Battery control system

Abstract

This more effectively suppresses the formation of Ni2O3H within the positive electrode of nickel-metal hydride batteries. [Solution] The battery control system comprises a nickel-metal hydride battery and a control device for controlling the charging and discharging of the nickel-metal hydride battery. The control device, when the amount of Ni2O3H produced by the nickel-metal hydride battery is equal to or greater than a reference amount, and the temperature of the nickel-metal hydride battery is equal to or greater than a reference temperature, sets the voltage of the nickel-metal hydride battery to a reference voltage and the change in the charge level of the nickel-metal hydride battery to a reference change amount.

Description

Technical Field

[0001] The present disclosure relates to a battery control system including a nickel - hydrogen battery.

Background Art

[0002] Ni2O3H is generated in the positive electrode of a nickel - hydrogen battery. When the amount of generation increases, the electrode reaction is partially restricted, promoting the memory effect and reducing the capacity of the nickel - hydrogen battery. In contrast, for example, Patent Document 1 proposes a method for recovering the reduced battery capacity. Specifically, in Patent Document 1, based on the full capacity of the nickel - hydrogen battery, an OCV (Open Circuit Voltage) - SOC (State of Charge) curve is obtained, and based on the OCV - SOC curve, the SOC is estimated from the current voltage. Then, when charging the nickel - hydrogen battery, if the estimated SOC belongs to the high - SOC region, charging is performed at a low rate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, by setting the charging rate low, generation of local overcharging in the positive electrode is suppressed while homogenizing the active material of the entire positive electrode, thereby aiming to recover the battery capacity. However, if the amount of Ni2O3H generation in the positive electrode increases, it accelerates the reduction of the battery capacity due to the memory effect. Therefore, it is desirable to suppress the generation of Ni2O3H.

[0005] The present disclosure has been made in view of the above problems, and an object thereof is to provide a technique for more effectively suppressing the generation of Ni2O3H in the positive electrode of a nickel - hydrogen battery. [Means for solving the problem]

[0006] One aspect of this disclosure is a battery control system. This battery control system comprises a nickel-metal hydride battery and a control device for controlling the charging and discharging of the nickel-metal hydride battery. The control device, when the amount of Ni2O3H produced by the nickel-metal hydride battery is equal to or greater than a reference amount, and the temperature of the nickel-metal hydride battery is equal to or greater than a reference temperature, sets the voltage of the nickel-metal hydride battery to a reference voltage and the change in the State of Charge (SOC) of the nickel-metal hydride battery to a reference change amount. [Effects of the Invention]

[0007] By limiting the voltage during charging and discharging to below a reference voltage and keeping the change in state of charge (SOC) below a reference change, it becomes possible to effectively suppress the generation of Ni2O3H, thereby suppressing the degradation of nickel-metal hydride batteries. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram shows the relationship between the State of Charge (SOC) and voltage of a nickel-metal hydride battery. [Figure 2] This figure shows the relationship between the cell temperature of a nickel-metal hydride battery and the amount of Ni2O3H produced. [Figure 3] This figure shows the relationship between the upper limit of the SOC change and the cell temperature in charge / discharge control of a nickel-metal hydride battery according to an embodiment of the present disclosure. [Figure 4] This figure shows the change in full charge capacity over time when the charge / discharge control according to the embodiment of this disclosure is performed. [Figure 5] This is a flowchart illustrating the control process performed by the control device of the battery control system according to the embodiment of the present disclosure. [Modes for carrying out the invention]

[0009] Embodiments of this disclosure will be described below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and their descriptions are simplified or omitted.

[0010] Embodiment. The battery control system according to this embodiment is installed, for example, in an electric vehicle. The electric vehicle may be a hybrid vehicle (including a plug-in hybrid vehicle), an electric vehicle, or a fuel-powered vehicle. Furthermore, the use of the battery control system is not limited to vehicles, but may also be for stationary use.

[0011] The battery control system comprises a nickel-metal hydride battery, a control device, and various sensors. The nickel-metal hydride battery in the battery control system is a battery pack in which multiple nickel-metal hydride battery cells (hereinafter referred to as "cells") are connected. Various known materials can be used as the electrode pairs and electrolyte materials for each cell. Specifically, for example, nickel hydroxide (Ni(OH)2 or NiOOH) is used as the positive electrode and a hydrogen storage alloy is used as the negative electrode. For the electrolyte, for example, an alkaline aqueous solution containing potassium hydroxide (KOH) or sodium hydroxide (NaOH) is used.

[0012] The battery control system includes at least a voltage sensor and a temperature sensor. The voltage sensor detects the terminal voltage (hereinafter referred to as "cell voltage") Vb of each individual cell. The temperature sensor detects the temperature (hereinafter referred to as "cell temperature") Tb of each cell. The values ​​detected by the voltage sensor and each sensor are input to the control unit.

