313 research outputs found
Effects of energy storage systems grid code requirements on interface protection performances in low voltage networks
The ever-growing penetration of local generation in distribution networks and the large diffusion of energy storage systems (ESSs) foreseen in the near future are bound to affect the effectiveness of interface protection systems (IPSs), with negative impact on the safety of medium voltage (MV) and low voltage (LV) systems. With the scope of preserving the main network stability, international and national grid connection codes have been updated recently. Consequently, distributed generators (DGs) and storage units are increasingly called to provide stabilizing functions according to local voltage and frequency. This can be achieved by suitably controlling the electronic power converters interfacing small-scale generators and storage units to the network. The paper focuses on the regulating functions required to storage units by grid codes currently in force in the European area. Indeed, even if such regulating actions would enable local units in participating to network stability under normal steady-state operating conditions,
it is shown through dynamic simulations that they may increase the risk of unintentional islanding occurrence. This means that dangerous operating conditions may arise in LV networks in case dispersed generators and storage systems are present, even if all the end-users are compliant with currently applied connection standards
Various approaches for power balancing in grid-connected and islanded microgrids
One of the promising solutions to reduce power imbalance, an undesired impact of intermittent renewable energy sources, is to supply the loads by means of local distributed energy resources in the form of a microgrid. Microgrids offer several benefits such as reduction of line losses, increased system reliability, and maximum utilisation of local energy resources. A microgrid, during its islanded operation, is more susceptible to the frequency and voltage fluctuation caused by a sudden dispatch either from the generation or load. Therefore, additional control is required to manage either the output power from the generation side or the demand from the end-user side. Thus, appropriate and efficient control and monitoring systems need to be installed. However, the cost of such a system will reduce the rate of investment return on microgrid projects. This research has focused on developing various techniques to maintain the voltage and frequency within acceptable limits in microgrids, taking into account various influencing factors.
This study proposes an additional active power management technique through the use of inverters, that can maintain the microgrid’s frequency when the generated power in the microgrid is much higher than its demand. Also, to facilitate the microgrid’s transition from grid-connected to islanded mode, the inverters can be controlled with a soft starting ramp. Moreover, a control function employing a droop control method is proposed in order to reduce the output power of the renewable sources when the microgrid frequency is much higher than the nominal frequency.
On the other hand, when the demand is higher than the generated power, managing the demand under a demand response program is proposed as a means of maintaining the microgrid stability. This is an inexpensive solution which will not reduce the rate of investment return on the microgrid project. However, this requires the installation of appropriate enabling technologies at the utility and end-user sides. Moreover, the participation from demand response participants is influenced by the profit earned from engaging in the program. Therefore, in this research, the technical and economic benefits of demand response deployment are analysed in detail.
The execution of the demand response program through load-shifting, reducing the appliances’ consumed power, and load-shedding causes customer discomfort. To minimise this discomfort, in this thesis, suitable strategies are suggested for various groups of loads. Furthermore, each load profile contains information on its capacity, flexibility, and operating time. The proposed approach ensures that the loads with a larger capacity and flexibility are the most preferred ones to be controlled during demand response events so that customer discomfort and the number of affected loads can be minimised. Also, this study examines the load’s economic value, power losses, emission factor, and cost of energy production to maximise the microgrid operator’s profit as a result of deploying the demand response program.
Meanwhile, to encourage end-users’ engagement in demand response programs, the microgrid operator should offer incentives to the customer as compensation for any incurred costs and discomfort felt. The given incentives should be such that both the microgrid operator and the end-user gain the maximum profit. Therefore, this study proposes an approach for calculating the level of incentives that should be given to the participants by comparing the differences between ongoing revenue and the cost of energy with and without demand response
Frequency-Based Decentralized Conservation Voltage Reduction Incorporated Into Voltage-Current Droop Control for an Inverter-Based Islanded Microgrid
Conservation voltage reduction (CVR) aims to decrease load demands by regulating bus voltages at a low level. This paper proposes a new strategy for decentralized CVR (DCVR), incorporated into the current-based droop control of inverter-interfaced distributed energy resources (IDERs), to improve the operational reliability of an islanded microgrid. An controller is developed as an outer feedback controller for each IDER, consisting of controllers for the DCVR and and controllers for power sharing. In particular, the controllers adjust the output voltages of the IDERs in proportion to the frequency variation determined by the controllers. This enables the output voltages to be reduced by the same amount, without communication between the IDERs. The controllers are responsible for reactive power sharing by adjusting the voltages while taking into account the controllers. Small-signal analysis is used to verify the performance of the proposed DCVR with variation in the and droop gains. Case studies are also carried out to demonstrate that the DCVR effectively mitigates an increase in the load demand, improving the operational reliability, under various load conditions determined by power factors and load compositions.11Ysciescopu
“Estrategia de control robusto descentralizado para una micro-red aislada con generación distribuida acoplada para mejorar la estabilidad de voltaje”
El constante avance de la tecnología
requiere una gran cantidad de energía, por
ello se ha propuesto la inclusión de fuentes
de energía renovable (RES) cerca de los
centros de carga. Estas RES son
implementadas también en sectores donde
el sistema eléctrico convencional no es
capaz de llegar, de esta manera se
garantiza el abastecimiento de energía
eléctrica a toda la población. Sin embargo,
la implementación de estos nuevos
sistemas implica retos de control para que
su funcionamiento sea correcto,
indiferente que la Micro-red funcione de
forma conectada o aislada a la red
convencional.
Este trabajo presenta una novedosa
estrategia de control de Micro-redes
aisladas, basado en el control jerárquico y
control droop modificado. Esta estrategia
robusta permite mejorar la estabilidad de
voltaje y su comportamiento transitorio.
Se implementa una Micro-red de
referencia con dos fuentes fotovoltaicas
con valores nominales. Lo que permite
verificar el desempeño de la estrategia
propuesta comparando con un controlador
PI convencional.Technological advances demand a huge
amount of electricity, therefore
Renewable Energy Resources (RES) must
be near the electrical demand is huge, in
addition they are implemented in rural
places, where electric utility is not able to
provide the service. However, the
implementation of these new systems
implies facing new challenges for the
correct operation of Microgrid connected
or islanded from the conventional system.
This research presents a novel control
strategy for islanded Microgrids, based on
hierarchical control and modified droop
control. The robust control strategy
presented allows stability voltage
improvement and its transient behavior.
Which subscribes to verify the
performance of the proposed strategy
compared with a conventional PI
controller
- …