Abstract:
Disclosed is a control device for a waste heat recovery system which enables improvement in the responsiveness of the output control for a power turbine and a steam turbine with respect to sudden changes in the inboard load. The control device for a waste heat recovery system is equipped with: a power turbine that provides drive using engine exhaust gas and a steam turbine that provides drive using steam generated with an engine exhaust gas economizer, and is equipped with a power turbine control means which controls the output of the power turbine and a steam turbine control means which controls the output of the steam turbine, and both of which drive an electrical generator by means of the power turbine and the steam turbine. The power turbine control means is equipped with: a power turbine feedback control means which calculates a control valve operation amount based on the deviation between a power turbine target value and; the actual power turbine output; and a power turbine feed-forward control means which extracts a control valve operation amount from a power turbine degree-of-opening command map wherein the relationship between the engine load, the power turbine output target value calculated from the engine load, and the control valve operation amount has been preset. The power turbine control means sets the degree of opening of the control valve by adding the operation amount from the feed-forward control means and the operation amount from the feedback control means.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a control device for an exhaust heat recovery system for vessels, in particular, a control device for an exhaust heat recovery system which sets the opening of a control valve by calculation of a PID controller and a deviation of the rotation speed of a power turbine. 
         [0003]    2. Description of the Related Art 
         [0004]    As a exhaust heat recovery system for vessels, there is a power generation system wherein a steam turbine is driven by performing heat exchange with exhaust gas discharged from a main engine with use of a exhaust gas economizer which utilizes the exhaust gas from the engine and a system wherein the power is generated by rotating a shaft generator by engine output so as to partially compensate for electric load within the vessel. These types of systems have been proposed in view of saving power in the vessel. For instance, Patent Document 1 (JP2007-001339A) discloses the system wherein the exhaust gas from the engine is utilized to drive the power turbine and to partially compensate for the electric load within the vessel. 
         [0005]    In the exhaust heat recovery system equipped with the power turbine, the power is distributed amongst a steam turbine, a power turbine, and a shaft generator depending on the engine load. The power generation by the power turbine is usually controlled by a valve such as ON/OFF valve. In such a case, when there is a chance that turbine trip occurs due to increased load in the vessel, the steam flow is completely shut off by closing the valve or bypassing the flow, and thus it is impossible to control the flow amount of the steam precisely. 
         [0006]      FIG. 7  is a block diagram illustrating a control logic performed in a conventional exhaust heat recovery system.  FIG. 8  is a flow chart of the control logic in relation to  FIG. 7 . The control logic of  FIG. 7  starts in a step S 21 , and a power generation output command computer  52  computes a target output value of the power turbine from the engine load in a step S 22 . An actual output value is measured in a step S 23 , and a subtractor  53  calculates the difference between the target output value and the actual output value of the power turbine in a step S 24 . Then, a PID controller  54  performs PID calculation based on a control deviation so as to obtain an operation amount O 1 . 
         [0007]    Next, a valve opening converter  51  converts an output signal of the feedback control into an operation amount O 2  based on a rotation difference between a target rotation and an actual rotation of the power turbine in a step S 26 . Then, an adder  55  adds the operation amount O 1  and the operation amount O 2  in a step S 27  so as to determine the opening amount of the control valve. After the step S 27 , the process returns to the step S 22 . 
         [0008]    In this manner, the opening amount of the control valve in the power turbine is set by performing the feedback control. 