[0013] The control unit comprises a processor, memory, and input / output buffers, etc. The memory includes ROM (Read Only Memory) and RAM (Random Access Memory). The control unit is configured to control each device so that the battery control system reaches a desired state, based on signals input from various sensors and maps, programs, etc., stored in memory.

[0014] In nickel-metal hydride batteries, it is known that if Ni2O3H is generated in the positive electrode and oxidation of the positive electrode progresses, the full charge capacity of the nickel-metal hydride battery decreases. The control device of this embodiment suppresses the generation of Ni2O3H in the positive electrode by performing charge and discharge control that controls the charging and discharging of the nickel-metal hydride battery.

[0015] The following is an overview of the charge and discharge control performed by the control device, with reference to the figures. Figure 1 shows the relationship between SOC (State of Charge) and voltage. Figure 2 shows the relationship between cell temperature and Ni2O3H production amount. Figure 3 shows the relationship between the upper limit of SOC change and cell temperature.

[0016] It is known that positive electrode oxidation proceeds more easily at high voltages, but in this study, it was confirmed that positive electrode oxidation proceeds more easily when the State of Charge (SOC) is in a low SOC range. Here, the low SOC region is the region where the change in SOC during charging and discharging, ΔSOC, is large. In other words, the amount of positive electrode oxidation is thought to depend on ΔSOC, and as ΔSOC increases, the amount of positive electrode oxidation also increases. Here, ΔSOC refers to the change in SOC from the start to the end of charging, or from the start to the end of discharging.

[0017] In the charge-discharge control of this embodiment, the cell voltage Vb is controlled so as not to exceed the first reference voltage V1, which is particularly conducive to positive electrode oxidation, and the SOC is controlled so that ΔSOC does not exceed a reference change amount.

[0018] The method for controlling ΔSOC is not particularly limited. For example, the amount of change in SOC per unit time, that is, ΔSOC, may be estimated by a conventional method, and the current value may be controlled so that ΔSOC does not become larger than the reference change amount. Also, the cell voltage and SOC have a correlation as shown in FIG. 1, and ΔSOC becomes large in a region where the cell voltage is low. Therefore, as shown in FIG. 1, a second reference voltage V2 corresponding to the boundary value in the region where positive electrode oxidation is likely to occur may be obtained, and the cell voltage Vb may be controlled to be equal to or higher than the second reference voltage. Alternatively, the amount of change in voltage ΔV during charging and discharging may be limited so as not to exceed the differential voltage between the first reference voltage V1 and the second reference voltage V2. Here, ΔV means the amount of change in voltage from the start to the end of charging or from the start to the end of discharging.

[0019] Also, the region of ΔSOC where positive electrode oxidation is likely to occur changes depending on the cell temperature Tb. Specifically, as shown in FIG. 2, in a region where the temperature is higher than the reference temperature T, the amount of Ni2O3H generated increases as the cell temperature increases.

[0020] Therefore, in the present embodiment, the reference change amount, which is the upper limit value of ΔSOC, is made to depend on the cell temperature Tb as shown in FIG. 3. Specifically, in a region where the cell temperature is lower than the reference temperature T, since almost no Ni2O3H is generated, the reference change amount for ΔSOC is increased or not limited. In a region where the cell temperature Tb is equal to or higher than the reference temperature T, the reference change amount is set to decrease as the cell temperature Tb increases.

[0021] In a specific control, based on the relationship as described above, a map defining the relationship between the reference change amount for ΔSOC and the cell temperature is created and stored in a memory in advance. Then, according to this, the reference change amount corresponding to the cell temperature is set. Alternatively, when limiting ΔSOC by limiting the amount of change in voltage ΔV, a map defining the relationship between the cell temperature and the amount of change in voltage (V1 - V2) may be created, and the amount of change in voltage corresponding to the cell temperature Tb may be set according to this.

[0022] Figure 4 shows the change in full charge capacity over time when the charge / discharge control of this embodiment is performed. For comparison, the case with charge / discharge control of this embodiment is shown by solid line A, and the conventional case is shown by dashed line B. As shown in Figure 4, the full charge capacity over time can be maintained at a high level by using charge / discharge control.

[0023] Figure 5 is a flowchart illustrating the control process performed by the control device. The process in Figure 5 is repeatedly executed at a predetermined control cycle from the start to the end of charging, or from the start to the end of discharging. In the following explanation, "unit time" corresponds to the control cycle.

[0024] In the process shown in Figure 5, first, in step S101, the cell voltage Vb, cell temperature Tb, and current Ib of each cell are acquired from each sensor.

