Grid-tie DC-AC inverter

Hi guys!

My friends and I are doing a student project - low cost but high efficiency grid-tie DC-AC inverter. It already works alright in a stand-alone mode but now we've faced the problem of connecting it to the grid and uploading power into the network. 

I found some articles about  connection method with real-time current control (current loop). But is there any way of doing it without Hall effect sensor?  Using current transformer for instance... Can anyone suggest any algorithm of connecting DC-AC inverter to the grid or some useful literature about it?

Thanks in advance,