Balanced control strategies for interconnected heterogeneous battery systems in smart grid applications
A battery network includes a plurality of heterogeneous batteries coupled to at least one energy source and one energy load, a plurality of switches coupled to the heterogeneous batteries, and the switches controllable having a duty cycle between 0 and 1. A controller is configured to characterize each of the plurality of heterogeneous batteries characteristics, determine duty cycles for each of the plurality of switches based on the characterization such that a charge applied from the at least one energy source or a discharge to the at least one energy load converges to a balanced state for the plurality of heterogeneous batteries, and apply the determined duty cycles to the plurality of switches.
1. A battery network, comprising:
a plurality of heterogeneous batteries coupled in parallel, the plurality of heterogeneous batteries coupled to an electric grid that includes at least one energy source and one energy load;
a plurality of switches coupled to the plurality of heterogeneous batteries, each battery having a switch in series, the plurality of switches each controllable via application of a pulse-width modulation (PWM) frequency such that a duty cycle is defined as a proportion of on time for each switch; and
a controller configured to:
characterize each battery of the plurality of heterogeneous batteries based at least on an RC equivalent model to determine a time constant for each of the plurality of heterogeneous batteries;
determine a respective duty cycle for each switch of the plurality of switches based on the characterization of the of the respective plurality of heterogeneous batteries; and
apply the determined duty cycle to each of the respective plurality of switches such that a charge applied from the grid or a discharge to the grid converges to a balanced state-of-charge (SOC) for each of the plurality of heterogeneous batteries.
2. The battery network of claim 1 , wherein the plurality of heterogeneous batteries is arranged having two or more modules that are connected serially, each module comprising its own plurality of heterogeneous batteries and each module having its own respective switch of the plurality of switches.
3. The battery network of claim 2 , wherein the controller is configured to determine a scalar value for each battery based on the characteristics of batteries within the two or more modules that, when applied to the switches, maintains the duty cycle between 0 and 1.
4. The battery network of claim 3 , wherein the duty cycles applied to each of the switches are determined based on a largest equivalent module capacitance of all of the modules.
5. The battery network of claim 4 , wherein the controller is configured to continuously re-characterize the SOC of each of the plurality of heterogeneous batteries in real time, and determine the scalar values based on the re-characterization.
6. The battery network of claim 1 , wherein the plurality of heterogeneous batteries are arranged having two or more batteries, of the plurality of heterogeneous batteries, arranged in parallel with one another, each of the two or more batteries having its own respective switch of the plurality of switches.
7. The battery network of claim 6 , wherein the controller is configured to determine the duty cycles based on a largest time constant of the determined time constants within each of the two or more batteries.
8. The battery network of claim 7 , wherein battery time constants are determined based on a product of an equivalent resistance and capacitance for each of the two or more batteries.
9. The battery network of claim 1 , wherein the at least one energy source includes one of a conventional electrical grid, a photovoltaic (PV) generator, and a wind farm.
10. The battery network of claim 1 , wherein the controller is configured to apply the determined duty cycles until the balanced SOC is achieved and without re-characterizing the plurality of heterogeneous batteries.
11. A method of balancing a network of batteries, comprising:
characterizing each battery of a plurality of heterogeneous batteries based on an RC equivalent model to determine a time constant for each battery, wherein the batteries are coupled in parallel and coupled to an electric grid that includes an energy source and an energy load, each battery having a switch in series such that a plurality of switches is coupled to the plurality of heterogeneous batteries, with each switch controllable via application of a pulse-width modulation (PWM) frequency;
determining duty cycles for each of the plurality of switches based on the characterization of each respective battery of the plurality of heterogeneous batteries, each duty cycle defined as a proportion of on time between 0 and 1 for a respective battery; and
applying the determined duty cycles via the PWM frequency to each of the respective plurality of switches such that a charge applied from the grid or a discharge to the grid converges to a balanced voltage state for each battery of the plurality of heterogeneous batteries.
12. The method of claim 11 , wherein the plurality of heterogeneous batteries is arranged having two or more modules that are connected serially, each module comprising a plurality of heterogeneous batteries and each module having its own respective switch of the plurality of switches.
13. The method of claim 12 , further comprising determining a scalar value based on the characteristics of batteries within the two or more modules that, when applied to the switches, maintains the duty cycle between 0 and 1.
14. The method of claim 13 , further comprising determining the duty cycles to each of the switches based on a largest equivalent module capacitance of all of the modules.
15. The method of claim 14 , further comprising continuously re-characterizing the state-of-charge (SOC) of the plurality of heterogeneous batteries in real time, and determine the scalar value based on the re-characterization.
16. The method of claim 11 , wherein the plurality of heterogeneous batteries is arranged having two or more of the plurality of heterogeneous batteries arranged in parallel with one another, each of the two or more batteries having its own respective switch.
17. The method of claim 16 , further comprising:
determining the duty cycles based on a largest time constant within each of the two or more batteries; and
determining the battery time constants based on a product of an equivalent resistance and capacitance for each of the two or more batteries.
18. The method of claim 11 , further comprising applying the duty cycle of the switches using a pulse-width modulation (PWM) control.
19. The method of claim 11 , wherein the step of applying the determined duty cycles comprises applying the determined duty cycles until the balanced SOC is achieved and without a step of re-characterizing the plurality of heterogeneous batteries.