JP4127256B2 - SOC measurement method for lead acid battery - Google Patents

Description

  The present invention relates to a method for measuring the state of charge (SOC) of a lead storage battery of a hybrid vehicle.

  Hybrid vehicles using an engine as the main power and an electric motor driven by a storage battery as auxiliary power have been put into practical use and are widely available on the market. The storage battery drives the electric motor and stores regenerative energy during vehicle braking. Therefore, unless the state of charge (SOC) of the storage battery is controlled at an appropriate level, sufficient electric power supply to the electric motor and reception of regenerative energy cannot be performed.

  Also, unlike nickel metal hydride storage batteries, especially when using lead storage batteries as storage batteries, if the SOC is excessively reduced, the electrode plate becomes sulfated (sulfation), and there is a problem that the battery life is drastically reduced. In order to control the SOC within an appropriate range, it is important to more accurately detect.

  In the lead storage battery, the sulfuric acid concentration in the electrolytic solution changes with the change in the SOC. Therefore, as in Patent Document 1, the SOC of the lead storage battery is estimated by measuring the electromotive force (open circuit voltage) of the lead storage battery. Is possible. However, this method cannot measure the SOC during charging / discharging because it needs to measure the open circuit voltage. Accordingly, it is necessary to temporarily limit the lead-acid battery to the open circuit state or charge / discharge current during charge / discharge to make it substantially open circuit, and to measure the open circuit voltage during this period.

  Further, the lead storage battery is fully charged once to make the SOC 100%, the charge / discharge current of the lead storage battery is detected, and the time integration value of these currents, that is, the discharge electricity quantity Qd and the charge electricity quantity of the lead storage battery. Qi is obtained, and the SOC of the lead storage battery can be obtained by the formula (1) using the rated capacity C of the lead storage battery.

  In equation (1), in consideration of charging efficiency η, it is common to use ηQi instead of Qi.

Since the method as described above stops charging / discharging of the lead-acid battery or forcibly charges, there is a disadvantage that auxiliary power by the motor cannot be obtained during this time, and regenerative energy cannot be recovered. is there. In addition, the method based on the integration of the charge / discharge current has a drawback in that errors due to measurement of the charge / discharge current and errors due to fluctuations in the charge efficiency η accumulate.
JP 2001-351698 A

  The present invention provides a highly accurate SOC measurement method suitable for a lead storage battery used in a hybrid vehicle. In addition, by eliminating charging / discharging of the storage battery and charging for adjusting the SOC to 100%, it is not possible to obtain auxiliary power from the motor during this time, and it is difficult to recover regenerative energy. This solves the inconvenience.

  In order to solve the above-described problems, an invention according to claim 1 of the present invention includes an engine and an electric motor as power sources, and includes a generator driven by the engine and a lead storage battery charged by the generator. A method for measuring the state of charge (SOC) of a lead storage battery in a vehicle, wherein the lead storage battery voltage E is detected every predetermined time when the vehicle is not in operation and the discharge load of the lead storage battery is below a predetermined value, With reference to the lead storage battery voltage (E) -SOC table obtained in advance, the SOC corresponding to the lead storage battery voltage (E) is sequentially obtained as the temporary SOC at each predetermined time interval, and the temporal change rate of these temporary SOCs is predetermined. If the value is less than the value, the temporary SOC is set as the reference SOC, the reference SOC is sequentially updated as time passes, and the charge / discharge current (I) during vehicle operation is integrated over time to charge / discharge power A method for measuring the SOC of a lead storage battery, comprising obtaining a quantity (Q) and obtaining an SOC of the lead storage battery during operation of the vehicle based on the reference SOC and the charge / discharge electrical quantity (Q). is there.

  The invention according to claim 2 of the present invention is a method for measuring the SOC of a lead storage battery in a vehicle comprising an engine and an electric motor as a power source, a generator driven by the engine, and a lead storage battery charged by the generator. In the state where the vehicle is not operated and the discharge load of the lead storage battery is below a predetermined value, the lead storage battery voltage (E) is detected every predetermined time, and the time change rate of the lead storage battery voltage (E) is In the case of the predetermined value or less, the open circuit voltage (OCV) of the lead storage battery is estimated based on the plurality of lead storage battery voltages (E), and the lead storage battery voltage (E) -SOC table obtained in advance is referred to. The SOC corresponding to (OCV) is set as the reference SOC, the charge / discharge current (I) during vehicle operation is integrated over time to obtain the charge / discharge electricity quantity (Q), and the reference SOC and the charge / discharge electricity quantity (Q). In Zui and shows the SOC measuring method of the lead-acid battery and obtains the SOC of the lead storage battery during the vehicle operation.

