394 research outputs found
Control of transient power during unintentional islanding of microgrids
No full textIn inverter-based microgrids, the paralleled inverters need to work in grid-connected mode and stand-alone mode and to transfer seamlessly between the two modes. In grid-connected mode, the inverters control the amount of power injected into the grid. In stand-alone mode, however, the inverters control the island voltage while the output power is dictated by the load. This can be achieved using the droop control. Inverters can have different power set-points during grid-connected mode but in stand-alone mode they all need their power set-points to be adjusted according to their power ratings. However, during sudden unintentional islanding (due to loss of mains), transient power can flow from inverters with high power setpoints to inverters with low power set-points, which can raise the DC link voltage of the inverters causing them to shut down. This paper investigates the transient circulating power between paralleled inverters during unintentional islanding and proposes a controller to limit it. The controller monitors the DC link voltage and adjusts the power set-point in proportion to the rise in the voltage. A small signal model of an islanded microgrid is developed and used to design the controller. Simulation and experimental results are presented to validate the design
Hybrid Generators-based AC Microgrid Performance Assessment in Island Mode
No full textAchieving an accurate steady-state averaged active power sharing between parallel inverters in islanded AC microgrids could be realized by a traditional droop control. For identical inverters having the same droop gains, it is assumed that the transient average power responses will be similar, and no circulating current will flow between the units. However, different line impedances could influence the instantaneous power significantly and thus circulating power flows among the inverters particularly during sudden disturbances such as load changes. This power, if absorbed by an inverter, will lead the DC link voltage to rise abruptly and trip the inverter, thus, degrading the performance of the whole microgrid. The problem becomes worse when hybrid generators are serving as unidirectional power source. This paper assesses the performance of hybrid generators within an islanded microgrid against the mismatch in line impedances. Two schemes to stabilize the microgrid are proposed. In addition, a participation factor analysis is developed to select the most effective controller scheme to bound the DC link voltage and minimize the circulating power. Simulation and experimental results are presented to verify the analysis and the capability of the proposed controller
A review of recent control techniques of drooped inverter‐based AC microgrids
No full textAs the penetration of distributed generation (DG) systems in the grid is increasing, the challenge of combining large numbers of DGs in the power systems has to be carefully clarified and managed. The control strategy and management concept of the interconnected systems should be flexible and reliable to handle the various types of DGs. This can be suitably met by microgrids. This paper introduces the microgrid structure and elements and states the main objectives that should be achieved by the microgrid controllers and each DG controller in both operation modes (grid-connected and island mode). It also presents the challenges of having multiple DG units in a microgrid in terms of accurate power control/sharing, voltage and frequency regulation, power management between DGs, different renewable energy sources integration and deployment, seamless mode transfer, and the modeling issues. The centralized and decentralized control techniques as potential solutions have been discussed and compared by highlighting the advantages and disadvantages of each. Furthermore, the recent control techniques for drooped alternating current microgrids and the main proposed solutions and contributions in the literature have been exposed to finally overcome the droop control limitations and obtain a flexible and smart distributed power system
A small signal model of an inverter-based microgrid including DC link voltages
No full textIn this paper, a small signal model of an island microgrid containing multi parallel inverters is
established. The inverters are dealt as ideal voltage sources with an equivalent output impedance as the
effect of the inner loops dynamics of the voltage controller can be neglected. In addition, this model
includes the DC link voltage state of each inverter. The model can be used to study the dynamic of the
DC link voltages during unintentional islanding by proper defining of the initial conditions. The model
is validated using detailed simulation
Improved reactive power sharing for parallel-operated inverters in islanded microgrids
No full textUnequal impedances of interconnecting cables between paralleled inverters in island mode of microgrids cause inaccurate reactive power sharing when traditional droop control is used. Many in the literature adopt low speed communications between the inverters and a central control unit to overcome this problem. However, the loss of this communication link can be very detrimental to the performance of the controller. This paper proposes an improved reactive power-sharing control method. It employs infrequent measurements of the voltage at the point of common coupling (PCC) to estimate the output impedance between the inverters and the PCC and readjust the voltage droop controller gains accordingly. The controller then reverts to being a traditional droop controller using the newly calculated gains. This increases the immunity of the controller against any loss in the communication links between the central control unit and the inverters. The capability of the proposed control method has been demonstrated in simulation and experiment using a laboratory scale microgrid
The Civilization Responsibility for the Judge Student Name: walid issa Obayat
No full textThe Purposed of the civilization Responsibility is the Responsibility about indemnity for
damage that caused because of the Lack of Obligation whether the source of the Obligation
was the contract , its called the Contractual Responsibility , and if the source of the
Obligation was Negligence in a work , it’s called Negligence Responsibility , where the
subject of this study about the Civilization Responsibility For the Judge , that judge will be
Responsible about indemnity for damage that caused by his false in his own work and here
will be controlled by special rules it’s called the Rules of adversary .
