Propulsion system and protection device for rotary electric machine

Abstract

A propulsion system according to one embodiment of the present invention comprises a motor, a rotary electric machine, a mechanical fuse, a sensor, and a protection device. The rotary electric machine is a permanent magnetic field-type rotary electric machine having a rotor connected to the motor. The mechanical fuse is connected between the motor and the rotary electric machine. The sensor monitors the state of the rotary electric machine. The protection device is configured to be capable of applying torsional vibration torque for breaking the mechanical fuse to the mechanical fuse on the basis of an output of the sensor.

Description

Propulsion system and protective device for rotating electrical machines

[0001] The present invention relates to a propulsion system, and more particularly to a protective device for a rotating electrical machine directly connected to a prime mover such as an engine or a turbine.

[0002] In recent years, in mobility applications such as ships and aircraft, systems have been under study in which rotating electric machines are directly connected to prime movers, such as engines and turbines, for hybrid propulsion and shaft power generation, which provide both power assist and electricity generation. In such systems, if a layer short circuit or bearing abnormality occurs and rotational force continues to be applied from the prime mover, permanent magnet rotating electric machines, in particular, are unable to reduce the field voltage, which can lead to fires caused by localized high heat or damage to the prime mover due to abnormal vibrations. Because crew members on ships and aircraft cannot immediately evacuate from the location of a fire, it is desirable to build a system that disconnects the rotating electric machine when signs of an accident are detected and allows evacuation by continuing to operate the prime mover.

[0003] Generally, a mechanism is required to mechanically separate the engine shaft and the generator shaft in the event of a malfunction, and examples of such mechanisms include a shear pin and a clutch mechanism. For example, Patent Document 1 describes a generator using a gas turbine as a prime mover, in which a shear pin is provided between the reducer and the generator to protect the prime mover from overload.

[0004] Japanese Patent Application Laid-Open No. 2000-37057

[0005] However, in cases of interlayer short circuits or bearing abnormalities, the transient torque at the time of the abnormality is small, so the shear pin does not operate. Meanwhile, the larger the capacity of the clutch mechanism, the larger and more expensive it becomes, which hinders its application to the mobility applications mentioned above. A new method is needed that can disconnect a failed rotating electric machine from the prime mover at any time before the accident spreads, while still allowing the prime mover to continue operating, using a system structure that minimizes increases in weight and cost compared to conventional methods.

[0006] In view of the above circumstances, the object of the present invention is to provide a propulsion system and a protective device for a rotating electric machine that can mechanically isolate a rotating electric machine showing signs of failure at any time while continuing to operate the prime mover when an abnormality in the rotating electric machine is detected.

[0007] A propulsion system according to one aspect of the present invention includes a prime mover, a rotating electric machine, a mechanical fuse, a sensor, and a protection device. The rotating electric machine is a permanent magnet field type rotating electric machine having a rotor connected to the prime mover. The mechanical fuse is connected between the prime mover and the rotating electric machine. The sensor monitors the state of the rotating electric machine. The protection device is configured to be able to apply to the mechanical fuse a torsional vibration torque that ruptures the mechanical fuse based on an output of the sensor.

[0008] According to the above-mentioned propulsion system, when an abnormality in the rotating electric machine is detected, a torsional vibration torque is applied to the mechanical fuse to cause the mechanical fuse to break, so that a rotating electric machine showing signs of failure can be mechanically disconnected at any time while the prime mover continues to operate.

[0009] The protection device may include a power converter, a protection load, and a control unit. The power converter is connected to the rotating electric machine. The protection load consumes power generated by the power converter. The control unit determines whether or not an abnormality exists in the rotating electric machine based on an output of the sensor, and inputs a control command to the power converter to generate the torsional vibration torque when it determines that the rotating electric machine is abnormal.

[0010] The control command may include a torque command value whose target torque value changes periodically.

[0011] The control unit may generate a torque command value that generates a torsional vibration torque having a frequency equivalent to a torsional resonance frequency of the mechanical fuse.

