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Differential analysis of battery first in series and then in parallel and parallel first and then in series

by:dcfpower     2021-03-13
u003cpu003eLithium-ion batteries are more and more widely used in the national economy, but their power and energy are an incompatible pair of performance. In actual design, users are often required to make trade-offs and balances between battery power and energy, and battery designers are in a dilemma. In addition, large-scale assembled battery packs need to be implemented in multiple strings. According to the usual theory, the consistency of the performance of the single cells participating in the combination should be controlled within a narrow range, otherwise it will be due to the performance difference between the individual cells in the battery pack. Seriously affect the cycle life of the battery pack. Therefore, the more monomers the battery requires, the more difficult it is to match, and the more batteries that cannot be matched, which will cause great waste. In order to solve the above problems, this article made a bold breakthrough on the basis of theoretical analysis, combining different types of batteries according to certain rules. Experiments have shown that this battery combination method can not only solve the contradiction problem of high power and high energy, but also A specific method to reduce the pressure of large-scale battery assembly is proposed. u003cpu003e Figure 1 is a schematic diagram of the assembled battery pack first in series and then in parallel, where: Bmn is the m-th parallel n-th series battery; Rm is the m-th parallel total series resistance (including battery internal resistance and line contact resistance); Im is The current of the m-th parallel; Ip is the total output current of the battery pack; Vm is the total series voltage of the m-th parallel; Vp is the total output voltage after paralleling. It can be seen from Figure 1 that Ipu003dI1+I2+I3+……+Imu003c/pu003eu003cpu003eFigure 1 Schematic diagram of combination first in series and then parallelu003c/pu003eu003cpu003e The same voltage platform is selected for the assembled battery (the positive and negative electrode materials of the battery) Consistent) battery, namely V1u003dV2u003d……u003dVmu003dV; each parallel series battery requires to be grouped according to the capacity, internal resistance and other parameters, namely Bm1, Bm2,……Bmn, which requires consistent performance matching. Between B1n, B2n, ...Bmn, the electrical parameters are not required to be consistent. u003c/pu003e Imu003d(Vm-Vp)/Rm, in the discharge process, the current of each parallel battery string is inversely proportional to the resistance value of the parallel circuit, that is to say, during the discharge process, due to the The series resistance is different, the current flowing through the parallel battery string is different, that is, I1, I2,...Im are not the same, and change constantly during the discharge process, but the overall maintain Ipu003dI1+I2+I3+...+In dynamic equilibrium. Vpu003dVm-ImRm, if the voltage (Vm) of a parallel battery string becomes lower during the discharge process (compared to the voltage of other parallel battery strings), because Imu003d(Vm-Vp)/Rm, the battery pack will automatically By reducing the current of the parallel battery string, the total voltage (Vm) of the parallel battery string will be raised, so the battery pack is in a dynamically balanced discharge state, so that the battery pack maintains a certain balance voltage (Vp), so In the process of dynamic voltage balance of the battery pack, each parallel battery string can discharge its own capacity without over-discharging. The charging process is opposite and the principle is similar. Due to the dynamic balance of the charging voltage, each string of batteries can be charged into its own capacity without overcharging. u003cpu003eFigure 2 Schematic diagram of the combination of first parallel and then seriesu003c/pu003e The connection method of first parallel and then series is shown in Figure 2. Since B11, B12...B1n are screened by matching groups, their electrical performance can be regarded as consistent In terms of electrical performance, B11, B12...B1n are the same, and Bm1, Bm2...Bmn are the same, so after paralleling, B and 1u003dB and 2u003d...u003dB and n (where B and n are B1n , B2n...Bmn parallel result). Then, the whole set of batteries is equivalent to the series of B parallel 1, B parallel 2...B parallel n after screening and matching, and there is no problem in charging and discharging. The parallel connection of Bm1, Bm2...Bmn is similar to the analysis in Figure 1. From the above analysis, it can be seen that the battery packs connected in parallel and then connected in series can be charged and discharged normally, which will not be repeated here. Through the above theoretical analysis, it can be concluded that if the conditions are met: the voltage platforms of all the batteries that make up the battery pack are the same (the positive and negative materials of the battery are the same), and the single cells corresponding to the series direction have undergone strict matching screening (maintain The internal resistance, capacity, etc. are the same), then the battery pack can be charged and discharged normally, regardless of whether the single batteries are connected in series and then paralleled or combined in series before the battery pack can be charged and discharged normally without affecting the cycle life of the battery pack. u003c/pu003eu003c/pu003e
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