Hello all, new to forum and fairly new to electronics. I am attempting to build a load controller for a windmill with a 3ph alternator, the objective being to unload the alternator at low wind speeds (so the windmill won't stall when the wind picks up) and to increase or decrease the load later as the wind speed increases or decreases. I have designed a circuit that rectifies the incoming AC and feeds it through an IGBT to the load. The IGBT is controlled by a Picaxe micro via a driver chip and PWM from the Picaxe. My test setup derrives input power from the 120VAC mains. I am running the PWM at 500Hz over duty cycles from 0 to 100%. The circuit seems to work fine once underway but the problem is the IGBT sometimes fails on power up (when plugging load power into the mains). What happens when it fails is that the load (incadescent lamps of 900W total) immediately come on full brightness and the IGBT is found to be shorted internally. I have placed diodes and caps across the load and IGBT C-E terminals to try to dampen voltage spikes. An external 5V zener is there to protect the gate. A schematic of the circuit is attached. I would appreciate any comments or suggestions of how to avoid this problem.