         [0009]    Moreover, Patent Document 2 (JP3804693B) proposes an invention to control the opening amount of the valve. According to Patent Document 2, a circulation water temperature sensor of load side is arranged on a downstream side of exhaust heat recovery point on a circulation pip of the load side and measures the temperature of circulation water of the load side; an exhaust heat recovery detection means outputs a first heat discharge signal when the temperature of the load side circulation water having been detected by the circulation water temperature sensor is not less than a first set temperature of the load side circulation water by comparing the measured temperature and the first set temperature of the load side circulation water; a flow state detection means is arranged on the load side circulation pipe and detects the flow state of the load side circulation water is normal or abnormal and outputs a second heat discharge signal depending when detecting the abnormal flow; a hold means outputs a heat discharge signal based on the second discharge signal to a point at which a temperature of cooling water measured by a cooling water temperature sensor becomes lower than a second set temperature; a feedforward side controller outputs a control output to set the opening of a discharge amount regulator to a set amount which is set in advance and smaller than the opening amount of the valve which allows a rated operation of the engine and allows the flow of the cooling water for the amount that is supplied to a heat exchanger when the there is no demand for the discharge heat; and a feedback side controller outputs a control output based on the temperature measured by the cooling water temperature sensor so as to control the regulator to increase the discharge heat as the measured temperature gets higher. The control output from the feedforward side controller is added to the control output from the feedback side controller so as to calculate a control output for controlling the discharge heat controller. 
         [0010]    The exhaust heat recovery system disclosed in Patent Document 2 was made in view of prevent the generation of an overshoot resulting from a sudden variation of the exhaust heat recovery amount. 
         [0011]    However, A rapid decline in the load in the vessel generates surplus power and thus it is necessary to immediately reduce the output of the power turbine. In such case, a fluctuation of frequency may be intensified depending on the responsiveness of controlling the output of the power turbine. 
         [0012]    Similarly in the power generation of the steam turbine, a rapid decline in the load in the vessel generates surplus power. To take measure against this, it is necessary to control the flow amount at the valve so as to reduce the output of the steam turbine. In such case, a fluctuation of frequency may be intensified depending on the responsiveness of controlling the output of steam turbine. 
         [0013]    As described above, when there is a rapid decline in the load in the vessel, it is necessary to consider the fluctuation of the frequency. However, Patent Document 2 discloses no solution thereto. Further, in order to control the output of the power turbine or the steam turbine due to the rapid decline in the load in the vessel, the time that takes to stabilize the power supply depends on the responsive speed. 
       [Related Art Document] 
       [0014]    [PATENT DOCUMENT 1] JP2007-1339A 
         [0015]    [PATENT DOCUMENT 2] JP3804693B 
       SUMMARY OF THE INVENTION 
       [0016]    In view of the problem above, an object of the present invention is to improve the responsiveness of controlling the output of the power turbine and the steam turbine in response to the rapid change of the load within the vessel. 
         [0017]    To solve the above issues, the present invention proposes a control device for an exhaust heat recovery system which comprises a power turbine which is driven with use of exhaust gas of an engine, a steam turbine which is driven with use of steam generated by an exhaust gas economizer using the exhaust gas of the engine, and a power generator which is driven by the power turbine and the steam turbine, the control device comprising: a first control valve mechanism which includes at least one control valve arranged on an upstream side of the power turbine and controlling output value of the power turbine by regulating a flow of the exhaust gas; a second control valve mechanism which includes at least one control valve arranged on an upstream side of the steam turbine and controlling output value of the steam turbine; a power turbine controller which controls a total operation amount of the first control valve mechanism; and a steam turbine controller which controls a total operation amount of the second control valve mechanism, wherein the power turbine controller includes a power turbine feedback control unit which calculates a difference between a target output value of the power turbine calculated from an engine load and an actual output value of the power turbine with use of a PID controller so as to compute a first operation amount of the first control valve mechanism, and a power turbine feedforward control unit which extracts a second operation amount of the first control valve mechanism from a preset opening-amount command map for the power turbine which indicates a relationship among the engine load, the target output value of the power turbine calculated from the engine load and an operation amount of the first control valve mechanism, wherein the power turbine controller calculates the total operation amount of the first control valve mechanism by adding the first operation amount obtained from the power turbine feedforward control unit and the second operation amount obtained from the power turbine feedback control unit. 
         [0018]    According to the invention, the preset opening-amount command map for the power turbine which indicates the relationship among the engine load, the target output value of the power turbine calculated from the engine load and an operation amount of the first control valve mechanism; the feedback control unit obtains the first operation amount of the first control valve mechanism from the preset opening-amount command map; and the power turbine controller calculates the total operation amount of the first control valve mechanism by adding the first operation obtained form the power turbine feedforward control unit and the second operation amount obtained from the power turbine feedback control unit. As a result, the responsiveness of controlling the output of the power turbine is improved and the fluctuation of the frequency is reduced. 
