System and method for saving energy when driving masses having periodic load variations

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 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.

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 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.