Method and device for balancing electrical voltages in electrical accumulator units

The invention provides a method for balancing the electrical voltages of at least two electrical accumulator units that are connected in series. According to the invention, one accumulator unit is connected to the winding of a coil in order to excite the coil, and the other accumulator unit is charged by the excited coil by the subsequent connection of the winding to the other accumulator unit. In addition, the invention provides a corresponding electrical accumulator.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 35 USC 371 application of PCT/EP 2009/065469 filed on Nov. 19, 2009.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a method for balancing the electrical voltages of at least two serially connected electrical accumulator units. The invention also relates to a corresponding electrical accumulator.

Description of the Prior Art

It is clear that in future, in both stationary applications, such as wind farms and non-stationary applications, such as in vehicles, for example hybrid and electric vehicles, new battery systems of which very stringent demands for reliability will be made will increasingly come into use. The background of these demands is that a failure of the battery systems can lead to either a failure of an entire system pertaining to the application, or to a safety-relevant problem. One conceivable example of such a failure is an electric vehicle that if its traction battery fails is “dead in the water”, since it is no longer capable of propelling itself. As an example of a safety-relevant problem, a wind farm is conceivable, in which electrical accumulators are used for protecting the farm against impermissible modes of operation by adjusting the rotor blades under strong wind conditions. Failure of these electrical accumulators can then lead to safety-relevant problems.

When many individual accumulator units, such as battery cells, connected in series are used, the individual accumulator units are not automatically equal. As a result, particularly over the service life of the accumulator units, this leads to unequal electrical voltages among the individual accumulator units, unless appropriate countermeasures are taken. Especially with lithium-ion batteries, excessive charging or deep discharging of individual accumulator units leads to irreversible damage. Such excessive charging or deep discharging can result when a battery management system regulates a charging or discharging operation based on one of the accumulator units, which is not representative all of the accumulator units. For that reason, balancing of the electrical voltages of the electrical accumulator units among one another must be done at regular intervals. This balancing is known as “cell balancing”. To that end, the individual accumulator units are discharged, by external wiring provisions, in such a way that after the balancing, they all have the same electrical voltage.

It is known for that purpose to perform so-called resistance balancing. To that end, an ohmic resistor or a resistor combination is assigned to each accumulator unit via switches. By means of the resistors, the accumulator units are discharged until such time as the accumulator units have the electrical voltage. It is disadvantageous here that energy stored in the electrical accumulator units is converted into heat by the resistors and is carried away unused, for the sake of achieving the desired charge balance. Hence there is a need for a way in which balancing the electrical voltages of a plurality of accumulator units among one another is attained with little energy loss and in which a substantial improvement in the efficiency of a complete electrical accumulator system is brought about.

SUMMARY OF THE INVENTION

According to the invention, it is provided that the one accumulator unit is connected to the winding of a coil for the excitation of that coil, and that next, by means of the excited coil, the other accumulator unit is charged by the connection of the winding to that other accumulator unit. It is provided that the same winding that is used for exciting the coil is also used for charging the other accumulator unit. In this way, it becomes possible for the energy stored in the accumulator units not to be merely converted into heat, but to be transferred from the one accumulator unit to the other, so that the electrical voltages of the various accumulator units are balanced with each other. Charging the other accumulator unit should be understood to mean that the coil is excited, and by means of the electrical energy that is thus available, the other accumulator unit is further charged. Charging should accordingly be understood to mean not full charging of the entire electrical accumulator, but rather transporting an electrical charge between the accumulator units and the coil for the sake of balancing the electrical voltages.

In a further feature of the invention, it is provided that the one accumulator unit, which is connected to the winding of the coil for its excitation, has a higher electrical voltage than the accumulator unit that is charged next, by the connection of the winding.

In a further feature of the invention, it is provided that as the accumulator units, one accumulator cell each, in particular a battery cell, is used.

In a further feature of the invention, it is provided that the coil is charged by closure of a switch. Using the switch makes it possible to charge at least one coil in a targeted manner. In this way, the method can be employed in targeted manner to individual accumulator units, without always having to include all the accumulator units in the method.

