CIRCUIT AND METHOD FOR BATTERY EQUALIZATION

• US 20140232347A1
• Filed: 02/19/2013
• Published: 08/21/2014
• Est. Priority Date: 02/19/2013
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: DROBNIK, Josef, BERNOUX, Beatrice
• Granted Patent: US 9,337,670 B2
• Time in Patent Office: Days
• US Class Current: 320/119
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries
• CPC Class Codes: H02J 7/0018 using separate charge circuits

Abstract

A battery equalization circuit is provided, including: a positive battery node connecting to a positive node of a battery cell in a battery circuit with a plurality of other battery cells; a negative battery node connected to a negative node of the battery cell; a transformer winding receiving an AC voltage, the transformer winding having an upper transformer node and a tower transformer node; an upper triac connected between the positive battery node and the upper transformer node; a lower triac connected between the negative battery node and the lower transformer node; a control circuit for controlling the upper triac and the lower triac based on a measured cell voltage between the positive battery node and the negative battery node, and a total battery voltage of the battery circuit; and an isolation element connected between the control circuit and a data bus.

Claims

1. A battery equalization circuit, comprising:

a first positive battery node configured to connect to a positive node of a first monitored battery cell contained in a battery circuit that includes a plurality of other battery cells connected in series with the first monitored battery cell;

a first negative battery node configured to connect to a negative node of the first monitored battery cell;

a first transformer winding configured to receive an output voltage of an AC generator, the first transformer winding having a first upper transformer node and a first lower transformer node;

a first upper triac connected between the first positive battery node and the first upper transformer node;

a first lower triac connected between the first negative battery node and the first lower transformer node; and

a multiplexers configured to control the operation of the first upper triac and the first lower triac based on instructions received from a central control unit,

wherein the instructions received from the central control unit are generated based on a first measured cell voltage between the first positive battery node and the first negative battery node, and a total battery voltage of the battery circuit.

2. The battery equalization circuit of claim 1, wherein the first upper triac and the first lower triac are both optically-coupled triacs.

3. The battery equalization circuit of claim 1, wherein

the first monitored battery cell and the plurality of other battery cells are all configured to have the same preset voltage, and

wherein the total battery voltage of the battery circuit is determined by measuring a voltage of all of the first monitored battery cell and the plurality of other battery cells arranged in series with each other, and dividing the resulting voltage by a total number of battery cells, including the first monitored battery cell and the plurality of other battery cells.

4. The battery equalization circuit of claim 1, further comprising

a first analog-to-digital converter connected between the first positive battery node and the first negative battery node, and configured to determine a first analog cell voltage, and to convert the first analog cell voltage into a first digital cell voltage,

wherein the central control circuit uses the first digital cell voltage as the first measured cell voltage.

5. The battery equalization circuit of claim 1, further comprising

a first switch connected between the first positive node and a voltage-measurement node;

a cluster analog-to-digital converter connected the voltage-measurement node, and configured to determine a first analog cell voltage at the first positive node when the first switch is closed, and to convert the first analog cell voltage into a first digital cell voltage; and

a cluster isolation element for electrically isolating the cluster analog-to-digital converter from the multiplexer,

wherein

the multiplexer controls the operation of the first switch.

6. The battery equalization circuit of claim 1, further comprising:

a second positive battery node configured to connect to a positive node of a second monitored battery cell selected from the plurality of other battery cells connected in series with the first monitored battery cell;

a second negative battery node configured to connect to a negative node of the second monitored battery cell;

a second transformer winding configured to receive the output voltage of the AC generator, the second transformer winding having a second upper transformer node and a second lower transformer node; and

a triac connected between the second positive battery node and the second upper transformer node,

wherein the multiplexer is further configured to control the operation of the second triac based on further instructions received from a central control unit,

wherein the further instructions received from the central control unit are generated based on a second measured cell voltage between the second positive battery node and the second negative battery node, and the total battery voltage of the battery circuit.

7. The battery equalization circuit of claim 6, wherein the second triac is an optically-coupled triac.

8. The battery equalization circuit of claim 6, further comprising

a second analog-to-digital converter connected between the second positive battery node and the second negative battery node, and configured to determine a second analog cell voltage, and to convert the second analog cell voltage into a second digital cell voltage,

wherein the central control circuit uses the second digital cell voltage as the second measured cell voltage.

