Patent Description:
The field of the disclosure relates generally to a control system for electric motors and, more specifically, a control system that enables approximately constant fluid-flow production from a fluid moving apparatus.

At least some electric motors are torque-calibrated when manufactured to ensure the torque output at the drive shaft of the electric motor matches the torque commanded. At least some electric motors, particularly electric motors driving blowers, such as a forward-curved blower, are further calibrated to produce an approximately constant fluid-flow or, more specifically, airflow during operation in either a torque-control mode or a speed-control mode. Such a calibration, or characterization, quantizes airflow output for a given speed and torque output when driving the blower. The actual airflow output can vary according to the blower construction or duct, space, or other airflow restriction, into which the airflow is directed.

Constant fluid-flow heating, ventilation, and air conditioning (HVAC) systems improve thermal comfort and energy savings. Constant fluid-flow systems may also be used in certain refrigeration systems or pumping systems. In a constant fluid-flow system, a control system for an electric blower motor receives a fluid-flow rate demand, for example, a value in cubic feet per minute (CFM), and then determines, for example, by a polynomial or constant fluid-flow algorithm, an appropriate motor torque or motor speed to produce approximately the fluid-flow demanded. In a torque-controlled implementation, for example, motor torque is regulated based on a monitored motor speed to produce the approximate fluid-flow.

Some certain types of blowers may produce multiple different fluid-flows when operated at a given torque and speed, particularly in certain operating ranges, such as at high fluid flows. Likewise, it is desirable to operate other fluid moving apparatuses, such as, for example, compressors, fans (e.g., axial fans, vane-axial fans, mix flow fans, dual stage axial flow fans, tube axial fans, multi-stage axial fans, or any other type of fan), impellers, and pumps, to produce an approximately constant fluid-flow. Consequently, a control system using known constant fluid-flow algorithms cannot effectively operate an electric blower or certain types of fans and compressors to produce a demanded fluid-flow by operating in a traditional torque-control or speed-control mode. A control system that overcomes this limitation for electric blowers, compressors, and certain types of fans is desired. <CIT> discloses a control system for an electric motor configured to drive a fluid moving apparatus to generate a fluid-flow. The control system includes a drive circuit configured to regulate power supplied to a stator of the motor to turn a rotor and generate the fluid-flow, and a processor that computes a value proportional to at least one of a system resistance or a static pressure for the fluid moving apparatus based on a fixed set point for a first control parameter and a feedback parameter. The processor receives a fluid-flow rate demand and computes an operating set point for a second control parameter based on the fluid-flow rate demand and the value proportional to the system resistance or the static pressure. The processor controls the drive circuit based on the operating set point to supply power to the motor and operate the fluid moving apparatus to generate the fluid-flow.

In one aspect, a control system for an electric motor configured to drive a fluid-moving apparatus to generate a fluid-flow is provided. The control system includes a drive circuit configured to regulate electrical power supplied to a stator of the electric motor to turn a rotor of the electric motor and generate the fluid-flow. The control system further includes a processor coupled in communication with the drive circuit. The processor is configured to control the drive circuit to operate the electric motor at a plurality of control values of a control parameter. The processor is further configured to determine, for each of the plurality of control values, a fluid-flow value and a feedback value. The processor is further configured to compute a mathematical relationship between fluid-flow rate and one of the control parameter or the feedback parameter. The feedback value corresponds to a feedback parameter. The processor is further configured to receive a fluid-flow rate demand value. The processor is further configured to compute an operating setpoint for the control parameter based on the fluid-flow rate demand value and the computed mathematical relationship. The processor is further configured to control the drive circuit to operate the electric motor at the operating setpoint.

In another aspect, a method for controlling an electric motor configured to drive a fluid-moving apparatus to generate a fluid-flow is provided. The method includes controlling a drive circuit to operate the electric motor at a plurality of control values of a control parameter. The drive circuit is configured to regulate electrical power supplied to a stator of the electric motor to turn a rotor of the electric motor and generate the fluid-flow. The method further includes measuring, for each of the plurality of control values, a fluid-flow value and a first feedback value. The method further includes computing a mathematical relationship between fluid-flow rate and one of the control parameter or the feedback parameter. The feedback value corresponds to a feedback parameter. The method further includes receiving a fluid-flow rate demand value. The method further includes computing an operating setpoint for the control parameter based on the fluid-flow rate demand value and the computed mathematical relationship. The method further includes controlling the drive circuit to operate the electric motor at the operating setpoint.

