CN102121973A - Method for testing net energy of electrical vehicle power battery - Google Patents

Abstract

The invention discloses a method for testing the net energy of a power battery of an electric vehicle. It charges the battery pack at the discharge cut-off voltage to the charge cut-off voltage with a rated current, records the charged energy, and then discharges the battery pack with a rated current to a preset value. Set the SOC, record the energy released for the first time, and then conduct a cycle test on the electric vehicle. After the test is completed, discharge the battery pack at the rated current to the discharge cut-off voltage, and record the energy released for the second time; The charge and discharge efficiency obtains the energy change of the battery in the cycle test of the working condition, corrects the energy change of the battery in the cycle test of the working condition according to the battery charge and discharge energy efficiency model, and obtains the actual stored electric energy of the battery during the cycle of the working condition, that is, the battery of net energy. On the one hand, the method considers the influence of charging and discharging efficiency on the net energy of the battery, and the test accuracy is high;

Description

Electric automobile power battery net energy method of testing

Technical field

The present invention relates to electric automobile energy consumption testing technical field, particularly a kind of electric automobile power battery net energy method of testing.

Background technology

Electrokinetic cell is an energy-storage travelling wave tube the most frequently used in all kinds of electric automobiles, and its power performance directly has influence on the operating cost and the serviceable life of electric automobile.The finite energy that therefore must make full use of the electric battery storage is with the operating cost that reduces electric automobile and increase the service life.The research of aspects such as at present energy-optimised to the Vehicular dynamic battery group, energy management system is more, but less for the research that changes with electric automobile energy consumption and the closely-related battery net energy of discharging.And research electric automobile power battery net energy has significant meaning: 1) provide technical support for heavy mixed power electric car car load energy consumption and emission test; 2) net energy of cells known can be tried to achieve the energy efficiency of battery in the car load test process, and then can analyze the battery generation of heat at work, is convenient to battery thermal management, optimizes integrated vehicle control tactics.

Existing battery net energy computing method are directly to calculate by voltage, electric current and time integral, obtain the battery net energy.This method is not owing to consider the influence of efficiency for charge-discharge, and electric current and voltage accurately obtain the restriction that is subjected to surveying instrument, the changing value that therefore obtains the battery net energy exactly is very difficult.

Therefore, be necessary to provide a kind of improved electric automobile power battery net energy method of testing to overcome the defective of prior art.

Summary of the invention

The purpose of this invention is to provide a kind of electric automobile power battery net energy method of testing, can accurately obtain the changing value of battery net energy.

To achieve these goals, the invention provides a kind of electric automobile power battery net energy method of testing, comprise the steps:

(1) determine the state-of-charge interval, calculate battery net energy in this state-of-charge interval according to the rated capacity of electric battery and battery open circuit voltage with the quantitative relationship of state-of-charge, computing formula is:

Wherein, Δ Q _nBe net energy, C _nBe rated capacity, SOC (0) is the state-of-charge interval to SOC (t), U _OCVBe battery open circuit voltage, SOC is a state-of-charge;

(2) battery is carried out the multiple discharge experiment, set up the battery discharging energy efficiency Model of discharge current and discharge energy relationship between efficiency;

(3) electric automobile is put between test carriage, the electric battery that will be in discharge cut-off voltage is charged to the charging cut-off voltage with rated current, the ENERGY E that the record charging consumes ₁, discharge into discharge cut-off voltage with rated current again, the ENERGY E that record is emitted ₂, according to formula The average efficiency for charge-discharge of counting cell group

(4) electric automobile is put between test carriage, the electric battery that will be in discharge cut-off voltage with the rated current constant-current charge to the cut-off voltage that charges, again with the rated current constant-current discharge to default SOC, the ENERGY E that record is emitted for the first time _Out1, again electric automobile being carried out the operating mode cyclic test on the chassis dynamometer revolving drum test table, the average current of record operating mode cyclic test after the operating mode cyclic test is finished, to discharge cut-off voltage, writes down the ENERGY E of emitting for the second time with the rated current constant-current discharge _Out2

(5) according to the average efficiency for charge-discharge of battery

The ENERGY E that charging consumes ₁, the ENERGY E of emitting for the first time _Out1With the ENERGY E of emitting for the second time _Out2The energy content of battery variation delta E of design condition circulation experiment ₀, computing formula is:

