Extractors#

Extractors create initial guesses for model parameters through model-specific algorithms. Many algorithms require data from battery cycling performed under specific operating conditions, which we refer to as Reference Performance Tests (RPTs).

For example, the OCVExtractor estimates the open circuit voltage from a cycle which completely charges and discharges a battery under minimal current.

This part of the documentation describes the general interface for extractors then each extractor available for each model.

Extractor Interface#

All extractors provide two operations:

  1. check_data evaluates whether a datasets contains data needed to perform the estimation.

  2. extract generates part of a health parameter object given a dataset.

Instantiate an extractor by providing configuration options for the algorithm and, in some cases, information gathered from other extractors.

from moirae.extractors.ecm import MaxCapacityExtractor, OCVExtractor, R0Extractor

cap = MaxCapacityExtractor().extract(dataset)
ex_ocv = OCVExtractor(capacity=cap)
ocv = ex_ocv.extract(dataset)
ex_r0 = R0Extractor(capacity=cap)
r0 = ex_r0.extract(dataset)

Available Extractors#

Extractors are model-specific, and we describe those available for each type of model below.

Equivalent Circuit Models#

Model: moirae.models.ecm.EquivalentCircuitModel

Demonstration: ECM Extractors

Extracting parameters for a Equivalent Circuit Models (ECM) require several steps, each generating parameters for different parts of the model.

Extractor

Parameters

Data Needs

MaxCapacityExtractor

Capacity of battery

Complete charge and discharge

OCVExtractor

Voltage with zero current

  • Capacity estimate

  • Complete charge and discharge

R0Extractor

Instantaneous resistance (measured in Ohms) of a battery observed from step changes in current

  • Capacity estimate

  • Step changes in current across various states of charge, measured across a small timestep

RCExtractor

Resistance (measured in Ohms) and Capacitance (measured in Farads) of RC couples observed from post-charge and discharge rests

  • Capacity estimate

  • Voltage relaxation from a sufficiently long post-charge or post-discharge rest