Method for testing a balanced circuit

Abstract

A method tests a balancing circuit for a battery having a plurality of battery cells. The method detects first voltage states of the battery cells by way of a control unit; activates the balancing circuit with the aim of achieving a voltage equalization of at least two of the battery cells; detects second voltage states of the battery cells by way of the control unit; and determines a functional capability of the balancing circuit based on the first voltage states and the second voltage states of the battery cells by way of the control unit.

Claims

1. A method for testing a balancing circuit for a battery that has a plurality of battery cells, the method comprising the steps of: a) detecting first voltage states of the battery cells by way of a control unit, including: a1) detecting a first group of voltages of the battery cells; and a2) calculating a first voltage difference between a highest voltage and a lowest voltage of the first group of voltages by way of the control unit; b) activating the balancing circuit for a purpose of achieving voltage equalization of at least two of the battery cells; c) detecting second voltage states of the battery cells by way of the control unit, including: c1) detecting a second group of voltages of the battery cells; and c2) calculating a second voltage difference between a highest voltage and a lowest voltage of the second group of voltages by way of the control unit; and d) determining, by way of the control unit, a functional capability of the balancing circuit on the basis of the first voltage states and the second voltage states of the battery cells, including: d1) calculating a difference value between the first voltage difference and the second voltage difference and comparing the difference value with a prescribed voltage value by way of the control unit and d2) determining, by way of the control unit, that the balancing circuit is not working if the difference value is smaller than a prescribed voltage value.

2. The method as claimed in claim 1, wherein the method further comprises the step of: determining, by way of the control unit, that the balancing circuit is working if the difference value is greater than or equal to the prescribed voltage value.

3. The method as claimed in claim 1, wherein step cl) is performed a specific time after step al).

4. The method as claimed in claim 3, wherein the specific time is determined depending on a duration of the voltage equalization; or the specific time is a prescribed value.

5. The method as claimed in claim 1, wherein the prescribed voltage value is between 0 mV and 10 mV.

6. The method as claimed in claim 2, wherein the prescribed voltage value is between 0 mV and 10 mV.

7. A device for testing a balancing circuit for a battery that has a plurality of battery cells, comprising: a control unit operatively configured to execute a process that: detects first voltage states of the battery cells; activates the balancing circuit for a purpose of achieving voltage equalization of at least two of the battery cells; detects second voltage states of the battery cells; and determines a functional capability of the balancing circuit on the basis of the first voltage states and the second voltage states of the battery cells; and at least one voltmeter, wherein the at least one voltmeter detects a first group of voltages of the battery cells; the control unit calculates a first voltage difference between a highest voltage and a lowest voltage of the first group of voltages; the at least one voltmeter detects a second group of voltages of the battery cells; the control unit calculates a second voltage difference between a highest voltage and a lowest voltage of the second group of voltages; the control unit calculates a difference value between the first voltage difference and the second voltage difference and compares the difference value with a prescribed voltage value; and the control unit determines that the balancing circuit is not working if the difference value is smaller than the prescribed voltage value.

8. The device as claimed in claim 7, wherein the prescribed voltage value is between 0 mV and 10 mV.

9. A battery system, comprising: at least one battery that has a plurality of battery cells; a balancing circuit whose purpose is to achieve voltage equalization of at least two of the battery cells; and a device for testing the balancing circuit as claimed in claim 7.

10. An electric vehicle or hybrid vehicle, comprising a battery system as claimed in claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart of one exemplary embodiment of the method according to the invention.

(2) FIG. 2 is another flow chart of another exemplary embodiment of the method according to the invention.

(3) FIG. 3 is a schematic depiction of one exemplary embodiment of the device according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) In step S1 in FIG. 1, first voltage states of the battery cells 30 are detected by way of a control unit 10. FIG. 3 schematically depicts a device according to an embodiment of the invention or the control unit 10, which is able to implement the method in FIG. 1 or the method in FIG. 2.

(5) Step S1 is preferably able to be implemented by step S11 and step S12 in FIG. 2. In step S11 in FIG. 2, a first group of voltages of the battery cells 30 is detected by way of e.g. at least one voltmeter.

(6) In step S12 in FIG. 2, a first voltage difference D1 between a highest voltage and a lowest voltage of the first group of voltages is calculated by way of the control unit 10. The first voltage difference D1 indicates the voltage difference between two battery cells 30 of the plurality of battery cells 30 prior to the step of voltage equalization or of balancing of the plurality of battery cells 30.

(7) As the voltages of the battery cells 30 are already measured or monitored by the battery system (not shown) for other reasons, no additional components or sensors are required to detect the voltages of the battery cells 30.

(8) The balancing circuit is activated in step S2. As mentioned above, the balancing circuit has the task of achieving voltage equalization of at least two of the battery cells 30. The balancing circuit thus serves to balance or to equalize the states of charge of battery cells 30 of a battery system that has at least two battery cells 30. A balancing circuit is assigned to a battery cell or to a battery module and connected thereto.

