Electric machinery system

Abstract

To reduce the magnitude of a fault current.SOLUTION: An electrical mechanical system 1 includes an electric machine 2 having a rotor 21 and a coil 221, a power converter 3 that outputs an output current to the coil 221 of the electric machine 2, and a controller 4 that controls the power converter 3. The controller 4 includes a signal output unit 42 that outputs a signal for controlling the mode of the output current to the power converter 3, and an abnormality detection unit 41 that receives an abnormality signal θ1 indicating an abnormality when an abnormality occurs in which generation of a fault current generated in the coil 221 by the rotation of the rotor 21 is to be suppressed. When the abnormality detection unit 41 receives the abnormality signal, the signal output unit 42 outputs a demagnetization control signal φ2 to the power converter 3. In response to the input of the demagnetization control signal φ2, the power converter 3 passes a demagnetization current through the coil 221 to cause demagnetization due to heat caused by eddy currents generated in a permanent magnet 211.SELECTED DRAWING: Figure 1

Description

Technical Field

[0004] , , , ,

[0001] The present disclosure relates to an electromechanical system. This application is based on Japanese Patent Application No. 2021-153869 filed on September 22, 2021. This application claims the benefit of priority with respect to Japanese Patent Application No. 2021-153869. The entire contents of Japanese Patent Application No. 2021-153869 are incorporated herein by reference.

Background Art

[0002] Patent Documents 1, 2, and 3 disclose technologies related to electromechanical devices such as motors and generators including coils and magnets. Patent Document 1 discloses an efficient slip-ringless synchronous motor. Patent Document 2 discloses a technology for suppressing an increase in magnetization current during demagnetization and magnetization, and enabling variable speed operation over a wide range from low speed to high speed with high output. Patent Document 3 discloses a flux amount variable rotating electrical machine system with good energy efficiency.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a rotor containing magnets rotates relative to a stator containing coils, a voltage is generated in the coils. This induced voltage continues to be generated even if an abnormality occurs, such as a short circuit in the coils or other circuits, as long as the rotational movement continues. The fault current that flows when such an abnormality occurs can cause unintended malfunctions. Therefore, electric machinery is required to be able to handle fault currents.

[0005] This disclosure describes an electric motor system that can reduce the magnitude of fault current. [Means for solving the problem]

[0006] The electric motor system of this disclosure comprises an electric motor having a rotor that includes a magnet and rotates together with a shaft, and coils fixedly arranged to surround the rotor; a power converter that outputs an output current to the coils of the electric motor; and a controller that controls the power converter. The controller has a signal output unit that outputs a signal to the power converter for controlling the manner of the output current, and an abnormality detection unit that receives an abnormality signal indicating an abnormal situation. When the abnormality detection unit receives an abnormality signal, the signal output unit outputs a demagnetization control signal to the power converter, and the power converter, upon input of the demagnetization control signal, causes a demagnetization current to flow through the coils to cause demagnetization due to heat generated by eddy currents in the magnets. [Effects of the Invention]

[0007] The electric motor system of this disclosure can reduce the magnitude of fault current. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows the configuration of the electric motor system of this disclosure. [Figure 2] Figure 2 shows the structure of the electric motor shown in Figure 1. [Figure 3] Figures 3(a), 3(b), and 3(c) show the demagnetizing flux synchronized with the rotation of the rotor. [Figure 4]Figure 4 is a diagram illustrating the demagnetization of the rotor's magnets due to external magnetic flux. [Figure 5] Figure 5 is a flowchart showing the operation of the controller shown in Figure 1. [Figure 6] Figures 6(a) and 6(b) show the current supplied from the power converter to the electric motor in the electric motor system of the second embodiment. Figures 6(c), 6(d), 6(e), and 6(f) show modified examples of the current supplied from the power converter to the electric motor in the electric motor system of the second embodiment. [Figure 7] Figure 7 is a diagram illustrating the demagnetization of the rotor's magnets due to heat. [Figure 8] Figures 8(a) and 8(b) are further diagrams showing the current supplied from the power converter to the electric motor in the electric motor system of the second embodiment. Figures 8(c), 8(d), 8(e), and 8(f) are further diagrams showing modified examples of the current supplied from the power converter to the electric motor in the electric motor system of the second embodiment. [Modes for carrying out the invention]

[0009] The electric motor system of this disclosure comprises an electric motor having a rotor that includes magnets and rotates together with a shaft, and coils fixedly arranged to surround the rotor; a power converter that outputs output current to the coils of the electric motor; and a controller that controls the power converter. The controller has a signal output unit that outputs a signal to the power converter for controlling the mode of the output current, and an abnormality detection unit that receives an abnormality signal indicating an abnormal situation. When the abnormality detection unit receives an abnormality signal, the signal output unit outputs a demagnetization control signal to the power converter. In response to the input of the demagnetization control signal, the power converter causes a demagnetizing current to flow through the coils for a demagnetizing flux that demagnetizes the magnets of the rotor.

[0010] A controller that detects an abnormal situation controls the power converter to generate a demagnetizing flux in the stator coils that demagnetizes the rotor magnets. When the rotor magnets are demagnetized, it is possible to reduce the magnitude of the fault current generated in the stator coils. The electric motor system of this disclosure can reduce the magnitude of the fault current by controlling the power converter that is inherently equipped in the system.

