Waste heat power generation system

Abstract

To provide a waste heat power generation system improved in startability.SOLUTION: A waste heat power generation system includes: an evaporator 11 for heating a refrigerant by waste heat to vaporize the same; an expander 12 for expanding the vaporized refrigerant; a condenser 13 for condensing the expanded refrigerant to liquefy the same; a pump 16 disposed between the condenser 13 and the evaporator 11 for circulating the refrigerant in a heat cycle; an electric valve 17 disposed between the pump 16 and the evaporator 11 and adjustable in opening; and a power generator 18 connected to the expander 12 for generating electric power. In starting, the waste heat power generation system is controlled so that an operation of the pump 16 is started in a state of reducing the opening of the electric valve 17, and the opening of the electric valve 17 is increased after a rotating speed of the pump 16 is increased.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a waste heat power generation system that generates electricity by utilizing waste heat generated in facilities and the like.

Background Art

[0002] In recent years, in facilities where waste heat is generated (such as hot springs and factories), generating electricity by utilizing waste heat has been widely practiced. Patent Document 1 discloses a waste heat power generation system that generates electricity using a Rankine cycle.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The waste heat power generation system of Patent Document 1 heats a working fluid (refrigerant) with waste heat and operates a generator with the working fluid circulating in a Rankine cycle (heat cycle) to generate electricity. In such a waste heat power generation system using a heat cycle, various controls are required to effectively operate the system. It is considered that, for example, the startability of the system can be improved by controlling the waste heat power generation system.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a waste heat power generation system with improved startability.

Means for Solving the Problems

[0006] In order to solve the above problems, a waste heat power generation system according to the present invention is a waste heat power generation system that generates electricity using waste heat, and includes an evaporator that heats a refrigerant with waste heat and vaporizes the refrigerant, an expander that expands the refrigerant vaporized in the evaporator, a condenser that condenses the refrigerant expanded by the expander and liquefies the refrigerant, a pump disposed between the condenser and the evaporator to circulate the refrigerant, an electric valve disposed between the pump and the evaporator and having an adjustable opening degree, and a generator connected to the expander to generate power from the expanding refrigerant and generate electricity. When starting up the waste heat power generation system, the operation of the pump is started with the opening degree of the electric valve reduced, and control is performed to increase the opening degree of the electric valve after the rotational speed of the pump has increased.

[0007] According to the above configuration, by reducing the opening degree of the electric valve when starting up the waste heat power generation system and increasing the outlet side pressure of the pump, it is possible to avoid surging of the pump even when the rotational speed of the pump is low immediately after startup, and the startup performance of the waste heat power generation system can be improved.

[0008] Further, the waste heat power generation system can be configured such that, when starting up the waste heat power generation system, control is performed to start driving the pump after the evaporator is heated.

[0009] According to the above configuration, since the pressure in the refrigerant piping is increased before starting the operation of the pump and the refrigerant can be completely liquefied at the inlet of the pump, the liquid delivery performance of the pump at startup is improved.

[0010] Further, in the waste heat power generation system, the driving of the pump at startup of the waste heat power generation system can be configured to start when the refrigerant temperature becomes equal to or higher than a preset reference value.

[0011] According to the above configuration, the operation of the pump can be started in a state where it is confirmed that the refrigerant is completely liquefied at the inlet of the pump.

[0012] Further, in the waste heat power generation system, the driving of the pump at the start of the waste heat power generation system may be configured to start when the temperature of the heat source medium that supplies waste heat to the evaporator becomes equal to or higher than a preset reference value.

[0013] According to the above configuration, the operation of the pump can be started in a state where the refrigerant is considered to be completely liquefied at the inlet of the pump with simple control.

[0014] In addition, in the waste heat power generation system, a system inverter that performs constant DC voltage control is connected to the output side of the generator. When it is detected in advance that the state of the system inverter approaches a state where constant DC voltage control becomes impossible, the waste heat power generation system may be configured to perform first output suppression control to suppress the output of the waste heat power generation system.

