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The Smart Grid (SG) implementation requires a constant monitoring and control of the power network. An Advanced Metering Infrastructure (AMI) allows the Distribution System Operator (DSO) to know what is happening on the power network. However, existing smart meters are not prepared for an emerging energy market nor to be integrated with LV/MV dispatch centres. The Unbundle Smart Meter (USM) concept...
Variable carrier single rate deadbeat control method for low carrier frequency was proposed. In the large capacity inverter system, the carrier frequency range is limited to relatively lower frequency range, the trade off between the control accuracy and the efficiency should be considered. Digital hysteresis control was applied to the inductor current, suitable carrier frequency was adopted in every...
The inverter with critical loads should be able to provide critical loads with a stable and seamless voltage during control mode change as well as clearing time. The indirect current control has been proposed for providing stable voltage with critical load during clearing time and seamless control mode transfer of inverters. However, the islanding detection is difficult since with the indirect current...
The aim of this paper is to explain a novel technique to improve voltage and frequency profiles on microgrids controlled using the droop control scheme. The method consists on retuning the controller according to the present load scenario by adjusting the droop coefficients in a way that is proportional to the load changes. The proposed technique is tested through numerical simulations and the results...
This study examines the P+ multi resonant based voltage control for the voltage harmonics compensation under the islanded mode of a microgrid. In islanded mode, the inverter is defined as a voltage source to supply the full local load demand without a connection to the grid. On the other hand, the output voltage waveform is distorted by the negative and zero sequence and current harmonics due to the...
This paper proposes a smoothing method of frequency fluctuations of power system due to the varying output of wind farms (WFs) by using High Voltage Direct Current (HVDC) transmission system. The proposed control method is designed to minimize the fluctuations of the power system frequency without any additional installation of energy storage systems such as batteries. Simulation analysis is performed...
Due to the low inductance of an LCL-filter, the grid current generated by an LCL-filtered Voltage Source Inverter (VSI) is sensitive to low-order grid-voltage harmonics. This issue is especially tough for the control system with Inverter Current Feedback (ICF), because the grid-current harmonics can freely flow into the filter capacitor without control. To cope with this issue, this paper develops...
Microgrids are key elements for integrating renewable resources as well as distributed energy storage systems as green sources of electricity. However, the presence of controllers is indispensable in confronting the intermittency and variable operation of renewable resources. This paper explores the control of active and reactive power flow through two modes of microgrid operations, namely islanded...
The increasing awareness of the need to reduce pollution and global warming, and the increasing price of conventional energy resources, encouraged many countries to adapt new energy policies by including renewable energy resources, such as solar energy, wind energy, tidal energy. These new energy sources are usually connected to the gird via inverters, which presents fast dynamics due to their small...
Lately, new solutions have been added to the control of autonomous grids, which improve the way the power grids operate. These changes may affect the reliability and safety of power distribution grids, the dynamic stability being a real concern. This issue is more prominent in autonomous microgrids (MGs) with high penetration of renewable energy sources. On this topic, this paper aims to study how...
In this paper is presented the design of PR controller for 3-phase current source inverter. The converter is implemented with IGBT transistors and is modelled as a CSI (Current Source Inverter). Current control loops based on resonant techniques and instantaneous power p-q theory are used to control the DC/AC converter. This control strategy achieves active and reactive power generation in a three-phase...
The feature of power current sources for pulse-arc welding is superimposing of current pulses with a defined shape, size and frequency on the main welding current. The purpose of this paper is to explore the possibilities to control the parameters of superimposed pulses by a particular (additional) welding inverter current source with improved parameters. The current pulse superimposed to the basic...
The future in electric power supplying is characterized by huge deployment of AC and DC distributed generations (DG). The main requirement was caused by the maximum use of local energy resources in countries with advanced technologies with good cost flows, into the usable energy forms. Huge possibility has especially photovoltaic generation together with accumulation systems or with others local power...
The advent of microgrids paved the way for energy decentralization and self-sufficiency among consumers. Reciprocating engine driven synchronous generators (also known as gensets) are one of the most commonly found distributed energy resources (DERs) installed in a microgrid. A key concern in microgrid operation is the frequency regulation, especially when it is islanded from the main grid. In recent...
This paper presents a control strategy for a flexible single-phase microgrid that can operate in grid-connected or in islanded mode. The microgrid adopted is composed of two voltage source inverters (VSIs) operated in parallel and two local nonlinear loads. This approach is based on a hierarchical structure which consists of inner, primary and secondary levels. The inner control regulates the output...
High-efficiency control of grid-tied inverters under unbalanced grid voltage condition is very important to improve the operation performance of the grid-tied inverters. On basis of instantaneous power theory of Current Source Inverter (CSI) under unbalanced grid voltage condition, this paper proposes a novel Quasi Direct Power Control (QDPC) strategy which adopts proportional resonant (PR) controller...
This paper addresses the optimal current control of grid-connected converters with uncertain parameters. The grid is modeled as a voltage source, affected by harmonics, in series with an uncertain inductance. As a main contribution, the comparison of ℋ2 state feedback strategies based on linear matrix inequalities is carried out. It is shown by means of examples that a suboptimal strategy can lead...
In this paper a comparison between grid-feeding and grid-supporting inverters is shown based on simulation and measurement of inverter output impedances. The output impedance of a grid-feeding inverter with current control shows capacitive behavior compared to inductive behavior of a grid-supporting inverter with voltage control.
In this paper, it is presented a procedure to simplify the well-known average model as well as to approximate the controller design for a Pulse-Width-Modulation (PWM) based power converter that transforms energy from some DC source (such as batteries or fuel cells) into an AC voltage source. The power converter studied is formed by two stages: a DC-DC bidirectional converter (boost) and a DC-AC H-bridge...
The microgrid is some part of the electric grid that can disconnect and operate autonomously, therefore it is becoming a broadly discussed theme in the ecosystem of the distribution domain. Moreover, distributed generation and distributed storage may function cooperatively towards balancing energy supply and demand, as well as managing system stability and power quality. In this context, the vastly...
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