JP2018186590A - Composite power storage system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite power storage system capable of suppressing an increase of cost even if another battery for supplementing capacity shortage of a capacity type battery is added.SOLUTION: A composite power storage system outputs DC power accumulated in a capacity type battery 15 to power supply objects (11, 12), and comprises a secondary battery 13 for supplementing capacity shortage of the capacity type battery 15. A limit value of voltage of the capacity type battery 15 is set so that total running cost of the capacity type battery 15 and the secondary battery 13 becomes nearly the lowest or nearly minimum.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a composite power storage system that supplies power to an electrical load by a plurality of types of power storage devices.

  An electric vehicle supplies electric energy using a single type of battery. As this battery, a capacity type battery that emphasizes capacity (Ah) performance is used. However, the capacity type battery alone may lack power.

  On the other hand, the prior art described in Patent Document 1 is known. In this prior art, a power type battery that emphasizes power performance is connected in parallel to a capacity type battery to supplement the power of the capacity type battery.

Japanese Patent Laid-Open No. 2006-152718

  In Patent Document 1, a capacity type battery, such as a Ni-rich or semi-solid battery, tends to be significantly deteriorated at a high potential. For this reason, if the potential is lowered in order to suppress the deterioration of the battery, it is necessary to compensate for the insufficient capacity of the battery as the potential is lowered. For this reason, there exists a possibility that the cost of the whole electrical storage system may increase.

  Therefore, the present invention provides a composite power storage system that can suppress an increase in cost even if another battery that compensates for the capacity shortage of the capacity type battery is added.

  In order to solve the above problems, a composite power storage system according to the present invention outputs a DC power stored in a capacity type battery to a power supply target, and includes a second battery that compensates for the capacity shortage of the capacity type battery. The limit value of the voltage of the capacity type battery is set so that the total running cost of the capacity type battery and the second battery is substantially minimized or substantially minimized.

  According to the present invention, even if another battery that compensates for the capacity shortage of the capacity type battery is added, an increase in the cost of the composite power storage system can be suppressed.

  Problems, configurations, and effects other than those described above will become apparent from the following description of embodiments.

1 shows a configuration of a composite power storage system that is Embodiment 1 of the present invention and an electric vehicle equipped with the same. A modification of the first embodiment. It is a flowchart which shows the setting method of the voltage limit value in a capacity type battery. An example of the data acquired by step S21 of FIG. 3 is shown. An example of the relationship between the number of charge / discharge cycles and a capacity ratio in a capacity-type battery is shown. The example of a relationship between SOC and an open circuit voltage is shown. An example of the relationship between a running cost and an upper limit voltage is shown. The structure of the composite electrical storage system which is Example 2 of this invention and the electric vehicle carrying it is shown.

  Hereinafter, embodiments of the present invention will be described with reference to the following Examples 1-2. In each figure, the same reference numerals indicate the same constituent elements or constituent elements having similar functions.

  FIG. 1 shows the configuration of a composite power storage system that is Embodiment 1 of the present invention and an electric vehicle equipped with the same.

  As shown in FIG. 1, the electric vehicle 10 includes a composite power storage system including a second battery 13 and a capacitive battery 15 connected in parallel to the second battery 13 via a DCDC converter 14 that is a power control device. . The composite power storage system is connected to the motor generator 11 via the inverter 12. Therefore, the second battery 13 is directly connected to the inverter 12 without going through the DCDC converter, and the capacitive battery 15 is connected to the inverter 12 through the DCDC converter 14. The inverter 12, the second battery 13, the DCDC converter 14 and the capacity type battery 15 are controlled by an ECU 16 ("ECU" is an abbreviation of "Electronic Control Unit").

  Here, the motor generator 11 is an AC machine, for example, an induction machine or a synchronous machine.

  Direct current power is output from the second battery 13 directly to the inverter 12 from the capacitive battery 15 via the DCDC converter 14. The inverter 12 converts the DC power supplied from the second battery 13 and the capacity type battery 15 into three-phase AC power. The motor generator 11 is rotationally driven as an electric motor by the three-phase AC power output from the inverter 12. Thereby, the electric vehicle 10 travels. The DCDC converter 14 controls the voltage of the capacity type battery 15 to be equal to or lower than an upper limit voltage described later.

