WO2012098968A1

WO2012098968A1 - Apparatus for estimating state of charge of secondary cell

Info

Publication number: WO2012098968A1
Application number: PCT/JP2012/050407
Authority: WO
Inventors: 尚志赤嶺
Original assignee: プライムアースＥｖエナジー株式会社
Priority date: 2011-01-17
Filing date: 2012-01-11
Publication date: 2012-07-26
Also published as: JPWO2012098968A1; JP5616464B2

Abstract

Provided is an apparatus that highly accurately estimates the state of charge of a secondary cell. The apparatus is provided with: a voltage measuring unit (22), which measures the terminal voltage of a secondary cell (30); a current measuring unit (23), which measures a charge/discharge current of the secondary cell (30); and a control unit (26), which estimates the state of charge (SOC) of the secondary cell (30). The control unit (26) estimates the SOC by integrating the charge/discharge current obtained by reducing a current offset from the charge/discharge current. Furthermore, the terminal voltage of the secondary cell (30) is estimated on the basis of a measurement model, a first correction value for an estimated current offset, and a second correction value for the estimated SOC are calculated using an error between the estimated terminal voltage and the terminal voltage measured by means of the voltage measuring unit (22), and the current offset and the SOC are corrected.

Description

Secondary battery charge state estimation device

The present invention relates to a charging state estimation device for a secondary battery, and more particularly to estimation of a charging state using an extended Kalman filter.

A technology for estimating the state of charge (SOC) of a secondary battery such as a nickel metal hydride secondary battery or a lithium ion secondary battery and controlling the charge / discharge of the secondary battery based on the estimated SOC is known. Yes.

The following patent documents include a sensing unit that measures charge / discharge current flowing through a battery, battery temperature and terminal voltage, a prediction unit that accumulates charge / discharge current to estimate battery SOC, battery temperature, charge / discharge current. A data rejection unit that generates information corresponding to an error generated by the measurement model according to at least one of the time change rate of SOC, SOC, and charge / discharge current, and the measurement model and information corresponding to the error are used A battery management system including a measurement unit that corrects the estimated SOC of the battery is disclosed. Specifically, the data rejection unit sets a modeled battery equivalent circuit as a measurement model, and generates a gain corresponding to the variance of errors generated by the measurement model. Then, a Kalman gain is generated using the dispersion gain of the measurement model error, and the estimated SOC is corrected using the generated Kalman gain.

Specifically, the prediction unit predicts the voltage Vdiff applied to the SOC and diffusion impedance of the battery, which is the state variable (x), using the state equation. The prediction unit generates a covariance for the predicted state variable and the estimation error of the state variable and supplies the generated covariance to the measurement unit. The measurement unit predicts a value that can be measured using the SOC predicted by the prediction unit and the voltage Vdiff, that is, the terminal voltage of the battery. The measurement unit solves the non-linearity between SOC and OCV and uses differential equations to use the Kalman filter. Then, the measurement unit generates a Kalman gain for correcting the predicted SOC and voltage Vdiff. The Kalman gain is set to a value that minimizes the covariance.

JP 2008-10420 A

In the above-described conventional technology, a reliable period and an unreliable period are set for the temperature, SOC, time change rate of current, and current magnitude, respectively, and the variance of the error is adjusted according to the interval. That is, the error variance is fixed to a predetermined value in a reliable period, but is changed by the data rejection unit in an unreliable period. For example, in an interval where the magnitude of the current exceeds a predetermined reference value and is not reliable, the error variance value increases, the Kalman gain decreases, and the SOC predicted by the prediction unit is corrected by the measurement model in the measurement unit. Decrease.

However, in the above-described conventional technology, the current offset that can be included in the current sensor (the value of the current sensor when no current flows) is not taken into consideration. Therefore, even if the current value itself does not exceed the predetermined reference value and is reliable, if the current offset is included, the current offset can be quickly corrected to improve the accuracy of the SOC. Where necessary, such correction is difficult with the prior art.

An object of the present invention is to provide a state of charge estimation device for a secondary battery that can improve the estimation accuracy of the SOC by considering the current offset included in the current sensor.

