Maintaining the synchronous operation of the power system generator is a necessary condition for the normal operation of the power system. Therefore, the concept of static and transient stability of the power system is also based on whether any generator in the power system loses synchronous operation. In the power system, once the power generation fund project: the national key basic research special fund project (G1998020311); Tsinghua University power system national key. The other three fuzzy controllers are analogously available. The fuzzy controller consists of four parts: fuzzy interface, fuzzy control rule, fuzzy reasoning and defuzzification interface. The fuzzification interface determines the membership of the linguistic variable value associated with it based on the exact input analog quantity and the corresponding membership function. The fuzzy control rule adopts the format: if A and B are C, that is, if the conditions A and B are satisfied, the control is performed. C. The control rule 15 obtained according to the derivative of the slip and the slip is as shown in Table 1.
Table 1 The control rule of X-Oper1 The derivation process of the d-control strategy The fuzzy inference uses the Mamdani method, and the de-fuzzification uses the median method. The reasoning process is as shown.
It is a three-dimensional control chart of control measures.
In order to realize additional intermittent control, the fuzzy controller should be composed of four fuzzy sub-controllers. Each fuzzy sub-controller completes one process stage of additional intermittent control, which is the structural diagram of the whole fuzzy controller. As can be seen from the figure, the four controllers correspond to four control stages, and the output of each controller has the function of the next controller in addition to the control operation (only the first three sub-controllers) Have this effect). Therefore, the control rules of the four sub-controllers are not the same, and the reasoning process is also different. For the first three controllers, the following three functions are implemented: control operation (meeting the control condition), no action (in the normal case), and excitation of the next fuzzy controller (when the above conditions are not met). The fourth fuzzy controller only needs to complete the first two functions. For the conditions of controller operation, the following three fuzzy controllers can not only operate under the condition of fuzzy reasoning, but also must implement the operation of the controller when the excitation state of the previous fuzzy control is true. Two conditions Indispensable.
4 Simulation results analysis 4.1 Single-infinite system and its simulation results According to the fuzzy control controller proposed in this paper, the MATLAB simulation tool is used to perform digital simulation of system out-of-synchronization for single-infinity system and multi-machine system.
A simple schematic of a stand-in-infinite system is shown.
See Appendix for the selection of model parameters for the generator and its excitation system. Since the model of the prime mover and the speed control system is to be added to the fast-closing valve control, the typical values ​​of the governor model and the prime mover model are used. When a power line in the system has a three-phase ground short circuit fault about 1km away from the generator end and delays the resection fault for some reason or a three-phase permanent short circuit occurs, the generator will be out of step and enter Asynchronous running state. In this case, if the system is allowed to run asynchronously for a short time, then using the fuzzy controller proposed in this paper, the generator can be quickly pulled into synchronous operation. The slip curve of the conventional control measures and the slip curve of the applied intermittent fuzzy controller are given under the condition that the delay is 0.4s and the line is no longer coincident. It can be seen from the figure that under additional control measures, the generator resumes synchronous operation after a period of time.
And for some reason, the fault is delayed by about 0.8s. Under normal control measures, the generator will lose synchronization and enter the asynchronous running state. The additional discontinuous fuzzy controller proposed in this paper is used to control it. Under the condition that the three-phase permanent short circuit occurs at the Gi busbar, the delay time is 0.8s, and the line no longer overlaps, the conventional control measures and plus The slip curve after adding the intermittent fuzzy controller.
Schematic diagram of multi-machine system Multi-machine system Additional resynchronization fuzzy intermittent control and conventional control slip curve As can be seen from the figure, the use of additional intermittent fuzzy controller can improve the variation of slip, using additional intermittent control measures The generator is quickly pulled into synchronization, allowing the system to quickly return to synchronous operation. It can be seen that the control effect of Gi is obvious, and the out-of-step generator can be quickly pulled into the synchronous operation state within about 45s, which proves the effectiveness of the additional intermittent control measures; since the fault occurs at a distance from Gi In the near place, the influence on Gi is very large, and the influence on G2 is relatively small. Therefore, the additional intermittent control device of G2 has basically no action, and the regulation of the conventional control system can achieve the stability requirement.
5 Conclusions This paper describes the working principle of fuzzy controllers, and proves that the fuzzy controller has better control effect on power system resynchronization through simulation results in single-infinite system and multi-machine system. It shows that the intelligent controller has practical application value.
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