  When the electric vehicle 10 is decelerated or braked, that is, when the motor generator 11 is regenerated, the AC power generated by the motor generator 11 is converted into DC power by operating the inverter 12 as a rectifier, and the second It is stored in the battery 13 or stored in the capacitive battery 15 via the DCDC converter 14.

  When the electric vehicle 10 is parked, the capacity type battery 15 and the second battery 13 are charged by a charging device (not shown).

  1 may be configured by separate motors and generators.

  The capacity type battery 15 has a high internal resistance and cannot flow a large current, but has a high capacity (Ah). As such a capacity type battery 15, a lithium ion battery, a lithium ion semi-solid battery, a lithium solid battery, etc. are applied. These batteries deteriorate at a high potential. For this reason, when the operating potential is lowered, a capacity shortage occurs with respect to the capacity required for the power storage system. This lack of capacity will be compensated with an additional battery. The addition of the battery affects the size and cost of the power storage system. Therefore, in the first embodiment, as will be described later, a means for setting the capacity of an additional battery suitable for the power storage system battery is applied including the cost.

  A lead battery may be applied as the capacity type battery. The lead battery deteriorates at a lower potential than the capacity type battery such as the above-described lithium ion battery, but means for setting the capacity of the additional battery, which will be described later, can be applied. As the capacity type battery 15, a battery whose Ah unit price (k ¥ / Ah) or Wh unit price (k ¥ / Wh) is lower than that of the second battery described later is applied. An additional battery is also used when raising the minimum voltage. The capacity setting means for this additional battery in this case will also be described later.

  In the first embodiment, the second battery 13 can pass a larger current than the capacity battery, but has a lower capacity (Ah). As such a second battery, a power type battery such as a lithium ion battery or a nickel metal hydride battery is applied. Further, instead of a lithium ion battery or a nickel metal hydride battery, a power storage device such as a lithium ion capacitor or an electric twentieth layer capacitor having high output characteristics similar to these may be used. In the following, these batteries and capacitors are collectively referred to as “second battery” or “power battery”.

  In the first embodiment, the second battery has a longer life than the capacity type battery, and the value obtained by dividing the initial cost by the battery replacement year, that is, the life cycle cost (k ¥ / year) is low. Further, the second battery has a higher unit price of Ah (k ¥ / Ah) or unit price of Wh (k ¥ / Wh) than the capacity type battery.

  The DCDC converter 14 according to the first embodiment may be a bidirectional one, or may be a step-up or step-down type in one direction (direction from the capacity battery 15 to the inverter 12 side). Also good. When a step-up DCDC converter is used, “(inverter voltage)> (maximum capacity battery voltage) × (capacity battery series number)”. When the step-down type is used, “(inverter voltage) <(minimum capacity battery voltage) × (capacity battery series number)”. As a circuit configuration of the bidirectional DCDC converter, the one-way step-up DCDC converter, and the one-way step-down DCDC converter, a known chopper circuit can be used (for example, “Atsuo Kawamura,“ Eco-future electric vehicle prototype) And Performance Evaluation Test ”, Denso Technical Review, Vol. 16, 2011, p.

  The voltage of the capacity type battery 15 is controlled by the DCDC converter 14 so that the voltage per cell of the capacity type battery is equal to or lower than the voltage limit value V0 regardless of charge / discharge. The setting means for V0 will be described later.

As a modification of the first embodiment, a current limiting circuit may be used instead of the DCDC converter having the step-up or step-down function as described above. Such a modification is shown in FIG.

As shown in FIG. 2, the DCDC converter 14 in the electric vehicle 10 of FIG. 1 is replaced with a current limiting circuit 21. In the current limiting circuit 21, a P-channel MOSFET 22 and an N-channel MOSFET 23 are connected in series, and these MOSFETs are ON / OFF driven by a gate driver 24. The on / off signal which is a command signal of the gate driver 24 is E
This is an on / off logic signal from the CU 16. P-channel MOSFET 22 and N-channel MO
By turning on and off the switch comprising the SFET 23, the current value is limited to a desired current value on a time average basis. Further, a voltage smoothing capacitor 25 is connected in parallel to the capacitive battery 15, and the current limiting circuit 21 is controlled so that the voltage of the voltage smoothing capacitor 25, that is, the voltage of the capacitive battery is equal to or lower than the voltage limit value V0. Is done.

