CN102590592A - Device for precisely detecting voltage of lithium battery pack - Google Patents

Abstract

The invention relates to a device for precisely detecting a voltage of a lithium battery pack, which comprises a lithium battery pack with batteries connected in series. A voltage current converter extracts a detection current of each battery of the lithium battery packs from two adjacent batteries of the lithium battery packs. The detection current generates a detection voltage of each battery through a corresponding divider resistance. The batteries share a same reference voltage. The detection voltage of each battery is output through a same comparator. The device for precisely detecting the voltage of the lithium battery pack adopts the method of current compensation and avoids the problem of imbalance among batteries caused by inter-battery current leakage. The device for precisely detecting the voltage of the lithium battery pack adopts a high precision line and the comparator to avoid the problem that the detection precision is not high due to a plurality of reference voltages adopted.

Description

Accurately detect lithium battery group voltage device

Technical field:

The present invention relates to technical field of lithium batteries, more specifically to the li-ion cell protection special IC.

Background technology:

Because the chemical characteristic of lithium battery self; If to its overcharge, overdischarge will cause lithium battery interior generation chemical side reactions; This subsidiary reaction meeting has a strong impact on the performance and the serviceable life of battery, even safety problem such as will set off an explosion, so all lithium batteries all need a holding circuit; Be used for the charge and discharge state of battery is effectively monitored, and turn-off charging and discharging circuit under given conditions and battery self is caused damage preventing.Because the overall performance of series battery depends on the poorest cell of performance in the electric battery; The voltage status of having only cell in the real-time detection series battery; Just can accomplish cell is effectively protected; And prolonging its serviceable life, the voltage that therefore accurately detects each batteries is very important.Testing circuit will be avoided causing because of extracting the unbalanced problem of battery that electric current causes from cell when accurately detecting each batteries voltage.

Serial lithium battery group voltage detection method mainly contains two kinds at present: resistance sampling method, differential amplifier detection method.

1, resistance sampling method; See shown in Figure 1; Resistance sampling method principle of work is that each batteries voltage passes through divider resistance dividing potential drop separately; Actual cell voltage is decayed to the voltage range that battery protection ic can be accepted, sampled value that obtains and the inner reference voltage for every batteries generation of protection IC are made comparisons, decide opening or turn-offing of charging and discharging circuit according to result relatively.BAT1～BATn represents each batteries; Each batteries voltage is V _BAT1～V _BATnR1～Rn is a divider resistance; Vref1～Vrefn is the reference voltage that battery protection ic produces for each batteries; V1～Vn is the detection voltage of each batteries; IB1～IBn is the electric current that flows through each batteries divider resistance string; COMP1～COMPn is the comparer of each batteries; IA1～IAn-1 is respectively the leakage current between adjacent two batteries.

In the ideal case,

$\mathrm{Vn}=\frac{\mathrm{Rn}-1}{\mathrm{Rn}+\mathrm{Rn}-1}={\mathrm{KV}}_{\mathrm{BATn}},$ Wherein K is a scale-up factor.

$\mathrm{IBn}=\frac{\mathrm{VDD}}{R1+R2+R3+\mathrm{L\; Rn}+\mathrm{Rn}-1}$

VDD＝V _BAT1+V _BAT2+L?V _BATn＝IBn[(R1+R2)+(R3+R4)+L(Rn+Rn-1)]。

It is equal to suppose that divider resistance between each batteries matees fully, and the electric current that flows through the divider resistance string of every batteries so equates, also is IB1=IB2=L IBn.Analyze by above: LA1=IA2=L IAn=0.

Under actual conditions, be example with BAT1, V _BAT1=IB1*R1, IB1=LA1+IBn.

Divider resistance between each batteries is not accomplished to mate fully equal, and resistance maybe be bigger than normal or less than normal, and the electric current that causes flowing through each batteries divider resistance string will be unequal.At VDD, V _BAT1, under the certain condition of IBn, IB1 can change along with the variation of R1, finally causes having between BAT1 and BAT2 leakage current IA1, occurrence depends on the mismatch degree of R1 and other resistance.The problem that has leakage current between other any adjacent two batteries too.As time goes on, leakage problem will cause unbalanced between each batteries, finally influences the life-span of electric battery.

The resistance sampling method; Need produce reference voltage V ref1～Vrefn separately for every batteries; Be difficult in reality guarantee that the reference voltage of each batteries is in full accord that the inconsistent protection point voltage of each batteries that finally causes of reference voltage is different, As time goes on; Also can cause unbalanced between each batteries, finally influence the life-span of electric battery.

2, differential amplifier detection method is seen shown in Figure 2ly, and differential amplifier detection method principle is to adopt differential amplifier that every batteries voltage difference is amplified, obtain detecting voltage Vn after, the reference voltage with each batteries compares again, exports VO at last.Corresponding two switches of every batteries in the switch matrix, a positive switch SP, a negative switch SN; The effect of switch matrix is that gating sampling battery gets into testing circuit.Sample voltage value Vn is obtained by following formula:

$\mathrm{Vn}=\frac{R3}{R2+R3}(1+\frac{R4}{R1})V_{\mathrm{BATn}+}+\frac{R2}{R2+R3}(1+\frac{R4}{R1})V_{\mathrm{ref}}-\frac{R4}{R1}{V}_{\mathrm{BATn}-}$

In the ideal case; R1=R2; During R3=R4,

In reality was made, R1 and R2, R3 did not accomplish to equate fully with R4, cause very accurately detecting cell voltage.

