JP2017084636A - Battery controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller for a secondary battery capable of preventing performance deterioration of the secondary battery more reliably.SOLUTION: A battery controller for controlling charge and discharge of a secondary battery connected with a dynamo-electric machine via a transformer includes a control unit for calculating an allowable input current value of the secondary battery based on a limit term indicating the increment and decrement of the allowable input current value due to continuation of the charge and discharge, and a recovery term indicating the recovery amount of the allowable input current value due to the secondary battery being left alone. The control unit changes the variable coefficient α of at least the limit term, according to the transformation switching frequency fc at least of the transformer.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a battery control device that controls charging / discharging of a secondary battery connected to a rotating electrical machine via a transformer.

Conventionally, a battery control device that controls charging / discharging of a secondary battery mounted on an electric vehicle is known. A vehicle-mounted secondary battery is usually connected to a rotating electrical machine via a transformer or an inverter. Further, the battery control device compares the voltage of the secondary battery (battery voltage) with a predetermined input power limit value Win _in order to prevent the secondary battery from being overcharged. but to control the charging of the secondary battery so as not to exceed the input power limit value W _in.

  By the way, it is known that the performance of some secondary batteries is reduced by taking a specific usage mode. For example, in the case of a lithium ion secondary battery, when charging at a high rate, charging from a high charging state (high SOC), continuing charging for a long time, charging at a low temperature (charging in a high resistance state), etc. Lithium (Li) metal may be deposited on the negative electrode surface, leading to overheating or performance degradation of the lithium ion secondary battery.

In order to prevent such precipitation of lithium metal, Patent Document 1 discloses an apparatus that increases or decreases the allowable input current value of a lithium ion secondary battery according to the state of charge / discharge of the secondary battery. According to this technique, with reference to the state of the secondary battery, allowable input current value to the secondary battery, and thus, the input power limit value W _in is limited, lithium metal deposition is suppressed, and thus, Secondary battery overheating and performance degradation can be avoided.

Japanese Patent No. 5223920

  Here, it is known that a pulsation (so-called ripple current) having substantially the same cycle as the switching cycle of the transformer occurs in the current of the secondary battery. Usually, the current of the secondary battery is detected by a current sensor at a predetermined sampling interval, and the battery control device calculates an allowable input current value and the like based on the detected current value. However, when the transformer switching interval is smaller than the current detection sampling interval, the ripple current described above cannot be accurately detected. In this case, an error occurs between the actual current value and the detected current value, and the allowable input current value cannot be calculated appropriately. As a result, the deposition of lithium metal cannot be appropriately suppressed, and the performance of the secondary battery may be degraded.

  Therefore, an object of the present invention is to provide a control device for a secondary battery that can more reliably prevent performance degradation of the secondary battery.

  The control device for a secondary battery of the present invention is a battery control device that controls charging / discharging of a secondary battery connected to a rotating electrical machine via a transformer, and the allowable input current value of the secondary battery A control unit that calculates based on a limit term indicating an increase / decrease amount of the allowable input current value caused by continuation of charging / discharging and a recovery term indicating a recovery amount of the allowable input current value caused by leaving the secondary battery And the control unit changes at least the limiting term according to at least a transformation switching frequency of the transformer.

  According to the present invention, since at least the limiting term changes according to the transformation switching frequency, the influence of the ripple current can be reflected in the allowable input current value. As a result, precipitation of lithium metal can be prevented more reliably, and performance deterioration of the secondary battery can be more reliably prevented.

It is a figure which shows the battery system incorporating the battery control apparatus which is embodiment of this invention. It is a figure which shows the change of the positive electrode electric potential according to SOC of an assembled battery, and a negative electrode electric potential. It is a figure which shows the relationship between the electric current value of an assembled battery, and an allowable input electric current value. It is an image figure which shows an actual electric current value and a detected electric current value. It is an image figure of the map group of variable coefficient (alpha). It is a figure which shows the relationship between variable coefficient (alpha) and switching frequency fc. It is a figure which shows the relationship between variable coefficient (beta) and switching frequency fc. It is a figure which shows the relationship between initial value _Ilim [0] and switching frequency fc. It is a flowchart showing a flow of calculation of the input power limit value W _in.

