Abstract:
Methods and apparatus for controlling a motor are provided. The motor may be operated in a fluid system having a variable static pressure acting on the motor. The method including operating the motor at a first substantially constant torque level, varying the static pressure of the system, receiving a torque selection signal from external to the motor, and operating the motor at a second substantially constant torque level, the level corresponding to the torque selection signal.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to electric motors, and more particularly, to methods and apparatus for controlling the operation of electric motors.  
         [0002]     At least some known fluid handling systems utilize a constant flow rate through a contained space of a system that may include an apparatus for conditioning the temperature of the fluid. Within such systems the rate of fluid flow may be related to the static pressure associated with the system wherein the static pressure may vary due to changes in system flow demands. The apparatus may include an electric motor coupled to a fluid driver such as a fan, a blower, or a pump. The speed and torque of the electric motor may be affected by the static pressure of the system and the rate of fluid flow. The static pressure of the system and the rate of fluid flow may vary according to the changing system demands. Providing systems with motor speed and torque characteristics matched to a fluid mover to provide an approximately constant fluid flow to the system may require laborious and time consuming attempts to match motor speed and torque with the proper fluid mover to at least approximate the desired fluid flow rate for the particular contained space and static pressure of the particular apparatus or the system in which such apparatus was employed.  
         [0003]     For example, if the fluid mover is a squirrel cage type blower, a decrease in the static pressure acting on the blower may result in a decrease in the speed of the blower and the electric motor driving it. Conversely, if the static pressure acting on the blower is increased, the speed of the fan and the electric motor may be correspondingly increased. Thus, the speed of squirrel cage type blowers and electric motors varies directly, i.e. in following relation, with a variation of the static pressure.  
         [0004]     However, maintaining a substantially constant fluid flow operation with a varying system static pressure may require auxiliary detection and control components that may increase procurement and manufacturing costs beyond those that a customer may be willing to incur.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0005]     In one embodiment, a method for controlling a motor is provided. The motor may be operated in a fluid system having a variable static pressure acting on the motor. The method includes operating the motor at a first substantially constant torque level, varying the static pressure of the system, receiving a torque selection signal from external to the motor, and operating the motor at a second substantially constant torque level, the level corresponding to the torque selection signal.  
         [0006]     In another embodiment, a motor is provided. The motor includes a stationary assembly including a plurality of winding stages for carrying motor current, a rotatable assembly in magnetic driving relation with the stationary assembly, and a commutation electronics configured to supply a pulsed DC voltage in a preestablished sequence to the plurality of winding stages, the commutation electronics configured to receive a constant torque selection signal from a source external to the motor, the commutation electronics further configured to control motor current in the plurality of winding stages such that the motor generates one of a plurality of constant torque levels corresponding to the constant torque selection signal.  
         [0007]     In yet another embodiment, a fluid system comprising a motor wherein the motor is configured to receive a constant torque selection signal from a source external to the motor, the commutation electronics further configured to control motor current in the plurality of winding stages such that the motor generates one of a plurality of constant torque levels corresponding to the constant torque selection signal, a fluid mover coupled to the motor, the fluid mover in fluid communication with a contained space within the fluid system, the fluid mover configured to generate a fluid flow through the fluid system in relation to a static pressure in the contained space and a rotational speed of the fluid mover, and at least one flow regulator configured to modify flow through the fluid system such that a static pressure acting on the fluid mover is variable based on a position of the fluid regulator. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic diagram of an exemplary fluid moving system such as a residential heating, ventilation and air conditioning (HVAC) system, a light industrial HVAC system, or a clean room filtering system;  
         [0009]      FIG. 2  is a perspective view of an exemplary selectable torque dynamoelectric machine that may be used in the system shown in  FIG. 1 ;  
         [0010]      FIG. 3  is a graph illustrating an exemplary flow versus static pressure relationship for a system that may be used with the blower and motor shown in  FIG. 1 ; and  
