Power supply system and management device capable of determining current upper limit for supressing cell deterioration and ensuring safety

Power supply system mounted in electric vehicle includes voltage measurement unit that measures a voltage of each of a plurality of cells to ensure both safety of an electric vehicle and convenience of a user. Current measurement unit therein measures a current flowing through the plurality of cells. Temperature measurement unit therein measures a temperature of the plurality of cells. Controller therein determines a current limit value defining an upper limit of a current for suppressing cell deterioration and ensuring safety based on the voltage, the current, and the temperature of each of the plurality of cells measured by voltage measurement unit, current measurement unit, and temperature measurement unit respectively, and that notifies a higher-level controller in electric vehicle of the determined current limit value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of the PCT International Application No. PCT/JP2019/029350 filed on Jul. 26, 2019, which claims the benefit of foreign priority of Japanese patent application No. 2018-181657 filed on Sep. 27, 2018, the contents all of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a power supply system and a management device that are mounted on an electric vehicle.

BACKGROUND ART

In recent years, hybrid vehicles (HVs), plug-in hybrid vehicles (PHVs), and electric vehicles (EVs) have become popular. These electric vehicles are each equipped with a power supply system provided with a secondary battery as a key device.

When the power supply system causes overcharging, overdischarging, or overheating, a protection function (hereinafter referred to as relay cut off) operates to open a contactor relay installed between the power supply system and an inverter that drives a running motor. The relay cut off is also activated when a measurement circuit for detecting overcharge, overdischarge, or overheat (e.g., a voltage measurement circuit, a current measurement circuit, or a temperature measurement circuit) has an anomaly (e.g., refer to PTL 1).

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

Even when the relay cut off is activated, a hybrid vehicle (HV) or a plug-in hybrid vehicle (PHV) can travel using an engine. However, a pure electric vehicle (EV) without an engine cannot travel when the relay cut off is activated. An electric vehicle (EV) equipped with the above protection function cannot travel when the measurement circuit has an anomaly, even with a battery itself having no anomaly, and thus the vehicle cannot be moved by itself to a car dealer or a repair shop.

The present invention is made in view of such a situation, and it is an object of the present invention to provide a technique for ensuring both safety of an electric vehicle and convenience of a user.

To solve the above problems, a power supply system according to an aspect of the present invention is mounted on an electric vehicle and includes a power storage unit connected to a plurality of cells, a voltage measurement unit that measures a voltage of each of the plurality of cells, a current measurement unit that measures a current flowing through each of the plurality of cells, a temperature measurement unit that measures a temperature of each of the plurality of cells, and a controller that determines a current limit value defining an upper limit of a current for suppressing cell deterioration and ensuring safety based on the voltage, the current, and the temperature of each of the plurality of cells measured by the voltage measurement unit, the current measurement unit, and the temperature measurement unit, respectively, and that notifies a higher-level controller in the electric vehicle of the determined current limit value.

Any combination of the components described above and a conversion of expression of the present invention between methods, devices, systems, and the like are also effective as aspects of the present invention.

According to the present invention, both safety of the electric vehicle and convenience of a user can be ensured.

DESCRIPTION OF EMBODIMENT

FIG.1is a diagram for illustrating electric vehicle1equipped with power supply system10according to an exemplary embodiment of the present invention. Electric vehicle1is assumed to be an EV that can be charged from charger3installed outside.

Power supply system10is connected to motor50through first relay RY1and inverter40. Inverter40converts DC power supplied from power supply system10into AC power and supplies it to motor50during power running. At the time of regeneration, the AC power supplied from motor50is converted into DC power and supplied to power supply system10. Motor50is a three-phase AC motor, and rotates in accordance with the AC power supplied from inverter40during power running. At the time of regeneration, rotational energy due to deceleration is converted into AC power and supplied to inverter40.

First relay RY1is a contactor inserted between wiring connecting power supply system10and inverter40. Vehicle ECU30controls first relay RY1in an on-state (closed state) during traveling, and electrically connects power supply system10and a power system of electric vehicle1. Vehicle ECU30controls first relay RY1in an off-state (open state) during non-traveling in principle, and electrically interrupts power supply system10and the power system of electric vehicle1. Instead of the relay, another type of switch such as a semiconductor switch may be used.

Power supply system10can be charged from commercial power system2when being connected to charger3installed outside electric vehicle1with charging cable4. Charger3is installed in homes, car dealers, service areas, commercial facilities, public facilities, and the like. Charger3is connected to commercial power system2and charges power supply system10in electric vehicle1using charging cable4. In electric vehicle1, second relay RY2is inserted between wiring connecting power supply system10and charger3. Instead of the relay, another type of switch such as a semiconductor switch may be used. Vehicle ECU30controls second relay RY2in the on-state (closed state) before start of charging, and in the off-state (open state) after the charging is completed.

In general, normal charging uses an alternating current for charging and quick charging uses a direct current for charging. When an alternating current is used for charging, AC power is converted to DC power by an AC/DC converter (not illustrated) inserted between second relay RY2and power supply system10.

Power supply system10includes power storage unit11and management unit12, and power storage unit11includes a plurality of cells E1to En connected in series. More specifically, power storage unit11includes one or more power storage modules. The one or more power storage modules are connected in series and series-parallel. Each of the power storage modules includes a plurality of cells connected in series and series-parallel. For each of the cells, a lithium ion battery cell, a nickel hydrogen battery cell, a lead battery cell, an electric double layer capacitor cell, a lithium ion capacitor cell, or the like is available. Hereinafter, in the present specification, an example using a lithium ion battery cell (having a nominal voltage of 3.6 V to 3.7 V) is assumed. A number of series of cells E1to En is determined in accordance with a drive voltage of motor50.

The plurality of cells E1to En is connected to shunt resistor Rs in series. Shunt resistor Rs functions as a current detection element. Instead of shunt resistor Rs, a Hall element may be used. Power storage unit11is provided inside with a plurality of temperature sensors T1, T2for detecting temperature of the plurality of cells E1to En. One temperature sensor may be provided for each of the power storage modules, or one temperature sensor may be provided for each of the plurality of cells. For example, a thermistor can be used for each of temperature sensors T1, T2.

Management unit12includes voltage measurement unit13, temperature measurement unit14, current measurement unit15, and controller16. Each of nodes of respective cells E1to En connected in series is connected to voltage measurement unit13with corresponding one of voltage lines. Voltage measurement unit13measures a voltage of each of cells E1to En by measuring a voltage between two adjacent voltage lines. Voltage measurement unit13transmits the measured voltage of each of cells E1to En to controller16.

