Multi-slope droop control

1. A method of controlling two or more sources of electrical power to supply electrical power to a shared bus for provision to an electrical load;

wherein each source of electrical power has a rated power P r , a maximum overload power P m , and is operable along a multi-voltage droop slope, the multi-voltage droop slope including a share region and a catch region, the share region being defined by an upper voltage limit, V high and a base voltage V base , and the catch region being defined by the base voltage V base and a lower voltage limit, V low ;

and the method comprises:

providing a scaling factor, K, for each of the sources of electrical power, the scaling factor operating on a process variable used to control an output of the respective source of electrical power in a control loop, such that the sources of electrical power operate on one of the share region and the catch region; and

when a power demand of the electrical load is less than the sum of the rated powers P r , setting one or more scaling factor K such that each source of electrical power is operating in the share region of the multi-voltage droop slope in which a power split between the sources of electrical power is equal to the ratio of P r for a given source of power to the sum of rated powers P r for the sources of electrical power; and

when the power demand of the electrical load is greater than the sum of the rated powers P r , setting one or more scaling factor K such that each source is operating in the catch region of the multi-voltage droop slope in which a power split between the sources of electrical power is equal to a ratio of P m for a given source of power to the sum of overload powers P m for the sources of electrical power.

2. The method of claim 1 , wherein the scaling factor K for each source of electrical power is defined as K=K r ×sƒ, where K r is set such that a transition point between the share region and the catch region of the multi-voltage droop slope for each source of power is at a value corresponding to the rated power for that source of electrical power, and sƒ is a slope factor greater than or equal to 1.

3. The method of claim 2 , wherein the share region is further defined as a region of the multi-voltage droop slope between 0 watts power output and a base power output P b =P r /sƒ, on the power scale.

4. The method of claim 1 , wherein the catch region is further defined as a region of the multi-voltage droop slope between the base power output P b =P r /sƒ and the maximum power output P m , on the power scale.

5. The method of claim 1 , where the share and catch regions are further defined by a plurality of piecewise linear slopes, each with respective knee points.

6. The method of claim 1 , wherein when the sources of power are operating in the catch region of their respective multi-voltage droop slope, a power manager control system adjusts the scaling factor of one or more sources of power so as to bring the sources of power operating in the catch region back into the share region.

7. The method of claim 1 , wherein a thermal state of each source of power is monitored, and wherein the maximum overload power P m of each source of power is adjusted in accordance with the monitored thermal state of the respective source of power.

8. The method of claim 1 , wherein the process variable used to control the output of the respective source of electrical power is an electrical current output to the shared bus I DC .

9. The method of claim 1 , wherein the two or more sources of electrical power are turbines, and the shared bus is connected to one or more electrical engines for an aircraft.

10. A power management controller, connected to two or more sources of electrical power configured to supply DC power to a shared bus, wherein:

each source of electrical power has a rated power P r , a maximum overload power P m , and is operable along a multi-voltage droop slope, the multi-voltage droop slope including a share region and a catch region, the share region being defined by an upper voltage limited, V high and a base voltage V base , and the catch region being defined by the base voltage V base and a lower voltage limit V low ; and

the power management controller is configured to perform the method of claim 1 .

11. An aircraft, including:

two or more sources of electrical power, connected to a shared bus;

the power management controller of claim 10 ; and

one or more electric engines, for propelling the aircraft, connected to the shared bus and driven by the two or more sources of electrical power.

12. A ship, including:

two or more sources of electrical power, connected to a shared bus;

the power management controller of claim 10 ; and

one or more electric loads, connected to the shared bus and provided with power by the two or more sources of electrical power.

13. A non-transitory computer readable medium comprising instructions which, when executed by a power management controller configured to control two or more sources of electrical power to supply electrical power to a shared bus for provision to an electrical load, causes the power management controller to perform the method of claim 1 .