PI-based controller for low-power distributed inverters to maximise reactive current injection while avoiding over voltage during voltage sags

This paper is a postprint of a paper submitted to and accepted for publication in IET Power Electronics and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at the IET Digital Library.In the recently deregulated power system scenario, the growing number of distributed generation sources should be considered as an opportunity to improve stability and power quality along the grid. To make progress in this direction, this work proposes a reactive current injection control scheme for distributed inverters under voltage sags. During the sag, the inverter injects, at least, the minimum amount of reactive current required by the grid code. The flexible reactive power injection ensures that one phase current is maintained at its maximum rated value, providing maximum support to the most faulted phase voltage. In addition, active power curtailment occurs only to satisfy the grid code reactive current requirements. As well as, a voltage control loop is implemented to avoid overvoltage in non-faulty phases, which otherwise would probably occur due to the injection of reactive current into an inductive grid. The controller is proposed for low-power rating distributed inverters where conventional voltage support provided by large power plants is not available. The implementation of the controller provides a low computational burden because conventional PI-based control loops may apply. Selected experimental results are reported in order to validate the effectiveness of the proposed control scheme.Peer ReviewedPostprint (updated version

Power quality and electromagnetic compatibility: special report, session 2

The scope of Session 2 (S2) has been defined as follows by the Session Advisory Group and the Technical Committee: Power Quality (PQ), with the more general concept of electromagnetic compatibility (EMC) and with some related safety problems in electricity distribution systems. Special focus is put on voltage continuity (supply reliability, problem of outages) and voltage quality (voltage level, flicker, unbalance, harmonics). This session will also look at electromagnetic compatibility (mains frequency to 150 kHz), electromagnetic interferences and electric and magnetic fields issues. Also addressed in this session are electrical safety and immunity concerns (lightning issues, step, touch and transferred voltages). The aim of this special report is to present a synthesis of the present concerns in PQ&EMC, based on all selected papers of session 2 and related papers from other sessions, (152 papers in total). The report is divided in the following 4 blocks: Block 1: Electric and Magnetic Fields, EMC, Earthing systems Block 2: Harmonics Block 3: Voltage Variation Block 4: Power Quality Monitoring Two Round Tables will be organised: - Power quality and EMC in the Future Grid (CIGRE/CIRED WG C4.24, RT 13) - Reliability Benchmarking - why we should do it? What should be done in future? (RT 15

Voltage Distortion Mitigation in a Distributed Generation-integrated Weak Utility Network Via a Self-tuning Filter-based Dynamic Voltage Restorer

The dynamic voltage restorer (DVR) is mainly used in a utility grid to protect sensitive loads from power quality problems, such as voltage sags and swells. However, the effectiveness of the DVR can wane under unbalanced grid voltage conditions. Recently, DVR control algorithms have been developed that enable the elimination of voltage harmonics in weak and distorted utility networks. This paper presents a modified control method for the DVR, which can (1) compensate the voltage swell and (2) eliminate the voltage harmonics in a combined utility condition consisting of voltage unbalance and harmonic distortion. A self-tuning filter (STF) is used along with the pq controlmethod to increase the control performance of the DVR. One of the advantages of STF is that it eliminates the need to have multiple filters as part of the control method, and thus reduces the controller complexity. Analysis of the fault ride-through capability of the new DVR revealed an improvement in the voltage stability offered to distributed generation-integrated weak utility networks. The proposed DVR control method is modeled in MATLAB/Simulink and tested in both off-line and real-time environments using theOPALRT real-time platform. Results are then presented as a verification of the proposed system

Voltage quality enhancement in distribution system using artificial neural network (ANN) based dynamic voltage restorer

Voltage quality issue and invariably power quality has become an important issue in distribution power system operation due to presence of increased use of nonlinear loads (computers, microcontrollers and power electronics systems). Voltage sags and swells as well as harmonics are problems for industrial, commercial and residential customers with sensitive loads, which need urgent attention for their compensation. In this paper, the modeling and simulations of a dynamic voltage restorer (DVR) was achieved u sing MATLAB/Simulink. The aim was to employ artificial intelligence to provide smart triggering pulses for the DVR to mitigate and to provide compensation against voltage sags and swells. The Artificial Neural Network (ANN) was trained online by data gener ated via a 3 - phase programmable voltage generator and these were used as inputs to the ANN, fault conditions were simulated to create voltage sags and swells in the source supply, while faultless condition of the system was simulated and the data obtained from it was used as targets of the ANN. A net fitting, feed forward back propagation, Lavenberg - Marquardt training algorithm and mean square error performance were used. ANN Simulink block was used as control for the gate of the full wave 3 - phase Insulated Gate Bipolar Transistor (IGBT) inverter employed in constructing the DVR. Three single phase injection transformers were employed to regulate the output amplitude voltage from the DVR, while filters were used to reduce the harmonics from 11.09% to 3.5%. A t the end, voltage sags and swells were effectively mitigated and harmonics in the system reduced to 3.5%, which is within the maximum acceptable IEEE standard 519 of 1992 for harmonic distortion. Key words : Voltage, Distribution System, ANN, Dynamic Volt age Restorer, Voltage quality enhancement, non - linear load

Development of a proposed single-phase series active power filter without external power sources

The quality of electric power is receiving more and more attention from part of consumers, Distribution System Operators (DSO), Transmission System Operators (TSO) and other competent entities related to the electrical power system. Once the electrical Power Quality (PQ) problems have direct implications for business productivity, causing high economic losses, it is mandatory to develop solutions that mitigate these problems. Active Power Filters (APFs) are power electronic equipment capable of compensating PQ problems that have the ability to dynamically adjust their modes of operation in response to changes in load or in the power system. Among these solutions, the Series Active Power Filter (SeAPF) is specially conceived to deal with problems related to the power system voltage amplitude and waveform. Despite the ability to compensate voltage sags, voltage swells, voltage harmonics, and voltage imbalances in three-phase systems, the SeAPF has not achieved much success neither has not been widely adopted. The lack of interest in this equipment can be largely justified by its high cost and also because of some limitations presented by the SeAPF conventional topology. In this paper is presented a novel topology, as well as the control algorithms of a single-phase SeAPF that is connected directly to the power grid without the use of coupling transformers and that does not require the use of external power sources. The topology and control algorithms of the SeAPF proposed in this paper were firstly evaluated by means of simulation results obtained with PSIM software and, once validated, a laboratory prototype was developed, being presented experimental results that support the correct operation of the proposed system.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019. This work is financed by the ERDF – COMPETE 2020 Programme, and by FCT within project SAICTPAC/0004/2015-POCI-01-0145-FEDER-016434 and by FCT within project PTDC/EEI-EEE/28813/2017. Mr. Luis A. M. Barros is supported by the doctoral scholarship PD/BD/143006/2018 granted by the Portuguese FCT agency