[0012] The protection device may further have a first circuit breaker capable of interrupting conduction between the power converter and a power load that operates by receiving power generated by the power converter, and the control unit may cause the first circuit breaker to interrupt conduction between the power converter and the power load when it determines that the rotating electric machine is abnormal.

[0013] The protection device may further have a second circuit breaker capable of interrupting conduction between the power converter and the protected load, and when the control unit determines that the rotating electric machine is not abnormal, it may cause the second circuit breaker to interrupt conduction between the power converter and the protected load.

[0014] The rotating electric machine may be a generator or a motor.

[0015] The mechanical fuse may be tubular in shape.

[0016] The sensor may be a temperature sensor that measures the temperature of the rotating electric machine, or a current sensor that detects the current flowing through the rotating electric machine.

[0017] The prime mover may be a jet engine.

[0018] A protection device according to one aspect of the present invention is a protection device for a rotating electric machine having a prime mover, a permanent magnet field type rotating electric machine having a rotor connected to the prime mover, and a mechanical fuse connected between the prime mover and the rotating electric machine, and includes a power converter, a protection load, and a control unit. The power converter is connected to the rotating electric machine. The protection load consumes power generated by the power converter. The control unit determines whether or not an abnormality exists in the rotating electric machine based on the output of a sensor that monitors the state of the rotating electric machine, and if it determines that the rotating electric machine is abnormal, inputs a control command to the power converter to generate a torsional vibration torque that will blow the mechanical fuse.

[0019] According to the present invention, when an abnormality in a rotating electric machine is detected, the rotating electric machine showing signs of failure can be mechanically separated at any timing while the prime mover continues to operate.

[0020] 1 is a schematic configuration diagram of a propulsion system according to an embodiment of the present invention. FIG. 1 is a schematic diagram showing the configuration of a generator. FIG. 2 is a control block diagram of the propulsion system during steady operation control. FIG. 3 is a schematic diagram showing a state when a layer short occurs in an electromagnetic coil of a generator wound in the same slot. FIG. 4 is an equivalent circuit diagram of a permanent magnet generator (PMSG). FIG. 5 is a control block diagram of the propulsion system during protection control. FIG. 6 is a waveform diagram showing an example of power oscillation. FIG. 7 is a diagram explaining the phase relationship between a prime mover and a generator. FIG. 8 is a diagram showing the relationship between the frequency of vibration torque and the response magnification. FIG. 9 is a diagram showing the relationship between the response torque acting on a mechanical fuse and the generator torque. FIG. 10 is a schematic configuration diagram of a propulsion system according to another embodiment of the present invention.

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0022] 1 is a schematic diagram of a propulsion system 100 according to an embodiment of the present invention. The propulsion system 100 according to the present embodiment is applied to a propulsion system installed in, for example, an aircraft, and includes a prime mover 10, a generator 20, and a protection device 40.

[0023] [Overview of Propulsion System] Examples of aircraft equipped with propulsion system 100 include aircraft equipped with prime mover 10 as a propulsion device, as well as electric aircraft that use electricity from generator 20 to drive auxiliary propulsion systems such as fans and propellers. In this propulsion system, prime mover 10 rotates a propulsion propeller to obtain thrust for cruising, and generates an electric load by operating generator 20 with surplus energy.

[0024] The prime mover 10 is, for example, a jet engine having a compressor, a combustor, a turbine, etc. The prime mover 10 drives a thruster 12 such as a propeller or a fan via gears 11, etc., and also drives a generator 20. The prime mover 10 is controlled by a prime mover controller 15 such as a Full Authority Digital Engine Control (FADEC). The prime mover controller 15 controls the fuel supply to the prime mover 10, etc., so as to maintain the speed by keeping the thruster 12 at a constant rotation speed during cruising.

