Dear Ralph,

Thanks for the reply. I don't know which SMPS controller your are talking about. But if you are talking about PWM controllers like SG3524/25 or even TC140 from the microchip family then I am afraid the only possibility of generating a sine wave is a resonant tank at the secondary side. I am talking about weighted sine through PWM lookup table. The Hardware PWM coupled with high speed would be choice. The trend is using DSP (from TI or AD) which have onboard peripherals specially useful for this type of applications. There are a family of PICs which has EPWM (enhanced) circuitry onboard but recent ones are not supported by pbp and I am not so conversant with either asm or C. In fact microchip had an appnote using the 17C familiy for an online UPS. You can go through AC induction motor appnotes to understand what I mean

Regards