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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A: Sustainable Energy".

Deadline for manuscript submissions: closed (31 August 2020) | Viewed by 19504

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Special Issue Editors

Prof. Dr. Teuvo Suntio

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Guest Editor

Department of Electrical Engineering, Tampere University, 33720 Tampere, Finland
Interests: power electronics; dynamic modeling; control design; renewable energy; photovoltaic energy system; battery energy storage; DC-DC converter; three-phase converter

Dr. Alon Kuperman

E-Mail Website1 Website2
Guest Editor

Applied Energy Laboratory, School of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
Interests: photovoltaics; power electronics; energy; renewable energy; power generation; energy conversion; distributed generation; energy engineering; power converters; power quality; wireless power transfer
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Special Issue Information

Dear Colleagues,

Renewable-energy-based generation of electricity remains a "hot" subject nowadays due to the common trend of increasing renewables share in energy generation mix. However, increasing the amount of energy coming from renewable sources both influences electric grid behavior due to the increased amount of grid-interfacing power electronic converters and calls for more efficient renewable energy conversion. As a consequence, enhanced approaches for renewable energy sources modeling, novel topologies of both renewable energy source and mains interfacing power converters and control and monitoring algorithms are required. In addition, energy storage units' role becomes more and more important due to the intermittent and inertia-less nature of the majority of renewable energy sources. The Energies’ Special Issue “Power Electronics in Renewable Energy Systems Ⅱ” is intended for closing the gap by disseminating new promising methods and techniques to cope with the above mentioned challenges.

Prospective authors are invited to submit original contributions, survey papers or tutorials for review for publication in this special issue. Topics of interest include but are not limited to:

Maximum power point tracking algorithms;
Operation of renewable energy sources in isolated micro-grids;
Combined source-converter dynamics;
Modeling techniques of renewable energy sources;
Grid interfacing of renewable energy converters;
Hybridization of energy storage with renewable energy systems;
Energy management of hybrid renewable energy systems;
Virtual inertia.

Prof. Dr. Teuvo Suntio
Prof. Dr. Alon Kuperman
Guest Editors

Manuscript Submission Information

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Keywords

photovoltaic generators
wind turbines
thermoelectric generators
renewable energy sources
power converters
analysis
modeling
control
electric grid
stability
dynamics
MPPT

Published Papers (7 papers)

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Research

16 pages, 1938 KiB

Open AccessArticle

Dynamic Effect of Input-Voltage Feedforward in Three-Phase Grid-Forming Inverters

by Matias Berg and Tomi Roinila

Energies 2020, 13(11), 2923; https://0-doi-org.brum.beds.ac.uk/10.3390/en13112923 - 07 Jun 2020

Cited by 3 | Viewed by 2685

Abstract

Grid-connected and grid-forming inverters play essential roles in the utilization of renewable energy. One problem of such a converter system is the voltage deviations in the DC-link between the source and the inverter that can disrupt the inverter output voltage. A common method to prevent these voltage deviations is to apply an input-voltage feedforward control. However, the feedforward control has detrimental effects on the inverter dynamics. It is shown that the effect of the feedforward in the input-to-output dynamics is not ideal due to the delay in the digital control system. The delay affects the input-to-output dynamics at high frequencies, and only a minor improvement can be achieved by low-pass filtering the feedforward control signal. Furthermore, the feedforward control can remarkably affect the inverter input admittance, and therefore, impedance-based stability problems may arise at the DC interface. This paper proposes a method based on linearization and extra element theorem to model the effect of the feedforward control in the inverter dynamics. Experimental measurements are shown to demonstrate the effectiveness of the proposed model. Full article

(This article belongs to the Special Issue Power Electronics in Renewable Energy Systems Ⅱ)

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18 pages, 2081 KiB

Open AccessArticle

Demodulation of Three-Phase AC Power Transients in the Presence of Harmonic Distortion

by Benjamin T. Gwynn and Raymond de Callafon

Energies 2020, 13(9), 2341; https://0-doi-org.brum.beds.ac.uk/10.3390/en13092341 - 08 May 2020

