CN104122447A - Online estimation method for direct current resistance of power battery of electric vehicle - Google Patents

Abstract

The invention relates to an online estimation method for direct current resistance of a power battery of a plug-in hybrid electric vehicle or a pure electric vehicle. The online estimation method includes that in the process of charging through a vehicle-mounted charger, charging to appointed equally spaced SOC points in sequence in a constant-current charging mode, and then using a constant-voltage charging mode; when the current is reduced to an equalizing current designed by a monomer equalizer, casually opening and closing the equalizer of each monomer in sequence, using the equalizer to generate a composite pulse excitation on each monomer, recording the change curve of the terminal voltage thereof changed along with the time, substituting into a corresponding mathematical model of direct current resistance of the power battery to obtain the direct current resistance and open-circuit voltage of the battery, and calculating the direct current resistance and open-circuit voltage of a power battery pack according to the direct current resistance and open-circuit voltage of the battery. The online estimation method for the direct current resistance of the power battery of the electric vehicle is simple and reliable and has high practicability and performability.

Description

A kind of estimation on line method of electric automobile power battery group DC impedance

Technical field

The present invention relates to a kind of electric automobile power battery group DC impedance estimation on line method, belong to electric automobile power battery electric energy management field.

Background technology

Electrokinetic cell is electric automobile important component part, in its use procedure, accurately grasps electrokinetic cell state parameter to improving electric automobile performance and safety, plays vital effect.Some state parameter of current driving force battery is as state of charge (state of charge, SOC), health status (state of health, and power rating (state of power SOH), SOP) cannot directly obtain by sensor or other device, need to contact electrokinetic cell electrical characteristic parameter, use certain mathematical method, carry out real-time estimation.

Power battery pack is most important is also that the electrical characteristic parameter that is difficult to directly obtain is DC internal resistance and the open-circuit voltage of electric battery.The method of research on-line prediction power battery pack DC internal resistance is extremely important: the electric characteristic models that 1) contributes to set up accurate electrokinetic cell; 2) contribute to improve the accuracy that battery status is estimated; 3) contribute to performance boost and the safety guarantee of electric automobile.

Current driving force electric battery DC internal resistance is all generally to use battery test apparatus to carry out off-line test to battery to obtain, and in the state estimation in later stage, sets it as constant constant processing.And along with the increase of service time of battery, and accelerate frequently in electric automobile actual moving process, slow down, the applying working condition that start and stop etc. are complicated, can cause power battery pack DC internal resistance that certain variation occurs, the method that off-line obtains data is not considered the time variation of parameter, and corresponding state estimation degree of accuracy also progressively reduces.And also there is no so far both at home and abroad an accurately method of on-line prediction power battery pack DC internal resistance and open-circuit voltage.

Summary of the invention

The object of the invention is to overcome above-mentioned the deficiencies in the prior art and a kind of electric automobile power battery group DC impedance estimation on line method is provided, and the method can realize the object of the inner parameter of estimation on line electric battery DC impedance.

The technical scheme that realizes the object of the invention employing is: a kind of electric automobile power battery group DC impedance estimation on line method, comprises the following steps:

By Vehicular charger to power battery charging, at default uniformly-spaced SOC point place constant voltage low current charge;

Unlatching, the closing motion of the balanced device of each battery cell distributed in utilization, produces the constant-current pulse of positive and negative 2 directions;

Gather the voltage signal of each battery cell, the variation relation data line curve to each monomer voltage to the time, obtains the curve of matching;

The matched curve obtaining is carried out to parameter identification, calculate DC impedance and the open-circuit voltage parameter of each battery cell;

According to the type of attachment of battery, the battery cell parameter obtaining is performed mathematical calculations, thereby draw whole power battery pack DC impedance and open-circuit voltage.

The DC impedance Data Update that estimation on line is gone out is to BMS (battery management system) controller, for follow-up BMS is to battery charge state (state of charge, SOC), health status (state of health, SOH) provides the data of online updating.

In technique scheme, first described Vehicular charger charges to electrokinetic cell with constant current charging mode, and calculates charge capacity with ampere-hour integral method; And in the time that electrokinetic cell is charged to default uniformly-spaced SOC point, make charge mode into constant voltage low current charge pattern.

In technique scheme, described balanced device should adopt two-way buck-boost circuit to produce the constant-current pulse with positive and negative 2 directions.

In technique scheme, time and the standing time of middle balanced device of 2 pulse currents of described buck-boost circuit generation should be consistent with the pulse curve of mixed pulses power characteristic test request.

In technique scheme, BMS collecting unit gathers the voltage of battery cell, and utilizes CAN network that data are sent to BMS main control unit.

In technique scheme, the voltage arithmetic mean value after the voltage using pulsed discharge and after leaving standstill and pulse charge also leave standstill is as battery open-circuit voltage at that time.

Compared with prior art, the present invention has the following advantages:

1, utilize Vehicular charger and monomer balanced device, online simulation mixed pulses power characteristic (hybrid pulse power characterization, HPPC) test, be different from traditional battery dynamic characteristic test method, the present invention, without vehicle mounted dynamic battery is dismantled, can estimate battery DC impedance in battery charging process.

