DC power grid voltage transient stability recovery control method based on additional electric quantity
A DC power grid, restoration control technology, applied in electrical digital data processing, special data processing applications, instruments, etc., can solve the problems of continuous oscillation, DC bus voltage fluctuation, etc., to delay the action time, prolong the drop to the limit point effect of time
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Embodiment 1
[0108] The present invention builds such as in Matlab / Simulink environment Figure 7 The simulation model of the multi-terminal flexible DC grid is shown. On the AC grid side, the power frequency three-phase AC power supply is filtered and transformed to connect to the VSC 1 The converter is connected to the DC grid, and the capacitor C is connected in parallel dc The voltage across both ends represents the DC bus voltage. The load side is connected to the converter VSC with constant power control 2 , to ensure that the connected load exhibits constant power characteristics. During the simulation, the wind power generation system is regarded as an equivalent unit. The basic parameters of the simulation model are shown in Table 1.
[0109] Table 1 Basic parameters of flexible DC grid simulation model
[0110]
[0111] Combined with the basic parameters of the flexible DC grid simulation in Table 1, the theoretical stable operating parameters of the system in this insta...
Embodiment 2
[0113] In order to verify the voltage operating limit of the DC grid, by changing VSC 1 The DC voltage reference value in the voltage droop controller makes the system operate at different degrees of step-down. The four step-down operation calculation examples are as follows: at 0.02s, the DC voltage droop control reference values are set to 485V, 470V, 455V, and 430V respectively, and the initial values are restored at 0.03s. The dynamic response of the system is as follows: Figure 8 shown.
[0114] Such as Figure 8 As shown, as the DC voltage reference value decreases and the capacitor discharges, the DC voltage drops rapidly from 498V in a stable operating state. In the four calculation examples, the system DC voltage drops to 450V, 375V and 230V in 0.03s respectively. After the disturbance is eliminated, the system can resume stable operation in the first two cases. In calculation example 3, the system runs stably around 235V, which slightly exceeds the theoretica...
Embodiment 3
[0116] In order to further analyze the limit time of DC voltage fault removal, a bipolar short-circuit fault is set at the DC bus at 0.02s. Under traditional droop control, the fault is removed at different times, and the dynamic response of the system is as follows: Figure 9 shown. In the five fault calculation examples, the cutting time is set to 0.025s, 0.0265s, 0.028s, 0.030s, 0.031s respectively.
[0117] In the first three calculation examples, after the short-circuit fault was removed at different times, the DC bus voltage dropped to 480V, 420V, and 315V respectively, which did not exceed the theoretical calculation limit of 224V. As shown in the figure, after the fault is cleared, the system returns to the initial stable operation state. When the fault duration is extended to 0.030s, in Example 4, the system voltage drops to the limit voltage during the fault period, even if the fault is cleared, the system cannot return to the initial operating state. In example 5...
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