The subject of this study is about the Civilization Responsibility for the Judge Which it is
related to his profession through the Civilization and commercial Procedures law Num (2)
for the year (2001) Whence the nature of this responsibility which it’s Contractual or
Negligence or a Legal Responsibility , in this study we Explained about the rules of
adversary and the legal Philosophy and the Legality To Exempt the judge From the
Responsibility during to the infraction Mandatory Law Num (36) for the year (1944) during
the Primary law that text about the Responsibility for the country of indemnity for the
mistakes of the judicial authority that texted in the Civilization and Commercial Procedures
Law in Palestine Under The Title THE RULES OF ADVERSARY , and we explained about
the Reasons and cases of the judges strife that texted in the Law .
This study Focusing on the Judges strife case and his Civilization Responsibility about big
mistakes that done by judge during to his Profession , and this study does not Focusing about
Administrator mistakes that causes Which can not be a Reason For Responsibility , and this
study does not Focusing about the Criminal Responsibility For Judge if he does a Crime .
And this study doesn’t Focusing on Judges Responsibilities of Contractual Correlation and
Mistakes in their Own life out of their Professions . and this rules of adversary Which is the
Subject of our study is Specialized in the Civilization Responsibility about Mistakes that
Causes by the Judge during his Judicial Profession and anything Related to that .
And these Rules includes all Judges that Known in the Judicial Authority Law , and its
important for the adversarial Case to be accepted the Existence OF Damage and a Reason
For the Adversarial .
And we studied Also in this search the Procedures and the rules of the adversary Case
through the Procedures Before the Lawsuit and the Parties of the LAwSuit and the Set up
Procedures for the Lawsuit and the Competent court in this Lawsuit , and also we studied
through this subject the Responsibility Range of the Supreme Judicial council about Judges
work By studying the Responsibility of the Country about the Judicial Authority Mistakes
and the Possibility of adversary about Deputations annulment , and the Possibility of
adversarial to the Administrator decisions that related in courts Forming and Judges
Advancement .
This study explained the Range to the Civilization Responsibility For Judge and to Achieve
this purpose we Settled the Comparision Analytical Method through collecting information
about the Civilization Responsibility and to fit the Texts on the Responsibility of the Judge ,
and to Analyze these Texts and compares Texts to Reach to the Main Purpose which it is The
civilization Responsibility for Judge .
The Summarization of this study that the Judge Responsibility in Palestine it is a Special
Responsibility cause it has a special texts about it that Differentiate it from others Lawsuits
and special Procedures and Purposes and Cases and effects, and it Also has a dual Nature
about indemnity and nullity, so this LawSuit has a special nature and a Dual Nature and it’s a
Personality Responsibility for the Judge in the face of the Adversary and to The country that
can Return on the judge.