  Hereinafter, setting means for the voltage limit value V0 in the capacity type battery will be described.

  FIG. 3 is a flowchart showing a method of setting the voltage limit value V0 in the capacity type battery. This method is executed, for example, when setting the battery mounting amount of an electric vehicle.

  First, in step S21, data relating to the battery replacement year indicating the deterioration characteristics of the capacity type battery is acquired.

  An example of data acquired in step S21 is shown in FIG. FIG. 4 shows the relationship between the upper limit voltage of the capacity type battery and the battery replacement year (hereinafter referred to as “replacement year”). The horizontal axis indicates the upper limit voltage per cell, and the vertical axis indicates the replacement year. The temperature and effective current are fixed to predetermined values. A plurality of data may be acquired using temperature and effective current as parameters.

  The data in FIG. 4 is based on the study of the present inventor. For example, when the upper limit voltage of the capacity type battery is 4.4V, CCCV (Constant Current-Constant Voltage) charging is performed so that the battery voltage becomes 4.4V. This is data when the battery is discharged with a simulated current waveform when the vehicle is driven. That is, the upper limit voltage is a voltage in a fully charged state.

  The simulated current waveform is obtained by using a vehicle simulator equipped with a battery [kWh] that can run a specified distance by using a predetermined driving test method such as JC08 (travel pattern specified by the Ministry of Land, Infrastructure, Transport and Tourism) or WLTP (Worldwide It is a current waveform when driving based on harmonized Light vehicles Test) or a constant current waveform. The data in FIG. 4 is data when the vehicle simulator is repeatedly run from the fully charged battery until the battery becomes empty with such a simulated current waveform. In addition, you may obtain data based on an actual driving | running | working test irrespective of a vehicle simulator.

  As FIG. 4 shows, the replacement year becomes shorter as the upper limit voltage becomes higher. That is, as the upper limit voltage increases, the progress of deterioration becomes faster.

  In addition, you may convert the exchange year in the vertical axis | shaft of FIG. 4 by applying a conversion factor (day / cycle) to the data of the number of charge / discharge cycles.

  Further, the data in FIG. 4 can be obtained from a change in capacitance ratio (Wh ratio or Ah ratio) or resistance ratio. This means will be described next.

  FIG. 5 shows an example of the relationship between the number of charge / discharge cycles and the capacity ratio (Wh ratio) in a capacity type battery. The horizontal axis indicates the number of cycles, and the vertical axis indicates the capacity ratio. Here, one cycle refers to one process in which charging is performed up to the upper limit voltage and then discharging is performed until the battery becomes empty with a simulated current waveform. The capacity ratio is the ratio of the battery capacity to the initial capacity.

  In FIG. 5, a threshold value η (for example, 0.6 in FIG. 5) for determining battery replacement is specified in advance, and when the Wh ratio decreases to η, the battery is replaced. In this case (η = 0.6), when the travelable distance decreases to 60% of the initial value, the battery is replaced.

  The number of cycles in which the capacity ratio curve 53 becomes η is the life cycle x in FIG. 5, and this x is the replacement cycle. As described above, the exchange cycle is converted to the exchange year by applying the conversion factor (day / cycle).

When using Ah ratio or resistance ratio data instead of the Wh ratio shown in FIG. 5, the lower limit voltage (per battery cell) in an electric vehicle (that is, required for a power storage system) is VL (for example, 2.3 V). Then, first, SOCe (SOC of the battery at the time of discharge (State of charge charge rate)) is obtained by Expression (1).
VL = Vo (SOCe) −current × R (SOCe) × resistance ratio (1)
In equation (1), R (SOC) and Vo (SOC) are the internal resistance of the battery and the open circuit voltage of the battery, respectively, and are both expressed as a function of the SOC. These function forms are obtained in advance by actual measurement or the like. Moreover, you may obtain | require SOCe using Formula (1) using a well-known Newton method or a bisection method.

