Process for controlling a plurality of turbo engines in parallel or tandem operation

Abstract

A plurality of turbo engines (1, 2, 3) cooperate in a station, and each turbo engine with the drive machine (4, 5, 6) driving it forms a machine unit, with which a machine controller (28, 29, 30) is associated. To control these turbo engines (1, 2, 3) in parallel or tandem operation to observe at least one process variable, which is preset by the station and is common to all turbo engines (1, 2, 3), the preset, common process variable is set directly to each of the machine controllers (28, 29, 30), and this preset, common process variable is controlled exclusively via the machine controllers (28, 29, 30) associated with the particular machine unit.

Description

FIELD OF THE INVENTION

[0001] The present invention pertains to a process for controlling a plurality of turbo engines cooperating in a station in parallel or tandem operation for observing at least one process variable that is preset by the station and is common to all turbo engines, wherein each turbo engine with the drive machine forming it forms a machine unit, with which a machine controller is associated.

BACKGROUND OF THE INVENTION

[0002] A process for operating a plurality of turbocompressors connected in parallel, which are provided each with a surge limit control to prevent surge, is described in EP-B 0 132 487. The turbocompressors are controlled jointly by load distribution controllers and individually by a pressure controller each. The load distribution controllers control the setting of the compressors among each other such that there are equal distances between the working point and the blow-off line for all compressors. Only one of the compressors is controlled by its pressure controller, whereas the others are adjusted by the load distribution control.

[0003] A process for the optimized operation of a plurality of compressors in parallel or tandem operation has been known from EP-B 0 431 287. Using algorithms, a combination of machine parameters in which the total shaft power of all drive machines becomes minimal is determined here for any working point. A higher-level master controller is used in this process.

[0004] A higher-level master controller, also called master controller, is bound to be always necessary according to the hitherto common state of the art in case of the tandem or parallel connection of turbo engines with individual control devices and individual controllers. The master controller has a higher-level task. It determines the necessary adjusting commands for the individual machine units from the required total capacity (desired pressure or desired flow of all compressors). Especially in the case of plants of an asymmetric design, the master controller calculates different manipulated variables for the individual machine controllers. According to the pertinent state of the art, it is emphasized time and time again that there must be only one controller for distributing the load among different compressors, which controller processes only one set point and only one actual value, because conflicts may otherwise arise in the downstream machine controllers. Each machine unit needs an unambiguous manipulated variable, which is coordinated with the other manipulated variables such that no conflicts can arise. In case of flow control, the flow may be measured at a single point only. In case of pressure control, the pressure may likewise be measured at a single point only. There may also be only a single set point for the common pressure or flow controller. Observing this rule is particularly important especially in case of use as a pressure controller for the final pressure or the suction pressure. If each machine unit were equipped with a pressure controller of its own, and if the set point of the pressure and the actual value of the pressure deviated even only slightly between the different controllers, which may be caused even by the analog/digital conversion of the input signals alone, the controllers of the parallel-connected compressors would work against each other such that one controller would slow down the machine and the other would speed it up. The machine controllers with their downstream machines work against each other until one of the two machines reaches the upper or lower limit of capacity. Moreover, the master controller is a complicated component, whose failure leads to the stoppage of the entire plant.

SUMMARY OF THE INVENTION

[0005] The basic object of the present invention is to simplify the control of this type, to increase the availability of the individual controllers and to avoid colliding interactions between the controllers.

[0006] According to the invention a process is provided for controlling a plurality of turbo engines cooperating in a station in parallel or tandem operation to observe at least one process variable, which is preset by the station and is common to all turbo engines. Each turbo engine with the drive machine forming it forms a machine unit, with which a machine controller is associated.

[0007] A master controller affecting all turbo engines for controlling the process variable is done away with in the process according to the present invention by the functionality of this process variable controller being divided among the individual machine controllers. The algorithm for the distribution of the load among the individual compressors, which takes place exclusively in the master controller according to the known state of the art, is embodied according to the present invention in every individual machine controller. The flow, the final pressure, the suction pressure, the pressure ratio, the temperature, the level in a tank, the power of the drive machine or the load distribution of the compressors can be used as the process variable individually or in a combination. Since storage space and computing power are available to a sufficient extent with modern hardware, there are no restrictions in this respect. Due to the elimination of the higher-level master controller, an existing station can be expanded by additional machine units without problems. Only a machine unit with a machine controller is to be added, which machine controller contains the same control and regulation as each of the existing machine units. No investment, operating or maintenance costs arise due to the use of the process according to the present invention. The elimination of the master controller is likewise unlikely to lead to disturbances in operation in a station. Since there are no higher-level and lower-level controllers, colliding interactions between different controllers are eliminated. The process according to the present invention is applicable to the parallel operation, the tandem operation and the combined parallel and tandem operation of the turbo engines in a station.

