Balancing method and battery system
According to an example embodiment, a battery system includes: a plurality of modules, each including a plurality of cells connected to each other in series and a cell balancing circuit performing a balancing operation between the plurality of the cells based on voltages of the plurality of the cells; and a module balancing circuit performing a balancing operation between the modules based on voltages of the modules.
1. A battery system comprising:
a plurality of modules, each of the plurality of modules including a plurality of cells connected in series and a cell balancing circuit,
the cell balancing circuit being configured to measure voltages of the plurality of cells,
the cell balancing circuit being configured to select a first number of the plurality of cells for cell balancing based on the voltages of the plurality of cells; and
a module balancing circuit configured to measure voltages of the plurality of modules,
the module balancing circuit being configured to select a second number of the plurality of modules for module balancing based on the voltages of the plurality of modules,
the module balancing circuit including,
bi-directional switches that are respectfully connected to the plurality of modules, the bi-directional switches being configured to hi-directionally control a flow of an electric current,
a module controller configured to determine the selected second number of modules for module balancing based on the voltages of the plurality of modules, the module controller being configured to turn on and turn off a selected number of the bi-directional switches that are connected to the selected modules, and
a multi-winding transformer connected to the bi-directional switches, the multi-winding transformer being configured to transfer energy between the selected modules when a selected number of the bi-directional switches are turned on, the selected number of bi-directional switches corresponding to the selected modules.
2. The battery system of claim 1 , wherein
the plurality of modules are connected in series,
the multi-winding transformer includes an inductor;
the module balancing circuit further includes a reset circuit connected to opposite terminals of the plurality of modules, and
the reset circuit includes a diode and a mutual inductor that is correlated with the inductor of the multi-winding transformer.
3. The battery system of claim 2 , wherein
an impedance of the mutual inductor in the reset circuit is greater than an impedance of the plurality of the modules, and
a number of windings of the mutual inductor in the reset circuit is greater than a number of windings of the inductor in the multi-winding transformer.
4. The battery system of claim 1 , wherein the module balancing circuit is configured to determine the selected modules based on selecting a module having a highest voltage and selecting a module having a lowest voltage among the plurality of modules.
5. The battery system of claim 1 , wherein the module controller is configured to determine the selected modules according to a priority that is set by the module controller.
6. The battery system of claim 5 , wherein the module controller is configured to determine the selected modules based on a connecting order of the plurality of modules when at least two of the plurality of modules have equal voltages.
7. A battery system comprising:
a plurality of modules, each of the plurality of modules including a plurality of cells connected in series and a cell balancing circuit,
the cell balancing circuit being configured to measure voltages of the plurality of cells,
the cell balancing circuit being configured to select a first number of the plurality of cells for cell balancing based on the voltages of the plurality of cells,
the cell balancing circuit including a buck booster circuit; and
a module balancing circuit configured to measure voltages of the plurality of modules,
the module balancing circuit being configured to select a second number of the plurality of modules for module balancing based on the voltages of the plurality of modules, and
the module balancing circuit including a multi-winding transformer.
8. The battery system of claim 7 , wherein the multi-winding transformer includes mutual inductors having an equal number of windings as each other.
9. The battery system of claim 7 , wherein the cell balancing circuit includes,
two switches connected to opposite terminals of every two adjacent cells in parallel, and
an energy storage device connected between the two adjacent cells and the two switches.
10. A balancing method of a battery system, the method comprising:
measuring voltages of a plurality of modules;
selecting a first number of the plurality of modules for module balancing based on the voltages of the plurality of modules,
the selecting the first number of the plurality of modules including one of,
determining the selected first number of the plurality of modules based on a priority set by a controller, and
determining the selected first number of the plurality of modules based on a connecting order of the plurality of modules when at least two of the plurality of modules have equal voltages,
each of the plurality of modules including a plurality of cells connected in series;
balancing the selected modules by controlling turning on and turning off switches that are connected to the selected modules;
selecting a second number of the plurality of cells for cell balancing based on voltages of the plurality of cells included in the plurality of modules; and
balancing the selected cells by controlling turning on and turning off switches connected to the selected cells.
11. The method of claim 10 , wherein the selecting the first number of the plurality modules includes selecting two of the plurality of modules for module balancing based on measured voltages of the plurality of modules.
12. The method of claim 10 , wherein the selecting the first number of the plurality of modules includes determining the selected first number of the plurality of modules based on the priority set by a controller.
13. The method of claim 10 , wherein the selecting the first number of the plurality of modules includes determining the selected first number of the plurality of modules based on the connecting order of the plurality of modules when at least two of the plurality of modules have equal voltages.
14. The method of claim 10 , wherein the selecting the second number of the plurality of cells includes selecting two adjacent cells for cell balancing based on measured voltages of the cells.
15. A tangible computer readable recording medium having embodied thereon a program for executing the method of claim 10 in a computer.