  Using this SOCe, the battery capacity (Wh) is obtained from the open-circuit voltage curve of the battery as follows. FIG. 6 shows an example of the relationship between the SOC and the open circuit voltage, that is, an example of an open circuit voltage curve. As for the discharge capacity (Wh), the area of the region between the open-circuit voltage curve and the horizontal axis is obtained between SOCe and 100% in FIG. Then, using this area, “area × capacity ratio × capacity battery capacity [Ah] ÷ 100”, that is, Wh ratio is obtained.

  In addition, about SOC, it is good also as SOC100% by the voltage at the time of a charge when a battery becomes unusable in 1 cycle, and good also as SOC100% by the maximum voltage in which metallic lithium does not precipitate inside a battery. Further, the SOC voltage may be 100% at a voltage at which the battery voltage suddenly rises and the battery capacity does not substantially change even when the voltage is further raised. Further, the SOC is set to 0% (for example, 2.3 V) as the lower limit value of the voltage set to suppress the deterioration of the battery.

  In FIG. 5, when the vertical axis is Ah ratio, the number of cycles when the Ah ratio becomes the same η as in FIG. 5 is defined as the life cycle, that is, the replacement cycle. The conversion year may be converted to the exchange year by multiplying (day / cycle).

  As described above, when step S21 of FIG. 3 is executed, the process proceeds to step S22.

  In step S22, the running cost of the capacity type battery is calculated by dividing the battery cost per year, that is, the total battery cost by the replacement year, from the capacity type battery replacement year data obtained in step 21 (FIG. 4). To do. Thereby, the relationship between the upper limit voltage and the running cost is obtained for the capacity type battery. Here, the total cost of the battery is calculated from the total battery capacity of the capacity type battery required for the power storage system and the unit price of Wh. The unit price of Wh is calculated from, for example, the price of one battery and the capacity (Wh) at the time of designing one battery. The calculation may be performed using Ah instead of Wh. Once step S22 is executed, the process proceeds to step S23.

  In step 23, the running cost of the second battery added to compensate for the insufficient capacity due to the lowered voltage of the capacity type battery is calculated. When the upper limit voltage V0 of the capacity type battery is lowered, the SOC obtained from the open-circuit voltage curve (FIG. 6) may be SOCu, and “(100−SOCu) × Ah ÷ 100 required for electric vehicle design” may be the insufficient capacity. . In addition, the area of the region between the open-circuit voltage curve and the horizontal axis is calculated from SOCu to 100%, and using this area, “area × Wh / 100 required for electric vehicle design” is set as an insufficient capacity. Also good.

  In step S23, the running cost of the second battery that compensates for the shortage of capacity of the capacity type battery obtained as described above is calculated in the same manner as the running cost of the capacity type battery in step S22. Thereby, the relationship between the upper limit voltage of the capacity type battery and the running cost of the second battery is obtained.

  Since the second battery has a longer life than the capacity type battery, the influence of the upper limit voltage on the running cost is smaller than that of the capacity type battery. For this reason, the upper limit voltage of the second battery itself may be a fixed value (in Example 1, this fixed value can be set independently of the upper limit voltage of the capacity type battery). In addition, the second battery may be used in a part of the SOC. For example, when the SOC is used in the range of 30% to 70% of SOC, the additional capacity is reduced by the capacity type battery. It is good also as a value which multiplied the value which remove | divided the area of the SOC range (100-SOCu) with respect to the shortage capacity | capacitance by the area of the SOC range capacity (70% -30% (= 40%)) used with a 2nd battery. Further, the additional capacity may be a value obtained by multiplying the aforementioned shortage by a margin magnification (for example, 1.5 times) in consideration of battery deterioration.

  As described above, when step S23 of FIG. 3 is executed, the process proceeds to step S24.

  In step 24, based on the running costs of the capacity type battery and the second battery calculated in steps S22 and S23, the upper limit voltage of a suitable capacity type battery, that is, the running cost of all the batteries used in the power storage system is minimized. The upper limit voltage V0 of the capacity type battery to be obtained is obtained.