2, open-circuit voltage (open circuit voltage, OCV) estimation is to utilize mixed pulses power characteristic (hybrid pulse power characterization, HPPC) in test, after the rear standing 40s magnitude of voltage of electric discharge and charging, the arithmetic mean of standing 40s magnitude of voltage is worth as it, the method that this is different from general tradition the battery operated rear standing long period is obtained its open-circuit voltage, has very high engineering operability.

Brief description of the drawings

Fig. 1 is the process flow diagram of the estimation on line method of electric automobile power battery group DC impedance of the present invention.

Fig. 2 is the two-way buck-boost circuit topological structure that balanced device is taked.

Fig. 3 is battery cell curent change curve in balanced device open and close process.

Fig. 4 is the time dependent curve of battery cell terminal voltage that balanced device open and close process gathers.

Fig. 5 carries out by matched curve the graph of a relation that open-circuit voltage that parameter identification goes out changes with SOC.

Fig. 6 carries out by matched curve the graph of a relation that time constant that parameter identification goes out changes with SOC.

Fig. 7 carries out by matched curve the graph of a relation that polarization capacity that parameter identification goes out changes with SOC.

Fig. 8 carries out by matched curve the graph of a relation that ohmic internal resistance that parameter identification goes out changes with SOC.

Fig. 9 carries out by matched curve the graph of a relation that polarization resistance that parameter identification goes out changes with SOC.

Figure 10 is the PNGV equivalent-circuit model schematic diagram of taking.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in further detail.

The present embodiment adopts the lithium-ion-power cell group of the ferric phosphate lithium ion monomer composition of certain company's production, object is the open-circuit voltage obtaining in its single order PNGV equivalent electrical circuit, ohmic internal resistance, the electrical characteristic parameter of polarization impedance, PNGV equivalent-circuit model schematic diagram is as shown in figure 10.

As shown in Figure 1, the estimation on line method of electric automobile power battery group DC impedance of the present invention comprises the following steps:

S100, Vehicular charger carry out constant-current charge to electrokinetic cell, at SOC point uniformly-spaced, (the present embodiment is got 5% uniformly-spaced point, for example: 5%, 10%, 15%,, 100%) and locate to change into the little electric current trickle charge of constant voltage, the now respectively SOC point (5% uniformly-spaced of magnitude of voltage and off-line calibration in battery test apparatus, 10%, 15%,, 100%) magnitude of voltage located is identical.

Unlatching, the closing motion of the balanced device of each battery cell distributed in S200, utilization, produces the constant-current pulse of positive and negative 2 directions.

In the present embodiment, as shown in Figure 2, loop forms typical two-way buck-boost circuit by inductance and field effect transistor to circuit of battery pack balancing topological structure.Stage 1: opening switch pipe Q1, energy is stored in inductance L 1 by battery B1, closed Q1, unlatching Q2, the energy being now stored in inductance L 1 is passed to adjacent battery B2, control constant current size 0.1C, duration 10s, produces the 0.1C pulse current by battery B1 to B2 thus.Stage 2: after keeping 40s, because topological structure has been designed to symmetrical structure, utilize identical principle to produce the reverse pulse of 0.1C, the pulse energy that is reached B2 by B1 is returned to B1.In this whole process, Vehicular charger to batteries charging, makes up by opening with the little electric current trickle of constant voltage mode, closed balanced device and the energy that brings consumes, therefore can think that SOC now keeps constant.

S300, record each SOC point place terminal voltage temporal evolution curve, use curve instrument to carry out minimum 2 to data and take advantage of matching, obtain similar mixed pulses power characteristic (hybrid pulse power characterization, HPPC) curve, this curve as shown in Figure 3.

S400, the HPPC matched curve obtaining is carried out to parameter identification with following formula, each magnitude of voltage and time point are as shown in accompanying drawing 3, accompanying drawing 4, draw the each parameter value of each SOC point place's DC impedance, obtain open-circuit voltage, time constant, polarization capacity, ohmic internal resistance and polarization resistance respectively as shown in Fig. 5～8.

Open-circuit voltage:

$U_{\mathrm{oc}}=\frac{1}{2}(U_4+U_6)---\left(1\right)$

Timeconstantτ:

$\mathrm{\τ}=-\frac{(t_4-t_3)}{\mathrm{In}(1-\frac{U_4-U_3}{U_1-U_3})}---\left(2\right)$

Capacitor C b:

$C_b=\frac{\mathrm{AmpSec}*U_{\mathrm{oc}}}{\frac{1}{2}*(U_{100\%\mathrm{SOC}}^2-U_{0\%\mathrm{SOC}}^2)}---\left(3\right)$

In formula, AmpSec is rated capacity, and Uoc is open-circuit voltage.