[0015] According to the above configuration, by performing the first output suppression control when the state of the system inverter approaches a state where constant DC voltage control becomes impossible, a state of constant DC voltage control (which is easy to control as a waste heat power generation system) can be maintained.

[0016] In addition, in the waste heat power generation system, the first output suppression control may be configured to be performed when at least one of the following occurs: when the received power from the system inverter falls below a predetermined received power threshold value, when the temperature of the system inverter exceeds a predetermined temperature threshold value, when the DC voltage in the system inverter exceeds a predetermined voltage threshold value, and when the power generation amount by the generator exceeds a predetermined power threshold value.

[0017] In addition, in the waste heat power generation system, the first output suppression control may be configured to be a control that operates by reducing the flow rate of the refrigerant compared to normal operation.

[0018] According to the above configuration, the output of the waste heat power generation system can be suppressed by reducing the flow rate of the refrigerant.

[0019] Further, in the waste heat power generation system, the first output suppression control can be configured to perform operation by raising the target value of the superheat degree of the refrigerant higher than that during normal operation.

[0020] According to the above configuration, by raising the target value of the superheat degree of the refrigerant, the refrigerant flow rate can be reduced during the first output suppression control compared to normal operation.

[0021] Further, when the waste heat power generation system detects that it has come closer to a state where constant DC voltage control becomes impossible in the system inverter after the implementation of the first output suppression control, the waste heat power generation system can be configured to perform second output suppression control to stop the output of the waste heat power generation system.

[0022] According to the above configuration, when the system inverter further approaches a state where constant DC voltage control becomes impossible even after the implementation of the first output suppression control, the safety of the system can be ensured by stopping the output of the waste heat power generation system through the second output suppression control.

[0023] Further, in the waste heat power generation system, the pump and the motor-operated valve can be configured to be arranged at a position lower than the evaporator.

[0024] According to the above configuration, during startup of the waste heat power generation system, etc., it becomes easier to actuate the pump and the motor-operated valve on the liquid-phase refrigerant.

Advantages of the Invention

[0025] The waste heat power generation system of the present invention has an effect of improving the startability of the waste heat power generation system.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a waste heat power generation system (hereinafter, this system) of the present invention. This system is a system that generates electricity using a heat cycle such as a Rankine cycle.

[0028] As shown in FIG. 1, this system includes an evaporator 11, an expander 12, a condenser 13, a receiver 14, a subcooling heat exchanger 15, a pump 16, an electric valve 17, and a generator 18 as components. In this system, a refrigerant (working fluid) circulates in the order of the pump 16, the electric valve 17, the evaporator 11, the expander 12, the condenser 13, the receiver 14, and the subcooling heat exchanger 15.

[0029] The evaporator 11 heats the refrigerant with waste heat generated in facilities such as hot springs and factories, and vaporizes the refrigerant. In this system, the waste heat is supplied by a heat source medium such as warm water or high-temperature gas, and the refrigerant is heated by heat exchange between the refrigerant and the heat source medium.

[0030] The expander 12 expands the vaporized refrigerant. This system generates power from the expanding refrigerant and generates electricity by this power. Specifically, the expanding refrigerant rotates a turbine in the expander 12, and electricity is generated by a generator 18 connected to this turbine.

[0031] The condenser 13 condenses the expanded refrigerant and liquefies the refrigerant. In the condenser 13, the temperature of the refrigerant is lowered by heat exchange with cooling water. However, in this system, not all of the refrigerant is liquefied in the condenser 13, and at the outlet of the condenser 13, the refrigerant is in a gas-liquid mixed state.

[0032] The receiver 14 functions as a gas-liquid separator within the thermal cycle. That is, the refrigerant in a gas-liquid mixed state at the inlet of the receiver 14 is separated into a liquid-phase refrigerant and a gas-phase refrigerant within the receiver 14, and only the liquid-phase refrigerant is discharged from the outlet of the receiver 14. The subcooling heat exchanger 15 further cools the liquid-phase refrigerant separated by the receiver 14 through heat exchange with cooling water to obtain a subcooled liquid.