Voltage measurement unit13has a higher voltage than controller16, so that voltage measurement unit13and controller16are connected with a communication line in an insulated state. Voltage measurement unit13can be composed of an application specific integrated circuit (ASIC) or a general-purpose analog front-end integrated circuit (IC). Voltage measurement unit13includes a multiplexer and an A/D converter. The multiplexer outputs the voltage between two adjacent voltage lines to the A/D converter in order from the top. The A/D converter converts an analog voltage received from the multiplexer into a digital value.

Temperature measurement unit14includes a voltage dividing resistor and an A/D converter. The A/D converter sequentially converts a plurality of analog voltages divided by the plurality of temperature sensors T1, T2and a plurality of voltage dividing resistors into digital values and outputs them to controller16. Controller16estimates temperatures of the plurality of cells E1to En based on the digital values. For example, controller16estimates a temperature of each of the cells E to En based on a value measured by the temperature sensor closest to the corresponding one of cells E1to En.

Current measurement unit15includes a differential amplifier and an A/D converter. The differential amplifier amplifies a voltage across shunt resistor Rs and outputs the voltage to the A/D converter. The A/D converter converts the voltage received from the differential amplifier into a digital value and outputs the digital value to controller16. Controller16estimates a current flowing through the plurality of cells E1to En based on the digital value.

When an A/D converter is mounted in controller16and an analog input port is provided in controller16, temperature measurement unit14and current measurement unit15may output analog voltages to controller16, and the A/D converter in controller16may convert the analog voltages into digital values.

Controller16manages a state of each of the plurality of cells E1to En based on the voltage, temperature, and current of the corresponding one of the plurality of cells E1to En measured by voltage measurement unit13, temperature measurement unit14, and current measurement unit15, respectively. Controller16and vehicle ECU30are connected through in-vehicle network20. In-vehicle network20is constructed using at least one of the standards such as a controller area network (CAN), a local interconnect network (LIN), FlexRay (registered trademark), and Ethernet (registered trademark). Hereinafter, in the present exemplary embodiment, an example is assumed in which the CAN is used for in-vehicle network20.

Controller16can be composed of a microcomputer and a non-volatile memory (e.g., an electrically erasable programmable read-only memory (EEPROM), or a flash memory). In the non-volatile memory, state of charge (SOC)-open circuit voltage (OCV) map16aand SOC-temperature map16bare held. SOC-OCV map16adescribes characteristic data on SOC-OCV curves of the plurality of cells E1to En.

SOC-temperature map16bdefines a relationship between an SOC and a temperature of a cell, and a current limit value. The current limit value defines an upper limit value of a current recommended for suppressing deterioration of a cell. A battery manufacturer determines a recommended current limit value for each of various combinations of an SOC and a temperature of a cell based on numerical simulations and experiments in advance, and maps a relationship between them. The recommended current limit value is set to, for example, a current value for avoiding progress of deterioration faster than an average life curve of a cell. The recommended current limit value is set separately for each of a charge current and a discharge current. SOC-temperature map16bgenerated by the battery manufacturer is registered in the non-volatile memory in controller16.

The relationship between the SOC and temperature of the cell, and the recommended current limit value may be defined as a function. Also in that case, the derived function is registered in the non-volatile memory in controller16. Instead of the recommended current limit value, a recommended power limit value may be used.

Controller16estimates the SOC and a state of health (SOH) of each of the plurality of cells E1to En. Controller16estimates the SOC by combining an OCV method and a current integration method. The OCV method is configured to estimate the SOC based on OCV of each of the cells E1to En measured by voltage measurement unit13and the characteristic data on the SOC-OCV curve described in SOC-OCV map16a. The current integration method is configured to estimate the SOC based on the OCV at the start of charging and discharging of each of cells E1to En and an integrated value of a current measured by current measurement unit15. In the current integration method, a measurement error of current measurement unit15accumulates as charging and discharging time increases. Thus, the estimated SOC by the current integration method needs to be corrected using the estimated SOC by the OCV method.

The SOH is defined as a ratio of current full charge capacity to initial full charge capacity, and the SOH having a lower value (closer to 0%) indicates that deterioration progresses more. The SOH may be acquired by measuring capacity by complete charge and discharge, or may be acquired by adding storage deterioration and cycle deterioration. The storage deterioration can be estimated based on the SOC, the temperature, and a storage deterioration rate. The cycle deterioration can be estimated based on a SOC range used, a temperature, a current rate, and a cycle deterioration rate. The storage deterioration rate and the cycle deterioration rate can be derived in advance by experiments or simulations. The SOC, the temperature, the SOC range, and the current rate can be determined by measurement.

The SOH can also be estimated based on a correlation with internal resistance of each of the cells. The internal resistance can be estimated by dividing a voltage drop caused by allowing a predetermined current to flow through the corresponding one of the cells for a predetermined time by the current value. The internal resistance decreases as the temperature rises, and increases as the SOH decreases.

Controller16notifies vehicle ECU30of a state of each of the plurality of cells E1to En through in-vehicle network20. For example, controller16totals the SOCs of the plurality of cells E1to En to calculate the SOC of the whole of power storage unit11, and notifies vehicle ECU30of the calculated SOC of the whole of power storage unit11. Controller16also notifies vehicle ECU30of a voltage applied to power storage unit11and a current flowing through power storage unit11, in real time. Vehicle ECU30notifies vehicle ECU30of the current limit value described above.

Vehicle ECU30controls the whole of electric vehicle1. Vehicle ECU30may be composed of, for example, an integrated vehicle control module (VCM). In electric vehicle1, instrument panel60is disposed facing a driver's seat. Instrument panel60includes a tachometer, a speedometer, and various telltale lamps. The teller tail lamps include a caution lamp indicating an anomaly in equipment in electric vehicle1. For example, a caution lamp indicating an anomaly in power supply system10and a caution lamp indicating an anomaly in in-vehicle network20are included.

When vehicle ECU30receives notification that an anomaly has occurred in any equipment in electric vehicle1through in-vehicle network20, vehicle ECU30turns on the corresponding caution lamp on instrument panel60. When a caution lamp requiring repair of equipment lights up, a driver moves to a car dealer or a repair shop with the vehicle itself when the vehicle can travel. When the vehicle cannot travel, the driver uses road service.