[0011] The power converter of the above-described electric motor system may, upon input of a demagnetization control signal, pass a demagnetizing current through the coil for a demagnetizing flux that includes a first demagnetizing flux component which is in the opposite direction to the magnetic field generated by the magnet and synchronized with the rotation of the magnet. With this configuration, the first demagnetizing flux component generated by the coil acts as an external magnetic flux on the rotor's magnet. As a result, the rotor's magnet can be demagnetized by the external magnetic flux.

[0012] The power converter in the above-described electric motor system controls the current flowing through the coils surrounding the rotor where the d-axis component is greater than the q-axis component relative to the rotor, in response to the input of a demagnetization control signal, so that the current flowing through the coils where the q-axis component is greater than the d-axis component is greater than the current flowing through the coils where the q-axis component is greater than the d-axis component. This operation can also reduce the magnitude of the fault current.

[0013] In the power converter of the above electromechanical system, it is not necessary to pass current through coils where the q-axis component is greater than the d-axis component.

[0014] In the above-described electric motor system, the intensity of the demagnetizing flux, including the first demagnetizing flux component, may be such that it causes irreversible demagnetization of the rotor's magnets. This configuration also reduces the magnitude of the fault current.

[0015] The demagnetization control signal of the electromechanical system described above may cause a demagnetization current for a demagnetizing magnetic flux including an alternating-current second demagnetizing component interlinking with the magnet of the rotor to be output from the power converter to the coil. According to this configuration, heat is generated in the magnet of the rotor due to the second demagnetizing magnetic flux component interlinking with the magnet of the rotor. As a result, the magnet of the rotor can be demagnetized by the heat.

[0016] The controller of the electromechanical system described above may have a demagnetization evaluation unit that evaluates the degree of irreversible demagnetization of the magnet of the rotor. When the degree of irreversible demagnetization of the magnet of the rotor is below a threshold value, the demagnetization evaluation unit may stop the output of the demagnetization control signal from the signal output unit. According to this configuration, the magnitude of the fault current can be reduced without continuously providing a demagnetization current.

[0017] The shaft of the electromechanical system described above may be connected to the rotating mechanism of the prime mover at a position different from the position where the rotor is provided. The shaft may receive power transmitted from the rotating mechanism and rotate the rotor. The electromechanical machine may generate electric power due to the rotation of the rotor. The electromechanical system of the present disclosure can reduce the magnitude of the fault current that may occur in the electromechanical machine that generates electric power by controlling the power converter that it originally includes.

[0018] Hereinafter, the electromechanical system of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are assigned to the same elements, and duplicate descriptions are omitted.

[0019] As shown in FIG. 1, the electromechanical system 1 includes an electromechanical machine 2, a power converter 3, and a controller 4. The electromechanical machine 2 includes a coil and a magnet. The electromechanical machine 2 is a generator. The electromechanical machine 2 receives kinetic energy from an external device 6 and generates electrical energy. The electromechanical machine 2 may be an electric motor. The electric motor receives electrical energy from the outside and generates kinetic energy. In the present disclosure, the electromechanical machine 2 will be described as a generator.

[0020] The electric motor 2 comprises a rotor 21 and a stator 22 as its main components. The rotor 21 is a cylindrical member. The rotor 21 is fixed to the shaft 5. Both ends of the shaft 5 are supported by bearings 23. The rotor 21 rotates together with the shaft 5. As shown in Figure 2, the rotor 21 has a permanent magnet 211 and an armor ring 212. The armor ring 212 may be provided as needed. Therefore, the rotor 21 may omit the armor ring 212. The cylindrical permanent magnet 211 is fixed to the shaft 5. The permanent magnet 211 may be, for example, a surface permanent magnet. As a result, two axes can be defined along the radial direction of the permanent magnet 211. The line connecting the north pole and south pole of the permanent magnet 211 is defined as the d-axis. The q-axis is defined as an axis perpendicular to the d-axis. The permanent magnet 211 may be covered by a cylindrical armor ring 212. A stator 22 is positioned around the rotor 21. The stator 22 is fixed to the housing of the electric motor 2 or the like. The stator 22 does not move relative to the housing of the electric motor 2 or the like. The stator 22 has a plurality of coils 221 formed by winding wires around teeth.

[0021] Refer to Figure 1 again. The power converter 3 can also convert AC power to DC power. The power converter 3 can also convert DC power to AC power. When the electric motor 2 is a generator, the power converter 3 receives power from the electric motor 2. The power converter 3 converts the form of the received power. The power converter 3 outputs the converted power to the load device 7. The power converter 3 can also perform phase control regarding the phase of the three-phase AC current. The power converter 3 can advance the phase of the three-phase AC current. The power converter 3 can also delay the phase of the three-phase AC current.

[0022] The electric motor 2, exemplified as a generator, has its shaft 5's input end connected to an external device 6 (prime mover), which is the drive source. The input end may be switchable between connected and disconnected from the rotating mechanism, which is the output end of the external device 6. Alternatively, the input end may be connected in a way that prevents disconnection from the output end of the external device 6. When the external device 6 rotates the shaft 5, the rotor 21 rotates in accordance with the rotation of the shaft 5. The electric motor 2 outputs three-phase alternating current power due to the rotation of the rotor 21.

[0023] Controller 4 controls the operation of the power converter 3. Controller 4 outputs control signals to the power converter 3. Controller 4 is connected to the power converter 3 by wire or wireless. Controller 4 is also connected to a device other than the power converter 3 in order to obtain information for outputting control signals. For example, Controller 4 may be connected to an electric motor 2. The electric motor 2 may be equipped with several sensors. Controller 4 may obtain sensor signals output by those sensors.

