Design and implementation of voltage source converter excitation system to improve power system stability

This paper presents the design of the voltage source converter(VSC) excitation system and an integrated prototype using digital signal processor(DSP) as the core of the excitation controller is developed. Compared with the static excitation systems with thyristor, the VSC excitation system owns one more channel offering positive damping to power system by controlling reactive power of VSC on its ac side, and this approach is approved much faster than field voltage regulation. To design the prototype, the VSC excitation system has to meet the practical condition of the selected synchronous generator(SG) set such as generator capacity, terminal voltage, field voltage and field current, etc. The designed VSC excitation system consists of converters containing a front-end three-phase VSC and a back-end H-bridge chopper, a step-down transformer, and a coordinate excitation controller. Through a series of experiments, it is demonstrated that the VSC excitation system is able to improve both transient stability and steady-state stability limit of power systems. It is a prospective substitute to the conventional thyristor based static excitation system and an attractive solution to strengthen power system stability as well as increase the capability of long-distance transmission systems.