FR3128327A1 - Protection of an electric propulsion chain of an aircraft - Google Patents

Abstract

Method for protecting an electric propulsion chain of an aircraft, the propulsion chain comprising an electric motor (2), a module (3) for power electronics and control of the electric motor and a DC voltage source ( 1), the power electronics and electric motor control module comprising an inverter (31), the power electronics and electric motor control module (3) being on the one hand connected to the voltage source (1) and on the other hand connected to the electric motor (2), characterized in that it comprises, in the case of detection of an electrical fault in the propulsion chain, a short- circuit at the level of the inverter (31) of the power electronics and control module of the electric motor. Figure for abstract: Figure 1

Description

Protection of an electric propulsion chain of an aircraft

The present invention relates to electric or hybrid motors, in particular for aircraft. It relates more particularly to the protection of an electric propulsion chain of an aircraft, comprising an electric motor, a power electronics module and control of the electric motor and a DC voltage source.

State of the prior art

The evolution of aircraft leads to an interest in electric and hybrid propulsion. In this context, we consider an electric propulsion chain of an aircraft, forming an electrical network and comprising an electric motor, a power electronics module and control of the electric motor and a DC voltage source.

To protect the electric propulsion chain in the event of an element failure, components can be added to the propulsion chain. Thus, it is possible for example to provide, between the DC voltage source and the power electronics and electric motor control module, additional diodes to impose a single direction of current or even current cut-off devices.

However, adding components is penalizing for the system. Indeed, this increases the cost and the mass of the electric propulsion chain. In addition, it is necessary to take into account the increase in heat dissipation and the reduction in the reliability of the electric propulsion chain. These constraints require oversizing of all components.

The invention aims to solve the problems of the prior art by providing a method for protecting an electric propulsion chain of an aircraft, the propulsion chain comprising
- an electric motor,
- a DC voltage source, and
- a power electronics and electric motor control module comprising an inverter, and being on the one hand connected to the DC voltage source and on the other hand connected to the electric motor, the inverter comprising power modules comprising each a high bridge arm and a low bridge arm,

characterized in that it comprises, in the case of detection of an electrical fault in the propulsion chain, a short-circuit control step at the level of the inverter of the power and control electronics module of the electric motor, among several predetermined types of short-circuit, the short-circuit command step comprising commanding a short-circuit of the high bridge arms, or of the low bridge arms, or of the high bridge arms and low simultaneously, or alternating short circuits of the high bridge arms and the low bridge arms, depending on the type of electrical fault detected.

Thanks to the invention, in the event of an electrical fault in the propulsion chain, if the motor behaves as a current generator, it is possible to contain the energy generated by the motor at the level of the motor.

This makes it possible, for example, to avoid resupplying a short circuit on the DC power circuit, thereby limiting the risk of fire.

This advantage is obtained without additional components.

The type of short-circuit which is controlled is selected according to the type of fault detected.

According to a preferred characteristic, the short-circuit control step comprises the control of a short-circuit of the low bridge arms in the event of a short-circuit between positive and negative input terminals of the power electronics module and control of the electric motor. This avoids supplying current generated by the motor to the short-circuit between the positive and negative input terminals of the power electronics and control module of the electric motor.

According to a preferred characteristic, the short-circuit command step comprises commanding a short-circuit of the upper bridge arms in the event of a short-circuit at the level of a coil of the electric motor.

According to a preferred characteristic, the short-circuit control step comprises the control of an alternation of short-circuit of the high bridge arms and of the low bridge arms in the event of a short-circuit at the level of a coil of the motor electric.

According to a preferred characteristic, the short-circuit control step comprises the control of a simultaneous short-circuit of the high bridge arms and the low bridge arms in the event of a short-circuit between the positive and negative terminals of a inverter power modules. Thus, it is possible to discharge an energy reservoir from the power electronics and control module of the electric motor.

According to a preferred characteristic, the short-circuit command step includes commanding a short-circuit of the high bridge arms, or a short-circuit of the low bridge arms, in the event of a broken bridge arm being closed or open .

The invention also relates to an electric propulsion chain for an aircraft, comprising
- an electric motor,
- a DC voltage source, and
- a power electronics and electric motor control module comprising an inverter, and being on the one hand connected to the DC voltage source and on the other hand connected to the electric motor, the inverter comprising power modules comprising each a high bridge arm and a low bridge arm,

characterized in that it comprises an inverter control sub-module, adapted, in the event of detection of an electrical fault in the propulsion chain, to control a short-circuit at the level of the inverter of the power and control electronics module of the electric motor, among several predetermined types of short-circuit, the short-circuit being a short-circuit of the high bridge arms, or of the low bridge arms, or of the bridge arms high and low simultaneously, or alternating short circuits of the high bridge arms and the low bridge arms, depending on the type of electrical fault detected.