[0008] Further advantages of the present invention will be mentioned in connection with the following description of exemplary embodiments of the present invention and the state of the art, which are shown in the drawings. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In the drawings:

[0010] FIG. 1 is a system diagram of a control system for compressors in parallel operation according to the state of the art;

[0011] FIG. 2 is a system diagram of a control system in tandem operation according to the state of the art;

[0012] FIG. 3 is a signal flow diagram for the control system according to FIG. 1 or 2;

[0013] FIG. 4 is a system diagram of a control system for compressors in parallel operation according to the present invention;

[0014] FIG. 5 is a system diagram of a control system for compressors in tandem operation according to the present invention;

[0015] FIG. 6 is a system diagram of a system for surge limit control according to the state of the art;

[0016] FIG. 7 is a signal flow diagram for the control system according to FIG. 4 or 5;

[0017] FIG. 8 is a system diagram of a control system for compressors in parallel operation according to another embodiment of the present invention;

[0018] FIG. 9 is a system diagram of a control system for compressors in parallel and tandem operation;

[0019] FIG. 10 is a system diagram of a control system for compressors in parallel and tandem operation, where the control of one of the compressors is faded in; and

[0020] FIG. 11 is a control system for compressors in parallel and tandem operation, where the control of one of the compressors is faded in, according to another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Referring to the drawings in particular, FIG. 1 shows three compressors 1, 2, 3 in parallel operation, which are driven by a turbine 4, 5, 6 each acting as a drive machine. One compressor each forms a machine unit with a drive machine. The three machine units are integrated within one station, which may in turn be part of a pipeline system or is bound in a process. The delivery capacity of the compressor 1, 2, 3 can be varied by varying the speed of the turbines. As an alternative, the turbines may also be replaced with motors with a fixed speed, and adjustable guide vanes are used with the adjusting drives 7, 8, 9 in the compressors 1, 2, 3 or butterfly valves are used in front of the compressors (not shown) in this application.

[0022] The compressors 1, 2, 3 are connected by inlet lines 10, 11, 12 to a suction-side bus bar 13, which in turn has a connection to a suction-side process 14 or to a pipeline or to a gas storage unit. On the pressure side, the compressors 1, 2, 3 are connected via outlet lines 15, 16, 17 to a pressure-side bus bar 18, which in turn has a connection to a pressure-side process 19 or to a pipeline or to a gas storage unit.

[0023] A station governor level, which presets as the set point presetter 20 the set points for the operation of the station, is superordinate to the entire station. The actual capacity of the mechanical equipment, usually the final pressure or the suction pressure of the compressor plant or the flow, is measured with a sensor 22 and transmitted as an actual value via a signal line 23 to a master controller 24. The set point of the process variable for the entire station is sent by the set point presetter 20 via a signal line 21 to the machine controller 24, which calculates the necessary load of the individual machine units according to a preset algorithm and presets the set point for the speed or the position of the guide vanes or the throttling fitting for the respective machine controllers 28, 29, 30 via the signal lines 25, 26 and 27. The machine controllers 28, 29, 30 in turn set the speed of the turbines 4, 5, 6 and the position of the butterfly valves or suction throttles to this set point.

[0024] The master controller 24 has a higher-level task. It determines the necessary adjusting commands for the individual machine units from the required total capacity (desired pressure or desired flow) of all three compressors 1, 2, 3. Especially in the case of plants of an asymmetric design, the master controller 24 calculates different manipulated variables for the individual machine controllers 28, 29, 30.

[0025] FIG. 2 shows the case of application for three compressors 1, 2, 3 in tandem operation. The design of this station extensively corresponds to that of the station shown in FIG. 1 for the parallel operation. The difference is only that the first compressor 1 is connected to the inlet line 11 and, via the outlet line 15, to the second compressor 2, and this is connected via the outlet line 16 and the inlet line 12 to the third compressor 3. The suction-side bus bar 13 is not present, and the process 14 is connected directly to the inlet line 10 acting as a suction line. The pressure-side bus bar is likewise absent, and the outlet of the third compressor 3 is connected directly to the process 19 via the outlet line 17.

[0026] According to the known state of the art, exactly the same statements apply to the control of compressors in tandem operation as to the parallel operation. If the compressors 1, 2, 3 are to be run at constant flow in tandem operation, the master controller 24 determines the speeds to which the individual machine units are to be run to reach the desired flow. If the compressors 1, 2, 3 are run at constant final pressure or constant pressure ratio, the master controller 24 determines the pressure ratio that every individual compressor 1, 2, 3 has to reach in order to reach the required total pressure ratio. It also applies to the tandem operation according to the general state of the art that there may be only one master controller, which receives only one set point and one actual value.

[0027] FIG. 3 shows a signal flow diagram for a control system for a station with three compressors 1, 2, 3. The station set point (flow set point or pressure set point) is sent via the signal line 21 and a converter 31 to a variance comparison unit 32. The actual value (measured flow or pressure) reaches the same comparison unit 32 via the signal line 23 and a converter 33. The difference between the set point and the actual value is formed in this comparison unit and is sent to a station controller 34. The station controller 34 adjusts its output variable until the actual value corresponds to the set point. The output of the station controller 34 is sent to the signal lines 25, 26, 27 via percentage setters 35, 36, 37 and converters 38, 39, 40. These signal lines 25, 26, 27 connect the station controller 34 to the three unit controllers 41, 42, 43. Each unit controller 41, 42, 43 has a converter 44, 45 and 46 for the input variable and another input converter (not shown) for the actual value of the machine, typically the speed of the drive turbine 4, 5, 6, or the position of the inlet guide vanes in guide vane-controlled compressors. The difference between the actual value of the machine and the set point of the machine is formed in the comparison units 47, 48 and 49 and is sent to the respective unit controllers 41, 42 and 43. These in turn now adjust the speed of the turbine 4, 5, 6 (or the position of the guide vanes) via converters 50, 51 and 52 such that the actual value of the machine will exactly correspond to the set point of the machine.

