CN105277791A - Method for on-line detection of internal resistance of a storage battery by performing low-direct-current discharge twice - Google Patents

Abstract

The present invention relates to a method for on-line detection of the internal resistance of a storage battery by performing low-direct-current discharge twice. The low current discharge is performed twice on the storage battery in a load state, and two discharge loops are composed of switches and two precision resistors having different resistances. The on-line detection method is provided based on the direct current high current discharge method, a sampling holder is employed in the process of the voltage acquisition to perform sampling holding of voltages acquired in the two-time discharge, then a required voltage difference in the two-time discharge is obtained through differential amplification, and the internal resistance of the storage battery is calculated according to the voltage difference in the two-time sampling. According to the on-line detection method provided by the invention, the problems of the damage of a high current discharge method to a storage battery and the defect of an inappropriate on-line detection may be overcome, voltage difference in the two-time discharge obtained through sampling holding and differential amplification may improve the precision of data acquisition, and the error is reduced, therefore, the exact value of the internal resistance of the storage battery is obtained and the accurate detection of the internal resistance of the storage battery in the load state is realized online.

Description

DC low current secondary discharge accumulator internal resistance online test method

Technical field

The present invention relates to a kind of internal resistance of cell pick-up unit, particularly a kind of DC low current secondary discharge accumulator internal resistance online test method.

Background technology

Accumulator plays an increasingly important role in modern society as the main carriers of energy storage, and accumulator is widely used in industry-by-industry as electrokinetic cell or back-up source, large to the little various aspects to daily life of military industry.Moreover, accumulator in support power supply be also widely used in industry-by-industry.Be no matter the performance of accumulator, capacity status or charge status, can embody from its internal resistance change.Therefore by measuring the internal resistance of accumulator, monitoring and evaluation can be carried out to its duty.The internal resistance of accumulator as the important parameter of reflection accumulator property, about its value Measurement accuracy particularly on-line checkingi tool be of great significance.

Current accumulator internal resistance detects conventional method and mainly contains densimetry, ac-current inject method, direct-current discharge method.Densimetry mainly estimates the internal resistance of accumulator by the density detecting battery liquid, be usually used in the internal resistance detection of open type lead-acid accumulator, be not suitable for the internal resistance detection of sealed type lead acid battery, the scope of application of the method is narrower.Ac-current inject method is by injecting a low-frequency ac electric current signal to accumulator, the response of battery can produce the phase shift of a voltage and current, the low-frequency voltage recording accumulator two ends and the low-frequency current flow through and both phase differential, thus the internal resistance of accumulator can be calculated.AC method, owing to not needing electric discharge, need not be in static state or off-line state, can realize safe on-line checkingi management.But, this method due to measuring amount too much, cause disturbing factor to increase, and add the complicacy of system, affect measuring accuracy, compare the detection being suitable for cell comparatively speaking.The ultimate principle of DC internal resistance method of testing is the load of accumulators series direct current, transient large current discharge is carried out to battery, be generally tens to hundreds of amperes, remove the discharge current of front and back and the change of accumulator voltage by detecting load, the internal driving of accumulator can be obtained thus.Accurately can detect the internal resistance of accumulator when the major advantage of DC-method is that accumulator is online, measurement result is not by the impact of charger ripple with other noises.In addition, measuring error can be controlled within 0.1%.Also there is certain defect in the method method, because discharge current is comparatively large, small-capacity cells may be difficult in seconds bear larger electric current.Meanwhile, when accumulator have large electric current by time, internal chemical reaction is complicated, there will be polarization resistance, also comparatively large to the infringement of accumulator, and heavy-current discharge is repeatedly unfavorable for on-line checkingi.

Summary of the invention

The present invention be directed to accumulator internal resistance and detect conventional method Problems existing, propose a kind of DC low current secondary discharge accumulator internal resistance online test method, overcome heavy-current discharge to the shortcoming of the infringement of accumulator with unsuitable on-line monitoring.

Technical scheme of the present invention is: a kind of DC low current secondary discharge accumulator internal resistance online test method, specifically comprises the steps:

1) set up two discharge loops, accumulator, be connected on the switch S at accumulator two ends ₁with sampling precision resistance R ₁the first discharge loop formed, accumulator, is connected on the switch S at accumulator two ends ₂with sampling precision resistance R ₂the discharge loop formed, single-chip microcomputer exports control signal and controls two switch S ₁, S ₂fragmentary works;

2) first by two discharge loop switch S ₁and S ₂all disconnect, record pull-up resistor both end voltage U ₀and electric current, the load resistor value R under accumulator presence can be tried to achieve by Ohm law _l;

