Disclosed herein are systems and methods for estimating a period and frequency of a waveform. In one embodiment, a system may comprise an input configured to receive a representation of the input waveform. A period determination subsystem may perform an iterative process to determine the variable period of the input waveform. The iterative process may comprise selection of an estimated window length, determination of an autocorrelation value based on the estimated window length, determination of an adjustment value to the window length to identify a maximum of the autocorrelation value; and determination of the variable period based on the window length associated with the maximum of the autocorrelation value. The period determination subsystem may perform the iterative process to track changes in the variable period of the input waveform. A control action subsystem may implement a control action based on the variable period of the input waveform.