[0025] The generator 20 is a permanent magnet synchronous generator (PMSG) that converts the rotational force of the rotating shaft 10a of the prime mover 10 into electrical energy. Fig. 2 is a schematic diagram showing the configuration of the generator 20. The generator 20 includes a rotor 21 having permanent magnets 21S, 21N, and a stator 22 around which multi-phase electromagnetic coils are wound.

[0026] The multi-phase electromagnetic coil is not particularly limited as long as it is an electromagnetic coil through which two or more alternating currents of different phases flow, and here, a three-phase electromagnetic coil of U-phase, V-phase, and W-phase is used. Electric power generated by generator 20 is supplied to power load 50 via a CVCF (Constant Voltage Constant Frequency) or the like. As will be described later, generator 20 may be a motor that performs power running to support the power of prime mover 10 (see FIG. 11 ).

[0027] The rotating shaft 20a (rotor 21) of the generator 20 is connected to the rotating shaft 10a of the prime mover 10 via a mechanical fuse 30. The mechanical fuse 30 transmits the rotational driving force of the prime mover 10 to the generator 20. A shear pin (also called a shear pin) is used as the mechanical fuse 30. The mechanical fuse 30 is formed in a tubular shape such as a cylindrical shape, or in a shape that is partially constricted to make it thinner, so that it can be broken by a predetermined torsional vibration torque that is electrically generated in a protection device 40, as will be described later.

[0028] The generator 20 is equipped with a monitoring sensor 31 that monitors the state of the generator 20. The monitoring sensor 31 may be a temperature sensor that measures the temperature of the generator 20 or a current sensor that detects the current generated by the generator 20. In this embodiment, the monitoring sensor 31 includes three temperature sensors 31a, 31b, and 31c that are attached to the stator 22 at equal angular intervals, as shown in FIG.

[0029] A current sensor 32 that detects the magnitude of the current flowing through the electromagnetic coil is attached between the generator 20 and the protection device 40 (power converter 41). This current sensor 32 is a sensor that feeds back the generator current to the control unit 43 so that the current generated in the generator 20 reaches a target current value. Note that the current sensor 32 may be used as the monitoring sensor 31 instead of or in addition to the temperature sensors 31a to 31c.

[0030] The protection device 40 functions as a power generation control device that controls the power generated by the generator 20 during normal operation when there is no abnormality in the generator 20, and has the function of protecting the generator 20 by disconnecting the generator 20 from the prime mover 10 when an abnormality is detected in the generator 20. More specifically, the protection device 40 monitors whether or not there is an abnormality in the generator 20, and when the generator 20 is normal, supplies the power generated by the generator 20 to the power load, and when an abnormality in the generator 20 is detected, generates a power oscillation to break the mechanical fuse 30 and disconnect the generator 20 from the prime mover 10. The protection device 40 will be described in detail below.

[0031] [Protection Device] The protection device 40 includes a power converter 41 , a protected load 42 , a control unit 43 , a first circuit breaker 51 , and a second circuit breaker 52 .

[0032] The power converter 41 is connected to the generator 20 and is a converter that converts AC power generated by the generator 20 into predetermined DC power consumed by the power load 50. The power load 50 is a power circuit or power equipment that operates by receiving the power generated by the power converter 41. Examples of the power load include electrical equipment such as fans and pumps installed on board the aircraft, as well as air conditioning equipment, batteries, and an auxiliary propulsion system.

[0033] The first circuit breaker 51 is a switch that can interrupt conduction between the power converter 41 and the power load 50. The first circuit breaker 51 is controlled to open and close by the control unit 43, and interrupts conduction between the power converter 41 and the power load 50 when an abnormality is detected in the generator 20, as will be described later.

[0034] The protective load 42 is an element that consumes the power generated by the power converter 41 to generate a power oscillation that breaks the mechanical fuse 30 and disconnects the generator 20 from the prime mover 10, and is configured as a resistive element in this embodiment. The resistive element that configures the protective load 42 may be a single resistive element or a group of resistive elements connected in series or in parallel.