The invention also relates to an aircraft comprising an electric propulsion chain.

The electric propulsion chain and the aircraft have advantages similar to those previously presented.

In a particular embodiment, the steps of the method according to the invention are implemented by computer program instructions.

Consequently, the invention also relates to a computer program on an information medium, this program being capable of being implemented in a computer, this program comprising instructions adapted to the implementation of the steps of a process as described above.

The invention also relates to an information medium readable by a computer, and comprising computer program instructions adapted to the implementation of the steps of a method as described above.

The information carrier can be any entity or device capable of storing the program.

Other characteristics and advantages will appear on reading the following description of a preferred embodiment, given by way of non-limiting example, described with reference to the figures in which:

illustrates an electric propulsion chain, according to one embodiment of the invention,

illustrates a fault in the electric propulsion chain of the ,

illustrates the method of protecting the electric propulsion chain of the .

Identical, similar or equivalent parts of the different figures bear the same reference numerals so as to facilitate passage from one figure to another.

The different parts shown in the figures are not necessarily shown on a uniform scale, to make the figures more readable.

The different possibilities (variants and embodiments) must be understood as not mutually exclusive and can be combined with each other.

E exposed d detailed d e m odes d e r realization p particular

According to a preferred embodiment, shown in , an electric propulsion chain of an aircraft comprises a DC voltage source 1, an electric motor 2 and a module 3 for power electronics and control of the electric motor. The electric motor 2 is connected to a propeller 4.

A DC power circuit 5 in the form of a DC power harness is on the one hand connected to output terminals of the DC voltage source 1. The DC power harness 5 is on the other hand connected to terminals input of module 3 of power electronics and control of the electric motor.

A three-phase power circuit 6 in the form of a three-phase power harness is on the one hand connected to output terminals of the module 3 of power electronics and control of the electric motor. The three-phase power harness 6 is also connected to input terminals of the electric motor 2.

The power electronics and electric motor control module 3 comprises a three-phase inverter 31 which comprises three power modules 31 ₁ , 31 ₂ and 31 ₃ respectively connected to one phase of the three-phase power harness 6. Each power module comprises two bridge arms, namely a high bridge arm and a low bridge arm.

Each bridge arm comprises a switch 31 _{1 1} , 31 _{1 2} , 31 _{2 1} 31 _{2 2} , 31 ₃₁ and 31 _{3 2} . Each of these switches is for example made in the form of an IGBT transistor with a diode in parallel.

The power electronics and electric motor control module 3 also includes an energy reservoir 32 in the form of one or more capacitors.

The power electronics and electric motor control module 3 further comprises a sub-module 35 for controlling the electric motor, and a sub-module 36 for controlling the inverter 31, in particular the bridge arms of the inverter 31. Of course, one or both of these sub-modules can be modules external to module 3 of power electronics and control of the electric motor and be connected to the latter.

Devices for measuring electrical quantities and electrical protection of the various elements of the propulsion chain equip them. These devices are conventional and are neither shown nor described to simplify the description of the invention.

Similarly, the architectures and equipment of the aircraft must comply with the installation and safety requirements defined by the regulatory and certification bodies. This requires in particular to provide means for detecting and eliminating the faults and preventing their propagation as well as that of their induced effects.

Consequently, the components are dimensioned to hold the time of detection of the breakdowns and tripping of the associated protections. Additional protection devices can be implemented in the architecture to provide redundancy. Moreover, to be efficient and competitive, these architectures must be optimized in terms of mass, reliability and cost. These aspects are not detailed here.

The motor 2 is for example a three-phase synchronous motor with permanent magnets. This type of motor has many advantages: it is compact, it has good efficiency, a good power/mass ratio and high torque. However, it is not possible for him to control the excitation of the inductor. Consequently, the electric motor 2 has the disadvantage of behaving as a generator when the motor is not controlled and the rotor is rotated under the effect of the propeller when it is rotating, or when the propeller is driven by the aerodynamic forces of the wind (in English: windmilling). This phenomenon creates an electromotive force (EMF) on the three phases connected to module 3 of power electronics and control of the electric motor.

