Experimental Comparison of Direct and Active Throttle Control of a 7 kW Turboelectric Power System for Unmanned Aircraft

Abstract

This article compares direct turbine throttle control and active turbine throttle control for a turboelectric system; the featured turboprop is rated for 7 kW of shaft output power. The powerplant is intended for applications in unmanned aerial systems and requires a control system to produce different amounts of power for varying mission legs. The most straightforward control scheme explored is direct turbine control, which is characterized by the pilot controlling the throttle of the turbine engine. In contrast, active control is characterized by the turbine reacting to the power demanded by the electric motors or battery recharge cycle. The transient response to electric loads of a small-scale turboelectric system is essential in identifying and characterizing such a system’s safe operational parameters. This paper directly compares the turbogenerator’s transient behavior to varying electric loads and categorizes its dynamic response. A proportional, integral, and derivative (PID) control algorithm was utilized as an active throttle controller through a microcontroller with battery power augmentation for the turboelectric system. This controller manages the turbine’s throttle reactions in response to any electric load when applied or altered. By comparing the system’s response with and without the controller, the authors provide a method to safely minimize the response time of the active throttle controller for use in the real-world environment of unmanned aircraft.

Integration and Flight Test of a 7 kW Turboelectric Vertical Take-Off and Landing Unmanned Aircraft

“…The turboelectric hybrid system includes a turbine engine with a mechanical response rate measured in seconds, whereas the battery and electrical power system have a response rate measured in microseconds. Therefore, an active throttle scheme was utilized that controlled the turbine engine based on the demands of the electrical system [16,17]. A controller reads the voltage of the system and throttles the turbine engine based on whether or not the system is under load.…”

“…Subsequent work was done to refine and measure the performance of three different turboelectric systems for unmanned aircraft [16]. The reader is directed to the previous work for details regarding the control scheme and experimental validation of the active throttle control system used to govern the turbogenerator inside the test vehicle utilized in the current study [17].…”