Protection system and protection device

Abstract

A protection system according to an embodiment of the present invention comprises a generator, a converter, a detector, and a protection device. The generator is connected to a rotating shaft of an engine. The converter converts AC power outputted from the generator into DC power. The detector monitors the power generation state of the generator. The protection device is connected to the generator, in parallel with the converter. The protection device has a load mechanism, a switch, and a control unit. The switch switches a connection state between the generator and the load mechanism. The control unit determines the presence or absence of an abnormality in the generator on the basis of an output of the detector and, when an abnormality is determined, controls the switch so as to generate, in the rotating shaft, a braking torque restraining the rotational speed of the rotating shaft to a predetermined rotational speed or less.

Description

Protection Systems and Devices

[0001] The present invention relates to a protection system and a protection device that can be applied to a generator connected to a rotating shaft of an engine installed in an aircraft.

[0002] A motor drive device that generates braking force by using a resistor in a DC section when using a synchronous motor as a generator is known. For example, Patent Document 1 discloses a motor drive device that controls a motor used to drive an electric vehicle, and that includes a connection configuration switching circuit that can switch between a drive connection configuration in which the three-phase motor is driven by battery power and a regenerative connection configuration in which the motor's generated power is charged to the battery during regenerative braking. The connection configuration switching circuit is an inverter with a total of six drive elements, each of which is a semiconductor switching element, connected in series, two on the positive voltage side and two on the negative voltage side for each phase. The connection configuration switching circuit is configured to be switchable to a short-circuit connection configuration in which the motor coil is short-circuited to generate braking force, and is equipped with a short-circuit current control means that controls the short-circuit current flowing in this short-circuit connection configuration.

[0003] Patent No. 5808923

[0004] Electrical equipment powered by a generator connected to the rotating shaft of an aircraft engine is typically equipped with a protective device that cuts off the power supply in the event of a malfunction. When the power supply is cut off by the protective device, the power required by the generator decreases, and the shaft torque also decreases, causing a temporary increase in generator rotation speed, i.e., engine rotation speed. If the power of the malfunctioning electrical equipment is small, the increase in the rotating shaft speed is also small, and can be ignored from the perspective of stable engine operation.

[0005] However, when the electrical equipment supplies large amounts of power, such as to a motor driving a propeller or other propulsion device, that power can be several tens of percent of the engine's shaft power, resulting in a significant increase in rotational speed. This can lead to mechanical malfunctions in the engine. Specifically, this can include engine compressor surging and excessive turbine centrifugal force. These malfunctions can impair not only the generator but also the engine's stable operation and ultimately safe flight, so it is necessary to prevent these malfunctions from occurring. To prevent such events, for example, a Full Authority Digital Engine Controller (FADEC) can adjust the fuel flow rate to return the engine to its original rotational speed. However, this system has a long time constant, requiring time for stabilization, leading to reduced control responsiveness. Furthermore, in a system with a load mechanism and protective devices installed in the DC section beyond the generator and converter, even if the generator is functioning normally, a converter failure can disable braking, reducing the reliability of the system.

[0006] In view of the above circumstances, an object of the present invention is to provide a protection system and a protection device that can improve the reliability of the system without causing a decrease in control responsiveness.

[0007] A protection system according to one aspect of the present invention includes a generator, a converter, a detector, and a protection device. The generator is connected to a rotating shaft of an engine. The converter converts AC power output from the generator into DC power. The detector monitors the power generation state of the generator. The protection device is connected to the generator in parallel with the converter. The protection device includes a load mechanism, a switch, and a control unit. The switch switches the connection state between the generator and the load mechanism. The control unit determines whether or not there is an abnormality in the generator based on the output of the detector, and if there is an abnormality, controls the switch to generate a braking torque on the rotating shaft that keeps the rotation speed of the rotating shaft below a predetermined rotation speed.

[0008] When the protection system detects an abnormality in the generator, it connects the generator to a load mechanism to generate a braking torque and suppress an increase in rotation speed, thereby improving system reliability without reducing control responsiveness.

[0009] The detector may be configured to monitor at least one of the number of rotations of the rotating shaft or the current generated by the generator.

[0010] In this case, the control unit may determine that an abnormality has occurred when a difference between the current rotation speed of the rotating shaft and a predetermined rotation speed during steady operation of the generator is equal to or greater than a predetermined value.

[0011] Alternatively, the control unit may determine that an abnormality has occurred when a difference between the current current and a predetermined current during steady operation of the generator is equal to or greater than a predetermined value.

[0012] Alternatively, the control unit may determine that an abnormality has occurred when oscillations different from oscillations in the current during steady-state operation of the generator are occurring in the current.

[0013] The control unit may control the switch in accordance with a torque pattern based on a time constant of the engine.

[0014] In this case, the torque pattern may include gradually attenuating the braking torque.

[0015] The control unit may generate a predetermined maximum value of the braking torque for a first predetermined time, and then gradually attenuate the braking torque over a second predetermined time that is longer than the first predetermined time.

[0016] The predetermined maximum value may be equal to or less than 50% of the rated torque of the generator.

[0017] The control unit may decay the braking torque logarithmically over the second predetermined time period.

[0018] The protection system may further include an engine control unit that controls the amount of fuel introduced into the engine to control the rotation speed so that it becomes a rotation speed command value, and the control unit may control the switch based on the rotation speed command value to the engine output from the engine control unit.

[0019] The predetermined rotation speed may be the rotation speed command value output from the engine control unit, and the control unit may determine the braking torque so as to maintain the rotation speed command value, and control the switch to generate the determined braking torque.

[0020] The load mechanism may be a resistor connected to an AC line between the generator and the converter and consuming the power generated by the generator.

[0021] Alternatively, the load mechanism may be a battery or a capacitor that is connected to an AC line between the generator and the converter and is capable of storing the power generated by the generator.

[0022] In this case, the switch may include a DC-AC converter capable of supplying power stored in the battery or capacitor to the AC line.

[0023] Alternatively, the switch may be provided between the AC line between the generator and the converter and the load mechanism, and configured to be able to convert or cut off power between the generator and the load mechanism.

[0024] The generator may have a stator wound with three-phase electromagnetic coils, and the load mechanism may be connected between AC lines of at least two of the three phases.

[0025] The switch may be provided between the AC line between the generator and the converter and the load mechanism.

[0026] The engine may be used in an aircraft, in which case the predetermined rotational speed may be a rotational speed of the engine during cruising of the aircraft, and the protection device may generate the braking torque so that the rotational speed of the rotary shaft becomes the rotational speed of the engine.

[0027] A protection device according to one aspect of the present invention includes a load mechanism, a switch, and a control unit. The load mechanism is connected to an AC line between a generator connected to a rotating shaft of an engine and a converter that converts AC power output from the generator into DC power. The switch switches the connection state between the generator and the load mechanism. The control unit determines whether or not there is an abnormality in the generator based on the output of the detector, and, if an abnormality is determined, controls the switch to generate a braking torque on the rotating shaft that keeps the rotation speed of the rotating shaft below a predetermined rotation speed.