[0035] The second circuit breaker 52 is a switch that can interrupt conduction between the power converter 41 and the protected load 42. The second circuit breaker 52 is controlled to open and close by the control unit 43, and as will be described later, when it is determined that the generator 20 is not abnormal, the second circuit breaker 52 interrupts conduction between the power converter 41 and the protected load 42.

[0036] 1, the control unit 43 includes a signal generating circuit 431. The signal generating circuit 431 generates a control signal for controlling the power generated by the power converter 41.

[0037] 3 is a control block diagram showing an example of the configuration of the propulsion system 100, illustrating details of the signal generation circuit 431 during steady operation control when no abnormality occurs in the generator 20. As shown in FIG. 3, the signal generation circuit 431 has a current command value generator 44, a current controller 45, and a power controller 46.

[0038] The current command value generator 44 generates a q-axis current command value i based on the torque target value τ* of the generator 20 and the power control signal output from the power controller 46. d * and q-axis current command value i q Generate *.

[0039] The torque target value τ* changes from moment to moment depending on the state of the power load 50, such as the fan or pump mounted on the aircraft. Since the generator 20 cannot control its speed, a new torque target value is calculated from the power measured on the load side and the generator speed and reset by the power controller 46 to balance the power consumed by the power load 50 and the power generated by the generator 20 and suppress voltage fluctuations to the equipment. If necessary, the accuracy of the current command value may be improved by feeding back information on the d-axis current, q-axis current, DC voltage, and speed.

[0040] The current controller 45 calculates the q-axis current command value i d * and q-axis current command value i q *Based on this, the voltage control amount V uvw * and supplies it to the power converter 41 as a control command. uvw The generator 20 is controlled based on the signal *, and the generated DC voltage Vdc is supplied to the power load 42.

[0041] The power controller 46 generates a power control signal to be fed back to the current command value generator 44 based on the output of the speed detector 33 that detects the rotation speed of the prime mover 10 and the power measurement value of the power load 50. The rotation speed of the prime mover 10 is determined by the engine speed command ω c * and the actual engine speed value ω detected by the speed detector 33 c The engine controller 15 controls the engine speed based on the above.

[0042] (Protection Control) The control unit 43 further has a determination unit 432 that determines an abnormality in the generator 20 based on the output of the monitoring sensor 31. When the determination unit 432 determines that the generator 20 is abnormal, the control unit 43 executes protection control to apply to the mechanical fuse 30 a torsional vibration torque that breaks the mechanical fuse 30 by inputting a torque command value, the target torque value of which changes periodically, to the power converter 41 as a control command to generate a torsional vibration torque.

[0043] As an example, Figure 4 shows the state of a generator 20 in which a layer short occurs in an electromagnetic coil C wound in the same slot (same tooth). The stator 22 has multiple slots partitioned by multiple teeth. In this example, a short circuit occurs between different layers of turns of the same phase (e.g., U-phase) electromagnetic coils housed in one slot, forming a short circuit, as shown by the thick solid line in the figure. The magnetic flux generated by the field coil corresponds to the magnetic flux generated in the teeth. If a rotor with a permanent magnet field magnet, which constantly generates field flux, continues to rotate in this state, a short-circuit current will continue to flow in the shorted section, attempting to cancel the magnetic flux generated by the rotor poles. This generates localized heat, increasing the risk of fire if the condition is left unattended.

[0044] On the other hand, when applied to ships and aircraft, it is necessary to use the minimum amount of power to move to a safe location such as a port, airport, etc. To do this, it is necessary to disconnect the prime mover 10 and the generator 20 by cutting the mechanical fuse 30, stop the generator 20 to prevent a fire, and then take evacuation action using the power of the prime mover 10.

[0045] One method for detecting signs of a rare short circuit is to detect an abnormality by managing the trend of temperature non-uniformity of temperature measuring elements embedded at equal intervals in the stator 22 of the generator 20. For example, if a failure occurs near the temperature measuring element 31a as shown in Figure 2, the detected temperatures T1 of the temperature measuring element 31a, T2 of the temperature measuring element 31b, and T3 of the temperature measuring element 31c are normally uniform, but it is expected that a gradient will occur in the detected temperatures, such as T1 > T2 > T3, and an abnormality is detected using a threshold value obtained from experience.

