Active Control and Excitation of Breathing Oscillations in a Hall Thruster with a Fast Digital Signal Processor

An experimental characterization of Hall thruster current discharge oscillations when moderate levels of oscillations are superimposed on the discharge voltage is performed in both open loop and closed loop configurations. Investigations of the dynamic behavior up to 200 kHz were made possible by the use of a custom-designed high power voltage regulator and a strongly optimized digital controller implementation on a fast digital signal processor. This new experiment with proportional-integral-derivative control has confirmed the authors’ earlier findings that proportional (resistive) control provides very large damping of breathing oscillations at low voltages, although its eectiveness decreases at high voltages. The destabilizing eect of positive feedback was also studied and confirmed for pure proportional, integral and derivative feedback. Open loop operation shows, in turn, a very clear resonance around 20kHz, while its gain and phase behaviors present striking similarities with those of the predator-prey model of breathing oscillations.