Patent Publication Number: US-2023138626-A1

Title: Electromechanical installation for an aircraft with a turbogenerator, method for emergency shutdown of an aircraft turbogenerator and corresponding computer program

Description:
The present invention relates to an electromechanical installation for an aircraft with a turbogenerator, a method for emergency shutdown of an aircraft turbogenerator and a corresponding computer program. 
     It is known from the prior art an electromechanical installation for an aircraft, of the type comprising: 
     an electrical network comprising electrical sub-networks electrically disconnected from each other and each comprising at least one electrical equipment; 
     a turbogenerator comprising: 
     a gas turbine, 
     a permanent magnet electrical generator designed to be mechanically driven by the gas turbine and having phase groups respectively connected to the electrical sub-networks, and 
     for each phase group, an isolation device designed to disconnect the phase group from its associated electrical sub-network; 
     a control device adapted to detect a short-circuit in at least one of the phase groups, each phase group in which a short-circuit is detected being referred to as defective and each other phase group being referred to as healthy, and, in response to the detection of the short-circuit, on the one hand, to control the isolation device associated with each defective phase group to disconnect that defective phase group from its associated electrical sub-network and, on the other hand, to control a shutdown of the gas turbine. 
     Specifically, in the prior art, the control device is designed to trigger a shutdown procedure consisting in controlling all the isolation devices to disconnect all the defective and healthy phase groups from the electrical sub-networks. The purpose of this disconnection is to prevent the failure from spreading downstream to the electrical network. 
     A problem with the aircraft propulsion system according to the prior art is that when a short-circuit is detected in the electrical generator, the shutdown procedure is triggered but the deceleration time of the gas turbine is long, for example in the order of several tens of seconds. During this time, the electrical generator is driven in rotation by the gas turbine and therefore continues to supply power. There is then a very high risk of local heating which could cause a fire departure in the electrical generator. In particular, an electrical and/or thermal insulator is usually provided in the electrical generator and the local heating can cause it to catch fire. Also, when the electrical generator is oil-cooled, the latter can ignite. 
     In the present invention, an attempt has been made to solve this problem of the risk of overheating which could cause a fire departure in the electrical generator, by providing an aircraft propulsion system which allows to avoid at least one portion of the aforementioned problems and constraints. 
     It is therefore an object of the invention to provide an aircraft propulsion system of the aforementioned type, characterised in that the control device is further designed, in response to the detection of the short-circuit, to keep each healthy phase group connected to its electrical sub-network. 
     Indeed, the inventors have found that the main problem with completely disconnecting the electrical network from the electrical generator in response to the detection of a short-circuit is that the electrical generator no longer has a charge and therefore no longer provides braking torque to decelerate the gas turbine. With the invention, the healthy phase group or groups remain connected to their respective sub-networks, thus allowing to keep a charge for the electrical generator and thus braking the gas turbine. 
     Optionally, the control device is advantageously designed, after keeping each healthy phase group connected to its electrical sub-network for some time, to disconnect all the phase groups from the electrical sub-networks by controlling the isolation device associated with each healthy phase group to disconnect that healthy phase group from its associated electrical sub-network. 
     Optionally also, the control device is further designed to receive a measurement of a rotational speed of the electrical generator, to detect whether a predefined condition relating to the received rotational speed is achieved, this predefined condition being for example that the rotational speed falls below a predefined threshold, and, in response to the detection of the achievement of the predefined condition, to carry out the step of disconnecting all phase groups of the electrical sub-networks. 
     Optionally also, the control device is designed, in response to the detection of the short-circuit, to increase an electrical power consumption of at least one equipment of an electrical sub-network connected to one of the healthy phase group or groups. 
     Optionally also, one of the electrical sub-networks comprises a battery, and, to increase the electrical power consumption of the battery, the control device is designed to increase an electrical voltage applied to the battery by its electrical sub-network so that the battery recharges. 
     Also optionally, to increase the electrical power consumption of a battery, the control device is designed to increase an electric voltage applied to the battery by its electrical sub-network so that the battery recharges and/or, to increase the electrical power consumption of an electric motor, the control device is designed to control the electric motor in order to increase a rotational speed of the electric motor and/or to control the electric motor so that the electric motor generates a reactive current. 
