WO2004011777A1

WO2004011777A1 - Rankine cycle system

Info

Publication number: WO2004011777A1
Application number: PCT/JP2003/009222
Authority: WO
Inventors: Akihisa Sato; Shigeru Ibaraki
Original assignee: Honda Giken Kogyo Kabushiki Kaisha
Priority date: 2002-07-25
Filing date: 2003-07-22
Publication date: 2004-02-05
Also published as: EP1536105A1; US20060101821A1; EP1536105A4; JP3901609B2; JP2004060462A; AU2003248085A1

Abstract

A Rankine cycle system, wherein a feed-forward value (NFF) is calculated based on the flow rate (Q) of a vapor-phase acting medium at the outlet of a evaporator (12) and a target pressure (PO) so that the pressure (P) of a vapor-phase acting medium at the inlet of an expander (13) agrees with a target pressure (PO), a feed-back value (NFB) is calculated by multiplying a deviation between the pressure (P) of a vapor-phase acting medium at the inlet of the expander (13) and a target pressure (PO) by feed-back gain (kp) calculated based on the flow rate (Q) of the above vapor-phase acting medium, and the rotation speed of the expander (13) is controlled based on the added/subtracted value of the feed-forward value (NFF) and the feed-back value (NFB). Accordingly, the pressure of a vapor-phase acting medium at the inlet of an expander can be controlled to a target pressure accurately without changing the supply amount of a liquid-phase acting medium to an evaporator.

Description

Specification

Field of the invention

The present invention relates to an evaporator that generates a gas-phase working medium by heating a liquid-phase working medium with exhaust gas of an engine, and a positive displacement type that converts heat energy of the gas-phase working medium generated by the evaporator into mechanical energy. And a Rankine cycle device comprising the expander.

Background art

Japanese Unexamined Patent Publication No. 2000-3344585 describes that in a waste heat recovery device that drives a turbine by heating refrigerant vapor of an engine cooling system by waste heat of the engine, the pressure of the cooling path or It describes that the thermal efficiency is improved by optimally controlling the temperature according to the operating state of the engine. Specifically, as the engine speed and the engine load increase, the target value of the cooling path pressure is set lower, and the discharge amount of the refrigerant circulation pump is controlled so that the actual pressure matches the target pressure. I have. In a Rankine cycle device equipped with a positive displacement expander, if the steam pressure at the inlet of the expander matches the target steam pressure (optimum steam pressure), as shown in Fig. 4, the steam pressure at the outlet of the expander Becomes a pressure commensurate with the expansion ratio of the expander, but if the steam pressure at the inlet is too high, excess energy is left in the steam discharged from the outlet of the expander, and energy is wasted. There is. Conversely, if the steam pressure at the inlet is too low, the steam discharged from the outlet of the expander will have a negative pressure. ^ There is a problem that the expander performs negative work and reduces efficiency.

Thus, it is important to match the steam pressure supplied to the expander to the target steam pressure.However, if the water pressure to the evaporator is changed to make the steam pressure match the target steam pressure, There is a problem that the steam temperature changes accordingly. In other words, as shown in Fig. 3, the efficiency of the evaporator and expander of the Rankine cycle device varies with the steam temperature.To maximize the combined efficiency of the two, the steam temperature must be optimized. If the steam temperature deviates from the optimal steam temperature by changing the amount of water supply so that the steam pressure matches the target steam pressure, the overall efficiency of the evaporator and expander will decrease. There is a problem. Disclosure of the invention

The present invention has been made in view of the above circumstances, and in a Rankine cycle device, a target pressure of a gas phase working medium at an inlet of an expander is set without changing a supply amount of a liquid phase working medium to an evaporator. The purpose is to precisely control the pressure.

