I am using carrier AC. Its very nice and cheap. I agree that It is pure sine wave inverter based on IGBT based PWM technology. The PWM(Pulse Width Modulation technology) is an updated technology that provides output that matches to grid supply. This feature assures safety of appliance against voltage fluctuation or overload. This feature supports optimal performance of the inverter.
The micro controller has embedded software that control working of the inverter. The sensor senses the status of power grid supply and provides a prompt supply appropriately.