Gas system and method for controlling same

Abstract

Provided are: a gas system for expanding, using a turbine, a gas compressed by a compressor, the gas system safely stopping at the time of a power failure; and a method for controlling the gas system. This gas system comprises: a compressor that generates a compressed gas, which is a gas compressed due to the rotation of a compression rotor; a first rotary electric machine that rotates the compression rotor and rotates together with the compression rotor; a first inverter that transmits and receives electric power to and from the first rotary electric machine and controls the rotational speed of the first rotary electric machine; an expansion turbine that expands the compressed gas to rotate a turbine rotor; a second rotary electric machine that rotates together with the turbine rotor; a second inverter that transmits and receives electric power to and from the second rotary electric machine and controls the rotational speed of the second rotary electric machine; and an electric power line that supplies driving electric power from the first inverter to the second inverter.

Description

Gas system and its control method

[0001] The present disclosure relates to a gas system and a control method thereof.

[0002] For example, Patent Document 1 discloses a low-temperature air generator and information related to the operation stop during a power outage.

[0003] The low-temperature air generator disclosed in Patent Document 1 includes a compressor that sucks and compresses air, a cooler that cools the compressed air, an expansion turbine that adiabatically expands the cooled compressed air to generate low-temperature air, and a braking blower directly connected to the expansion turbine.

[0004] In Patent Document 1, in a gas system that expands a gas such as air compressed by a compressor with a turbine to generate, for example, low-temperature air, when a power outage occurs, the control circuit may stop and the gas system may not be safely stopped. Specifically, when a power outage occurs in the gas system as described above, the rotational speed control of the turbine may stop (the brake may not work), and the rotational speed of the turbine may rise above the rated value. That is, even if the power outage occurs and the compressor stops operating, the pressure of the gas in the piping compressed by the compressor does not immediately decrease and continues to be supplied to the turbine at a high pressure. However, since the braking device of the turbine also stops operating due to the power outage, the turbine cannot be braked and may rise to a rotational speed exceeding the rated value. When the rotational speed exceeds the rated value in this way, the turbine may be destroyed.

[0005] Therefore, in the low-temperature air generator disclosed in Patent Document 1, a path for introducing the atmosphere to the suction side of the braking blower is provided, and a path for merging the discharge side of the braking blower into the path from the compressor to the cooler is provided. In this low-temperature air generator, since the atmosphere is always introduced to the suction side of the braking blower, the braking action on the expansion turbine is not lost even when the compressor suddenly stops, and the expansion turbine does not undergo dangerous high-speed rotation.

[0006] Patent Document 2 discloses a turbine expander comprising an adiabatic expansion device with a turbine impeller built in, and an induction motor generator connected coaxially to the turbine impeller and used to brake it.

[0007] Patent Document 3 discloses an expansion turbine equipped with a mechanism for braking using eddy currents. Patent Document 3 points out that, as a problem with the braking method of the expansion turbine, the blower braking method may reduce the turbine efficiency, and the power generation braking method is complex and expensive due to the braking resistance when recovering and releasing power with an inverter, as well as the equipment and control for power regeneration. In addition, it is pointed out that with the power generation control method, braking force cannot be exerted unless the motor rotation conditions are met.

[0008] Japanese Patent Publication No. Hei 6-180156, Japanese Patent Publication No. 2001-132410, Japanese Patent Publication No. 2008-255787

[0009] As mentioned above, in conventional gas systems where compressed gas is expanded by a turbine, the challenges have been improving turbine efficiency, avoiding complexity of equipment and control, and improving the reliability of control (braking). Therefore, there is a need for a system that avoids a decrease in turbine efficiency, avoids complexity of equipment and control, and can reliably brake according to the situation. In particular, from the perspective of equipment maintenance during power outages, there is a need for a system and control method that can more safely shut down a gas system where compressed gas is expanded by a turbine during a power outage.

[0010] This disclosure has been made in view of the above circumstances, and its purpose is to provide a gas system in which a gas compressed by a compressor is expanded by a turbine, and which can be safely shut down in the event of a power outage, and a control method thereof.

[0011] A gas system according to the present disclosure for achieving the above objectives comprises: a compressor that produces compressed gas, which is a gas compressed by the rotation of a compression rotor; a first rotating electric machine that rotates the compression rotor and rotates together with the compression rotor; a first inverter that transmits and receives power to and from the first rotating electric machine and controls the rotational speed of the first rotating electric machine; an expansion turbine that expands the compressed gas and rotates a turbine rotor; a second rotating electric machine that rotates together with the turbine rotor; a second inverter that transmits and receives power to and from the second rotating electric machine and controls the rotational speed of the second rotating electric machine; and a power line that supplies power from the first inverter to the second inverter.

[0012] In the gas system according to this disclosure, the power line can supply power from the first inverter to the second inverter for driving the second inverter during a power outage.

[0013] The gas system according to this disclosure may further include a voltage detection unit that detects a voltage drop of at least one of the following: the power supply voltage supplied to the first inverter, the internal voltage of the first inverter, and the internal voltage of the second inverter.

[0014] In the gas system according to this disclosure, the second inverter can apply the brakes to the second rotating electric machine when the voltage detection unit detects a voltage drop.

[0015] In the gas system according to this disclosure, the power line can supply the regenerative current as power for driving the second inverter.

[0016] In the gas system according to this disclosure, the first rotating electric machine is a permanent magnet type rotating electric machine, and the first inverter can supply the regenerative current generated when the first rotating electric machine is rotating by inertia to the second inverter.

[0017] In the gas system relating to this disclosure, the first rotating electric machine may be a permanent magnet type rotating electric machine.

[0018] In the gas system according to this disclosure, the first inverter includes a first smoothing circuit for smoothing the supplied power, and a first inverter circuit that converts the DC current smoothed by the first smoothing circuit into AC current and supplies it to the first rotating electric machine, and rectifies the regenerative current and returns it to the first smoothing circuit; the second inverter includes a second smoothing circuit for smoothing the supplied power, and a second inverter circuit that converts the DC current smoothed by the second smoothing circuit into AC current and supplies it to the second rotating electric machine; and the power line can supply power from the first smoothing circuit to the second smoothing circuit.

[0019] A control method for a gas system according to the present disclosure for achieving the above objective is a control method for a gas system as described above, wherein when a voltage drop occurs in at least one of the power supply voltage supplied to the first inverter, the internal voltage of the first inverter, and the internal voltage of the second inverter, a regenerative brake is applied to the first rotating electric machine to generate a regenerative current, the regenerative current is supplied to the second inverter to maintain the operation of the second inverter, and the second inverter applies a brake to the second rotating electric machine.

[0020] A control method for a gas system according to the present disclosure for achieving the above objective is a control method for a gas system in which the first rotating electric machine is a permanent magnet type rotating electric machine as described above, wherein when a voltage drop occurs in at least one of the power supply voltage supplied to the first inverter, the internal voltage of the first inverter, and the internal voltage of the second inverter, the first inverter supplies a regenerative current generated while the first rotating electric machine is rotating by inertia to the second inverter, thereby maintaining the operation of the second inverter, and the second inverter applies the brakes to the second rotating electric machine.

[0021] A control method for a gas system according to the present disclosure to achieve the above objective is a control method for a gas system comprising: a compressor that produces compressed gas, which is a gas compressed by the rotation of a compression rotor; a first rotating electric machine that rotates the compression rotor and rotates together with the compression rotor; a first inverter that transmits and receives power to and from the first rotating electric machine and controls the rotational speed of the first rotating electric machine; an expansion turbine that expands the compressed gas and rotates a turbine rotor; a second rotating electric machine that rotates together with the turbine rotor; a second inverter that transmits and receives power to and from the second rotating electric machine and controls the rotational speed of the second rotating electric machine; and a power line that supplies power for driving from the first inverter to the second inverter, wherein when a voltage drop occurs in at least one of the power supply voltage supplied to the first inverter, the internal voltage of the first inverter, and the internal voltage of the second inverter, a regenerative brake is applied to the first rotating electric machine to generate a regenerative current, the regenerative current is supplied to the second inverter to maintain the operation of the second inverter, and the second inverter applies a brake to the second rotating electric machine.

[0022] A control method for a gas system according to the present disclosure to achieve the above objective is a control method for a gas system comprising: a compressor that produces compressed gas, which is a gas compressed by the rotation of a compression rotor; a first rotating electric machine that rotates the compression rotor and rotates together with the compression rotor; a first inverter that transmits and receives power to the first rotating electric machine and controls the rotational speed of the first rotating electric machine; an expansion turbine that expands the compressed gas and rotates a turbine rotor; a second rotating electric machine that rotates together with the turbine rotor; a second inverter that transmits and receives power to the second rotating electric machine and controls the rotational speed of the second rotating electric machine; and a power line that supplies power for driving from the first inverter to the second inverter, wherein the first rotating electric machine is a permanent magnet type rotating electric machine, and when a voltage drop occurs in at least one of the power supply voltage supplied to the first inverter, the internal voltage of the first inverter, and the internal voltage of the second inverter, the first inverter supplies a regenerative current generated while the first rotating electric machine is rotating by inertia to the second inverter, thereby maintaining the operation of the second inverter, and the second inverter applies the brakes to the second rotating electric machine.

[0023] According to this disclosure, it is possible to provide a gas system in which a gas compressed by a compressor is expanded by a turbine, and which can be safely shut down in the event of a power outage, as well as a control method thereof.

[0024] This is an explanatory diagram of the configuration of the gas system according to this embodiment. This is an explanatory diagram of the electrical circuit of the gas system according to this embodiment. This is a graph illustrating the control method of the gas system according to this embodiment.

[0025] A gas system and a control method thereof according to the embodiments of this disclosure will be described with reference to the drawings.

[0026] Figure 1 shows an explanatory diagram illustrating the configuration of the gas system 100 according to this embodiment.

[0027] The gas system 100 includes a compressor 1 that produces compressed gas, which is gas compressed by the rotation of a compression rotor 10; a first rotating electric machine 11 that rotates the compression rotor 10 and rotates together with the compression rotor; a first inverter 3 that transmits and receives power to and from the first rotating electric machine 11 and controls the rotational speed of the first rotating electric machine 11; an expansion turbine 2 that expands the compressed gas and rotates a turbine rotor 20; a second rotating electric machine 21 that rotates together with the turbine rotor 20; a second inverter 4 that transmits and receives power to and from the second rotating electric machine 21 and controls the rotational speed of the second rotating electric machine 21; and a power line 93 that supplies power for driving from the first inverter 3 to the second inverter 4.

[0028] The control method for the gas system according to this embodiment is realized by the gas system 100 described above. Specifically, in the control method for the gas system according to this embodiment, when a voltage drop occurs in at least one of the power supply voltage supplied to the first inverter 3, the internal voltage of the first inverter 3, and the internal voltage of the second inverter 4, regenerative braking is applied to the first rotating electric machine 11 to generate a regenerative current, and this regenerative current is supplied to the second inverter 4, thereby maintaining the operation of the second inverter 4, and the second inverter 4 applies the brakes to the second rotating electric machine 21.

[0029] The gas system 100 and the control method for the gas system realized thereby can achieve safe shutdown in the event of a power outage.

[0030] The gas system 100 and the control method for the gas system realized thereby will be described in detail below.

[0031] As shown in Figure 1, the gas system 100 includes a compressor 1 having a compression rotor 10 and a first rotating electric machine 11, an expansion turbine 2 having a turbine rotor 20 and a second rotating electric machine 21, a first inverter 3, a second inverter 4, a voltage detection unit 7 that detects a voltage drop of at least one of the power supply voltage supplied to the first inverter 3, the internal voltage of the first inverter 3, and the internal voltage of the second inverter 4, and a power line 93 that supplies power from the first inverter 3 to the second inverter 4.

[0032] The gas system 100 is supplied with power for operation from a power source 9, such as a factory connected to a commercial power source (external power source). In this embodiment, the gas system 100 is electrically connected to the power source 9 and the first inverter 3 via a power line 90, and power is supplied from the power source 9 to the first inverter 3.

[0033] The gas system 100 can be used, for example, as part of a heat pump mechanism in a low-temperature air generator or refrigerator (hereinafter referred to as a cooling system) that produces cooled gas. The general outline of the case in which the gas system 100 is used as part of the heat pump mechanism of a cooling system is as follows. In this case, the gas system 100 is compressed in the compressor 1 and supplied to the expansion turbine 2 as compressed gas (see gas G1 in Figure 1). The compressed gas is cooled, for example, in the heat exchanger 81 and then further adiabatically expanded. The expansion turbine 2 extracts the kinetic energy of the compressed gas during adiabatically expanding gas (compressed gas) as the energy of the rotational motion of the turbine rotor 20, and promotes the cooling of the gas after adiabatically expanding gas. The gas after adiabatically expanding gas (see gas G2 in Figure 1) that has passed through the expansion turbine 2 exchanges heat with another gas to be cooled, for example (see gas G3 in Figure 1), in the heat exchanger 82 and returns to the compressor 1.

[0034] The following describes each part of the gas system 100.

[0035] As described above, the compressor 1 is a device that compresses a gas (refrigerant) supplied as a heat transfer medium and delivers compressed gas. The type of gas is not limited as long as it functions as a heat transfer medium. The compressor 1 includes a compression rotor 10 that compresses the gas by rotational force, and a first rotating electric machine 11 that generates the rotational force to drive the compression rotor 10. The compressor 1 may be, for example, a turbo compressor having an impeller-type compression rotor 10. The first rotating electric machine 11 is electrically connected to the first inverter 3 via a power line 91 and is driven or braked (brakes applied) by the first inverter 3.

[0036] In this embodiment, a rotating electric machine refers to an electric machine such as a motor or generator that comprises a stator having stator windings and a rotor that is rotatably mounted on the stator around a predetermined axis of rotation.

[0037] Furthermore, in this embodiment, when an inverter drives a rotating electric machine, it means that the inverter supplies power to the rotating electric machine and rotates the rotor, and when an inverter brakes a rotating electric machine, it means that the inverter applies some kind of brake to the rotor of the rotating electric machine to rotate the rotor at a constant speed or to decelerate it.

[0038] The first rotating electric machine 11 is a so-called rotating electric machine. The first rotating electric machine 11 may be, for example, an induction motor, a permanent magnet motor (PM motor, an example of a permanent magnet type rotating electric machine), or a mechanical structure part having these functions. A permanent magnet type rotating electric machine includes a rotating electric machine that uses permanent magnets in its rotor. A permanent magnet motor also includes a motor that uses permanent magnets in its rotor.

[0039] The first rotating electric machine 11 is connected to the compression rotor 10 so as to rotate together with it (for example, as a single unit). When the first rotating electric machine 11 is driven by the first inverter 3 and rotates, the compression rotor 10 rotates in conjunction with this rotation. When the first rotating electric machine 11 is braked by the first inverter 3, which will be described later, while the compression rotor 10 is rotating, the compression rotor 10 is braked by the first rotating electric machine 11 and stops rotating.

[0040] The compression rotor 10 and the first rotating electric machine 11 may be a combination of separate devices, or they may be integrated as a single compressor 1 (configured as a single mechanical device). For example, in the compressor 1, the main shaft of the compression rotor 10 and the main shaft of the first rotating electric machine 11 may be separate and mechanically connected via a power transmission mechanism such as gears or chains to enable mutual transmission of rotational power between these main shafts. Alternatively, in the compressor 1, the main shaft of the compression rotor 10 and the main shaft of the first rotating electric machine 11 may be common, and the rotor of the first rotating electric machine 11 may be configured to rotate integrally with the compression rotor 10.

[0041] The first inverter 3 is a power supply circuit or power supply device that converts the power supplied from the power supply 9 (for example, three-phase alternating current) into alternating current (for example, three-phase alternating current) power adjusted to a desired frequency and voltage, and supplies it to the first rotating electric machine 11, and also supplies power based on the regenerative current (regenerative power) of the first rotating electric machine 11 to the inverter 4, which will be described later.

[0042] The first inverter 3 adjusts the frequency and voltage of the current supplied to the first rotating electric machine 11 to drive the first rotating electric machine 11 at a desired rotational speed, and also adjusts the frequency and voltage of the current supplied to the first rotating electric machine 11 to regeneratively brake the first rotating electric machine 11 (applying regenerative braking) to control the rotational speed of the first rotating electric machine 11 and the rotational speed of the compression rotor 10.

[0043] The first inverter 3, as shown in Figure 2 for example, includes a rectifier circuit 31 that rectifies the supplied power into a DC current and outputs it, a smoothing circuit 32 (an example of a first smoothing circuit) including a capacitor or the like (in this embodiment, a capacitor) to smooth the DC current output from the rectifier circuit 31, and an inverter circuit 33 (an example of a first inverter circuit) that converts the DC current smoothed by the smoothing circuit 32 into an AC current of a desired frequency and voltage and supplies it to the first rotating electric machine 11. The inverter circuit 33 may perform PWM (Pulse Width Modulation) control and may include a switching device and a freewheeling diode in its circuit. The first inverter 3 may further have a control circuit that controls the operation of internal circuits such as the inverter circuit 33. A power-storable smoothing circuit 32 can be selected.

[0044] When the first inverter 3 is supplied with regenerative current from the first rotating electric machine 11, the inverter circuit 33 can rectify this current and return (output) it to the smoothing circuit 32. The smoothing circuit 32 is connected to the power line 93, and can send power (direct current in this embodiment) based on this regenerative current (the regenerative current generated by the regenerative brake applied by the first inverter 3 to the first rotating electric machine 11) to the power line 93. Note that the first inverter 3 may be configured to be driven (operated) by the regenerative current supplied from the first rotating electric machine 11 or the power stored in the smoothing circuit 32.

[0045] The first inverter 3 may further include a brake unit such as a resistor that thermally consumes part or all of the regenerative current generated when the first rotating electric machine 11 is regeneratively braked. This may prevent regenerative failure in some cases.

[0046] As described above, the expansion turbine 2 is a device that expands the compressed gas sent out from the compressor 1, extracts energy, and promotes cooling of the gas after adiabatic expansion. The expansion turbine 2 has a turbine rotor 20 that rotates by the airflow when the compressed gas expands, and a second rotating electric machine 21 that rotates with the turbine rotor 20 and regulates (brakes) the rotation of the turbine rotor 20. The second rotating electric machine 21 is connected to the second inverter 4 via the power line 92 and is braked (braked upon) by the second inverter 4.

[0047] The second rotating electric machine 21 may be a so-called rotating electric machine, for example, an induction motor, a permanent magnet motor, or a generator. The second rotating electric machine 21 is connected so as to rotate with the turbine rotor 20. When the turbine rotor 20 is driven and rotated by the airflow due to the expansion of the compressed gas, the second rotating electric machine 21 rotates along with this rotation. When the second rotating electric machine 21 is rotating and is braked by the second inverter 4, the turbine rotor 20 is braked by the second rotating electric machine 21. In this embodiment, the second inverter 4 brakes (controls the rotational speed) the rotation of the second rotating electric machine 21 so that the turbine rotor 20 does not rotate at a rotational speed exceeding the rated value.

[0048] Note that the turbine rotor 20 and the second rotating electric machine 21 may be a combination of separate devices, or may be integrally configured (configured as one mechanical device) as the expansion turbine 2. For example, in the expansion turbine 2, the main shaft of the turbine rotor 20 and the main shaft of the second rotating electric machine 21 are separate, and they may be mechanically connected via a power transmission mechanism such as a gear or a chain so that the rotational power can be mutually transmitted between these main shafts. Also, in the expansion turbine 2, the main shaft of the turbine rotor 20 and the main shaft of the second rotating electric machine 21 may be common, and the rotor of the second rotating electric machine 21 may be configured to rotate integrally with the turbine rotor 20.

[0049] The second inverter 4 is a power supply circuit or a power supply device that adjusts the frequency and voltage of the current supplied to the second rotating electric machine 21 to maintain (control) the rotational speed of the second rotating electric machine 21 at a desired rotational speed. The second inverter 4 is driven (operates) by the power supplied from the first inverter 3.

[0050] In the present embodiment, the second inverter 4 is electrically connected to the first inverter 3 via the power line 93 and is supplied with the driving (operating) power from the first inverter 3 (the power for operating the second inverter 4). Note that the driving power supplied to the second inverter 4 by the power line 93 is the power for the second inverter 4 to perform various operations (the driving power of the second inverter 4). The driving power of the second inverter 4 includes the meaning of the power for the second inverter 4 itself to operate and the meaning of the power used for the braking performed by the second inverter 4 (the braking of the second rotating electric machine 21 described later). The power supplied from the first inverter 3 to the second inverter 4 is the power based on the power supplied from the power source 9 or the power based on the regenerative current supplied from the first rotating electric machine 11.

[0051] The second inverter 4 brakes the second rotating electric machine 21, which rotates together with the turbine rotor 20, at least (for example, by regenerative braking or DC braking), thereby controlling the rotational speed of the second rotating electric machine 21 and the rotational speed of the turbine rotor 20, for example, by braking so that they do not exceed a predetermined rotational speed (for example, the rated rotational speed). When braking the second rotating electric machine 21, the second inverter 4 preferably uses regenerative braking to improve power efficiency.

[0052] As shown in Figure 2, the second inverter 4 includes a smoothing circuit 42 (an example of a second smoothing circuit) which includes a capacitor or the like (in this embodiment, a capacitor) for smoothing the DC current supplied from the first inverter 3, and an inverter circuit 43 (an example of a second inverter circuit) which converts the DC current smoothed by the smoothing circuit 42 into an AC current (in this embodiment, three-phase AC) of a desired frequency and voltage and supplies it to the second rotating electric machine 21. The inverter circuit 43 may perform PWM (Pulse Width Modulation) control and may include a switching device and a freewheeling diode in its circuit. The second inverter 4 may further have a control circuit that controls the operation of internal circuits such as the inverter circuit 43. A device capable of storing energy can be selected as the smoothing circuit 42.

[0053] When the second inverter 4 receives regenerative current from the second rotating electric machine 21, it can rectify this current in the inverter circuit 43 and return it to the smoothing circuit 42 (output it). The second inverter 4 may be configured to be driven (operated) by the power stored in the smoothing circuit 42 or by the regenerative current supplied from the second rotating electric machine 21.

[0054] The second inverter 4 may further include a brake unit such as a resistor that dissipates some or all of the regenerative current generated when the second rotating electric machine 21 is regeneratively braked as heat. This may prevent regenerative braking failure.

[0055] The compressor 1 and the expansion turbine 2 are connected by a circulation path 80, which is a pipe that circulates gases (gases G1 and G2) between them. The circulation path 80 may include an upward pipe 80a through which gas (gas G1) flows from the compressor 1 to the expansion turbine 2, and a downward pipe 80b through which gas (gas G2) flows from the expansion turbine 2 to the compressor 1. The compressed gas compressed by the compressor 1 flows through the upward pipe 80a and is supplied to the expansion turbine 2 via the heat exchanger 81. The gas expanded by the expansion turbine 2 flows through the downward pipe 80b, passes through the heat exchanger 82 and the heat exchanger 81 in that order, and returns from the expansion turbine 2 to the compressor 1.

[0056] The voltage detection unit 7 is a voltage detection device or sensor that detects a voltage drop in at least one of the following: the power supply voltage supplied to the first inverter 3, the internal voltage of the first inverter 3, and the internal voltage of the second inverter 4. Hereinafter, the power supply voltage supplied to the first inverter 3, the internal voltage of the first inverter 3, and the internal voltage of the second inverter 4 may be collectively referred to as the voltage to be detected.

[0057] The voltage detection unit 7 may, for example, include at least one of the following: a voltage sensor 70 for detecting the voltage of the power line 90, a voltage sensor 71 for detecting the internal voltage of the first inverter 3 (for example, the voltage smoothed by the smoothing circuit 32), and a voltage sensor 72 for detecting the internal voltage of the second inverter 4 (for example, the voltage smoothed by the smoothing circuit 42).

[0058] The voltage detection unit 7 may be a detection device or sensor provided separately from the first inverter 3 and the second inverter 4, or it may be a detection device or sensor incorporated into the first inverter 3 and the second inverter 4. For example, voltage sensor 70 and voltage sensor 71 may be detection devices or sensors provided by the first inverter 3. Voltage sensor 71 may be a detection device or sensor provided by the second inverter 4.

[0059] In the gas system 100, when the voltage detection unit 7 detects that the voltage to be detected has fallen below a predetermined voltage (i.e., a threshold voltage, hereinafter sometimes referred to as the detection voltage), it can be assumed that the power supply from the power source 9 has been cut off (i.e., a power outage has occurred) or that there is a possibility that the power supply from the power source 9 will be cut off (i.e., a power outage will occur), and the gas system 100 can be safely shut down.

[0060] In other words, in the gas system 100, if a voltage drop occurs in at least one of the following: the power supply voltage supplied to the first inverter 3, the internal voltage of the first inverter 3, and the internal voltage of the second inverter 4, the first inverter 3 applies regenerative braking to the first rotating electric machine 11 to generate a regenerative current, and the first inverter 3 supplies this regenerative current to the second inverter 4 via the power line 93. The gas system 100 thereby maintains the operation of the second inverter 4, that is, the braking control (brake) of the second rotating electric machine 21, or brakes the second rotating electric machine 21 more strongly, maintaining the rotational speed of the turbine rotor 20, or decelerating the rotation of the turbine rotor 20. In other words, the second inverter 4 continues to apply braking to the second rotating electric machine 21, or increases the braking strength, even when the voltage detection unit 7 detects a voltage drop. As a result, even in the event of a power outage, the braking control of the turbine rotor 20, which rotates using the energy of the compressed gas remaining in the upstream piping 80a, is maintained, preventing the turbine rotor 20 from rotating at a rotational speed exceeding its rated speed, and allowing the gas system 100 to be safely stopped.

[0061] In the following explanation, the detection by the voltage detection unit 7 when the target voltage drops below the detection voltage will be referred to as power outage detection by the voltage detection unit 7.

[0062] As described above, the voltage detection unit 7 detects a power outage by detecting that the target voltage has dropped below the detection voltage. The detection voltage may be set to a separate value for each of the following: the power supply voltage supplied to the first inverter 3, the internal voltage of the first inverter 3, and the internal voltage of the second inverter 4.

[0063] The voltage detection unit 7's power outage detection may be performed based on at least one of the power supply voltage supplied to the first inverter 3, the internal voltage of the first inverter 3, and the internal voltage of the second inverter 4. The voltage detection unit 7 may perform power outage detection based on two or more voltages, or it may perform power outage detection based on any one of the voltages.

[0064] For example, the voltage detection unit 7 may perform power outage detection based only on the power supply voltage supplied to the first inverter 3. In other words, the voltage detection unit 7 may perform power outage detection based only on a detection voltage defined for the power supply voltage supplied to the first inverter 3. This prevents the first inverter 3 and the second inverter 4 from shutting down due to power loss, and ensures reliable execution of the gas system 100 shutdown control.

[0065] Furthermore, if the voltage detection unit 7 performs power outage detection based solely on a detection voltage defined for the power supply voltage supplied to the first inverter 3, the voltage detection unit 7 only needs to have at least a voltage sensor 70, and it is not essential for the voltage detection unit 7 to have voltage sensors 71 and 72.

[0066] When setting a detection voltage for the first inverter 3 or the second inverter 4, these detection voltages are set to a value equal to or greater than the internal voltage at which the first inverter 3 or the second inverter 4 stops operating (hereinafter sometimes referred to as the inverter stop voltage). This prevents the first inverter 3 and the second inverter 4 from ceasing to function due to power loss, and ensures reliable execution of the stop control of the gas system 100. The concept of inverter stop voltage includes cases where the first inverter 3 or the second inverter 4 becomes unable to operate due to a voltage drop (cases where they become inoperable due to power loss), and cases where the first inverter 3 or the second inverter 4 is set to an internal voltage at which it stops its own operation. The internal voltages of the first inverter 3 and the second inverter 4 can be the voltages (terminal voltages) of the smoothing circuit 32 and the smoothing circuit 42, respectively.

[0067] Furthermore, when controlling the stopping of the gas system 100 based on the power outage detection by the voltage detection unit 7, the first inverter 3 applies regenerative braking to the first rotating electric machine 11 as described above. However, in this case, the operation of the first inverter 3 differs in the following respects depending on whether the first rotating electric machine 11 is an induction motor type or a permanent magnet type rotating electric machine such as a permanent magnet motor.

[0068] When controlling the stopping of the gas system 100, if the first rotating electric machine 11 is an induction-motorized rotating electric machine, the first inverter 3 needs to continuously supply a rotating magnetic field current to the induction motor coil of the first rotating electric machine 11 in order to perform regenerative braking of the first rotating electric machine 11.

[0069] In contrast, if the first rotating electric machine 11 is a permanent magnet type rotating electric machine such as a permanent magnet motor, when the first inverter 3 regenerates braking the first rotating electric machine 11, it does not require control to continuously supply a rotating magnetic field current, as is required when regenerating braking an induction motor type rotating electric machine.

[0070] Therefore, it is preferable to use a permanent magnet type rotating electric machine, such as a permanent magnet motor, as the first rotating electric machine 11, as this avoids situations where, for example, the internal voltage of the first inverter 3 unintentionally falls below the inverter stop voltage, making it impossible to brake the first rotating electric machine 11, and thus enabling more reliable stopping control of the gas system 100.

[0071] To elaborate, if the first rotating electric machine 11 is a permanent magnet type rotating electric machine such as a permanent magnet motor, and a power outage occurs, the first inverter 3 and the first rotating electric machine 11 will operate as follows.

[0072] In other words, if a power outage occurs and the first inverter 3 stops driving the first rotating electric machine 11 as a result, the first rotating electric machine 11 and the compression rotor 10 will continue to rotate due to inertia. The stopping of the first rotating electric machine 11 by the first inverter 3 may be based on the detection of a power outage by the voltage detection unit 7 (for example, the voltage sensor 71), or it may occur when the first inverter 3 becomes inoperable due to a power loss.

[0073] When the first inverter 3 stops driving the first rotating electric machine 11, since the first rotating electric machine 11 is a permanent magnet motor, if the first rotating electric machine 11 and the compression rotor 10 continue to rotate due to inertia, the first rotating electric machine 11 will naturally switch to a power generation state and begin to send regenerative current to the first inverter 3. Furthermore, the first inverter 3 is configured so that the electrical connection between the inverter circuit 33 of the first inverter 3 and the first rotating electric machine 11 is not interrupted even if a power outage occurs. If the first rotating electric machine 11 is rotating while the first inverter 3 has stopped driving it, the first inverter 3 will naturally apply regenerative braking to the first rotating electric machine 11.

[0074] Therefore, in the event of a power outage, since the first rotating electric machine 11 is a permanent magnet motor, the first inverter 3 can automatically switch to a state where it supplies power based on the regenerative current sent from the first rotating electric machine 11 to the second inverter 4. In this way, the second inverter 4 can maintain operation with the power supplied from the first inverter 3, and the second inverter 4 can apply the brakes to the second rotating electric machine 21 to stop the rotation of the turbine rotor 20. If the first rotating electric machine 11 is a permanent magnet type rotating electric machine such as a permanent magnet motor, in this way the gas system 100 can be safely stopped in the event of a power outage.

[0075] Furthermore, if the first rotating electric machine 11 is an induction-powered rotating electric machine rather than a permanent magnet-type rotating electric machine such as a permanent magnet motor, the first inverter 3 should be set to start regenerative braking of the first rotating electric machine 11 (start applying regenerative braking) before the first inverter 3 stops due to a voltage drop (when the internal voltage of the first inverter 3 drops to the inverter stop voltage). In other words, when setting a detection voltage for the first inverter 3, the value of that voltage should be set to a value that exceeds the inverter stop voltage. In this way, if the first rotating electric machine 11 is an induction-powered rotating electric machine, the safe stopping of the gas system 100 during a power outage can be achieved.

[0076] Furthermore, even if the first rotating electric machine 11 is a permanent magnet type rotating electric machine such as a permanent magnet motor, it is preferable that the first inverter 3 is set to start regenerative braking of the first rotating electric machine 11 (start applying regenerative brakes) before the second inverter 4 stops due to a voltage drop. In other words, it is preferable that the detection voltage of the first inverter 3 is set to a voltage higher than the inverter stop voltage of the first inverter 3. This ensures that the gas system 100 can be safely stopped in the event of a power outage.

[0077] Whether the first rotating electric machine 11 is a permanent magnet type rotating electric machine such as a permanent magnet motor, or an induction motor type rotating electric machine, the relationship between the detection voltage and the inverter stop voltage should be as follows. For example, if the first inverter 3 and the second inverter 4 each have a voltage V0 set as the internal voltage setting value (threshold, inverter stop voltage) at which they stop their own operation, it is preferable to set the internal voltage threshold (V1, detection voltage) for the first inverter 3 that stops the drive of the first rotating electric machine 11 to a value higher than the internal voltage threshold (V0) at which the second inverter 4 stops due to a drop in its internal voltage (i.e., V1 > V0). This is preferable because the first inverter 3 can reliably stop the drive of the first rotating electric machine 11 before the second inverter 4 stops due to a voltage drop.

[0078] In the gas system 100, in order to ensure the safe shutdown of the gas system 100 during a power outage, the electrical circuits of the gas system 100 and the electrical connection state between the first inverter 3 and the second inverter 4 may be configured such that the internal voltage of the first inverter 3 drops before the internal voltage of the second inverter 4. This ensures that the safe shutdown of the gas system 100 during a power outage is reliably achieved. Specifically, it is preferable that the second inverter 4 is configured to regenerate braking the second rotating electric machine 21. In this case, immediately after a power outage, the gas system 100 is in a state where the first inverter 3 is supplying power to the first rotating electric machine 11, and the second inverter 4 is receiving regenerative current from the second rotating electric machine 21. Therefore, even if the first inverter 3 (smoothing circuit 32) and the second inverter 4 (smoothing circuit 42) are electrically connected by the power line 93 (equal voltage on the circuit), in actual operation, the internal voltage of the first inverter 3 drops before the internal voltage of the second inverter 4, which is preferable.

[0079] The following describes a specific example of the safe shutdown of the gas system 100 during a power outage.

[0080] Figure 3 shows an illustrative graph of the changes in the rotational speed of the compression rotor 10 of the compressor 1, the rotational speed of the turbine rotor 20 of the expansion turbine 2, the internal voltage of the first inverter 3, the internal voltage of the second inverter 4 (see Figure 1), and the power supply voltage in the gas system 100 when a power outage occurs. In this example, the first rotating electric motor 11 of the compressor 1 (see Figure 1) is a permanent magnet motor. Also in this example, the second inverter 4 is configured to regenerate braking the second rotating electric motor 21 (see Figure 1).

[0081] In the graph, the horizontal axis represents elapsed time, and the vertical axis represents rotational speed or voltage. The graph also shows the internal voltage threshold (inverter stop voltage; in this example, the set value that is set as the voltage at which the inverter stops its own operation and is detected by the voltage sensor 71) at which the first inverter 3 stops driving the first rotating electric motor 11 of the compressor 1, and the internal voltage threshold (Vs) at which the second inverter 4 stops braking the second rotating electric motor 21 of the expansion turbine 2. In the following explanation, Figure 1 will be referred to as appropriate when describing the configuration of the gas system 100.

[0082] As shown in Figure 3, before the power outage (the section indicated by symbol α), the internal voltage of the first inverter 3, the internal voltage of the second inverter 4, the rotational speed of the compression rotor 10, and the rotational speed of the turbine rotor 20 are constant.

[0083] When a power outage occurs (at point A), and the power supply voltage drops as a result, the internal voltages of the first inverter 3 and the second inverter 4 both decrease. At this time, since the second inverter 4 is configured to regenerate braking the second rotating electric machine 21 (see Figure 1), the rate at which the internal voltage of the second inverter 4 decreases is slower than the rate at which the internal voltage of the first inverter 3 decreases. Therefore, the internal voltage of the first inverter 3 reaches voltage Vs (drops to voltage Vs) before the internal voltage of the second inverter 4.

[0084] When the internal voltage of the first inverter 3 reaches voltage Vs (at point B, when a power outage is detected by the voltage sensor 71 acting as the voltage detection unit 7), the first inverter 3 stops driving the first rotating electric machine 11, and as a result, the first rotating electric machine 11 stops driving the compression rotor 10.

[0085] Even when the first inverter 3 stops driving the first rotating electric machine 11, the compression rotor 10 of the compressor 1 continues to rotate due to inertia. This generates a regenerative current in the first rotating electric machine 11, and this regenerative current continues to be supplied to the first inverter 3 (the section indicated by symbol β). At this time, the first rotating electric machine 11 is in a regenerative braking state (a state where regenerative braking is applied), so the rotation of the compression rotor 10 decelerates in a shorter time compared to when it is free-running. Then, the power based on the regenerative current supplied to the first inverter 3 is supplied to the second inverter 4 as power for driving the second inverter 4, so the second inverter 4 can maintain its operation, that is, the rotational speed control (at least braking) of the second rotating electric machine 21. As a result, the second rotating electric machine 21 and the turbine rotor 20 are maintained at a predetermined rotational speed (for example, rated rotational speed or set rotational speed).

[0086] Subsequently, when the compressor 1 stops, that is, when the first rotating electric machine 11 (compression rotor 10) stops rotating (at point C), the supply of regenerative current to the first inverter 3 stops. As a result, the internal voltages of the first inverter 3 and the second inverter 4 decrease (the section indicated by symbol γ).

[0087] Subsequently, when the internal voltage of the second inverter 4 reaches voltage Vs (at point D), the rotational speed control of the second rotating electric machine 21 by the second inverter 4 stops. As a result, the second rotating electric machine 21 and the turbine rotor 20 enter a free-running state and then stop rotating. Note that when the compressor 1 stops, the pressure of the compressed gas in the upstream pipe 80a has also decreased sufficiently, so the rotational speed of the turbine rotor 20 does not increase when the rotational speed control of the second rotating electric machine 21 by the second inverter 4 stops.

[0088] Thus, in the gas system 100, even after a power outage, the regenerative current (regenerative power) of the compressor 1 (first rotating electric machine 11) maintains the braking of the second rotating electric machine 21 (turbine rotor 20). Therefore, even in the event of a power outage, it is possible to prevent the turbine rotor 20 from rotating at an overspeed exceeding its rated speed and to prevent failure of the turbine rotor 20 due to overspeed.

[0089] Furthermore, in order to achieve the safe shutdown of the gas system 100 during such a power outage, it is not necessary to add any new control equipment or devices to the gas system 100, thus avoiding increased complexity of equipment and control.

[0090] As described above, a gas system that safely shuts down during a power outage and a control method thereof can be provided.

[0091] The embodiments described herein are not limited thereto and may be modified as appropriate without departing from the purpose of this disclosure.

[0092] This disclosure is applicable to gas systems and methods for controlling them.

[0093] 1: Compressor 10: Compression rotor 11: First rotating electric machine 100: Gas system 2: Expansion turbine 20: Turbine rotor 21: Second rotating electric machine 3: First inverter 31: Rectifier circuit 32: Smoothing circuit (first smoothing circuit) 33: Inverter circuit (first inverter circuit) 4: Second inverter 42: Smoothing circuit (second smoothing circuit) 43: Inverter circuit (second inverter circuit) 7: Voltage detection unit 70: Voltage sensor 71: Voltage sensor 72: Voltage sensor 80: Circulation path 80a: Upward piping 80b: Downward piping 81: Heat exchanger 82: Heat exchanger 9: Power supply 90: Power line 91: Power line 92: Power line 93: Power line G1: Gas G2: Gas G3: Gas

Claims

1. A gas system comprising: a compressor that produces compressed gas, which is a gas compressed by the rotation of a compression rotor; a first rotating electric machine that rotates the compression rotor and rotates together with the compression rotor; a first inverter that transmits and receives power to and from the first rotating electric machine and controls the rotational speed of the first rotating electric machine; an expansion turbine that expands the compressed gas and rotates a turbine rotor; a second rotating electric machine that rotates together with the turbine rotor; a second inverter that transmits and receives power to and from the second rotating electric machine and controls the rotational speed of the second rotating electric machine; and a power line that supplies power for driving from the first inverter to the second inverter.

2. The gas system according to claim 1, wherein the power line supplies power from the first inverter to the second inverter for driving the second inverter during a power outage.

3. The gas system according to claim 1 or 2, further comprising a voltage detection unit that detects a voltage drop in at least one of the following: the power supply voltage supplied to the first inverter, the internal voltage of the first inverter, and the internal voltage of the second inverter, wherein when the voltage detection unit detects the voltage drop, the first inverter applies regenerative braking to the first rotating electric machine and supplies the regenerative current generated by the regenerative braking applied to the first rotating electric machine to the second inverter.

4. The gas system according to claim 3, wherein the second inverter applies the brakes to the second rotating electric machine when the voltage detection unit detects a voltage drop.

5. The gas system according to claim 4, wherein the power line supplies the regenerative current as power for driving the second inverter.

6. The gas system according to claim 1, wherein the first rotating electric machine is a permanent magnet type rotating electric machine, and the first inverter supplies a regenerative current generated when the first rotating electric machine is rotating by inertia to the second inverter.

7. The gas system according to any one of claims 1 to 5, wherein the first rotating electric machine is a permanent magnet type rotating electric machine.

8. The gas system according to any one of claims 3 to 6, wherein the first inverter comprises a first smoothing circuit for smoothing the supplied power, and a first inverter circuit for converting the DC current smoothed by the first smoothing circuit into AC current and supplying it to the first rotating electric machine, and for rectifying the regenerative current and returning it to the first smoothing circuit, and the second inverter comprises a second smoothing circuit for smoothing the supplied power, and a second inverter circuit for converting the DC current smoothed by the second smoothing circuit into AC current and supplying it to the second rotating electric machine, and the power line supplies power from the first smoothing circuit to the second smoothing circuit.

9. A method for controlling a gas system according to claim 1, wherein when a voltage drop occurs in at least one of the power supply voltage supplied to the first inverter, the internal voltage of the first inverter, and the internal voltage of the second inverter, a regenerative brake is applied to the first rotating electric machine to generate a regenerative current, the regenerative current is supplied to the second inverter to maintain the operation of the second inverter, and the second inverter applies the brakes to the second rotating electric machine.

10. A control method for a gas system according to claim 7, wherein when a voltage drop occurs in at least one of the power supply voltage supplied to the first inverter, the internal voltage of the first inverter, and the internal voltage of the second inverter, the first inverter supplies a regenerative current generated while the first rotating electric machine is rotating by inertia to the second inverter, thereby maintaining the operation of the second inverter, and the second inverter applies the brakes to the second rotating electric machine.

11. A control method for a gas system comprising: a compressor that produces compressed gas, which is a gas compressed by the rotation of a compression rotor; a first rotating electric machine that rotates the compression rotor and rotates together with the compression rotor; a first inverter that transmits and receives power to and from the first rotating electric machine and controls the rotational speed of the first rotating electric machine; an expansion turbine that expands the compressed gas and rotates a turbine rotor; a second rotating electric machine that rotates together with the turbine rotor; a second inverter that transmits and receives power to and from the second rotating electric machine and controls the rotational speed of the second rotating electric machine; and a power line that supplies power for driving from the first inverter to the second inverter, wherein when a voltage drop occurs in at least one of the power supply voltage supplied to the first inverter, the internal voltage of the first inverter, and the internal voltage of the second inverter, a regenerative brake is applied to the first rotating electric machine to generate a regenerative current, the regenerative current is supplied to the second inverter to maintain the operation of the second inverter, and the second inverter applies the brake to the second rotating electric machine.

12. A control method for a gas system comprising: a compressor that produces compressed gas, which is a gas compressed by the rotation of a compression rotor; a first rotating electric machine that rotates the compression rotor and rotates together with the compression rotor; a first inverter that transmits and receives power to and from the first rotating electric machine and controls the rotational speed of the first rotating electric machine; an expansion turbine that expands the compressed gas and rotates a turbine rotor; a second rotating electric machine that rotates together with the turbine rotor; a second inverter that transmits and receives power to and from the second rotating electric machine and controls the rotational speed of the second rotating electric machine; and a power line that supplies power for driving from the first inverter to the second inverter, wherein the first rotating electric machine is a permanent magnet type rotating electric machine, wherein when a voltage drop occurs in at least one of the power supply voltage supplied to the first inverter, the internal voltage of the first inverter, and the internal voltage of the second inverter, the first inverter supplies a regenerative current generated while the first rotating electric machine is rotating by inertia to the second inverter, thereby maintaining the operation of the second inverter, and the second inverter applies the brakes to the second rotating electric machine.

Images