In another aspect, a fluid moving system is provided. The fluid moving system includes a fluid-moving apparatus. The fluid moving system further includes an electric motor coupled to the fluid moving apparatus. The electric motor is configured to drive the fluid-moving apparatus to generate a fluid-flow. The fluid moving system further includes a drive circuit configured to regulate electrical power supplied to a stator of the electric motor to turn a rotor of the electric motor and generate the fluid-flow. The fluid moving system further includes a processor coupled in communication with the drive circuit. The processor is configured to control the drive circuit to operate the electric motor at a plurality of control values of a control parameter. The processor is further configured to determine, for each of the plurality of control values, a fluid-flow value and a feedback value. The processor is further configured to compute a mathematical relationship between fluid-flow rate and one of the control parameter or the feedback parameter. The feedback value corresponds to a feedback parameter. The processor is further configured to receive a fluid-flow rate demand value. The processor is further configured to compute an operating setpoint for the control parameter based on the fluid-flow rate demand value and the computed mathematical relationship. The processor is further configured to control the drive circuit to operate the electric motor at the operating setpoint.

Embodiments of the control system and methods of operating an electric motor for a constant fluid-flow system described herein provide improved characterization of the constant fluid-flow system based on motor torque, motor speed, fluid-flow, and/or values proportional thereto. The improved characterization enables constant fluid-flow production using a fluid moving apparatus, or fluid mover, such as, for example, a backward-curved electric blower, a compressor, an impeller, or a fan (e.g., a vane-axial fan), while maintaining the benefits of such fluid moving apparatus, for example, the benefits of a backward-curved electric blower over a radial or forward-curved blower, namely the improved efficiency and greater pressure generation. The improved characterization also enables constant fluid-flow production using, for example, a forward-curved electric blower or a radial electric blower.

The control system, as described herein, performs this characterization based on a correlation between speed, fluid-flow, and another control parameter such as torque. The control system performs a characterization process where the electric motor is operated at a plurality of control setpoints corresponding to, for example, torque or speed, and fluid-flow and other feedback parameters are measured at each setpoint. Using the measurements, the control system computes a mathematical relationship that defines the correlation between speed, fluid-flow, and torque. Using this relationship, the control system may determine, for a demanded fluid-flow value, a control (e.g., speed or torque) value for the electric motor that will cause the fluid-flow system to produce the demanded-fluid flow. These relationships or correlations are apparatus-agnostic, and, as such, may be applied to any fluid moving apparatus.

As used herein, "fluid moving apparatus" or "fluid mover" may include any fluid moving apparatus, such as, but not limited to, compressors, blowers, fans (e.g., axial fans, vane-axial fans, mix flow fans, dual stage axial flow fans, tube axial fans, multi-stage axial fans, or any other type of fan), impellers, and pumps. "Air moving apparatus" or "air mover" may more specifically include, for example, blowers and/or fans. It should be readily understood that "air" may refer to any gaseous fluid.

Embodiments of the control system and methods described herein characterize the constant fluid-flow system utilizing, for example, correlations among torque (T), speed (N), demanded fluid-flow (Q), or one or more additional parameter. More specifically, the constant fluid-flow system may be characterized by a fluid-flow algorithm, or "torque correlation," that defines, for example, torque (T) as a function of speed (N) and demanded fluid-flow (Q). In alternative embodiments, the constant fluid-flow system is characterized by a "speed correlation" that defines speed (N) as a function of torque (T) and demanded fluid-flow (Q). Using these correlations, together referred to as the "constant fluid-flow algorithm," a fluid moving apparatus, or fluid mover, such as, for example, a backward-curved, forward-curved, or radial electric blower motor, a compressor, an impeller, or a fan such as an axial or vane-axial fan can be operated in a torque control mode, a speed control mode, or both to produce an approximately constant fluid-flow from the fluid mover.

In alternative embodiments, the electric motor may be characterized utilizing correlations among torque (T) or speed (N) and one or more of power input to the electric motor, current supplied to the electric motor, power output at the drive shaft of the motor, motor efficiency, or power output from the fluid mover itself, i. e, fluid power. For example, power output at the drive shaft is correlated to torque (T) and speed (N), i.e., Pshaft = TN, as well as to power input to the electric motor and motor efficiency, i.e., Pin = Pshaft/motor efficiency. Moreover, power input to the electric motor is a function of voltage and current supplied to the stator windings of the electric motor, i.e., Pin = VI.

In a torque-controlled implementation or speed-controlled implementation, for example, the characterization embodied in the control system and methods described herein produces one or more torque-speed-fluid-flow data points that characterize a relation between fluid flow data and other parameters. That relationship is then approximated by fluid-flow algorithm such as a polynomial function, power function, exponential function, or other formula that defines a relationship between fluid flow data points and other parameters such as motor torque (T), motor speed (N).