         [0011]      FIG. 4  is a graph illustrating another exemplary flow versus static pressure relationship for a system that may be used with the blower and motor shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]      FIG. 1  is a schematic diagram of an exemplary fluid moving system  100  such as a residential heating, ventilation and air conditioning (HVAC) system, a light industrial HVAC system, or a clean room filtering system. System  100  may include a characteristic static pressure that may be determined based on the dimensions and configuration of a contained space  102 , a temperature conditioning apparatus  104 , for example an evaporator coil of an air conditioner or a heat pump, or furnace heat exchanger, a position of a flow regulator, such as, damper  106 , and a vent or register  108 . System  100  may include a ductwork channel  110  for directing a flow of fluid, for example, air to an inlet  112  of a blower  114 . Channel  110  may include a filter  115  that, over time, may be subject to clogging. A motor  116  may be coupled to blower  114  through a shaft  118  for rotationally driving blower  114 . In the exemplary embodiment, motor  116  is an electronically commutated motor (ECM). In various embodiments, motor  116  is coupled to blower  114  through a power transmission device, such as, but not limited to a belt, a chain, and a fluid drive. Temperature conditioning apparatus  104 , may be positioned within ductwork channel  110  for conditioning the fluid flowing through blower  114  and into contained space  102 . Temperature conditioning apparatus  104  may be in fluid communication with a firebox of a furnace (not shown) or evaporator of a heat pump (not shown) through a heat exchanger inlet  120  and may discharge gases to a flue (not shown) or a heat pump return (not shown) through an outlet  122 . Dampers  106  and/or registers  108  may selectively be positioned manually and/or automatically in relation to demand for conditioned fluid. The varying positions of dampers  106  and registers  108  or clogging of air filter  115  may cause the static pressure, into which blower  114  is directing a flow of fluid, to change. The change in static pressure may in turn cause a change in fluid flow and speed of rotation of blower  114  and motor  116 .  
         [0013]     In the exemplary embodiment, motor  116  is configured to generate a selectable level of substantially constant torque. As the static pressure in system  100  increases, a rotational speed of blower  114  and fluid flow through blower  114  decreases. The rotational speed of blower  114  may be detected continuously or intermittently to determine that the static pressure of system  100  and consequently the flow through blower  114  is decreased. The rotational speed may be compared to a predetermined rotational speed threshold for selecting a next level of substantially constant torque at which motor  116  may operate. Increasing the level of torque at which motor  116  is operating increases the rotational speed of blower  114  and the fluid flow generated by blower  114 . In the exemplary embodiment, the level of substantially constant torque of motor  116  is selectable by selecting one of a plurality of selection lines  124  that are communicatively coupled to motor  116  through a commutation electronics  126 . In an alternative embodiment, the level of substantially constant torque of motor  116  is selectable through a signal line (not shown) communicatively coupled to commutation electronics  126 . The signal line may transmit a digital signal to a processor (not shown) programmed to change the level of substantially constant torque of motor  116 .  
         [0014]      FIG. 2  is a perspective view of an exemplary selectable torque motor  116 , such as for example, an ECM. A stationary assembly  200  includes a core or stator  202  of a ferromagnetic material, and a winding arrangement  204 . In the exemplary embodiment, the windings associated with winding arrangement  204  are configured to be electronically commutated in at least one preselected sequence. In an alternative embodiment, the windings associated with winding arrangement  204  are configured to be selectable separately or in combination to affect different discrete torque operating levels. A rotatable assembly  206  of motor  116  is rotatably associated with stationary assembly  200  and may include a permanent magnet rotor  208  operable generally for rotatably driving blower  114 . Rotatable assembly  206  may be associated, in selective magnetic coupling relation, with permanent magnet rotor  208 , so as to be rotatably driven about a longitudinal axis  209  by multistage winding arrangement  204  upon the electronic commutation thereof. Permanent magnet rotor  208  includes a plurality of magnet material elements  210  secured to a rotor  212  generally about the circumference thereof, and the rotor is secured about a shaft  214 . Rotor shaft  214  may be journaled by one or more bearings (not shown) in a pair of opposite end frames (not shown) forming a part of stationary assembly  200 , and rotor shaft  214  is configured to be coupled in rotatable driving relation with blower  114 . Motor  116  may include a commutation electronics  216  configured to sense a rotational position of rotatable assembly  206  within stationary assembly  200  and to provide signals to the winding stage in a preselected order to magnetically drive rotatable assembly  206  about longitudinal axis  209 . In the exemplary embodiment, commutation electronics  216  may include a plurality of input lines that may be used to transmit selection signals from a user&#39;s control device (not shown) to motor  116 . In one embodiment, each of the input lines corresponds to a constant torque configuration of motor  116 . In another embodiment, the input lines may be used in combination to transmit selection signals from a user&#39;s control device to motor  116 . The selection signals may be used to select one of a plurality of constant torque configurations of motor  116 . In an alternative embodiment, a processor  220  may be used to receive a selection signal or message from a user&#39;s control device through a cable  222 . Processor  220  may be programmed to control motor  116  to provide one of a plurality of selectable constant torque output levels based on the selection signal or message.  
