Topologies for compact compensated pulsed alternators

Increasing the compactness of compensated pulsed alternators (compulsators) has been an ongoing effort supported by the US Army and others since the mid-1980s, when interest in electric armaments began to emerge. Today, the compulsator is the best approach for achieving compact energy storage and pulsed power generation for multi-MJ, multi-GW applications requiring voltages of up to 15-20 kV and discharge durations between 1 and 10 milliseconds. Electromagnetic railguns, coil launchers, and directed energy systems requiring high-power, high-energy pulsed-power in compact form are ideal candidate loads for compulsators. Since the initial validation of compulsator theory in the late 1970s, a transition from iron-core to air-core magnetic circuits and the associated incorporation of composite materials and self-excitation has provided substantial increases in both stored energy density and power density. On a per unit mass basis, the current state of the art is more than 1 kW/g peak power in a machine that provides greater than 10 J/g inertial energy storage. While the advancement has been significant, further gains in compactness are possible by exploiting continued innovation in the topology of the machine, the mode in which it operates, and by developing new technologies specifically for compulsator application. This paper focuses on practical machine topologies that offer promise for obtaining higher specific energy and power. The evaluation presented also contemplates current and potential future improvements in compulsator component technologies, including composite materials and switching devices that can substantially impact the magnitude of possible improvements as well as the selection of the most promising topology.