Vehicle propulsion system having an energy storage system and optimized method of controlling operation thereof

1. A control system for controlling the supply of power from an energy storage system to a DC bus of a vehicle propulsion system, the control system comprising a controller configured with a database comprising a degradation model for each energy storage unit (ESU) of the energy storage system, the controller programmed to:

determine an initial power split between a high-specific power ESU and a high-specific energy ESU of the energy storage system;

monitor a state of charge (SOC) of the high-specific power ESU and the high-specific energy ESU;

monitor a power demand of the vehicle propulsion system;

input the initial power split and monitored SOC of each ESU into the different degradation models for the high-specific power ESU and high-specific energy ESU to determine a change in the SOC for each ESU;

determine whether the change in the SOC for each ESU exceeds a threshold value for the change in the SOC;

and

selectively allocate power to the DC bus from the high-specific power ESU and high-specific energy ESU during real-time operation of the vehicle propulsion system based on the degradation models and the power demand such that the threshold value for the change in the SOC for each ESU is not exceeded.

2. The control system of claim 1 wherein the power demand of the vehicle propulsion system is based on at least one of a user input and a predetermined vehicle duty cycle.

3. The control system of claim 2 wherein the controller is further programmed to iteratively adjust the allocation of power to the DC bus in real-time to maximize at least one of a performance of the vehicle propulsion system and an operating life of the energy storage system.

4. The control system of claim 3 wherein the controller is further programmed to run a power split algorithm that defines a power split coefficient for each ESU of the energy storage system.

5. The control system of claim 3 wherein the controller is further programmed to selectively operate a bi-directional DC-DC converter coupled between the energy storage system and the DC bus.

6. The control system of claim 1 wherein the controller is further programmed to run a multi-objective optimization algorithm.

7. A method for supplying power to a DC bus from an energy storage system of a vehicle propulsion system, the vehicle propulsion system including a controller configured with a database comprising a charging degradation model for each energy storage unit (ESU) of the energy storage system, the method comprising:

determining a power split between a high-specific power ESU and a high-specific energy ESU at a first time;

monitoring a state of charge (SOC) of the high-specific power ESU and high-specific energy ESU at the first time and at a second time;

inputting the initial power split and monitored SOC of each ESU into the different degradation models for the high-specific power ESU and high-specific energy ESU to determine a change in the SOC for each ESU;

determining a first power demand of the vehicle propulsion system based on at least one of a first user input and a predetermined vehicle duty cycle;

defining a first power allocation between the high-specific power ESU and high-specific energy ESU based on the first power demand, the SOC at the first time, and the degradation models;

inputting the change in the SOC into a system constraint function;

modifying the first power allocation if the change in the SOC violates the system constraint function;

determining a second power demand of the vehicle propulsion system based on at least one of a second user input and the predetermined vehicle duty cycle; and

defining a second power allocation between the high-specific power ESU and high-specific energy ESU based on the second power demand, the SOC at the second time, and the degradation models in a manner that does not violate the system constraint function, wherein the second power allocation differs from the first power allocation.

8. The method of claim 7 further comprising defining the first power allocation and the second power allocation using a multi-objective optimization algorithm.

9. The method of claim 7 further comprising controlling at least one bi-directional DC-DC voltage converter assembly to cause the energy storage system to supply power to a DC bus in accordance with the first and second power allocations.

10. The method of claim 7 further comprising accessing a database having stored thereon the predetermined duty cycle for the vehicle propulsion system.

11. A vehicle propulsion system comprising:

a bi-directional converter coupled to a DC bus;

an energy storage system comprising a high-specific power energy storage unit (ESU) and a high-specific energy ESU, wherein the high-specific power ESU is coupled to the first bi-directional converter; and

a controller configured with a database comprising degradation models for the high-specific power ESU and high-specific energy ESU, the controller programmed to:

determine an initial power split between the high-specific power ESU and the high-specific energy ESU;

determine a power demand of the vehicle propulsion system;

monitor a state of charge (SOC) of the high-specific power ESU and the high-specific energy ESU;

input the initial power split and monitored SOC of each ESU into the different degradation models for the high-specific power ESU and high-specific energy ESU to determine a change in the SOC for each ESU;

define a plurality of power allocations for the energy storage system based on the different degradation models for the high-specific power and high-specific energy ESUs such that a threshold value for the change in the SOC for each ESU is not exceeded;

control the first bi-directional converter to transfer power from the high-specific power ESU to the DC bus based on a power allocation of the plurality of power allocations; and

selectively supply power to the DC bus from the high-specific power and high-specific energy ESUs during real-time operation of the vehicle propulsion system based on the power demand and the plurality of power allocations.

12. The vehicle propulsion system of claim 11 wherein a power allocation of the plurality power allocations allocates a first portion of the power demand to the high-specific power ESU and a second portion of the power demand to the high-specific energy ESU.

13. The vehicle propulsion system of claim 11 wherein the controller is further programmed to define the plurality of power allocations using a multi-objective optimization algorithm.