the inertia adjustability capability. Furthermore, for inertia deficits, a sensitivity-based inertia allocation approach is proposed for credible contingencies. Finally, the efficacy of the proposed ISR approach is validated using case studies on a modified 39-bus system and a practical large-scale power grid in China.