Power generation system

Abstract

This power generation system (10) comprises: a planetary gear mechanism (23) which has a first shaft, a second shaft and a third shaft; a rotary body (11) which is connected to the first shaft and rotates due to the flow of a fluid; a first rotary electric machine (21) which is connected to the second shaft and generates power by rotation of the second shaft; and a second rotary electric machine (22) which is connected to the third shaft. Said power generation system (10) causes the first rotary electric machine to perform AC power generation by rotation of the rotary body. Furthermore, the power generation system comprises: a first inverter (51) which converts AC power outputted from the first rotary electric machine into DC power; a second inverter (52) which converts DC power outputted from the first inverter into AC power and causes the second rotary electric machine to rotate by means of the AC power; an acquisition unit (41) which acquires a parameter indicating a rotation state of the first rotary electric machine; and a rotation control unit (42) which, on the basis of the acquired parameter, controls the rotation speed of the third shaft by using the rotation state of the second rotary electric machine due to the operation of the inverters and uses said rotation speed control to adjust the rotation speed of the first rotary electric machine.

Description

Power generation system CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-004835, filed on January 16, 2024, the contents of which are incorporated herein by reference.

[0002] The disclosure in this specification relates to a power generation system that generates power using energy sources such as hydraulic power and wind power.

[0003] Various power generation systems have been proposed that generate electricity using renewable energy sources such as hydropower and wind power. For example, in a hydroelectric power generation system described in Patent Document 1, a water pressure sensor detects changes in the water level of the source stream or changes in water pressure due to water intake from a water intake, and the opening of a flow regulator for a hydroelectric turbine is adjusted according to the detected changes in water intake, and the rotation speed of the hydroelectric turbine is controlled according to the adjusted opening. This configuration makes it possible to control the rotation speed of the hydroelectric turbine to optimize the output power.

[0004] JP 2018-71100 A

[0005] In a power generation system, it is conceivable that the power generated by the generator as a result of the rotation of the water turbine is directly output to the power grid. In this case, if the rotation of the water turbine fluctuates due to changes in water pressure or the like, the output voltage of the generator may deviate from the frequency of the grid voltage (e.g., 50 Hz or 60 Hz), which may result in grid interconnection being impossible. Therefore, there is room for improvement in power generation systems that output grid voltage.

[0006] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a power generation system that can appropriately output power to a power grid.

[0007] a first rotating electric machine connected to the second shaft and generating electric power by the rotation of the second shaft; and a second rotating electric machine connected to the third shaft, wherein the rotation of the rotating body causes the first rotating electric machine to generate AC power, and the generated AC power can be output to an electric power system via an AC power line extending from the first rotating electric machine; a first inverter connected to the AC power line and converting the AC power output from the first rotating electric machine into DC power; a second inverter having high-potential and low-potential DC terminals connected to the first inverter, converting the DC power output from the first inverter into AC power and rotating the second rotating electric machine with the AC power; and an acquisition unit that acquires parameters indicating the rotation state of the first rotating electric machine. and a rotation control unit that controls the rotation speed of the third shaft according to the rotation state of the second rotating electric machine through operation of each inverter based on the parameters acquired by the acquisition unit, and adjusts the rotation speed of the first rotating electric machine through the rotation speed control.

[0008] In the power generation system configured as described above, a rotor that rotates due to a fluid flow, a first rotating electric machine, and a second rotating electric machine are connected to the three shafts (first shaft, second shaft, and third shaft) of the planetary gear mechanism, respectively, and the first rotating electric machine can be driven by the rotation of the rotor to generate electricity. The AC power generated by the first rotating electric machine is output to a power grid via an AC power line. The second rotating electric machine can be driven by power supplied from the AC power line of the first rotating electric machine via a first inverter and a second inverter.

[0009] In a planetary gear mechanism, the rotation speed of the remaining shaft is determined by the rotation speed of two shafts. Therefore, when the first shaft rotates due to the rotation of a rotor caused by a fluid flow, the rotation speed of the first rotating electric machine (generator) connected to the second shaft can be increased or decreased depending on the rotation speed of the third shaft. In this case, the rotation speed of the third shaft is controlled based on the rotation state of the second rotating electric machine operated by each inverter, based on a parameter indicating the rotation state of the first rotating electric machine, and the rotation speed of the first rotating electric machine is adjusted by this rotation speed control. This allows the rotation speed of the first rotating electric machine to be adjusted to the desired rotation speed even if the rotation speed of the rotor fluctuates due to changes in the flow velocity of a fluid such as water or air, and ultimately makes it possible to maintain the frequency of the grid voltage at an appropriate frequency. As a result, electric power can be output appropriately to the power grid.

[0010] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is an overall configuration diagram of a power generation system, Fig. 2 is a skeleton diagram showing an example configuration of a transaxle, Fig. 3 is a diagram showing a schematic configuration of a hybrid vehicle, Fig. 4 is a nomogram showing the operation of a planetary gear mechanism, Fig. 5 is a nomogram showing changes in the rotation speeds of three shafts of the planetary gear mechanism, Fig. 6 is a flowchart showing the procedure for power generation control in the power generation system, Fig. 7 is an overall configuration diagram of a power generation system in a second embodiment, Fig. 8 is a flowchart showing the procedure for power generation control in the second embodiment, Fig. 9 is a nomogram showing changes in the rotation speeds of three shafts of the planetary gear mechanism, Fig. 10 is an overall configuration diagram of a power generation system in a third embodiment, and Fig. 11 is a flowchart showing the procedure for power generation control in the third embodiment.

