As Artificial Intelligence (AI) data centers transition into the era of high-performance computing, the power consumption of a single AI server rack has surged from a traditional 10kW to over 200kW. When navigating the Electrical Design Power peak (EDPp) generated by GPU workloads, systems demand instantaneous power compensation. Consequently, the Power Capacitor Shelf (PCS) has become an indispensable solution. By utilizing electric double-layer capacitors (EDLCs) for instantaneous high-power discharge, the PCS provides "peak shaving and valley filling" capabilities, ensuring stable power output under dynamic heavy current loads.

The Critical Impact of ESR on PCS Design

In PCS system design, the equivalent series resistance (ESR) of the EDLC is the fundamental physical quantity determining power performance. The impact of ESR is no longer confined to the individual cell level; once cells are assembled into modules, minute resistance deviations produce a cumulative effect. This leads to non-linear deviations at the module design level, amplifying power loss and thermal risks. ESR is closely correlated with the following four parameters:

1. Maximum Power: Power output limits are inversely proportional to ESR.
2. Runtime: As ESR increases, voltage drops intensify, causing the system to reach the cutoff voltage prematurely and shortening actual runtime.
3. Self-Heating: ESR is the primary cause of energy converting into heat, significantly impacting system-level thermal management.
4. Lifetime: Higher ESR leads to increased temperature rise, accelerating EDLC degradation and shortening its lifespan.

Addressing Measurement Discrepancies in International Standards

Currently, the industry evaluates EDLC ESR using three mainstream standards:

1. IEC 62391: Focuses on voltage drop measurements during constant current discharge.
2. Maxwell Six-Step Method: Captures voltage differences through discharge and rest phases.
3. QC/T 741: Calculates pulse characteristics specifically for traction capacitors (Figure 1).

These three standards can typically be met using standard charge-discharge testing equipment. However, ESR measurement faces a technical paradox: to achieve high data precision and stability, conventional testers often apply "moving average" algorithms to filter signal noise. Nevertheless, because ESR is resistive, it relies heavily on the equipment's ability to capture transient changes. Excessive data smoothing can lead to an underestimation of the EDLC potential transient, resulting in underestimated ESR values (Figure 2). When products undergo dual verification by end customers on actual machines, unexpected gaps between actual power capability and nominal specifications can emerge, leading to design failure or the risk of being disqualified from the supply chain.

▲[Figure 1] ESR measurement diagram: IEC 62391 standard, Maxwell six-step method, and QC/T 741 standard

▲[Figure 2] Diagram of ESR measurement differences caused by over-smoothed data

Chroma's Solution: High-Resolution Transient Capture

To address the limitations of conventional data processing methods, Chroma has developed specialized testing functions for EDLCs ranging from 200µA to 2400A, fully compliant with international standards. By utilizing firmware-level data acquisition with 1ms resolution, Chroma systems precisely capture  instantaneous voltage changes during transitions. The system automatically calculates ESR and capacitance, integrating these results directly into test reports. This design provides R&D engineers with high-fidelity ESR data, eliminating design deviations and potential risks in PCS modules caused by measurement distortion.

For more information on the full capabilities of the Chroma 17010/17010H Battery Reliability Test Systems, or to learn more about our solutions for preventing data over-averaging, please visit our official website linked below.