Research

14 pages, 3307 KiB

Open AccessArticle

Reliability Assessment of Power Systems with Photovoltaic Power Stations Based on Intelligent State Space Reduction and Pseudo-Sequential Monte Carlo Simulation

by Wenxia Liu, Dapeng Guo, Yahui Xu, Rui Cheng, Zhiqiang Wang and Yueqiao Li

Energies 2018, 11(6), 1431; https://doi.org/10.3390/en11061431 - 03 Jun 2018

Cited by 29 | Viewed by 2938

Abstract

As the number and capacity of photovoltaic (PV) power stations increase, it is of great significance to evaluate the PV-connected power systems in an effective, reasonable, and quick way. In order to overcome the challenge of PV’s time-sequential characteristic and improve upon the [...] Read more.

As the number and capacity of photovoltaic (PV) power stations increase, it is of great significance to evaluate the PV-connected power systems in an effective, reasonable, and quick way. In order to overcome the challenge of PV’s time-sequential characteristic and improve upon the computational efficiency, this paper presents a new methodology to evaluate the reliability of the power system with photovoltaic power stations, which combines intelligent state space reduction and a pseudo-sequential Monte Carlo simulation (PMCS). First, a non-aggregate Markov model of photovoltaic output is established, which effectively retains some time-sequential representation of the PV output. Then, the differential evolution algorithm (DE) is introduced into the sampling stage of PMCS to carry out an intelligent state space reduction (ISSR). By using the DE algorithm, success states are searched out and removed, thus the state space is reduced and formed with a high density of loss-of-load. Hence, unnecessary samplings are avoided, which optimizes the PMCS sampling mechanism and improves the computational efficiency. Finally, the proposed method is tested in the modified IEEE RTS-79 system. The results indicate that this new method has a better computational efficiency than the time-sequential Monte Carlo simulation method (TMCS) and pure PMCS. In addition, the effectiveness and feasibility of this method are also verified. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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25 pages, 6464 KiB

Open AccessArticle

Proposals for Enhancing Frequency Control in Weak and Isolated Power Systems: Application to the Wind-Diesel Power System of San Cristobal Island-Ecuador

by Danny Ochoa and Sergio Martinez

Energies 2018, 11(4), 910; https://doi.org/10.3390/en11040910 - 12 Apr 2018

Cited by 19 | Viewed by 4336

Abstract

Wind-diesel hybridization has been emerging as common practice for electricity generation in many isolated power systems due to its reliability and its contribution in mitigating environmental issues. However, the weakness of these kind of power systems (due to their small inertia) makes the [...] Read more.

Wind-diesel hybridization has been emerging as common practice for electricity generation in many isolated power systems due to its reliability and its contribution in mitigating environmental issues. However, the weakness of these kind of power systems (due to their small inertia) makes the frequency regulation difficult, particularly under high wind conditions, since part of the synchronous generation has to be set offline for ensuring a suitable tracking of the power demand. This reduces the power system’s ability to absorb wind power variations, leading to pronounced grid frequency fluctuations under normal operating conditions. This paper proposes some corrective actions aimed at enhancing the frequency control capability in weak and isolated power systems: a procedure for evaluating the system stability margin intended for readjusting the diesel-generator control gains, a new wind power curtailment strategy, and an inertial control algorithm implemented in the wind turbines. These proposals are tested in the San Cristobal (Galapagos Islands-Ecuador) hybrid wind-diesel power system, in which many power outages caused by frequency relays tripping were reported during the windiest season. The proposals benefits have been tested in a simulation environment by considering actual operating conditions based on measurement data recorded at the island. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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6024 KiB

Open AccessArticle

Hosting Capacity of the Power Grid for Renewable Electricity Production and New Large Consumption Equipment

by Math H. J. Bollen and Sarah K. Rönnberg

Energies 2017, 10(9), 1325; https://doi.org/10.3390/en10091325 - 02 Sep 2017

Cited by 119 | Viewed by 9569

Abstract

After a brief historical introduction to the hosting-capacity approach, the hosting capacity is presented in this paper as a tool for distribution-system planning under uncertainty. This tool is illustrated by evaluating the readiness of two low-voltage networks for increasing amounts of customers with [...] Read more.