[0024] Specifically, controller 4 receives an abnormality signal θ1 and a current signal θ2 as input signals. Controller 4 outputs an operation control signal φ1 and a demagnetization control signal φ2 as output signals.

[0025] The controller 4 is implemented by a computer. The controller 4 includes one or more computers. A computer has an arithmetic unit (processor), a main memory unit, an auxiliary memory unit, a communication control unit, an input device, and an output device. The controller 4 is composed of one or more computers consisting of this hardware and software such as programs. When the controller 4 is composed of multiple computers, these computers may be connected locally. The multiple computers that make up the controller 4 may be connected via a communication network such as the Internet or an intranet. Through this connection, a single logical controller 4 is constructed.

[0026] The controller 4 has several functional components that are realized by the execution of a program on the above hardware. The controller 4 has an abnormality detection unit 41, a signal output unit 42, and a demagnetization evaluation unit 43 as functional components.

[0027] The abnormality detection unit 41 receives an abnormality signal θ1. The abnormality signal θ1 indicates that the electric motor 2 is not in a normal operating state. Specifically, the abnormality signal θ1 indicates that an abnormality, such as a short circuit, has occurred in the coil 221 of the electric motor 2. The abnormality signal θ1 may be input from, for example, a current sensor that senses the current generated by the abnormality. The abnormality signal θ1 may be input from, for example, a sensor that detects the heat or light generated by the short circuit. The abnormality signal θ1 may be input from, for example, a magnetic sensor. In other words, the abnormality signal θ1 may be input from various sensors. The abnormality signal θ1 may be output by a processing unit that has received output signals from these sensors. The processing unit receives output signals from sensors. The processing unit performs predetermined signal processing on the received signals. As a result, the processing unit generates a processed signal. The processing unit may output the processed signal as the abnormality signal θ1. The abnormality signal θ1 may also be a signal that a person inputs to the abnormality detection unit 41 via an input device when a person determines that an abnormality has occurred through visual inspection. The controller 4, which has an abnormality detection unit 41, switches the operation of the electric motor 2 to the operation when an abnormality occurs, in response to the input of an abnormality signal θ1.

[0028] The circumstances under which the abnormal signal θ1 is input to the controller 4 are not limited to a short circuit. For example, the abnormal signal θ1 may be input to the controller 4 due to a decrease in the supply amount of refrigerant used to cool the electric motor 2. For example, the abnormal signal θ1 may be input to the controller 4 due to a supply abnormality such as a blockage of the refrigerant. As a result, demagnetization of the permanent magnet 211, as described later, may occur.

[0029] The electric motor 2 of this disclosure may be, for example, a generator mounted on an aircraft. The aircraft is equipped with external devices 6, such as an internal combustion engine (prime mover), in addition to the electric motor 2. The external devices 6 include a rotating body such as a turbine. The shaft 5 of the electric motor 2 is directly connected to the rotating body of the external devices 6. Therefore, the rotor 21 rotates in conjunction with the rotation of the rotating body of the external devices 6. As a result, current is generated in the coil 221. Even if an abnormality such as a short circuit occurs in the coil 221, it is difficult for the external devices 6, such as the internal combustion engine, to stop immediately. Therefore, even if an abnormality occurs, rotational power continues to be transmitted from the external devices 6 to the rotor 21 via the shaft 5.

[0030] The signal output unit 42 outputs either the operation control signal φ1 or the demagnetization control signal φ2 to the power converter 3. The signal output unit 42 outputs the demagnetization control signal φ2 when the abnormality detection unit 41 receives an abnormal signal. Conversely, if the abnormality detection unit 41 does not receive an abnormal signal, the signal output unit 42 outputs the operation control signal φ1.

[0031] The operation control signal φ1 is for operating the electric motor 2 as a generator. As long as the electric motor 2 is brought to the desired operating state, the operation of the power converter 3 realized by the operation control signal φ1 is not subject to any limitations.

[0032] For example, if the electric motor 2 is an Interior Permanent Magnet (IPM) motor, the power converter 3, upon receiving the operation control signal φ1, may output a current that includes both a d-axis component and a q-axis component. If the electric motor 2 is a Surface Permanent Magnet (SPM) motor, the power converter 3, upon receiving the operation control signal φ1, may output a current that includes a q-axis component. Ideally, a current that includes a q-axis component means that the current output from the power converter 3 includes only the q-axis component and does not include the d-axis component. However, in practice, the current output from the power converter 3 only needs to include the q-axis component as its main component and may include a small amount of the d-axis component.

[0033] The demagnetization control signal φ2 is used to demagnetize the permanent magnet 211 of the rotor 21.

[0034] As described above, the abnormal signal θ1 was explained as indicating that an abnormality such as a short circuit has occurred. If current (fault current) continues to be generated in coil 221 while this abnormal condition persists, it can cause unintended malfunctions. For example, if the electric motor 2 is cooled by oil, the oil may ignite due to the short-circuit current. There is also a risk of wear and tear on surrounding equipment due to the heat generated by the short circuit. If there is an abnormality in the supply of refrigerant, there is a risk of wear and tear on surrounding equipment due to the heat generated by the fault current flowing through coil 221. Therefore, it is necessary to take measures to address the fault current.