[0028] As described above, according to the present invention, the reliability of the system can be improved without causing a decrease in control responsiveness.

[0029] FIG. 1 is a schematic configuration diagram of a power generation system according to a first embodiment. FIG. 2 is a block diagram showing the configuration of a protection system. FIG. 3 is a graph showing the relationship between engine rotation speed, generator torque, and engine command torque. FIG. 4 is a flowchart showing control of the protection system. FIG. 5 is a diagram showing an example of generation of an opening / closing signal by a control unit. FIG. 6 is a diagram showing another example of generation of an opening / closing signal by a control unit. FIG. 7 is a block diagram showing the configuration of a protection device according to a second embodiment. FIG. 8 is a block diagram showing the configuration of a protection device according to a third embodiment. FIG. 9 is a block diagram showing the configuration of a protection device according to a fourth embodiment. FIG. 10 is a diagram showing the configuration and operation of a switch. FIG. 11 is a timing chart showing a schematic attenuation pattern of braking torque generated by a protection device according to each embodiment.

[0030] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0031] 1 is a schematic diagram of a power generation system 100 according to a first embodiment of the present invention. The power generation system 100 of this embodiment is an engine with a generator mounted on an aircraft, and includes an engine 10, a generator 20, a FADEC 30, and a protection device 40.

[0032] Aircraft equipped with the power generation system 100 include, for example, aircraft equipped with the engine 10 as a propulsion device, as well as electric aircraft that use electricity from the generator 20 to drive propulsion systems such as fans and propellers.

[0033] The engine 10 is a jet engine and includes a compressor 11 , a combustor 12 , and a turbine 13 .

[0034] The compressor 11 has a rotary shaft 110 as an engine shaft, and a low-pressure compression section 11a and a high-pressure compression section 11b connected to the rotary shaft 110. The compressor 11 introduces air adiabatically compressed in the low-pressure compression section (LPC) 11a and the high-pressure compression section (HPC) 11b into a combustor 12 at a downstream stage.

[0035] The low-pressure compression section 11a and the high-pressure compression section 11b each have a plurality of rotor blades and a plurality of stator vanes. The rotor blades rotate together with the rotary shaft 110 and compress air between the rotor blades and the stator vanes. Although not shown, a fan that introduces air into the low-pressure compression section 11a may be installed upstream of the compressor 11. The fan is connected to the rotary shaft 110 and rotates integrally with the compressor 11.

[0036] The combustor 12 has a mixing chamber that mixes the air compressed by the compressor 11 with the fuel injected from the fuel injector 121, and a combustion chamber that burns the mixture, and discharges high-pressure combustion gas toward the downstream turbine 13. The flow rate of fuel introduced from the fuel injector 121 to the combustor 12 is controlled by the FADEC 30. Normally, the flow rate of fuel is adjusted based on the rotation speed of the rotating shaft 110 detected by the rotation speed sensor 111.

[0037] The turbine 13 has a high-pressure turbine section (HPT) 13a and a low-pressure turbine section (LPT) 13b connected to a rotary shaft 110, and is rotated by receiving combustion gas discharged from the combustor 12. The rotation of the high-pressure turbine section 13a and the low-pressure turbine section 13b is transmitted to the compressor 11 via the rotary shaft 110, and is used as driving force for continuously drawing in and compressing air.

[0038] The generator 20 has a drive shaft 21 directly connected to the rotating shaft 110. In this embodiment, the generator 20 is a polyphase generator equipped with electromagnetic coils for three phases, namely, U-phase, V-phase, and W-phase, but is not limited to this and may be a single-phase generator. The generator 20 is an AC generator that includes a rotor with a permanent magnet attached to the drive shaft 21 and a stator around which polyphase electromagnetic coils are wound, and converts the rotational force of the rotating shaft 110 into electrical energy.

[0039] The drive shaft 21 may be formed by a part of the rotating shaft 110. The generator 20 is not particularly limited to a multi-phase electromagnetic coil, as long as it is an electromagnetic coil through which two or more alternating currents of different phases flow. The generator 20 is not limited to being connected to the rear stage of the engine 10 (the turbine 13 side), but may be connected to the front stage of the engine 10 (the compressor 11 side).

[0040] The FADEC 30 controls the engine 10. For example, as described above, the FADEC 30 adjusts the flow rate of fuel introduced from the fuel injector 121 to the combustor 12 based on the output of the rotation speed sensor 111. In this embodiment, the FADEC 30 controls the rotation speed of the engine 10 (rotating shaft 110), which has increased due to torque loss, by adjusting the fuel flow rate so that the rotation speed of the engine 10 becomes equal to a rotation speed command value. For example, the rotation speed command value is the rotation speed of the engine 10 during steady operation. In other words, the rotation speed of the engine 10 when the aircraft is cruising without any problems (hereinafter referred to as a stable rotation speed) may be stored, and the rotation speed command value may be determined based on the stable rotation speed. In this embodiment, the FADEC 30 also outputs the rotation speed command value to the protection system 40.

[0041] The sensors used to control the FADEC 30 are not limited, and various sensors capable of measuring torque, pressure, temperature, etc. may be used to measure operational disturbances of the engine 10 .

[0042] The power generation system 100 further includes an ammeter 35. The ammeter 35 is connected between the generator 20 and a converter (transformer) 51. The ammeter 35 detects the magnitude of the current generated by the generator 20 and outputs the detection signal to the FADEC 30 and the protection device 40.

[0043] The protection device 40 is configured to be able to generate a braking torque on the rotating shaft 110 to suppress the rotation speed of the rotating shaft 110 to a predetermined rotation speed based on the outputs of the sensors (the ammeter 35 and the rotation speed sensor 111). For example, when an abnormality occurs, the protection device 40 controls the rotation speed of the engine 10 to a rotation speed command value output from the FADEC 30.

[0044] Here, an abnormal situation includes a situation in which the load 61 described below is lost due to some kind of trouble, causing the load on the engine 10 to disappear and the rotation speed of the engine 10 to suddenly increase, i.e., a so-called torque loss (load loss).

[0045] That is, in this embodiment, the protection device 40 functions to return the rotation speed of the rotating shaft 110, which has increased due to the torque drop, to the rotation speed command value (for example, the rotation speed during steady operation). In addition, in this embodiment, the detection signals output from the ammeter 35 and the rotation speed sensor 111 are used to determine whether an abnormality has occurred.

[0046] For example, based on the detection signal, the protection device 40 determines that an abnormal situation has occurred from behavior such as a sudden decrease in the current generated by the generator 20, the generation of a current with vibrations different from those during steady operation, or the difference in the rotation speed of the rotating shaft 110 exceeding the acceleration / deceleration rate during steady operation.

