Self-tuning pull-down fuzzy logic temperature control for refrigeration systems

A method of controlling flow of refrigerant in a refrigeration system during an operation to adjust a temperature of a secondary refrigerant in the refrigeration system to a predetermined setpoint temperature, the method comprising the steps of:

• generating a temperature signal for the secondary refrigerant in the refrigeration system;
• generating an error signal using the temperature signal;
• generating a rate signal using the error signal;
• generating an control signal using fuzzy logic reasoning in response to the error signal and the rate signal to control the flow of refrigerant in the refrigeration system;
• and
• controlling the flow of refrigerant in the refrigeration system in response to the control signal to adjust the temperature of the secondary refrigerant in the refrigeration system to minimize or eliminate overshoot of the predetermined setpoint temperature.

A method of calculating a control signal for an actuator of a plurality of vanes to control flow of refrigerant from an evaporator during a pull-down operation to adjust a temperature of leaving water from the evaporator to a predetermined setpoint temperature, the method comprising the steps of:

• measuring, at predetermined intervals, a temperature of the leaving water from the evaporator;
• calculating an error value from the difference between the measured temperature and the predetermined setpoint temperature;
• and
• calculating a pull-down rate value from a difference between the error value and a previously calculated error value from a prior interval;
• generating a control signal at each predetermined interval using a fuzzy logic control algorithm in response to the error value, the pull-down rate value and an adjustable rate sensitivity value, wherein the control signal, when transmitted to the actuator, operates the actuator to position the plurality vanes to control flow of refrigerant from the evaporator to minimize or eliminate overshoot of the predetermined setpoint temperature during adjustment of the temperature of the leaving water from the evaporator to the predetermined setpoint temperature.

A refrigeration system comprising:

• a compressor, a condenser, and an evaporator connected in a closed refrigeration circuit, through which refrigerant is circulated, the compressor having a plurality of inlet guides vanes adjustable by an actuator;
• a sensor for detecting a leaving fluid temperature in the evaporator to provide a temperature signal;
• means for generating an error signal, an error rate of change signal and an adjustable rate sensitivity signal at a predetermined interval during a pull-down operation on the leaving fluid temperature in the evaporator in response to receiving the temperature signal;
• and
• means for generating a control signal for the actuator of the plurality of inlet guide vanes in response to the error signal, the error rate of change signal and the adjustable rate sensitivity signal as inputs, to control refrigerant flow to the evaporator to minimize or eliminate overshoot of a setpoint temperature for the leaving fluid temperature of the evaporator during the pull-down operation.

A computer program product embodied on a computer readable medium and executable by a microprocessor for calculating a control signal for an actuator of a plurality of vanes to control flow of refrigerant from an evaporator during a pull-down operation to adjust a temperature of leaving water from the evaporator to a predetermined setpoint temperature, the computer program product comprising computer instructions for executing the steps of:

• measuring, at predetermined intervals, a temperature of the leaving water from the evaporator;
• calculating an error value from the difference between the measured temperature and the predetermined setpoint temperature;
• calculating a pull-down rate value from a difference between the error value and a previously calculated error value from a prior interval;
• calculating an adjustable rate sensitivity value using a fuzzy logic algorithm;
• and
• generating a control signal at each predetermined interval using a fuzzy logic control algorithm in response to the error value, the pull-down rate value and the adjustable rate sensitivity value, wherein the control signal, when transmitted to the actuator, operates the actuator to position the plurality vanes to control flow of refrigerant from the evaporator to minimize or eliminate overshoot of the predetermined setpoint temperature during adjustment of the temperature of the leaving water from the evaporator to the predetermined setpoint temperature.