To achieve the above object, according to the present invention, an evaporator for heating a liquid-phase working medium with exhaust gas of an engine to generate a gas-phase working medium, and a heat energy of the gas-phase working medium generated by the evaporator, In a Rankine cycle device equipped with a positive displacement expander that converts oil into mechanical energy, the pressure of the gas phase working medium at the inlet of the expander should be matched with the target pressure. The feedforward value was calculated based on the flow rate of the phase working medium and the target pressure, and the difference between the pressure and the target pressure of the gas phase working medium at the inlet of the expander was calculated based on the flow rate of the gas phase working medium. Control means is provided to calculate the feedback value by multiplying the feedback gain, and to control the rotation speed of the expander based on the feedforward value and the addition / subtraction value of the feedback value. Rankine cycle system is proposed which is characterized in that the.

According to the above configuration, the feedforward value is calculated based on the flow rate of the gas-phase working medium at the outlet of the evaporator and the target pressure of the gas-phase working medium at the inlet of the expander, and the feedforward value at the inlet of the expander is calculated. The feedback value is calculated by multiplying the deviation between the pressure of the gas phase working medium and the target pressure by the feedback gain calculated based on the flow rate of the gas phase working medium, and the expansion is performed based on the feedforward value and the addition / subtraction value of the feedback value. Control the rotation speed of the expander, compensating that the change characteristics of the pressure of the gas-phase working medium when the rotation speed of the expander changes vary depending on the flow rate of the gas-phase working medium. The pressure of the gas phase working medium at the inlet of the expander can be made to match the target pressure with good responsiveness and high accuracy without changing the supply amount of the liquid phase working medium. The controller 20 in the embodiment corresponds to the control means of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

1 to 12 show a first embodiment of the present invention. Fig. 1 is a block diagram of a Rankine cycle device and its control system. Fig. 2 searches for a target steam pressure from steam energy and a target steam temperature. Fig. 3 is a graph showing the relationship between the optimum steam temperature and the maximum overall efficiency of the evaporator and the expander. Fig. 4 is a graph showing the relationship between the inlet pressure and the outlet pressure of the expander. 5A and 5B are graphs showing changes in steam pressure when the rotational speed of the expander is changed in steps, and Figs. 6A and 6B are when the feedback gain is fixed. 7A and 7B are diagrams showing the convergence state of the steam pressure when the feedback gain is variable, and FIG. 8 is a flowchart of the main routine of the steam pressure control. 9 is a flowchart of the subroutine of step S3 of the main routine, FIG. 10 is a flowchart of the subroutine of step S4 of the main routine, and FIG. A map for retrieving the feedforward value N _FF of the number. Figure 12 is a table for retrieving the feedback gain kp from the steam flow Q. Figs. 13 to 16 show a second embodiment of the present invention. Fig. 13 is a block diagram of a Rankine cycle device and its control system. Fig. 14 is a flowchart of a main routine of steam pressure control. 15 is a flowchart of a subroutine of step S34 of the main routine, and FIG. 16 is a map for retrieving a specific volume V of steam from a steam pressure P and a steam temperature. FIGS. 17 to 20 show a third embodiment of the present invention. FIG. 17 is a block diagram of a Rankine cycle device and its control system. FIG. 18 is a front view of a main routine of steam pressure control. FIG. 19 is a flowchart of a subroutine of step S53 of the main routine, and FIG. 20 is a flowchart of a subroutine of step S54 of the main routine. FIGS. 21 to 25 show a fourth embodiment of the present invention. FIG. 21 is a block diagram of a Rankine cycle ^ / device and its control system, and FIG. 22 is a flow chart of a main routine of steam pressure control. FIG. 23 is a flowchart of the subroutine of step S72 of the main routine. FIG. 24 is a flowchart of a subroutine of step S73 of the main routine. FIG. 25 is a flowchart of the subroutine of step S73. 15 is a flowchart of a subroutine of step S74.

BEST MODE FOR CARRYING OUT THE INVENTION

1 to 12 show a first embodiment of the present invention.

As shown in Fig. 1, the Rankine cycle device for recovering the thermal energy of the exhaust gas from the engine 11 of the vehicle uses a high-temperature and high-pressure gas by heating the liquid-phase working medium (water) with the exhaust gas from the engine 11. An evaporator 1 2 that generates a phase working medium (steam), and a volume that converts the thermal energy of the high-temperature, high-pressure steam generated by the evaporator 1 2 into mechanical energy Type expander 13, condenser 14 that cools steam discharged from expander 13 and condenses it into water, tank 15 that stores water discharged from condenser 14, tank A water supply pump 16 for sucking water in 15 and an injector 17 for injecting water sucked by the water supply pump 16 into the evaporator 12 are arranged on a closed circuit.

