MOTOR CONTROLLER SYSTEM AND METHOD FOR MAXIMIZING ENERGY SAVINGS
A motor controller (4) and method for maximizing the energy savings in an AC induction motor (3) at every load wherein the motor is calibrated at two or more load points to establish a control line (6), 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 (23), voltage (37), current (9) 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 claims the benefit of U.S. Provisional Application Nos. 60/933,706 filed Sep. 14, 2007; and 61/135,402 filed Jul. 21, 2008.
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.
The relevant patents of prior art includes the following references:
The 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:
For purposes of describing the preferred embodiment, the terminology used in reference to the numbered components in the drawings is as follows:
- 1. digital system processor (DSP)
- 2. hardware inputs
- 3. motor
- 4. motor controller
- 5. observed phase angle
- 6. control line
- 7. observed calibration data curve from sweep of control space
- 8. supply divider resistors
- 9. current
- 10. target phase angle
- 11. phase error signal
- 12. proportional integral derivative (PID) controller
- 13. root square mean (RMS) motor voltage
- 14. power control device outputs
- 15. phase A line voltage zero crossing
- 16. phase B line voltage zero crossing
- 17. phase C line voltage zero crossing
- 18. positive phase rotation
- 19. negative phase rotation
- 20. power-on-reset (POR)
- 21. stall point
- 22. a,c,b phase turn on times
- 23. firing angle/duty cycle
- 24. percent load
- 25. parametrical control line
- 26. operating point
- 27. low output impedance amplifier
- 28. phase error
- 29. control voltage
- 30. point b
- 31. knee
- 32. calibration button
- 33. power control device
- 34. point c
- 35. voltage minimum (Vmin)
- 36. phase zero crossing inputs
- 37. phase line voltage
- 38. phase motor voltage
- 39. time is measured
- 40. is time greater or less than 90°
- 41. ABC rotation
- 42. ACB rotation
- 43. point d
- 44. place in loaded configuration
- 45. place in unloaded configuration
- 46. run calibration
- 47. control line ends calibrated
- 48. calculate control line
- 49. saves control line
- 50. line voltages
- 51. set firing angle/duty cycle to 90°
- 52. measure motor parameters
- 53. detects knee
- 54. decrease firing angle/duty cycle by 2°
- 55. save phase angle and motor voltage
- 56. repeat four times
- 57. compute average values
- 58. firing angle/duty cycle is increased
- 59. measure next step
- 60. fixed voltage clamp
- 61. synthesize control segment
- 62. analog to digital converter
- 63. phase computation
- 64. phase error is computed
- 65. voltage error is computed connection
- 66. RMS motor voltage is compared to fixed voltage threshold
- 67. is control target positive
- 68. voltage loop is run
- 69. control line loop is run
- 70. motor placed on dynamometer
- 71. motor is connected to computer
- 72. firing angle/duty cycle is increased and voltage decreased
- 73. record calibration point
- 74. start motor
- 75. firing angle/duty cycle is adjusted
- 76. form control line
- 77. differential-to-single-ended amplifiers
- 78. input resistors
- 79. attenuator
- 80. feedback resistor
- 81. ground reference resistor
- 82. protection diodes
- 83. summing amplifier
- 84. DC blocking capacitors
- 85. summing resistors
- 86. neutral
- 87. jumper block for alternate neutral
- 88. window comparator
- 89. motor current is provided
- 90. positive voltage is provided
- 91. negative voltage is provided
- 92. voltage passes through two comparators
- 93. voltage passes through operation (OR) gate
- 94. zero-cross digital signal is created
- 95. current waveform
- 96. positive voltage half cycle
- 97. negative voltage half cycle
- 98. OR function
- 99. DSP monitors for increase in current
- 100. increase is observed
- 101. motor voltage is turned to full on
- 102. motor voltage is reduced to control line
- 103. load on the motor
- 104. power applied to motor
- 105. point a
- 106. count sweeps
With reference to
Referring now to
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.
Referring now to
Referring to
Referring now to
Referring now to
Now referring to
As further illustrated in
Further,
Now referring to
Referring now to
Referring now to
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
As illustrated in
Further, as shown in
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
As shown in
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
As shown in
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.
As further shown in
Referring now to
As further shown in
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.
21. The system of claim 1 further comprising:
- a means for preventing said AC induction motor to run at voltages below minimum voltage.
22. The system of claim 1 further comprising:
- a means for determining virtual neutral as a reference.
23. The system of claim 1 further comprising:
- a means for detecting zero-crossings of positive and negative halves of a current waveform in said AC induction motor.
24. The system of claim 23 wherein:
- said means for detecting zero-crossings of positive and negative halves of a current waveform is at least one window comparator.
25. The system of claim 24 wherein:
- a positive voltage is provided to the at least one window comparator as a reference for a positive half cycle;
- a negative voltage is provided to the at least one window comparator as a reference for a negative half cycle;
- signals form the at least one window comparator pass through an OR gate to create composite current zero-cross digital signals.
26. The system of claim 1 further comprising:
- a means for protecting against stalling in said AC induction motor.
27. The system of claim 26 wherein:
- a DSP actively controls said AC induction motor while constantly sweeping said AC induction motor for increases in motor current;
- said DSP turns motor voltage to full on when an increase in motor current is detected; and
- said DSP reduces the motor voltage to follow a control line after current returns to a lower level.
28. A method for controlling an AC induction motor to maximize energy savings comprising the steps of:
- a. connecting a motor controller to an AC induction motor;
- b. sweeping a control space of the AC induction motor and observing and measuring operating parameters of the AC induction motor throughout the control space;
- c. establishing a control line for said AC induction motor from said parameters;
- d. storing said control line in said motor controller;
- e. controlling the operating parameters along the control line; and
- f. performing closed-loop control of said AC induction motor to keep the motor running in accordance with said control line.
29. The method of claim 28 wherein step b comprises:
- placing said AC induction motor in a fully loaded configuration;
- determining said AC induction motor's fully loaded point;
- placing said AC induction motor in a fully unloaded configuration; and
- determining said AC induction motor's fully unloaded point.
30. The method of claim 28 further comprising:
- connecting the AC induction motor's fully loaded and fully unloaded point to establish the control line of the motor.
31. The method of claim 28 further comprising a step after step d of:
- increasing firing angle/duty cycle of the AC induction motor from eighty degrees to one-hundred-fifty degrees and recording current and phase angles along the control line.
32. The method of claim 28 further comprising a step of:
- recording current and phase angles along the control line.
33. The method of claim 28 wherein step e comprises:
- controlling the operating parameters of voltage along the control line using pulse width modulation.
34. The method of claim 28 wherein:
- said pulse width modulation is performed using at least one TRIAC driver.
35. The method of claim 32 wherein:
- said pulse width modulation is performed using at least one SCR driver.
36. The method of claim 32 wherein:
- said pulse width modulation is performed using at least one IGBT driver.
37. The method of claim 32 wherein:
- said pulse width modulation is performed using at least one MOSFET driver.
38. The method of claim 28 wherein step e further comprises:
- clamping the operating parameters of voltage at minimum voltage and not allowing said AC induction motor to run at voltages below minimum voltage.
39. The method of claim 28 further comprising a step after step b of:
- determining virtual neutral for use as a reference.
40. The method of claim 28 further comprising a step after step b of:
- detecting zero-crossings of positive and negative halves of a current waveform in said AC induction motor.
41. The method of claim 40 wherein:
- a positive voltage is provided to at least one window comparator as a reference for a positive half cycle;
- a negative voltage is provided to the at least one window comparator as a reference for a negative half cycle;
- signals form the at least one window comparator pass through an OR gate to create composite current zero-cross digital signals.
42. The method of claim 28 further comprising a step after step f of:
- protecting against stalling in said AC induction motor.
43. The method of claim 42 wherein:
- a DSP actively controls said AC induction motor while constantly sweeping said AC induction motor for increases in motor current;
- said DSP turns motor voltage to full on when an increase in motor current is detected; and
- said DSP reduces the motor voltage to follow a control line after current returns to a lower level.
Type: Application
Filed: Sep 10, 2008
Publication Date: Jan 21, 2010
Inventor: Paul H. Kelley (Boca Raton, FL)
Application Number: 12/207,913