In certain embodiments, the constant fluid-flow system is first characterized to determine a set of constants for a fluid-flow algorithm. In one embodiment, the fluid mover, for example, a blower, vane axial fan, etc., is operated at a first constant torque (T) or speed (N), for example, <NUM>%, and an output speed (N) or torque (T) is measured to produce a first torque-speed pair from which a torque-speed-fluid-flow data point can be computed using a fluid-flow algorithm, or "torque correlation," for example, T=f(Q,N), similar in form to a traditional constant fluid-flow algorithm for a forward-curved blower, for example. For example, the fluid-flow algorithm may take the following form: <MAT> where, k<NUM>, k<NUM>, k<NUM>, k<NUM>, k<NUM> are constants. Generally, the constants are predetermined for the fluid mover prior to installation.

The fluid mover may be further operated at a second fixed torque (T) or speed (N), for example, <NUM>%, and speed (N) or torque (T) is measured to produce a second torque-speed pair. The second torque-speed pair, and EQ. <NUM> may be used to determine a linear relationship between speed and fluid flow as expressed by the following equation: <MAT> where, x<NUM> and x<NUM> are constants.

<NUM>, when a demanded fluid-flow (Q) is received, a corresponding speed (N) may be determined, and accordingly, using EQ. <NUM>, a torque (T) setpoint at which to operate the fluid mover may be determined.

Generally, a fluid-flow algorithm having more terms produces a finer fit to the data collected during characterization and, therefore, yields more accurate estimates of actual fluid-flow. The fit of a given fluid-flow algorithm may be further improved by enabling non-integer (e.g., real number) values for one or more coefficients or exponents. Consequently, electric motors and motor controllers must have sufficient processors, memory, communication interfaces, and software to program, store, recall, and execute such fluid-flow algorithms. Moreover, a greater number of terms and non-integer coefficients in the fluid-flow algorithm generally correlates to heavier computation loads in deriving the necessary coefficients.

The fluid flow system may be further characterized by its system resistance (R). In many constant fluid-flow systems, the system resistance is generally considered constant over a period of time. In practice, that system resistance may shift over time, for example, due to dirt, dust, or other contamination buildup on the a filter or other changing components of the system, path, or space into which the fluid-flow is directed. In other systems, the system resistance is controllable, for example, by configuring dampers, louvres, ducts, or vents to increase or decrease the resistance of the system to the fluid-flow. In such systems, the control system detects a change in system resistance (R), for example, by detecting a change in torque (T), and adjusts the operating point accordingly. For example, when operating in a speed-controlled mode and the system resistance (R) increases, the motor controller detects a change in torque output of the electric motor. This new torque-speed pair results in a recalculation of the relationship between speed and fluid-flow (EQ. This procedure iterates until the system converges on a stable operating point for the increased system resistance (R).

<FIG> is a block diagram of a constant fluid-flow system <NUM>. Constant fluid-flow system <NUM> includes a control system <NUM>, an output path <NUM>, a fluid mover <NUM>, and an electric motor <NUM>. Control system <NUM> includes a motor controller <NUM>, and a system controller <NUM>. In other embodiments, constant fluid-flow system <NUM> may include additional, fewer, or alternative components, including those described elsewhere herein. For example, fluid mover <NUM> may be configured to generate a fluid-flow into a space other than a defined duct, plenum, or other output path.

Fluid mover <NUM> is configured to generate a fluid-flow <NUM> directed through output path <NUM>. Output path <NUM> is configured to guide the fluid-flow for circulation and distribution within a system, building, vehicle, or other structure. Output path <NUM>, or alternatively the space into which fluid-flow <NUM> is directed, has a fluid-flow restriction, or system resistance (R), that affects the fluid-flow output from fluid mover <NUM>. The fluid-flow restriction is based on various parameters that may affect fluid-flow within constant fluid-flow system <NUM>, such as, but not limited to, the internal dimensions of output path <NUM>, open or closed dampers, contaminants (e.g., dust) within output path <NUM>, the geometry of output path <NUM>, or alternatively the space into which fluid-flow <NUM> is directed, and the like.

Electric motor <NUM> is configured to drive fluid mover <NUM> to generate the fluid-flow <NUM> into output path <NUM>. In at least some embodiments, electric motor <NUM> is an induction motor configured to convert electrical power into mechanical power. In alternative embodiments, electric motor <NUM> is a permanent magnet motor. In one example, electric motor <NUM> is coupled to a wheel (not shown) of fluid mover <NUM> and is configured to rotate the wheel. In the exemplary embodiment, electric motor <NUM> is configured to operate at a plurality of torque output levels (i.e., torque-controlled) to increase or decrease a corresponding motor speed. Increasing or decreasing the motor speed of electric motor <NUM> causes electric motor <NUM> to drive fluid mover <NUM> to generate corresponding fluid-flows. The fluid-flow <NUM> generated by fluid mover <NUM> is at least partially a function of the motor speed of electric motor <NUM> and the fluid-flow restriction of output path <NUM>. In some embodiments, electric motor <NUM> is integrated with fluid mover <NUM>.

