What is the relation between state of charge of battery and its output power?
In constraint handling ...
Hi,
there isn't a formal relationship between maximum discharge power and SOC and it also depends on the type/size/chemistry/temperature/SOH of the cell, but an example graph is attached for one particular cell, under one particular set of test conditions.
Maximum power is governed by the maximum allowable voltage drop, which in turn comes from the internal resistance of the cell. So, a low internal resistance means a high maximum discharge power available. Obviously, the load can draw any power it wants, provided it is less than this maximum power limit.
Regards,
Robert
I cannot show you the publications on this topic.
As rightly stated by Dr. Robert Ball: "…low internal resistance means a high discharge power available". Usually this condition is fulfilled the available range of the electrochemical capacitance. But from my experience, it can be said that the internal resistance at the edges of C sharply increases (for C=0 and C=Cmax). It's necessary to emphasize that for C = 0 this high internal resistance depends on the prehistory (it is high immediately after the charge, and then gradually decreases).
If you write the expression for power: P=U*I, and take into account, that I = U/R, you will receive equation: P=U2/R. In case of homogeneous type of electrochemical reaction (for example for LiCoO2 and its “clones” = NMC etc.), voltage during discharge decreases. Therefore, the maximum power will be reached at the beginning of the discharge (excluding the very beginning of the discharge). In the case of heterogeneous type of electrochemical reaction (LiFePO4 cathode material, for example) dependence of power on the degree of discharge will have a "desk" form, as U close to constant. See in attachment practical results for industrial power source (20 A*hrs for low and high power respectively). Take in account, please, that all this logic works only for traditional for laboratory testing galvanostatic mode (I=const).
Basically, for all chemistries the inner restistance of the cell increases with decreasing SOC.
So, while there are a lot of additional parameters (cell chemistry, cell "form factor", SOH - to name just a few), the maximum available output power is somewhat proportional to the SOC.
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