[0028] The manipulated variable of the station controller 34 is divided among the individual machine units in the percentage setters 38, 39 and 40. The adjustment law may be linear or nonlinear depending on the needs of the plant. If necessary, it may be dependent on various parameters. A linear adjustment law, according to which the turbines 4 and 6 are each to contribute 30% of the total power and the turbine 5 shall contribute 40%, shall be assumed for simplicity's sake. Consequently, a factor of 0.3 is set in the percentage setters 35 and 37, and a factor of 0.4 is set in the percentage setter 36. Should the station controller 34 call for 10% more power, the machine set point, which is sent to the turbine 4 via the signal line 25, increases by 3%, the machine set point of turbine 5 increases by 4%, and the machine set point of turbine 6 increases by 3%.

[0029] According to FIG. 3, the elements 31 through 40 belong to the common master controller 24, the components 44, 47, 41 and 50 belong to the machine controller 28 of turbine 4 with the compressor 1, the components 45, 48, 42 and 51 belong to the machine controller 29 of turbine 5 with the compressor 2, and the components 46, 49, 43 and 52 belong to the machine controller 30 of turbine 6 with the compressor 3.

[0030] In many applications, the machine controller usually contains an additional control function. For example, a pressure control circuit may be designed such that flow controllers, which control the particular flow through the individual machines, are subordinated to the master pressure controller. Speed controllers, which will then control the speed, are in turn subordinated to these flow controllers. The flow controller associated with the machines is part of the respective unit controller 41, 42, 43 in these applications.

[0031] Each turbocompressor needs a surge limit control, which is part of each machine control and whose task it is to protect the compressor from operating in the unstable working range. The operation in the unstable working range is called compressor surge. FIG. 6 shows a block diagram of a typical surge limit control for a compressor with variable suction pressure. A compressor 53 is equipped with a suction line 54 and a delivery line 55. A blow-by valve 56 in a blow-by line 57 may be opened in a controlled manner when needed, thus increasing the flow through the compressor when the gas consumption by the process is smaller than the minimum allowable compressor flow. A blow-by valve 56, also called surge limit control valve, is actuated via a control line 58 by the surge limiter 59, whose input variables are the inlet pressure measured with the sensor 60, the inlet flow measured with the sensor 61, the final pressure measured with the sensor 62, and the inlet temperature measured with the sensor 63. Since the surge limiter 59 is usually embodied within the same controller hardware as the machine controller (it is an essential part of the machine controller), signals such as compressor flow as well as pressure before and after the compressor are available within the machine controller and can thus be also used for the load distribution controller and the capacity controller.

[0032] FIGS. 4 and 5 show the control process according to the present invention for three compressors 1, 2, 3 integrated to form a station in parallel operation and in tandem operation. As was already described in connection with FIGS. 1 and 2, the compressors 1, 2 and 3 are coupled with turbines 4, 5 and 6 as drive machines and are driven by these. The delivery capacity of the compressor 1, 2, 3 can be varied by varying the speed of the turbine. As an alternative, the drive turbines may also be replaced with motors with a fixed speed, and adjustable guide vanes with the adjusting drives 7, 8, 9 are used in the compressors 1, 2, 3 or butterfly valves are used in front of the compressors (not shown) in this case of application.

[0033] The compressors 1, 2, 3 shown in FIG. 4 are connected by the inlet lines 10, 11, 12 to the suction-side bus bar 13, which in turn has a connection to the suction-side process 14 or to a pipeline or to a gas storage unit. On the pressure side, the compressors 1, 2, 3 are connected via the outlet lines 15, 16, 17 to the pressure-side bus bar 18, which in turn has a connection to a pressure-side process 19 or to a pipeline or to a gas storage unit. According to FIG. 5, the first compressor 1 of the compressors 1, 2, 3 connected in tandem is connected to the inlet line 11 and, via the outlet line 15, to the second compressor 2. This is connected to the third compressor 3 via the outlet line 16 and the inlet line 12. The process 14 is directly connected to the suction line 10, and the outlet of the third compressor 3 is directly connected to the process 19 via the outlet line 17.

[0034] The master controller is eliminated in the control process according to the present invention. The total set point is sent, instead, to each of the machine controllers 28, 29, 30 from the set point presetter 20 of the station directly via the signal line 21. The actual value is likewise sent directly to each machine controller 28, 29, 30 via the signal line 23, so that each machine controller 28, 29, 30 can perform the necessary calculations on its own and can adjust the downstream control units just as if a common, higher-level master controller were used.

[0035] FIG. 7 shows the signal flow diagram for a parallel or tandem connection of three compressors 1, 2, 3 according to the present invention. The station set point of the set point presetter 20 is divided, sent in parallel to three converters 64, 65, 66, and passed on to the comparison units 70, 71, 72. The actual value from the signal line 23 is sent to three converters 67, 68, 69 and passed on to the comparison units 70, 71, 72. In the percentage setters 35, 36 and 37, which are arranged between the converters 64, 65, 66, the set point is divided among the individual machine units, comprising the compressors 1, 2, 3 and the turbines 4, 5, 6. The difference between the set point and the actual value is formed in the comparison units 70, 71, 72 and is sent to an amplifier 73, 74, 75 each to the controllers 76, 77, 78 of the units. The unit controllers 76, 77, 78 adjust in turn the turbine speed or the guide vanes of the respective compressor 1, 2 or 3 via the converters 79, 80 and 81. The converters 67, 64, the percentage setter 35, the comparison unit 70, the amplifier 73, the unit controller 76, and the converter 79 are common parts of the machine controller 28, which is associated with the machine unit, which is formed by the turbine 4 and the compressor 1. The converters 68, 65, the percentage setter 36, the comparison unit 71, the amplifier 74, the unit controller 77, and the converter 80 are common parts of the machine controller 29, which is associated with the machine unit, which is formed by the turbine 5 and the compressor 2. The converters 69, 66, the percentage setter 37, the comparison unit 72, the amplifier 75, the unit controller 78, and the converter 81 are common parts of the machine controller 30, which is associated with the machine unit, which is formed by the turbine 5 and the compressor 3.

