## 5 Simulation Cases
### DFIG and EV Coordinating to Participate in FR  
In order to verify the effectiveness of the coordinated FR strategy of DFIG and EV, Scenario 3 is set up. In Scenario 3, DFIG and EV cluster coordinates to participate in system FR, and the lack of FR demand power is compensated by the conventional unit. Other conditions are the same as with Scenario 1 and Scenario 2. The system FR task in Scenario 3 is shown in Figure 16, which will be allocated to EV and DFIG, respectively, according to the proposed real-time allocation strategy. Figure 14: The Operation state change of DFIG (double-fed induction generator). (**a**) The rotor speed change of DFIG; (**b**) The pitch angle change of DFIG. Figure 15: Comparison of FR (frequency regulation) effect in Scenario 1 and Scenario 2. The FR capacity of EV cluster for up-regulation and down-regulation is shown in Figure 17a,b, respectively. With EVs accessing and leaving the grid according to the driving rules, the FR capacity of EV cluster will vary with time. The FR output of EV cluster for up-regulation and down-regulation is shown in Figure 18a,b, respectively. It can be seen from the figure that as EVA is given priority in down-regulation in the proposed FR task allocation strategy, EVA's down-regulation task is more than up-regulation task. EV cluster will participate in up-regulation only when the up-regulation capacity of EVA cannot fulfill the FR task. In 9:00-10:00 of Figure 18a as well as 8:30-9:00 and 17:30-19:00 of Figure 18b, the FR output of EV cluster is constrained by the FR capacity. The FR output of DFIG is shown in Figure 19. It can be seen from the figure that as DFIG is given priority in up-regulation in the proposed FR task allocation strategy, DFIG's up-regulation task is more than down-regulation task. DFIG will participate in down-regulation only when the down-regulation capacity of EVA cannot fulfill the FR task. The FR task allocated to DFIG is almost accomplished, except for some up-regulation moment that the FR output of DFIG is constrained by the FR capacity. If the joint FR output of EV cluster and DFIG cannot fulfill the system FR task, the conventional unit will output power to compensate for the lack of FR demand power. The FR task allocated to the conventional unit is shown in Figure 20.  
Figure 16: System FR (frequency regulation) task. Figure 17: FR (frequency regulation) capacity of EV (electric vehicle) cluster. (**a**) EV’s FR capacity for up-regulation; (**b**) EV’s FR capacity for down-regulation. In Scenario 1, DFIG coordinates with the conventional unit to participate in FR, while in Scenario 3, DFIG coordinates with EVA to participate in FR. The comparison of the FR effect in Scenario 1 and Scenario 3 is shown in Figure 21. The RMS value of frequency deviation in Scenario 1 and Scenario 3 is 0.0346 Hz and 0.0267 Hz, respectively. It can be seen that the FR effect of DFIG coordinating with EVA is obviously better than the situation when DFIG is coordinating with the conventional unit. This is because EVs can respond to the FR signal more quickly than the conventional unit, so the system FR  
Figure 19: FR (frequency regulation) output of DFIG (double-fed induction generator). Figure 20: FR (frequency regulation) task of a conventional unit. Figure 18: FR (frequency regulation) output of EV (electric vehicle) cluster. (**a**) EV’s FR output for up-regulation; (**b**) EV’s FR output for down-regulation. task can be better accomplished. Therefore, through the proposed coordinated FR strategy, EV cluster is able to assist DFIG to participate in FR effectively. The proposed coordinated FR strategy is based on the real-time allocation of system FR task, which considers the FR capacity of DFIG and EV cluster to make the allocation more reasonable. In order to verify the superiority of this method, Scenario 4 is set up. In Scenario 4, the system FR task is allocated to the DFIG and EV cluster at a fixed ratio of 5:5.