According to the average current of the operating mode cyclic test of rated current and record, utilize the battery discharging energy efficiency Model to calculate the default discharge energy efficiency eta that discharges and recharges under the system respectively _OutWith the discharge energy efficiency eta in the operating mode cyclic test _Dis0, according to formula Δ E _t=(Δ E ₀/ η _Out) η _Dis0The battery net energy Δ E of design condition circulation experiment _t

In one embodiment of the invention, definite step of the rated capacity of electric battery is in the described step (1):

With electric battery with the rated current constant-current discharge to discharge cut-off voltage, to the cut-off voltage that charges, this moment, the electric weight that charges into was the rated capacity of electric battery with the rated current constant-current charge.

In another embodiment of the present invention, battery open circuit voltage with definite step of the quantitative relationship of state-of-charge is in the described step (1):

With electric battery with the rated current constant-current discharge to discharge cut-off voltage, the test electric automobile is when being pure electric automobile, rated current is C/3, when the test electric automobile was mixed power electric car, rated current was 1C;

Again electric battery is stopped the charging curve that the record total voltage changes with state-of-charge after with 0.04C electric current constant-current charge 25h;

Again with electric battery with 0.04C electric current constant-current discharge 25h after or stop the discharge curve that the record total voltage changes with state-of-charge to cut-off voltage;

The utilization linear interpolation method obtains the open circuit voltage variations curve that the monomer average open-circuit voltage changes with state-of-charge with charging curve and discharge curve stack,

Utilize the relational expression of battery open circuit voltage with state-of-charge And the unknown parameter k in the above-mentioned open circuit voltage variations curve acquisition relational expression ₁, k ₂, k ₃, k ₄, k ₅, k ₆, k ₇, k ₈, k ₉, k ₁₀, obtain the quantitative relationship of battery open circuit voltage with state-of-charge, wherein y is an open-circuit voltage in the relational expression, x is a state-of-charge.

In an embodiment more of the present invention, described step (2) is specially:

Battery is discharged to the termination SOC of setting with different constant currents from the initial SOC that sets, at each constant current, the extraneous energy Q of battery output behind the record discharge off _OutAnd battery net energy Δ Q _n, according to formula η _Dis=Q _Out/ Δ Q _nCalculate the discharge energy efficiency eta of each constant current correspondence _Dis, all constant currents and corresponding discharge energy efficient are carried out curve fitting, thereby set up the battery discharging energy efficiency Model.

Compared with prior art, electric automobile power battery net energy method of testing of the present invention has been considered the influence of efficiency for charge-discharge to the battery net energy, battery net energy accuracy of test height.

In addition, this method of testing need not the voltage, the current value that adopt expensive surveying instrument to obtain battery, only need measure the energy that electric automobile fills into and emits before and after test, thereby obtain the energy variation amount of battery in the operating mode circulation, and then obtaining the net energy of battery by correction, method of testing realizes easily.

By following description also in conjunction with the accompanying drawings, it is more clear that the present invention will become, and these accompanying drawings are used to explain embodiments of the invention.

Description of drawings

Fig. 1 is an electric automobile power battery net energy method of testing process flow diagram of the present invention.

Fig. 2 be in the electric automobile power battery net energy method of testing shown in Figure 1 LiFePO4 batteries monomer average open-circuit voltage with the SOC change curve.

Fig. 3 has showed the LiFePO4 batteries charging energy efficiency model in the electric automobile power battery net energy method of testing shown in Figure 1, wherein the battery charge energy efficiency that obtains for actual measurement of black side's point.

Fig. 4 has showed the LiFePO4 battery power discharge energy efficiency model in the electric automobile power battery net energy method of testing shown in Figure 1, wherein the battery discharging energy efficient that obtains for actual measurement of black side's point.

Embodiment

With reference now to accompanying drawing, describe embodiments of the invention, the similar elements label is represented similar elements in the accompanying drawing.

Principle below in conjunction with accompanying drawing and instantiation detailed description electric automobile power battery net energy method of testing of the present invention.The electric battery that the present embodiment electric automobile adopts is the LiFePO4 type lithium-ion-power cell that domestic certain company produces.