FIG.2is a diagram summarizing alternative strategies and fail-safe actions when power supply system10has an anomaly in a comparative example and an example. As described later, the fail-safe action of the comparative example is suitable for controlling a hybrid vehicle (HV) and a plug-in hybrid vehicle (PHV), and the fail-safe action of the example is suitable for controlling a pure electric vehicle (EV) without an engine. In the comparative example, when any of overcharge, overdischarge, and overheat is detected in a cell by external control from a vehicle to power supply system10, controller16transmits a relay cut off request to vehicle ECU30through in-vehicle network20. When receiving the relay cut off request, vehicle ECU30turns off first relay R1.

Controller16compares the voltage of each of the cells measured by voltage measurement unit13with an OV threshold value for detecting overvoltage, and determines that a cell having a voltage higher than the OV threshold value is overcharged. Controller16also compares the voltage of each of the cells measured by voltage measurement unit13with a UV threshold value for detecting undervoltage, and determines that a cell having a voltage lower than the UV threshold value is overdischarged. The OV threshold value is typically set to a value lower than an upper limit of a working voltage of a cell by a protection margin. The UV threshold value is typically set to a value higher than a lower limit of the working voltage of the cell by the protection margin. Controller16compares the temperature of each of the cells measured by temperature measurement unit14with an OT threshold value for detecting overtemperature (OT), and determines that a cell having a temperature higher than the OT threshold value is excessively increased in temperature.

In the comparative example, also when a circuit that implements a cell protection function (specifically, voltage measurement unit13, temperature measurement unit14, or current measurement unit15) has an anomaly, controller16transmits the relay cut off request to vehicle ECU30. As described above, the fail-safe action of the comparative example can prevent use of battery system10in an uncertain state by performing relay cut off when any of the measurement units fails. In particular, hybrid vehicles (HVs) and plug-in hybrid vehicles (PHVs) each can travel using an engine, so that relay cut off performed as a fail-safe action for an anomaly having occurred in the circuit causes little inconvenience. Thus, the fail-safe action of the comparative example is suitable for controlling a battery system mounted on this type of vehicle.

However, a pure electric vehicle (EV) without an engine may not be stopped in a safe place when power supply system10suddenly stops. Even when the vehicle can be stopped in a safe place, the vehicle cannot travel by itself after that, and thus reducing convenience of a user. Thus, a pure electric vehicle (EV) is required to achieve both ensuring vehicle safety and continuing basic performance (running, turning, stopping).

In the example, an anomaly of a cell is detected with a current limit (hereinafter, also referred to as a power limit as appropriate) using SOC-temperature map16b.

The power limit using the SOC-temperature map is a value indicating an allowable current value from the viewpoint of suppressing cell deterioration. The power limit using the SOC-temperature map only indicates a recommended value for suppressing cell deterioration in conventional power supply systems and electric vehicles, so that whether the vehicle ECU executes the power limit in accordance with a current limit value transmitted from the controller to the vehicle ECU is left to a design concept of a vehicle manufacturer. A typical vehicle ECU of a conventional electric vehicle controls charge and discharge such that the power limit is executed when an economic mode for emphasizing battery life is selected, and the power limit is not executed when a normal mode without traveling restriction is selected.

In contrast, the example is configured such that a power limit signal transmitted from the power supply system is treated as an abnormal signal. Specifically, the vehicle ECU is configured such that when the power limit signal indicating a value at which the current limit value is zero is received, relay cut off is executed when safety can be checked from another data acquired by the vehicle ECU. This enables the example to determine an anomaly of a cell before an abnormal state such as OV, UV, or OT occurs by detecting the anomaly of the cell with the power limit using SOC-temperature map16b. What is especially important is that a boundary related to both the SOC and the temperature can be identified by treating the power limit as an abnormal signal, and thus enabling multiple anomalies, which are conventionally determined individually as OV, UV or OT, to be integrated and evaluated.

Specifically, as described above, the SOC can be estimated by combining the OCV method and the current integration method, and the SOC also can be estimated by only one of the OCV method and the current integration method. Additionally, the OCV method uses voltage measurement unit13that measures OCV and has a redundant configuration, and the current integration method uses current measurement unit15that measures a current integrated value and has a redundant configuration. Thus, even when the alternative strategy illustrated inFIG.5is executed, the redundant configuration is maintained in a circuit that measures a measurement value for calculating the power limit. For example, even when a circuit anomaly occurs in voltage measurement unit13, the power limit can be calculated based on a measurement value of current measurement unit15having the redundant configuration.

The comparative example has the configuration in which there is no correlation between determination of OV/UV and determination of OT. Thus, when an alternative strategy as in the example is applied to voltage measurement unit13by assuming that a circuit anomaly occurs, operation under conditions where no redundant configuration is maintained is allowed. Thus, the configuration of the comparative example is not allowed to use such a configuration from the viewpoint of reliability.

When executing the power limit, vehicle ECU30sets the current limit value received from controller16of power supply system10to inverter40. When a DC/DC converter (not illustrated) is provided between inverter40and first relay RY1and a current is controlled by the DC/DC converter, vehicle ECU30sets the received current limit value to the DC/DC converter. Inverter40or the DC/DC converter controls an output current (discharge current from power storage unit11) within a range of the set current limit value.

At the time of charging from charger3to power supply system10, vehicle ECU30sets the current limit value received from controller16of power supply system10to charger3through a communication line (not illustrated). When an AC/DC converter or DC/DC converter is provided between charger3and second relay RY2, and a charge current is controlled by the AC/DC converter or the DC/DC converter, vehicle ECU30sets the received current limit value to the AC/DC converter or the DC/DC converter.

In the example, the power limit using the SOC-temperature map16bis used not only for suppressing cell deterioration but also for ensuring safety of electric vehicle1. In the example, the current limit value may be zero. The current limit value is zero when a cell has a state estimated to be equivalent to a state in which any of overcharging, overdischarging, and overheating has occurred. To ensure safety more, SOC-temperature map16bmay be generated in which the current limit value is zero in a state before the state in which any of overcharging, overdischarging, and overheating has occurred. In this case, vehicle ECU30turns off first relay RY1when the current limit value received from controller16of power supply system10is zero.

In the example, when a circuit that implements a cell protection function (specifically, voltage measurement unit13, temperature measurement unit14, or current measurement unit15) has an anomaly, controller16executes an alternative strategy and notifies vehicle ECU30of a transfer request to a degenerate mode.

