Data processing: generic control systems or specific application – Generic control system – apparatus or process – Optimization or adaptive control
Reexamination Certificate
2001-09-24
2004-08-17
Patel, Ramesh (Department: 2121)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Optimization or adaptive control
C700S019000, C700S017000, C700S083000, C700S034000, C700S073000, C700S074000, C340S007100, C340S007510, C340S870030, C340S870030
Reexamination Certificate
active
06778865
ABSTRACT:
The invention relates to a method and an apparatus for monitoring and controlling an appliance or a system comprising a number of appliances, having a two-dimensional or multidimensional operating envelope, whose limits represent different technical, procedure, financial or contractual restrictions.
One example of an appliance having a two-dimensional (planar) operating envelope, which is referred to as an operating characteristic, is a compressor. The gas volume flow V and the enthalpy difference H are chosen, for example, as characteristic variables for the operating point of a compressor. These characteristic variables are used as co-ordinate axes for representing the operating characteristic, which is defined as the totality of all those points (operating points) at which the compressor may be operated in the V′H plane. In practice, the operating characteristic is mainly in the form of a curved polygon. The sides of the polygon are referred to as bounds whose infringement results in certain secondary conditions no longer being satisfied. One of the bounds is, for example, the pump bound, which defines a minimum gas volume flow at which there is still protection against pump surges; beyond the pump bound, operation of the compressor becomes unstable. Further bounds correspond to the maximum rating of the compressor drive, the maximum flow rate, and the minimum and the maximum rotation speed.
The monitoring of a compressor has two tasks:
1. Preventative monitoring, to protect the equipment against dangerous and unstable operating conditions, for example protection against pump surging.
2. Functional monitoring in order, for example, to set a specific compressor rotation speed as a function of the operating state (for example the load), or to maintain a predetermined nominal value.
Known monitoring systems for compressors are based on the measurement of a number of characteristic variables for the compressors and their controllers. If the operating point infringes what is referred to as a control line, which runs parallel to a bound, and at a specific distance from it, in the operating characteristic, suitable measures are taken in order to return the operating point to an area on this side of the control line once again.
In EP-B-0 332 888, the rate of movement of the operating point in the direction of the pump limit in the operating characteristic is determined; if a pump control line, which occurs at a variable distance from the pump limit depending on the speed, is infringed, a blow-out or bypass valve is opened quickly, in addition to the normal blow-out control.
U.S. Pat. No. 3,994,623 discloses the linking of a number of originally independent control loops. A method is proposed which can be carried out using a cascade circuit. The method comprises the control loops for the rotation speed, the feed pressure and the gas volume flow being linked to one another, with the output signal from each outer loop representing the input signal for the next inner loop.
In known control methods, a separate control loop is provided for each of the control lines. If a control line is infringed, measures are taken, which depend on the respectively infringed control line and its specific shape. These methods are thus based on an independent description of each individual control line. If the operating point is in an area close to two bounds (a “corner” of the operating envelope), control of the operating point is very complicated. The control loops associated with the various bounds thus often operate independently of one another and conflict with one another, or else the interaction of the various control loops is incomplete.
Similar difficulties also occur when controlling other appliances or systems which comprise a number of appliances, having an operating envelope with two, three or more dimensions.
In the case of a three-dimensional operating envelope, the boundary conditions, which must not be infringed in either direction, are generally represented as, possibly curved, surfaces. The operating envelope is then an irregular polyhedron with curved side surfaces. If the operating point is in the vicinity of more than one of the side surfaces, this results in a complicated control response. In the general case of an N-dimensional operating envelope, the boundary conditions can generally be represented as, possibly curved, (N−1)-dimensional hyperplanes. In this case as well, particular control difficulties arise when the operating point approaches more than one of the hyperplanes.
A first object of the present invention is to provide a standard method for monitoring or controlling the position of the operating point in a two-dimensional or multidimensional operating envelope, which is independent of the specific shape of the operating envelope and which avoids said difficulties when the operating point approaches the limits of the operating envelope. The method is intended to allow the user to be warned reliably of unacceptable or dangerous operating conditions (monitoring), and to avoid them, or to maintain a predetermined nominal value (control).
This object is achieved by a method for monitoring or controlling an appliance or a system comprising a number of appliances, having a two-dimensional or multidimensional operating envelope, in which, according to the invention, the operating envelope, or a part of it, is mapped onto a unit domain or onto the operating envelope of another appliance for monitoring or control.
In this method, an operating point or set point in the operating envelope is advantageously transformed by means of the map to a point in the unit domain or in the operating envelope of the other appliance. The monitoring or control is in this case carried out on the basis of the position of the image of the operating point which results from the map.
The term unit domain in this case means intrinsically any desired region which is selected and is cohesive as an entity. For two-dimensional operating envelopes, for example, the unit circle or a half plane can advantageously be used as the unit domain. The unit sphere or a semi-infinite body advantageously carries out this role for operating envelopes with more dimensions.
If a map is made of the operating envelope onto a unit domain, the method according to the invention can be used to identify when the operating point is approaching a limit of the operating envelope, since the image of the operating point approaches a limit of the unit domain. One advantage of the method according to the invention is in this case that, provided the unit domain, the mapping rule and the co-ordinate representation of the image are selected appropriately, the situation where the image of the operating point is approaching a limit of the unit domain can be defined and controlled by monitoring a single limit.
A further advantage of the method according to the invention is that the monitoring of the operating point of different appliances can be carried out in a standard way by using differently shaped operating envelopes.
If the operating envelope of the appliance to be monitored is mapped onto the operating envelope of another appliance, the operating point of the appliance to be monitored can be monitored and controlled in the same way as for the other appliance. In particular, in this way, methods which have been proven for monitoring the operating point of a specific appliance can be transferred to the monitoring of the operating point of any other desired appliances with operating envelopes of any shape in the same dimension.
The method according to the invention is suitable for a large number of fields of application, in particular for monitoring a compressor.
In the method according to the invention, one or more process parameters are advantageously determined by means of the map, or the inverse transformation with respect to it.
In one advantageous refinement, the method for monitoring according to the invention contains the following steps:
a) determination of the operating point in the operating envelope;
b) transforma
Bauer Herbert
Huijnk Jan
Ostromuhov Leonid
Patel Ramesh
WINGAS GmbH
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