Ohmic internal resistance:

$R_0=\frac{U_1-U_1^{\′}}{I}---\left(4\right)$

Polarization resistance:

$R_{\mathrm{pp}}=\frac{U_4-U_3}{I}---\left(5\right)$

S500, according to battery cell type of attachment, therefore the total open-circuit voltage of electric battery is:

Total ohmic internal resistance and polarization resistance are respectively:

Total polarization capacity is:

In above formula, t ₁for starting pulsed discharge zero hour, t ₂for electric discharge cut-off time, t ₃for leaving standstill the zero hour, t ₄for leaving standstill the finish time, t ₅for pulse charge cut-off time; The corresponding t that gets ₁moment final voltage value is U ₁, the value after voltage dip is U ₁', t2 moment magnitude of voltage is U ₂, t ₃moment magnitude of voltage is U ₃, t ₄moment magnitude of voltage is U ₄, t ₅moment magnitude of voltage is U ₅, after charging leaves standstill, magnitude of voltage is U ₆.

Finally, the DC impedance that above-mentioned estimation on line is gone out is updated to BMS controller, for follow-up BMS provides the data of online updating to battery charge state, health status.

Claims (7)

1. an estimation on line method for electric automobile power battery group DC impedance and open-circuit voltage, is characterized in that, comprises the following steps:

By Vehicular charger to power battery charging, at default uniformly-spaced SOC point place constant voltage low current charge;

Unlatching, the closing motion of the balanced device of each battery cell distributed in utilization, produces the constant-current pulse of positive and negative 2 directions;

Gather the voltage signal of each battery cell, the variation relation data line curve to each monomer voltage to the time, obtains mixed pulses power characteristic;

The curve of the matching obtaining is carried out to parameter identification, calculate DC impedance and the open-circuit voltage parameter of each battery cell;

According to the type of attachment of battery, the battery cell parameter obtaining is performed mathematical calculations, thereby draw whole power battery pack DC impedance and open-circuit voltage.

2. the estimation on line method of electric automobile power battery group DC impedance according to claim 1, it is characterized in that: first described Vehicular charger charges to electrokinetic cell with constant current charging mode, and calculate charge capacity with ampere-hour integral method, in the time that electrokinetic cell is charged to default uniformly-spaced SOC point, make charge mode into constant voltage low current charge pattern.

3. the estimation on line method of electric automobile power battery group DC impedance according to claim 1, is characterized in that: described balanced device should adopt two-way buck-boost circuit to produce the constant-current pulse with positive and negative 2 directions.

4. the estimation on line method of electric automobile power battery group DC impedance according to claim 3, is characterized in that: time and the standing time of middle balanced device of 2 pulse currents of described buck-boost circuit generation should be consistent with the pulse curve of mixed pulses power characteristic test request.

5. the estimation on line method of electric automobile power battery group DC impedance according to claim 1, is characterized in that: gather the voltage of battery cell by BMS collecting unit, and utilize CAN network that data are sent to BMS main control unit.

6. the estimation on line method of electric automobile power battery group DC impedance according to claim 1, is characterized in that: the voltage arithmetic mean value after the voltage using pulsed discharge and after leaving standstill and pulse charge also leave standstill is as battery open-circuit voltage at that time.

7. the estimation on line method of electric automobile power battery group DC impedance according to claim 1, is characterized in that BMS utilizes following formula to estimate DC impedance and the open-circuit voltage of each battery cell:

Open-circuit voltage:

$U_{\mathrm{oc}}=\frac{1}{2}(U_4+U_6)---\left(1\right)$

Timeconstantτ:

$\mathrm{\τ}=-\frac{(t_4-t_3)}{\mathrm{In}(1-\frac{U_4-U_3}{U_1-U_3})}---\left(2\right)$

Capacitor C b:

$C_b=\frac{\mathrm{AmpSec}*U_{\mathrm{oc}}}{\frac{1}{2}*(U_{100\%\mathrm{SOC}}^2-U_{0\%\mathrm{SOC}}^2)}---\left(3\right)$

In formula, AmpSec is rated capacity, and Uoc is open-circuit voltage;

Ohmic internal resistance:

$R_0=\frac{U_1-U_1^{\′}}{I}---\left(4\right)$

Polarization resistance:

$R_{\mathrm{pp}}=\frac{U_4-U_3}{I}---\left(5\right)$

Then, according to battery cell type of attachment, draw DC impedance and the open-circuit voltage of whole electric battery by mathematical operation, concrete computation process is as follows:

The total open-circuit voltage of electric battery is:

Total ohmic internal resistance and polarization resistance are respectively:

Total polarization capacity is:

In above formula, t ₁for starting pulsed discharge zero hour, t ₂for electric discharge cut-off time, t ₃for leaving standstill the zero hour, t ₄for leaving standstill the finish time, t ₅for pulse charge cut-off time; The corresponding t that gets ₁moment final voltage value is U ₁, the value after voltage dip is U ₁', t2 moment magnitude of voltage is U ₂, t ₃moment magnitude of voltage is U ₃, t ₄moment magnitude of voltage is U ₄, t ₅moment magnitude of voltage is U ₅, after charging leaves standstill, magnitude of voltage is U ₆.