For in-vehicle applications, a redundant configuration is typically used for voltage measurement unit13in many cases. Current measurement unit15also uses a redundant configuration in many cases. As an alternative strategy, operation is continued using a redundant function when an anomaly occurs in a main function of the redundant configuration. When an anomaly occurs in the redundant function of the redundant configuration, the operation is continued using only the main function. When an anomaly occurs in both the main function and the redundant function of the redundant configuration, an alternative value is generated based on a value measured by another measurement circuit and the operation is continued. In any case, the measurement circuit is not in a perfect state, so that electric vehicle1is transferred to the degenerate mode to improve safety, and accordingly compensating reduced reliability of the measurement circuit. Specific examples of the alternative strategy and the degenerate mode will be described later.

FIG.3is a flowchart for illustrating a protection function of power supply system10according to a comparative example. When a power supply of electric vehicle1is turned on (corresponding to ignition-on of an engine vehicle), controller16acquires the voltage, temperature, and current of the plurality of cells E1to En measured by voltage measurement unit13, temperature measurement unit14, and current measurement unit15, respectively (S11). When the measurement circuit has an anomaly (Y in S12), controller16notifies vehicle ECU30of the relay cut off request signal (S15). When the measurement circuit has no anomaly (N in S12), controller16estimates the SOC of the plurality of cells E1to En based on the acquired voltage and current (S13).

Controller16compares the acquired voltage with the OV threshold value, the acquired voltage with the UV threshold value, and the acquired temperature with the OT threshold value (S14). When overcharge, overdischarge, or overheat is detected (Y in S14), controller16notifies vehicle ECU30of the relay cut off request signal (S15). When overcharge, overdischarge, or overheat is not detected (N in S14), processing proceeds to step S11, and the processing after step S11is repeated.

When receiving the relay cut off request signal from controller16of power supply system10, vehicle ECU30turns off first relay RY1and executes relay cut off (S16).

FIG.4is a flowchart for illustrating a protection function of power supply system10according to an example. When a power supply of electric vehicle1is turned on, controller16acquires the voltage, temperature, and current of the plurality of cells E1to En measured by voltage measurement unit13, temperature measurement unit14, and current measurement unit15, respectively (S21). When the measurement circuit has an anomaly (Y in S22), controller16executes an alternative strategy (S26). When finishing the alternative strategy, controller16notifies vehicle ECU30of the relay cut off request signal (S27).

When the measurement circuit has no anomaly in step S22(N in S22), controller16estimates the SOC of the plurality of cells E1to En based on the acquired voltage and current (S23). Controller16determines the current limit value of each of the cells by referring to SOC-temperature map16bbased on the estimated SOC of the corresponding one of the cells and the temperature of the corresponding one of the cells (S24).

Controller16selects the smallest current limit value among determined current limit values of the respective cells, and notifies vehicle ECU30of the selected current limit value (S25). Then, the processing proceeds to step S21and the processing after step S21is repeated.

FIG.5is a block diagram illustrating a specific example of a redundant configuration of power supply system10, in-vehicle network20, and vehicle ECU30, illustrated inFIG.1. In the example illustrated inFIG.5, voltage measurement unit13includes main voltage measurement circuit13aof a measurement system and secondary voltage measurement circuit13bof a monitoring system.

In the present example, both main voltage measurement circuit13aand secondary voltage measurement circuit13buse a circuit configuration capable of software control using a processor. For example, the same ASIC is used for main voltage measurement circuit13aand secondary voltage measurement circuit13b. Main voltage measurement circuit13amay use a relatively high-spec ASIC, and secondary voltage measurement circuit13bmay use a relatively low-spec ASIC.

In general, when a circuit anomaly occurs as shown in the comparative example ofFIG.2, i.e., when any one of main voltage measurement circuit13aand secondary voltage measurement circuit13bhas an anomaly, relay cut off is performed. Thus, the main voltage measurement circuit is often designed with a circuit configuration capable of software control using a processor, and the sub voltage measurement circuit is often designed with a circuit configuration capable of only hardware control without using a processor. In contrast, the present example is configured to continue operation using an alternative strategy, so that main voltage measurement circuit13aand secondary voltage measurement circuit13bare each not composed of a circuit capable of only hardware control without using a processor. Anomaly detection with a power limit is determined by using SOC-temperature map16bas described above in the present example, so that the anomaly detection with a power limit can be continued even with deterioration in reliability of a measured voltage value. Thus, the present example is configured to allow the degenerate mode to be used by using together the anomaly detection with a power limit.

Temperature measurement unit14includes temperature measurement circuit14a. Current measurement unit15includes first current measurement circuit15ain a high range and second current measurement circuit15bin a low range. First current measurement circuit15ain a high range uses a differential amplifier and an A/D converter, each having a relatively wider voltage input range than second current measurement circuit15bin a low range. In general, a differential amplifier and an A/D converter each have a larger offset error as a range widens, so that second current measurement circuit15bin a low range has higher detection accuracy. In-vehicle network20includes main network20aand sub network20b.

The configuration of current measurement unit15described above is an example, and thus current measurement unit15does not necessarily include a current measurement circuit in a high range and a current measurement circuit in a low range. For example, first current measurement circuit15aand second current measurement circuit15bmay be each composed of the same current sensor, or may be composed of a combination of a current measurement circuit using a Hall element and a current measurement circuit using a shunt resistor.

FIG.6is a diagram summarizing alternative strategies and fail-safe actions when power supply system10has an anomaly in the example. Examples of an anomaly in both main voltage measurement circuit13aand secondary voltage measurement circuit13b(the entire voltage measurement function) include an ASIC power supply anomaly and a serial peripheral interface (SPI) communication anomaly. When an anomaly occurs in the entire voltage measurement function, voltage information on some cells constituting power supply system10cannot be obtained. Thus, controller16replaces data on the ASIC having an anomaly has occurred with data on another normal ASIC as an alternative strategy, and calculates the power limit described above. The power limit is not calculated only using a voltage value, so that an abnormal state of power supply system10can be detected from another parameter even with deterioration in reliability of some data. Battery system10mounted on electric vehicle1has several hundred volts, so that many cells are connected in series. A number of cells (measurement unit) for which one ASIC measures voltages is generally10to20. Thus, one power supply system10is provided with a plurality of ASICs. Even when an anomaly occurs in an ASIC of any measurement unit (both main voltage measurement circuit13aand secondary voltage measurement circuit13b), only a measurement value of the ASIC cannot be used, and thus a measurement value of a normal ASIC of another measurement unit can be used.

