Pure sine wave inverter
There are two possibilities:
 1. HV DC, H Bridge (low current) -> PWM, LC filter removes switching HF and what remains is a sine wave.
 2. Low voltage DC, H Bridge (high current)-> PWM, LC filter (high current), transformer iron core 50/60Hz; on secondary you get sine wave.
 3. Low voltage DC, push-pull converter with ferrite transformer, HV DC output, same as point 1.   

The ferrite choke is a part of LC filter for elimination the HF transistir switching frequency.