  Hereinafter, a battery control apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a battery system 10 in which a battery control device is incorporated. The battery system 10 is mounted on an electric vehicle such as a hybrid vehicle or an electric vehicle. The hybrid vehicle includes an engine or a fuel cell as a power source for running the vehicle, in addition to the assembled battery 100 described later. The electric vehicle includes only the assembled battery 100 described later as a power source for running the vehicle.

  The assembled battery 100 includes a plurality of unit cells 102 connected in series. The unit cell 102 is a lithium ion secondary battery. The number of unit cells 102 constituting the assembled battery 100 can be appropriately set in consideration of the required output of the assembled battery 100 and the like. In this embodiment, all the unit cells 102 are connected in series to form the assembled battery 100. However, the assembled battery 100 is configured to connect a battery group including a plurality of unit cells 102 connected in series in parallel. It is good.

  The positive electrode of the unit cell 102 is formed of a material that can occlude and release lithium ions. As a positive electrode material, for example, lithium cobaltate or lithium manganate can be used. The negative electrode of the unit cell 102 is formed of a material that can occlude and release lithium ions. As the negative electrode material, for example, carbon can be used. When the unit cell 102 is charged, the positive electrode releases ions into the electrolytic solution, and the negative electrode occludes ions in the electrolytic solution. Moreover, when discharging the unit cell 102, the positive electrode occludes ions in the electrolytic solution, and the negative electrode releases ions into the electrolytic solution.

  The assembled battery 100 is connected to a motor / generator 108 via a transformer 104 and an inverter 106. The inverter 106 converts the DC power output from the assembled battery 100 into AC power, and outputs the AC power to the motor / generator 108. For example, a three-phase AC rotating electric machine can be used as the motor / generator 108. Motor generator 108 receives AC power from inverter 106 and generates kinetic energy for running the vehicle. The motor generator 108 is connected to wheels, and the kinetic energy generated by the motor generator 108 is transmitted to the wheels. Thereby, the vehicle can be driven.

  The motor / generator 108 converts kinetic energy generated during braking of the vehicle and kinetic energy supplied from an engine (not shown) into electric energy (AC power). The inverter 106 converts the AC power output from the motor / generator 108 into DC power, and outputs the DC power to the assembled battery 100. The transformer 104 boosts the output voltage of the assembled battery 100 and outputs the boosted power to the inverter 106. When the motor / generator 108 generates power, the output voltage from the inverter 106 is stepped down, and the stepped down power is output to the assembled battery 100. The transformer 104 has a plurality of switching elements, and switches the plurality of switching elements at a predetermined frequency fc for voltage transformation. The switching frequency fc of the transformer 104 is alternatively selected from a plurality of predetermined frequencies f1, f2,..., Fn.

  The battery control device that controls charging / discharging of the assembled battery 100 includes a plurality of sensors for detecting the state of the assembled battery 100 and a control unit 20. The sensor includes a voltage sensor 12 that detects a voltage value of the assembled battery 100, a current sensor 14 that detects a current value IB of the assembled battery 100, and a temperature sensor 16 that detects a temperature TB of the assembled battery 100. The voltage sensor 12 detects a voltage between terminals of the assembled battery 100 (hereinafter referred to as “battery voltage”), and outputs a detection result to the control unit 20. The current sensor 14 detects the current flowing through the assembled battery 100 and outputs the detection result to the control unit 20. In the present embodiment, the current value (discharge current value) that flows when the battery pack 100 is discharged is treated as positive, and the current value (charge current value) that flows when the battery pack 100 is charged is treated as negative.

  The temperature sensor 16 detects the temperature of the assembled battery 100 (battery temperature). The temperature sensor 16 outputs the detection result to the control unit 20. The temperature sensor 16 can be provided at one place of the assembled battery 100, or can be provided at a plurality of places in the assembled battery 100. In the case of using a plurality of detected temperatures, the temperature of the assembled battery 100 can appropriately use a minimum value, a maximum value, a median value or an average value of the plurality of detected temperatures, among the plurality of detected temperatures.