Then, controller16executes transition to the degenerate mode as a fail-safe action to compensate for deterioration in reliability. As the degenerate mode, for example, a SOC usage range of a cell is limited. For example, when the SOC usage range in a normal mode is 20% to 80%, the SOC range in the degenerate mode is limited to 40% to 60%. Additionally, as the degenerate mode, for example, a predetermined offset value is added to a current value measured by current measurement unit15. A positive offset value is added for charging and a negative offset value is added for discharging. For the offset value, a value determined in advance by the battery manufacturer based on numerical simulations and experiments is used. The offset value may be a fixed value or a variable value in accordance with a measured current value. For example, the offset value may be a value obtained by multiplying a measured current value by a constant rate.

This allows controller16to estimate the SOC based on a current value with an absolute value larger than a current actually flowing. Thus, the estimated SOC by controller16is smaller at the time of discharging and larger at the time of charging than an actual SOC. This allows the charging and the discharging to easily reach an upper limit value and a lower limit value of the SOC, respectively.

As the degenerate mode, controller16multiplies the estimated SOC by a predetermined coefficient. For charging, a coefficient more than one is multiplied, and for discharging, a coefficient less than one is multiplied. For charging, a coefficient less than one may be multiplied, and for discharging, a coefficient more than one may be multiplied. For the coefficients for charging and discharging, values determined in advance by the battery manufacturer based on numerical simulations and experiments are used. When the SOC is multiplied by a predetermined coefficient, the estimated SOC by controller16is smaller at the time of discharging and larger at the time of charging than the actual SOC. This allows the charging and the discharging to easily reach an upper limit value and a lower limit value of the SOC, respectively. Instead of multiplying the estimated SOC by a predetermined coefficient, a positive offset may be added for charging and a negative offset may be added for discharging.

The degenerate mode is performed on both power supply system10and vehicle ECU30. For example, vehicle ECU30executes processing of limiting an SOC usage range of a cell described above. For example, vehicle ECU30also executes power limit control based on a current limit value transmitted from controller16as essential control. For example, power supply system10executes processing of adding a predetermined offset value to the measured current value described above and/or processing of multiplying the estimated SOC described above by a predetermined coefficient. In the degenerate mode, the current value and SOC transmitted from controller16of power supply system10to vehicle ECU30may be an original measured value or an estimated value, or a measured value or an estimated value subjected to the above processing.

FIG.7is a flowchart for illustrating a protection function of power supply system10after transition to an alternative strategy caused when an anomaly occurs throughout a voltage measurement function. Controller16acquires the voltage, temperature, and current of the plurality of cells E1to En measured by voltage measurement unit13, temperature measurement unit14, and current measurement unit15, respectively (S261). During a period where yet another measurement circuit has no anomaly after the alternative strategy is executed (N in S262), controller16replaces a voltage value of each of main voltage measurement circuit13aand secondary voltage measurement circuit13bof a failed measurement unit with a voltage value measured by voltage measurement unit13of another normal measurement unit (S263). Controller16limits the SOC usage range of the cell as a fail-safe action (S264).

Controller16estimates an SOC of each of the plurality of cells E1to En based on the acquired or replaced voltage and the acquired current (S265). Controller16determines a current limit value of each of the cells by referring to SOC-temperature map16bbased on the estimated SOC of the corresponding one of the cells and the temperature of the corresponding one of the cells (S266). Controller16selects the smallest current limit value among determined current limit values of the cells, and notifies vehicle ECU30of the selected current limit value (S267). Then, processing proceeds to step S261and the processing after step S261is repeated. When another measurement circuit has an anomaly in step S262(Y in S262), the alternative strategy is terminated.

As described above, even when an anomaly occurs in the entire voltage measurement function of a certain measurement unit, replacement of a voltage value with a voltage value measured by voltage measurement unit13of another normal measurement unit as an alternative strategy enables electric vehicle1to continue to travel within a range of the degenerate mode. Transition to the degenerate mode allows electric vehicle1to be operated according to a standard requiring higher safety, so that deterioration in reliability due to the anomaly of the voltage measurement function can be compensated. This enables ensuring both safety of electric vehicle1and convenience of a user when an anomaly occurs in the entire voltage measurement function. In contrast, when an anomaly occurs in the entire voltage measurement function in the comparative example, relay cut off is performed. Thus, electric vehicle1cannot travel, so that convenience of a user is impaired.

Return toFIG.6. Examples of an anomaly of main voltage measurement circuit13ainclude an anomaly in that output of an A/D converter sticks. When main voltage measurement circuit13ahas an anomaly, controller16uses data measured by secondary voltage measurement circuit13bas an alternative strategy.

When main voltage measurement circuit13ahas an anomaly, data measured by main voltage measurement circuit13aand data measured by secondary voltage measurement circuit13bcannot be compared with each other, and thus reliability of the data is deteriorated.

Controller16executes transition to the degenerate mode as a fail-safe action. As the degenerate mode, for example, vehicle ECU30executes the processing of limiting the SOC usage range of the cell described above. For example, vehicle ECU30also executes power limit control based on a current limit value transmitted from controller16as essential control.

Even when main voltage measurement circuit13ahas an anomaly as described above, electric vehicle1can continue to travel within the range of the degenerate mode by using the data measured by secondary voltage measurement circuit13bas an alternative strategy. This enables ensuring both safety of electric vehicle1and convenience of a user when main voltage measurement circuit13ahas an anomaly.

In contrast, the comparative example is often configured to use a circuit configuration in which secondary voltage measurement circuit13bis capable of only hardware control without using a processor. In this case, when main voltage measurement circuit13ahas an anomaly, transition to the degenerate mode cannot be executed. In this regard, the present example includes secondary voltage measurement circuit13bthat uses a circuit configuration capable of software control using a processor, so that secondary voltage measurement circuit13bcan substitute for the function of main voltage measurement circuit13a. This enables electric vehicle1to continue to travel within the range of the degenerate mode.

Examples of an anomaly of secondary voltage measurement circuit13binclude an anomaly in that output of an A/D converter sticks. When secondary voltage measurement circuit13bhas an anomaly, controller16continues to use data measured by main voltage measurement circuit13ain a state where data measured by secondary voltage measurement circuit13bcannot be acquired.

Even when secondary voltage measurement circuit13bhas an anomaly, the data measured by main voltage measurement circuit13aand the data measured by secondary voltage measurement circuit13bcannot be compared with each other, and thus reliability of the data is deteriorated.

