The HPPC test is a controlled sequence of high-current discharge and charge pulses performed at multiple battery charge levels. On a laboratory battery testing platform, the cell is fully charged, moved through defined Depth of Discharge (DOD) or State of Charge (SOC) steps, and subjected to short current pulses while voltage, current, and temperature are recorded at high speed. The resulting voltage response is used to determine internal resistance and calculate the battery’s allowable peak discharge and charge power before reaching voltage limits.
Core takeaway: HPPC testing converts transient voltage response into a map of dynamic resistance and usable power across SOC or DOD. Peak power is limited by both the battery’s effective resistance and the minimum or maximum permitted terminal voltage.
What the HPPC Test Measures
Dynamic power capability
HPPC characterizes how much power a cell, module, or pack can deliver or accept for a short period.
It is more representative of real operation than a slow capacity test because it captures voltage sag during acceleration-like discharge and voltage rise during regenerative charging.
Internal resistance and impedance
The test identifies the effective resistance associated with discharge and charge pulses.
More detailed analyses may also extract ohmic resistance, polarization resistance, transient capacitance, and Area Specific Impedance (ASI) for use in equivalent-circuit models.
Power across SOC or DOD
The test is repeated across the usable battery range, commonly in 10% SOC or DOD increments.
This produces discharge-power and charge-power curves that show where the battery has the greatest and least dynamic capability.
How the Test Is Performed on a Laboratory Platform
1. Connect and configure the test article
The cell, module, or pack is installed in a suitable test fixture and connected to a programmable battery cycler.
The platform should provide accurate bidirectional current control, fast sampling, temperature monitoring, and sufficient voltage and current range for the test article.
2. Fully charge the battery
The test typically begins with a complete charge using the required charging protocol.
After charging, the battery is allowed to rest so that electrochemical and thermal transients can settle and the measured voltage approaches an open-circuit condition.
3. Move through DOD or SOC steps
The battery is discharged in defined increments, commonly 10% DOD per step.
A constant-current discharge is used to reach each target point, followed by a rest period—often approximately one hour in the stated procedure—before the pulse sequence is applied.
4. Apply the pulse sequence
At each DOD point, the platform applies a controlled pulse sequence:
- A short discharge pulse, typically 10 seconds.
- A rest period to observe voltage recovery.
- A short charge or regeneration pulse, typically 10 seconds.
- A further rest period, if required by the selected protocol.
The exact pulse current and rest duration depend on the applicable standard, cell chemistry, and test objective. Example current levels include 25% of the maximum current for a lower-current test or 75% for a higher-current test.
5. Record fast voltage and current data
The system records current, terminal voltage, elapsed time, and temperature throughout each pulse.
Fast sampling is important because the initial voltage change may occur within milliseconds, while slower voltage changes reflect polarization and diffusion effects.
6. Repeat across the operating range
The charge, rest, discharge, and rest sequence is repeated at each selected SOC or DOD point.
The result is a set of resistance and power values indexed by battery operating condition.
How Internal Resistance Is Calculated
Discharge resistance
During a discharge pulse, the current increase causes the terminal voltage to fall.
A basic effective discharge resistance can be calculated from the voltage change and current change:
[ R_{\text{discharge}} = \frac{\Delta U_{\text{discharge}}}{\Delta I_{\text{discharge}}} ]
For a pulse beginning from an approximately open-circuit voltage:
[ R_{\text{discharge}} \approx \frac{U_{\text{OCV}}-U_{\text{pulse}}}{I_{\text{discharge}}} ]
The precise value depends on which point in the pulse is used. An initial value emphasizes ohmic resistance, while a later value includes more polarization and diffusion effects.
Charge resistance
During a charge pulse, the terminal voltage rises toward the upper voltage limit.
The effective charge resistance is calculated similarly:
[ R_{\text{charge}} = \frac{\Delta U_{\text{charge}}}{\Delta I_{\text{charge}}} ]
Using the open-circuit voltage as the reference:
[ R_{\text{charge}} \approx \frac{U_{\text{pulse}}-U_{\text{OCV}}}{I_{\text{charge}}} ]
Charge and discharge resistance are not necessarily equal. Electrode polarization, diffusion, temperature, SOC, and the direction and duration of the pulse can produce different values.
Model-based parameter identification
For more detailed characterization, the pulse data can be fitted to an equivalent-circuit model such as a Thevenin or PNGV model.
These methods can estimate parameters including:
- Open-circuit voltage, (U_{\text{OCV}})
- Ohmic resistance, (R_0)
- Polarization resistance, (R_P)
- Transient capacitance, (C_P)
The model parameters can then be used to estimate real-time State of Power rather than only reporting a single measured pulse result.
How Peak Discharge Power Is Calculated
Determine the maximum permissible current
During discharge, the terminal voltage must not fall below the minimum allowable voltage, (U_{\min}).
Using an effective discharge resistance:
[ I_{\text{discharge,max}} = \frac{U_{\text{OCV}}-U_{\min}} {R_{\text{discharge}}} ]
This is the highest current predicted to bring the terminal voltage to the lower voltage limit.
Calculate the corresponding power
The battery terminal voltage at this limiting condition is (U_{\min}). Therefore:
[ P_{\text{discharge}} = U_{\min} \cdot I_{\text{discharge,max}} ]
Substituting the current expression gives:
[ \boxed{ P_{\text{discharge}} = \frac{ U_{\min} \left(U_{\text{OCV}}-U_{\min}\right) }{ R_{\text{discharge}} } } ]
This is the peak discharge power under the stated voltage-limit and resistance assumptions.
Interpretation
Discharge power increases when:
- (U_{\text{OCV}}) is higher.