[0025] Next, in step S102, the State of Charge (SOC) of each cell is estimated. Known methods can be used to calculate the SOC. Specifically, the SOC may be calculated based on data showing a predetermined correlation between the SOC and the OCV, or it may be calculated based on the integrated value of the current Ib and the full charge capacity of the cell.

[0026] Next, in step S103, an estimated value of the amount of Ni2O3H produced per unit time in each cell is calculated. Here, the amount of Ni2O3H produced is correlated with SOC, cell temperature Tb, and cell voltage Vb. For example, under conditions where SOC is the same, the amount of Ni2O3H produced per unit time increases as the voltage or cell temperature Tb increases. In this embodiment, a map is created in advance by experiment or other means, defining the relationship between SOC, cell voltage, and Ni2O3H produced for each cell temperature Tb, and is stored in memory. In the process of step S103, the amount of Ni2O3H produced per unit time is calculated according to this map, corresponding to SOC, cell temperature Tb, and cell voltage Vb.

[0027] Next, in step S104, the amount of Ni2O3H produced per unit time calculated in step S103 is added to the previous amount of Ni2O3H produced to calculate the current amount of Ni2O3H produced in each cell.

[0028] Next, in step S105, it is determined whether the amount of Ni2O3H produced calculated in step S104 is equal to or greater than a predetermined baseline amount. The baseline amount is the threshold at which control to suppress Ni2O3H production should be initiated, and is set in advance based on the relationship between the amount of Ni2O3H produced and the decrease in battery capacity. If in step S105 there are no cells with a Ni2O3H production amount equal to or greater than the baseline amount, that is, if the result in step S105 is NO, the process is terminated.

[0029] On the other hand, if it is determined in step S105 that there is at least one cell with Ni2O3H in an amount equal to or greater than the standard amount, the process proceeds to step S106. In step S106, it is determined whether the cell temperature Tb of the cell with Ni2O3H in an amount equal to or greater than the standard temperature T is equal to or greater than the standard temperature T. If it is determined in step S106 that the cell temperature Tb is not equal to or greater than the standard temperature T, the process is terminated.

[0030] In step S106, if it is determined that the cell temperature Tb of a cell whose Ni2O3H production amount is equal to or greater than the reference production amount is equal to or greater than the reference temperature T, the process proceeds to step S107. In step S107, for cells whose Ni2O3H production amount is equal to or greater than the reference production amount, the cell voltage Vb is limited to the first reference voltage or less, and ΔSOC is limited to be equal to or less than the reference change amount. Here, the reference change amount for ΔSOC is set according to the map, depending on the cell temperature Tb and the cell voltage Vb. After this, the process is considered complete.

[0031] As described above, the charge / discharge control of this embodiment can suppress the decrease in the full charge capacity of the nickel-metal hydride battery and prevent the full charge capacity from falling below the required amount. Furthermore, since the amount of Ni2O3H produced can be suppressed, the decrease in full charge capacity over time can be suppressed.

[0032] In the embodiments described above, sensors such as voltage sensors and temperature sensors are installed in all cells, and the voltage and temperature are detected for each cell, and the voltage and ΔSOC (or ΔV) are controlled for each cell. However, multiple cells of a nickel-metal hydride battery may be divided into multiple areas, and each sensor may be installed in only one or more cells in each area. In this case, the cell voltage and cell temperature are detected for each area, and the voltage Vb and ΔSOC of the entire area can be limited when the estimated amount of Ni2O3H produced is equal to or greater than the reference amount and the cell temperature Tb is equal to or greater than the reference temperature T. Alternatively, the voltage and ΔSOC (or ΔV) of the entire nickel-metal hydride battery may be limited when there is a cell or area where the estimated amount of Ni2O3H produced is equal to or greater than the reference amount and the cell temperature Tb is equal to or greater than the reference temperature T. Furthermore, one voltage sensor and one temperature sensor may be installed in the entire nickel-metal hydride battery, and the voltage and temperature of the entire battery may be detected, and the voltage and ΔSOC (or ΔV) of the entire nickel-metal hydride battery may be limited.

Claims

[Claim 1] Nickel-metal hydride batteries and A control device for controlling the charging and discharging of the nickel-metal hydride battery, Equipped with, The control device is The Ni of the aforementioned nickel-metal hydride battery ２ O ３ If the amount of H produced is equal to or greater than the standard production amount, and the temperature of the nickel-metal hydride battery is equal to or greater than the standard temperature, The voltage of the nickel-metal hydride battery is set to be below the reference voltage, and the change in the State of Charge (SOC) of the nickel-metal hydride battery is set to be below the reference change amount. Battery control system

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