[0011] First Embodiment A power generation system according to one embodiment of the present disclosure will be described below with reference to the drawings. The power generation system 10 of this embodiment is a hydroelectric power generation system constructed using a transaxle and a power control unit (PCU) removed from a used hybrid vehicle, and generates power using hydroelectric energy, which is renewable energy, and outputs the generated power as grid power.

[0012] The configuration of a power generation system 10 will be described using Figure 1. The power generation system 10 includes a water turbine 11 as a rotating body rotated by hydraulic power, a transaxle 13 and a PCU 14 taken out of a hybrid vehicle, and a power generation control device 15, with AC power output from the PCU 14 to an electric power grid 90. The power generation system 10 uses water flowing from, for example, a water tank or reservoir as an energy source, and is configured such that the water turbine 11 is installed in a water channel extending from the water tank or reservoir. The water flow in the water channel rotates the water turbine 11 and a rotating shaft 12 fixed to the water turbine 11.

[0013] The transaxle 13 has a first rotating electric machine 21 (MG1), a second rotating electric machine 22 (MG2), a planetary gear mechanism 23, and a differential gear 24. The planetary gear mechanism 23 and the second rotating electric machine 22 are connected via a drive shaft 25, and the differential gear 24 is connected to the drive shaft 25 via a gear portion 26. The differential gear 24 has a pair of side gears 24a, 24b, and shaft portions 27a, 27b are connected to the side gears 24a, 24b, respectively.

[0014] The first rotating electric machine 21 and the second rotating electric machine 22 are, for example, three-phase AC motors formed by permanent magnet motors or field winding motors. In the power generation system 10, the first rotating electric machine 21 functions as a generator that generates electricity in conjunction with the rotation of the water turbine 11.

[0015] 2 is a skeleton diagram showing an example configuration of the transaxle 13. The planetary gear mechanism 23 includes a sun gear 31, a ring gear 32 that rotates coaxially with the sun gear 31, a plurality of pinion gears 33 that mesh with both the sun gear 31 and the ring gear 32, and a planetary carrier 34 that rotates coaxially with the sun gear 31 as the pinion gears 33 rotate. In the planetary gear mechanism 23, the water wheel 11 is connected to the planetary carrier 34 via a rotating shaft 12. The sun gear 31 is connected to the first rotating electric machine 21. The ring gear 32 is connected to the second rotating electric machine 22 and the differential gear 24 via a drive shaft 25 and a gear unit 26. In the planetary gear mechanism 23, the sun gear 31, the ring gear 32, and the planetary carrier 34 correspond to three axes: a first axis, a second axis, and a third axis.

[0016] As an example of the configuration of the gear unit 26, a counter driven gear 35 is integrally provided on the ring gear 32. The counter driven gear 35 is connected to the second rotating electric machine 22 via a reduction gear 36. The counter driven gear 35 is also connected to the differential gear 24 via a reduction gear 37.

[0017] The transaxle 13 also has a parking lock mechanism 38 (P / L). The parking lock mechanism 38 includes, for example, an actuator, a parking lock gear, and a parking ball (not shown). The actuator drives a parking pawl as an engagement member to engage with the parking lock gear, thereby establishing a parking lock state (activated state). In the parking lock state, rotation of the ring gear 32 meshing with the parking lock gear is restricted. Note that the parking lock mechanism 38 may also mesh the parking lock gear with the counter driven gear 35 to restrict rotation of the counter driven gear 35. In any case, the parking lock mechanism 38 may be any mechanism that switches between a state in which rotation of the ring gear 32 of the planetary gear mechanism 23 is permitted and a state in which rotation is prohibited, i.e., that is capable of restricting rotation of the ring gear 32.

[0018] As shown in Figure 3, when the transaxle 13 is mounted on the hybrid vehicle 100, an internal combustion engine 101 is connected to the planetary carrier 34 of the planetary gear mechanism 23, the first rotating electric machine 21 is connected to the sun gear 31, and the second rotating electric machine 22 is connected to the ring gear 32. In the hybrid vehicle 100, power is generated in the first rotating electric machine 21 as the engine 101 rotates. Furthermore, shafts 27a, 27b on both sides of the differential gear 24 are connected to left and right wheels 102. The hybrid vehicle 100 can travel by driving the wheels with the second rotating electric machine 22.

[0019] 1 , a rotation angle sensor 28 is provided on the rotating shaft (rotor rotating shaft) of the first rotating electric machine 21 to detect the rotation angle of the rotating shaft. The first rotating electric machine 21 also has a three-phase stator coil, and a generated voltage sensor 29 is provided on a power line connected to the stator coil to detect the generated voltage of the first rotating electric machine 21. The detection signals of these sensors 28, 29 are input sequentially to the power generation control device 15.

[0020] The PCU 14 has a first inverter 51, a second inverter 52, a DC-DC converter 53, and an MG control device 54. The first inverter 51 and the second inverter 52 are three-phase inverters. As is well known, the first inverter 51 and the second inverter 52 have an upper arm switch 61 and a lower arm switch 62 for each phase, and perform orthogonal power conversion by switching the upper and lower arm switches 61, 62 in each phase at a predetermined cycle.

