Abstract:
A fan arrangement ( 20 ) has a fan ( 24 ) driven by an electric motor ( 22 ), also an apparatus for detecting the electrical power (P IST ) consumed by the electric motor ( 22 ) during operation; an input apparatus ( 28 ) for inputting a desired rotation speed (n SOLL ) of said electric motor ( 22 ); a converter ( 26 ) for converting said desired rotation speed (n SOLL ) into a desired electrical power (P SOLL ); and a controller ( 44 ), which regulates the control input controlling the electric motor ( 22 ) in such a way that the difference between the electrical power (P IST ) consumed in operation and the desired electrical power (P SOLL ) is reduced, in order thereby to improve the air output characteristic curve ( 49, 58 ) of the fan arrangement ( 20 ) at least in a portion of the overall operating range.

Description:
CROSS-REFERENCE 
     The present application is a section 371 of PCT/EP08/09701 filed 17 Nov. 2008, published 28 May 2009 as WO-2009-065539, claiming priority of German application DE 10 2007 057 099.8 filed 19 Nov. 2007, the disclosure of which is incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a fan arrangement having a fan driven by an electric motor. 
     BACKGROUND 
     When a fan is driven by an electric motor, what results is a combination of the properties of the fan and the properties of the electric motor. 
     A variety of fan designs exist, e.g. radial fans, transverse-flow blowers, axial fans, and diagonal fans. Radial fans are divided into radial fans having backward-curved blades, and radial fans having forward-curved blades. There are likewise further sub-types in the case of the other designs. 
     The properties of a fan result from the so-called fan characteristic curve, which indicates the quantity of air per hour (m 3 /h) delivered by the fan at a particular static pressure, and from the motor characteristic curve, which indicates how much power the motor needs in order to deliver a specific quantity of air per hour. 
     The power requirement is further determined by the operating conditions of the fan. For example, when a fan is blowing air from outside into a room in which all the doors and windows are closed, the fan is operating at maximum static pressure. “Free outlet” blowing, conversely, means that the fan is located unrestrictedly in a space, and that no physical separation, and also no pressure difference, exists between its intake side and delivery side. This therefore means that a free outlet fan has a different power requirement than a fan that is delivering into a closed space. 
     An examination of the curve for a fan arrangement&#39;s power consumption plotted against generated volumetric air flow rate reveals that this power is highly dependent on the working point that is set, or on the pressure buildup in the fan. In the case of a radial fan, for example, maximum power is usually reached with free outlet, i.e. at a pressure elevation Δpf=0, whereas for an axial fan, it is reached at a maximum pressure elevation Δpf=maximum. 
     Radial fans are normally used at a higher static pressure. When they work without static pressure, i.e. in free-outlet fashion, they are being operated at their power limit, i.e. a radial fan must be designed for this operating point even though in practice it occurs seldom and in rather arbitrary fashion. This limits the power of such a fan under other operating conditions. Analogous considerations apply to other fan types. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to make available a novel fan arrangement. 
     This object is achieved by employing a controller which reduces any difference between operating electrical power P IST  and desired electrical power P SOLL  to thereby improve the air output characteristic curve. 
     Fan arrangements are normally designed so that the maximum permissible winding temperature of the electric motor is not exceeded at maximum electrical power consumption. This means that a fan arrangement of this kind is “understressed” for many applications, i.e. at most working points it is operating below its maximum permissible power level. 
     What is achieved, by means of the invention, is that a fan arrangement of this kind can be operated at its permissible power limit, i.e. an improved air output characteristic curve is obtained with the same fan. The approach in this context is to operate the fan arrangement always in the region of its maximum permissible power, i.e. at the power limit or close to it, and thereby to achieve a greater volumetric flow rate for the same counterpressure, i.e. to increase the air output without requiring a larger fan arrangement for that purpose. Different solutions may be produced in this context, depending on the type of fan arrangement. 
    
    
     
       BRIEF FIGURE DESCRIPTION 
       Further details and advantageous refinements of the invention are evident from the exemplifying embodiments, in no way to be understood as a limitation of the invention, that are described below and depicted in the drawings. 
