CA1286713C - Method of limiting motor power output - Google Patents
Method of limiting motor power outputInfo
- Publication number
- CA1286713C CA1286713C CA000535475A CA535475A CA1286713C CA 1286713 C CA1286713 C CA 1286713C CA 000535475 A CA000535475 A CA 000535475A CA 535475 A CA535475 A CA 535475A CA 1286713 C CA1286713 C CA 1286713C
- Authority
- CA
- Canada
- Prior art keywords
- motor
- speeds
- speed
- representative
- fan
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
- H02H7/085—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against excessive load
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B5/00—Anti-hunting arrangements
- G05B5/01—Anti-hunting arrangements electric
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S388/00—Electricity: motor control systems
- Y10S388/923—Specific feedback condition or device
- Y10S388/93—Load or torque
Abstract
METHOD OF LIMITING MOTOR
POWER OUTPUT
ABSTRACT
The power output of a variable speed motor is limited to a safe level by determining the maximum allowable speed corre-sponding to a maximum power output limit over a range of load conditions and then maintaining the speed of the motor below those maximum allowable speeds at the particular load condi-tions existing at the time.
POWER OUTPUT
ABSTRACT
The power output of a variable speed motor is limited to a safe level by determining the maximum allowable speed corre-sponding to a maximum power output limit over a range of load conditions and then maintaining the speed of the motor below those maximum allowable speeds at the particular load condi-tions existing at the time.
Description
~Z~6~ 3 - ~ETHOD OF LIMITING MOTOR
PO~ER OUTPUT
Back~round of the Invention This invention relates generally to the control of motors and, more particularly, to a method of limiting to a safe level ~he power output of a variable speed motor operating under variable load conditions.
The use of variable speed motors is now being made for various applications. In order to vary the speeds as de-sired, various control techniques have been employed. One approach is that of pulse width modulation wherein the voltage is controlled by varying the duration and/or width of the output pulses. Pulse width modulation can be used, for example, with inverter controls or with electrically commu-tated motors (ECM's).
In the application of motor controls, it is common to limit the speed of the motor to a safe operating level as deter-mined by the particular design specifications. Even when operating within this limit, a motor or its associated electronics may become overstressed if its power output exceeds a certain level for a given load on the motor. For example, where a motor is used to drive a fan for the circu-lation of air from a furnace, the speed of the motor is controlled such that the power output will not normally exceed a safe level. However, where a high volume of air delivery is called for under nons~andard conditions such as static pressures in excess of .5 inches of water, the associ-ated higher torque requirements may cause the safe power output level to b~ exceeded. This may occur, for example, where the air filter becomes dirty or the ductwork is overly restrictive because of improper sizing or because of too many dampers being closed off.
~2~t~ 13 In Canadian Patent Application No. 524,283, filed Decem~er 2, 1986 by ~be common assignee of the present invention, a technique is described for calibrating a variable ~peed mo~or. As part of this t~chnigue, ~ motor fan combination is tested to empirically determine ~he relationship between the speed of the motor and the volume flow of air being delivereo by the fan. Th,s relationship is ther. used, in combination with ~he fan law equations and a measured torque output of the motor, to calculate the desired motor ~peed to obtain a desired air delivery volume. However, such a motor and control 6ystem is suscep~ible to the problem mentioned above relatlng to excessive power conditions.
It is therefore an object of the present inventlon to provide a means of protecting a variable 8p~ed motor from eJ~ceeding a safe level of power output.
Another object of the present invention is the provision fGr controlling the power output of a variable speed motor to which an unusually high load may be applied.
Yet another object of the present invention is the provisior.
for controllin~ the output of a variable speed motor without the use of special equipment and apparstus.
Still another object of the present invention is the provi-sion for an improved motor control system that is ~cono~ic~l to manufacture and effective in use.
These objects and other features and advsn~age6 become more ~eadily apparent upon reference to ~he following description ~hen taken in conjunction with the appended drawin~s.
Summary ~f the Invention ~riefly, in accordance with one aspect of the invention, ~
motor fan combination is empirically tested to aetermine the ~213~13 relationship between the motor speed and the volume flow of air. The motor is ~hen operated at maximum power over a range of s~atic pressure conditions~ while t~e corresponding volume flow, motor speed, and motor power output are record-ed. A maximum power output limit is established, and, usingthe fan laws, maximum allowable motor speeds are calculated over the range of static pressure conditions. The actual motor speed is ~hen limited to these maximum allowable motor speeds during all periods of operation.
In accordallce with another aspect of the invention, again using the fan laws, reference speeds are determined, as a function of motor speeds and volume flow, over the range of the static load conditions. These reference speeds are then related to the ma~imum allowable motor speeds to derive a representative equa~ion wherein the maximum allowable motor speed is expressed as a function of the reference speeds. A
microprocessor then uses the equation ~o compute ~he maximum allowable motor speed for ~he existing static load conditions, and to limit the actual speed of the motor to those values.
