Forward synchronization and reverse synchronization

Q: I know what is forward synchronization and reverse synchronization. But in the article I read its mentioned that reverse synchronization is dangerous.

1) Why is reverse synchronization dangerous?
2) What are the differences in parameters in auto synchronization for both types of synchronization?
3) If there is no auto sync relay, is there any difference when synchronized manually?

A: In the old days when you had mechanical governors with a lot of droop (the RPM - Frequency difference of a generator between a no load condition and a loaded condition) you always wanted the generator coming on line to be a little faster than the bus frequency because as soon as the generator would be placed on line and loaded, the speed of the generator would drop and if you knew what the droop was, you could come close to matching the amount of speed it would take to share some of the load.. If it was less than the frequency of the bus, when it would be placed on line, the drop of the generator could drag down the bus as the generator would not accept the load but have reverse power until someone adjusted the speed control up to accept more of the load.

When synchronizing the generator, the system is settled already, so even off by a little bit, the generator will follow. The generator will assume some load based on the droop settings (whatever that is). You can't introduce a voltage dip on the grid, but you might have to adjust voltage at the generator to match system. When going the other way around, both the grid and the generator are under some load. You would need to mess with the generator to match the grid while it's loaded. I haven't seen difference in auto synchronizing, but have someone do that manually (which it used to be done all the time), it's definitely a challenge. You still need to match the speed, but also any voltage difference the grid could introduce. How easy does the engine recover already being under load?

If your solution is constructed from interleaved and modular converters, why wouldn't you just measure the efficiency at the module level first?

There are many issues with developing such a converter, especially in a modular fashion. The source impedance and the converter impedance must be stable over all operating conditions including turn on (so 0-170V). In other considerations the turn on of the multiple modules needs to assure a well behaved startup and that none of the individual modules go into a fault state during turn-on.

Once you are ready to test your complete system I strongly suggest testing it in a very similar way that it is intended to be used. We often see "interesting" problems that crop up between idealized test conditions and operational test conditions. In my book I strongly recommend testing the power supply within the system. I have many "bloopers" type stories about such projects and how they can go wrong very quickly.