Alternatively, electric motor <NUM> is configured to operate at a plurality of speed output levels (i.e., speed-controlled) to increase or decrease a corresponding motor torque. As in the torque-controlled embodiments, increasing or decreasing the torque of electric motor <NUM> causes electric motor <NUM> to drive fluid mover <NUM> to generate corresponding fluid-flows.

System controller <NUM> and motor controller <NUM> are communicatively coupled to electric motor <NUM> to operate electric motor <NUM>. More specifically, motor controller <NUM> supplies electrical power of a certain current amplitude, phase, and frequency to the stator windings of electric motor <NUM> to operate electric motor <NUM> according to instructions or commands from system controller <NUM>. By adjusting the amplitude, phase, and frequency, motor controller <NUM> controls the torque (or alternatively speed in a speed-controlled embodiment) of the electric motor <NUM>, thereby facilitating control of the speed of electric motor <NUM>. In other embodiments, motor controller <NUM> may be communicatively coupled to a second controller (not shown) associated with electric motor <NUM>. In such embodiments, motor controller <NUM> may be configured to transmit control signals to the second controller to instruct the second controller to operate electric motor <NUM>. In such an embodiment, motor controller <NUM> may be separated, or remote, from electric motor <NUM>. For example, motor controller <NUM> may be located within an HVAC assembly along with fluid mover <NUM> and electric motor <NUM>. In another embodiment, for example, motor controller <NUM> may be located with a thermostat system or system controller <NUM>.

Motor controller <NUM> includes a processor <NUM>, a memory <NUM> communicatively coupled to processor <NUM>, and a sensor system <NUM>. Processor <NUM> is configured to execute instructions stored within memory <NUM> to cause motor controller <NUM> to function as described herein. For example, memory <NUM> is configured to store a constant fluid-flow algorithm to be executed by processor <NUM>. Memory <NUM> is further configured to store a plurality of coefficient values for use in the constant fluid-flow algorithm. Moreover, memory <NUM> is configured to store data to facilitate calibrating electric motor <NUM>. In some embodiments, motor controller <NUM> may include a plurality of processors <NUM> and/or memories <NUM>. In other embodiments, memory <NUM> may be integrated with processor <NUM>. In one example, memory <NUM> includes a plurality of data storage devices to store instructions and data as described herein. In alternative embodiments, an additional processor and memory may be incorporated into system controller <NUM> for the purpose of storing a constant fluid-flow algorithm and coefficient values, and for executing the constant fluid-flow algorithm for the purpose of controlling motor controller <NUM> to produce a demanded constant fluid-flow. Control system <NUM> is described herein as allocating the function of storing and executing the constant fluid-flow algorithm at motor controller <NUM>, it should be understood that any processor and memory within control system <NUM> may carry out the functions of controlling fluid mover <NUM> to produce an approximately constant fluid-flow.

Prior to operation of motor controller <NUM> described herein, motor controller <NUM> receives values for coefficients that result from a regression analysis of characterization data for electric motor <NUM> and fluid mover <NUM>. The coefficients correspond to programmable variables within the constant fluid-flow algorithm stored in memory on motor controller <NUM> and executable by processor <NUM> during operation. In certain embodiments, certain other constants for the constant fluid-flow algorithm, or alternative constant fluid-flow algorithms, may be defined and stored, for example, in memory <NUM>, such as an EEPROM. In certain embodiments, the values for coefficients may be received from external system controller <NUM> or other device over a wired or wireless communication channel. In another alternative embodiment, the values for coefficients may be programmed into motor controller <NUM> by a technician or installer when motor controller <NUM> is installed.

During operation, motor controller <NUM> generally receives a fluid-flow rate demand (Q) from external system controller <NUM> and one of motor torque (T) and motor speed (N) measured at electric motor <NUM>. The other of motor torque (T) and motor speed (N) is computed. For example, in a torque-controlled embodiment, system controller <NUM> transmits a fluid-flow rate demand (Q) to motor controller <NUM>, and motor controller <NUM> computes a motor torque (T) to be commanded of electric motor <NUM> based on a computed required motor speed (N). In an alternative embodiment, system controller <NUM> transmits a discrete selection, or an index, of a particular fluid-flow rate demand (Q) from among a plurality of values stored in a table in memory <NUM>. Motor speed (N) may be determined from the current signal supplied to the stator windings or, alternatively, may be measured directly by sensor system <NUM>. The torque control loop then recursively executes, or iterates, until motor torque (T) converges on an objective torque. The torque control loop may execute, for example, once every <NUM> milliseconds. In alternative embodiments, the torque control loop period may be lengthened or shortened depending on, for example, the specific electric motor, fluid mover, or output path configuration.