The present invention is a secondary battery charge state estimation device, comprising: a current detection means for detecting a charge / discharge current of the secondary battery; a voltage detection means for detecting a terminal voltage of the secondary battery; and the current detection. A charge state estimating means for estimating a current state included in the means and correcting a charge / discharge current detected by the current detecting means based on the current offset to estimate a charge state of the secondary battery; and a predetermined measurement model. A first correction of the estimated current offset using an error between the terminal voltage estimating means for estimating the terminal voltage of the secondary battery, the estimated terminal voltage, and the terminal voltage detected by the voltage detecting means. Correction value calculation means for calculating a value, and offset correction means for correcting the estimated current offset using the first correction value calculated by the correction value calculation means. .

In one embodiment of the present invention, the correction value calculation means uses the error between the estimated terminal voltage and the terminal voltage detected by the voltage detection means to perform the second correction of the estimated charge state. Charge state correction means for calculating a value and correcting the estimated state of charge using the second correction value is further provided. In another embodiment of the present invention, the predetermined measurement model is based on an equivalent circuit model of a polarization voltage of the secondary battery.

In another embodiment of the present invention, the terminal voltage estimation means includes the long-term polarization voltage, the short-term polarization voltage, the voltage drop due to internal resistance in the equivalent circuit model, and the charge estimated by the charge state estimation means. The terminal voltage is estimated using the electromotive force corresponding to the state.

Also, in another embodiment of the present invention, the correction value calculation means is an extended Kalman filter.

In another embodiment of the present invention, the correction value calculation means is an extended Kalman filter, and the extended Kalman filter includes a third correction of the long-term polarization voltage in addition to the first correction value and the second correction value. A long-term polarization voltage correction means for correcting the long-term polarization voltage using the third correction value calculated by the correction value calculation means, and a correction value. Short-term polarization voltage correction means for correcting the short-term polarization voltage using the fourth correction value calculated by the calculation means.

According to the present invention, the SOC estimation accuracy can be improved by considering the current offset included in the current detection means (current sensor).

It is a system configuration figure of an embodiment. It is a lineblock diagram of the rechargeable battery and battery ECU of an embodiment. It is a functional block diagram of a control part of an embodiment. It is an equivalent circuit diagram of a polarization voltage. It is a graph which shows the relationship between an electromotive force and charge condition SOC. It is a processing flowchart of an embodiment. It is a graph which shows the current offset simulation result using two models.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, taking a hybrid electric vehicle as an example. In addition, although this embodiment illustrates the hybrid electric vehicle which is one of the electric vehicles, it can be applied to other electric vehicles including a motor as a drive source.

1. Basic Configuration FIG. 1 shows a schematic configuration of a hybrid electric vehicle. The vehicle ECU 10 controls the inverter 50 and the engine ECU 40. The engine ECU 40 controls the engine 60. The battery ECU 20 functions as a charge state estimation device, receives information such as the battery voltage V, the charge / discharge current I, and the battery temperature T from the secondary battery 30 and estimates the state of charge (SOC) of the secondary battery 30. In addition, the battery ECU 20 transmits battery information such as the SOC and battery temperature of the secondary battery 30 to the vehicle ECU 10. The vehicle ECU 10 controls charging / discharging of the secondary battery 30 by controlling the engine ECU 40, the inverter 50, and the like based on various battery information.

The secondary battery 30 supplies electric power to the motor 52. The inverter 50 converts DC power supplied from the secondary battery 30 into AC power and supplies it to the motor 52 when the secondary battery 30 is discharged.

The engine 60 transmits power to the wheels via the power split mechanism 42, the speed reducer 44, and the drive shaft 46. The motor 52 transmits power to the wheels via the speed reducer 44 and the dry shaft 46. When the secondary battery 30 needs to be charged, a part of the power of the engine 60 is supplied to the generator 54 via the power split mechanism 42 and used for charging.