[0047] How the protection device 40 restores the rotation speed of the engine 10 to normal will be explained later with reference to FIGS. 2 and 3.

[0048] In this embodiment, the protection device 40 operates on an independent power supply system that is different from the power generation system 100 (aircraft, etc.). This allows the protection system to operate even if the power supply system of the aircraft, etc., is lost. In other words, it is possible to constantly generate braking torque, and the operation of restoring the rotation speed to normal is performed stably.

[0049] The generated power obtained by utilizing the rotational force of the engine 10 is supplied to a power distribution line 60 connected to a load 61, a battery 62, etc. via a converter 51 that converts AC to DC. The converter 51 is a power conversion device that converts the power generated by the generator 20 into a predetermined power and supplies it to the power distribution line 60.

[0050] The power distribution line 60 may be provided with a protective device such as a circuit breaker that cuts off the power supply to the load 61 in the event of a malfunction such as a short circuit or a ground fault in the load 61. An auxiliary generator 70 driven by a power source other than the engine 10 may also be connected to the power distribution line 60. An example of the other power source is a propeller or other such drive mechanism. In this case, the auxiliary generator 70 generates power by the rotation of the propeller. The power generated by the auxiliary generator 70 is supplied to the power distribution line 60 via a power converter such as the converter 52.

[0051] The load 61 is, for example, a hydraulic pump that drives various hydraulic devices in the aircraft, an air conditioner, and other electronic devices, and in the case of an electric aircraft, includes a motor that drives a propeller or other thruster.

[0052] The battery 62 is a rechargeable secondary battery used as an auxiliary power source, and includes the battery itself and a charge / discharge circuit that controls the charging and discharging of the battery.

[0053] Fig. 2 is a block diagram showing the configuration of the protection device 40. For simplification, Fig. 2 only shows a portion of the engine 10, converter 51, etc. Also, the FADEC 30, ammeter 35, rotation speed sensor 111, auxiliary generator 70, etc. are omitted from the illustration.

[0054] 2, the protection device 40 includes a resistor unit 41, a switch 42, and a control unit 43. The protection device 40 is connected to the generator 20 in parallel with the converter 51.

[0055] The resistance unit 41 is connected to the AC lines 9 (9U, 9V, 9W) between the generator 20 and the converter 51, and consumes the power generated by the generator 20. In this embodiment, the resistance unit 41 has resistors of the same value arranged in parallel for each of the three phases, U phase, V phase, and W phase. Also in this embodiment, the resistance unit 41 is arranged in parallel with the converter 51. Note that the resistance value and number of the resistance unit 41 are not limited, and resistors of different values ​​may be arranged, or the resistance unit 41 may be connected to at least two of the three phases.

[0056] The switches 42 are semiconductor switches that switch between an open and closed connection state based on an open / close signal output from the control unit 43. In the present embodiment, the switches 42 are connected to the AC lines 9 (9U, 9V, 9W) via the protection lines 45U, 45V, 45W, and are disposed between the AC lines 9 and each of the resistance units 41.

[0057] The control unit 43 controls the switch 42 when an abnormality occurs. In this embodiment, the control unit 43 determines whether an abnormality has occurred based on the rotation speed of the rotating shaft 110 detected by the rotation speed sensor 111 and the current of the generator 20 detected by the ammeter 35. In this embodiment, the control unit 43 also outputs an opening / closing signal to control the switch 42 based on the rotation speed command value output from the FADEC 30 so that the rotation speed of the rotating shaft 110, which has increased due to the abnormality, returns to an appropriate rotation speed (typically the rotation speed immediately before the abnormality occurred).

[0058] In this embodiment, the switching signal is a PWM signal. The switch 42 starts a switching operation based on the switching signal. For example, when the switch 42 is short-circuited and the generator 20 is connected to the resistor 41, a braking torque is generated. In other words, the lost load torque seen from the engine 10 side is compensated for, and the torque that contributes to an increase in the rotation speed of the engine 10 is reduced, thereby suppressing the increase in the rotation speed.

[0059] In this embodiment, the control unit 43 controls the switch 42 so that the current rotation speed, which has increased due to torque loss, returns to a predetermined rotation speed. Here, the predetermined rotation speed is a rotation speed command value output from the FADEC 30. That is, the control unit 43 determines the value of the braking torque using a speed control system that maintains the rotation speed, using the rotation speed command value of the engine 10 during steady operation, and reflects this value in the switching operation of the switch 42.

[0060] The specified rotation speed is not limited to the rotation speed during steady-state operation, and an upper limit may be set based on the rotation speed (rotational speed) allowable by the engine 10, or a lower limit may be set based on the rotation speed at which aircraft, etc., cannot fly.

[0061] Here, the difference between the case where the rotation speed of the engine 10 is reduced using only the FADEC 30 and the case where the rotation speed of the engine 10 is reduced using the FADEC 30 and the protection device 40 will be described with reference to FIG.

[0062] 3A and 3B are graphs showing the relationship between the rotation speed of the engine 10, the generator torque, and the engine command torque. Fig. 3A shows the relationship when only the FADEC 30 is used. Fig. 3B shows the relationship when the FADEC 30 and the protection device 40 are used. In Fig. 3, the horizontal axis represents time, the left vertical axis represents torque, and the right vertical axis represents rotation speed.

[0063] As shown in FIG. 3A, when torque loss occurs due to loss of load 61 (see the time indicated by dashed line 80), generator torque 81, which had been a negative value, becomes zero, and the rotation speed 82 of engine 10 increases.

[0064] Furthermore, in order to reduce the rotation speed 82 of the engine 10, the engine command torque 83 output to the engine 10 is reduced. In this embodiment, this is achieved by adjusting the flow rate of fuel introduced from the fuel injector 121 to the combustor 12 by the FADEC 30.

[0065] However, the time constant for fuel adjustment by the FADEC 30 is long, and it takes time for the rotation speed of the engine 10 to return to the rotation speed during steady operation. In other words, the FADEC 30, which throttles the flow rate of fuel in response to an increase in rotation speed, cannot completely suppress the increase in rotation speed of the engine 10.

[0066] The time constant here refers to the time constant of the engine 10 including the control system of the FADEC 30, and refers to the time from when fuel control is started until the rotation speed of the engine 10 settles down (reaches a predetermined rotation speed, which is a target value). Typically, the time constant is a value specific to the type of engine, etc.

[0067] As shown in FIG. 3B, when torque loss occurs (see the time indicated by the dashed line 80), the engine command torque 85 is reduced and an opening / closing signal is output to the switch 42 in order to reduce the rotation speed of the engine 10.

