JP2002238171A - System and method for non-dissipative lithium-ion battery management - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system and a method for charge management of a battery pack. SOLUTION: This battery pack 1 comprises a plurality of charge cells C1-n, a means 3 for measuring charges of the rechargeable cells C1-n, a switch matrix 2 for switching a current among the charge cells and a current control DC-DC converter means 4 for supplying charges for recharging of cells. The current control DC-DC converter means 4 discharges the first cell Ci or a battery charge V as a whole via the switch matrix 2, in order to charge in direct the second cells Cj, Cp and thereby prevents dissipation of electrical power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a system and method for managing charge associated with a lithium ion (Li-ion) battery. More specifically, the present invention relates to Li-
The present invention relates to managing charge associated with various cells forming an ion battery pack. The management is such that charge is transferred from the higher voltage cells of the pack to the lower voltage cells in a controlled manner, thereby eliminating the need to dissipate the overcharge of the higher voltage cells. It is. Further, the system of the present invention utilizes a very simple circuit configuration to achieve the desired result, said circuit being based on the use of a single DC / DC converter associated with a switch matrix, wherein the DC / DC converter The converter uses an internal charging power supply to charge the cells. The present invention is particularly, but not exclusively, applicable to the space industry application.

[0002]

BACKGROUND OF THE INVENTION The use of Li-ion battery technology is relatively new. The tendency to use this battery has several implications for its use, such as its smaller weight and size compared to known aqueous cells, reduced production costs and no capacitance effect. This is because there is an advantage. Heretofore, this battery has been used especially for mobile phones, portable computers, video recorders and electric vehicles.

[0003] Li-ion batteries typically include a series of cells arranged in series to obtain the overall battery voltage. The battery capacity depends primarily on the individual cell capacity and on the secondary
Is determined by the parallel number of individual cells.

[0004] Li-ion cells have special restrictions compared to classic battery cells. That is, during use, the cell charge must be controlled so that the cell charge does not drop below a certain minimum voltage and does not exceed a certain maximum voltage. Thus, each cell has an allowable charging range between a minimum charge and a maximum charge. Deviating from this allowable charging range of the cell can destroy the cell below the lower limit (minimum) or above the upper limit (maximum).

Accordingly, there is a need to provide a procedure for managing Li-ion batteries to control the charge of individual cells based on accurate measurements of cell charge. Such a procedure would in principle be based on the following criteria. That is, if the charge of the cell exceeds a certain value, the cell must be discharged, and similarly, if the charge reaches a certain minimum value, the cell must be charged. This procedure is basically the classical approach to battery management known in the art. These approaches are usually based on dissipating overcharges found in cells with high voltage values into so-called bleeder resistors. The major drawback of this approach is that it increases heat dissipation and consequently results in poor system efficiency with respect to utilizing the energy generated by the solar panels.

[0006] Attempts have been made in the art to avoid heat dissipation during the management of battery (or cell) charge. A few such techniques have been published by the IEEE and are described in N.W. H. "Dynamic" by Kutkut et al.
equalization technologies f
or series battery stacks
(Dynamic Equalization Technology for Series Battery Stacks) ", The 18th Annual Interneti, Boston, Mass., USA, Oct. 6-10, 1996.
online Telecommunications E
energy Conference (INTELEC)
At pages 515 to 521 in the editorial filed at No. 5, pp. 515-521, the contents of which are incorporated herein by reference.

[0007] According to one of the techniques taught in the above references, charge equalization is achieved by using separate current controlled DC / DC converter modules for all of the battery cells. A disadvantage associated with this solution is the use of as many converters as battery cells, which substantially increases circuit complexity and cost.

Another approach suggested in the same literature uses a lumped converter with a multi-winding transformer. This solution also has the disadvantage that the circuitry involved is complex and expensive.

A further solution of the prior art suggested by said document concerns a different approach than the solution presented by the present invention.