The control unit 20 includes a CPU 22 that performs various calculations, a memory 24, and the like. In the memory 24, information for the control unit 20 to execute a specific process (particularly, a process described in the present embodiment), for example, a variable coefficient α, a variable coefficient β, and an initial value I _lim [0] which will be described in detail later. The map group etc. which are referred when specifying etc. are memorize | stored.

  Next, charge / discharge control of the battery pack 100 of this embodiment will be described. FIG. 2 is a diagram illustrating changes in the positive electrode potential and the negative electrode potential according to the SOC of the battery pack 100. When the unit cell 102 is charged, the voltage value VB of the unit cell 102 increases. As shown in FIG. 2, the voltage value VB of the unit cell 102 is the difference between the positive electrode potential and the negative electrode potential. Therefore, as the cell 102 is charged, the positive electrode potential increases and the negative electrode potential decreases. Here, when the negative electrode potential is lower than a reference potential (for example, 0 [V]), lithium metal may be deposited on the surface of the negative electrode.

Therefore, in this embodiment, in order to suppress the deposition of lithium metal, the allowable input current value I _lim [t] is set, and the input current value (charging current value) of the unit cell 102 (the assembled battery 100) is the allowable input. The current value is not exceeded. The allowable input current value I _lim [t] is the maximum allowable current value when charging the unit cell 102. As described above, in this embodiment, since the charging current value (input current value) is negative, I _lim [t] is also a negative value.

When the absolute value of the allowable input current value I _lim [t] increases, the absolute value of the current value when charging the unit cell 102 can also be increased, and the input performance of the unit cell 102 can be improved. On the other hand, when the absolute value of the allowable input current value decreases, the absolute value of the current value when charging the unit cell 102 cannot be increased, and charging of the unit cell 102 is likely to be limited.

The control unit 20 calculates the allowable input current value I _lim [t] at a predetermined sampling interval. The allowable input current value I _lim [t] of the assembled battery 100 is calculated based on the following equation (1).

In Expression (1), I _lim [t] is an allowable input current value at the time of the t-th sampling, and I _lim [t−1] is an allowable input current value at the time of the previous sampling. The second term of Equation (1) is a term indicating the amount of increase / decrease in the allowable input current value I _lim [t] resulting from charging / discharging of the assembled battery 100, and is hereinafter referred to as “limit term”. In addition, the third term of the expression (1) is a term indicating a recovery amount of the allowable input current value I _lim [t] caused by leaving the assembled battery 100, and is hereinafter referred to as a “recovery term”.

Here, as described above, since the charging current value (input current value) is a negative value, the allowable input current values I _lim [t] and I _lim [t−1] are also negative values. Therefore, the absolute value of the allowable input current value I _lim [t] decreases if the limiting term (α · IB · dt) is negative, and increases if it is positive. The limiting term is negative if the battery current value IB is a charging current (negative), and positive if the battery current value IB is a discharging current (positive). Therefore, the absolute value of the allowable input current value I _lim [t] decreases during charging (the input current limit becomes strict) and increases during discharge (the input current limit becomes loose). Further, α in the limiting term is a variable coefficient that changes according to the battery temperature TB or the like. Conventionally, the variable coefficient α has changed according to the battery temperature TB and SOC. In the present embodiment, the variable coefficient α is changed not only in accordance with the battery temperature TB and SOC but also in accordance with the switching frequency of the transformer 104. The specific description thereof will be described later.

The recovery term indicates an amount (recovery amount) by which the absolute value of the allowable input current value I _lim increases per unit time when the assembled battery 100 is left unattended. In this recovery term, β is a variable coefficient that changes according to the battery temperature TB or the like. Conventionally, the variable coefficient β has been changed according to the battery temperature TB and SOC. In the present embodiment, the variable coefficient β is also changed according to not only the battery temperature TB and SOC but also the switching frequency of the transformer 104, as with the variable coefficient α. Will be described later.

