Hybrid Pulse Power Characterization (HPPC) Testing with Arbin MITS Pro

1Introduction to HPPC Testing

The HPPC test is defined in the US Department of Energy battery test manuals for hybrid and electric vehicles [1][2]. A short discharge pulse and a short charge (regen) pulse are applied at a series of SOC levels and the voltage response is recorded. The voltage change during each pulse gives the discharge resistance and regen resistance at that SOC, from which the pulse power that the battery can deliver or absorb within its voltage limits is calculated [1].

Capacity measurements quantify stored energy but not the rate at which energy can be delivered or accepted. HPPC provides this information and is used to:

• set the power limits a battery management system (BMS) allows at each SOC;
• parameterise the equivalent circuit models used for SOC and state-of-health estimation [5][6];
• compare cell designs, chemistries or suppliers;
• track resistance growth as a cell ages.

Cell resistance increases and pulse power decreases at lower temperature [4]; HPPC is therefore performed at a controlled temperature and repeated at each temperature of interest.

2HPPC Methodology

2.1HPPC Pulse Profile

The HPPC pulse profile is a 10-second discharge pulse, a 40-second rest and a 10-second regen pulse at 75% of the discharge current [1][3]. In a full test the profile is applied at every 10% SOC step; between steps the cell is discharged at a constant rate and rested for one hour, so that each pulse starts from a relaxed, near open-circuit condition [1].

2.2Pulse Resistance and Power Calculation

With t₀ just before the discharge pulse, t₁ at the end of the discharge pulse, t₂ at the end of the rest and t₃ at the end of the regen pulse (Figure 1) [1]:

OCV_dis and OCV_regen are the rested voltages before the discharge and regen pulses. Plotted against SOC, these values give the resistance and pulse power curves of the cell.

The measured resistance depends on the time at which it is evaluated (for example 1 s or 10 s after the start of the pulse); the evaluation time is therefore reported with the results [7].

3Cycler Requirements for HPPC

HPPC results are calculated from voltage and current readings taken at defined times during fast current steps in both directions. Measurement errors and deviations from the programmed waveform propagate directly into the calculated resistance and power. Table 2 lists the cycler characteristics that affect HPPC results and the corresponding test-setup considerations.

3.1Test Instrument

A precision cycler facilitates meeting the requirements in Table 2. The test in this note was performed on an Arbin HPS ultra-high precision cycler with integrated temperature chambers (Figure 2). Its specifications are listed in Table 3 [9].

Arbin HPS key specifications [9]

In the integrated-chamber version, each channel has a dedicated chamber (10 to 60 °C, ±0.5 °C stability) and a PT100 input mapped to the channel, so that temperature is controlled and recorded together with the electrical data.

4Cell, Module and Pack Level Testing

HPPC can be performed at cell, module or pack level. The pulse profile is the same at each level; currents, voltages and limits are scaled to the device under test [2].

The experiment described in this note is performed at cell level.

5Device Under Test: XCell N18650-35E

The device under test is an XCell N18650-35E, a 3350 mAh cylindrical 18650 lithium-ion cell (Figure 3). The datasheet values [8] are listed in Table 5 and were entered in the MITS Pro cell definition.

6Experimental Setup

The HPPC pulse sequence is applied at a single SOC point, 90% SOC, with the cell at 25 °C in the integrated chamber of the Arbin HPS. 25 °C lies within the datasheet charge and discharge temperature ranges and is the common reference temperature for HPPC [1][8]. A full SOC sweep is obtained by repeating steps 5 to 11 at each 10% SOC step.

6.1Test Procedure at 90% SOC and 25 °C

1. 1Soak at 25 °C for 1 hour.log every 1 minute
2. 2Charge at 0.5C (CC) to 4.20 V.log every 30 seconds and every 10 mV change
3. 3Hold at 4.20 V (CV) until the current falls to 0.01C.log every 30 seconds
4. 4Rest for 1 hour.log every 10 seconds
5. 5Reset the charge and discharge capacity counters. 
6. 6Discharge at 0.5C until 10% of nominal capacity (0.335 Ah) has been removed, bringing the cell to 90% SOC. End test if 2.50 V is reached.log every 10 seconds and every 10 mV change
7. 7Rest for 1 hour.log every 10 seconds
8. 8HPPC discharge at 2.50 A for 10 seconds. End test if 2.50 V is reached.log every 0.1 second and every 5 mV change
9. 9HPPC rest for 40 seconds.log every 0.1 second
10. 10HPPC regen at 1.88 A for 10 seconds. End test if 4.20 V is reached.log every 0.1 second and every 5 mV change
11. 11Rest for 1 hour, then end the test.log every 10 seconds

