Objectives The characteristics of low inertia and low damping in “double-high” (high renewable energy penetration and high power electronics application) power system pose significant challenges to grid stability, particularly in terms of frequency and voltage. Grid-forming energy storage (GFM-ES), which has the capability of frequency regulation and voltage control, is reviewed in terms of its characteristics, application scenarios, and research outlook. Methods Firstly, the main characteristics of GFM-ES are described from the aspects of the differences between GFM-ES and grid-following energy storage, as well as the control methods. Then, the main application scenarios of GFM-ES, including frequency support, voltage support, and black start, are elaborated. Finally, the research outlook is presented, focusing on the stability, optimal configuration, and practical engineering applications of GFM-ES. Conclusions The stability of GFM converters has an important impact on the operational characteristics of energy storage units, and further attention needs to be paid to the induced causes of the stability problem, parameter tuning, and switching of control and current limiting strategies. The GFM-ES configuration requires trade-offs in terms of functionality, complexity, and cost, and the hybrid configuration of grid-forming and grid-following energy storage needs to be further investigated. Coordination and interoperability between GFM-ES units should be strengthened, and technical test specifications and standards should be improved to promote their application in hybrid AC-DC grids and high-voltage transmission grids.

With the increasing proportion of new energy in power system, the safety and stability of large-scale new energy has become a common concern. Taking the 1 000 kV Zhangbei—Xiong’an UHVAC transmission line from the 10 million kilowatt new energy base in Zhangbei area as an example, this paper builds a PSASP electromechanical transient simulation model, which includes new energy model and distributed condenser model with low voltage crossing function. The paper analyzes the constraints of the new energy transmission capacity. And then the influence of different configuration schemes on short-circuit ratio of new energy and the suppression effect of transient overvoltage are studied. Finally, the optimization effect of transient overvoltage problem is verified by ADPSS all electromagnetic transient simulation. The results show that transient overvoltage and steady-state low voltage are the main factors restricting the transmission capacity of UHVAC line from new energy base. The distributed small-scale condenser is installed at the generator end with low short-circuit ratio of new energy, which can effectively restrain the transient overvoltage problem and improve the overall output capacity of new energy. The results of the study are of great reference value for planning, operation and design of the same kind of new energy delivery project in China.

In order to study the ralationship between grid-forming （GFM） and grid-following （GFL） units that can support the stable operation of renewable systems, this paper firstly takes the single wind farm integrated system as an example to analyze the dynamic characteristics of the GFL and GFM units. Then, from the perspective of maintaining the oscillation stability of wind farms both in low frequency and subsynchronous frequency bands, the calculation principle of the GFM unit capacity to be deployed in wind farms is proposed. On this basis, based on the three-machine-nine-bus system, the feasibility of the stable operation of the 100% renewable system is explored, and the influence of the proportion and location of the GFM units on the dynamics of the system are studied. The results show that the subsynchronous oscillation （SSO） risk can be effectively improved by deploying a small number of GFM units in the wind farm, and the capacity of GFM units is mainly constrained by the low-frequency mode stability. Besides, in the 100% renewable system, the SSO due to inadequate support of GFM to the remote GFL units is the key constraint in determining the need for GFM units.

A grid-forming photovoltaic energy storage access optimization control strategy based on improved chaotic particle swarm optimization is proposed to address the issues of voltage fluctuations, low utilization of renewable energy, and line losses caused by the integration of traditional photovoltaic energy storage grid-forming inverters into active distribution stations. Firstly, a multi-objective optimization model is constructed with the objectives of minimizing load voltage deviation, maximizing photovoltaic power generation, and minimizing line losses. According to system requirements, the optimization priority for load voltage deviation is set to be the highest and the line loss is the lowest. Multi-objective problems are transformed into three single objective optimization problems through priority sorting. To improve the efficiency of solving, the initial parameter selection strategy of the chaotic particle swarm algorithm is improved. The simulation results show that the proposed method has faster convergence speed and higher solution accuracy, which verify the effectiveness of the control strategy.