In a Grid Tie Inverter design, I need a circuit which can detect only one zero crossing of the Grid signal, (when the signal will change from negative to positive half cycle). I have made a circuit, which detects both the zero crossings. So please guide me, that which circuit will perform this function? I have made the circuit attached herewith, but it detects both the zero crossings.
You could use any safe method of illuminating an LED directly from mains which only conducts on one of the half cycles.
Two common arrangements are:
The LEDs represents the LED in the optocoupler.
The diodes are included to protect the LED from reverse voltage on the other half-cycle. You have to be careful in selecting the resistor value and the protection diode.
Target just a few milliamps -- perhaps even just 1 mA -- for the LED current. Also remember to do a power dissipation calculation for the resistor. You may need to go to a 1/2-watt resistor or use two resistors in series.