The vehicle ECU 10 receives information on the operating state of the engine 60 from the engine ECU 40, the operation amount of the accelerator pedal, the operation amount of the brake pedal, the operation information such as the shift range set by the shift lever, and the battery information such as the SOC from the battery ECU 20. Is output to the engine ECU 40 or the inverter 50 to drive the engine 60 or the motor 52.

FIG. 2 shows the configuration of the secondary battery 30 and the battery ECU 20. The secondary battery 30 is configured, for example, by connecting battery blocks B1 to B20 in series. Battery blocks B1 to B20 are housed in a battery case 32. Each of the battery blocks B1 to B20 is configured by electrically connecting a plurality of battery modules in series, and each battery module is configured by electrically connecting a plurality of single cells (cells) in series. A plurality of temperature sensors 34 are provided in the battery case 32.

Next, the configuration of the battery ECU 20 will be described.

The voltage measuring unit 22 measures the terminal voltage of the secondary battery 30. The voltage measuring unit 22 measures the terminal voltages of the battery blocks B1 to B20 and outputs them to the control unit 26. The control unit 26 stores the voltage measurement value in the storage unit 28. The output of the voltage data to the control unit 26 is performed at a preset period, for example, 100 msec. The control unit 26 calculates the battery voltage V by summing the terminal voltages of the battery blocks B1 to B20.

The current measuring unit 23 measures the charging / discharging current I at the time of charging / discharging the secondary battery 30 and outputs it to the control unit 26. The control unit 26 stores the current measurement value in the storage unit 28. The current measuring unit 23 generates a current measurement value, for example, when charging is negative and when discharging is positive.

The temperature measurement unit 24 measures the battery temperature of the secondary battery 30 and outputs it to the control unit 26. The control unit 26 stores temperature data in the storage unit 26.

The control unit 26 includes a DCIR (internal resistance) unit 261, a polarization voltage calculation unit 262, an electromotive force calculation unit 263, a charge state estimation unit 264, an extended Kalman filter (EKF) 265, and a correction unit 266. The control unit 26 estimates the state of charge (SOC) of the secondary battery 30 based on the charge / discharge current I. Specifically, the SOC of the secondary battery 30 is estimated by integrating the charge / discharge current I, and information corresponding to the error generated by the measurement model is generated. Then, a Kalman gain is generated using the dispersion gain of the measurement model error, and the estimated SOC is corrected or updated using the generated Kalman gain.

FIG. 3 shows a detailed functional block diagram of the control unit 26. Based on a predetermined measurement model, the control unit 26 uses an internal resistance voltage drop calculated by the DCIR unit 261, a long-term polarization voltage and a short-term polarization voltage calculated by the polarization voltage calculation unit 262, and an electromotive force calculation unit 263. The estimation unit 267 that estimates the terminal voltage of the secondary battery 30 using the calculated electromotive force, the error calculation unit 268 that calculates the error between the voltage measured by the voltage measurement unit 22 and the estimated terminal voltage, and the error An extended Kalman filter (EKF) 265 that generates a Kalman gain by using it and calculates various correction values, and a correction unit 266 that performs correction using the calculated correction values are provided. The electromotive force calculation unit 263 calculates the estimated SOC obtained by integrating the charging current in the charge state estimation unit 264 by converting it into an electromotive force using a predetermined electromotive force map. The extended Kalman filter (EKF) 265 calculates a current sensor offset correction value (first correction value) and an SOC correction value (second correction value) as correction values, and a long-term polarization voltage correction value (third correction value). A short-term polarization correction value (fourth correction value) is calculated. The correction unit 266 corrects the estimated current sensor offset value included in the current measurement unit 23 using the current sensor offset correction value, and corrects the estimated SOC calculated by the charging state estimation unit 264 using the SOC correction value. . Further, the correction unit 266 corrects the long-term polarization voltage and the short-term polarization voltage using the long-term polarization voltage correction value and the short-term polarization correction value, respectively.

In the present embodiment, not only the SOC is corrected using the extended Kalman filter (EKF) 265, but also the charge / discharge current measured by the current measurement unit 23 includes a measurement error, that is, a current sensor offset. Assuming that the current sensor offset value is estimated to estimate the SOC, and using the extended Kalman filter (EKF) 265 to correct the estimated value of the current sensor offset, the accuracy of the current sensor offset estimation is improved. A major feature is that the accuracy of estimation is improved.