[0068] The switch 42 performs a switching operation in accordance with a switching signal based on a rotation speed command value output from the FADEC 30. Note that in FIG. 3B, a time lag occurs between the operation period 84 during which the switching operation is performed and the timing 80 at which torque loss occurs. This occurs because the occurrence of torque loss is detected by detecting fluctuations in rotation speed and current. However, this time lag can be ignored because it is almost negligible from the engine's perspective.

[0069] The operation period 84 may be set based on the time constant of the engine 10, or the switching operation may be continued until the rotation speed of the engine 10 falls within a predetermined range.

[0070] The control unit 43 also controls the braking torque (generator torque 86) in synchronization with the fuel adjustment (engine command torque 85) by the FADEC 30, and transitions to a steady operation state in which there is no output from the generator 20. At this time, the switch 42 returns to the open state. That is, the control unit 43 controls the generator torque by outputting an open / close signal to the switch 42, and controls the rotation speed of the engine 10 to a predetermined rotation speed that is a target value.

[0071] FIG. 4 is a flowchart showing the control of the protection device 40.

[0072] As shown in FIG. 4, the rotational speed of the rotating shaft 110 is detected by the rotational speed sensor 111, and the current of the generator 20 is detected by the ammeter 35 (step 101).

[0073] The control unit 43 determines whether an abnormal situation has occurred (step 102). In this embodiment, it is determined that an abnormal situation has occurred when at least one of the following cases is detected: a sudden decrease in the current of the generator 20, generation of a current with vibration different from that during steady operation, or a difference in the rotation speed of the rotating shaft 110 (for example, the difference between the current rotation speed and the rotation speed one frame before) exceeds the acceleration / deceleration rate during steady operation of the equipment.

[0074] If no abnormality has occurred (NO in step 102), the process returns to step 101. The timing at which the detection signal is output or the timing at which the protection device 40 requests a detection signal is not limited. For example, the detection signal may be output constantly, or the detection signal may be requested at predetermined time intervals. Furthermore, for example, the detection signal may be requested based on the timing at which the FADEC 30 performs fuel adjustment.

[0075] If an abnormal situation occurs (YES in step 102), the control unit 43 controls the switch 42 (step 103).

[0076] FIG. 5 is a diagram showing an example of generation of an opening / closing signal by the control unit 43. In FIG.

[0077] 5, in this embodiment, PI control is performed based on the rotation speed command value output from the FADEC 30 and the current shaft rotation speed of the generator 20. A switching signal (open / close signal) is obtained by comparing the duty ratio in the PWM control of the resistor unit 41 obtained by the PI control with a triangular wave.

[0078] Furthermore, based on the opening and closing signal, the current when the resistor unit 41 is on or off is calculated, and the current is calculated taking into account the time constant of the generator 20. The time constant of the generator 20 in this embodiment is the electrical time constant of the generator 20, and takes into account the response delay time from when the pulse-like voltage after switching obtained by the triangular wave comparison is applied to the generator 20 until it appears as a current value flowing through the generator 20.

[0079] When performing the calculation, the AC generator is treated as a DC generator and the calculation is performed using values ​​equivalent to DC current, so the shape of the current is sawtooth, similar to the torque waveform. The calculated current is converted to torque. Furthermore, the converted torque is controlled by the PWM controlled switching of the resistor unit 41 as described above and is obtained from the sawtooth current, so it becomes torque that changes over time in a sawtooth pattern. Note that the sawtooth shape refers to a shape like the generator torque 86 during the operating period 84 shown in Figure 3B.

[0080] This opening / closing signal is given to the switch 42. For example, the rotation speed of the engine 10 is constant in a stable state (for example, a state in which the aircraft is flying at a constant speed), and the braking torque is controlled in accordance with the current shaft rotation speed of the generator 20 using that rotation speed as a rotation speed command value.

[0081] In this embodiment, the control unit 43 controls the switch 42 to perform a switching operation so that the braking torque gradually decreases in synchronization with the fuel adjustment (engine command torque) by the FADEC 30 .

[0082] It is determined whether the rotation speed of the rotating shaft 110 has reached a predetermined rotation speed through the switching operation of the switch 42 by the control unit 43 and the fuel adjustment by the FADEC 30 (step 104). Note that the rotation speed of the rotating shaft 110 reaching the predetermined rotation speed does not only mean that the rotation speed matches the predetermined rotation speed, but also means that the rotation speed of the rotating shaft 110 has converged (stabilized) within a certain range of the predetermined rotation speed for a predetermined period of time. In other words, the rotation speed does not need to match the rotation speed command value output from the FADEC 30 without error, and some error is acceptable.

[0083] If the rotation speed falls within the predetermined range (YES in step 104), the control unit 43 opens the switch 42.

[0084] As described above, according to this embodiment, even if the load on the generator 20, such as the load 61, is lost, the load on the engine 10 is eliminated and the rotation speed of the rotating shaft 110 increases, the rotation speed of the engine 10 can be returned to the stable rotation speed when the vehicle was cruising safely before reaching the danger zone.

[0085] In particular, according to this embodiment, a resistance unit 41, which is a three-phase resistor for absorbing power, and a switch 42 having a mechanism for continuously switching the resistance unit 41 are provided in the AC section between the generator 20 and the converter 51, which is the controller for the generator 20. Therefore, the resistance unit 41 is connected via the switch 42, and when torque loss occurs, a braking torque of any magnitude can be generated from the generator 20 as a regenerative brake in coordination with fuel adjustment by the FADEC 30.

[0086] <Modifications> For example, in the above embodiment, the switch 42 is controlled by an opening / closing signal that feeds back the rotation speed of the rotating shaft 110 in response to a rotation speed command value, and the value of the braking torque is determined using a speed control system, but this is not limited to this. For example, according to the present invention, since the time constant of the FADEC 30 that adjusts the engine 10 is specific to each individual engine, the way in which the braking torque is reduced may be determined in advance using a fixed torque pattern that corresponds to the time constant.

[0087] 6A and 6B are diagrams showing other examples of generation of an opening / closing signal by the control unit 43. Fig. 6A is a diagram showing an example in which the opening / closing signal is controlled by a fixed torque pattern. Fig. 6B is a diagram showing an example of the fixed torque pattern.

[0088] As shown in Fig. 6A, for example, the rotation speed command value output from the FADEC 30 is treated as a duty ratio in the PWM control of the resistor unit 41, and a switching signal (open / close signal) is obtained by comparing the duty ratio with a triangular wave. For example, in the graph of Fig. 6B, the vertical axis represents the braking force (duty) and the horizontal axis represents the time from braking. In this case, the fixed torque pattern may include a ramp decay section (a section in which the torque decreases linearly) between a duty ratio of 1 (constant braking) and a duty ratio of 0 (brake release). In other words, a torque pattern may be set that gradually weakens the braking torque value.