US Pat. No. 5,656,915 discloses a battery management arrangement utilizing a switch arrangement for passing current through a preselected group of cells within a battery pack. The cell groups that need to be charged here are connected to the charging power supply via a switch arrangement. One of the differences that exists between the teachings of this document and that of the present invention is that the arrangement in the prior art document is intended to balance cells in a collective manner, i.e., charging is performed on a preselected cell group. And not for individual cells. Further, according to the teachings of U.S. Pat. No. 5,656,915, the overcharge obtained from a cell with a large charge is not charged directly to a cell with a small charge, but the overcharge is transferred to an external RC circuit via a power bus. When discharged and discharged, the high charge cell groups are disconnected. The less charged cell group is then connected to the RC circuit via the power bus, and this new connection transfers energy there. Thus, by storing energy in the RC circuit for the time during which high charge cells discharge and charge low charge cells, there should be some amount of heat loss in the RC circuit. This drawback is very problematic in space applications, since one is trying to eliminate energy losses and on the other hand any energy dissipation that generates heat is highly undesirable. Finally, it should be noted that the overall system disclosed in said document is relatively complex.

[0011]

Therefore, Li in an efficient and non-dissipative manner without the need to use complex circuits.
-It is desired to provide battery charge management for ion battery cells.

[0012]

This object is achieved by using the solution presented by the present invention.
According to the present invention, charging is performed from a battery cell having a charge exceeding a predetermined upper limit to a cell having a charge smaller than the predetermined lower limit. Thus, the overcharge is transferred from the higher charge cells to the lower charge cells without being dissipated as heat.

This solution is achieved by a simple circuit configuration utilizing a single DC / DC converter to transfer charge between cells, wherein charge transfer between cells is implemented by utilizing a switch matrix. The switch matrix establishes a connection between the appropriate cells via a DC / DC converter to allow charge transfer.

Furthermore, the same switch matrix is also used for measuring individual cell charges in cooperation with the charge measuring means described further below. The measurement is performed using a simple algorithm, whereby all cells are continuously measured by the charge measuring means. Therefore, it is possible to map the state of charge of each cell in a given short time.

Based on the mapping information obtained, charge transfer is performed from overcharged cells to cells that have less charge and therefore need to be charged.

Accordingly, it is an object of the present invention to provide a system for managing the charge of a battery pack having a plurality of rechargeable cells, the system comprising a system for controlling the charge of each of the plurality of rechargeable cells. , A switch matrix for switching current flowing between each of said plurality of rechargeable cells, and a current control DC / DC for supplying charge to recharge the cells.
DC / DC converter means;
The converter means is adapted to extract charge from the first cell or from the whole battery and is characterized by charging the second cell directly via the switch matrix.

According to one aspect of the present invention, the charge level of the first cell of the battery pack is higher than a predetermined first level.

[0018] According to another aspect of the present invention, the charge level of the second cell of the battery pack is lower than a predetermined second level.

According to a further aspect of the invention, the current controlled DC / DC converter means is arranged to extract electrical energy from the cell via the switch matrix.

According to yet another aspect of the present invention, the switch matrix is used for measuring individual cell charges in cooperation with the charge measuring means.

According to yet another aspect of the present invention, the switch matrix of the present invention provides a first switch matrix portion for balancing the charge of the cells and a connection for the charge measuring means to make a measurement. And a second switch matrix unit for performing the operation.

According to still another aspect of the present invention, the battery cell is made of a lithium-ion material.

Another object of the present invention is to provide a switch matrix as disclosed in the system of the present invention.

It is another object of the present invention to provide a method for managing the charge of a battery pack having a plurality of rechargeable cells, wherein the step of measuring the charge of each of the plurality of rechargeable cells, and a switch Switching a current between each of the plurality of rechargeable cells by a matrix, and supplying a charge for recharging the cells by current controlled DC / DC converter means; It is characterized in that the / DC converter means takes out charge from the first cell or the whole battery and charges the charge directly to the second cell via the switch matrix.