[0046] Similarly, when a bearing abnormality occurs and it is necessary to stop the rotating electrical machine, the abnormality can be detected by trend management of the temperatures of the direct-coupled side and the non-direct-coupled side. In this embodiment, when such an abnormality is detected, the determination unit 432 detects an abnormality in the generator 20 and issues a command to disconnect the prime mover 10 and the generator 20.

[0047] In the existing method, it was necessary to generate a transiently large torque in order to cut the mechanical fuse 30. Intentionally generating a transient excessive torque requires a large capacity inverter that constitutes the power converter 41, but this has the drawback of increasing the size of the device.

[0048] On the other hand, in this embodiment, at any timing when an abnormality is detected, the first circuit breaker 51 is first opened to disconnect the generator 20 from the power load 50. Thereafter, the second circuit breaker 52 is closed to switch the load from the power load 50 to the protected load 42. The control unit 43 generates vibration torque by controlling the power consumed by the protected load 42. Since the generator does not completely lose its function when a layer short occurs, it is possible to control the load.

[0049] Generally, in a permanent magnet generator (PMSG), the rated power P and torque τ are expressed by the following equations (1) and (2), respectively. However, V a : each phase voltage, E0: induced voltage, x s : synchronous reactance, δ: load angle, ω: power supply frequency, p: number of pole pairs.

[0050] The voltage amplitude applied by the power converter 41 is expressed as Va=Va{1−k+k sin(ω s t)}, then the power P s , torque τ s is expressed by the following equation: where k is a constant and ω s : vibration frequency, δ s : Any load angle.

[0051] sinω in equation (3) s When we look at the term, we see that the frequency ω s In (k sin δ s By adjusting each parameter as desired in the power conversion device, it is possible to generate torque vibration with the desired amplitude.

[0052] (Principle of torque vibration generation) During steady-state operation (see Figure 3), ω, which depends on the rotation speed in equation (2), is constant because there is no change in the prime mover speed, which depends on the rotation speed of the propeller (thruster 12), and under this condition, the induced voltage E0 is also constant. For this reason, the power load expressed by equation (1) is the product of each phase voltage and the load angle (V a As will be described later, the generator torque τ expressed by equation (2) is adjusted by the d-axis current i d and q-axis current i q This is equivalent to adjusting each phase voltage and load angle.

[0053] 5 is an equivalent circuit diagram of a permanent magnet generator (PMSG), where A indicates the d-axis current circuit and B indicates the q-axis current circuit. The generator torque is calculated by dividing the magnetic flux of the permanent magnet by ψ a , the d-axis and q-axis currents that contribute to the torque are respectively i od , i oq (Generally, the current for iron loss is small, so i od ≒d-axis current i d , i oq ≒q-axis current i q ), d-axis and q-axis inductances are L d , L q Using this, the torque τ is expressed as follows:

[0054] At this time, the torque command value τ pre *, the current command value i od *, i oq * is set as follows, with K being a constant.

[0055] 6 is a control block diagram of the propulsion system 100 showing details of the signal generating circuit 431 during protective control when an abnormality is detected in the generator 20. When the protective device 40 executes protective control as shown in FIG. 5, the first circuit breaker 51 and the second circuit breaker 52 are switched to connect the protected load 42 to the power converter 41 instead of the power load 50.

[0056] Before the protective control is started, the torque command value is controlled according to the state of the power load 50. However, when the protective control is executed, the torque is oscillated to control the torsional frequency ω of the weak point (mechanical fuse 30). ts In other words, the power generated by the generator 20 is consumed by the protected load 42, but since it does not need to be connected to equipment that requires a guarantee of power quality, any load may be generated without speed feedback to the torque target value.

[0057] The torque can be varied over time t to generate vibration torque, and the equation is, for example, as follows: where k is a constant (0<k<1), t is time, and τ ave is the average value of the vibration torque, which corresponds to the vibration amplitude.

[0058] At this time, the current command value i od *, i oq * is set as follows, with K being a constant:

[0059] In addition, since the fuel of the prime mover 10 is controlled to maintain the current operation, the rotation speed does not change (ω e = constant). Even if the speed changes, it does not have a significant effect because the frequency of the torque fluctuation is important. As described above, unlike the case of the power load 50 (during steady operation), the protected load 42 only needs to consume a specified amount of power, so feedback of the power consumption of the protected load 42 is not necessary.

[0060] (Power Oscillation) The protection device 40 oscillates the torque as described above, thereby applying power oscillation (torsional oscillation torque) to the mechanical fuse 30. An example waveform of the power oscillation is shown in FIG.

[0061] In vibration torque resonance, the GD2 (flywheel effect) of the generator 20 is normally small compared to the load, so when torsional resonance occurs in a mode where only the phase of the generator 20 is different from that of the propeller 12, the prime mover 10, and the shaft (mechanical fuse 30), as shown in Figure 8, the resonance torque becomes maximum.

[0062] Figure 9 shows the frequency and response magnification of the vibration torque. When the frequency of the vibration torque is gradually increased, the response magnification is approximately 1 when the frequency is low, but by matching the vibration frequency as closely as possible to the resonance frequency f0, the torque can be increased by resonance. Note that the torque can be amplified by several tens of times depending on the frequency adjustment.

[0063] By utilizing this phenomenon, it is preferable to tune the frequency of the vibration torque during protection control to the resonance frequency f0. As a result, as shown in Figure 10, the response torque acting on the mechanical fuse 30 is greatly amplified relative to the torque of the generator 20. Because the magnitude of the vibration torque can be amplified up to about 10 times the rated value, this can be utilized to repeatedly generate a large torque to cut the mechanical fuse 30 without increasing the power supply capacity. As for the resistor that constitutes the protective load 42, it is only necessary to have a short-term capacity to generate the vibration torque, which prevents the device from becoming larger, and is expected to be particularly effective in mobility applications.

[0064] As described above, according to this embodiment, when an abnormality in the generator 20 is detected, a torsional vibration torque is applied to the mechanical fuse 30, so that the generator 20 showing signs of failure can be mechanically isolated at any timing while the operation of the prime mover 10 continues.

[0065] Furthermore, according to this embodiment, a control command that generates a torsional vibration torque with a torque command value whose target torque value changes periodically is input to the power converter 41, so that a vibration torque sufficient to cut the mechanical fuse 30 can be generated without generating a transiently large torque.

[0066] Furthermore, since the vibration torque can be generated by the power converter 41 used during steady-state operation control, there is no need to increase the capacity of the inverter that constitutes the power converter 41, and therefore it is possible to prevent the device from becoming too large.

[0067] Although the embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the above-described embodiments and that various modifications can be made.

[0068] For example, in the above embodiment, a layer short circuit was used as an example of the cause of an accident, but even in the case of a ground fault in a winding or a fault between two independent windings, the above-mentioned effects can be obtained by similar control depending on the severity of the accident.

[0069] In addition, in the above embodiment, the protective load 42 is used to generate the vibration torque required to break the mechanical fuse 30, but this is not limiting, and the vibration torque may be generated using the power load 50. In this case, the installation of the protective load 42, the first circuit breaker 51, and the second circuit breaker 52 can be omitted.

[0070] In the above embodiment, the AC power generated by the generator 20 is converted into DC power by the power converter 41 and supplied to the power load 50, but this is not limiting. An AC (Alternating Current) converter may be provided between the power converter 41 and the power load 50, thereby connecting an AC load as the power load.

[0071] Furthermore, in the above embodiment, the rotating electric machine is a permanent magnet synchronous generator 20, but this is not limiting, and an AC motor may be used as the rotating electric machine. As an example, Fig. 11 shows a parallel hybrid propulsion system 200. This propulsion system 200 includes a motor 60 having a rotor connected to the prime mover 10, and a battery 61 that is a power source for driving the motor 60, and is configured so that the motor 60 connected to the battery 61 can assist a portion of the shaft power of the prime mover 10.

[0072] 11 , power converter 41 converts DC power from battery 61 into AC power and outputs it to motor 60 based on instructions from control unit 43. When control unit 43 detects an abnormality in motor 60, it closes second circuit breaker 52 to connect power converter 51 and protected load 42, and generates a torsional vibration torque that breaks mechanical fuse 30, thereby disconnecting motor 60 from prime mover 10. This provides the same effects as those of the above-described embodiment.

[0073] DESCRIPTION OF SYMBOLS 10 Prime mover 20 Generator (rotating electric machine) 30 Mechanical fuse 31 Monitoring sensor 40 Protection device 41 Power converter 42 Protected load 43 Control unit 50 Power load 51 First circuit breaker 52 Second circuit breaker 60 Motor (rotating electric machine) 100, 200 Propulsion system

Claims

1. A propulsion system comprising: a prime mover; a permanent magnet field type rotating electric machine having a rotor connected to the prime mover; a mechanical fuse connected between the prime mover and the rotating electric machine; a sensor that monitors the condition of the rotating electric machine; and a protection device configured to be able to apply a torsional vibration torque to the mechanical fuse that breaks the mechanical fuse based on the output of the sensor.

2. A propulsion system as claimed in claim 1, wherein the protection device comprises: a power converter connected to the rotating electric machine; a protective load which consumes the power generated by the power converter; and a control unit which judges whether or not there is an abnormality in the rotating electric machine based on the output of the sensor, and which inputs a control command to the power converter to generate the torsional vibration torque when it judges that there is an abnormality in the rotating electric machine.

3. A propulsion system according to claim 2, wherein the control command includes a torque command value whose target torque value changes periodically.

4. A propulsion system according to claim 3, wherein the control unit generates a torque command value that generates a torsional vibration torque having a frequency equivalent to a torsional resonance frequency of the mechanical fuse.

5. A propulsion system as described in claim 2, wherein the protection device further has a first circuit breaker capable of interrupting electrical continuity between the power converter and an electrical load that operates by receiving electrical power generated by the power converter, and when the control unit determines that there is an abnormality in the rotating electrical machine, the control unit causes the first circuit breaker to interrupt electrical continuity between the power converter and the electrical load.

6. A propulsion system as claimed in claim 5, wherein the protection device further has a second circuit breaker capable of interrupting conduction between the power converter and the protected load, and when the control unit determines that there is no abnormality in the rotating electric machine, it causes the second circuit breaker to interrupt the conduction between the power converter and the protected load.

7. A propulsion system according to any one of claims 1 to 6, wherein the rotating electric machine is a generator.

8. A propulsion system according to any one of claims 1 to 6, wherein the rotating electric machine is a motor.

9. A propulsion system according to any one of claims 1 to 6, wherein the mechanical fuse is tubular in shape.

10. A propulsion system according to any one of claims 1 to 6, wherein the sensor is a temperature sensor that measures the temperature of the rotating electric machine, or a current sensor that detects the current flowing through the rotating electric machine.

11. A propulsion system according to any one of claims 1 to 6, wherein the prime mover is a jet engine.

12. A protection device for a rotating electric machine having a prime mover, a permanent magnet field type rotating electric machine having a rotor connected to the prime mover, and a mechanical fuse connected between the prime mover and the rotating electric machine, comprising: a power converter connected to the rotating electric machine; a protective load that consumes power generated by the power converter; and a control unit that determines whether or not there is an abnormality in the rotating electric machine based on the output of a sensor that monitors the state of the rotating electric machine, and inputs a control command to the power converter to generate a torsional vibration torque that breaks the mechanical fuse when it is determined that the rotating electric machine is abnormal.

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