Abstract:
A modular system for the control of at least one compression system for the compression a fluid medium, said compression system comprising compressors (C 1 -C 7 ) and their controllers (A 1 -A 7 ) for the compression of the fluid medium, secondary treatment devices for the treatment of the medium delivered from the compressors, and piping systems ( 17 - 19, 23 ) for conducting the fluid medium to a place of consumption ( 16, 22 ), said control system comprising a control unit ( 3 ) containing a data processing system ( 34 ) for controlling the compression system, a user interface ( 35 ) including a display associated with it and transmission means for the transmission of control data between the control unit, the controllers and pressure sensors. The transmission means consist of data communication buses, preferably serial communication buses ( 30 - 32 ) and a data communication port unit ( 33 ) serving to connect the bus to the control unit ( 34 ). The controllers and pressure sensors are connected to common data communication buses.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a continuation of application Ser. No. 10/470,996, filed Oct. 14, 2003, which was a national phase filing of PCT/FI02/00082, filed 4 Feb. 2002, which was based on Finland Application No. 20010199, filed Feb. 2, 2001. All priorities are claimed. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method for controlling a compression system for the compression of a fluid medium. 
   2. The Prior Art 
   In industrialized countries, about 10% of the electric energy consumed by industry is spent on the production of compressed air. In addition, compressed air is a critical production factor, and consequently quality problems appearing in compressed air are in many cases economically much more significant than the energy spent on producing it. Ineffective use of compressed air has been found to be a significant problem in many countries. 
   In the compression systems of compressed air networks, compressors are used to produce compressed air, which is conducted via a cooler and a pressure tank into a secondary treatment apparatus, which is provided with filters and driers, and into a second pressure tank, from where the compressed air is supplied to the place of consumption. The compressors are controlled by means of controllers connected via a data communication bus to a control computer controlling the system. Connected to the computer are additionally e.g. pressure sensors, and the data obtained from these is used in the control of the system. 
   WO specification 91/06762 discloses a compressor control apparatus of this type, which can be connected to a computer. Via a data communication bus, several compressors can be connected to the computer. An individual controller can control the mode of operation of an individual compressor, said modes being on/off-line, modulating operation and deloaded operation. In WO specification 91/06762, each controller of the compressor can be controlled individually by means of signal obtained from a computer. In addition, the apparatus comprises a graphic display, such as a LED display, on which it is possible to present e.g. controller parameters, and the operator of the apparatus can operate it via a user interface by pressing different switches. 
   To save energy in the production of compressed air, various methods have been developed. Among the most typical solutions are standard controllers provided by compressor manufacturers and having their own control programs, which can not be customized to suit other manufacturers&#39; compressors and which comprise no verification of efficiency of control. In addition, partly modular methods have been developed that are customizable for several compressor types and permit the connection of several pressure sensors. There are also measuring methods that can be used to ascertain the benefit regarding energy economy achieved by the control. However, these measuring methods are of a single-operation nature, and they have to be repeated at regular intervals if the aim is to ensure a continuous high quality of performance. The prices of customizable solutions are high due to the large amount of programming work needed, among other things. Under these circumstances, the equipments have to be built in small production series, and consequently they are expensive. 
   A large proportion, even 80% of maintenance visits associated with control systems are attributable to a misuse failure. This is because present control systems are separate systems that, after their introduction, are not maintained except sporadically. When users are changed out for new ones, the training they have once received is no longer useful. This leads to a situation where, in the course of time, even a well performing system does not necessarily answer its purpose. 
   The object of the present invention is to achieve a new type of control system in order to enable the operation of pneumatic systems and equivalent to be rendered more effective on a large scale at a reasonable cost and with limited personnel resources. The details of the features characteristic of the system of the invention are presented in the claims below. 
   SUMMARY OF THE INVENTION 
   In the system of the invention, one or more compressors and the associated secondary treatment apparatus, connected to one or more compressed air networks or equivalent, are controlled and monitored. The system of the invention is based on a modular technique as far developed as possible, utilization of parameters and inter-modular fault diagnostics. By additionally combining these features with a possibility of remote monitoring and programmability, a maximally reliable solution of favorable cost is guaranteed. In addition, the system contains useful analyzing and reporting features that make it possible to verify the benefit provided by the system and to maintain a good performance of the network and to improve it on a continuous basis. 
