title: Distinguishability of rechargeable battery equivalent circuit models

authors: Poihipi, Eden Kathleen

subjects: ECM

abstract: The contention made by Berthier et al. - that competing fractional-element equivalent- circuit models of battery cells are indistinguishable in the presence of noise - is revisited in this work. A set of six equivalent circuit models (ECMs) were chosen as a subset of West- erhoff’s generalised ECM from 2016. These six ECMs had increasing complexity, and gave a simulated output similar to that of an idealised Lithium battery impedance spec- trum. By extending the frequency range of Berthier, using methods suggested by both Mauracher & Karden, and Hasan & Scott, sets of simulated electrochemical impedance spectra (EIS) are generated. A Nelder-Mead based optimisation method, which em- ploys multiple restarts, is used to fit each ECM to the sets simulated data. The data was produced with 0%, 1%, 3% and 5% noise. The optimisations showed that all six ECMs were distinguishable at 0% noise, but as the noise increased - distinguishability is lost. Typically a 4-element ECM is shown to model the simulated data with preci- sion which is comparable to the error in the data. When optimising the ECMs against measured data (measured with an Egilent 66332A, E5270 and a Keithley 2460A) from INR and NCA batteries, it is seen that the 3-element ECMs are an adequate model. However there is some variation between the two battery chemistries. Battery ageing and the measurement system used also contribute to variation in which ECM models the data best. Further work on this project should include repeating this fitting method on different battery chemistries, and collating and fitting ECMs to a battery which is measured at different points as it ages.

text: Distinguishability of rechargeable battery equivalent circuit models The contention made by Berthier et al. - that competing fractional-element equivalent- circuit models of battery cells are indistinguishable in the presence of noise - is revisited in this work. A set of six equivalent circuit models (ECMs) were chosen as a subset of West- erhoff’s generalised ECM from 2016. These six ECMs had increasing complexity, and gave a simulated output similar to that of an idealised Lithium battery impedance spec- trum. By extending the frequency range of Berthier, using methods suggested by both Mauracher & Karden, and Hasan & Scott, sets of simulated electrochemical impedance spectra (EIS) are generated. A Nelder-Mead based optimisation method, which em- ploys multiple restarts, is used to fit each ECM to the sets simulated data. The data was produced with 0%, 1%, 3% and 5% noise. The optimisations showed that all six ECMs were distinguishable at 0% noise, but as the noise increased - distinguishability is lost. Typically a 4-element ECM is shown to model the simulated data with preci- sion which is comparable to the error in the data. When optimising the ECMs against measured data (measured with an Egilent 66332A, E5270 and a Keithley 2460A) from INR and NCA batteries, it is seen that the 3-element ECMs are an adequate model. However there is some variation between the two battery chemistries. Battery ageing and the measurement system used also contribute to variation in which ECM models the data best. Further work on this project should include repeating this fitting method on different battery chemistries, and collating and fitting ECMs to a battery which is measured at different points as it ages.

year: 2023

title: To what extent are public savings offset by private savings in the OECD

authors: Holmes, Mark J.

subjects: OECD

abstract: The substitutability of private and public savings has implications for the effectiveness of fiscal policy. Using annual data for the period 1970–2004, this study re-examines long-run relationships between OECD private and public savings rates. However, unlike previous work, panel data unit root and cointegration tests are employed. The results confirm substitutability where strong Ricardian Equivalence is rejected for the entire OECD panel. There is support for weak Ricardian Equivalence with less than perfect substitutability. Indeed, it is argued that existing studies most likely overstate the extent of long-run substitutability particularly with regard to EU countries.

text: To what extent are public savings offset by private savings in the OECD The substitutability of private and public savings has implications for the effectiveness of fiscal policy. Using annual data for the period 1970–2004, this study re-examines long-run relationships between OECD private and public savings rates. However, unlike previous work, panel data unit root and cointegration tests are employed. The results confirm substitutability where strong Ricardian Equivalence is rejected for the entire OECD panel. There is support for weak Ricardian Equivalence with less than perfect substitutability. Indeed, it is argued that existing studies most likely overstate the extent of long-run substitutability particularly with regard to EU countries.

year: 2006

title: The development of an indigenous knowledge program in a New Zealand Maori-language immersion school

authors: Harrison, Barbara

subjects: knowledge

abstract: In 1985, Te Wharekura o Rakaumangamanga initiated a Maori-language immersion program for children ages 5 through 18. In recent years, a program based on Waikato-Tainui tribal epistemology has been incorporated into the language immersion program. This article describes the community context and the language immersion and tribal knowledge programs. We consider the relationship of these programs to individual and tribal self-determination and to theories of minority achievement, particularly the work of John Ogbu.

text: The development of an indigenous knowledge program in a New Zealand Maori-language immersion school In 1985, Te Wharekura o Rakaumangamanga initiated a Maori-language immersion program for children ages 5 through 18. In recent years, a program based on Waikato-Tainui tribal epistemology has been incorporated into the language immersion program. This article describes the community context and the language immersion and tribal knowledge programs. We consider the relationship of these programs to individual and tribal self-determination and to theories of minority achievement, particularly the work of John Ogbu.

year: 2005-03