16,726 research outputs found
Ancillary Services in Hybrid AC/DC Low Voltage Distribution Networks
In the last decade, distribution systems are experiencing a drastic transformation
with the advent of new technologies. In fact, distribution networks are no longer passive
systems, considering the current integration rates of new agents such as distributed generation,
electrical vehicles and energy storage, which are greatly influencing the way these systems are
operated. In addition, the intrinsic DC nature of these components, interfaced to the AC system
through power electronics converters, is unlocking the possibility for new distribution topologies
based on AC/DC networks. This paper analyzes the evolution of AC distribution systems,
the advantages of AC/DC hybrid arrangements and the active role that the new distributed agents
may play in the upcoming decarbonized paradigm by providing different ancillary services.Ministerio de Economía y Competitividad ENE2017-84813-RUnión Europea (Programa Horizonte 2020) 76409
Local Control of Reactive Power by Distributed Photovoltaic Generators
High penetration levels of distributed photovoltaic (PV) generation on an
electrical distribution circuit may severely degrade power quality due to
voltage sags and swells caused by rapidly varying PV generation during cloud
transients coupled with the slow response of existing utility compensation and
regulation equipment. Although not permitted under current standards for
interconnection of distributed generation, fast-reacting, VAR-capable PV
inverters may provide the necessary reactive power injection or consumption to
maintain voltage regulation under difficult transient conditions. As side
benefit, the control of reactive power injection at each PV inverter provides
an opportunity and a new tool for distribution utilities to optimize the
performance of distribution circuits, e.g. by minimizing thermal losses. We
suggest a local control scheme that dispatches reactive power from each PV
inverter based on local instantaneous measurements of the real and reactive
components of the consumed power and the real power generated by the PVs. Using
one adjustable parameter per circuit, we balance the requirements on power
quality and desire to minimize thermal losses. Numerical analysis of two
exemplary systems, with comparable total PV generation albeit a different
spatial distribution, show how to adjust the optimization parameter depending
on the goal. Overall, this local scheme shows excellent performance; it's
capable of guaranteeing acceptable power quality and achieving significant
saving in thermal losses in various situations even when the renewable
generation in excess of the circuit own load, i.e. feeding power back to the
higher-level system.Comment: 6 pages, 5 figures, submitted to IEEE SmartGridComm 201
Options for Control of Reactive Power by Distributed Photovoltaic Generators
High penetration levels of distributed photovoltaic(PV) generation on an
electrical distribution circuit present several challenges and opportunities
for distribution utilities. Rapidly varying irradiance conditions may cause
voltage sags and swells that cannot be compensated by slowly responding utility
equipment resulting in a degradation of power quality. Although not permitted
under current standards for interconnection of distributed generation,
fast-reacting, VAR-capable PV inverters may provide the necessary reactive
power injection or consumption to maintain voltage regulation under difficult
transient conditions. As side benefit, the control of reactive power injection
at each PV inverter provides an opportunity and a new tool for distribution
utilities to optimize the performance of distribution circuits, e.g. by
minimizing thermal losses. We discuss and compare via simulation various design
options for control systems to manage the reactive power generated by these
inverters. An important design decision that weighs on the speed and quality of
communication required is whether the control should be centralized or
distributed (i.e. local). In general, we find that local control schemes are
capable for maintaining voltage within acceptable bounds. We consider the
benefits of choosing different local variables on which to control and how the
control system can be continuously tuned between robust voltage control,
suitable for daytime operation when circuit conditions can change rapidly, and
loss minimization better suited for nighttime operation.Comment: 8 pages, 8 figure
Synchronous frequency support of photovoltaic power plants with inertia emulation
©2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Grid stability is one of the main concerns in renewable energies. The lack of inertia and their low capability to provide frequency support has created the need for implementing new control strategies to solve this problem. In current networks, frequency and voltage support are performed through synchronous generators, which provide an inherent grid support due to the inertia presented in their mechanical rotors. Based on the same concept, renewable energies based on power converters have introduced synchronous controllers to emulate the dynamic behavior of synchronous generators and provide voltage and frequency support. However, most synchronous control strategies integrate their controllers as an add-on firmware embedded in each power converter, without presenting a coordinated synchronous performance when several converters operate in a PV power plant. The aggregation of several power converters operating with a coordinated synchronous response would be advantageous in these cases, since they can provide a harmonic response with an automatic power distribution when grid support is required. This paper presents a synchronous control strategy for photovoltaic power plants, which manages several power converters as an aggregated synchronous system.Peer ReviewedPostprint (author's final draft
Chance-Constrained ADMM Approach for Decentralized Control of Distributed Energy Resources
Distribution systems are undergoing a dramatic transition from a passive
circuit that routinely disseminates electric power among downstream nodes to
the system with distributed energy resources. The distributed energy resources
come in a variety of technologies and typically include photovoltaic (PV)
arrays, thermostatically controlled loads, energy storage units. Often these
resources are interfaced with the system via inverters that can adjust active
and reactive power injections, thus supporting the operational performance of
the system. This paper designs a control policy for such inverters using the
local power flow measurements. The control actuates active and reactive power
injections of the inverter-based distributed energy resources. This strategy is
then incorporated into a chance-constrained, decentralized optimal power flow
formulation to maintain voltage levels and power flows within their limits and
to mitigate the volatility of (PV) resources
Power Quality Improvement and Low Voltage Ride through Capability in Hybrid Wind-PV Farms Grid-Connected Using Dynamic Voltage Restorer
© 2018 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission.This paper proposes the application of a dynamic voltage restorer (DVR) to enhance the power quality and improve the low voltage ride through (LVRT) capability of a three-phase medium-voltage network connected to a hybrid distribution generation system. In this system, the photovoltaic (PV) plant and the wind turbine generator (WTG) are connected to the same point of common coupling (PCC) with a sensitive load. The WTG consists of a DFIG generator connected to the network via a step-up transformer. The PV system is connected to the PCC via a two-stage energy conversion (dc-dc converter and dc-ac inverter). This topology allows, first, the extraction of maximum power based on the incremental inductance technique. Second, it allows the connection of the PV system to the public grid through a step-up transformer. In addition, the DVR based on fuzzy logic controller is connected to the same PCC. Different fault condition scenarios are tested for improving the efficiency and the quality of the power supply and compliance with the requirements of the LVRT grid code. The results of the LVRT capability, voltage stability, active power, reactive power, injected current, and dc link voltage, speed of turbine, and power factor at the PCC are presented with and without the contribution of the DVR system.Peer reviewe
- …