   Due to its architecture, the system can be constructed from standard components produced by automation manufacturers. The invention allows a decisive reduction to be achieved in the amount of work required at installation time. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     In the following, the invention will be described in detail with reference to the attached drawing, which presents a block diagram of a pneumatic system comprising a control unit  3  according to the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The pneumatic system comprises two compressed air networks  1 ,  2 , which are connected to a control system that controls them. The first network  1  comprises six compressors C 1 -C 6  with their controllers A 1 -A 6 , a pressure tank  11  connected to three compressors C 2 -C 4 , four secondary treatment units  12 - 15 , a place of consumption  16  and piping systems  17 - 19  for their interconnection. The second network  2  correspondingly comprises one compressor C 7  with its controller A 7 , a secondary treatment unit  21 , a place of consumption  22  and a piping system  23  for their interconnection. 
   In addition, both networks are provided with pressure sensors PI 1 -PI 5 , of which PI 1  is connected to the pressure tank piping  17  between compressor C 1  and secondary treatment unit  12 , PI 2  to the pressure tank,  11 , PI 3  to the piping  19  between compressors C 5 , C 6  and secondary treatment unit  14 ,  15 , PI 3  and PI 4  to the place of consumption  16  and PI 5  to the piping  23  between compressor C 7  and secondary treatment unit  21  as well as to the place of consumption  22 , and of pneumatic station controllers AS 1 -AS 3 , of which AS 1  is connected to sensors PI 2 , PI 4 , PI 1  and to secondary treatment unit  13 , AS 2  is connected to controllers A 5 , A 6  and sensor PI 3 , while AS 3  is connected to sensors PI 5 . 
   The above-described controllers and sensors are connected via three serial communication buses  30 - 32  common to both devices to a serial port  33  of the control unit  3  and further to the control computer  34 , which comprises a display and a user interface  35 . The user interface is provided with a user interface program, and the control computer is provided with a group control program and a controller unit. 
   Via the user interface  35 , the user can observe the operation of the pneumatic system, configure the control and monitoring system and output reports concerning the functioning of the system. The control program regulates and controls the pneumatic system via the pneumatic station controllers and compressor controllers, based on the information obtained by means of the data communication devices and programs and on the instructions given by the user. 
   The pneumatic station controller AS 1 -AS 3  reads pneumatic station-specific data, such as pressure and alarm data from the pneumatic system. The compressor controller A 1 -A 7  reads data regarding the compressor and the control commands sent by the control program via the data communication bus  30 - 32  and executes the commands, such as start, stop and load. 
   The number of compressors can be given as parameters to the group control program. The control program need not be altered in any way when compressors are added or removed. This is because, as far as the compressors are concerned, the program has been constructed according to a modular design such that each compressor C 1 -C 7  is an embodiment of its category that, depending on the parameter given, is either commissioned or decommissioned. 
   Each compressor C 1 -C 7  can be configured via the user interface  35  as any compressor type by means of one parameter given. Therefore, when the control system is being configured for the first time or when an individual compressor type is later changed, the control system need not be tailored at all. This is due to the fact that, by means of a single parameter, the above-described embodiments of compressor category can be configured as any basic compressor type. These are two-stage, three-stage and five-stage modulating control and kinetic machine control. 
   It is possible to connect to the control system a required number of pressure sensors PI 1 -PI 5  to read the delivery pressure of each compressor and the desired network pressures. This makes easier to control the compressors and gives a general view of the state of the pneumatic network. Any one of the pressure sensors can be configured to indicate the delivery pressure of any one of the compressors, and any of the pressure sensors can be configured to function as the control pressure of the entire system. The number of pressure sensors can be configured with one value, which is input via the user interface  35 . The addition or removal of pressure sensors does not involve any changes in the control program. 
   Each pressure data item also contains information as to how large a volume it pertains to and what is the rate of change of the pressure. Based on these data, it is possible to calculate the exact change in the amount of compressed air for the volume in question. By computing the change in the amount of air for each volume and combining this information with the data regarding the state of all the compressors, real-time actual consumption of compressed air is obtained. This method considerably improves the accuracy and reacting capability of the control. 
