Abstract:
The invention relates to a method for operating a power generating device ( 2 ) comprising an combustion engine, in particular a gas motor or a gas turbine, and an energy accumulator. Said combustion engine and the energy accumulator are electrically coupled together. Said combustion engine ( 16 ) can be operated in accordance with a first estimated value and in accordance with a second estimated value.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a method for operating a power generating device according to the preamble of claim  1  and to a power generating device according to an independent claim. 
         [0002]    It is known that lean-burn gas motors having output powers in the range of above 400 kW have a slow-acting load alteration response in comparison with diesel motors in this power range. However, gas motors have a better emission behaviour in comparison with diesel motors. Furthermore, gas motors can be operated using waste gases or unrefined gases that result during the extraction of natural gas and/or petroleum. 
         [0003]    It is also known that these lean-burn gas motors can be operated in a low partial-load range only for short periods of time. Furthermore, manufacturer instructions regarding the start-up and turn-off behaviour of the lean-burn gas motor have to be respected. 
         [0004]    DE 10 2006 037 649 A1 discloses, for example, a gas motor having improved non-steady behaviour. Upstream of a turbine of an exhaust gas turbocharger, an additional fuel injection valve is arranged in the exhaust gas line. 
         [0005]    U.S. Pat. No. 6,724,098 B2 discloses a generator system having a gas turbine, a generator driven by the gas turbine, and an energy accumulator, in which system the generator is operated as a motor in order to accelerate the gas turbine. 
       SUMMARY OF THE INVENTION 
       [0006]    The object of the invention is therefore to provide a method for operating a power generating device and a power generating device, in order to improve operation of the power generating device by means of an combustion engine that has a slow-acting load alteration response. 
         [0007]    The object addressed by the invention is achieved by a method according to claim  1  and by a power generating device according to an independent claim. The dependent claims relate to advantageous developments. Features that are important to the invention are also stated in the following description and in the drawings, it being possible for the features to be important to the invention both in isolation and in different combinations without this being explicitly indicated again. 
         [0008]    An combustion engine and an energy accumulator are electrically coupled together. An actual power of the combustion engine is determined. A first estimated value for energy that would be generated during a turn-off process of the combustion engine is determined on the basis of the actual power of the combustion engine. A second estimated value for energy that the energy accumulator can reliably absorb is determined on the basis of a state of charge of the energy accumulator. The combustion engine is operated on the basis of the first estimated value and on the basis of the second estimated value. Advantageously, the energy source in the form of the combustion engine is thus not operated directly on the basis of the behaviour of the load. Rather, as a result of using the first estimated value and the second estimated value, taking the state of charge into account results in the operation of the combustion engine being only indirectly influenced. This results in considerable advantages both for the combustion engine and for the energy accumulator. Since the combustion engine is not operated directly on the basis of the actual power of the load, but rather on the basis of the state of charge of the energy accumulator, the energy accumulator has a filter function with regard to the energy output of the power generating device. Changes or fluctuations in the power output of the combustion engine can be attenuated by means of the energy accumulator. Consequently, by preventing fluctuations in the energy output, wear of the combustion engine is significantly reduced, which has a positive influence on the maintenance costs for the combustion engine. 
         [0009]    On account of the proposed method, the energy accumulator, in turn, is not in a permanent state of charge or discharge. A number of charging and discharging cycles is also kept to a minimum. This also reduces wear of the energy accumulator, which is a relatively expensive component of the power generating device. It can therefore also be said that the energy of the energy accumulator is the most expensive in comparison with the energy of the remaining system components. Thus, the energy accumulator advantageously acts not as an energy supply for the load, but rather as a buffer, since the load is preferably operated directly using the energy generated by the combustion engine. Accordingly, in the method according to the invention, the load draws the minimum energy required from the energy accumulator, and therefore the efficiency and service life of the energy accumulator, which are strongly influenced by the discharging and charging behaviour, are maximised. 
