I Get a giggle every time someone says something has to be complex just to make it simple. I Laugh every time!
I make simple to be simple. Because I am simple. How simple is that?
As I have pointed out in several past posts there are countless ways to make one of these and as a simple man I came to the conclusion for my designs that the simple iron core low frequency method was the simplest, easiest, and cheapest way to feed the power back to the grid. And with the right Pi circuit it does give a clean sine wave that follows the grid wave form very cleanly and effectively.
I have never needed to monitor anything more than the instantaneous voltage of the line side wave form in order to get good clean returning power. All other line monitoring is just for safety, to make sure the line power is at the right voltage and frequency.
If the output amps get too high thats what fuses and circuit breakers are for. Same with the input side. If the input power exceeds the GTI capacity for too long the thermal protection limits shut it down and redirect the incoming power to a load dump circuit.
If the line voltage or frequency get to far off it again diverts the incoming power to the load dump device and then waits until the line side power returns to normal.
As far as using the HF switching to isolate the input from the output I see some gains and some losses. It does give a better and slightly more efficient use of the low end input power but is more complex and honestly does not have any overall great operating efficiency gains over a simple transformer. HF switching is much lighter physically but when you factor in the actual physical volume its actually bigger per watt than a standard transformer of the same capacity so nothing was gained size wise.
The LF iron core transformers are going to make the GTI heavier. But I figure, so what! The wind generators, solar panels or micro hydroelectric power source and the line connection are all stationary so what purpose does it serve or what gain do you get if the GTI is more portable? It cant actually go any place while its doing its job!
A lighter unit will save a customer a few dollars on shipping cost but a simpler and less complex unit is cheaper to build. And that savings will off set any added shipping costs.
From my personal experiences the standard voltage controlled switching device H-Bridge cant be beat! Its simple, easy to control, and protect.
It eliminates a need for multiple H-bridges or switching circuits to be used.
With the right control circuit design its capable of both current limiting and voltage limiting and PWM wave form shaping at 10's of KHz drive frequencies.
All other functions are done in the control side of the system. And once the control circuit is built and can do all of the input and output monitoring then its just a matter of changing voltage and current sensing
components in order to adapt it from a multi watt to a multi kilowatt control and monitoring capacity.
Just my opinion, but I do like the conceptual ideas and I am open to the possibilities that there could be other ways too.
I just think simple is simple and complex never makes anything actually simpler.