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20 pages, 3485 KiB

Open AccessArticle

Control Strategy for MGT Generation System Optimized by Improved WOA to Enhance Demand Response Capability

by Jiecheng Zhu, Xitian Wang, Da Xie and Chenghong Gu

Energies 2019, 12(16), 3101; https://doi.org/10.3390/en12163101 - 13 Aug 2019

Cited by 5 | Viewed by 2606

Abstract

The grid-connected micro gas turbine (MGT) generation system is playing an important role in power systems because of its demand response capability and application in combined heat and power (CHP) systems. When applied to promote demand response, the generation system is expected to [...] Read more.

The grid-connected micro gas turbine (MGT) generation system is playing an important role in power systems because of its demand response capability and application in combined heat and power (CHP) systems. When applied to promote demand response, the generation system is expected to respond to follow instructions quickly, but a rapid response harms the safety and is not conducive to the benefits of customers, which leads to a contradiction. In this paper, a closed-loop power control is introduced for the MGT to improve demand response capability. The rate of fuel valve opening is limited so as to protect the equipment from thermal fatigue threats. An optimization method is developed for identifying the control parameters, balancing the response time and unrealized energy in the regulation process. An improved whale optimization algorithm (IWOA) is proposed to implement the optimization. Results of the algorithm performance verify that WOA is competitive with other heuristic algorithms, and IWOA is more suitable for parameter optimization problems than WOA because of better efficiency and exploitation capability. Results of power response further indicate that the proposed control strategy can achieve expected aims and is suitable for the MGT generation system. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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17 pages, 2813 KiB

Open AccessArticle

Research on Evaluation of Power Supply Capability of Active Distribution Network with Distributed Power Supply with High Permeability

by Jiafeng Ren, Haifeng Liang and Yajing Gao

Energies 2019, 12(11), 2223; https://doi.org/10.3390/en12112223 - 11 Jun 2019

Cited by 9 | Viewed by 3387

Abstract

With the large number of distributed generation (DG) access to the distribution network, the traditional distribution network with a single-supply radial structure has been transformed into an active distribution system (ADS) with source and bidirectional currents. This transformation makes the calculation of the [...] Read more.

With the large number of distributed generation (DG) access to the distribution network, the traditional distribution network with a single-supply radial structure has been transformed into an active distribution system (ADS) with source and bidirectional currents. This transformation makes the calculation of the power supply capacity (PSC) of the ADS face new challenges, and the uncertainty of the DG output increases the difficulty in calculating the PSC. At the same time, the power market transaction check needs to meet the safety constraints of the distribution network operation, and is required to know the PSC information of the ADS more quickly and accurately. Therefore, in order to quickly evaluate the PSC of the ADS, this paper proposes a fast evaluation method of the PSC based on the DG output rolling prediction and the information gap decision theory (IGDT). The method first establishes a rolling prediction model of the DG output, and calculates the PSC of the ADS at the corresponding time. Next, it establishes a risk avoidance model (RAM) and a risk speculation model (RSM) for the PSC of the ADS based on the IGDT. These models further calculate the probability of the range of the PSC at the corresponding time, so as to better evaluate the PSC of the ADS. Finally, the improved IEEE-14 node is used to verify that the model can consider the influence of the DG output uncertainty and quickly calculate the information of PSC. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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23 pages, 25087 KiB

Open AccessArticle

Time-Aware Monitoring of Overhead Transmission Line Sag and Temperature with LoRa Communication

by Michal Wydra, Pawel Kubaczynski, Katarzyna Mazur and Bogdan Ksiezopolski

Energies 2019, 12(3), 505; https://doi.org/10.3390/en12030505 - 5 Feb 2019

Cited by 30 | Viewed by 8057

Abstract

The techniques of Dynamic Line Rating (DLR) for Overhead Transmission Line (OTL)’s are currently dynamically developed. DLR systems typically rely on weather, temperature, inclination, and current measurements to calculate tension and sag, where sensors need to be installed directly on wires. Such systems [...] Read more.