According to another aspect of the present invention, there is provided a method for managing the charge of a battery pack, wherein the current control DC / DC converter means draws electrical energy from cells through the switch matrix.

According to yet another aspect of the present invention, the switch matrix measures the charge of individual cells in cooperation with the charge measuring means.

These and further advantages of the present invention are:
Further details are set forth in the following description, with the help of the accompanying drawings, as well as the claims.

[0028]

DETAILED DESCRIPTION OF THE INVENTION According to the schematic diagram shown in FIG.
The battery pack 1 has a plurality of cells C arranged in series.
_{1 to n} . The battery pack 1 includes a plurality of switches S
It is bidirectionally connected to a switch matrix 2 having 1 to _m as shown in the figure by a double arrow. This switch matrix can be implemented by a relay matrix or by other known switching devices.

As discussed further above, during normal operation the cell charge must be controlled so that the cell charge does not fall below a certain minimum and does not exceed a certain maximum. . Therefore, it is necessary to measure the charge level of each cell in a simple manner so that the cells do not become overcharged or undercharged.

The charge measuring means 3 is used to measure the charge of the cell. The charge measuring means 3 measures the charge of each cell by selectively connecting to each cell via the switch matrix 2. The charge measuring means 3 is a cell C
_{The 1 to n} charges are measured continuously and the state of charge in each cell is mapped at a given time. The switch matrix is also bidirectionally connected to the current control DC / DC converter means 4.

In this arrangement, the charge management process according to the invention is preferably implemented in the following manner.

Based on the charge mapping of each cell, it is detected that one cell has a charge less than a predetermined lower value and another cell has a charge greater than a predetermined higher value. .

[0033] In FIG. 1, the cell C _j is in the charge level lower than the value of the predetermined, lower, hence the cell is assumed to need to be charged. Low charge levels of the cell C _j is detected by the charge measuring means 3 for reading the charges of all cells in the battery pack via the switch matrix 2. Charge measurement unit 3 is also over-charge, i.e. to detect the cell C _i having a charge greater than the value of the higher predetermined. This information is sent in a known manner to a central processing unit, not shown for simplicity. The switch matrix 2 then switches the appropriate first from the overcharged cells C _i to the current controlled DC-DC converter means 4.
The first connection by closing a single switch S _k of
Forming a second connection by closing the second single switch S _l to likewise current control DC-DC converter cell that has been detected from the unit 4 with a smaller charge than the predetermined level C _j . In this way, the connection is made from the overcharged cell C _i via the switch S _k to the current controlled DC-DC
To the converter unit 4, and from the current control DC-DC converter unit 4, it is formed into a cell C _j that need to be charged through the switch S _l. Therefore, charging is C
from _i to C _j . The charging current is applied to the receiving cell _Cj.
Continue until the charge level of is charged to a value within the allowable range.

FIG. 2 illustrates an alternative embodiment of the present invention. In this figure, the same parts as those shown in FIG. 1 are given the same reference numbers. Similarly, the method for measuring the charge of the cells C1- _n is implemented using the charge measuring means 3 via the switch matrix 2 as described with respect to the embodiment of FIG.

[0035] In FIG 2, the charge level of the cell with a reference numeral C _p is lower than the value of a predetermined low one. However, in this embodiment, the cell C _p is not from the in and individual cells receive the charging current obtained from the charge of the entire battery. As clearly shown in FIG. 2, the current control DC-
The DC converter 4 is provided with an output terminal V for the electric charge of the entire battery.
Directly connected and to charge the cell C _p to be charged via a switch S _q closed therefrom a switch matrix.

In this case, the input side of the current control DC-DC converter 4 is fixed at the full voltage V of the battery, so that there is no need to switch.

FIG. 3 illustrates another alternative embodiment of the present invention.
Again, in this figure, the same parts as in FIG. 1 are given the same reference numbers. However, the switch matrix in this embodiment has two parts 2 and 2 '. According to the embodiment of FIG. 3, the first switch matrix part 2 has a plurality of switches responsible for the reciprocal connection between the battery cells C1 to _n for the process of balancing the charges, while the first The two switch matrix sections 2 'are used to provide a connection for the charge measuring means 3 to make a measurement.

