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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A2: Solar Energy and Photovoltaic Systems".

Deadline for manuscript submissions: closed (31 August 2019) | Viewed by 56393

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Dr. Dezso Sera

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Department of Energy Technology, Aalborg University, DK-9220 Aalborg, Denmark
Interests: photovoltaic systems; power electronics; PV systems modelling, diagnostics and monitoring; PV+ energy storage; PV grid integration
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Prof. Dr. Tamás Kerekes

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Department of Energy Technology, Aalborg University, Pontoppidanstræde 111, 9220 Aalborg-East, Denmark
Interests: converter topologies and control algorithms for grid connected renewable energy systems including storage
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Special Issue Information

Dear Colleagues,

We invite you to submit your original research or overview papers to this Special Issue on the “Integration of PV in Distribution Networks”, in Energies.

Solar photovoltaics is one of the fastest-growing energy technologies worldwide, and residential and small commercial installations play an important role in the global PV market. A continued increase in the penetration of PV systems in the distribution network can be expected as the prices of these systems keep falling. Energy storage provides a further boost to this trend.

Due to the high penetration of PV in the distribution network, the fast power fluctuations from individual PV installations will pose challenges for maintaining the voltage quality. Furthermore, the high density of grid-feeding power electronic converters creates further challenges related to harmonics and interhamonics, resonances, active anti-islanding, and so on.

Therefore, in this Special Issue we welcome contributions within the general area of PV grid integration, especially for low voltage distribution systems and issues related to high PV penetration.

Topics include, but are not limited to:

Grid current harmonics, interhamonics, and their mitigation
Grid voltage fluctuations due to fast irradiance variations (e.g., passing clouds)
Operation of large number of paralleled PV inverters: resonance, harmonics, active anti-islanding, operation under grid faults.
Advanced control strategies for higher PV penetration, grid voltage support via reactive power, frequency support, active power control
Coordinated control of PV inverters to, e.g., allow higher penetration

Assoc. Prof. Dr. Dezso Sera
Assoc. Prof. Dr. Tamas Kerekes
Guest Editor

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Keywords

PV grid integration
PV inverter control
Grid support by PV inverters
High PV penetration in distribution network
PV inverter harmonics and interhamonics

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Published Papers (12 papers)

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Research

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21 pages, 3387 KiB

Open AccessArticle

Online Parametric Estimation of Grid Impedance Under Unbalanced Grid Conditions

by Nabil Mohammed, Mihai Ciobotaru and Graham Town

Energies 2019, 12(24), 4752; https://doi.org/10.3390/en12244752 - 13 Dec 2019

Cited by 24 | Viewed by 3806

Abstract

Whereas power-electronics-based power systems are expected to enable more integration of renewable energy sources, they could pose crucial challenges including stability issues due to the Thévenin impedance seen by inverters. Such problems could be mitigated by enabling the inverters to estimate the grid impedance by including a grid impedance estimation technique into their control loop. However, one aspect which has been overlooked thus far is that the accuracy of such grid impedance estimation techniques is significantly affected by various grid conditions. For instance, the unbalance in three-phase power systems causes unwanted oscillations at double the fundamental frequency in the inverters control loops. Therefore, this paper proposes a simple and reliable online estimation of the grid impedance under unbalanced conditions. The technique is based on wide-band impedance estimation incorporated into the control loop of the positive sequence of a three-phase grid-connected inverter equipped with a positive- and negative-sequence control (PNSC) strategy. Additionally, complex curve fitting is utilized to obtain parametric models of the grid impedance. To demonstrate the efficacy of the proposed grid impedance estimation technique, extensive case studies are performed. These include: (1) unbalanced operations of both resistive-inductive (RL) and resistive-inductive-capacitive (RLC) models of the grid, (2) background harmonics, and (3) asymmetrical impedances of the network. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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20 pages, 5360 KiB

Open AccessFeature PaperArticle

Theoretical and Experimental Study to Determine Voltage Violation, Reverse Electric Current and Losses in Prosumers Connected to Low-Voltage Power Grid

by Igor Cavalcante Torres, Gustavo F. Negreiros and Chigueru Tiba

Energies 2019, 12(23), 4568; https://doi.org/10.3390/en12234568 - 29 Nov 2019

Cited by 13 | Viewed by 3212

Abstract

The impact of PV generation distributed in a low voltage transmission line depends on many factors: The distribution lines and PV generators characteristics, its location, operational control, local meteorological conditions, electricity consumption profile, and the electricity cost variation. An atypical and challenging behavior of photovoltaic distributed generation (DG) insertion in consumer units (CUs), implies in some circumstances, as the reverse directionality of the power flow between the load equipped with a photovoltaic system generator and the electrical grid, when a CU contains a distributed generation and low power consumption, the power flow will be directed to the power electric grid. In this work, the modeling of a low-voltage real feeder was performed, setting the variables of the system under real operating conditions. As result, voltage levels variability throughout the feeder, the electrical losses, and the asymmetry between the phases were observed. Through simulation scenarios, the occurrence of voltage increase under different penetration scenarios of distributed generation was verified and there was a 10% increase in reference voltage as well as the occurrence of higher electrical losses by reverse current, reaching 1200% more with a DG penetration, in the massive presence of the photovoltaic generator. The mitigatory action used in this work was able to attenuate the negative impacts to the feeder circuit, ensuring the integrity grid and the consumer unit. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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23 pages, 10600 KiB