In the drawings as hereinafter describéd, a preferred embodi-ment is depicted; however, various other modifications in alternate constructions can be made thereto withcut departing from the true spirit and scope o the invention.
Brief Description of the Drawings Figure 1 is a perspective view, partizlly broken away, of a furnace having an installed motor and control system in accordance with the present inven~ion.
Figure 2 is a schematic illustration of the motor and con~rol portion of the present inventi.on.
t71;3 Figure 3 is a schematic illustration of the process of controlling a motor in accordance with the present invention.
Figure 4 is a graphic illustration, of how the motor operat-ing conditions are controlled in accordance with the present invention.
Description of the Preferred Embodiment Referring now to Figure 1, there is shown generally at 10, a motor con~rol system as applied to a furnace 11 in accordance with the design of the present invention. The furnace 11 includes a cabinet 12 which houses in its lower portion a blower 13, a motor 14 for driving the blower 13 and a control apparatus 16 which is electrically connected to the motor and various other devices to provide the necessary control and coordination between the various components of the system.
One of the functions performed by the control 16 is that of controlling the speed of the motor 14 such that the blower 13 provides the desired volume flow of air through the furnace.
The furnace 11 includes an intake vent 17 which brings in outdoor air for combustion, and a burner (not shown) where the fuel-air mixture is burned. The résulting hot combustion gases are then drawn through a primary heat exchanger 18 and a condensing heat exchanger 19, with the exhaust gases then flowing out the exhaust vent 21. At the same time, the cool household air is being brought back to the furnace by the blower 13 and then recircula~ed upwardly through the fan discharge opening 22 and across the outer surfaces of the condensing heat exchanger 19 and the primary heat exchanger 18 where it is heated on its way to the duct 23 for distribut,on throughout the house.
In addition to controlling the blower motor 14, ~he control 16 functions to regulate and coordinate the operation of a draft inducer blower, the flow of fuel to the burners, and -` ~2~36~7~
the operation of the pilo~ and primary ignition devices. Ir.
Figure 2, there is shown a schematic illustration of the microprocessor control 16 with its electrical interconnec~
tions with the fan motor 14 and with the other devices which it controls. Typically the ignition devices ~4 include a pilo~ which, after being proved, sends a signal to ~he microprocessor control 16 which then opens the fuel valves 27 to send fuel to the burners. In order to provide for the proper miY.ture of air to ~he burners, the microprocessor control 16 also turns on the inducer motor 27 to drive the inducer blower 28, which then causes air to flow from the air inlet 17 into the burner to mix with the fuel in the desired proportions. After ignition has occurred in the burners, and hot exhaust gases have been drawn into the heat exchangers to heat up their outer surfaces, the microprocessor control 16 turns on the fan motor 14 to drive the fan 13 for circulating the hot air throughout the house. When the house is heated to the point that the thermostat 29 is satisfied, then a signal is sent to the microprocessor control 16 ~o de-energize, in a sequentia-l and controlled fashion, the fuel valves 26,-the ignition devices 24, the inducer motor 27 and the fan motor 14.
The motor 14 is of the variable speed type such tha~ it~
speed ¢an be controlled so as to maintain the desired ~ir delivery for a particular air tempera~ure rise or cooling load desired. One such motor is an electronically commutated motor which is commercially available from General Electric as Part Number 5SME39HGH69IT. However, it will be understood that other variable speed motor and control combinations, such as, for example, any AC motor and inverter combination, could be used in practicing the presen~ invention. Similar-ly, although the present invention is being described herein as applied to a motor which drives a furnace blower fan, it will be recognized that the invention can be used with other variable load applications ac well.
~2~ 13 . ~
Referring now ~o Figure 3, ~he various steps in the inventive process are set forth, wi~h the particular sequence as showr being exemplary and not necessarily required to be performed in that order, Further, although it will be recognized that some of the steps are set forth in specific terms, it will be understood that their function as set forth in the claims may be accomplished by other specific means while still remaining within the scope of the invention, In order to establish the output of the fan 13 when the motor is operating at maximum power conditions, laboratory tests were conducted with the motor mentioned hereinabove as driving a Morrison blower wheel manufactured by Morrision Products Inc. of Cleveland, Ohio and available as a commercial product as Part No. 10-7~D03-42007-0.
These laborator,7 tests were necessary to determine, for the motor-blower assembly, the air flow ra~e of the blower (CPM), and the power outputs (HP) 'and speeds (RPM) of the motor operating at maximum power conditions over a ran8e of load conditions. It should be mentioned here that the present invention can be used in variable speed applic~tions other than in driving fans, in which case the measurements to be made are not air flow (CFM) but some other form of work output. Accordingly, where CF~ is used hereinafter it should be construed in the narrow sense only to the extent it is being applied to the blower assembly described, but in G
broader sense to mean work output of a system being controlled by the present invention, To obtain the desired values mentioned above, the assembly is run at maximum power under conditions with static pressure varying from ,1 to .7 inches W.C, The results are set forth in the ~ollowing table:
STAIIC HP TEST
PRESSU~E (IN. W.C.)(WATTS) RPM CFM
.1 421 924 1413 .2 431 95~ 138Q
.3 439 992 1343 .4 447 1026 1304 .5 457 105 1269 .6 465 1091 1242 .7 475 1128 1214 Since it is under high load conditions (i.e., high motor RP2:
under high seatic pressure conditions) that the power l~mit may be exceeded, it is necessary to choose an associated design point that represents the limit on the power output of the motor. An analysis of ~he data in Table 1 showed th~ 2 safe power li~it for the particular motor/blower co~binatior mentioned hereinabov~ would be 457 watts, which corresponds to 1059 RPM and 1269 CF~.
