### Background  
Few small-scale turbine-based power systems are rated for approximately under 30 kW of power production. Turbine powerplants are commercially available, ranging near the 30 kW capability intended for grid power applications. However, those from Capstone turbines are not designed for UAS applications and tend to be too heavy for said uses. The turboelectric variant of the commercial Monarch 5 turboprop is the only other system of a similar class that may be flightworthy to the authors' awareness. However, publicly available information is limited, and the system does not appear to have been flown.  
Because of this market gap, there were no commercially available turboelectric systems for UAS applications. The team had to modify an existing turbopro to act as the powerplant. The turbopro's output shaft was modified to drive a generator instead of a propellor, as typically suited. The turbine used for experimentation is a model K-60 TP. According to Kingtech, the manufacturer, this engine can produce approximately 7.3 kW of shaft power at approximately 7000 RPM. This constraint meant that the team had to design the electrical portion of the turboelectric system from the ground up to operate at this design point. It also meant implementing a way to control the turbine to operate the turbogenerator effectively was needed.  
Research has been conducted at Oklahoma State University for active throttle control for UAS turboelectric systems [18; 19]. The need for a dynamic, transient throttle control had been identified in this paper, and there was a preliminary attempt to implement a throttle controller. Some challenges were highlighted, and a fully realized controller was not implemented.  
Figure 2: A basic schematic of the turboelectric system. The meter-controller determines the throttle sent to the turbine.  
The active throttle control implemented in this paper directs the turboelectric system without input from the pilot. The source voltage from the rectifier bus of the turboelectric system is used as the input variable for the active throttle controller. The voltage must be maintained within a particular window to ensure safe operation for the entire system. Each component must be sized and appropriated to fit within the voltage constraints of the system. This voltage window also acts as the target voltage margin for the throttle controller, with the median being the target voltage. The controller monitors the source voltage and responds, as necessary, with the proper PWM throttle signal to the turbine electronic control unit to maintain the desired system source voltage.  
Characterized by the velocity constant of the electric generator, \(K_{V}\), the rotational velocity of the output shaft of the turboprop is directly proportional to the generator's voltage production because of the mechanical coupling of the output shaft to the generator. For example, if the known supplied voltage to an electric motor under no load is multiplied by that motor's \(K_{V}\) value, then one would derive the instantaneous angular velocity of said motor. This detail is essential when compiling and sizing the various components that make up the turboelectric system.  
With the application of an electric load to the turboelectric system, the generator rotational speed will lower as the electric motor uses increased torque levels on the turbine shaft, and the electric demand increases. This reduction in angular velocity results in a measurable source voltage drop from the turbogenerator combination. A sudden voltage increase, or \"spike\", can occur when an electric load is removed or reduced. The active throttle controller monitors these voltage discrepancies and reacts accordingly to maintain the proper system voltage. The relationship between an electric motor's \(K_{V}\), voltage, and \(RPM_{Mot}\) is detailed in Equation (1) [20].  
\[RPM_{Mot}=K_{V}*V_{mat} \tag{1}\]