[0021] The first inverter 51 and the second inverter 52 are provided with their respective high-potential and low-potential DC terminals connected to each other. That is, in each of the inverters 51 and 52, a high-potential path 63, which is an electrical path on the high-potential side, and a low-potential path 64, which is an electrical path on the low-potential side, are continuous with each other. A smoothing capacitor 65 is connected between the high-potential path 63 and the low-potential path 64.

[0022] AC terminals of the first inverter 51 are connected to the stator coil of the first rotating electric machine 21 and the power system 90. In this case, the first rotating electric machine 21 and the power system 90 are connected to each other by an AC power line 56 extending from the first rotating electric machine 21, and the first inverter 51 is connected to the AC power line 56. AC terminals of the second inverter 52 are connected to the stator coil of the second rotating electric machine 22.

[0023] The first inverter 51 converts the AC voltage output from the first rotating electric machine 21 into a DC voltage. The second inverter 52 reconverts the DC voltage converted by the first inverter 51 into an AC voltage and outputs it to the second rotating electric machine 22. The second rotating electric machine 22 can be rotated by the AC power output from the second inverter 52.

[0024] As is well known, the DC-DC converter 53 has an upper arm switch, a lower arm switch, and a reactor and a capacitor connected to the midpoint between the upper and lower arms, and boosts the voltage of the battery 55 by switching the upper and lower arms. The battery 55 is an electricity storage device with a terminal voltage of, for example, several hundred volts, and is, for example, a lithium-ion secondary battery or a nickel-metal hydride secondary battery. In this power generation system 10, the DC-DC converter 53 and the battery 55 can be omitted from the PCU 14.

[0025] In the hybrid vehicle 100 shown in FIG. 3 , the first inverter 51 is provided as a power conversion circuit for the first rotating electric machine 21, and the second inverter 52 is provided as a power conversion circuit for the second rotating electric machine 22. That is, in the hybrid vehicle 100, the PCU 14 having the two inverters 51, 52 and the DC-DC converter 53 is provided as a rotating electric machine drive component for driving the two rotating electric machines 21, 22. In the power generation system 10 shown in FIG. 1 , the PCU 14 is reused with the inverters 51, 52 and the DC-DC converter 53 connected to each other as they are. However, a difference from the hybrid vehicle 100 is that in the power generation system 10, in addition to the first inverter 51, a power grid 90 is connected to the AC power line 56 extending from the first rotating electric machine 21.

[0026] The MG control device 54 is mainly composed of a microcomputer including a processor, memory, etc. The MG control device 54 performs switching control by turning on and off the upper and lower arm switches 61, 62 for each phase in the first inverter 51 and the second inverter 52. In this embodiment, the MG control device 54 performs switching control based on an output command and a phase command received from the power generation control device 15. The output command is a torque command or a current command for the first rotating electric machine 21. Feedback control may be performed based on the deviation of the detected current from the torque command or current command given as d-axis and q-axis components of the permanent magnet motor. Regarding the phase command, phase information based on the phase of the grid voltage may be provided as angle information during two-phase to three-phase conversion calculation used in the feedback control, thereby controlling the phase or frequency of the first rotating electric machine 21. The MG control device 54 performs power factor correction (PFC) operations in each of the inverters 51, 52 to convert AC current to DC current so as to bring the power factor closer to 1.0 or reduce high-frequency components. By this grid-connected operation of the PCU 14, a grid voltage is output at a frequency of, for example, 60 Hz.

[0027] The power generation control device 15 is primarily composed of a microcomputer (equivalent to a "computer"). The microcomputer includes a processor and a memory (storage unit). The microcomputer provides various functions, such as an acquisition unit 41 and a rotation control unit 42. The functions provided by the microcomputer can be provided by software stored in a physical memory device and a computer executing the software, software alone, hardware alone, or a combination thereof. For example, when the microcomputer is provided by a hardware electronic circuit, the function can be provided by a digital circuit including multiple logic circuits or an analog circuit. For example, the microcomputer executes a program stored in a non-transitory tangible storage medium that serves as its own storage unit. The program includes, for example, a program for the process shown in FIG. 6 . Execution of the program results in the execution of a method corresponding to the program. The storage unit is, for example, a non-volatile memory. The program stored in the storage unit can be updated, for example, via a network such as the Internet.

[0028] FIG. 4 shows an example of a nomographic diagram of the planetary gear mechanism 23. In FIG. 4, the S-axis represents the rotation speed of the sun gear 31, i.e., the rotation speed of the first rotating electric machine 21; the C-axis represents the rotation speed of the planetary carrier 34, i.e., the rotation speed of the water turbine 11; and the R-axis represents the rotation speed of the ring gear 32. In the nomographic diagram, the rotation speeds of the three shafts of the planetary gear mechanism 23 are represented linearly. In FIG. 4, in the basic state, the rotation speed of the ring gear 32 is zero, and the planetary carrier 34 rotates in conjunction with the rotation of the water turbine 11 due to the water flow. The first rotating electric machine 21 then rotates at a rotation speed that conforms to the relationship between the reduction ratios of the three shafts of the planetary gear mechanism 23. Power generation is generated by the rotation of the first rotating electric machine 21.

