## 1 Introduction  
With the penetration rate of wind power in micro-grid increasing, the indeterminacy and volatility of wind power generation will directly affect the balance of supply and demand of active power in the micro-grid system, causing frequency fluctuations. Countries around the world have introduced grid codes, which stipulate that wind farms must be able to regulate active power and provide frequency support [1; 2]. At present, the most widely used kind of wind turbines (WTs) is a double-fed induction generator (DFIG), which is connected to the grid through power electronic devices, thus is unable to respond to system frequency deviations without supplementary active power control methods, which includes rotor speed control, pitch angle control, and their combination. In Ref. [3], only pitch angle control is applied in the frequency regulation (FR) by DFIG, while the potential of rotor speed control is not exploited. However, the power regulation through rotor speed control is faster than pitch angle control, so its FR performance is better. The combination of two control methods is adopted in the FR strategy presented by Ref. [4], but the de-loading of DFIG is not studied; thus, DFIG can only participate in down-regulation. Only DFIG in the de-loading state can participate in both system up-regulation and down-regulation. Constrained by operation limit of DFIG, the de-loading strategy for different wind speed (WS) region is different, and the combination of rotor speed and pitch angle control is commonly applied in the researches about DFIG de-loading. In the DFIG de-loading strategy of Ref. [5], the dividing of WS regions is proposed based on the operation characteristic of DFIG. However, the dividing method does not designate the starting point of low WS region; thus, the FR reserve capacity cannot reach the expected value due to the lower limit of rotor speed. In addition, the pitch angle control is only applied in high WS region, which will result in the lack of reserve capacity in median WS region due to the upper limit of rotor speed. In both reference. [6] and reference [7], the dividing of WS regions is used for appointing different de-loading mode or FR type to WTs under different WS in the wind power plant, which does not consider the smooth transition between control methods. In other words, most existing researches ignored the continuous change of rotor speed or pitch angle at the junctions of different WS regions and the probability of not reaching expected FR reserve capacity in each WS region. Therefore, it is necessary to establish a DFIG FR model, which is applicable under continuously varying WS in whole WS range. However, WTs underperform in providing FR service due to the volatility and indeterminacy of wind power. Therefore, it is difficult for WT to provide frequency support independently. The energy storage system is often used to assist renewable energy generation to provide auxiliary services [8]. The coordinated control strategy in Ref. [9] uses battery energy storage system (BESS) as a secondary energy resource to assist wind power plant to provide FR service for long-term operation. In Ref. [10], the proposed cooperation strategy employs wind power to track the FR signal in priority and battery storage to compensate for insufficient and inaccurate power. Nevertheless, the auxiliary energy storage system requires a large amount of additional equipment, which will greatly increase the operation cost of the wind farm. Meanwhile, the method only improves the frequency response on the power supply side but does not exploit the potential of the load side in system FR. The quantity of electric vehicle (EV) will increase significantly in the future because the development of EV is attached great importance by countries around the world in consideration of the global environmental pollution and energy shortage crisis. Through proper price guidance, EV cluster can provide reserve capacity for FR.