In order to solve the problems of power jump caused by direct switching between energy storage frequency regulation control modes in critical mode and the limitation of energy storage output caused by too high or too low State of Charge（SOC）of energy storage,an integrated control strategy of energy storage participating in primary frequency regulation based on fuzzy control is proposed.Firstly,the influence of energy storage virtual droop,virtual inertia and virtual negative inertia control parameters on the frequency response of the system is analyzed,and the frequency modulation advantage and stable variation range of each control parameter are determined;Secondly,a fuzzy controller with virtual negative inertia control is designed to realize smooth switching and complementary advantages between control modes and accelerate frequency recovery;Finally,the feedback control strategy of SOC and the selfrecovery control strategy of energy storage SOC are designed by using the logistics function,so that the energy storage capacity can be better maintained and the frequency modulation ability of energy storage can be improved. The effectiveness of the proposed strategy is verified by Matlab/Simulink simulation.

In order to accommodate high-penetration wind & PV power sources with strong fluctuation and randomness, the access of renewables and planning of transmission grids not only need to consider the balance of electricity, but also the balance of flexibility capacity. On this occasion, the conventional method of transmission expansion cannot economically realize the above-said objectives, thus joint expansion planning of energy storage and transmission becomes the new solution. A joint expansion planning method for energy storage and transmission based on quantitative assessment of flexibility is established. Firstly, from the perspective of flexibility, we qualitatively analyze the technical characteristics and advantages of the joint ‘storage-transmission’ planning in power balance and flexible adjustment capacity. Then, a joint storage-transmission planning model considering flexibility is established, and the solution method is given with combination of heuristic and mathematical programming. Finally, the feasibility of the proposed method is verified based on the modified Garver-6 system. The results show that under the scenario of high-penetration of renewable energy sources, the joint ‘storage-transmission’ planning has better economy. The energy storage can effectively improve the system’s up-regulation flexibility, but the cost is an important factor for restricting its planning capacity.