Controller16executes transition to the degenerate mode as a fail-safe action. As the degenerate mode, for example, vehicle ECU30executes the processing of limiting the SOC usage range of the cell described above. For example, vehicle ECU30also executes power limit control based on a current limit value transmitted from controller16as essential control.

Even when secondary voltage measurement circuit13bhas an anomaly as described above, electric vehicle1can continue to travel within the range of the degenerate mode. This enables ensuring both safety of electric vehicle1and convenience of a user when secondary voltage measurement circuit13bhas an anomaly.

Examples of an anomaly of temperature measurement circuit14ainclude output sticking of a thermistor and an output drift anomaly. When temperature measurement circuit14ahas an anomaly, controller16replaces temperature estimated using abnormal thermistor output with temperature estimated using normal thermistor output as alternative strategy 1. Controller16uses a measurement value of an abnormal thermistor by adding an offset value to the measurement value as alternative strategy 2. When abnormal thermistors include an abnormal thermistor exhibiting behavior identical to that of a normal thermistor, controller16replaces a measurement value of the abnormal thermistor with a measurement value of the normal thermistor identical in behavior as alternative strategy 3.

When one of a plurality of thermistors has an anomaly and there is no change in temperature distribution estimated from measurement values of the other thermistors, controller16executes alternative strategy 1. When one of the plurality of thermistors has an anomaly and there is a change in temperature distribution estimated from measurement values of the other thermistors, controller16executes alternative strategy 2.

FIG.8is a diagram for illustrating a first specific example of alternative strategy 2 when temperature measurement circuit14ahas an anomaly. When one of the plurality of thermistors has an anomaly, controller16adds a predetermined offset value to each of measurement values of the plurality of thermistors. For the offset value, a value determined in advance by the battery manufacturer based on numerical simulations and experiments is used. In the first specific example, an offset with an identical value is uniformly added to each of measurement values of all the thermistors.

FIG.9is a diagram for illustrating a second specific example of alternative strategy 2 when temperature measurement circuit14ahas an anomaly. When one of the plurality of thermistors has an anomaly, controller16calculates a median value of measurement values of the plurality of thermistors. Instead of the median value, an average value may be calculated. Controller16identifies a measurement value out of a predetermined range centered on the median value. Controller16adds an offset value only to the identified measurement value. As the offset value, a predetermined fixed value may be used, or a variable value may be used. As the variable value, for example, an average value of deviations between the median value and respective measurement values may be used.

This allows controller16to determine a current limit value with reference to SOC-temperature map16bbased on a temperature higher than an actually measured temperature. SOC-temperature map16bsets an absolute value of a current limit value that decreases as temperature increases. Thus, when the current limit value is determined based on the temperature higher than the actually measured temperature, a more suppressive current limit value is selected.

Controller16executes transition to the degenerate mode as a fail-safe action. As the degenerate mode, for example, vehicle ECU30executes the processing of limiting the SOC usage range of the cell described above. For example, vehicle ECU30also executes power limit control based on a current limit value transmitted from controller16as essential control.

Even when temperature measurement circuit14ahas an anomaly as described above, electric vehicle1can continue to travel within the range of the degenerate mode by executing any of alternative strategies 1 to 3 described above. This enables ensuring both safety of electric vehicle1and convenience of a user when temperature measurement circuit14ahas an anomaly. In contrast, when one of the plurality of thermistors has an anomaly in the comparative example, relay cut off is performed, and thus electric vehicle1cannot travel. In this regard, the present example enables electric vehicle1to continue to travel within the range of the degenerate mode.

Return toFIG.6. Examples of an anomaly in both first current measurement circuit15aand second current measurement circuit15b(the entire current measurement function) include power failure of a current sensor (e.g., Hall element, differential amplifier, A/D converter). When an anomaly occurs in the entire current measurement function, controller16uses an SOC estimated by the OCV method as an alternative strategy.

Controller16executes transition to the degenerate mode as a fail-safe action. As the degenerate mode, for example, a SOC usage range of a cell is limited. Additionally, as the degenerate mode, for example, a predetermined offset value is added to a voltage value measured by voltage measurement unit13. A positive offset value is added for charging and a negative offset value is added for discharging. For the offset value, a value determined in advance by the battery manufacturer based on numerical simulations and experiments is used. The offset value may be a fixed value or a variable value in accordance with a measured voltage value. For example, the offset value may be a value obtained by multiplying the measured voltage value by a constant rate. This allows controller16to use a cell voltage that is lower than actual cell voltage during discharge and higher during charging. Thus, the cell voltage is likely to reach the UV threshold value or the OV threshold value.

The degenerate mode is performed on both power supply system10and vehicle ECU30. For example, vehicle ECU30executes processing of limiting an SOC usage range of a cell described above. For example, vehicle ECU30also executes power limit control based on a current limit value transmitted from controller16as essential control. For example, power supply system10executes processing of adding a predetermined offset value to the measured voltage value described above. In the degenerate mode, the voltage value transmitted from controller16of power supply system10to vehicle ECU30may be an original measured value or a measured value subjected to the above processing.

FIG.10is a flowchart for illustrating a protection function of power supply system10after transition to an alternative strategy caused when an anomaly occurs throughout a current measurement function. Controller16acquires voltages and temperatures of the plurality of cells E1to En measured by voltage measurement unit13and temperature measurement unit14, respectively (S261a). During a period where yet another measurement circuit has no anomaly after the alternative strategy is executed (N in S262), controller16limits the SOC usage range of each of the cells as a fail-safe action (S264).

Controller16estimates an SOC of each of the plurality of cells E1to En based on the acquired voltage values (S265a). For example, the SOC can be estimated by the OCV method. Controller16determines a current limit value of each of the cells by referring to SOC-temperature map16bbased on the estimated SOC of the corresponding one of the cells and the temperature of the corresponding one of the cells (S266). Controller16selects the smallest current limit value among determined current limit values of the cells, and notifies vehicle ECU30of the selected current limit value (S267). Then, processing proceeds to step S261and the processing after step S261is repeated. When another measurement circuit has an anomaly in step S262(Y in S262), the alternative strategy is terminated.

As described above, even when an anomaly occurs in the entire current measurement function, estimation of the SOC based on the voltage value, and determination of the current limit value based on the SOC and the temperature, as an alternative strategy, enable electric vehicle1to continue to travel within the range of the degenerate mode. This enables ensuring both safety of electric vehicle1and convenience of a user when an anomaly occurs in the entire current measurement function.