  The means for obtaining the upper limit voltage V0 in step S24 will be described with reference to FIG.

  FIG. 7 shows an example of the relationship between the running cost of the battery and the upper limit voltage. The horizontal axis represents the upper limit voltage. The vertical axis represents the running cost when the running cost ratio, that is, the running cost of the reference capacity battery (running cost for the upper limit voltage 4.4 V in FIG. 7) is 1. The reference running cost is selected based on the replacement year (life) of the capacity type battery allowed in the power storage system. Hereinafter, in the description of FIG. 7, “running cost” is synonymous with “running cost ratio” indicated by the vertical axis of FIG. 7.

  In FIG. 7, curves A, B, and C indicate the running cost of the capacity type battery (step S22), the running cost of the second battery that is added to compensate for the capacity shortage of the capacity type battery (step 23), and these. The total running cost of all batteries included in the power storage system that is the sum of

  In FIG. 7, as curve A shows, when the upper limit voltage increases within a predetermined range (4 to 4.4 V) of the upper limit voltage of the capacity type battery, the running cost of the capacity type battery increases almost monotonously. On the other hand, as shown by the curve B, the running cost of the second battery is relatively smaller than that of the capacity type battery, and decreases substantially monotonically when the upper limit voltage increases in the same voltage range. For this reason, the total running cost has a minimum value or a minimum value. The upper limit voltage value V0 that gives such a minimum value or minimum value of the total running cost is set as the upper limit voltage value of the capacity-type battery suitable for the power storage system.

  Next, means for numerically obtaining the preferred value of V0 as described above will be described.

In this means, the capacity type battery running cost function F1 (V0) and the second battery running cost function F2 (V0) are set based on the calculation results of steps S22 and S23, and further, the total running is calculated by the equation (2). A cost function F is set.
F = F1 (V0) + F2 (V0) (2)
V0 at which the value of the function obtained by differentiating the total running cost function F by V0 is 0 is obtained by the Newton method or the bisection method. At this time, the obtained V0 is the upper limit voltage value V0 that gives the minimum value or the minimum value of the total running cost.

  In the power storage system, the second battery bears a part of the current flowing to the load side (in FIG. 1, the inverter 12 and the motor generator 11 side). For this reason, it is preferable to consider current and temperature as variables related to running cost.

  In this case, a capacity type battery running cost function f1 (v1, Ie1, temp1) and a running cost function per capacity of the second battery f2 (Ie2, temp2) are set (the capacity may be Ah or Wh). Here, v1 is the upper limit voltage of the capacity type battery, Ie1 is the effective current of the capacity type battery, and temp1 is the temperature of the capacity type battery. Ie2 is the effective current of the second battery, and temp2 is the temperature of the second battery. For the second battery, the running cost is not affected by the upper limit voltage of the second battery itself.

  Ie1 is a function Ie1 (Q) that is corrected according to the capacity Q (Ah or Wh) of the second battery. For example, when a current x times as large as 10 s can be supplied to the capacity Q (Ah) of the second battery, the correction is made by reducing the current. Such Ie1 may be converted into a function based on relational data obtained by an electric vehicle simulator. Ie2 is also a function Ie2 (Q) of Q, and similarly, it may be converted into a function based on relational data obtained by an electric vehicle simulator.

  temp1 is a function that varies depending on the outside air temperature and Ie1. Therefore, temp1 is also a function of the capacity Q of the second battery. Further, temp2 is a function that varies depending on the outside air temperature and Ie2, and is also a function temp2 (Q) of the capacity Q of the second battery. temp and temp2 may be converted into a function based on relational data obtained by the electric vehicle simulator.

With these functions, f1, f2, Ie1, Ie2, temp1, and temp2, a total running cost function f is set according to Equation (3).
f = f1 (v1, Ie1 (Q), temp1 (Q)) + Q × f2 (Ie2 (Q), temp (Q)) × λ (3)
Q is set by “Q = S (v1) × Q0”. Here, S (v1) is the area [V%] of the region between the open-circuit voltage curve and the horizontal axis between SOCu and SOC 100% corresponding to the upper limit voltage v1 in the capacity type battery (see FIG. 6). Or (100-SOCu) [%]. Q0 is the initial set capacity (Wh or Ah) of the capacity type battery, and λ is the SOC usage range rate of the second battery.