[0089] Based on the switching signal, the current when the resistor unit 41 is on or off is calculated, and the current is calculated taking into account the time constant of the engine 10. When making the calculation, the AC generator is treated as a DC generator and the calculation is performed using values ​​equivalent to DC current, so the shape of the current is sawtooth, similar to the torque waveform. The calculated current is converted into torque. Furthermore, since the converted torque is controlled by the PWM controlled switching of the resistor unit 41 as described above and is obtained from the sawtooth current, the torque changes in a sawtooth pattern over time.

[0090] In this case, the speed control system only determines the maximum value of the braking torque, so that coordination with fuel adjustment by the FADEC 30 can be simplified, and the system configuration can be simplified and made highly reliable.

[0091] Second Embodiment Next, a second embodiment of the present invention will be described. In the following description, the description of the same components and functions as those of the power generation system 100 described in the first embodiment will be omitted or simplified.

[0092] 7 is a block diagram showing the configuration of the protection device 140 according to this embodiment. For the sake of simplicity, only the engine 10, the converter 51, and other components are shown in the figure, and the FADEC 30, the ammeter 35, the rotation speed sensor 111, the auxiliary generator 70, and other components are omitted (the same applies to FIG. 8 relating to a third embodiment and FIG. 9 relating to a fourth embodiment, which will be described later).

[0093] In this embodiment, the generator 20 is a three-phase synchronous generator that is connected to the engine 10 and generates three-phase AC power. For example, the generator 20 generates power using a permanent magnet field.

[0094] 7 , the protection device 140 is connected to the AC line 90 (90U, 90V, 90W) that connects the generator 20 and the converter 51. The protection device 140 has a battery 141, a switch 142, and a switch controller 143. As in the first embodiment, the protection device 140 is connected to the generator 20 in parallel with the converter 51, and is configured to be able to generate a braking torque that limits the rotation speed of the rotating shaft 110 to a predetermined rotation speed based on the outputs of sensors (the ammeter 35 and the rotation speed sensor 111).

[0095] The battery 141 is connected to the AC line 90 (90U, 90V, 90W) via a switch 142, and is capable of charging (storing) the power generated by braking torque. The power charged in the battery 141 is used to assist the power supply of the aircraft's auxiliary machinery. The battery 141 is an example of a load mechanism.

[0096] The battery 141 is connected in series with the switch 142 and is connected to at least two of the three phases of the protection lines 145U, 145V, and 145W that are connected in parallel with the three-phase AC lines 90U, 90V, and 90W, respectively. Note that the battery 141 is not limited to any particular type as long as it is capable of storing power, and a capacitor or the like may be used.

[0097] The switch 142 is connected to the AC lines 90 (90U, 90V, 90W) via protection lines 145U, 145V, 145W. The switch 142 is configured to be able to convert or cut off power between the generator 20 and the battery 141. In other words, the switch 142 has a function as a switch that switches the connection state between the generator 20 and the battery 141 based on a control signal output from the switch controller 143, and a function as a converter that converts the input current from AC to DC.

[0098] For example, the switch 142 includes a switching circuit that connects any two of the three-phase protection lines 145U, 145V, and 145W to the positive and negative electrodes of the battery 141, and an AC-DC converter including a diode circuit, a chopper circuit, or the like. The chopper circuit may function as the switching circuit. Note that the switch 142 requires conversion from three-phase AC to DC to generate braking torque, but does not necessarily require conversion from DC to three-phase AC.

[0099] When an abnormal situation occurs, the switch controller 143 controls the switch 142. For example, the occurrence of an abnormal situation is determined by sensors (the ammeter 35 and the rotation speed sensor 111) based on at least one of the rotation speed of the rotating shaft 110, the current generated by the generator 20, the voltage generated by the generator 20, and the power generation state.

[0100] In this embodiment, the switch controller 143 outputs a control signal to the switch 142 upon receiving a signal indicating an abnormality that is output when the power generation state of the generator 20 or a difference in rotation speed is detected.

[0101] The control signal is a signal suitable for the operation of the switch 142. In this embodiment, since the switch 142 is a switch having a converter function, an electrical signal corresponding to a current command value for generating a braking torque is output as the control signal.

[0102] In this embodiment, the switch controller 143 outputs to the switch 142 a control signal for generating a braking torque that suppresses the rotation speed of the rotating shaft 110 to a predetermined rotation speed or less, based on the time constant of the engine 10. The predetermined rotation speed includes the rotation speed of the engine 10 when the aircraft is in cruising flight. Details of the torque pattern of the braking torque based on the time constant of the engine 10 will be described later.

[0103] In this embodiment, the control signal output to the switch 142, i.e., the torque pattern of the braking torque that keeps the rotational speed of the rotating shaft 110 below a predetermined rotational speed, aims to smoothly suppress the rotational speed (rotational speed) of the rotating shaft 110 that has increased due to torque loss (load loss) caused by the loss of the load 61 for some reason, without causing re-load loss and while maintaining an approximately constant deceleration.

[0104] Here, torque drop refers to a phenomenon in which the rotation speed of the rotating shaft 110 increases when the load is removed (see dashed line 80 in FIG. 3), as in the first embodiment. Reload drop refers to a phenomenon in which the rotation speed increases again, similar to torque drop, when the operation of the protection device 140 (braking torque) is stopped after the protection device 140 has suppressed the fluctuation in rotation speed caused by load drop.

[0105] Furthermore, in this embodiment, it is assumed that the converter 51, which is a converter for driving the three-phase generator, and the various loads 61 connected thereto have experienced some kind of trouble and are disconnected (in a load-disconnected state) when the protection device 140 operates. In other words, the protection device 140 does not require the presence or absence of the converter 51 and the load 61. Furthermore, even if a device that converts the power obtained from the generator 20 is connected or not connected to the output of the generator 20, the protection device 140 can operate without being affected by the connection of the load 61.

[0106] As described above, according to this embodiment, the regenerative power obtained by braking can be stored in the battery 141, and the stored power can be used to assist the auxiliary power supply of the aircraft. This makes it possible to use the stored power as a function that contributes to the management of the aircraft's onboard power supply.

[0107] Furthermore, because the protection device 140 is connected in parallel with the converter 51 to the AC line 90 of the generator 20, the protection device 140 can function independently even if a malfunction occurs in the converter 51 or the load 61 connected thereto. This makes it possible to improve the operating frequency and controllability of the protection device 140. Furthermore, it is possible to suppress the increase in the speed (rotational speed) of the rotating shaft 110, without causing reload loss behavior, and to obtain a smooth deceleration tendency. Furthermore, a protection system can be constructed even if the power supply specifications of the generator 20 and the power supply specifications of the load mechanism are different. Furthermore, the protection device 140 can operate regardless of the load connected to the generator 20. Therefore, the protection device 140 can improve the reliability of the power generation system 100.

[0108] 8 is a block diagram showing the configuration of a protection device 240 according to a third embodiment. This embodiment differs from the second embodiment in that a capacitor 241 is used instead of the battery 141. The following mainly describes the differences from the second embodiment.

