METHOD FOR DRIVING AN AIR VEHICLE, AND AIR VEHICLE

Abstract

The invention relates to a method for driving an air vehicle using a multilevel converter with at least two converter modules. A first operating voltage is applied to at least one of the converter modules in a first operating state, and a second operating voltage which is lower than the first operating voltage is applied to the converter module in a second operating state. The air vehicle is designed to carry out such a method and comprises an electric drive which has at least one multilevel converter with at least two converter modules, each of which is designed and connected so as to be supplied with a first operating voltage in a first operating state and with a second operating voltage which is lower than the first operating voltage in a second operating state. Advantageously, the air vehicle is an airplane, in particular a hybrid electric airplane.

Claims

1. A method for driving an aircraft (10), using a multilevel inverter (70) having at least two inverter modules (SM), wherein, in a first operating state, a first operating voltage is applied to at least one of the inverter modules (SM) and, in a second operating state, a second operating voltage, lower than the first one, is applied to at least one of the inverter modules (SM).

2. The method as claimed in claim 1, wherein, in the first operating state, a respective first operating voltage is applied to at least two of the inverter modules (SM) and, in a second operating state, a respective second operating voltage, in each case lower than the first one, is applied to at least two of the inverter modules (SM).

3. The method as claimed in either of the preceding claims, wherein, in the first operating state, a respective first operating voltage is applied to all of the inverter modules (SM) and, in a second operating state, a respective second operating voltage, in each case lower than the first one, is applied to all of the inverter modules (SM).

4. The method as claimed in one of the preceding claims, wherein the first and the second operating voltage are applied in a pulsed manner, wherein the second operating voltage has longer pulse durations than the first operating voltage.

5. The method as claimed in one of the preceding claims, wherein the multilevel inverter is used to convert a generated AC voltage of a generator into an AC voltage feeding a drive motor.

6. The method as claimed in one of the preceding claims, wherein the power provided by way of the multilevel inverter (70) in the second operating state amounts to at most 80 percent of the maximum power in the first operating state, preferably amounts to at most 70 percent and ideally at most 60 percent.

7. The method as claimed in one of the preceding claims, wherein the second operating state is implemented during or after a takeoff and/or ended before or during a landing of the aircraft.

8. The method as claimed in one of the preceding claims, wherein the first operating state is implemented before and/or during at least part of the takeoff of the aircraft (10) and/or before and/or during at least part of the landing of the aircraft (10).

9. The method as claimed in one of the preceding claims, wherein the second operating state is implemented above a minimum altitude of the aircraft (10).

10. The method as claimed in one of the preceding claims, performed in order to drive a hybrid airplane.

11. An aircraft for performing a method as claimed in one of the preceding claims, having an electric drive (20) that comprises at least one multilevel inverter having at least two inverter modules (SM) that are in each case designed and connected so as to be fed with a first operating voltage in a first operating state and with a second operating voltage, lower than the respective first one, in a second operating state.

12. The aircraft as claimed in the preceding claim, wherein a control device is present, which control device is designed in each case to switch the first and/or the second operating state depending on the altitude or a flight maneuver, in particular depending on a takeoff or landing procedure that is initiated or imminent.

13. The aircraft as claimed in either of the preceding claims, which is an airplane (10), in particular an electric hybrid airplane (10).

Description

[0028] The invention is explained in more detail below with reference to an exemplary embodiment illustrated in the drawing.

[0029] In the figures:

[0030] FIG. 1 schematically shows an aircraft having a drivetrain with a multilevel inverter in a block diagram,

[0031] FIG. 2 schematically shows the multilevel inverter of the aircraft according to FIG. 1 in a block diagram, and

[0032] FIG. 3 schematically shows an inverter module of the multilevel inverter according to FIG. 2 in a block diagram.

[0033] The aircraft illustrated in FIG. 1 is an electric hybrid airplane 10 and has a drivetrain 20. The drivetrain 20 comprises a turbine 30, which provides mechanical rotational energy when required in a manner known per se by combustion of fuel and transmits it to a generator 40 for converting the mechanical energy into electrical energy. The generator 40 makes the electrical energy available by way of an AC voltage on the output side.

[0034] The generator 40 feeds a rectifier 50, which rectifies the AC voltage of the generator 40. Instead of a rectifier 50, in a further exemplary embodiment not illustrated specifically, an active inverter may be provided. In the event of excess energy provided by way of the generator 40, an electric battery 60 of the electric hybrid airplane 10 is charged with the rectified voltage. The battery 60 is provided as a permanent energy source for the electric airplane 10. In the event of drainage of the battery 60 or a greatly increased energy demand, the turbine 30 and the generator 40 may be called upon for the increased supply of energy.

[0035] On the output side of the rectifier 50 and the battery 60 a multilevel inverter 70 of modular construction is connected thereto, which multilevel inverter converts the DC voltage delivered by the rectifier 50 and/or the battery 60 into an AC voltage of appropriate frequency suitable for operating a propeller motor 80 of the airplane 10. The propeller motor 80 is connected mechanically to the drive of a propeller 90 of the airplane 10.

[0036] The multilevel inverter 70 constitutes a voltage intermediate circuit inverter, which (see also FIG. 3) has in each case three parallel-connected series circuits of in case two inverter modules SM per phase U, V, W. The individual inverter modules SM in each case comprise two switches T0, T1 formed by way of IGBTs (IGBTinsulated-gate bipolar transistor) with two freewheeling diodes D0, D1. In principle, in further exemplary embodiments, which otherwise correspond to the one shown, other transistors, for example power MOSFETS, may also be used as switches. The switches T0, T1 are switched by way of pulse width modulation (in principle, other modulation methods may also be used in further exemplary embodiments). The intermediate circuit voltage V.sub.C, applied here to the capacitor C, of the intermediate circuit between P and N is in each case converted into the phase voltage V.sub.SM of an inverter module by way of the inverter module SM.

[0037] During the flight of the airplane 10, the propeller motor 80 generally requires a highly predictable load profile: power peaks thus occur only at the beginning during a takeoff and an ascent of the airplane 10. During the rest of the flight time, in particular during cruising, only around 60% of this power is required.

[0038] Accordingly, power peaks are catered for by way of the battery 60, whereas the turbine 30 and the generator 40 have smaller dimensions.

[0039] The power fed to the propeller motor 80 is controlled by way of the multilevel inverter 70 via the current of the multilevel inverter 70, by switching voltage pulses of appropriate magnitude and length at individual semiconductor components of submodules of the multilevel inverter 70, here at the switches T0, T1.

[0040] These voltages prove to be highly critical in the case of high altitudes of the airplane 10: in principle, above a specific altitude of the airplane 10, the probability of failure of the switches T0, T1 increases greatly on account of cosmic radiation.

[0041] In this case, the probability of failure on account of cosmic radiation at such an altitude is related to the respectively applied voltage: if a specific value of the voltage is exceeded, then so much charge is generated in the semiconductor component, when the semiconductor component interacts with cosmic radiation, that it becomes conductive for a short time and is permanently destroyed by heating.

[0042] In the multilevel inverter 70 of the airplane 10 according to the invention, this problem does not occur in the method according to the invention, by way of which method the multilevel inverter 70 is controlled.

[0043] The airplane 10 is now driven by way of the method according to the invention as follows:

[0044] Since, during takeoff and during the beginning of the ascent phase, the airplane 10 still reaches a comparatively low altitude, the particle flux of the cosmic radiation at the location of the airplane 10, and therefore at the location of the multilevel inverter 70, is very small (by way of comparison: the particle flux at sea level is less than at an altitude of 12 kilometers by about a factor of 150). Consequently, the particle flux of the cosmic radiation does not pose a problem during takeoff and at the start of the ascent phase of the airplane 10.

[0045] By contrast, during cruising at an altitude of 12 kilometers, that is to say the typical cruising altitude, cosmic radiation is particularly critical: to counter it, the altitude of the airplane 10 is continuously acquired by way of a control device that is not illustrated explicitly in the drawing.

[0046] Above a threshold altitude that the airplane 10 passes after takeoff and during the ascent phase, the voltage applied to the intermediate circuit of the multilevel inverter 70, and consequently also the voltage V.sub.C at the inverter modules SM of the multilevel inverter 70, is then reduced, such that the inverter modules SM are switched with voltage pulses having a reduced voltage in this operating state. In this case, the voltage pulses are switched at the same time with in each case a longer-lasting pulse duration. To provide the required power, higher currents, which are distributed over a plurality of individual, smaller submodules 200 of the multilevel inverter 70, also flow. Details of the multilevel inverter 70 are illustrated by way of example in FIG. 3.