Patent Publication Number: US-2006004470-A1

Title: Multivalue control system and method for controlling a multivalue controlled system

Description:
FIELD OF THE INVENTION  
      The present invention relates to a multivalue control system, to a method for controlling a multivalue controlled system and to a method for controlling a propeller power unit.  
     BACKGROUND INFORMATION  
      The starting point for control technology or for a control task is a system or a device for which a value that changes with time is to be influenced in a certain manner. The value to be controlled is designated as the controlled variable, and the given system or device is designated as the controlled system. The controlled variable is an output variable of the controlled system, and a measured value of the controlled variable is termed the actual value of same. The controlled variable is to be influenced such that the controlled variable is equal to a desired quantity, which is called the setpoint value. The real actual value of the controlled variable is compared to the desired setpoint value, the corresponding deviation, a so-called system deviation, being supplied to a controller. Based on the system deviation, the controller generates a regulating variable, the regulating variable being an input variable of the controlled system.  
      Frequently, controlled systems are to be controlled in which several variables that vary over time, that is, several controlled variables, are to be influenced and thereby controlled. Such controlled systems are termed controlled multivalue systems or multivalue controlled systems. Examples of such multivalue control tasks are the following: 
          propeller power units, such as turboprop power units for aircraft, in which the speed and the performance of a propeller are to be controlled,     distillation columns, in which the liquid level and temperatures in the bottom and the top of the column are to be controlled, or     air conditioning, in which the temperature and the humidity of a space are to be controlled.        

