That is the similar circuit I gave you here, which uses the zener diode idea:
http://www.fieldlines.com/index.php/topic,146791.msg1009845.html#msg1009845except I did all three phases, not one phase, and I added three tiny diodes for the DC gate power, instead of tapping gate power from the power DC side rectifiers, of your circuit. I don't think I need a capacitor. I could add one.
Mine would take six SCRs (ignore the pairs) for 3 phases. Yours is three SCRs for three phases because it shares the DC side rectifiers.
I can locate mine outside, separate and away from my boost converter rectifier.
Not using the MC3423 controller has a disadvantage that the SCR gate current might be high, and my variable resistor might need to be higher wattage. MC3423 can use low watt resistors and it can do any voltage level without swapping different zeners. I am happy with the zener idea for mine, though. I have no wind to test it yet.
I think your 50K resistor might be too large. Maybe my SCRs are unusual, needing so much current. Check the gate current and be sure 50K will not drop too much voltage and mess up your zener setting.
My power is AC to turn off the SCRs on each cycle.