Open AccessArticle

Behaviour of Distribution Grids with the Highest PV Share Using the Volt/Var Control Chain Strategy

by Daniel-Leon Schultis and Albana Ilo

Energies 2019, 12(20), 3865; https://doi.org/10.3390/en12203865 - 12 Oct 2019

Cited by 4 | Viewed by 3356

Abstract

The large-scale integration of rooftop PVs stalls due to the voltage limit violations they provoke, the uncontrolled reactive power flow in the superordinate grids and the information and communications technology (ICT) related challenges that arise in solving the voltage limit violation problem. This paper attempts to solve these issues using the LINK-based holistic architecture, which takes into account the behaviour of the entire power system, including customer plants. It focuses on the analysis of the behaviour of distribution grids with the highest PV share, leading to the determination of the structure of the Volt/var control chain. The voltage limit violations in low voltage grid and the ICT challenge are solved by using concentrated reactive devices at the end of low voltage feeders. Q-Autarkic customer plants relieve grids from the load-related reactive power. The optimal arrangement of the compensation devices is determined by a series of simulations. They are conducted in a common model of medium and low voltage grids. Results show that the best performance is achieved by placing compensation devices at the secondary side of the supplying transformer. The Volt/var control chain consists of two Volt/var secondary controls; one at medium voltage level (which also controls the TSO-DSO reactive power exchange), the other at the customer plant level. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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19 pages, 6463 KiB

Open AccessArticle

Towards Energy Neutral Wireless Communications: Photovoltaic Cells to Connect Remote Areas

by Sovan Das, Enrique Poves, John Fakidis, Adrian Sparks, Stefan Videv and Harald Haas

Energies 2019, 12(19), 3772; https://doi.org/10.3390/en12193772 - 3 Oct 2019

Cited by 26 | Viewed by 4540

Abstract

In this work, we have designed, developed and deployed the world’s first optical wireless communication (OWC) system using off-the-shelf lasers and solar photovoltaics. Four bidirectional OWC prototypes have been installed on the Orkney Islands of Scotland at a 30 m link distance for the provision of high-speed internet access to two residential properties. The silicon-made solar panels can harvest power up to 5 W from sunlight and they offer data rates as high as 8 Mb/s. Using additional analogue processing, data rates higher than the existing landline broadband connection are achieved. This breakthrough opens the development path to low cost, self-powered and plug-and-play free-space optical (FSO) systems. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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17 pages, 658 KiB

Open AccessFeature PaperArticle

A Review on Transformerless Step-Up Single-Phase Inverters with Different DC-Link Voltage for Photovoltaic Applications

by Wenjie Liu, Kamran Ali Khan Niazi, Tamas Kerekes and Yongheng Yang

Energies 2019, 12(19), 3626; https://doi.org/10.3390/en12193626 - 23 Sep 2019

Cited by 19 | Viewed by 4807

Abstract

Photovoltaic (PV) energy has been competitive in power generation as an alternative to fossil energy resources over the past decades. The installation of grid-connected solar energy systems is expected to increase rapidly with the fast development of the power electronics technology. As the key to the interface of the PV energy and the grid, power converters should be reliable, efficient and comply with the grid requirements. Considering the nature of PV energy, the power conversion should be flexible (e.g., high step-up DC-DC conversion and harmonic-free DC-AC conversion). Accordingly, many power electronic converters have been reported in literature. Compared with isolated inverters, transformerless inverters show great advantages. This paper thus presents an overview of the transformerless step-up single-phase inverters for PV applications based on the dc-link configurations. Grid-connected PV inverters are classified as constant dc-link voltage structures, pseudo-dc-link voltage structures, pulsating dc-link voltage structures and integrated dc-link voltage structures. The discussion on the composition of different dc-link structures is presented, which provides guidance to select appropriate transformerless inverter topologies for PV applications. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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14 pages, 2343 KiB