         [0019]    Therefore, even when the load within the vessel rapidly decreases, the responsiveness of controlling the output of the power turbine can be improved. 
         [0020]    It is preferable in the present invention that the total operation amount of the first control valve mechanism is an opening amount of a flow control valve for controlling an inflow of the exhaust gas to the power turbine. It is also preferable that the total operation amount of the first control valve mechanism is an opening amount of a bypass valve for controlling a flow of the exhaust gas bypassing the power turbine. 
         [0021]    In the case of controlling the opening amount of the flow control valve, the inflow of the exhaust gas to the power turbine is directly controlled and thus the output of the power turbine can be controlled efficiently and the inflow can be shut out completely. As a result, the power generation of the power turbine can be reduced instantaneously when the load within the vessel decreases. 
         [0022]    Meanwhile, in the case of controlling the opening amount of the bypass valve, the inflow of the exhaust gas to the power turbine can be indirectly controlled by controlling the flow of the exhaust gas bypassing the power turbine. As a result, the output of the power turbine can be precisely controlled. 
         [0023]    Further, it is also preferable that the steam turbine controller comprises a steam turbine feedback control unit which calculates a difference between a target output value of the steam turbine calculated from the engine load and an actual output value of the steam turbine with use of a PID controller so as to compute a first operation amount of the second control valve mechanism, and a steam turbine feedforward control unit which extracts a second operation amount of the second control valve mechanism from a preset opening-amount command map for the steam turbine which has a relationship among the engine load, the target output value of the steam turbine calculated from the engine load and an operation amount of the second control valve mechanism, and that the steam turbine controller calculates the total operation amount of the second control valve mechanism by adding the first operation amount obtained from the steam turbine feedforward control unit and the second operation amount obtained from the steam turbine feedback. 
         [0024]    By this, in the manner similar to the power turbine, the first operation amount obtained from the steam turbine feedforward control unit is added to the second operation amount obtained from the steam turbine feedback so as to obtain the total operation amount of the second control valve mechanism, thereby improving the responsiveness of controlling the output of the steam turbine and also reducing the fluctuation of the frequency. As a result, the responsiveness of controlling the output of the steam turbine can be improved even when the load within the vessel decreases. 
         [0025]    To control the output of the steam turbine, the total operation amount of the second control valve mechanism may be an opening amount of a flow control valve for controlling an inflow of the exhaust gas to the steam turbine or an opening amount of a bypass valve for controlling a flow of the exhaust gas bypassing the steam turbine. 
         [0026]    In the manner similar to controlling the output of the power turbine, in the case of controlling the opening amount of the flow control valve, the inflow of the exhaust gas to the steam turbine can be directly controlled and thus the output of the steam turbine can be efficiently controlled and the flow can be completely shut out. As a result, the power generation of the steam turbine can be reduced instantaneously when the load within the vessel decreases. 
         [0027]    Meanwhile, in the case of controlling the opening amount of the bypass valve, the inflow of the exhaust gas to the steam turbine can be indirectly controlled by controlling the flow of the exhaust gas bypassing the steam turbine. As a result, the output of the steam turbine can be precisely controlled. 
         [0028]    Furthermore, in the present invention, the control device preferably comprises a power turbine target output value correcting unit for correcting the target output value of the power turbine in accordance with a change of a steam turbine load so as to obtain a corrected target output value of the power turbine, wherein the power turbine feedback control unit and the power turbine feedforward control unit perform calculation based on the corrected target output value of the power turbine 
         [0029]    By this, the power turbine and the steam turbine can be controlled in conjunction with each other instead of independently. 
         [0030]    That is, steam-type units are slower in response and thus, the steam turbine is operated as a master unit and the power turbine is operated as a slave unit to set the operation amount. 
         [0031]    Specifically, the power turbine target output value correcting unit corrects the target output value of the power turbine in accordance with the change of the steam turbine load being monitored. 