In known manner, the DC voltage source 1 is equipped with a protection system 11 capable of isolating the voltage source in the event of an electrical fault in the propulsion chain. The protection system 11, symbolized by a switch, is arranged between the DC voltage source 1 and the DC power circuit 5. A source monitoring system, not shown, controls the opening of the protection system in the event of electrical fault. When DC voltage source 1 is isolated, electric motor 2 is no longer controlled. It can then switch to freewheel mode and let the propeller spin due to the previous torques applied. It is also possible that aerodynamic forces (wind) on the propeller during any phase of flight maintain or rotate the electric motor 2.

When the electric motor is thus set in rotation, it then behaves as a generator. A current source is then created and, in the absence of corrective measures, resupplies the propulsion chain and therefore the electrical fault.

In the following, we consider the case of an electrical fault in the propulsion chain.

There represents the case where the electrical fault is a DC short circuit on the DC power harness 5. In other words, the positive and negative input terminals of the module 3 of power electronics and control of the electric motor are in short circuit. In this case, the source protection circuit 11 opens upstream of the DC electrical fault to protect the DC voltage source 1. Following this opening, the electric motor 2 continues to rotate and becomes a generator, which has as a consequence of feeding the short circuit on the continuous power harness 5.

The current generated by the electric motor in generator mode becomes equal to the electromotive force divided by the impedance of the electric motor 2, where the electromotive force is the image of the motor speed. There is no opening element between the electric motor 2 and the power electronics and electric motor control module 3 for reasons of weight and size limitation.

In such a case of an electrical fault, the method for protecting the electric propulsion chain is implemented.

There represents the method of protection of the electric propulsion chain of the , implemented in the sub-module 36 for controlling the bridge arms of the inverter 31. The method comprises steps E1 to E2.

Step E1 is an electrical fault detection in the propulsion chain and the identification of the type of fault.

The sub-module 36 monitors the propulsion chain by receiving the results of measurements carried out by the devices for measuring electrical quantities of the various elements of the propulsion chain and by comparing them with nominal values. If one or more measurement results deviate(s) from the nominal values, then an electrical fault is detected and the type of fault is identified.

This is for example the detection of the DC short-circuit at the level of the DC power circuit 5, illustrated in .

Following the detection of an electrical fault, the switch 11 is opened to protect the DC voltage source 1. The electric propulsion chain is then in the configuration of the .

Other electrical faults taken into account and detectable in step E1 are in particular:

- A short-circuit at the level of a coil of the electric motor 2;
- A short circuit between the positive and negative terminals of one of the power modules of the inverter 31;
- A closed or open broken bridge arm.

The next step E2 is a short-circuit command at the level of the inverter 31 of the module 3 of power electronics and control of the electric motor. The short circuit is selected from among several predetermined short circuit types, depending on the type of electrical fault detected in the previous step.

More precisely, the sub-module 36 for controlling the bridge arms of the inverter 31 controls the closing of at least some of the switches of the inverter 31. Thus, if the electric motor 2 behaves as a generator, as explained previously, the current generated by motor 2 is diverted so that it no longer passes through the electrical fault, for example the DC short circuit.

The best protection strategy is applied according to the type of fault detected in the propulsion chain.

In the event of a short-circuit between the positive and negative input terminals of the power electronics and electric motor control module, as shown in , the short-circuit commanded in step E2 is a short-circuit of the low bridge arms.

Shorting the low bridge arms creates a midpoint on the motor phases. The current generated by the motor no longer feeds the existing DC short circuit in the DC power circuit 5. This procedure stops the motor after a certain time.

In the event of a short-circuit at the level of a coil of the electric motor, the short-circuit commanded in step E2 is a short-circuit of the upper bridge arms.

As a variant, in the event of a short-circuit at the level of a coil of the electric motor, the short-circuit commanded in step E2 is an alternation of short-circuit of the high bridge arms and of the low bridge arms. This makes it possible to distribute the thermal stress caused by the short circuits alternately on all the bridge arms.

In the event of a short-circuit between the positive and negative terminals of one of the power modules of the inverter 31, the short-circuit commanded in step E2 is a simultaneous short-circuit of the upper bridge arms and the Low bridge. This allows the thermal stress caused by short circuits to be distributed over all the bridge arms.

It should be noted that a simultaneous short-circuit of the low and high bridge arms simultaneously should only be carried out when the DC voltage source 1 is disconnected, in order to avoid short-circuiting the positive and negative terminals of DC voltage source 1.

In the event of a bridge arm broken closed or open, the short-circuit commanded in step E2 is either a short-circuit of the high bridge arms, or a short-circuit of the low bridge arms. For example, if a high bridge arm is broken closed, the commanded short is a high bridge arm short. If a high bridge arm is broken open, the commanded short is a low bridge arm short.