9. The battery equalization circuit of claim 6, further comprising

a second switch connected between the second positive node and the voltage-measurement node;

wherein

the cluster analog-to-digital converter is further configured to determine a second analog cell voltage at the second positive node when the second switch is closed, and to convert the second analog cell voltage into a second digital cell voltage, and

the multiplexer controls the operation of the second switch.

10. A battery equalization circuit, comprising:

a primary battery equalization cluster comprising N primary cluster cells;

a central control circuit configured to control the operation of the primary battery equalization cluster, and to provide signals to a data bus; and

wherein

an i^th primary cluster cell further comprises

an i^th positive primary battery node configured to connect to a positive node of an i^th monitored primary battery cell contained in a primary battery circuit that includes N primary battery cells connected in series with each other,

an i^th negative primary battery node configured to connect to a negative node of the i^th monitored primary battery cell,

an i^th primary transformer winding configured to receive an output voltage of an AC generator, the i^th primary transformer winding having an i^th upper primary transformer node and an i^th lower primary transformer node,

an i^th primary triac connected between the i^th positive primary battery node and the i^th upper primary transformer node, and

wherein

the central control circuit is configured to control the operation of the i^th primary triac based on an i^th measured primary cell voltage between the i^th positive primary battery node and the i^th negative primary battery node, and a total primary battery voltage of the primary battery circuit,

the first through N^th primary transformer windings are connected in series such that an i^th lower primary transformer node is connected to an (i+1)^th upper primary transformer node,

an i^th negative primary battery node is connected to an (i+1)^th positive primary battery node, and

i is an integer index that varies from 1 to N.

11. The battery equalization circuit of claim 10, further comprising

a secondary battery equalization cluster comprising M secondary cluster cells,

wherein

a j^th secondary cluster cell further comprises

a j^th positive secondary battery node configured to connect to a positive node of a j^th monitored secondary battery cell contained in a secondary battery circuit that includes N secondary battery cells connected in series with each other,

a j^th negative secondary battery node configured to connect to a negative node of the j^th monitored secondary battery cell,

a j^th secondary transformer winding configured to receive the output voltage of the AC generator, the j^th secondary transformer winding having a j^th upper secondary transformer node and an i^th lower secondary transformer node,

a j^th secondary triac connected between the j^th positive secondary battery node and the j^th upper secondary transformer node, and

wherein

the central control circuit is further configured to control the operation of the j^th secondary triac based on a j^th measured secondary cell voltage between the j^th positive secondary battery node and the j^th negative secondary battery node, and a total secondary battery voltage of the secondary battery circuit,

the first through M^th secondary transformer windings are connected in series such that a j^th lower secondary transformer node is connected to a (j+1)^th upper secondary transformer node,

a jth negative secondary battery node is connected to a (j+1)^th positive secondary battery node,

the central control circuit is further configured to provide signals to the data bus, and

j is an integer index that varies from 1 to M.

12. The battery equalization circuit of claim 10, wherein

an i^th primary cluster cell further comprises

an i^th primary analog-to-digital converter connected between the i^th positive primary battery node and the an i^th negative primary battery node, and configured to determine an i^th primary analog cell voltage, and to convert the i^th primary analog cell voltage into an i^th primary digital cell voltage, and

an i^th isolation element located between the i^th primary analog-to-digital converter and the data bus, and configured to electrically isolate the i^th primary analog-to-digital converter from the data bus,

wherein the central control circuit uses the i^th primary digital cell voltage as the i^th measured primary cell voltage.

13. The battery equalization circuit of claim 10, further comprising

an i^th primary switch connected between the i^th positive primary battery node and the control circuit;

and

wherein

the central control circuit controls the operation of the i^th primary switch;

the i^th primary cluster cell further comprises

an analog-to-digital converter connected to the i^th primary switch, and configured to measure an i^th primary analog cell voltage of the i^th monitored primary battery cell when the i^th primary switch is closed, and configured to convert the i^th primary analog cell voltage into an i^th primary digital cell voltage,

an isolation element located between the analog-to-digital converter, and configured to electrically isolate the analog-to-digital converter from the data bus, and

the control circuit uses the i^th primary digital cell voltage as the i^th measured primary cell voltage.

