Discharge Current Amplitude Detection in Power Processing Units for Hall Thrusters

Discharge current oscillation in Hall thrusters can cause noise or, in the worst case, severe damage to the satellite. An amplitude detection system senses the discharge current and can shut off the thruster if excessive oscillations occur. The system divides a waveform 100 ms long and sampled at 1 MHz into 1000 segments and calculates the current amplitude in each segment. Next, a Power Processing Unit (PPU) calculates the number of segments where the current threshold is exceeded and determines whether the thruster should stop running. The proposed system was installed in a PPU2, PPU for 6 kW thrusters, and PPU Technology Development Unit 2 (PPU-TDU2) for 1 kW thrusters. In a test of the PPU2, the system detected 905 peaks over the threshold of 5.1 A during the 100 ms period, which agrees with the actual number of peaks, 931. In addition, the thruster can be automatically changed to a state with a low-amplitude discharge current by changing the magnetic field. In a test of the PPU-TDU2, the maximum amplitude of 4.3 A calculated by the system agreed well with the peak value of 4.07 A calculated from the current waveform on an oscilloscope. These results reveal that the amplitude detection system is sufficiently accurate for thrusters of different power levels.