JP6451585B2 - Plug-in vehicle battery management system - Google Patents

Description

  The present invention relates to a battery management system for a plug-in vehicle, and more particularly to a management system for obtaining a battery SOC (State Of Charge).

  A battery (DC power supply) is mounted on an electric vehicle or a hybrid vehicle including a rotating electrical machine as a drive source. In a so-called plug-in vehicle that can charge a battery from an external charging source, a full charge capacity FCC (Full Charge Capacity) [Ah] of the battery is calculated upon charging. The full charge capacity FCC is obtained by using SOC (State Of Charge) [%] of the battery before and after charging.

  In acquiring the SOC, for example, in Patent Document 1, a correspondence relationship between the SOC and the open circuit voltage OCV (Open Circuit Voltage) [V] is used. The open circuit voltage OCV refers to the voltage across the battery in a state where the connection between the load and the battery is disconnected and no current flows through the battery. It is known that the SOC and the open circuit voltage OCV are in a correspondence relationship (for example, linear correlation), and the correspondence relationship between the SOC and the open circuit voltage OCV is stored in advance in a map (SOC-OCV map) or the like, so that the open circuit voltage before and after the charging is stored. The SOC corresponding to the OCV can be obtained.

JP 2013-101072 A

  By the way, in the SOC-OCV map, generally, the voltage value at the time (polarization time) when the polarization of the battery is eliminated is stored as the open circuit voltage OCV. That is, when a battery is connected to a load and a current flows through the battery, a loss occurs due to movement of a reactive substance in the battery, activation energy, or the like, and polarization in which the voltage across the battery drops occurs. In the SOC-OCV map, an open circuit voltage OCV_E (= equilibrium potential Eeq) at the equilibrium time when polarization is eliminated (voltage drop is eliminated) is stored. In this sense, among the voltage across the battery (open circuit voltage in a broad sense) when the battery is disconnected from the load (current stops flowing to the battery), the open circuit voltage OCV_E at the equilibrium time is expressed as the open circuit voltage OCV (open circuit voltage in the narrow sense). Sometimes called. Hereinafter, as the definition of the open circuit voltage, the former definition (open circuit voltage in a broad sense) is used for convenience.

  It is known that polarization does not immediately disappear even when the load is disconnected (even when no current flows through the battery), and it takes a certain amount of time to reach an equilibrium state. Therefore, even if the open circuit voltage OCV is measured immediately after the connection with the load is disconnected, the value is lower than the open circuit voltage OCV_E when the polarization is canceled by the polarization voltage ΔV. By plotting a value lower than the open circuit voltage OCV_E at the time of depolarization in the SOC-OCV map, an SOC different from the actual value is extracted.

  In order to obtain the open circuit voltage OCV_E when the polarization is eliminated, it is conceivable to measure the open circuit voltage OCV after a predetermined waiting time (for example, 30 minutes) has elapsed after disconnection from the load. However, for example, in the case of a plug-in vehicle, if the waiting time as described above is provided, a problem arises from the viewpoint of user convenience. For example, if the user inserts the charging plug into the charging inlet of the vehicle immediately after running the vehicle to the charging stand and charging is not started at this time, the user may erroneously recognize that the charging system has failed. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a plug-in vehicle battery management system capable of accurately obtaining an open circuit voltage at the time of battery polarization elimination even before the battery polarization is eliminated. .

  The present invention relates to a plug-in vehicle battery management system including a current sensor that detects a current flowing through a battery and a calculation unit. The calculation unit obtains a polarization voltage generated in the battery according to a current flowing through the battery when connected to a load. In addition, the polarization voltage of the battery at the charging start time is obtained from the polarization voltage at the time of disconnection from the load and the forgetting factor according to the elapsed time from the connection disconnection time to the charging start time.

  In the present invention, the polarization voltage of the battery at the start of charging is obtained. Based on the obtained polarization voltage and the voltage across the battery at the start of charging, the open circuit voltage at the time of depolarization at the start of charging can be obtained. Thus, according to the present invention, the open circuit voltage at the time of depolarization can be obtained with high accuracy even before the polarization of the battery is eliminated.

It is a figure which illustrates the structure of a plug-in vehicle including the battery management system which concerns on this embodiment. It is a figure explaining the voltage change of a battery. It is the graph which contrasted the calculated value and measured value of the polarization voltage which arose in the battery. It is a graph explaining a forgetting factor.

