The present invention relates to a device for detecting remaining battery capacity, a battery system including the same, a method of detecting remaining battery capacity and a program for executing the same. The present invention relates particularly to a device for detecting remaining battery capacity, a battery system including the same, a method of detecting remaining battery capacity and a program for executing the same which allow total power storage amount of storage battery to be detected even when charging is started with certain power storage amount remaining.
Conventionally, a battery pack has been known in which a plurality of storage batteries, for example lithium ion secondary batteries, are connected to one another. As a method of detecting a power storage amount of such storage batteries, for example, Patent Document 1 discloses that values of current inputted/outputted in/from storage batteries are measured, the values of current are integrated to thereby calculate actual remaining capacity.
Patent Document 1: Japanese Patent Laid-Open No. 63-208733
In such a system in which current value is simply measured as disclosed in Patent Document 1, there is a problem that accumulation of measurement errors in values of current causes a large error in calculated value from actual remaining capacity. To correct the error, it is necessary to pass through a discharge end point and a full charge point as measurement reference points, however, such a system is not practical for typical use of battery.
The object of the present invention is thus to provide a device for detecting remaining battery capacity, a battery system including the same, a method of detecting remaining battery capacity and a program for executing the same which allow total power storage amount of storage battery to be detected even when charging is started with certain power storage amount remaining.
In order to achieve the above-mentioned object, a device for detecting remaining battery capacity according to an embodiment of the present invention includes:
a voltage detection unit configured to detect voltage of a storage battery;
a current detection unit configured to detect current for charging during charging the storage battery; and
a control unit for computing,
the control unit is configured to
(a) detect actual voltage of the storage battery at start of charging storage battery,
(b) obtain power storage amount corresponding to the actual voltage (hereinafter referred to as “power storage amount at start”) by using a look-up table representing a relationship between voltages and power storage amounts corresponding thereto,
(c) calculate power storage amount in the storage battery charged by implemented charging (hereinafter referred to as “calculated power storage amount”), and
(d) calculate total power storage amount of the charged storage battery, by adding the calculated power storage amount and the power storage amount at start.
“Device for detecting remaining battery capacity” includes both a device in which a voltage detection unit, a current detection unit and a control unit are disposed in one place, for example disposed in housing, and a device in which they are disposed separately and connected to one another.
“Control unit” may be a computer unit with for example a CPU (Central Processing Unit) for computing, a memory, an interface, which can provide various functions by executing a computer program stored in the memory. So-called one-chip microcomputer can be used in which hardware such as a CPU, a ROM, a RAM, an I/F and a program are provided. Alternatively, the control unit may be one provided as an electric circuit.
“Connection”: when it is said, for example, that an element is connected to another element in the specification, this means both an embodiment in which the both are connected directly to each other and an embodiment in which the both are connected indirectly to each other via one or more intermediate elements. Both wired connection and wireless connection can be used for connection between elements for transmitting electric signals or performing any data communication to each other.
The present invention can provided a device for detecting remaining battery capacity and the like which allow total power storage amount of a storage battery to be detected even when charging is started with certain power storage amount remaining.
Embodiments of the present invention are described with reference to the drawings. It is noted that configurations, functions, operations and the like described below are just according to embodiment of the present invention and are not intended to limit the present invention.
As illustrated in
The battery unit 11 has a plurality of battery cells 12a to 12c (each of which is also referred to simply as “battery cell 12”). The battery cells 12 are lithium ion batteries by way of example and are connected in series. It is noted that the number of the battery cells 12 is not limited specific value. One battery cell 12 may be provided instead of limiting to be plural. Other secondary batteries such as nickel-cadmium batteries and nickel-metal hydride batteries other than lithium ion batteries can be used as battery cells 12.
It is noted that the device for detecting remaining battery capacity 10 may have an enclosure for housing at least one of or all of the current detection unit 13, the voltage detection unit 15, and the control unit 17, for example.
The embodiment is described by way of example with battery cells 12 which show charging curve and discharging curve as illustrated in
As illustrated in
The current detection unit 13 is configured to detect current inputted/outputted in/from the battery cells 12. The voltage detection unit 15 is configured to detect voltages of the battery cells 12a to 12c.