The techniques of Dynamic Line Rating (DLR) for Overhead Transmission Line (OTL)’s are currently dynamically developed. DLR systems typically rely on weather, temperature, inclination, and current measurements to calculate tension and sag, where sensors need to be installed directly on wires. Such systems are very reliable and ensure high accuracy in determining maximum allowable current. However, their installation may require switching off the transmission line from the operation. In order to receive precise values regarding the actual operating conditions of the whole transmission line, DLR sensors measuring wire temperature or tension should be installed at many points of OTL. The minimum number of installation points should cover at least each tension section and critical spans, thereby increasing installation costs. The alternative method that allows for the monitoring of OTL is the use of the vision system based on cameras. Installed on the OTLs’ poles, cameras can take photos which, appropriately processed, can provide data about the sag and temperature of wires, without the necessity of switching OTL from the operation for installation or further maintenance. Such a vision system facilitates also data transmission, because it does not require measurement data to be transmitted from the sensor station installed on the wire to the base station located on the pole (for instance, via radio). This article aims to present the concept of a vision system that monitors sag and temperature of Overhead Transmission Lines (OTLs)’ using Long Range (LoRa) wireless communication and data transmission. The developed system consists of a camera and a microcomputer equipped with LoRa communication module. The whole system monitors OTLs’ spans by taking photos, processing images for wire sag-temperature estimation, and sending results to the operator’s Supervisory Control And Data Acquisition (SCADA). The system communication architecture is also proposed and investigated for data transmission time when monitoring the whole OTL. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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18 pages, 14461 KiB

Open AccessArticle

DC Voltage Adaptive Droop Control Strategy for a Hybrid Multi-Terminal HVDC System

by Yingpei Liu, La Zhang and Haiping Liang

Energies 2019, 12(3), 380; https://doi.org/10.3390/en12030380 - 25 Jan 2019

Cited by 5 | Viewed by 3729

Abstract

To solve the problems of DC voltage control and power allocation in the hybrid multi-terminal high voltage direct current system effectively, a DC voltage adaptive droop control strategy based on DC voltage-current characteristics is proposed. Based on adjustment of the droop coefficient of [...] Read more.

To solve the problems of DC voltage control and power allocation in the hybrid multi-terminal high voltage direct current system effectively, a DC voltage adaptive droop control strategy based on DC voltage-current characteristics is proposed. Based on adjustment of the droop coefficient of the converter station, the proposed control strategy introduces the influence factor of the droop coefficient, which considers the dynamic power margin of the converter station according to the direction of DC current variation in the converter station. When changes in the hybrid multi-terminal high voltage direct current system power flow occur, the droop coefficient of the converter station can be adjusted by the influence factor of the droop coefficient, so that the converter station can participate in power regulation according to its own power regulating ability. Consequently, the proposed control strategy can reasonably allocate the active power and minimize the deviation of the DC voltage. Besides, the stability analysis of the proposed control strategy is also carried out. Simulation results have verified the feasibility and effectiveness of the proposed control strategy. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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18 pages, 3501 KiB

Open AccessArticle

A New Method for Computing the Delay Margin for the Stability of Load Frequency Control Systems

by Ashraf Khalil and Ang Swee Peng

Energies 2018, 11(12), 3460; https://doi.org/10.3390/en11123460 - 11 Dec 2018

Cited by 19 | Viewed by 3671

Abstract

Open communication is an exigent need for future power systems, where time delay is unavoidable. In order to secure the stability of the grid, the frequency must remain within its limited range which is achieved through the load frequency control. Load frequency control [...] Read more.

Open communication is an exigent need for future power systems, where time delay is unavoidable. In order to secure the stability of the grid, the frequency must remain within its limited range which is achieved through the load frequency control. Load frequency control signals are transmitted through communication networks which induce time delays that could destabilize power systems. So, in order to guarantee stability, the delay margin should be computed. In this paper, we present a new method for calculating the delay margin in load frequency control systems. The transcendental time delay characteristics equation is transformed into a frequency dependent equation. The spectral radius was used to find the frequencies at which the root crosses the imaginary axis. The crossing frequencies were determined through the sweeping test and the binary iteration algorithm. A one-area load frequency control system was chosen as a case study. The effectiveness of the proposed method was proven through comparison with the most recent published methods. The method shows its merit with less conservativeness and less computations. The impact of the proportional integral (PI) controller gains on the delay margin was investigated. It was found that increasing the PI controller gains reduces the delay margin. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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33 pages, 3829 KiB