As shown in Figure 1, described electric automobile power battery net energy method of testing comprises the steps:

Step S1, according to national standard, (rated current of dissimilar batteries is determined by corresponding national battery performance test standard and electric automobile type with rated current with electric battery, when the test electric automobile is pure electric automobile (EV), the LiFePO4 type lithium-ion-power cell rated current that this paper selects for use is 0.33C, be C/3, when the test electric automobile is mixed power electric car (HEV), the LiFePO4 type lithium-ion-power cell rated current that this paper selects for use is 1C) constant-current discharge is to discharge cut-off voltage, leave standstill 1h (after the national Specification battery discharge finishes, leave standstill 1h and treat to carry out again after battery performance recovers ensuing charging experiment) after, to the cut-off voltage that charges (being about to electric battery is full of), the electric weight that charge into this moment is the rated capacity C of electric battery with the rated current constant-current charge _n

Step S2, according to national standard, (determined with power accumulator performance test standard by 2008 annual EV, HEV: when the test electric automobile was pure electric automobile (EV), rated current was C/3 with rated current with electric battery; When the test electric automobile is mixed power electric car (HEV), rated current is 1C) constant-current discharge is to discharge cut-off voltage, leave standstill 1h (after the national Specification battery discharge finishes, leave standstill 1h and treat to carry out again after battery performance recovers ensuing charging experiment) after, with 0.04C (C/25, determining that by document and experiment test the low range electric current is C/25) constant-current charge 25h is (with 0.04C constant-current charge 25h, battery capacity (C/25) * 25=C, be that battery is full of, and the battery cell average voltage can not arrive charging cut-off voltage 3.6V)) after stop, the battery charge curve that the record total voltage changes with SOC (state-of-charge), leave standstill 5h (because during with C/25 electric current constant-current charge, duration of charging reaches 25h, and before guaranteeing to carry out follow-up discharge test, battery performance recovers and is in steady state (SS) fully, make the measured value of after discharge experiment enough accurate, therefore time of repose is longer herein, be 5h) after, to stop (with 0.04C constant-current discharge 25h behind the 0.04C electric current constant-current discharge 25h or to discharge cut-off voltage, in theory that the battery tele-release is intact, after considering that battery is formed battery module, the monomer inconsistency strengthens, some monomer voltage has reached discharge cut-off voltage in the time of might causing battery discharge to be less than 25h, cause potential safety hazard for avoiding battery to cross putting, also should stop discharge this moment), the battery discharge curve that the record total voltage changes with SOC, the utilization linear interpolation method can obtain monomer average open-circuit voltage U with charging curve and discharge curve stack _OCVThe open circuit voltage variations curve that changes with SOC is (according to document (periodical JOURNAL OF POWER SOURCES, article is called Extended Kalman filtering for battery management systems of LiPB-based HEV battery packs Part2.Modeling and identification, author Gregory L.Plett) and experiment test as can be known, discharge and recharge for a long time with the low range electric current, the gained charging and discharging curve is superposeed, can obtain the relation curve that open-circuit voltage (OCV) changes with state-of-charge (SOC), the OCV-SOC relation curve error that this curve and actual measurement obtain is very little, the open-circuit voltage that can correctly reflect battery under certain state-of-charge), (voltage among Fig. 2 is that total voltage is divided by the monomer number as shown in Figure 2, it is the monomer average open-circuit voltage, round dot is the cell open-circuit voltage values that actual measurement obtains, measuring method be battery with electric weight be charged to certain SOC after having put, (open-circuit voltage refers to battery under off working state to leave standstill 3h, be that battery does not have under the condition of external any load, when the circuit no current flows through, directly measure magnitude of voltage between gained battery two binding posts with ammeter.Battery must be in steady state (SS) when therefore carrying out the open-circuit voltage measurement, so when being charged to certain SOC, must leave standstill the regular hour, treat that battery performance is stable, currently used time of repose is generally 2-4h, the time of repose that we choose when experimentizing is 3h, this moment, the inside battery chemical reaction tended to balance, performance is recovered substantially fully, leave standstill the longer time again, cell voltage, temperature does not have to change substantially) back surveys total voltage, then divided by the monomer number), can obtain the open-circuit voltage U of corresponding state-of-charge (SOC) point according to this open circuit voltage variations curve _OCVThe relational expression of utilizing the same state-of-charge of LiFePO4 battery open circuit voltage (SOC) is (by document (periodical JOURNAL OF POWER SOURCES, article is called Solid-state diffusion limitations on pulse operation of a lithium ion cell for hybrid electric vehicles, author Kandler Smith, Chao-Yang Wang) obtains, this relational expression can accurately reflect the open-circuit voltage of battery under certain state-of-charge, this function curve is compared with above-mentioned measured curve, error is very little, the mean square deviation of fitting function curve is less than 0.002, and related coefficient is greater than 0.999) but and above-mentioned open circuit voltage variations curve iteration try to achieve unknown parameter k in (1) formula ₁, k ₂, k ₃, k ₄, k ₅, k ₆, k ₇, k ₈, k ₉, k ₁₀, obtain the quantitative relationship of LiFePO4 battery open circuit voltage with SOC, wherein the LiFePO4 battery open circuit voltage is as follows with the relational expression of SOC:

$y=k_1{x}^6+k_2{x}^5+k_3{x}^4+k_4{x}^3+k_5{x}^2+k_{6}x+{\mathrm{<figure-callout\; id="7"\; label="k"\; filenames="HDA0000042715030000011.png"\; state="\{\{state\}\}">k</figure-callout>}}_7+k_8{e}^{(k_9-x^{k_{10}})}---\left(1\right)$

(1) in the formula, y is open-circuit voltage U _OCV, x is SOC (state-of-charge);

Step S3 determines state-of-charge (SOC) interval, calculates the interval interior battery net energy of this state-of-charge (SOC) according to the LiFePO4 battery open circuit voltage with the quantitative relationship of state-of-charge:

Wherein, Δ Q _nBe battery net energy, C _nBe the battery rated capacity, SOC (0) is the state-of-charge interval to SOC (t), U _OCVBe battery open circuit voltage, SOC is a state-of-charge;

Step S4 is according to national Specification, under 20 ℃ ± 5 ℃ environmental baselines, with different charging currents (0.1C, 0.33C, 0.5C, 1C, the 2C) experiment of charging, charge to certain SOC, to each charging current, the energy Q of extraneous input battery after the record charging is finished _In, and calculate charging according to the formula among the step S3 and cause SOC to change pairing battery net energy Δ Q _n, by rechargeable energy efficiency calculation formula η _Ch=Δ Q _n/ Q _InCalculate the rechargeable energy efficiency eta of each charging current correspondence _ChExperimental data is carried out curve fitting, set up battery charge energy efficiency model (as shown in Figure 3, the battery charge energy efficiency that obtains for actual measurement of black point wherein, solid line is the matched curve of rechargeable energy efficient second order, be the line of a plurality of black points, the quadratic function equation is the rechargeable energy efficiency Model of being set up); According to national Specification, under 20 ℃ ± 5 ℃ environmental baselines, (0.1C, 0.33C, 0.5C, 1C, 2C, 3C) carries out discharge test with different discharge currents, is discharged to certain SOC, to each discharge current, the extraneous energy Q of battery output after the record discharge is finished _Out, and calculating discharge according to the formula among the step S3, to cause SOC to change pairing battery net energy be Δ Q _n, by discharge energy efficiency calculation formula η _Dis=Q _Out/ Δ Q _nCalculate the discharge energy efficiency eta of each discharge current correspondence _DisExperimental data is carried out curve fitting, set up the battery discharging energy efficiency Model (as shown in Figure 4, the battery discharging energy efficient that obtains for actual measurement of black side's point wherein, solid line is the matched curve of discharge energy efficient second order, be the line of a plurality of black points, the quadratic function equation is the battery discharging energy efficient mathematical model of being set up);

Step S5 puts into electric automobile between test carriage, with the rated current I of electric battery with national Specification ₀(pure electric automobile rated current I ₀Be C/3, mixed power electric car rated current I ₀Being 1C) constant-current discharge is to discharge cut-off voltage (be about to electric battery dump energy give out light), leaves standstill 1h (national Specification battery discharge finish after, leave standstill 1h and treat to carry out after battery performance recovers ensuing charging experiment again), with rated current I ₀Constant-current charge is to charging cut-off voltage, the energy value E that record charges and consumed ₁, leave standstill 1h after, with rated current I ₀Constant-current discharge writes down the energy value E that emits to discharge cut-off voltage from battery ₂, then the average efficiency for charge-discharge of electric battery is:

