Analysis of the applicability of the IEEE 2030.8 standard for testing a microgrid control system

To coordinate the operation of the different generating units, storage systems and loads belonging to a microgrid, typically a Microgrid Control System (MGCS) is needed. This MGCS defines the set points to be delivered to the controllable devices to guarantee the appropriate operation of the microgrid both from the technical and the economic perspectives. The MGCS must be able to operate the microgrid in islanded mode, grid-connected, and withstand the transitions between the two operatingmodes. Recently two international standards have been approved dealing with microgrid con-trollers, “IEEE 2030.7-2017 – IEEE Standard for the Specification of Microgrid Control-ler” and “IEEE 2030.8-2018 - IEEE Standard for the Testing of Microgrid Controllers”.The research leading to this publication has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654113 via the Trans-national Access (TA) User Project 05.024-2018

A Universal Formulation for Multilevel Selective Harmonic Elimination - PWM with Half-Wave Symmetry

Selective harmonic elimination - pulse width modulation (SHE-PWM) can be utilized to improve the efficiency of multilevel voltage source converters due to its ability to provide low switching frequency and tight control of low-order harmonics. In addition, SHE-PWM with half-wave (HW) symmetry provides a higher number of solutions than quarter-wave (QW) symmetry and therefore, the waveform design can be improved. This work proposes a universal formulation, which can be utilized with HW symmetry, that provides a unique system of equations valid for any possible multilevel waveform. Thereby, without using predefined waveforms, this formulation provides the ability to search simultaneously both the firing angles and the switching patterns, simplifying significantly the search process and providing a high number of solutions. With the aim of selecting the optimum sets of firing angles, the solutions provided by HW and QW symmetries are compared, based on several metrics of harmonic performance, for particular test cases. Experimental results also validate the universal formulation with HW symmetry.Eusko Jaurlaritza; Secretaria de Estado de Investigacion Desarrollo e Innovacio

Circulating current control for modular multilevel converter based on selective harmonic elimination with ultra-low switching frequency

Multilevel converters (MCs) are utilized in medium voltage (MV) high power applications due to its higher efficiency than two level converters. On the other hand, modular multilevel converters (MMCs) provide several advantages with regard to other MCs, such as higher scalability, reliability and no requirement of a common DC capacitor. Particularly, low switching frequency modulations, such as (2N+1) selective harmonic elimination (SHE) - pulse width modulation (PWM), may improve the efficiency of MMCs when they are utilized in MV and high power applications, where the number of sub-modules is not high. This work presents a new circulating current control for MMC when (2N+1) SHE-PWM is utilized. Therefore, it is possible to operate the converter simultaneously with low switching frequency and low capacitor voltage ripple at every sub-module besides a correct energy balance between arms. In addition, a new method to implement (2N+1) SHE-PWM for MMCs, which is also valid to implement standard SHE-PWM for any MC, is provided. Using this method, different equation systems are not required for every switching pattern. In this way, this technique provides simultaneously both the switching patterns and the firing angles which solve the SHE problem, simplifying the searching task. Simulation results which have been obtained from a MMC with 5 sub-modules at every arm, have validated the novel proposed circulating current control. Furthermore, the spectrum of the simulated line to line voltage waveform has proved the correct performance of the proposed (2N+1) SHE-PWM implementation method. Several sets of angles have been provided throughout the ma range, where 17 harmonics have been controlled

A universal formulation for selective harmonic elimination PWM with half-wave symmetry for multilevel voltage source converters

Publisher Copyright: © 2016 IEEE.Selective harmonic elimination (SHE) - pulse with modulation (PWM), when applied to multilevel converters (MCs), can be optimized in case a half-wave (HW) symmetry is implemented. This kind of symmetry is able to provide a wide variety of solutions. This paper proposes a novel method, based on optimization algorithms, which provides a universal formulation of the SHE-PWM problem with HW symmetry, in such a way that different equation systems are not required to find a solution when different switching patterns are considered. In this way, the proposed technique is able to search simultaneously both the switching patterns and their associated firing angles that solve the SHE-PWM problem, without using predefined waveforms. Therefore, the search process is significantly simplified and the flexibility to find solutions with different waveforms, throughout the reference modulation index, ma, range, is increased. Different sets of solutions provided by this method have been presented and simulation results, obtained from a five-level modular multilevel converter (MMC), have proved the validity of the new proposed technique.Peer reviewe

Selective Harmonic Mitigation (SHM-PWM) and THD Minimization: Performance Comparison of Different Formulations

Publisher Copyright: © 2022 IEEE.Selective harmonic mitigation (SHM-PWM) is a low switching frequency modulation technique commonly employed in medium voltage-high power multilevel converters to increase their efficiency. Several different formulations, based on multi-objective cost functions, have been published in the technical literature to implement SHM-PWM together with total harmonic distortion (THD) minimization. However, a comparison is required to determine which formulation is more effective to solve the problem. In this way, this paper provides a novel comparison based on a study of the formulation equations and a brute force analysis. The formulation parameters have been optimized to offer a fair comparison in the brute force analysis. With the aim of considering the effect on the convergence of search algorithm effectiveness, the formulations have also been compared considering the results provided by a hybrid meta-heuristic-numerical search algorithm. As a result, the advantages and disadvantages of every formulation, besides some rules to optimize their parameters, have been extracted.This work has been supported by the Basque Government within the Research program ELKARTEK under projects: CONVADP (KK-2020/00091) and EP4H2 (KK-2022/00039).Peer reviewe

Adaptive Reclosing Technique Using Variational Mode Decomposition Algorithm in BESS-Based Microgrid

This study introduces a novel adaptive technique to accelerate the process of reclosing in a Battery Energy Storage System (BESS)-based microgrid system to provide uninterrupted power supply (UPS). Two different methodologies, Fault Current Contribution Ratio (FCCR) and Variational Mode Decomposition (VMD) are used to implement the proposed technique. First, the FCCR between the healthy and faulty phases is estimated in the relay after the occurrence of the transient. In the next stage, exact fault occurrences and clearance instances are detected using the VMD technique. The exact detection of fault clearance time will help reduce the conventional outage time. This will reduce the unwanted burden on the BESS as it can be used adaptively during the fault only. The comparative assessment is done to show the efficacy of the proposed reclosing method. The proposed technique will also help distinguish faults from switching operations. The performance of the proposed method is validated through a modified IEEE 13-bus BESS-based microgrid architecture. The EMTDC/PSCAD software is used for simulation. The algorithms are developed on the MATLAB platform. Real-time test results are also provided for the signals obtained from the Smart Grid Technology Laboratory (SGTL) lab setup. The results prove the efficacy of the proposed technique

SHC-PWM Closed-Loop Control Based on PI Controllers for Active Power Filters

Publisher Copyright: © 2023 IEEE.The increase of non-linear loads connected to the grid has led to the use of active power filters (APF) to reduce the low-order current harmonics injected by this kind of loads. In case of high-power medium-voltage applications, low switching frequency optimized modulators are preferred over standard carrier based-PWM. Therefore, in this work the selective harmonic control - PWM (SHC-PWM) modulation technique is used. SHC-PWM allows to synthesize low-order harmonics in amplitude and phase with low switching frequency. A closed-loop control system for APFs is proposed in order to address the control dynamic challenges related to low switching frequency modulation techniques. The closed-loop control uses a Kalman filter to estimate the harmonic currents in the grid side, a proportional-integral controller and SHC-PWM modulator based on artificial neural network. Simulation results are provided for a 3-level NPC converter to verify the effectiveness of the proposed control.Peer reviewe

Error Tolerance Analysis for SHE-PWM Calculation in a 3L-NPC Converter

Publisher Copyright: © 2021 IEEE.Medium-voltage high-power converters are usually modulated using low switching frequency techniques such as Selective Harmonic Elimination-Pulse Width Modulation (SHE-PWM) in order to improve their efficiency. To calculate the firing angles, SHE-PWM transcendental equations are usually solved by offline calculation methods, whose computational burden depends on the number of firing angles or eliminated harmonics and the required accuracy in the solutions. Consequently, with the aim of reducing this computational burden, this paper presents an analysis that estimates the maximum accuracy required in the calculated SHE-PWM solutions considering the main non-idealities of the converter. In this sense, a systematic methodology to evaluate the error in the harmonic amplitudes due to control and dead time effects has been developed, providing an optimal error tolerance for the calculation methods that solve the SHE-PWM problem.This work has been supported by the Basque Government within the Research program ELKARTEK under projects: CONVADP (KK-2020/00091) and BIKAINTEK (005-B2-2020).Peer reviewe

SiC modular multilevel converters: sub-module voltage ripple analysis and efficiency estimations

Two important technical challenges associated with the Modular Multilevel Converter (MMC) are the reduction of the voltage ripple of the Sub-Module (SM) capacitors and the reduction of the converter losses. This paper conducts a study focused on these two topics. Firstly, the effect of a circulating current with a predefined second harmonic on the SM voltage ripple is assessed. Secondly, an efficiency study for two different MMCs, one with silicon (Si) and the other with silicon carbide (SiC) devices is carried out. Results suggest that a SiC MMC converter with a circulating current including a second harmonic represent a good solution since it achieves a reduction of the SM capacitors together with a high efficiency operation.Peer Reviewe