<Overall configuration>
FIG. 1 shows an electrical system of a plug-in vehicle 10 including a battery management system according to the present embodiment. As will be described later, the battery management system according to the present embodiment includes a voltage sensor 34, a current sensor 36, a temperature sensor 30, and a calculation unit 40. In addition, illustration is abbreviate | omitted about the apparatus which is not related to this embodiment (or few). In addition, a one-dot chain line in FIG. 1 represents a signal line.

  The plug-in vehicle 10 is an electric vehicle or a plug-in hybrid vehicle that includes a rotating electrical machine 12 as a drive source. A battery 14 serving as a power source for the rotating electrical machine 12 is connected to the rotating electrical machine 12 via a system main relay 16. The battery 14 is a rechargeable secondary battery such as a nickel metal hydride battery or a lithium ion battery.

  When the system main relay 16 is connected (ON), the DC power of the battery 14 is boosted by the step-up / down converter 18 and further orthogonally converted by the inverter 20. The rotating electrical machine 12 is driven by supplying the converted AC power. This driving force is transmitted to a wheel (not shown).

  A power branch path 21 (charging path) is provided between the battery 14 and the system main relay 16. The battery 14 and the connector 26 (inlet) are connected via the branch path 21 and the charging relay 22.

  When the connector 28 (charging plug) of an external AC power supply 27 (for example, commercial power supply) is connected to the connector 26 (inlet) and the charging relay 22 is connected (ON), the AC power of the AC power supply 27 is converted into the charger 24. To improve power factor, boost and AC / DC conversion. The converted DC power is supplied to the battery 14. In addition to the charger 24 and the connector 26, a connector that can be connected to an external DC power source may be added.

  Further, as an instrument related to the battery 14, a temperature sensor 30 that detects the temperature of the battery 14 is attached to the plug-in vehicle 10. Furthermore, a voltage sensor 34 that detects the voltage across the battery 14 is connected between the bus bars 32 a and 32 b connected to the battery 14. Further, a current sensor 36 for detecting a charge / discharge current I flowing through the battery 14 is attached to the plus bus bar 32 a between the battery 14 and the system main relay 16.

  The control unit 38 is a computer that includes an arithmetic unit 40 that performs arithmetic processing and signal processing and a memory 42 therein. The memory 42 stores an SOC-OCV map and a full charge capacity calculation program which will be described later.

  The temperature sensor 30 transmits the battery temperature value, the voltage sensor 34 transmits the voltage across the battery 14, and the current sensor 36 transmits the charge / discharge current value of the battery 14 to the control unit 38. In addition, a start command and a shutdown command for the vehicle system are transmitted from the ignition switch 41 to the control unit 38. Further, a signal indicating whether or not the connector 28 (charging plug) is connected is transmitted from the connector 26 (inlet) or the charger 24 to the control unit 38. The arithmetic unit 40 activates a program for calculating the full charge capacity stored in the memory 42 and performs arithmetic processing on various signals received by the control unit 38. In such a configuration, the battery management system according to the present embodiment includes the voltage sensor 34, the current sensor 36, the temperature sensor 30, and the calculation unit 40.

<Calculation of full charge capacity>
The full charge capacity FCC [Ah] is calculated by the following formula (1) using the SOC _C0 [%] at the start of charging of the battery 14, the SOC _C1 at the end of charging, and the current integrated value I _itg [Ah] _therebetween . Desired.

In the above formula (1), the current integrated value I _itg can be obtained by integrating the value of the current I detected by the current sensor 36. The SOC _C0 and SOC _C1 before and after charging are acquired using the SOC-OCV map stored in the memory 42. As described above, it is known that there is a correspondence between the SOC and the battery open circuit voltage OCV_E at the time of depolarization (at equilibrium) (hereinafter referred to as the open circuit voltage at the time of depolarization). The calculation unit 40 calculates the open circuit voltage OCV_E at the time of depolarization before charging and after charging as described below, and then refers to the SOC (SOC _C0 and SOC _C1 corresponding to the open circuit voltage OCV_E at the time of depolarization with reference to the SOC-OCV map. ) To get.

