Power conversion system

Abstract

To sufficiently consume electric energy of an electric machine when an anomaly occurs in the electric machine while avoiding an increase in the size of a device configuration.SOLUTION: A power conversion system 1 according to an embodiment of the present disclosure comprises: an electric machine 2; a power converter 11 that has a plurality of switching elements 211; and a controller 13 that controls a switching operation of each of the switching elements 211. The controller 13 has: a mode switching unit 32 that can switch a control mode of the switching operation of each switching element 211; and an anomaly detection unit 31b that detects an anomaly in an operating state of the electric machine 2. The control mode includes: a sinusoidal wave control mode M1 in which each switching element 211 is controlled so that a voltage waveform becomes sinusoidal; and a rectangular wave control mode M2 in which the switching element 211 is controlled so that the voltage waveform becomes rectangular. When the anomaly detection unit 31b detects an anomaly, the mode switching unit 32 switches the control mode from the sinusoidal wave control mode M1 to the rectangular wave control mode M2.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to power conversion systems. [Background technology]

[0002] Patent Documents 1 to 4 disclose techniques related to power conversion systems. Such power conversion systems have a configuration in which a generator is connected to a power grid via a power converter. A fuse is usually provided between the power converter and the power grid. In such a configuration, if the fuse blows, power from the generator cannot be supplied to the power grid, and the electrical energy of the generator is added as rotational energy of the rotor of the generator, which may cause over-rotation of the rotor. To prevent such over-rotation of the rotor, a switch and a resistor are sometimes provided downstream of the power converter. In such a configuration, if the fuse blows, the switch is driven to cause the electrical energy of the generator to be consumed by the resistor, thereby suppressing over-rotation of the rotor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 1-107686 [Patent Document 2] International Publication No. 2009 / 025243 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-236935 [Patent Document 4] Japanese Patent Application Laid-Open No. 2001-268973 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-described configuration, if all of the generator's power, which could cause rotor over-rotation, were to be consumed by a resistor, a large resistor would be required, which could result in an increased device size. On the other hand, there is a limit to how much power can be consumed by a resistor by increasing its size. Therefore, with the above-described configuration, it is difficult to sufficiently suppress rotor over-rotation. Furthermore, when an abnormality occurs in the generator, not just over-rotation, it may be necessary to consume electrical energy to recover or prevent damage.

[0005] The present disclosure describes a power conversion system that can sufficiently consume the electric energy of an electric machine when an abnormality occurs in the electric machine while avoiding an increase in the size of the device configuration. [Means for solving the problem]

[0006] A power conversion system according to one embodiment of the present disclosure comprises: an electric machine having a rotor and a coil; a power converter having a plurality of switching elements electrically connected to the coil, and converting the state of power input and output to the coil by switching operation of the plurality of switching elements; and a controller communicatively connected to the power converter and controlling the switching operation of each of the switching elements included in the plurality of switching elements, wherein the controller has a mode switching unit capable of switching the control mode of the switching operation of the switching elements, and an abnormality detection unit that detects abnormalities in the operating state of the electric machine, wherein the control modes include a normal control mode in which the switching operation of the switching elements is controlled so that the voltage waveform of power input to the coil is sinusoidal, and an abnormality control mode in which the switching operation of the switching elements is controlled so that the voltage waveform differs in at least one of waveform shape and phase from the voltage waveform in the normal control mode, and the mode switching unit switches the control mode from the normal control mode to the abnormality control mode when the abnormality detection unit detects an abnormality.

[0007] In the above-described power conversion system, when an abnormality in the operating state of the electric machine due to overspeed of the rotor of the electric machine is detected, the control mode of the switching operation of the switching elements of the power converter is switched from the normal control mode to the abnormal control mode. In the abnormal control mode, the voltage waveform differs from the voltage waveform in the normal control mode in at least one of the waveform shape and phase. When the voltage waveform is non-sinusoidal (e.g., rectangular), losses such as iron loss and copper loss increase within the electric machine, resulting in increased power consumption in the electric machine compared to when the voltage waveform of the power input to the coil is sinusoidal. As a result, the electric machine can consume power that could cause overspeed of the rotor. Furthermore, when the voltage waveform is out of phase, the current that does not contribute to the torque of the electric machine increases. This increase in current increases losses within the electric machine and increases power consumption in the electric machine. Therefore, in this case as well, the electric machine can consume power that could cause overspeed of the rotor. In this way, when an abnormality in the operating state of the electric machine is detected, the control mode of the switching elements is deliberately switched to an abnormal control mode that increases power consumption in the electric machine, thereby enabling the electric machine to be used as a device that consumes power that could cause rotor overspeed. In other words, the power that could cause rotor overspeed can be consumed not only by the resistor but also by the electric machine. This eliminates the need to increase the size of the resistor to consume power that could cause rotor overspeed, thereby avoiding an increase in the size of the device configuration. Furthermore, by having the electric machine take on the role of consuming power that could cause rotor overspeed, this power can be consumed effectively. This makes it possible to sufficiently suppress rotor overspeed. In this way, the above-mentioned power conversion system makes it possible to sufficiently consume electrical energy that could be generated when an abnormality occurs in the electric machine.

[0008] In the above aspect, the mode switching unit may output, in the normal control mode, a normal control signal to the switching element that instructs the switching element to perform a switching operation according to the normal control mode, and in the abnormal control mode, output, to the switching element, an abnormality control signal that instructs the switching element to perform a switching operation according to the abnormal control mode, the duty ratio of the normal control signal may be set to change over time, and the duty ratio of the abnormality control signal may be set to a constant. In this case, the voltage waveform can be controlled using the normal control signal and the abnormality control signal.

[0009] In the above aspect, the controller may further include a frequency control unit that controls the switching frequency of the abnormality control signal, and the frequency control unit may set the switching frequency of the abnormality control signal higher than the switching frequency of the normal control signal. In this case, the number of switching operations of the switching circuit increases in the abnormality control mode, resulting in an increase in switching loss of the switching circuit. This increases the power consumption of the power converter accordingly. Therefore, the power converter can be used in addition to the electric machine as a device that consumes power that may cause rotor over-rotation. This allows the electric machine and the power converter to more effectively consume power that may cause rotor over-rotation. As a result, the above-mentioned effect of being able to sufficiently consume electrical energy that may be generated in the event of an abnormality in the electric machine can be more effectively achieved while avoiding an increase in the size of the device configuration.

[0010] In the above aspect, the controller may further include an information acquisition unit that acquires at least one of the rotor rotation speed and the DC voltage of the power output from the power converter as an index value indicating the operating state of the electric machine, and the frequency control unit may change the switching frequency of the abnormality control signal in the abnormality control mode in accordance with the difference between the index value and a preset tolerance. The rotor rotation speed and the DC voltage of the power output from the power converter may fluctuate depending on the amount of power that could cause the rotor to overspeed, and therefore can be used as index values ​​indicating the operating state of the electric machine. Therefore, if the controller is configured to change the switching frequency of the abnormality control signal in accordance with the difference between the index value and the preset tolerance, it is possible to increase or decrease the power consumption in the power converter in accordance with the amount of power that could cause the rotor to overspeed, thereby enabling the power to be consumed efficiently.

[0011] In the above aspect, the mode switching unit may switch the control mode from the abnormality control mode to the normal control mode when, in the abnormality control mode, the switching frequency of the abnormality control signal is equal to or less than a reference value that is a criterion for determining whether the operating state of the electric machine is abnormal. In this way, by returning from the abnormality control mode to the normal control mode when it is determined that there is no abnormality in the operating state of the electric machine, it is possible to return the electric machine to a state in which it operates efficiently.

[0012] In some embodiments, the abnormal control mode includes a square-wave control mode in which switching operations of switching elements are controlled to obtain a square-wave voltage waveform. The square-wave control mode includes a first square-wave control mode in which switching operations of switching elements are controlled to obtain a square-wave voltage waveform including a first harmonic, and a second square-wave control mode in which switching operations of switching elements are controlled to obtain a square-wave voltage waveform including the first harmonic and a second harmonic higher than the first harmonic. The mode switching unit may be capable of switching from the first square-wave control mode to the second square-wave control mode in the square-wave control mode. In the second square-wave control mode, losses within the electric machine are greater than in the first square-wave control mode, resulting in greater power consumption in the electric machine. Therefore, for example, when the electric power that may cause rotor overrotation is large, switching from the first square-wave control mode to the second square-wave control mode enables the electric power to be consumed more effectively in the electric machine. [Effects of the Invention]

[0013] According to some aspects of the present disclosure, a power conversion system is provided that can sufficiently consume the electric energy of an electric machine when an abnormality occurs in the electric machine, while avoiding an increase in the size of the device configuration. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing the configuration of a power conversion system according to the present disclosure. [Figure 2] FIG. 2 is a diagram showing the structure of the electric machine of FIG. [Figure 3] FIG. 3 is a diagram illustrating the configuration of the controller in FIG. [Figure 4] Fig. 4(a) is a graph showing a U-phase sine wave control signal output in the sine wave control mode, Fig. 4(b) is a graph showing a V-phase sine wave control signal output in the sine wave control mode, and Fig. 4(c) is a graph showing a W-phase sine wave control signal output in the sine wave control mode. [Figure 5]Fig. 5(a) is a graph showing a U-phase square wave control signal output in the square wave control mode, Fig. 5(b) is a graph showing a V-phase square wave control signal output in the square wave control mode, and Fig. 5(c) is a graph showing a W-phase square wave control signal output in the square wave control mode. [Figure 6] FIG. 6 is a graph showing an example of a voltage waveform that switches stepwise from the sine wave control mode to the square wave control mode. [Figure 7] FIG. 7 is a flowchart showing the control flow of the controller. [Figure 8] Figure 8(a) is a graph showing a voltage waveform output in the first square wave control mode, Figure 8(b) is a graph showing a voltage waveform output in the second square wave control mode, and Figure 8(c) is a graph showing a voltage waveform output in the third square wave control mode. [Figure 9] FIG. 9 is a graph showing an example of a voltage waveform that switches stepwise from the first square wave control mode to the third square wave control mode. [Figure 10] Fig. 10(a) is a graph showing a voltage waveform in the phase control mode, and Fig. 10(b) is a graph showing a current waveform generated based on Fig. 10(a). DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, a power conversion system according to the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0016] As shown in FIG. 1, the power conversion system 1 includes an electric machine 2 and a power conversion unit 3. The power conversion system 1 is applied to, for example, an electric compressor, an electric blower, or a vehicle. The electric machine 2 is, for example, a generator that receives kinetic energy from an external device and generates electric energy. As the kinetic energy, for example, fluid energy such as steam can be used. Note that the electric machine 2 may also be an electric motor that receives electric energy from an external device and generates kinetic energy.

[0017] As shown in FIG. 2 , the electric machine 2 includes, as its main components, a rotor 21 and a stator 22. The rotor 21 is a cylindrical member fixed to the shaft 20. Both ends of the shaft 20 are supported by bearings, and the rotor 21 rotates integrally with the shaft 20. The rotor 21 has a permanent magnet 121 fixed to the shaft 20. The permanent magnet 121 may be, for example, a so-called surface permanent magnet. A stator 22 is disposed around the rotor 21. The stator 22 is fixed to a housing of the electric machine 2 or the like. The stator 22 has a plurality of coils 221 formed by winding conducting wires around the teeth. When the shaft 20 rotates due to external kinetic energy, the rotor 21 rotates in response to the rotation of the shaft 20. Due to the rotation of the rotor 21, the electric machine 2 outputs AC power. The electric machine 2 may be an internal rotation motor in which the rotor 21 is surrounded by the stator 22, or an external rotation motor in which the stator 22 is surrounded by the rotor 21.

[0018] Referring again to FIG. 1 , the power conversion unit 3 is electrically connected between the electric machine 2 and the power grid 5. The power conversion unit 3 converts the form of power from the electric machine 2 into a form of power compatible with the power grid 5 and outputs the converted power to the power grid 5. The form of power from the electric machine 2 and the form of power compatible with the power grid 5 are, for example, three-phase AC power. The power conversion unit 3 can also convert the form of power received from the power grid 5 into a form of power compatible with the electric machine 2 and output the converted power to the electric machine 2. If the electric machine 2 is a generator, at the start of power generation, the rotor 21 of the electric machine 2 is rotated using electrical energy, so the power conversion unit 3 converts the form of power received from the power grid 5 into a form of power required by the electric machine 2. As such, in the present disclosure, the power conversion unit 3 is configured to perform bidirectional power conversion between the electric machine 2 and the power grid 5. The following description will mainly focus on a case where the power conversion unit 3 converts power from the electric machine 2 and outputs the power to the power grid 5.

[0019] The power conversion unit 3 includes, for example, a power converter 11, a power converter 12, a controller 13, and a controller 14. The power converters 11 and 12 are connected in series with each other via DC buses 6a and 6b between the electric motor 2 and the power grid 5. The power converter 11 is connected to the electric motor 2 and receives AC power from the electric motor 2. The power converter 11 functions as a converter (rectifier) ​​that converts AC power from the electric motor 2 into DC power. The power converter 11 is an example of a "power converter" according to the present disclosure.

[0020] The power converter 12 functions as an inverter that converts the DC power from the power converter 11 into AC power. The power converter 12 is connected to the power grid 5 and provides the converted AC power to the power grid 5. When power from the power grid 5 is provided to the electric machine 2 via the power conversion unit 3, the power converter 11 functions as an inverter and the power converter 12 functions as a converter.

[0021] The power converter 11 has a U-phase terminal 11a, a V-phase terminal 11b, a W-phase terminal 11c, and input / output terminals 11d and 11e. The U-phase terminal 11a is connected to a U-phase coil 221. The V-phase terminal 11b is connected to a V-phase coil 221. The W-phase terminal 11c is connected to a W-phase coil 221. The U-phase terminal 11a, the V-phase terminal 11b, and the W-phase terminal 11c function as inputs of the power converter 11 to which AC power from the electric machine 2 is input. The input / output terminals 11d and 11e function as outputs of the power converter 11 to which DC power converted by the power converter 11 is output. The input / output terminals 11d and 11e are connected to DC buses 6a and 6b, respectively. A capacitor 7 is electrically connected between the DC buses 6a and 6b. The capacitor 7 smoothes the DC voltage on the DC buses 6a and 6b.

[0022] The power converter 11 has a switching circuit 111 having a plurality of (e.g., six) switching elements 211. The switching circuit 111 has a configuration in which three upper and lower arms, each including a pair of switching elements 211 connected in series to each other, are connected in parallel. Three intermediate potentials of each upper and lower arm are connected to a U-phase terminal 11a, a V-phase terminal 11b, and a W-phase terminal 11c, respectively. The switching elements 211 switch between on (conducting) and off (insulating) in accordance with instructions from the controller 13. A transistor may be used as the switching element 211. In the present disclosure, a case in which the switching element 211 is an insulated gate bipolar transistor (IGBT) will be described. The power converter 11 converts AC power from the electric machine 2 into DC power by the switching operation of the switching circuit 111.

[0023] Power converter 12 has U-phase terminal 12a, V-phase terminal 12b, W-phase terminal 12c, input / output terminal 12d, and input / output terminal 12e. Input / output terminal 12d is connected to input / output terminal 11d of power converter 11 via DC bus 6a. Input / output terminal 12e is connected to input / output terminal 11e of power converter 11 via DC bus 6b. DC power output from power converter 11 is input to input / output terminals 12d and 12e. AC power converted by power converter 12 is output from U-phase terminal 12a, V-phase terminal 12b, and W-phase terminal 12c. U-phase terminal 12a, V-phase terminal 12b, and W-phase terminal 12c are connected to power grid 5 via filter 4. Filter 4 is, for example, an EMC filter for removing electromagnetic noise. AC power output from U-phase terminal 12a, V-phase terminal 12b, and W-phase terminal 12c is provided to power grid 5 via filter 4. A fuse is provided between the power converter 12 and the power system 5. The fuse is blown by an overcurrent, so that an overcurrent flowing in the power system 5 can be suppressed.

[0024] The power converter 12 has a switching circuit 112 having a plurality of (e.g., six) switching elements 212. The switching circuit 112 has a configuration in which three upper and lower arms, each including a pair of switching elements 212 connected in series with each other, are connected in parallel. Three intermediate potentials of each upper and lower arm are connected to a U-phase terminal 12a, a V-phase terminal 12b, and a W-phase terminal 12c, respectively. The switching elements 212 switch between on (conducting) and off (insulating) in accordance with instructions from the controller 14. A transistor may be used as the switching element 212. In the present disclosure, a case in which the switching element 212 is an insulated gate bipolar transistor (IGBT) will be described. The power converter 12 converts DC power from the power converter 11 into AC power by the switching operation of the switching circuit 112.

[0025] The controller 13 is communicatively connected to the power converter 11 by wire or wirelessly. The controller 13 is an electronic control unit that controls the power converter 11, and is configured by a computer including, for example, a CPU, a ROM, and a RAM. The controller 13 has several functional components that are realized by executing a program on this hardware. The controller 14 is communicatively connected to the power converter 12 by wire or wirelessly. The controller 14 is an electronic control unit that controls the power converter 12, and is configured by a computer including, for example, a CPU, a ROM, and a RAM. The controller 14 has several functional components that are realized by executing a program on this hardware. The controller 14 may have the same functional components as the controller 13. The controllers 13 and 14 may be configured by a single computer.

[0026] As shown in FIG. 3 , the controller 13 has, as functional components, for example, an operation monitoring unit 31 and a mode switching unit 32. The operation monitoring unit 31 monitors the current operating state of the electric machine 2. The operation monitoring unit 31 includes, for example, an information acquiring unit 31a, an abnormality detecting unit 31b, a frequency control unit 31c, and a rotation speed control unit 31d. The information acquiring unit 31a acquires operation information D13 indicating the current operating state of the electric machine 2. The operation information D13 includes, for example, the current rotation speed of the rotor 21 and the current DC voltage applied to the DC buses 6a, 6b between the power converter 11 and the power converter 12 (hereinafter referred to as the "DC bus voltage"). The information acquiring unit 31a can acquire the rotation speed of the rotor 21, for example, by receiving a detection result D11 from a rotation speed sensor for detecting the rotation speed of the rotor 21. Furthermore, the information acquiring unit 31a can acquire the DC bus voltage by receiving a detection result D12 from a bus voltage sensor for detecting the DC bus voltage. The information acquiring unit 31a provides operation information D13 acquired from the detection results D11 and D12 to the mode switching unit 32. The operation information D13 may include other information in addition to the rotation speed and the DC bus voltage. For example, the operation information D13 may include the phase of the rotor 21. In this case, the information acquiring unit 31a may acquire the phase of the rotor 21 by receiving a detection result from a rotation speed sensor for detecting the phase of the rotor 21, or may estimate the phase of the rotor 21 from the detection result of the rotation speed sensor.

[0027] The abnormality detection unit 31b detects an abnormality in the operating state of the electric machine 2. An abnormality in the operating state of the electric machine 2 is an event that causes the electric machine 2 to generate excess electrical energy that should be consumed, such as an abnormality caused by over-rotation of the rotor 21. An abnormality caused by over-rotation of the rotor 21 is, for example, a state in which a fuse provided between the power conversion unit 3 and the power grid 5 is blown. When over-rotation of the rotor 21 occurs, excessive power is generated in the electric machine 2. In this case, the fuse melts and blows to prevent the excessive power from being provided to the power grid 5. When the fuse is blown in this way, the abnormality detection unit 31b receives an abnormality detection signal D21 that notifies the mode switching unit 32 of an abnormality in the operating state of the electric machine 2 caused by over-rotation of the rotor 21. Upon receiving the abnormality detection signal D21, the abnormality detection unit 31b detects that the operating state of the electric machine 2 is abnormal and provides an abnormality notification signal D22 that notifies the mode switching unit 32 of the abnormality in the operating state of the electric machine 2. The abnormality in the operating state of the electric machine 2 may be an abnormality caused by a factor other than the over-rotation of the rotor 21, as long as it causes the electric machine 2 to generate excess electrical energy that should be consumed.

[0028] An abnormality in the operating state of the electric machine 2 caused by over-rotation of the rotor 21 is not limited to when a fuse is blown. For example, when over-rotation of the rotor 21 occurs, the rotation speed of the rotor 21 increases compared to when the operating state of the electric machine 2 is normal (during normal driving). Furthermore, when a fuse is blown due to over-rotation of the rotor 21, the DC bus voltage increases compared to when it is during normal driving in response to the increase in the rotation speed of the rotor 21. Therefore, an abnormality in the operating state of the electric machine 2 caused by over-rotation of the rotor 21 may occur when the rotation speed of the rotor 21 increases compared to when it is during normal driving, or when the DC bus voltage increases compared to when it is during normal driving.

[0029] The frequency control unit 31c controls the switching frequency of the switching circuit 111 based on the operation information D13 acquired by the information acquisition unit 31a. The rotation speed control unit 31d controls the rotation speed of the rotor 21 of the electric machine 2 based on the operation information D13 acquired by the information acquisition unit 31a. Specific control methods of the frequency control unit 31c and the rotation speed control unit 31d will be described later.

[0030] The mode switching unit 32 switches the control mode of the switching operation of each switching element 211 included in the switching circuit 111. The mode switching unit 32 includes, for example, a mode selection unit 32a, a signal output unit 32b, a sine wave control signal generation unit 32c, and a square wave control signal generation unit 32d. The mode selection unit 32a selects either a sine wave control mode (normal control mode) or a square wave control mode (abnormal control mode) as the control mode for the switching operation of the switching element 211. The sine wave control mode is a control mode in which the switching operation of the switching element 211 is controlled so that the voltage waveform of the power input to the coil 221 becomes a sine wave. The square wave control mode is a control mode in which the switching operation of the switching element 211 is controlled so that the voltage waveform of the power input to the coil 221 becomes a square wave, which is different from a sine wave.

[0031] The mode selection unit 32a selects the sine wave control mode during normal driving before receiving the abnormality notification signal D22 from the abnormality detection unit 31b. On the other hand, when the mode selection unit 32a receives the abnormality notification signal D22 from the abnormality detection unit 31b, it determines that an abnormality has occurred in the electric machine 2 due to over-rotation of the rotor 21, and selects the square wave control mode as a control mode (rapid braking mode) for suppressing the over-rotation of the rotor 21. The mode selection unit 32a provides the signal output unit 32b with control mode information D51 indicating whether the selected control mode is the sine wave control mode or the square wave control mode.

[0032] The signal output unit 32b receives control mode information D51 from the mode selection unit 32a and outputs a control signal to the switching element 211 to instruct the switching operation of the switching element 211 according to the control mode indicated by the control mode information D51. When the mode selection unit 32a selects the sinusoidal control mode, the signal output unit 32b outputs a sinusoidal control signal D61 (normal control signal) generated by the sinusoidal control signal generation unit 32c to the switching element 211. The sinusoidal control signal D61 is a switching signal that instructs the switching operation of the switching element 211 so that the voltage waveform becomes sinusoidal. The state in which the voltage waveform becomes sinusoidal refers to a state in which the time waveform of the voltage exhibits periodic sinusoidal changes. The phase of the sinusoidal voltage waveform is synchronized with the phase of the rotor 21. While the mode selection unit 32a selects the sinusoidal control mode, the signal output unit 32b may continuously output the sinusoidal control signal D61 to the switching element 211.

[0033] The sine-wave control signal generator 32c generates, as the sine-wave control signal D61, a U-phase sine-wave control signal D61a shown in FIG. 4(a), a V-phase sine-wave control signal D61b shown in FIG. 4(b), and a W-phase sine-wave control signal D61c shown in FIG. 4(c). FIGS. 4(a), 4(b), and 4(c) also show sinusoidal voltage waveforms V1a, V1b, and V1c, respectively, that are converted by switching the switching elements 211 on and off in accordance with the sine-wave control signals D61a, D61b, and D61c for each phase. The sine-wave control signals D61a, D61b, and D61c for each phase are, for example, PWM signals that are pulse-width modulated by PWM control. PWM control is a control method that arbitrarily changes the pulse width by temporally varying the on / off duty ratio of the switching elements 211. The duty ratio means the ratio of an on-period to the total period of an on-period in which the switching element 211 is on and an off-period in which the switching element 211 is off.

[0034] The sine-wave control signal generator 32c compares the U-phase voltage command value with the carrier wave to generate a sine-wave control signal D61a that controls the on / off switching of the U-phase switching element 211. The U-phase voltage command value is a sine-wave reference signal corresponding to the U-phase voltage waveform V1a. The carrier wave is, for example, a triangular wave that oscillates with a predetermined amplitude at a carrier frequency (switching frequency) set by the frequency controller 31c. The sine-wave control signal generator 32c turns on the sine-wave control signal D61a when the U-phase voltage command value exceeds the carrier wave, and turns off the sine-wave control signal D61a when the U-phase voltage command value falls below the carrier wave. In this manner, the U-phase sine-wave control signal D61a shown in FIG. 4(a) is generated. The V-phase sine-wave control signal D61b and the W-phase sine-wave control signal D61c are also generated in the same manner as the U-phase sine-wave control signal D61a.

[0035] In the sine wave control mode M1, the signal output unit 32b outputs sine wave control signals D61a, D61b, and D61c for each phase to the corresponding switching elements 211. As a result, the switching elements 211 are switched on and off in accordance with the sine wave control signals D61a, D61b, and D61c for each phase, and the voltage waveforms V1a, V1b, and V1c input to the coils 221 for each phase become sine waves. Hereinafter, when the sine wave control signals D61a, D61b, and D61c for each phase are described without distinction, they will be collectively referred to as the "sine wave control signal D61."

[0036] On the other hand, when the mode selection unit 32a selects the square wave control mode, the signal output unit 32b outputs a square wave control signal D62 (abnormality control signal) generated by the square wave control signal generation unit 32d to the switching element 211. The square wave control signal D62 is a switching signal that instructs the switching element 211 to perform a switching operation so that the voltage waveform becomes square wave-like. A state in which the voltage waveform becomes square wave-like refers to a state in which the time waveform of the voltage exhibits periodic square wave-like changes. The square wave-like voltage waveform may be a waveform in which harmonics are superimposed on a constant-period fundamental wave (e.g., an undistorted sine wave). More specifically, the square wave-like voltage waveform may be a waveform that includes, in addition to the fundamental wave (frequency Ω), harmonic components having frequencies that are odd multiples of the fundamental frequency Ω (3Ω, 5Ω, 7Ω, etc.). Therefore, the rectangular voltage waveform includes not only an ideal rectangular wave but also a waveform that deviates from a fundamental wave (typically a sine wave) due to the superposition of harmonics, i.e., a waveform that deviates from the fundamental wave and approaches an ideal rectangular wave. The fundamental wave is an ideal sine wave that is synchronized with the phase of the rotor 21 to increase output efficiency. While the mode selection unit 32a selects the rectangular wave control mode, the signal output unit 32b may continuously output a rectangular wave control signal D62 to the switching element 211.

[0037] The square-wave control signal generator 32d generates, as the square-wave control signal D62, a U-phase square-wave control signal D62a shown in Fig. 5(a), a V-phase square-wave control signal D62b shown in Fig. 5(b), and a W-phase square-wave control signal D62c shown in Fig. 5(c). Figs. 5(a), 5(b), and 5(c) also show square-wave voltage waveforms V2a, V2b, and V2c converted by switching the switching elements 211 on and off in accordance with the square-wave control signals D62a, D62b, and D62c for each phase. The square-wave control signals D62a, D62b, and D62c for each phase have a fixed on-off duty ratio for the switching elements 211 so that the voltage remains constant during a predetermined conduction period.

[0038] In the example shown in FIG. 5(a), the U-phase square-wave control signal D62 alternates between a 120-degree conduction period and a 60-degree non-conduction period. During the first 60-degree period of the 120-degree conduction period, the signal is alternately on and off, and during the second 60-degree period, the signal is on. The V-phase square-wave control signal D62b and the W-phase square-wave control signal D62c are generated in the same manner as the U-phase square-wave control signal D62a. The square-wave control signals D62a, D62b, and D62c are configured so that when one phase is in a non-conduction period, the other two phases are in a conduction period. The conduction periods of the square-wave control signals D62a, D62b, and D62c are not limited to 120 degrees, but may be periods corresponding to other phases, such as 150 degrees or 110 degrees.

[0039] In the square-wave control mode M2, the signal output unit 32b outputs square-wave control signals D62a, D62b, and D62c for each phase to the corresponding switching elements 211. As a result, the switching elements 211 are switched on and off in accordance with the square-wave control signals D62a, D62b, and D62c for each phase, and the voltage waveforms V2a, V2b, and V2c input to the coils 221 for each phase have a square waveform. Hereinafter, when the square-wave control signals D62a, D62b, and D62c for each phase will not be distinguished from one another, they will be collectively referred to as the "square-wave control signal D62."

[0040] The frequency control unit 31c sets the switching frequency of the square-wave control signal D62 to be higher than the switching frequency of the sine-wave control signal D61. For example, the frequency control unit 31c sets the switching frequency of the square-wave control signal D62 to be higher than the switching frequency of the sine-wave control signal D61 during the first 60-degree period of the 120-degree conduction period. The period during which the switching frequency of the square-wave control signal D62 is set high may be at least a portion of the 120-degree conduction period, or may be the entire 120-degree conduction period. As an example, the frequency control unit 31c sets the switching frequency of the sine-wave control signal D61 to 10 kHz and the switching frequency of the square-wave control signal D62 to 40 kHz. Hereinafter, the term "switching frequency" simply refers to the switching frequency of the square-wave control signal D62.

[0041] As described above, in the sine-wave control mode M1 before the abnormality detection unit 31b detects an abnormality, the mode switching unit 32 outputs a sine-wave control signal D61 to the switching element 211, thereby controlling the voltage waveforms V1a, V1b, and V1c input to the coil 221 to be sinusoidal (see FIGS. 4(a), 4(b), and 4(c)). On the other hand, when the abnormality detection unit 31b detects an abnormality, the mode switching unit 32 switches from the sine-wave control mode M1 to the square-wave control mode M2. Then, in the square-wave control mode M2, the mode switching unit 32 outputs a square-wave control signal D62 to the switching element 211, thereby controlling the voltage waveforms V2a, V2b, and V2c input to the coil 221 to be square waves (see FIGS. 5(a), 5(b), and 5(c)).

[0042] In the square-wave control mode M2, square-wave voltage waveforms V2a, V2b, and V2c are input to the electric machine 2. In this case, sixth-order harmonic currents are generated in the current flowing through the electric machine 2, which increases losses such as iron loss and harmonic copper loss inside the electric machine 2 due to the high-order harmonic currents. As a result, the electric machine 2 consumes more power in the square-wave control mode M2 ​​than in the sine-wave control mode M1. Furthermore, the square-wave control mode M2 ​​has a higher switching frequency than the sine-wave control mode M1. Therefore, in the square-wave control mode M2, the switching element 211 switches more frequently, which increases the switching loss in the switching element 211 and increases the power consumed by the power converter 11. As a result, in the square-wave control mode M2, it is possible to consume more excess power in the electric machine 2 and the power converter 11, which may cause the rotor 21 to over-rotate.

[0043] Here, excessive power that may cause over-rotation of the rotor 21 affects the rotation speed of the rotor 21 and the DC bus voltage, and the higher the power, the higher the rotation speed and DC bus voltage of the rotor 21. Therefore, the rotation speed and DC bus voltage can be used as index values ​​that indicate the operating state of the electric machine 2 caused by over-rotation of the rotor 21. If the index value is large, it can be said that the power that may cause over-rotation of the rotor 21 is large, and therefore, in order to suppress over-rotation of the rotor 21 caused by the power, it is necessary to consume more power in the power conversion system 1.

[0044] Therefore, in the square-wave control mode M2, the frequency control unit 31c acquires an index value from the operation information D13 provided by the information acquisition unit 31a and changes the switching frequency of the square-wave control signal D62 according to the magnitude of the index value. The "index value" may be a value indicating at least one of the rotation speed of the rotor 21 and the DC bus voltage. The frequency control unit 31c sets a tolerance value for the index value and changes the switching frequency according to the difference between the index value and the tolerance value. The "tolerance value" may be, for example, an index value when no abnormality in the operating state of the electric machine 2 due to overspeed of the rotor 21 occurs (i.e., during normal driving). If the index value indicates the rotation speed of the rotor 21, the frequency control unit 31c may set the upper limit of the rotation speed of the rotor 21 during normal driving as the tolerance value. If the index value indicates the DC bus voltage, the frequency control unit 31c may set the upper limit of the DC bus voltage during normal driving as the tolerance value.

[0045] For example, when the index value exceeds the allowable value, the frequency control unit 31c increases the switching frequency as the difference between the index value and the allowable value increases. The frequency control unit 31c outputs a frequency control signal D31 that instructs the square wave control signal generation unit 32d to change the switching frequency of the square wave control signal D62. As a result, when the power that could cause over-rotation of the rotor 21 is large, power consumption in the power converter 11 increases, and this power can be consumed more in the power conversion system 1. Note that when the index value does not exceed the allowable value, the frequency control unit 31c may control the switching frequency to decrease as the difference between the index value and the allowable value increases.

[0046] Here, in the power converter 11, in order to convert the form of input power, an operation in which the switching element 211 of one arm is turned on and the switching element 211 of the other arm is turned off is repeated. If the switching elements 211 of the upper and lower arms are both turned on, a short circuit occurs, resulting in a malfunction. In the sine-wave control mode M1, to avoid such a short circuit, it is necessary to ensure a period (dead time) in which both the switching elements 211 of the upper and lower arms are turned off. Therefore, in the sine-wave control mode M1, there is a limit to how high the switching frequency of the sine-wave control signal D61 can be increased.

[0047] On the other hand, in the square-wave control mode M2, when the switching element 211 of one arm is on, the switching element 211 of the other arm is off. Therefore, both the upper and lower arm switching elements 211 are not on. Increasing the switching frequency of the square-wave control signal D62 increases the number of repetitive on-off cycles of the switching element 211 of one arm, but the switching element 211 of the other arm is always off. Therefore, in the square-wave control mode M2, even if the switching frequency is increased, a short circuit between the upper and lower arm switching elements 211 is not generated, and therefore there is no need to ensure dead time. Therefore, the switching frequency can be increased as far as the processing capacity of the controller 13 allows. Therefore, in the square-wave control mode M2, the frequency control unit 31c can, in principle, set the switching frequency as high as possible depending on the amount of power that may cause the rotor 21 to over-rotate.

[0048] In the square-wave control mode M2, the rotation speed control unit 31d controls the rotation speed of the rotor 21 so that the current rotation speed of the rotor 21 is equal to or less than a tolerable value in order to directly prevent the rotor 21 from over-rotating. The rotation speed control unit 31d acquires the current rotation speed of the rotor 21 from the operation information D13 and outputs a rotation speed control signal D41 to the electric machine 2, which controls the rotation speed of the rotor 21 to be equal to or less than the tolerable value. In accordance with the rotation speed control signal D41, the rotation speed of the rotor 21 is controlled to be equal to or less than the tolerable value. The tolerable value here may be, for example, an upper limit of the rotation speed of the rotor 21 during normal operation. When the rotation speed of the rotor 21 is controlled to be equal to or less than the tolerable value in this manner, excess power that could cause the rotor 21 to over-rotate is stored in the capacitor 7 connected to the DC buses 6a and 6b, causing an increase in the DC bus voltage.

[0049] Therefore, the frequency control unit 31c may control the switching frequency using only the DC bus voltage as an index value so that the DC bus voltage is equal to or less than the allowable value. In this case, for example, when the DC bus voltage exceeds the allowable value, the frequency control unit 31c may increase the switching frequency as the difference between the DC bus voltage and the allowable value increases. In this way, under the square-wave control mode M2, an attempt to keep the rotation speed of the rotor 21 equal to or less than the allowable value increases the DC bus voltage, and an attempt to further keep the DC bus voltage equal to or less than the allowable value increases the switching frequency. Therefore, when both the rotation speed of the rotor 21 and the DC bus voltage are within the allowable values ​​and the switching frequency is equal to or less than the reference value, it can be said that the abnormal operating state of the electric machine 2 caused by overspeed of the rotor 21 has been eliminated.

[0050] Therefore, the mode switching unit 32 acquires the switching frequency from the frequency control unit 31c, and switches the control mode of the power converter 11 from the square wave control mode M2 ​​to the sine wave control mode M1 when the switching frequency falls below a reference value. The "reference value" may be, for example, the upper limit of the switching frequency when the operating state of the electric machine 2 is normal. The "reference value" may be the same value as the switching frequency of the sine wave control signal D61, or may be a value higher or lower than the switching frequency.

[0051] In this case, the mode selection unit 32a determines whether the switching frequency is equal to or lower than the reference value. If the mode selection unit 32a determines that the switching frequency is not equal to or lower than the reference value, it maintains the control mode of the switching operation of the switching element 211 in the square-wave control mode M2. On the other hand, if the mode selection unit 32a determines that the switching frequency is equal to or lower than the reference value, it changes the control mode of the switching operation of the switching element 211 from the square-wave control mode M2 ​​to the sine-wave control mode M1. In response to this, the control signal output from the signal output unit 32b to the switching element 211 switches from the square-wave control signal D62 to the sine-wave control signal D61. As a result, the voltage waveform input to the coil 221 returns from a square wave to a sine wave.

[0052] As shown in Fig. 6, the mode switching unit 32 may switch from the sine wave control mode M1 to the square wave control mode M2, and then switch from the square wave control mode M2 ​​back to the sine wave control mode M1 after a certain time has elapsed since the square wave control mode M2 ​​was started. In this case, the square wave control mode M2 ​​can be automatically ended after a certain time has elapsed since the square wave control mode M2 ​​was started. In Fig. 6, the voltage waveform V1 corresponds to any one of the voltage waveforms V1a, V1b, or V1c described above, and the voltage waveform V2 corresponds to any one of the voltage waveforms V2a, V2b, or V2c described above.

[0053] Next, the control flow of the controller 13 will be described with reference to Fig. 7. As shown in Fig. 7, first, the mode selection unit 32a selects the sine wave control mode M1 during normal driving before the abnormality detection unit 31b detects an abnormality in the operating state of the electric machine 2 (step S11). At this time, the signal output unit 32b outputs a sine wave control signal D61 to the switching element 211, thereby controlling the voltage waveform input to the coil 221 to be sinusoidal.

[0054] Next, the mode selection unit 32a determines whether the abnormality detection unit 31b has detected an abnormality in the operating state of the electric machine 2 (step S12). If the mode selection unit 32a has not received the abnormality notification signal D22 from the abnormality detection unit 31b, the mode selection unit 32a determines that the abnormality detection unit 31b has not detected an abnormality (No in step S12) and repeats step S12 again. On the other hand, if the mode selection unit 32a has received the abnormality notification signal D22 from the abnormality detection unit 31b, the mode selection unit 32a determines that the abnormality detection unit 31b has detected an abnormality (Yes in step S12) and switches the control mode of the switching element 211 from the sine wave control mode M1 to the square wave control mode M2 ​​(step S13). At this time, the signal output unit 32b outputs a square wave control signal D62 to the switching element 211, thereby controlling the voltage waveform input to the coil 221 to be square.

[0055] Next, the frequency control unit 31c controls the switching frequency of the square-wave control signal D62 while referring to the operation information D13 (step S14). For example, the frequency control unit 31c uses the current DC bus voltage as an index value and changes the switching frequency according to the difference between the index value and an allowable value. Furthermore, the rotation speed control unit 31d controls the current rotation speed of the rotor 21 so that the current rotation speed of the rotor 21 is equal to or less than the allowable value (step S15). Steps S14 and S15 may be performed in parallel (simultaneously) or at different times.

[0056] Next, the mode selection unit 32a determines whether the switching frequency controlled by the frequency control unit 31c has fallen below the reference value. If the mode selection unit 32a determines that the switching frequency has not fallen below the reference value (No in step S16), it repeats steps S14 to S16 until it determines that the switching frequency has fallen below the reference value. On the other hand, if the mode selection unit 32a determines that the switching frequency has fallen below the reference value (Yes in step S16), it switches the control mode of the switching element 211 from the square wave control mode M2 ​​to the sine wave control mode M1 (step S17). In this case, the series of processes from step S12 to step S17 are repeated again. The control flow shown in FIG. 7 may include, for example, a step of increasing the cooling capacity of a cooler for cooling the power converter 11 and the electric machine 2 in order to avoid thermal failure of the power converter 11 and the electric machine 2. For example, when switching from sine wave control mode M1 to square wave control mode M2, the cooling capacity of the cooler for at least one of the power converter 11 and the electric machine 2 may be made larger than that during normal driving (when sine wave control mode M1 is selected).

[0057] The following describes the effects and advantages of the power conversion system 1 according to this embodiment.

[0058] In the power conversion system 1 according to this embodiment, when an abnormality in the operating state of the electric machine 2 caused by over-rotation of the rotor 21 is detected, the control mode of the switching element 211 is switched from the sine-wave control mode M1 to the square-wave control mode M2. As a result, the voltage waveform input to the coil 221 becomes square-wave. In this case, losses such as iron loss and copper loss increase inside the electric machine 2, and therefore the power consumption of the electric machine 2 increases compared to when the voltage waveform of the power input to the coil 221 is sinusoidal. As a result, it becomes possible for the electric machine 2 to consume power that could cause over-rotation of the rotor 21.

[0059] In this way, when an abnormality in the operating state of the electric machine 2 is detected, the control mode of the switching element 211 is switched to the square-wave control mode M2, which intentionally increases the power consumption of the electric machine 2. This allows the electric machine 2 to be used as a device that consumes power that could cause overrotation of the rotor 21. In other words, the power that could cause overrotation of the rotor 21 can be consumed not only by the resistor but also by the electric machine 2. This eliminates the need to increase the size of the resistor to consume power that could cause overrotation of the rotor 21, thereby preventing an increase in the size of the device configuration. For example, the resistor can be made smaller or can be omitted. Furthermore, since the electric machine 2 takes on the role of consuming power that could cause overrotation of the rotor 21, this power can be consumed effectively. This makes it possible to sufficiently suppress overrotation of the rotor 21. In this way, the power conversion system 1 according to this embodiment allows sufficient consumption of electrical energy that could be generated when an abnormality occurs in the electric machine 2.

[0060] As in this embodiment, the duty ratio of the sine wave control signal D61 may be set to change over time, and the duty ratio of the square wave control signal D62 may be set to a constant value. In this case, the voltage waveform can be controlled using the sine wave control signal D61 and the square wave control signal D62.

[0061] As in the present embodiment, the frequency control unit 31c may set the switching frequency of the square-wave control signal D62 higher than the switching frequency of the sine-wave control signal D61. In this case, in the square-wave control mode M2, the number of times the switching element 211 is switched increases, resulting in an increase in the switching loss of the switching element 211. This increases the power consumption of the power converter 11 accordingly. Therefore, the power converter 11, in addition to the electric machine 2, can be used as a device consuming power that may cause the rotor 21 to over-rotate. This allows the electric machine 2 and the power converter 11 to more effectively consume the power that may cause the rotor 21 to over-rotate. As a result, the above-mentioned effect of being able to sufficiently consume electrical energy that may be generated in the event of an abnormality in the electric machine 2 can be more effectively achieved while avoiding an increase in the size of the device configuration.

[0062] As in the present embodiment, in the square-wave control mode M2, the frequency control unit 31c may change the switching frequency of the square-wave control signal D62 in accordance with the difference between the index value and a preset allowable value. The rotation speed of the rotor 21 and the DC bus voltage may fluctuate due to the magnitude of power that may cause the rotor 21 to over-rotate, and therefore can be used as index values ​​that indicate the operating state of the electric machine 2. Therefore, if the switching frequency of the square-wave control signal D62 is changed in accordance with the difference between the index value and the allowable value, it becomes possible to increase or decrease the power consumption in the power converter 11 in accordance with the magnitude of power that may cause the rotor 21 to over-rotate, thereby enabling the power to be consumed efficiently.

[0063] As in this embodiment, the mode switching unit 32 may switch the control mode from the square-wave control mode M2 ​​to the sine-wave control mode M1 when the switching frequency of the square-wave control signal D62 is equal to or lower than a reference value in the square-wave control mode M2. In this way, when it is determined that there is no abnormality in the operating state of the electric machine 2 due to over-rotation of the rotor 21, by switching back from the square-wave control mode M2 ​​to the sine-wave control mode M1, the electric machine 2 can be restored to a state in which it operates efficiently.

[0064] In this embodiment, the mode switching unit 32 may change the control mode from the square-wave control mode M2 ​​to the sine-wave control mode M1 when the switching frequency is equal to or lower than a reference value and the index value is equal to or lower than a tolerance value. As described above, the index value can be used to indicate the operating state of the electric machine 2. Therefore, by taking this index value into consideration in addition to the switching frequency, it is possible to more reliably determine that there is no abnormality in the operating state of the electric machine 2 due to over-rotation of the rotor 21. This makes it possible to prevent a situation in which the control mode is returned to the sine-wave control mode M1 while an abnormality exists in the operating state of the electric machine 2.

[0065] The control method by the controller 13 is not limited to the above-described example. For example, the square-wave control mode M2 ​​selected by the mode selection unit 32a may include a first square-wave control mode M21 shown in FIG. 8(a), a second square-wave control mode M22 shown in FIG. 8(b), and a third square-wave control mode M23 shown in FIG. 8(c). The voltage waveform V21 shown in FIG. 8(a) is the voltage waveform output from the power converter 11 in the first square-wave control mode M21. The voltage waveform V22 shown in FIG. 8(b) is the voltage waveform output from the power converter 11 in the second square-wave control mode M22. The voltage waveform V23 shown in FIG. 8(c) is the voltage waveform output from the power converter 11 in the third square-wave control mode M23.

[0066] In the first square-wave control mode M21, a square-wave control signal D62 for obtaining a voltage waveform V21 shown in FIG. 8(a) is output to the switching element 211. The switching element 211 performs a switching operation in accordance with the square-wave control signal D62, thereby outputting the voltage waveform V21 from the power converter 11. The voltage waveform V21 is a waveform that includes, for example, a fifth-order harmonic and a seventh-order harmonic in addition to a fundamental wave (sine wave). The fifth-order harmonic and the seventh-order harmonic are examples of the "first harmonic" according to the present disclosure. In the second square-wave control mode M22, a square-wave control signal D62 for obtaining a voltage waveform V22 shown in FIG. 8(b) is output to the switching element 211. The switching element 211 performs a switching operation in accordance with the square-wave control signal D62, thereby outputting the voltage waveform V22 from the power converter 11. The voltage waveform V22 is a waveform that includes, for example, a ninth-order harmonic and an eleventh-order harmonic in addition to the voltage waveform V21. The 9th harmonic or the 11th harmonic are examples of the "second harmonic" according to the present disclosure.

[0067] In the third square-wave control mode M23, a square-wave control signal D62 for obtaining the voltage waveform V23 shown in FIG. 8(c) is output to the switching element 211. The switching element 211 performs a switching operation in response to the square-wave control signal D62, thereby outputting the voltage waveform V23 from the power converter 11. The voltage waveform V23 is, for example, a waveform that includes higher-order harmonics in addition to the voltage waveform V22. The voltage waveform V23 is close to an ideal square wave. Among the voltage waveforms V21, V22, and V23, when the voltage waveform V21 is input to the coil 221, the loss in the electric machine 2 is smallest. When the voltage waveform V22, which includes higher-order harmonics than the voltage waveform V21, is input to the coil 221, the loss in the electric machine 2 is larger than when the voltage waveform V21 is input to the coil 221. Furthermore, when the voltage waveform V23, which includes higher-order harmonics than the voltage waveform V22, is input to the coil 221, the loss in the electric machine 2 is largest.

[0068] Therefore, in the first square-wave control mode M21, the power consumption of the electric machine 2 is minimized, and in the third square-wave control mode M23, the power consumption of the electric machine 2 is maximized. Therefore, in the square-wave control mode M2, the mode switching unit 32 switches the control mode of the switching element 211 in stages depending on the magnitude of power that may cause over-rotation of the rotor 21. For example, the mode switching unit 32 sets a first permissible value, a second permissible value greater than the first permissible value, and a third permissible value greater than the second permissible value for an index value indicating at least one of the rotation speed of the rotor 21 and the DC bus voltage. The mode switching unit 32 selects the first square-wave control mode M21 when the index value is greater than the first permissible value and equal to or less than the second permissible value. Then, the mode switching unit 32 switches from the first square-wave control mode M21 to the second square-wave control mode M22 when the index value is greater than the second permissible value and equal to or less than the third permissible value. If the index value is greater than the third allowable value, the mode switching unit 32 switches from the second square wave control mode M22 to the third square wave control mode M23. For example, as shown in Fig. 9, the mode switching unit 32 may switch in stages from the first square wave control mode M21 to the third square wave control mode M23 via the second square wave control mode M22.

[0069] In this way, by gradually switching from the first square-wave control mode M21 to the third square-wave control mode M23, the power consumption of the electric machine 2 can be gradually increased. This makes it possible to efficiently consume the power depending on the magnitude of the power that may cause the rotor 21 to over-rotate. Note that in the square-wave control mode M2, the voltage waveform may be controlled so that the phase of the current is shifted by 120 degrees relative to the fundamental wave. By shifting the phase of the voltage waveform in this way, the power consumption of the electric machine 2 can be increased.

[0070] The mode selection unit 32a may select the phase control mode M2A shown in FIG. 10(a) instead of the square-wave control mode M2. As shown in FIG. 10(a), the phase of the voltage waveform V11 in the phase control mode M2A is shifted relative to the phase of the voltage waveform V1 in the sine-wave control mode M1. In the phase control mode M2A, the shape of the voltage waveform V11 is maintained sinusoidal. In FIG. 10(a), the voltage waveform V1 corresponds to any one of the voltage waveforms V1a, V1b, or V1c described above. The voltage waveform V1 is, for example, an ideal sine wave (fundamental wave) that is synchronized with the phase of the rotor 21 to increase output efficiency. In contrast, the phase of the voltage waveform V11 is shifted relative to the phase of the voltage waveform V1, and therefore deviates from the ideal phase synchronized with the phase of the rotor 21, resulting in an increase in current that does not contribute to the torque of the electric machine 2.

[0071] For example, as shown in the current waveform A11 in FIG. 10(b), the current value output from the power converter 11 is larger than that of the current waveform A1 in FIG. 10(b). The current waveform A11 is a waveform representing a current generated based on the voltage waveform V11, and the current waveform A1 is a waveform representing a current generated based on the voltage waveform V1. When the current increases in this way, loss within the electric machine 2 increases, and the electric power consumed by the electric machine 2 increases. Therefore, even in the phase control mode M2A shown in FIG. 10(a), as in the square-wave control mode M2, it is possible for the electric machine 2 to consume power that could cause over-rotation of the rotor 21. Note that in the square-wave control mode M2, control to change the voltage waveform V1 into a square wave shape may be performed in addition to control to shift the phase of the voltage waveform V1, as in the phase control mode M2A described above. Alternatively, in the phase control mode M2A, control to change the voltage waveform V1 into a square wave shape may be performed in addition to control to shift the phase of the voltage waveform V1.

[0072] The present disclosure is not limited to the above-described examples and may be modified in various ways. In the above-described examples, the power converter 11 converts three-phase AC. However, the present disclosure is not limited to three-phase AC, and may also convert two-phase AC or single-phase AC. In the above-described examples, the power conversion system 1 includes the power converter 11 and the power converter 12. However, if the power grid requires DC power, the power converter 12 may be omitted. In addition, in the above-described examples, the electric machine 2 is a generator. However, the power conversion system 1 of the present disclosure can also be applied to cases where the electric machine 2 is a motor. For example, when the motor suddenly stops, the motor rotates due to inertia, generating electrical energy in the same way as a generator. In this case, the motor can be considered a generator, and therefore the same description as in the above-described embodiment can be applied. [Explanation of symbols]

[0073] 1 Power Conversion System 2 Electric machines 11 Power Converter 13 Controller 21 rotor 31a Information acquisition section 31b Abnormality detection unit 31c Frequency Control Section 32 Mode switching section 211 Switching element 221 Coil D61, D61a, D61b, D61c Sine wave control signal (normal control signal) D62, D62a, D62b, D62c Square wave control signal (abnormal control signal) M1 Sine wave control mode (normal control mode) M2 Square wave control mode (abnormal control mode) M21 1st square wave control mode M22 Second square wave control mode V1, V1a, V1b, V1c, V2, V2a, V2b, V2c, V21, V22, V23 voltage waveforms

Claims

1. an electric machine having a rotor and a coil; a power converter having a plurality of switching elements electrically connected to the coil, the power converter converting a mode of power input / output to the coil by switching operations of the plurality of switching elements; a controller communicatively connected to the power converter and configured to control a switching operation of each of the plurality of switching elements; The controller a mode switching unit capable of switching a control mode of a switching operation of the switching element; an abnormality detection unit that detects an abnormality in the operating state of the electric machine, the control modes include a normal control mode in which a switching operation of the switching element is controlled so that the voltage waveform of the power input to the coil becomes sinusoidal, and an abnormal control mode in which a switching operation of the switching element is controlled so that the voltage waveform differs in at least one of waveform shape and phase from the voltage waveform in the normal control mode, The mode switching unit switches the control mode from the normal control mode to the abnormality control mode when the abnormality detection unit detects an abnormality.

2. The mode switching unit In the normal control mode, a normal control signal instructing a switching operation of the switching element according to the normal control mode is output to the switching element; In the abnormal control mode, an abnormality control signal is output to the switching element to instruct a switching operation of the switching element according to the abnormal control mode; the duty ratio of the normal control signal is set to change over time; The power conversion system according to claim 1 , wherein the duty ratio of the abnormality control signal is set to a constant value.

3. The controller a frequency control unit that controls a switching frequency of the abnormality control signal; The power conversion system according to claim 2 , wherein the frequency control unit sets a switching frequency of the abnormality control signal higher than a switching frequency of the normal control signal.

4. the controller further includes an information acquisition unit that acquires at least one of a rotation speed of the rotor and a DC voltage of the power output from the power converter as an index value indicating an operating state of the electric machine; The power conversion system according to claim 3 , wherein the frequency control unit changes the switching frequency of the abnormality control signal in the abnormality control mode in accordance with a difference between the index value and a preset allowable value.

5. 5. The power conversion system according to claim 4, wherein the mode switching unit switches the control mode from the abnormality control mode to the normal control mode when, in the abnormality control mode, a switching frequency of the abnormality control signal is equal to or lower than a reference value that is a criterion for determining whether an operating state of the electric machine is abnormal.

6. the abnormality control mode includes a square wave control mode in which a switching operation of the switching element is controlled so that the voltage waveform has a square wave shape; The square wave control mode is a first square wave control mode in which the switching operation of the switching element is controlled so as to obtain the square wave-shaped voltage waveform including a first harmonic; a second square wave control mode in which a switching operation of the switching element is controlled so as to obtain the voltage waveform having a square wave shape including the first harmonic and a second harmonic that is higher in order than the first harmonic, The power conversion system according to any one of claims 1 to 5, wherein the mode switching unit is capable of switching from the first square wave control mode to the second square wave control mode in the square wave control mode.

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