[0033] The pump 16 is a power source for circulating the refrigerant within the thermal cycle. By being arranged on the downstream side of the subcooling heat exchanger 15, it acts on the liquid-phase refrigerant. The electric valve 17 is an opening adjustment valve whose opening can be adjusted and is used for controlling the flow rate of the refrigerant within the thermal cycle. That is, increasing the opening of the electric valve 17 can increase the flow rate of the refrigerant, and decreasing the opening can decrease the flow rate of the refrigerant. Note that the pump 16 and the electric valve 17 are preferably arranged at a low position within this system, at least lower than the evaporator 11, in order to act on the liquid-phase refrigerant.

[0034] Also, in this system, a drier 19 for removing moisture in the refrigerant and a filter 20 for removing dust in the refrigerant may be provided. Furthermore, in this system, a temperature sensor T and a pressure sensor P for detecting the temperature and pressure of the refrigerant at a predetermined location within the thermal cycle are appropriately provided.

[0035] The above is the basic configuration of this system. Subsequently, the characteristic control method in this system will be described in the following Embodiments 1 to 4.

[0036] [Embodiment 1] In Embodiment 1, a control method for improving the startup performance of the present system will be described. As shown in FIG. 1, in the present system, an electric valve 17 is arranged directly downstream in the refrigerant flow direction (between the pump 16 and the evaporator 11) with respect to the pump 16. As a control method according to Embodiment 1, the opening degree of the electric valve 17 is reduced when the present system is started up. Specifically, the operation of the pump 16 is started with the opening degree of the electric valve 17 reduced, and the opening degree of the electric valve 17 is increased after the rotational speed of the pump 16 has increased. Note that the timing for increasing the opening degree of the electric valve 17 is preferably when a parameter (for example, the drive frequency) reflecting the rotational speed of the pump 16 reaches a predetermined reference value. Alternatively, after a predetermined time has elapsed since the start of the operation of the pump 16, the opening degree of the electric valve 17 may be increased on the assumption that the rotational speed of the pump 16 has sufficiently increased.

[0037] FIG. 2 is a timing chart showing an example of the startup performance improvement control according to Embodiment 1. Here, it is assumed that the maximum drive frequency of the pump 16 is 60 Hz. Note that the rotational speed of the pump 16 increases as the drive frequency increases. In the example of FIG. 2, when the present system is started up, the drive of the pump 16 is started with the opening degree of the electric valve 17 reduced to 20%, and the drive frequency of the pump 16 is gradually increased. Then, when the drive frequency of the pump 16 reaches 50 Hz, the opening degree of the electric valve 17 is set to 100%, and the drive frequency of the pump 16 is further increased to 60 Hz.

[0038] By this startup performance improvement control, surging of the pump 16 at the startup of this system can be avoided. Here, the surging of the pump refers to a phenomenon in which vibrations occur in the pump and piping when operating in a state where the discharge amount of the pump is small (the rotational speed of the pump is low). In the control according to the first embodiment, at the startup of this system, the opening degree of the motor-operated valve 17 is reduced, and the outlet-side pressure of the pump 16 is increased, so that surging of the pump 16 can be avoided even in a state where the rotational speed of the pump 16 is low immediately after startup. Then, when the rotational speed of the pump 16 has risen sufficiently (to a level where surging does not occur), the opening degree of the motor-operated valve 17 can be increased to set the refrigerant flow rate to the required level. Incidentally, after the rotational speed of the pump 16 has risen, by increasing the opening degree of the motor-operated valve 17 to increase the refrigerant flow rate, the power consumption of the pump 16 can be suppressed.