Using the data from Iable 1, it i6 then necessary to calcu-late, at the various systematic pressures, an equivalent reference motor speed (RPMr~f) which would occur during a "coast down" measure~ent, as conducted in accordance w.~h Canadian Application Serial No. 524,283 referenced heremabove and as illustrated in the following equation which has been derived empirically by operating the above-mentioned motor and blower wheel assembly to obtain the relatior.ship between the motor speed and the fan output:
CF~ref = 865.893 - (.74539 x RP~ref) (Eq. 1) ~2 ~ 3 Where: CFMref is the reference air volume flow rate expressed ln cubic fest per minute and RPMref is the reerence motor speed in revolutions per minute.
Using the empirical relationship set forth in Equation 1 and the following fan law equation:
RPM = CFM (Eq. 2) ref ref A reference motor speed RPMr~f is found to be:
ref 865.893 x RPM (Eq.3) CFM ~ (.74539 x RPM) Using the RPM and CFM values of Table 1, Equation 3 is then used to obtain the RPMref values as set forth in column 2 of Table 2 and are used as a reference in determining system load conditions to thereby obtain the corresponding maximum allowable RP~ (RPM457). These values as shown in column 3 of Table 2 are ob~ained using the follo~-ing fan law equation:
( 457)3 = max (Eq. 4) RPM HP
rearranging:
30RPM457 =RPM x (HP 1/3 (Eq. 5) Where: RPM457 is the ~otor speed at which the power input will be 457 watts.
~86~
HPmax i9 457 watts and RPM and ~P are the respective values from Table 1.
10STATIC PRESSURE RPMref RPM457 (IN. W.C.? (EQ. 3) (EQ. 5) .1 380.7 949.6 .2 396.1 976.9 ,3 412.5 lOQ5.4 .4 429,4 1033.6 .5 445.5 1059.0 .~ 459.6 1084.7 .7 475.3 1113.6 Thus, by limiting the speed of the motor to the indicated RPM457 value corresponding to the particular system operating condition, the power output of the motor can be limited to 457 watts to thereby protect the motor and its electronic components from damage that may otherwise occur. Such an application, requires no means for sensing the static pressure condition but rather uses the calculated RPMref which has been obtalned in the coast down technique. Since these are discrete values between which it would be necessary to interpolate, an empirical relationship is derived to provide for control over 2 continuous range of P~Mref values.
Assuming a straight line rela~ionship (y = mx ~ b) between RPMref, and RPMma~, and designating RPM457 as RPMmaX we obtain the following equation:
l 3 RP~.may = 297.18 ~ (1.715 x RP~.re~) (Eq. 6) In applying E~uation 6, the RPMref is obtained at the beginning of each h~ating cycle when performing the calibra-tion technique set forth in Canadian Patent Application Serial No. 524,283 referenced hereinabove. Thus, when the sy~te~
goes through a coast down measurement of the system load and computes the desired RPM to obtain the desired CFM of a~r delivery, it can no~ compare the desired RPM and limit it to RPMm~y to prevent the motor from being overstressed.
Further, whenever the desired RPM ic greater than RP~m~, it msy be dtsirable to cause some type of fsult ~i~nal to be displayed to thereby indicate that ~ load condition exists which is causing the power limiting feature to be brought into play. The operator c~n then check for such things as blocked filters or closed damper6 to remove the excessive load condition.
Referring now to Figure 4, ~he principles discussed herein-~`G above sre illustrateG on a blower performance greph. In thet graph line A is a maximu~ power line representing those ~alues in Table 1 wherein the sy6tem was run at maximum po~er conditions. Line B is a constant power line representing those values in Table 2, column 3, wherein the syste~ ~-as run at a constant power output level of 330 ~atts (i.e. 457 watts oS input power). The use of Equation 6 allows one to recognize the crossing point of these two lines ~nd, where ~he desired RPM is less than the RPMmaX, the 6ystem will be allowed to operat~ within the confines of line A. But if the desired RP~; is greater than the RPMmaX the syste~ will rat~,er be made to operate on line B, It should be understood that the control method and appar~tus of the present invention can be used to control any variable speed motor which is susceptible to variable load cor.citions.
Thus, ~he preceding description of the inventior; as appli~c 6t713 `` 11 to a blower of a furnace has been provided merely for the purpose of presenting a more complet~ illustration of the invention and its application and should not be consider~d as limited to that application or particulàr embodiment.
