Patent Application
20100289453
A lithium-ion battery typically includes an anode, cathode and electrolyte. Lithium ions move from the anode to the cathode during discharge and from the cathode to the anode during charge.
Graphite may be used for the anode. A layered oxide (lithium cobalt oxide), polyanion (lithium iron phosphate) or spinel (lithium manganese oxide) may be used for the cathode. Other materials may also be used. Depending on the choice of material for the anode, cathode and electrolyte, the voltage, capacity and life of the lithium-ion battery may change.
Lithium-ion batteries may be electrically connected in series to form a battery pack for an automotive vehicle. Power from such a battery pack may be used to generate motive power, via an electric machine, to move the vehicle. This use of the battery pack may result in charge imbalances among the batteries.
A vehicle power system may include a plurality of series connected power storage units configured to supply power to move a vehicle, and a transformer including a plurality of primary windings and a secondary winding. Each of the primary windings may be configured to be selectively electrically connected with a respective one of a set of the power storage units. The secondary winding may be electrically connected with a different set of the power storage units.
A vehicle power system may include a plurality of charge balancing modules, each including a plurality of series connected power storage units configured to supply power to move a vehicle, and at least one transformer including a plurality of primary coils and a secondary coil. Each of the primary coils may be configured to be selectively electrically connected with at least one of the power storage units via at least one switch. The secondary coil may be electrically connected with power storage units of another of the charge balancing modules. Each of the charge balancing modules may further include circuitry configured to selectively activate the at least one switch.
A vehicle power system may include a plurality of series connected power storage units configured to supply power to move a vehicle, and at least one flyback switch mode converter having a plurality of primary windings and a single secondary winding. Each of the primary windings may be configured to be selectively electrically connected with a respective one of a set of the power storage units. The secondary winding may be electrically connected with a different set of the power storage units.
While example embodiments in accordance with the invention are illustrated and disclosed, such disclosure should not be construed to limit the invention. It is anticipated that various modifications and alternative designs may be made without departing from the scope of the invention
Referring now to
Referring now to
Referring now to
The cell module 18a may also include transformers 22a, 22b. The transformer 22a includes a plurality of primary windings 26a-26d, a core 28a, and secondary winding 30a. Likewise, the transformer 22b includes a plurality of primary windings 26e-26h, a core 28b, and secondary winding 30b. A primary winding is associated with each of the power storage units. (That is, the number of power storage units 20n matches the number of primary windings 26n.) In other embodiments, however, these numbers need not match. For example, every two power storage units may be associated with a primary winding, etc. As discussed below, the transformer 22a may be electrically connected with the power storage units 20a-20d; the transformer 22b may be electrically connected with the power storage units 20e-20h.
The cell module 18a may further include a plurality of electrical switches 32n (32a-32d), 34n (34a-34d), 36n (36a-36d), 38n (38a-38d). The electrical switches 32n, 34n may electrically connect the power storage units 20a-20d with the transformer 22a. The electrical switches 36n, 38n may electrically connect the power storage units 20e-20h with the transformer 22b. In the embodiment of
The secondary windings 30a, 30b may be electrically connected with power storage units of other cell modules 18n. Similarly, the power storage units 20n may be electrically connected with a secondary winding of another cell module 18n, etc. In the embodiment of
Diodes 40a, 40b and capacitors 42a, 44b may be associated with the electrical connections between the secondary windings 30a, 30b and the cell modules 18b, 18c. As known in the art, the diode 40a prevents current from flowing through the secondary winding 30a while current is ramping up in any of the primary windings 26a-26d; the diode 40b prevents current from flowing through the secondary winding 30b while current is ramping up in any of the primary windings 26e-26h. As also known in the art, the capacitors 42a, 42b smooth the current output by the secondary windings 30a, 30b respectively.
To electrically connect the power storage unit 20a with the primary winding 26a, the switches 32a, 34a may be activated. Current will flow (clockwise as illustrated) from the positive terminal of the power storage unit 20a, through the primary winding 26a (thus building an electromagnetic field), and to the negative terminal of the power storage unit 20a. As discussed above, while current is ramping up in the primary winding 26a, the diode 40a will prevent current flow through the secondary winding 30a (given the dot convention of the primary winding 26a and secondary winding 30a). Once the switches 32a, 34a are deactivated, current will flow (clockwise as illustrated) from the secondary winding 30a (due to the collapse of the electromagnetic field built up by the primary winding 26a) to power storage units of the cell module 18b. (Of course, the turns ratio of the primary winding 26a to the secondary winding 30a may be selected such that an appropriate voltage is output to the cell module 18b.) The other power storage units 20b-20h may be electrically connected with their associated transformer 22a, 22b by similar operation.
As apparent to those of ordinary skill, the transformers 22a, 22b, and associated components, each form a flyback switch mode converter with multiple primary windings and a single secondary winding. The cell module 18a of
The cell module 18a may further include a balance control circuit 44. The control circuit 44 facilitates the activation/deactivation of the switches 32n, 34n, 36n, 38n based on received state of charge information (determined in any suitable manner) regarding the power storage units 20n. In the embodiment of
Each of the cell modules 18n need not have its own control circuit 44. In some embodiments, a single balance control circuit may be arranged to facilitate the activation/deactivation of switches of some/all of the cell modules 18n. Other arrangements are also possible.
To activate the switches 32a, 34a, the control circuit 44 pulls the gate voltages of the switches 32a, 34a negative (with respect to their source leads) via connection to the reference of the control circuit 44. Switches 32b-32d, 34b-34d may be activated in a similar manner. To activate the switches 36a, 38a, the control circuit 44 drives the gate voltages of the switches 36a, 38a positive (with respect to their source leads) via connection to the reference of the control circuit 44. Switches 36b-36d, 38b-38d may be activated in a similar manner.
If any of the power storage units 20n has a state of charge greater than a desired threshold, its additional energy may be passed to power storage units of other cell modules 18n. For example, if the power storage unit 20g has a state of charge greater than the desired threshold (as indicated by state of charge information received by the control circuit 44), the control circuit 44 may drive gates of the switches 36c, 38c positive (activating the switches 36c, 38c). Energy stored by the power storage unit 20g may thus be transferred (via the transformer 22b) to power storage units of the cell module 18c until the state of charge of the power storage unit 20g achieves the desired range.
If any of the power storage units 20n has a state of charge less than a desired threshold, energy from the other power storage units 20n may be passed to power storage units of other cell modules 18n. For example, if the power storage unit 20d has a state of charge less than the desired threshold, the control circuit 44 may utilize the switches 32a, 34a to transfer power from the power storage unit 20a via the transformer 22a; the control circuit 44 may utilize the switches 32b, 34b to transfer power from the power storage unit 20b via the transformer 22a, etc. This power transfer may continue until the states of charge of the power storage units 20a-20h are approximately equal. Energy may then be driven into the power storage units 20a-20h (from other cell modules 18n) to raise their states of charge to a desired level. Other control schemes are also possible.
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