     Optionally also, the installation further comprises a device for connecting the electrical sub-networks and the control device is designed, in response to the detection of the short-circuit, to control the connection device to connect the electrical sub-network associated with each defective phase group to the electrical sub-network associated with one of the healthy phase group or groups. 
     Optionally also, the installation further comprises an electrical charging device and a connection system designed to selectively connect the electrical charging device to one or more of the electrical sub-networks and the control device is designed, in response to the detection of the short-circuit, to connect the electrical charging device to an electrical sub-network associated with a healthy phase group. 
     The invention also relates to an aircraft comprising an installation according to the invention. 
     The invention also relates to a method for emergency shutdown of a turbogenerator comprising a gas turbine and a permanent magnet electrical generator designed to be mechanically driven by the gas turbine, the method comprising: 
     a detection of a short-circuit in each of at least one of the phase groups of the electrical generator, the phase groups being respectively connected to electrical sub-networks of an electrical network, the electrical sub-networks being electrically disconnected from each other and each comprising at least one electrical equipment, each phase group in which a short-circuit is detected being referred to as defective and each other phase group being referred to as healthy; and 
     in response to the detection of the short-circuit: 
     a disconnection of each defective phase group from its associated electrical sub-network, and 
     a shutdown of the gas turbine; 
     characterised in that it further comprises, in response to the detection of the short-circuit, keeping of each healthy phase group connected to its electrical sub-network. 
     Also proposed is a computer program downloadable from a communication network and/or stored on a computer-readable medium, characterised in that it comprises instructions for executing the steps of a method, according to the invention, of emergency shutdown of a turbogenerator, when said program is executed on a computer. 
    
    
     
       The invention will be better understood with the aid of the following description, given only by way of example and made with reference to the attached drawings in which: 
         FIG.  1    is a simplified view of an electromechanical installation for an aircraft with a turbogenerator, according to one embodiment of the invention, 
         FIG.  2    is a block diagram illustrating the steps of an emergency shutdown method of the turbogenerator of  FIG.  1   , according to one embodiment of the invention, 
         FIG.  3    is a view similar to  FIG.  1   , showing a first configuration of the installation during operation, and 
         FIG.  4    is a similar view to  FIG.  1   , showing a second configuration of the installation during operation. 
     
    
    
     With reference to  FIG.  1   , an electromechanical installation  100  for an aircraft, according to one embodiment of the invention, will now be described. 
     The installation  100  firstly comprises an electrical network  102  comprising electrical sub-networks, two in the example described, designated by the references  104 ,  106 . The electrical sub-networks  104 ,  106  are electrically disconnected from each other and each comprise at least one electrical equipment. In the example described, the first electrical sub-network  104  comprises a battery  108 , an isolation device  110  for the battery  108  and another electrical equipment  112 , while the second electrical sub-network  106  comprises an electric motor  114  and other electrical equipment  116 . The electric motor  114  is used, for example, to drive a propeller (not shown) of the aircraft. 
     To allow the electrical sub-networks  104 ,  106  to be connected together, the installation  100  further comprises a device  117  for connecting the sub-networks. 
     Optionally, the electrical network  102  may further comprise an electrical charging device  119  consisting of, for example, one or more charging resistors, as well as a connection system  121  designed to selectively connect the electrical charging device  119  to one or more of the electrical sub-networks  104 ,  106 . The connection system  121  comprises, for example, switches connecting the electrical charging device  119  respectively to at least some of the electrical sub-networks. In the example described, the connection system  121  is designed to connect the electrical charging device  119  selectively to all sub-networks  104 ,  106 , and for this purpose comprises two respective switches. 
     The installation  100  further comprises a turbogenerator  118  forming a propulsion system for the aircraft. 
     The turbogenerator  118  firstly comprises a gas turbine  120  and a valve  123  for supplying fuel to the gas turbine  120 . 
