Integrating rugged hybrid energy and power supplies in military UAVs

Story

August 05, 2024

In a combat unmanned aerial vehicle (UAV) platform, the power source primarily consists of an energy-storage system consisting of advanced batteries and high-voltage capacitors. The power source must meet the demand of mobility, lethality, survivability as well as for uses including command, control, communications, computers, intelligence, surveillance and reconnaissance (C4ISR).

The demand for electric power becomes even more challenging when the power draw must be provided solely from energy storage systems for extended range and periods of time. The power supply must be delivered in two forms, continuous for mobility and pulsed for the directed-energy weapons. Depending on the size and weight of the UAV, the continuous power requirements can range from a few tens to several hundreds of kilowatts (KWs) supplied by the prime battery system. The pulsed power needs can range from a few to hundreds of megawatts (MWs) depending on the loads and rep rates. In addition, the pulsed power loads require pulse forming networks (PFN), which impose another integration burden with their own space requirements.

Since electric power is used for continuous loads such as mobility and for pulsed loads such as electric weapons, it is necessary to have a common power and energy management system onboard the UAV to distribute electric power to various users according to a defined precedence strategy.

Creating a rugged military-ready power system

To design and integrate the various components for a combat-ready UAV system, it is important to consider critical and enabling technologies that include state-of-the-art high-temperature power electronics, high-energy-density and high-power-density batteries, high-voltage capacitors, and high-torque-density traction motors. These components and auxiliary systems need to be integrated within the power needs, loads, and size constraints of the UAV.

To meet the established goals for weight, volume, and power needs, aggressive design goals need to be pursued for the energy-storage systems as well as the associated power electronics, motor controllers, converters, inverters as well as the thermal-­management system. Another aggressive metric is needed for the pulse forming network (PFN), which must be optimized and minimized to install in the UAV. Integration of the power converters and the PFN hinges on leveraging wide bandgap semiconductors, such as SiC and GaN [silicon carbide and gallium nitride]. These types of semiconductors enable engineers to build converters that operate at high temperature, high frequency (50 kHz to 100 kHz), and higher efficiency.

For the PFN, another critical technology component is the use of compact, high-energy, and high-voltage-discharge capacitors that provide energy densities over 2 Joules/cc. The high-energy capacitors combined with SiC-based solid state switches provide significant reduction of PFN weight and volume.

Continuous power requirements

In a combat UAV, there are two primary users of continuous power – mobility and thermal management – in addition to other smaller loads. Power is supplied to most of the mobility and thermal loads from the prime mover, the battery-storage system. For optimum performance, the power is split between capacitor and battery for either best efficiency or burst power according to the specified duty cycle of the UAV.

Military UAVs must be able to operate under extreme environmental conditions, from the frigid temperatures of the Arctic Circle to the intense heat of deserts, as well as rough terrain conditions. They must withstand vibrations, shocks, and violent twisting experienced during travel and they must be able to operate for long periods of time with very little or no maintenance. Future UAVs must be lighter, faster, and more deployable but at the same time more lethal and sturdier. These constraints impose a departure from the traditional methods of making UAVs. Therefore, new enabling technologies should be integrated to meet the technical challenges of future vehicles.

Pulsed power requirements

Directed-energy weapons (DEWs) are electromagnetic systems that convert electrical energy into radiated energy, focusing it on targets to cause physical damage and neutralize adversaries. These include high-energy lasers (HEL) emitting photons and high-power microwaves (HPM) emitting radio-frequency waves. The military uses them for power projection and integrated defense missions. The effectiveness of DEWs is measured by their ability to reliably and precisely focus energy at range, producing controllable effects and measurable damage or mission defeat.

Integrating high-power microwave (HPM) devices into UAVs for targeting adversarial autonomous aircraft involves several complex technical challenges. Firstly, there is the issue of power management: HPM devices require a lot of energy, and providing a compact, lightweight, and efficient power source within the UAV’s limited payload capacity is critical. The integration also demands ruggedization: advanced thermal-management systems to dissipate the heat generated by HPM devices, ensuring they do not overheat or damage other onboard electronics.

Secondly, targeting precision is paramount. The HPM system must include sophisticated tracking and guidance systems to accurately lock onto fast-moving, potentially evasive UAV targets. This upgrade involves integrating advanced sensors and algorithms for real-time target acquisition and engagement. Moreover, designers must consider maintaining UAV stability and maneuverability while deploying the HPM system. The electromagnetic emissions from the HPM device can interfere with the UAV’s own electronics and control systems, necessitating robust electromagnetic shielding and isolation techniques. (Figure 1.)