Open AccessArticle

FLISR Approach for Smart Distribution Networks Using E-Terra Software—A Case Study

by Duy Phuc Le, Duong Minh Bui, Cao Cuong Ngo and Anh My Thi Le

Energies 2018, 11(12), 3333; https://doi.org/10.3390/en11123333 - 29 Nov 2018

Cited by 29 | Viewed by 6938

Abstract

A smart grid concept has been defined in recent years, which emphasizes the importance on smart protection and measurement devices, reliable data communication and high security, optimal energy management system, and fault detection, location, isolation and service restoration (FLISR) of distribution networks (DNs). [...] Read more.

A smart grid concept has been defined in recent years, which emphasizes the importance on smart protection and measurement devices, reliable data communication and high security, optimal energy management system, and fault detection, location, isolation and service restoration (FLISR) of distribution networks (DNs). The main objectives of the FLISR approach are to achieve fast fault processing time, reduce the minimum number of interrupted customers, and improve the power supply reliability of the distribution. The conventional FLISR approach is to use signals of fault indicators (FIs) with distribution network states. The discrete installation of FIs to switches or reclosers may slow the processing time of fault detection and location, so it is necessary to develop a more efficient FLISR approach for smart distribution networks using functions of feeder terminal units (FTUs). In this paper, pick-up and tripping signals of overcurrent (OC) relays in combination with distribution grid states (e.g., switching status of devices, loss of voltage…) sent from feeder terminal units (FTUs) are used to detect and locate different fault types. Fault isolation and service restoration of black-out areas are then performed by solving an objective function with two main constraints, including (i) restoring the possible maximum number of out-of-service loads; and (ii) limiting the minimum number of switching operation. Thirteen performance factors (PF) are used for the post-fault service restoration process, consisting of: (i) Power Flow Violations (PFV), (ii) Bus Voltage Violations (BVV), (iii) Total Operation Cost (TOC), (iv) Lost Power (LP), (v) Outage Customer (OC), (vi) Number of Switching Steps (NSS), (vii) Power Losses (LOSS); (viii) Customer Minutes Interruption (CMI), (ix) Load Minutes Interruption (LMI), (x) MAIFI, (xi) SAIFI, (xii) SAIDI, and (xiii) Protection Validation (PRV). E-Terra platform of a distribution management system (DMS) is used to implement the proposed FLISR approach. Simulation and experiment results from a real 22 kV distribution network are also analysed to validate this FLISR approach. As a result, the novel FLISR approach has the ability to identify effectively the over-reaching of OC relays, indicate a mis-coordination risk of adjacent protection devices on the same feeder, and get the total processing time of fault detection, location and isolation as well as ranking all possible service restoration plans in distribution network at less than two minutes. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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17 pages, 5942 KiB

Open AccessArticle

Research on Automatic Generation Control with Wind Power Participation Based on Predictive Optimal 2-Degree-of-Freedom PID Strategy for Multi-area Interconnected Power System

by Xilin Zhao, Zhenyu Lin, Bo Fu, Li He and Na Fang

Energies 2018, 11(12), 3325; https://doi.org/10.3390/en11123325 - 28 Nov 2018

Cited by 75 | Viewed by 4186

Abstract

High penetration of wind power in the modern power system renders traditional automatic generation control (AGC) methods more challenging, due to the uncertainty of the external environment, less reserve power, and small inertia constant of the power system. An improved AGC method named [...] Read more.