Likewise, in a speed-controlled embodiment, system controller <NUM> transmits a fluid-flow rate demand (Q) to motor controller <NUM>, and motor controller <NUM> computes a motor speed (N) to be commanded of electric motor <NUM> based on a required motor torque (T). As described above with respect to motor speed (N), motor torque (T) may be determined from the current signal supplied to the stator windings or, alternatively, may be measured directly by sensor system <NUM>. The speed control loop then iterates until motor speed (N) converges on an objective speed.

Sensor system <NUM> includes one or more sensors that are configured to monitor electric motor <NUM>. In certain embodiments, sensor system <NUM> is omitted and motor torque and speed are determined from the current signal supplied to the stator windings of electric motor <NUM>. In one embodiment, sensor system <NUM> is configured to monitor a frequency output of motor controller <NUM> to electric motor <NUM>. Sensor system <NUM> may monitor other data associated with electric motor <NUM>, such as, but not limited to, motor speed, torque, power, and the like. In certain embodiments, sensor system <NUM> is configured to monitor a fluid-flow output of fluid mover <NUM>. For example, sensor system <NUM> may include an air pressure sensor configured to monitor static pressure within output path <NUM>, such as a duct or plenum. In some embodiments, sensor system <NUM> monitors electric motor <NUM> from motor controller <NUM>. In such embodiments, sensor system <NUM> may be integrated with processor <NUM>. In other embodiments, at least some sensors of sensor system <NUM> may be installed on electric motor <NUM> and transmit sensor data back to motor controller <NUM>.

In one embodiment, motor controller <NUM> is configured to calibrate electric motor <NUM> for a plurality of fluid-flow output levels to determine corresponding pairs of torque and speed. The resulting fluid-flow-torque-speed data points define a surface that further defines the operating profile of constant fluid-flow system <NUM>.

Motor controller <NUM> includes a drive circuit <NUM>. Drive circuit <NUM> supplies electric power to the stator windings of electric motor <NUM> based on control signals received from processor <NUM>. Drive circuit <NUM> may include, for example, various power electronics for conditioning line frequency alternating current (AC) power to be supplied to the stator windings of electric motor <NUM> with a desired current, i.e., phase, amplitude, and frequency. Such power electronics may include, for example, and without limitation, one or more rectifier stages, power factor correction (PFC) circuits, filters, transient protection circuits, EMF protection circuits, inverters, or power semiconductors.

Motor controller <NUM> includes a communication interface <NUM>. Communications interface <NUM> may include one or more wired or wireless hardware interface, such as, for example, universal serial bus (USB), RS232 or other serial bus, CAN bus, Ethernet, near field communication (NFC), WiFi, Bluetooth, or any other suitable digital or analog interface for establishing one or more communication channels between system controller <NUM> and motor controller <NUM>. For example, in certain embodiments, one or more parameters, such as a maximum fluid-flow rate (expressed in cubic feet per minute), fluid-flow rate demand, or one or more coefficient values, may be communicated to motor controller <NUM> through communications interface <NUM> using a pulse-width modulated signal. In certain embodiments, system controller <NUM> or another processor (not shown) may communicate operating parameters such as torque, speed, or power to motor controller <NUM> through communications interface <NUM>. Communications interface <NUM> further includes a software or firmware interface for receiving one or more motor control parameters and writing them, for example, to memory <NUM>. In certain embodiments, communication interface <NUM> includes, for example, a software application programming interface (API) for supplying one or more coefficient values for a constant fluid-flow algorithm. In such embodiments, received coefficient values are supplied to processor <NUM>, processed, and stored in memory <NUM> along with a constant fluid-flow algorithm for subsequent execution by processor <NUM> during operation of electric motor <NUM>.

In certain embodiments, memory <NUM> is configured to store two or more constant fluid-flow algorithms. Alternatively, memory <NUM> may be configured to store a single constant fluid-flow algorithm, and one or more sets of constants to be utilized by the algorithm. In certain embodiments, electric motor <NUM> and motor controller <NUM> are configured to receive through communication interface <NUM> and utilize those coefficients with the constant fluid-flow algorithm.