In a further feature of the invention, it is provided that the two accumulator units are located adjacent one another. Being located adjacent one another should be understood to mean that the accumulator units are connected directly in series with one another, and a positive pole of one of the accumulator units is connected directly to a negative pole of the other accumulator unit via a line.

In a further feature of the invention, it is provided that each adjacent accumulator unit is assigned a coil. When there is a plurality of adjacent accumulator units, it is provided in particular that each adjacent accumulator unit is assigned its own coil, with a winding.

In a further feature of the invention, it is provided that the coil charges the other accumulator unit by opening the switch. By appropriate interconnection, it becomes possible to end the charging of the coil by opening the switch, and by reinduction, or in other words de-excitation, the coil makes the energy stored in it available. In that case, the coil outputs the stored electrical energy, and that energy is taken up by the other accumulator unit, which is being charged. The combination here of closing the switch to charge the coil and opening the switch to charge the accumulator unit is advantageous, since by means of only two positions of the switch, both the charging of the coil and the charging of the accumulator unit can be brought about in succession in a simple way.

In a further feature of the invention, it is provided that the other accumulator unit is charged by the coil via at least one diode. This is especially advantageous whenever a flow of current, which flows into the coil upon charging, is reversed and flows out of the coil again, for charging the accumulator unit in the reverse manner. Thus the coil can be connected to two accumulator units simultaneously, and the charging of the other accumulator unit depends on whether the coil is being charged or discharged.

The invention relates further to an electrical accumulator having at least two serially connected electrical accumulator units and one electrical balancing circuit, in particular for performing the method described above, in which the balancing circuit has at least one coil having a winding and its winding is connectable to one of the accumulator units for exciting the coil, and in which, for charging the other accumulator unit, the winding can be connected to that accumulator unit.

In a further feature of the invention, it is provided that the balancing circuit has at least one diode and/or at least one switch.

In a further feature of the invention, it is provided that the switch is embodied as a semiconductor switch, in particular a transistor, thyristor, or the like. By the use of semiconductor elements, very easy automation is made possible, by means of electrical components, such as circuits. Moreover, in this way the device of the invention can be embodied in a space-saving way and can be produced economically.

In a further feature of the invention, it is provided that each of the accumulator units has an accumulator cell, in particular a battery cell.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1shows a detail of an electrical accumulator101, comprising three accumulator units102in the form of accumulator cells103that are connected in series adjacent to one another. The electrical accumulator101is embodied as a battery104, and the accumulator cells103are embodied as battery cells105. The accumulator units102form the electrical accumulator101by means of the fact that a first accumulator unit106is connected via its negative pole106″ and a line107to a node point108, which leads via a line109to a positive pole110′ of a second accumulator unit110. The second accumulator unit110is connected in turn via its negative pole110″ and a line111to a node point112, which leads via a line113to a positive pole114′ of a third accumulator unit114. A balancing circuit115, a detail of which is shown inFIG. 1, is assigned to the accumulator101. The balancing circuit115is connected via a line116to a positive pole106′ of the first accumulator unit105. It is also connected to the node point108via a line117, to the node point112via a line118, and to a negative pole114″ of the third accumulator unit114via a line119. The balancing circuit115has a plurality of electric coils121, each with a winding120. The balancing circuit115furthermore has diodes122and switches123. The line116is connected via a node point124to a further line125, which leads to a first winding126. The first winding126is connected via a line127to a node point128, which has a further line129which leads to a first switch130. Beginning at the first switch130, a line131leads to a node point132. From the node point132, a line133leads to a further node point134, which in turn is connected via a line135to a second winding136. The second winding136is connected via a line137to a node point138, which is connected via a line139to a further node point140. The node point140is also connected to the line117. Via a line141, a first diode142is connected to the node point140. The diode142is also connected to the node point128via a line143. The diode142is disposed between the lines141and143in such a way that it has a conducting direction from the line141to the line143. The node point134is connected via a line144to a second diode145, which in turn is connected via a line146to the node point124. The second diode145has a conducting direction from the line144to the line146. Beginning at the node point132, a further line149leads to a second switch150. From the switch150, a line151leads to a node point152. From the node point152, a line153leads to a further node point154, which in turn is connected via a line155to a third winding156. The winding156is connected via a line157to a node point158, which is connected via a line159to a further node point160. The node point160is also connected to the line118. Via a line161, a third diode162is connected to the node point160. The diode162is also connected to the node point134via a line163. The diode162is disposed between the lines161and163in such a way that it has a conducting direction from the line161to the line163. The node point154is connected via a line164to a fourth diode165, which in turn is connected via a line166to the node point138. The fourth diode165has a conducting direction from the line164to the line166. Beginning at the node point152, a further line169leads to a third switch170. Beginning at the switch170, a line171leads to a node point174. The node point174is in turn connected via a line175to a fourth winding176. The winding176is connected via a line177to a node point180. The node point180is also connected to the line119. Via a line181, a fifth diode182is connected to the node point180. The diode182is also connected to the node point154via a line183. The diode182is disposed between the lines181and183in such a way that it has a conducting direction from the line181to the line183. The node point174is connected via a line184to a sixth diode185, which in turn is connected to the node point158via a line186. The sixth diode185has a conducting direction from the line184to the line186. The switches123are assigned to an electronic control unit190. For that purpose, they are embodied as semiconductor switches191in the form of transistors192, so that the control unit190forms an integrated circuit193. Dashed lines179indicate that both the electrical accumulator101and the balancing circuit115are continued logically onward in the direction of the lines179.

