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The system inertia and the primary frequency modulation capacity are decreased by the reduction of the traditional conventional unit start-up capacity as the rapid development of wind power. The active power disturbance is increased after system frequency change rate. It is indispensable to study the inertia compensation and primary frequency modulation methods provided by wind turbines. A fuzzy adaptive virtual frequency modulation control strategy for wind power is proposed by analyzing the frequency modulation characteristics of wind turbines. Firstly, the mathematical model of wind power participation in frequency modulation and the frequency response model of the high proportion system is established. Secondly, analyzing the frequency change characteristics of the system after the disturbance, and establishing the wind power fuzzy control rules for the shortcomings of insufficient fixed parameter control, the stability of the fuzzy control rule parameters are analyzed by the root locus method. Finally, the effectiveness of the fuzzy control is verified by simulation, and the system stability is improved.

Aiming at the characteristics of the large-scale power electronic equipment access in modern power system, the inertia is continuously reduced. Based on the stability graph theory, the inertia evaluation method for power electronic system is proposed and designed. The method derives the relationship between inertia and active power from the second-order rocking equation model of the power system. Then, based on the output equivalence principle, the equivalent model of the new energy generation system is established by the synchronous machine rocking model. Further, the combination is stable. The graph method identifies the equivalent inertia of the wind farm and the fan based on the active power of the grid connection point. The simulation and measured tests show that the inertia estimated by this method can effectively adapt to the evaluation of the equivalent inertia of the wind farm, thus significantly improving the level of inertia assessment of the power system.

In order to solve the voltage over-limit problem of distributed photovoltaic(PV) connected to string lines, it is feasible to fully utilize the reactive power regulation ability of PV systems to adjust the line's voltage. In this paper, based on analyzing the mechanism of the point of interconnection(POI) of PV systems voltage over-limit and the voltage sensitivity of low-voltage string lines, a reactive power voltage control strategy named Q(U, P) was proposed, which is based on the POI voltage and the active power of PV. This control strategy inherits the advantages of Q(U) and cosφ(P) control strategies, determines the reactive power reference value by detecting the POI voltage and active power output of the PV systems. The simulation results show that the proposed control strategy satisfies the grid voltage within the rated range, the total absorbed amount of reactive power is lower and the active and reactive loss of grid are less than the existing control strategies.