[0029] In the power generation system 10, for example, if the rotational speed of the water turbine 11 fluctuates in response to changes in the flow velocity of the water flowing through the water channel, the rotational speed of the first rotating electric machine 21 fluctuates accordingly, which in turn fluctuates the frequency of the grid voltage output to the power grid 90. This change in the frequency of the grid voltage may result in a loss of grid interconnection. Specifically, as shown by the dashed-dotted line in FIG. 4 , for example, if the rotational speed (carrier rotational speed) of the water turbine 11 increases from N1 to N2, the rotational speed (sun gear rotational speed) of the first rotating electric machine 21 increases accordingly. This increases the frequency of the grid voltage output from the first rotating electric machine 21, making it impossible to continue grid interconnection. Although not shown, if the rotational speed (carrier rotational speed) of the water turbine 11 decreases, the rotational speed (sun gear rotational speed) of the first rotating electric machine 21 also decreases accordingly, which may also result in a loss of grid interconnection.

[0030] Therefore, in this embodiment, in the planetary gear mechanism 23, when rotational fluctuations occur in the two axes, the sun gear 31 and the planetary carrier 34, due to changes in the water flow velocity, the rotational speed of the remaining axis, the ring gear 32, is controlled to suppress changes in the rotational speed of the first rotating electric machine 21, i.e., changes in the frequency of the system voltage.

[0031] In this embodiment, in the power generation control device 15 shown in FIG. 1 , the acquisition unit 41 acquires a parameter indicating the rotational state of the first rotating electric machine 21. Here, the parameter indicating the rotational state of the first rotating electric machine 21 is the mechanical or electrical frequency of the rotation of the first rotating electric machine 21, or the frequency, voltage, current, or power of the AC output (AC output voltage waveform) of the first rotating electric machine 21. In this embodiment, a rotation angle sensor 28 provided on the rotating shaft of the first rotating electric machine 21 is used as a parameter detection means, and the rotation speed Nm of the first rotating electric machine 21 is acquired as a parameter based on the detection value of the rotation angle sensor 28. The rotation speed Nm corresponds to the mechanical frequency of the rotation of the first rotating electric machine 21. The parameter may be obtained by converting the mechanical frequency (rotation speed) into an electrical frequency taking into account the number of pole pairs of the first rotating electric machine 21. Other parameter detection means may include the generated voltage sensor 29 and current sensors that detect the phase currents of each phase of the first rotating electric machine 21.

[0032] The rotation control unit 42 adjusts the rotation speed of the first rotating electric machine 21 by operating the second inverter 52 to control the rotation speed of the second rotating electric machine 22 based on the parameters acquired by the acquisition unit 41. At this time, the rotation control unit 42 controls the rotation speed of the second rotating electric machine 22 by operating the second inverter 52 based on the deviation state between the mechanical or electrical frequency of the rotation of the first rotating electric machine 21 or the frequency of the AC output voltage and a specified frequency defined by the system voltage frequency of the power grid 90. The system voltage frequency is 50 Hz or 60 Hz. It is preferable that the voltage, current, or power of the AC output voltage waveform of the first rotating electric machine 21 be similarly controlled based on the deviation state from the system voltage waveform of the power grid 90.

[0033] Changes in the rotation speed of the three shafts of the planetary gear mechanism 23 when the rotation speed of the ring gear 32 is adjusted by the second rotating electric machine 22 will be described with reference to FIGS.

[0034] 5(a), similarly to FIG. 4, it is assumed that the rotation speed of the water turbine 11 (carrier rotation speed) increases from N1 to N2, and the rotation speed of the ring gear 32 increases in the positive direction as the second rotating electric machine 22 is rotated in the positive direction. In this case, the rotation speed of the sun gear 31 decreases as the positive rotation speed of the ring gear 32 increases. Therefore, even if the rotation speed of the water turbine 11 changes to the increasing direction, the increase in the rotation speed of the first rotating electric machine 21 (sun gear rotation speed) is suppressed.

[0035] 5(b) assumes that the rotational speed of the water turbine 11 (carrier rotational speed) decreases from N1 to N3, and in this case, the second rotating electric machine 22 is rotated in the negative direction, causing the rotational speed of the ring gear 32 to increase in the negative direction. In this case, the rotational speed of the sun gear 31 increases as the negative-side rotational speed of the ring gear 32 increases. Therefore, even if the rotational speed of the water turbine 11 decreases, the decrease in the rotational speed of the first rotating electric machine 21 (sun gear rotational speed) is suppressed.

[0036] 6 is a flowchart showing the procedure for power generation control in the power generation system 10. This process is executed by the power generation control device 15 at predetermined intervals.

[0037] 6 , in step S11, the rotation speed Nm of the first rotating electrical machine 21 is acquired. Then, in step S12, it is determined whether the rotation speed Nm is less than a first threshold value TH1 corresponding to the grid voltage frequency, and in step S13, it is determined whether the rotation speed Nm is equal to or greater than a second threshold value TH2 corresponding to the grid voltage frequency. The threshold values ​​TH1 and TH2 satisfy the relationship TH1>TH2 and are determined based on the upper and lower limit values ​​allowed for the grid voltage frequency. For example, if the grid voltage frequency is 60 Hz, the first threshold value TH1 may be a value corresponding to 60.1 Hz, and the second threshold value TH2 may be a value corresponding to 59.9 Hz.

[0038] If the results of both steps S12 and S13 are affirmative, the process proceeds to step S 14. In step S 14, the second rotating electrical machine 22 is brought into a rotation-stop state.

[0039] If the result of step S12 is negative, i.e., if the rotation speed Nm is equal to or greater than the first threshold value TH1, the process proceeds to step S15, where the second rotating electrical machine 22 (MG2) is rotated in the forward direction. As a result, as shown in FIG. 5A, the rotation speed of the ring gear 32 increases in the forward direction, and the rotation speed Nm (sun gear rotation speed) is reduced to less than the first threshold value TH1.

