Hey gentleman!
Hi
It is very very simple.
In first step you should build a H bridge converter with HF trans and with HF Pwm frequency (for increase voltage up to 240V) and then rectify it and give it to another H bridge or Half bridge or.... (without transformer) as supply. and switch them with SPWM . for example you need a 50HZ 240v sine wave , you can make spwm with 50KHZ carrier and 50HZ message . and after amplifying it with your Second H bridge , you will need a filter on 5KHZ cut off frequency and a simple feed back . i can guess your next question! your next question will be this: why F0= 5KHZ? it is simple ! because of that the least frequency that you have , will 50HZ and LPF for 50HZ will be large and expensive. LPF on 5KHZ will small and cheap . and your least frequency is 50HZ and you will have 50HZ sine wave in your out put as well as.
Respect
Goldsmith