The control unit 17 is connected to the current detection unit 13 and the voltage detection unit 15. The control unit 17 performs (i) controlling operations of the detection units 13 and 15, and (ii) various computing by using detected values from the detection units 13 and 15. The control unit 17 may be configured to implement the above operations with a program, and moreover, to perform various processes as mentioned later with the program.
Although illustration is omitted in
“Power storage amount” in a right column of the table refers to power storage amount of a battery cell, each amount corresponds to each charging voltage. Numerical values of the “power storage amount” would vary under influence of aging degradation of the battery cell. Preferably, data in the look-up table is updated properly to calculate power storage amount more accurately. Data updating will also be described later.
The look-up table allows power storage amount of battery cell 12 at start of charge to be estimated, for example: a power storage amount is 200 Ah when a detected voltage of the battery cell 12 is 3.1 V (3100 mV), whereas the amount is 5000 Ah at 3.8 V (3800 mV). If voltage of the battery cell 12 is 3.75 V (3750 mV) for example, 5000 Ah is estimated when the voltage reaches 3800 mV after charging is performed.
It is noted that the control unit 17 also performs measuring a power storage amount consumed from the state of full charging (used power storage amount) on the basis of the detection value from the current detection unit 13, and then calculating a remaining battery capacity, after usage, on the basis of a total power storage amount at full charge and a measured used power storage amount.
Next, charging operation of the battery cell by the battery system 1 according to the embodiment is described.
First of all, the charging device (not shown) is connected to the battery unit 11 to start charging, followed by detecting charging current with the current detection unit 13 in step S1. The voltage detection unit 15 detects voltage of the battery cell 12. Timing for starting and/or ending of these detections and the like is not limited to a specific timing but may be arbitrary one. As a system for performing each detection, a conventionally known methods can be properly used.
In step S2, it is determined whether the actual voltage of battery cell 12 is substantially larger than a discharge end voltage (3.0 V in this example). For example, when voltage of the voltage cell 12 is less than 3000 mV, total power storage amount of the battery cell is calculated on the basis of charging current and charging time (step S3-2) after determining that charging has been performed up to the discharge end value and the voltage has reached discharge end voltage. It is noted that determination as above may be automatically performed by the control unit 17, for example.
On the other hand, in step S2 when it is determined that voltage of the battery cell is substantially larger than the discharge end voltage (in other words, in case that charging is started except from the discharge end voltage), remaining battery capacity detection of step S3-1 is performed. As a specific example, assume that voltage of the battery cell 12 is 3.75 V (3750 mV) as illustrated in
Power storage amount is calculated by multiplying charging current and charging time (this is referred to as “measured power storage amount”) after the voltage exceeds 3800 mV till discharge end. Total power storage amount is then calculated by adding the “power storage amount at start” and the measured power storage amount.
According to such a calculation of the power storage amount, total power storage amount of the battery cell after charging can be obtained more accurately even when charging is performed except from the discharge end voltage, since the power storage amount remaining in the battery cell 12 is obtained with reference to the look-up table and the power storage amount stored in the actual charging is added thereto to calculate the total power storage amount of the battery cell 12.
Next, updating data of the look-up table is described. When charging from a discharge end voltage (step S4-2) is started, relationship between each voltage and corresponding power storage amount during constant-current charging point is monitored. Specifically, relationship between each voltage and power storage amount at that time point is measured, for example, the power storage amount at the time of reaching 3100 mV being a1 [Ah], the power storage amount at the time of reaching 3200 mV being a2 [Ah], . . . , the power storage amount at the time of reaching 3900 mV being a9 [Ah], and the power storage amount at the time of reaching 3100 mV being a10 [Ah]. Then, by using such monitored data, data of power storage amounts in the look-up table (
It is noted that updating may be performed during charging or after charging. For the data update, the control unit 17 may be configured to automatically update data in the look-up table using information such as the power storage amounts a1 and a2 to a9 as above.
On the other hand, when charging is started except from the discharge end voltage (step S4-1), updating is performed only for part of the “power storage amounts” in the look-up data as mentioned below. As a specific example, similarly to the above, a case is supposed where the voltage of the battery cell 12 is 3750 mV. In this case, power storage amounts corresponding to the battery sections of 3900 mV and 4000 mV are newly calculated respectively, and data of the “power storage amounts” in the look-up table are to be updated.
