Abstract:
A fan arrangement ( 20 ) has a fan ( 24 ) driven by an electric motor ( 22 ). It further has an apparatus for continuously detecting an actual electrical value associated with the electric motor ( 22 ) during operation, an input apparatus for inputting a desired electrical value for the operation of said electric motor, 
     a comparison apparatus ( 26 ) for comparing said electrical value with the actual electrical value, and a controller which regulates said electrical value by pulse width modulation ( 36 ).

Description:
CROSS-REFERENCE 
     The present application is a section 371 of PCT/EP08/09702, filed 17 Nov. 2008, published 28 May 2009 as WO-2009-065540, and further claims priority from German application DE 10 2007 057 100.5, filed 19 Nov. 2007, the disclosure of which is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a fan arrangement with influence on the electrical power that it consumes. 
     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 many further sub-types in the case of the other designs. 
     The properties of a fan result from the so-called fan output characteristic curve, which indicates the quantity of air per hour (m 3 /h) delivered by the fan at a particular static pressure Δpf [Pascal], 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 means that a free outlet fan has a different power requirement than a fan that is delivering air into the interior of 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. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to make available a novel fan arrangement. 
     This object is achieved by employing both a controller which compares the electrical power being consumed with a predetermined maximum motor power, and a limiting arrangement for adjusting pulse-width modulation signals if the power being consumed exceeds the maximum permissible motor power. 
     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. 
     It is also important, in practical terms, that users are accustomed to modifying the air output of an axial fan by way of a rotation speed control system. The result of this can be, however, that the power consumed by the fan at maximum rotation speed becomes too high, with the consequence that the electric motor becomes too hot. With an axial fan this is normally the case only when the static pressure Δpf to the left of the so-called saddle becomes very high. This is because the normal working range of an axial fan is just below the saddle, since flow detachments at the fan blades occur in the area of the saddle and produce a drastic increase in fan noise. 
     For this reason, a fan of this kind is operated with normal rotation speed control over a large portion of its operating range. If the electrical power consumed by the fan motor becomes too high, however, said power is limited, in the embodiment described below, to a permissible value. This makes it possible to operate the fan in speed-controlled fashion up to a predetermined volumetric flow rate, and then in power-limited fashion at even higher pressure. The advantage of this is that the air output of the fan can be modified, as usual, by way of the rotation speed control system. Only in maximum rotation speed ranges does power limiting become active, in this case, at high static pressure. For an axial fan, this is normally the case only with a static pressure to the left of the “saddle.” The normal working range of an axial fan is just below the “saddle,” and in this range the fan can be operated normally with its speed control system. 
     By operating the fan motor at its power limit, it is possible to achieve considerably greater air output with the same fan; this can be important in terms of cooling, especially on hot days. 
    
    
     
       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. In the drawings: 
         FIG. 1  shows an embodiment of a fan arrangement having a power-limited rotation speed controller; 
         FIG. 2  is a perspective depiction of an axial fan, here in the form of a device fan that is used, for example, to cool desktop computers; 
         FIG. 3  shows an example of a fan characteristic curve of a fan arrangement according to  FIG. 1 ; 
         FIG. 4  shows a characteristic curve of power consumption as a function of air volume delivered per hour (m 3 /h) for an arrangement according to  FIG. 1 ; 
         FIG. 5  is a diagram to explain a problem that can occur in practical use in the context of  FIG. 1 ; 
         FIG. 6  shows a variant of  FIG. 1 ; 
         FIG. 7  is a diagram to explain  FIG. 6 ; 
         FIG. 8  shows measurement curves that were recorded using the variant according to  FIG. 6 ; 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. 9  shows measurement curves for  FIG. 6 ; they show rotation speed as a function of volumetric flow rate at a low constant power and at a higher constant power. 
         FIG. 10  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. 11  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. The latter can be an axial fan, a radial fan, a diagonal fan, a transverse-flow blower, etc. 
     The rotation speed n ist  of motor  22  can be regulated to a value n soll . n soll  is often determined by the temperature in the vicinity of fan arrangement  20 , for example by means of a temperature sensor  23  as depicted in  FIG. 2 . This sensor can also be arranged outside fan  24 . 
     For rotation speed control, the present rotation speed n ist  of motor  22  is also continuously detected and is delivered to a comparator  26 , along with the desired rotation speed n soll  (see  FIG. 1 ). 
     The output signal of comparator  26  is delivered to a controller  27  which, depending on requirements, can be, for example, a P controller, a P 1  controller, or a PID controller. Controller  27  has an output  28  at which a control input is obtained and is delivered to a limiter  29 . The latter limits the control input to a predetermined value. 
     The limited signal at output  32  of limiter  29  is delivered to a PWM module  34  and transformed there into a PWM signal  36  that is delivered to motor  22  and controls current i mot  therein. PWM modules of this kind are known. 
     A fan arrangement according to  FIG. 1  is normally designed so that its fan characteristic curve ( FIG. 3 ), at a predetermined static pressure Δpf that is equal to, for example, 1400 Pa in  FIG. 3 , reaches a delivery output of 0 m 3 /h with no need to take particular actions for that purpose (see curves  44  in  FIGS. 3 and 46  in  FIG. 4 ). 