[0039] Also, in the first embodiment, even when this system is stopped, surging of the pump 16 can be avoided by performing control opposite to that at startup. That is, when this system is stopped, first, the driving frequency of the pump 16 is decreased with the opening degree of the motor-operated valve 17 being small, and after the pump 16 has completely stopped, the motor-operated valve 17 is closed. In this case, by reducing the opening degree of the motor-operated valve 17 until the pump 16 has completely stopped, surging of the pump 16 can be avoided even in a state where the rotational speed of the pump 16 is low until the operation stops.

[0040] Also, the opening degree control of the motor-operated valve 17 at the startup and stop of this system may be a composite control of the pump 16 and the motor-operated valve 17. That is, the opening degree of the motor-operated valve 17 may be controlled such that the opening degree of the motor-operated valve 17 increases as the driving frequency of the pump 16 increases, by multi-step opening degree control or continuous opening degree control more than the example shown in FIG. 2.

[0041] In such a composite control, it becomes possible to more appropriately adjust the opening degree of the motor-operated valve 17 in accordance with the driving frequency of the pump 16, and it is possible to more appropriately improve the startability of this system while avoiding surging of the pump 16. Incidentally, regarding the relationship between the driving frequency of the pump 16 and the opening degree of the motor-operated valve 17, data obtained experimentally in advance may be stored in the storage unit of this system as a LUT (Look-Up Table), and the control unit of this system may refer to this LUT to adjust the opening degree of the motor-operated valve 17.

[0042] 〔Embodiment 2〕 In this Embodiment 2, another control method for improving the startability of this system will be described. In this system, power generation is performed by heating the refrigerant in the evaporator 11 (supply of the heat source medium to the evaporator 11) and sending the refrigerant by the pump 16 (circulation of the refrigerant in the heat cycle). Here, the pump 16 can obtain good liquid-sending performance because the refrigerant is completely in the liquid phase at the inlet of the pump 16. If this system is operating stably, the refrigerant circulating in the heat cycle is sent to the pump 16 in a completely liquefied state by the action of the receiver 14 and the subcooling heat exchanger 15.

[0043] However, at the start of this system, the refrigerant is not completely liquefied at the inlet of the pump 16 (it is in a gas-liquid mixed state), and if the operation of the pump 16 is started in that state, the liquid-sending performance of the pump 16 may decrease, and the startability of this system may deteriorate.

[0044] Therefore, in this system, at the start, control is performed such that the heating of the refrigerant in the evaporator 11 is performed first, and subsequently, the sending of the refrigerant by the pump 16 is started. By this control, the pressure in the refrigerant piping in the heat cycle can be increased by supplying the heat source medium to the evaporator 11 before starting the operation of the pump 16. If the pressure in the refrigerant piping increases, the degree of subcooling of the refrigerant increases accordingly, so that the refrigerant can be completely liquefied at the inlet of the pump 16, and the liquid-sending performance of the pump 16 is improved.

[0045] In the above control, it is preferable that the operation start of the pump 16 is performed after confirming that the refrigerant is completely in the liquid phase at the inlet of the pump 16. Whether the refrigerant is completely in the liquid phase can be confirmed by the refrigerant temperature (including the degree of subcooling of the refrigerant). For example, a thermometer T1 (see FIG. 1) and a pressure gauge P1 (see FIG. 1) are arranged upstream of the pump 16 in the refrigerant flow direction, and the refrigerant temperature (degree of subcooling) at the inlet of the pump 16 can be calculated from the outputs of the thermometer T1 and the pressure gauge P1. That is, the above control can be realized by starting the operation of the pump 16 after the calculated refrigerant temperature becomes equal to or higher than a preset reference value.

[0046] However, in the above control, the operation start timing of the pump 16 may be determined by a simpler method. For example, a thermometer T2 (see FIG. 1) is arranged in the pipe for supplying the heat source medium to the evaporator 11, and the above control can be realized by starting the operation of the pump 16 after the heat source medium temperature confirmed by the thermometer T2 becomes equal to or higher than a preset reference value. In this case, the heat source medium temperature when the refrigerant is completely in the liquid phase at the inlet of the pump 16 may be obtained experimentally in advance and set as the above reference value.

[0047] 〔Embodiment 3〕 It is assumed that the system according to the third embodiment is connected to a distribution system of an electric power company via a system inverter (not shown) downstream (output side) of the generator 18. In this case, the alternating current obtained by the power generation of the generator 18 is converted into a current synchronized with the system side (for example, an alternating current with a frequency of 60 Hz and a voltage of 200 V) by the system inverter and output. Further, when performing the above output conversion, the system inverter needs to temporarily convert the alternating current into a direct current. At this time, in this system, the system inverter performs constant DC voltage control so that the voltage becomes constant in the converted direct current. In the constant DC voltage control, the power generation amount corresponding to the temperature of the heat source fluid supplied to the evaporator 11 can be obtained. Such constant DC voltage control is also generally adopted in conventional waste heat power generation systems.

[0048] However, in the DC voltage constant control in the system inverter, there may be a case where this cannot be performed because the balance between the output of the system inverter and the rotation speed of the pump 16 in this system is disrupted. For this reason, in a conventional waste heat power generation system, for example, when the following states (1) to (4) occur, it is determined that the DC voltage constant control becomes impossible, and the control is switched from the DC voltage constant control to the received power constant control. Here, the received power refers to the power (self-consumption power) received by a facility equipped with this system from the system inverter. In the received power constant control, the power generation amount can be suppressed to be constant regardless of the temperature of the heat source fluid supplied to the evaporator 11. (1) Decrease in received power: When the received power decreases, the power generation amount exceeds the self-consumption amount and surplus power is generated, and there is a possibility of reverse flow occurring in the waste heat power generation system. In order to prevent reverse flow, it is necessary to suppress the power generation amount. (2) Temperature rise: When the temperature of the system inverter rises, the power generation amount is suppressed for inverter protection. (3) Voltage rise: When the DC voltage in the system inverter rises, the power generation amount is suppressed for system protection connected to the system inverter. (4) Power excess: When the power generation amount by the generator 18 exceeds the maximum output of the system inverter, the power generation amount is suppressed.

[0049] In the received power constant control, it is necessary to perform the rotation speed control (speed governing control) of the turbine in the expander 12 by the pump 16 and the motor-operated valve 17. That is, if the refrigerant flow rate is reduced by lowering the rotation speed of the pump 16 or reducing the opening degree of the motor-operated valve 17, the power generation amount can be suppressed. However, in reality, it is difficult to maintain the speed governing performance by the pump 16 and the motor-operated valve 17.

[0050] For this reason, in this system according to the third embodiment, it is detected in advance that the state in which the DC voltage constant control in the system inverter becomes impossible is approaching, and when it is detected that the state is approaching, output suppression control is performed to enable the DC voltage constant control state to be maintained in the system inverter. This output suppression control will be described below.

[0051] <First Output Suppression Control> The first output suppression control is implemented before the DC voltage constant control becomes impossible in this system (before shifting to the states (1) to (4) described above), and it is a control to continue operation while suppressing the output of this system. As a method for suppressing the output of this system, for example, a method of changing the target degree of overheating and performing operation can be mentioned. Usually, a waste heat power generation system using a heat cycle sets a target value for the degree of overheating in order to operate the system efficiently, and controls the flow rate of the refrigerant so that the degree of overheating is maintained at the target value. For example, when the target value of the heating degree during normal operation is 5°C, if the target value is increased to 20°C, this system will decrease the flow rate of the refrigerant in order to increase the degree of overheating, and as a result, the output of this system will be suppressed. Incidentally, the degree of overheating is calculated from the outputs of the thermometer T3 (see FIG. 1) and the pressure gauge P3 (see FIG. 1) arranged on the downstream side of the evaporator 11.

