Device for supplying power to a wired drone

Abstract

The present invention relates to a device for supplying electrical power to a wired system for a drone (1). The device according to the invention includes at least one power converter (4) on the ground and one power converter (2) at the level of the drone (1), regulation at the level of the converter on the ground ensures that the output voltage of the power converter (4) on the ground increases when the output current of the power converter (4) on the ground increases. The method according to the invention is intended for all wired drones, the wire (3) of which is used to supply electrical power to the drone (1).

Claims

1. A device for supplying power to a wired drone, including at least: a ground based power converter, a power converter at a level of the drone, a cable connecting the power converters and, wherein a regulation of the ground based power converter ensures that a voltage U.sub.B delivered by the ground based power converter increases when a current I.sub.B delivered by the ground based power converter increases, and the voltage U.sub.B occurs over a power range of normal use of the drone and wherein the regulation of the ground based power converter ensures a voltage U.sub.D at an input of the power converter at the level of the drone, is close to an optimal operating voltage of the power converter at the level of the drone, wherein the power converter at the level of the drone has a fixed ratio of output voltage with respect to the voltage U.sub.D at the input of the power converter at the level of the drone.

2. The device according to claim 1, wherein the regulation of the ground based power converter compensates at least partially a voltage drop between an output of the ground based power converter and the input of the power converter at the level of the drone, due to a resistance R.sub.F of the cable.

3. The device according to claim 2, wherein the voltage U.sub.B delivered by the ground based power converter increases linearly with the current I.sub.B, according to an affine law U.sub.B=U.sub.0+R.sub.BI.sub.B where U.sub.0 designates a constant voltage, close to the optimal operating voltage of the power converter at the level of the drone, and R.sub.B designates a constant approximately equal to the resistance R.sub.F of the cable.

4. The device according to claim 1, wherein the voltage U.sub.B delivered by the ground based power converter increases linearly with the current I.sub.B, according to an affine law U.sub.B=U.sub.0+R.sub.BI.sub.B where U.sub.0 designates a constant voltage, close to the optimal operating voltage of the power converter at the level of the drone, and R.sub.B designates a constant approximately equal to a resistance R.sub.F of the cable.

5. The device according to claim 1, wherein the voltage U.sub.B delivered by the ground based power converter increases linearly with the current I.sub.B, according to an affine law U.sub.B=U.sub.0+R.sub.BI.sub.B wherein U.sub.0 is defined by a function U.sub.0(I.sub.B), such that this function is close to a function that describes the optimal operating voltage of the power converter at the level of the drone as a function of the current I.sub.B and R.sub.B designates a constant approximately equal to a resistance R.sub.F of the cable.

6. The device according to claim 1, wherein a variation of a resistance R.sub.F of power supply strands of the cable with temperature is taken into account, by measuring a temperature of the cable in one or several location(s), or measuring an ambient temperature, or both.

7. The device according to claim 1, wherein a resistance R.sub.F of the cable is reevaluated regularly using measurements of U.sub.B, U.sub.D, I.sub.B and Ohm's law.

8. The device according to claim 1, wherein the regulation of the ground based power converter prevents oscillations of a voltage in the power converter at the level of the drone or the ground based power converter.

9. The device according to claim 1, wherein a circuit on the drone, interposed between the cable and the power converter at the level of the drone, includes at least one energy storage device and absorbs voltage variations during a sudden variation in a power consumed by the drone.

10. The device according to claim 1, wherein U.sub.B is servo-controlled directly to a measurement of a voltage U.sub.D at the input of the power converter at the level of the drone, a value of the voltage U.sub.D being transmitted via the cable.

11. The device according to claim 1, wherein the regulation of the ground based power converter maximizes a ratio P.sub.M/T.sub.F or a ratio P.sub.M/I.sub.B, wherein P.sub.M designates a power available for motors of the drone, and T.sub.F is a temperature of the cable.

12. The device according to claim 1, wherein the voltage U.sub.B delivered by the ground based power converter increases linearly with the current I.sub.B, according to an affine law U.sub.B=U.sub.0+R.sub.BI.sub.B wherein U.sub.0 is defined by a function U.sub.0(I.sub.B), such that this function is close to a function that describes the optimal operating voltage of the power converter at the level of the drone as a function of a power supply current of the power converter at the level of the drone and R.sub.B designates a constant approximately equal to a resistance R.sub.F of the cable.

13. The device according to claim 12, wherein a variation of the resistance R.sub.F of power supply strands of the cable with temperature is taken into account, by measuring a temperature of the cable in one or several location(s), or measuring an ambient temperature, or both.

14. The device according to claim 13, wherein the resistance R.sub.F of the cable is reevaluated regularly using measurements of U.sub.B, U.sub.D, I.sub.B and Ohm's law.

15. The device according to claim 14, wherein the regulation of the ground based power converter prevents oscillations of a voltage in the power converter at the level of the drone or the ground based power converter.

16. The device according to claim 1, wherein the fixed ratio of output voltage of the power converter at the level of the drone is 1/16.