High penetration of wind power in the modern power system renders traditional automatic generation control (AGC) methods more challenging, due to the uncertainty of the external environment, less reserve power, and small inertia constant of the power system. An improved AGC method named predictive optimal 2-degree-of-freedom proportion integral differential (PO-2-DOF-PID) is proposed in this paper, which wind farm will participate in the load frequency control process. Firstly, the mathematical model of the AGC system of multi-area power grid with penetration of wind power is built. Then, predictive optimal 2-degree-of-freedom PID controller is presented to improve the system robustness considering system uncertainties. The objective function is designed based on the wind speed and whether wind farm takes part in AGC or not. The controller solves the optimization problem through the predictive theory while taking into account given constraints. In order to obtain the predictive sequence of output of the whole system, the characteristic of the 2-DOF-PID controller is integrated in the system model. A three interconnected power system is introduced as an example to test the feasibility and effectiveness of the proposed method. When considering the penetration of wind power, two cases of high wind speed and low wind speed are analyzed. The simulation results indicate that the proposed method can effectively deal with the negative influence caused by wind power when wind power participates in AGC. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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22 pages, 1155 KiB

Open AccessArticle

Peer-to-Peer Energy Trading among Microgrids with Multidimensional Willingness

by Ning Wang, Weisheng Xu, Zhiyu Xu and Weihui Shao

Energies 2018, 11(12), 3312; https://doi.org/10.3390/en11123312 - 27 Nov 2018

Cited by 87 | Viewed by 7417

Abstract

Networked microgrids are emerging for coordinating distributed energy resources in distribution networks in the future Energy Internet, for which developing an efficient energy market model is crucial for facilitating multi-directional trading among microgrids. In this paper, a peer-to-peer energy trading mechanism is presented [...] Read more.

Networked microgrids are emerging for coordinating distributed energy resources in distribution networks in the future Energy Internet, for which developing an efficient energy market model is crucial for facilitating multi-directional trading among microgrids. In this paper, a peer-to-peer energy trading mechanism is presented using non-cooperative bidding among microgrids. Multidimensional willingness, including time pressure and counter behavior for mimicking the personalized behaviors of microgrids, was taken into account in the design of the bidding strategy. Under a parallel trading framework based on a blockchain, the proposed multidimensional willingness bidding strategy turns out to be able to make rational decisions with sufficient flexibility in the bidding process. The simulation results of a realistic case of microgrids from Guizhou Province, China, validate that the proposed peer-to-peer energy trading mechanism is capable of raising the microgrids’ profits and renewable energy source utilization. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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20 pages, 1642 KiB

Open AccessArticle

Hierarchical Look-Ahead Conservation Voltage Reduction Framework Considering Distributed Energy Resources and Demand Reduction

by Davye Mak and Dae-Hyun Choi

Energies 2018, 11(12), 3250; https://doi.org/10.3390/en11123250 - 22 Nov 2018

Cited by 8 | Viewed by 3302

Abstract

This paper proposes a hierarchical look-ahead framework to conduct conservation voltage reduction (CVR) when distributed energy resources such as solar photovoltaic (PV) systems and energy storage systems (ESSs), and demand response programs are integrated into distribution systems. With the increasing deployment of PV [...] Read more.

This paper proposes a hierarchical look-ahead framework to conduct conservation voltage reduction (CVR) when distributed energy resources such as solar photovoltaic (PV) systems and energy storage systems (ESSs), and demand response programs are integrated into distribution systems. With the increasing deployment of PV systems in distribution systems, their frequently varying power output due to cloud movements could have a detrimental impact on the consumer’s voltage quality, consequently leading to degraded CVR performance. A two-level CVR framework for the coordination of an on-load tap changer (OLTC), capacitor banks (CBs), and the smart inverters of PV systems/ESSs is presented, in which these elements operate to reduce the voltage profile along the distribution feeder at different temporal scales. At the global level, the operations of the OLTC and the CBs are scheduled every hour to achieve the best CVR performance in an optimization problem using mixed-integer linear programming. When voltage violations occur rapidly, the smart inverters of PV systems and ESSs help to maintain a lower voltage profile every second based on the proposed piecewise droop control functions at the local level. A simulation study is carried out in an IEEE 33-bus distribution system with an OLTC, CBs, PV systems, and ESSs, and our results demonstrate the advantages of the proposed approach in terms of voltage level and energy savings. Furthermore, the impact of demand reduction on the proposed approach is quantified, and we verify that a higher demand reduction yields more energy savings in the proposed framework. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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20 pages, 7692 KiB

Open AccessArticle

Design of Low-Ripple and Fast-Response DC Filters in DC Distribution Networks

by Jianquan Liao, Niancheng Zhou and Qianggang Wang

Energies 2018, 11(11), 3128; https://doi.org/10.3390/en11113128 - 12 Nov 2018

Cited by 8 | Viewed by 5696

Abstract

The design and parameter selection of low-ripple and fast-response direct current (DC) filters are discussed in this study with the aim of alleviating the influence of a DC-side low-frequency voltage pulsation on a sensitive load in a DC distribution network. A method for [...] Read more.