Cited by 1 | Viewed by 2227

Abstract

Load switches in power systems may cause oscillations in active and reactive power flow. Such oscillations can be damped by synthetic inertia provided by smart inverters providing power from DC sources such as photovoltaic or battery storage. However, AC current provided by inverters is inherently non-sinusoidal, making measurements of active and reactive power subject to harmonic distortion. As a result, transient effects due to load switching can be obscured by harmonic distortion. An RLC circuit serves as a reference load. The oscillation caused by switching in the load presents as a dual-sideband suppressed-carrier signal. The carrier frequency is available via voltage data but the phase is not. Given a group of candidate signals formed from phase voltages, an algorithm based on Costas Loop that can quickly quantify the phase difference between each candidate and carrier (thus identifying the best signal for demodulation) is presented. Algorithm functionality is demonstrated in the presence of inverter-induced distortion. Full article

(This article belongs to the Special Issue Power Electronics in Renewable Energy Systems Ⅱ)

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19 pages, 4811 KiB

Open AccessArticle

Multi-Target Control Strategy of DFIG Using Virtual Synchronous Generator Based on Extended Power Resonance Control under Unbalanced Power Grid

by Dan Sun, Yangming Wang, Tianlong Jiang, Xiaohe Wang, Jun Sun and Heng Nian

Energies 2020, 13(9), 2232; https://0-doi-org.brum.beds.ac.uk/10.3390/en13092232 - 03 May 2020

Cited by 5 | Viewed by 1761

Abstract

Virtual synchronous generator control is considered as an effective solution to optimize the frequency response characteristics of doubly fed induction generator. However, due to the insufficient control bandwidth of the original virtual synchronous generator, it has little control effect over the oscillating components of the power caused by the unbalanced grid voltage. Therefore, long-term unbalanced voltage will cause a series of problems, such as distortion of stator and rotor currents, as well as oscillations of power and electromagnetic torque, which seriously affect the power quality and the operating performance of the doubly fed induction generator. To solve these problems, the concept of extended power is introduced, and the second-order generalized integrator-based resonant controller is used to control the extended power and traditional power. Control targets of the extended power method are discussed and extended, so that the doubly fed induction generator system using extended power resonant control-based virtual synchronous generator control can realize three different control targets under the unbalanced grid condition. The three control targets are: balanced and sinusoidal stator current, sinusoidal stator current and constant active power, and sinusoidal stator current and constant reactive power and electromagnetic torque. The three control targets can also be flexibly switched according to the real-time requirements of the grid with unbalanced voltage. The simulation results verify the effectiveness of the control method. Full article

(This article belongs to the Special Issue Power Electronics in Renewable Energy Systems Ⅱ)

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15 pages, 12056 KiB

Open AccessArticle

Impedance-Based Stability Analysis of Paralleled Grid-Connected Rectifiers: Experimental Case Study in a Data Center

by Henrik Alenius and Tomi Roinila

Energies 2020, 13(8), 2109; https://0-doi-org.brum.beds.ac.uk/10.3390/en13082109 - 24 Apr 2020

Cited by 13 | Viewed by 3465

Abstract

Grid-connected systems often consist of several feedback-controlled power-electronics converters that are connected in parallel. Consequently, a number of stability issues arise due to interactions among multiple converter subsystems. Recent studies have presented impedance-based methods to assess the stability of such large systems. However, only few real-life experiences have been previously presented, and practical implementations of impedance-based analysis are rare for large-scale systems that consist of multiple parallel-connected devices. This work presents a case study in which an unstable high-frequency operation, caused by multiple paralleled grid-connected rectifiers, of a 250 kW data center in southern Finland is reported and studied. In addition, the work presents an experimental approach for characterizing and assessing the system stability by using impedance measurements and an aggregated impedance-based analysis. Recently proposed wideband-identification techniques based on binary injection and Fourier methods are applied to obtain the experimental impedance measurements from the input terminals of a single data center rectifier unit. This work provides a practical approach to design and implement the impedance-based stability analysis for a system consisting of multiple paralleled grid-connected converters. It is shown that the applied methods effectively predict the overall system stability and the resonant modes of the system, even with very limited information on the system. The applied methods are versatile, and can be utilized in various grid-connected applications, for example, in adaptive control, system monitoring, and stability analysis. Full article

(This article belongs to the Special Issue Power Electronics in Renewable Energy Systems Ⅱ)

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19 pages, 8066 KiB

Open AccessArticle

Fuzzy Logic Control for Low-Voltage Ride-Through Single-Phase Grid-Connected PV Inverter

by Eyad Radwan, Mutasim Nour, Emad Awada and Ali Baniyounes

Energies 2019, 12(24), 4796; https://0-doi-org.brum.beds.ac.uk/10.3390/en12244796 - 16 Dec 2019

Cited by 17 | Viewed by 2725

Abstract

This paper presents a control scheme for a photovoltaic (PV) system that uses a single-phase grid-connected inverter with low-voltage ride-through (LVRT) capability. In this scheme, two PI regulators are used to adjust the power angle and voltage modulation index of the inverter; therefore, controlling the inverter’s active and reactive output power, respectively. A fuzzy logic controller (FLC) is also implemented to manage the inverter’s operation during the LVRT operation. The FLC adjusts (or de-rates) the inverter’s reference active and reactive power commands based on the grid voltage sag and the power available from the PV system. Therefore, the inverter operation has been divided into two modes: (i) Maximum power point tracking (MPPT) during the normal operating conditions of the grid, and (ii) LVRT support when the grid is operating under faulty conditions. In the LVRT mode, the de-rating of the inverter active output power allows for injection of some reactive power, hence providing voltage support to the grid and enhancing the utilization factor of the inverter’s capacity. The proposed system was modelled and simulated using MATLAB Simulink. The simulation results showed good system performance in response to changes in reference power command, and in adjusting the amount of active and reactive power injected into the grid. Full article

(This article belongs to the Special Issue Power Electronics in Renewable Energy Systems Ⅱ)

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14 pages, 9944 KiB

Open AccessArticle

Study on Surface Charge Accumulation Characteristics of Resin Impregnated Paper Wall Bushing Core Under Positive DC Voltage

by Ming Chen, Xuandong Liu, Chengjun Liang, Yi Zhao and Hao Tang

Energies 2019, 12(23), 4420; https://0-doi-org.brum.beds.ac.uk/10.3390/en12234420 - 21 Nov 2019

Cited by 3 | Viewed by 2579

Abstract

As a critical component of a high-voltage direct current (HVDC) transmission system, resin impregnated paper (RIP) wall bushing has become a weak point because of its surface charge accumulation. This paper studies a model RIP wall bushing core designed by the equal capacitance method. The stationary resistive field along the gas–solid interface of the RIP wall bushing core is investigated theoretically by a gas model, which considers the non-linearly field-dependent volume conductivity. The results show that the gas conductivity along the core surface tends to be an arched distribution from the high-voltage conductor to the end shielding screen. The surface charge mainly accumulates at the turning point of the radius, which may threaten the core’s insulation. Then, the surface charge is obtained through a measurement system, where the experimental results are highly consistent with the simulation results. Considering the time constant of charge dissipation is nearly 15 min, it would be better to measure the surface charge on one axial direction of RIP wall bushing core after each voltage application. The simulation and experimental results of this paper can guide the design of a RIP wall bushing core. Full article

(This article belongs to the Special Issue Power Electronics in Renewable Energy Systems Ⅱ)

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19 pages, 5825 KiB

Open AccessArticle

Maximum Perturbation Step Size in MPP-Tracking Control for Ensuring Predicted PV Power Settling Behavior

by Teuvo Suntio and Alon Kuperman

Energies 2019, 12(20), 3984; https://0-doi-org.brum.beds.ac.uk/10.3390/en12203984 - 19 Oct 2019

Cited by 5 | Viewed by 2001

Abstract

The heuristic perturb-and-observe-based maximum-power-point tracking (MPPT) algorithm of photovoltaic (PV) generator is still the most popular technique in use, despite the broad spectrum of developed other MPPT algorithms. The correct direction of the next perturbation step requires that the previous perturbation is settled down properly and the applied perturbation step size is large enough to overcome the PV-power changes induced by the varying irradiation level and/or the power-grid-originated PV-voltage ripple. The requirements for the minimum perturbation step size are well defined in the available literature. The design equations to predict the PV-power settling time are derived by assuming that the PV-interfacing converter operates in continuous conduction mode (CCM). A large perturbation step size may drive the interfacing converter to enter into discontinuous conduction mode (DCM), which will delay the PV-power settling process and destroy the validity of the predicted settling times. In order to avoid confusing the MPPT process, the maximum perturbation step size has to be limited as well. This paper provides theoretical foundations for the proper design of the maximum step size based on the DC-DC interfacing-converter dynamic behavior. The theoretical findings are validated with experiments as well as by simulations by means of a boost-type DC-DC converter and real PV panel. Full article

(This article belongs to the Special Issue Power Electronics in Renewable Energy Systems Ⅱ)

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