The motor generator 18 connected to the expander 13 is arranged between the engine 11 and the driving wheels, and the motor generator 18 functions as the motor and the output of the engine 11 In addition to assisting the vehicle, when the vehicle decelerates, the motor generator 18 can function as a generator to recover the kinetic energy of the vehicle as electric energy. Note that the motor generator 18 may be connected to the expander 13 as a single unit and have only the function of generating electric energy. In the present invention, the load applied to the expander 13 from the motor generator 18 is adjusted by adjusting the load (power generation amount) of the motor generator 18 to rotate the expander 13. Control the number. The controller 20 has a signal from a steam flow sensor 21 for detecting the steam flow at the outlet of the evaporator 12 and a signal from a steam pressure sensor 22 for detecting the steam pressure at the inlet of the expander 13. And a signal.

The controller 20 includes target steam pressure setting means 23 for setting a target steam pressure that is a target value of the steam pressure at the inlet of the expander 13. As shown in FIG. 2, the target steam pressure setting means 23 retrieves the target steam pressure based on the target steam temperature and the steam energy (steam flow rate). The steam temperature at the outlet of the evaporator 12 is adjusted so that the total efficiency of the evaporator 12 and the expander 13 is maximized (that is, the optimum steam temperature). It is controlled by adjusting the amount of water supplied from 6 to the evaporator 12. That is, as shown in FIG. 3, the efficiency of the evaporator 12 and the efficiency of the expander 13 change depending on the steam temperature. When the steam temperature increases, the efficiency of the evaporator 12 decreases and the efficiency of the expander 13 increases. When the steam temperature decreases and the steam temperature decreases, the efficiency of the evaporator 12 increases and the efficiency of the expander 13 decreases.Therefore, there is an optimum steam temperature that maximizes the combined efficiency of the two. The steam temperature at the outlet of the evaporator 12 is controlled to the optimum steam temperature.

The steam pressure at the inlet of the expander 13 is controlled to the target steam pressure for the following reasons. That is, as shown in FIG. 4, the steam pressure at the inlet of the expander 13 is If the steam pressure matches the target steam pressure, the steam pressure at the outlet of the expander 13 becomes a pressure corresponding to the expansion ratio of the expander 13, but if the inlet steam pressure is too high, the steam from the outlet of the expander 13 will There is a problem that excess energy is left in the discharged steam and energy is wasted. Conversely, if the inlet steam pressure is too low, the steam discharged from the outlet of the expander 13 will have a negative pressure, and there will be a problem that the expander 13 will perform negative work and reduce efficiency. .

Control the steam pressure at the inlet of the expander 13 to the target steam pressure while maintaining the steam temperature at the outlet of the evaporator 12 at the optimum steam temperature, that is, without changing the amount of water supplied to the evaporator 12 To do so, the load applied to the expander 13 from the motor generator 18 may be adjusted to control the number of revolutions of the expander 13. As shown in FIGS. 5A and 5B, the steam pressure increases when the rotation speed of the expander 13 is reduced, and conversely, the steam pressure decreases when the rotation speed of the expander 13 is increased. However, the response of the change in steam pressure changes depending on the steam flow rate, and when the steam flow rate is low, the response is low, and it takes more than 100 seconds for the steam pressure to reach a steady state. However, when the steam flow rate is high, the response becomes high, and it takes less than 10 seconds for the steam pressure to reach a steady state.

It should be noted that the pressure difference before and after the injector 17 is detected and the Ti value is controlled so as to match the target water supply amount, or the discharge pressure of the water supply pump 16 is detected, and the rotation speed of the water supply pump 16 is determined. If controlled, the amount of water supplied to the evaporator 12 is kept constant even if the number of revolutions of the expander 13 changes, and the steam temperature at the outlet of the evaporator 11 can be kept at the optimum steam temperature. it can.

