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Introduction to IEEE 450 Annex J battery model

Introduction to IEEE 450 Annex J battery model. Before we can delve into battery impedance, we have to make sure some key electrical principles are understood. DC electrical theory (constant voltage, frequency is 0) The element that limits the flow of electricity is called Resistance .

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Introduction to IEEE 450 Annex J battery model

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  1. Introduction to IEEE 450 Annex J battery model

  2. Before we can delve into battery impedance, we have to make sure some key electrical principles are understood. DC electrical theory (constant voltage, frequency is 0) The element that limits the flow of electricity is called Resistance. It can be calculated with Ohms Law.

  3. AC electrical theory (changing voltage, frequency is greater than 0) The property that limits electricity flow is called Impedance. When an AC voltage is applied there is resistance like DC but there are 2 new electrical elements. Capacitance Inductance

  4. Impedance = Resistance + Capacitance Resistance + Inductance Resistance The term for Capacitance and Inductance Resistance is Reactance (X).

  5. The resistance of the 2 new elements is more complicated because they depend on the frequency of the voltage applied. Capacitance reactance XC = Inductance reactance XL= f stands for frequency

  6. Impedance (Z)= Resistance (R) + Reactance (X) However because of the Reactance, Impedance is more complicated and can be best represented as vectors. X = XL - XC ) Impedance is a complex number it has a modulus (Z) and an Angle (q).

  7. The inverse of Impedance(Z) is Admittance(Y), and the inverse of Resistance(R) is Conductance(G). Admittance Conductance Impedance can be represented in the following format.

  8. A battery can be represented by a simplified lumped model so that Electrical Theory can be utilised to quantify the battery behaviour. Source IEEE 450-2010 Annex J

  9. The Warburg Impedance Zw can be ignored because it’s effect is at extremely low frequencies outside the range of the existing technology in the market for online battery impedance measurements. = The battery inductance is very small and the battery capacitance is large. Therefore it is typical to only use one vertical axis, and the convention is for the axis to point upwards.

  10. The battery impedance is dependent on frequency therefore if we take two measurements with different frequencies it can be represented as follows by points f1 and f2. The battery impedance decreases as the frequency increases because the battery’s capacitance is much greater than its inductance. Therefore f1is a higher frequency than f2, so Z1 is smaller than Z2. The above result shows if two battery instruments with different test frequencies measure the same battery the readings are different.

  11. In the battery/electrochemical industry a graph as per the previous slide is used when a battery’s impedance has been measured across a range of frequencies, this is known as a Nyquist plot. Battery model Nyquist plot. Battery Nyquist plots are unique, like human finger prints, batteries have different plots and the differences are more significant for different types and sizes of batteries.

  12. Thank you.

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