[0109] 8 , the protection device 240 is connected to the AC line 90 (90U, 90V, 90W) that connects the generator 20 and the converter 51. The protection device 240 has a capacitor 241, a switch 242, and a switch controller 243. As in the first embodiment, the protection device 240 is connected to the generator 20 in parallel with the converter 51, and is configured to be able to generate a braking torque that limits the rotation speed of the rotating shaft 110 to a predetermined rotation speed based on the outputs of the sensors (the ammeter 35 and the rotation speed sensor 111).

[0110] The capacitor 241 is connected to the AC line 90 via the switch 242 and is capable of charging (storing) the power generated by the braking torque. For example, an electric double layer capacitor or the like is used as the capacitor 241. The capacitor 241 can also discharge the charged power to compensate for momentary power shortages during normal operation due to normal load fluctuations other than when the converter 51 or the like fails. The capacitor 241 is an example of a load mechanism.

[0111] The capacitor 241 is connected in series with the switch 242, and is connected to at least two of the three phases of the protection lines 245U, 245V, and 245W that are connected in parallel with the three-phase AC lines 90U, 90V, and 90W, respectively. Note that the capacitor 241 is not limited to any particular configuration as long as it can store power, and a battery or the like may be used.

[0112] The switch 242 is connected to the AC lines 90 (90U, 90V, 90W) via protection lines 245U, 245V, 245W. The switch 242 is configured to be able to convert or cut off power between the generator 20 and the capacitor 241. In other words, the switch 242 has a function as a switch that switches the connection state between the generator 20 and the capacitor 241 based on a control signal output from the switch controller 243, and a function that bidirectionally converts the input current from AC to DC or from DC to AC.

[0113] That is, when braking torque is generated on the rotating shaft 110, the switch 242 converts the power on the AC line 90 from three-phase AC to DC and supplies it to the capacitor 241, and when a normal load fluctuation occurs other than when the converter 51 or the like fails, the switch 242 converts the power stored in the capacitor 241 from DC to three-phase AC and supplies it to the AC line 90. For example, an inverter circuit or a converter for controlling a generator is used as the switch 242. Alternatively, the switch 242 may be configured to have a function of coordinating with the three-phase AC system, such as the AC line 90 of the generator 20 and the converter 51. Note that the three-phase AC is not released into the system when a failure occurs, but is released during normal operation.

[0114] In this embodiment, the switch controller 243 receives a signal indicating an abnormality that is output when the power generation state or the difference in current between the generator 20 and the normal operation state of the generator 20 is detected, and outputs a control signal to the switch 242.

[0115] In addition, in this embodiment, the difference in current from that during normal operation of the generator 20 is detected, so if the engine 10 is at a constant speed, it is possible to determine an abnormality from the difference in current from that during normal operation, and therefore the protective function of generating a braking torque by the protective device 240 can be used.

[0116] As described above, according to this embodiment, regenerative power obtained by braking can be stored in the battery 241. Furthermore, when a normal load fluctuation occurs other than when the converter 51 or the like fails, the stored power can be returned to the grid, thereby stabilizing control of the grid load fluctuation. This makes it possible to utilize this function as a contribution to the management of the aircraft's onboard power supply. Furthermore, the conversion function of the switch 242 does not require a special circuit, and a general converter configuration can be used, thereby contributing to the robustness of the system.

[0117] Furthermore, by connecting the battery 241 and the switch 242 in parallel with the converter 51 and the load 61 to the AC line 90 of the generator 20, the protection device 240 can function independently of the converter 51 and the load 61, thereby improving the operating frequency and controllability of the protection device 240. Furthermore, it is possible to suppress the increase in the speed (rotational speed) of the rotating shaft 110, without causing reload loss behavior, and to obtain a smooth deceleration trend. Furthermore, a protection system can be constructed even when the power supply specifications of the generator 20 and the power supply specifications of the load mechanism are different. Furthermore, the protection device 240 can operate regardless of the load connected to the generator 20. Therefore, the protection device 240 can improve the reliability of the power generation system 100.

[0118] <Fourth embodiment> Fig. 9 is a block diagram showing the configuration of a protection device 340 according to a fourth embodiment. This embodiment differs from the second embodiment in that a dual three-phase synchronous generator is used as the generator 20. Only the differences from the second embodiment will be described below, and the description of the commonalities will be simplified.

[0119] 9, the generator 20 and the converter 51 are connected by two sets of three-phase AC lines 90U, 90V, 90W, 90U', 90V', 90W'. Hereinafter, one of the three-phase AC lines (90U, 90V, 90W) will be referred to as group A, and the other three-phase AC lines (90U', 90V', 90W') will be referred to as group B (see FIG. 10).

[0120] 9 , the protection device 340 is connected to the two sets of three-phase AC lines 90U, 90V, 90W, 90U′, 90V′, 90W′. The protection device 340 includes a battery 341, a switch 342, and a switch controller 343. As in the first embodiment, the protection device 340 is connected to the generator 20 in parallel with the converter 51, and is configured to be able to generate a braking torque that limits the rotation speed of the rotating shaft 110 to a predetermined rotation speed based on the outputs of sensors (the ammeter 35 and the rotation speed sensor 111).

[0121] Fig. 10 is a diagram showing the configuration and operation of the switch 342. Fig. 10A is a diagram showing the configuration of the switch 342. Fig. 10B is a diagram showing an example of the operation of the switch 342.

[0122] As shown in FIG. 10A, the switch 342 has a group A converter 342A connected to group A AC lines 90U, 90V, and 90W, and a group B converter 342B connected to group B AC lines 90U', 90V', and 90W'.

[0123] The group A converter 342A is connected to each of the three-phase AC lines 90U, 90V, and 90W of the group A via protection lines 345U, 345V, and 345W. The group A converter 342A includes a switching circuit capable of connecting the three-phase protection lines 345U, 345V, and 345W to the positive and negative electrodes of the battery 341, and an AC-DC converter including a diode circuit, a chopper circuit, or the like that converts the current input from the protection lines 345U, 345V, and 345W into DC.

[0124] Similarly, the group B converter 342B is connected to the group B three-phase AC lines 90U', 90V', 90W' via protection lines 345U', 345V', 345W', respectively. The group B converter 342B includes a switching circuit capable of connecting the three-phase protection lines 345U', 345V', 345W' to the positive and negative electrodes of the battery 341, and an AC-DC converter including a diode circuit, chopper circuit, etc. that converts the current input from the protection lines 345U', 345V', 345W' into DC. The chopper circuit may function as the switching circuit.