     The turbogenerator  118  further comprises a permanent magnet electrical generator  122  designed to be mechanically driven by the gas turbine  120  via a rotating shaft  124 . The electrical generator  122  may be associated with a cooling system (not shown), for example forced air for the low power (typically less than 100 kW) and oil for higher power. The electrical generator  122  has phase groups respectively connected to the electrical sub-networks. Thus, in the written example, the electrical generator  122  comprises two phase groups  126 ,  128  respectively connected to the electrical sub-networks  104 ,  106 . Each phase group  126 ,  128  is carried by a stator of the electrical generator  122 . The phases of each phase group  126 ,  128  are for example arranged in star or triangle. Each phase usually comprises a winding, also referred to as reel, designed to have a phase current flowing through it and to have a phase voltage. 
     The turbogenerator  118  further comprises a system  129  for measuring operating parameters of the electrical generator  122 , such as phase currents, phase voltages, phase temperatures and/or an oil temperature, in case the electrical generator  122  is oil-cooled. 
     In the example described, the electrical sub-networks  104 ,  106  use a direct voltage, referred to as HVDC (High Voltage Direct Current), while the phase groups  126 ,  128  each provide alternating phase voltages. Thus, the turbogenerator  118  comprises, for each phase group  126 ,  128 , an alternating-direct voltage converter  130 ,  132  designed to convert the phase voltages of that phase group  126 ,  128  to the HVDC voltage of the associated electrical sub-network  104 ,  106 . 
     The turbogenerator  118  further comprises, for each phase group  126 ,  128 , an isolation device  134 ,  136  designed to disconnect the phase group  126 ,  128  from its associated electrical sub-network  104 ,  106 , and thereby isolate that electrical sub-network  104 ,  106 . For example, each isolation device  134 ,  136  comprises an electromechanical contactor, a pyrofuse or a Solid State Power Controller (SSPC). 
     In addition, the turbogenerator  118  comprises a speed sensor  138  designed to measure a rotational speed of the electrical generator  122 . The speed sensor  128  is for example mounted on the rotation shaft  124 . 
     The installation  100  further comprises a control device  140 . 
     In the example described, the control device  140  firstly comprises a unit  142  for controlling in particular the voltage converters  130 ,  132 , generally referred to as the Generator Control Unit (GCU). 
     The control device  140  further comprises a unit  144  for controlling in particular the gas turbine  120 , generally referred to as the Electronic Engine Control Unit (EECU) or Full Authority Digital Engine Control (FADEC). 
     The control device  140  further comprises a unit  146  for controlling in particular the electrical network  102 , referred to as Supervisor of the propulsion system. 
     In the example described, each of the modules  142 ,  144 ,  146  of the control device  140  comprises a computer system comprising a processing unit (such as a microprocessor) and a memory (such as a main memory) into which a computer program is intended to be charged, the computer program containing computer program instructions designed to be executed by the processing unit. Thus, the functions implemented by the control device  140  that will be described later, with reference to the method of  FIG.  2   , are implemented in the example described in the computer program, in the form of software bricks. In other embodiments, several of the modules  142 ,  144 ,  146  could be combined into a single computer system. 
     Alternatively, all or part of these software bricks could be implemented as hardware bricks, i.e., in the form of an electronic circuit, for example micro-wired, not involving a computer program. 
     With reference to  FIG.  2   , a method  200  according to one embodiment of the invention, for emergency shutdown of the turbogenerator  118  will now be described. 
     In a step  202 , the GCU  142  detects a short-circuit in at least one of the phase groups  126 ,  128 . In the following, each phase group  126 ,  128  in which a short-circuit is detected will be referred to as defective and each other phase group will be referred to as healthy. In other words, each phase group  126 ,  128  has the status “healthy” as long as the GCU  142  has not detected a short-circuit in that phase group  126 ,  128 . 
     A short-circuit in a phase group  126 ,  128  is most often caused by an insulation defect in one or more windings. This short-circuit results in a significant increase in the electric current circulating in the phases, leading to very high local heating of the phases of the stator, which may lead to the initiation of a fire, for example in the electrical and/or thermal insulator, and/or to the ignition of the oil in the case of an oil-cooled electrical generator  122 . Furthermore, as the risk of short-circuit is generally constant per phase group, the more phase groups there are, the greater the overall risk. 