  The invention according to claim 3 of the present invention is the method for measuring the SOC of the lead storage battery according to claim 1 or 2, wherein the data pair comprising the average voltage Ea and the average current Ia of the lead storage battery during a predetermined time T during vehicle operation. (Ea, Ia) is obtained, Ea at Ia = 0 is estimated by regression analysis from these plural data pairs (Ea, Ia), and this Ea value and the lead acid battery voltage (E) -lead acid battery Based on the difference (SOC-SOC (regression)), the SOC (regression) by regression analysis is obtained from the SOC table, and the SOC obtained from the reference SOC and the charge / discharge electricity quantity Q and the SOC (regression) are compared. Then, the SOC is corrected.

  The invention according to claim 4 of the present invention is the method for measuring the SOC of the lead storage battery according to claim 3, wherein the charge / discharge electric quantity (Q) is corrected based on the difference (SOC-SOC (regression)). It is characterized by.

  According to the SOC measuring method of the lead storage battery of the present invention, the SOC can be measured without shutting off the charging / discharging of the storage battery or charging for adjusting the SOC to 100% during operation of the vehicle. it can. Therefore, it is possible to eliminate the inconvenience in the control of the hybrid vehicle that the auxiliary power by the electric motor cannot be obtained during this period and the regenerative energy cannot be recovered. In addition, accumulation of errors caused by time integration of the charge / discharge current can be eliminated, and an accurate SOC value can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing the configuration of a vehicle to which the SOC measurement method for a lead storage battery of the present invention is applied.

  The vehicle 10 includes an engine 4 and an electric motor 2 as power sources. The generator 3 is driven by part of the power of the engine 4, and the lead storage battery 1 is charged by the generator 3.

  The output from the lead storage battery 1 is supplied to the electric motor 2 to generate auxiliary power. The vehicle 10 travels using power from the engine or power generated by the electric motor 2. The lead storage battery 1 also supplies electric power to the ECU 7, and the ECU 7 controls on-vehicle equipment such as the engine 4, the electric motor 2, the generator 3, and the inverter 6.

  The ECU 7 outputs a signal to the inverter 6 and the engine 4 in response to an engine ignition (I / G) signal from the I / G key 12 or a charge request or discharge request of the lead storage battery 1 from the battery ECU 11, thereby managing vehicle operation or lead. Charging and discharging of the storage battery 1 can be controlled.

  The battery ECU 11 performs charge / discharge current measurement and temperature measurement of the lead storage battery 1 and performs SOC measurement of the lead storage battery 1. From these measurement results, the battery ECU 11 can make a discharge request and a charge request for the lead storage battery 1 to the ECU 7.

  The functions of the ECU 7 and the battery ECU 11 described above are merely examples of functions in a normal hybrid vehicle, and are not the essence of the present invention. The present invention relates to a method for measuring the SOC of the lead-acid battery 1, and whether or not the measurement function is provided on the battery ECU 11 side or the ECU 7 side or individually is a design matter that a vehicle designer should appropriately determine. In order to specify the present invention, the transmission 5, the differential gear 8 and the wheels 9 are unnecessary, but are described only for the purpose of facilitating the understanding of FIG.

  Hereinafter, a method for measuring the SOC of the lead storage battery of the present invention will be described.

  First, it is determined whether the vehicle 10 is in an operating state or not in an operating state. This is usually determined by the state of the I / G key 12. It may be determined that the vehicle 10 is not in the operating state when the I / G key is OFF, and the vehicle 10 is in the operating state at other ACC, ON, and I / G positions.

1. The state where the vehicle is not operating When the state where the vehicle is not operating is detected, the lead-acid battery voltage (E) is measured every predetermined time (t). From a lead storage battery voltage (E), a preset lead storage battery voltage (E) -SOC table is referenced, and an SOC corresponding to the lead storage battery voltage (E) is set as a temporary SOC (hereinafter referred to as SOCt) at a predetermined time interval (t ) It asks every time sequentially. In the present invention, the state in which the vehicle is not operated assumes a state in which the I / G key 12 is parked with the I / G key 12 turned off.