[0036] The actual value and the set point of the process variable may be any variables as inputs of the converters 67 through 66. They are frequently the flow through the compressors, the pressure before or after the station, but they may also be the load distribution of the compressors in tandem or parallel operation. The pressure ratio of the entire station or a temperature or a liquid level in a tank is also conceivable.

[0037] The essential difference between the state of the art according to FIG. 3 and the present invention according to FIG. 7 is that the master controller 24 shown in FIG. 3 with the elements 31 through 40 may be eliminated altogether, and its function is divided among the machine controllers 28, 29, 30, which are present anyway. The elements 31 through 34 have been eliminated without replacement and are replaced with three elements 64, 70 and 76; 65, 71 and 77 as well as 66, 72 and 78 each. The converters 38 through 46 are eliminated. However, it is much more essential that the functionalities being shown are auxiliary functions embodied purely in software in the machine controllers which are already present anyway.

[0038] The advantages of the solution according to the present invention over the state of the art shall be described below based on an example by comparing the state of the art with the present invention. Three compressors 1, 2, 3 according to FIG. 2 are operated with a control system according to FIG. 3 in tandem operation (state of the art). Each of the compressors 1, 2, 3 shall operate at the beginning of the control process with a pressure ratio of 3. The controlled variable shall be the pressure in the pressure-side bus bar 19. The set point shall be 99 bar and the actual value 90 bar. The compressors 1 through 3 shall contribute one third to the total pressure ratio each. The comparison unit 32 detects a deviation of 9 bar and transmits this to the station controller 34. This station controller 34 increases its power by a percentage that corresponds to an increase in the pressure ratio by 10% from 90 bar to 99 bar, and an increase in the output signal from 45% to 50% shall be assumed here as an example. Each of the three machine units increases its power by the same extent until the measured actual value corresponds to the set point.

[0039] The function will be the following in a system according to the present invention according to FIG. 7. The actual value on the signal line 23 is 90 bar and the set point on the signal line 21 is 99 bar. Via the converters 67 through 69, all three unit controllers (capacity controllers) 76, 77 and 78 receive the same deviation of 9 bar. Each of the three unit controllers 76, 77 and 78 reacts in exactly the same way as the master controller 24 in FIG. 3. Each of the three machine units increases its power by the same extent until the measured actual value corresponds to the set point.

[0040] The final pressure is always controlled in the compressors in tandem operation with variable suction pressure such that the controlled variable is the pressure ratio over the entire station, i.e., the tandem connection of all compressors. The ratio of the pressure ratios of the individual compressors is also the variable to be controlled for the unit controllers in the case of compressors in tandem operation, which are run at constant flow.

[0041] It must be assumed according to the state of the art that problems may arise if the input controllers for the set point and the actual value of the individual unit controllers have different drifts or determine different numerical values for the set point or the actual value of the individual machine controllers due to the incremental analog/digital conversion. A deviation of the total delivery capacity of all compressors from the required power will arise in this case. According to the state of the art, this drawback is considered to be reason for the absolute need for a higher-level master controller. This drawback was pointed out already in the introduction in connection with the use of three individual pressure controllers.

[0042] This problem is solved according to the present invention by the use of a load distribution controller. This load distribution controller acts in addition to the unit controller 76 through 78 (capacity controller) and uses the same machine controller 28, 29, 30. Only the function of the load distribution controller will be described below with the use of the prior-art functional groups. The combination of capacity controller and load distribution controller will be subsequently described. This load distribution controller has exactly the same design as the unit controller 76 through 78 (capacity controller) according to FIG. 7. However, the set point of a load distribution control is the set point of the load percentage of the compressor and the actual value is the current load. The distance between the working point and the stability limit is usually the controlled variable in the case of compressors in parallel operation, and the pressure ratio is usually the controlled variable in compressors in tandem operation. In the case of a load distribution control for tandem operation according to FIG. 7, the actual value for each machine unit is the particular pressure ratio of the particular compressor, and the set point is the set point of the percentage contributed by the particular compressor to the total pressure ratio. The actual value of the pressure ratio can be determined by dividing the final pressure obtained for the surge limit control by the suction pressure measured for the surge limit control. The total pressure ratio is calculated by dividing the station's outlet pressure by the station's inlet pressure. All compressors are usually operated with the same pressure ratio in tandem operation, so that the set point is one third of the total station pressure ratio for every individual load distribution controller. Should the ratio be different for individual machines, a scaling factor may be taken into account within the set point formation. Should the load percentage of the individual machine units depend on additional process variables, variable scaling factors may be introduced.

[0043] The load distribution algorithm calculates a partial load for each of the compressors and, in the case of compressors in parallel operation, e.g., a preset percentage of the total flow. In tandem operation, the algorithm presets, e.g., a fixed, preset percentage of the total required pressure ratio. The unit controller of each compressor now adjusts the individual machine unit to this value.

[0044] If the actual value processed in the controller deviates from the actual value at which the compressor is actually operating in one of the three unit controllers due to a measurement error or a converter error, all load distribution controllers detect this alleged deviation from the set point of the load distribution, and control this deviation by adjusting all three compressors such that the load distribution controllers will see a uniform load distribution. If the converter 67 delivers, e.g., a value that is too high by 10% for the actual value of unit 1, each of the unit controllers (load distribution controllers) associated with each compressor notices this deviation and adjusts its downstream control unit by the preset ratio. In the equalized state, the machine unit 1 operates in a stable manner with a load that is too low by 6.66%, and the machine units 2 and 3 operate in a stable manner with a load that is too high by 3.33%. The consequence of this is an imbalance of all three compressors. However, this is smaller than the individual error of the machine unit in question.

