The voltage dip is the sudden drop of the voltage amplitude of the AC power system to an unacceptable level, resulting in the disconnection and collapse of the interconnected system. A voltage dip is an unstable condition that occurs when the system load is too high. Because the load increases, the system voltage first changes slightly, then abruptly accelerates and decreases, eventually causing the system to collapse. In the event of a voltage dip, voltage-controlled electrical appliances, such as switching transformers, may experience small voltages before the voltage suddenly drops. The change is within the allowable range and no action is taken. A faster decrease may cause the undervoltage relay to act before the transformer switches. In this way, the operator of the control center will not observe the alarm sound, because at this time the phase angle, frequency and voltage amplitude of the power system may also remain in the normal range. Then, the sudden drop in voltage caused the immediate action of the system protection device, the disconnection of the interconnection system, and the immediate collapse of the system.
In this paper, by introducing the perturbation of the load characteristic parameters, the voltage sag characteristics of the power system can be suppressed. The simulation shows that the perturbation suppression method is feasible.
1 System Model The power system model discussed in this paper is shown as a model based on the Dobson and Chiang research. Dobson and Chiang applied the power system model to describe some of the dynamic characteristics of voltage sags. It can be regarded as the equivalent circuit of the local power system connected with the external large power system; the external large power system can be regarded as an unlimited-capacity bus, ie, a power source whose voltage amplitude and phase angle do not change regardless of the load size. In the figure, the terminal voltage amplitude and phase angle of the bus with unlimited capacity are respectively %° and 0.°, ie, 匕>0; the terminal voltage of the generator in the local system can also be described as the conduction of the transmission line. We connect a generator, an unlimited power bus, a load, and a capacitor. The load's terminal voltage is the capacitance C. It is used to keep the voltage amplitude close to 1 unit (units of domestication Dobson and C Wang's model is large Power system models, saddle-shaped branches occur when approaching 11.41 units.
The three-bus power system model 2 introduces the perturbation voltage sag characteristics to suppress the introduction of perturbation in the load characteristic parameter r term, which can be obtained by equation (1) = 0.98, initial value (0.350, 0.151, 0.150, 0.980) for simulation. The relationship between system load voltage and time is shown in b. When the time is taken 〖=5000s, there is no voltage drop. Near the point of collapse, by introducing perturbations, the system can operate stably, delaying or avoiding the occurrence of voltage dips.
=l, when perturbation was not introduced (b). 98, the time behavior of the load voltage when the perturbation is 0.980) 3 Conclusion This paper introduces the perturbation of the load characteristic parameters, which effectively suppresses the occurrence of voltage dips in the power system. The simulation results show the feasibility of the perturbation suppression method. It is effective for delaying or suppressing the voltage sag and system collapse of the power system. How to control the chaotic phenomenon in the power system more effectively and completely avoid the voltage sag and the system The collapse has yet to be studied.
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