Implementation and test of on-line embedded grid impedance estimation for PV-inverters

New and stronger power quality requirements are issued due to the increase amount of photovoltaic (PV) installations. In this paper different methods are used for continuous grid monitoring. By injecting a noncharacteristic harmonic current and measuring the grid voltage response it is possible to evaluate the grid impedance directly by the PV-inverter, providing a fast and low cost implementation. This principle theoretically provides a correct result of the grid impedance but when using it into the context of PV integration, different implementation issues strongly affect the quality of the results. This paper presents a new impedance estimation method including typical implementation problems encountered and it also presents adopted solutions for on-line grid impedance measurement. Practical tests on an existing PV-inverter validate the chosen solutions.