Control structures of grid-tied photovoltaic systems
Abstract
Photovoltaic (PV) systems have emerged as one of the most widely used source of renewable and clean energy and have the aptitude to provide a considerable contribution to electricity generation in the future. One major area of interest which has dominated the field for many years concerns controlling grid-connected PV systems, in which specific primary requirements such as maximum power point tracking (MPPT) under both uniform or non-uniform solar radiation figures and injecting high-quality currents in terms of a low total harmonic distortion (THD) must be met. From this perspective, the control system for grid-connected PV systems has two cascaded loops, including outer and inner loops. While the former is the power /voltage control loop and responsible for producing the current references for the inner loop, the latter is the current control loop and in charge of regulating the injected currents. Increasing the penetration of PV systems into the grid has caused adverse effects on the whole distribution network. These undesirable effects, which are actually led by the fluctuating nature of the power generated by the PV systems, undoubtedly further complicate the efficient performance of the electricity grid and have major implications on the accessibility, reliability, and quality of the distribution network to which the PV system is connected. One solution to rectify these problems and provide reliable and efficient power generation is to continuously upgrade grid integration guidelines corresponded to momentous customers’ demands, but it gives rise to more issues for the PV intermediate inverters. Afterwards, advisable for the majority of PV systems is to present multiple operations. Consequently, new generation of multi-purpose PV inverter systems involve more developed and smart control policies to meet enhanced controllability. In the matter, low voltage ride-through (LVRT) capability, compensating reactive power, improving power quality, frequency control using active power curtailment, flexible control of active power (e.g., the P restrictions), and reliability-focused thermal control are of ancillary and intelligent services deemed to provide the new generation of PV systems with a substantial degree of control flexibility. Meanwhile, controlling the PV interfaced inverters is the major part to which intelligent control functions for grid-connected PV systems are applied. Altogether, the chief to further reduce the total cost of an efficient and reliable PV system is of those control functions applied to the future PV inverters, giving rise to higher penetration level of cost-efficient PV systems into the electricity grid. Fundamental and up-to-date control functions implemented in the grid-tied PV systems have been discussed in this chapter. © 2021 by Nova Science Publishers, Inc.