     Curves  44 ,  46  of an axial fan as depicted in  FIG. 2  have a so-called “saddle” that is labeled  48  in  FIGS. 4 and 50  in  FIG. 3 . 
     Such fans are normally operated just below saddle  48  and  50  and at a low static pressure, i.e. in the case of  FIGS. 3 and 4  at, for example, a delivery output of approximately 400 to 500 m 3 /h. The reason is that in the region of saddle  48 ,  50  and above it, a fan of this kind can generate very intense noise. 
       FIG. 2  shows, as an example for explanation, a typical axial fan  24  having a fan housing  56 , which is depicted in section and in which is mounted, by means of struts  58 , a hub  60  on which is journaled a rotor  62  on whose outer side are mounted fan blades  64  that rotate during operation in the direction of an arrow  66  and thereby deliver air in the direction of arrows  68 . 
     Motor  22  of an axial fan of this kind is normally designed so that it operates on curves  44 ,  46  of  FIGS. 3 and 4 . This means, for example in  FIG. 4 , that at a maximum power of 340 W, the delivery output is equal to 0 m 3 /h. Motor  22  of a normal fan therefore automatically limits the power P ist  that it consumes, and is physically designed for that purpose. 
     The present case is different: as  FIG. 4  shows, in accordance with curve  52  fan motor  22 , as a result of how it is constructed, limits the power P ist  that it consumes in the range from 250 to 800 m 3 /h to a value that is less than P max , i.e. in this range motor  22  can be operated with a normal rotation speed control system because its power consumption P ist  is less than P max , so that no additional interventions are necessary here. 
     Proceeding farther to the left in  FIGS. 3 and 4 , however, i.e. Into the range from 0 to 250 m 3 /h, it is evident that at values below approximately 250 m 3 /h the permissible power P max  of motor  22  would be exceeded, since motor  22  (unlike a “normal” motor having air output curve  46 ) has a lower induced voltage, i.e. it has fewer stator windings that are produced from a thicker wire, so that in accordance with curve  52  in  FIG. 4 , in the range between 0 and 250 m 3 /h it would exceed the permissible power P max  which, in this example, is equal to 340 W. 
     This would create the risk that motor  22  might overheat and consequently be damaged or destroyed. This must be prevented, and for that reason the fan arrangement according to  FIG. 1  has a power limiter that prevents P max  from being exceeded. The fan arrangement thus operates here with Power_CTL, as indicated in  FIG. 4 . This power limiter detects voltage u mot  at motor  22  and current i mot  through motor  22 , the latter e.g. at a measuring resistor  136 . These two values are multiplied by one another in a multiplier  70  and this yields, at output  72  of multiplier  70 , power P ist  which is delivered to an input  74  of a comparator  76  whose other input  78  has delivered to it a value for the permissible power P max . The signal at output  80  of comparator  76  is delivered to limiter  29  and thereby limits the control input at output  32  of limiter  29 , but not until P ist  becomes greater than P max . This means that the permissible power P max  cannot be exceeded. Alternatively, the duty factor of PWM signal  36  can also be directly influenced in the required fashion by the signal at output  80 . 
     As a result of the invention, fan arrangement  22  is therefore influenced so that fan  24  (of whatever type) operates at its full output specifically at high static pressures and delivers more air in that context, of course with a higher power consumption. 
     It is very advantageous that a standard control circuit, in which the fan rotation speed is regulated by pulse width modulation, can be used for rotation speed control. In a deviation from the standard solution, however, the setting signal for PWM module  34  is limited as soon as the maximum motor power P max  is reached. Alternatively, the duty factor of PWM signal  36  can also be limited directly when the power limit is reached. 
     Characteristic curves  52  in  FIGS. 4 and 53  in  FIG. 3  show, by way of example, the manner of operation. Up to a volumetric flow rate of approximately 250 m 3 /h, fan arrangement  20  runs in speed-controlled fashion, and at even higher pressure its power is then limited. This has the advantage that the air output of fan arrangement  20  can be modified, as is usual, by way of rotation speed control system n_CTL. Only at maximum rotation speed does the power limiter additionally become active in this case at high static pressure. 
     The arrangement described is very advantageous for all types of fans, since the user will still encounter the usual characteristics of a speed-controlled fan, but with increased fan air output. 
     Because fan motor  22  is operated at its maximum power limit (P max  in  FIG. 4 ), a considerably higher air output can be achieved with the same fan. It thus becomes possible always to operate such fans at the maximum permissible power, and thereby to achieve more volumetric flow at the same counterpressure, i.e. the fan&#39;s characteristic curve is electronically modified so the fan can be better utilized. 
     The same working principle is also possible, for example, with radial fans, where once again a considerable increase in air output is obtained. Such radial fans can then also preferably have a reduced number of stator windings, the wire diameter being increased in order to achieve the same copper fill factor. 