[0125] The battery 341 is connected in common to the group A converter 342A and the group B converter 342B. As shown in Fig. 10A, the positive electrodes of the group A converter 342A and the group B converter 342B are connected to the positive electrode of the battery 341 via one DC line 346, and the negative electrodes of the group A converter 342A and the group B converter 342B are connected to the negative electrode of the battery 341 via the other DC line 346'. Note that the battery 341 is not limited as long as it has a configuration capable of storing power, and a capacitor or the like may be used. Alternatively, a battery for the group A and a battery for the group B may be provided separately as the battery 341.

[0126] The switch 342 may operate either the group A converter 342A or the group B converter 342B, or may simultaneously operate both the group A converter 342A and the group B converter 342B. In this embodiment, the switch 342 individually determines whether there is an abnormality based on the AC current input to the group A converter 342A and the group B converter 342B, and operates as follows.

[0127] If an abnormality occurs in the load connected to group A, only the group A converter 342A is operated. If an abnormality occurs in the load connected to group B, only the group B converter 342B is operated. If an abnormality occurs in the load connected to groups A and B, both the group A converter 342A and the group B converter 342B are operated. If an abnormality occurs in the load connected to groups A and B, only the group A converter 342A is operated. If an abnormality occurs in the load connected to groups A and B, only the group B converter 342B is operated.

[0128] In other words, the protection device 340 may be operated only in the group A or B in which an abnormality has occurred, and the healthy group in which no abnormality has occurred may be allowed to operate normally, or if an abnormality has occurred in both groups, the protection device 340 may be operated in only one of the groups.

[0129] 10B, when abnormalities occur in both groups, the protection device 340 can also operate the group A converter 342A and the group B converter 342B alternately and complementarily for a predetermined period. This type of operation does not affect the charging of the battery 341 caused by the alternating operation of the group A converter 342A and the group B converter 342B. Furthermore, since the alternating operation of the group A converter 342A and the group B converter 342B does not result in a loss of torque from the generator 20, there is no problem in terms of braking force.

[0130] In addition, since the combined power of the A group converter 342A and the B group converter 342B is output from the switch 342 to the battery 341 via DC lines 346, 346', the switching circuit (or chopper circuit) as a switch may be a single switching circuit common to the A group converter 342A and the B group converter 342B.

[0131] As described above, according to this embodiment, regenerative power obtained by braking can be stored in the battery 341. Furthermore, the power stored in the battery 41 can be used to assist the auxiliary power supply of the aircraft. This enables the battery 41 to be used as a function that contributes to the management of the aircraft's onboard power supply. Furthermore, because the power stored in the battery 41 is not regenerated and fed back to the AC line 90 of the generator 20, the switch 342 can be realized with a simple circuit configuration, which contributes to weight reduction.

[0132] Furthermore, by connecting the battery 341 and the switch 342 in parallel with the converter 51 and the load 61 to the AC line 90 of the generator 20, the protection device 340 can function independently of the converter 51 and the load 61, thereby improving the operating frequency and controllability of the protection device 340. Furthermore, it is possible to suppress the increase in the speed (rotational speed) of the rotating shaft 110, without causing reload loss behavior, and to obtain a smooth deceleration trend. Furthermore, a protection system can be constructed even when the power supply specifications of the generator 20 and the power supply specifications of the load mechanism are different. Furthermore, the protection device 340 can operate regardless of the load connected to the generator 20. Therefore, the protection device 340 can improve the reliability of the power generation system 100.

[0133] Furthermore, in this embodiment, the use of a multi-phase generator increases the flexibility of the phases or groups to be used, contributing to redundancy. Furthermore, because the DC portion of the switch 342 (DC lines 346, 346') can combine power, it is easy to simultaneously handle power from each phase or group. Furthermore, using a single load mechanism contributes to weight reduction, and if the load mechanisms are separated for each phase or group, they do not interfere with each other, allowing the protection device 340 to operate stably.

[0134] [Regarding the Torque Pattern of the Braking Torque Based on the Time Constant of the Engine] Next, a description will be given of the torque pattern of the braking torque by the protection devices 40, 140, 240, and 340 based on the time constant of the engine 10. Note that the following description is applicable to each of the switch controllers in the first to fourth embodiments.

[0135] The time constant of the engine 10 is the time constant of the entire system including the control system of the engine 10 and the FADEC 30. Because the mechanical and control parameters of the engine 10 are eigenvalues ​​determined for each aircraft, the time constant of the engine 10 is uniquely determined. For this reason, the time constant of the engine 10 is significantly related to determining the operation period 84 (see FIG. 3B ) of the protection device that generates braking torque. Here, the behavior of the low-pressure shaft speed due to a load loss event will be described as an example, assuming an engine size of a twin-engine, single-aisle passenger aircraft.

[0136] First, engine requirements for load shedding include preventing engine speed from rising to a dangerous range and preventing sudden torque fluctuations in the engine's low-pressure shaft. Therefore, in this embodiment, the torque pattern of the braking torque is set based on the following algorithm. This allows for smooth suppression of increases in the speed of the rotating shaft while maintaining a substantially constant deceleration rate without causing reload shedding. (A) The braking torque pattern is a damping pattern that initially applies maximum torque and then damps it. (B) The maximum torque continues for an initial first predetermined time, and the damping pattern gradually damps the braking torque over a second predetermined time, which is longer than the first predetermined time, after the first predetermined time has elapsed. (C) The maximum torque value is set to 50% of the load shedding amount. (D) The damping pattern is based on a logarithmic function. Details of this pattern are described below.

[0137] (1) Damping Pattern The damping pattern of the braking torque will be described with reference to Fig. 11. Fig. 11 is a timing chart showing a typical damping pattern of the braking torque generated by the protection devices 40, 140, 240, 340, and 342 according to the embodiment, with the horizontal axis representing the time when torque loss occurs (t １ The vertical axis shows the braking torque, and the vertical axis shows the time when the braking torque is applied. １ for a certain period of time (time t ２１ ~Time t ２２ ) and then stop the operation (see FIG. 11A). ２ for a certain period of time (time t ３１ ~Time t ３２ ) and time t ３２ From time t ３３ The second method (see FIG. 11B) gradually reduces the torque over a certain period of time. The first method is based on the premise that, in principle, speed increase will not occur if the lost torque is compensated for at a constant rate. However, if braking operation is stopped after torque fluctuations are suppressed, a speed increase (reload loss) similar to torque loss may occur again, making it unavoidable for the engine speed to increase. For this reason, this embodiment employs the second method described above, in which, after braking operation has been performed for a certain period of time, the torque is gradually attenuated without stopping the braking operation.

[0138] (2) Regarding the duration of application of braking torque: Factors that determine the braking torque pattern include the duration of constant operation, the decay time, the magnitude of the constant torque, and the decay method. In order to suppress fluctuations in the rotation speed of the rotating shaft, it is preferable to apply braking torque to the rotating shaft for a time period equivalent to or longer than the time constant of the engine 10. More preferably, by continuing the braking torque for a time period longer than the time constant of the engine 10, it is possible to stably suppress an increase in the rotation speed of the rotating shaft without causing re-acceleration due to reload loss.