PO~ER OUTPUT
Back~round of the Invention This invention relates generally to the control of motors and, more particularly, to a method of limiting to a safe level ~he power output of a variable speed motor operating under variable load conditions.
The use of variable speed motors is now being made for various applications. In order to vary the speeds as de-sired, various control techniques have been employed. One approach is that of pulse width modulation wherein the voltage is controlled by varying the duration and/or width of the output pulses. Pulse width modulation can be used, for example, with inverter controls or with electrically commu-tated motors (ECM's).
In the application of motor controls, it is common to limit the speed of the motor to a safe operating level as deter-mined by the particular design specifications. Even when operating within this limit, a motor or its associated electronics may become overstressed if its power output exceeds a certain level for a given load on the motor. For example, where a motor is used to drive a fan for the circu-lation of air from a furnace, the speed of the motor is controlled such that the power output will not normally exceed a safe level. However, where a high volume of air delivery is called for under nons~andard conditions such as static pressures in excess of .5 inches of water, the associ-ated higher torque requirements may cause the safe power output level to b~ exceeded. This may occur, for example, where the air filter becomes dirty or the ductwork is overly restrictive because of improper sizing or because of too many dampers being closed off.
~2~t~ 13 In Canadian Patent Application No. 524,283, filed Decem~er 2, 1986 by ~be common assignee of the present invention, a technique is described for calibrating a variable ~peed mo~or. As part of this t~chnigue, ~ motor fan combination is tested to empirically determine ~he relationship between the speed of the motor and the volume flow of air being delivereo by the fan. Th,s relationship is ther. used, in combination with ~he fan law equations and a measured torque output of the motor, to calculate the desired motor ~peed to obtain a desired air delivery volume. However, such a motor and control 6ystem is suscep~ible to the problem mentioned above relatlng to excessive power conditions.
It is therefore an object of the present inventlon to provide a means of protecting a variable 8p~ed motor from eJ~ceeding a safe level of power output.
Another object of the present invention is the provision fGr controlling the power output of a variable speed motor to which an unusually high load may be applied.
Yet another object of the present invention is the provisior.
for controllin~ the output of a variable speed motor without the use of special equipment and apparstus.
Still another object of the present invention is the provi-sion for an improved motor control system that is ~cono~ic~l to manufacture and effective in use.
These objects and other features and advsn~age6 become more ~eadily apparent upon reference to ~he following description ~hen taken in conjunction with the appended drawin~s.
Summary ~f the Invention ~riefly, in accordance with one aspect of the invention, ~
motor fan combination is empirically tested to aetermine the ~213~13 relationship between the motor speed and the volume flow of air. The motor is ~hen operated at maximum power over a range of s~atic pressure conditions~ while t~e corresponding volume flow, motor speed, and motor power output are record-ed. A maximum power output limit is established, and, usingthe fan laws, maximum allowable motor speeds are calculated over the range of static pressure conditions. The actual motor speed is ~hen limited to these maximum allowable motor speeds during all periods of operation.
In accordallce with another aspect of the invention, again using the fan laws, reference speeds are determined, as a function of motor speeds and volume flow, over the range of the static load conditions. These reference speeds are then related to the ma~imum allowable motor speeds to derive a representative equa~ion wherein the maximum allowable motor speed is expressed as a function of the reference speeds. A
microprocessor then uses the equation ~o compute ~he maximum allowable motor speed for ~he existing static load conditions, and to limit the actual speed of the motor to those values.
In the drawings as hereinafter describéd, a preferred embodi-ment is depicted; however, various other modifications in alternate constructions can be made thereto withcut departing from the true spirit and scope o the invention.
Brief Description of the Drawings Figure 1 is a perspective view, partizlly broken away, of a furnace having an installed motor and control system in accordance with the present inven~ion.
Figure 2 is a schematic illustration of the motor and con~rol portion of the present inventi.on.
t71;3 Figure 3 is a schematic illustration of the process of controlling a motor in accordance with the present invention.
Figure 4 is a graphic illustration, of how the motor operat-ing conditions are controlled in accordance with the present invention.
Description of the Preferred Embodiment Referring now to Figure 1, there is shown generally at 10, a motor con~rol system as applied to a furnace 11 in accordance with the design of the present invention. The furnace 11 includes a cabinet 12 which houses in its lower portion a blower 13, a motor 14 for driving the blower 13 and a control apparatus 16 which is electrically connected to the motor and various other devices to provide the necessary control and coordination between the various components of the system.
One of the functions performed by the control 16 is that of controlling the speed of the motor 14 such that the blower 13 provides the desired volume flow of air through the furnace.
The furnace 11 includes an intake vent 17 which brings in outdoor air for combustion, and a burner (not shown) where the fuel-air mixture is burned. The résulting hot combustion gases are then drawn through a primary heat exchanger 18 and a condensing heat exchanger 19, with the exhaust gases then flowing out the exhaust vent 21. At the same time, the cool household air is being brought back to the furnace by the blower 13 and then recircula~ed upwardly through the fan discharge opening 22 and across the outer surfaces of the condensing heat exchanger 19 and the primary heat exchanger 18 where it is heated on its way to the duct 23 for distribut,on throughout the house.