[Figure 1 ǀ Real-time target acquisition and engagement on an unmanned aerial vehicle means adding sophisticated tracking and guidance systems, which involves advanced sensors and algorithms for delivery of data and video.]

Additionally, addressing potential countermeasures is crucial. Adversarial UAVs may employ shielding or other protective measures against HPM attacks, requiring continuous advancements in HPM technology to overcome these defenses.

Design considerations

Designing and integrating power supplies and energy storage systems for a military UAV equipped with a DEW system involves meticulous planning and consideration of multiple factors to ensure efficiency, reliability, and operational effectiveness. A hybrid electric platform is the most suitable type to use for power demand for both continuous and pulsed loads. Although the power management and distribution to both types of loads is feasible within the hybrid architecture, the integration burden could be challenging and depends largely on the pulsed load specifications.

The benefits of ruggedizing power supply and energy storage systems include:

• Extended ranges/durations: High-performance power systems enable military UAVs to operate over extended ranges and durations without the need for frequent recharging. This capability enhances the strategic mobility and endurance of military forces, enabling them to sustain operations in remote or austere environments for longer periods.
• Ability to integrate advanced technology payloads: Reliable and high-performance power systems enable the integration of advanced payloads into defense platforms, which include not only UAVs but also DEWs, high-power radar, and electronic countermeasures.
• Combating harsh electromagnetic environments: Defense UAV systems are often exposed to harsh electromagnetic environments that can interfere with sensitive electronics. High-quality power systems with built-in EMI [electro­magnetic interference] filtering and protection mechanisms ensure that critical equipment remains immune to external electromagnetic disturbances, maintaining operational integrity in hostile electromagnetic environments.
• Flexibility/scalability: Modern defense operations require flexible and scalable power solutions that can adapt to evolving mission requirements and operational environments. An appropriately designed, reliable power system gives the option of modular designs and scalability, enabling easy integration into a wide range of defense UAV platforms and applications.

Rugged design calls for balanced approach

Designing and integrating power supplies and energy storage systems for military UAVs with DEW systems necessitates a balanced approach that addresses high power demands, stringent reliability, and operational flexibility.

Integrating hybrid energy sources and high-performance power supplies in military UAVs is a design challenge that demands a comprehensive approach to ensure operational efficiency, reliability, and mission effectiveness. Key considerations must include the optimization of energy density and power-to-weight ratios, which are critical for extending flight endurance and enhancing payload capacities. By leveraging advanced battery technologies alongside capacitors, designers can achieve a balance between sustained power output and the ability to respond to peak demand scenarios. Additionally, the integration of sophisticated energy-management systems is essential to seamlessly coordinate the various power sources, ensuring that the UAV can autonomously switch between or combine them to maintain optimal performance under stressful, varying operational conditions.

Furthermore, the ruggedness and resilience of the power-supply systems must be prioritized to withstand the harsh environments and potential adversarial conditions typical of military operations. This includes using robust thermal-management solutions to prevent overheating and ensuring that all components meet stringent military standards for shock, vibration, and electromagnetic compatibility. The integration process should also emphasize modularity and ease of maintenance, allowing for rapid field repairs and upgrades. As these UAVs are often deployed in remote and hostile areas, the ability to quickly replace or service energy components can be crucial to mission success.

Ultimately, the successful integration of hybrid energy sources and high-performance power supplies will not only enhance the operational capabilities of military UAVs but will also give troops a significant strategic advantage through improved reliability, versatility, and endurance.

Carol Brower is Vice President of Operations at Custom Electronics Inc. (CEI), with more than two decades of experience in manufacturing operations. At CEI, she is responsible for management, fiscal oversight, audit preparation, human resources, process improvement, reporting, research, and analysis.

Pradeep Haldar serves as Management and Technology Commercialization Lead for Custom Electronics Inc. He has extensive experience in business development, strategic planning, research and development, financial and operations management, technology transfer, innovation, and technology commercialization. He has a Ph.D. from Northeastern University and an MBA from Rensselaer Polytechnic Institute.

Custom Electronics Inc. (CEI) • https://www.customelec.com/