Hereinafter, a method of correcting the estimated current sensor offset value in the control unit 26 and a method of estimating the SOC using this correction method will be described.

2. SOC estimation method
The control unit 26 considers that the current measurement value from the current measurement unit 23 includes the current sensor offset, sets the current sensor offset estimated value δI, and sets the current measurement value I and the current sensor offset estimated value δI. Perform a difference operation. That is, I−δI is calculated. The difference value is supplied to a DCIR (internal resistance) unit 261, a polarization voltage calculation unit 262, and a charge state estimation unit 264.

The DCIR (internal resistance) unit 261 plots a set of current measurement values and voltage measurement values in advance, calculates the DCIR (internal resistance) of the secondary battery 30 from the slope of the primary approximate line, and uses this DCIR voltage Calculate the drop (voltage drop). That is, DCIR · (I−δI) is calculated. The DCIR unit outputs the calculation result to the terminal voltage estimation unit 267.

The polarization voltage calculation unit 262 calculates the polarization voltage based on the equivalent circuit model of the polarization voltage. The polarization voltage is calculated based on the change amount of the integrated capacity in a predetermined period. The polarization voltage includes a short-term polarization voltage and a long-term polarization voltage, and the polarization voltage calculation unit 262 calculates a short-term polarization estimated value and a long-term polarization estimated value. The polarization voltage calculation unit 262 outputs each calculation result to the terminal voltage estimation unit 267.

The charging state estimation unit 264 calculates the SOC estimated value by integrating the amount (I−δI) obtained by subtracting the current sensor offset from the current measured value. The charge state estimation unit 264 outputs the estimated SOC value obtained by integrating the current to the electromotive force calculation unit 263.

The electromotive force calculation unit 263 stores an electromotive force map that preliminarily defines the relationship between the SOC and the electromotive force in the memory, and obtains an electromotive force corresponding to the estimated SOC value with reference to the electromotive force map. The electromotive force calculation unit outputs the obtained electromotive force to the terminal voltage estimation unit 267.

The terminal voltage estimation unit 267 estimates the voltage of the secondary battery 30 based on a predetermined measurement model. The measurement model is different for discharging and charging.

And the voltage from this model is

It becomes.

On the other hand, in the case of charging,

And the voltage from this model is

It becomes.
However,
x: state estimated value Vpl: long-term polarization Vps: short-term polarization δI: current sensor offset estimated value u = I: measured current value y = Vb: measured voltage value Cpl: long-term polarization capacitor Cps: polarization voltage in an equivalent circuit model of polarization voltage Short-term polarization capacitor Rpl in the equivalent circuit model of the long-term polarization resistance Rps in the equivalent circuit model of the polarization voltage RIR: short-term polarization resistance in the equivalent circuit model of the polarization circuit DCIR: internal resistance ηc: charging efficiency τ _δI : correlation time Vemf of the current sensor offset (SOC): An electromotive force calculated from the estimated SOC value. In the present embodiment, the current sensor offset is modeled by a so-called ECRP (Exponentially correlated Random Process) in which the amount of time change is determined by the current value, and δI (·) = − δI / τ _δI + σ (2 / τ) _δI ) ^0.5 Ω. Here, (•) represents time differentiation, and ω represents random noise.

FIG. 4 shows an equivalent model of the polarization voltage. The change in polarization voltage over time is

It is.

FIG. 5 shows an example of an electromotive force map, that is, a map that defines the relationship between the SOC estimated value and the electromotive force.

The terminal voltage estimator 267 performs the long-term polarization voltage Vpl, the short-term polarization voltage Vps, the electromotive force Vemf (SOC) calculated from the estimated SOC value, and the internal resistance drop DCIR in accordance with the above formula (2) or (4) The measured voltage Vb is calculated using (I−δI).