3) first time low discharging current is carried out to accumulator, switch S ₁closed, switch S ₂disconnect, detect accumulator both end voltage U ₁, then second time low discharging current is carried out to accumulator, switch S ₂closed, switch S ₁disconnect, detect accumulator both end voltage U ₂, send Signal-regulated kinase to process after signal after gathering, the U after Signal-regulated kinase process ₁, U ₂send into two sampling holders respectively to keep, two sampling holder outputs are sent into differential amplifier circuit again and are obtained U ₂-U ₁value;

4) detected value is sent into internal resistance calculating formula and obtain internal resistance R _s

$R_S=\frac{R_1{R}_2{R}_L(U_2-U_1)}{R_L(U_1{R}_2-U_2{R}_1)-R_1{R}_2(U_2-U_1)}.$

Described sampling hold circuit selects LF398 as sampling holder.

Described step 3) first time low discharging current time, switch S ₁closed, switch S ₂disconnect, the first sampling holder is in sample states; When then carrying out low discharging current, now switch S ₂closed, switch S ₁disconnect, the first sampling holder is in hold mode, and the second sampling holder is in sample states; So latter two sampling holder is all in hold mode, finally by the data U of sampling holder output ₁, U ₂with the U that differential amplifier circuit exports ₂-U ₁send into the internal resistance value calculating accumulator in the single-chip microcomputer of band AD conversion.

Beneficial effect of the present invention is: DC low current secondary discharge accumulator internal resistance online test method of the present invention, not only overcome Big Current Discharge to the shortcoming of the infringement of accumulator with unsuitable on-line monitoring, and to be kept by sampling and differential amplification obtains the precision that twice sparking voltage value difference also improves data acquisition, reduce error, thus obtain the exact value of accumulator internal resistance, realize the accurate detection to the internal resistance of accumulator under tape carries state.

Accompanying drawing explanation

Fig. 1 is DC low current secondary discharge method equivalent circuit diagram of the present invention;

Fig. 2 is DC low current secondary discharge accumulator internal resistance on-line measuring device block diagram of the present invention;

Fig. 3 is that the present invention samples retaining part circuit diagram.

Embodiment

Fig. 1 is DC low current secondary discharge method equivalent circuit diagram, is the circuit model of accumulator under direct-current discharge state, accumulator, is connected on the switch S at accumulator two ends ₁with precision resistance R ₁the discharge loop I formed, accumulator, is connected on the switch S at accumulator two ends ₂with precision resistance R ₂the discharge loop II formed.

Be the equivalent model of accumulator under direct-current discharge state in frame, R _sbe the equivalent internal resistance of accumulator, R _lfor the equivalent load under presence, R ₁, R ₂for electric discharge precision resistance.

First switch S ₁, S ₂all disconnect, can R be recorded _lboth end voltage U ₀with flow through R _lelectric current I _s, can be obtained by Ohm law:

$R_L=\frac{U_0}{I_S}---\left(1\right)$

Secondly, first time low discharging current is carried out to accumulator, S ₁closed, S ₂disconnect, if R ' ₁=R ₁//R _l(R ₁, R _lvalue in parallel), R ₁both end voltage is U ₁, can be obtained by Ohm law:

$U_1=\frac{R_1^{\′}E}{R_1^{\′}+R_S}---\left(2\right)$

Then, second time electric discharge is carried out to accumulator, S ₂closed, S ₁disconnect, if R' ₂=R ₂//R _l(R ₂, R _lvalue in parallel), R ₂both end voltage is U ₂, can be obtained by Ohm law:

$U_2=\frac{R_2^{\′}E}{R_2^{\′}+R_S}---\left(3\right)$

Arranged can be obtained by formula (2), (3):

$R_S=\frac{R_1^{\′}{R}_2^{\′}(U_2-U_1)}{U_1{R}_2^{\′}-U_2{R}_1^{\′}}---\left(4\right)$

By R ' ₁, R' ₂(4) formula of substitution arranges can obtain internal resistance R _sfinal expression formula:

$R_S=\frac{R_1{R}_2{R}_L(U_2-U_1)}{R_L(U_1{R}_2-U_2{R}_1)-R_1{R}_2(U_2-U_1)}---\left(5\right)$

Therefore, by the known equivalent load R first obtained under accumulator presence of formula _l, then record U by twice electric discharge ₁, U ₂, U ₂-U ₁, the internal resistance R of accumulator can be tried to achieve thus _s.

By the known magnitude of voltage U that need measure precision resistance two ends in twice discharge loop of the expression formula of internal resistance ₁with U ₂, and both difference U ₂-U ₁, due to U ₂with U ₁difference very little, in order to reduce measuring error, improve measuring accuracy, herein first with sampling holder to U ₂and U ₁carry out sampling to keep, then obtain U by differential amplification ₂-U ₁value.Then data are sent into and carry the internal resistance value calculating accumulator in the single-chip microcomputer of AD conversion.