(9) The balancing procedure comprises the following method steps: acquiring the battery cell voltages; identifying a battery cell having the lowest voltage; transferring the balancing circuit of the battery cell having the lowest battery cell voltage from an active state into a sleep mode; operating the balancing circuit in the active state, which balancing circuit is connected to battery cells 30 whose battery cell voltages are in each case higher than the lowest battery cell voltage; transferring the balancing circuit operated in the active state into the sleep mode as soon as the respective battery cell voltage of the battery cells 30 respectively assigned to the balancing circuit in the active state is in each case equal to the lowest battery module voltage of the multiplicity of battery cells 30.

(10) Second voltage states of the battery cells 30 are detected in step S3 by way of the control unit 10.

(11) Step S3 is preferably able to be implemented by step S14 and step S15 in FIG. 2. In step S14 in FIG. 2, a second group of voltages of the battery cells 30 is detected by way of e.g. at least one voltmeter. In step S15 in FIG. 2, a second voltage difference D2 between a highest voltage and a lowest voltage of the second group of voltages is calculated by way of the control unit 10. The second voltage difference D2 indicates the greatest voltage difference between two battery cells 30 of the plurality of battery cells 30 following balancing of the plurality of battery cells 30. The second group of voltages of the battery cells 30 is detected a specific time T after the detection of the first group of voltages of the battery cells 30 or after step S11, wherein the specific time T is determined depending on a duration of the voltage equalization or balancing or is a prescribed value.

(12) In accordance with the principle of balancing, the voltage of the battery cell that has a highest voltage prior to the balancing of the plurality of battery cells 30 is reduced by the balancing if the balancing circuit is working. Therefore, the greatest voltage difference D2 between a highest voltage and a lowest voltage of the plurality of battery cells 30 should be reduced following the balancing of the plurality of battery cells 30 if the balancing circuit is working, that is to say the second voltage difference D2 should be smaller than the first voltage difference D1.

(13) In step S4 in FIG. 1, a functional capability of the balancing circuit is determined on the basis of the first voltage states and the second voltage states of the battery cells 30 by way of the control unit 10.

(14) Step S4 is preferably able to be implemented by step S16 and step S17 in FIG. 2. In step S16, a difference value D3 between the first voltage difference D1 and the second voltage difference D2 is calculated using the following equation:
D3=D1D2.

(15) In step S16, the control unit 10 furthermore compares the difference value D3 with a prescribed voltage value D4 and determines, in step S17, that the balancing circuit is not working if the difference value D3 is smaller than a prescribed voltage value D4. The prescribed voltage value D4 is set between 0 mV and 10 mV. The prescribed voltage value D4 is preferably 4 mV.

(16) Furthermore, in step S18 in FIG. 2, the control unit may determine that the balancing circuit is working if the difference value D3 is greater than or equal to the prescribed voltage value D4.

(17) The control unit may evaluate the functional capability of the balancing circuit on the basis of the difference value D3 and the prescribed voltage values or ranges in graded form, e.g. working very well, adequate, poor and defective.

(18) The existing controller or microcontroller inside the battery system may serve as the control unit. This leads to no additional expenditure. The present invention thus provides a solution for testing a balancing circuit without increasing the costs of the battery system.

(19) FIG. 3 shows a schematic depiction of a device that is able to test a balancing circuit for a battery that has a plurality of battery cells 30. The device comprises a control unit 10 and a plurality of voltmeters 20, wherein the device detects first voltage states of the battery cells 30 and activates the balancing circuit (not shown) for the purpose of achieving voltage equalization of at least two of the battery cells 30, and detects second voltage states of the battery cells 30, and determines a functional capability of the balancing circuit on the basis of the first voltage states and the second voltage states of the battery cells 30.

(20) The voltmeters 20 serve to measure the voltages of the battery cells 30. The control unit 10 calculates a first voltage difference D1 between a highest voltage and a lowest voltage of the battery cells 30 prior to the balancing step, and a second voltage difference D2 between a highest voltage and a lowest voltage of the battery cells 30 following the balancing. As the voltages of the battery cells 30 are already measured or monitored by the battery system for other reasons, the voltmeters are already present inside a battery system. No additional components are therefore required to measure the voltages of the battery cells 30.

(21) The control unit 10 calculates a difference value D3 between the first voltage difference D1 and the second voltage difference D2 and compares the difference value D3 with a prescribed voltage value D4. The control unit 10 determines that the balancing circuit is not working if the difference value D3 is smaller than a prescribed voltage value D4. On the other hand, the balancing circuit is working if the difference value D3 is greater than or equal to the prescribed voltage value D4.

(22) A controller that is already present or a microcontroller that is already present in the battery system may serve as the control unit. This therefore leads to no additional expenditure. The present invention thus provides a solution for testing a balancing circuit without increasing the costs of the battery system. As no additional components need to be used, the installation space for the battery system remains unchanged.

(23) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.