The design and parameter selection of low-ripple and fast-response direct current (DC) filters are discussed in this study with the aim of alleviating the influence of a DC-side low-frequency voltage pulsation on a sensitive load in a DC distribution network. A method for determining the DC filter parameters by using a mofatching most flat response algorithm is presented. The voltage transfer function of the DC-side filter in the DC distribution network is deduced to analyze its voltage transfer characteristics. The resonance peak value of the filter network is an important factor affecting the transfer speed of a filter. A pole-circle-based parameter optimization method is proposed to move the poles of the filter transfer function down and to the left of pole plane for finding the appropriate capacitance, inductance, and damping parameters. This approach effectively restricts the resonance peak value, accelerates the transfer speed, and maintains steady filtering results. Simulation and test results verify that the filter has low resonance value, rapid convergence ability, and an excellent filtering effect. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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28 pages, 2673 KiB

Open AccessArticle

A CVaR-Robust Risk Aversion Scheduling Model for Virtual Power Plants Connected with Wind-Photovoltaic-Hydropower-Energy Storage Systems, Conventional Gas Turbines and Incentive-Based Demand Responses

by Liwei Ju, Peng Li, Qinliang Tan, Zhongfu Tan and GejiriFu De

Energies 2018, 11(11), 2903; https://doi.org/10.3390/en11112903 - 25 Oct 2018

Cited by 14 | Viewed by 3415

Abstract

To make full use of distributed energy resources to meet load demand, this study aggregated wind power plants (WPPs), photovoltaic power generation (PV), small hydropower stations (SHSs), energy storage systems (ESSs), conventional gas turbines (CGTs) and incentive-based demand responses (IBDRs) into a virtual [...] Read more.

To make full use of distributed energy resources to meet load demand, this study aggregated wind power plants (WPPs), photovoltaic power generation (PV), small hydropower stations (SHSs), energy storage systems (ESSs), conventional gas turbines (CGTs) and incentive-based demand responses (IBDRs) into a virtual power plant (VPP) with price-based demand response (PBDR). Firstly, a basic scheduling model for the VPP was proposed in this study with the objective of the maximum operation revenue. Secondly, a risk aversion model for the VPP was constructed based on the conditional value at risk (CVaR) method and robust optimization theory considering the operating risk from WPP and PV. Thirdly, a solution methodology was constructed and three cases were considered for comparative analyses. Finally, an independent micro-grid on an industrial park in East China was utilized for an example analysis. The results show the following: (1) the proposed risk aversion scheduling model could cope with the uncertainty risk via a reasonable confidence degree β and robust coefficient Γ. When Γ ≤ 0.85 or Γ ≥ 0.95, a small uncertainty brought great risk, indicating that the risk attitude of the decision maker will affect the scheduling scheme of the VPP, and the decision maker belongs to the risk extreme aversion type. When Γ

\in

(0.85, 0.95), the decision-making scheme was in a stable state, the growth of β lead to the increase of CVaR, but the magnitude was not large. When the prediction error e was higher, the value of CVaR increased more when Γ increased by the same magnitude, which indicates that a lower prediction accuracy will amplify the uncertainty risk. (2) when the capacity ratio of (WPP, PV): ESS was higher than 1.5:1 and the peak-to-valley price gap was higher than 3:1, the values of revenue, VaR, and CVaR changed slower, indicating that both ESS and PBDR can improve the operating revenue, but the capacity scale of ESS and the peak-valley price gap need to be set properly, considering both economic benefits and operating risks. Therefore, the proposed risk aversion model could maximize the utilization of clean energy to obtain higher economic benefits while rationally controlling risks and provide reliable decision support for developing optimal operation plans for the VPP. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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19 pages, 3474 KiB

