DC motor phase estimation with phase-locked loop

A method of automatically adapting an instantaneous frequency to a component of a single frequency of a primary signal, said primary signal representing an electrical current provided to a direct current (DC) motor, comprising:

• synthesizing an incident frequency to produce a complex exponential incident signal;
• multiplying said complex exponential incident signal by an adaptive coefficient to produce a reference signal, said adaptive coefficient having a magnitude and a phase;
• subtracting said reference signal from said primary signal to produce an error signal;
• adapting said adaptive coefficient in a complex single frequency adaptive filter according to a coefficient gradient as a function of at least said error signal;
• adapting said incident frequency in a phase lock loop (PLL) having an incident frequency adaptation component as a function of a frequency gradient;
• and
• responsive to said adapting said incident frequency, calculating a distance traveled by a load coupled to said DC motor from said adapted incident frequency.