The error calculation unit 268 calculates a difference between the voltage measurement value actually measured by the voltage measurement unit 22 and the measurement voltage Vb calculated by the terminal voltage estimation unit 267, that is, an error caused by the measurement model. The calculated error is supplied to an extended Kalman filter (EKF) 265.

The extended Kalman filter (EKF) 265 generates a Kalman gain by using the dispersion gain of the measurement model error, calculates an SOC correction value by using the generated Kalman gain, and also calculates a current sensor offset correction value, a long-term polarization. A correction value and a short-term polarization correction value are calculated. These correction values are supplied to the correction unit 266.

The SOC correction value is supplied to a correction unit 266 that corrects the SOC. Correction unit 266 corrects the SOC estimated value obtained by charge state estimating unit 264 using the SOC correction value. The corrected SOC is transmitted to the vehicle ECU 10.

The current sensor offset correction value is supplied to the correction unit 266 that corrects the current sensor offset. The correction unit 266 corrects the current sensor offset estimated value using the current sensor offset correction value.

The long-term polarization correction value and the short-term polarization correction value are supplied to the respective correction units 266 and used for correcting the long-term polarization estimation value and the short-term polarization estimation value.

FIG. 6 shows a processing flowchart in the present embodiment. First, the measurement model is linearized (S101). Nonlinear systems are

Where x is a state vector, u is an input vector, and function f is a non-linear function with respect to x and u. This is approximated so that the derivative of x becomes a gain independent of x. That is, in continuous time,

And in discrete time,

It is. Here, A is a state matrix and B is an input matrix. Specifically, A is obtained by differentiating equations (1) and (3). In the case of discharge,

In the case of charging,

It is.

The discretized (k-1) component Adk-1 of A is

Given in. Where E is

It is. ΔT is the minimum time unit (sampling time) in discrete time. In processing by software, an operation cycle (for example, 100 msec) is used as a minimum time unit.

After linearization, next, time update processing is performed (S102). The time update process

It is. Hat (^) represents an estimated value. Also,

Is the time update state estimate,

Is the observed update state estimate.

The error covariance estimate is

It is. P is a covariance value of the error between the true state and the estimated value, and is a matrix of the number of states × the number of states, which is 4 × 4 in this embodiment. If xk is true, the error is

And the error covariance estimate is

It is. The diagonal component is the error covariance value of the state estimation value. In particular,

It is.

Further, Q in the equation (16) is a weight matrix of the state estimation error,

Defined by For example, if the estimation error of long-term polarization by the polarization model can be estimated to be 0.1 V, Q1 = 0.01.

After performing the time update process, linearization is performed (S103). That is,

It is.

Finally, observation update processing is performed (S104). The observation update process

It is. (−) in xk is a value before being corrected with the correction value, and (+) is an updated value after being corrected with the correction value. Here, the second term on the right side of equation (27) is the correction value, and the Kalman gain, that is, the observation update gain is

Is calculated as Specifically, the long-term polarization voltage estimated value, the short-term polarization voltage estimated value, the SOC estimated value, and the current sensor offset estimated value are respectively

Is updated.

Note that R in equation (25) is a measurement error weight matrix,

Is defined as

By adjusting the balance between the state estimation error weight matrix Q and the measurement error weight matrix R, it is possible to set which of the estimation based on the measurement model and the observed value is used more. For example, when the estimation accuracy of the measurement model is high and the reliability is high, the SOC estimation by the measurement model is emphasized by setting Q <R. On the other hand, when it is assumed that the actual deviation from the measurement model is large, it is possible to perform SOC estimation based on the measured voltage by setting Q> R.

As described above, correction values for correcting the long-term polarization voltage estimated value, the short-term polarization voltage estimated value, the current sensor offset estimated value, and the SOC estimated value can be calculated and corrected by the extended Kalman filter (EKF). Therefore, the accuracy of SOC estimation can be improved. In particular, in the present embodiment, a correction value for correcting the estimated value of the current sensor offset is calculated, and the current sensor offset estimated value is corrected by the equation (32) using the calculated correction value. The offset can be estimated with high accuracy, and as a result, the SOC estimation accuracy can be improved. Further, in the present embodiment, the correction of the current sensor offset estimated value that is performed when the vehicle is normally stopped can be performed even during traveling, so that the SOC estimation accuracy can be improved even in the case of long-distance traveling that does not stop for a long time. it can.

