• Fast discharge
• Continuous Fast discharge

This thesis provides contributions for a general description for the derivation of a non-contacting charge estimation and discharge actuation algorithm for the LISA Pathfinder test masses free-flying in a gravitational field in open space. The estimation principle is based on the application of forces that depend on the charge present on the mass. The discharge principle is based on the photoelectric emission of surfaces illuminated by UV light. The discharge actuation can be supported via the application of constant bias voltages.
The content of this work contributes to the derivation of a linearized time variant model valid for any combination of constant or variable voltages that could be present on the electrodes surrounding the test mass. In particular this thesis investigates the application of constant voltages and sinusoidal test signal voltages simultaneously, such that charge estimation and discharge actuation supported by constant bias voltages is possible.
Furthermore, the discharge process is analyzed in order to obtain a model suitable for on-board utilization. As a result of this analysis, possible improvements of this model are provided and discussed.
Integral part of this thesis is the identification of a control scheme that is able to perform discharge actuation in the fastest way possible. Therefore, a closed-loop control scheme has been designed which is based on continuously estimating the test mass charge and to apply discharge actuation using constant bias voltages at the same time. Finally, the designed fast discharge closed-loop control scheme is traded against an alternative approach currently used as a baseline. This baseline scheme sequentially estimates the test mass charge and then discharges it. The two strategies are compared in terms of robustness against uncertainties in the plant, afterwards as well as in terms of discharge duration.