Return toFIG.6. Examples of an anomaly of first current measurement circuit15ain a high range include output sticking of a current sensor and an offset anomaly of the current sensor. When first current measurement circuit15ain a high range has an anomaly, controller16uses data measured by second current measurement circuit15bin a low range, and limits a range of input-output current of power storage unit11to an input range of second current measurement circuit15bin a low range, as an alternative strategy. In a specific example, controller16notifies vehicle ECU30to limit the range of input-output current of power storage unit11to the input range of second current measurement circuit15bin a low range. Vehicle ECU30sets an upper limit current value and a lower limit current value corresponding to the input range received from controller16of power supply system10in inverter40.

FIGS.11(a) and11(b)are each a diagram for illustrating an alternative strategy when first current measurement circuit15ahas an anomaly.FIG.11(a)illustrates the input-output current before the anomaly occurs in first current measurement circuit15a, andFIG.11(b)illustrates the input-output current after the anomaly occurs in first current measurement circuit15a. As illustrated inFIGS.11(a) and11(b), when first current measurement circuit15ain a high range has an anomaly, a current in a range acquired by excluding a low range measurable by second current measurement circuit15bfrom a high range measurable by first current measurement circuit15acannot be measured. Thus, the input-output current of power storage unit11needs to be limited in the low range measurable by second current measurement circuit15b.

When first current measurement circuit15ain a high range has an anomaly, data measured by first current measurement circuit15ain a high range cannot be compared with data measured by second current measurement circuit15bin a low range, and thus reliability of the data deteriorates.

Controller16executes transition to the degenerate mode as a fail-safe action. As the degenerate mode, for example, vehicle ECU30executes the processing of limiting the SOC usage range of the cell described above. For example, vehicle ECU30also executes power limit control based on a current limit value transmitted from controller16as essential control.

Even when first current measurement circuit15ahas an anomaly as described above, data measured by second current measurement circuit15bis used while the input-output current of power storage unit11is limited to the low range measurable by second current measurement circuit15b, as an alternative strategy, and thus electric vehicle1can continue to travel within the range of the degenerate mode. This enables ensuring both safety of electric vehicle1and convenience of a user when first current measurement circuit15ahas an anomaly.

Return toFIG.6. Examples of an anomaly of second current measurement circuit15bin a low range include output sticking of a current sensor and an offset anomaly of the current sensor. When second current measurement circuit15bin a low range has an anomaly, controller16uses only data measured by first current measurement circuit15ain a high range as an alternative strategy.

FIGS.12(a) and12(b)are each a diagram for illustrating an alternative strategy when second current measurement circuit15bhas an anomaly.FIG.12(a)illustrates SOC estimation before the anomaly occurs in second current measurement circuit15b, andFIG.12(b)illustrates the SOC estimation after the anomaly occurs in second current measurement circuit15b. As illustrated inFIGS.12(a) and12(b), when second current measurement circuit15bin a low range has an anomaly, the SOC is estimated based on a current value measured by first current measurement circuit15ain a high range. When second current measurement circuit15bis normal and a current value is within the input range of second current measurement circuit15b, using a current value measured by second current measurement circuit15bmore increases estimation accuracy of the SOC.

When first current measurement circuit15ain a high range has an anomaly, data measured by first current measurement circuit15ain a high range cannot be compared with data measured by second current measurement circuit15bin a low range, and thus reliability of the data deteriorates.

Controller16executes transition to the degenerate mode as a fail-safe action. As the degenerate mode, for example, vehicle ECU30executes the processing of limiting the SOC usage range of the cell described above. For example, vehicle ECU30also executes power limit control based on a current limit value transmitted from controller16as essential control.

Even when second current measurement circuit15bhas an anomaly as described above, electric vehicle1can continue to travel within the range of the degenerate mode by estimating the SOC based on a current value measured by first current measurement circuit15aas an alternative strategy. This enables ensuring both safety of electric vehicle1and convenience of a user when second current measurement circuit15bhas an anomaly.

Return toFIG.6. Examples of an anomaly of controller16include an anomaly in a CPU. The anomaly in the CPU includes an anomaly in an ALU, an anomaly in a ROM, and an anomaly in a RAM. When controller16has an anomaly, relay cut off under hardware control is executed. When receiving a hardware stop signal from management unit12of power supply system10, vehicle ECU30turns off first relay RY1and executes the relay cut off. When controller16has an anomaly, controller16cannot detect an anomaly of a cell, and then CAN communication between controller16and vehicle ECU30also cannot be performed. Thus, when controller16has an anomaly, relay cut off is used as in the comparative example.

Examples of an anomaly in main network20ainclude disconnection of a CAN bus and communication timeout. When main network20ahas an anomaly, controller16notifies vehicle ECU30of various data only through sub network20bas an alternative strategy. Vehicle ECU30controls electric vehicle1based on the data received through sub network20b. Vehicle ECU30lights a caution lamp in instrument panel60, the caution lamp indicating an anomaly in in-vehicle network20. When main network20ahas an anomaly, vehicle ECU30may or may not transfer to the degenerate mode. Regular data is transmitted to vehicle ECU30from power supply system10, so that only lighting of the caution lamp may be performed.

Examples of an anomaly in sub network20binclude disconnection of a CAN bus and communication timeout. When sub network20bhas an anomaly, controller16notifies vehicle ECU30of various data only through main network20aas an alternative strategy. Vehicle ECU30controls electric vehicle1based on the data received through main network20a. Vehicle ECU30lights a caution lamp in instrument panel60, the caution lamp indicating an anomaly in in-vehicle network20. When sub network20bhas an anomaly, vehicle ECU30may or may not transfer to the degenerate mode. Regular data is transmitted to vehicle ECU30from power supply system10, so that only lighting of the caution lamp may be performed.

The present example includes secondary voltage measurement circuit13bthat uses a circuit configuration capable of software control using a processor, so that secondary voltage measurement circuit13bdoes not directly control main network20aor sub network20bto stop hardware.

As described above, according to the present exemplary embodiment, when the measurement circuit has an anomaly, the alternative strategy is executed together with transition to the degenerate mode without performing the relay cut off. This enables ensuring both safety of electric vehicle1and convenience of a user. This is especially effective in pure electric vehicles (EVs) equipped with no engine.