6.2MITS Pro Schedule Implementation

Figure 5 shows the schedule in MITS Pro, programmed as one step per line (sequential method). Table 7 lists the control, step limits and log limits of each step. Capacity-based limits refer to MV_NominalCapacity, the nominal capacity in the MITS Pro cell definition (3.35 Ah), which allows the schedule to be reused for other cells. The CV step holds 1 × LS_CHAN_Voltage, the voltage at the end of the CC step (4.20 V). Charge current is positive and discharge current is negative.

7Results

Figure 6 shows the complete test recorded in MITS Pro: soak, CC-CV charge to 4.20 V, rest, 0.5C discharge to 90% SOC, rest, HPPC pulse sequence and final rest. Figure 7 shows the pulse sequence in detail.

The recorded data show the following:

• Pulse current. The current steps to −2.50 A and +1.88 A and remains constant for the full 10 s, so that the resistance is calculated against a defined current.
• Transitions. Discharge, rest and charge follow each other within one minute without visible overshoot or dead time, as provided by bipolar circuitry.
• Data logging. Time- and voltage-based logging records the voltage step at the start of each pulse, the response during the pulse and the subsequent relaxation, while the long rest periods are logged at a lower rate.
• Voltage limits. The voltage remained between 2.50 V and 4.20 V throughout the test, with step limits programmed to end the test if either limit was reached.

V_t0 to V_t3 are taken from the data file, and the resistance and pulse power at this SOC are calculated with Equations (1) to (4).

8Conclusion

HPPC is a short protocol consisting of a 10 s discharge pulse, a 40 s rest and a 10 s charge pulse, repeated across the SOC range. It characterises the power delivery and acceptance of a battery, which capacity testing does not.

Since the results are derived from small voltage changes measured during fast current steps, the quality of HPPC results depends largely on the cycler. Accurate voltage and current measurement, suitable current ranges, fast current steps, flexible data logging, bipolar operation, step-level limit handling and integrated temperature control allow small differences between cells, and small changes as a cell ages, to be measured reproducibly.

A precision cycler with these characteristics improves the reliability and comparability of HPPC results. In MITS Pro, the protocol is programmed once as a schedule, uses the cell definition for capacity-based limits, and applies the appropriate logging and limits to each step.

References

1. [1]FreedomCAR Battery Test Manual for Power-Assist Hybrid Electric Vehicles, DOE/ID-11069, Idaho National Engineering and Environmental Laboratory, October 2003.
2. [2]Battery Test Manual for Electric Vehicles, Revision 3, INL/EXT-15-34184, Idaho National Laboratory, June 2015.
3. [3]R. Rogers, "HPPC Test with Arbin," Arbin Instruments, 2021.
4. [4]W. Waag, S. Käbitz, D. U. Sauer, "Experimental investigation of the lithium-ion battery impedance characteristic at various conditions and aging states and its influence on the application," Applied Energy, 102, 885-897 (2013).
5. [5]H. He, R. Xiong, J. Fan, "Evaluation of lithium-ion battery equivalent circuit models for state of charge estimation by an experimental approach," Energies, 4, 582-598 (2011).
6. [6]G. L. Plett, Battery Management Systems, Volume I: Battery Modeling, Artech House, 2015.
7. [7]A. Barai, K. Uddin, W. D. Widanage, A. McGordon, P. Jennings, "A study of the influence of measurement timescale on internal resistance characterisation methodologies for lithium-ion cells," Scientific Reports, 8, 21 (2018).
8. [8]energy inside GmbH, "Specification for Lithium-Ion Rechargeable Cell XCell N18650-35E," document 148187. Datasheet (PDF)
9. [9]Arbin Instruments, "HPS Ultra-High Precision Battery Cycler," arbin.com/battery-research/high-precision-tester.html