In the present embodiment, the current sensor offset is modeled by so-called ECRP in which the amount of time change is determined by the current value, and δI (·) = − δI / _τδI + σ (2 / _τδI ) ^0.5 ω However, the present invention includes a case where the current sensor offset is modeled so as to change with time by ω (random noise) so that δI (·) = ω. In this case, −1 / _τδI is “0” in the numbers (1), (3), (9), and (10). However, the model using ECRP is preferable because it reaches the true error earlier and has less variation. FIG. 7 shows simulation results of a model using ECRP and a model that changes with time at ω. In the figure, the horizontal axis represents time, and the vertical axis represents the current sensor offset δI. Reference numeral 100 denotes a model using ECRP, and reference numeral 102 denotes a model that changes over time with ω. In the model that changes over time with ω, a phenomenon occurs in which the estimated value varies near the true value. On the other hand, in the model using ECRP, the estimated value quickly approaches the true value and no variation occurs. From this simulation result, it is understood that a model using ECRP is more desirable.

In this embodiment, the correction is calculated using the extended Kalman filter from the error between the estimated terminal voltage and the terminal voltage detected by the voltage detection unit. The correction value, particularly the current sensor, is calculated using this error. As long as the offset correction value is calculated, the adaptive filter is not limited to the extended Kalman filter, and other adaptive filters such as an Unscented Kalman filter and a particle filter can also be used.

10 vehicle ECU, 20 battery ECU, 22 voltage measurement unit, 23 current measurement unit, 26 control unit.

Claims

A rechargeable battery state of charge estimation device comprising:
Current detection means for detecting a charge / discharge current of the secondary battery;
Voltage detecting means for detecting a terminal voltage of the secondary battery;
A charge state estimation unit that estimates a current offset included in the current detection unit, corrects a charge / discharge current detected by the current detection unit based on the current offset, and estimates a charge state of the secondary battery;
Terminal voltage estimating means for estimating the terminal voltage of the secondary battery according to a predetermined measurement model;
Correction value calculating means for calculating a first correction value of the estimated current offset using an error between the estimated terminal voltage and the terminal voltage detected by the voltage detecting means;
Offset correcting means for correcting the estimated current offset using the first correction value calculated by the correction value calculating means;
A charging state estimating device for a secondary battery, comprising:
The rechargeable battery state of charge estimation device according to claim 1,
The correction value calculating means calculates a second correction value of the estimated charging state using an error between the estimated terminal voltage and the terminal voltage detected by the voltage detecting means,
A charging state estimating device for a secondary battery, further comprising: a charging state correcting unit that corrects the estimated charging state using the second correction value.
The rechargeable battery state of charge estimation device according to claim 1,
2. The secondary battery state estimation device according to claim 1, wherein the predetermined measurement model is based on an equivalent circuit model of a polarization voltage of the secondary battery.
In the secondary battery charge state estimation device according to claim 3,
The terminal voltage estimation means uses a terminal voltage using a long-term polarization voltage, a short-term polarization voltage, a voltage drop due to internal resistance in the equivalent circuit model, and an electromotive force corresponding to the charge state estimated by the charge state estimation means. A state of charge estimation device for a secondary battery, wherein
The rechargeable battery state of charge estimation device according to claim 1,
The correction value calculation means is an extended Kalman filter.
In the rechargeable battery state of charge estimation device according to claim 4,
The correction value calculation means is an extended Kalman filter,
The extended Kalman filter calculates a third correction value of the long-term polarization voltage and a fourth correction value of the short-term polarization in addition to the first correction value and the second correction value,
further,
Long-term polarization voltage correction means for correcting the long-term polarization voltage using the third correction value calculated by the correction value calculation means;
Short-term polarization voltage correction means for correcting the short-term polarization voltage using the fourth correction value calculated by the correction value calculation means;
A charging state estimating device for a secondary battery, comprising: