A Simplified Analytical Approach for Hybrid Exciters of Wound-Field Generators

Midpower wound-field generators are predominantly used for grid applications, marine naval ships, industrial buildings, and critical standby power applications. They are often equipped with brushless excitation systems (ESs), where an exciter supplies the generator through a diode rectifier. Here, the uncontrolled nature of the rectification process can determine a significant reduction of the mean value of the output voltage. Hence, the root causes must be identified and properly modeled for an accurate evaluation of the system performance. In this article, a simplified analytical model is proposed for such purposes, taking as case study a consequent-pole, hybrid exciter of a wound-field generator for naval applications. The approach is based on the calculation of the diodes' commutation angle, which permits to estimate the exciter's armature current waveforms. Special focus is given to the voltage waveforms, which are determined using the estimated current waveforms as an input, thus removing the need for a numerical resolution. In addition, simplified equivalent functions calculated without relying upon finite-element (FE) analyses are employed to determine the machine inductances. Being fully released from any numerical computation, the proposed model permits a fast but accurate evaluation of the exciter performance. For validation purposes, FE and experimental investigations are finally performed.