Multi-motor switching control system and method for increased efficiency and energy savings
A multi-motor switching system and method for obtaining a global optimization of performance criteria that takes into account variables and conditions across an entire driving cycle. The controller of the system is adapted to conduct a global optimization in that it determines the most optimal distribution of motor loads over an entire trip or driving cycle, as opposed to sequentially determining the optimized solution for a given point of time and localized set of current condition. In one embodiment where the control system provides for global optimization, the controller receives trip information through a trip planning tool. The controller utilizes the trip information to generate a driving cycle and further incorporates this information into the optimization process performed by the controller to determine the optimal solution for the entire trip.
1. A multi-motor system capable of performing a global optimization in order to determine an optimal contribution of torque from motors in the system based on a given torque demand in order to achieve a target efficiency value over an entire driving cycle while remaining within one or more constraints, the system comprising:
a plurality of motors mechanically coupled to a shaft, wherein the plurality of motors are electric motors;
a database that stores efficiency data associated with each of the plurality of motors, wherein the efficiency data represents an efficiency of a motor across possible combinations of speed and torque;
a controller for receiving driving cycle information for a driving cycle, and for generating torque commands for the plurality of motors;
wherein the controller generates torque commands for the plurality of motors by performing an optimization analysis across all time periods in the driving cycle with respect to potential combinations of torque contributions by the motors, the optimization analysis comprising:
determining based on the driving cycle information a required shaft speed and torque across all time periods in the driving cycle;
calculating, based on the efficiency data, a cost function for an amount of energy used across all time periods in the driving cycle for each of the potential combinations of torque contributions by the plurality of motors;
identifying from the potential combinations of torque contributions one or more combinations of torque contributions that meet the target efficiency value based on the cost function and that remains within the one or more constraints; and
generating, for each time period in the driving cycle, torque command signals for each of the plurality of motors in order to cause the plurality of motors to drive the shaft according to the one or more combinations of torque contributions that meet the target efficiency value while remaining within the one or more constraints.
2. The system of claim 1 wherein the target efficiency value is the maximum efficiency capable over the driving cycle.
3. The system of claim 2 wherein the controller estimates for each time period in the driving cycle the energy consumed, and wherein the controller outputs an estimated total energy consumption for the driving cycle.
4. The system of claim 1 wherein the one or more constraints includes the temperature for each motor.
5. The system of claim 1 wherein the optimization analysis further comprises, with respect to each potential combination of torque contributions by the motors and for each time period in the driving cycle, calculating as part of the cost function the effect on the efficiency of each motor in the plurality of motors at future periods in the driving cycle based on the efficiency data and one or more transients.
6. The system of claim 1 wherein the one or more transients includes thermal transients, wherein the efficiency data further represents the efficiency of a motor across different operating temperatures, and wherein the optimization analysis performed by the controller further comprises calculating thermal transients to determine an estimated temperature for each of the plurality of motors at the end of the next time period.
7. The system of claim 1 wherein the system is housed within an electric vehicle.
8. The system of claim 1 wherein the system further comprises a trip planning tool, and wherein the trip planning tool generates the driving cycle information.
9. The system of claim 1 wherein the optimization analysis performed by the controller further comprises integrating an optimization of energy regeneration from braking.
10. A method of performing a global optimization in order to determine an optimal contribution of torque from motors in a vehicle based on a given torque demand in order to achieve a target efficiency value over an entire driving cycle while remaining within one or more constraints, the method comprising:
storing efficiency data associated with each of the plurality of motors, wherein the plurality of motors are electric motors, and wherein the efficiency data represents an efficiency of a motor across possible combinations of speed and torque;
receiving driving cycle information for a driving cycle;
generating torque commands for the plurality of motors by performing an optimization analysis across all time periods in the driving cycle with respect to potential combinations of torque contributions by the motors, the optimization analysis comprising:
determining based on the driving cycle information a required shaft speed and torque across all time periods in the driving cycle;
calculating, based on the efficiency data, a cost function for an amount of energy used across all time periods in the driving cycle for each of the potential combinations of torque contributions by the plurality of motors;
identifying from the potential combinations of torque contributions one or more combinations of torque contributions that meet the target efficiency value based on the cost function and that remains within the one or more constraints;
and generating, for each time period in the driving cycle, torque command signals for each of the plurality of motors in order to cause the plurality of motors to drive the shaft according to the one or more combinations of torque contributions that meet the target efficiency value while remaining within the one or more constraints.
11. The method of claim 10 wherein the target efficiency value is the maximum efficiency capable over the driving cycle.
12. The method of claim 11 further comprising estimating for each time period in the driving cycle the energy consumed, and outputting an estimated total energy consumption for the driving cycle.
13. The method of claim 10 wherein the one or more constraints includes the temperature for each motor.
14. The method of claim 10 wherein the optimization analysis further comprises, for each potential combination of torque contributions by the motors and for each time period in the driving cycle, calculating as part of the cost function the effect on the efficiency of each motor in the plurality of motors at future periods in the driving cycle based on the efficiency data and one or more transients.
15. The method of claim 14 wherein the one or more transients includes thermal transients, wherein the efficiency data further represents the efficiency of a motor across different operating temperature, and wherein the optimization analysis further comprises calculating thermal transients to determine an estimated temperature for each of the plurality of motors at the end of the next time period.
16. The method of claim 10 wherein the method is performed by a controller housed within an electric vehicle.
17. The method of claim 10 wherein the step of generating the driving cycle information is performed using a trip planning tool.
18. The method of claim 10 wherein the optimization analysis performed by the controller further comprises integrating an optimization of energy regeneration from braking.