Electronic – Need help on 2N3055 12v DC to 220v AC Inverter Circuit

Some people claim that certain loads "may" not work as well, or "may" be damaged, with anything other than a pure sine wave.

Since the power coming out of my wall sockets is significantly different from a pure sinewave, I suspect these sincere and well-meaning people are merely repeating propaganda from the manufacturer of a pure sinewave inverter, much like people repeat urban legends.

There is only one kind of device that I know doesn't work as well with a non-sine-wave inverter: devices that use a "capacitive power supply" -- see How efficient is a capacitive power supply? for details.

Since a "capacitive power supply" has a power factor near 0, it is questionable whether any "capacitive power supply" meets EU-mandated power factor laws, such as EN61000-3-2.

I suspect that all products -- as long as they were designed after EU-mandated power factor laws went into effect -- should work just as well on "modified sine wave" as with "pure sine wave" inverters.

Of course, I can't possibly know about every product ever designed -- if there is any specific product (that was designed after those EU-mandated power factor laws went into effect) that can't work or doesn't work as well with "modified sine wave" power, I would be interested. If anyone can explain why it doesn't work, in enough detail that I can try to avoid that kind of failure, I would be fascinated and grateful.

You say you're not familiar with digital oscillators yet, but I think it's worth looking into. Using a microcontroller with PWM output you can input the signal directly in the amplifier's format. So you won't need an A/D conversion at the amplifier's input stage.
The code for the microcontroller is very simple. Basically it's like this: you need a sine lookup table, and a timer interrupt generating your sample clock. This can be 5kHz, for instance, then you get 100 samples per cycle, which is enough for an inverter application; the transformer will work as a low-pass filter. Every 200\$\mu\$s you take the next value from the table and set the PWM register with this value. The output will be pulse-width modulated following the sine pattern.
This means that your class-D amplifier doesn't need the input stage with the triangle wave generator + comparator (this would otherwise be you A/D converter), so it only consists of the driver stage for driving the output MOSFETs.
You get a crystal precision frequency virtually for free.

PS: a center-aligned PWM signal will give you a cleaner sine approximation, but many microcontrollers only can generate edge-aligned PWM. This Freescale controller is available in an SOIC-8 package and is an example of a microcontroller which can do center-aligned PWM.

image from this document