System and method for saving energy when driving masses having periodic load variations
First Claim
1. A method of saving energy for an electric motor having periodic load variations, the method comprising the steps of:
- detecting a supply voltage and a current applied to said motor;
observing a phase angle between the supply voltage and the current;
obtaining a time segment value corresponding to a duration of the periodic load variations;
comparing the observed phase angle with a threshold phase angle;
adjusting the supply voltage when the observed phase angle approaches the threshold phase angle, the supply voltage being adjusted by changing a firing angle of a switching device that electrically couples the supply voltage and the motor, the supply voltage being adjusted to maintain the observed phase angle at a value corresponding to a target phase angle;
applying the supply voltage to said motor when the firing angle falls below a threshold firing angle;
identifying at least one off-time period during the time segment value, the at least one off-time time period corresponding to when the adjusted supply voltage is applied to the motor;
decoupling the supply voltage to the motor during the at least one off-time period; and
coupling the supply voltage to the motor during a remainder of the time segment value, the remainder of the time segment value including at least one turn-on time period.
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Abstract
A system and method are described for conserving energy by decoupling a supply voltage to an electric motor operating under periodic load variations. A time segment value corresponding to a duration of periodic load variations is obtained and the supply voltage is adjusted to maintain an observed phase angle for a supply voltage and current at a value corresponding to a target phase angle. At least one off-time period is identified during the time segment value that corresponds to when the adjusted supply voltage is applied to the motor. During a remainder of the time segment value, at least one turn-on time period is provided when the supply voltage is coupled to the motor. The system may enter to a closed-loop control process after a predetermined period of time to adjust to any changes in the periodic load variations.
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Citations
20 Claims
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1. A method of saving energy for an electric motor having periodic load variations, the method comprising the steps of:
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detecting a supply voltage and a current applied to said motor; observing a phase angle between the supply voltage and the current; obtaining a time segment value corresponding to a duration of the periodic load variations; comparing the observed phase angle with a threshold phase angle; adjusting the supply voltage when the observed phase angle approaches the threshold phase angle, the supply voltage being adjusted by changing a firing angle of a switching device that electrically couples the supply voltage and the motor, the supply voltage being adjusted to maintain the observed phase angle at a value corresponding to a target phase angle; applying the supply voltage to said motor when the firing angle falls below a threshold firing angle; identifying at least one off-time period during the time segment value, the at least one off-time time period corresponding to when the adjusted supply voltage is applied to the motor; decoupling the supply voltage to the motor during the at least one off-time period; and coupling the supply voltage to the motor during a remainder of the time segment value, the remainder of the time segment value including at least one turn-on time period. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of saving energy for an electric motor having periodic load variations, the method comprising the steps of:
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detecting a supply voltage and a current applied to the electric motor; observing a phase angle between the supply voltage and the current applied to said motor; obtaining a time segment value corresponding to a duration of the periodic load variations; comparing the observed phase angle with a threshold phase angle; controlling the supply voltage to said motor when the observed phase angle approaches the threshold phase angle, the supply voltage being controlled to maintain the observed phase angle at a value corresponding to a target phase angle; controlling a real component of the current to be substantially zero and an imaginary component of the current to be greater than zero; applying the supply voltage to said motor when the observed phase angle decreases below a stall phase angle; identifying at least one off-time period during the time segment value, the at least one off-time time period corresponding to when the supply voltage is controlled; setting a duration of the at least one turn-off time period during the time segment value; decoupling the supply voltage to said motor during said at least one turn-off time period; and coupling the supply voltage to the motor during a remainder of the time segment value. - View Dependent Claims (15, 16, 17)
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18. A method of saving energy for an electric motor having periodic load variations, the method comprising the steps of:
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detecting a supply voltage and a current applied to the electric motor; observing a phase angle between the supply voltage and the current applied to the electric motor; obtaining a time segment value corresponding to a duration of the periodic load variations; comparing the observed phase angle with a threshold phase angle; adjusting the supply voltage when the observed phase angle approaches the threshold phase angle, the supply voltage being adjusted to maintain the observed phase angle at a value corresponding to a target phase angle; applying the supply voltage to said motor when a firing angle of a switching device that electrically couples the supply voltage and the motor falls below a threshold firing angle; identifying at least one off-time period during the time segment value, the at least one off-time time period corresponding to when the adjusted supply voltage is applied to the motor; decoupling the supply voltage to said motor during the at least one off-time period; and coupling the supply voltage to the motor during a remainder of the time segment value, the remainder of the time segment value including at least one turn-on time period; observing a turn-on phase angle, the turn-on phase angle occurring at a beginning of the corresponding turn-on time period; comparing said turn-on phase angle with an ideal phase angle; increasing the duration of the at least one turn-off time period during the time segment value if the turn-on phase angle is greater than the ideal phase angle, and decreasing the duration of the at last one turn-off time period if the turn-on phase angle is less than the ideal phase angle. - View Dependent Claims (19, 20)
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Specification