润色下面文字在Case 1和Case 2中研究了故障检测延迟对GFM-GCI系统暂态稳定性的影响。电网正常运行期间GFM-GCI系统采用功率外环、电压电流双环控制模式P+ ref和Q+ ref分别为-1pu和0pu图12中P+和Q+分别为1pu和0pu表明有功、无功功率可以准确跟随指令值。在故障持续阶段为使系统存在平衡点由式10可得GFM-GCI系统的有功功率给定值范围可将P+ ref设置为-05

In Case 1 and Case 2, the impact of fault detection delay on the transient stability of the GFM-GCI system was studied. During normal operation of the grid, the GFM-GCI system adopts a power outer loop and voltage-current dual-loop control mode, with P+ ref and Q+ ref set to -1 p.u. and 0 p.u. respectively. In Figure 12, P+ and Q+ are set to 1 p.u. and 0 p.u. respectively, indicating that the active and reactive powers can accurately follow the command values. During the fault duration phase, in order to maintain a balance point in the system, the active power set point range of the GFM-GCI system can be obtained from equation (10), and P+ ref can be set to -0.5 p.u. By using equation (9), the reactive power command Q+ ref can be determined as 0.28 p.u. Equation (18) gives the critical clearing time tcr of the system, which is 48 ms in this case. In Case 1, with td set to 40 ms, the delay time is less than the critical clearing time. At this time, the GFM-GCI system outputs power P+ and Q+ as -0.5 p.u. and 0.28 p.u. respectively. It can quickly follow the command values and maintain stability during the fault. In Case 2, with td set to 60 ms, which is greater than the critical clearing time, the kinetic energy accumulated during the detection delay process cannot be released in the subsequent phase. The excess kinetic energy will drive the GFM-GCI system to cross the transient instability boundary, leading to frequency deviation. As shown in Figure 12, the system output power P+ and Q+ fluctuate widely, the system frequency is higher than the nominal frequency and exhibits oscillation, and the system power angle continues to rise and oscillate. The simulation verifies the correctness of the theoretical derivation