- (R_{\text{discharge}}) is lower.
- The allowable voltage window is wider.
The calculation is performed at every SOC or DOD point, producing a discharge-power capability curve.
How Peak Charge Power Is Calculated
Determine the maximum permissible charge current
During charging, the terminal voltage must not exceed the upper allowable voltage, (U_{\max}).
Using the effective charge resistance:
[ I_{\text{charge,max}} = \frac{U_{\max}-U_{\text{OCV}}} {R_{\text{charge}}} ]
This is the largest charging current predicted to bring the terminal voltage to the upper voltage limit.
Calculate the corresponding power
At the limiting condition, the terminal voltage is (U_{\max}). Thus:
[ P_{\text{charge}} = U_{\max} \cdot I_{\text{charge,max}} ]
Substituting the current expression gives:
[ \boxed{ P_{\text{charge}} = \frac{ U_{\max} \left(U_{\max}-U_{\text{OCV}}\right) }{ R_{\text{charge}} } } ]
This represents the maximum short-duration charge or regenerative-braking power under the selected voltage and resistance assumptions.
Interpretation
Charge power generally decreases as SOC increases because the open-circuit voltage moves closer to the upper voltage limit.
With less voltage headroom available, the allowable charge current falls even if the cell’s resistance remains unchanged.
What the Laboratory System Must Control
Pulse accuracy
The cycler must generate the commanded current quickly and accurately.
Current overshoot, slow rise time, or control instability can distort the measured voltage response and produce an incorrect resistance estimate.
Sampling speed
The system must capture both the immediate voltage step and the slower transient response.
Insufficient sampling speed can miss the initial voltage drop and underestimate the ohmic component of resistance.
Temperature
Cell temperature should be measured continuously and, where necessary, controlled.
Resistance and power capability are strongly temperature-dependent, so results from different temperatures should not be compared without qualification.
Fixture and wiring resistance
The measured response includes not only the cell but also cables, contacts, busbars, and fixtures.
Four-wire sensing, suitable current paths, and fixture compensation are important when measuring milliohm-level resistance.
Understanding the Trade-offs
A simple resistance model is useful but limited
The equations above treat the battery as an open-circuit voltage source in series with an effective resistance.
This is practical for calculating pulse-power limits, but it does not fully represent time-dependent polarization, diffusion, hysteresis, or temperature behavior.
Pulse duration changes the result
A 10-second pulse, a 30-second pulse, and a high-rate pulse lasting only a few seconds will not necessarily produce the same resistance or power capability.
Longer pulses include more polarization and diffusion effects, so the selected duration must match the intended application.
Charge and discharge values are asymmetric
It is incorrect to assume that charge resistance equals discharge resistance.
The two directions can experience different electrochemical limitations, and regenerative charging may be restricted by voltage rise even when discharge power remains high.
Voltage limits are not the only limits
The calculated power must also be checked against:
- Maximum allowable current
- Battery temperature limits
- Manufacturer charge and discharge limits
- Safety constraints
- Aging and State of Health
- Pack-level cell imbalance
The final usable power limit is the most restrictive of these constraints.
SOC and DOD must be defined consistently
SOC describes the remaining charge, while DOD describes the portion already removed.
A test reported in DOD increments must be mapped carefully if the results are later used in an SOC-based battery-management system.
Cell-level results do not directly equal pack-level performance
A module or pack has additional resistance from interconnects, busbars, fuses, contactors, and cell imbalance.
Pack-level HPPC testing or a validated scaling model is needed for reliable system-level power limits.
Making the Right Choice for Your Goal
The correct HPPC implementation depends on whether the objective is screening, modeling, qualification, or battery-management-system development.
- If your primary focus is quick power screening: Use a repeatable pulse sequence at defined SOC or DOD points and calculate effective charge and discharge resistance from the measured voltage response.
- If your primary focus is equivalent-circuit modeling: Use high-rate sampling and fit the pulse data to a Thevenin or PNGV model to separate ohmic and polarization behavior.
- If your primary focus is regenerative-braking capability: Pay particular attention to charge resistance, upper voltage limits, temperature, and the reduction in charge power at high SOC.
- If your primary focus is pack design: Test representative modules or packs and include interconnect resistance, thermal conditions, cell imbalance, and system current limits.
- If your primary focus is accurate comparison between chemistries: Keep pulse duration, current level, rest time, temperature, SOC/DOD definition, and voltage limits identical.
A well-controlled HPPC test turns transient battery behavior into defensible resistance, current-limit, and peak-power data across the full operating range.
Summary Table:
| Step | Action | Purpose |
|---|---|---|
| 1 | Connect and configure the test article | Ensure accurate bidirectional current control and data logging |
| 2 | Fully charge the battery | Start from a known state with settled open-circuit voltage |
| 3 | Move through DOD/SOC steps | Discharge to target levels, rest for stabilization |
| 4 | Apply pulse sequence | 10s discharge, rest, 10s charge, rest |
| 5 | Record fast voltage/current data | Capture transient response for resistance and power calculation |
| 6 | Repeat across SOC/DOD range | Build power capability curve across operating range |
Key Calculations:
- Discharge Resistance: ( R_{dis} = \frac{U_{OCV} - U_{pulse}}{I_{dis}} )
- Charge Resistance: ( R_{chg} = \frac{U_{pulse} - U_{OCV}}{I_{chg}} )
- Peak Discharge Power: ( P_{dis} = \frac{U_{min}(U_{OCV} - U_{min})}{R_{dis}} )
- Peak Charge Power: ( P_{chg} = \frac{U_{max}(U_{max} - U_{OCV})}{R_{chg}} )
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