[0035] When an abnormality such as a short circuit occurs, the magnetic flux from the permanent magnet 211 of the rotor 21 rotates in link with the coil 221, inducing a back electromotive force in the coil 221. As a result, a current is generated in the coil 221. In other words, if the magnetic flux does not link with the coil 221 when the rotor 21 rotates, no back electromotive force is induced in the coil 221. In other words, no fault current is generated in the coil 221. Therefore, the electric motor system 1 of this disclosure demagnetizes the permanent magnet 211 of the rotor 21. Demagnetizing the permanent magnet 211 reduces the magnetic flux that links with the coil 221. As a result, the magnitude of the induced voltage and the magnitude of the fault current generated in the coil 221 are suppressed. Furthermore, if the permanent magnet 211 is demagnetized, there is no magnetic flux that links with the coil 221. As a result, no induced voltage is generated in the coil 221, and no fault current is generated.

[0036] Demagnetization of the permanent magnet 211 can be caused by several factors. In the first embodiment, an example utilizing demagnetization by external magnetic flux will be described. In the second embodiment, an example utilizing demagnetization by heat will be described.

[0037] Upon receiving the demagnetization control signal φ2, the power converter 3 outputs a demagnetization current to the stator 22. The stator 22, upon receiving the demagnetization current, generates a demagnetization flux D3 (see Figure 3). The demagnetization flux D3 includes a first demagnetization flux component that is in the opposite direction to the magnetic flux D2 generated by the permanent magnet 211. The demagnetization current that generates the demagnetization flux D3 can also be called the d-axis current. In other words, the first demagnetization flux component is aligned with the d-axis. The demagnetization current that generates the demagnetization flux D3 only needs to include the d-axis current as its main component. That is, the demagnetization current that generates the demagnetization flux D3 may additionally include the q-axis current. The demagnetization flux D3 is synchronized with the rotation of the permanent magnet 211. That is, the demagnetization flux D3, including the first demagnetization flux component, is a rotating magnetic field. As a result, as shown in Figures 3(a), 3(b), and 3(c), the direction of the demagnetizing flux D3 synchronized with the rotation of the rotor 21 is always opposite to the direction of the magnetic flux D2 of the permanent magnet 211. From the perspective of the permanent magnet 211, it appears that the permanent magnet 211 is always receiving a magnetic flux in the opposite direction to the magnetic flux D2 it generates. The magnitude of the demagnetizing flux D3 is constant. In other words, the first demagnetizing flux component included in the demagnetizing flux D3 is synchronized with the rotation of the rotor 21. On the other hand, the magnitude of the first demagnetizing flux component does not fundamentally need to change over time.

[0038] In other words, the magnitude of the first demagnetizing flux component may or may not change over time.

[0039] The demagnetizing flux D3 only needs to include the first demagnetizing flux component. Therefore, the demagnetizing flux D3 may include a flux component that does not lie along the d-axis. If the demagnetizing flux D3 includes a flux component that does not lie along the d-axis, the direction of the demagnetizing flux D3, which is a combination of the first demagnetizing flux component and the flux component that does not lie along the d-axis, will not perfectly coincide with the direction of the d-axis.

[0040] A permanent magnet 211 subjected to an external magnetic flux undergoes either reversible or irreversible demagnetization, depending on the strength of the external magnetic flux. Demagnetization due to the demagnetizing flux D3 may be reversible demagnetization. Demagnetization due to the demagnetizing flux D3 may be irreversible demagnetization. In the case of reversible demagnetization, the magnitude of the fault current can be reduced when the demagnetizing flux D3 is applied. In the case of irreversible demagnetization, if the degree of demagnetization is large, the generation of a fault current can be suppressed even if the application of the demagnetizing flux D3 is stopped.

[0041] Whether the demagnetizing flux D3 causes reversible demagnetization or irreversible demagnetization can be understood by referring to the magnetization curve shown in Figure 4. If the magnetization curve of the permanent magnet 211 of the rotor 21 is known, it becomes possible to arbitrarily select and induce either reversible or irreversible demagnetization.

[0042] The horizontal axis of Figure 4 shows the magnetic field strength (H: unit A / m). The vertical axis shows the magnetic flux density (B: unit T). Graph G51 is the BH curve (magnetic hysteresis curve) showing the characteristics of the permanent magnet 211. The BH curve shows the magnetic flux density, which is the sum of the external magnetic flux and the magnetic flux of the permanent magnet 211. Graph G52 is the JH curve showing the characteristics of the permanent magnet 211. The JH curve shows how much the magnitude of the magnetic flux of the permanent magnet 211 changes due to the external magnetic flux.

[0043] Let's assume that the state of the permanent magnet 211 is currently at the operating point P51 on the BH curve (graph G51). The operating point P51 is the same as the operating point P52 on the JH curve (graph G52). Next, we determine a straight line G53 connecting the operating point P52 and the origin. Then, let's assume that a demagnetizing flux D3, which is an external magnetic flux with an intensity of Hs, is applied to the permanent magnet 211. As a result, the operating point P52 on the JH curve (graph G52) changes to the operating point P53. The operating point P53 on the JH curve (graph G52) is the same as the operating point P54 on the BH curve. When the application of the demagnetizing flux D3 is stopped at the operating point P54, the magnetic field of the permanent magnet 211 tries to return to its original state by following the straight line G55. The straight line G55 has a slope corresponding to the BH curve (graph G51). Therefore, the state of the permanent magnet 211 cannot return to the original operating point P51. The permanent magnet 211 returns to its original state at the intersection of the line G55 connecting the original operating point P51 and the origin (operating point P55). The magnetic flux density at operating point P55 is smaller than that at the original operating point P51. In other words, irreversible demagnetization has occurred in the permanent magnet 211.