         [0010]    In an advantageous embodiment, an increase in the actual power is enabled if the first estimated value is no greater than the second estimated value. Thus, a state of the power generating device is identified in which the actual power of combustion engine can be readily increased. By increasing the power of the load, the state of charge of the energy accumulator is initially reduced. As a result of the energy accumulator initially being discharged when the power of the load is increased, the energy in the energy accumulator can be used optimally. Accordingly, the running time of the combustion engine and therefore also the maintenance costs for the combustion engine are reduced. 
         [0011]    In an advantageous embodiment, the actual power of the combustion engine is reduced if the first estimated value is greater than the second estimated value. 
         [0012]    In an advantageous development, the actual power of the combustion engine is reduced if the actual power is greater than a minimum continuous power of the combustion engine. This ensures that the combustion engine is not operated beyond its specification. 
         [0013]    In an advantageous development, the actual power of the combustion engine is reduced if the actual power of the combustion engine is greater than the minimum continuous power of the combustion engine and if a state of charge of the energy accumulator increases. In particular, this also ensures that, as a result of a power sink suddenly being removed, all of the energy generated during a turn-off process of the combustion engine can be absorbed by the energy accumulator. As a result of the energy accumulator initially being charged when the power of the load is reduced, which increases the state of charge of the energy accumulator, and the actual power of the combustion engine only then being reduced, all of the surplus energy generated by the combustion engine can be stored in the energy accumulator and an optimal use of energy can thus be achieved. 
         [0014]    In an advantageous development, the actual power of the combustion engine is reduced if the actual power of the combustion engine is greater than a maximum charging capacity of the energy accumulator. This ensures that the energy accumulator is not operated beyond its specification or the service life thereof is not shortened. 
         [0015]    In an advantageous embodiment, a turn-off process is started if the first estimated value is greater than the second estimated value. 
         [0016]    In an advantageous embodiment, the turn-off process is started if the actual power of the combustion engine is lower than a minimum continuous power of the combustion engine. A turn-off time point for an combustion engine is determined on the basis of an actual power of the combustion engine and on the basis of a state of charge of an energy accumulator. A turn-off process of the combustion engine is started at the turn-off start time. Advantageously, this makes it possible for lean-burn gas motors that have a low-transient performance to also be usable for high-transient applications. Thus, a lean-burn gas motor can advantageously be operated using unrefined gas and, at the same time, by means of the method, high amounts of power can be provided for short periods of time in order to operate, for example, oil drilling rigs or the like. 
         [0017]    In particular, it is ensured that, as a result of a power sink suddenly being removed, all of the energy generated during a turn-off process of the combustion engine can be absorbed by the energy accumulator. In particular, when using gas motors, a slow shutdown in the form of an overrun can ensure that maintenance intervals and outages of the gas motor can be reduced. 
         [0018]    Furthermore, this method ensures that the accumulator has a high state of charge most of the time, which has a positive influence on the service life thereof when using, for example, a lithium ion battery. The increased charge of the accumulator which is thus possible results in an increased availability of the power generating device. 
         [0019]    Advantageously, a power generating device that has a slow-acting energy source, such as a gas motor, and has an increased service life, together with reduced exhaust gas emissions and high-transient power output, can thus be provided. Advantageously, the efficiency of the entire system is improved since no braking apparatus, such as a braking resistor, is required to consume surplus energy generated by the gas motor. 
         [0020]    In an advantageous embodiment, a first estimated value for energy that is generated during an overrun of the combustion engine is determined on the basis of the actual power. A second estimated value for energy that the energy accumulator can reliably absorb during the overrun is determined on the basis of the state of charge. The turn-off process is started if the first estimated value is greater than the second estimated value. Advantageously, the energy accumulator is thus operated in an acceptable range. Furthermore, the combustion engine advantageously does not have to be provided with a braking apparatus in order to consume surplus energy generated by the combustion engine. Of course, a braking apparatus can also continue to be provided for an emergency shutdown or the like. 
         [0021]    In an advantageous embodiment, the turn-off process is started if the actual power of the combustion engine is greater than a maximum charging capacity of the energy accumulator. This prevents destruction of the power generating device, in particular in the converter region. 
         [0022]    In an advantageous embodiment, the actual power of the combustion engine is reduced as a function of an increasing state of charge of the energy accumulator. The actual turn-off start time for the turn-off process of the combustion engine can advantageously be further delayed thereby, as a result of which the operating time of the combustion engine can advantageously be increased. 
         [0023]    In an advantageous embodiment, the turn-off process is started if the actual power of the combustion engine is lower than a minimum continuous power of the combustion engine. This means that the combustion engine can advantageously be operated in the range of the minimum continuous power or above the minimum continuous power until the turn-off time point has been reached. Advantageously, the turn-off time point is therefore moved further into the future. 
         [0024]    In an advantageous embodiment, a start-up enabling time point for the combustion engine is determined on the basis of the state of charge of the energy accumulator, on the basis of a performance during a run-up of the combustion engine, and on the basis of a performance during an overrun of the combustion engine. A start-up process of the combustion engine is enabled at the start-up enabling time point. Advantageously, this ensures that, when the combustion engine has been turned off, the combustion engine is only started up again if it has been ensured that energy generated by starting the combustion engine can be reliably absorbed in the energy accumulator during a run-up and an overrun. 
         [0025]    Further features, possibilities for application and advantages of the invention can be found in the following description of embodiments of the invention, which are shown in the figures of the drawing. All the features that are described or shown, taken in isolation or in any desired combination, form the subject matter of the invention, independently of the manner in which they are worded or shown in the description or in the drawings, respectively. For functionally equivalent variables and features, the same reference signs are used in all the figures, even in different embodiments. Embodiments of the invention given by way of example are explained in the following, with reference to the drawing, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a schematic block diagram; 
           [0027]      FIG. 2  is a schematic view of a power generating device, a load, and a controller; 
           [0028]      FIGS. 3 and 4  are each power/time diagrams; 
           [0029]      FIG. 5  is a schematic energy/power diagram; and 
           [0030]      FIGS. 6 and 7  are each schematic flow diagrams. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]      FIG. 1  is a schematic block diagram for the operation of a power generating device  2  comprising an combustion engine and an energy accumulator. A turn-off start time  4  for the combustion engine is determined by the block  10  on the basis of an actual power Pq of the combustion engine and on the basis of a state of charge SOC. The block  10  is, for example, part of a controller for the power generating device. A turn-off process of the combustion engine is started at the turn-off start time  4 . 
         [0032]      FIG. 2  is a schematic view of the power generating device  2  and a load  12 , which can also be referred to as an energy sink and is electrically coupled to the power generating device  2 . A controller  14  for operating the power generating device  2  is also shown. The variables  4 , Pq and SOC are supplied to the controller  14 . Furthermore, other variables (not shown) can, of course, also be supplied to the controller  14 . Of course, equivalent variables can also be used instead of the variables  4 , Pq and SOC, or alternatively the variables  4 , Pq and SOC are inherent to the correspondingly used variables. The power generating device  2  comprises an combustion engine  16  that is designed in particular as a gas motor or gas turbine. The combustion engine  16  is mechanically coupled to a generator  20  according to the mechanical connection  18 , the generator  20  supplying electrical energy to an electrical connection  22  which can be designed, in particular, as a direct-current network. The electrical connection  22  interconnects the generator  20 , the load  12 , and an energy accumulator  24  within the meaning of an electrical coupling. The electrical connection  22  comprises cable connections, converters and similar devices in order to allow energy to be exchanged between the units  20 ,  12  and  24 . The variables Pq and SOC relate to the electrical level according to the connection  22 . Of course, the device  2  can comprise a plurality of drives, even of different kinds, which supply energy to the connection  22 . Accordingly, a plurality of loads  12  can also be connected to the power generating device  2 . A plurality of energy accumulators, even of different kinds, are also conceivable. 
         [0033]      FIG. 3  is a schematic power/time diagram. By way of example, two curves  26  and  28  of the actual power Pq of the combustion engine  16  are shown. The curve  26  has a higher value of actual power Pq than the curve  28  during normal operation  30 . From the turn-off start time  4 , a turn-off process  32  or  34  is started that ends at a time point  36  for the curve  26  and ends at a time point  38  for the curve  28 . At the time points  36  and  38 , the combustion engine  16  is substantially turned off and no longer outputs any power. 
         [0034]    In particular, a gas motor should not be turned off immediately, and a step-like curve of the actual power Pq arises, which is shown, in the present case, in an idealised manner in the regions of the turn-off process  32  and  34 . At the turn-off time point  4 , on the basis of the actual power Pq turn-off processes  32  and  34  of different lengths arise that result in different amounts of generated energy. Shortly before or at the time point  4 , on the basis of the actual power Pq of the combustion engine  16  a corresponding estimated value  40  for the energy that is still anticipated is formed, which value can, in the present case, be determined for example as an integral below the curves  26  or  28  in the region of the turn-off processes  32  or  34 , respectively. The turn-off processes  32  and  34  can each also be referred to as an overrun. 
         [0035]      FIG. 4  is schematic view of a power/time diagram. A curve  42  of the actual power Pq of the combustion engine  16  over time is shown. At a start-up enabling time point  44 , the generator  20  receives energy from the energy accumulator  24  in order to start the combustion engine  16 , as a result of which a negative curve  42  arises. An estimated value  46  for the reception of energy from the energy accumulator  24  is found from a negative integral. 
         [0036]    From a time point  48 , the combustion engine  16  outputs energy to the connection  22  and increases the energy output up to a minimum continuous power Pqmin at a time point  50 . 
         [0037]    From the time point  50 , the curve  42  remains at the level of the minimum continuous power Pqmin up to a time point  52 , in order to fall to a value of zero from the time point  52  up to the time point  54 . 
         [0038]    For a run-up of the combustion engine  16  from the time point  48  up to the time point  50 , an estimated value  56  for the energy outputted by the combustion engine  16  in the time period between the time points  48  and  50  is determined. An estimated value  58  is also determined that ascertains the energy output by the combustion engine  16  between the time points  50  and  52 . A further estimated value  60  is determined in the same way as the estimated value  40   
         [0039]    The composition of the curve  42  depends on the configuration and requirements of the combustion engine  16 . For example, the curve  42  may also be composed only of the parts between the time point  48  and the time point  50  and between the time point  52  and the time point  54 . Pqmin may also be dispensed with. The portions of the curve  42  between the time points  44  and  48  and the between the time points  50  and  52  are therefore optional and are intended to be provided depending on the configuration of the power generating device  2 . In particular, the time point  48  may also be selected as the start-up enabling time point. Therefore, all estimated values between the time points  44  and  54  are totaled to an estimated value  62  that describes a minimum energy output of the combustion engine  16  during a start-up or turn-off of the combustion engine  16 . 
         [0040]    The start-up enabling time point  44  enables the starting or start-up for other functions that determine the starting of the combustion engine  16 . This means that a start-up of the combustion engine  16  is allowed temporally after the start-up enabling time point  44 , but need not necessarily occur. Temporally prior to the start-up enabling time point  44 , a start-up of the combustion engine  16  is prevented. 
         [0041]      FIG. 5  is schematic view of an energy/power diagram having a curve  64 . The diagram or the curve  64  can be stored in the controller  14  as a characteristic map, in order to determine, on the basis of an actual power Pq of the combustion engine  16 , overrun energy Eq that would still be generated by the combustion engine  16  during an overrun or during a turn-off process and that the energy accumulator must be able to safely absorb. The curve  64  arises, by way of example, if it is assumed that there is a substantially triangular area under the curves  26  and  28  according to  FIG. 3  in the regions  32  and  34 . 
         [0042]    In the same way, an energy/power diagram and a corresponding characteristic that is similar to the curve  64  can be determined for the estimated value  62  from  FIG. 4 . 
         [0043]      FIG. 6  is a schematic flow diagram. During normal operation  30  of the power generating device  2 , a block  66  is carried out. Two blocks  68  and  70  are arranged in the block  66 . The block  68  determines, from the actual power Pq, the estimated value  40  for energy Eq that is generated by the combustion engine  16  during an overrun  32 ,  34 . The estimated value  40  is also referred to as the first estimated value. The block  70  determines, on the basis of the state of charge SOC, a second estimated value  72  for energy that the energy accumulator  24  can reliably absorb during the overrun  32 ,  34 . The energy received by the load  12  is indirectly observed by means of the second estimated value  72  being determined. 
         [0044]    The second estimated value  72  can, of course, be linked to a fixed value; for example, the fixed value can be added to the second estimated value  72  in order to carry out an adjustment to the particular type of energy accumulator  24  and to thus improve operation of the energy accumulator  24  by means of a desired target state of charge. Specifying a fixed value in such a manner may be necessary for deliberately discharging the energy accumulator  24 , in particular when taking the power generating device  2  out of operation in a planned manner. 
         [0045]    At a branching point  74 , the first estimated value  40  and the second estimated value  72  are compared with one another. If the first estimated 40 is greater than the second estimated value  72 , a transition is made to the branching point  76 . If the first estimated value  40  is no greater than the second estimated value  72 , a transition is made to the block  78 . The block  78  enables a further increase in the actual power Pq. 
         [0046]    In order to protect the energy accumulator  24 , the aforesaid condition for transitioning to the branching point  76  can be AND-linked to the following condition: the actual power Pq of the combustion engine  16  is greater than a maximum charging capacity of the energy accumulator  24 . Of course, a direct transition to a state  80  can also be made. 
         [0047]    Starting from the branching point  76 , a transition is made to a block  80 , and the turn-off process  32 ,  34  is started if the actual power Pq of the combustion engine  16  is lower than the minimum continuous power Pqmin of the combustion engine  16 . This prevents the combustion engine  16  from remaining in an operative state that is beyond the specification of the combustion engine  16 . Of course, a transition can also be made from the branching point  74  directly to the state  80 , the turn-off process  32 ,  34  being started if the first estimated value  40  is greater than the second estimated value  72 . 
         [0048]    If, at the branching point  76 , the actual power Pq of the combustion engine  16  is greater than the minimum continuous power Pqmin, the actual power Pq of the combustion engine  16  is reduced in a block  82 , in particular as a function of an increasing state of charge SOC of the energy accumulator  24 . 
         [0049]      FIG. 7  is a schematic flow diagram. A transition is made from a state  84 , in which the combustion engine  16  is turned off, to a block  86 . 
         [0050]    In a block  88 , the estimated value  62  from  FIG. 4  is generated. Of course, the estimated value  62  can also be stored as a fixed value. A block  90  determines, on the basis of the state of charge SOC of the energy accumulator  24 , an estimated value  92  for the energy that the accumulator  24  can still reliably absorb at the present point in time. 
         [0051]    At a branching point  94 , the estimated values  62  and  92  are compared with one another. If the estimated value  62  is no greater than the second estimated value  92 , a transition is made to the block  96 , in which a start-up process of the combustion engine is then enabled at the start-up enabling time point  44  or  48 . This ensures that a specification of the gas motor with regard to its performance when being started up and turned off can be readily adhered to, since the generated energy can be absorbed by the energy accumulator  24 . Of course, the start-up time point can also occur later if this allows for a more advantageous operation of the power generating device  2 .