It is easy to use a step down transformer and then feed this to the controller to measure the phase of the grid for example. I am looking for an alternative method which solely uses power electronics without the step down transformer.

All I care about is the phase of the voltage. But extension to current phase measurements would also be welcomed.

The cheaper the better, I assume using power electronics would be cheaper than buying a transformer. Efficiency matters too, I could use some resistance voltage dividers but what else?

I found these to be helpful:

http://www.digikey.com/en/articles/techzone/2015/sep/synchronizing-small-scale-pv-systems-with-the-grid

"In its simplest form, a suitable PLL structure relies on a zero-crossing detector on the grid waveform and a counter to measure the time between zero crossings — adjusting inverter output as needed to match grid-voltage zero crossings (Figure 2). Designers can implement this simple PLL using a differential op amp such as the Maxim Integrated MAX9939, Microchip Technology MCP6022T, or Texas Instruments THS4121CD to trigger the next cycle of the sinusoidal output waveform from a reference sine-wave generator implemented in hardware or software."

What is the best power electronics scheme for voltage phase measurement? - ResearchGate. Available from: https://www.researchgate.net/post/What_is_the_best_power_electronics_scheme_for_voltage_phase_measurement#581e566b3d7f4bf3d262c371 [accessed Nov 5, 2016].

https://en.wikipedia.org/wiki/Phase_detector

I am still looking for the name of power electronics ICs that work similar to this one http://www.avrfreaks.net/sites/default/files/zerocrossingdetector.gif

http://www.rotwang.co.uk/projects/triac.html

In all of these it is easy to see how zero crossing happen after using  a transformer but it seems that this operation definitely needs the transformer ...

I know the transformer isolates the circuits. More specifically, I am looking for a phase detector IC which could be optocoupled later, I think there is not such a thing!