In The End , this Study Recommends to Add the Cheating situation and justice denial and
Perfidy and Bribery and stealing and Spoliation and hiding and not to signature the
Adjudication or it’s draft and the embezzlement and Exploitation of the job to The adversary
Reasons , and this study also Recommends to Cancel the Text of the article Number (154)
From the Palestinian Civilization and commercial Procedures Law which it must be removed
a condition that must Notify the high Judicial court Before Submitting the Adversary
Lawsuit Because this can Restricts The Right of Litigation and this is a Legal right For Every
Body
Stability Analysis and Control of a Microgrid against Circulating Power between Parallel Inverters
No full textIn grid-connected mode, the grid normally absorbs all the power generated by each inverter in a microgrid. Droop control-based microgrid power management employs the frequency as a wireless communication to determine the power outage. However, in the cases of grid loss, each inverter should receive, from a supervisory controller, new settings of the output power suitable to the microgrid load. Because of the supervisory controllers are slower than the droop control loops, this might produce unstable dynamics caused by the excess generated power circulating between the inverters if the microgrid load is low. This case degrades the microgrid stability leading the DC link voltage of each inverter to rise to trip point. In this paper, a PD voltage control loop is proposed to stabilize the system and minimize the circulating power so providing more time for the supervisory control to respond without tripping any inverter. A detailed small signal model is developed and stability analysis is performed to tune the controller’s gain. Matlab/Simulink results validate the performance of the proposed controller
DC link voltage control during sudden load changes in AC microgrids
No full textParallel inverters in AC microgrids can achieve accurate power sharing using droop control. However, different grid line impedances will result in different transient power and thus different energy being delivered or absorbed by the inverters during sudden load changes. This might lead the DC link voltage to rise beyond the trip limit causing the inverter to shut down, which reduces the reliability of the whole microgrid. This paper investigates the effect of the mismatch in line impedances on the stability of the DC link voltage during a sudden load changes and proposes a scheme to control the DC link voltage during disturbances. Simulation and experimental results are presented to verify the efficacy of the proposed controller
Roundtable Discussion with Rose Issa and Mohammad El Rawas on the Exhibition Contemporary Lebanese Artists at London’s Kufa Gallery in Early 1988
No full textIn December 1986, Kufa Gallery opened in London’s Westbourne Grove. After exhibitions of Old Maps of the Arab and Islamic World (3–30 June 1987), three Europe-based Kurdish artists Walid Mustafa, Tahir Hamid and Karim Azad (15 July–8 August 1987), and an exhibition in memory of the Palestinian cartoonist Naji al Ali shortly after his assassination in London on 29 August 1987 (29 October–4 November 1987), Rose Issa dedicated an exhibition to Contemporary Lebanese Artists (15 January–24 February 1988). This exhibition took place during a period of war in Lebanon and in parallel with preparations for the landmark exhibition that was to take place at the Barbican Centre the following year, Lebanon—The Artist’s View (15 April–4 June 1989). Contemporary Lebanese Artists not only aimed to raise awareness about Lebanon’s artists and the country’s plight, but also to raise funds both for the artists and for the Lebanese Red Cross, which received part of the gallery’s commission. In this roundtable discussion, the main protagonists behind Contemporary Lebanese Artists, gallerist Rose Issa and artist Mohammad El Rawas, discuss the creation and reception of the exhibition
Development of smart glazing techniques for efficient buildings
No full textIn recent times, the buildings sector has emerged as a major consumer of energy in urban areas. Among various contributors, windows in the external envelope of buildings are particularly responsible for a significant portion of energy consumption due to their high thermal conductivity. The integration of smart films with traditional glazing has been explored as a means to modify the opt properties of windows. However, this integration can affect the visual connection between occupants and the outside views. This thesis focuses on advancing smart windows to enhance their thermal and daylight performance, with two main developments proposed.
The first development involves the use of double-glazed ventilated windows in cold climate regions. These windows utilise waste air from the building for ventilation. However, existing research indicates that under certain conditions, the waste air may be insufficient to maintain proper ventilation. To address this, the thesis proposes validated procedures that optimise the utilisation of waste air, enabling sustained ventilation for longer periods. This optimisation contributes to improved thermal efficiency of ventilated windows and energy savings in buildings. Experimental results obtained from a small-scale test room demonstrate that implementing the proposed optimisation process can achieve energy savings of up to 83% compared to conventional double-glazed windows.
The second development focuses on integrating a double-glazed window with a polymer dispersed liquid crystal (PDLC) film for hot climate regions. Previous research overlooked the impact of reduced optical transmission on the window's visual clarity. This thesis introduces an image-processing quantification algorithm for evaluating the visual experience through PDLC windows. The algorithm identifies the comfortable visible range and determines the lowest acceptable transparency level to maintain satisfactory visual communication with the outdoor environment. Experimental results from a small-scale test room indicate that implementing the proposed quantification process enables the provision of a customized range of visual quality based on user preferences. The system also ensures that the operating visibility does not fall below a pre-defined threshold level. The trial illustrates that altering the PVR ratio from 0 to 1 has the potential to alter the mean contrast value in a clear sky setting, shifting it from 0.18 to 0.37. Additionally, in order to ensure a minimum acceptable vision quality, the proposed algorithm ensures that the optical transmittance of the window remains above a specified threshold value
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