PID-controller with single frequency

Hi, I am using simulink to control piezo-actuators which are commanded by a card. The card receives via dll the orders from the pid-controller in form of single Magnitude, phase-angle and SINGLE FREQUENCY. It means that the discrete pid-controller should give AT EVERY PROCESS-TIME-POINT an output signal composed SOLELY of a single frequency (but not a continuous spectrum in form of linear combination of different frequencies weighted by the corresponding magnitudes). Is there a specific pid-controller working with discrete single frequency-signal? If not, is there a method to determine in real time (at every time step) the main frequency, magnitude and phase-angle of the pid-output signal, in order to transfer it via dll to the actuators? Could a real time fft help with this issue? Thanks!