In all cases, the purpose of the short-circuit commanded in step E2 is to impose a path for the current generated by the motor to maintain it in the windings of the motor and to brake the motor.

The inventors have shown by simulation that the temperature constraints remain bearable by the various components of the inverter, regardless of the type of short-circuit implemented in the inverter 31.

Thus, each of the chips used to form a power module (bridge arm) has for example a maximum junction temperature of 175°C. The worst-case generated current flowing in the bridge arms after shorting at least part of the bridge arms does not heat the chip beyond its maximum junction temperature.

It should be noted that the alternation of short-circuiting of the low bridge arms and short-circuiting of the high bridge arms makes it possible to distribute the temperature rise over the two switches of the same arm, as well as the short -simultaneous circuit of low and high bridge arms.

This makes it possible to limit the discharge circuits, and therefore the weight and volume of the inverter.

Claims (9)

Method for protecting an electric propulsion chain of an aircraft, the propulsion chain comprising

• an electric motor (2),
• a DC voltage source (1), and
• a module (3) for power and control electronics of the electric motor comprising an inverter (31), and being on the one hand connected to the DC voltage source (1) and on the other hand connected to the electric motor (2 ), the inverter (31) comprising power modules (31 ₁ , 31 ₂ , 31 ₃ ) each comprising an upper bridge arm (31 ₁₁ , 31 ₂₁ , 31 ₃₁ ) and a lower bridge arm (31 ₁₂ , 31 ₂₂ , 31 ₃₂ ),

characterized in that it comprises, in the case of detection of an electrical fault in the propulsion chain, a short-circuit control step at the level of the inverter (31) of the power electronics module and controlling the electric motor, among several predetermined types of short-circuit, the step of controlling a short-circuit comprising controlling a short-circuit of the high bridge arms, or of the low bridge arms, or of the arms high and low bridge arms simultaneously, or alternating short circuits of the high bridge arms and the low bridge arms, depending on the type of electrical fault detected. Method for protecting an electric propulsion chain of an aircraft according to claim 1, in which the step of controlling a short-circuit comprises controlling a short-circuit of the lower bridge arms in the event of a short-circuit (CC) between positive and negative input terminals of the module (3) of power electronics and control of the electric motor. Method for protecting an electrical propulsion chain of an aircraft according to one of Claims 1 to 2, in which the step of controlling a short-circuit comprises controlling a short-circuit of the upper bridge arms in case of short-circuit at the level of a coil of the electric motor (2). Method for protecting an electric propulsion chain of an aircraft according to one of claims 1 to 2, in which the short-circuit control step comprises controlling an alternating short-circuit of the bridge arms top and bottom bridge arms in the event of a short circuit at the level of a coil of the electric motor (2). Method for protecting an electric propulsion chain of an aircraft according to one of Claims 1 to 4, in which the short-circuit control step comprises controlling a simultaneous short-circuit of the upper bridge arms and low bridge arms in the event of a short-circuit between the positive and negative terminals of one of the power modules (31 ₁ , 31 ₂ , 31 ₃ ) of the inverter (31). Method for protecting an electrical propulsion system of an aircraft according to one of Claims 1 to 5, in which the short-circuit command step comprises commanding a short-circuit of the upper deck arms, or a short circuit of the low bridge arms, in the event of a broken bridge arm closed or open. Electrical propulsion chain of an aircraft, comprising

• an electric motor (2),
• a DC voltage source (1), and
• a module (3) for power and control electronics of the electric motor comprising an inverter (31), and being on the one hand connected to the DC voltage source (1) and on the other hand connected to the electric motor (2 ), the inverter (31) comprising power modules (31 ₁ , 31 ₂ , 31 ₃ ) each comprising an upper bridge arm (31 ₁₁ , 31 ₂₁ , 31 ₃₁ ) and a lower bridge arm (31 ₁₂ , 31 ₂₂ , 31 ₃₂ ),

characterized in that it comprises a sub-module (36) for controlling the inverter (31), adapted, in the event of detection of an electrical fault in the propulsion chain, to control a short-circuit at the level of the inverter (31) of the power electronics and electric motor control module (3), from among several predetermined types of short-circuit, the short-circuit being a short-circuit of the upper bridge arms, or low bridge arms, or high and low bridge arms simultaneously, or alternating short circuits of high bridge arms and low bridge arms, depending on the type of electrical fault detected. Aircraft comprising an electric propulsion chain according to claim 7. Computer program comprising instructions for the execution of the steps of the method according to any one of Claims 1 to 6 when the said program is executed by a computer.