MOTOR CONTROLLER SYSTEM AND METHOD FOR MAXIMIZING ENERGY SAVINGS
A motor controller and method for maximizing the energy savings in an AC induction motor at every load wherein the motor is calibrated at two or more load points to establish a control line, which is then programmed into a non-volatile memory (30) of the motor controller. A DSP-based closed-loop motor controller observes the motor parameters of the motor such as firing angle/duty cycles, voltage, current and phase angles to arrive at a minimum voltage necessary to operate the motor at any load along the control line. The motor controller performs closed-loop control to keep the motor running at a computed target control point, such that maximum energy savings are realized by reducing voltage through pulse width modulation.
This application is a continuation of co-pending U.S. application Ser. No. 12/207,913, filed on Sep. 10, 2008, which claims the benefit of U.S. Provisional Application Nos. 60/993,706 filed Sep. 14, 2007; and 61/135,402 filed Jul. 21, 2008, which applications are hereby incorporated by reference in their entirety.
BACKGROUND OF THE INVENTIONThis invention relates to a system and method for maximizing the energy savings in AC induction motors at every load, more particularly one that uses a digital signal processor that calibrates control lines to determine the most efficient operational characteristics of the motors.
In prior systems and methods related to energy saving motor controllers using control lines of a motor, constant phase angle and/or constant power factor control were used to determine the control lines. This meant that the control lines were horizontal and the motor controllers were not able to control the motor to specific calibrated operating point at every load to maximize energy savings.
Thus, a need exists for a method and system for AC induction motors which controls the motor to a specific calibrated operating point at every load. Operating points taken across all loads will define a control line or a control curve. Furthermore, a need exists for a method and system for AC induction motors which is capable of recognizing when a motor begins to slip and is about to stall and uses that information to determine calibrated control line so as to maximize energy savings at every load.
SUMMARY OF THE INVENTIONThe primary object of the present invention is to provide a system and method of maximizing energy savings in AC induction motors at every load.
Another object of the present invention is to provide a system and method which recognizes when a motor begins to slip and when the motor is about to stall.
A further object of the present invention is to provide a system and method which controls the motor to a specific calibrated operating point at every load.
Another object of the present invention is to provide a motor controller that is capable of observing the operational characteristics of AC induction motors.
A further object of the present invention is to provide a motor controller capable of making corrections to the RMS motor voltage as an AC induction motor is running and under closed loop control.
Another object of the present invention is to provide a motor controller capable of responding to changes in the load of an AC induction motor in real-time.
The present invention fulfills the above and other objects by providing a motor controller system and method for maximizing the energy savings in the motor at every load wherein a motor is calibrated at one or more load points, establishing a control line or curve, which is then programmed into a non-volatile memory of the motor controller. A digital signal processor (DSP) a part of a closed loop architecture of the motor controller possesses the capability to observe the motor parameters such as current, phase angles and motor voltage. This DSP based motor controller is further capable of controlling the firing angle/duty cycle in open-loop mode as part of a semi-automatic calibration procedure. In normal operation, the DSP based motor controller performs closed-loop control to keep the motor running at a computed target control point, such that maximum energy savings are realized. The method described here works equally well for single phase and three phase motors.
The preferred implementation of this method uses a DSP to sample the current and voltage in a motor at discrete times by utilizing analog to digital converters. From these signals, the DSP can compute key motor parameters, including RMS motor voltage, RMS current and phase angle. Furthermore, the DSP based motor controller can use timers and pulse width modulation (PWM) techniques to precisely control the RMS motor voltage. Typically the PWM is accomplished by using power control devices such as TRIACs, SCRs, IGBTs and MOSFETs.
The above and other objects, features and advantages of the present invention should become even more readily apparent to those skilled in the art upon a reading of the following detailed description in conjunction with the drawings wherein there is shown and described illustrative embodiments of the invention.
In the following detailed description, reference will be made to the attached drawings in which:
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Next, computations 63 of motor phase angle for each phase are calculated to yield an observed phase angle 5. Next, a target phase angle 10 which has been derived from a preprogrammed control line 6 is compared to the observed phase angle 5. The difference between the target phase angle 10 and observed phase angle 5 yields a resulting phase error signal 11 which is processed by a digital filter called a proportional integral derivative (PID) controller 12 which has proportional, integral and differential components. The output from the PID controller 12 is the new control voltage 13 to the motor 3, which can be obtained through the use of power control devices 33, such as TRIACs, SCRs, IGBTs or MOSFETS, to yield power control device outputs 14 of RMS motor voltage 13 supplied with line voltages 50 for each phase for maximum energy savings.
In this closed loop system, the voltage 13 of each phase of the motor 3 and the current are continually monitored. The motor controller 4 will drive the observed phase angle 5 to the point on the calibrated control line 6 corresponding to the load that is on the motor. At this point, maximum energy savings will be realized because the control line 6 is based on known calibration data from the motor 3. The motor controller 4 can control the motor 3 just as if a technician set the voltage 13 by hand. The difference is that the DSP 1 can dynamically respond to changes in the load in real-time and make these adjustments on a cycle by cycle basis.
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Every motor operates along a parametrical control line 25 within its operating space.
For example, when a given motor is 50% loaded and the firing angle/duty cycle 23 is set to 100°, a phase angle 5 of approximately 55° is observed.
The parametrical control line 25 shown in
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Referring back to the block diagram of
As stated above, the motor controller 4 will drive the observed phase angle 5 to the point on the control line 25 that corresponds to the load presently on the motor 3. This operating point 26 provides the maximum energy savings possible because the control line 25 is calibrated directly from the motor 3 that is being controlled.
This preferred method for calibration is called semi-automatic calibration. The semi-automatic calibration is based on the DSP 1 sweeping the control space of the motor. As shown in
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There is little danger of stalling during the semi-automatic sweep because of the controlled environment of the setup. A technician or operator helps to insure that no sudden loads are applied to the motor 3 under test while a semi-automatic calibration is in progress.
The process of sweeping the control space can be performed at any fixed load. For example, it can be performed once with the motor 3 fully loaded and once with the motor 3 unloaded. These two points become the two points that define the control line 25. It is not necessary to perform the calibration at exactly these two points. The DSP 1 will extend the control line 25 beyond both these two points if required.
There are many numerical methods that can be applied to find the stall point 21 in the plot of the current motor voltage 23. As shown in
The continuation of this method is shown in
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Semi-automatic calibration may be performed in the field. Referring now to
Next the motor 3 is placed in an unloaded configuration 45. Ideally this configuration is less than 25% of the rated load. Then a calibration button 32 on the motor controller 4 is pressed 47 to tell the DSP 1 to perform an unloaded measurement. The DSP 1 runs the calibration 46 to determine the unloaded point. The motor controller 4 indicates that it has finished calibrating both ends 47 of the control line 25 by turning on a light emitting diode (LED). The DSP 1 then determines the control line 48 using the two measurements and applies this control line when it is managing the motor 3. The values of the control line 25 are stored in non-volatile memory 49.
An alternative method for calibration is called manual calibration.
When the RMS line voltage is greater than a programmed fixed-voltage, the DSP controller clamps the RMS motor voltage at that fixed voltage so energy savings are possible even at full load. For example, if the mains voltage is above the motor nameplate voltage of 115V in the case of a single phase motor then the motor voltage is clamped at 115V. This operation of clamping the motor voltage, allows the motor controller to save energy even when the motor is fully loaded in single-phase or three-phase applications.
In some cases, it may not be possible to fully load the motor 3 during the calibration process. Perhaps 50% is the greatest load that can be achieved while the motor is installed in the field. Conversely, it may not be possible to fully unload the motor; it may be that only 40% is the lightest load that can be achieved.
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Although a preferred embodiment of a motor controller method and system for maximizing energy savings has been disclosed, it should be understood, it is not to be limited to the specific form or arrangement of parts herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not be considered limited to what is shown and described in the specification and drawings.
Claims
1. A system for controlling an AC induction motor to maximize energy savings compromising:
- a means for connecting a motor controller to an AC induction motor;
- a means for placing a load on said AC induction motor;
- a means for removing a load from said AC induction motor;
- a means for sweeping a control space of the AC induction motor and taking measurements of operating parameters of the AC induction motor;
- a means for establishing a control line from said measurements;
- a means for storing said control line in said motor controller;
- a means for controlling said operating parameters; and
- a means for performing closed-loop control of said AC induction motor to keep the motor running in accordance with said control line.
2. The system of claim 1 further comprising:
- a means for placing said AC induction motor in a fully loaded configuration.
3. The of claim 1 further comprising:
- a means for placing said AC induction motor in a fully unloaded configuration.
4. The system of claim 1 further comprising:
- measuring a current of said AC induction motor.
5. The system of claim 4 wherein:
- the current measurement of the AC induction motor is accomplished by a digital signal processor.
6. The system of claim 1 further comprising:
- measuring phase angles of the AC induction motor.
7. The system of claim 6 wherein:
- the phase angles measurements of the AC induction motor are accomplished by a digital signal processor.
8. The system of claim 1 further comprising:
- a means for controlling a firing angle/duty cycle of said AC induction motor.
9. The system of claim 8 wherein:
- said means for controlling said firing angle/duty cycle of said AC induction motor is accomplished by a digital signal processor.
10. The system of claim 1 wherein:
- said means for sweeping the control space of the AC induction motor and observing and measuring said operating parameters is accomplished by varying root square means motor voltage of the AC induction motor.
11. The system of claim 10 wherein:
- said means for varying the root square means motor voltage of the AC induction motor is a digital signal processor.
12. The system of claim 1 wherein:
- said means for establishing a control line from said measurements is accomplished by a digital signal processor.
13. The system of claim 1 wherein:
- said means for storing said control line in said motor controller is a non-volatile memory.
14. The system of claim 1 wherein:
- said means for performing closed-loop control of said AC induction motor to keep the motor running in accordance with said control line is a digital signal processor.
15. The system of claim 1 wherein:
- said means for performing closed-loop control of said AC induction motor to keep the motor running in accordance with said control line is pulse width modulation.
16. The system of claim 15 wherein:
- said pulse width modulation is performed using at least one TRIAC driver.
17. The system of claim 15 wherein:
- said pulse width modulation is performed using at least one SCR driver.
18. The system of claim 15 wherein:
- said pulse width modulation is performed using at least one IGBT driver.
19. The system of claim 15 wherein:
- said pulse width modulation is performed using at least one MOSFET driver.
20. The system of claim 1 further comprising:
- a means for clamping voltage of the motor at maximum voltage.
Type: Application
Filed: Aug 19, 2014
Publication Date: Jul 9, 2015
Inventor: Paul H. Kelley (Boca Raton, FL)
Application Number: 14/462,940