AC vs. DC Power: Understanding the Different Electrical Systems Used in Aircraft

Modern aircraft rely on complex electrical systems to power everything from essential flight controls to passenger conveniences. At the very center of this electrical infrastructure are alternating current (AC) and direct current (DC), two fundamental types of power that bring their own unique advantages and limitations to aviation system design. Read on as we delve further into what AC and DC power are, how they contribute to aircraft performance, and how they generally tend to be implemented.

DC Power in Aviation

DC power has been a foundational part of aviation electrical systems since the earliest aircraft. Flowing in one direction, this power type is known to provide consistent voltage with relatively simple control mechanisms. This stability makes it indispensable in smaller aircraft and rotary-wing platforms, and it remains vital in larger airframes for powering essential systems during non-standard conditions.

DC systems are typically supported by a combination of onboard and external sources that ensure steady voltage delivery, including aircraft batteries, auxiliary power units (APUs), and ground power units (GPUs). Batteries act as a power source when engines are off, assisting start-up sequences or standby systems. Similarly, APUs function as onboard generators when the engines are offline during taxiing or preflight operations. Meanwhile, GPUs supply DC power externally during ground maintenance or preflight preparations to preserve onboard resources. Together, these accessories allow DC systems to seamlessly support tasks like:

• Powering avionics during engine-off conditions
• Operating electric actuators in flight control surfaces or landing gear systems
• Delivering backup power for flight-critical systems and emergency lighting in emergencies

Challenges and Modern Adaptations

Despite its reliability, DC power is less efficient for long-distance transmission. It requires heavier cabling to prevent voltage drops over extended runs, adding unwanted, excess weight to aircraft. To address this, modern aircraft incorporate DC-to-AC inverters and hybrid distribution systems that enable selective conversion, delivering DC directly to low-voltage systems while converting it to AC where higher voltage is necessary. Moreover, advancements in solid-state electronics have empowered DC power systems to offer better voltage control, fault tolerance, and overall system integration.

AC Power in Aviation

In contemporary aircraft, AC power systems are usually the primary electrical source for their ability to transmit high voltage over long distances using relatively lightweight cabling. AC current alternates direction periodically, typically at 400 Hz in aviation–compared to the 50 or 60 Hz standard on the ground–allowing for the use of smaller, lighter transformers and motors. Usually generated by engine-driven or APU-driven alternators, AC power is used to support numerous high-demand systems, such as:

• Cabin and cockpit lighting systems
• Hydraulic pump motors that actuate essential systems like landing gear and flight control surfaces
• Galley equipment, including ovens, coffee makers, and refrigeration units
• Environmental control systems (ECSs) like compressors, fans, and heaters

Limitations and System Considerations

While AC power systems excel at transmitting energy over long distances, supporting high loads, and facilitating scalable layouts, they introduce more complexity in regulation. Rapid load fluctuations can cause voltage spikes or drops, leading to harmonic interference or distortion that can disrupt sensitive electronics. Additionally, as AC frequency is tied to generator speed, it can be difficult to maintain consistent output during varying flight phases like startup or descent. To overcome these challenges, modern aircraft incorporate support systems like:

• Power Conditioning Units (PCUs): These devices regulate and filter the electrical output from generators to ensure a clean waveform, protecting sensitive electronic subsystems from degradation or malfunction.
• Solid-State Power Controllers (SSPCs): Replacing traditional circuit breakers and relays, SSPCs offer precise digital control over power distribution. These devices serve to quickly isolate faults, reduce wiring complexity, and optimize load management.
• Frequency Converters: These systems decouple power output from generator speed, allowing for stable frequency output regardless of engine RPM. This is especially useful in variable-speed configurations and in aircraft that use a combination of AC and DC power systems.

The Integration and Coexistence of Power Types

Rather than choosing one over the other, modern aircraft merge AC and DC systems to take advantage of each type’s strengths. DC power remains ideal for low-voltage applications that demand consistency, such as avionics, emergency systems, and linear actuators. Meanwhile, AC power is preferred for high-load systems requiring efficient transmission and compact component design, such as ECS units and hydraulic systems. By allocating AC and DC power strategically across different subsystems, designers can mitigate the limitations of each and introduce redundancy, allowing for far more flexible operation across diverse flight conditions.

Veritable Aerospace: A One-Stop Shop for Avionics and More

Whether part of an AC, DC, or combination system, every electrical component onboard an aircraft must adhere to rigorous standards for compliance and durability under the challenging conditions of flight. Veritable Aerospace, an ASAP Semiconductor-owned platform, stands out as a dependable source for high-quality electrical components and a broad range of other aviation products that come from leading manufacturers.

Our platform is easy to navigate, presenting offerings by familiar designations like NSNs, part types, AS standards, and more. Beyond our expansive inventory, we are committed to streamlining fulfillment and meeting specialized requirements with tailored solutions. Knowing that we boast quality assurance, competitive procurement options, and expert support, do not hesitate to check out our selection and get in touch with our specialists.