<FIG> is a logical block diagram of constant fluid-flow system <NUM>, including electric motor <NUM> and control system <NUM> (shown in <FIG>). A processor <NUM> (e.g., processor <NUM> of motor controller <NUM>, or a processor of system controller <NUM>) transmits control signals to drive circuit <NUM> to control the current amplitude, phase, and frequency of the electric power supplied to electric motor <NUM>. Processor <NUM> executes, for example, a constant fluid-flow algorithm <NUM>, such as that described above in EQ. <NUM> and EQ. <NUM> to compute one of a torque set point and a speed set point for controlling drive circuit <NUM> and electric motor <NUM>. Execution of the algorithm is typically carried out periodically, for example, at <NUM> Hertz, to update the torque set point or the speed set point. During operation, processor <NUM> receives a fluid-flow rate demand value, Q <NUM> that is used in constant fluid-flow algorithm <NUM>. Processor <NUM>, in certain embodiments, may receive fluid-flow rate demand value, Q <NUM>, directly from a system controller, such as system controller <NUM> (shown in <FIG>). Alternatively, system controller <NUM> may supply fluid-flow rate demand value, Q <NUM> using discrete inputs representing an index into a table of fluid-flow rate demand values stored in a memory from which processor <NUM> receives fluid-flow rate demand value, Q <NUM>. Alternatively, system controller <NUM> may supply a pulse width modulated (PWM) signal that proportionately varies between two fluid-flow rate demand values. In yet another alternative embodiment, system controller <NUM> may supply a digital command including fluid-flow rate demand value, Q <NUM>.

Processor <NUM> also receives coefficient values, A <NUM> that are used in constant fluid-flow algorithm <NUM>. Coefficient values, A <NUM> may be received, for example, from system controller <NUM>, from a memory, such as memory <NUM> (shown in <FIG>), or from another external device. In certain embodiments, processor <NUM> receives coefficient values, A <NUM> when constant fluid-flow system <NUM> is, for example, manufactured, installed, or powered on, and processor <NUM> operates with those same values from that point on unless it is reset, reprogrammed, or recalibrated by a technician or other user. In other embodiments, processor <NUM> may receive a periodic update of coefficient values A <NUM> from a remote device and constant fluid-flow algorithm <NUM> utilizes the latest values for a given iteration.

In certain embodiments, constant fluid-flow algorithm <NUM> is selected from among multiple algorithms stored in memory, such as memory <NUM>. The memory may include, for example, read-only memory such as an EEPROM. Constant fluid-flow algorithm <NUM> is retrieved from the memory based on a user selection or a selection by system controller <NUM>. In turn, for example, system controller <NUM> then transmits corresponding coefficient values, A <NUM>, a corresponding memory address for the space in the memory containing the appropriate coefficient values, A <NUM>, or an identifier, or "pointer," to such a memory address to processor <NUM>. Processor <NUM> then gains access to the corresponding space in the memory and reads coefficient values, A <NUM>.

Processor <NUM> receives at least one of a measured speed, N <NUM> and a measured torque, T <NUM> of electric motor <NUM>. That is used in constant fluid-flow algorithm <NUM>. Measured speed, N <NUM>, for example, may be derived from a current signal supplied to the stator windings of electric motor <NUM>. For example, such a current signal may be measured by a current sensor and measured speed, N <NUM> is derived from that measurement. Alternatively, processor <NUM> may receive a frequency measurement from a frequency sensor on electric motor <NUM>, the output of which may be converted to measured speed, N <NUM>. Alternatively, motor speed may be measured by any other suitable method, such as by further analyzing the current signal supplied to the stator windings of electric motor <NUM>. Measured torque, T <NUM>, for example, may be derived from the current signal supplied to the stator windings of electric motor <NUM>. For example, such a current signal may be measured by a current sensor and measured torque, T <NUM> is derived from that measurement, for example, by inference that torque output is equal to the commanded torque by virtue of a closed loop control system. Alternatively, processor <NUM> may receive a torque measurement from a torque sensor on electric motor <NUM> or, alternatively, by any other suitable method.

During operation, processor <NUM> executes constant fluid-flow algorithm <NUM> using the several inputs described above, including fluid-flow rate demand value, Q <NUM>, and at least one of measured speed, N <NUM> and measured torque, T <NUM>. Upon execution of constant fluid-flow algorithm <NUM>, processor <NUM> computes one of a torque set point and a speed set point that is used to control drive circuit <NUM>. Drive circuit <NUM> then supplies the desired current and frequency of AC electric power to electric motor <NUM> to turn fluid mover <NUM> (shown in <FIG>).

<FIG> is a schematic diagram of one embodiment of constant fluid-flow control loop <NUM> for use in controlling a torque-controlled electric motor, such as electric motor <NUM> of constant fluid-flow system <NUM> (shown in <FIG> and <FIG>). Control loop <NUM> may be embodied, for example, in motor controller <NUM>, processor <NUM>, processor <NUM>, or another processor in system controller <NUM> or other remote device, and illustrates control of electric motor <NUM> by execution of constant fluid-flow algorithm <NUM> to compute a torque set point <NUM>. Constant fluid-flow algorithm <NUM> receives fluid-flow rate demand, Q <NUM> and measured speed, N <NUM>, and computes torque set point <NUM> based on, for example, the formulas shown in EQ. <NUM> and EQ.