  The lead storage battery voltage (E) -SOC table depends on the model of the lead storage battery 1 to be used, and is obtained by adjusting the SOC of the lead storage battery 1 and measuring the open circuit voltage of the lead storage battery 1 at this time. It is done. An example of a lead storage battery voltage (E) -SOC table in a 12V lead storage battery is shown in FIG. In addition, as shown in FIG. 2, since the detection system of temporary SOCt increases, it is preferable to set a table for every temperature of the lead storage battery 1. In this case, it goes without saying that a temperature sensor (not shown) for measuring the temperature of the lead storage battery 1 is required.

  The temporary SOCt is detected when the discharge load of the lead storage battery is equal to or lower than a predetermined value. The SOC of the lead storage battery has a linear correlation with the voltage when the lead storage battery 1 is in an unloaded state, that is, the open circuit voltage. Therefore, the open circuit voltage when the lead storage battery 1 is in an unloaded state should be measured. However, in an actual vehicle, a backup load to the ECU 7 and the battery ECU 11 is necessary, and the load of the lead storage battery 1 is cut off. To do is not realistic.

  Therefore, this invention determines that the discharge load of a lead acid battery is below predetermined, and handles the lead acid battery voltage (E) at this time as a pseudo open circuit voltage. In addition, it can be set as about 0.001 CA when lead storage battery capacity is set to C (Ah) as a predetermined value of this discharge load. Depending on the type of the lead storage battery 1, there is a case where there is almost no difference between the lead storage battery voltage (E) and the open circuit voltage even at a discharge load higher than this. In such a case, it is of course possible to set a value exceeding the above-mentioned 0.001 CA.

  When the temporal change rate of the temporary SOCt obtained for each measurement time is within a predetermined range, the temporary SOCt is set as the reference SOC (SOCr). The reference SOCr is positioned at the SOC of the lead storage battery 1 when the vehicle is stopped. The reason for monitoring the time rate of change is that the lead storage battery voltage (E) is not stable due to the concentration polarization of sulfuric acid in the electrolytic solution based on the charge / discharge of the lead storage battery 1 immediately after the operation of the vehicle 10 is finished. This is because an error occurs in the SOC measurement. In the present invention, when the temporary SOCt is in a stable state, the temporary SOCt is used as the SOC of the lead storage battery 1 when the vehicle is stopped, that is, the reference SOCr.

  As an example of the measurement frequency of the lead-acid battery voltage (E), it is 10 minutes, and the change amount (maximum value-minimum value) of the temporary SOCt of n = 6 obtained in 60 minutes is, for example, 5% or less and obtained in the 60th minute. The provisional SOCt can be used as the reference SOCr.

  In addition, when the vehicle operation stop state lasts for a long time, the SOC of the lead storage battery 1 decreases due to a backup load on the ECU 7 and the battery ECU 11 and self-discharge. In the present invention, even after the reference SOCr is once measured, the temporary SOCt measurement is continued and the reference SOCr is sequentially updated.

  In addition to the above-described method, the following method can be used as a method for measuring the reference SOCr. That is, when a plurality of lead storage battery voltages (E1, E2,... En) are measured at predetermined time intervals and the difference between E1 and En is a predetermined value or less, for example, 5% or less, the lead circuit battery is opened from E1 to En. The voltage (OCV) is estimated, the SOC is obtained from the open circuit voltage (OCV) and the lead storage battery voltage (E) -SOC table, and this SOC can be handled as the reference SOCr.

  An approximate expression obtained in advance by experiments can be used as the estimated value of the open circuit voltage. As an approximate expression for this estimation, for example, Expression (2) can be used.

  If E1 = E2 = E3, this value may be OCV. The above approximate expression has been experimentally confirmed that the estimation accuracy of OCV decreases when the difference between E1 and E2 exceeds 5%, and therefore the expression (2) is used when the difference between E1 and E2 is 5%. Is preferred.

