Online frequency response characterization system and method

A tangible, non-transitory, machine-readable medium, comprising machine-readable instructions to:

• add a perturbation signal to an error signal representing a difference between a desired measurement output of a control system and a measurement output of the control system, thereby generating a perturbation-error signal;
• perform a discrete Fourier transform on the perturbation-error signal and the measurement output at a frequency that corresponds to the perturbation signal, thereby determining a transformed perturbation-error signal and a transformed measurement output;
• and
• compare a first amplitude and a first phase of the transformed perturbation-error signal to a second amplitude and a second phase of the transformed measurement output, thereby determining a frequency response of the control system at the frequency.

A method, comprising:

• receiving a range of frequencies;
• adding one or more perturbation signals at one or more frequencies of the range to a node of a control loop in a control system;
• performing one ore more discrete Fourier transforms on at least two signals in the control loop at each of the one or more frequencies, thereby determining at least two transformed signals at each of the one or more frequencies;
• and
• determining a complex ratio between any two of the at least two transformed signals at each of the one or more frequencies, thereby determining one or more frequency responses of the control system at the one or more frequencies.