[0040] If step S13 is negative, i.e., if the rotation speed Nm is less than the second threshold value TH2, the process proceeds to step S16, where the second rotating electrical machine 22 (MG2) is rotated in the negative rotation direction, thereby increasing the rotation speed of the ring gear 32 to the negative side, as shown in FIG. 5B, and thereby increasing the rotation speed Nm (sun gear rotation speed) to or above the second threshold value TH2.

[0041] In steps S15 and S16, the second inverter 52 performs switching control of the switches 61 and 62 of each phase so that the mechanical or electrical frequency of the rotation of the first rotating electric machine 21 or the frequency of the AC output voltage matches a specified frequency defined by the system voltage frequency of the power grid 90. At this time, the power generation control device 15 calculates an output command and a phase command for driving the second rotating electric machine 22 based on the deviation (deviation) between the current rotation speed Nm of the first rotating electric machine 21 and the rotation speed corresponding to the system voltage frequency, and transmits these commands to the MG control device 54 of the PCU 14. The MG control device 54 then operates the inverters 51 and 52. As a result, the rotation speed of the first rotating electric machine 21 is controlled in conjunction with the driving of the second rotating electric machine 22, and the output voltage of the first rotating electric machine 21 is adjusted to conform to the system voltage.

[0042] Note that instead of a configuration in which the second inverter 52 is controlled so that the mechanical or electrical frequency of the rotation of the first rotating electric machine 21 or the frequency of the AC output voltage matches a specified frequency specified by the system voltage frequency of the power grid 90, a configuration in which the second inverter 52 is controlled so that the phase of the AC output voltage of the first rotating electric machine 21 matches a phase specified by the system voltage frequency of the power grid 90 may be adopted. Also, a configuration in which the parking lock mechanism 38 is turned on (activated) in step S14 and turned off (inactivated) in steps S15 and S16 may be adopted. Step S11 corresponds to an "acquisition unit," and steps S12 to S16 correspond to a "rotation control unit."

[0043] According to the present embodiment described above in detail, the following excellent effects can be obtained.

[0044] In the power generation system 10, the water turbine 11, the first rotating electric machine 21, and the second rotating electric machine 22 are connected to three shafts of the planetary gear mechanism 23, respectively. The first rotating electric machine 21 generates power as the water turbine 11 rotates and outputs it to the power grid via an AC power line 56. The second rotating electric machine 22 is driven by power supplied from the AC power line 56 via a first inverter 51 and a second inverter 52. The rotation speed of the first rotating electric machine 21 is adjusted by controlling the inverters 51 and 52 based on parameters indicating the rotation state of the first rotating electric machine 21. This allows the rotation speed of the first rotating electric machine 21 to be adjusted to a desired value, even if the rotation speed of the water turbine 11 fluctuates due to, for example, a change in the water flow velocity. This ultimately makes it possible to maintain the frequency of the system voltage at an appropriate frequency. As a result, power can be appropriately output to the power grid 90.

[0045] The power generation system 10 is constructed using a transaxle 13 and a PCU 14 that are mounted on a hybrid vehicle 100. This makes it possible to simultaneously contribute to the creation of a recycling-oriented society and the spread of renewable energy.

[0046] The rotation speed of the second rotating electric machine 22 is controlled by operating the inverters 51, 52 so that the mechanical or electrical frequency of the rotation of the first rotating electric machine 21, or the frequency or phase of the AC output voltage, coincides with a specified frequency or phase specified by the system voltage frequency of the power system 90. This makes it possible to appropriately control the frequency of the system voltage output from the first rotating electric machine 21 to the power system 90.

[0047] Second Embodiment The second embodiment will be described below, focusing on the differences from the first embodiment.

[0048] FIG. 7 is a configuration diagram showing the power generation system 10 according to this embodiment. FIG. 7 differs from FIG. 1 in that a brake device 111 is connected to each of the shafts 27a, 27b fixed to the pair of side gears 24a, 24b of the differential gear 24. The brake device 111 is, for example, an electromagnetic brake that generates an electromagnetic force by energizing a coil to hold the shafts 27a, 27b on both sides of the differential gear 24 in a rotationally stopped state. The brake device 111 applies a braking force to the rotation of the drive shaft 25. Note that instead of the configuration in which the brake device 111 is connected to both sides of the shafts 27a, 27b, a configuration in which the brake device 111 is connected to one side of the shafts 27a, 27b and the other side is fixed in a non-rotatable state may be used. The brake device 111 may also be a hydraulic brake.

[0049] The braking force of the brake device 111 may be controlled by a duty ratio, or may be adjusted by the friction resistance of an intermediate connection state, such as a clutch mechanism.

[0050] In this embodiment, when the first rotating electric machine 21 is generating power, if the second rotating electric machine 22 is in a rotating state due to operation of the inverters 51, 52 and a predetermined braking force is being applied to the drive shaft 25 by the brake device 111, the rotation control unit 42 increases or decreases the braking force of the brake device 111 based on the parameters acquired by the acquisition unit 41. That is, the rotation control unit 42 controls the rotation speed of the ring gear 32 by increasing or decreasing the braking force of the brake device 111. In this case, when the first rotating electric machine 21 is generating power, as shown in the collinear diagram of FIG. 9 , the ring gear 32 is in a forward rotation state (rotation speed Na) due to forward rotation drive of the second rotating electric machine 22, and the brake device 111 adjusts the rotation speed of the ring gear 32 under this state.

[0051] 8 is a flowchart showing the power generation control process in this embodiment. In FIG. 8, the same steps as those in FIG. 6 are denoted by the same step numbers, and the description thereof will be omitted.

[0052] In Figure 8, if the rotation speed Nm of the first rotating electric machine 21 is less than the first threshold value TH1 and greater than or equal to the second threshold value TH2 (if steps S12 and S13 are both positive), in step S21, the second rotating electric machine 22 (MG2) is set to a predetermined rotation state, and the brake device 111 is turned on to apply a predetermined braking force to the drive shaft 25.

[0053] If step S12 is negative, that is, if the rotation speed Nm is equal to or greater than the first threshold value TH1, the process proceeds to step S22, where the braking force of the brake device 111 is reduced. At this time, the second rotating electric machine 22 is maintained in the same rotational state, but the rotation speed of the ring gear 32 increases as the braking force is reduced. According to step S22, as shown in FIG. 9A , when the ring gear 32 is rotated forward by the second rotating electric machine 22, the rotation speed of the ring gear 32 increases from Na to Nb, and the rotation speed Nm (sun gear rotation speed) becomes less than the first threshold value TH1.

[0054] On the other hand, if step S13 is negative, i.e., if the rotation speed Nm is less than the second threshold value TH2, the process proceeds to step S23, where the braking force of the brake device 111 is increased. At this time, the second rotating electric machine 22 is maintained in the same rotational state, but the rotation speed of the ring gear 32 is reduced as the braking force increases. According to step S23, as shown in FIG. 9B , when the ring gear 32 is rotating forward by the second rotating electric machine 22, the rotation speed of the ring gear 32 is reduced from Na to Nc, so that the rotation speed Nm (sun gear rotation speed) becomes equal to or greater than the second threshold value TH2.

[0055] In steps S22 and S23, the braking force of the brake device 111 (electromagnetic force of the electromagnetic brake) is controlled so that the mechanical or electrical frequency of the rotation of the first rotating electric machine 21, or the frequency of the AC output voltage, matches the specified frequency determined by the system voltage frequency of the power system 90.

[0056] When the first rotating electric machine 21 generates electricity in accordance with the rotation of the water turbine 11, if the second rotating electric machine 22 is rotating and a predetermined braking force is applied to the drive shaft 25 by the brake device 111, the braking force of the brake device 111 is increased or decreased based on the rotation speed Nm of the first rotating electric machine 21. In this case, the rotation speed of the ring gear 32 of the planetary gear mechanism 23 is adjusted by the braking force of the brake device 111, and thus the rotation speed of the first rotating electric machine 21 can be controlled to an appropriate value.

[0057] Third Embodiment A third embodiment will be described below, focusing on the differences from the first embodiment.

[0058] Fig. 10 is a configuration diagram showing a power generation system 10 according to this embodiment. Fig. 10 differs from Fig. 1 in that a resistive load 122 is connected via a switch 121 to AC terminals of the second inverter 52 that output AC power. The resistive loads 122 are provided on power lines extending from AC terminals of each phase in the second inverter 52. The resistive loads 122 are, for example, resistors. By turning the switch 121 on and off (opening and closing), switching is performed between a first state in which the resistive load 122 is disconnected from the AC terminals of the second inverter 52 and a second state in which the resistive load 122 is connected to the AC terminals of the second inverter 52.

[0059] The power generation control device 15 has an acquisition unit 41, a rotation control unit 42, and a switching control unit 123. When the first rotating electric machine 21 is generating power, the switching control unit 123 switches between a first state (a state in which the resistive load 122 is disconnected) and a second state (a state in which the resistive load 122 is connected) based on parameters acquired by the acquisition unit 41. The switch 121 is initially off (open). When in the second state, the rotation control unit 42 controls the rotation speed of the ring gear 32 by energizing the resistive load 122 through operation of the inverters 51, 52.

[0060] 11 is a flowchart showing the power generation control process in this embodiment. In FIG. 11, the same steps as those in FIG. 6 are denoted by the same step numbers, and the description thereof will be omitted.

[0061] 11 , if the rotation speed Nm of the first rotating electric machine 21 is equal to or greater than the first threshold value TH1 (if step S12 is negative), then in step S31 it is determined whether the rotation speed Nm is less than a threshold value THA that is greater than the first threshold value TH1. If the rotation speed Nm is less than the threshold value THA, then the process proceeds to step S32, where the switch 121 is turned off. This disconnects the resistive load 122 from the second inverter 52. Then, in step S15, the second rotating electric machine 22 (MG2) is driven to rotate in the forward direction.

[0062] If the rotation speed Nm is equal to or greater than the threshold value THA, the process proceeds to step S33, where the switch 121 is turned on. This connects the resistive load 122 to the second inverter 52. Then, in step S34, the inverters 51 and 52 switch the switches 121 to energize the resistive load 122. In this case, a portion of the output power from the first rotating electrical machine 21 is consumed as resistance loss associated with the load energization. This reduces the rotation speed Nm (sun gear rotation speed) to less than the first threshold value TH1. It is also possible to utilize the heat generated by the resistance loss for other purposes.

[0063] According to the above configuration, even if the rotation speed of the water turbine 11 increases excessively, the rotation speed of the first rotating electric machine 21 can be controlled to an appropriate value by consuming electrical energy by passing current from the second inverter 52 to the resistive load 122.