     SUMMARY  
      Example embodiments of the present invention relate to such multivalue control systems or controlled multivalue systems. In the following, an example embodiment of the present invention is described with reference to the regulation of a propeller power unit. However, it should be understood that the present invention should not be considered to be limited to the regulation of a propeller power unit.  
      In such multivalue control systems, in general, there are interrelationships or couplings between the several controlled variables and the several correcting variables of such a kind that one correcting variable acts not only upon one but on a plurality of controlled variables. Furthermore, in general, nonlinearities occur between the several correcting variables and the several controlled variables. The interrelationships and the nonlinearities between the correcting variables and the controlled variables may pose considerable difficulties for the arrangement of a suitable controller, e.g., if an optimal control result is required over the entire operating range of the controlled system, and not only in the area of a preferred operating point of the controlled system.  
      In the article by Harold L. Wade, entitled “Inverted Decoupling: A Neglected Technique,” Advances in Instrumentation and Control, Instrument Society of America, Vol. 51, pp. 357 to 369 (1996), and in U.S. Pat. No. 5,403,074, a controlled multivalue system having a controlled multivalue system is described, the controlled multivalue system having several correcting variables as input variables and several controlled variables as output variables, having several comparators for ascertaining control deviations, having several controllers, to each controller one control deviation being able to be supplied as input variable, and having a conversion device whose input variables are the output variables made available by the controllers, the conversion device calculating the correcting variables for the controlled multivalue system at least from the output variables of the controllers. In the article by Axel Graeser, entitled “Cross-Profile Control in the Paper Industry—Sensors and Actuators as Determining Elements of the Control Quality,” Automatisierungstechnik (Automation Technology), Oldenbourg Verlag, Vol. 45, pp. 271 to 281 (1997), a control method is described that has decoupling of the individual loops and a compensation of the system or path coupling.  
      Using conventional multivalue control systems or methods for controlling a controlled multivalue system, it has not been, or has only insufficiently been, possible to control in a satisfactory manner controlled multivalue systems having interrelatinships and nonlinearities between the correcting variables and the controlled variables.  
     SUMMARY  
      According to example embodiments of the present invention, an improved multivalue control system and an improved method for controlling a controlled multivalue system, e.g., for controlling a propeller power unit, may be provided.  
      According to an example embodiment of the present invention, a conversion device, when calculating the correcting variables, superimposes on the output variables of the controllers an input control component that is a function of actual values of the controlled variables. Thereby may be achieved a good decoupling of the correcting variables and the controlled variables of the controlled multivalue system which is used for compensating for the system nonlinearity.  
      There may be provided a first controlled variable conversion device and a second controlled variable conversion device. The output variables of the controlled multivalue system, e.g., the controlled variables, are able to be supplied to the first controlled variable conversion device as input variables, the first controlled variable conversion device ascertaining output variables, from the controlled variables, which are able to be supplied to the comparators as first input variables. Furthermore, the setpoint values of the controlled variables are able to be supplied to the second controlled variable conversion device as input variables, the second controlled variable conversion device ascertaining output variables, from the setpoint values, which are able to be supplied to the comparators as second input variables. The control result may be optimized by the controlled variable conversion, and the structure of the control may be considerably simplified.  
      An exemplary embodiment of the present invention is explained in greater detail with reference to the appended Figure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       FIG. 1  illustrates a closed-loop control circuit for a propeller power unit to illustrate a multivalue control system according to an example embodiment of the present invention and a method according to an example embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION  
       FIG. 1  illustrates a multivalue control system  10  according to an example embodiment of the present invention. In the multivalue control system  10  illustrated in  FIG. 1 , a controlled multivalue system  11 , that is to be controlled, is arranged as a propeller power unit of an aircraft. It should be understood that example embodiments of the present invention may be applied to other controlled multivalue systems.  