<FIG> is a schematic diagram of one embodiment of a constant fluid-flow control loop <NUM> for use in controlling a speed-controlled electric motor, such as electric motor <NUM> of constant fluid-flow system <NUM> (shown in <FIG> and <FIG>). Control loop <NUM> may be embodied, for example, in motor controller <NUM>, processor <NUM>, processor <NUM>, or another processor in system controller <NUM> or other remote device, and illustrates control of electric motor <NUM> by execution of constant fluid-flow algorithm <NUM> to compute a speed set point <NUM>. Constant fluid-flow algorithm <NUM> receives fluid-flow rate demand, Q <NUM> and measured torque, T <NUM>, and computes speed set point, N, <NUM> based on, for example, the formulas shown in EQ. <NUM> and EQ.

<FIG> is a flow diagram of an embodiment of a method <NUM> of operating an electric motor configured to drive a fluid moving apparatus, or fluid mover, such as electric motor <NUM> and fluid mover <NUM> of constant fluid-flow system <NUM> (shown in <FIG>). Fluid mover <NUM> then generates a fluid-flow into a space, such as output path <NUM>. Referring to <FIG> and <FIG>, method <NUM> may be embodied in a control system such as control system <NUM> having a processor, such as processor <NUM> of motor controller <NUM> or processor <NUM> of another device such as system controller <NUM> (all shown in <FIG> and <FIG>).

Control system <NUM> controls <NUM> drive circuit <NUM> to operate electric motor <NUM> at a plurality of control values of a control parameter. For example, in some embodiments, control system <NUM> controls drive circuit <NUM> to operate the electric motor <NUM> at a first control value of a control parameter and a second control value of the control parameter. The control parameter may be torque (T) output from electric motor <NUM>. Alternatively, the control parameter may be speed (N). Alternatively, the control parameter may be another parameter such as shaft power, input power, or current. In some embodiments, the first and second control values are expressed as a percentage, for example, <NUM>% and <NUM>% of a maximum rated torque (T) or speed (N) of electric motor <NUM>.

Control system <NUM> determines <NUM>, for each of the plurality of control values, a fluid-flow value and a feedback value. The feedback value corresponding to a feedback parameter, such as speed (N) or torque (T). For example, in embodiments wherein the control parameter is torque (T), the feedback parameter may be speed (N), and in embodiments wherein the control parameter is speed (N), the feedback parameter may be torque (T). The fluid-flow values and the feedback values are associated with the control value, such that each fluid-flow value, the feedback value, and the control value a first data point from which a mathematical relationship between the feedback parameter and fluid-flow may be obtained as described below.

Control system <NUM> computes <NUM> a mathematical relationship between fluid-flow rate and one of the control parameter or the feedback parameter. In some embodiments control system <NUM> computes the mathematical relationship based on the plurality of control values, the fluid flow values, and the feedback values. In some embodiments, mathematical relationship is defined by a linear equation such as, for example, EQ. Alternatively, the mathematical relationship may be defined by another type of equation such as, for example, a polynomial equation, an exponential equation, or a power equation.

Control system <NUM> receives <NUM> a fluid-flow rate demand value (Q). This value may be received, for example, from remote system controller <NUM>. The fluid-flow rate demand value may be transmitted as, for example, a digital formatted value or, alternatively, a continuous pulse-width modulated signal representing the desired fluid-flow rate demand (Q).

Control system <NUM> computes <NUM> an operating setpoint for the control parameter based on the fluid-flow rate demand value (Q) and the computed mathematical relationship. Using, for example, EQ. <NUM>, control system <NUM> determines a speed (N) corresponding to the demanded torque (Q), from which control system <NUM> may determine a torque setpoint at which to operate electric motor <NUM> to produce the demanded torque (Q). Control system <NUM> controls <NUM> drive circuit <NUM> to operate electric motor <NUM> at the computed operating setpoint.

In certain embodiments, control system <NUM> uses additional control parameter, feedback parameter, and fluid-flow data points to compute the operating setpoint or the mathematical relationship between the control parameter or the feedback parameter and fluid-flow. In certain such embodiments, control system <NUM> is configured to control drive circuit <NUM> to operate electric motor <NUM> at a third control value of the control parameter (e.g., <NUM>% torque or speed), determine a third fluid-flow value and a third feedback value, and compute the operating setpoint further based on the third fluid-flow value and the third feedback value. In such embodiments, control system <NUM> may use further data points to compute the operating setpoint. Utilizing more data points in some cases may increase the accuracy with which the computed operating setpoint corresponds to the demanded fluid-flow (Q).

Over time, in certain embodiments, the system resistance (R) may shift, for example, the system resistance may increase due to dust buildup on a filter or other pathway. Alternatively, the system resistance (R) may be deliberately changed by adjusting one or more dampers on the constant fluid-flow system. Under such circumstances, control system <NUM> is configured to determine a difference between a current fluid-flow rate value and the demanded fluid-flow rate demand value is greater than a threshold difference; and recompute the mathematical relationship in response to a determination the difference is greater than the threshold difference. Control system <NUM> iterates these computations until the operating point stabilizes at a new torque (T) and speed (N).