         [0015]     In the exemplary embodiment, motor  116  is a permanent magnet electrical machine with magnet material elements  210  spaced substantially circumferentially along an out periphery of permanent magnet rotor  208  and multiple, spatially distributed winding arrangement  204  on stator  202 . Current in the windings of winding arrangement  204  interacts with the permanent magnetic field to produce the motor&#39;s torque. To maintain a constant torque as the rotor turns, the current distribution in stator  202  is continually adjusted to maintain a constant spatial relationship with the magnetic field of rotor  208 . The adjustment in current distribution is accomplished by switching (“commutating”) current among the various stator winding phases. Commutation may be effected electronically by controlling the conduction states of a multiplicity of electronic power devices (not shown) electrically coupling the various stator phase windings to a power bus.  
         [0016]      FIG. 3  is a graph  300  illustrating an exemplary flow versus static pressure relationship for a system that may be used with blower  114  and motor  116  (shown in  FIG. 1 ). Graph  300  includes an x-axis  302  graduated in divisions of fluid flow expressed in cubic feet per minute (CFM) and a y-axis  304  graduated in divisions of system static pressure expressed in units of inches of water (in H 2 O). A plurality of constant torque lines define the operating characteristics for the combination of blower  114 , motor  116 , and system  100 . A first constant torque line  306  defines an fluid flow response of blower  114  for a system static pressure that is defined by the positions of dampers  106  and registers  108  when a first torque operating level for motor  116  is selected. Similarly, a second constant torque line  308 , a third constant torque line  310 , a fourth constant torque line  312 , and a fifth constant torque line  314  respectively define an fluid flow response of blower  114  for an associated system static pressure when respective torque operating levels are selected. A line  316  illustrates a desired constant fluid flow through system  100 , a line  318  illustrates a lower limit of fluid flow, and a line  320  illustrates an upper limit of fluid flow for system  100 . Together, lines  318  and  320  define a band  321  of desired fluid flows through system  100  that is generally equally spaced about line  316 , although band  321  may be selected to be spaced about line  316  in non-equally.  
         [0017]     In operation, system  100  may initially be operating at a point  322 , for example, wherein motor  116  is selected to be outputting a first level of torque and blower  114  is outputting the desired fluid flow as indicated by operating point  322  being at the intersection of constant torque line  306  and fluid flow line  316 . If a change in system  100  causes an increase in system static pressure, such as a repositioning of dampers  106  and/or registers  108 , the system operating parameters will change such that system  100  will operate at a new operating point  324  along line  306 . Because motor  116  is configured to maintain the selected torque output substantially constant, when system static pressure increases the system operating point changes such that the fluid flow will decrease to a value corresponding to the intersection of line  306  and the value of static pressure the system is operating at. In this example, changes to system  100  caused system static pressure to increase from approximately 0.25 in H 2 O to approximately 0.31 in H 2 O. The system operating point moves along line  316  to operating point  324  wherein the fluid flow through system  100  and the speed of rotation of motor  116  decreases correspondingly. A further change in the position of dampers  106  and/or registers  108 , or other device that may affect system static pressure may cause the system parameters to change such that the system will operate at another new operating point  326  along line  306 . If at this point the speed of motor  116  reaches a value that corresponds to an fluid flow defined by lower limit  318 , a speed sensor or a sensor configured to sense a parameter that may correspond to the rotational speed of motor  116 , may transmit a signal that causes motor  116  to operate at a second torque level defined by second constant torque line  308 . Motor  116  will accelerate rotationally to operating point  328  such that motor  116  speed and fluid flow through blower  114  increases to a value corresponding to the intersection of the value of static pressure and constant torque line  308 .  