  Calculation of the open circuit voltage OCV_E at the time of depolarization will be described with reference to FIG. FIG. 2 illustrates time-series changes in the voltage of the battery 14 associated with travel and charging of the plug-in vehicle. First, from time t0 to time t1, the ignition switch 41 is not pressed, and the system main relay 16 is in a disconnected (off) state. The charging relay 22 is also disconnected. At this time, the battery 14 is not connected to the load or the AC power source 27 and the current I does not flow. Further, the polarization of the battery 14 is eliminated, and the voltage across the battery 14 (open circuit voltage) at this time is equal to the open circuit voltage OCV_E when the polarization is eliminated.

When the ignition switch 41 is pressed and turned on at time t1, the control unit 38 switches the system main relay 16 from the disconnected state to the connected (on) state. At this time, a load such as the battery 14 and the rotating electrical machine 12 is connected, and the current I is supplied from the battery 14 to the rotating electrical machine 12. As the current is supplied, polarization occurs in the battery 14, and the voltage across the both ends becomes lower than the open circuit voltage OCV_E when the polarization is eliminated. At this time, the calculation unit 40 obtains the polarization voltage ΔV _run (n) at the time of load connection using the following mathematical formulas (2) and (3).

In Equation (2), I _itg (n) represents the current integrated value at time n, and I (n) represents the charge / discharge current value (instantaneous value) of the battery 14 at time n. In the present embodiment, the charge / discharge current value I (n) is positive and the charge current is negative. Further, the increment interval of the counter n is, for example, 0.1 [sec].

In Formula (2), the current integrated value that causes the polarization voltage ΔV _run at time n is obtained. The first term on the right side is _{obtained by multiplying the} current integrated value I _itg (n-1) at time n-1 by a forgetting factor (weighting factor) 0.9 corresponding to the passage of time. The initial value I _itg (0) represents the current value when the ignition is on, and is 0 [A], for example.

Since the initial value I _itg (0) = 0 and the discharge current takes a positive value, if I (1) = a (> 0), for example, I _itg (1) = 0−a, I _itg (1) takes a negative value. Thereafter, since the power running (discharge) exceeds the regeneration (charge) during driving of the vehicle, the current integrated value I _itg (n) generally takes a negative value.

In Equation (3), seeking polarization voltage [Delta] V _{the run} (n) at time n is multiplied by the coefficient 0.001 indicating the internal resistance on the current integrated value at time n. As described above, when the vehicle is driven, the integrated current value I _itg (n) is generally a negative value, so the polarization voltage ΔV _run (n) is also generally a negative value.

FIG. 3 shows a graph comparing the actually measured polarization voltage ΔV _run (n) (CCV−OCV difference) with ΔV _run (n) obtained by Equations (2) and (3). The horizontal axis represents time, and the vertical axis represents voltage. The actual measurement value is a closed circuit voltage CCV (Closed Circuit Voltage), that is, the difference value obtained by subtracting the open circuit voltage OCV_E at the time of depolarization from the voltage across the battery 14 at the time of load connection (at the time of current flow). As shown in this figure, it is understood that the actually measured values and the calculated values by the formulas (2) and (3) are in good agreement.

  Returning to FIG. 2, when the ignition switch 41 is pushed again and turned off at time t2, the control unit 38 switches the system main relay 16 from the connected state to the disconnected state. As described above, since it takes time to eliminate the polarization, the polarization voltage ΔV remains even after time t2 (connection disconnection time) when the connection between the battery 14 and the rotating electrical machine 12 is disconnected.

  Further, when connector 28 (charge plug) is inserted into connector 26 (inlet) at time t3, control unit 38 sets open circuit voltage OCV_E at the time of depolarization of battery 14 before switching charge relay 22 from the disconnected state to the connected state. The calculation unit 40 is instructed to calculate.

The memory 42 stores the polarization voltage ΔV _run (n) at time t2 when the system main relay 16 switches from the connected state to the disconnected state (connection disconnection time) t2. In addition, an elapsed time T _int from time t2 that is the disconnection time point to time t3 that is the charging start time point is measured by a timer (not shown).

  The computing unit 40 extracts a forgetting factor corresponding to the elapsed time and the temperature of the battery 14 from the forgetting factor graph as shown in FIG. The forgetting factor graph represents the elimination process of the polarization voltage ΔV. The horizontal axis represents the square root of the elapsed time, and the vertical axis represents the forgetting factor k (0 ≦ k ≦ 1). Since the polarization is eliminated as time passes, the forgetting factor takes a smaller value as time elapses.