[0044] It can be seen that irreversible demagnetization occurs in the permanent magnet 211 when a demagnetizing flux D3 is applied to the permanent magnet 211 such that the change in state on the JH curve (graph G52) exceeds the inflection point P56 of the JH curve.

[0045] The demagnetization evaluation unit 43 can evaluate the demagnetization state of the permanent magnet 211 of the rotor 21 by, for example, utilizing the magnitude of the fault current generated in the coil 221. The demagnetization state refers to the state of the permanent magnet 211 in which a fault current smaller than an acceptable current value is generated. For example, during the period when the demagnetization control signal φ2 is output, the permanent magnet 211 is sufficiently demagnetized. Next, the output of the demagnetization control signal φ2 is stopped for a predetermined period of time. In this case, demagnetization of the permanent magnet 211 caused by the application of the demagnetizing flux D3 does not occur. The magnitude of the magnetic flux generated by the permanent magnet 211 becomes the magnitude that has been reduced by irreversible demagnetization. A fault current corresponding to the magnitude of the magnetic flux density reduced by irreversible demagnetization is generated in the coil 221. If the strength of the magnetic flux has been sufficiently reduced by irreversible demagnetization, it is not necessary to continue applying the demagnetizing flux D3. In other words, if the magnitude of the fault current is acceptable, it is not necessary to continue applying the demagnetizing flux D3. Therefore, the demagnetization evaluation unit 43 applies the demagnetizing flux D3 and then stops applying the demagnetizing flux D3 for a predetermined period of time. The demagnetization evaluation unit 43 obtains the magnitude of the fault current that occurs when the application of the demagnetizing flux D3 is stopped. Then, the demagnetization evaluation unit 43 selects whether to continue or stop applying the demagnetizing flux D3 according to the magnitude of the fault current.

[0046] The above is an example of a case where a current sensor that detects the magnitude of the current generated in the coil 221 is installed. For example, if a sensor that detects heat or light is installed, the demagnetization evaluation unit 43 may stop applying the demagnetizing flux D3 provided that these sensors have not detected any abnormal conditions and are not outputting any abnormal signals. Alternatively, the demagnetization evaluation unit 43 may use the results of measuring the magnetic flux of the linked rotor to determine whether or not to stop applying the demagnetizing flux D3.

[0047] If the electric motor 2 is equipped with a sensor that directly measures the magnitude of the magnetic field of the permanent magnet 211, the demagnetization evaluation unit 43 may choose to continue or stop the application of the demagnetizing flux D3 by comparing the measured value with a threshold value. In this case, it is not necessary to stop the demagnetizing current for a predetermined period of time.

[0048] Next, the operation of the controller 4 will be explained with reference to the flowchart shown in Figure 5. First, the signal output unit 42 outputs an operation control signal φ1 (S1). Next, the abnormality detection unit 41 determines whether or not an abnormality signal θ1 is input (S2). If there is no input of abnormality signal θ1 (S2:NO), a predetermined waiting period is observed, and then the presence or absence of abnormality signal θ1 is determined again. In other words, the operation of determining whether or not an abnormality signal θ1 is input and the waiting operation are repeated until an abnormality signal θ1 is input.

[0049] If an abnormal signal θ1 is input (S2: YES), the signal output unit 42 stops outputting the operation control signal φ1 and starts outputting the demagnetization control signal φ2 (S3). The strength of the demagnetization flux D3 determined by the demagnetization control signal φ2 may be determined by the type of demagnetization (reversible demagnetization, irreversible demagnetization, or demagnetization). The demagnetization flux D3 is synchronized with the rotation of the rotor 21. It is difficult to directly know the rotation of the rotor 21 when it is in an abnormal state. Therefore, the signal output unit 42 may use feedback control to control the phase of the demagnetization flux D3 so that the magnitude of the fault current is reduced.

[0050] As an example, the power converter 3, upon receiving the demagnetization control signal φ2, may control the current flowing through the coils 221 surrounding the rotor 21 that are located at positions where the d-axis component is greater than the q-axis component relative to the rotor 21, so as to be greater than the current flowing through the coils located at positions where the q-axis component is greater than the d-axis component. The power converter 3 does not need to allow current to flow through the coils located at positions where the q-axis component is greater than the d-axis component.

[0051] In other words, the power converter 3, upon receiving the demagnetization control signal φ2, controls the current flowing through the coils 221 surrounding the rotor 21 such that the d-axis component is greater than the q-axis component. As a result, a state is achieved where the current flowing through the coils located relative to the rotor 21 where the d-axis component is greater than the q-axis component is greater than the current flowing through the coils located where the q-axis component is greater than the d-axis component. Note that current does not need to flow through the coils located where the q-axis component is greater than the d-axis component.

[0052] Next, the demagnetization evaluation unit 43 evaluates the degree of demagnetization of the permanent magnet 211 (S4). The specific evaluation method is as described above, for example. If the degree of demagnetization is insufficient (S4: NO), the demagnetization evaluation unit 43 continues to output the demagnetization control signal φ2. If the degree of demagnetization is sufficient (S4: YES), the demagnetization evaluation unit 43 stops outputting the demagnetization control signal φ2.

[0053] The following describes the operation and effects of the electric motor system 1 of the first embodiment.