         [0032]    When the power demand within the vessel decreases sharply, it is necessary to reduce both the load of the steam turbine and the load of the power turbine. However, the responsiveness of the steam-type units is low and thus the output of the steam turbine decreases following the decline of the output of the power turbine. In such an occasion, as it is necessary to ensure the minimum electricity needed within the vessel, the target output of the power turbine should be increased in response to the output (load) of the steam turbine, i.e. the reduction of the output of the steam turbine. 
         [0033]    In this manner, the target output of the power turbine is corrected while the load state of the steam turbine is monitored. As a result, to respond to the decline in the load within the vessel, both the power turbine and the steam turbine are controlled in conjunction with each other, instead of controlling the output of the power turbine disproportionately. 
         [0034]    Furthermore, it is also preferable that the power turbine target output value correcting device calculates the corrected target output value of the power turbine from the engine load and the steam turbine load, based on a preset correction opening-amount command map for the power turbine which indicates a relationship among the steam turbine load, the engine load and the corrected target output value of the power turbine. In this manner, the corrected target output value of the power turbine can be easily obtained by using the preset correction opening-amount command map for the power turbine. 
         [0035]    According to the present invention, it is possible to provide the control device for the exhaust heat recovery system, that can improve the responsiveness of controlling the output of the power turbine and the steam turbine in response to the rapid change of the load within the vessel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    [ FIG. 1 ] A configuration diagram illustrating schematically an exhaust heat recovery system and a general structure of a control device in relation to the present invention. 
           [0037]    [ FIG. 2 ] A block diagram showing a control logic performed in the exhaust heat recovery system of a first preferred embodiment. 
           [0038]    [ FIG. 3 ] A flow chart showing the control logic of the first preferred embodiment. 
           [0039]    [ FIG. 4 ] Maps with an opening amount of a control valve B of a first control valve mechanism on the x-axis. 
           [0040]    [ FIG. 5 ] A block diagram showing a control logic performed in the exhaust heat recovery system of a second preferred embodiment. 
           [0041]    [ FIG. 6 ] A flow chart showing the control logic of the second preferred embodiment. 
           [0042]    [ FIG. 7 ] A block diagram showing a control logic performed in a conventional exhaust heat recovery system. 
           [0043]    [ FIG. 8  ] A flow chart showing the control logic of the conventional case in relation to  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0044]    A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, shape, its relative positions and the like shall be interpreted as illustrative only and not limitative of the scope of the present. 
       First Preferred Embodiment  
       [0045]    First, a configuration of the exhaust heat recovery system in relation to the present invention will be explained in reference to  FIG. 1 .  FIG. 1  shows an engine  22  for propelling the vessel, a propeller being rotated by the output of the engine  22 , a supercharger  21  for compressing the air to be supplied to the engine  22 , a cooler  31  for cooling the air from the supercharger  21 , a power turbine (gas turbine)  23 , a steam turbine  26 , and a generator  28 . 
         [0046]    The power turbine  23  is connected to the steam turbine  26  via a decelerator  24  and the steam turbine  26  is connected to the generator  28  via another decelerator  27 . The decelerators  24  and  27  are different in size and the number of gear teeth. A rotation shaft connecting the power turbine  23  and the steam turbine  26 , and a rotation shaft connecting the steam turbine  26  and the generator  28  are connected via a clutch  25  such that rotative power is transmitted or cut off. 
         [0047]    Further, an exhaust gas economizer  150  is provided. The exhaust gas discharged from the engine  22  is supplied to the exhaust gas economizer  150  via the supercharger  21  or via both the supercharger  21  and the power turbine  23 . The steam generated in the exhaust gas economizer  150  is introduced to the steam turbine  26  so as to actuate the steam turbine  26  and then to rotate the generator  28  with the power of the power turbine  23 . The steam returns to the water in a condenser  29  arranged on a downstream side of the steam turbine  57 . Subsequently, the water is heated by the heat of the cooler  31  and the heat used for cooling walls of the engine  22  and then supplied to the exhaust gas economizer  150  in which the water evaporates, thereby generating the steam. 