Open AccessArticle

An Improved Directional Relay Adapted to a Distribution Network with IIG Integration

by Yifan Zhu, Tao Zheng, Minghao Wang, Hongcheng Zhao and Xingguo Wang

Energies 2019, 12(17), 3345; https://doi.org/10.3390/en12173345 - 30 Aug 2019

Cited by 4 | Viewed by 2631

Abstract

The integration of distributed generation (DG) into a distribution network changes the network’s topology. Three-stage current protection for a radial distribution network cannot meet the requirements of relay protection for a distribution network with DG. A directional relay that is based on the positive sequence fault component (PSFC) can effectively identify faults in the positive and negative directions and can be used to solve the adaptability problem with three-stage current protection in a multi-source distribution network. However, DG and the traditional generators have different fault characteristics and are affected by different control strategies, which may lower the sensitivity of a directional relay based on the PSFC or even cause mal-operation. Focusing on this problem, this paper proposes an improved directional relay that is adapted to a distribution network with inverter-interfaced generation (IIG) integration. The improved scheme divides the operation zone of the directional relay based on the PSFC into sensitive and insensitive areas. If the result of a phase comparison is located in the insensitive area, further identification is needed according to a comparison of the current amplitudes. Simulation experiments are carried out based on PSCAD/EMTDC, and their results verify the correctness of the proposed scheme. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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22 pages, 2090 KiB

Open AccessArticle

Optimised Heat Pump Management for Increasing Photovoltaic Penetration into the Electricity Grid

by Cristian Sánchez, Lionel Bloch, Jordan Holweger, Christophe Ballif and Nicolas Wyrsch

Energies 2019, 12(8), 1571; https://doi.org/10.3390/en12081571 - 25 Apr 2019

Cited by 15 | Viewed by 6285

Abstract

Advanced control of heat pumps with thermal storage and photovoltaics has recently been promoted as a promising solution to help decarbonise the residential sector. Heat pumps and thermal storage offer a valuable flexibilisation mean to integrate stochastic renewable energy sources into the electricity grid. Heat pump energy conversion is nonlinear, leading to a challenging nonlinear optimisation problem. However, issues like global optimum uncertainty and the time-consuming methods of current nonlinear programming solvers draw researchers to linearise heat pump models that are then implemented in faster and globally convergent linear programming solvers. Nevertheless, these linearisations generate some inaccuracies, especially in the calculation of the heat pump’s coefficient of performance (

C O P

). In order to solve all of these issues, this paper presents a heuristic control algorithm (HCA) to provide a fast, accurate and near-optimal solution to the original nonlinear optimisation problem for a single-family house with a photovoltaic system, using real consumption data from a typical Swiss house. Results highlight that the HCA solves this optimisation problem up to 1000 times faster, yielding an operation that is up to 49% cheaper and self-consumption rates that are 5% greater than other nonlinear solvers. Comparing the performance of the HCA and the linear solver intlinprog, it is shown that the HCA provides more accurate heat pump control with an increase of up to 9% in system Operating Expense OPEX and a decrease of 8% in self-consumption values. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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16 pages, 16820 KiB

Open AccessArticle

Static Operational Impacts of Residential Solar PV Plants on the Medium Voltage Distribution Grids—A Case Study Based on the Danish Island Bornholm

by Ziyu Wang and Guangya Yang

Energies 2019, 12(8), 1458; https://doi.org/10.3390/en12081458 - 17 Apr 2019

Cited by 4 | Viewed by 5129

Abstract

Driven by the Energy Strategy 2050 of Denmark, renewable energy sources (RESs) are increasingly integrated into the Danish power grid. Solar photovoltaic (PV) plants play an important role in this process. This paper conducted a study to investigate the impacts of residential solar PV integration in the distribution grid on voltage security and grid loss based on the 10 kV distribution grid in Bornholm. Three case studies are performed to test three different reactive power control methods, i.e., PF(P), constant PF and constant Q, at different penetration levels. The assessment of the impacts of PV integration and different control methods are done in the DIgSILENT PowerFactory. It was found that PV integration can contribute to reducing the loss of the system, increased overvoltage in buses and overload in transformers, and 40% penetration at the low voltage is considered to be an optimal level based on the result. PF(P) control gives the best performance among all three methods under the current grid codes. With constant PF control, it was found that the system loss can be significantly reduced if the PV systems operate with a power factor of 0.9 leading, which is not the norm of the current Danish grid code. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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15 pages, 4137 KiB

Open AccessArticle

Comparative Study of Ramp-Rate Control Algorithms for PV with Energy Storage Systems

by João Martins, Sergiu Spataru, Dezso Sera, Daniel-Ioan Stroe and Abderezak Lashab

