How Electrification Is Changing Capacitor Selection

Capacitors have long performed fundamental functions in power electronics, including storing energy, smoothing voltages, and filtering the byproducts of switching. Those functions aren’t changing, but as electrification reshapes how electricity is generated, converted, and consumed, the conditions under which capacitors must perform them are becoming increasingly demanding.

As rotating generators give way to inverter-based resources and mechanical and electromechanical systems are rebuilt around power electronics, systems are incorporating more power conversion stages operating at higher voltages, switching frequencies, and power densities. As a result, capacitor selection increasingly requires engineers to look beyond capacitance alone and consider factors such as impedance, ripple current capability, thermal performance, operating lifetime, and energy storage duration.

Familiar Functions in New Applications

Two capacitor technologies are playing particularly important roles in these evolving power systems: film DC link capacitors and supercapacitors.

Film DC link capacitors provide both filtering and energy storage within power converters, inverters, motor drives, and onboard chargers. Supercapacitors provide fast, high-cycle energy storage that complements batteries in applications where power must be delivered or absorbed almost instantly.

As electrification advances, these familiar capabilities are taking on new importance in emerging applications such as:

• Solid-state transformers (SSTs), where multiple power conversion stages create additional requirements for DC link filtering and energy storage
• E-STATCOMs, which combine power electronics with energy storage to support both voltage and frequency response
• Virtual inertia systems, where fast energy storage can help replace some of the stabilizing effects traditionally provided by rotating generators.
  

Designing for More Demanding Power Systems

These applications illustrate a broader change in capacitor design requirements. Filtering is moving to higher frequencies, making equivalent series resistance (ESR), equivalent series inductance (ESL), and impedance across frequency increasingly important. At the same time, energy storage requirements are stretching from millisecond-scale bursts toward seconds-long support for functions such as ride-through and grid stabilization. In the end, the underlying capacitor functions remain familiar, but engineers must perform them under increasingly demanding electrical and thermal conditions.

Download our full white paper, Familiar Jobs, Harder Conditions: How Electrification Is Redefining the Capacitor’s Role, to learn more.