17. The device according to claim 16, wherein the power converter at the level of the drone has a maximum efficiency point at about 400V.

18. The device according to claim 15, wherein the fixed ratio of output voltage of the power converter at the level of the drone is 1/16.

19. The device according to claim 18, wherein the power converter at the level of the drone has a maximum efficiency point at about 400V.

Description

SUMMARY DESCRIPTION OF THE FIGURES

(1) FIG. 1 represents a drone (1) provided with a power converter (2) connected by a wire (3) to a ground base (5) provided with a power converter (4) connected to the mains grid (6).

(2) FIG. 2 allows comparing the voltages U.sub.B and U.sub.D as a function of the current I.sub.B for a conventional power supply device (FIG. 2a) and a power supply device according to a particular embodiment of the invention (FIG. 2b). In full line, the voltage U.sub.B in Volt is represented as a function of the current I.sub.B in Ampere, in dotted line the voltage U.sub.D in Volt as a function of the current I.sub.B in Ampere. It can be seen that the voltage U.sub.D available for the drone (1) drops with the power demanded for a conventional power supply device, whereas the voltage U.sub.D available for the drone (1) remains constant regardless of the power demanded for the power supply device according to a particular embodiment of the invention.

(3) FIG. 3 illustrates the reaction of different power supply devices according to the invention when the power of the drone (1) increases suddenly.

(4) FIG. 3a represents the current I.sub.B in Ampere as a function of time in seconds. This current doubles suddenly at an instant called t.

(5) FIGS. 3b, 3c, 3d represent the reactions as a function of time of three different power supply devices according to the principle illustrated in FIG. 2b. For these three figures, we find in full line the voltage U.sub.B as a function of time in seconds and in dotted line the voltage U.sub.D as a function of time in seconds.

(6) FIG. 3b corresponds to a device whose servo-control corresponds to a second-order system. It can be seen that the voltage U.sub.D varies strongly just after the instant t, which could lead to a major malfunction, either by overvoltage or under-voltage.

(7) FIG. 3c corresponds to a device whose servo-control corresponds to a first-order system. It can be seen that the voltage U.sub.D also varies strongly just after the instant t but there is no oscillation. The only possible malfunction is under-voltage.

(8) FIG. 3d corresponds to the same device as in FIG. 3c but was added immediately upstream of the power converter (2) of the drone (1) a small capacity to cope with voltage variations and to smoothen U.sub.D.

(9) FIG. 4 illustrates the reaction of different devices according to the invention when the power of the drone (1) decreases suddenly.

(10) FIG. 4a represents the current I.sub.B in Ampere as a function of time in seconds. This current is suddenly divided by 2 at an instant called t.

(11) FIGS. 4b and 4c represent the reactions as a function of time of two different power supply devices according to the principle illustrated in FIG. 2b. For these two figures, we find in full line the voltage U.sub.B as a function of time in seconds and in dotted line the voltage U.sub.D as a function of time in seconds.

(12) FIG. 4b corresponds to the same device as that of FIG. 3c, and FIG. 4c corresponds to the same device as that of FIG. 3d.

(13) It can thus be seen that the device of FIG. 3d or 4c is optimal for the operation of the system.

(14) FIG. 5a represents, in dotted line, the power supply voltage U.sub.D which ensures a maximum efficiency of a power converter (2) located on the drone (1) as a function of the current I.sub.B which traverses the wire (3). It can be seen here that the optimal voltage U.sub.D varies considerably with the input current I.sub.B.

(15) FIG. 5b represents in full line the voltage U.sub.B delivered by a power supply device according to the invention which allows obtaining the optimal voltage U.sub.D to offer the drone (1) a maximum power as a function of the current I.sub.B.

DETAILED DESCRIPTION

(16) The ways of achieving the invention and their variants which follow illustrate precisely the invention and are not limiting other ways of achieving the power supply device according to the invention.

(17) An optimal embodiment of the power supply device according to the invention is achieved as follows.

(18) A drone (1) with a maximum power of 2600 W supplied with 25V direct voltage is used. This drone (1) has a power converter (2) with a 1/16 fixed ratio connected to a wire or cable. This wire or cable, 100 m length, is constituted by two electric strands, an aramid strand, all in a plastic sheath. The resistance of the used electric strands is 0.06 ohm per meter. This wire or cable (3) is connected to a power converter (4) in a ground base (5). The converter of the ground base (5) is supplied by the mains grid (6) with 230V alternating voltage. The ground base (5) includes a winding drum of the wire, a motor connected to the winding drum of the wire or cable (3) for winding or unwinding the wire or cable (3). A fan cools the winding drum of the wire (3). A temperature sensor is present on the winding drum of the wire (3) to prevent the user from possible overheating of the wound wire (3).

(19) The drone (1) has various on-board instruments and communicates in real-time with the ground base (5) through the technique called Power-Line Communication, well known to those skilled in the art. The information therefore passes via the power supply strands.

(20) The power converter (2) at the level of the drone (1) has its maximum efficiency point at about 400V, requires not exceeding 410V at the input, otherwise it stops operating, and also requires never being supplied at more than 480V under penalty of irreparable damage. This power converter (2) being with a 1/16 fixed ratio, it outputs a 25V voltage for an input voltage equal to 400V.

(21) The power converter (4) at the level of the ground base (5) uses the so-called Power Factor Correction technique, well known to those skilled in the art. The power controller is modified so that the output voltage U.sub.B follows the law expressed in Volt U.sub.B=min (400+R.sub.BI.sub.B, 480) where I.sub.B is the output current of the power converter (4) expressed in Ampere, and R.sub.B a constant expressed in Ohm, in our case equal to 12, which one has been selected equal to R.sub.F the resistance of the wire. To obtain such a law, the modification of the power controller requires simple electronic components such as diodes, resistors, current sensors at the output of the converter, analog multipliers. Particular care is taken to ensure that the components are adjusted in such a way that the regulation, in case of sudden power variations, ensures that the voltage does not undergo oscillations. Thus, the voltage at the level of the power converter (2) of the drone (1) does not exceed 410V which would cause the converter of the drone (1) to stop and the drone (1) to fall. The selection and the way in which the components are adjusted are known to those skilled in the electronics industry and do not require further explanation.

(22) At the input of the power converter (2) of the drone (1), the voltage U.sub.D is equal to U.sub.B minus the ohmic losses in the wire (3) namely min (400+R.sub.BI.sub.B, 480)R.sub.FI.sub.B Volts. Thus, as long as I.sub.B does not exceed 80/12=6.7 A, the voltage U.sub.D is almost constant and equal to 400V.

(23) Based on the heat-up of the wires at the level of the ground base (5), it is estimated that the current flowing in the wires should not exceed 6.7 A in continuous operation mode. The maximum power available for the drone (1) in continuous operation mode is therefore equal to 400*6.7=2700 W at the input of the power converter (2) of the drone (1), and the maximum power at the output of the power converter (2) of the drone (1) is equal to about 2600 W. With a conventional 400V fixed voltage power supply at the level of the ground base (5), the maximum available power would be only 320*6.7=2150 W at the input of the power converter (2) of the drone (1), and only 1800 W at the output of the power converter (2) because the efficiency is not optimal at 320V.

(24) With our device according to the invention, a gain in power of 45% is thus obtained on the maximum power supplied to the drone (1) in continuous operation mode compared to a conventional system, and especially with equal heat-up of the wires.

(25) In the embodiment of the device according to the preceding invention, the variation of the resistance R.sub.F of the power supply strands with temperature is not taken into account. The power supply strands of this first embodiment are made of copper, and the resistivity of copper varies with temperature: the resistivity increases by about 50% between 20 degrees Celsius and 70 degrees Celsius. To take into account the change of resistance R.sub.F of the wire (3) as a function of the temperature, two variations of the embodiment are possible.

(26) The first variation of the first embodiment according to the invention consists in using the information of the temperature sensor on the winding drum of the wire. The temperature measured by this sensor is called T.sub.F. In addition, a revolution counter on the winding drum of the wire (3) allows knowing the length l of the wire (3) still wound on the drum. Finally, a temperature sensor on the ground base (5) allows estimating the temperature T.sub.A of the ambient air. We notice then that the resistance RE of the wire (3) is a function f of T.sub.A, T.sub.F, and I: R.sub.F=f (T.sub.A, T.sub.F, I), a function that has been determined theoretically and experimentally verified. The output law of the power converter (4) is then replaced by the law U.sub.B=min (U.sub.Bf(T.sub.A, T.sub.F, I) I.sub.B, 480).

(27) The second variation of the embodiment according to the invention consists in measuring regularly, every minute, U.sub.D the voltage at the input of the power converter (2) located on the drone (1), U.sub.B the voltage at the output of the power converter (4) of the ground base (5), and I.sub.B the current flowing in the wire. The measurement of U.sub.D is sent to the ground base (5) via the power-line communication technique. The resistance R.sub.F of the power supply strands of the wire (3) is then reevaluated by the Ohm law, by dividing the difference U.sub.BU.sub.D by I.sub.B, and the regulation regulates according to the law min(400+R.sub.FI, 400).

(28) Another variation of the embodiment of the invention consists in carrying out a software-type rather than electronic voltage regulation of U.sub.B as previously described.

(29) A third variation of the embodiment according to the invention consists in regulating U.sub.B directly on the measured value of U.sub.D, this then requires a measurement of U.sub.D at high frequency, very significantly higher than one Herz, preferably in the range of a dozen kilohertz.

(30) The ways of achieving the invention and their variants disclosed in the foregoing illustrate precisely the invention and are not limiting other ways of achieving the power supply device according to the invention.

POSSIBILITIES OF INDUSTRIAL APPLICATIONS

(31) The power supply system according to the invention is capable of supplying power to all wired drones to the extent that it allows increasing the range and the payload compared to existing power supply systems.