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The inertia response and primary frequency regulation capability of synchronous grids are declining owing to the increasing penetration of inverter-based resources. The fast frequency response (FFR) of inverter-based resources is an important mitigation option for maintaining grid security under the conditions of low inertia and insufficient primary frequency response capability. However, the understanding and technical characteristics of the FFR of inverter-based resources are still unclear. Aiming at solving the aforementioned problems, this paper proposes a definition for FFR based on the impact mechanism of FFR on system frequency. The performance requirements of FFR are clarified. Then, the effects of FFR on system frequency characteristics are further analyzed based on steady-state frequency deviation, the initial rate of change of frequency, and the maximum transient frequency deviation. Finally, the system requirements for FFR and its application effects are verified by simulating an actual bulk power grid, providing technical support for subsequent engineering application.

This paper proposes a novel transmission network planning method under the background of Transmission and Distribution Price reform. Firstly, a multi-stage transmission network planning model considering the transmission and distribution price is established. The objective function of the planning model is to maximize the profit during the whole planning period. The constraints contains the nodal power balance, AC power flow, construction sequence, construction time, limitation of the total investment cost, and so on. Then, genetic algorithm is applied to solve the planning model. Finally, case studies are carried out on the modified IEEE 24- bus transmission network. And the results show the effectiveness of the proposed method.

As the penetration of RES (renewable energy sources) in large scale grid increases continuously, the inertia support capability and primary frequency regulation of synchronous power grid are both declining. A decrease in inertia is problematic because it negatively influences the dynamic characteristic of the system’s frequency. But its concrete impact is still not clearly distinguished from that caused by the decline of primary frequency regulation. Aiming at the above problem, firstly, the inertia support capability and its physical meaning of synchronous generator are analyzed in depth, and the expression formula of inertia support power of synchronous generator is deduced. Secondly, the distinction between the inertia support capability and primary frequency regulation of synchronous generator is analyzed in detail. Thirdly, the respective impacts of the inertia support and of the primary regulation on the dynamic characteristic of system frequency during power shortage disturbances in large scale synchronous grid are simulated and analyzed. Finally, all the study above points to a conclusion that the large synchronous power grids with increasing penetration of RES require more relatively continuous power support of the primary frequency regulation than the short term inertia support, because the impact brought by the decrease of system inertia support is less serious than that brought by reduction of primary frequency regulation ability in large scale power grid.

Saturated load is city's maximum affordable load, which is very important for urban development planning. As the power grid matures, the short-circuit current gradually becomes the key factor affecting the security of power grid, it is urgent to analysis the saturated load based on grid technology constraint of short-circuit current. In the paper, firstly, the regular pattern of power supply partition is put forward. Secondly, the typical partition structure model is extracted and the relationship between the model parameters and the actual power supply is deduced. Furthermore, a new method of calculating the saturated load level of power grid is proposed with the consideration of different partition structures and different power supply growth modes. Finally, the saturated load of an actual grid is calculated and the accuracy and effectiveness of the method is verified.

One type of bifurcation named oscillation emergence bifurcation (OEB) found in time-delayed linear time invariant (abbr. LTI) systems is fully studied. The definition of OEB is initially put forward according to the eigenvalue variation. It is revealed that a real eigenvalue splits into a pair of conjugated complex eigenvalues when an OEB occurs, which means the number of the system eigenvalues will increase by one and a new oscillation mode will emerge. Next, a method to determine OEB bifurcation in the time-delayed LTI system with single lag is developed based on Lambert W function. A one-dimensional (1-dim) time-delayed system is firstly employed to explain the mechanism of OEB bifurcation. Then, methods to determine the OEB bifurcation in 1-dim, 2-dim, and high-dimension time-delayed LTI systems are derived. Finally, simulation results validate the correctness and effectiveness of the presented method. Since OEB bifurcation occurs with a new oscillation mode emerging, work of this paper is useful to explore the complex phenomena and the stability of time-delayed dynamic systems.