         [0048]    The power generation by the power turbine  23  is controlled by the first valve mechanism formed by control valves A, B, and C. The power generation by the steam turbine  26  is controlled by the second valve mechanism formed by control valves D, E, and F. In the first preferred embodiment, the first control valve mechanism is explained from a perspective of controlling the opening of the control valve in such a state that the control valves A and C are fully-open or open with a certain amount and the second control valve mechanism is explained from a perspective of controlling the opening of the control valve E in such a state that the control valves D and F are fully-open or open with a certain amount. 
         [0049]    A control device of the control device  1000  of the exhaust heat recovery system comprises a power turbine controller  101  for controlling which controls a total operation amount of the first control valve mechanism formed by the control valves A, B, and C, and a steam turbine controller  102  which controls a total operation amount of the second control valve mechanism formed by the control valves D, E, and F. 
         [0050]    Further, the power turbine controller  101  includes a power turbine feedback control unit  104  which calculates a difference between a target output value of the power turbine calculated from an engine load and an actual output value of the power turbine with use of a PID controller so as to compute a first operation amount of the first control valve mechanism, and a power turbine feedforward control unit  106  which extracts a second operation amount of the first control valve mechanism from a preset opening-amount command map  105  for the power turbine which indicates a relationship among the engine load, the target output value of the power turbine calculated from the engine load and an operation amount of the first control valve mechanism. 
         [0051]    Furthermore, the steam turbine controller  102  comprises a steam turbine feedback control unit  108  which calculates a difference between a target output value of the steam turbine calculated from the engine load and an actual output value of the steam turbine with use of a PID controller so as to compute a first operation amount of the second control valve mechanism, and a steam turbine feedforward control unit  110  which extracts a second operation amount of the second control valve mechanism from a preset opening-amount command map  109  for the steam turbine which has a relationship among the engine load, the target output value of the steam turbine calculated from the engine load and an operation amount of the second control valve mechanism. 
         [0052]    A control logic performed by the control device in the exhaust heat recovery system is described in reference to  FIG. 2  and  FIG. 3 .  FIG. 2  is a block diagram showing a control logic performed in the exhaust heat recovery system of a first preferred embodiment.  FIG. 3  is a flow chart showing the control logic of the first preferred embodiment.  FIG. 2  and  FIG. 3  show a case in which the power generation of the power turbine  26  is controlled by the control valve B of the first control valve mechanism. 
         [0053]    In the control logic of  FIG. 2 , the process starts in a step S 1 , and an opening-amount map of the control valve B is prepared by calculating or measuring such a opening amount of the control valve B that obtains the desired output of the power turbine for each load of the engine in a step S 2 .  FIG. 4  shows opening-amount maps (opening-amount command map for the power turbine)  105  of the control valve B. 
         [0054]    The opening-amount map of the control valve is determined by a target output value of the power turbine calculated from an engine load and the engine load. The target output value of the power turbine is set in response to the engine load. And the map can be used so that the opening amount of the control valve B can be adjusted with respect to the output.  FIG. 4  shows three of the control valve opening-amount maps in the case of the engine load being 50%, 60%, and 100%. When the engine load is below 50%, the energy of the entire exhaust gas from the engine decreases. 
         [0055]    In a step S 3 , a target generator output calculation unit  2  (ref.  FIG. 2 ) calculates the target output value for the power turbine from the engine load. In a step S 4 , the actual output value of the power turbine is measured. In a step S 5 , a subtractor  3  (ref.  FIG. 2 ) calculates a difference between the target output value of the power turbine and the actual output value of the power turbine. In a step S 6 , a PID control unit  4  (ref.  FIG. 2 ) performs PID calculation based on the difference so as to obtain an operation amount O 1 . 
