An extremum-seeking control system for a plant includes a feedback controller for operating the plant to achieve a value of a manipulated variable, and an extremum-seeking controller. The extremum-seeking controller is configured to provide the value of the manipulated variable to the feedback controller and to determine a value for the manipulated variable. The extremum-seeking controller determines the value for the manipulated variable by perturbing the manipulated variable with an excitation signal and monitoring a performance variable of the plant resulting from the perturbed manipulated variable, estimating a normalized correlation coefficient relating the performance variable to the manipulated variable, and modulating the manipulated variable to drive the normalized correlation coefficient toward zero using a general set of tuning parameters. The general set of tuning parameters are adapted for use with the normalized correlation coefficient, independent of a scale of the performance variable.