The initial value I _lim [0] is the maximum allowable input current value at which lithium metal deposition can be suppressed within a unit time when charging is performed from a state where there is no charge / discharge history. As apparent from the above formula, the recovery term increases as the difference value ΔI _lim between the initial value I _lim [0] and the previous allowable input current value I _lim [t−1] increases. This indicates that the larger the ΔI _lim is, the larger the recovery amount per unit time of the allowable input current value I _lim is. In the present embodiment, the initial value I _lim [0] is also changed according to the switching frequency fc, which will be described in detail later.

Next, limiting control of the charging power of the assembled battery 100 using the allowable input current value I _lim [t] calculated based on the formula (1) will be described. The controller 20 calculates the allowable input current value I _lim [t] at a predetermined period when the assembled battery 100 is being charged / discharged or when the assembled battery 100 is left unattended. After calculating the allowable input current value I _lim [t], the control unit 20 controls input / output (charging / discharging) of the assembled battery 100 based on the allowable input current value I _lim [t]. In this embodiment, charging / discharging (input / output) of the assembled battery 100 is controlled by a power-based battery output or battery input, and the control unit 20 controls the input power limit value W based on the allowable input current value I _lim [t]. _in [t] is set, and the input power of the assembled battery 100 can be controlled using the set input power limit value W _in [t]. If the input power limit value W _in [t] is set, the control unit 20 controls the input power of the assembled battery 100 so that the input power of the assembled battery 100 does not exceed the input power limit value W _in [t]. To do. Hereinafter, the setting of the input power limit value W _in [t] will be described.

FIG. 3 is a diagram illustrating a relationship between the current value IB of the assembled battery 100 and the allowable input current value I _lim [t] in the lithium deposition suppression control. If the allowable input current value I _lim [t] can be calculated, the control unit 20 then calculates the input current limit value I _tag (shown by a broken line in FIG. 3). The input current limit value I _tag is a value for specifying the input power limit value W _in [t], and is a value obtained by offsetting the allowable input current value I _lim [t] by a predetermined amount toward 0 [A]. It is. This offset amount is a margin provided so that the current value IB does not exceed the allowable input current value I _lim [t] even if there is a control delay or the like. This offset amount can be freely set according to the capacity of the assembled battery 100 and the like. While the current value IB of the assembled battery 100 does not exceed the input current limit value I _tag (until time a in FIG. 3), the input power of the assembled battery 100 is not limited. On the other hand, when the current value IB of the assembled battery 100 exceeds the input current limit value I _tag (after time a in FIG. 3), the restriction of the input power of the assembled battery 100 is started.

If the input current limit value I _tag can be calculated, the control unit 20 subsequently calculates the input power limit value W _in [t]. The input power limit value W _in [t] can be calculated based on the following formula (2), for example.

In the equation, W _in [t] is an input power limit value at the time of the t-th sampling, and SW _in [t] is an input power limit value W set in advance in consideration of input characteristics of the assembled battery 100 and the like. _This is the upper limit value of _in [t]. Kp and Ki represent preset gains. I _{tag1, I tag2} shows the input current limit value corresponds to an input current limit value _{I tag} described above. In the above formula (2), as the input current limit value _{I tag,} and set the two input current limit value _{I tag1, I tag2.} Here, the input current limit value _{I tag1, I tag2} may be equal to each other, may be different from each other.

If the input power limit value W _in [t] can be calculated, the control unit 20 adjusts the torque command of the motor / generator 108 so that the input power of the assembled battery 100 is equal to or less than the input power limit value W _in [t]. .

  By the way, as described above, the electric power input / output to / from the assembled battery 100 is transformed by the transformer 104. At the time of this voltage transformation, the transformer 104 performs switching control of a plurality of switching elements. Due to this switching operation, the actual current IBr flowing through the assembled battery 100 has the same switching cycle Cc as shown in FIG. Pulsation (ripple current) occurs in the cycle. When the switching cycle Cc of the transformer 104 is, for example, less than 100 ms and is smaller than the sampling cycle Cd of the current sensor 14, an error may occur in the above-described calculation result.