      As illustrated in  FIG. 1 , in the case of the controlled multivalue system  11  arranged as a propeller power unit, a propeller speed n p  and a propeller performance P PR  are to be controlled as controlled variables  12 ,  13 . The two controlled variables  12 ,  13  represent the output variables of controlled multivalue system  11 .  
      Two correcting variables  14 ,  15  are supplied as input variables to controlled multivalue system  11  that is arranged as a propeller power unit. In the case of first correcting variable  14 , in the exemplary embodiment illustrated, a propeller blade angle of incidence β is involved. In the case of second correcting variable  15 , a fuel stream w F  is involved.  
      Thus, in the case of the propeller power unit, a controlled multivalue system  11  is involved, having two input variables and two output variables. There are close interrelationships and nonlinearities between the input variables, e.g., correcting variables  14 ,  15  and the output variables, e.g., controlled variables  12  and  13 , of the controlled multivalue system  11  arranged as a propeller power unit. With the aid of multivalue control system  10  according to an example embodiment of the present invention and the method according to an example embodiment of the present invention for controlling controlled value system  11 , a solution is provided by which the interrelationships and the nonlinearities between correcting variables  14 ,  15  and controlled variables  12 ,  13  may be eliminated to the greatest extent possible, and consequently one may also achieve an optimized control result, using simple control structures, over a broad operating range of controlled multivalue system  11  that is to be controlled.  
      As mentioned above, the speed of the propeller n p  is to be controlled as the first controlled variable  12 , and the power of the propeller P PR  is to be controlled as the second controlled variable  13 . Measured values of these controlled variables are designated as actual values. It is within the meaning of the control task that the actual values of controlled variables  12 ,  13  should be brought into agreement with corresponding setpoint values  16 ,  17  for the speed of the propeller and the power of the propeller. Thus  FIG. 1  illustrates, as first setpoint value  16 , a setpoint value for the propeller&#39;s speed n Psoll , and as second setpoint value  17  a setpoint value for the power of the propeller P PRsoll .  
      According to an example embodiment of the present invention, the actual values of controlled variables  12 ,  13  are not directly compared to setpoint values  16 ,  17  of the same. Rather, for both the actual values of controlled variables  12 ,  13  and for the corresponding setpoint values  16 ,  17 , there is present in each case a controlled variable conversion device  18 ,  19 .  
      A first controlled variable conversion device  19  is assigned to the measured actual values of controlled variables  12 ,  13 . A second controlled variable conversion device  18 , however, is assigned to the corresponding setpoint values  16 ,  17 . First controlled variable conversion device  19  ascertains output variables  20 ,  21  from the actual values of controlled variables  12 ,  13 . Correspondingly, second controlled variable conversion device  18  ascertains output variables  22 ,  23  from setpoint values  16 ,  17 . The output variables  20 ,  21  of first controlled variable conversion device  19  and output variables  22 ,  23  of second controlled variable conversion device  18  are supplied to comparators  24 ,  25  as input variables. In comparators  24 ,  25 , the corresponding output variables  20 ,  21 ,  22 ,  23  of controlled variable conversion devices  18 ,  19  are offset against one another. This is described in greater detail below.  
      In advance, at this point, the conversions of the actual values of controlled variables  12 ,  13  as well as their setpoint values  16 ,  17  that are executed in controlled variable conversion devices  18 ,  19  are described. Thus, first controlled variable conversion device  19 , to which, as input variables, controlled variables  12 ,  13  are supplied, e.g., actual values of the propeller&#39;s speed n p  and the propeller&#39;s power P PR , makes available two output variables  20 ,  21 , which are calculated from the input variables of controlled variable conversion device  19  and from characteristics values of controlled multivalue system  11 . Thus, in the exemplary embodiment illustrated, first controlled variable conversion device  19  outputs as first output variable  20  controlled variable  12 , e.g., propeller speed n p, , as the first output variable. On the other hand, as second output variable  21 , first controlled variable conversion device  19  outputs a quantity ascertained from the actual values of controlled variables  12 ,  13 , e.g., in the exemplary embodiment illustrated, an ascertained value of turbine output P LPT . Accordingly, propeller speed n p  and propeller performance P PR  are supplied to first controlled variable conversion device  19  as input variables. As output variables  20 ,  21 , controlled variable conversion device  19  outputs propeller speed n p  and turbine output P LPT . In order to ascertain turbine output P LPT  from controlled variables  12 ,  13 , one proceeds according to the following equation: 
 
 P   LPT   =P   PR   +n   p   *dn   p   /dt*Θ* 4π 2  
 
 in which: 
          P LPT =turbine output;     P PR =propeller performance;     n p =propeller speed;     dn p /dt=first derivative of the propeller&#39;s speed; and     Θ=mass moment of inertia of the propeller power unit.        

      By using the above equation, output variables  20 ,  21  of the first controlled variable conversion device may simply be ascertained from controlled variables  12 ,  13  in first controlled variable conversion device  19 .  
      In an analogous manner, the above equation is also used in second controlled variable conversion device  18 , in which output variables  22 ,  23  are calculated from setpoint values  16 ,  17 .  
      In addition, a time delay device for the setpoint value of the propeller speed is also integrated into second controlled variable conversion device  18 . Output variable  22  of controlled variable conversion device  18  thus corresponds to the setpoint value for propeller speed n Psoll  at a time delay of, e.g., 200 milliseconds. Because of this time-delayed passing through of the setpoint value for the propeller speed, the dynamic time delaying effect of the propeller power unit is compensated for.  
      At this point, it is noted that output variables  20 ,  21  of first controlled variable conversion device  19  may also be designated as auxiliary controlled variables, and output variables  22 ,  23  of second controlled variable conversion device  18  may also be designated as auxiliary setpoint values.  
      As was mentioned above, output variables  20 ,  21  of first controlled variable conversion device  19  and output variables  22 ,  23  of second controlled variable conversion device  18  are supplied to comparators  24 ,  25  as input variables. As illustrated in  FIG. 1 , output variables  20 ,  22  of controlled variable conversion devices  18 ,  19  are supplied to a first comparator  24 . In the exemplary embodiment illustrated, in this connection, the recalculated actual values and setpoint values for propeller speed n p  are involved. In comparator  24 , a difference is formed between this auxiliary setpoint value for the propeller&#39;s speed and the auxiliary actual value for the propeller&#39;s speed, and from this, a control deviation  26  for the propeller&#39;s speed is calculated. The control deviation for the propeller&#39;s speed is designated in  FIG. 1  as n Perr .  
      In analogous manner, in second comparator  25 , a difference is calculated between output variable  23  of second controlled variable conversion device  18  and output variable  21  of first controlled variable conversion device  19 . Accordingly, in the exemplary embodiment illustrated, in second comparator  25 , a difference is ascertained between a calculated actual value of turbine output P LPT , that is used as auxiliary controlled variable, and a correspondingly calculated setpoint value for this auxiliary controlled variable. A corresponding control deviation  27  between the actual value and the setpoint value of the turbine output used as auxiliary controlled variable is designated in  FIG. 1  as P LPTerr .  
      Control deviations  26 ,  27  of auxiliary variables  20 ,  21  are supplied to controllers. 28 ,  29 , as illustrated in  FIG. 1 . Control deviation  26  of auxiliary controlled variable  20  is supplied to first controller  28 . In the case of control deviation  26  supplied to first controller  28 , accordingly, a control difference is involved between auxiliary setpoint value  22  of the propeller rotational speed and auxiliary actual value  20  for the propeller speed. Accordingly, first controller  28  is arranged as a speed controller. First controller  28  ascertains an output variable  30  from control deviation  26 . In the exemplary embodiment illustrated, in the case of output variable  30  a torque request ΔT is involved.  
      Analogously, control deviation  27  of auxiliary controlled variable  21  is supplied to second controller  29 . Thus, in the case of control deviation  27 , the difference is involved between setpoint value  23  and corresponding actual value  20  of turbine output P LPT  that is used as auxiliary controlled variable. As a result, second controller  29  is arranged as a power controller. Second controller  29  ascertains an output variable  31  from control deviation  27 . In the case of output variable  31  of second controller  29 , in the exemplary embodiment illustrated, a power request ΔP is involved.  
      The two controllers  28 ,  29  may be arranged, for example, as PID controllers.  
      Output variables  30 ,  31  of controllers  28 ,  29  are not used directly as correcting variables for controlled multivalue system  11 , but are rather supplied to a conversion device  32 . Output variables  30 ,  31  of controllers  28 ,  29  are accordingly used as input variables by conversion device  32 . Output variables  30 ,  31  are offset against each other in conversion device  32 . Conversion device  32  ascertains correcting variables  14 ,  15  for controlled multivalue system  11  from output variables  30 ,  31  of controllers  28 ,  29  and from characteristics values of controlled multivalue system  11 . In the exemplary embodiment illustrated, this means that torque request ΔT and power request ΔP are supplied as input variables to conversion device  32 . From these two input variables, conversion device  32  ascertains propeller blade angle of incidence β and fuel stream w F  as correcting variables for propeller power unit  11 . In this instance, one may proceed according to the following model equations: 
 
 T=β   E1   *n   p   E2  
 
 P=w   F   E3   * n   p   E4  
 
 in which: 
          P=turbine output, output variable of speed controller;     T=torque, output variable of power controller;     n p =propeller speed;     w F =fuel stream, the correcting variable wanted;     β=propeller blade angle of incidence, correcting variable wanted; and     E 1 , E 2 , E 3 , E 4 =exponents of the model.        

      According to a further aspect of an example embodiment of the present invention, in conversion device  32 , for ascertaining controlled variables  14 ,  15 , not only are output variables  30 ,  31  of the two controllers  28 ,  29  offset against one another, but rather an input control component is additionally taken into consideration in conversion device  32 . Accordingly, characteristics of controlled multivalue system  11 —in the current exemplary embodiment, characteristics of the turbine and of the propeller are involved—are looped into the control paths of multivalue control system  10 .  
      In this connection, in the exemplary embodiment illustrated, characteristics maps of the propeller and the turbine are taken into consideration. Such characteristics maps are obtained from the mathematical or system-dynamic modelling of controlled multivalue system  11 , in the exemplary embodiment illustrated, of the propeller power unit.  
      As input variables, output variables  30 ,  31  of the two controllers  28 ,  29  and, in addition, the measured corresponding actual values that are used as input control components, are supplied to these characteristics maps. In output variables  30 ,  31  of the two controllers  28 ,  29 , the respective input control component is added, and this sum is supplied to the corresponding characteristics map as input variable. In this connection, the following applies: 
 
 T=f (β,  n   p , . . .) and  T=ΔT+T   ist  
 
 P=f ( w   F   , n   p , . . .) and  P=ΔP+P   ist  
 
 in which: 
          f(β, n p , . . .), f(w F , n p , . . .)=characteristics maps; and     T ist ,P ist =input control components.        