The methods and systems described herein may be implemented using computer programming or engineering techniques including computer software, firmware, hardware or any combination or subset thereof, wherein the technical effect may include at least one of: (a) enabling use of a backward-curved blower, compressor, impeller, or certain types of fans, such as axial and vane-axial, in constant fluid-flow systems while maintaining the benefits provided by such fluid mover over, for example, forward-curved or radial equivalent blowers; (b) improving accuracy of estimations of actual fluid-flow for backward-curved blowers, compressors, impellers, and fans; (c) reducing fluid mover size and power consumption for a given range of fluid-flows in a constant fluid-flow system by use of, for example, a backward-curved blower versus a forward-curved or radial equivalent; (d) reducing fluid mover speed for a given range of fluid-flows in a constant fluid-flow system by use of, for example, a backward-curved blower versus a forward-curved or radial equivalent; and (e) improving thermal comfort and energy savings for operation of constant fluid-flow systems in HVAC systems.

In the foregoing specification and the claims that follow, a number of terms are referenced that have the following meanings.

As used herein, an element or step recited in the singular and preceded with the word "a" or "an" should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to "example implementation" or "one implementation" of the present disclosure are not intended to be interpreted as excluding the existence of additional implementations that also incorporate the recited features.

Here, and throughout the specification and claims, range limitations may be combined or interchanged. Such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

Some embodiments involve the use of one or more electronic processing or computing devices. As used herein, the terms "processor" and "computer" and related terms, e.g., "processing device," "computing device," and "controller" are not limited to just those integrated circuits referred to in the art as a computer, but broadly refers to a processor, a processing device, a controller, a general purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a microcomputer, a programmable logic controller (PLC), a reduced instruction set computer (RISC) processor, a field programmable gate array (FPGA), a digital signal processing (DSP) device, an application specific integrated circuit (ASIC), and other programmable circuits or processing devices capable of executing the functions described herein, and these terms are used interchangeably herein. The above embodiments are examples only, and thus are not intended to limit in any way the definition or meaning of the terms processor, processing device, and related terms.

In the embodiments described herein, memory may include, but is not limited to, a non-transitory computer-readable medium, such as flash memory, a random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and non-volatile RAM (NVRAM). As used herein, the term "non-transitory computer-readable media" is intended to be representative of any tangible, computer-readable media, including, without limitation, non-transitory computer storage devices, including, without limitation, volatile and non-volatile media, and removable and non-removable media such as a firmware, physical and virtual storage, CD-ROMs, DVDs, and any other digital source such as a network or the Internet, as well as yet to be developed digital means, with the sole exception being a transitory, propagating signal. Alternatively, a floppy disk, a compact disc - read only memory (CD-ROM), a magnetooptical disk (MOD), a digital versatile disc (DVD), or any other computer-based device implemented in any method or technology for short-term and long-term storage of information, such as, computer-readable instructions, data structures, program modules and sub-modules, or other data may also be used. Therefore, the methods described herein may be encoded as executable instructions, e.g., "software" and "firmware," embodied in a non-transitory computer-readable medium. Further, as used herein, the terms "software" and "firmware" are interchangeable, and include any computer program stored in memory for execution by personal computers, workstations, clients and servers. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein.

Also, in the embodiments described herein, additional input channels may be, but are not limited to, computer peripherals associated with an operator interface such as a mouse and a keyboard. Alternatively, other computer peripherals may also be used that may include, for example, but not be limited to, a scanner. Furthermore, in the exemplary embodiment, additional output channels may include, but not be limited to, an operator interface monitor.

The systems and methods described herein are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein.

Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.

Claim 1:
A control system for an electric motor configured to drive a fluid-moving apparatus to generate a fluid-flow, said control system comprising:
a drive circuit configured to regulate electrical power supplied to a stator of the electric motor to turn a rotor of the electric motor and generate the fluid-flow; and
a processor coupled in communication with said drive circuit and configured to:
control said drive circuit to operate the electric motor at a plurality of control values of a control parameter;
determine, for each of the plurality of control values, a fluid-flow value and a feedback value, the feedback value corresponding to a feedback parameter;
compute a mathematical relationship between fluid-flow rate and one of the control parameter or the feedback parameter;
receive a fluid-flow rate demand value;
compute an operating setpoint for the control parameter based on the fluid-flow rate demand value and the computed mathematical relationship;
control said drive circuit to operate the electric motor at the operating setpoint;
determine a difference between a current fluid-flow rate value and the fluid-flow rate demand value is greater than a threshold difference; and
recompute the mathematical relationship in response to a determination the difference is greater than the threshold difference.