This paper proposes a novel proportional-integral-derivative (PID) control approach that enables variable ballast systems on an autonomous underwater vehicle (AUV) to complement the underwater vehicle's hydroplanes when altitude-keeping over a variable seabed. This control approach is tested on an AUV computer simulator that features a variable ballast system model, which includes the capacity for free flow of seawater into and out of the ballast tank. The new control approach uses hydroplane deflection angle feedback as inputs to the variable ballast system controller in combination with a lowpass filter to ensure that the variable ballast system does not react to high hydroplane deflection rates and unnecessarily deplete the underwater vehicle's onboard energy supply. For the conditions modeled in this research, the resulting simulation case studies showed that this control approach enables the variable ballast system to effectively return control authority back to the hydroplanes while altitude-keeping to a variable seabed. [ABSTRACT FROM AUTHOR]
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