Photovoltaic Distributed Generation (PV-DG) produces some technical, commercial, and regulatory challenges in distribution systems. The most important technical challenge are the overvoltages produced by a high PV-DG penetration, which modifies the voltage profiles along the network and disturbs the operation of conventional voltage regulation devices. Extensive research has been carried out using various regulation devices under different control schemes to mitigate this impact. This paper presents a review of the literature dedicated to mitigate these overvoltage problems, proposing the classification and definition of regulation devices and control schemes used.

Frequency stability analysis of large power systems are extremely time consuming, laborious and may even exceed the computational capacity of modern computers. Hence, simplified power system models have being developed in the literature. These models are usually called System Frequency Response (SFR). In SFR models, generators are represented by transfer functions, nonlinearities are generally neglected and the grid is not taken into account. Conventional SFR models only contemplate the mechanical behavior of speed governors, turbines and synchronous machines of generators. This is because, a common simplification is to consider that frequency and voltage can be controlled independently. However, it is demonstrated that there is an interaction between them, so frequency can be affected by the effect of power system stabilizers (PSSs) over excitation system controllers. In this work, a modified SFR model is proposed, considering the influence of generators excitation control on frequency. Simulation results show an improvement of the accuracy in the estimation of frequency response of the power system.

This study proposes a novel methodology for optimal sizing of a vanadium redox flow battery (VRFB) aiming at providing the load frequency control (LFC) of power system (PSs) with renewable generation, such as wind generation. This methodology utilises a new optimisation problem, where the optimal size of the VRFB is an endogenous result from the model of optimisation problem. To resolve the new optimisation problem, a hybrid optimisation model (HOM) is employed in order to calculate the optimal investment for the VRFB (optimal size) while taking into account both its impact on the PS costs and on the quality of the system frequency. Through stochastic optimisation, the HOM allows computing the variable operating costs and VRFB investment costs, considering the uncertainties associated to the PS. This stochastic optimisation utilises a new quasi‐stationary simulations of the PS operation, which demands lower computing effort. To this aim, this study proposes a novel modelling approach of both the VRFB and the PS operation. Moreover, statistical indexes are proposed as new factor used in sizing the LFC operating reserve. The results show that the developed methodology allows evaluating with precision the stochastic characteristics of the PS.

This article aims to provide a comprehensive review of control strategies for AC microgrids (MG) and presents a confidently designed hierarchical control approach divided into different levels. These levels are specifically designed to perform functions based on the MG’s mode of operation, such as grid-connected or islanded mode. The primary control ensures frequency (f) and voltage (V) stability, whereas the secondary control adjusts their values to their references and the tertiary control efficiently manages the power of distributed generators (DGs) in a cost-effective manner. The article extensively discusses centralized, decentralized, and distributed strategies for each control level, highlighting their differences, advantages, disadvantages, and areas of application. Finally, the usefulness of different control strategies at different levels is demonstrated through practical examples.

Wind generation (WG) is the most widespread renewable energy resource in the world. However, this implementation inevitably leads to an increase in the problems caused by WG, e.g. frequency oscillations, power fluctuations or voltage variations. To overcome these problems, the use of a power conditioning system (PCS) coupled with a vanadium redox flow battery (VRFB) is proposed in this study. The PCS is composed of a distribution static synchronous compensator connected to a dc/dc chopper. The PCS/VRFB detailed model is presented and a three‐level control system is developed. This control system allows the PCS/VRFB to perform a decoupled reactive and active power flow control. The dynamic response of the PCS/VRFB is evaluated through simulation tests, and performance characteristics of the device are obtained by means of the variation of the power references. The results obtained demonstrate that the PCS/VRFB offers a good transient response and the control system proposed allows mitigating the problems caused by wind power generation.

La incorporación de potencia eólica en microredes está creciendo progresivamente. Esta integración puede introducir problemas en la dinámica y calidad de potencia del sistema eléctrico debido a fluctuaciones del viento. Este trabajo propone un controlador compuesto por un sistema de acondicionamiento de potencia (PCS), un almacenador flywheel (FESS) y una batería de flujo redox de vanadio (VRFB) para mitigar problemas introducidos por la generación eólica en microredes. Se presenta un modelo del PCS/FESS-VRFB y se propone un método para controlar la potencia intercambiada entre el controlador y la red eléctrica. El método tiene dos modos: nivelación de potencia y control de frecuencia. A través de simulaciones, se estudia el desempeño del PCS/FESS-VRFB cuando opera con generación eólica en microredes. Los resultados demuestran un adecuado desempeño del método propuesto y una alta efectividad para nivelar las fluctuaciones de potencia eólica y proveer soporte para el control de frecuencia de la microred.