Step S6 puts into electric automobile between test carriage, with electric battery with rated current I ₀(pure electric automobile rated current I ₀Be C/3, mixed power electric car rated current I ₀Being 1C) constant-current discharge is to discharge cut-off voltage (be about to electric battery dump energy give out light), leaves standstill 1h, with rated current I ₀(pure electric automobile is 0.33C, and mixed power electric car is 1C) constant-current charge writes down the energy value that charging consumes to the cut-off voltage that charges

Be the E among the step S5 ₁, leave standstill 1h after, with rated current I ₀(this value is generally 80% to constant-current discharge to default SOC value, used for electric vehicle power accumulator state-of-charge scope commonly used is 20%-80%, electric automobile is in operating mode circulation driving process, the stored electric weight of battery is used for the steam supply car and travels, battery is emitted electric weight, and the SOC value reduces, so the default SOC value that operating mode circulates before travelling generally is made as 80%-90%, low excessively with battery electric quantity after avoiding the operating mode circulation to travel), the energy value E that record is emitted _Out1, leave standstill 1h after, on the chassis dynamometer revolving drum test table, carry out the operating mode cyclic test, the average current I of record operating mode cyclic test with Chinese typical urban public transport circulation _Av(average current I _AvBy selected operating mode circulation decision, under the different operating mode circulations, the electric current of battery changes different, and the electric current in the whole working condition cyclic process is carried out sum-average arithmetic, can obtain the average current I under the operating mode cyclic test _Av), after the operating mode cyclic test is finished, leave standstill 1h after, with rated current I ₀Constant-current discharge writes down the energy value E that emits to discharge cut-off voltage _Out2

Step S7, the average efficiency for charge-discharge of battery that obtains by step S5

The energy that obtains the actual acquisition of battery is The energy content of battery variation delta E of operating mode circulation experiment then ₀For:

$\mathrm{\&Delta;}{E}_0=E_{\mathrm{in}}*\stackrel{\&OverBar;}{\mathrm{\&eta;}}-E_{\mathrm{out}1}-E_{\mathrm{out}2}=E_2-(E_{\mathrm{out}1}+E_{\mathrm{out}2});$

Step S8 is according to the rated current I of step S6 ₀Average current I with the operating mode cyclic test of writing down _Av, utilize the battery discharging energy efficiency Model of step S4 to calculate default system (the rated current I that discharges and recharges respectively ₀) under the discharge energy efficiency eta _OutWith the discharge energy efficiency eta in the operating mode cyclic test _Dis0, according to default system (the rated current I that discharges and recharges that calculates ₀) under the discharge energy efficiency eta _OutWith the discharge energy efficiency eta in the operating mode cyclic test _Dis0, and the energy content of battery variation delta E of the operating mode circulation experiment of trying to achieve among the step S7 ₀, the battery net energy variable quantity of design condition circulation experiment, computing formula is:

ΔE _t＝(ΔE ₀/η _put)·η _dis0 (2)

Battery net energy variation delta E _tBe the energy of battery physical holding of the stock in the operating mode cyclic test process, i.e. the net energy of battery in the operating mode cyclic process.

The following describes the principle of step S8.Evidence is when the average current of pulse charge is I _{Av, ch}, the energy efficiency of pulse charge with identical average current I _{Av, ch}The energy efficiency of constant-current charge is basic identical; When the average current of pulsed discharge is I _{Av, dis}, the energy efficiency of pulsed discharge with identical average current I _{Av, dis}The energy efficiency of constant-current discharge is basic identical.The charge and discharge electric current of battery constantly changes in the operating mode cyclic test, so the current value of the constant current charge-discharge system of the average current of battery charge and discharge and setting (is rated current I in the operating mode cyclic test ₀) when equating, the energy efficiency of pulse charge and discharge equates that with the energy efficiency of constant current charge and discharge the energy variation amount of operating mode cyclic test is the actual energy variable quantity of battery, is the net energy of battery in the operating mode cyclic test process.

