Flexible Power Point Tracking for Active Power Regulation in String-Inverter PV Plants with Power Optimizers

Abstract

Large integration of variable renewable resources into modern power grids, has forced grid operators to look for maximizing the available flexibility that can be provided by generators, storage, and loads. In particular, PV plants can provide flexibility by decreasing their active-power injection, following a grid requirement, by using a Flexible Power Point Tracking (FPPT) method. These methods are capable of tracking an external active-power setpoint, that is usually sent by the grid operator, or of tracking the maximum available PV power when the setpoint is larger than what is capable to inject due to the current irradiance. On the other hand, power optimizers (POs) have been proposed as an alternative to minimize the effects of non-uniform conditions in PV systems, by maximizing the power extraction of each PV module. However, FPPT methods have not been implemented on PV plants with POs, where a portion of the active-power requested by the grid must be allocated to each PO. In this paper, we consider a string-inverter PV configuration where the active-power request is distributed among the POs on each PV module. We propose a power-distribution technique that accounts for the individual restrictions of each PV module and PO, while being capable of following the grid's active-power setpoint. We show the results of this proposal through simulations using PLECS®.