In addition to controlling the blower motor 14, ~he control 16 functions to regulate and coordinate the operation of a draft inducer blower, the flow of fuel to the burners, and -` ~2~36~7~
the operation of the pilo~ and primary ignition devices. Ir.
Figure 2, there is shown a schematic illustration of the microprocessor control 16 with its electrical interconnec~
tions with the fan motor 14 and with the other devices which it controls. Typically the ignition devices ~4 include a pilo~ which, after being proved, sends a signal to ~he microprocessor control 16 which then opens the fuel valves 27 to send fuel to the burners. In order to provide for the proper miY.ture of air to ~he burners, the microprocessor control 16 also turns on the inducer motor 27 to drive the inducer blower 28, which then causes air to flow from the air inlet 17 into the burner to mix with the fuel in the desired proportions. After ignition has occurred in the burners, and hot exhaust gases have been drawn into the heat exchangers to heat up their outer surfaces, the microprocessor control 16 turns on the fan motor 14 to drive the fan 13 for circulating the hot air throughout the house. When the house is heated to the point that the thermostat 29 is satisfied, then a signal is sent to the microprocessor control 16 ~o de-energize, in a sequentia-l and controlled fashion, the fuel valves 26,-the ignition devices 24, the inducer motor 27 and the fan motor 14.
The motor 14 is of the variable speed type such tha~ it~
speed ¢an be controlled so as to maintain the desired ~ir delivery for a particular air tempera~ure rise or cooling load desired. One such motor is an electronically commutated motor which is commercially available from General Electric as Part Number 5SME39HGH69IT. However, it will be understood that other variable speed motor and control combinations, such as, for example, any AC motor and inverter combination, could be used in practicing the presen~ invention. Similar-ly, although the present invention is being described herein as applied to a motor which drives a furnace blower fan, it will be recognized that the invention can be used with other variable load applications ac well.
~2~ 13 . ~
Referring now ~o Figure 3, ~he various steps in the inventive process are set forth, wi~h the particular sequence as showr being exemplary and not necessarily required to be performed in that order, Further, although it will be recognized that some of the steps are set forth in specific terms, it will be understood that their function as set forth in the claims may be accomplished by other specific means while still remaining within the scope of the invention, In order to establish the output of the fan 13 when the motor is operating at maximum power conditions, laboratory tests were conducted with the motor mentioned hereinabove as driving a Morrison blower wheel manufactured by Morrision Products Inc. of Cleveland, Ohio and available as a commercial product as Part No. 10-7~D03-42007-0.
These laborator,7 tests were necessary to determine, for the motor-blower assembly, the air flow ra~e of the blower (CPM), and the power outputs (HP) 'and speeds (RPM) of the motor operating at maximum power conditions over a ran8e of load conditions. It should be mentioned here that the present invention can be used in variable speed applic~tions other than in driving fans, in which case the measurements to be made are not air flow (CFM) but some other form of work output. Accordingly, where CF~ is used hereinafter it should be construed in the narrow sense only to the extent it is being applied to the blower assembly described, but in G
broader sense to mean work output of a system being controlled by the present invention, To obtain the desired values mentioned above, the assembly is run at maximum power under conditions with static pressure varying from ,1 to .7 inches W.C, The results are set forth in the ~ollowing table:
STAIIC HP TEST
PRESSU~E (IN. W.C.)(WATTS) RPM CFM
.1 421 924 1413 .2 431 95~ 138Q
.3 439 992 1343 .4 447 1026 1304 .5 457 105 1269 .6 465 1091 1242 .7 475 1128 1214 Since it is under high load conditions (i.e., high motor RP2:
under high seatic pressure conditions) that the power l~mit may be exceeded, it is necessary to choose an associated design point that represents the limit on the power output of the motor. An analysis of ~he data in Table 1 showed th~ 2 safe power li~it for the particular motor/blower co~binatior mentioned hereinabov~ would be 457 watts, which corresponds to 1059 RPM and 1269 CF~.
Using the data from Iable 1, it i6 then necessary to calcu-late, at the various systematic pressures, an equivalent reference motor speed (RPMr~f) which would occur during a "coast down" measure~ent, as conducted in accordance w.~h Canadian Application Serial No. 524,283 referenced heremabove and as illustrated in the following equation which has been derived empirically by operating the above-mentioned motor and blower wheel assembly to obtain the relatior.ship between the motor speed and the fan output:
CF~ref = 865.893 - (.74539 x RP~ref) (Eq. 1) ~2 ~ 3 Where: CFMref is the reference air volume flow rate expressed ln cubic fest per minute and RPMref is the reerence motor speed in revolutions per minute.