  V1 at which the value of the function obtained by differentiating the total running cost function f by V1 becomes 0 is obtained by the Newton method or the bisection method. At this time, V1 to be obtained is an upper limit voltage value V1 that gives a minimum value or a minimum value of the total running cost.

  In the process of obtaining the upper limit voltage value of the capacity type battery by the above means, the capacity of the second battery added to compensate for the capacity shortage of the capacity type battery is obtained. The capacity of the second battery in the composite power storage system is set to an initial value Y or more.

  The upper limit voltage V0 is one specific value that minimizes or minimizes the running cost, but V0 may be a value in a certain voltage range. This means will be described.

  In the example shown in FIG. 7, the sensitivity of the total running cost (c) with respect to the upper limit voltage is relatively low between 4.2 V and 4.3 V, and the total running cost is almost the same value that is minimal or close to the minimum value. Indicates. For this reason, the upper limit voltage V0 can be set to an arbitrary value in the range between 4.2V and 4.3V. In this case, the range of the upper limit voltage V0 is a range in which the voltage sensitivity of the total running cost function, that is, the voltage differential value of the total running cost function is substantially zero. Note that a range in which the voltage differential value is equal to or less than a predetermined minute positive constant ε may be set as the range of the upper limit voltage V0.

  The upper limit value of the second battery may be set in accordance with the upper and lower limit values in the above-described V0 range. However, when the second battery is a power battery, there may be a power limitation. At this time, if the capacity for obtaining the desired power is Q0, the lower limit of the capacity of the second battery is preferably set to Q0 or more.

  Next, the setting of the voltage limit value when a battery that deteriorates when the voltage is relatively low, such as a lead battery, is used as a capacity type battery will be described.

  In the lead battery, the lower limit voltage Vl is set, and the DCDC converter is controlled so that the voltage at the connection between the DCDC converter (FIGS. 1 and 2) and the capacity type battery does not become lower than Vl. Then, in the relationship between the upper limit voltage of the capacity type battery and the replacement year in FIG. 4, data is acquired with the horizontal axis as the lower limit voltage. In the Wh conversion example of FIG. 6, the area of the region between SOCe and the larger one of the SOCs corresponding to the lower limit voltage is obtained from the SOC 100%. In FIG. 7, the value of the lower limit voltage that minimizes or minimizes the total running cost is obtained with the horizontal axis as the lower limit voltage.

  Next, using a function (hereinafter referred to as “deterioration function”) representing the deterioration and life of the article, life cycle data, that is, a function form of the capacity ratio with the charge / discharge cycle as shown in FIG. 5 as a variable. A means for acquiring will be described. In addition, when this means is used, the life cycle can be estimated from fewer data, so the time required for obtaining the life cycle data can be shortened.

First, as a degradation function, a so-called root rule (root (square root) cycle) representing the degradation of the battery accompanying the precipitation of a solid substance (for example, Li) in the battery (for example, Yancheng Zhang, Chao-Yang Wang, “Cycle- A linear function using Life Characterization of Automotive Lithium-Ion Batteries with LiNiO ₂ Cathode ”, Journal of The Electrochemical Society, 156 (7) A527-A535_2009) is applied.

In addition, in the case of batteries, when deterioration factors include mechanical electrode peeling and current collector corrosion, the deterioration function is expressed as a so-called Weibull distribution (for example, Chiakihiko Sugaya, “Statistical distribution immediately useful”, Tokyo Books, see). Expression (4) shows an example of a function form of the capacity ratio (= capacity (cycle) / capacity initial value: capacity is a function of the number of cycles) to which the Weibull distribution is applied. As is well known, there is a correlation between the capacitance and the internal resistance (see, for example, JP 2012-247339 A), so that the resistance ratio can be used instead of the capacitance ratio. Therefore, a function form of an admittance ratio (= admittance (cycle) / initial value of admittance: where admittance is a function of the number of cycles) is also written as equation (5). The admittance ratio becomes a value smaller than 1 as the capacity ratio because the internal resistance becomes larger than the initial value when the number of charge / discharge cycles increases and the deterioration proceeds. For this reason, data processing can be performed in the same manner as when the capacity ratio is used. It is also possible to use a resistance ratio.
Capacity (cycle) / capacity initial value = exp {− (cycle / τ1) ⁿ¹ } (4)
Admittance (cycle) / Admittance initial value = exp {− (cycle / τ2) ⁿ² } (5)
Here, τ1, τ2, n1, and n2 are constants.