2. During vehicle operation Detects a transition from a vehicle operation stop state to an operation state. This detection method can be detected by setting the I / G key 12 to the ACC position, the ON position, or the I / G position because the vehicle operator operates the vehicle. Further, since the discharge load of the lead storage battery 1 is monitored when the vehicle operation is stopped, the operation of the vehicle can be detected when the discharge load exceeds the predetermined value.

  During vehicle operation, a charge / discharge current (I) is measured by a current sensor (not shown), and the charge / discharge current (I) is integrated over time to obtain a charge / discharge electricity quantity (Q). By subtracting the increase / decrease in the SOC due to the amount of charge / discharge electricity (Q) from the reference SOCr, the SOC at an arbitrary time during vehicle operation can be obtained.

  Here, assuming that the charging current is Ic, the discharging current is Id, the capacity of the lead storage battery is C, and the charging efficiency is η, the SOC can be obtained from the reference SOCr using equation (3). In addition, since charging efficiency (eta) changes with SOC as shown in FIG. 3, it is preferable to correct | amend to charging efficiency value according to the SOC value to measure.

  In the equation (3), the charging electric quantity and discharging electric quantity obtained by integrating the charging current Ic and discharging current Id over time until time t in the minute time Δt are ΣIcΔt and the discharging electric quantity is ΣIdΔt, respectively.

  In the present invention, the reference SOCr is obtained for each operation. In addition, since the time integration of the charge / discharge current is performed continuously only in one operation, the SOC measurement error due to the error accumulation can be reduced. Further, the reference SOCr is separately obtained from the lead storage battery voltage (E) when the vehicle operation is stopped, separately from the conventional charge / discharge operation for fully charging the lead storage battery. Therefore, the SOC can be obtained at an arbitrary time without interrupting charging / discharging of the lead storage battery during vehicle operation.

  As a more preferable configuration of the present invention, the following configuration can be used.

  That is, during the operation of the vehicle, a plurality of data pairs (Ea, Ia) composed of the average voltage Ea and the average current Ia of the lead storage battery during a predetermined time T are acquired. For example, the voltage (E) and charge / discharge current (I) of the lead storage battery are measured every 10 μsec for 10 minutes, and the average values of E and I are defined as Ea and Ia. A plurality of data pairs (Ea, Ia) composed of Ea and Ia, for example, about 6 sets (Ea, Ia) are acquired.

  Then, Ea at Ia = 0 is estimated from the plurality of data pairs by regression analysis.

  The SOC (regression) by regression analysis is obtained from the Ea value and the above-described lead storage battery voltage (E) -lead storage battery SOC table. And if SOC is calculated | required by Formula (3) and SOC (regression) is compared and SOC is correct | amended based on the difference (SOC-SOC (regression)), more accurate SOC measurement can be performed. .

  Since the SOC (regression) obtained by this regression analysis is not affected by the measurement error of the charge / discharge current and the fluctuation of the charging efficiency η, a relatively high-accuracy SOC is obtained, but a huge amount of data processing is required. The SOC at an arbitrary time cannot be obtained. For example, when processing 6 sets of one data pair every 10 minutes, 60 minutes are required. Therefore, in the preferred embodiment of the present invention, if the SOC obtained by the equation (3) of the present invention is corrected with the SOC (regression) obtained every certain time, a more accurate SOC measurement value can be obtained arbitrarily. Can be obtained at the time.

  In the SOC measurement according to equation (3), SOCr is performed only by voltage measurement. The voltage is easy to measure and can be measured with little error, and it is considered that the SOCr measurement error accounts for a small percentage of the SOC measurement error. On the other hand, the time integration of the charge / discharge current has a measurement error larger than that of SOCr due to the measurement error of the current sensor and the fluctuation of the charging efficiency η.

  Therefore, it is preferable to correct the time integration portion of the charge / discharge current based on the difference (SOC-SOC (regression)). As an example of this correction method, Expression (4) in which the correction coefficient k is introduced into Expression (3) is used. Here, the corrected SOC is assumed to be SOCx.

  Here, the correction coefficient k in Equation (4) can be obtained by the following procedure.

  When the second term on the right side of Expression (3) is Q, Expression (4) is expressed by Expression (4-1), and Expression (3) is expressed by Expression (3-1).