As another method, in any of the above embodiments, the current control DC-DC converter can apply overcharge to all the battery packs.

Further, a flying capacitor can be connected in parallel with the charge measuring means 3 in order to suppress the common mode voltage in the charge measurement.

The solution presented by the present invention has the advantage of substantially reducing power dissipation, which increases system efficiency and reduces thermal problems. Furthermore, the solution according to the invention makes it possible to reduce the complexity of battery management since only one single DC / DC converter is used.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a first embodiment of a battery management system according to the present invention.

FIG. 2 is a schematic diagram of an alternative embodiment of a battery management system according to the present invention.

FIG. 3 is a schematic diagram of another alternative embodiment of a battery management system according to the present invention.

[Explanation of symbols]

1 battery pack 2, 2 'switch matrix 3 charge measuring means 4 a current control DC / DC converter means C _{1 to n} cell C _i over charge cell C _{j, C p} insufficient charge cells S _{1 to m} switches S _k C _i from means Switch S ₁ to S 4, Switch from S _q means 4 to C _j V Output terminal of charge of entire battery

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5G003 BA02 CA11 CC02 DA07 EA09 FA08 GB03 5H030 AA03 AA04 BB01 BB21 FF43 FF44

Claims (11)

[Claims] 1. A system for managing the charge of a battery pack (1) having a plurality of rechargeable cells (C 1 to _n ), wherein the system comprises a plurality of rechargeable cells (C 1 _{to n).} Means for measuring each charge of (3)
And a switch matrix (2) for switching current flowing between each of the plurality of rechargeable cells;
Current-controlling DC-DC converter means (4) for supplying a charge for recharging the cell, wherein the current-controlling DC-DC converter means (4) comprises a first cell (C
_i ) or from the charge (V) of the entire battery, said current-controlled DC-DC converter means (4) transferring said charge via said switch matrix (2) to a second A system for managing charge, characterized in that it is directly transferred to a cell (C _j , C _p ). 2. The first cell (C) of a battery pack (1).
The system of claim 1, wherein _i ) has a charge level that is higher than a predetermined first level. 3. The second cell (C) of the battery pack (1).
3. The system of claim 1, wherein _j , C _p ) has a charge level lower than a predetermined second level. 4. The method as claimed in claim 1, wherein the current-controlled DC-DC converter means (4) is adapted to extract electrical energy from cells via the switch matrix (2). The described system. 5. The system according to claim 1, wherein the switch matrix is used for measuring individual cell charges in cooperation with the charge measuring means. 6. The first switch matrix section (2) for balancing the charge of the cell, and the second switch matrix for providing a connection for the charge measuring means to perform the measurement. A system according to any of the preceding claims, comprising a part (2 '). 7. The system according to claim 1, wherein the battery cells (C 1 _-n ) are made of a lithium ion material. 8. A switch matrix as disclosed in claim 1 or 6. 9. A method of managing a plurality of charge of rechargeable cells (C _{1 to n)} battery pack having a (1), each of charge of the plurality of rechargeable cells (C _{1 to n)} Measuring; switching a current flowing between each of said plurality of rechargeable cells by a switch matrix (2); and cells (C _j , C _p ) by current-controlled DC-DC converter means (4). Supplying a charge to recharge the current control DC-
DC converter means (4) is provided for the first cell (C _i )
Or from the charge (V) of the entire battery, and the current-controlled DC-DC converter means (4) transfers the charge via the switch matrix (2) to a second cell (C _j , C _p ). Transported directly to
How to manage charge. 10. The current-controlled DC-DC converter means (4) draws electrical energy from cells (C 1 _-n ) via the switch matrix (2).
The method described in. 11. The switch matrix (2)
The method according to claim 9 or 10, wherein the charge of the individual cells is measured in cooperation with the charge measuring means (3).