Further, in the case where both the above-described mechanical deterioration and deterioration due to precipitation of the solid substance occur, two Weibull distributions are used as shown in Expression (6) and Expression (7). Equations (6) and (7) show a functional form consisting of the product of two Weibull distributions. Equations (8) and (9) show a function form that is the sum of two Weibull distributions. In Expressions (8) and (9), constant coefficients (1-P1, P1, 1-P2, P2) are set so that both the capacity ratio and the admittance ratio are 1 or less (P1 <1). , P2 <1). The function form is appropriately selected according to the deterioration factor.
Capacity (cycle) / capacity initial value = exp {− (cycle / τ1) ⁿ¹ } × exp {− (cycle / τ1 ′) ^{n1 ′} } (6)
Admittance (cycle) / Admittance initial value = exp {-(cycle / τ2) ⁿ² } × exp {− (cycle / τ2 ′) ^{n2 ′} } (7)
Here, τ1, τ2, n1, n2, τ1 ′, τ2 ′, n1 ′, and n2 ′ are constants.
Capacity (cycle) / capacity initial value = (1-P1) exp {-(cycle / τ1) ⁿ¹ } + P1exp {− (cycle / τ1 ′) ^{n1 ′} } (8)
Admittance (cycle) / Admittance initial value = (1−P2) exp {− (cycle / τ2) ⁿ² } + P2exp {− (cycle / τ2 ′) ^{n2 ′} } (9)
Here, τ1, τ2, n1, n2, τ1 ′, τ2 ′, n1 ′, n2 ′, P1, and P2 are constants.

  In the first embodiment, cycle deterioration is considered. However, as battery deterioration, storage deterioration depending on the storage time of the battery per day may be considered. In this case, the battery replacement year is similarly calculated based on the life cycle data (capacity ratio, resistance ratio (admittance ratio)) corresponding to cycle deterioration and storage deterioration.

  As described above, according to the first embodiment, by limiting the voltage of the capacity type battery, even if a second battery that compensates for the capacity shortage of the capacity type battery is added, an increase in cost can be suppressed. . In addition, since the capacity of the second battery to be added is optimized so as to suppress an increase in cost, an increase in the size of the composite power storage system accompanying the addition of the second battery is suppressed.

  FIG. 8 shows the configuration of a composite power storage system that is Embodiment 2 of the present invention and an electric vehicle equipped with the same. Hereinafter, differences from the first embodiment will be mainly described.

  In the second embodiment, unlike the first embodiment, the capacity type battery and the second battery are directly connected in parallel without going through the power control device (DCDC converter 14 in FIG. 1). Thereby, the apparatus size and cost of a composite power storage system are reduced.

In Example 2, the upper limit voltage V0 of the capacity type battery is defined by the upper limit voltage (voltage at SOC 100%) of the second battery, as shown in Expression (10).
V0 = the upper limit voltage of the second battery × the number of series of the second battery / the number of series of the capacity type battery (10)
As equation (10) shows, V0 takes a discrete value. For example, the upper limit voltage of the second battery is 4.2 V, and the series number of the second batteries is 14 according to the motor voltage. In this case, the upper limit voltage V0 of the capacity type battery is “V0 = 14 × 4.2 / n (n: the number of series of capacity type batteries)”. If the voltage range of the capacity type battery is 2.3 V or more and 4.52 V or less, n is 13 or more and 25 or less. For this reason, when V0 optimization shown in FIG. 7 is performed, n = 13 or more and only 4.2V and 4.52V as upper limit voltages are candidates for the optimum value. In this case, since the running cost is minimized at 4.2 V, the upper limit voltage of the capacity type battery set as the initial value is 4.2 V (n = 14).

