Impedance estimation of photovoltaic modules for inverter start-up analysis

Abstract

Starting-up of photovoltaic (PV) inverters involves pre-charging of the input dc bus capacitance. Ideally, direct pre-charging of this capacitance from the PV modules is possible as the PV modules are current limited. Practically, the parasitic elements of the system such as the PV module capacitance, effective wire inductance and resistance determine the start-up transient. The start-up transient is also affected by the contactor connecting the PV modules to the inverter input dc bus. In this work, the start-up current and voltages are measured experimentally for different parallel and series connections of the PV modules. These measurements are used to estimate the stray elements, namely the PV module capacitance, effective inductance and resistance. The estimation is based on a linear small-signal model of the start-up conditions. The effect of different connections of the PV modules and the effect of varying irradiation on the scaling of the values of the stray elements are quantified. The System model is further refined by inclusion of connecting cable capacitance and contactor resistance. Dynamics of the resulting fifth-order model are seen to be consistent with those of the simplified third-order model. The analysis of this paper can be used to estimate the expected peak inrush current in PV inverters. It can also be used to arrive at a detailed modelling of PV modules to evaluate the transient behaviour.

Modeling of PV Module and DC/DC Converter Assembly for the Analysis of Induced Transient Response Due to Nearby Lightning Strike

“…Focusing on low irradiation conditions (about 100 W/m 2 ), reference [42] describes that the parallel capacitance at MPP and OC conditions could achieve a 294% and 340% value, respectively, compared to that of the SC condition. The resulting parallel capacitance is also irradiance-dependent [42,46,51,59,60]. Thus, for different voltage biases, this capacitance could decrease in the range 15% to 70% when irradiance decreases from high to low irradiation [42,60].…”

“…Modelling and value setting of dynamic AC circuit parameters for a PV module gives important insight to characterize and diagnose its behavior in case of lightning events. Extensive studies on the determination of parameters of the active electrical circuitry for PV cells and modules are available in the literature, mostly focused on calculating both the DC and AC electrical parameters [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53]. The most widely used method to study the PV dynamic behavior is the impedance spectroscopy [40,43,[54][55][56][57][58].…”

All SiC Grid-Connected PV Supply with HF Link MPPT Converter: System Design Methodology and Development of a 20 kHz, 25 kVA Prototype

“…Therefore, in the analysis and design of such systems, a proper dynamic model of the multi-string PV system is to be used. Several attempts have been made to obtain dynamic models of a PV module [35][36][37][38][39][40][41]. However, in this research work, the dynamic model parameters of the roof-mounted multistring PV system shown in Figure 2 were obtained from a set of experimental data.…”

High-Power Closed-Loop SMPC-Based Photovoltaic System Characterization under Varying Ambient Conditions

“…These SMPC systems are promising to be one of the best methods of characterizing PV arrays owing to their controllable and fast response, designed ability to handle high power and optional power conditioning capability [29]. These converters are further useful in transient characterization of PV panels for dynamic modeling [38] and can therefore be instrumental in fault diagnosis. SMPC systems also work well in fast changing environmental conditions wherein special cautions such as high characterization speeds are needed when irradiation changes fast [26].…”