The AC signal from WG is connected to a PN junction through a 1 kOhm resistor. Other end of the PN junction is conencted to the DC supply PV1. The input is monitored by A1 and the signal after the resistor by A2. The AC signal gets clipped at the diode drop (~ 0.7 volts) when PV1 is set to zero. The clipping level changes with the value of PV1.
Reverse the diode direction a apply negative voltages to clip the negative half.