[0139] Furthermore, the braking torque pattern is such that the maximum torque F ２ After that, the brake is applied for a predetermined time (time t ３２ ~Time t ３３) is applied to gradually attenuate the braking torque. ３１ ~Time t ３２ ) is set as the first predetermined time, the first predetermined time is the period during which the engine speed increases immediately after the load drop. ３３ ) is defined as the second predetermined time, which is a period longer than the first predetermined time and is the period from when the engine speed, which has increased immediately after the load is released, starts to decrease until it returns to its original speed.

[0140] For example, if the time constant of the engine system is set to 4 seconds (the rotation speed increases in 1 second, decreases in 3 seconds, and returns to the original rotation speed) after torque loss occurs, the first predetermined time is set to, for example, 1 second, and the second predetermined time is set to, for example, 3 to 5 seconds. This makes it possible to effectively suppress a sudden increase in rotation speed immediately after load loss, while also suppressing re-information on the rotation speed due to re-load loss.

[0141] (3) Maximum Torque With respect to a sudden increase in rotation speed immediately after load loss, the greater the braking torque applied to the rotating shaft, the greater the effect of reducing the increase in rotation speed. However, as the torque increases, there is a tendency for the speed to increase beyond the initially suppressed speed after load loss occurs, so there is a limit to the maximum value of the torque that can be applied. Therefore, in this embodiment, the maximum value of the braking torque is set to 50% or less of the torque that has been lost due to load loss (in this embodiment, 50% of the rated torque of the generator), thereby significantly suppressing the increase in rotation speed due to load loss.

[0142] (4) Regarding the Decay Pattern of the Braking Torque In order to reduce the rotational speed without causing a reload drop, it is necessary to smooth out torque fluctuations during braking and maintain a constant deceleration rate. More specifically, examples of the deceleration pattern of the braking torque executed during the second predetermined time period include a linear deceleration pattern and a logarithmic deceleration pattern. In this embodiment, a torque pattern based on a logarithmic function is adopted as the deceleration pattern of the braking torque. This makes it possible to reduce the rotational speed of the rotating shaft to its original speed at a substantially constant deceleration rate while suppressing torque fluctuations in the rotating shaft after switching the braking torque from the maximum torque to the deceleration pattern.

[0143] DESCRIPTION OF SYMBOLS 10... Engine 11... Compressor 12... Combustor 13... Turbine 20... Generator 21... Drive shaft 30... FADEC 35... Ammeter 40... Protection device 41... Resistor section 42... Switch 43... Control section 51, 52... Converter 61... Load 62... Battery 70... Auxiliary generator 100... Power generation system 111... Rotational speed sensor 121... Fuel injector 140, 240, 340... Protection device 141, 341... Battery 142, 242, 342... Switch 143, 243, 343... Switch controller 242... Capacitor

Claims

1. A protection system comprising: a generator connected to a rotating shaft of an engine; a converter that converts AC power output from said generator into DC power; a detector that monitors the power generation state of said generator; and a protection device connected to said generator in parallel with said converter, said protection device having a load mechanism, a switch that switches the connection state between said generator and said load mechanism, and a control unit that determines the presence or absence of an abnormality in said generator based on the output of the detector, and when said abnormality is determined, controls said switch to generate a braking torque on said rotating shaft that keeps the rotation speed of said rotating shaft below a predetermined rotation speed.

2. A protection system according to claim 1, wherein the detector monitors at least one of the number of revolutions of the rotating shaft or the current generated by the generator.

3. A protection system as claimed in claim 2, wherein the control unit judges that an abnormality has occurred when the difference between the current rotation speed of the rotating shaft and a predetermined rotation speed during steady operation of the generator is equal to or greater than a predetermined value.

4. A protection system as claimed in claim 2, wherein said control unit judges that an abnormality has occurred when the difference between the present current and a predetermined current during steady operation of said generator is equal to or greater than a predetermined value.

5. A protection system as claimed in claim 2, wherein said control unit judges that an abnormality has occurred when oscillations different from oscillations of the current during steady-state operation of said generator are occurring in the current.

6. A protection system according to claim 1, wherein the control unit controls the switch in accordance with a torque pattern based on a time constant of the engine.

7. A protection system according to claim 6, wherein said torque pattern includes gradually decaying said braking torque.

8. A protection system as claimed in claim 7, wherein the control unit generates a predetermined maximum value of the braking torque for a first predetermined time, and then gradually attenuates the braking torque over a second predetermined time that is longer than the first predetermined time.

9. A protection system according to claim 8, wherein the predetermined maximum value is equal to or less than 50% of the rated torque of the generator.

10. A protection system according to claim 8, wherein said control unit decays said braking torque logarithmically over said second predetermined time period.

11. A protection system as claimed in claim 1, further comprising an engine control unit which controls the amount of fuel introduced into the engine to control the engine speed to a command value, and the control unit controls the switch based on the command value for the engine speed output from the engine control unit.

12. A protection system as claimed in claim 11, wherein the predetermined rotation speed is the rotation speed command value output from the engine control unit, and the control unit determines the braking torque so as to maintain the rotation speed command value, and controls the switch to generate the determined braking torque.

13. A protection system according to claim 1, wherein the load mechanism is a resistor connected to an AC line between the generator and the converter and consuming the power generated by the generator.

14. A protection system according to claim 1, wherein the load mechanism is a battery or a capacitor connected to an AC line between the generator and the converter and capable of storing power generated by the generator.

15. A protection system according to claim 14, wherein the switch includes a DC-AC converter capable of supplying the power stored in the battery or capacitor to the AC line.

16. A protection system according to claim 1, wherein the switch is provided between the load mechanism and an AC line between the generator and the converter, and is configured to be able to convert or cut off power between the generator and the load mechanism.

17. A protection system according to claim 1, wherein the generator has a stator wound with a three-phase electromagnetic coil, and the load mechanism is connected between AC lines of at least two of the three phases.

18. A protection system according to claim 1, wherein the switch is provided between the AC line between the generator and the converter and the load mechanism.

19. A protection system as claimed in claim 1, wherein the engine is used in an aircraft, the predetermined rotation speed is the rotation speed of the engine when the aircraft is cruising, and the protection device generates the braking torque so that the rotation speed of the rotating shaft becomes the rotation speed of the engine.

20. A protective device comprising: a generator connected to a rotating shaft of an engine, a load mechanism connected to an AC line between a converter that converts AC power output from the generator into DC power, a switch that switches the connection state between the generator and the load mechanism, and a control unit that determines whether or not there is an abnormality in the generator based on the output of the detector, and when an abnormality is determined, controls the switch to generate a braking torque on the rotating shaft that keeps the rotation speed of the rotating shaft below a predetermined rotation speed.

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