DC low current secondary discharge accumulator internal resistance on-line measuring device block diagram as shown in Figure 2.12V, 38Ah analysing valve control type lead-acid accumulator battery selected by accumulator, in Fig. 2, main control chip selects C8051F350 single-chip microcomputer, having electrification reset in sheet, VDD monitor, band 24 or 16 single-ended/difference ADC, WatchDog Timer and clock oscillators, is the SOC (system on a chip) that really can work alone.Precision resistance R in discharge loop I, II ₁, R ₂get 20 Ω and 10 Ω respectively, twice discharge current is all no more than 2A, and data acquisition selects Hall element to realize voltage acquisition.Hall element gathers U ₀, U ₁, U ₂signal-regulated kinase is sent to process after signal, by internal resistance R _sexpression formula knownly need measure U ₂-U ₁value, due to U ₂with U ₁difference very little, in order to reduce measuring error, herein first to U ₂and U ₁carry out sampling to keep, the U after sampling keeps ₁, U ₂send into A/D modular converter and carry out analog to digital conversion feeding single-chip microcomputer, the U after sampling simultaneously keeps ₁, U ₂send into differential amplifier circuit and obtain U ₂-U ₁value, then send A/D modular converter to carry out analog to digital conversion, the U that Signal-regulated kinase exports ₀through A/D modular converter output digit signals to single-chip microcomputer, single-chip microcomputer carries out internal resistance calculating.

Sampling retaining part circuit diagram as shown in Figure 3, sampling holder selects LF398, utilizes logic level to control its duty.Sampling holder has two stable duties.Sample states: its reception analog input signal fast as far as possible during this period, and the change of accurately trace simulation input signal, until till receiving hold instruction; Hold mode: to flashy analog signal sampling before receiving hold instruction.Sampling holder was equivalent to " analog signal storage " in the maintenance stage.Fig. 3 is sampling retaining part circuit diagram, switch S during first time electric discharge ₁closed, S ₂disconnect, sampling holder L1 is in sample states; Then second time electric discharge is carried out, now S ₂closed, S ₁disconnect, sampling holder L1 is in hold mode, and L2 is in sample states; Then L1, L2 are in hold mode, finally the data collected are given differential amplifier and obtain calculating the data needed for the internal resistance of electric power storage group, completed the calculating of internal resistance by single-chip microcomputer.

Claims (3)

1. a DC low current secondary discharge accumulator internal resistance online test method, is characterized in that, specifically comprise the steps:

1) set up two discharge loops, accumulator, be connected on the switch S at accumulator two ends ₁with sampling precision resistance R ₁the first discharge loop formed, accumulator, is connected on the switch S at accumulator two ends ₂with sampling precision resistance R ₂the discharge loop formed, single-chip microcomputer exports control signal and controls two switch S ₁, S ₂fragmentary works;

2) first by two discharge loop switch S ₁and S ₂all disconnect, record pull-up resistor both end voltage U ₀and electric current, the load resistor value R under accumulator presence can be tried to achieve by Ohm law _l;

3) first time low discharging current is carried out to accumulator, switch S ₁closed, switch S ₂disconnect, detect accumulator both end voltage U ₁, then second time low discharging current is carried out to accumulator, switch S ₂closed, switch S ₁disconnect, detect accumulator both end voltage U ₂, send Signal-regulated kinase to process after signal after gathering, the U after Signal-regulated kinase process ₁, U ₂send into two sampling holders respectively to keep, two sampling holder outputs are sent into differential amplifier circuit again and are obtained U ₂-U ₁value;

4) detected value is sent into internal resistance calculating formula and obtain internal resistance R _s

$R_S=\frac{R_1{R}_2{R}_L(U_2-U_1)}{R_L(U_1{R}_2-U_2{R}_1)-R_1{R}_2(U_2-U_1)}.$

2. DC low current secondary discharge accumulator internal resistance online test method according to claim 1, it is characterized in that, described sampling hold circuit selects LF398 as sampling holder.

3. DC low current secondary discharge accumulator internal resistance online test method according to claim 1 or 2, is characterized in that, described step 3) first time low discharging current time, switch S ₁closed, switch S ₂disconnect, the first sampling holder is in sample states; When then carrying out low discharging current, now switch S ₂closed, switch S ₁disconnect, the first sampling holder is in hold mode, and the second sampling holder is in sample states; So latter two sampling holder is all in hold mode, finally by the data U of sampling holder output ₁, U ₂with the U that differential amplifier circuit exports ₂-U ₁send into the internal resistance value calculating accumulator in the single-chip microcomputer of band AD conversion.