  In addition, it is known that the higher the temperature of the battery 14 is, the more the polarization is eliminated. In the forgetting coefficient graph, a forgetting coefficient line is provided for each temperature. In the example shown in FIG. 4, since the reaction rate doubles when the temperature rises by 10 ° C. from the Arrhenius theorem, the slope of the 10 ° C. forgetting factor line is halved with respect to the 0 ° C. forgetting factor line. The inclination of the forgetting factor line at 20 ° C. is ½ with respect to the forgetting factor line. Such a forgetting coefficient graph is created in advance by actual measurement, simulation, or the like, and stored in the memory 42.

The computing unit 40 calculates the elapsed time t _int (= t3−t2) from time t2 to time t3 and the forgetting factor k (t _int , Tb) corresponding to the temperature Tb of the battery 14 at time t3 from the forgetting factor graph. Extract. Further, the calculation unit 40 calculates the polarization voltage ΔV (t3) at time t3 based on the following mathematical formula (4).

  Further, the calculation unit 40 obtains the voltage across the battery 14 (open circuit voltage) OCV (t3) from the voltage sensor 34, and based on the following formula (5), eliminates the polarization of the battery 14 at time t3, that is, at the start of charging. The hourly open circuit voltage OCV_E (t3) is calculated.

  ΔV (t) in the second term on the right side of Equation (5) takes a negative value during discharge due to the configuration of Equation (2). Therefore, in Equation (5), the polarization voltage ΔV (t3) is substantially added to the both-ends voltage (open circuit voltage) OCV (t3) of the battery 14.

  The calculation unit 40 obtains the polarization elimination open circuit voltage OCV_E (t3) at time t3, and then refers to the SOC-OCV map stored in the memory 42 to correspond to the polarization elimination open circuit voltage OCV_E (t3). Extract (t3).

  In response to the completion of the extraction of the SOC (t3) by the calculation unit 40, the control unit 38 switches the charging relay 22 from the disconnected state to the connected state. As a result, power is supplied from the AC power supply 27 to the battery 14.

The calculation unit 40 obtains a current integrated value I _itg (n) during charging using the charging current value sent from the current sensor 36 and the mathematical expression (2). Further, the polarization voltage ΔV _run is obtained based on the formula (3).

  When the charging is completed at time t4, the control unit 38 switches the charging relay 22 from the connected state to the disconnected state. The calculation unit obtains the polarization release open circuit voltage OCV_E (t4) at time t4, that is, at the end of charging based on the equations (4) and (5), and then refers to the SOC-OCV map stored in the memory 42. Thus, the SOC (t4) corresponding to the open circuit voltage OCV_E (t4) at the time of polarization elimination is extracted.

  Further, the calculation unit 40 substitutes the SOC (t3) and SOC (t4) before and after charging and the current integrated value from the time t3 to t4 into the formula (1) to obtain the full charge capacity FCC of the battery 14.

  In the above-described embodiment, the polarization elimination open circuit voltage OCV_E (t4) at the end of charging is obtained based on the formulas (4) and (5), but this is not a limitation. For example, the voltage between both ends of the battery 14 may be measured after a predetermined waiting time (for example, 30 minutes) at which the polarization is eliminated, and this may be used as the polarization elimination open circuit voltage OCV_E (t4). For example, when plug-in charging is performed at the end of the day and the connectors 26 and 28 are left connected until the next day, the user may confirm the start of charging and thereafter not check the charging state until the next day. Many. In such a case, even if the open circuit voltage OCV_E (t4) at the time of termination of charging is measured after the waiting time has elapsed, the convenience for the user is not greatly affected.

  10 plug-in vehicle, 12 rotating electrical machine, 14 battery, 16 system main relay, 22 charging relay, 24 charger, 26 connector (inlet), 27 AC power supply, 28 connector (charging plug), 30 temperature sensor, 34 voltage sensor, 36 current sensor, 38 control unit, 40 calculation unit, 41 ignition switch, 42 memory.

Claims (1)

A current sensor for detecting the current flowing in the battery;
A polarization voltage generated in the battery according to a current flowing through the battery at the time of connection to the load is obtained, and a forgetting factor corresponding to a polarization voltage at the time of disconnection from the load and an elapsed time from the connection disconnection time to the charging start time And a calculation unit for determining the polarization voltage of the battery at the start of charging,
A battery management system for a plug-in vehicle.