Date of Award

August 2018

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical and Aerospace Engineering


Thong Q. Dang

Second Advisor

Tomislav Bujanovic


hybrid power, nonlinear control, power systems, Propulsion, transitional flight, VTOL

Subject Categories



This research effort explores the interactions between aerodynamics and hybridelectric power system (HEPS) design and control for vertical takeoff and landing (VTOL) aircraft applications. Specifically, this research focuses on embedded distributed electric propulsion systems, for which the aerodynamic forces and moments are inextricably linked to power input.

This effort begins by characterizing the performance of two similar embedded propulsion systems using computational fluid dynamics (CFD). From this initial analysis, a wind tunnel model is constructed and the systems are tested across the operating conditions required to characterize the performance of a VTOL aircraft, where 0 deg ≤ α ≤ 90 deg. One of these configurations is selected for evaluating the interaction with the hybrid-power system.

An experimental HEPS is constructed based on a small two-stroke internal combustion engine as well, with a rated continuous power output of 2kW. This experiment is used to develop a validated dynamical HEPS model in MATLAB and Simulink, where the control systems are refined and the performance of the system is extended to accommodate the VTOL power demand during transitional flight. A robust control design is developed using a second order sliding mode controller (2-SMC), implemented using the super-twisting algorithm and integrated with classical linear control schemes in an interleaved-cascade architecture. The resulting system has a variable voltage output and a robust response to rapid changes in power demand. Additionally, the HEPS is also demonstrated to fully utilize the mechanical power output capability of the two-stroke engine.

Ultimately, the HEPS is demonstrated, via the dynamical model, to be capable of supplying power for an embedded propulsion VTOL aircraft. This performance is further extended with the addition of an actively controlled slack bus, utilizing battery energy storage and a buck-converter integrated with the HEPS control system. In this configuration, the peak power demands of the system can exceed the maximum sustained power threshold (MSPT) of the HEPS.


Open Access

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