FIG. 2shows the electrical accumulator101and the balancing circuit115ofFIG. 1with all their features. Unlike inFIG. 1, inFIG. 2the second switch150is closed, for performing a first method step. The accumulator unit110furthermore has a higher voltage than the other accumulator units106and114. As a result, there is a closed electric circuit195for the second accumulator unit110, the second winding136and the third winding156. The electric circuit195inFIG. 2is shown in heavy lines and is provided with current direction arrows196. The electric circuit195extends from the positive pole110′ of the second accumulator unit110via the line109and onward via the line117to the node point140, so that by means of the lines137and139, the coil121of the second winding136is charged. The electric circuit195also extends via the lines135,133and149to the closed second switch150. It continues via the lines151,153and154to the third winding156. Beginning at the third winding156, the electric circuit195is closed via the lines157,159,118and111to the negative pole110″ of the second accumulator unit110. By means of this closed electric circuit195, a charge is transferred into the second and third windings136and156and stored there. The closure of the second switch150is effected by the control unit190. It is provided that each accumulator unit102charges two windings120. By closure of the switch150, the electric circuit195is closed, and it is opened again either after a certain period of time or after a certain level of the current that flows through the switch is reached.

FIG. 3shows the accumulator101and the balancing circuit115ofFIG. 1with all their features. The switches123are all opened for a second method step, and the coils assigned to the second winding136and the third winding156are excited. The result is two electric circuits197and198; the electric circuit197is assigned to the first accumulator unit106, and the second electric circuit198is assigned to the third accumulator unit114. The electric circuit197extends from the second winding136to the second diode145, via the lines135and144. Beginning at the second diode145, the electric circuit197extends onward via the lines146and116into the positive pole106′ of the first accumulator unit106. From the negative pole106″ of the accumulator unit106, the electric circuit197extends via the lines107,117,139and138back to the second winding136. The electric circuit198begins at the third winding156, which is connected via the lines157,159,118and113to the positive pole114′ of the third accumulator unit114. From the negative pole114″ of the third accumulator unit114, the fifth diode182is connected via the lines119and181, so that beginning at the diode182, the electric circuit198is closed via the lines183and155. Within the electric circuits197and198, the various current directions are represented by current direction arrows196. The current directions run in the directions that correspond to the conducting directions of the second diode145and the fifth diode182. Via the electric circuits197and198, the coils of the windings136and156can be de-excited; that is, they give up their charges, which flow into the corresponding accumulator units106and114and as a result further charge those accumulator units. For that purpose it is unnecessary to employ further control means for the second method step, since this process ensues automatically because of the balancing circuit shown.

The method steps shown inFIGS. 2 and 3describe the possibility of charging the first accumulator unit106and the second accumulator unit114with an electrical charge from the second accumulator unit110. This process is highly energy-efficient, since electrical charges are transferred among the accumulator units.

The foregoing relates to the preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.