Motor control topology for airborne power generation and systems using same

1. A system comprising:

a plurality of drive units coupled to a plurality of propellers, wherein each drive unit comprises a single motor/generator and a single motor controller, and wherein the plurality of drive units includes a first drive-unit pair and a second drive-unit pair; and

a high-voltage bus connecting the motor controllers in the first drive-unit pair to a tether,

a low-voltage bus connecting the motor controllers in the second drive-unit pair to the tether, and

an intermediate-voltage bus connecting the motor controllers of the first drive-unit pair in series with the motor controllers of the second drive-unit pair;

wherein the motor controllers in the first drive-unit pair are connected in parallel via the high-voltage bus and the intermediate-voltage bus; and

wherein the motor controllers in the second drive-unit pair are connected in parallel via the intermediate-voltage bus and the low-voltage bus.

2. The system of claim 1 , further comprising a motor control system operable to send control signals to each motor controller, such that each drive unit is separately controllable.

3. The system of claim 2 , wherein the motor control system is configured to generate control signals that balance the voltage across the plurality of drive units.

4. The system of claim 3 , wherein the motor control system is configured to generate control signals for two or more of the motor controllers such that a desired torque is applied to an aerial vehicle of the system.

5. The system of claim 2 , wherein the motor control system is configured to receive data related to the plurality of drive units.

6. The system of claim 5 , wherein the control system is operable to determine the control signals based at least in part on the received data related to the plurality of drive units.

7. The system of claim 2 , wherein the control system is configured to:

detect a failure of at least one motor or motor controller in a particular pair of drive units; and

in response to the failure, generate control signals for one or more of the motor controllers that bypass the particular drive-units pair.

8. The system of claim 1 , wherein the motor/generators comprise a number of phase windings, and wherein the motor controllers are configured to source power to the motor/generators at times corresponding to the number of phase windings.

9. The system of claim 1 , wherein each pair of drive units comprises a first drive unit arranged at a first location of an aerial vehicle of the system and a second drive unit arranged at a second location on the aerial vehicle, and wherein, for each pair of drive units, the location of the first drive unit mirrors the location of the second drive unit about a center of mass of the aerial vehicle.

10. The system of claim 1 , further comprising at least one override switch that is operable to bypass at least one pair of drive units.

11. The system of claim 1 , further comprising on-ground equipment adapted to adjust tether voltage when a motor controller fails so as to maintain equal bus voltage over each drive-unit pair.

12. The system of claim 1 , wherein each motor controller is a low-voltage motor controller, wherein the tether comprises a high-voltage transmission line, and wherein the arrangement of the at least two drive units allows for interfacing of the low-voltage motor controllers with the high-voltage transmission line.

13. The system of claim 1 , wherein the drive units are located on an aerial vehicle of the system such that, if any drive-unit pair of the plurality is disabled, control authority and force balance on each of pitch, yaw, and thrust axis of the aerial vehicle is maintained.

14. A system comprising:

a plurality of drive units coupled to a plurality of propellers, wherein each drive unit comprises a single motor/generator and a single motor controller, and wherein the plurality of drive units form a plurality of drive-unit pairs;

a tether;

a high-voltage bus connecting the motor controllers in a first drive-unit pair of the plurality to the tether;

a low-voltage bus connecting the motor controllers in a second drive-unit pair of the plurality to the tether; and

an intermediate-voltage bus configured to connect the plurality of drive-unit pairs in series via the motor controllers in each of the plurality of drive-unit pairs;

wherein the motor controllers in the first drive-unit pair of the plurality are connected in parallel via the high-voltage bus and the at least one intermediate-voltage bus; and

wherein the motor controllers in the second drive-unit pair of the plurality are connected in parallel via the at least one intermediate-voltage bus and the low-voltage bus.

15. The system of claim 14 , wherein the plurality of drive units further comprise a third drive-unit pair and a fourth drive-unit pair, and wherein the intermediate-voltage bus comprises a first intermediate-voltage bus, a second intermediate-voltage bus, and a third intermediate-voltage bus, wherein:

(i) the first intermediate-voltage bus is configured to connect the first drive-unit pair in series with the third drive-unit pair via the motor controllers in the first and third drive-unit pairs,

(ii) the second intermediate-voltage bus is configured to connect the third drive-unit pair in series with the fourth drive-unit pair via the motor controllers in the third and fourth drive-unit pairs,

(iii) the third intermediate-voltage bus is configured to connect the fourth drive-unit pair in series with the second drive-unit pair via the motor controllers in the fourth and second drive-unit pairs,

(iv) the first and second intermediate-voltage buses are configured to connect the motor controllers in the third drive-unit pair in parallel, and

(v) the second and third intermediate-voltage buses are configured to connect the motor controllers in the fourth drive-unit pair in parallel.

16. The system of claim 14 , further comprising a motor control system operable to send control signals to each motor controller, such that each drive unit is separately controllable.

17. The system of claim 16 , wherein the motor control system is configured to generate control signals that balance the voltage across the plurality of drive units.

18. The system of claim 14 , wherein an average voltage at the at least one intermediate-voltage bus is approximately half of an incoming voltage on the tether.

19. A system comprising:

an aerial vehicle comprising a plurality of propellers;

a plurality of drive units coupled to the plurality of propellers, wherein each drive unit comprises a single motor/generator and a single motor controller, and wherein the plurality of drive units includes a first drive-unit pair and a second drive-unit pair; and

a high-voltage bus connecting the motor controllers in the first drive-unit pair to a tether,

a low-voltage bus connecting the motor controllers in the second drive-unit pair to the tether, and

an intermediate-voltage bus connecting the motor controllers of the first drive-unit pair in series with the motor controllers of the second drive-unit pair;

wherein the motor controllers in the first drive-unit pair are connected in parallel via the high-voltage bus and the intermediate-voltage bus; and

wherein the motor controllers in the second drive-unit pair are connected in parallel via the intermediate-voltage bus and the low-voltage bus.

20. The system of claim 19 , further comprising a motor control system operable to send control signals to each motor controller, such that each drive unit is separately controllable, wherein the motor control system is configured to apply a control scheme that generates control signals that, for each drive unit, evens power outtake across each motor/generator of the plurality of the motor/generators.