Open AccessArticle

Synchronous Compensator Based on Doubly Fed Induction Generator to Improve the Power Quality under Unbalanced Grid Voltage Conditions

by Paulo H. P. Silva, Francisco Kleber de A. Lima, Jean M. L. Fonseca, Carlos Gustavo C. Branco and Celso R. Schmidlin Júnior

Energies 2018, 11(10), 2803; https://doi.org/10.3390/en11102803 - 18 Oct 2018

Cited by 1 | Viewed by 2832

Abstract

Currently, power quality is a major issue for all sorts of customers. End users of the electricity service in industrial, commercial and residential sectors have nonlinear loads or loads that are sensitive to disturbances in the electric power supply. In this context, this [...] Read more.

Currently, power quality is a major issue for all sorts of customers. End users of the electricity service in industrial, commercial and residential sectors have nonlinear loads or loads that are sensitive to disturbances in the electric power supply. In this context, this paper presents a study on four different control strategies for the application of synchronous compensator based on a doubly-fed induction generator (DFIG). The mathematical modeling developed to support the proposal of this article is validated through computational simulations and experimental results. This work contains strong arguments that support the idea that the proposed synchronous compensator can be employed to cancel oscillations caused by imbalances in the grid, and can furthermore inject or absorb reactive and active power without the characteristic oscillations that arise when negative sequence components are present in the system. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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22 pages, 3427 KiB

Open AccessArticle

Unbalanced Current Sharing Control in Islanded Low Voltage Microgrids

by Foad Najafi, Mohsen Hamzeh and Matthias Fripp

Energies 2018, 11(10), 2776; https://doi.org/10.3390/en11102776 - 16 Oct 2018

Cited by 26 | Viewed by 3930

Abstract

This paper reports a new control strategy to improve sharing of unbalanced currents in islanded LV microgrids. This technique provides fast and effective sharing of positive-, negative- and zero-sequence currents, and is the first example of zero-sequence current sharing in the literature. The [...] Read more.

This paper reports a new control strategy to improve sharing of unbalanced currents in islanded LV microgrids. This technique provides fast and effective sharing of positive-, negative- and zero-sequence currents, and is the first example of zero-sequence current sharing in the literature. The controllers are designed in the stationary frame. The control structure consists of four loops: (1) the current controller; (2) the voltage controller; (3) the droop controller and the (4) negative and zero sequence current controllers. The output current is considered unknown for the controller and is added to the control system as a disturbance. The proposed controller features a high gain in fundamental and harmonic frequencies, hence a good voltage quality is obtained in the presence of unbalanced and nonlinear loads. To this aim, a proportional-resonant (PR) controller is adopted as the current controller. By using a multi-resonant controller as current controller, a unified control structure is obtained which is suitable for both grid-connected and islanded modes. The voltage controller is designed using a resonant controller so that the voltage can have low VUF and THD in the presence of unbalanced and nonlinear loads. Furthermore, in this paper, the droop method is applied to the control structure to share real and reactive powers. Simulation studies show that the conventional droop method cannot share the oscillatory part of the output power that is due to the presence of unbalanced loads in the microgrid. This paper relies on using zero and negative sequence virtual impedance controller to share the oscillatory part of output power. By using zero-sequence virtual impedance controller (ZSVIC) and negative-sequence virtual impedance controller (NSVIC), the zero and negative sequence currents in the microgrid are controlled and shared effectively. By compensating zero- and negative-sequence currents locally, the flow of these currents in the microgrid is minimized, and the overall power quality of the islanded LV microgrid is improved. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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16 pages, 857 KiB

Open AccessFeature PaperArticle

Voltage Harmonic Suppression by Means of Grid-Connected Converters Using only Local Measurements

by Ya Zhang, Maurice G. L. Roes, Marcel A. M. Hendrix and Jorge L. Duarte

Energies 2018, 11(10), 2515; https://doi.org/10.3390/en11102515 - 21 Sep 2018

Cited by 1 | Viewed by 2816

Abstract

A single-phase grid-connected converter is considered in this paper in the presence of harmonic problems introduced non-linear loads. In order to compensate the harmonics caused by the loads, a local voltage support scheme is proposed. This is an added feature because its implementation [...] Read more.

A single-phase grid-connected converter is considered in this paper in the presence of harmonic problems introduced non-linear loads. In order to compensate the harmonics caused by the loads, a local voltage support scheme is proposed. This is an added feature because its implementation is in parallel with a conventional current control method. Distinctively, the measurements of the grid or load current are not needed since the scheme is based on only local measurements. On top of a fundamental part for desired power injection, the converter output current comprises a harmonic part for compensation. Thus, the grid current harmonic distortion is minimized and the enhancement of the local voltage quality is achieved. A comprehensive model analysis indicates that the proposed strategy can help to attenuate harmonics of the local voltage without compromising on the quality of the fundamental current injection. Experimental results validate the effectiveness of the proposed control scheme. Moreover, the impact of grid frequency estimation error on the control strategy’s performance is quantified theoretically and experimentally. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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17 pages, 2200 KiB

Open AccessArticle

Microgrid Spinning Reserve Optimization with Improved Information Gap Decision Theory

by Hong Zhang, Hao Sun, Qian Zhang and Guanxun Kong

Energies 2018, 11(9), 2347; https://doi.org/10.3390/en11092347 - 6 Sep 2018

Cited by 10 | Viewed by 4006

Abstract

Distributed generation (DG) is an important method of energy generation that accelerates the decentralization process of centralized systems, and has been widely deployed in modern society due to its economical, sustainable, and environmentally friendly characteristics. However, with the tremendous development of DG, system [...] Read more.

Distributed generation (DG) is an important method of energy generation that accelerates the decentralization process of centralized systems, and has been widely deployed in modern society due to its economical, sustainable, and environmentally friendly characteristics. However, with the tremendous development of DG, system reliability operations are facing increasingly severe challenges because of the fluctuations of the renewable generation. In this paper, a novel spinning reserve optimization method is proposed to maximize the maximum allowance of system uncertainty (MAoSU) under the premise of satisfying the preset system operational cost. Then, the success rate of DG off-grid operation is calculated by comparing the magnitude of optimal spinning reserve capacity with the power exchange between the main grid and the distributed grid. The simulation results show that decision-makers need to increase the operational cost to compensate for system uncertainty, and the percentage increase of the operational cost is in proportional to the MAoSU and system renewable energy penetration rate. Additionally, with the increase of the MAoSU, the system needs to prepare more spinning reserve capacity to maintain system reliability operations. Finally, with the decrease of the MAoSU, the success rate of system off-grid operation decreases sharply, especially when the MAoSU is less than 0.5. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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14 pages, 6936 KiB

Open AccessCase Report

Arc Voltage and Current Characteristics in Low-Voltage Direct Current

by Wooho Kim, Yong-Jung Kim and Hyosung Kim

Energies 2018, 11(10), 2511; https://doi.org/10.3390/en11102511 - 20 Sep 2018

Cited by 25 | Viewed by 11029

Abstract

Recently, Low-Voltage DC (direct current) distribution systems have received high lights according to the expansion of DC generations and DC loads such as photovoltaics (PV) generations, electric vehicles (EVs), light emitting diodes (LEDs), computers, DC homes, etc. Low-Voltage DC distribution systems have optimistic [...] Read more.

Recently, Low-Voltage DC (direct current) distribution systems have received high lights according to the expansion of DC generations and DC loads such as photovoltaics (PV) generations, electric vehicles (EVs), light emitting diodes (LEDs), computers, DC homes, etc. Low-Voltage DC distribution systems have optimistic perspectives since DC has various good aspects compared to alternating current (AC). However, ensuring safety of human and electric facility in Low-Voltage DC is not easy because of arc generation and difficulty of arc-extinguishing. This paper constructs a low-voltage DC circuit and studies the arc interruption that occurs when separating electrodes from where load currents flow. Also, arc extinguishers are experimented upon and analysed in various levels of source voltage and load currents conditions. Voltage and current characteristics for arc interruption are identified based on experimental results, and we establish the electric generation for arc interruption. Further, the voltage–current characteristics and the correlation of arc during arc duration time arc are verified, and the voltage–current equation and DC arc resistance model for the breaking arc are developed. Full article

(This article belongs to the Special Issue Operation and Control of Power Distribution Systems)

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