         [0056]    In a step S 7 , a valve opening converter  1  (ref.  FIG. 2 ) converts an output signal of the feedback control into an operation amount O 2  based on a rotation difference between a target rotation and an actual rotation of the power turbine. In a step S 8 , an opening-amount calculation unit  5  (ref.  FIG. 2 ) extracts an operation amount  0   3  to achieve the target output value of the power turbine from the opening-amount command map  105  of the control valve B having been prepared in the step S 1 . In a step S 9 , an adder  6  adds the operation amount O 2  and the operation amount O 3  and another adder  7  further adds the operation amount O 1  so as to determine the opening amount of the control valve B. After completing the step S 9 , the process returns to the step S 2 . In this manner, the opening-amount map indicating the relationship between  21 , line generated, and the opening amount command is generated by performing the above feedforward control. 
         [0057]    Therefore, the opening-amount command value of the control valve B for the power turbine  23  is set as a total operation amount obtained by adding the operation amount Os obtained in the feedforward control to the operations amount O 1  and O 2  obtained in the feedback control. By further adding the operation amount 3 obtained in the feedforward control, the responsiveness of controlling the output of the power turbine is improved and the fluctuation of the electric frequency is reduced. 
         [0058]    Further, as for the steam turbine control, the steam turbine controller  102  performs the control process in the same way as the power turbine control. 
         [0059]    Specifically, the flow chart of  FIG. 3  may be interpreted as follow for the steam turbine control. The process starts in the step S 1 , and an opening-amount map  109  of the control valve E is prepared by calculating or measuring such a opening amount of the control valve E that obtains the desired output of the steam turbine for each load of the engine in the step S 2 . In this case, the control valve E is equivalent of the control valve B of the previous case and the prepared opening-amount map (opening-amount command map for the steam turbine)  109  are equivalent of the opening-amount maps  105  for the power turbine 
         [0000]      FIG. 4  shows opening-amount maps (opening-amount command map for the power turbine)  105  of the control valve B of the previous case. 
         [0060]    In the step S 3 , the target output value of the steam turbine is obtained in the same manner as calculating the target output value of the power turbine. In the step S 4 , the actual output value of the steam turbine is measured. In the step S 5 , the subtractor  3  calculates a difference between the target output value of the steam turbine and the actual output value of the steam turbine. In the step S 6 , the PID control unit  4  performs PID calculation based on the difference so as to obtain an operation amount O 1 ′. In the step S 7 , the valve opening converter  1  converts an output signal of the feedback control into an operation amount O 2 ′ based on a rotation difference between a target rotation and an actual rotation of the steam turbine. In the step S 8 , an operation amount O 3 ′ is extracted to achieve the target output value of the steam turbine from the opening-amount command map  109  of the control valve E having been prepared in the step S 1 . In the step S 9 , the sum of the operation amounts O 1 ′, O 2 ′ and O 3 ′ is calculated so as to determine the opening amount of the control valve E. 
         [0061]    In this manner, the opening-amount command value of the control valve E for the steam turbine  26  is set as a total operation amount obtained by adding the op 
         [0062]    Therefore, the opening-amount command value of the control valve B for the power turbine  23  is set as a total operation amount obtained by adding the operation amount O 3 ′ obtained in the feedforward control to the operations amount O 1 ′ and O 2 ′ obtained in the feedback control. By further adding the operation amount O 3 ′ obtained in the feedforward control, the responsiveness of controlling the output of the steam turbine is improved and the fluctuation of the electric frequency is reduced. 
         [0063]    In the preferred embodiment, the control valve B is provided as an inflow control valve arranged in such a place that the inflow amount to the power turbine can be directly controlled. Meanwhile, the control valve E is provided as an inflow controlled valve arranged in such a place that the inflow amount to the steam turbine  26  can be directly controlled. With the structure, the output control for the power turbine  23  and the steam turbine  26  can be efficiently achieved, and the inflow thereto can be completely shut off. As a result, it is possible to immediately reduce the power output of the power turbine  23  and the steam turbine  26  when the load within the vessel drops dramatically. 
         [0064]    Further, the control valves B and E were explained in the preferred embodiment. However, it is possible to control the opening amount of the control valve C which controls the amount bypassing the power turbine  23 , and the control valve F which controls the amount bypassing the steam turbine  26 . In such a case, the output of the power turbine  23  and the steam turbine  26  can be precisely controlled. 
         [0065]    Furthermore, the example of using the control valve opening-amount map for the control valve B was explained in the preferred embodiment. However, the opening amount can be sequentially calculated by using a calculation model instead of the map. 
       Second Preferred Embodiment  
       [0066]    The control logic performed by the control device in the exhaust heat recovery system in relation to the second preferred embodiment is explained in reference to  FIG. 5  and  FIG. 6 .  FIG. 5  is a block diagram showing a control logic performed in the exhaust heat recovery system of a second preferred embodiment.  FIG. 6  is a flow chart showing the control logic of the second preferred embodiment.  FIG. 5  and  FIG. 6  illustrate the case about the control valve B for controlling the power generation by the power turbine. 
         [0067]    In the second preferred embodiment, control algorithm is established to control the power turbine and the steam turbine in conjunction with each other instead of controlling them independently. In general, steam-type units are slower in response and thus, the steam turbine is operated as a master unit and the power turbine is operated as a slave unit to generate the command for the power turbine. 
         [0068]    Specifically, the control logic of  FIG. 5  starts in a step S 11 . In a step S 12 , an opening-amount map of the control valve B is prepared by calculating or measuring such a opening amount of the control valve B that obtains the desired output of the power turbine for each load of the engine.  FIG. 4  shows opening-amount maps (opening-amount command map for the power turbine)  105  of the control valve B. The opening-amount map of the control valve B is the same as that of the first preferred embodiment shown in  FIG. 4 . However, the calculation of the target output value of the power turbine is different from the first preferred embodiment. 
         [0069]    In a step S 13 , a target generator output calculation unit (ref.  FIG. 5 ) calculates the target output value for the steam turbine from the engine load. In the first preferred embodiment, the target output value of the power turbine is calculated from the engine load alone. In contrast, in the second preferred embodiment, the target output value of the power turbine is further corrected in response to the change of the load of the steam turbine. Specifically, the target output value of the power turbine increases as the load of the steam turbine decreases and the output of the power turbine comes down. 
         [0070]    Further, a correcting unit (a power turbine target output value correcting unit)  120  for correcting the target output value of the power turbine is provided. The target output value of the power turbine may be corrected by the correcting unit or calculated based on a correction map (correction opening-amount command map for the power turbine)  122  that indicates the relationship among the load of the steam turbine, the engine load and the corrected target output value of the power turbine. The corrected target output value of the power turbine can be easily obtained by using the correction map. 
         [0071]    Next, in a step S 14 , the actual output value of the power turbine is measured. In a step S 15 , a subtractor  13  (ref.  FIG. 5 ) calculates a difference between the target output value of the power turbine and the actual output value of the power turbine. In a step S 16 , a PID control unit  14  (ref.  FIG. 5 ) performs PID calculation based on the difference so as to obtain an operation amount O 1 . 
         [0072]    In a step S 17 , a valve opening converter  11  (ref.  FIG. 5 ) converts an output signal of the feedback control into an operation amount O 2  based on a rotation difference between a target rotation and an actual rotation of the power turbine. In a step S 18 , an opening-amount calculation unit  15  (ref.  FIG. 5 ) extracts an operation amount O 3  to achieve the corrected target output value of the power turbine from the opening-amount command map of the control valve B having been prepared in the step S 11 . In a step S 19 , the sum of the operation amounts O 1 , O 2  and O 3  is calculated in adders  16  and (ref.  FIG. 5 ) so as to determine the opening amount of the control valve B. After completing the step S 19 , the process returns to the step S 12  to repeat the process. 
         [0073]    In the preferred embodiment, the target output value of the power turbine is corrected in response to the change of the load of the steam turbine. Specifically, the opening amount of the control valve is controlled while the load of the steam turbine side is monitored by the power turbine side, and thus the fluctuation of the surplus power can be suppressed by controlling amount of the control valve without monitoring the power turbine side disproportionately. 
       INDUSTRIAL APPLICABILITIES 
       [0074]    According to the present invention, it is possible to improve the responsiveness of controlling the output of the power turbine and the steam turbine in response to the rapid change of the load within the vessel. Therefore, the present invention is beneficial to be applied to the control device for the exhaust heat recovery system for vessels