[0064] Furthermore, when the rotation speed Nm of the first rotating electric machine 21 is equal to or greater than the first threshold value TH1, if the rotation speed Nm is less than the threshold value THA, control is performed to adjust the rotation speed of the first rotating electric machine 21 by rotationally driving the second rotating electric machine 22, whereas if the rotation speed Nm is equal to or greater than the threshold value THA, control is performed to adjust the rotation speed of the first rotating electric machine 21 by energizing the resistive load 122. In this case, for example, by increasing the degree of adjustment of the system voltage by energizing the resistive load 122, the rotation speed of the first rotating electric machine 21 can be adjusted quickly even if the deviation of the rotation speed of the first rotating electric machine 21 from the system voltage frequency is large.

[0065] Other Embodiments The above embodiment may be modified as follows, for example.

[0066] In the above embodiment, the planetary gear mechanism 23 is configured such that the water turbine 11 is connected to the planetary carrier 34, the first rotating electric machine 21 is connected to the sun gear 31, and the second rotating electric machine 22 and the differential gear 24 are connected to the ring gear 32. However, it is also possible to change the connection partners of the shafts in the planetary gear mechanism 23. For example, the planetary gear mechanism 23 may be configured such that the water turbine 11 is connected to the sun gear 31, the first rotating electric machine 21 is connected to the planetary carrier 34, and the second rotating electric machine 22 and the differential gear 24 are connected to the ring gear 32.

[0067] In the above embodiment, the PCU 14 is configured to use the first inverter 51 to convert the three-phase AC voltage from the first rotating electric machine 21 into a DC voltage, but this may be changed to a configuration in which a full-wave rectifier circuit consisting of multiple diodes is used.

[0068] A configuration may be adopted in which a plurality of power generation systems 10 shown in FIG. 1 are provided and each of these power generation systems 10 is connected to the power grid 90 .

[0069] The power generation system 10 may be a wind power generation system that generates power using wind energy as renewable energy and outputs the generated power to a power grid. In this case, the water turbine 11 in Fig. 1 is replaced with a wind turbine.

[0070] In the above embodiment, the power generation system 10 is constructed by reusing the transaxle 13 and the PCU 14 from the hybrid vehicle 100, but this may be changed. For example, the power generation system 10 may be constructed by reusing only the transaxle 13 from the hybrid vehicle 100 and combining the transaxle 13 with a power control unit that is a separate component from the hybrid vehicle 100. It is also possible to construct the power generation system 10 without using any components repurposed from the hybrid vehicle 100.

[0071] The control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described herein may be implemented by one or more special-purpose computers configured by combining a processor and memory programmed to perform one or more functions with a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by a computer on a computer-readable non-transitory tangible storage medium.

[0072] The technical concepts extracted from the above-described embodiments are described below. [Configuration 1] A planetary gear mechanism (23) having a first shaft, a second shaft, and a third shaft, a rotating body (11) connected to the first shaft and rotated by a fluid flow, a first rotating electric machine (21) connected to the second shaft and generating electricity by the rotation of the second shaft, and a second rotating electric machine (22) connected to the third shaft, wherein the rotation of the rotating body causes the first rotating electric machine to generate AC power, and the generated AC power can be output to an electric power system (90) via an AC power line (56) extending from the first rotating electric machine, a first inverter (51) connected to the AC power line and converting the AC power output from the first rotating electric machine into DC power, and a second inverter (52) having high-potential and low-potential DC terminals connected to the first inverter, converting the DC power output from the first inverter into AC power and rotating the second rotating electric machine with the AC power, a rotation control unit (42) that controls the rotation speed of the third shaft in accordance with the rotation state of the second rotating electric machine by operating each of the inverters based on the parameters acquired by the acquisition unit, and adjusts the rotation speed of the first rotating electric machine by controlling the rotation speed. [Configuration 2] The power generation system according to Configuration 1, wherein the rotation control unit controls the rotation speed of the third shaft by operating each of the inverters based on the parameters acquired by the acquisition unit. [Configuration 3] The power generation system according to Configuration 1, wherein the second rotating electric machine is connected to the third shaft of the planetary gear mechanism via a drive shaft (25), and the power generation system further comprises a brake device (111) that applies a braking force to the rotation of the drive shaft, and the rotation control unit controls the rotation speed of the third shaft by increasing or decreasing the braking force of the brake device based on the parameters acquired by the acquisition unit when the second rotating electric machine is in a rotating state due to operation of each of the inverters and a predetermined braking force is applied to the drive shaft by the brake device.[Configuration 4] The power generation system according to any one of configurations 1 to 3, wherein the acquisition unit acquires, as the parameter, a mechanical or electrical frequency of rotation of the first rotating electric machine, or a frequency, voltage, current or power of an AC output of the first rotating electric machine, and the rotation control unit controls the rotation speed of the third shaft so that the mechanical or electrical frequency of rotation of the first rotating electric machine, or the frequency or phase of the AC output voltage, matches a specified frequency or phase specified by a system voltage frequency of the power system. [Configuration 5] The power generation system according to Configuration 1, wherein a resistive load (122) is connected via a switch (121) to an AC terminal of the second inverter that outputs AC power, and wherein a switching control unit (123) is configured to switch between a first state in which the resistive load is disconnected from the AC terminal of the second inverter and a second state in which the resistive load is connected to the AC terminal of the second inverter based on the parameters acquired by the acquisition unit when the first rotating electric machine is generating power in accordance with the rotation of the rotating body, and wherein the rotation control unit controls the rotation speed of the third shaft by energizing the resistive load by operating each of the inverters when in the second state. [Configuration 6] The power generation system according to any one of configurations 1 to 5, wherein the planetary gear mechanism has a sun gear (31), a ring gear (32) that rotates coaxially with the sun gear, a plurality of pinion gears (33) that mesh with both the sun gear and the ring gear, and a planetary carrier (34) that rotates coaxially with the sun gear as the pinion gears rotate, the sun gear is connected to the first rotating electric machine as the second shaft, the ring gear is connected to the second rotating electric machine as the third shaft, and the planetary carrier is connected to the rotating body as the first shaft, and the rotation control unit controls the rotation speed of the ring gear by the second rotating electric machine based on the parameters acquired by the acquisition unit.[Configuration 7] The power generation system according to any one of Configurations 1 to 6, wherein the planetary gear mechanism, the first rotating electric machine, and the second rotating electric machine are on-board components mounted as a transaxle (13) in a hybrid vehicle, the rotating body is connected to the first shaft of the planetary gear mechanism in the transaxle instead of an engine of the hybrid vehicle, and the first inverter and the second inverter are power converters in the hybrid vehicle that adjust the input and output of power to and from the first rotating electric machine and the second rotating electric machine, respectively.

