An amplitude-modulated pseudo-random binary sequence approach to broadband impedance spectroscopy for photovoltaic module system identification

Pseudo-random binary sequence (PRBS) has been used for internal impedance identification and shown to be faster and easier to implement than analogue multiple frequency signals. To implement this technique on PV modules – which have a wider impedance bandwidth, the following needs to be considered. Both converter and PV module are non-linear, and since a varying frequency module excitation signal is induced through a bandwidth limited non-linear converter, this presents linearity issues. This study demonstrates the use of a parametric APRBS excitation signal, designed by defining the signal design points as a series of ramp functions This parametric profile mitigates the frequency induced system non-linearities, while producing fast and accurate online impedance estimation across a wide bandwidth. The results show that the APRBS achieves good tolerance for the induced system non-linearities – this is demonstrated by a small impedance error between the designed system and a Frequency Response Analyzer (FRA) for all frequencies within the bandwidth of the module.