When the steam pressure is feedback-controlled to the target steam pressure, assuming that the feedback gain kp (proportional term) is a constant value as shown in Fig. 6A, an appropriate response when the steam flow rate is large as shown in Fig. 6B If the feed pack gain kp is set so as to obtain high responsiveness, sufficient responsiveness cannot be obtained when the steam flow rate is small. On the other hand, as shown in Figure 7A, by using the feedpack gain kp retrieved from the gain table with the steam flow as a parameter, even when the steam flow is large as shown in Figure 7B. Appropriate responsiveness can be obtained even when it is small.

That is, the gist of the present invention is that the steam pressure at the inlet of the expander 13 is equal to the target steam pressure. In performing feedback control of the number of revolutions of the expander 13 in order to match the feedback gain, the feedback gain must be changed according to the steam flow rate. Hereinafter, the specific contents will be described based on the block diagram of FIG. 1 and the flowcharts of FIG. 8 to FIG. First, in step S1 of the flowchart of FIG. 8, the steam flow rate Q at the outlet of the evaporator 12 is detected by the steam flow rate sensor 21 in step S1, and in step S2, the inlet of the expander 13 is detected by the steam pressure sensor 22. after detecting the steam pressure P in, calculating the rotational speed of the feed-forward value N _FF of the expander 1 3 step S 3. That is, searches Ficoll one Dofowado value N _FF step S 1 rotational speed of the expander 1 3 1 from the map of FIG 1 the steam flow rate Q and the target steam pressure P o as parameters Isseki of the flowchart of FIG. As is evident from FIG. 11, the feedforward value N _FF is set so as to decrease as the steam flow rate Q decreases and the target steam pressure P o increases, and to increase as the steam flow rate Q increases and the target steam pressure P o decreases. ing.

Returning to the flowchart of FIG. 8, in step S4, a feedback value N _FB of the rotation speed of the expander 13 is calculated. That is, the steam pressure P at the inlet of the expander 13 detected by the steam pressure sensor 22 in step S 21 of the flowchart of FIG. 10 and the target steam pressure P o set by the target steam pressure setting means 23 The deviation Δ Δ = I Ρ-の ο I is calculated, and the gain kp is searched by applying the steam flow rate Q detected by the steam flow rate sensor 21 in the following step S22 to the table of FIG. As is evident from the table in FIG. 12, the gain kp decreases as the steam flow rate Q increases. Then, in step S23, the gain kp is multiplied by the deviation ΔΡ to calculate a feedback value N _FB of the rotational speed of the expander 13.

Returning to the flowchart of FIG. 8, if the vapor pressure P is a target steam pressure P ₀ or more in step S 5, by adding the feedback value N _FB to the rotational speed of the feed-forward value N _FF of the expander 1 3 Step S 6 To calculate the rotation speed command value N of the expander 13, and if the steam pressure P is lower than the target steam pressure P o in step S5, the feed speed of the rotation speed of the expander 13 is determined in step S7. By subtracting the feedback value N _FB from the command value N _FF, the rotation speed command value N of the expander 13 is calculated. Then, by controlling the rotation speed of the motor generator 18 based on the rotation speed command value N, that is, the rotation speed of the expander 13, the steam pressure P at the inlet of the expander 13 is set to the target steam pressure. Good response to P ₀ And converges with high accuracy, and as a result, excessive energy remains in the steam discharged from the outlet of the expander 13 or the steam discharged from the outlet of the expander 13 becomes negative pressure. The problem that the expander 13 performs a negative work and the efficiency is reduced can be solved.

FIGS. 13 to 16 show a second embodiment of the present invention.

