Control strategy to share reactive power and regulate voltage in microgrids with autonomous mode operation

The objective of this thesis is to develop control strategies for distributed generation (DG) systems, that allows to achieve reactive power sharing and regulate voltage in microgrids operated autonomously. The proposed control strategies present different alternatives to improve reactive power sharing among DGs that conform the microgrid and to regulate the voltage in the nodes. Thus, it is possible to contribute to the overcoming problems caused by the continuous connection and disconnection of power loads, avoiding DG tripping under this situation. The scope of the proposed strategies covers a wide range of possibilities, from regulating voltage in the nodes of the microgrid based on electric vehicle connection and disconnection, to urban and rural residential loads. The usefulness of these control strategies is focused on DG systems that operate in isolated mode with great integration of renewables, mainly located in remote areas. Therefore, in this research we worked on the comparison of both the consumption of rural and urban communities to obtain different load variations to test the control strategy in the microgrid. The control strategies included in this research are: virtual RMS voltage, variable virtual impedance, virtual current, and virtual voltage.El objetivo de esta tesis es desarrollar una estrategias de control para los sistemas de generación distribuida (DG), que permitan lograr compartir la potencia reactiva y regular el voltaje en las microrredes operadas de manera autónoma. Las estrategias de control propuestas presentan diferentes alternativas para mejorar la compartición de potencia reactiva entre las diferente DG que conforman la microrred y para regular el voltaje en los nodos. Por lo tanto, es posible contribuir a la superación de los problemas causados por la conexión y desconexión continua de las cargas, evitando el disparo de DG en esta situación. El alcance de las estrategias propuestas cubre una amplia gama de posibilidades, desde la regulación del voltaje en los nodos de la microrred basada en la conexión y desconexión del vehículo eléctrico, hasta las cargas residenciales urbanas y rurales. La utilidad de estas estrategias de control se centra en los sistemas de DG que funcionan en modo autónomo con una gran integración de energías renovables, principalmente ubicadas en áreas remotas. Por lo tanto, en esta investigación trabajamos en la comparación del consumo de las comunidades rurales y urbanas para obtener diferentes variaciones de cargas para probar la estrategia de control en la microrred. Las estrategias de control incluidas en esta investigación son: voltaje RMS virtual, impedancia virtual variable, corriente virtual y voltaje virtual.ColcienciasThesis presented as a partial requirement to obtain the title of: Doctor en Ingeniería - Línea de Investigación en Automática.Doctorad

State-Space Modeling and Stability Analysis for Microgrids with Distributed Secondary Control

© 2018 IEEE. High penetration of renewable energies in power systems leads to the necessity of comprehensive modelling of a microgrid (MG) for its appropriate control. The distributed secondary control in the MG can be used for complementing the role of primary droop-based control. This paper presents a systematic way of developing a linearized small signal state space model with distributed secondary control as well as stability analysis of an islanded AC MG. The MG considered here, consists of three distributed generations (DGs) represented in the synchronous (DQ) reference frame. To show the effect of controller parameters on system stability, the eigenvalue analysis is presented here. The MATLAB/Simulink model of islanded MG with both primary and secondary control strategies is also developed to verify the outcomes of small-signal analysis. The simulation results show that the voltage controller simultaneously achieves the critical voltage restoration and accurate reactive power sharing

Review on Control of DC Microgrids and Multiple Microgrid Clusters

This paper performs an extensive review on control schemes and architectures applied to dc microgrids (MGs). It covers multilayer hierarchical control schemes, coordinated control strategies, plug-and-play operations, stability and active damping aspects, as well as nonlinear control algorithms. Islanding detection, protection, and MG clusters control are also briefly summarized. All the mentioned issues are discussed with the goal of providing control design guidelines for dc MGs. The future research challenges, from the authors' point of view, are also provided in the final concluding part

Droop control in DQ coordinates for fixed frequency inverter-based AC microgrids

This paper presents a proof-of-concept for a novel dq droop control technique that applies DC droop control methods to fixed frequency inverter-based AC microgrids using the dq0 transformation. Microgrids are usually composed of distributed generation units (DGUs) that are electronically coupled to each other through power converters. An inherent property of inverter-based microgrids is that, unlike microgrids with spinning machines, the frequency of the parallel-connected DGUs is a global variable independent from the output power since the inverters can control the output waveform frequency with a high level of precision. Therefore, conventional droop control methods that distort the system frequency are not suitable for microgrids operating at a fixed frequency. It is shown that the proposed distributed droop control allows accurate sharing of the active and reactive power without altering the microgrid frequency. The simulation and hardware-in-the-loop (HIL) results are presented to demonstrate the efficacy of the proposed droop control. Indeed, following a load change, the dq droop controller was able to share both active and reactive power between the DGUs, whereas maintaining the microgrid frequency deviation at 0% and the bus voltage deviations below 6% of their respective nominal values