   The control system can control and monitor several separate pneumatic systems  1 ,  2 . This makes it possible to select any one of the pressure sensors PI 1 -PI 5  connected to the system as a control pressure sensor for each compressor C 1 -C 7 , and in addition any one of the compressors can be set via the user interface to be controlled according to a pressure sensor value selected in accordance with separate pressure settings. 
   For each compressor C 1 -C 7  and for the pneumatic system, maximum and minimum pressure limits can be set. When these values are exceeded, control of the compressors is handed over to their own control system. 
   The order in which the compressors C 1 -C 7  are started and loaded is determined by an operating sequence table. The compressors can be set to work in accordance with as many operating sequence tables as desired. This is possible because each individual operating sequence is an embodiment of its category that can be commissioned or decommissioned by changing a program parameter determining the number of embodiments. Therefore, the program need not be altered at all when operating sequences are added or removed. 
   The manner of changing the operating sequence is selected by changing one control parameter. The operating sequence can be changed e.g. on the basis of a weekly calendar, stoppage of compressors or an automatic arrangement. 
   Automatic alternation is based on continuous computation of the required idling power for all compressor combinations possible, which, combined with the observation of the required compressors C 1 -C 7  to be kept active and free selection of the observation interval, results in automatic selection of the most effective operating sequence possible. 
   The method of starting and stopping a compressor C 1 -C 7  can be selected via the user interface. These are pulse starting and stopping and pulse duration, continuous starting and stopping, run-on stopping or stopping based on allowed numbers of starts. 
   The starting, loading and deloading delays for each compressor C 1 -C 7  can be adjusted separately. This allows correct operation of the method in every situation regardless of the pneumatic system&#39;s own dynamics. 
   The information regarding compressor states and pressure values received by the control program via the data communication means  30 - 32  is continuously stored on a mass storage medium (in the control computer  34 ). The state of operation and pressure level of the compressors can be presented in the same diagram so that they can be viewed in a graphic form from instant to instant. This enables the pneumatic system to analyzed in real time or afterwards. 
   The control program calculates the total output and power input of the pneumatic system on a continuous basis. These data are stored on a mass storage medium. In the user interface, these data can be presented in the same diagram so that they can be viewed in a graphic form from instant to instant. In addition, the user interface calculates the average consumption and power over a selected period of time. Moreover, the points of the diagram can be printed to a file with a desired time interval. The report thus produced allows verification of the actual benefit yielded by the control system and continuous measurement of performance even over a long period. 
   The compressor controller A 1 -A 7  reads information from the compressor and transmits it to the control program, reads the control commands from the group control program and executes them in accordance with its own control program while also monitoring the validity of the commands and the condition of the data communication bus and the programs. The compressor program is a compressor type and model-specific program. As an example, consider a pressure-switch-controlled model that is stopped and started by a run-on timer. About 50% of all compressors are of this type. About 5 different compressor controller models cover about 95% of the entire compressor capacity. In current solutions, even a single non-standard compressor model to be incorporated under the control system requires relatively extensive tailoring of the control programs. This problem is now limited to the tailoring of a simple compressor controller program. Even this tailoring work will be reduced when this solution gains ground, because it will be easy to form a library of compressor controller programs. 
   The basic architecture of the method allows the use of a device of any manufacturer in the compressor controller. This makes it possible to utilize the invention in many cases in which it has not been possible before. 
   When a disturbance, e.g. a connection fault, occurs in any part of the system, the compressor controller hands over the control to the compressor&#39;s own control system. This guarantees disturbance-free production of compressed air in almost all situations. 
   The operation of the compressor controller can be tested either by means of a group controller or any device that is capable of writing the run and load commands to the controller. This is made possible by the structure of the controller program, in which the outward interface can be kept as simple and standard as possible regardless of compressor type and model. Only the run/stop commands and the desired load factor are written via the interface. 
   It is obvious to the person skilled in the art that different embodiments of the invention are not limited to the examples described above, but that they may be varied within the scope of the following claims.