As shown in FIG. 13, the second embodiment does not include the steam flow sensor 21 of the first embodiment (see FIG. 1), and instead has a water supply amount sensor 24 at the inlet side of the evaporator 12. And a steam temperature sensor 25 on the inlet side of the expander 13. In the first embodiment, the steam flow rate Q is directly detected by the steam flow sensor 21, whereas in the second embodiment, the steam flow rate Q is detected by the steam pressure P detected by the steam pressure sensor 22, and the water supply amount sensor 24. The calculation is performed using the detected feedwater mass flow rate Gw and the steam temperature detected by the steam temperature sensor 25, and other configurations and operations are the same as those of the first embodiment. The operation of the second embodiment will be described with reference to a flowchart. First, in step S31 of the flowchart in FIG. 14, the steam temperature sensor 25 detects the steam temperature T at the inlet of the expander 13 in step S31. In step S32, the steam pressure P at the inlet of the expander 13 is detected by the steam pressure sensor 22 in step S32, and the mass flow rate Gw of water supply to the evaporator 12 is detected by the water supply amount sensor 24 in step S33. To detect.

In the following step S34, the steam flow Q to the expander 13 is calculated without using the steam flow sensor 21. That is, in step S41 of the flow chart of FIG. 15, the specific volume V of steam is searched from the map of FIG. 16 using the steam temperature T and the steam pressure P as parameters. As is evident from Fig. 16, the specific volume V of the steam is set so as to increase as the steam pressure P decreases and the steam temperature T increases. In the following step S42, the steam flow rate Q is calculated by multiplying the specific volume V by the feedwater mass flow rate Gw detected by the feedwater sensor 24.

When the steam flow rate Q is calculated as described above, the process proceeds to steps S35 to S39 in the flowchart of FIG. These steps are exactly the same as steps S3 to S7 in the flowchart of FIG. 8 (first embodiment), and thus redundant description will be omitted. Thus, according to the second embodiment, the steam flow sensor 21 can be eliminated. FIG. 17 to FIG. 20 show a third embodiment of the present invention.

As shown in Fig. 17, the third embodiment uses the water supply amount sensor of the second embodiment (see Fig. 13).

The temperature controller 26 is provided in the controller 20 instead of the controller 24. In the second embodiment, the water supply mass flow rate Gw is detected by the water supply amount sensor 24, whereas in the third embodiment, the command water supply mass flow rate G output by the temperature control unit 26 is used. , The steam mass flow rate Gs corresponding to the feedwater mass flow rate Gw is calculated, and other configurations and operations are the same as in the second embodiment.

The operation of the third embodiment will be described with reference to a flow chart. First, in step S51 of the flow chart of FIG. 18, the steam temperature T at the inlet of the expander 13 is determined by the steam temperature sensor 25 in step S51. Is detected, the steam pressure P at the inlet of the expander 13 is detected by the steam pressure sensor 22 in step S52, and the steam mass flow rate Gs is calculated in step S53.

That is, the command water supply mass flow rate G output by the temperature control unit 26 which controls the steam temperature T by controlling the water supply amount of the injector 17 or the water supply pump 16 in step S61 of the flowchart of FIG. Is read, and in step S62, the commanded water supply flow rate G. Lag filter processing to calculate the steam mass flow rate G s. In this delay filter processing, the temperature control unit 26 sets the commanded feedwater mass flow rate G. This is for compensating for the time delay from when is output to when the evaporator 12 actually generates steam. Subsequently, the steam flow rate Q is calculated in step S54 of the flowchart of FIG. The subroutine of this step S54 is shown in FIG. 20, but the flowchart of FIG. 20 is substantially the same as the flowchart of FIG. 15 of the second embodiment. The example feedwater mass flow Gw has only changed to the steam mass flow Gs, which is substantially the same.

When the steam flow rate Q is calculated as described above, the process proceeds to steps S55 to S59 in the flowchart of FIG. These steps are exactly the same as steps S3 to S7 in the flowchart of FIG. 8 (first embodiment), and thus redundant description will be omitted. Thus, according to the third embodiment, the water supply amount sensor 24 can be eliminated.

