WO2015118364A1

WO2015118364A1 - Charge balancing device

Info

Publication number: WO2015118364A1
Application number: PCT/HU2015/000006
Authority: WO
Inventors: Gábor FARKAS
Original assignee: Farkas Gábor
Priority date: 2014-02-04
Filing date: 2015-01-26
Publication date: 2015-08-13
Also published as: HUP1400051A2; HUP1400051A3

Abstract

The invention is a charge balancing device for a battery, comprising a charge balancing structural element (10) being connectable to a negative terminal (1 1a) and to a positive terminal (1 1 b) of the battery (24) and carrying a charge balancing circuit, and a transistor (14) forming a part of the charge balancing circuit and having a casing, and a heat transfer element (12) being galvanically connectable to any of the terminals (1 1 b), being galvanically connected to the charge balancing structural element (10) at the side thereof facing the battery (24), being electrically conductive, and being adapted for conducting off heat, and the casing of the transistor (14) is arranged on the side of the charge balancing structural element (10) being opposite the heat transfer element (12), at least partly in the region determined by the heat transfer element (12) and is arranged to be in heat transfer connection with the heat transfer element (12).

Description

CHARGE BALANCING DEVICE

TECHNICAL FIELD

The invention relates to a charge balancing device being connectable to a battery. BACKGROUND ART

Nowadays, the use of simple batteries or battery assemblies consisting of several cells is becoming more and more widespread. For operation of larger battery assemblies, battery management systems (BMS), or, in alternative terms, cell balancing or charge balancing systems are customarily applied. These systems consist of a central unit responsible for control, and subunits being connectable to the individual batteries. To avoid the use of extensive wiring, in certain solutions the central control unit is connected to the subunits via wireless connection. Such solutions are disclosed in US 2006/0152190 A1 , US 2008/0071483 A1 , US 2010/0196748 A1 , US 2012/0112685 A1 , US 2013/0017421 A1 , US 2013/0271072 A1 and WO 2013/139921 A2. A serious problem of battery management is caused by the heat generated, by e.g. the heat generating components (most frequently: transistors) of the cell balancing subunits during the battery charging process. Of the above listed documents, in US 2013/0017421 A1 a solution is disclosed wherein the batteries are enclosed in a material capable of absorbing heat. In WO 2013/139921 A2 a solution is disclosed wherein the temperature of the individual subunits is measured.

In view of the known solutions, there is a demand for a solution wherein the heat generated by the transistors is managed more effectively on the subunits of the charge balancing system compared to known solutions. DESCRIPTION OF THE INVENTION

The primary object of the invention is to provide a charge balancing device which is free of the disadvantages of prior art solutions to the greatest possible extent.

A further object of the invention is to provide a charge balancing device which is adapted for managing heat generated by the transistors on the subunits of the system more effectively compared to known solutions. The objects according to the invention can be achieved by the device according to claim 1 . Preferred embodiments of the invention are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below by way of example with reference to the following drawings, where

Fig. 1 is a schematic side view illustrating the charge balancing device according to an embodiment of the invention,

Fig. 2 is a schematic top view illustrating the charge balancing device shown in Fig. 1 ,

Fig. 3A is a schematic drawing illustrating series-connected batteries fitted with the charge balancing device according to the invention,

Fig. 3B is a schematic drawing illustrating a charge control module belonging to the arrangement shown in Fig. 3A,

Fig. 4 is a schematic circuit diagram illustrating the charge balancing device according to the invention, and

Fig. 5 is a circuit diagram illustrating a detail of a further embodiment of the charge balancing device according to the invention.

MODES FOR CARRYING OUT THE INVENTION

The invention relates to a charge balancing device for a battery. An embodiment of the device according to the invention is illustrated in Fig. 1. The charge balancing device according to the invention comprises a charge balancing structural element 10 being connectable to a negative terminal 1 1 a and to a positive terminal 11 b of a battery 24 and carrying a charge balancing circuit, and further comprises a transistor 14 forming a part of the charge balancing circuit and having a casing. In the context of the invention the casing of the transistor is taken to comprise all parts of the transistor except the pins, for example particularly a mounting/carrier plate connected to an optionally comprised plastic cover. The charge balancing device according to the invention further comprises a heat transfer element 12 being galvanically connectable to any of the terminals, in the present embodiment, to terminal 1 1 b, being galvanically connected to the charge balancing structural element 10 at the side thereof facing the battery 24, being electrically conductive, and being adapted for conducting off heat. In the charge balancing device according to the invention the casing of the transistor 14 is arranged on the side of the charge balancing structural element 10 being opposite the heat transfer element 12, at least partly in the region defined by the heat transfer element 12, and is arranged to be in heat transfer connection with the heat transfer element, such that the heat transfer element 12 is able to efficiently carry off heat generated by the transistor 14. The region defined by the heat transfer element 12 is meant to refer to the region assignable on the charge balancing structural element where the heat transfer element 12 is either in contact with the charge balancing structural element 10 or is positioned close to it.

By way of example, the heat transfer element is configured as a rectangular plate comprising holes adapted to receive the terminals of the battery. The heat transfer element may be ring-shaped, in which case the terminals of the battery can be connected inside the ring. Provided that an appropriate heat transfer connection is ensured between the casing of the transistor and the heat transfer element, i.e. that heat is adequately transferred from the transistor casing to the heat transfer element, it is conceivable that another object (by way of example, a washer or a metal plate) is arranged between the casing of the transistor and the heat transfer element in addition to the charge balancing structural element.

In the embodiments illustrated herein the charge balancing structural element is implemented as a printed circuit board, and the transistor is arranged on the reverse side of the printed circuit board opposite the heat transfer element.

In other embodiments the charge balancing structural element can also be implemented as a cable. In case the charge balancing structural element is implemented as a cable, the transistor is disposed at the cable end proximate to the heat transfer element 12.

Since the heat transfer element 12 is in contact with the charge balancing structural element 10, configured as a printed circuit board, through the conductive layer thereof, heat can be conducted off efficiently in the device according to the invention. In the configuration illustrated in Fig. 1 , the conductive layer of the charge balancing structural element 10 and the heat transfer element 12 are in contact over a sufficiently large surface area. In the present embodiment the conductive layer of the charge balancing structural element 10 is constituted by the wiring of the printed circuit board. In the operation of the charge balancing device, current flows in the conductive layer. In the device according to the invention the current of the charge balancing device also flows through the heat transfer element 12, hence it is required that the heat transfer element 12 is electrically conductive. This current is limited typically to a value about 10 A (ampere).

In the embodiment of the device according to the invention shown in Fig. 1 an additional conductive layer is arranged on the side of the charge balancing structural element 0 (implemented as a printed circuit) which is opposite the heat transfer element 12. Applying the additional conductive layer a measurement path independent from the above high current (even as high as 10 A) can be established, which measurement path may for example be utilised for control measurement.

The application of the heat transfer element 12 in a manner according to the invention is also particularly advantageous because thereby the heat generated during operation of the transistor 14 arranged on the charge balancing structural element 10 can be transferred to the heat transfer element 12. The heat transfer element 12 has high heat conductivity, and thus heat transferred to the heat transfer element 12 is carried off into the battery 24, that is, the battery 24 behaves as a heat absorber with high thermal inertia. With the application of the device according to the invention, therefore, no additional measures have to be taken in order to conduct off heat generated during operation of the charge balancing device; applying the heat transfer element 12 heat generation does not affect the operation of the battery.

The heat transfer element 12 is preferably made from copper. The heat transfer element 12 is arranged between the charge balancing structural element 10 and the battery 24, and the width of the heat transfer element 12 between the charge balancing structural element 10 and the battery 24 is in the range of 3-30 mm to provide for the appropriate rigidity of the heat transfer element 12. The above mentioned width of the heat transfer element 12 is preferably in the range of 5-10 mm such that it may be preferably arranged on the terminals 11 a, 1 1 b of the battery 24 without overhanging to a too large extent with respect to the terminals 1 1a, 1 1 b of the battery 24. Particularly preferably a plate having a width of 7-9 mm is applied as heat transfer element in case of the most widely applied battery dimensions, the thickness of the heat transfer element is, by way of example, 8 mm. Although the battery 24 is not part of the invention, the device according to the invention is illustrated in Fig. 1 and Fig. 2 connected to the battery 24. In Fig. 1 the battery 24 is shown schematically, with only the portions around the terminals 1 1 a, 1 1b being indicated in the drawing.

According to the embodiment illustrated in Fig. 1 a respective heat transfer element 12 is comprised in the charge balancing device for both terminals 1 1 a, 1 1b of the battery 24. In the present embodiment the transistor 14 is arranged on the charge balancing structural element 10 at the terminal 1 1 b, i.e. in the right of the drawing. In Fig. 1 pins 15 of the transistor 14 are also shown. Due to the arrangement of the transistor 14 shown in the drawing, a significant amount of heat is generated by the operation of the transistor 14 at this terminal 11 b during operation of the charge balancing device. In the region of the heat transfer element 12 shown in the left of the drawing, however, i.e. at the terminal 11a, no significant heat is generated.

The arrangement according to Fig. 1 , i.e. arranging a respective heat transfer element 12 at both sides, is advantageous from the aspect of the optimisation of the manufacturing process. As the charge balancing structural element 10, implemented as a printed circuit board, is expediently arranged parallel with the top edge of the battery 24, some kind of spacer element should be applied in any case to the terminal not located near the transistor 14. Accordingly, the charge balancing structural element 10 has to be raised by including some element, i.e. a spacer of some kind has to be applied at both of the terminals. It is not preferred to arrange a heat transfer plate as a spacer only at one of the terminals.

As it is shown in Fig. 1 , the charge balancing structural element 10 is secured to the battery 24 applying a respective screw 16, 8 at each of the terminals. In case the charge balancing structural element 10 is secured in such a way, therefore, the screw 18 is included between the heat transfer element 12 and the battery 24. In the embodiment according to Fig. 1 the charge balancing structural element 10 is attached to the heat transfer element 12 by screws 20 on both the left and right sides of the drawing. In the present embodiment a circuit board 22 is also attached to the charge balancing structural element 0.

In Fig. 2 the embodiment of Fig. 1 is illustrated in top plan view. It is also illustrated in this figure that in an embodiment of the invention at least two transistors 14 being connected in parallel are applied, but three, four, or even more transistors may also be arranged. In the embodiment according to Fig. 2 two transistors 14 are arranged on the charge balancing structural element 10. The application of two or more transistors is advantageous because thereby more independent heat paths and independent current paths are established on the charge balancing structural element 10, which may have a positive effect on the service life of the device according to the invention. Furthermore, in the present embodiment the casings of the transistors 14 are arranged at the middle of the region defined by the heat transfer element 12. Since the components of the transistors that are subjected to heating are the casings, from the aspect of providing appropriate heat transfer the arrangement of the casing is important. It is expedient to arrange the transistors in such a way that their casings tend to heat are situated to the greatest possible extent in the region defined by the heat transfer element 12. Therefore, the transistors are preferably arranged near or at the middle of this region. In the embodiment shown in Fig. 1 and Fig. 2 field effect transistors 14 (FETs) are applied. For conducting off the heat generated by the transistor 14 it is expedient to arrange the transistor 14 in a manner shown in the drawing, i.e. above the heat transfer element 12 such that its pins 15 are not situated in the region of (i.e., in the drawing, above) the contact surface of the charge balancing structural element 10 and the heat transfer element, and thus the side of the transistor opposite its pins is situated precisely at the midline of the heat transfer element 12. This way the heat generated by the field-effect transistor can be transferred to the heat transfer element 12 in the most effective manner.

In the present embodiment n-type field-effect transistors are applied, with the transistor 14 being arranged at the positive terminal 1 1 b. In other embodiments p- type field-effect transistors are applied, arranged at the negative terminal 1 1a. It is more expedient to apply n-type transistors because most commercially available field-effect transistors are of the n-type. The screw joints of the n-type transistors are situated on the drain side of the transistors; and, as it is illustrated in Fig. 5, the drain electrode has to be connected to the positive terminal.

It is also shown in Fig. 2 that in the present embodiment a first temperature sensor 25b is disposed at the positive terminal 1 1b, and a second temperature sensor 25 is disposed at the negative terminal 1 1 a. The temperature sensors 25a and 25b are independent of each other. During operation of the charge balancing device the positive terminal 1 1 b is heated up and the temperature sensor 25b is arranged at the terminal 1 1 b to provide means for limiting this heating if it becomes necessary. Because the heating of the transistor 14 occurs at terminal 1 1b, compared to this terminal the other terminal 1 a heats up only very slowly. Thereby the values measured by the temperature sensor 25a well represent the internal temperature of the battery 24. In accordance with the above, by arranging the temperature sensors 25a, 25b according to Fig. 2 both the temperature of the terminal 1 1 b and the internal temperature of the battery 24 can be monitored. In Fig. 3A a system of charge balancing devices 26 according to an embodiment of the invention comprising radio frequency modules 28 (in short: radio modules), and batteries 32 connected thereto is illustrated. In a manner illustrated in the drawing, an arbitrary number of units comprising, among others, a battery 32 and a charge balancing device 26 may be added, and therefore the charge balancing device according to the invention can be applied for battery systems. Fig. 3B shows a central charge controller 34 comprising radio frequency modules 36. The charge balancing device 26 is controlled by a central charge controller 34 via a radio frequency module 28. Charge control of the batteries 32 shown in Fig. 3A, i.e. cell- or charge balancing of the batteries, is realised collectively by the components according to Fig 3A and Fig. 3B. The temperature of the individual charge balancing devices 26 can be monitored applying a temperature sensor 30. The central charge controller 34 may issue other control signals, and may communicate with a display or monitoring system.

By way of example, radio frequency communication can operate at a frequency of 2.4 GHz with a transfer speed of 2 MBps. Appropriate scheduling is performed by the central charge controller 34. The duration of each polling cycle is approximately 100 ps, and a measurement should be performed for all of the battery cells in every second. Thereby, as many as 1000 series-connected cells can be managed at the same time. In case the battery is not operating, it is sufficient to carry out only one measurement every day. In Fig. 4 the configuration of the charge balancing device 26 is illustrated by a block diagram. The charge balancing device 26 comprising a charge balancing structural element 27, on which, in addition to the radio frequency module 28, a microcontroller 40 and a measurement unit 42 are preferably arranged. The measurement unit 42 is a high-precision voltage-, current-, and temperature measurement unit. The charge balancing structural element 27 is controlled, by way of example, by a 32-bit microcontroller 40 which provides for transferring information arriving from the measurement unit 42 towards the central charge controller 34 via wireless communication. Additionally, the balancing current is also controlled by the microcontroller 40. In case more than one charge balancing device is applied, communication between the microcontrollers of the charge balancing devices may be implemented applying wireless data transfer which allows for the complete elimination of wiring. A big advantage of the charge control device according to the invention is that it can be fully integrated with the battery, and it may be even applied for monitoring a battery while it is out of operation. In the present embodiment, a transistor 38, which, similarly to other embodiments, is implemented as a field-effect transistor, is connected to the charge balancing structural element 27. Fig. 4 also shows the temperature sensor 30 and the battery 32. Fig. 5 is a circuit diagram illustrating the connections of transistors 44 and 46. In the embodiment according to Fig. 5 a respective shunt resistor 48, 50 is connected to the source electrode of each transistor 44, 46. In the example illustrated in the figure the source electrode of each field-effect transistor is connected to the ground through a fuse and a 22 mOhm shunt resistor. The control measurement signal is carried from the so-called hot points of the shunt resistors through a respective resistor. This resistor has much higher resistance than the shunt resistor, and thus essentially the entire current of the source flows through the shunt resistor. As shown in Fig. 5, the inputs of the field-effect transistors are controlled from a PWM (pulse width modulator) driver. To prevent autoresonance high-impedance separation is applied between the inputs of the two field-effect transistors. As it is shown in Fig. 5, the drain electrode of each field-effect transistor is connected to the positive terminal of the battery. In the example illustrated in the figure a current of 5A per field-effect transistor is calculated, i.e. according to the example a total current of 10A can be used for charge balancing. For a completely wireless system consisting of charge balancing devices according to the invention and batteries connected thereto, a passive balancing solution can be applied, since in that case excess energy is transformed into heat.

The invention is, of course, not limited to the preferred embodiments described in details above, but further variants, modifications and developments are possible within the scope of protection determined by the claims.

Claims

1 . A charge balancing device for a battery, comprising

- a charge balancing structural element (10, 27) being connectable to a negative terminal (1 1 a) and to a positive terminal (1 1 b) of the battery (24, 32) and carrying a charge balancing circuit, and

- a transistor (14, 38, 44, 46) forming a part of the charge balancing circuit and having a casing,

c h a r a c t e r i s e d by

- further comprising a heat transfer element (12) being galvanically connectable to any of the terminals (1 1 b), being galvanically connected to the charge balancing structural element (10, 27) at the side thereof facing the battery (24, 32), being electrically conductive, and being adapted for conducting off heat, and

- the casing of the transistor (14, 38, 44, 46) is arranged on the side of the charge balancing structural element (10, 27) being opposite the heat transfer element (12), at least partly in the region defined by the heat transfer element (12) and is arranged to be in heat transfer connection with the heat transfer element (12).

2. The device according to claim 1 , characterised by comprising at least two transistors (14, 44, 46) being connected in parallel.

3. The device according claim 1 or claim 2, characterised in that the charge balancing structural element (10, 27) is configured as a printed circuit board, and the transistor (14, 38, 44, 46) is arranged on the reverse side of the printed circuit board opposite the heat transfer element (12).

4. The device according to claim 3, characterised in that the casing of the transistor (14) is arranged at the middle of the region defined by the heat transfer element (12).

5. The device according to claim 3 or claim 4, characterised in that an additional conductive layer is arranged on the side of the charge balancing structural element (10, 27) being opposite the heat transfer element (12).

6. The device according to any of claims 1 to 5, characterised in that the heat transfer element (12) is made from copper, the heat transfer element (12) is arranged between the charge balancing structural element (10, 27) and the battery (24, 32), and the width of the heat transfer element (12) between the charge balancing structural element (10, 27) and the battery (24, 32) is in the range of 3-30 mm, preferably in the range of 5-10 mm, particularly preferably in the range of 7-9 mm, and by way of example 8 mm.

7. The device according to any of claims 1 to 6, characterised in that the transistor (14, 38, 44, 46) is a field-effect transistor.

8. The device according to claim 7, characterised in that the field-effect transistor is of n-type, and it is arranged at the positive terminal (11b).

9. The device according to claim 7, characterised in that the field-effect transistor is of p-type, and it is arranged at the negative terminal (11a).

10. The device according to any of claims 7 to 9, characterised in that a shunt resistor (48, 50) is connected to a source electrode of the field-effect transistor.

1 1. The device according to any of claims 1 to 10, characterised in that a first temperature sensor (25b) is arranged at the positive terminal (1 1 b), and a second temperature sensor (25a) is arranged at the negative terminal (11 a).

12. The device according to any of claims 1 to 11 , characterised by comprising a radio frequency module (28) through which the charge balancing device (26) is controlled by a central charge controller (34).