How to boost ac voltage?

I have an air x wind generator and the internal controller died so i converted it to an ac turbine and put a rectifier in the building then it goes to grid tie but im having an issue. It puts out a low voltage spinning at the speed it used to charge batteries it gets 6 volts high amps and spinning at the speed whare it used to output 25 amps and charge the batterys i get about 11 volts high current ...way to low for a grid tie what can i do to double or boost this voltage? either on the ac or dc end whatever works ...somthing i can do/build myself? anyone have any ideas?