When safety control corresponding to determination of each of the voltage and temperature, using a threshold value, is incorporated into power limit control, the control can be unified and simplified as compared with when the safety control by determination of each of the voltage and temperature, using a threshold value, and the power limit control coexist. At a stage prior to relay cut off, stepwise current limiting also enables safety to be ensured.

Conventional power limit control is intended only to suppress cell deterioration, and ensuring safety is left to OV/UV determination and OT determination. In contrast, the power limit control according to the present exemplary embodiment can achieve suppression of cell deterioration, ensuring safety, and ensuring degenerate traveling time. The power limit control also enables preventing the relay cut off from being suddenly activated by detection of OV, UV, or OT, and ensuring the degenerate traveling time while ensuring the safety at the stage prior to the relay cut off.

The present invention has been described above based on the exemplary embodiment. The exemplary embodiment is exemplified, and it is understood by those skilled in the art that various modifications are available for combinations of each of components of the exemplary embodiment and each of processing processes thereof, and that such modifications are also within the scope of the present invention.

In the exemplary embodiment described above, an example of determining a current limit value based on SOC-temperature map16bis described. In this regard, the current limit value derived based on SOC-temperature map16bmay be corrected based on the SOH and/or internal resistance. This correction algorithm is also created by the battery manufacturer for each type of battery. In an algorithm that determines a current limit value based on SOC-temperature map16b, processing of setting the current limit value to zero when the cell voltage exceeds the OV threshold value or when the cell voltage falls below the UV threshold value may be incorporated. The OV threshold value may be lower than the OV threshold value used in the control according to the comparative example. The UV threshold value may be higher than the UV threshold value used in the control according to the comparative example.

In the exemplary embodiment described above, limitation of the SOC usage range of a cell is mainly described as the degenerate mode executed by vehicle ECU30. In this regard, the degenerate mode can be controlled in various ways determined by a vehicle manufacturer. For example, a predetermined upper limit speed may be set for traveling of electric vehicle1.

The exemplary embodiment may be specified by the following items.

Power supply system (10) that is mounted on electric vehicle (1), and that includes power storage unit (11) connected to a plurality of cells (E1to En), voltage measurement unit (13) that measures a voltage of each of the plurality of cells (E1to En), current measurement unit (15) that measures a current flowing through each of the plurality of cells (E1to En), temperature measurement unit (14) that measures a temperature of each of the plurality of cells (E1to En), and controller (16) that determines a current limit value defining an upper limit of a current for suppressing cell deterioration and ensuring safety based on the voltage, the current, and the temperature of each of the plurality of cells (E1to En) measured by voltage measurement unit (13), current measurement unit (15), and temperature measurement unit (14), respectively, and that notifies higher-level controller (30) in electric vehicle (1) of the determined current limit value.

This enables both suppressing cell deterioration and ensuring safety to be achieved by using the current limit value.

Power supply system (10) described in Item 1, wherein controller (16) estimates a state of charge (SOC) of each of the plurality of cells based on the voltage of the corresponding one of the cells measured by voltage measurement unit (13) and the current of the corresponding one of the cells measured by current measurement unit (15), and determines the current limit value based on the estimated SOC and the temperature measured by temperature measurement unit (14).

This enables the current limit value to be determined based on the SOC and the temperature.

Power supply system (10) described in Item 2, wherein when voltage measurement unit (13) of a certain measurement unit among the plurality of cells (E1to En) has an anomaly, controller (16) replaces a voltage of a cell included in the certain measurement unit with a voltage measured by voltage measurement unit (13) of another normal measurement unit.

This enables the current limit value to be obtained, even when voltage measurement unit (13) of a certain measurement unit has an anomaly, by using a value of voltage measurement unit (13) of another normal measurement unit as a substitute.

Power supply system (10) described in Item 3, wherein controller (16) adds a positive offset value to an absolute value of a current measured by current measurement unit (15) when voltage measurement unit (13) has an anomaly.

This enables need criteria for safety to be raised by adding the positive offset value to the absolute value of the measured current when voltage measurement unit (13) has an anomaly.

Power supply system (10) described in Item 3, wherein controller (16) multiplies the estimated SOC by a positive coefficient less than one when voltage measurement unit (13) has an anomaly during discharge from power storage unit (11), and multiplies the estimated SOC by a positive coefficient more than one when voltage measurement unit (13) has an anomaly during charge on power storage unit (11).

This enables need criteria for safety to be raised by multiplying the estimated SOC by a coefficient when voltage measurement unit (13) has an anomaly.

Power supply system (10) described in Item 1, wherein controller (16) estimates an SOC of each of the plurality of cells based on a voltage of the corresponding one of the cells measured by voltage measurement unit (13) when current measurement unit (15) has an anomaly, and determines the current limit value based on the estimated SOC and the temperature measured by the temperature measurement unit.

This enables electric vehicle (1) to continue to travel within the range of the degenerate mode by changing a method for detecting an anomaly of a cell when current measurement unit (15) has an anomaly.

Power supply system (10) described in Item 6, wherein controller (16) adds a negative offset value to the voltage measured by voltage measurement unit (13) when current measurement unit (15) has an anomaly during discharge from power storage unit (11), and adds a positive offset value to the voltage measured by voltage measurement unit (13) when current measurement unit (15) has an anomaly during charge on power storage unit (11).

This enables need criteria for safety to be raised by adding an offset value to the measured voltage when current measurement unit (15) has an anomaly.

Power supply system (10) described in any one of Items 3 to 7, wherein controller (16) narrows a usage range of SOCs of the plurality of cells (E1to En).

This enables safety of power supply system (10) to be improved, and deterioration in reliability of a measurement function to be compensated.

Management device (12) that is provided in power supply system (10) for a vehicle and that includes voltage measurement unit (13) that measures a voltage of each of a plurality of cells (E1to En) provided in power storage unit (11) provided in the power supply system for a vehicle, current measurement unit (15) that measures a current flowing through each of the plurality of cells (E1to En), temperature measurement unit (14) that measures a temperature of each of the plurality of cells (E1to En), and controller (16) that calculates a current limit value defining an upper limit of a current for suppressing cell deterioration and ensuring safety based on the voltage, the current, and the temperature of each of the plurality of cells (E1to En) measured by voltage measurement unit (13), current measurement unit (15), and temperature measurement unit (14), respectively, and that notifies higher-level controller (30) in electric vehicle (1) of the calculated current limit value.

This enables both suppressing cell deterioration and ensuring safety to be achieved by using the current limit value.

REFERENCE MARKS IN THE DRAWINGS