Study Of Digital Excitation Control System For Use With 1000 KW Synchronous Generators

In power system, enhancing and maintaining synchronous generators stability is one of the basic conditions to ensure safe and economical power system operation. Moreover, enhancing the performance of excitation control is one of the most effective methods to improve synchronous generators stability, which is widely accepted. The traditional main circuit of static excitation system is three-phase full-bridge controlled Rectifier. The lost-control period of phase-control system and the low operation frequency of thyristor result in the long regulation time and slow dynamic response of excitation control system. In addition, equivalent series reactance of excitation transformer worsens the condition of the thyristor operation, and it can bring transient over-voltage at the moment of switching thyristor. The transient over-voltage will endanger the field winding. According to the characteristic of excitation control system of small and medium synchronous generators, DC chopping circuit is presented based on scheme simulation. Because of the high switch frequency of Intelligent Power Modules (IPM), the corresponding control circuit is simpler than conventional thyristor controlled circuit by using IPM. Which leave out the reactor, and thus increase the dynamic regulating speed of excitation control system. Modern excitation control system for use with synchronous generators is prone to high stability and computer control. Digital Signal Processor (DSP) TMS320LF2407A made by TI is our digital excitation control chip. The event manager module of LF2407A can substitute complicated digital trigger circuit and many peripheral circuits. The excitation control, fault protection and communication are integrated to provide a true single-chip DSP controller. The main circuit and control circuit of excitation control system are introduced. Saber model of synchronous generators is built by using MAST. Chopping excitation approach simulation and control strategy is presented. Design of hardware circuits and system program is discussed. Parameter in p.u. of synchronous generators is applied in excitation control program, so excitation control program can be used for different synchronous generators excitation control system. Experimental results show that DC chopping circuit can produce field current with quick adjusting speed and wide regulating range. At the same time, digital excitation regulator based on DSP has been fully testified, which has faster dynamic response speed and useful for engineering application with chopping control excitation approach.