While method for calculating values of “power storage amounts” to be updated is not limited specific one, but any method can be used, for example, it may be one described below:
e1: obtaining power storage amount at start corresponding to the actual voltage of the storage battery from the look-up table (5000 Ah in the case of 3750 mV, 5000 Ah corresponding to 3800 mV after charging);
e2: calculating power storage amount stored by charging during one voltage section (for example, from 3800 mV to 3900 mV), for example, by multiplying the charging current by the charging time;
e3: adding the power storage amount in e2 as above and the power storage amount at start and calculate total power storage amount at the voltage (3900 mV) (for example, 5950 Ah); and
e4: storing the total power storage amount as power storage amount at the voltage (3900 mV) in the table.
Updating data of the “power storage amounts” in look-up table in response to actual condition of the battery cell allows remaining capacity to be detected more accurately in consideration of the situation of degradation of battery cell, since the look-up table is to be prepared in accordance with the condition of the cell, even if performance of the battery vary under influence of aging degradation of battery cell.
(Case where Recharging is Performed After Discharge Only for Short Time After Constant-Voltage Charging)
Battery system 1 according to the embodiment may perform operations below in consideration of charging performed for lithium ion batteries by constant-current/constant-voltage method:
the control unit 17 is configured to (i) determine whether battery cell 12 is in a state where power storage amount stored by the constant-voltage charging has been discharged, when the charging of the battery cell 12 is performed; and to (ii) perform remaining battery capacity detection using the look-up table and/or updating of the look-up table as mentioned above only when state of having been discharged is determined.
For example, voltage become constant (approximately 4.15 V in this example) in constant-voltage charging as illustrated in
On the other hand, in the case where following charging is started from a position where all of the power storage amount stored by the constant-voltage charging has been discharged completely (for example, the position of P2), the following charging is to be the constant-current charging, and therefore, the remaining battery capacity detection using the look-up table and the data update of the look-up table as mentioned above are performed. By doing so, the advantageous effects similar to the above can be obtained.
While the embodiments of the present invention have been described as above, the present invention is not limited to the contents of the above disclosure but can be modified in various manners.
Incidentally, other than the inventions according to the battery system and the device for detecting remaining battery capacity, the following invention is disclosed in the description:
a method of detecting remaining battery capacity, comprising:
(a) detecting actual voltage of a storage battery with voltage detection means at start of charging storage battery;
(b) obtaining power storage amount corresponding to the actual voltage (hereinafter referred to as “power storage amount at start”) by using a look-up table representing a relationship between voltages and power storage amounts corresponding thereto;
(c) calculating power storage amount in the storage battery charged by implemented charging (hereinafter referred to as “calculated power storage amount”); and
(d) calculating total power storage amount of the charged storage battery, by adding the calculated power storage amount and the power storage amount at start.
For example, in the case where the remaining battery capacity detection as above is performed by a device, the present invention can also be expressed as follows:
a method of detecting remaining battery capacity, performed by one or more computers, including:
obtaining, by the computer, power storage amount corresponding to the detected actual voltage of a storage battery (hereinafter referred to as “power storage amount at start”) by using a look-up table representing a relationship between the voltage and the power storage amount corresponding thereto;
calculating, by the computer, power storage amount in the storage battery charged by implemented charging (hereinafter referred to as “calculated power storage amount”); and
calculating, by the computer, total power storage amount of the storage battery by adding the calculated power storage amount and the power storage amount at start.
There is provided a program causing a computer (which may be one or more computers) to execute the processes of;
(a) referring to a actual voltage of a storage battery, at start of charging storage battery, detected by voltage detection means ;
(b) obtaining power storage amount corresponding to the actual voltage (hereinafter referred to as “power storage amount at start”) by using a look-up table representing a relationship between the voltages and the power storage amounts corresponding thereto;
(c) calculating power storage amount stored in the storage battery charged by implemented charging (hereinafter referred to as “calculated power storage amount”); and
(d) calculating total power storage amount of the charged storage battery, by adding the calculated power storage amount and the power storage amount at start.
The present application discloses a method, a program, and a medium that stores the program, which correspond to the invention of the above-described device, other than the inventions according to the methods and program.
Number | Date | Country | Kind |
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2012-195069 | Sep 2012 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2013/073701 | 9/3/2013 | WO | 00 |