[0073] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A planetary gear mechanism (23) having a first axis, a second axis, and a third axis, a rotating body (11) connected to the first axis and rotated by a fluid flow, a first rotating electrical machine (21) connected to the second axis and generating electric power by rotation of the second axis, and a second rotating electrical machine (22) connected to the third axis, wherein alternating current power generation of the first rotating electrical machine is caused by rotation of the rotating body, and the generated alternating current power can be output to a power system (90) via an alternating current power line (56) extending from the first rotating electrical machine; a first inverter (51) connected to the alternating current power line and converting the alternating current power output from the first rotating electrical machine into direct current power; a second inverter (52) having its high-potential side and low-potential side DC terminals connected to the first inverter, converting the direct current power output from the first inverter into alternating current power, and rotating the second rotating electrical machine by the alternating current power; an acquisition unit (41) for acquiring a parameter indicating a rotation state of the first rotating electrical machine; and a rotation control unit (42) for controlling the rotation speed of the third axis in a rotation state of the second rotating electrical machine by operation of each inverter based on the parameter acquired by the acquisition unit, and adjusting the rotation speed of the first rotating electrical machine by the rotation speed control. A power generation system (10).

2. The power generation system according to claim 1, wherein the rotation control unit controls the rotation speed of the third axis by controlling the rotation speed of the second rotating electrical machine by operation of each inverter based on the parameter acquired by the acquisition unit.

3. The second rotating electrical machine is connected to the third axis of the planetary gear mechanism via a drive shaft (25), and a brake device (111) for applying a braking force to rotation of the drive shaft is provided. The rotation control unit increases or decreases the braking force of the brake device based on the parameter acquired by the acquisition unit when the second rotating electrical machine is in a rotating state by operation of each inverter and a predetermined braking force is applied to the drive shaft by the brake device, thereby controlling the rotation speed of the third axis. The power generation system according to claim 1.

4. The acquisition unit acquires, as the parameter, the mechanical or electrical frequency of the rotation of the first rotating electrical machine, or the frequency, voltage, current, or power of the AC output of the first rotating electrical machine. The rotation control unit controls the rotational speed of the third axis so that the mechanical or electrical frequency of the rotation of the first rotating electrical machine, or the frequency or phase of the AC output voltage, matches the specified frequency or phase defined by the system voltage frequency of the power system. The power generation system according to any one of claims 1 to 3.

5. A resistive load (122) is connected to an AC terminal that outputs AC power in the second inverter via a switch (121). In a power generation state by the first rotating electrical machine accompanying the rotation of the rotating body, based on the parameter acquired by the acquisition unit, a switching control unit (123) that switches between a first state in which the resistive load is disconnected from the AC terminal of the second inverter and a second state in which the resistive load is connected to the AC terminal of the second inverter is provided. The rotation control unit controls the rotational speed of the third axis by energizing the resistive load by operating each inverter when in the second state. The power generation system according to claim 1.

6. The planetary gear mechanism includes a sun gear (31), a ring gear (32) that rotates coaxially with the sun gear, a plurality of pinion gears (33) that mesh with both the sun gear and the ring gear, and a planetary carrier (34) that rotates coaxially with the sun gear as the pinion gears rotate. The sun gear is connected to the first rotating electrical machine as the second axis, the ring gear is connected to the second rotating electrical machine as the third axis, and the planetary carrier is connected to the rotating body as the first axis. The rotation control unit controls the rotational speed of the ring gear by the second rotating electrical machine based on the parameter acquired by the acquisition unit. The power generation system according to claim 1.

7. The planetary gear mechanism, the first rotating electric machine, and the second rotating electric machine are in-vehicle components mounted as a transaxle (13) in a hybrid vehicle. In the transaxle, the rotating body is connected to the first shaft of the planetary gear mechanism in place of the engine of the hybrid vehicle. The first inverter and the second inverter are power converters that adjust the input and output of power to the first rotating electric machine and the second rotating electric machine, respectively, in the hybrid vehicle. The power generation system according to claim 1.

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