Using the empirical relationship set forth in Equation 1 and the following fan law equation:
RPM = CFM (Eq. 2) ref ref A reference motor speed RPMr~f is found to be:
ref 865.893 x RPM (Eq.3) CFM ~ (.74539 x RPM) Using the RPM and CFM values of Table 1, Equation 3 is then used to obtain the RPMref values as set forth in column 2 of Table 2 and are used as a reference in determining system load conditions to thereby obtain the corresponding maximum allowable RP~ (RPM457). These values as shown in column 3 of Table 2 are ob~ained using the follo~-ing fan law equation:
( 457)3 = max (Eq. 4) RPM HP
rearranging:
30RPM457 =RPM x (HP 1/3 (Eq. 5) Where: RPM457 is the ~otor speed at which the power input will be 457 watts.
~86~
HPmax i9 457 watts and RPM and ~P are the respective values from Table 1.
10STATIC PRESSURE RPMref RPM457 (IN. W.C.? (EQ. 3) (EQ. 5) .1 380.7 949.6 .2 396.1 976.9 ,3 412.5 lOQ5.4 .4 429,4 1033.6 .5 445.5 1059.0 .~ 459.6 1084.7 .7 475.3 1113.6 Thus, by limiting the speed of the motor to the indicated RPM457 value corresponding to the particular system operating condition, the power output of the motor can be limited to 457 watts to thereby protect the motor and its electronic components from damage that may otherwise occur. Such an application, requires no means for sensing the static pressure condition but rather uses the calculated RPMref which has been obtalned in the coast down technique. Since these are discrete values between which it would be necessary to interpolate, an empirical relationship is derived to provide for control over 2 continuous range of P~Mref values.
Assuming a straight line rela~ionship (y = mx ~ b) between RPMref, and RPMma~, and designating RPM457 as RPMmaX we obtain the following equation:
l 3 RP~.may = 297.18 ~ (1.715 x RP~.re~) (Eq. 6) In applying E~uation 6, the RPMref is obtained at the beginning of each h~ating cycle when performing the calibra-tion technique set forth in Canadian Patent Application Serial No. 524,283 referenced hereinabove. Thus, when the sy~te~
goes through a coast down measurement of the system load and computes the desired RPM to obtain the desired CFM of a~r delivery, it can no~ compare the desired RPM and limit it to RPMm~y to prevent the motor from being overstressed.
Further, whenever the desired RPM ic greater than RP~m~, it msy be dtsirable to cause some type of fsult ~i~nal to be displayed to thereby indicate that ~ load condition exists which is causing the power limiting feature to be brought into play. The operator c~n then check for such things as blocked filters or closed damper6 to remove the excessive load condition.
Referring now to Figure 4, ~he principles discussed herein-~`G above sre illustrateG on a blower performance greph. In thet graph line A is a maximu~ power line representing those ~alues in Table 1 wherein the sy6tem was run at maximum po~er conditions. Line B is a constant power line representing those values in Table 2, column 3, wherein the syste~ ~-as run at a constant power output level of 330 ~atts (i.e. 457 watts oS input power). The use of Equation 6 allows one to recognize the crossing point of these two lines ~nd, where ~he desired RPM is less than the RPMmaX, the 6ystem will be allowed to operat~ within the confines of line A. But if the desired RP~; is greater than the RPMmaX the syste~ will rat~,er be made to operate on line B, It should be understood that the control method and appar~tus of the present invention can be used to control any variable speed motor which is susceptible to variable load cor.citions.
Thus, ~he preceding description of the inventior; as appli~c 6t713 `` 11 to a blower of a furnace has been provided merely for the purpose of presenting a more complet~ illustration of the invention and its application and should not be consider~d as limited to that application or particulàr embodiment.
Claims (7)
1. A method of controlling the power output of a variable speed motor operating to drive a device under variable load conditions comprising the steps of:
(a) driving a representative device by operating said representative motor over a range of speeds and sensing parameters to determine the relationship of representative motor speed to work output of said represen-tative device;
(b) driving said representative device with said motor operating at maximum power conditions over a range of variable load conditions, and sensing parameters to determine the work outputs and the corresponding speeds and power outputs of said representative motor over said range;
(c) establishing a particular power output limit for the motor;
(d) using the above determinations to calculate the maximum allowable motor speeds corresponding to said power output limit over said range of variable load conditions;
(e) sensing the actual speed of the variable speed motor driving the device under variable load condi-tions; and (f) limiting said actual speed to said maximum allowable motor speeds while operating within said range of variable load conditions.
(a) driving a representative device by operating said representative motor over a range of speeds and sensing parameters to determine the relationship of representative motor speed to work output of said represen-tative device;
(b) driving said representative device with said motor operating at maximum power conditions over a range of variable load conditions, and sensing parameters to determine the work outputs and the corresponding speeds and power outputs of said representative motor over said range;
(c) establishing a particular power output limit for the motor;
(d) using the above determinations to calculate the maximum allowable motor speeds corresponding to said power output limit over said range of variable load conditions;
(e) sensing the actual speed of the variable speed motor driving the device under variable load condi-tions; and (f) limiting said actual speed to said maximum allowable motor speeds while operating within said range of variable load conditions.