     In a practical embodiment, the GCU  142  detects a short-circuit from measurements of the phase currents, phase voltages and/or phase temperatures. The GCU  142  can also take into account the measurement of the temperature of the oil in order to avoid false short-circuit detections (when the oil temperature measurement does not reveal an abnormal heating of the oil). 
     In response to the detection of the short-circuit, the following steps are implemented. 
     In a step  204 , the GCU  142  controls the isolation device associated with each defective phase group to disconnect that defective phase group from its associated electrical sub-network. This electrical sub-network thus becomes isolated from the defective phase group. In addition, the GCU  142  keeps each healthy phase group connected to its electrical sub-network, leaving every other isolation device open (closed state). 
     For example, if in the installation illustrated in  FIG.  1   , the GCU  142  detects a short-circuit in the phase group  126 , the following situation is obtained as illustrated in  FIG.  3   : the isolation device  134  is activated in the open state (isolating state) to isolate the electrical sub-network  104  from the defective phase group  126  while the isolation device  136  is left in the closed state to keep the healthy phase group  128  connected to its electrical sub-network  106 . 
     Returning to  FIG.  2   , in a step  206 , the GCU  142  monitors the measurement of the rotational speed of the electrical generator  122  provided by the sensor  138 , to detect when the rotational speed is low enough to completely disconnect the electrical generator  122  from the electrical network  102 . For this purpose, the GCU  142  detects, for example, whether a predefined condition relating to the received rotational speed is achieved. This predefined condition is, for example, that the rotational speed falls below a predefined threshold or becomes zero. 
     In a step  208 , after keeping each healthy phase group connected to its associated electrical sub-network for a period of time, the GCU  142  disconnects all the phase groups  126 ,  128  from the electrical sub-networks  104 ,  106  by controlling the isolation device associated with each healthy phase group to disconnect that healthy phase group from its associated electrical sub-network. 
     For example, considering the situation in  FIG.  3    in which the defective phase group  126  had been isolated from the electrical sub-network  104  in step  204 , the GCU  142  disconnects the healthy phase group  128  in step  208  by controlling the isolation device  136  to the open state (isolating state), as illustrated in  FIG.  4   . 
     Thus, in the example described, the time during which each healthy phase group is kept connected to its electrical sub-network corresponds to the time that the rotational speed of the electrical generator  122  takes to reach the predefined condition. Alternatively, the step  206  could be omitted and the keeping time could be a fixed, predefined time. 
     Returning to  FIG.  2   , in parallel to the steps  204  to  208 , in a step  210 , the GCU  142  sends an emergency shutdown request to the FADEC  144 . 
     In a step  212 , in response to the emergency shutdown request, the FADEC  144  controls a shutdown of the gas turbine  120 . To this end, in the example described, the FADEC  144  controls the closure of the fuel supply valve  123 . 
     In the example described, following the step  204  of isolating one or more of the electrical sub-networks  104 ,  106 , the electrical network  102  is modified, in a step  215 , to increase the electrical power it collects from the electrical generator  122 . 
     The step  215  comprises, for example, one or more of the steps  216 ,  217 ,  218  that will now be described. 
     In the step  216 , the Supervisor  146  (e.g., in response to an emergency shutdown request from the GCU) and/or the GCU  142  causes the electrical charging of at least one equipment on an electrical sub-network associated with a healthy phase group to be increased, in order to increase the electrical power collected from the electrical network  102  to the electrical generator  122 . Thus, if the healthy phase group or groups are not fully charged prior to the emergency shutdown procedure, the step  216  has the effect of further charging them to further brake the electrical generator  122 . 
     For example, to increase the electrical charging of the battery  108 , the GCU  142  increases the HVDC voltage of the electrical sub-network  104  to which the battery  108  belongs, so that the HVDC voltage becomes sufficiently higher than that of the battery  108  to impose a significant recharge current on it. This voltage increase is achieved, for example, by appropriately controlling the voltage converter  130  of the electrical sub-network  104  to which the battery  108  belongs. The voltage increase  130  is preferably calculated by the GCU  142  so that the recharge current remains within the operating limits of the battery  108 , in particular below a maximum permissible recharge current, and to respect a maximum charge level of the battery  108 . 
