The 'Hybrid Pulse Power Characterization (HPPC) Test' is a test employed in battery performance characterization. It provides data for battery management systems (BMS) to assess cell performance, particularly the maximum deliverable power & state of charge (SOC). It primarily focuses on assessing the battery's ability to deliver & absorb power, establishing its power limits, & identifying the changes in its parameters with respect to the state of charge (SOC).
The HPPC test involves applying a current pulse to the battery while recording the voltage response. The current pulse includes a discharge pulse followed by a relaxation period & then a charge pulse. This sequence is repeated at various SOC levels to comprehensively characterize the battery's performance over its entire operating range.
The power pulses reflect typical usage conditions, such as accelerating or braking in an electric vehicle, & the test identifies the maximum power the battery can deliver or absorb under these conditions.
✔️Normal Procedure of HPPC Test:
The HPPC test begins with the battery at full charge, and the initial SOC is noted. A discharge pulse, typically around 10% of the battery's capacity, is applied for a specific duration (for instance, 10 seconds). Following the pulse, the battery is allowed to relax for a certain period (e.g., 40 seconds), during which no current is drawn.
Subsequently, a charge pulse of the same magnitude & duration as the discharge pulse is applied, followed by a similar relaxation period. This sequence is known as a 'pulse pair'.
The pulse pair sequence is repeated at different SOC levels (for example, every 10% SOC decrease), until the battery is fully discharged. The voltage responses to the pulse pairs across different SOC levels are then analyzed to characterize the battery's performance.
✔️Interpreting HPPC Data:
The HPPC test provides various pieces of critical data about the battery's performance, including:
1. Pulse resistance (Rp): This is calculated as the change in voltage divided by the change in current during the pulse. This value is crucial as it represents the instantaneous internal resistance of the battery during high current operations.
2. Pulse power: This is the maximum power the battery can deliver or absorb during the pulse, calculated by multiplying the pulse current by the voltage just before the pulse.
3. Change in SOC: The SOC decreases after a discharge pulse & increases after a charge pulse. By monitoring these changes, we can evaluate the battery's efficiency in delivering and absorbing power.
4. Open-circuit voltage (OCV) and state of health (SOH): By examining the voltage response during the relaxation period, the battery's OCV can be inferred, which in turn gives an indication of the battery's SOC. Changes in OCV at the same SOC over time can also provide information about the battery's SOH.