2. A method as set forth in claim 1 wherein the variable speed motor is connected to drive a fan and the work output is the volume of air being moved over a period of time.
3. A method as set forth in claim 2 wherein the variable load conditions are expressed in terms of static pressure.
4. A method as set forth in claim 1 and including the steps of:
(a) determining reference speeds expressed as a function of motor speeds and work output over said range of variable load conditions; and (b) using these reference speeds in limiting the actual motor speeds.
(a) determining reference speeds expressed as a function of motor speeds and work output over said range of variable load conditions; and (b) using these reference speeds in limiting the actual motor speeds.
5. A method as set forth in claim 4 and including the further steps of:
(a) relating said reference speeds to said maximum allowable motor speeds and deriving an equation which expresses the maximum allowable motor speed as a function of said reference speed; and (b) using the equation in limiting the actual motor speed.
(a) relating said reference speeds to said maximum allowable motor speeds and deriving an equation which expresses the maximum allowable motor speed as a function of said reference speed; and (b) using the equation in limiting the actual motor speed.
6. A method as set forth in claim 5 wherein said equation is a best fit straight line equation.
7. A method of limiting the power output of variable speed motor which is applied to drive a fan comprising the steps of:
(a) operating a representative motor and fan combination and sensing parameters to determine the volume flow rates of said representative fan as a function of said representative motor speeds;
(b) operating said representative motor and fan combination and sensing parameters to determine, for various static pressure conditions of said representative fan, with said representative motor operating under maximum power conditions, the volume flow rate of said representa-tive fan and the corresponding speeds and power outputs of said representative motor;
(c) establishing a particular power output limit for the motor;
(d) using the known fan law relationship of motor speed and power output, determining the maximum motor speeds corresponding to said power output limit for each of said various static pressure conditions;
(e) using the volume flow rates and motor speeds obtained in step (a) and using the known fan law relation-ship of speed versus volume flow rate, determining reference speeds for each of said various static pressure conditions;
(f) using the maximum motor speeds and the reference speeds obtained in respective steps (d) and (e), establishing a best fit straight line equation to express the maximum allowable motor speeds as a function of said reference speeds;
(g) sensing the actual speed of the variable speed motor driving the fan; and (h) limiting said control speeds to said maximum allowable motor speeds found in step (f).
(a) operating a representative motor and fan combination and sensing parameters to determine the volume flow rates of said representative fan as a function of said representative motor speeds;
(b) operating said representative motor and fan combination and sensing parameters to determine, for various static pressure conditions of said representative fan, with said representative motor operating under maximum power conditions, the volume flow rate of said representa-tive fan and the corresponding speeds and power outputs of said representative motor;
(c) establishing a particular power output limit for the motor;
(d) using the known fan law relationship of motor speed and power output, determining the maximum motor speeds corresponding to said power output limit for each of said various static pressure conditions;
(e) using the volume flow rates and motor speeds obtained in step (a) and using the known fan law relation-ship of speed versus volume flow rate, determining reference speeds for each of said various static pressure conditions;
(f) using the maximum motor speeds and the reference speeds obtained in respective steps (d) and (e), establishing a best fit straight line equation to express the maximum allowable motor speeds as a function of said reference speeds;
(g) sensing the actual speed of the variable speed motor driving the fan; and (h) limiting said control speeds to said maximum allowable motor speeds found in step (f).
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/868,378 US4707646A (en) | 1986-05-29 | 1986-05-29 | Method of limiting motor power output |
| US868,378 | 1986-05-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1286713C true CA1286713C (en) | 1991-07-23 |
Family
ID=25351559
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000535475A Expired - Lifetime CA1286713C (en) | 1986-05-29 | 1987-04-24 | Method of limiting motor power output |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4707646A (en) |
| JP (1) | JPS62290383A (en) |
| KR (1) | KR900008037B1 (en) |
| CA (1) | CA1286713C (en) |
| DE (1) | DE3717870A1 (en) |
| FR (1) | FR2606526B1 (en) |
| GB (1) | GB2193398B (en) |