  In the second embodiment, the same calculation as in the first embodiment is performed using the discrete values as described above.

  As described above, according to the second embodiment, as in the first embodiment, even if a second battery that compensates for the capacity shortage of the capacity type battery is added, an increase in cost can be suppressed. In addition, since the capacity of the second battery to be added is optimized so as to suppress an increase in cost, an increase in the size of the composite power storage system accompanying the addition of the second battery is suppressed.

  In addition, this invention is not limited to embodiment mentioned above, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  For example, the composite power storage system in each of the embodiments described above can be applied to a building management system, a plug-in hybrid vehicle, a hybrid vehicle, a ship, a railway vehicle, and the like.

DESCRIPTION OF SYMBOLS 10 ... Electric vehicle 11 ... Motor generator 12 ... Inverter 13 ... Second battery 14 ... DCDC converter 15 ... Capacity type battery 16 ... ECU
21 ... Current limiting circuit 22 ... P-channel MOSFET
23 ... N-channel MOSFET
24 ... Gate driver 25 ... Voltage smoothing capacitor

Claims (21)

In a composite power storage system that outputs DC power stored in a capacity type battery to a power supply target,
A second battery that compensates for the capacity shortage of the capacity type battery;
A composite power storage system, wherein a limit value of a voltage of the capacity type battery is set so that a total running cost of the capacity type battery and the second battery is substantially minimized or substantially minimized. In the composite power storage system according to claim 1,
The second battery has a lower life cycle cost than the capacity type battery,
The composite battery system, wherein the second battery has a higher unit price of Wh than the capacity type battery. In the composite power storage system according to claim 1,
The composite battery system, wherein the second battery is a power battery. In the composite power storage system according to claim 3,
The power storage battery has a capacity equal to or greater than a lower limit capacity corresponding to a power limit. In the composite power storage system according to claim 1,
The total power storage system is calculated based on a battery replacement year that changes according to the limit value. In the composite power storage system according to claim 5,
The battery replacement year is determined based on a capacity ratio, a resistance ratio, or an admittance ratio, which changes according to the number of charge / discharge cycles. In the composite power storage system according to claim 1,
The composite power storage system, wherein the limit value is a value of an upper limit voltage. In the composite power storage system according to claim 7,
The capacity type battery is any one of a lithium ion battery, a lithium ion semi-solid battery, and a lithium solid battery. In the composite power storage system according to claim 1,
The composite power storage system, wherein the limit value is a value of a lower limit voltage. In the composite power storage system according to claim 9,
The composite battery system, wherein the capacity type battery is a lead battery. In the composite power storage system according to claim 1,
The composite power storage system, wherein the limit value gives a minimum value or a minimum value of the total running cost. In the composite power storage system according to claim 1,
The limit value is set in a voltage range in which the total running cost becomes a substantially minimum value or a substantially minimum value. In the composite power storage system according to claim 1,
The composite power storage system, wherein the total running cost is a function having the limit value as a variable. In the composite power storage system according to claim 1,
The composite power storage system, wherein the total running cost is a function having the limit value, battery current, and battery temperature as variables. In the composite power storage system according to claim 6,
A composite power storage system, wherein a function form of the capacity ratio or the resistance ratio or the admittance ratio is a deterioration function. In the composite power storage system according to claim 15,
The composite power storage system, wherein the deterioration function is a Weibull distribution. In the composite power storage system according to claim 16,
The composite power storage system, wherein the deterioration function is a product or sum of two Weibull distributions. In the composite power storage system according to claim 1,
The capacity type battery and the second battery are connected in parallel via a power control device,
The power control apparatus controls a voltage of the capacity type battery based on the limit value. The composite power storage system according to claim 18,
The composite battery system, wherein the power control device is a DCDC converter. The composite power storage system according to claim 18,
The composite battery system, wherein the power control device is a current limiting circuit. In the composite power storage system according to claim 1,
The capacity type battery and the second battery are directly connected in parallel,
The composite battery system, wherein the limit value is defined by an upper limit voltage (voltage at 100% SOC) of the second battery.

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