System and method for a variable gain proportional-integral (PI) controller

A variable gain PI controller comprising:

• a proportional function for weighting an error signal with a proportional gain factor to generate a proportional signal;
• an integral function that includes an integral gain factor to generate an integral signal, said integral gain factor is equal to:
• a first gain function for a normalized set-point signal less than a predetermined percentage of a maximum normalized set-point signal;
• a second gain function for said normalized set-point signal greater than said predetermined percentage of said maximum normalized set-point signal;
• and
• an adder for summing said proportional signal and said integral signal to generate a control signal.

A mass flow controller for controlling the flow of a liquid or gas in a manufacturing process, said mass flow controller comprising:

• valve drive circuitry for controlling a solenoid-activated valve that controls an actual flow rate of said liquid or gas in said manufacturing process;
• a flow sensor for measuring said actual flow rate of said substance and outputting a sensed flow rate signal;
• a derivative controller for converting said sensed flow rate signal into a feedback signal that more closely approximates said actual flow rate than said sensed flow rate signal;
• and
• a variable gain PI controller that converts an error signal between a set-point signal and said feedback signal into said valve drive signal, said variable PI controller comprising:
• a proportional function for weighting an error signal with a proportional gain factor to generate a proportional signal;
• an integral function for implementing a weighted integral of said error signal with an integral gain factor to generate an integral signal, said integral gain factor is equal to:
• a first gain function for a normalized set-point signal less than a predetermined percentage of a maximum normalized set-point signal;
• a second gain function for said normalized set-point signal greater than said predetermined percentage of said maximum normalized set-point signal;
• and
• an adder for summing said proportional signal and said integral signal to generate a valve drive signal to be input into said valve drive circuitry.

A method for generating a valve drive signal using a variable gain PI controller in a mass flow controller, said method comprising the steps of:

• multiplying an error signal by a proportional gain factor to generate a proportional signal;
• implementing an integral function including an integral gain factor on said error signal to generate an integral signal, said integral gain factor equal to:
• a first gain function for a normalized set-point signal less than a predetermined percentage of a maximum normalized set-point signal;
• said first gain function equal to [ ( 1 0.1 - 1 ) ⁢ ⁢ A + B ] ,
• where A is a first gain constant and B is a second gain constant;
• a second gain function for said normalized set-point signal greater than a predetermined percentage of said maximum normalized set-point signal;
• and
• summing said integral signal and said proportional signal to generate said valve drive signal.

A variable gain PI controller comprising:

• a proportional function for weighing an error signal with a proportional gain factor to generate a proportional signal;
• an integral function that includes an integral gain factor to generate an integral signal, said integral gain factor is equal to:
• a first gain function for a normalized set-point signal less than a predetermined percentage of a maximum normalized set-point signal;
• said first gain function equal to [ ( 1 0.1 - 1 ) ⁢ ⁢ A + B ] ,
• where A is a first gain constant and B is a second gain constant;
• a second gain function for said normalized set-point signal greater than said predetermined percentage of said maximum normalized set-point signal;
• and
• an adder for summing said proportional signal and said integral signal to generate a control signal.

A mass flow controller for controlling the flow of a liquid or gas in a manufacturing process, said mass flow controller comprising:

• valve drive circuitry for controlling a solenoid-activated valve that controls an actual flow rate of said liquid or gas in said manufacturing process;
• a flow sensor for measuring said actual flow rate or said substance and outputting a sensed flow rate signal;
• a derivative controller for converting said sensed flow rate signal into a feedback signal that more closely approximates said actual flow rate than said sensed flow rate signal;
• and
• a variable PI controller that converts an error signal between a set-point signal and said feedback signal into said valve drive signal, said variable PI controller comprising:
• a proportional function for weighing an error signal with a proportional gain factor to generate a proportional signal;
• an integral function for implementing a weighted integral of said error signal with an integral gain factor to generate an integral signal, said integral gain factor is equal to:
• a first gain function for a normalized set-point signal less than a predetermined percentage of a maximum normalized set-point signal;
• said first gain function equal to [ ( 1 0.1 - 1 ) ⁢ ⁢ A + B ] ,
• where A is a first gain constant an B is a second gain constant;
• a second gain function for said normalized set-point signal greater than said predetermined percentage of said maximum normalized set-point signal;
• and
• an adder for summing said proportional signal and said integral signal to generate a valve drive signal to be input into said valve drive circuitry.