The differential amplifier detection method, Vref is generally GND, has I1 ≠ I2 ≠ 0 equally, the unbalanced problem of the battery that also promptly exists the leakage current between two batteries to cause.

Summary of the invention:

The object of the invention is exactly the deficiency to prior art, and a kind of accurate detection lithium battery group voltage device is provided, and it has avoided the electric leakage problem of resistance sampling method and the not high problem of voltage detecting precision of differential amplifier detection method, detects effective.

Technological solution of the present invention is following:

Accurately detect lithium battery group voltage device; Comprise the serial lithium battery group; Voltage current adapter is from extracting the detection electric current of each batteries of lithium battery group between adjacent two batteries of serial lithium battery group; This detects electric current produces each batteries again through corresponding divider resistance detection voltage, the shared same reference voltage of each batteries, and the detection voltage of each batteries is exported through same comparer.

Said current compensation circuit produces with equivalent electric current and the compensation of each batteries output current and gives each batteries.

Beneficial effect of the present invention is:

1, it has adopted the method for current compensation, has stopped the unbalanced problem of battery that the existence because of the internode leakage current causes.

2, adopt high precision line and comparer, evaded the not high problem of accuracy of detection that adopts a plurality of reference voltages to cause.

3, it has avoided the electric leakage problem of resistance sampling method and the not high problem of voltage detecting precision of differential amplifier detection method, detects effective.

Description of drawings:

Fig. 1 detects the circuit diagram of serial lithium battery group voltage for the resistance sampling method

Fig. 2 detects the circuit diagram of serial lithium battery group voltage for the differential amplifier detection method

Fig. 3 is the circuit diagram of embodiment 1

Fig. 4 is the circuit diagram of embodiment 2

Embodiment:

Embodiment 1: see shown in Figure 3; Accurately detect lithium battery group voltage device; Comprise serial lithium battery group BAT1, BAT2, BATn-1......BATn; Voltage current adapter is from extracting the detection electric current of each batteries of lithium battery group between serial lithium battery group BAT1, BAT2, adjacent two batteries of BATn-1......BATn; This detects electric current produces each batteries again through corresponding divider resistance detection voltage, the shared same reference voltage of each batteries, and the detection voltage of each batteries is exported through same comparator C OMP.

Embodiment 2: see shown in Figure 4ly, said current compensation circuit produces with equivalent electric current and the compensation of each batteries output current and gives each batteries.

Principle of work: see shown in Figure 3ly, voltage current adapter is realized converting cell voltage into electric current, and the voltage current adapter that every batteries is used is all identical; Each batteries voltage is respectively V _BAT1, V _BAT2, V _BATnI1, I2 ... In-1 is the electric current of voltage current adapter from extracting between adjacent two batteries; IA1, IA2 ... IAn is for flowing out the electric current between per two batteries, I1=IA1 wherein, I2=IA2, In-1=IAn-1.Used high precision line and multichannel comparator C OMP among Fig. 3, a plurality of comparers are combined into a comparer, the shared same reference voltage of each batteries has guaranteed the consistance of reference voltage, has evaded the not high problem of the accuracy of detection of using a plurality of reference voltages to cause.

For making the leakage current that flows out two joint adjacent cell is 0, even also IA1=IA2=... IAn-1=0 needs and IA1, IA2 ... The electric current that IAn equates flows into each batteries.The present invention has adopted the method for current compensation, has accomplished IA1=IA2=... IAn-1=0, as shown in Figure 4, on the basis of Fig. 3, add current compensation circuit.

With BAT1 is example, for making IA1=IA2=among Fig. 3 ... IAn-1=0 has adopted current compensation circuit in Fig. 4.Voltage current adapter is IA1 from the electric current that extracts between BAT1 and the BAT2, and current compensation circuit produces the IB1 that equates with IA1, and I1=IB1, compensation process get into the electric current I B1 compensation that current compensation circuit produces among the BAT1.Because I1=IB1 can get IA1=0 by the KCL equation, final equivalent result is 0 for the electric current that flows out BAT1.The compensation of other each batteries electric currents is all identical with BAT1.The present invention has stopped the unbalanced problem between battery that the existence because of the internode leakage current causes fully.

Among the present invention, the voltage of each batteries converts electric current to through voltage current adapter, makes this electric current flow through the corresponding divider resistance of each batteries, produces final detection voltage.Detection voltage between each batteries does not disturb mutually, has guaranteed the accuracy of the sampled voltage of every batteries.

Detecting magnitude of voltage is obtained by following formula: wherein K is a scale-up factor,

V1＝I1×R1＝KV _BAT1、V2＝I2×R2＝KV _BAT2L、Vn＝In×Rn＝KV _BATn。

Claims (2)

1. accurately detect lithium battery group voltage device; Comprise serial lithium battery group (BAT1, BAT2, BATn-1......BATn); It is characterized in that: voltage current adapter is from extracting the detection electric current of each batteries of lithium battery group between adjacent two batteries of serial lithium battery group (BAT1, BAT2, BATn-1......BATn); This detects electric current produces each batteries again through corresponding divider resistance detection voltage; The shared same reference voltage of each batteries, the detection voltage of each batteries is exported through same comparer (COMP).

2. accurate detection lithium battery group voltage device according to claim 1 is characterized in that: current compensation circuit produces with equivalent electric current and the compensation of each batteries output current and gives each batteries.

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