Energies 2019, 12(7), 1342; https://doi.org/10.3390/en12071342 - 8 Apr 2019

Cited by 83 | Viewed by 5812

Abstract

The high variability of solar irradiance, originated by moving clouds, causes fluctuations in Photovoltaic (PV) power generation, and can negatively impact the grid stability. For this reason, grid codes have incorporated ramp-rate limitations for the injected PV power. Energy Storage Systems (ESS) coordinated by ramp-rate (RR) control algorithms are often applied for mitigating these power fluctuations to the grid. These algorithms generate a power reference to the ESS that opposes the PV fluctuations, reducing them to an acceptable value. Despite their common use, few performance comparisons between the different methods have been presented, especially from a battery status perspective. This is highly important, as different smoothing methods may require the battery to operate at different regimes (i.e., number of cycles and cycles deepness), which directly relates to the battery lifetime performance. This paper intends to fill this gap by analyzing the different methods under the same irradiance profile, and evaluating their capability to limit the RR and maintain the battery State of Charge (SOC) at the end of the day. Moreover, an analysis into the ESS capacity requirements for each of the methods is quantified. Finally, an analysis of the battery cycles and its deepness is performed based on the well-established rainflow cycle counting method. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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13 pages, 4299 KiB

Open AccessArticle

Integration of Photovoltaic Power Units to Power Distribution System through Modular Multilevel Converter

by Seyed Mehdi Hakimi and Amin Hajizadeh

Energies 2018, 11(10), 2753; https://doi.org/10.3390/en11102753 - 15 Oct 2018

Cited by 8 | Viewed by 3001

Abstract

With the growing of using photovoltaic (PV) units in power distribution systems, the role of high-performance power electronic converters is increasing. In this paper, modelling and control of Modular Multilevel Converter (MMC) are addressed for grid integration of PV units. Designing a proper controller for MMC is crucial during faulty conditions to make the converter stable and provide proper dynamic performance. To achieve this goal, a dynamic model of MMC is presented which it includes symmetrical components of voltage and current. Then, adaptive robust current controllers are developed based on sliding mode and fuzzy controllers for MMC and then the robustness and stability of the controllers are proved by the Lyapunov theory. To implement the proposed controllers under unbalanced grid voltage fault, positive and negative sequences current controllers are implemented to compensate the effect of grid voltage fault and load power variation. Finally, numerical results are shown to evaluate the performance of MMC. In the end, the experimental results are given to prove the controller performance. The outcome indicates that the proposed current controllers are more effective under voltage disturbance conditions and could satisfy the stability of MMC. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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13 pages, 7805 KiB

Open AccessArticle

Voltage Stability of Low-Voltage Distribution Grid with High Penetration of Photovoltaic Power Units

by Majid Ghaffarianfar and Amin Hajizadeh

Energies 2018, 11(8), 1960; https://doi.org/10.3390/en11081960 - 27 Jul 2018

Cited by 31 | Viewed by 5460

Abstract

Voltage stability analysis of power distribution systems with high photovoltaic (PV) penetration is a challenging problem due to the stochastic generation of a solar power system. Voltage stability is an important benchmark for defining PV’s penetration level in active distribution networks considering loading capacity. The massive integration of PV power units, the effect of distribution system characteristics, like high ratio of R/X, and the reported collapses in power networks come up in serious studies that investigate their impact and upcoming problems on distribution networks. Therefore, this paper proposes analytical voltage stability and it is implemented on IEEE 34 nodes radial distribution systems with 24.9 kV and 4.16 kV voltage levels. In this regard, in addition to given properties in stability and power loss analysis, a penetration coefficient for PVs is considered. Simulation results prove that the applied method can illustrate the positive and negative effects of PV in distribution networks. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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Review

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16 pages, 2577 KiB

Open AccessReview

Large Photovoltaic Power Plants Integration: A Review of Challenges and Solutions

by Nouha Mansouri, Abderezak Lashab, Dezso Sera, Josep M. Guerrero and Adnen Cherif

Energies 2019, 12(19), 3798; https://doi.org/10.3390/en12193798 - 8 Oct 2019

Cited by 53 | Viewed by 6876

Abstract

Renewable energy systems (RESs), such as photovoltaic (PV) systems, are providing increasingly larger shares of power generation. PV systems are the fastest growing generation technology today with almost ~30% increase since 2015 reaching 509.3 GW_p worldwide capacity by the end of 2018 and predicted to reach 1000 GW_p by 2022. Due to the fluctuating and intermittent nature of PV systems, their large-scale integration into the grid poses momentous challenges. This paper provides a review of the technical challenges, such as frequency disturbances and voltage limit violation, related to the stability issues due to the large-scale and intensive PV system penetration into the power network. Possible solutions that mitigate the effect of large-scale PV system integration on the grid are also reviewed. Finally, power system stability when faults occur are outlined as well as their respective achievable solutions. Full article

(This article belongs to the Special Issue Integration of PV in Distribution Networks)

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