Thermoacoustic power generation system

Abstract

This invention provides a thermoacoustic power generation system that reduces the number of parameters that need to be adjusted for acoustic bonding. [Solution] A thermoacoustic power generation system comprising a thermoacoustic core that converts thermal energy into vibrational flow energy, a linear generator that converts vibrational flow energy into electrical energy, and an inverter circuit, wherein the linear generator has a movable element having a piston and a magnet that reciprocates using the vibrational flow energy, a coil section, an elastic member that applies elastic force to the piston, and a detection unit that detects the movement speed of the piston, and the inverter circuit has a plurality of switching elements connected to the coil section, and a control unit that controls the operation of the plurality of switching elements, the control unit controlling the operation of the plurality of switching elements based on the movement speed detected by the detection unit.

Description

[Technical Field]

[0001] This invention relates to a thermoacoustic power generation system. [Background technology]

[0002] Technologies for reusing waste heat from factories, automobiles, and other sources are being researched. One possible method for reusing waste heat is the use of external combustion engines. Examples of such engines include steam turbines using the Rankine cycle and Stirling engines using the Stirling cycle. These external combustion engines are configured to output power from a heat source.

[0003] Another type of external combustion engine is the thermoacoustic core, which is equipped with a heat accumulator that converts thermal energy into the energy of an oscillating fluid flow. In a thermoacoustic core, the compression and expansion of the oscillating flow act as a piston, allowing it to output oscillating flow energy from input thermal energy without any moving parts. Since the energy conversion in a thermoacoustic core is similar to that of a Stirling cycle, it has the potential to achieve high thermal efficiency. For this reason, thermoacoustic cores are attracting attention as highly efficient heat engines that have no moving parts in the energy conversion section and can reuse waste heat.

[0004] As a thermoacoustic core, for example, Non-Patent Document 1 discloses a thermoacoustic core configured as a thermoacoustic prime mover that generates and amplifies an oscillating flow from thermal energy such as waste heat, and a thermoacoustic core configured as a thermoacoustic cooler that performs refrigeration using the oscillating flow generated and amplified in the thermoacoustic prime mover, arranged in series along the flow path axis. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Jiaxin Chi, Yupeng Yang, Zhanghua Wu, Rui Yang, Ping Li, Jingyuan Xu, Limin Zhang, Jianying Hu, Ercang Luo,Numerical and experimental investigation on a novel heat-driven thermoacoustic refrigerator for room-temperature cooling, Applied Thermal Engineering, Volume 218, 2023, 119330, ISSN 1359-4311 [Overview of the project] [Problems that the invention aims to solve]

[0006] A thermoacoustic power generation system has been proposed that outputs the energy of the oscillating flow generated in a thermoacoustic core, comprising a thermoacoustic core and a linear generator that converts the energy of the oscillating flow into electrical energy. The linear generator comprises a magnet attached to a piston that reciprocates due to the oscillating flow, a coil surrounding the magnet, and an output circuit electrically connected to the coil, and is configured to extract the induced current generated in the coil from the output circuit.

[0007] In the thermoacoustic power generation system described above, in order to stably reciprocate the piston using oscillating flow, it is necessary to perform acoustic coupling to match the impedance of the acoustic system on the thermoacoustic engine side with the impedance of the mechanical and electrical systems of the linear generator. Acoustic coupling requires adjusting the mechanical and electrical parameters of the linear generator so that the impedance of the acoustic system on the thermoacoustic engine side matches the impedance of the mechanical and electrical systems of the linear generator. However, there was a challenge in that there were many parameters to consider when performing acoustic coupling.

[0008] This invention has been made in view of these circumstances, and one of its objectives is to provide a thermoacoustic power generation system that can reduce the number of parameters that need to be adjusted in order to perform acoustic bonding. [Means for solving the problem]

[0009] To solve the above problems, one aspect of the present invention includes the following aspects.

[0010] [1] A thermoacoustic power generation system comprising: a thermoacoustic core that converts thermal energy into the energy of a fluid oscillating flow; a linear generator that converts the energy of the oscillating flow into electrical energy; a waveguide that houses the thermoacoustic core, the linear generator, and the fluid; and an inverter circuit electrically connected to the linear generator, wherein the linear generator has a movable element having a piston that reciprocates in a first direction by the energy of the oscillating flow and a magnet held by the piston; a coil section surrounding the magnet; an elastic member connected to the piston and applying an elastic force to the piston in the first direction; and a detection unit that detects the moving speed of the piston in the first direction; wherein the inverter circuit has a plurality of switching elements electrically connected to the coil section and a control unit that controls the operation of the plurality of switching elements, and the control unit controls the operation of the plurality of switching elements based on the moving speed detected by the detection unit.

[0011] [2] The thermoacoustic power generation system according to [1], wherein the control unit controls the operation of a plurality of switching elements based on the moving speed, thereby arbitrarily setting the force acting on the movable element, and controls the impedance of the mechanical and electrical systems of the linear generator. [Effects of the Invention]

[0012] According to one aspect of the present invention, a thermoacoustic power generation system can be provided that can reduce the number of parameters that need to be adjusted in order to perform acoustic bonding. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic cross-sectional view showing a thermoacoustic power generation system according to an embodiment. [Figure 2] Figure 2 is a cross-sectional view showing a linear generator according to an embodiment. [Figure 3] Figure 3 is a conceptual diagram showing the pressure and velocity of the oscillating flow in the embodiment. [Figure 4] Figure 4 shows an example of the absolute value of the acoustic system impedance of the oscillating flow in the waveguide of the embodiment. [Figure 5] Figure 5 shows an example of the phase angle of the oscillating flow in the waveguide of the embodiment. [Figure 6] Figure 6 is a schematic diagram showing the equivalent circuit of the electrical system of a comparative example thermoacoustic power generation system. [Figure 7] Figure 7 is a schematic diagram showing the equivalent mechanical circuit of a comparative example thermoacoustic power generation system. [Figure 8] Figure 8 is a schematic diagram showing the equivalent circuit of the electrical system of the thermoacoustic power generation system of the embodiment. [Figure 9] Figure 9 is a schematic diagram showing the equivalent circuit of the electrical system of the thermoacoustic power generation system of the embodiment, and is a diagram illustrating the details of the control unit. [Figure 10] Figure 10 is a graph showing the analysis results of the thermoacoustic power generation system of the embodiment, and is a graph showing the relationship between the current of one phase and the back electromotive force. [Figure 11] Figure 11 is a graph showing the analysis results of the thermoacoustic power generation system of the embodiment, and is a graph showing the relationship between the velocity of the movable element and the applied force. [Figure 12] Figure 12 is a graph showing the analysis results of the thermoacoustic power generation system of the embodiment, and is a graph showing the amount of power generated by the thermoacoustic power generation system. [Modes for carrying out the invention]

[0014] In each drawing, the first direction D1 is indicated as appropriate. In this embodiment, the first direction D1 is the direction in which the piston reciprocates. The first direction D1 is also the direction in which the oscillating flow propagates within the branch pipe. In the following description, the side in which the arrow of the first direction D1 points (+D1 side) will be referred to as the "right side," and the side opposite to the side in which the arrow of the first direction D1 points (-D1 side) will be referred to as the "left side." Note that "right side" and "left side" are merely names used to describe the relative positional relationship of each part, and the actual arrangement may be different from the arrangement indicated by these names.

[0015] The central axis J, as indicated in each drawing, is the central axis of the piston. The central axis J is a virtual axis extending in the first direction D1. In the following explanation, the radial direction centered on the central axis J is simply referred to as the "radial direction," and the circumferential direction centered on the central axis J is simply referred to as the "circumferential direction." The circumferential direction is indicated by the arrow θ.

[0016] [Embodiment] Figure 1 is a schematic cross-sectional view showing the thermoacoustic power generation system 10 of this embodiment. Figure 2 is a cross-sectional view showing the linear generator 30 of this embodiment. The thermoacoustic power generation system 10 shown in Figure 1 is a thermoacoustic power generation system that generates and amplifies an oscillating flow C of a fluid F contained in a waveguide 15 using thermal energy Et supplied to a thermoacoustic core 20, converts the energy of the oscillating flow C into electrical energy in a linear generator 30, and outputs electrical energy in an inverter circuit 50. The heat source that supplies thermal energy Et to the thermoacoustic core 20 can be any heat source that can supply thermal energy Et, such as mobile bodies such as automobiles, ships, and aircraft, waste heat from factories, waste disposal plants, and water heaters, or heat collected from sunlight, and is not limited to these. The thermoacoustic power generation system 10 of this embodiment comprises a waveguide 15, a thermoacoustic core 20, a linear generator 30, an inverter circuit 50, and a fluid F.

[0017] Waveguide 15 houses a thermoacoustic core 20, a linear generator 30, and a fluid F. Waveguide 15 has an annular tube 16, branch tubes 17, and a housing 19.

[0018] The annular pipe 16 is a roughly rectangular annular conduit. A thermoacoustic core 20 is housed inside the annular pipe 16. The branch pipe 17 is a conduit that extends linearly from the annular pipe 16 to the right (+D1 side). In this embodiment, the branch pipe 17 is a roughly cylindrical conduit that extends in the first direction D1. The inside of the branch pipe 17 is connected to the inside of the annular pipe 16. A portion of the oscillating flow C circulates inside the annular pipe 16. Another portion of the oscillating flow C propagates to the right inside the branch pipe 17. The housing 19 is a box-shaped structure connected to the right end of the branch pipe 17. A linear generator 30 is housed inside the housing 19.

[0019] The fluid F is sealed inside the waveguide 15. The fluid F can be any fluid capable of transmitting an oscillating flow C, such as air, helium, and argon gases, water and ethanol liquids and vapors, or mixtures of gases, liquids, and vapors. However, the fluid F is not limited to the above materials and may be composed of other materials as long as it can transmit the oscillating flow C. In this embodiment, air is used as the fluid F, and the average pressure of the fluid F is set to 0.1 MPa. The average pressure of the fluid F may be the same as atmospheric pressure, greater than atmospheric pressure, or less than atmospheric pressure.

[0020] The thermoacoustic core 20 converts thermal energy Et, such as waste heat, into energy in the oscillating flow C of the fluid F. The thermoacoustic core 20 is housed inside the annular tube 16. The thermoacoustic core 20 is held in the annular tube 16. The thermoacoustic core 20 has a heat accumulator 21, a first heat exchanger 22, and a second heat exchanger 23.

[0021] The heat accumulator 21 converts thermal energy Et into the energy of the oscillating flow C of the fluid F. When a temperature difference occurs between one end 21a and the other end 21c of the heat accumulator 21, a thermoacoustic phenomenon occurs, which generates and amplifies the oscillating flow C. Although not shown in the figures, the heat accumulator 21 has one or more small-diameter channels. The channels extend along the direction in which the annular pipe 16 extends and open on both sides. The oscillating flow C flows inside the channels. The channels are formed, for example, by a honeycomb structure made of ceramics and a structure made of a large number of stacked stainless steel mesh sheets. Alternatively, the channels may be made of foamed metal or steel wool, or by rolling up an uneven film, or by combining thin sheets having different channel diameters and channel shapes. The channels are formed, for example, with a circular pipe shape, a parallel plate shape, a polygonal shape, or a pin array shape in cross-section.

[0022] The first heat exchanger 22 is located on one side of the heat accumulator 21. The first heat exchanger 22 is attached to one end 21a of the heat accumulator 21. The first heat exchanger 22 is the heat exchanger on the high-temperature side of the thermoacoustic core 20. The first heat exchanger 22 exchanges heat with one end 21a of the heat accumulator 21 via a heat medium that is at a higher temperature than the heat medium of the second heat exchanger 23. Thermal energy Et is supplied to the first heat exchanger 22 from the heat source. This supplies thermal energy Et to the thermoacoustic core 20.

[0023] The second heat exchanger 23 is located on the other side of the heat accumulator 21. The second heat exchanger 23 is attached to the other end 21c of the heat accumulator 21. The second heat exchanger 23 is the heat exchanger on the low-temperature side of the thermoacoustic core 20. The second heat exchanger 23 exchanges heat with the other end 21c of the heat accumulator 21 via a heat transfer medium at room temperature. The temperature of the second heat exchanger 23 is lower than the temperature of the first heat exchanger 22. In this embodiment, the second heat exchanger 23 is water-cooled with water at room temperature. This maintains the temperature of the heat transfer medium in the second heat exchanger 23 at approximately room temperature. As the heat transfer medium for the second heat exchanger 23, a medium that maintains a stable temperature, such as groundwater, seawater, river water, or factory cooling water, may be used. Alternatively, as the heat transfer medium for the second heat exchanger 23, a medium with a temperature lower than room temperature may be used, such as liquid nitrogen or natural gas, or a chiller. In this embodiment, "room temperature" refers to the temperature of the external atmosphere surrounding the thermoacoustic power generation system 10. Specifically, this includes the room temperature and the ambient temperature.

[0024] As described above, the first heat exchanger 22 circulates a heat transfer medium that is at a higher temperature than the heat transfer medium in the second heat exchanger 23. As a result, high-temperature heat is supplied to one end 21a of the accumulator 21, and the temperature of that end 21a can be maintained at a temperature higher than room temperature. Also, as described above, the second heat exchanger 23 circulates a heat transfer medium such as a gas or liquid at room temperature. As a result, the temperature of the other end 21c of the accumulator 21 can be maintained at approximately room temperature. Therefore, a temperature difference is formed between the high-temperature end 21a and the room-temperature end 21c of the accumulator 21, causing a thermoacoustic phenomenon to occur, which enables the generation and amplification of the oscillating flow C of the fluid F. In this way, the accumulator 21 converts thermal energy Et into the energy of the oscillating flow C of the fluid F. A portion of the oscillating flow C generated and amplified in the heat storage unit 21 propagates through the annular pipe 16, while another portion of the oscillating flow C propagates through the branch pipe 17 toward the right (+D1 side).

[0025] The linear generator 30 is a generator that converts the energy of an oscillating flow C into electrical energy. As described above, the linear generator 30 is housed inside the housing 19. As shown in Figure 2, the linear generator 30 has a movable element 31, a coil section 34, an elastic member 36, and a detection section 37. The linear generator 30 of this embodiment is a linear generator that generates an induced current Ia in the coil section 34 by the reciprocating motion of the movable element 31 inside the coil section 34 in a first direction D1. In addition, in the linear generator 30, a damping force is applied to the movable element 31 due to friction and other factors associated with the reciprocating motion. For this reason, Figures 1 and 2 schematically show a damper that applies a damping force to the movable element 31.

[0026] The movable element 31 is capable of reciprocating motion in a first direction D1. In this embodiment, the movable element 31 has a piston 32 and a plurality of magnets 33. That is, the linear generator 30 has a piston 32 and a plurality of magnets 33.

[0027] The piston 32 is cylindrical in shape, extending in a first direction D1 with respect to the central axis J. The piston 32 is subjected to a force F due to the oscillating flow C. f The material and shape are not limited as long as it can receive the current. The left end (-D1 side) of the piston 32 is located inside the branch pipe 17. The outer diameter of the piston 32 is slightly smaller than the inner diameter of the branch pipe 17. The outer circumferential surface of the piston 32 is supported on the inner circumferential surface of the branch pipe 17 so as to be movable in the first direction D1. This allows the piston 32 to reciprocate in the first direction D1. Therefore, the movable element 31 can reciprocate in the first direction D1. As shown in Figure 1, the piston 32 is located to the right (+D1 side) of the connection position Pc where the annular pipe 16 and the branch pipe 17 are connected. In this embodiment, the distance in the first direction D1 between the connection position Pc and the piston 32 is the first distance X L That is the case.

[0028] The plurality of magnets 33 are supported by the piston 32. The magnets 33 are permanent magnets. The plurality of magnets 33 are arranged in the first direction D1 with their magnetization directions aligned with the first direction D1. Note that the number of magnets 33 and the arrangement of the magnets 33 are merely examples and are not limited to this embodiment. When the piston 32 reciprocates in the first direction D1, the magnets 33 reciprocate in the first direction D1 together with the piston 32.

[0029] The coil portion 34 is substantially annular and surrounds the central axis J. The coil portion 34 surrounds the magnets 33 from the outside in the radial direction. In this embodiment, the coil portion 34 is composed of a coil wire wound in the circumferential direction.

[0030] The elastic member 36 is a spring extending in the first direction D1. In this embodiment, the elastic member 36 is a coil spring. The left (-D1 side) end of the elastic member 36 is connected to the right (+D1 side) end of the piston 32. That is, the elastic member 36 is connected to the end of the piston 32 in the first direction D1. The right end of the elastic member 36 is connected to the housing 19. The spring constant K g of the elastic member 36 is denoted as such. When the position of the piston 32 is x, the elastic member 36 applies a spring force F g (=K g x) to the piston 32, which is a force directed to the left (-D1 side). Note that the elastic member 36 is not limited to a spring as long as it elastically deform and applies an elastic force corresponding to the above-mentioned spring force to the piston 32.

[0031] ​​​​​​​​As a result, the piston 32 reciprocates in the first direction D1. When the piston 32 reciprocates in the first direction D1, the magnet 33 reciprocates, causing the magnetic flux passing through the coil section 34 to fluctuate, thus inducing a current I in the coil section 34. a This occurs. As a result, the linear generator 30 converts the energy of the oscillating flow C into electrical energy. In this embodiment, the induced current I a This is alternating current.

[0032] Induced current I in coil section 34 a When the current flows, the electromagnetic force between the electromagnet and the magnet 33, which constitute the coil section 34, causes the magnet 33 to generate a regenerative braking force F. l This is added. As a result, an induced current I is generated in the coil section 34. a When the current flows, the regenerative braking force F is applied to the movable element 31. l The following is added. Furthermore, the piston 32 is subjected to a damping force by an equivalent damper. With these factors, if the mass of the movable element 31 is m, the damping constant is D, and the position of the movable element 31 is x, then the equation of motion for the movable element 31 is defined by equation (1). Note that in equation (1) and the following equations, a single dot above a variable indicates that the variable has been differentiated once with respect to time, and two dots above a variable indicate that the variable has been differentiated twice with respect to time. Therefore, a single dot above x represents velocity, and two dots above x represent acceleration.

[0033]

number

[0034] The detection unit 37 detects the moving speed v of the piston 32 as it reciprocates in the first direction D1. That is, the detection unit 37 detects the moving speed v of the piston 32 in the first direction D1. The moving speed v of the piston 32 is the same as the moving speed of the movable element 31. Therefore, the moving speed v of the piston 32 is the same as the moving speed of the magnet 33 as it moves inside the coil section 34 in the first direction D1. The detection unit 37 can also detect the position x of the piston 32 in the first direction D1. A measuring instrument such as a linear encoder can be used as the detection unit 37. In this embodiment, the position x of the piston 32 can be calculated based on the amount of movement of the piston 32 detected by the detection unit 37. The moving speed v of the piston 32 can be calculated by differentiating the amount of movement of the piston 32 with respect to time.

[0035] As shown in Figure 1, the inverter circuit 50 is electrically connected to the coil section 34 via cables 39a and 39b. In other words, the inverter circuit 50 is electrically connected to the linear generator 30. As a result, the inverter circuit 50 receives the induced current I generated in the coil section 34. a A current flows. The induced current I that flows into the inverter circuit 50 a This is output from the inverter circuit 50. As a result, in the thermoacoustic power generation system 10, thermal energy Et is converted into the energy of the oscillating flow C of the fluid F in the thermoacoustic core 20, the energy of the oscillating flow C is converted into electrical energy in the linear generator 30, and the electrical energy is output from the inverter circuit 50. The inverter circuit 50 of this embodiment will be described in detail later.

[0036] Figure 3 shows the pressure P of the oscillating flow C in this embodiment. f and the velocity v of the oscillating flow C f This is a conceptual diagram illustrating the concept. The horizontal axis of Figure 3 represents the distance X in the first direction D1 from the connection point Pc in the branch pipe 17. In the following explanation, the distance X in the first direction D1 from the connection point Pc in the branch pipe 17 may be simply referred to as distance X. The vertical axis of Figure 3 represents the pressure P of the fluid F. f and the flow velocity v of fluid F fThe third axis is time t. Next, the acoustic impedance Z of the oscillating flow C in this embodiment. f I will explain this.

[0037] The thermoacoustic core 20 generates and amplifies the oscillating flow C of the fluid F, which propagates through the branch pipe 17. As a result, as shown in Figure 3, the pressure P of the fluid F inside the branch pipe 17 f and the flow velocity v of fluid F f Each of them vibrates. Pressure P of fluid F f and the flow velocity v of fluid F f Each magnitude differs depending on the distance X. Also, the pressure P of the fluid F. f The vibration and the fluid velocity v of fluid F f Between the oscillations, there is a temporal phase angle φ of the oscillating flow C. f There is a phase angle φ of the oscillating flow C involved. f This varies depending on the distance X. Here, if the cross-sectional area of ​​the branch pipe 17 is A, the acoustic power Pa of the oscillating flow C, which is the output of the thermoacoustic core 20, is defined by equation (2).

[0038]

number

[0039] Furthermore, the force F due to the oscillating flow within the branch pipe 17. f and the fluid velocity v f The ratio is the impedance Z of the acoustic system of the oscillating flow C. f It is defined as equation (3).

[0040]

number

[0041] Figure 4 shows the impedance Z of the acoustic system of the oscillating flow C inside the waveguide 15 of this embodiment. f This figure shows an example of the absolute value of [the variable]. The horizontal axis in Figure 4 is distance X. The vertical axis in Figure 4 is the impedance Z of the acoustic system of the oscillating flow C. f The absolute value of |Z f |. As shown in Figure 4, in this embodiment, |Z f| varies depending on the distance X. First distance X L |Z fL | is at the left end (-D1 side) of piston 32 |Z f | is.

[0042] Figure 5 shows the impedance Z of the acoustic system of the oscillating flow C inside the waveguide 15 of this embodiment. f Phase angle φ f This figure shows an example. The horizontal axis in Figure 5 represents distance X. The vertical axis in Figure 5 represents the phase angle φ. f As shown in Figure 5, in this embodiment, the phase angle φ of the oscillating flow C is... f This varies depending on the distance X. First distance X L Phase angle φ of the oscillating flow C in fL This is the phase angle φ at the left end (-D1 side) of the piston 32. f That is the case.

[0043] In the thermoacoustic power generation system 10, in order to continue the reciprocating motion of the piston 32 and continue power generation in the linear generator 30, the absolute value of the impedance of the acoustic system of the oscillating flow C is |Z f | and, phase angle φ f It is necessary to match the absolute value |Z'| and its phase angle φ' of the mechanical-electrical impedance Z' represented by the equivalent circuit of the mechanical-electrical system of the linear generator 30 and the inverter circuit 50. The mechanical-electrical impedance Z' is defined by equation (4) with respect to the force Fm acting on the movable part and the velocity v of the movable part.

[0044]

number

[0045] In the following explanation, |Z f | and |Z'|, as well as φ f Matching and φ′ to each other is called acoustic joining.

[0046] Figure 6 is a schematic diagram showing the equivalent electrical circuit of the comparative example thermoacoustic power generation system 910. Figure 7 is a schematic diagram showing the equivalent mechanical circuit of the comparative example thermoacoustic power generation system 910. Next, the acoustic junction in the comparative example thermoacoustic power generation system 910 will be described. Although not shown in the figures, the thermoacoustic power generation system 910 comprises a waveguide 15 (see Figure 1), a thermoacoustic core 20 (see Figure 1), a linear generator 30 (see Figure 1), an output circuit 990, and a fluid F. The configuration of the waveguide 15, thermoacoustic core 20, linear generator 30, and fluid F in the thermoacoustic power generation system 910 is the same as the configuration of the waveguide 15, thermoacoustic core 20, linear generator 30, and fluid F in this embodiment. The thermoacoustic power generation system 910 has a configuration in which the inverter circuit 50 of the embodiment is replaced with the output circuit 990. The output circuit 990 does not have multiple switching elements.

[0047] As shown in Figure 6, in the comparative example thermoacoustic power generation system 910, the output circuit 990 is a ring-shaped circuit through which the induced current Ia generated in the coil section 34 flows. The output circuit 990 is provided with an external resistor 991 and a capacitor 992. In the comparative example thermoacoustic power generation system 910, the electrical energy generated in the linear generator 30 is output from the external resistor 991. In Figure 6, the back electromotive force K e v is the induced voltage generated in the coil section 34 when the magnetic flux of the magnet 33 links with the coil section 34. Back electromotive force K e v is an AC voltage. a This is the resistance value of the coil section 34. a This is the inductance of the coil section 34. Capacitance C r R is the capacitance of capacitor 992. L This is the resistance value of the external resistor 991.

[0048] As shown in Figure 7, in the comparative example thermoacoustic power generation system 910, the equivalent mechanical circuits of the linear generator 30 and the output circuit 990 are annular circuits. In Figure 7, the force F due to the oscillating flow is shown. fAs described above, the force applied by the oscillating flow C to the piston 32 is the force exerted by the oscillating flow C on the piston 32. The damping constant D is the constant of the damping force applied to the piston 32. The mass m is the mass of the movable element 31. The spring constant K g This is the spring constant of the elastic member 36.

[0049] From the equivalent electrical circuits of the linear generator 30 and output circuit 990 shown in Figure 6, and the equivalent mechanical circuits of the linear generator 30 and output circuit 990 shown in Figure 7, the absolute value |Z'| of the mechanical-electrical impedance Z' is defined by equation (5), and its phase angle φ' is defined by equation (6). Note that in equations (5) and (6), K f K is the thrust constant. f This is determined by the magnetic force of the magnet 33, the number of turns in the coil section 34, and the distance between the magnet 33 and the coil section 34. The angular frequency ω is the frequency of the reciprocating motion of the piston 32, defined by the reciprocal of the reciprocating period when the piston 32 performs reciprocating motion in the first direction D1.

[0050]

number

[0051]

number

[0052] As mentioned above, in order to perform acoustic bonding, the impedance Z of the acoustic system of the oscillating flow C is f The absolute value of |Z f | and its phase angle φ f Each of these must be matched with the absolute value |Z'| of the mechanical-electrical impedance Z' and its phase angle φ'. It is assumed that the angular frequency ω on the thermoacoustic engine side is predetermined. Also, the mechanical parts of the linear generator—damping constant D, mass m, and spring constant K—are also considered. g It is assumed that this is predetermined by the specifications of the device. Furthermore, in the electrical circuit, the thrust constant K f , the inductance L of the coil section 34 aand the internal resistance R of the coil section 34 a This is predetermined. Therefore, when actually constructing the thermoacoustic power generation system 10, the external resistance R, which is a variable parameter, is also determined. L , and capacitor C r It is very complex because it requires proper configuration.

[0053] Figure 8 is a schematic diagram showing the equivalent circuit of the electrical system of the thermoacoustic power generation system 10 of this embodiment. The inverter circuit 50 of the thermoacoustic power generation system 10 of this embodiment generates an AC induced current i u ,i v ,i w This is an AC-AC inverter that converts AC current into alternating current. As described above, the inverter circuit 50 is electrically connected to the coil section 34 via cables 39a, 39b, and 39c.

[0054] The linear generator 30 of this embodiment has three coil sections 34. Although not shown in the figures, each coil section 34 is roughly annular in shape, surrounding the central axis J. Each coil section 34 is composed of coil wire wound in the circumferential direction. Each coil section 34 is arranged in a line in the first direction D1. Although not shown in the figures, each coil section 34 surrounds the magnet 33 (see Figure 2) from the radial outside. One end of each coil section 34 is electrically connected to each other and grounded. The other end of each coil section 34 is electrically connected to the inverter circuit 50 via cables 39a, 39b, and 39c.

[0055] When the piston 32 (see Figure 2) reciprocates in the first direction D1, the magnetic flux flows radially outward from the magnet 33 and passes through each coil section 34, causing fluctuations in the magnetic flux. As a result, an induced current i is generated in each of the multiple coil sections 34. u ,i v ,i w This occurs. As a result, the linear generator 30 converts the energy of the oscillating flow C into a three-phase alternating current. In other words, the linear generator 30 converts the energy of the oscillating flow C into electrical energy.

[0056] The inverter circuit 50 is electrically connected to each coil section 34 via cables 39a, 39b, and 39c. In other words, the inverter circuit 50 is electrically connected to the linear generator 30. As a result, the inverter circuit 50 receives the induced current i generated in each coil section 34. u ,i v ,i w It plays.

[0057] The inverter circuit 50 includes a wiring pattern 51, a plurality of switching elements 56, a power supply 57, a capacitor 58, and a control unit 59.

[0058] In this embodiment, the inverter circuit 50 has six switching elements 56. The six switching elements 56 include a first switching element 56a, a second switching element 56b, a third switching element 56c, a fourth switching element 56d, a fifth switching element 56e, and a sixth switching element 56f.

[0059] The number of switching elements 56 in the inverter circuit 50 may be 5 or less, or 7 or more. In this embodiment, the switching elements 56 are insulated gate bipolar transistors (hereinafter referred to as IGBTs). The switching elements 56 may be power semiconductor elements other than IGBTs. For example, the switching elements 56 may be field-effect transistors such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors).

[0060] The wiring pattern 51 is provided on a substrate (not shown). The wiring pattern 51 is electrically conductive. Copper and gold or other metals can be used as materials to make up the wiring pattern 51. The wiring pattern 51 electrically connects the linear generator 30, the multiple switching elements 56, and the power supply 57.

[0061] The wiring pattern 51 electrically connects the linear generator 30, a plurality of switching elements 56, a power supply 57, and a capacitor 58. The wiring pattern 51 includes a first wiring pattern 52, a second wiring pattern 53, a third wiring pattern 54, and a fourth wiring pattern 55.

[0062] One end 52a of the first wiring pattern 52 is connected to the positive arm of the first switching element 56a, and the other end 52b of the first wiring pattern 52 is connected to the negative arm of the second switching element 56b. A power supply 57 is provided between the one end 52a and the other end 52b of the first wiring pattern 52. The positive arm of the third switching element 56c, the positive arm of the fifth switching element 56e, and one end of the capacitor 58 are connected to the portion between the one end 52a of the first wiring pattern 52 and the power supply 57. The negative arm of the fourth switching element 56d, the negative arm of the sixth switching element 56f, and the other end of the capacitor 58 are connected to the portion between the other end 52b of the first wiring pattern 52 and the power supply 57.

[0063] One end 53a of the second wiring pattern 53 is connected to the negative arm of the first switching element 56a, and the other end 53b of the second wiring pattern 53 is connected to the positive arm of the second switching element 56b. A cable 39a is connected to the portion of the second wiring pattern 53 between the one end 53a and the other end 53b.

[0064] One end 54a of the third wiring pattern 54 is connected to the negative arm of the third switching element 56c, and the other end 54b of the third wiring pattern 54 is connected to the positive arm of the fourth switching element 56d. A cable 39b is connected to the portion between the one end 54a and the other end 54b of the third wiring pattern 54.

[0065] One end 55a of the fourth wiring pattern 55 is connected to the negative arm of the fifth switching element 56e, and the other end 55b of the fourth wiring pattern 55 is connected to the positive arm of the sixth switching element 56f. A cable 39c is connected to the portion between the one end 55a and the other end 55b of the fourth wiring pattern 55. In this way, each of the multiple switching elements 56 is electrically connected to each coil section 34 via the wiring pattern 51.

[0066] As described above, the power supply 57 is provided in the first wiring pattern 52. In this embodiment, the power supply 57 is a DC power supply. For example, a storage battery can be used as the power supply 57.

[0067] The control unit 59 controls the operation of multiple switching elements 56. The control unit 59 is electrically connected to the multiple switching elements 56. The control unit 59 can communicate with the detection unit 37. The control unit 59 may communicate with the detection unit 37 via wired communication means such as cables, or via wireless communication means such as wireless LAN.

[0068] In this embodiment, the control unit 59 is a computer that controls the operation of each switching element 56. The control unit 59 has a control program installed that performs control of the operation of each switching element 56. At least part of the functions of each component of the control unit 59 are realized by a processor such as a CPU (Central Processing Unit) executing a control program, i.e., software, stored in a memory unit (not shown). At least part of the functions of each component of the control unit 59 may be realized by hardware including circuit units such as an LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), and GPU (Graphics Processing Unit), or by the cooperation of software and hardware. The control unit 59 may include a memory unit (not shown). In this case, the memory unit (not shown) is realized by a storage medium such as RAM, ROM, HDD (hard disk drive), and flash memory.

[0069] Next, the acoustic junction in the thermoacoustic power generation system 10 of this embodiment will be described. In Figure 8, the back electromotive force K e v is the induced voltage generated in the coil section 34 when the magnetic flux generated from the magnet 33 links with the coil section 34. Back electromotive force K e v is an AC voltage. a This is the resistance value of the coil section 34. a This is the inductance of the coil section 34. The resistance value R b This is the internal resistance value of power supply 57. Power supply voltage V b This is the internal voltage of power supply 57.

[0070] In this embodiment, the control unit 59 controls the operation of each switching element 56, thereby controlling the power supply voltage V bis virtually adjusted. Therefore, the control unit 59 controls the operation of each switching element 56 to adjust the potential difference between the back electromotive force K e v and the power supply voltage V b . As a result, the control unit 59 can adjust the induced current i u , i v , i w flowing through the coil unit 34 and the inverter circuit 50, and the phase of the induced current i u , i v , i w . As described above, the control unit 59 can communicate with the detection unit 37. Also, as described above, the detection unit 37 detects the moving speed v of the piston 32 in the first direction D1. In the present embodiment, the control unit 59 controls the operation of the plurality of switching elements 56 based on the moving speed v of the piston 32 detected by the detection unit 37. As a result, the control unit 59 can adjust the current value and the phase of the induced current i u , i v , i w based on the moving speed v of the piston 32.

[0071] FIG. 9 is a schematic diagram showing an equivalent circuit of the electrical system of the thermoacoustic power generation system 10 of the present embodiment. In FIG. 9, the control unit 59 of FIG. 8 is described in more detail as a block diagram. In the present embodiment, vector control is adopted as the control method of the inverter circuit 50. The control unit 59 feeds back the displacement of the mover 31 and the value of the current flowing through each phase, determines the control voltage using vector control, and performs current control of the inverter circuit 50 by inputting a PWM signal to the inverter circuit 50. Note that the control method of the inverter circuit 50 is not limited to the present embodiment.

[0072] In the schematic diagram shown in FIG. 9, a motion equation for calculating the displacement of the mover 31 based on the power generation braking force F l , the spring force F g , the frictional force F r , and the force F f by the oscillating flow C is shown. In the thermoacoustic power generation system 10, the displacement of the mover 31 is input as a measured value of the detection unit 37 (see FIG. 8).

[0073] The displacement of the movable element 31 is used for vector control. Furthermore, the displacement of the movable element 31 is differentiated with respect to time using the differential block 59b to calculate the velocity v. The calculated velocity v is used to consider the induced electromotive force generated in the three-phase circuit. Additionally, velocity v is used in the control of the inverter circuit 50 to control the braking force of the linear generator 30.

[0074] As shown in Figure 9, the control unit 59 of this embodiment receives a command v*=0. That is, the control unit 59 of this embodiment applies a regenerative braking force F so that the speed v of the movable element 31 becomes 0. l The inverter circuit 50 is controlled to generate a regenerative braking force F. Therefore, the control unit 59 in this embodiment controls the inverter circuit 50 to apply a force proportional to the velocity v of the movable element 31 and in the opposite direction to the direction of motion of the movable element 31, thereby generating a regenerative braking force F. l This generates a regenerative braking force F. l This braking force is similar to the braking force generated by a damper in a so-called spring-mass-damper system.

[0075] Furthermore, the control unit 59 calculates a target q-axis current iq* to set the speed v to 0 based on the speed v, applies voltage control via the PI control 59c, performs three-axis control through the conversion unit 59d, and then sends commands to each switching element 56 via the PWM generator 59e. In this way, the control unit 59 controls the inverter circuit 50.

[0076] Furthermore, the PI control 59c receives the command id*=0. This causes the PI control 59c to control the d-axis current to be zero, matching the phase of the back electromotive force of each phase with the phase of the current of each phase, and allowing the current phase to be controlled regardless of the values ​​of Ra and La, which are parameters of the windings of the linear generator 30. In addition, the magnitude of the braking force acting on the movable element 31 can be set arbitrarily.

[0077] As described above, by inputting a command v*=0 to the control unit 59, a regenerative braking force F proportional to the speed of the movable element 31 is generated. lIt also becomes possible to give the proportionality constant K. l If defined as such, the braking force F acting on the movable element 31 l This is expressed by equation (7).

[0078]

number

[0079] Braking constant K l Since can be set to any value, the mechanical-electrical impedance Z' can also be adjusted. By utilizing the above, according to this embodiment, the acoustic coupling conditions of equations (5) and (6) described as comparative examples can be simplified to equations (8) and (9) below. However, the range that can be adjusted in this invention is limited to the real number parts in the mathematical formulas shown in equations (8) and (9).

[0080]

number

[0081]

number

[0082] Equations (8) and (9) of the acoustic bonding conditions in this embodiment have fewer parameters compared to equations (5) and (6) of the acoustic bonding conditions in the comparative example. According to this embodiment, since the external resistor and resonant capacitor are not connected, R L and C r It has been removed. Furthermore, the inverter can control the phase angle φ′ and amplitude of the current and voltage flowing through the winding to any value, so the inductance L a , winding resistance R a This can be excluded from the joining condition.

[0083] Figures 10 to 12 are graphs showing the analysis results of the thermoacoustic power generation system 10 of this embodiment.

[0084] Figure 10 is a graph showing the relationship between the current and back electromotive force of one phase (in this case, the U phase) of a three-phase circuit. As described above, the control unit 59 of this embodiment receives a command id*=0 and controls the d-axis current of the three-phase circuit to be 0. Therefore, the phase of the current of each phase and the phase of the back electromotive force almost coincide, and Figure 10 shows a linear relationship. Although the graph here shows the U phase, the same results are obtained for the V phase and W phase.

[0085] Figure 11 is a graph showing the relationship between the force F applied to the movable element 31 and the velocity v of the movable element 31. As described above, by inputting the command v*=0 to the control unit 59, a regenerative braking force F proportional to the velocity of the movable element 31 is generated. l The absolute value |Z'| and phase angle φ' of the mechanical-electrical impedance Z' are given by the acoustic impedance Z of the oscillating flow C. f The absolute value of |Z f |, and the phase angle φ of the oscillating flow C f A good agreement was found.

[0086] Figure 12 is a graph showing the output power of the thermoacoustic power generation system 10. In Figure 12, a negative region of the output power shown on the vertical axis indicates that power generation occurred, and a positive region indicates that power consumption (motoring) occurred. According to this analysis, the power generated by the thermoacoustic power generation system 10 of this embodiment was 0.36W. In Figure 12, the positive region where power is consumed is considered to be the power consumed because current flows from the capacitor that smooths the inverter circuit 50 to the power supply 57.

[0087] According to this embodiment, the thermoacoustic power generation system 10 comprises a thermoacoustic core 20 that converts thermal energy into the energy of an oscillating flow C of a fluid F, a linear generator 30 that converts the energy of the oscillating flow C into electrical energy, a waveguide 15 that houses the thermoacoustic core 20, the linear generator 30, and the fluid F, and an inverter circuit 50 that is electrically connected to the linear generator 30. The linear generator 30 comprises a movable element 31 having a piston 32 that reciprocates in a first direction D1 by the energy of the oscillating flow C, and a magnet 33 held by the piston 32, a coil section 34 surrounding the magnet 33, and a spring force F connected to the piston 32 that is directed toward the piston 32 in the first direction D1 g (=K g The inverter circuit 50 includes an elastic member 36 that applies x) and a detection unit 37 that detects the moving speed v of the piston 32 in the first direction D1. The inverter circuit 50 includes a plurality of switching elements 56 electrically connected to a coil unit 34, and a control unit 59 that controls the operation of the plurality of switching elements 56. The control unit 59 controls the operation of the plurality of switching elements 56 based on the moving speed v of the piston 32 detected by the detection unit 37. Therefore, as described above, the control unit 59 controls the induced current i based on the moving speed v of the piston 32. u ,i v ,i w This allows adjustment of the regenerative braking force F applied to the movable element 31, as described above. l This can be set arbitrarily. Therefore, as described above, the control unit 59 can control the absolute value |Z'| and phase angle φ' of the mechanical-electrical impedance Z' of the linear generator 30 and the inverter circuit 50. As a result, in the thermoacoustic power generation system 10 of this embodiment, the acoustic impedance Z of the oscillating flow C f The absolute value of |Z f |, and the phase angle φ of the oscillating flow C f The mechanical-electrical impedance Z′ can be controlled so that each of these satisfies equations (7) and (8). As a result, the number of parameters that need to be adjusted to achieve acoustic coupling can be reduced compared to the case where the thermoacoustic power generation system 10 does not have an inverter circuit 50, as described above.

[0088] According to this embodiment, the control unit 59 controls the operation of a plurality of switching elements 56 based on the moving speed v of the piston 32, thereby setting the braking constant K that acts on the movable element 31. l The braking constant K can be set arbitrarily. l By setting this, the absolute value |Z'| and phase angle φ' of the mechanical-electrical impedance Z' of the linear generator 30 and inverter circuit 50 are controlled. Therefore, as described above, the acoustic impedance Z of the oscillating flow C f The absolute value of |Z f |, and the phase angle φ of the oscillating flow C f The absolute value |Z'| and phase angle φ' of the mechanical-electrical impedance Z' can be controlled so that each of them satisfies equations (7) and (8). Therefore, as described above, the number of parameters that need to be adjusted to achieve acoustic bonding can be reduced.

[0089] Although embodiments of the present invention have been described above, the configurations and combinations thereof in the embodiments are merely examples, and additions, omissions, substitutions, and other modifications are possible without departing from the spirit of the present invention. Furthermore, the present invention is not limited by the embodiments.

[0090] The number of thermoacoustic cores in a thermoacoustic power generation system is not limited to the embodiments described above, and the thermoacoustic power generation system may have multiple thermoacoustic cores. The number of thermoacoustic cores can be appropriately determined, for example, by the amount of heat supplied to the thermoacoustic cores and the energy of the oscillating flow supplied to the linear generator. Furthermore, the thermoacoustic power generation system may be equipped with multiple linear generators or multiple inverter circuits.

[0091] The waveguide configuration is not limited to this embodiment; for example, the branch tube may be curved from the connection point toward the linear generator. Alternatively, the branch tube may have other shapes, such as a rectangular tube extending in the first direction. [Explanation of Symbols]

[0092] 10…Thermoacoustic power generation system, 15…Waveguide, 20…Thermoacoustic core, 30…Linear generator, 31…Modifier, 32…Piston, 33…Magnet, 34…Coil section, 36…Elastic member, 37…Detection section, 50…Inverter circuit, 56…Switching element, 59…Control section, C…Oscillating flow, D1…First direction, F…Fluid, K f …Thrust constant, K l ...braking constant, v...piston speed, |Z'|...absolute value of the mechanical-electrical impedance Z', φ'...phase angle of the mechanical-electrical impedance Z'

Claims

1. A thermoacoustic core that converts thermal energy into the energy of a fluid's oscillating flow, A linear generator that converts the energy of the aforementioned oscillating flow into electrical energy, The thermoacoustic core, the linear generator, and the waveguide containing the fluid, An inverter circuit electrically connected to the linear generator, Equipped with, The aforementioned linear generator is A movable element having a piston that reciprocates in a first direction by the energy of the oscillating flow, and a magnet held by the piston, The coil portion surrounding the aforementioned magnet, An elastic member connected to the piston and applying an elastic force to the piston in a first direction, A detection unit for detecting the movement speed of the piston in the first direction, It has, The inverter circuit includes a plurality of switching elements electrically connected to the coil section, and a control unit that controls the operation of the plurality of switching elements. A thermoacoustic power generation system in which the control unit controls the operation of a plurality of switching elements based on the moving speed detected by the detection unit.

2. The thermoacoustic power generation system according to claim 1, wherein the control unit can arbitrarily set a braking constant for setting the force acting on the movable element by controlling the operation of a plurality of switching elements based on the moving speed, and by setting the braking constant, the absolute value and phase angle of the mechanical-electrical impedance of the linear generator and the inverter circuit are controlled.

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