Analysis and design of the flight control system for battery powered mini drones.

Abstract

This doctoral dissertation studies how the electrical subsystem of a battery-powered quadrotor mini drone affects its altitude and attitude dynamics, and how to compensate for the negative effects on the performance caused by the drop in battery voltage during flight. The presented study shows that the closed-loop dynamic behavior degrades as the battery discharges during flight, due to the electrical subsystem being ignored during the flight controller design phase. A study of the relevant bibliography is conducted, showing that this research topic is of interest to the academic community, but has not been explored to the degree presented in this work. A model of a battery-powered quadrotor is constructed, from which a mathematical analysis is conducted showing how the electrical subsystem parameters and the battery discharge affect the closed-loop altitude and attitude dynamics. This system model included the modeling of a LiPo battery, which resulted in the proposal of a lumped parameter model for this type of battery. The mathematical analysis of the quadrotor model showed that the system dynamics get slower as the battery discharges. Compensation for this effect is proposed through two approaches: a battery-aware controller design and by generating the motor commands based on the actual battery voltage instead of the nominal voltage value. A discussion is conducted regarding the impact of the aggressiveness of the attitude controller reference dynamics over the energy consumption, stating that the more aggressive controllers lead to a slower battery discharge. These proposals were tested in simulated and experimental environments using a Parrot Mambo mini drone. The results showed that the proposed compensation techniques positively impacted both the altitude and attitude loops, resulting in a consistent closed-loop behavior for different battery voltage values, along with a smaller steady-state error. The effect of the proposed compensation approaches over the attitude loop was less pronounced than over the altitude loop. These improvements present a trade-off in the form of increased energy consumption. The choice of a more aggressive control strategy when performing a test flight was shown to result in a slower battery discharge when compared to a less aggressive one.