  Next, when the difference ΔS = (SOC−SOC (regression)) (Equation 5) between the SOC before correction obtained by the equation (3-1) and the SOC (regression) obtained by the regression analysis is obtained, this equation The SOC (%) in (5) is replaced with the formula (3-1), and the SOC (regression) is replaced with the formula (4-1) to obtain the formula (6).

  By applying the value of the correction coefficient k obtained by the equation (7) to the equation (4), the SOC can be corrected by the SOC (regression) obtained by the regression analysis, and a more accurate SOC can be obtained. Note that the value of the correction coefficient k is preferably updated every time the SOC (regression) is measured. If ΔS is small enough to be ignored, the calculation of the correction coefficient k can be canceled.

  By using the configuration of the present invention as described above, it is possible to correct the measurement error of the current sensor and the error due to the fluctuation of the charging efficiency η. The SOC measurement of the lead storage battery becomes possible.

  The SOC measurement method for a lead storage battery according to the present invention is particularly suitable for a hybrid vehicle in which SOC management of the storage battery is particularly important in order to enable accurate measurement of the SOC at any time even in vehicles where the use and suspension of the lead storage battery are intermittent. Is preferred.

The figure which shows the structural example of the vehicle which applies the SOC measuring method of the lead acid battery of this invention. The figure which shows an example of a lead storage battery voltage (E) -SOC table The figure which shows the relationship between SOC and charge efficiency (eta)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lead acid battery 2 Electric motor 3 Generator 4 Engine 5 Transmission 6 Inverter 7 ECU
8 Differential gear 9 Wheel 10 Vehicle 11 Battery ECU
12 I / G key

Claims (4)

Equipped with engine and electric motor as power source,
A generator driven by the engine;
A method for measuring a state of charge (SOC) of a lead storage battery in a vehicle including a lead storage battery charged by the generator,
When the vehicle is not in operation and the discharge load of the lead storage battery is below a predetermined value, the lead storage battery voltage E is detected every predetermined time,
With reference to the lead storage battery voltage (E) -SOC table obtained in advance, the SOC corresponding to the lead storage battery voltage (E) is sequentially obtained as the temporary SOC at each predetermined time interval,
When the temporal change rate of these temporary SOCs is not more than a predetermined value, the temporary SOC is set as a reference SOC,
The standard SOC is updated sequentially over time,
The charge / discharge current (I) during vehicle operation is integrated over time to obtain a charge / discharge electricity amount (Q). Based on the reference SOC and the charge / discharge electricity amount (Q), the lead storage battery during vehicle operation is An SOC measurement method for a lead-acid battery, characterized in that the SOC is obtained. Equipped with engine and electric motor as power source,
A generator driven by the engine;
A method for measuring the SOC of a lead storage battery in a vehicle equipped with a lead storage battery charged by the generator,
When the vehicle is not operated and the discharge load of the lead storage battery is below a predetermined value, the lead storage battery voltage (E) is detected every predetermined time, and the time change rate of the lead storage battery voltage (E) is below a predetermined value In the case of
Estimate the open circuit voltage (OCV) of the lead acid battery based on the plurality of lead acid battery voltages E,
With reference to the lead-acid battery voltage (E) -SOC table obtained in advance, the SOC corresponding to the open circuit voltage (OCV) is set as a reference SOC,
The charge / discharge current (I) during vehicle operation is integrated over time to obtain a charge / discharge electricity quantity Q. Based on the reference SOC and the charge / discharge electricity quantity (Q), the SOC of the lead storage battery during vehicle operation is calculated. A method for measuring the SOC of a lead storage battery, characterized in that: During vehicle operation, a plurality of data pairs (Ea, Ia) consisting of the average voltage Ea and average current Ia of the lead storage battery during a predetermined time T are obtained, and regression analysis is performed from these multiple data pairs (Ea, Ia), Estimate Ea at Ia = 0,
From this Ea value and the lead storage battery voltage (E) -lead storage battery SOC table, SOC (regression) by regression analysis is obtained,
The SOC calculated from the reference SOC and the charge / discharge electric quantity Q and the SOC (regression) are compared, and the SOC is corrected based on the difference (SOC-SOC (regression)). The SOC measuring method of the lead acid battery of 1 or 2. The SOC measurement method for a lead-acid battery according to claim 3, wherein the charge / discharge electricity quantity (Q) is corrected based on the difference (SOC-SOC (regression)).

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