Control algorithm for induction motor/blower system

• US 6,353,303 B1
• Filed: 10/18/2000
• Issued: 03/05/2002
• Est. Priority Date: 10/19/1999
• Status: Expired due to Fees

• Current Assignee: Fasco Industries, Inc. (Schneider Electric SE)
• Original Assignee: Fasco Industries, Inc. (Schneider Electric SE)
• Inventors: Ramachandran, Parimelalagan, Ciardo, Vincent C.
• Primary Examiner(s): Nappi, Robert E.
• Assistant Examiner(s): Leykin, Rita
• Application Number:
  US09/691,342
• Time in Patent Office: 503 Days
• Field of Search: 318/432, 318/727, 318/807, 318/806, 318/808, 454/229, 454/236, 417/42
• US Class Current: 318/727
• CPC Class Codes: F04D 27/004 by varying driving speed
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

An apparatus and method for controlling an induction motor having a variable frequency drive in a blower system so that the blower system provides a specific fluid flow. A start-up program causes the motor to ramp up to approximately a predetermined steady state speed. A required blower torque is calculated by operating on a table of blower constants, a selected flow rate and a motor speed which is read from a speed sensor in the motor/blower system. A developed motor torque is calculated by operating on a table of motor specific constants, a voltage-frequency index and the motor speed taken from the speed sensor. The calculated required blower torque is repeatedly compared with the calculated developed motor torque. The voltage-frequency index to the variable frequency drive is modified to force the developed motor torque to converge with the required blower torque in a steady state.

Claims

1. A method having an automatic controller of an induction motor/blower system providing a specified flow output, comprising the steps of:

providing an induction motor/blower system having an induction motor coupled to a blower such that a motor-torque by rotor-speed product (T_m×

N_m) of the induction motor substantially corresponds to a blower-torque by impeller-speed product (T_b×

N_b) of the blower at steady state and where the ratio of rotor-speed to blower-speed (N_m/N_b) is known;

providing a controller linked to a motor drive that adjusts motor speed N_m in response to control signals from the controller corresponding to a voltage-frequency index R;

serving the controller information corresponding to flow command information F;

serving the controller information corresponding to one of rotor speed N_m or impeller speed N_b and solving for the other of impeller speed N_b or rotor speed N_m by the known ratio N_m/N_b;

solving for required blower torque T_b by a polynomial equation expanded through at least second order terms and such that the blower-torque equation'"'"'s coefficients vary with the flow command information F according to;

2. The method of claim 1 further comprising:

idling for a pre-determined settling time, and then returning to the step of serving the controller information corresponding to flow command information F, and repeating the succeeding steps.

3. The method of claim 1 wherein the step of responding as following the step of comparing, in cases of the ratio N_m/N_b being substantially unity, the required blower-torque (required-T_b) to the delivered motor-torque (delivered-T_m), further comprises:

not modifying the most recent voltage-frequency index R if the required blower-torque (required-T_b) is substantially the same as the delivered motor-torque (delivered-T_m);

increasing the most recent voltage-frequency index R by a given increment if the required blower-torque (required-T_b) is not substantially the same as and is greater than the delivered motor-torque (delivered-T_m); and

decreasing the most recent voltage-frequency index R by a given decrement if the required blower-torque (required-T_b) is not substantially the same as and is less than the delivered motor-torque (delivered-T_m).

4. The method of claim 1 wherein the step of responding as following the step of comparing the product of required blower-torque by impeller-speed (required-T_b×

N_b) to the product of delivered motor-torque by rotor-speed (delivered-T_m×

N_m), further comprises;

not modifying the most recent voltage-frequency index R if the product of required blower-torque by impeller-speed (required-T_b×

N_b) is substantially the same as the product of delivered motor-torque by rotor-speed (delivered-T_m×

N_m);

increasing the most recent voltage-frequency index R by a given increment if the product of required blower-torque by impeller-speed (required-T_b×

N_b) is not substantially the same as and is greater than the product of delivered motor-torque by rotor-speed (delivered-T_m×

N_m); and

decreasing the most recent voltage-frequency index R by a given decrement if the product of required blower-torque by impeller-speed (required-T_b×

N_b) is not substantially the same as and is less than the product of delivered motor-torque by rotor-speed (delivered-T_m×

N_m).