But, owing to the average current and the default rated current I that discharges and recharges system of battery charge and discharge in the actual condition circulation ₀And unequal, therefore need to proofread and correct the energy content of battery variation delta E of design condition circulation experiment ₀The time, E ₂, E _Out1, E _Out2All be at rated current I ₀Obtain down, the discharge energy efficient of being calculated under this electric current as can be known by the discharge energy efficiency Model is η _OutThereby, E as can be known ₂, E _Out1, E _Out2Actual value should be E ₂/ η _Out, E _Out1/ η _Out, E _Out2/ η _OutAverage current under the known operating mode cyclic test is I _Av, the discharge energy efficient of being calculated under this electric current as can be known by the discharge energy efficiency Model is η _Dis0, the emitting energy accordingly and should be respectively (E of this moment record ₂/ η _Out) η _Dis0, (E _Out1/ η _Out) η _Dis0, (E _Out2/ η _Out) η _Ids0Thereby the net energy variable quantity of battery is in the operating mode circulation experiment process as can be known: Δ E _t=(E ₂/ η _Out) η _Dis0-(E _Out1/ η _Out) η _Dis0-(E _Out2/ η _Out) η _Dis0, i.e. Δ E _t=η _Dis0(E ₂-E _Out1-E _Out2)/η _Out=(Δ E ₀/ η _Out) η _Dis0So the energy content of battery is proofreaied and correct efficient:

η wherein _Dis0Be the discharge energy efficient under the state of cyclic operation, η _OutBe default discharge system (rated current I ₀) under discharge energy efficient, proofread and correct efficiency eta according to the energy content of battery and obtain Δ E _t==Δ E ₀η.

As from the foregoing, electric automobile power battery net energy method of testing of the present invention is by the ENERGY E of instrument record input battery _InENERGY E with battery output _Out1, E _Out2(step S6) is by the average efficiency for charge-discharge of battery

Obtain the energy variation amount Δ E of battery in the operating mode circulation ₀(step S5 and step S7), energy variation amount Δ E ₀Be the poor of the input energy content of battery and battery output energy; According to the energy variation amount Δ E of energy content of battery efficiency Model to the operating mode cyclic test ₀Proofread and correct, thereby draw the net energy variation delta E of battery before and after the operating mode loop test _t(step S8) is the battery net energy in the operating mode cyclic test process.

Need to prove: 1) step S5 and S6 all need to carry out on the chassis dynamometer revolving drum test table; When 2) carrying out battery net energy engine bench test, the residing external environment condition of step S4, S5 and S6 (as environment temperature etc.) should be identical; 3) since electric automobile in operating mode circulation driving process, the electrokinetic cell most of the time is in discharge condition, therefore in the process of carrying out follow-up energy correction, what mainly consider is the influence of discharge energy efficient, and ignored the influence of rechargeable energy efficient, therefore do not use the rechargeable energy efficiency Model, evidence considers that simultaneously the influence of the influence of rechargeable energy efficient and discharge energy efficient is about the same with the effect correction effect of only considering discharge energy efficient.

The advantage of this electric automobile power battery net energy method of testing is:

1) the battery charge and discharge energy efficiency model of setting up by step S4, make and considered that in the process of step S8 counting cell net energy the charge and discharge electric current to the influence of energy efficiency and carried out corresponding correction, has improved the accuracy of battery net energy test.

2) the operating mode circulating energy variable quantity that records by step S5 and S6 has been considered the influence of charge and discharge efficient, and then makes that the operating mode circulating energy variable quantity of trying to achieve is more accurate.And what test was concerned about is the energy of input battery and the energy of battery output, therefore the test request to operating mode circulation dynamic process amount reduces, need not to adopt expensive high precision measurement instrument, reduced testing cost and difficulty of test, thereby have very strong operability and practicality.

Above invention has been described in conjunction with most preferred embodiment, but the present invention is not limited to the embodiment of above announcement, and should contain various modification, equivalent combinations of carrying out according to essence of the present invention.

