Gas system and its control method

Abstract

A gas system in which gas compressed by a compressor is expanded by a turbine, the gas system being capable of safely stopping in the event of a power outage, and a control method thereof are provided. [Solution] The gas system 100 includes a compressor 1 that produces compressed gas by rotating a compression rotor 10, a first rotating electric motor 11 that rotates the compression rotor 10 and rotates together with the compression rotor, a first inverter 3 that exchanges electric power with the first rotating electric motor 11 and controls the rotation speed of the first rotating electric motor 11, an expansion turbine 2 that expands the compressed gas to rotate a turbine rotor 20, a second rotating electric motor 21 that rotates together with the turbine rotor 20, a second inverter 4 that exchanges electric power with the second rotating electric motor 21 and controls the rotation speed of the second rotating electric machine 21, and a power line 93 that supplies driving power from the first inverter 3 to the second inverter 4.

Description

[Technical field]

[0001] The present disclosure relates to a gas system and a method for controlling the same. [Background technology]

[0002] For example, Patent Document 1 discloses a cold air generator and information regarding the shutdown of the generator in the event of a power outage.

[0003] The low-temperature air generator disclosed in Patent Document 1 includes a compressor that draws in 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 brake blower directly connected to the expansion turbine.

[0004] Patent Document 1 points out that in a gas system in which gas such as air compressed by a compressor is expanded by a turbine to generate, for example, low-temperature air, when a power outage occurs, the control circuit stops and the gas system may not be able to be stopped safely. Specifically, when a power outage occurs in such a gas system, the turbine speed control stops (the brake does not work) and the turbine speed may increase beyond the rated speed. In other words, even if a power outage occurs and the compressor stops working, 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 high pressure, but since the turbine braking device also stops working due to the power outage, the turbine cannot be braked and the speed may increase to a speed that exceeds the rated speed. If the speed reaches a speed that exceeds the rated speed in this way, the turbine may be destroyed.

[0005] Therefore, in the low-temperature air generator disclosed in Patent Document 1, a path is provided to introduce air into the suction side of the brake blower, and a path is provided to merge the discharge side of the brake blower with the path from the compressor to the cooler. In this low-temperature air generator, air is always introduced into the suction side of the brake blower, so that the braking action on the expansion turbine is not lost even when the compressor suddenly stops, and the expansion turbine does not rotate at dangerously high speeds.

[0006] Patent Document 2 discloses a turbine expander including an adiabatic expansion device incorporating a turbine impeller, and an induction motor-generator that is coaxially connected to the turbine impeller and brakes it.

[0007] Patent Document 3 discloses an expansion turbine equipped with a braking mechanism using eddy currents. Patent Document 3 points out that problems with the expansion turbine braking method include the risk of reduced turbine efficiency in the blower braking method, and that the braking method using power generation requires complex and expensive equipment and controls for braking resistance and power regeneration when recovering and releasing power with an inverter. In addition, it is pointed out that the control method using power generation cannot exert braking force unless the motor rotation conditions are met. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 6-180156 [Patent Document 2] JP 2001-132410 A [Patent Document 3] JP2008-255787A Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, in the conventional technology, problems associated with a gas system in which gas compressed by a compressor is expanded by a turbine are to improve turbine efficiency, avoid complication of equipment and control, and improve the reliability of control (braking). Therefore, it is desirable to provide a system for such a gas system that can be braked reliably according to the situation while avoiding a decrease in turbine efficiency and avoiding complication of equipment and control. In particular, from the viewpoint of equipment maintenance during a power outage, it is desirable to provide a system and a control method thereof that can be safely stopped during a power outage in a gas system in which gas compressed by a compressor is expanded by a turbine.

[0010] The present disclosure has been made in consideration of the above-mentioned circumstances, and its purpose is to provide a gas system in which gas compressed by a compressor is expanded by a turbine, which can be safely shut down in the event of a power outage, and a control method for the same. [Means for solving the problem]

[0011] In order to achieve the above object, the gas system according to the present disclosure comprises: a compressor that generates compressed gas by rotating 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 electric power to and from the first rotating electric machine and controls a rotation speed of the first rotating electric machine; an expansion turbine that expands the compressed gas to rotate a turbine rotor; a second rotating electric machine which rotates together with the turbine rotor; a second inverter that transmits and receives electric power to and from the second rotating electric machine and controls a rotation speed of the second rotating electric machine; and a power line for supplying power from the first inverter to the second inverter.

[0012] In order to achieve the above object, a method for controlling a gas system according to the present disclosure includes: A method for controlling a gas system as described above, comprising the steps of: When a voltage drop occurs in at least one of a power supply voltage supplied to the first inverter, an internal voltage of the first inverter, and an internal voltage of the second inverter, applying regenerative braking to the first rotating electric machine to generate a regenerative current; supplying the regenerative current to the second inverter, thereby maintaining operation of the second inverter; The second inverter brakes the second rotating electric machine. Effect of the Invention

[0013] According to the present disclosure, it is possible to provide a gas system in which gas compressed by a compressor is expanded by a turbine, which can be safely stopped in the event of a power outage, and a control method for the gas system. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is an explanatory diagram of a configuration of a gas system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an explanatory diagram of an electrical circuit of the gas system according to the embodiment. [Diagram 3] 5 is a graph illustrating a control method for a gas system according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A gas system and a control method thereof according to an embodiment of the present disclosure will be described with reference to the drawings.

[0016] FIG. 1 shows an explanatory diagram illustrating the configuration of a gas system 100 according to this embodiment.

[0017] The gas system 100 includes a compressor 1 that generates 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 exchanges electric power with the first rotating electric machine 11 and controls the rotation speed of the first rotating electric machine 11, an expansion turbine 2 that expands the compressed gas to rotate a turbine rotor 20, a second rotating electric machine 21 that rotates together with the turbine rotor 20, a second inverter 4 that exchanges electric power with the second rotating electric machine 21 and controls the rotation speed of the second rotating electric machine 21, and a power line 93 that supplies driving power from the first inverter 3 to the second inverter 4.

[0018] The control method for the gas system according to this embodiment is realized by the above-mentioned gas system 100. That is, in the control method for the gas system according to this embodiment, when 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 drops, regenerative braking is applied to the first rotating electric machine 11 to generate a regenerative current, and the 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.

[0019] The gas system 100 and the method of controlling the gas system implemented thereby provide a safe shutdown in the event of a power failure.

[0020] The gas system 100 and the method of controlling the gas system realized thereby will now be described in detail.

[0021] As shown in FIG. 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 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, and a power line 93 that supplies power from the first inverter 3 to the second inverter 4.

[0022] The gas system 100 is supplied with operating power 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 a first inverter 3 via a power line 90, and power is supplied from the power source 9 to the first inverter 3.

[0023] The gas system 100 can be used as a part of a heat pump mechanism such as a low-temperature air generator or a refrigerator (hereinafter referred to as a cooling system) that produces cooled gas, for example. The gas system 100 can be used as a part of a heat pump mechanism of a cooling system as follows. In the gas system 100 in this case, a gas that serves as a heat medium is compressed in a compressor 1 and supplied to an expansion turbine 2 as compressed gas (see gas G1 in FIG. 1). The compressed gas is cooled, for example, in a heat exchanger 81, and then further adiabatically expanded. The expansion turbine 2 extracts kinetic energy when the compressed gas is adiabatically expanded from the adiabatically expanding gas as the energy of the rotational motion of the turbine rotor 20, and promotes cooling of the gas after adiabatic expansion. The gas (see gas G2 in FIG. 1) that has passed through the expansion turbine 2 exchanges heat with, for example, another gas to be cooled (see gas G3 in FIG. 1) in a heat exchanger 82, and returns to the compressor 1.

[0024] Each part of the gas system 100 will now be described.

[0025] As described above, the compressor 1 is a device that compresses a gas (refrigerant) supplied as a heat medium and delivers the compressed gas. The type of gas is not limited as long as it functions as a heat medium. The compressor 1 has a compression rotor 10 that compresses the gas by a rotational force, and a first rotating electric machine 11 that generates a rotational force that drives 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 (braked) by the first inverter 3.

[0026] In this embodiment, a rotating electric machine refers to an electric machine such as a motor or generator that includes a stator having a stator winding and a rotor that is rotatable relative to the stator around a predetermined rotation axis.

[0027] In addition, in this embodiment, the inverter driving the rotating electric machine means that the inverter supplies power to the rotating electric machine to rotate the rotor, and the inverter braking the rotating electric machine 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 the rotor.

[0028] 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 or a permanent magnet motor (PM motor, an example of a permanent magnet type rotating electric machine), or a mechanical structure having the functions of these. Note that the permanent magnet type rotating electric machine includes a rotating electric machine using a permanent magnet in the rotor. Also, the permanent magnet motor includes a motor using a permanent magnet in the rotor.

[0029] The first rotating electric machine 11 is connected to rotate together with (for example, rotate integrally with) the compression rotor 10. When the first rotating electric machine 11 is driven to rotate by the first inverter 3, 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.

[0030] The compression rotor 10 and the first rotating electric machine 11 may be a combination of separate devices, or may be configured as an integrated 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 bodies, and may be mechanically connected to each other via a power transmission mechanism such as gears or a chain so that rotational power can be transmitted between these main shaft pipes. Also, 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 a common shaft, and the rotor of the first rotating electric machine 11 may be configured to rotate integrally with the compression rotor 10.

[0031] The first inverter 3 is a power supply circuit or a power supply device that converts the power supplied from the power source 9 (for example, three-phase alternating current) into electric power of an alternating current (for example, three-phase alternating current) adjusted to a desired frequency and voltage, supplies it to the first rotating electric machine 11, and also supplies the power based on the regenerative current (regenerative power) of the first rotating electric machine 11 to an inverter 4 described later.

[0032] 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 perform regenerative braking on the first rotating electric machine 11 (apply a regenerative brake), thereby controlling the rotational speed of the first rotating electric machine 11 and the rotational speed of the compression rotor 10.

[0033] As shown in FIG. 2, for example, the first inverter 3 includes a rectifier circuit 31 that rectifies the supplied power into a direct current and outputs it, a smoothing circuit 32 (an example of a first smoothing circuit) including a capacitor or a condenser (in this embodiment, a capacitor) that smooths the direct current output from the rectifier circuit 31, and an inverter circuit 33 (an example of a first inverter circuit) that converts the direct current smoothed by the smoothing circuit 32 into an alternating 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 the circuit. The first inverter 3 may further include a control circuit that controls the operation of internal circuits such as the inverter circuit 33.

[0034] When the first inverter 3 is supplied with a regenerative current from the first rotating electric machine 11, it can rectify this by the inverter circuit 33 and return it (output it) to the smoothing circuit 32. The smoothing circuit 32 is connected to the power line 93, and can send out the 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.

[0035] The first inverter 3 may further include a brake unit such as a resistor that consumes, as heat, a part or all of the regenerative current generated when regenerative braking is performed on the first rotating electric machine 11. This may prevent regeneration failure.

[0036] As described above, the expansion turbine 2 is a device that expands the compressed gas sent from the compressor 1 and also extracts energy to promote cooling of the gas after adiabatic expansion. The expansion turbine 2 has a turbine rotor 20 that rotates with the airflow generated when the compressed gas expands, and a second rotating electric machine 21 that rotates together 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 a power line 92, and is braked (braked) by the second inverter 4.

[0037] The second rotating electric machine 21 may be a so-called rotating electric machine, for example, an induction electric motor, a permanent magnet motor, or a generator. The second rotating electric machine 21 is connected to rotate together with the turbine rotor 20. When the turbine rotor 20 is driven to rotate by an airflow caused by the expansion of compressed gas, the second rotating electric machine 21 rotates in association with the rotation. When the second rotating electric machine 21 is braked by the second inverter 4 while the second rotating electric machine 21 is rotating, the turbine rotor 20 is braked by the second rotating electric machine 21. In this embodiment, the second inverter 4 brakes the rotation of the second rotating electric machine 21 (controls the rotation speed) so that the turbine rotor 20 does not rotate at a rotation speed exceeding the rated speed.

[0038] The turbine rotor 20 and the second rotating electric machine 21 may be a combination of separate devices, or may be configured as an integral part (configured as one mechanical device) of 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 may be separate bodies, and may be mechanically connected to each other via a power transmission mechanism such as gears or a chain so that rotational power can be transmitted between these main shaft pipes. 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.

[0039] 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 rotation speed of the second rotating electric machine 21 at a desired rotation speed. The second inverter 4 is driven (operated) by the power supplied from the first inverter 3.

[0040] In this embodiment, the second inverter 4 is electrically connected to the first inverter 3 via a power line 93, and is supplied with power for driving (operation) from the first inverter 3 (power for operating the second inverter 4 is supplied). The power for driving supplied to the second inverter 4 by the power line 93 refers to power for the second inverter 4 to perform various operations. The power for driving the second inverter 4 includes the meaning of power for operating the second inverter 4 itself and the meaning of power used for braking performed by the second inverter 4 (braking of the second rotating electric machine 21, which will be described later). The power supplied to the second inverter 4 by the first inverter 3 is power based on the power supplied from the power source 9 or power based on the regenerative current supplied from the first rotating electric machine 11.

[0041] The second inverter 4 at least brakes (for example, regenerative braking or DC braking) the second rotating electric machine 21 which rotates together with the turbine rotor 20, thereby controlling the rotation speed of the second rotating electric machine 21 and the rotation speed of the turbine rotor 20, for example, braking so that the rotation speed does not exceed a predetermined rotation speed (as an example, a rated rotation speed). When braking the second rotating electric machine 21, the second inverter 4 preferably regeneratively brakes the second rotating electric machine 21 in order to increase power efficiency.

[0042] 2, the second inverter 4 has a smoothing circuit 42 (an example of a second smoothing circuit) including a capacitor or the like (a capacitor in this embodiment) that smoothes the DC current supplied from the first inverter 3, and an inverter circuit 43 (an example of a second inverter circuit) that converts the DC current smoothed by the smoothing circuit 42 into an AC current (three-phase AC in this embodiment) of a desired frequency and voltage and supplies the AC current 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 free wheel 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.

[0043] When the second inverter 4 is supplied with a regenerative current from the second rotating electric machine 21, the second inverter 4 can rectify the current in the inverter circuit 43 and return (output) the current to the smoothing circuit .

[0044] The second inverter 4 may further include a brake unit such as a resistor that consumes, as heat, a part or all of the regenerative current generated when regenerative braking is performed on the second rotating electric machine 21. This may make it possible to prevent regeneration failure.

[0045] The compressor 1 and the expansion turbine 2 are connected by a circulation path 80, which is a pipe for circulating gas (gases G1, G2) between them. The circulation path 80 may include an upstream pipe 80a through which gas flows from the compressor 1 to the expansion turbine 2, and a downstream pipe 80b through which gas flows from the expansion turbine 2 to the compressor 1. The compressed gas compressed by the compressor 1 flows through the upstream pipe 80a and is supplied to the expansion turbine 2 via a heat exchanger 81. The gas expanded by the expansion turbine 2 flows through the downstream pipe 80b and passes through a heat exchanger 82 and a heat exchanger 81 in this order, and returns from the expansion turbine 2 to the compressor 1.

[0046] The voltage detection unit 7 is a voltage detection device or sensor that detects a voltage drop 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. 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 a detection target voltage.

[0047] As an example, the voltage detection unit 7 may have at least one of a voltage sensor 70 that detects the voltage of the power line 90, a voltage sensor 71 that detects the internal voltage of the first inverter 3 (e.g., the voltage smoothed by the smoothing circuit 32), and a voltage sensor 72 that detects the internal voltage of the second inverter 4 (e.g., the voltage smoothed by the smoothing circuit 42).

[0048] The voltage detection unit 7 may be a detection device or a sensor provided separately from the first inverter 3 or the second inverter 4, or may be a detection device or a sensor built into the first inverter 3 or the second inverter 4. For example, the voltage sensor 70 or the voltage sensor 71 may be a detection device or a sensor included in the first inverter 3. The voltage sensor 71 may be a detection device or a sensor included in the second inverter 4.

[0049] In the gas system 100, when the voltage detection unit 7 detects that the voltage to be detected has dropped below a predetermined voltage (i.e., a threshold voltage, hereinafter sometimes referred to as the detection voltage), it is assumed that the power supply from the power source 9 has been cut off (i.e., a power outage has occurred) or 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.

[0050] That is, in the gas system 100, when at least one of the voltage drop 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 occurs, 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. As a result, the gas system 100 maintains the operation of the second inverter 4, i.e., maintains the braking control (brake) of the second rotating electric machine 21, or brakes the second rotating electric machine 21 more strongly, and maintains the rotation speed of the turbine rotor 20, or decelerates the rotation of the turbine rotor 20. In other words, even when the voltage detection unit 7 detects a voltage drop, the second inverter 4 continues to apply the brake to the second rotating electric machine 21, or brakes it more strongly. As a result, even when a power outage occurs, the braking control of the turbine rotor 20, which rotates by the energy of the expansion of the compressed gas remaining in the upflow pipe 80a, is maintained, and the turbine rotor 20 is prevented from rotating at a rotation speed exceeding the rated speed, and the gas system 100 can be safely stopped.

[0051] In the following description, the detection by the voltage detection unit 7 that the detection target voltage has dropped below the detection voltage will be referred to as detection of a power outage by the voltage detection unit 7 or the like.

[0052] As described above, the voltage detection unit 7 detects a power outage by detecting that the detection target voltage has dropped below the detection voltage. The detection voltage may be set to an individual value for each 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.

[0053] The power outage detection by the voltage detection unit 7 needs to 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, and the power outage detection by the voltage detection unit 7 may be performed based on two or more voltages, or the power outage detection by the voltage detection unit 7 may be performed based on any one of the voltages.

[0054] For example, the voltage detection unit 7 may detect a power outage based only on the power supply voltage supplied to the first inverter 3. In other words, the voltage detection unit 7 may detect a power outage based only on a detection voltage determined for the power supply voltage supplied to the first inverter 3. This makes it possible to prevent the first inverter 3 and the second inverter 4 from stopping functioning due to a loss of power, and to reliably execute stop control of the gas system 100.

[0055] In addition, when the voltage detection unit 7 detects a power outage based only on the detection voltage defined for the power supply voltage supplied to the first inverter 3, it is sufficient for the voltage detection unit 7 to have at least the voltage sensor 70, and it is not essential for the voltage detection unit 7 to have the voltage sensors 71, 72.

[0056] When the detection voltage is determined for the first inverter 3 or the second inverter 4, the detection voltage is set to a value equal to or higher than the internal voltage (hereinafter, may be referred to as the inverter stop voltage) at which the first inverter 3 or the second inverter 4 stops operating. This makes it possible to prevent the first inverter 3 and the second inverter 4 from stopping functioning due to a loss of power supply, and to reliably execute the stop control of the gas system 100. The concept of the inverter stop voltage includes a case where the first inverter 3 or the second inverter 4 becomes unable to operate due to a voltage drop (a case where the first inverter 3 or the second inverter 4 becomes unable to operate due to a loss of power supply), and a case where the inverter stop voltage is set as a set value for the first inverter 3 or the second inverter 4 as an internal voltage at which the operation of the first inverter 3 or the second inverter 4 stops.

[0057] In addition, when the gas system 100 is stopped based on the power outage detection by the voltage detection unit 7, the first inverter 3 applies regenerative braking to the first rotating motor 11 as described above. In this case, however, the operation of the first inverter 3 differs in the following respects between when the first rotating motor 11 is an induction motor type rotating motor and when the first rotating motor 11 is a permanent magnet type rotating motor such as a permanent magnet motor.

[0058] When controlling the stoppage of the gas system 100, if the first rotating motor 11 is an induction type rotating motor, the first inverter 3 needs to continuously pass a rotating magnetic field current through the induction coil of the first rotating motor 11 to perform regenerative braking of the first rotating motor 11.

[0059] In contrast, when the first rotating motor 11 is a permanent magnet type rotating motor such as a permanent magnet motor, when the first inverter 3 performs regenerative braking on the first rotating motor 11, there is no need to perform control to continuously flow a rotating magnetic field current as in the case of performing regenerative braking on an induction motor type rotating motor.

[0060] Therefore, using a permanent magnet type rotating electric machine such as a permanent magnet motor as the first rotating electric machine 11 is preferable, as it can avoid an event in which, 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, thereby making it possible to more reliably execute stop control of the gas system 100.

[0061] More specifically, when a power outage occurs in a case where the first rotating electric machine 11 is a permanent magnet type rotating electric machine such as a permanent magnet motor, the first inverter 3 and the first rotating electric machine 11 operate as follows.

[0062] That is, when a power outage occurs and the first inverter 3 stops driving the first rotating electric machine 11 accordingly, the first rotating electric machine 11 and the compression rotor 10 continue to rotate by inertia. Note that the first inverter 3 may stop driving the first rotating electric machine 11 based on the detection of a power outage by the voltage detection unit 7 (e.g., the voltage sensor 71), or may stop the first inverter 3 from operating due to a loss of power supply.

[0063] 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, the first rotating electric machine 11 naturally switches to a power generating state and sends a regenerative current to the first inverter 3. 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 cut off even if a power outage occurs, and if the first rotating electric machine 11 is rotating in a state where the first inverter 3 has stopped driving the first rotating electric machine 11, the first inverter 3 naturally applies regenerative braking to the first rotating electric machine 11.

[0064] Therefore, in the event of a power outage, the first inverter 3 can naturally switch to a state in which it supplies power based on the regenerative current sent from the first rotating electric machine 11 to the second inverter 4. The second inverter 4 can thus maintain operation with the power supplied from the first inverter 3, and the second inverter 4 can brake the second rotating electric machine 21 to stop the rotation of the turbine rotor 20. When the first rotating electric machine 11 is a permanent magnet type rotating electric machine such as a permanent magnet motor, it is possible to thus realize a safe stop of the gas system 100 in the event of a power outage.

[0065] If the first rotating electric machine 11 is not a permanent magnet type rotating electric machine such as a permanent magnet motor but an induction motor type rotating electric machine, the first inverter 3 may be set so as to start regenerative braking of the first rotating electric machine 11 (start regenerative braking) before the first inverter 3 stops due to a voltage drop (the internal voltage of the first inverter 3 drops to the inverter stop voltage). In other words, when determining a detection voltage for the first inverter 3, the voltage value is set to a value exceeding the inverter stop voltage. If the first rotating electric machine 11 is an induction motor type rotating electric machine, the gas system 100 can be safely stopped in the event of a power outage in this manner.

[0066] Incidentally, even when 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 braking) 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 can reliably achieve a safe stop of the gas system 100 in the event of a power outage.

[0067] Regardless of 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 may be as follows: For example, when the first inverter 3 and the second inverter 4 are each set to a voltage V0 as the internal voltage setting value (threshold, inverter stop voltage) at which they stop operating, it is preferable to set the internal voltage threshold (V1, detection voltage) at which the first inverter 3 stops driving 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), since this allows the first inverter 3 to reliably stop driving the first rotating electric machine 11 before the second inverter 4 stops due to a voltage drop.

[0068] In the gas system 100, in order to realize a safe stop of the gas system 100 in the event of a power outage, the electric circuit of the gas system 100 and the electrical connection state between the first inverter 3 and the second inverter 4 may be in a connection state in which the internal voltage of the first inverter 3 drops earlier than the internal voltage of the second inverter 4. This can reliably realize a safe stop of the gas system 100 in the event of a power outage. Specifically, it is preferable that the second inverter 4 is configured to perform regenerative braking of the second rotating electric machine 21. In this case, in the gas system 100 immediately after the occurrence of a power outage, the first inverter 3 is in a state of supplying power to the first rotating electric machine 11, and the second inverter 4 is in a state of receiving a 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 in the circuit), in actual operation, the internal voltage of the first inverter 3 drops earlier than the internal voltage of the second inverter 4, which is preferable.

[0069] The following provides an example of a safe shutdown of the gas system 100 in the event of a power outage.

[0070] 3 shows an image diagram (graph) of the transition of the rotation speed of the compression rotor 10 of the compressor 1, the rotation 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 FIG. 1) and the power supply voltage in the gas system 100 when a power outage occurs. In this example, the first rotating electric machine 11 (see FIG. 1) of the compressor 1 is a permanent magnet motor. Also, in this example, the second inverter 4 is configured to regeneratively brake the second rotating electric machine 21 (see FIG. 1).

[0071] In the graph, the horizontal axis indicates elapsed time, and the vertical axis indicates rotation speed or voltage. Also, in the graph, the internal voltage threshold at which the first inverter 3 stops driving the first rotating electric machine 11 of the compressor 1 (inverter stop voltage; in this example, this is a set value set as the voltage at which its own operation is stopped, and is a value detected by the voltage sensor 71) and the internal voltage threshold at which the second inverter 4 stops braking the second rotating electric machine 21 of the expansion turbine 2 are indicated as voltage Vs. Note that in the following explanation, the explanation of the configuration of the gas system 100 will refer to FIG. 1 as appropriate.

[0072] As shown in FIG. 3, before a power outage occurs (the section indicated by the symbol α), the internal voltage of the first inverter 3, the internal voltage of the second inverter 4, the rotation speed of the compressor rotor 10, and the rotation speed of the turbine rotor 20 are constant.

[0073] When a power outage occurs (time point A) and the power supply voltage drops as a result, the internal voltages of the first inverter 3 and the second inverter 4 drop. At this time, since the second inverter 4 is configured to perform regenerative braking on the second rotating electric machine 21 (see FIG. 1), the rate at which the internal voltage of the second inverter 4 drops is slower than the rate at which the internal voltage of the first inverter 3 drops. 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 does.

[0074] 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 as the voltage detection unit 7), the first inverter 3 stops driving the first rotating motor 11, thereby stopping the driving of the compression rotor 10 by the first rotating motor 11.

[0075] Even if the driving of the first rotating electric machine 11 by the first inverter 3 is stopped, the compressor rotor 10 of the compressor 1 continues to rotate due to inertia. As a result, a regenerative current is generated in the first rotating electric machine 11, and this regenerative current continues to be supplied to the first inverter 3 (section indicated by symbol β). At this time, the first rotating electric machine 11 is in a regenerative braking state (a state in which regenerative braking is applied), so the rotation of the compressor rotor 10 decelerates in a short time compared to when the first rotating electric machine 11 is free-running. Then, power based on the regenerative current supplied to the first inverter 3 is supplied to the second inverter 4, so that the second inverter 4 can maintain its operation, that is, the control of the rotation speed of the second rotating electric machine 21 (at least the braking). As a result, the second rotating electric machine 21 and the turbine rotor 20 are maintained in a state in which they do not exceed a predetermined rotation speed (for example, a rated rotation speed or a set rotation speed).

[0076] Thereafter, when the compressor 1 stops, that is, when the first rotating electric machine 11 (compression rotor 10) stops rotating (time C), the supply of regenerative current to the first inverter 3 stops. As a result, the internal voltage of the first inverter 3 and the internal voltage of the second inverter 4 decrease (the section indicated by γ).

[0077] Thereafter, when the internal voltage of the second inverter 4 reaches the voltage Vs (time point D), the rotation speed control of the second rotating electric machine 12 by the second inverter 4 is stopped. 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 is stopped, the pressure of the compressed gas in the upstream pipe 80a is also sufficiently reduced, so that the rotation speed of the turbine rotor 20 does not increase when the rotation speed control of the second rotating electric machine 12 by the second inverter 4 is stopped.

[0078] In this way, in the gas system 100, even after a power outage, the braking of the second rotating motor 21 (turbine rotor 20) is maintained by the regenerative current (regenerative power) of the compressor 1 (first rotating motor 11), so that even in the event of a power outage, the turbine rotor 20 can be prevented from rotating at an overspeed beyond its rated speed, and breakdown of the turbine rotor 20 due to overspeed can be prevented.

[0079] Furthermore, to realize a safe shutdown of the gas system 100 in the event of such a power outage, it is not necessary to add new control equipment or devices to the gas system 100, and it is possible to avoid complicating the equipment and control.

[0080] In this manner, a gas system that safely shuts down in the event of a power outage and a control method thereof can be provided.

[0081] Note that the embodiments of the present disclosure are not limited to the above and may be modified as appropriate without departing from the scope of the present disclosure. [Industrial Applicability]

[0082] The present disclosure is applicable to gas systems and methods of controlling the same. [Explanation of symbols]

[0083] 1: Compressor 10: Compression rotor 11: Daiichi Electric Machinery 100: Gas systems 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 section 70: Voltage sensor 71: Voltage sensor 72: Voltage sensor 80: Circulation path 80a: Upstream piping 80b: Downstream 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 compressor that generates compressed gas by rotating 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 electric power to and from the first rotating electric machine and controls a rotation speed of the first rotating electric machine; an expansion turbine that expands the compressed gas to rotate a turbine rotor; a second rotating electric machine which rotates together with the turbine rotor; a second inverter that transmits and receives electric power to and from the second rotating electric machine and controls a rotation speed of the second rotating electric machine; a power line for supplying driving power from the first inverter to the second inverter; a voltage detection unit that detects a voltage drop in at least one of a power supply voltage supplied to the first inverter, an internal voltage of the first inverter, and an internal voltage of the second inverter, When the voltage detection unit detects the voltage drop, the first inverter applying regenerative braking to the first rotating electric machine; A gas system that supplies a regenerative current generated by regenerative braking applied to the first rotating electric machine to the second inverter.

2. The gas system according to claim 1 , wherein the second inverter brakes the second rotating electric machine when the voltage detection unit detects a voltage drop.

3. The gas system according to claim 2 , wherein the power line supplies the regenerative current as power for driving the second inverter.

4. A compressor that generates compressed gas, which is gas compressed by 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 electric power to and from the first rotating electric machine and controls a rotation speed of the first rotating electric machine; an expansion turbine that expands the compressed gas to rotate a turbine rotor; a second rotating electric machine which rotates together with the turbine rotor; a second inverter that transmits and receives electric power to and from the second rotating electric machine and controls a rotation speed of the second rotating electric machine; a power line for supplying driving power from the first inverter to the second inverter, the first rotating electric machine is a permanent magnet type rotating electric machine, The first inverter supplies a regenerative current generated when the first rotating electric machine rotates by inertia to the second inverter.

5. 4. The gas system according to claim 1, wherein the first rotating electric machine is a permanent magnet type rotating electric machine.

6. The first inverter is a first smoothing circuit for smoothing the supplied power; a first inverter circuit that converts the DC current smoothed by the first smoothing circuit into an AC current and supplies the AC current to the first rotating electric machine, and rectifies a regenerative current generated by regenerative braking applied to the first rotating electric machine and returns the regenerative current to the first smoothing circuit, The second inverter is a second smoothing circuit for smoothing the supplied power; a second inverter circuit that converts the DC current smoothed by the second smoothing circuit into an AC current and supplies the AC current to the second rotating electric machine, 5. The gas system of claim 1, wherein the power line supplies power from the first smoothing circuit to the second smoothing circuit.

7. A compressor that generates compressed gas, which is gas compressed by 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 electric power to and from the first rotating electric machine and controls a rotation speed of the first rotating electric machine; an expansion turbine that expands the compressed gas to rotate a turbine rotor; a second rotating electric machine which rotates together with the turbine rotor; a second inverter that transmits and receives electric power to and from the second rotating electric machine and controls a rotation speed of the second rotating electric machine; and a power line for supplying driving power from the first inverter to the second inverter, When a voltage drop occurs in at least one of a power supply voltage supplied to the first inverter, an internal voltage of the first inverter, and an internal voltage of the second inverter, applying regenerative braking to the first rotating electric machine to generate a regenerative current; supplying the regenerative current to the second inverter, thereby maintaining operation of the second inverter; A control method for a gas system in which the second inverter brakes the second rotating electric machine.

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

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