14. A method of equalizing a battery, including:

measuring a total voltage of a battery containing N battery cells arranged in series with each other;

determining an optimum cell voltage based on the measured total voltage and the value of N;

measuring a selected cell voltage of a selected battery cell from the N battery cells;

determining whether the measured cell voltage is less than the optimum cell voltage;

connecting the selected battery cell to a voltage output of a generator during a portion of a positive cycle of the voltage output of the generator, when it is determined that the measured cell voltage is less than the optimum cell voltage;

determining whether the measured cell voltage is greater than the optimum cell voltage; and

connecting the selected battery cell to the voltage output of the generator during a negative cycle of the voltage output of the generator, when it is determined that the measured cell voltage is greater than the optimum cell voltage,

where N is an integer greater than 1.

15. The method of claim 14, wherein the optimum cell voltage is equal to the measured total voltage divided by the total number of the battery cells in the plurality of battery cells.

16. The method of claim 14, wherein the operations of measuring the total voltage of the battery, determining the optimum cell voltage, measuring the selected cell voltage, determining whether the measured cell voltage is less than the optimum cell voltage, connecting the selected battery cell to the voltage output of a generator during a positive cycle of the generator when it is determined that the measured cell voltage is less than the optimum cell voltage, determining whether the measured cell voltage is greater than the optimum cell voltage, and connecting the selected battery cell to the voltage output of the generator during a negative cycle of the generator when it is determined that the measured cell voltage is greater than the optimum cell voltage are repeated N times to allow each of the N battery cells to serve as the selected cell once.

17. The method of claim 14, wherein the operation of connecting the selected battery cell to the voltage output of a generator during a positive cycle of the generator when it is determined that the measured cell voltage is less than the optimum cell voltage further comprises:

determining a connection duration of the positive cycle during which the selected cell should be connected to the voltage output of the generator;

determining a connection starting point during the positive cycle at which the selected cell should be connected to the voltage output of the generator so that the selected cell will be connected to the voltage output of the generator for the connection duration, when a connection ending point during the positive cycle at which the selected cell will be disconnected from the voltage output of the generator is a zero crossing of the voltage output of the generator;

connecting the selected battery cell to the voltage output of the generator at the determined connection starting point; and

disconnecting the selected battery cell from the voltage output of the generator at a next zero crossing of the voltage output of the generator.

18. The method of claim 17, wherein the operation of connecting the selected battery cell to the voltage output of the generator at the determined connection starting point further comprises

activating a first triac connected between a positive terminal of the selected battery cell and a first terminal of the output voltage of the generator to connect the positive terminal of selected battery cell to the first terminal of the output voltage of the generator;

and

activating a second triac connected between a negative terminal of the selected battery cell and a second terminal of the output voltage of the generator to connect the negative terminal of selected battery cell to the second terminal of the output voltage of the generator.

19. The method of claim 18, wherein the selected battery cell is connected to the output voltage of the generator through a transformer.

20. The method of claim 14, wherein the operation of connecting the selected battery cell to the voltage output of a generator during a negative cycle of the generator when it is determined that the measured cell voltage is greater than the optimum cell voltage further comprises:

determining a connection duration of the negative cycle during which the selected cell should be connected to the voltage output of the generator;

determining a connection starting point during the negative cycle at which the selected cell should be connected to the voltage output of the generator so that the selected cell will be connected to the voltage output of the generator for the connection duration, when a connection ending point during the positive cycle at which the selected cell will be disconnected from the voltage output of the generator is a zero crossing of the voltage output of the generator;

connecting the selected battery cell to the voltage output of the generator at the determined connection starting point; and

disconnecting the selected battery cell from the voltage output of the generator at a next zero crossing of the voltage output of the generator.

21. The method of claim 20, wherein the operation of connecting the selected battery cell to the voltage output of the generator at the determined connection starting point further comprises:

activating a first triac connected between a positive terminal of the selected battery cell and a first terminal of the output voltage of the generator to connect the positive terminal of selected battery cell to the first terminal of the output voltage of the generator; and

activating a second triac connected between a negative terminal of the selected battery cell and a second terminal of the output voltage of the generator to connect the negative terminal of selected battery cell to the second terminal of the output voltage of the generator.

22. The method of claim 21, wherein the selected battery cell is connected to the output voltage of the generator through a transformer.