The self-excitation process in electrical rotating machines operating in pulsed power regime

The self-excitation process in pulsed air-core rotating generators is fundamental in assuring record values of power density and compactness. This paper analyzes the conditions for the self-excitation process in pulsed electrical machines used as power supplies for electromagnetic launchers, using the analogy and methods of the positive-feedback in control systems. In the classical "ferromagnetic" electrical machines in the self-excitation process, the machine output is used in order to gradually excite the generator until the steady-state voltage is finally reached. The end of the process and, consequently, the stability and repeatability, is assured by the intersection of the strongly nonlinear magnetization characteristic and the excitation straight line. In the air-core, pulsed power machines such as homopolar generators and compulsators, the two characteristics are apparently linear and both the end and the initiation of the process must be forced. The paper shows that the pattern of the self-excitation process is very similar in all the EML power supplies (homopolar, compulsators, asynchronous) and the initially unstable process reaches stability in a very controlled way. The paper also shows how the self-excitation can create a new EML power supply with an original use, from a classical electrical machine.