After a brief historical introduction to the hosting-capacity approach, the hosting capacity is presented in this paper as a tool for distribution-system planning under uncertainty. This tool is illustrated by evaluating the readiness of two low-voltage networks for increasing amounts of customers with PV panels or with EV chargers. Both undervoltage and overvoltage are considered in the studies presented here. Probability distribution functions are calculated for the worst-case overvoltage and undervoltage as a function of the number of customers with PV or EV chargers. These distributions are used to obtain 90th percentile values that act as a performance index. This index is compared with an overvoltage or undervoltage limit to get the hosting capacity. General aspects of the hosting-capacity calculations (performance indices, limits, and calculation methods) are discussed for a number of other phenomena: overcurrent; fast voltage magnitude variations; voltage unbalance; harmonics and supraharmonics. The need for gathering data and further development of models for existing demand is emphasised in the discussion and conclusions. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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3264 KiB

Open AccessArticle

A Piecewise Bound Constrained Optimization for Harmonic Responsibilities Assessment under Utility Harmonic Impedance Changes

by Tianlei Zang, Zhengyou He, Yan Wang, Ling Fu, Zhiyu Peng and Qingquan Qian

Energies 2017, 10(7), 936; https://doi.org/10.3390/en10070936 - 06 Jul 2017

Cited by 7 | Viewed by 3003

Abstract

Considering the effect of the utility harmonic impedance variations on harmonic responsibility, a method based on piecewise bound constrained optimization is proposed in this paper to evaluate the load harmonic responsibilities. The wavelet packet transform is employed to determine the change times of [...] Read more.

Considering the effect of the utility harmonic impedance variations on harmonic responsibility, a method based on piecewise bound constrained optimization is proposed in this paper to evaluate the load harmonic responsibilities. The wavelet packet transform is employed to determine the change times of the utility harmonic impedances. The harmonic monitoring data is divided into several segments where the utility harmonic impedances are considered as constants. Then, the problem of harmonic responsibility assessment under utility harmonic impedance changes are settled by the piecewise bound constrained optimization model. Furthermore, the interior point, the sequential quadratic programming and the active set algorithm are respectively adopted to calculate all the instantaneous harmonic responsibilities of harmonic loads. Finally, the weighted summation is used to calculate the total harmonic responsibility. To demonstrate the validity, simulation tests are carried out on an experimental circuit and the IEEE 13-bus distribution system. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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3707 KiB

Open AccessFeature PaperArticle

Double-Carrier Phase-Disposition Pulse Width Modulation Method for Modular Multilevel Converters

by Fayun Zhou, An Luo, Yan Li, Qianming Xu, Zhixing He and Josep M. Guerrero

Energies 2017, 10(4), 581; https://doi.org/10.3390/en10040581 - 23 Apr 2017

Cited by 8 | Viewed by 5299

Abstract

Modular multilevel converters (MMCs) have become one of the most attractive topologies for high-voltage and high-power applications. A double-carrier phase disposition pulse width modulation (DCPDPWM) method for MMCs is proposed in this paper. Only double triangular carriers with displacement angle are needed for [...] Read more.

Modular multilevel converters (MMCs) have become one of the most attractive topologies for high-voltage and high-power applications. A double-carrier phase disposition pulse width modulation (DCPDPWM) method for MMCs is proposed in this paper. Only double triangular carriers with displacement angle are needed for DCPDPWM, one carrier for the upper arm and the other for the lower arm. Then, the theoretical analysis of DCPDPWM for MMCs is presented by using a double Fourier integral analysis method, and the Fourier series expression of phase voltage, line-to-line voltage and circulating current are deduced. Moreover, the impact of carrier displacement angle between the upper and lower arm on harmonic characteristics is revealed, and further the optimum displacement angles are specified for the circulating current harmonics cancellation scheme and output voltage harmonics minimization scheme. Finally, the proposed method and theoretical analysis are verified by simulation and experimental results. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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2445 KiB

Open AccessArticle

Impedance Decoupling in DC Distributed Systems to Maintain Stability and Dynamic Performance

by Ahmed Aldhaheri and Amir Etemadi

Energies 2017, 10(4), 470; https://doi.org/10.3390/en10040470 - 02 Apr 2017

Cited by 17 | Viewed by 4781

Abstract

DC distributed systems are highly reliable and efficient means of delivering DC power or adopting renewable energy resources. However, DC distributed systems are prone to instability and dynamic performance degradation due to the negative incremental input impedance of DC-DC converts. In this paper, [...] Read more.

DC distributed systems are highly reliable and efficient means of delivering DC power or adopting renewable energy resources. However, DC distributed systems are prone to instability and dynamic performance degradation due to the negative incremental input impedance of DC-DC converts. In this paper, we propose a generic method to eliminate the impact of the negative input impedance on DC systems by shaping the source output impedance such that its bode-plot is restricted in the area that is contained below the product of the source’s duty ratio and its characteristic impedance. The performance deterioration originates whenever the output impedance of the source exceeds, in magnitude, the input impedance of the load converter due to deficiency in stability margins. Hence, confining the impedance in the proposed region helps decouple the interaction between the converters and preserve their own dynamic performances. The proposed method was proven by analytical analysis, time-based simulation, and practical experiments. All of their outcomes were in agreement, proving the effectiveness of the proposed method in preserving the dynamic performance of distributed systems. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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7292 KiB

Open AccessArticle

Consideration of Reactor Installation to Mitigate Voltage Rise Caused by the Connection of a Renewable Energy Generator

by Yeonho Ok, Jaewon Lee and Jaeho Choi

Energies 2017, 10(3), 344; https://doi.org/10.3390/en10030344 - 10 Mar 2017

Cited by 1 | Viewed by 3466

Abstract

This paper describes the detailed analysis of a reactor application for a power plant to mitigate the voltage rise of a distribution line (DL) caused by the connection of distributed resources (DRs). The maximum capacity of renewable energy generators (REGs) that meets the [...] Read more.

This paper describes the detailed analysis of a reactor application for a power plant to mitigate the voltage rise of a distribution line (DL) caused by the connection of distributed resources (DRs). The maximum capacity of renewable energy generators (REGs) that meets the acceptable voltage rise of a DL and the necessary capacity of the reactor to mitigate that voltage rise according to the different types of REGs are analyzed. The re-coordination of a protection relay and the loss of generation revenue as well as the installation location of a reactor are described. Finally, the ON/OFF conditions of the reactor, such as the magnitudes of the grid voltage and generator voltage, and the duration time of the voltage rise are analyzed. As the voltage rise is mitigated and self-limited in small power plants, it is confirmed that the capacity of the DRs connected to the DL can be increased through a field demonstration. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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11323 KiB

Open AccessArticle

Power Quality Disturbance Classification Using the S-Transform and Probabilistic Neural Network

by Huihui Wang, Ping Wang and Tao Liu

Energies 2017, 10(1), 107; https://doi.org/10.3390/en10010107 - 17 Jan 2017

Cited by 62 | Viewed by 5521

Abstract

This paper presents a transient power quality (PQ) disturbance classification approach based on a generalized S-transform and probabilistic neural network (PNN). Specifically, the width factor used in the generalized S-transform is feature oriented. Depending on the specific feature to be extracted from the [...] Read more.

This paper presents a transient power quality (PQ) disturbance classification approach based on a generalized S-transform and probabilistic neural network (PNN). Specifically, the width factor used in the generalized S-transform is feature oriented. Depending on the specific feature to be extracted from the S-transform amplitude matrix, a favorable value is determined for the width factor, with which the S-transform is performed and the corresponding feature is extracted. Four features obtained this way are used as the inputs of a PNN trained for performing the classification of 8 disturbance signals and one normal sinusoidal signal. The key work of this research includes studying the influence of the width factor on the S-transform results, investigating the impacts of the width factor on the distribution behavior of features selected for disturbance classification, determining the favorable value for the width factor by evaluating the classification accuracy of PNN. Simulation results tell that the proposed approach significantly enhances the separation of the disturbance signals, improves the accuracy and generalization ability of the PNN, and exhibits the robustness of the PNN against noises. The proposed algorithm also shows good performance in comparison with other reported studies. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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2580 KiB

Open AccessArticle

A Wavelet-Modified ESPRIT Hybrid Method for Assessment of Spectral Components from 0 to 150 kHz

by Luisa Alfieri, Antonio Bracale, Guido Carpinelli and Anders Larsson

Energies 2017, 10(1), 97; https://doi.org/10.3390/en10010097 - 14 Jan 2017

Cited by 18 | Viewed by 3726

Abstract

Waveform distortions are an important issue in distribution systems. In particular, the assessment of very wide spectra, that include also components in the 2–150 kHz range, has recently become an issue of great interest. This is due to the increasing presence of high-spectral [...] Read more.

Waveform distortions are an important issue in distribution systems. In particular, the assessment of very wide spectra, that include also components in the 2–150 kHz range, has recently become an issue of great interest. This is due to the increasing presence of high-spectral emission devices like end-user devices and distributed generation systems. This study proposed a new sliding-window wavelet-modified estimation of signal parameters by rotational invariance technique (ESPRIT) method, particularly suitable for the spectral analysis of waveforms that have very wide spectra. The method is very accurate and requires reduced computational effort. It can be applied successfully to detect spectral components in the range of 0–150 kHz introduced both by distributed power plants, such as wind and photovoltaic generation systems, and by end-user equipment connected to grids through static converters, such as fluorescent lamps. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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3401 KiB

Open AccessArticle

Stability Analysis and Stability Enhancement Based on Virtual Harmonic Resistance for Meshed DC Distributed Power Systems with Constant Power Loads

by Huiyong Hu, Xiaoming Wang, Yonggang Peng, Yanghong Xia, Miao Yu and Wei Wei

Energies 2017, 10(1), 69; https://doi.org/10.3390/en10010069 - 09 Jan 2017

Cited by 9 | Viewed by 3878

Abstract

This paper addresses the stability issue of the meshed DC distributed power systems (DPS) with constant power loads (CPLs) and proposes a stability enhancement method based on virtual harmonic resistance. In previous researches, the network dynamics of the meshed DC DPS are often [...] Read more.

This paper addresses the stability issue of the meshed DC distributed power systems (DPS) with constant power loads (CPLs) and proposes a stability enhancement method based on virtual harmonic resistance. In previous researches, the network dynamics of the meshed DC DPS are often ignored, which affects the derivation of the equivalent system impendence. In addition, few of them have considered the meshed DC DPS including multiple sources with voltage-controlled converters and CPLs. To tackle the aforementioned challenge, this paper mainly makes the following efforts. The component connection method (CCM) is employed and expanded to derive the stability criterion of the meshed DC DPS with CPLs. This stability criterion can be simplified to relate only with the network node admittance matrix, the output impendences of the sources, and the input admittances of the CPLs. A virtual harmonic resistance through the second-order generalized integrator (SOGI) is added in the source with the voltage-controlled converter to lower the peak of the source output impendence, which can enhance the stability of the meshed DC DPS. The effectiveness of the proposed stability criterion and stability enhancement method are verified by nonlinear dynamic simulations. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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