5. The method of claim 1 wherein the voltage-frequency index comprises a normalized ratio of voltage to frequency (V/f) that either is linear such as when an arbitrarily chosen index value of unity®

=1) corresponds to 100 V per 50 hertz and then the ratio of 200 V per 100 hertz corresponds to R=2, or is non-linear as when an arbitrarily chosen index value of unity®

=1) corresponds to 100 V per 50 hertz and then the ratio of 200 V per 90 hertz corresponds to R=2.

6. The method of claim 1 wherein the step of serving the controller information corresponding to flow command information F further comprises:

one of receiving from an input device or extracting from a database the flow command information F.

7. The method of claim 1 wherein the step of serving the controller information corresponding to one of rotor speed N_m or impeller speed N_b further comprises:

providing one of the motor or the blower with a speed transducer.

8. The method of claim 1 wherein the blower has a given impeller chosen from one of a fan blade or a blower wheel.

9. Apparatus for controlling flow output of an induction motor/blower system that has an induction motor coupled to a blower such that a motor-torque by rotor-speed product (T_m×

N_m) of the induction motor substantially corresponds to a blower-torque by impeller-speed product (T_b×

N_b) of the blower at steady state and where the ratio of rotor-speed to blower-speed (N_m/N_b) is known, said apparatus comprising;

a data processor;

a motor drive, operably coupled to the data processor, which adjusts motor speed N_m in response to control signals from the data processor corresponding to a voltage-frequency index R;

a device serving the data processor information corresponding to flow command information F; and

,

another device serving the data processor information corresponding to one of rotor speed N_m or impeller speed N_b;

wherein said data processor is operational to;

fetch the most recent voltage-frequency index R, the flow command information F, and the known ratio N_m/N_b from either storage or inputs;

solve for the other of impeller speed N_b or rotor speed N_m;

solve for required blower torque T_b by a polynomial equation expanded through at least second order terms and such that the blower-torque equation'"'"'s coefficients vary with the flow command information F according to;

10. The apparatus of claim 9 wherein the data processor is further operational to:

idle for a pre-determined settling time after the activities of compare and respond (if any response), and then repeating all over.

11. The apparatus of claim 9 wherein:

the data processor includes circuitry incorporating one of a micro-processor, a micro-controller, or a digital signal processor.

12. The apparatus of claim 9 wherein the activity of responding as following the activity of comparing, in cases of the ratio N_m/N_b being substantially unity, the required blower-torque (required-T_b) to the delivered motor-torque (delivered-T_m), further comprises:

not modifying the most recent voltage-frequency index R if the required blower-torque (required-T_b) is substantially the same as the delivered motor-torque (delivered-T_m);

increasing the most recent voltage-frequency index R by a given increment if the required blower-torque (required-T_b) is not substantially the same as and is greater than the delivered motor-torque (delivered-T_m); and

decreasing the most recent voltage-frequency index R by a given decrement if the required blower-torque (required-T_b) is not substantially the same as and is less than the delivered motor-torque (delivered-T_m).

13. The apparatus of claim 9 wherein the activity of responding as following the activity of comparing the product of required blower-torque by impeller-speed (required-T_b×

N_b) to the product of delivered motor-torque by rotor-speed (delivered-T_m×

N_m), further comprises;

not modifying the most recent voltage-frequency index R if the product of required blower-torque by impeller-speed (required-T_b×

N_b) is substantially the same as the product of delivered motor-torque by rotor-speed (delivered-T_m×

N_m);

increasing the most recent voltage-frequency index R by a given increment if the product of required blower-torque by impeller-speed (required-T_b×

N_b) is not substantially the same as and is greater than the product of delivered motor-torque by rotor-speed (delivered-T_m×

N_m); and

decreasing the most recent voltage-frequency index R by a given decrement if the product of required blower-torque by impeller-speed (required-T_b×

N_b) is not substantially the same as and is less than the product of delivered motor-torque by rotor-speed (delivered-T_m×

N_m).

14. The apparatus of claim 9 wherein the voltage-frequency index comprises a normalized ratio of voltage to frequency (V/f) that either is linear such as when an arbitrarily chosen index value of unity®

=1) corresponds to 100 V per 50 hertz and then the ratio of 200 V per 100 hertz corresponds to R=2, or is non-linear as when an arbitrarily chosen index value of unity®

=1) corresponds to 100 V per 50 hertz and then the ratio of 200 V per 90 hertz corresponds to R=2.

15. The apparatus of claim 9 wherein said other device that serves the data processor information corresponding to one of rotor speed N_m or impeller speed N_b further comprises a speed transducer operably coupled to either the motor or the blower.

16. An apparatus for providing a constant fluid flow comprising:

an induction motor having at least one rotor, at least one speed sensor and at least one variable frequency drive;

at least one fluid impeller attached to said at least one rotor wherein said at least one fluid impeller is constrained to rotate with an annular velocity equal to an angular velocity of said at least one rotor;

means for calculating motor speed by manipulating a signal from said at least one speed sensor wherein said means for calculating a motor speed is in electrical communication with said speed sensor;

means for storing and reading electrical signals to represent specific blower constant data and specific motor constant data;

means to provide an electrical signal to represent a selected fluid flow rate;

electrical signals representing an array of specific blower constant data wherein said array is indexed by an electrical signal representing a selected fluid flow rate;

means for monitoring a voltage-frequency index of said variable frequency drive;

electrical signals representing an array of specific motor constant data wherein said array is indexed by an electrical signal representing said voltage-frequency index of said variable frequency drive;

means to calculate a required blower torque T_b by reading specific blower constant data A_2F, A_1F and A_0F from memory as indexed by said electrical signal representing a selected flow rate F and manipulating said specific blower constant data together with said blower speed N_b according to the equation;

17. The apparatus of claim 16 further comprising means to modify said voltage-frequency index so as to cause said motor speed to increase from a specific speed approximating a steady state speed during a start-up period.

18. The apparatus of claim 16 wherein said means to calculate motor speed, means for storing and reading electrical signals, means for monitoring a voltage-frequency index, means to calculate a required blower torque, means to calculate a developed motor torque, means to compare the required blower torque with the developed motor torque, and means to modify the voltage-frequency index of a variable frequency drive comprises either a microprocessor system or a digital signal processor.

19. A method of causing an impeller driven by an induction motor having a variable frequency drive to provide a specific fluid flow, comprising the steps of:

attaching a fluid impeller to an induction motor such that said fluid impeller is constrained to rotate with an angular velocity N equal to the angular velocity of said induction motor rotor;

monitoring a magnitude of said angular velocity N by reading an angular velocity electrical signal from a speed sensor;

maintaining an array of specific blower constant values A_2F, A_1F and A_0F as indexed by a selected fluid flow rate F;

maintaining an array of specific motor constant values B_2R, B_1R and B_0R as indexed by a voltage-frequency index R of said variable frequency drive;

calculating a required blower torque T_b by multiplying a second entry A_2F of said blower constant array for a selected flow rate F by the motor speed squared, N², to obtain a first blower result, multiplying a first array entry A_1F of said blower constant array for a selected flow rate F by the motor speed N to obtain a second blower result, and adding said first blower result to said second blower result and to a zero^th array entry A_0F of said blower constant array for said selected flow rate F;

calculating a developed motor torque T_m by multiplying a second entry B_2R of said motor constant array for the voltage-frequency index R by the motor speed squared, N², to obtain a first motor result, multiplying a first array entry B_1R of said motor constant array for the voltage-frequency index R by the motor speed N to obtain a second motor result, and adding said first motor result to said second motor result and to a zero^th array entry B_0R of said motor constant array for the voltage-frequency index R;

comparing said required blower torque T_b to said developed motor torque T_m;

maintaining a constant voltage-frequency index R to said variable frequency drive if the required blower torque T_b equals the delivered motor torque T_m;

modifying the voltage-frequency index R to said variable frequency drive to increase the delivered motor torque T_m if the delivered motor torque T_m is less than the required blower torque T_b;

modifying the voltage-frequency index R to said variable frequency drive to decrease the delivered motor torque T_m if the delivered motor torque T_m is greater than the required blower torque T_b; and

repeating the steps of monitoring the angular velocity N, calculating the required blower torque T_b, calculating the developed motor torque T_m, comparing the delivered motor torque T_m to the required blower torque T_b and maintaining and modifying the voltage-frequency index R, thereby causing the values of delivered motor torque T_m to converge with the required blower torque T_b.

20. The method of claim 19 further comprising the step of changing said voltage-frequency index during a start-up period to cause said motor speed to increase from zero to a specific speed approximating a steady state speed.