ePropelled White Paper – Introduction and download link posted with permission from ePropelled.

Introduction

Electrical power systems are critical to a UAV’s design and operation. Weight, operating temperature and efficiency of the power components have a major influence on performance parameters such as flight duration, payload, operating ceiling and range.

The choices in selecting an electric power system are dictated largely by the duration of continuous and peak power requirements for the mission profile. Unlike many other UAV subsystems, the power system supports both the platform and the payload. Depending on the mission, the payload will require electrical power while in flight. This power demand may range from tens or hundreds of watts for sensors or communications, or it may be tens of kilowatts or more for complex payloads.

Thermal management is also a consideration because much of the thermal load is often generated by electrical devices. The operation of hydraulic system components and other actuators is also closely related to electrical system design requirements for peak versus average power.

Electrical power is generated by a starter generator which is a critical component for ensuring the electrical system can meet the design objectives of the aircraft. The starter generator is mounted on the engine so that the drive shaft turns the rotor to produce electricity or connected to the engine via mechanical means such as a belt system.

If the electrical machine is only used to generate power for the onboard systems, it may be referred to as an alternator. A starter generator is also capable of starting the internal combustion engine (ICE) itself. It would be paired with an Electronic Engine Starter, a power electronics component that provides the commutation to the starter generator in order to rotate the ICE shaft to the cranking speed and torque.

Starter generators produce 3-phase AC voltages that varies with RPM and load. These are converted to DC voltage output by a Power Management Unit (PMU) or an intelligent Power System (iPS) which uses active rectification and regulation to supply outputs of one or more DC voltages from the variable AC input. Different onboard systems require different DC voltages. For example, the payload may use 12 volts while the avionics may use 5 volts.

A battery pack stores energy to ensure a continuous supply over the required minimum operating time. It can also be used for power to start the engine.

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