Mosfet Driver for V/F single phase inverter for driving single AC motor

Hello
I am making a V/F inverter as a part of my graduation project to control the speed of a single phase 1 hp AC motor by rectifying the 220 V AC then inverting it again into AC voltage with variable V/f with PWM from AVR ATmega32
but i have some problems
1- the output wave gets kinda scrambled when the frequency is over 25 hz but works fine before that
2- i wonder if i can drive the mosfets with just optocoupler PC817 or co i need mosfet driver like IR2110 or IR2112 and if i have to use the IR2110 can you please show me how to connect it ??
3- what is the max timer frequency to use in order that the optocoupler can cope up with (i am using timer 0 & 2 with crystal 12MHz and a prescalar of 8) ??
4- what is the best filter to use for the output (RC or LC ) ??

Thanks alot in advance

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And also do i have to create 4 20V supplies for the Mosfet gate voltages ?? and can i do that with one transformer and 4 bridges ??? or 4 transformers and 4 bridges ??

It is difficult to control a single ph motor using v/f=const. Torque of motor is proportional to V*V. So reducing speed by a small amount reduces the torque to square of it. For wider range successful speed control, use DTC or Vector ctrl.

can you recommend where can i learn to do DTC or vector control

You can get the book Modern Power Electronics and AC Drives: Bimal K. Bose. If you want to learn while simulating, go for MATLAB/Simulink demos.