  That is, as the current value IB of the assembled battery 100 used in the calculations described so far, the current value detected by the current sensor 14, that is, the detected current value IBd is used. On the other hand, a ripple current having the same cycle as the switching cycle Cc of the transformer 104 is generated in the current value that actually flows through the assembled battery 100, that is, the actual current IBr. It is known that the amplitude of the ripple current increases as the switching period Cc increases (the switching frequency fc decreases).

When the sampling period Cd of the current sensor 14 is longer than the switching period Cc, the amplitude of the ripple current cannot be accurately detected. As a result, an error occurs between the current value IB (= IBd) used in the calculation and the actual current IBr, and the absolute value of the calculated allowable input current value I _lim [t] is the actual current. There was a risk of an increase in IBr. In this case, even if the input power is limited so as not to exceed the allowable input current value I _lim [t], lithium deposition may occur.

In order to avoid such a problem, it is conceivable to increase the offset amount (margin amount) at the time of calculating I _tag and to further restrict the input power. However, regardless of the switching frequency fc, if the input power is strictly limited, the input power is limited more than necessary, resulting in deterioration of fuel consumption. Therefore, in this embodiment, the variable coefficients α and β and the initial value I _lim [0] used for calculating the allowable input current value I _lim [t] are changed according to the switching frequency fc of the transformer 104. This will be described below.

FIG. 5 is an image diagram of a map group of the variable coefficient α stored in the memory 24. The control unit 20 refers to the map group of the variable coefficient α and specifies α used for calculating the allowable input current value I _lim [t]. As shown in FIG. 5, the variable coefficient α is generally lower as the battery temperature TB is higher and higher as the SOC is higher. In the present embodiment, a map of the variable coefficient α that changes according to the battery temperature TB and SOC is prepared for each switching frequency fc. That is, the switching frequency fc used in the transformer 104 is alternatively selected from a plurality of preset frequencies f1, f2,. A map of the variable coefficient α is prepared for each of the plurality of frequencies f1, f2,.

FIG. 6 is a graph showing the variable coefficient α when the switching frequency fc is taken on the horizontal axis. As shown in FIG. 6, in this map group, the variable coefficient α is set to be higher as the switching frequency fc is lower. The variable coefficient α is changed in this way because the amplitude of the ripple current increases as the switching frequency fc decreases. If the amplitude of the ripple current is large, the error between the detected current value IBd and the actual current IBr tends to increase accordingly. For this reason, in the present embodiment, when the switching frequency fc is small and a large detection error is assumed, the variable coefficient α is increased. If the variable coefficient α increases, the absolute value of the limiting term (that is, the current limiting amount due to charging / discharging) also increases, so the absolute value of the allowable input current value I _lim [t] is small, that is, the input The current value becomes more restrictive. As a result, lithium deposition due to an excessive input current can be effectively suppressed.

On the other hand, when the switching frequency fc is large and the error in the detected current value is assumed to be small, the variable coefficient α is decreased. If the variable coefficient α decreases, the absolute value of the limiting term (that is, the current limiting amount due to charging / discharging) also decreases, so the absolute value of the allowable input current value I _lim [t] increases, that is, the input The current limit is relaxed. As a result, excessive power limitation can be prevented and fuel consumption can be prevented from deteriorating.

By the way, it is desirable that the influence of the ripple current can be absorbed only by the variable coefficient α, but actually, even if only the variable coefficient α is changed according to the switching frequency fc, an appropriate allowable input current value I _{lim is achieved.} [T] may not be calculated. Therefore, in order to absorb an error that cannot be absorbed only by the variable coefficient α, in the present embodiment, the variable coefficient β and the initial value I _lim [0] are also changed according to the switching frequency fc. Specifically, the memory 24 stores a map group of the variable coefficient β and a map group of the initial value I _lim [0] as well as the map group of the variable coefficient α. Similar to the variable coefficient α, the variable coefficient β and the initial value I _lim [0] are values that change according to the battery temperature TB and the SOC. In the present embodiment, a map of the variable coefficient β and the initial value I _lim [0] depending on the battery temperature and the SOC is prepared for each of the plurality of frequencies f1, f2,.