     If the operating voltage Ub of a fan arrangement  20  of this kind fluctuates, different motor currents i mot  are produced at different voltages Ub. An arrangement  20  of this kind is designed, as standard, so that the maximum required power is achieved at rated voltage, and so that motor current i mot  is reduced in the event of overvoltage. Motor  22  is therefore not utilized less effectively than in the case of comparable arrangements  20  of the existing art. 
     In the arrangement according to  FIG. 1 , the power limiter (multiplier  70 , comparator  76 ) is of a higher order than the speed controller (elements  26 ,  27 ). This means that once the measured power P ist  exceeds the value P max  (at input  78  of comparator  76 ), no further increase in rotation speed is possible. 
     This situation is depicted schematically in  FIG. 5 , where the duty factor at the output of PWM module  34  is depicted on the abscissa, and the desired rotation speed (target rotation speed) n soll  on the ordinate. 
     Also depicted is the target rotation speed n soll *, shown in this case as 4000 rpm as an example, at which motor  22  is working at its maximum power P max , in this case 100 W as an example. This speed n soll * is not a constant value. In the case of a fan, for example, it depends on the so-called static pressure Δpf, i.e. if the fan is a radial fan and if the air flow at its outlet is throttled, the static pressure increases and the maximum permissible power, i.e. 100 W in the example, is already reached e.g. at a target rotation speed n soll =3500 rpm. In this case, it would therefore not be possible to set a speed greater than 3500 rpm, since that would be prevented by the power controller. 
     When the maximum power is reached, the rotation speed therefore cannot be increased further, i.e. even though the user sets a higher rotation speed n soll , this setting has no influence on the actual rotation speed n ist  of motor  22 . 
     This is depicted schematically in  FIG. 5 , where only the rotation speeds in a range 90 up to rotation speed n soll * can be set, but not the speeds in a region  92  from n soll * to n max . This part of the n soll  curve is therefore marked with Xs. 
     An operator might get the impression, from this, that speed controller  26 ,  27  is defective. 
       FIG. 5  also depicts the curve for the actual value n ist  of the rotation speed. Up to the value n soll * the curves for n soll  and n ist  proceed identically, but above n soll *n ist  remains constant even as n soll  is further increased. 
     This problem is avoided by the arrangement according to  FIG. 6 , in which the same reference characters as in  FIG. 1  are used for identical or identically functioning parts. 
     In  FIG. 7 , a control signal U CTL  is converted into a signal for a permissible target power value P soll  which can be e.g. between P min =5 W and P max =100 W, and rotation speed n ist  of motor  20  is modified until it generates the power set by means of U CTL . This is therefore a power controller. 
     In  FIG. 6 , a controller  98  is provided which can be identical in construction to controller  27  of  FIG. 1 . Its output  100  is connected to the input of PWM unit  34 , i.e. the magnitude of the signal at output  100  determines the duty cycle of PWM signal  36  at the output of PWM unit  34 . To facilitate comprehension, it is assumed here that a rise in the signal at output  100  corresponds to a rise in the duty cycle and to a rise in motor current i mot , as is the case for most motors. 
     The power P ist  consumed by motor  22  is calculated in multiplier  70  by multiplying i mot  and u mot , and this value P ist  is delivered to a comparator  102 . 
     The target power value P soll  is also delivered to comparator  102  from a target value unit  104 , and the output signal  106  of comparator  102  is delivered to controller  98 , which (via PWM unit  34 ) modifies the value P ist  until P ist =P soll . 
       FIG. 6  also shows, as an example, how control signal U CTL , which is delivered to an input of target value unit  104 , can be generated from a PWM signal  160  that is delivered to a terminal  162 . 
     Input  164  is connected to the cathode of a Zener diode  166  whose anode is connected to ground  168  and with which a capacitor  170  is connected in parallel. A resistor  172  is located between input  164  and terminal  162 . Terminal  162  is connected via a resistor  174  to a positive voltage, e.g. +5 V. 
     PWM signal  160  is smoothed by RC element  172 ,  170 . Zener diode  166  prevents voltage peaks in control signal U CTL . The latter is converted in target value unit  104  into a target power value P soll  for motor  22 , which is delivered as described to comparator  102 . PWM signal  160  can be converted in this fashion into a target power value for motor  22 , and this target value increases as the duty cycle of PWM signal  160  increases. 
       FIG. 7  explains target value unit  104  of  FIG. 6 . This unit converts a control signal U CTL  into a signal P soll  for the desired power of motor  22 . The value P max  can be set in suitable fashion, for example using a Zener diode with which a constant voltage, which can correspond e.g. to maximum power P max , is generated. A voltage divider, at which a value between P min  and P max  can be set, is then connected to this voltage.  FIG. 7  shows as an example a voltage U 1  that is converted into a target power P 1 . 
       FIGS. 8 to 11  show measured values for the power control system according to  FIG. 6 , 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. 8  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. 9  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. 10  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. 6 , 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 Å. Here as well, the volumetric flow was modified using a measurement nozzle (not depicted). 
       FIG. 11  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). 
     The constant power was set in  FIGS. 6 to 11  by means of control voltage U CTL , which in this case was 5 V for the lower power (135 W) and 10 V for the higher power (235 W). 
     Many variants and modifications are of course possible in the context of the present invention.