     Again, for example, to increase the electrical charging of the electric motor  114 , the supervisor  146  controls the electric motor  114  to increase its rotational speed. Alternatively, the Supervisor  146  controls the electric motor to generate a reactive current. Indeed, this reactive current heats up the electric motor  114  without changing its rotational speed. The additional electrical power consumed by the electric motor  114  is thus dissipated as heat in the electric motor  114 . It will be appreciated that, in another embodiment, the generation of the reactive current could be carried out in addition to the increase in the rotational speed. 
     In step  217 , the electrical charging device  119  is used, for example, in the case where the one or more healthy phase groups are already fully charged, in particular if, for example, the battery  108  is already fully charged and it is not desired to change the charging of the electric motor  114  so as not to change the aerodynamics of the flight. The connection system  119  is thus controlled by the control device  140  to connect the electrical charging device  119  to at least one electrical sub-network associated with a healthy phase group in order to increase the electrical power collected by this electrical sub-network. 
     In the example shown in  FIG.  3   , the connection system  121  is controlled in step  217  to connect the electrical charging device  119  to the electrical sub-network  106  associated with the healthy phase group  128 . 
     Returning to  FIG.  2   , in step  218 , at least one electrical sub-network isolated in step  204  is used to increase the electrical power collected from the electrical generator  122 . To do this, the Supervisor  146  controls the connection device  117  to connect this isolated electrical sub-network to the electrical sub-network associated with a healthy phase group. Thus, the isolated electrical sub-network is connected to the electrical generator  122  through the healthy phase group and can collect electrical power from the electrical generator  122 . 
     In the example shown in  FIG.  3   , the connection device  117  connects the isolated electrical sub-network  104  to the electrical generator  122  through the electrical sub-network  106 , so that electrical power can be collected from it. 
     Returning to  FIG.  2   , in an optional step  220 , the electrical charging of the equipment in the previously isolated electrical sub-network may then be increased, for example in the same manner as described in step  216 . 
     In the example shown in  FIG.  3   , the electrical charging of the equipment  112 ,  108  of the electrical sub-network  104  is for example increased in this step  220 . 
     Precautions may need to be taken when switching equipment from one phase group  126 ,  128  to another, particularly for the battery  108 . Thus, preferably, the method  200  further comprises a step  222  prior to step  218 , in which the Supervisor  146  controls the isolation device  110  of the battery  108  to isolate the battery  108  from the rest of the electrical sub-network  104 . Thus, the equipment  112  other than the battery  108  may be used to increase the electrical power collected from the electrical generator  122 . 
     Alternatively, the isolation device  110  may be replaced by an accommodation device, allowing the battery  108  to be used to increase the electrical power collected from the electrical generator  122 . 
     For example, the accommodation device comprises a pre-charge resistor that limits the electrical current of the battery  108  until the voltages of the battery  108  and the electrical sub-network  104  equalise. This pre-charge resistor is temporarily connected when the electrical sub-network  104  is connected to the electrical sub-network  106  and then disconnected when the voltages are equalized. 
     Alternatively, the accommodation device comprises, for example, a direct-direct voltage converter that achieve the voltage adaptation between the battery  108  and the electrical sub-network  104 . In this case, the voltage converter is usually present and active at all times. 
     It is clear that an installation and a method such as those described above allow the electrical generator to be stopped in a short time. 
     It will be further noted that the invention is not limited to the embodiments described above. It will indeed appear to the person skilled in the art that various modifications can be made to the above-described embodiments, in the light of the teaching just disclosed. 
     In particular, the electrical generator could comprise more than two phase groups, connected to as many electrical sub-networks. 
     In the foregoing detailed presentation of the invention, the terms used should not be interpreted as limiting the invention to the embodiments exposed in the present description, but should be interpreted to include all equivalents the anticipation of which is within the reach of the person skilled in the art by applying his general knowledge to the implementation of the teaching just disclosed.