[0054] The electric motor system 1 includes an electric motor 2 having a rotor 21 that includes a permanent magnet 211 and rotates with a shaft 5, and a coil 221 fixedly arranged to surround the rotor 21; a power converter 3 that outputs output current to the coil 221 of the electric motor 2; and a controller 4 that controls the power converter 3. The controller 4 has a signal output unit 42 that outputs a signal to the power converter 3 for controlling the mode of output current, and an abnormality detection unit 41 that receives an abnormality signal θ1 indicating an abnormal situation when the generation of fault current in the coil 221 due to the rotation of the rotor 21 should be suppressed. When the abnormality detection unit 41 receives the abnormality signal θ1, the signal output unit 42 outputs a demagnetization control signal φ2 to the power converter 3. The demagnetization control signal φ2 causes the power converter 3 to output a demagnetization current to the coil 221 for a demagnetizing flux D3 that demagnetizes the permanent magnet 211 of the rotor 21.

[0055] Upon detecting an abnormal situation, the controller 4 controls the power converter 3 to supply a demagnetizing flux D3 to the coil 221 of the stator 22, thereby demagnetizing the permanent magnets 211 of the rotor 21. When the permanent magnets 211 of the rotor 21 are demagnetized, it is possible to suppress the magnitude of the fault current generated in the coil 221 of the stator 22. The electric motor system 1 can reduce the magnitude of the fault current by controlling the power converter 3 that it is equipped with.

[0056] The electric motor system 1 of this disclosure does not have a circuit breaker installed in the electrical output path of the electric motor 2. The electric motor system 1 also does not have any other devices to counter fault currents, such as a clutch that physically interrupts the rotation of the shaft 5. Therefore, the electric motor system 1 can be made lighter than systems that have such circuit breakers. The electric motor system 1 of this disclosure has a controller 4 that controls the power generation or operation of the electric motor 2 in a normal state to take measures when an abnormality occurs.

[0057] In other words, when the electric motor system 1 detects a fault in the electric motor 2, which is a generator, it applies a reverse magnetic field to the permanent magnet 211 of the rotor 21 by utilizing the current control function of the inverter or converter that drives the electric motor 2. As a result, the permanent magnet 211 is demagnetized or demagnetized, which reduces or eliminates the power generation function that generates fault current. Therefore, it is possible to suppress the continuous flow of a large fault current.

[0058] The electric motor system 1 is equipped with a fault protection system that does not require additional components such as circuit breakers and clutches. Furthermore, safety devices that are provided separately from the electric motor 2, such as circuit breakers, cannot cope with internal short-circuit faults within the electric motor 2. However, the electric motor system 1 can cope with internal short-circuit faults within the electric motor 2. If additional components are not provided, the increase in the number of parts constituting the electric motor system 1 is also suppressed. As a result, the maintainability (maintainability) of the electric motor system 1 can also be improved.

[0059] The direction of the demagnetizing flux D3 generated by the demagnetizing control signal φ2 is opposite to the direction of the magnetic flux D2 generated by the permanent magnet 211. The power converter 3 outputs a demagnetizing current to the coil 221 for the demagnetizing flux D3, which includes a first demagnetizing flux component synchronized with the rotation of the permanent magnet 211. With this configuration, the first demagnetizing flux component generated by the coil 221 acts as an external magnetic flux on the permanent magnet 211 of the rotor 21. As a result, the magnets of the rotor 21 can be demagnetized by the external magnetic flux.

[0060] The intensity of the demagnetizing flux D3, which includes the first demagnetizing flux component, is strong enough to cause irreversible demagnetization of the permanent magnet 211 of the rotor 21. This configuration also reduces the magnitude of the fault current.

[0061] The controller 4 has a demagnetization evaluation unit 43 that evaluates the degree of irreversible demagnetization of the permanent magnets 211 of the rotor 21. If the degree of irreversible demagnetization of the permanent magnets 211 of the rotor 21 is below a threshold, the demagnetization evaluation unit 43 stops outputting the demagnetization control signal φ2 from the signal output unit 42. With this configuration, fault current can be suppressed without continuously supplying demagnetization current.

[0062] The electric motor system 1 of the second embodiment will now be described. The principle employed for demagnetization in the electric motor system 1 of the second embodiment differs from that of the first embodiment. Therefore, since the physical components of the electric motor system 1 are the same as those of the first embodiment, a detailed explanation will be omitted. In the electric motor system 1 of the second embodiment, the operation of the power converter 3 and the operation of the stator 22, which follow the demagnetization control signal φ2 generated by the signal output unit 42 of the controller 4, differ from those of the first embodiment. Specifically, in the controller 4 of the first embodiment, the permanent magnets 211 of the rotor 21 were demagnetized by external magnetic flux. In the controller 4 of the second embodiment, the permanent magnets 211 of the rotor 21 are demagnetized by heat. In other words, the demagnetization control signal φ2 output by the controller 4 of the second embodiment generates a magnetic field that heats the permanent magnets 211 of the rotor 21.

[0063] Figure 6(a) shows the demagnetizing current output to the stator 22 by the power converter 3 upon receiving the demagnetizing control signal φ2. As shown in Figure 6(a), the demagnetizing current is an alternating current. The demagnetizing current shown in Figure 6(a) includes an AC component whose magnitude changes on both the positive and negative sides, with zero in between. The demagnetizing current does not include a DC component (bias component) that does not change over time. As a result, the demagnetizing flux D3 is also an alternating magnetic field whose magnitude changes over time. By applying an alternating magnetic field to the rotor 21, eddy currents can be intentionally generated in the rotor 21. These eddy currents cause the magnets to heat up.

[0064] As shown in Figure 6(b), the demagnetizing current only needs to include an AC component. The demagnetizing current may also include a DC component in addition to the AC component. When the demagnetizing current includes both AC and DC components, the switching frequency can be lowered. As a result, an effect of increasing eddy currents based on high-frequency ripple currents (see enlarged section in Figure 6(b)) can also be obtained.