      From this, it follows that: 
 
β= f (Δ T+T   ist   , n   p , . . .) 
 
 w   F=f (Δ P+P   ist   , n   p , . . .) 
 
      This means that the characteristics maps are not only impinged upon by nominal or measured inputs T ist  and P ist , but also by dynamically ascertained output variables of the two controllers  28 ,  29 . Output variables  30 ,  31  of the two controllers  28 ,  29  are looped in by the characteristics maps of controlled multivalue system  11 , and thus undergo additional conversion.  
      Multivalue control system  10  described herein and the method for controlling controlled multivalue system  11  includes the following three aspects:  
      According to a first aspect, the output variables of controlled multivalue system  11 , e.g., controlled variables  12 ,  13  as well as corresponding setpoint values  16 ,  17  for controlled variables  12 ,  13 , are recalculated in controlled variable conversion devices  18 ,  19  into auxiliary controlled variables  20 ,  21  as well as corresponding setpoint values  22 ,  23  for the auxiliary controlled variables. According to a second aspect, output values  30 ,  31  of controllers  28 ,  29  that are ascertained from control deviations  26 ,  27  of auxiliary controlled variables  20 ,  21  are supplied to a setpoint value conversion device  32 . In conversion device  32 , correcting variables  14 ,  15  for controlled multivalue system  11  are formed from output variables  30 ,  31  of controllers  28 ,  29 . According to a third aspect, at least one input control component is superimposed on output variables  30 ,  31  of controllers  28 ,  29 , in conversion device  32 . This input control component is a function of the modelling of controlled multivalue system  11 . In the case of the input control components, characteristics maps of controlled multivalue system  11  are involved, as the input variables for these characteristics maps the dynamically ascertained output variables  30 ,  31  of controllers  28 ,  29  and the measured corresponding actual values, so-called input control components, being used.  
      While using the structure of multivalue control system  10 , one may, in a simple manner, eliminate interrelationships between correcting variables  14 ,  15  and controlled variables  12 ,  13  of controlled multivalue system  11 , as well as nonlinearities in the dynamic behavior of controlled multivalue system  11 . The multivalue control problem of controlled multivalue system  11  may thus be attributed to decoupled, linear closed-loop control circuits having one input variable as well as one output variable. Using simple control laws, such as PID controllers, one may then implement a satisfactory control of controlled multivalue system  11  over the entire operating range of controlled multivalue system  11 .  
      Multivalue control system  10  may be used with certain advantages for controlling a propeller power unit. The pronounced nonlinearities in the dynamic transmitting behavior that occur in a propeller power unit, as well as the pronounced interrelationships between the correcting variables and the controlled variables of the propeller power unit may be easily eliminated. With the aid of the controlled variable conversion, and the correcting variable conversion, propeller speed n p  and propeller performance P PR  may be controlled decoupled from each other and linearly to a great extent. Using a simple set of control parameters, an optimized control of a propeller power unit may be achieved over the entire operating range of the propeller power unit. Multivalue control system  10  may provide a robust control behavior.  
     LIST OF REFERENCE NUMERALS  
     
         
          multivalue control system  10   
          controlled multivalue system  11   
          controlled variable  12   
          controlled variable  13   
          correcting variable  14   
          correcting variable  15   
          setpoint value  16   
          setpoint value  17   
          controlled variables conversion device  18   
          controlled variables conversion device  19   
          output variable  20   
          output variable  21   
          output variable  22   
          output variable  23   
          comparator  24   
          comparator  25   
          control deviation  26   
          control deviation  27   
          controller  28   
          controller  29   
          output variable  30   
          output variable  31   
          controlled variables conversion device  32