THere are two basic GTI's Voltage driver and Current driver.
Using V and I sense, a simple regulator dumps all the power that is available from battery or PV as long as ;
1) the current is sinusoidal ,
2) input voltage range does not cause undervoltage ( impedance ratio)
3) does not cause over current or overtemp or affect PMMT on PV)
Then Phase of driver is simple I follows a filtered V with zero phase error. Or in other words, separating I & Q components of generated power making Q=0 ( reactive) or PF=1 by adjusting phase of driver or average time delay to switch stored energy to grid. As such this is a phase comparator can be called PLL but not using a VCO, rather some sort of timing control to adjust phase.
Protection for OVP, OCP, OTP for output and UVP for both input and output may be wise to include, but then you dont really need a PLL in a traditional sense.
Current mode control is better for stability with current sense feedback as it is more linear. PWM control is best method using Sine waveform to follow to minimize THD and make life easier for controlling sine current out.
The realization of a simple transformerless design can be very few parts, as long as the requirements are clearly defined with consideration to above. THe cost of the active components may be higher than expected for higher power transfer with inductive storage of energy for 1 cycle minimum and Ride-Through (RT) management as previously mentioned by FVM.
Solid grounding is required but isolation from peripheral communication.