Excitation Controller for a Synchronous Generator with a DC Exciter

In this paper, the excitation controlling structure for a synchronous generator with a field-controlled dc exciter is presented. Control unit represents a microprocessor-based device with buck converter within its power stage. Presented controlling structure offers a novel solution with a exciter self-excitation path. Namely, a buck converter is supplied directly from the dc exciter stator terminals, which are also used for the excitation of the synchronous generator field winding. However, since the field voltage of the synchronous generator varies significantly for the different modes of operation, especially during transients, this introduces significant nonlinearity in the control system. Additional blocks and loops in the control structure are avoided by introducing the appropriate linearization. Presented solution offers better large signal performance of excitation control system during transients, and some cost benefits compared to the more common solution proposed in IEEE 421.5 standard model DC4B, with synchronous generator self-excitation path established via its terminal voltage. Pole-zero cancellation excitation controller parameter tuning technique is, also, presented. Dynamic performance of the presented controlling structure is verified through the set of simulation and experimental tests presented in the paper. The simulations are carried out using the full order generator and exciter models. The experimental tests were carried out on a 15MVA synchronous generator.