FIGS. 21 to 25 show a fourth embodiment of the present invention. As shown in FIG. 21, the fourth embodiment does not include the steam temperature sensor 25 of the third embodiment (see FIG. 13), and instead, the temperature control unit 26 of the controller 20 issues a command. Feedwater mass flow G. And the command steam temperature T ₀ is output. The specific volume map contains the steam temperature T obtained by delaying the command steam temperature Τ ₀ by the delay filter 2, and the target steam pressure P. Is input, and the specific steam volume V found there is multiplied by the steam mass flow rate G s to calculate the steam flow rate Q. Further, instead of the map for searching the feedforward value N _FF of the rotation speed of the expander 13 using the steam flow rate Q and the target steam pressure P o of the first to third embodiments as parameters, only the steam flow rate Q is used as a parameter. In the evening, a _table for retrieving the feedforward value NFF of the rotation speed of the expander 13 is provided, and the other configuration and operation are the same as those of the third embodiment.

The specific volume V of steam is shown by replacing the "steam pressure P" with the "target steam pressure P o" on the horizontal axis in Fig. 16.

The operation of the fourth embodiment will be described with reference to a flow chart. First, in step S71 of the flow chart of FIG. 22, the steam pressure sensor 22 detects the flow at the inlet of the expander 13 at step S71. The steam pressure P is detected, and the steam mass flow rate Gs is calculated in step S72. The flowchart of FIG. 23, which is a subroutine of step S72, is substantially the same as the flowchart of FIG. 19 of the third embodiment, but distinguishes a time constant r from a second time constant 2 described later. The only difference is that the first time constant is set to 1.

Subsequently, the steam flow rate Q is calculated in step S73 of the flowchart of FIG. The subroutine of this step S73 is shown in FIG. 24, and the command steam temperature T output by the temperature control unit 26 in step S91 of the flowchart of FIG. 24. Is delayed in a delay filter 2 to calculate the steam temperature T. In step S92, the steam temperature T and the target steam pressure P output by the target steam pressure setting means 23 are calculated. Is applied to the specific volume map to find the specific volume V of steam. In step S93, the steam mass flow rate Gs output from the delay filter 1 is multiplied by the steam specific volume V to calculate the steam flow rate Q. Subsequently, in step S74 of the flowchart of FIG. 22, that is, in step S101 of the flowchart of FIG. 25, the steam flow rate Q is applied to the expander rotational speed table to apply the rotational speed of the expander 13 to the rotational speed of the expander 13. Search of the feedforward value N _FF. This expander speed table is different from the first to third embodiments in that the target steam pressure P o is not set as a parameter. However, since the target steam pressure P o is applied to the specific volume map in the process of calculating the steam flow rate Q, the target steam pressure Ρ ₀ is consequently taken into account. Thus, the feedforward value N _FF of the rotation speed of the expander 13 retrieved from the steam flow rate Q is proportional to the steam flow rate Q regardless of the steam temperature and the steam pressure. Actually, there is a case where it is not exactly proportional to the steam flow rate Q due to the influence of steam leak or the like, and the error is compensated by the feed pack control of the rotation speed of the expander 13. The last steps S75 to S78 of the flowchart of FIG. 22 are exactly the same as steps S4 to S7 of the flowchart (first embodiment) of FIG. I do. Thus, according to the fourth embodiment, the steam temperature sensor 25 can be eliminated. '

Although the embodiments of the present invention have been described in detail, various design changes can be made in the present invention without departing from the gist thereof.

For example, the working medium is not limited to water (steam), and any other suitable working medium can be employed.

Claims

The scope of the claims

1. The evaporator (12), which heats the liquid-phase working medium with the exhaust gas of the engine (11) to generate a gas-phase working medium; In a Rankine cycle device equipped with a positive displacement expander (13) for converting mechanical energy,

In order to match the pressure of the gas phase working medium at the inlet of the expander (13) to the target pressure, the feedforward value is determined based on the flow rate of the gas phase working medium at the outlet of the evaporator (12) and the target pressure. (N _FF ) is calculated, and the feedback gain (kp) calculated based on the flow rate of the gas phase working medium is added to the deviation between the pressure of the gas phase working medium and the target pressure at the inlet of the expander (13). The multiplication is performed to calculate a feedback value (N _FB ), and the control means (for controlling the rotation speed of the expander (13) based on the addition and subtraction values of the feed forward value (N _FF ) and the feed pack value (N _FB )) 20) A Rankine cycle device comprising: