Transient Analysis of Air-Core Pulsed Alternators in Self-Excitation Mode

In pulsed-power supply for electromagnetic launchers, air-core pulsed alternators have obvious advantages to enhance the power and energy densities. Compared with conventional machines, self-excitation mode is usually adopted due to the requirement of the large excitation current to establish the high flux densities in the air-core magnetic circuits. In this paper, a detailed description of the transient process involved with the air-core pulsed alternator operating at self-excitation mode is presented. First, it is necessary to supply a seed current rapidly prompting the alternator into the self-excitation mode. The capacitance and precharged voltage of the capacitor in excitation initialization module, which determine the seed current, are analyzed, and reasonable value ranges of the capacitance and the voltage are obtained. Then, when the machine is in self-excitation mode, a detailed study about the current and the voltage of the windings is carried out. Some innovational concepts, such as the equivalent impedance of the excitation winding R_feq and the growth rate of the excitation current K_fi, are proposed to simplify the transient analysis. They play a significant role to guide the optimization of our systems. Finally, the analysis is verified through the comparison with the Saber simulation results.