[0052] Also, the first output suppression control is started based on a predetermined threshold determination. For example, for the received power at which the state (1) occurs above, a received power value higher than this is set as the received power threshold. Then, if the first output suppression control is implemented when the received power falls below the received power threshold, before the state (1) occurs, this system can be shifted from normal operation to operation by the first output suppression control. As a result, the output of this system is suppressed, the shift to the state (1) can be avoided, so the switching to the received power constant control can also be avoided, and the state of the DC voltage constant control can be maintained.

[0053] Similarly, for the temperature of the system inverter in which the state of (2) above occurs, if a temperature lower than this is set as the temperature threshold, it is possible to shift to the operation by the first output suppression control before the state of (2) occurs. For the DC voltage in the system inverter in which the state of (3) above occurs, if a DC voltage lower than this is set as the voltage threshold, it is possible to shift to the operation by the first output suppression control before the state of (3) occurs. For the power generation amount by the generator 18 in which the state of (4) above occurs, if a power generation amount lower than this is set as the power threshold, it is possible to shift to the operation by the first output suppression control before the state of (4) occurs.

[0054] Incidentally, the first output suppression control is a control for suppressing the output of the system by reducing the flow rate of the refrigerant. In the above description, the flow rate control of the refrigerant based on the superheat degree is exemplified. However, the present invention is not limited to this, and as long as it reflects the flow rate of the refrigerant, it is also possible to perform the first output suppression control based on parameters other than the superheat degree. For example, it is also possible to directly detect the flow rate of the refrigerant with a flow meter and perform the first output suppression control based on the detected flow rate of the refrigerant (so that the flow rate of the refrigerant becomes less than that during normal operation).

[0055] <Second Output Suppression Control> In this system, when approaching the states of (1) to (4) above during normal operation, the output of this system is suppressed by shifting to the first output suppression control. Basically, if shifting to the first output suppression control, it moves away from the states of (1) to (4), but in some cases, it is also conceivable that it approaches the states of (1) to (4) even after shifting to the first output suppression control. In such a case, this system shifts to the stop sequence before the system inverter shifts to the states of (1) to (4) above by the second output suppression control, and once stops the output of this system.

[0056] Also, similar to the first output suppression control, the second output suppression control is started based on a predetermined threshold determination. In this case, the threshold value for transitioning to the second output suppression control is a threshold value that occurs after the first output suppression control and before the states of (1) to (4) above. For example, regarding the temperature of the system inverter, if the temperature at which the state of (2) is reached is 90°C and the temperature threshold for transitioning to the first output suppression control is 80°C, then the temperature threshold for transitioning to the second output suppression control is set to a temperature in between (e.g., 85°C).

[0057] In this system, by performing the second output suppression control in addition to the first output suppression control, it is possible to completely eliminate the need to switch to the constant power reception control in the system inverter. That is, the safety of this system can be ensured without performing the switch to the constant power reception control. However, this system is not limited to this, and it may be configured to perform only the first output suppression control and not perform the second output suppression control. In this case, if the states of (1) to (4) are reached after transitioning to the first output suppression control, a control sequence in which the switch to the constant power reception control is performed may be used. However, even in a configuration where the second output suppression control is not performed, if the output suppression degree of this system is increased during the implementation of the first output suppression control, it is also possible to almost surely avoid the switch from the constant DC voltage control to the constant power reception control.

[0058] 〔Embodiment 4〕 In this Embodiment 4, a control method for reducing the output for component protection and then stopping the system when the system is stopped will be described. Specifically, regarding the expander 12, there are concerns about contact of the scroll blades when it over-rotates, but by using the system stop control of Embodiment 4, such damage to the scroll can be suppressed. Also, regarding the system inverter, when it over-rotates, high voltages are applied to electrical components such as the rectifier and IPM, and there are concerns about failures due to overvoltage, but damage to such electrical components can be suppressed.

[0059] As described in the above Embodiment 3, this system sets a target value for the superheat degree during normal operation, and controls the refrigerant flow rate by the pump 16 and the electric valve 17 so that the superheat degree is maintained at the target value. In the system stop control according to Embodiment 4 of the present invention, the target value of the superheat degree is increased from that during normal operation to reduce the refrigerant flow rate, and after confirming that the output of this system has become low, the system is stopped, thereby protecting the components. For example, the target value of the superheat degree during normal operation is set to 5°C, and the target value of the superheat degree during system stop control is set to 50°C. Thereby, when the superheat degree reaches the target value of 50°C in the system stop control, it can be confirmed that the output of this system has become low.

[0060] The embodiments disclosed this time are illustrative in all respects and are not a basis for restrictive interpretation. Therefore, the technical scope of the present invention is not interpreted only by the above-described embodiments, but is defined based on the description of the claims. Also, all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0061] 11 Evaporator 12 Expander 13 Condenser 14 Receiver 15 Subcooling Heat Exchanger 16 Pump 17 Electric Valve 18 Generator

Claims

1. A waste heat power generation system that generates power using waste heat, comprising: an evaporator that heats a refrigerant with waste heat and vaporizes the refrigerant; an expander that expands the refrigerant vaporized in the evaporator; a condenser that condenses the refrigerant expanded by the expander and liquefies the refrigerant; a pump disposed between the condenser and the evaporator to circulate the refrigerant; an electric valve disposed between the pump and the evaporator and having an adjustable opening degree; a generator connected to the expander, which generates power from the expanding refrigerant to generate electricity, and when starting up the waste heat power generation system, the operation of the pump is started with the opening degree of the electric valve reduced, and control is performed to increase the opening degree of the electric valve after the rotational speed of the pump has increased. When stopping the waste heat power generation system, the drive frequency of the pump is reduced with the opening degree of the electric valve reduced, and control is performed to close the electric valve after the pump has stopped. A waste heat power generation system characterized by this.

2. The waste heat power generation system according to claim 1, when starting up the waste heat power generation system, control is performed to start driving the pump after the evaporator has been heated. A waste heat power generation system characterized by this.

3. The waste heat power generation system according to claim 2, when starting up the waste heat power generation system, the driving of the pump is started when the degree of supercooling becomes equal to or greater than a preset reference value. A waste heat power generation system characterized by this.

4. The waste heat power generation system according to claim 2, when starting up the waste heat power generation system, the driving of the pump is started when the temperature of the heat source medium that supplies waste heat to the evaporator becomes equal to or greater than a preset reference value. A waste heat power generation system characterized by this.

5. The waste heat power generation system according to any one of claims 1 to 4, a system inverter that performs constant DC voltage control is connected to the output side of the generator, and when it is detected in advance that the state of the system inverter approaches a state where constant DC voltage control becomes impossible, first output suppression control is performed to suppress the output of the waste heat power generation system. A waste heat power generation system characterized by this.

6. The waste heat power generation system according to claim 5, The first output suppression control is performed when at least one of the following occurs: when the power received from the system inverter is below a predetermined received power threshold, when the temperature of the system inverter exceeds a predetermined temperature threshold, when the DC voltage in the system inverter exceeds a predetermined voltage threshold, and when the power generation amount by the generator exceeds a predetermined power threshold. A waste heat power generation system characterized by this.

7. The waste heat power generation system according to claim 5 or 6, wherein the first output suppression control is a control that operates by reducing the flow rate of the refrigerant compared to normal operation. A waste heat power generation system characterized by this.

8. The waste heat power generation system according to claim 7, wherein the first output suppression control is a control that operates by raising the target value of the superheat degree of the refrigerant higher than during normal operation. A waste heat power generation system characterized by this.

9. The waste heat power generation system according to any one of claims 5 to 8, when it is detected that the system inverter has further approached a state where constant DC voltage control becomes impossible after the implementation of the first output suppression control, a second output suppression control for stopping the output of the waste heat power generation system is performed. A waste heat power generation system characterized by this.

10. The waste heat power generation system according to any one of claims 1 to 9, wherein the pump and the motor-operated valve are arranged at a position lower than the evaporator. A waste heat power generation system characterized by this. ​

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