Digital process control method avoiding windup

Claim 1

The method for automatically calculating valves for the control signal necessary to provide control action during each control interval of a digital computer control system to correct a process variable with minimum windup from constraints placed on the control action, comprising the steps of: automatically calculating the desired change in the manipulated variable for each control interval in accordance with the computed deviation of the controlled variable from its set point as modified by a previously stored windup correcting signal, automatically calculating the maximum change in the manipulated variable permissible during each control interval in accordance with said constraints, automatically comparing said maximum change and said desired change, automatically producing in response to said comparison a control signal which is of magnitude sufficient to effect said desired change when said desired change does not exceed in magnitude said maximum change and sufficient to effect said maximum change when said desired change does exceed said maximum change, and automatically producing and storing the windup correcting signal for the next subsequent control interval by automatically calculating the desired change in the manipulated variable which could not be effected during the control interval for which it was calculated due to the existence of said constraints.

Claim 2

The method for automatically calculating valves for the control signal necessary to provide control action during each control interval of a digital computer control system to correct a process variable with minimum windup from constraints placed on the control action, comprising the steps of: automatically calculating the desired change in the manipulated variable for each control interval in accordance with the computed deviation of the controlled variable from its set point as modified by a previously stored windup correcting signal, automatically calculating the maximum change in the manipulated variable permissible during each control interval in accordance with said constraints, automatically comparing said maximum change and said desired change, automatically producing in response to said comparison a control signal which is of magnitude sufficient to effect said desired change when said desired change does not exceed in magnitude said maximum change and sufficient to effect said maximum change when said desired change does exceed said maximum change, and automatically producing and storing the windup correcting signal for the next subsequent control interval by automatically calculating the desired change in the manipulated variable which could not be effected during the control interval for which it was calculated due to the existence of said constraints.

Claim 5

The method for calculating the control signal necessary to provide control action during each control interval of a digital computer control system to correct a process variable with maximum windup from constraints placed on the control action, comprising the steps of: producing a desired control signal representative of the desired change in the manipulated variable for a particular control interval as modified by a windup correcting signal, storing in memory said desired control signal, calculating a maximum control signal representing the maximum permissible control action for the particular control interval, storing in the memory said maximum control signal, comparing the value of the stored desired control signal with the value of the stored maximum control signal, outputting said desired control signal and storing a zero value signal as the windup correction signal when the magnitude of the desired control signal does not exceed the magnitude of the stored maximum control signal, outputting the stored maximum control signal and updating the value of the windup correcting signal when the magnitude of the desired control signal exceeds the magnitude of the stored maximum control signal, said updating including producing a signal representing the difference between the stored maximum control signal and the stored desired control signal and storing the difference as the windup correcting signal when the sign of the reset portion of the desired control signal for the control interval is not the same as the sign of the stored desired control signal, and producing a signal representing the difference between the sum of the stored maximum control signal and any fraction of the reset portion of the desired control signal which cannot be utilized from the stored control signal and storing the difference as a correcting signal when the sign of said reset portion is the same as the sign of said desired control signal.

Claim 6

The method for calculating the control signal necessary to provide control action during each control interval of a digital computer control system to correct a process variable with maximum windup from constraints placed on the control action, comprising the steps of: producing a desired control signal representative of the desired change in the manipulated variable for a particular control interval as modified by a windup correcting signal, storing in memory said desired control signal, calculating a maximum control signal representing the maximum permissible control action for the particular control interval, storing in the memory said maximum control signal, comparing the value of the stored desired control signal with the value of the stored maximum control signal, outputting said desired control signal and storing a zero value signal as the windup correction signal when the magnitude of the desired control signal does not exceed the magnitude of the stored maximum control signal, outputting the stored maximum control signal and updating the value of the windup correcting signal when the magnitude of the desired control signal exceeds the magnitude of the stored maximum control signal, said updating including producing a signal representing the difference between the stored maximum control signal and the stored desired control signal and storing the difference as the windup correcting signal when the sign of the reset portion of the desired control signal for the control interval is not the same as the sign of the stored desired control signal, and producing a signal representing the difference between the sum of the stored maximum control signal and any fraction of the reset portion of the desired control signal which cannot be utilized from the stored control signal and storing the difference as a correcting signal when the sign of said reset portion is the same as the sign of said desired control signal.