         [0018]     System  100  operates similarly for further increases in system static pressure by stepping to a next higher selectable constant torque level when the speed of motor  116  and correspondingly, the fluid flow through blower  114  decreases to lower a value defined by lower fluid flow limit  318 .  
         [0019]      FIG. 4  is a graph  400  illustrating another exemplary flow versus static pressure relationship for a system that may be used with blower  114  and motor  116  (shown in  FIG. 1 ). Graph  400  includes an x-axis  402  graduated in divisions of fluid flow expressed in cubic feet per minute (CFM) and a y-axis  404  graduated in divisions of system static pressure expressed in units of inches of water (in H 2 O). A plurality of constant torque lines define the operating characteristics for the combination of blower  114 , motor  116 , and system  100 . A first constant torque line  406  defines an fluid flow response of blower  114  for a system static pressure that is defined by the positions of dampers  106  and registers  108  when a first torque operating level for motor  116  is selected. Similarly, a second constant torque line  408 , a third constant torque line  410 , a fourth constant torque line  412 , and a fifth constant torque line  414  respectively define an fluid flow response of blower  114  for an associated system static pressure when respective torque operating levels are selected. A line  416  illustrates a desired constant fluid flow through system  100 , a line  418  illustrates a lower limit of fluid flow, and a line  420  illustrates an upper limit of fluid flow for system  100 . Together, lines  418  and  420  define a band  421  of desired fluid flows through system  100  that is generally equally spaced about line  416 , although band  421  may be selected to be spaced about line  416  in non-equally.  
         [0020]     In operation, system  100  may initially be operating at a point  422 , for example, wherein motor  116  is selected to be outputting a third level of torque and blower  114  is outputting the desired fluid flow as indicated by operating point  422  being at the intersection of constant torque line  410  and fluid flow line  416 . If a change in system  100  causes an decrease in system static pressure, such as a repositioning of dampers  106  and/or registers  108 , the system operating parameters will change such that system  100  will operate at a new operating point  424  along line  410 . Because motor  116  is configured to maintain the selected torque output substantially constant, when system static pressure decreases, the system operating point changes such that the fluid flow will increase to a value corresponding to the intersection of line  410  and the value of static pressure the system is operating at. In this example, changes to system  100  caused system static pressure to decrease from approximately 0.62 in H 2 O to approximately 0.57 in H 2 O. The system operating point moves along line  410  to operating point  424  wherein the fluid flow through system  100  and the speed of rotation of motor  116  increases correspondingly. A further change in the position of dampers  106  and/or registers  108 , or other device that may affect system static pressure may cause the system parameters to change such that the system will operate at another new operating point  426  along line  410 . If at this point the speed of motor  116  reaches a value that corresponds to a fluid flow defined by upper limit  420 , a speed sensor or a sensor configured to sense a parameter that may correspond to the rotational speed of motor  116 , may transmit a signal that causes motor  116  to operate at a different torque level defined by second constant torque line  408 . Motor  116  will decelerate rotationally to operating point  428  such that motor  116  speed and fluid flow through blower  114  decreases to a value corresponding to the intersection of the value of static pressure and constant torque line  408 .  
         [0021]     System  100  operates similarly for further decreases in system static pressure by stepping to a next lower selectable constant torque level when the speed of motor  116  and correspondingly, the fluid flow through blower  114  increases to an upper value defined by upper fluid flow limit  420 .  
         [0022]     The above-described embodiments of methods and apparatus for discrete speed compensated torque step motor control are cost-effective and highly reliable for maintaining a relatively constant flow through a fluid system using relatively less expensive control components such that a selectable substantially constant torque is generated by the motor in response to an input signal indicative generally of motor speed.  
         [0023]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.