[0045] The system even operates robustly when the set point and the actual value for each machine unit are determined separately and there are greater deviations between the set points and the actual values of the individual controllers as a result. This represents another advantage of the process according to the present invention. A disturbance in a common actual value measurement affects the operation of all machine units in the station. This also applies to a disturbance in the set point setter. The actual value measurement can be associated with every individual machine unit according to this process. FIG. 8 shows, e.g., an arrangement with individual actual value measurement. Instead of a common actual value measurement in the pressure-side bus bar 18, the actual value (final pressure after the compressors, before the compressors or flow through the compressors) can be measured in the respective outlet lines 15, 16 and 17 with sensors, which are connected to converters 90, 91 and 92. The individual actual values are then sent via the converters 69, 64 and 65 to the comparison units 70, 71 and 72 according to FIG. 7 and are sent to the machine controllers 28, 29, 30. It is also possible to preset the set point individually. Thus, all necessary functionalities are now individually associated with each machine unit. Conversion errors of the set point and actual value determination are compensated in the same manner with the use of the control process according to the present invention as capacity controllers (flow controllers, pressure controllers).

[0046] The advantage of such an arrangement is, on the one hand, that each of the actual value measurements can be associated with one machine unit, and the converters can be supplied with auxiliary energy from the control box of the respective associated machine unit. Furthermore, the corresponding units of the other machine units are active even in case of total failure of set point or actual value converters of one machine unit, and they reduce as a result the negative effects of this failure. It is also possible to form the set point and the actual value separately for each machine unit. It is advantageous that there are no common components any more and only identical machine systems without higher-level system parts are used.

[0047] The above-described case shall be mentioned as an example with the use of the unit controller as a pressure controller. The desired final pressure is 99 bar. The compressors 1 through 3 shall contribute each one third of the total power currently needed. Each turbine 4 through 6 shall contribute for this 20% of the total available power each. Now let the actual value measurement fail in the delivery line 17 of the compressor 3 and furnish an actual value of 0 bar. The turbine 6 runs up to its maximum power because of the missing actual value and contributes 33% of the total power as a result. The pressure rises as a result in the pressure-side bus bar 18 and so does consequently the final pressure of all compressors 1, 2 and 3. The two intact measuring means in the compressor outlet lines 15 and 16 of the compressors 1 and 2 notice this increase and reduce the power of the compressors 1 and 2 to the extent that the final pressure of all three compressors 1, 2, 3 will again correspond to the set point of 99 bar. A station that is controlled according to the state of the art by means of a master controller brings all compressors to 100% power in this case of operation. The same thing happens in case of failure of a set point. A master controller brings all machines to zero and the entire station ceases to offer any power any longer. In case of a control according to the present invention, the power of the compressor whose set point drops to zero will drop the zero, the other two compressor controls notice this deviation and eliminate it by increasing their own power, so that the operation of the station as an entirety is not affected.

[0048] The advantage of the solution according to the present invention is obvious; the master controller can be eliminated, as a result of which costs are saved and the availability is increased. Moreover, this process offers the advantage that a common actual value measurement and a common set point generation are eliminated and both the actual value measurement and the set point setting are associated with each compressor unit. Furthermore, it is very essential that the availability is increased and the entire plant is less liable to fault.

[0049] Some variants and embodiments for the distribution of the load among the individual compressors will be described below.

[0050] It is necessary in many applications to have the possibility of affecting the percentage contributed by the individual machine units to the total load. In some cases, the personnel presetting the operating characteristics of the station may intentionally affect the load percentage of individual machine units. If, e.g., a machine unit shall be put out of operation, it is meaningful to reduce the percentage contributed by that unit to the total load. This may happen by adding to the summing unit 70, 71 or 72 a fixed value to offset the equilibrium. The result of this is that the load distribution controller will no longer load all machine units uniformly, but differently. An example is as follows: Each of the three compressors operates with one third of the total pressure ratio in tandem operation without this offset. If an offset variable of minus 20% is now added to the summing unit 71 (for the middle compressor), the three machine controllers will make adjustments until the pressure ratio of the middle compressor becomes exactly 20% smaller than that of the other two.

[0051] Another possibility is to preset the set point individually and differently for the load distribution for each of the compressors. This may be necessary, e.g., when there is an asymmetry in the machine units. For example, machine units of various sizes may operate together in one station. The factor must be adapted to the size of the machine units in this case.

[0052] Another possibility is for an optimizing algorithm to determine a combination of the machine load of the individual machine units that is optimal for the particular working point. Such optimizing algorithms are described, e.g., in EP-B 0 431 287, which was mentioned in the introduction. If the present invention is applied to this prior-art process, a higher-level computer and master controller may be eliminated even in the prior-art process if the algorithm is programmed in each machine controller.

