Perhaps your project depends more on the sensor and current regulator than you may think.
AC is usually measured in RMS or peak values, so that catching the peaks of an undistorted sine wave will be sufficient. A diode and a RC filter can do that, in addition to the isolation (transformer, opto coupler?) you need anyhow.
But when the current control enters the scene, does it affect the wave shape of the primary current?
A PID may be useful, but its parameters depend on the entire closed loop circuit.
So please describe your circuits in more detail, or give a circuit diagram. What's the primary voltage and desired current range?