Claims (4)

1. A method for testing the net energy of an electric vehicle power battery, comprising the steps of: (1) Determine the state of charge interval, and calculate the net energy of the battery within the state of charge interval according to the rated capacity of the battery pack and the quantitative relationship between the open circuit voltage of the battery and the state of charge. The calculation formula is:

Among them, ΔQ _n is the net energy, C _n is the rated capacity, SOC(0) to SOC(t) is the state of charge interval, U _OCV is the open circuit voltage of the battery, and SOC is the state of charge; (2) Carry out multiple discharge experiments on the battery, and establish a battery discharge energy efficiency model of the relationship between discharge current and discharge energy efficiency; (3) Charge the battery pack at the discharge cut-off voltage to the charge cut-off voltage with the rated current, record the energy E ₁ consumed by charging, and then discharge it to the discharge cut-off voltage at the rated current, record the energy E ₂ released by the discharge, according to the formula

Calculate the average charge and discharge efficiency of the battery pack

(4) Charge the battery pack at the discharge cut-off voltage to the charge cut-off voltage with a rated current constant current, then discharge it to the preset SOC with a rated current constant current, record the energy E _out1 released for the first time, and then put the electric vehicle on the chassis Carry out the working condition cycle test on the hub test bench of the dynamometer, record the average current of the working condition cycle test, after the working condition cycle test is completed, discharge at the rated current constant current to the discharge cut-off voltage, and record the second released energy E _out2 ; (5) According to the average charge and discharge efficiency of the battery

The energy E ₁ consumed by charging, the energy E _out1 released for the first time, and the energy E _out2 released for the second time are used to calculate the battery energy change ΔE ₀ in the cycle test of the working condition. The calculation formula is:

According to the average current of the rated current and the recorded operating condition cycle test, the battery discharge energy efficiency model is used to calculate the discharge energy efficiency η _out under the preset charge and discharge system and the discharge energy efficiency η _dis0 in the operating condition cycle test respectively, according to The formula ΔE _t =(ΔE ₀ /η _out )·η _dis0 calculates the net energy ΔE _t of the battery in the cycle test under working conditions. 2. The electric vehicle traction battery net energy test method as claimed in claim 1, is characterized in that, the determination step of the rated capacity of battery pack in the described step (1) is: After the battery pack is discharged to the discharge cut-off voltage with the rated current constant current, it is charged to the charge cut-off voltage with the rated current constant current, and the charged power at this time is the rated capacity of the battery pack. 3. The electric vehicle power battery net energy test method as claimed in claim 1, is characterized in that, in the described step (1), the determination step of the quantitative relationship between battery open circuit voltage and state of charge is: Discharge the battery pack at the rated current and constant current to the discharge cut-off voltage. When the electric vehicle tested is a pure electric vehicle, the rated current is C/3. When the electric vehicle tested is a hybrid electric vehicle, the rated current is 1C; Then charge the battery pack with a constant current of 0.04C for 25 hours and then stop, and record the charging curve of the total voltage changing with the state of charge; Then discharge the battery pack at a constant current of 0.04C for 25 hours or until the cut-off voltage is stopped, and record the discharge curve of the total voltage changing with the state of charge; Using the linear interpolation method to superimpose the charging curve and the discharging curve, the open circuit voltage variation curve of the average open circuit voltage of the monomer changes with the state of charge is obtained, Using the relationship between battery open circuit voltage and state of charge

And the unknown parameters k ₁ , k ₂ , k ₃ , k ₄ , k ₅ , k ₆ , k ₇ , k ₈ , k ₉ , k ₁₀ in the relationship formula obtained from the above open circuit voltage change curve, and the battery open circuit voltage is obtained with the same charge Quantitative relationship of the state, where y in the relational formula is the open circuit voltage, and x is the state of charge. 4. The method for testing the net energy of an electric vehicle power battery as claimed in claim 1, wherein said step (2) is specifically: Discharge the battery at different constant currents from the set initial SOC to the set end SOC. For each constant current, record the battery output external energy Q _out and the battery net energy ΔQ _n after discharge. According to the formula η _dis =Q _out /ΔQ _n calculates the discharge energy efficiency η _dis corresponding to each constant current, and performs curve fitting on all constant currents and corresponding discharge energy efficiencies to establish a battery discharge energy efficiency model.

Images