[0053] Another need for interfering with the selection of the load distribution among the individual machine units may also be encountered, e.g., when a limit of the permissible operating range is reached at one of the components. If, e.g., gas turbines of various designs are used as drive machines for compressors, one of the gas turbines may have reached, e.g., the maximum exhaust gas temperature, while the other gas turbines still have reserves for adjustment. The present invention offers two approaches to solving this problem. One approach is that the factor for the splitting of the load among the machine units that are not at the limit is changed such that the factors are increased at the ratio of the machine units that are no longer available. The factor for the machine operating at the limit is set to zero as long as the machine is being operated at the limit. However, the process according to the present invention also compensates this process without this intervention. Since the unit being operated at the limit does not offer any power any longer, the capacity controller determines a deviation from the set point and increases the power of the other unit such that the process variable to be controlled will exactly correspond to the set point. The control unit and the point of intervention for all these offsetting factors are the percentage setters 35 through 37 and the addition of a fixed value to the summing units 70 through 72.

[0054] FIGS. 9 through 11 show three parallel-connected compressors of the low-pressure stage (LP-A, LP-B, LP-C) with three parallel-connected compressors of the medium-pressure stages (MP-A, MP-B, MP-C) and three parallel-connected compressors of the high-pressure stage (HP-A, HP-B, HP-C) connected in tandem. The control system for the compressor MP-B is enlarged in FIGS. 10 and 11. The usual compressors are equipped with an identical control system. Each compressor is provided with a surge limit control, which was already described in connection with FIG. 6. Furthermore, a machine controller 85 is associated with each machine unit comprising a compressor and a turbine.

[0055] A sensor for determining the actual value of the final pressure of the station is arranged in the pressure-side bus bar 18. The measured value is sent to a converter 86, which is connected to a comparison unit 88 via a signal line 87. In addition, the set point of the final pressure is sent to this comparison unit 88 by the set point presetter.

[0056] Furthermore, a sensor for determining the actual value of the flow of the station is arranged in the pressure-side bus bar 18. The measured value is sent to a converter 89, which is connected to a comparison unit 91 via a signal line 90. In addition, the set point of the flow is sent to this comparison unit 91 by the set point presetter.

[0057] A sensor for determining the actual value of the suction pressure of the station is arranged in the suction-side bus bar 13. The measured value is sent to a converter 92, which is connected to a comparison unit 94 via a signal line 93. In addition, the set point of the suction pressure is sent to this comparison unit 94 by the set point presetter.

[0058] The signal line 93 of the suction pressure and the signal line 87 of the final pressure are led to a computing site 95, in which the total pressure ratio is calculated. The pressure ratio may be additionally rated with a fixed factor or even a factor that depends on other variables. The factor is 1/3 in the first approach, i.e., all three compressors are loaded equally. A signal line 96, which is led to a computing site 97, is branched off after the converter 62 for the final pressure of the compressor MP-B. A signal line 98, which is likewise led to a computing site 97, is branched off after the converter 61 for the suction pressure of the compressor MP-B. The pressure ratio of an individual compressor is determined in the computing site 97. The computing sites 95 and 97 are connected to a comparison unit 99, in which the individual pressure ratio of this compressor MP-B is compared with its percentage set point relative to the total pressure ratio (which is rated with a factor).

[0059] A signal line 100 is led from the surge limiter 59 to a computing site 101. The signal line 100 carries a signal containing the distance of the working point of an individual compressor. In addition, the corresponding signals of the other parallel-connected compressors are sent to the computing site 101. The mean value of the distance of the working points is determined in the computing site 101. The mean value of the distances is compared with the individual value of a compressor in a comparison unit 102. The comparison units 88, 91, 94 are connected to a summing unit 104 via signal lines, in which a changeover switch 103 each is arranged. The comparison units 99, 102 are connected to a summing unit 106 via signal lines, in which a changeover switch 105 each is arranged. The summing units 104 are also connected to the summing unit 106.

[0060] Via a signal line 107, in which a manual intervention means 108 is arranged, the summing units 104, 106 are connected to the machine controller 85, which belongs to a machine unit and performs the functions of a capacity, final pressure, suction pressure, flow and load distribution controller.

[0061] The control system shown in FIG. 11 also contains additionally a maximum selection means 109 and a minimum selection means 110 in order to limit the speed and the load of the drive machine or other variables.

[0062] In the control system being shown for the tandem or parallel operation, the capacity control and the load distribution control of the station are performed by a single machine controller each which is associated with each machine unit. Deviations for the capacity control, the load distribution control in parallel operation and the load distribution control in tandem operation are formed by the machine controller. Three different capacity control algorithms (flow control, final pressure control after the high-pressure compressor and suction pressure control before the low-pressure compressor) can be selected in this control system. Since the capacity controller can control only one variable, the other two deviations of the capacity control are switched to zero via the switches 103. A mutual interlocking is meaningful here. If, e.g., the flow control shall be active, the deviation for the suction pressure control and the final pressure control is switched to zero. As an alternative, the set point for the non-active controller may also be switched to the actual value. This also causes the deviation to become zero.

[0063] The same thing happens if one of the load distribution controllers is to be deactivated. The corresponding deviation is simply switched to zero. This can be done in an elegant manner by switching the optimizing variable (actual value of the load distribution) to the set point. The same thing also happens when a compressor is out of operation. The load distribution controllers of the other compressors simply assume that the compressors that are out of operation are optimized and therefore do not affect the load distribution among the other compressors.

[0064] It is also possible to operate the machines exclusively by manual operation. All deviations are switched to zero for this purpose, i.e., all controllers are switched off. The manual intervention means shown in FIGS. 10 and 11 can be used to impose an artificial deviation as an actuating variable in a manually controlled manner. The particular machine controller follows this difference as long as the variable is present. Since the controller usually also has an integral behavior (PI--proportional, integral or PID--proportional, integral, differential controller), the integral part of the controller responds to this fixed deviation in the input by continuously adjusting the output. In a special embodiment, this manual adjustment can act only on the integral part of the controller, so that the proportional (P) and the differential percentage (D) do not respond to this manual intervention. As an alternative, the manual adjustment may also be performed by switching the controller 85 to "Manual."

[0065] An example shall be described below for illustration. The compressors in tandem are called the low-pressure (LP) compressor, medium-pressure (MP) compressor and high-pressure compressor (HP). The parallel-connected compressors are called A, B, C. It shall be assumed that the plant is in the flow control mode and all compressors are in operation.

[0066] The flow set point shall be 2% greater in parallel operation than the actual value, and compressor LP-A shall deliver exactly 1/3 of the total mass flow, compressor LP-B 5% too little, and compressor LP-C 5% too much. Compressor MP-A and compressor MP-B shall deliver 30% of the mass flow and compressor MP-C shall deliver 40%. Each of the HP compressors shall deliver an equal mass flow.

[0067] In tandem operation, compressor LP-A shall be loaded 2% too low, compressor MP-A shall be loaded correctly, and compressor HP-A shall be loaded 2% too high. Compressor LP-B is loaded correctly, compressor MP-B is loaded 3% too high, and compressor HP-B 3% too low. Compressor LP-C shall be loaded at a rate of 29%, MP-C at 36%, and HP-C at 35%.

[0068] The following deviations become established on the summing units:

1 Summing unit of compressor MP-B HP-A HP-B HP-C Capacity +2 +2 +2 Parallel +2 0 -2 Tandem -2 +3 -1.7 MP-A MP-B MP-C Capacity (104) +2 +2 +2 Parallel (102) +3.3 +3.3 -6.6 Tandem (99) 0 -3 -3.3 LP-A LP-B LP-C Capacity +2 +2 +2 Parallel 0 0 0 Tandem +2 0 +5.1

[0069] The control algorithm now forms the resulting deviation before the controllers. The following is obtained from this:

2 HP-A HP-B HP-C Capacity +2 +2 +2 Parallel +2 0 -2 Tandem -2 +3 -1.7 Sum +2 +5 -1.7 Capacity +2 +2 +2 Parallel +3.3 +3.3 -6.6 Tandem 0 -3 -3.3 Sum +5.3 +2.3 -7.9 Capacity +2 +2 +2 Parallel 0 0 0 Tandem +2 0 +5.1 Sum +4 +2 +7.1

[0070] Despite the sometimes conflicting requirements of the individual control tasks (the capacity controller requires an increase in power, the load distribution controller a reduction), each machine controller receives an unambiguous adjusting command in the necessary direction in order to reach the optimum. An interaction between the different requirements is ruled out by design.

[0071] In another embodiment, additional algorithms may be added as well. The drive machines of one or more compressors may reach, e.g., a power limit. This can be additionally processed in the algorithm such that the deviation of the machine controllers of the drive machines, which are being operated at the limit, are brought to zero (as in manual operation). These drive machines will then not participate in a further power increase any longer. To compensate this effect, the difference between the optimal adjusting difference according to the above table and the actual effective difference can be added to the deviation of the other parallel and tandem compressors. This intervention is thus optimally compensated as well. The process also functions, of course, for a plurality of limiting controllers per machine unit.

[0072] In another embodiment, the limiting controllers may be switched, as is shown in FIG. 11, via an extreme value selection means (maximum selection or minimum selection means). In addition to the above-described deviations, deviations for the distances of the working points from the limits are formed, e.g., from the maximum speed and the minimum speed in FIG. 11. In addition, the formation of another deviation each for a maximum limitation and a minimum limitation are shown. The deviations for limitations to maxima are switched to a minimum selection, and the deviations for a minimum limit act on a maximum selection. The effective deviation for the machine controller is thus either the deviation according to the above algorithm or the distance of the working point from the limit when this distance is shorter. When a limit is exceeded, the output of the max/min selection means 109/110 also always controls the machine unit in case of conflicting requirements of capacity or load distribution controllers primarily such that the limit is not exceeded in steady-state operation.

[0073] According to the above example, the power of compressor LP-C shall be increased by a deviation of 6.3%. However, the drive turbine shall be 3% below the maximum operating speed. The effective deviation is thus limited to 3%. As soon as the turbine has reached the maximum operating speed, the deviation of the speed limiting control becomes zero and prevents any positive deviation on the machine controller via the minimum selection. Only negative deviations in the direction of a speed reduction can occur. When the maximum speed is exceeded, the controller of the unit reduces the speed.

[0074] It may be occasionally necessary for the individual control circuits (pressure controller, flow controller, load distribution controller in tandem, load distribution in parallel) to be set to different control parameters, because the path time behavior of the control system is different for the individual controlled variables. This can be achieved in a simple manner by imposing different gain factors on the particular deviations. If, e.g., the deviation of the pressure controller is multiplied by a factor of 1, the deviation of the flow controller by a factor of 2, and that of the load distribution controller by a factor of 3, this causes the circuit gain of the load distribution controller to become 3 times that of the pressure controller.

[0075] If the controller adjustment time is to be adapted individually, this can be achieved in a simple manner. The variable that is the leading variable can be identified from a comparison of the individual inputs of the maximum and minimum selection with the output. The position of the changeover switch for the deviations of the capacity controllers and the load distribution controllers makes it possible to determine which of these controllers is in operation. A selection matrix can now determine which controller adjustment time shall be effective at which controller combination. The controller time constant effective in the machine controller can now be accurately adjusted adaptively as is required by the selection matrix.

[0076] FIG. 11 shows an application with a total of nine control circuits. If such a system were composed of nine individual controllers according to the state of the art, extensive adjustments and mutual interlocking, which would prevent individual non-active controllers from running into saturation, would be necessary. Furthermore, there is a risk that the nine controllers will mutually dynamically affect each other. All these drawbacks are circumvented according to the present invention. There is only one machine controller per machine unit. Any adjustment can be eliminated, and an interaction between controllers cannot occur, either. The machine controllers of the other compressors cannot mutually affect each other, because all machine controllers are set to the same parameters for the same controlled variables. Since all load distribution controllers are optimized with the same parameters, they have the same time characteristic. Consequently, it cannot happen that individual machines run in different directions and consequently against each other.

[0077] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

Claims

What is claimed is:

1. A process for controlling a plurality of turbo engines cooperating in a station in parallel or tandem operation to observe at least one process variable, the process comprising: presetting at least one process variable common to all turbo engines of the station; forming a machine unit of each turbo engine with a drive machine, with which a machine controller is associated; sending the preset common process variable directly to each of the machine controllers; and controlling the preset common process variable based on a deviation of the preset common process variable and an actual value associated with the variable sensed at the particular machine unit exclusively via the machine controllers associated with the particular machine unit.

2. A process in accordance with claim 1, wherein the final pressure of the compressors is used as the process variable.

3. A process in accordance with claim 1, wherein the flow through the compressors is used as the process variable.

4. A process in accordance with claim 1, wherein the suction pressure of the compressors is used as the process variable.

5. A process in accordance with claim 1, wherein the pressure ratio of the compressors is used as the process variable.

6. A process in accordance with claim 1, wherein the load distribution in parallel operation is used as the process variable.

7. A process in accordance with claim 1, wherein the load distribution in tandem operation is used as the process variable.

8. A process in accordance with claim 1, wherein the power of the turbines used as drive machines is used as the process variable.

9. A process in accordance with claim 1, wherein the inlet pressure of the turbines used as drive machines is used as the process variable.

10. A process in accordance with claim 1, wherein the outlet pressure of the turbines used as drive machines is used as the process variable.

11. A process in accordance with claim 1, wherein the tapping pressure of the turbines used as drive machines is used as the process variable.

12. A process in accordance with claim 1, wherein the flow through a turbine used as a drive machine is used as the process variable.

13. A process in accordance with claim 1, wherein the current of an electric drive machine is used as the process variable.

14. A process in accordance with claim 1, wherein a plurality of process variables are combined within a station.

15. A process in accordance with claim 1, wherein the output variables of the capacity controllers are at the same ratio to one another in order to reach a uniform load of all machines.

16. A process in accordance with claim 1, wherein the set points for the load distribution controllers are at a fixed but not equal ratio to each other in order to reach a predetermined, nonuniform load of all machines.

17. A process in accordance with claim 1, wherein the factor by which the set points of the load distribution controllers deviate from each other is a function of a process variable in order to reach a desired load of all machines.

18. A process in accordance with claim 17, wherein the power of the turbine used as the drive machine is used as the influencing process variable.

19. A process in accordance with claim 17, wherein the distance of a process variable from a limit or any other optimization algorithm is determined.

20. A process in accordance with claim 1, wherein the factor by which the set points of the load distribution controllers deviate from each other can be influenced arbitrarily in order to reach a desired load of all machines.

21. A process in accordance with claim 1, wherein set points and actual values are preset and measured jointly for all machine units.

22. A process in accordance with claim 1, wherein set points and actual values are preset and measured individually for each machine unit.

23. A process in accordance with claim 1, wherein one deviation is selected among the deviations of a plurality of process variables and the other, not needed deviations are switched to zero.

24. A process in accordance with claim 1, wherein one deviation is selected among the deviations of a plurality of process variables, and the set point of one of the non-selected process variables is switched to zero.

25. A process in accordance with claim 1, wherein the deviations of all process variables are switched to zero and that the control is performed manually.

26. A process in accordance with claim 23, wherein a machine controller with a proportional part and an integral part is used and the control is performed manually such that the manual intervention acts only on the integral part.

27. A process in accordance with claim 1, wherein the deviation of the machine controllers of the machine units, which are operated at the upper power limit, is reduced to zero, and that the actually effective deviation is added to the deviation of the other machine units.

28. A process in accordance with claims 1, wherein the deviation is switched via an extreme selection.

29. A process in accordance with claim 1, wherein the deviations for limitations are switched to a maxima of a minimum selection and that the deviations for a minimum limit act on a maximum selection.

30. A process in accordance with claim 1, wherein the deviations for different process variables are multiplied by different gain factors.

31. A process in accordance with claim 1, wherein the adjustment time of the controllers is adapted individually such that the process variable that is the leading process variable is determined from a comparison of the individual inputs of the maximum and minimum selection with the output and the controller that is in operation is determined from the position of changeover switches of the controllers for the process variables, and it is determined via a selection matrix of control functions which adjustment time shall be effective at which controller combination.

32. A control system for a plurality of turbo engines, comprising: a plurality of turbo engines cooperating in parallel or in tandem and forming a turbo engine station; a machine unit formed by each turbo engine, each machine unit including a drive machine driving the operation of the turbo engine; a machine controller at each a machine unit; a station input for at least one process variable to control the turbo engines in parallel or tandem operation, the at least one process variable being preset by the station and being in common to all turbo engines; connections for setting the preset common process variable directly to each of the machine controllers with the preset common process variable being controlled exclusively via the machine controllers associated with the particular machine unit.