[0065] The technique for reducing the switching frequency is not limited to the example shown in Figure 6(b). The technique for reducing the switching frequency is also applicable to the example in Figure 6(a). Furthermore, the technique for reducing the switching frequency can also be applied to the operations shown in the examples in Figures 6(c), 6(d), 6(e), and 6(f), which will be described later. Because the technique for reducing the switching frequency includes high-frequency components, the heating effect can be enhanced.

[0066] Figure 8(a) also shows the demagnetizing current output to the stator 22 by the power converter 3 upon receiving the demagnetizing control signal φ2. As shown in Figure 8(a), the demagnetizing current is an alternating current. The demagnetizing current shown in Figure 8(a) includes an AC component whose magnitude changes on both the positive and negative sides, with zero in between. The demagnetizing current shown in Figure 8(a) does not include a DC component (bias component) that does not change over time. As a result, the demagnetizing flux D3 is also an alternating magnetic field whose magnitude changes over time. By applying an alternating magnetic field to the rotor 21, eddy currents can be intentionally generated in the rotor 21. These eddy currents cause the magnets to heat up.

[0067] As shown in Figure 8(b), the demagnetizing current only needs to include an AC component. The demagnetizing current may also include a DC component in addition to the AC component. In particular, in Figure 8(b), the sign of the combined current of the AC and DC components does not change over time. That is, the sign of the combined current may always be positive or always negative.

[0068] In the examples shown in Figures 8(a) and 8(b), the switching frequency can be reduced. As a result, an effect of increasing eddy currents based on high-frequency ripple current can also be obtained. High-frequency ripple current is shown as an example in the enlarged sections of Figures 8(a) and 8(b).

[0069] The techniques for reducing the switching frequency are not limited to the examples shown in Figures 8(a) and 8(b). These techniques can also be applied to the examples shown in Figures 8(c), 8(d), 8(e), and 8(f), which will be described later. Because the techniques for reducing the switching frequency include high-frequency components, the heating effect can be enhanced.

[0070] In demagnetization due to external magnetic flux, if the magnetization characteristics of the permanent magnet 211, as shown in Figure 4, are known, it is possible to intentionally select between reversible and irreversible demagnetization. Similarly, in demagnetization due to heat, if the magnetization characteristics of the permanent magnet 211 are known, it is possible to intentionally select between reversible and irreversible demagnetization.

[0071] Figure 7 shows the BH curves illustrating the magnetization characteristics of the permanent magnet 211. The BH curve shown in graph G71 shows the magnetization characteristics of the permanent magnet 211 when the temperature of the permanent magnet 211 is room temperature. The BH curve shown in graph G72 shows the magnetization characteristics of the permanent magnet 211 when the temperature of the permanent magnet 211 is high. As shown in graphs G71 and G72, the magnetization characteristics of the permanent magnet 211 change with temperature.

[0072] Let's assume that the permanent magnet 211 is at room temperature and in the operating point P71 state. Next, let's assume that as a result of heating the permanent magnet 211, its magnetization characteristics change to those shown in graph G72. The operating point P72 is determined by the temperature coefficient of the residual magnetic flux density (Br) of the permanent magnet 211. Now, a straight line G73 can be defined by the temperature coefficient of the residual magnetic flux density (Br). The permanent magnet 211 operates in the state shown on the straight line G73 depending on the temperature. In other words, the operating point P72 of the heated permanent magnet 211 is the intersection of the BH curve, which is graph G72, and the straight line G73. Looking back at the explanation of demagnetization in the first embodiment, irreversible demagnetization occurred when the operating point exceeded the inflection point Ps on the BH curve. Similarly, irreversible demagnetization occurs when the permanent magnet 211 is heated until it reaches the characteristics shown in graph G72. For example, let's assume the temperature is higher than room temperature and is the temperature shown on the BH curve in graph G74. In this case, the operating point P73 has not crossed the inflection point. Therefore, in this case, reversible demagnetization occurs.

[0073] The degree of heating of the permanent magnet 211 can be controlled, for example, by the amplitude and frequency of the AC component. The degree of heating of the permanent magnet 211 can also be adjusted by controlling the switching speed and changing the magnitude of the ripple.

[0074] The demagnetization control signal φ2 causes the power converter 3 to output a demagnetizing current to the coil 221 for a demagnetizing magnetic flux that includes a second demagnetizing component of alternating current linked to the permanent magnets 211 of the rotor 21. With this configuration, the second demagnetizing magnetic flux component linked to the permanent magnets 211 of the rotor 21 generates heat in the permanent magnets 211 of the rotor 21. As a result, the permanent magnets 211 of the rotor 21 can be demagnetized by the heat.

[0075] The electric motor system of this disclosure has been described in detail above based on its embodiments. However, the electric motor system of this disclosure is not limited to the above. Various modifications are possible without departing from the spirit of this disclosure.

[0076] In the second embodiment, as shown in Figures 6(a) and 6(b), the demagnetizing current was described as the d-axis current. For example, the demagnetizing current may be the q-axis current, as shown in Figure 6(c). The demagnetizing current, which is the q-axis current, may contain only an AC component, as shown in Figure 6(c). The demagnetizing current, which is the q-axis current, may contain both an AC component and a DC component, as shown in Figure 6(d).

[0077] The demagnetizing current may be a composite current of the d-axis current component and the q-axis current component, as shown in Figure 6(e). In this case as in Modification 1, the demagnetizing current, which is the dq-axis composite current, may contain only the AC component, as shown in Figure 6(e). The demagnetizing current, which is the dq-axis composite current, may contain both the AC component and the DC component, as shown in Figure 6(f).

[0078] [Note] This disclosure includes the following components:

[0079] The electric motor system of the present disclosure is [1] "an electric motor having a rotor that includes magnets and rotates together with a shaft and coils fixedly arranged to surround the rotor, a power converter that outputs an output current to the coils of the electric motor, and a controller that controls the power converter, wherein the controller has a signal output unit that outputs a signal to the power converter for controlling the manner of the output current, and an abnormality detection unit that receives an abnormality signal indicating an abnormal situation, wherein when the abnormality detection unit receives the abnormality signal, the signal output unit outputs a demagnetization control signal to the power converter, and the power converter, upon input of the demagnetization control signal, causes a demagnetizing current for a demagnetizing magnetic flux to demagnetize the magnets of the rotor to flow through the coils."

[0080] The electric motor system of the present disclosure is [2] "the electric motor system according to [1] above, wherein the power converter, in response to the input of the demagnetization control signal, causes the coil to pass a demagnetizing current for the demagnetizing flux, which includes a first demagnetizing flux component that is in the opposite direction to the direction of the magnetic field generated by the magnet and synchronized with the rotation of the magnet."

[0081] The electric motor system of the present disclosure is [3] "the electric motor system according to [2] above, wherein the power converter controls the current flowing through the coils surrounding the rotor that are located at a position where the d-axis component is greater than the q-axis component relative to the rotor, in response to the input of the demagnetization control signal, so that the current flowing through the coils that are located at a position where the q-axis component is greater than the d-axis component."

[0082] The electric motor system of the present disclosure is [4] "the electric motor system according to [3] above, wherein the power converter does not pass current through coils where the q-axis component is greater than the d-axis component."

[0083] The electric motor system of the present disclosure is [5] "the electric motor system according to any one of the above [2] to [4], wherein the intensity of the demagnetizing flux including the first demagnetizing flux component is such that irreversible demagnetization occurs to the magnet of the rotor."

[0084] The electric motor system of the present disclosure is [6] "the electric motor system according to any one of the above [1] to [5], wherein the demagnetization control signal causes the power converter to output to the coil a demagnetization current for the demagnetization flux, which includes a second demagnetization component of alternating current linked to the magnet of the rotor."

[0085] The electric motor system of the present disclosure is [7] "the electric motor system according to any one of the above [1] to [6], wherein the controller has a demagnetization evaluation unit that evaluates the degree of irreversible demagnetization of the magnets of the rotor, and the demagnetization evaluation unit stops outputting the demagnetization control signal from the signal output unit when the degree of irreversible demagnetization of the magnets of the rotor is below a threshold."

[0086] The electric motor system of the present disclosure is [8] "the electric motor system according to any one of the above [1] to [7], wherein the shaft is connected to a rotating mechanism of a prime mover at a position different from the position in which the rotor is provided, the shaft receives power transmitted from the rotating mechanism to rotate the rotor, and the electric motor generates electricity due to the rotation of the rotor." [Explanation of Symbols]

[0087] 1. Electric Machinery System 2 Electric machines 3 Power Converters 4. Controller 5 shafts 6. External equipment (prime mover) 7 Load device 21 Rotors 22 stata 23 Bearings 41 Anomaly detection unit 42 Signal output section 43 Demagnetization Evaluation Unit 211 Permanent Magnet 212 Armoring D3 Demagnetizing flux θ1 Abnormal signal θ2 current signal φ1 Operation control signal φ2 Demagnetization control signal

Claims

1. An electric motor having a rotor that includes a magnet and rotates together with a shaft, and coils fixedly arranged to surround the rotor, A power converter that outputs an output current to the coil of the electric machine, The system includes a controller for controlling the power converter, The controller is, A signal output unit that outputs a signal to the power converter for controlling the mode of the output current, It has an abnormality detection unit that receives an abnormality signal indicating an abnormal situation, When the abnormality detection unit receives the abnormality signal, the signal output unit outputs a demagnetization control signal to the power converter. The power converter is an electric motor system that, in response to the input of the demagnetization control signal, causes the coil to flow a demagnetizing current that includes a DC component and an AC component superimposed on the DC component, which is used to cause demagnetization due to heat generated by eddy currents in the magnet, and whose polarity does not reverse over time.

2. The electric motor system according to claim 1, wherein the controller causes the power converter to output the demagnetizing current in the coil to generate a magnetic flux in the coil that includes an alternating current component that fluctuates within the magnet, causing the magnetic flux formed in the coil to link with the magnet.

3. The electric motor system according to claim 1, wherein the controller causes the power converter to output the demagnetizing current in which at least one of the current components of the d axis and the q axis includes an AC component.

4. The electric motor system according to claim 1, wherein the controller causes the power converter to output the demagnetizing current, in which at least one of the current components of the d axis and the q axis includes an AC component and also includes the DC component.

5. The electric motor system according to claim 4, wherein the controller reduces the switching frequency of the power converter when the abnormality detection unit receives the abnormality signal.

6. The electric motor system according to claim 1, wherein the controller controls the amplitude of the AC component of the demagnetizing current and the frequency of the demagnetizing current to generate the eddy current in the magnet for irreversible demagnetization of the magnet.

7. The electric motor system according to claim 1, wherein the controller controls the switching frequency of the power converter to cause the demagnetizing current superimposed with ripple to be output from the power converter to the coil.

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