The main strength of EIS is its ability to effectively deconvolute complex electrochemical processes into a series of basic processes based on the different relaxation times. Generally, such processes involve the dynamics of bound or mobile charge in the bulk or interfacial regions of any liquid or solid material: ionic, semiconducting, mixed electronic-ionic and even insulators (dielectrics) 1. Discharge/charge to next step at prescribed discharge/charge C-rate (per manufacturer’s data sheet)Įach cell type can be tested at each SOC, including across various temperatures and various C-rates for the pulses (discharge and charge).Electrochemical impedance spectroscopy (EIS) is a powerful technique for investigating processes occurring in electrochemical systems.Pulse, regeneration: 1C or 0.75C for 10 seconds.Rest for 10 minutes (relaxation period).The steps are made from 100% to 0% SOC, and can continue back to 100% SOC for the second half of the test profile. HPPC Testįor the HPPC test, 10% SOC steps are used based on the battery capacity determined from the static capacity test above. The discharge capacity is generally used for consistency, especially if only performing the first half (discharge) of the next section of the test profile – the HPPC test. Typically, you should find it is consistent with the charge capacity measured. The discharge capacity from 100% to 0% SOC is taken as the battery capacity. Another rest period is employed before recharging back to 100% SOC using the CCCV scheme. The discharge capacity can be measured directly via a dedicated battery tester, or determined from the current drawn in the time period from 100% SOC to 0% SOC. Next, the battery is discharged at a prescribed C-rate to a minimum voltage cutoff. The battery has reached 100% SOC, and a sufficient rest period is used to allow the cell to come to equilibrium. This is known as a constant-current, constant-voltage (CCCV) charge scheme. The battery is charged at a constant current until the charge voltage is reached (the voltage at full capacity), and then is switched over to constant voltage charging until a minimum current is reached. For example, if a cell has a nominal rated capacity of 2000 mA-hr, and a C-rate of 1.5 was used to discharge the battery, the current in use would be 3 A. The C-rate is defined as the current in use divided by the theoretical current under which the battery would deliver its nominal rated capacity in one hour. This is typically done at a set C-rate, representing the rate of current supplied (charge) or current drawn (discharge) relative to its maximum capacity. The static capacity test starts by taking a battery from an unknown SOC to 100% SOC per the manufacturer's charging instructions. The test profile itself comprises two sections:įigure 1: Test profile comprised of static capacity and HPPC tests Static Capacity Test This profile mimics the discharge and charge that can occur on hybrid EVs during acceleration and regenerative breaking. A discharge pulse is a relatively short load drawn on the battery, and a regeneration pulse is a relatively short charge to the battery. It is a test profile that incorporates both discharge and regeneration pulses that take place at various states of charge (SOC), and which can be performed under various temperature stressors and current loads. This testing determines battery power capability over the cell’s usable voltage range. HPPC testing is a methodology used to determine the dynamic performance characteristics of a battery. Watch the webinar to learn more: HPPC Testing for ECM Modeling and Battery Reliability What is HPPC Testing? Hybrid pulse power characterization (HPPC) testing can be applied to determine the dynamic performance over the usable voltage ranges of the cell - resulting in accurate battery parameter identification to create robust battery models for simulation. Replicating these use environments and capturing the dynamic behavior of the battery in test is key to accurately modeling the performance of the battery. The ECM parameter identification requires test data that covers the dynamic range of the battery operating conditions. The commonly used model for such applications is the battery equivalent circuit model (ECM), which is an electrical representation of the charging and discharging characteristics using a set of resistors and capacitors with a voltage source and current. To test for battery reliability, battery parameters must be identified. According to BloombergNEF, by 2040 over half of all passenger vehicle sales will be electric.
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