Islanding Detection and Power Quality Analysis in Microgrid

芝浦工業大学2019年

Implementing UPQC based Intelligent Islanding for the Microgrid System

Increased penetration of small scale renewable energy sources in the electrical distribution network, improvement of power quality has become more critical than where the current harmonics or disturbances and level of voltage can vary widely. For this reason, Custom Power Devices (CPDs) such as the Unified Power Quality Conditioner (UPQC) can be the most appropriate solution used for improving the dynamic performance of the distribution network, where accurate prior knowledge may not be available. Therefore, the main objectives are (i) placement (ii) integration (iii) capacity enhancement and (iv) real time control of the Unified Power Quality Conditioner (UPQC) to improve the power quality of a distributed generation (DG) network connected to the grid or microgrid. A new integration method of the UPQC has been developed: helps to the DGs to deliver quality of power in the case of islanding and help to reintegrate with the grid seamlessly post fault. It perform both control operation such as Detection of Islanding and reconnection techniques, hence, it is termed UPQC?G. The DG Inverter with storage supplies the active fundamental power only and the shunt part of the UPQC compensates the reactive and harmonic power of the load during both interconnected and islanding mode

Power Quality Improvement of Distributed Generation Integrated Network with Unified Power Quality Conditioner.

With the increased penetration of small scale renewable energy sources in the electrical distribution network, maintenance or improvement of power quality has become more critical than ever where the level of voltage and current harmonics or disturbances can vary widely. For this reason, Custom Power Devices (CPDs) such as the Unified Power Quality Conditioner (UPQC) can be the most appropriate solution for enhancing the dynamic performance of the distribution network, where accurate prior knowledge may not be available. Therefore, the main objective of the present research is to investigate the (i) placement (ii) integration (iii) capacity enhancement and (iv) real time control of the Unified Power Quality Conditioner (UPQC) to improve the power quality (PQ) of a distributed generation (DG) network connected to the grid or microgrid

A reliable micro-grid with seamless transition between grid connected and islanded mode for residential community with enhanced power quality

This paper presents a reliable micro-grid for residential community with modified control techniques to achieve enhanced operation during grid connected, islanded and resynchronization mode. The proposed micro-grid is a combination of solar photo-voltaic (PV), battery storage system and locally distributed DG systems with residential local loads. A modified power control technique is developed such that, local load reactive power demand, harmonic currents and load unbalance is compensated by respective residential local DG. However, active power demand of all local residential load is shared between the micro-grid and respective local DG. This control technique also achieves constant active power loading on the micro-grid by supporting additional active power local load demand of respective residential DG. Hence, proposed modified power control technique achieves transient free operation of the micro-grid during residential load disturbances. An additional modified control technique is also developed to achieve seamless transition of micro-grid between grid connected mode and islanded mode. The dynamic performance of this micro-grid during grid connected, islanded and re-synchronization mode under linear and non-linear load variations is verified using real time simulator (RTS)

Improved Droop Controller for Distributed Generation Inverters in Islanded AC Microgrids

Stability in island microgrids is crucial for efficient power distribution among distributed generation (DG) inverters. Conventional droop control, while effective in power sharing, poses challenges with voltage stability due to frequency and voltage deviations resulting from changing load power. Such deviations can lead to system instability, impacting power flows within each inverter. Therefore, this paper introduces a proposed droop control approach that effectively tackles the issues of frequency and voltage deviation, aiming to restore them to their rated values and significantly enhance transient response in power flows among inverters. The novel method incorporates integrating controllers for frequency and voltage, coupled with the utilization of virtual impedances. These virtual impedances, comprising virtual positive/negative-sequence impedance (VPI/VNI) loops at the fundamental frequency and a virtual harmonic impedance (VHI) loop at harmonic frequencies, play a crucial role in overcoming mismatched line impedance conditions, ultimately improving overall system performance. Simulation results demonstrate the effectiveness and outstanding performance of inverters operating in parallel within an island AC microgrid. The proposed approach ensures stable voltage and frequency levels in all operational states, regardless of varying load conditions

Control contributions to the universal operation of wind turbines

Ante la creciente dependencia energética de los países de la Unión Europea y los informes de contaminación atmosférica, la generación distribuida mediante energías renovables está modificando el sistema eléctrico actualmente basado en el paradigma centralizado. Dentro de las energías renovables con mayor impacto actual se encuentra la energía eólica. Un aspecto importante a mejorar en el marco de la calidad de potencia por parte del operador de la red de transmisión, es la continuidad del suministro. En estas circunstancias se define el concepto de microgrid como un sistema compuesto de al menos una fuente de generación distribuida asociada a cargas locales que pueden intencionalmente desconectarse del sistema de distribución con el objetivo de mejorar la fiabilidad del suministro. Este trabajo introduce la Operación Universal de aerogeneradores, donde éstos pueden trabajar conectados a red eléctrica y desconectarse de ella cuando ocurre un hueco o interrupción del suministro operando en modo isla. Es una aplicación específica del concepto de microgrid a aerogeneradores que evita el uso de sistemas de almacenamiento empleando únicamente las capacidades de almacenamiento y disipación intrínsecas de los aerogeneradores y se centra en contrarrestar interrupciones del suministro eléctrico del orden de unidades de minutos. Este trabajo se centra en abordar la problemática asociada a la Operación Universal de aerogeneradores desde el punto de vista del control de los convertidores de potencia: regulación del balance energético, compartición de la carga y control de la tensión local en modo isla y transiciones suaves entre modos de operación. Además, el sistema debe seguir manteniendo un rendimiento óptimo en modo conectado a red respetando los códigos de red: respuesta en potencia, calidad de potencia y respuesta ante perturbaciones

Buffered-microgrid Structure for Future Power Networks; a Seamless Microgrid Control

This paper proposes a new structure and control scheme for future microgrid-based power system, which is designed to achieve a seamless operation in both islanded and grid-connected modes, while the load is appropriately shared by all units (i.e. renewable sources, energy storage systems and the grid). The proposed method, which involves physical separation of the microgrid from the grid by using AC/DC/AC converters, ensures safe, secure and seamless operation of both modes. Such a “buffered” structure enables reduction in the transmission losses by reducing the exchanged energy with the grid through using a dead-zone in the control of the buffering AC/DC/AC converter. An inverse-droop control technique has been implemented to control the voltage magnitude and frequency, using current control in the dq-frame. PSCAD/EMTDC software has been used to validate the proposed method through simulating different scenarios. The solution provides a simple, smooth, and communication-free decentralized control for multi-sources microgrids. Moreover, the proposed buffered structure separates the dynamics of the microgrid and the grid, which enables a faster microgrid voltage and frequency control and protects the grid and the microgrid from faults on the other side