         FIG. 1  shows an embodiment of an air output controller; 
         FIG. 2  shows the fan characteristic curve of a radial fan with and without the output controller of  FIG. 1 ; 
         FIG. 3  depicts the fan power with and without an output controller; 
         FIG. 4  is a partial depiction of a radial fan wheel  100  whose fan blades  102  are “forward-curved”; 
         FIG. 5  depicts a radial fan wheel  104  whose fan blades  106  are “backward-curved”; 
         FIG. 6  shows measurement curves that were recorded using the motor according to  FIG. 1 ; they show static pressure Δpf as a function of volumetric flow rate V/t at a constant low power and at a constant higher power; 
         FIG. 7  shows measurement curves for  FIG. 1 ; they show rotation speed as a function of volumetric flow rate at a low constant power and at a higher constant power. 
         FIG. 8  shows motor current i MOT  as a function of volumetric flow rate V/t at a constant low power and at a higher constant power; and 
         FIG. 9  shows the electrical power P (watts) consumed by motor  12  at a low constant power (curve  122 ) and at a higher constant power (curve  124 ); it is evident that the power during operation is held practically constant, so that the motor&#39;s power can be fully utilized. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a preferred embodiment of a fan arrangement  20  having an electric motor  22  and a fan  24  driven thereby, which fan arrangement  20  operates with power control. Fan arrangement  20  is continuously operated with power control in order to achieve an increase in air output in the context of fan  24 , at least in portions of its fan characteristic curve, and thus to better utilize fan arrangement  20 . 
     Fan arrangement  20  can be, for example, a usual equipment fan whose motor  22  will usually be a collectorless DC motor since, in the case of the latter, the rotation speed can be more easily modified than in the case of an AC or three-phase motor. The use of an AC or three-phase motor is, however, also not excluded. 
     The users of such fans are accustomed to fan arrangements that work with a rotation speed control system, and in which the rotation speed can be adjusted. For this reason, the desired rotation speed n SOLL  specified by the user is delivered to input  28  of a target value converter  26 , and converted there into a target power value P SOLL . This conversion is based, for example, on the rotation speed n assumed by fan arrangement  20  when a predetermined electrical power P is delivered to motor  22 , and fan  24  is blowing freely at its outlet  30 , e.g. into a room having open windows and doors. The inlet of fan  24  is labeled  32 , and in this case is unthrottled. 
     For example, if a rotation speed n SOLL  of 1000 rpm is specified to target value converter  26 , target power P SOLL  is then modified until fan arrangement  20  is running (with free outlet) at 1000 rpm, e.g. at 2.3 watts. The value pair 1000 rpm=2.3 W is then inputted into converter  26 . This is repeated for the entire value range that fan arrangement  20  can cover during operation, e.g. for 500, 600, 700, 1000, 2000 . . . rpm; interpolation between these values usually occurs. 
     Alternatively, it is also possible to determine a mathematical approximation formula with which the value for n SOLL  can be converted directly into values for P SOLL . 
     Because the values are measured while fan  24  is blowing freely at its outlet  30 , the rotation speeds during actual operation are of course somewhat different from n SOLL  but, in any case, the behavior obtained for fan arrangement  20  is similar to that of a speed-controlled fan. 
     Electrical power P IST  consumed by motor  22  is ascertained, for example, by measuring voltage u MOT  at motor  22  and motor current i MOT  (e.g. at a measuring resistor  36 ). These values are delivered to a multiplier  38 , at whose output  40  a value is obtained for electrical power P IST  consumed by motor  22 . This, along with value P SOLL  from target value converter  26 , is delivered to a comparator  42  whose output signal is delivered to a controller  44 . 
     Depending on the speed and accuracy requirements, this latter can be, for example, a P controller, a PI controller, or a PID controller. Controller  44  has an output  45  at which a control input is obtained and is delivered to a limiter  46 . The latter limits the control input to a predetermined value, which can be different depending on the rotation direction. 
     The limited signal at output  47  of limiter  46  is delivered to a PWM module  48  and transformed there into a PWM signal  50  that is delivered to motor  22  and controls current i MOT  therein. 
     In order to prevent motor  22  from overloading, its power is therefore limited to a maximum value, e.g. by limiting current i MOT . 
       FIGS. 2 and 3  show, by way of example, the effect of the invention on a radial fan whose fan blades are forward-curved, i.e. curved in the rotation direction. Fan blades of this kind are depicted by way of example in  FIG. 4 . 
       FIG. 5  likewise shows a fan wheel whose fan blades are backward-curved and in which the invention can be used in the same fashion, although the curves that are obtained look somewhat different. 
       FIG. 2  shows, as an example, fan characteristic curve  49  without the invention, i.e. static pressure Δpf as a function of volumetric flow rate. For a radial fan, the maximum power is usually reached at a point  50  at which static pressure Δpf has a value of 0, i.e. at a point where fan  24  is blowing in free-outlet fashion, for example into a room having open windows and doors. 
     Moving from point  50  to the left, i.e. as the windows and doors are successively closed, the load on electric motor  22  decreases because static pressure Δpf increases. For curve  49  in  FIG. 2 , for example, at a static pressure of 700 Pa air is no longer being delivered, i.e. no further cooling is occurring, and the electrical power necessary for motor  22  decreases (as shown in  FIG. 3 ) in the range from 200 to 0 m 3 /h, as shown by curve  54  of  FIG. 3 . Unutilized power reserves of fan arrangement  20  thus exist in this range. 
     Motor  22  is operated, for example, in a specific operating state with a target power value P SOLL  of 100 W (see curve  56  of  FIG. 3 ). When power P IST  decreases here, as a result of the increasing static pressure, the rotation speed of fan  24  is increased, for example by raising the duty factor of PWM signal  50 , until the desired power P SOLL  is reached. This results, according to  FIG. 2 , in an improved fan characteristic curve  58 , in which air is still delivered up to a static pressure of approximately 1200 Pa. The power reserves of fan  24  are made usable in this fashion, and the cooling of a device cooled by fan  24  is improved. These mobilized power reserves are labeled  60  in  FIG. 2  and are highlighted in gray. 
     The description above refers to a radial fan. Application is likewise possible, however, for transverse-flow blowers, axial fans, diagonal fans, etc. The influence on the air output characteristic curve is more or less pronounced depending on the fan type. 
     A motor  22  is designed, as standard, approximately so that it reaches the maximum required power P IST  when operating voltage Ub corresponds to the rated voltage, and so that, if voltage Ub becomes too high, the power delivered to motor  22  is limited. 
     This is done by way of a corresponding reduction in motor current i MOT  (by modifying the duty factor of signal  50 ). The arrangement according to  FIG. 1  thereby automatically adapts to different values of voltage Ub that may occur during operation, and the risk of overloading motor  22  is ruled out. 
       FIGS. 6 to 9  show measured values for the power control system according to  FIG. 1 , for an RER190 radial fan of the EBM-PAPST company and for two different power settings, namely a low power of approximately 135 W and a higher power of approximately 235 W. 
       FIG. 6  shows static pressure Δpf as a function of volumetric flow rate. Curve  110  shows the result at a constant power that was regulated to 135 W, and curve  112  shows the result at a constant power of approximately 235 W. The curves run approximately parallel to one another. The volumetric flow rate was modified in the usual way by means of a measurement nozzle. 
       FIG. 7  shows rotation speed n IST  as a function of volumetric flow rate. The curve for 135 W is labeled  114 , and the curve for 235 W is labeled  116 . The volumetric flow rate was modified in the usual way by means of a measurement nozzle. 
       FIG. 8  shows motor current i MOT  as a function of volumetric flow rate. Because DC voltage Ub (in this case 48 V) was held constant in  FIG. 1 , current i MOT  is held constant by output controller  98 . The curve for 135 W is labeled  118 , the resulting current having been approximately 2.8 A; and the curve for 235 W is labeled  120 , the current having been equal to about 5 A. Here as well, the volumetric flow was modified using a measurement nozzle (not depicted). 
       FIG. 9  shows electrical power P IST  consumed by motor  22  as a function of volumetric flow. Curve  122  shows the result for a constant power of 135 W, and curve  124  shows the result for a constant power of 235 W. The volumetric flow rate was modified by means of a measurement nozzle (not depicted). 
     Many variants and modifications are of course possible in the context of the present invention.