Families Citing this family (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5220255A (en) * | 1990-10-12 | 1993-06-15 | Lennox Industries Inc. | Interface for interconnecting a thermostat and an electronically commutated motor |
| US5060722A (en) * | 1990-11-06 | 1991-10-29 | American Standard, Inc. | Furnace heat exchanger |
| US5616995A (en) * | 1993-02-22 | 1997-04-01 | General Electric Company | Systems and methods for controlling a draft inducer for a furnace |
| KR950001114A (en) * | 1993-06-19 | 1995-01-03 | 이헌조 | Fan Drive Control and Method of Fan |
| JP3295553B2 (en) * | 1994-10-05 | 2002-06-24 | 三菱電機株式会社 | Variable speed device |
| US5590642A (en) * | 1995-01-26 | 1997-01-07 | Gas Research Institute | Control methods and apparatus for gas-fired combustors |
| US5818194A (en) * | 1996-04-01 | 1998-10-06 | Emerson Electric Co. | Direct replacement variable speed blower motor |
| US5865611A (en) * | 1996-10-09 | 1999-02-02 | Rheem Manufacturing Company | Fuel-fired modulating furnace calibration apparatus and methods |
| US6168430B1 (en) | 1999-12-06 | 2001-01-02 | Duncan Higgins | Orthodontic appliance for treating overjet |
| GB2457534A (en) * | 2008-01-16 | 2009-08-26 | Ebm Papst Uk Ltd | Electric-motor driven fan speed control |
| US8070481B2 (en) | 2008-05-27 | 2011-12-06 | Honeywell International Inc. | Combustion blower control for modulating furnace |
| US8123518B2 (en) | 2008-07-10 | 2012-02-28 | Honeywell International Inc. | Burner firing rate determination for modulating furnace |
| US8143828B2 (en) | 2008-08-08 | 2012-03-27 | Rbc Manufacturing Corporation | Retrofit motor system for heating, ventilation, and air conditioning applications |
| US9071183B2 (en) * | 2011-05-27 | 2015-06-30 | Regal Beloit America, Inc. | Methods and systems for providing combined blower motor and draft inducer motor control |
| US8876524B2 (en) | 2012-03-02 | 2014-11-04 | Honeywell International Inc. | Furnace with modulating firing rate adaptation |
| US10295236B2 (en) * | 2014-08-13 | 2019-05-21 | Trane International Inc. | Compressor heating system |
Family Cites Families (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE878759C (en) * | 1948-07-06 | 1953-06-05 | Escher Wyss Maschinenfabrik G | Device for regulating an engine controlled by a speed controller and a power controller |
| DE948117C (en) * | 1951-09-12 | 1956-08-30 | Dr Hans Bender | Method for speed control of prime movers |
| DE1078873B (en) * | 1957-06-08 | 1960-03-31 | Motorenfabrik Darmstadt G M B | Overload shutdown device for engines with speed governors, especially for internal combustion engines |
| DE1958411A1 (en) * | 1969-11-21 | 1971-05-27 | Siemens Ag | Process and device to improve the shutdown safety when operating turbo systems |
| DE2254250C3 (en) * | 1972-11-06 | 1980-06-19 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Speed limiter for a turbine |
| US4102604A (en) * | 1977-05-04 | 1978-07-25 | Compressor Controls Corporation | Method and apparatus for noninteracting control of a dynamic compressor having rotating vanes |
| US4177649A (en) * | 1977-11-01 | 1979-12-11 | Borg-Warner Corporation | Surge suppression apparatus for compressor-driven system |
| US4248194A (en) * | 1979-08-23 | 1981-02-03 | Trw Inc. | Method and apparatus for controlling the operation of a pump |
| US4279013A (en) * | 1979-10-31 | 1981-07-14 | The Valeron Corporation | Machine process controller |
| US4317176A (en) * | 1980-03-24 | 1982-02-23 | Black & Decker Inc. | Microcomputer controlled power tool |
| US4526513A (en) * | 1980-07-18 | 1985-07-02 | Acco Industries Inc. | Method and apparatus for control of pipeline compressors |
| DE3125157A1 (en) * | 1981-06-26 | 1983-01-13 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Rotation-speed regulating circuit for a motor |
| US4513381A (en) * | 1982-06-07 | 1985-04-23 | The Singer Company | Speed regulator for power tool |
| DE3329971A1 (en) * | 1983-08-19 | 1985-03-07 | Robert Bosch Gmbh, 7000 Stuttgart | CONTROL AND OPERATING DEVICE FOR AN ELECTRIC HAND TOOL |
| US4628233A (en) * | 1984-03-23 | 1986-12-09 | Black & Decker Inc. | Microprocessor based motor control |
-
1986
- 1986-05-29 US US06/868,378 patent/US4707646A/en not_active Expired - Fee Related
-
1987
- 1987-04-24 CA CA000535475A patent/CA1286713C/en not_active Expired - Lifetime
- 1987-05-13 GB GB8711261A patent/GB2193398B/en not_active Expired - Lifetime
- 1987-05-27 DE DE19873717870 patent/DE3717870A1/en not_active Withdrawn
- 1987-05-28 KR KR1019870005315A patent/KR900008037B1/en not_active IP Right Cessation
- 1987-05-29 FR FR8707585A patent/FR2606526B1/en not_active Expired - Fee Related
- 1987-05-29 JP JP62134800A patent/JPS62290383A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| GB2193398B (en) | 1990-03-21 |
| US4707646A (en) | 1987-11-17 |
| GB2193398A (en) | 1988-02-03 |
| FR2606526B1 (en) | 1993-12-03 |
| DE3717870A1 (en) | 1987-12-03 |
| FR2606526A1 (en) | 1988-05-13 |
| KR900008037B1 (en) | 1990-10-31 |
| JPS62290383A (en) | 1987-12-17 |
| KR870011726A (en) | 1987-12-26 |
| GB8711261D0 (en) | 1987-06-17 |
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