As shown in FIGS. 7 and 8, in these map groups, the variable coefficient β and the initial value I _lim [0] are both set to increase as the switching frequency fc increases. As described above, not only the variable coefficient α but also the variable coefficient β and the initial value I _lim [0] are changed according to the switching frequency fc, so that the influence of the ripple current caused by the switching frequency fc is more appropriately allowed. This can be reflected in the input current value I _lim [t]. As a result, it is possible to prevent deterioration of fuel consumption while more reliably preventing lithium deposition.

Next, the flow of calculating the input power limit value W _in [t] will be described with reference to FIG. FIG. 9 is a flowchart showing a flow of calculation of the input power limit value W _in [t]. When calculating the input power limit value W _in [t], the control unit 20 first determines whether the assembled battery 100 is being discharged or charged (S10). If neither charging nor discharging is performed, the process waits as it is. On the other hand, when charging or discharging is performed, the control unit 20 subsequently acquires the current battery temperature TB, current value IB, and SOC (S12). Next, the control unit 20 specifies the current switching frequency fc of the transformer 104 (S14 to S18). As described above, the switching frequency fc is alternatively selected from a plurality of preset frequencies f1, f2,..., Fn. Therefore, the control unit 20 identifies the value of the current switching frequency fc by sequentially comparing the current switching frequency fc and the plurality of frequencies f1, f2,..., Fn.

If the value of the switching frequency fc is specified, the control unit 20 subsequently selects a map corresponding to the switching frequency fc in order to specify the variable coefficients α and β and the initial value I _lim [0] (S20). ). Then, the obtained battery temperatures TB and SOC are compared with the selected map to specify the variable coefficients α and β and the initial value I _lim [0] (S22).

If the variable coefficients α and β and the initial value I _lim [0] can be specified, the control unit 20 _adds the specified variable coefficients α and β, the initial value I _lim [0], and the current to the above equation (1). The value IB is applied to calculate the allowable input current value I _lim [t] (S24). The calculated allowable input current value I _lim [t] is temporarily stored in the memory 24 and used as I _lim [t−1] in the next calculation. Next, the control unit 20 _applies this I _lim [t] to the above equation (2) to calculate the input power limit value W _in [t]. If the input power limit value W _in [t] can be calculated, the control unit 20 returns to step S10, and thereafter repeats the same processing.

As is clear from the above description, according to the present embodiment, the value of the variable coefficient α of the limiting term (a term indicating the increase or decrease in the allowable input current value caused by charging / discharging) according to the switching frequency fc of the transformer 104. Is fluctuating. Therefore, even if an error occurs between the actual current IBr and the detected current value IBd due to the ripple current, an appropriate allowable input current value I _lim [t] can be set. As a result, it is possible to effectively prevent lithium deposition in the assembled battery 100 while suppressing deterioration in fuel consumption due to excessive input power limitation. In the present embodiment, not only the variable coefficient α but also the variable coefficient β and the initial value I _lim [0] are varied according to the switching frequency fc. However, if at least the variable coefficient α varies according to the switching frequency fc, the variable coefficient β and the initial value I _lim [0] may not vary according to the switching frequency fc.

  DESCRIPTION OF SYMBOLS 10 Battery system, 12 Voltage sensor, 14 Current sensor, 16 Temperature sensor, 20 Control part, 22 CPU, 24 Memory, 100 assembled battery, 102 Single battery, 104 Transformer, 106 Inverter, 108 Motor generator.

Claims (1)

A battery control device that controls charging / discharging of a secondary battery connected to a rotating electrical machine via a transformer,
The allowable input current value of the secondary battery is a limit term indicating an increase / decrease amount of the allowable input current value due to continuation of the charge / discharge, and a recovery amount of the allowable input current value due to leaving the secondary battery left A recovery term, and a controller that calculates based on the recovery term,
The control unit changes at least the limiting term according to at least a transformation switching frequency of the transformer.
A battery control device.

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