Grid-connected PV system: Introduction to behavior matching

Abstract

This paper presents a PV grid-connected system in centralized configuration and constructed with a three- phase dual-stage inverter. In this topology, usually, a DC- DC converter performs the maximum power point tracking (MPPT) and an inverter is responsible for controlling of the grid-current. For the DC-DC stage the three-phase series resonant converter (SRC3) is chosen thanks to the very advantages that it exhibit. However, it is inadequate for the accomplishment of MPPT, due that its efficiency extremely depends on the implemented deadtime and switching frequency. Then, this paper proposes a conceptual modification, i.e., a dual-stage inverter in which the inverter stage is responsible for the MPPT and the grid-current control. In addition, the DC-DC converter operates with constant duty cycle and frequency. Such configuration requires a new concept, introduced as behavior matching. It serves as fundamental feature for the DC-DC converter to reproduce the PV array I-V characteristic when they are connected, without control action. The maximum power operating point (MPOP) is finding maximizing the direct axis current, obtained by Park's transformation from the inverter, through the perturbation and observation algorithm (P&O). Any specific measurement to MPPT is made. The isolation is performed by a high-frequency transformer becoming the system most compact. The structure is appropriate for high power applications, above 10 kW.