The excitation system of synchronous generator directly affects the characteristics of the generator during the steady state or transient state. Excellent excitation system can not only guarantee the high quality of electric energy, the reliability and stability of the generator operation, but also effectively improve the technical and economic index of the generator and its related power system. Before the synchronous generator is put into the power grid, its voltage is required to maintain the given value, that is, the excitation control system must run stably under the condition of no-load operation of the generator. When the generator is integrated into the power grid, it runs in parallel with all the generator sets in the power system, so it is required that the excitation control system of the generator can have a beneficial effect on the stable operation of the power system. In the calculation of power system stability, it is difficult to get a satisfactory result if the role of excitation regulation system is ignored. In addition to stability problems, dynamic performance indexes and control accuracy of excitation control systems are often required in operation. The requirements for excitation control system in power system design regulations are: Stability index: amplitude margin m > 30 db, phase margin y > 50°; Dynamic indicator: overshoot M. If < 15 ranges from 30, adjust the time t. < 10 s; Control accuracy: steady state error e (oo) < 1% ~ ~2%; According to the regulations, the excitation control system should be analyzed and designed from three aspects: stability, dynamic performance and steady-state performance.
1. Principle of excitation control system The excitation control system of synchronous generator generally consists of two parts: excitation power unit and excitation regulator. The excitation power unit provides DC current to the rotor of synchronous generator, namely, excitation current. The excitation regulator controls the output of the excitation power unit according to the input signal and the given regulation criteria. The whole excitation automatic control system is a feedback control system composed of excitation regulator, excitation power unit and generator.
