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When a greatly varying load is connected to a weak system, stability of the system becomes a problem. In these days, because the use of renewable energy is accelerating, not only the loads but also the distributed power sources can be critical factors in destabilizing the system. The virtual synchronous generator (VSG) control allows a static inverter to behave similar to a synchronous generator (SG)...
The paper presents a microgrid energy management strategy (MEMS) for a Medium-Voltage Isolated microgrid, which is China's 10kv island microgrid demonstration project to accommodate the increasing power needs of customers and solve problems of island power supply. When the SOC is restored in security zone, the energy storage system (ESS) would increase the sensitivity and adjust the maximum charging...
Due to the increasing penetration of distributed generation resources, more and more microgrids can be found in distribution systems. This paper proposes a phasor measurement unit based distance protection strategy for microgrids in distribution system. At the same time, transfer tripping scheme is adopted to accelerate the tripping speed of the relays on the weak lines. The protection methodology...
Owing to the increasing penetration of distributed generation, there are some challenges for the conventional protection in distribution system. Bidirectional power flow and variable fault current because of the various operation modes may lead to the selectivity and sensitivity of the overcurrent protection decreased. This paper adopts distance protection for one mid-voltage level microgrid in Aalborg,...
Compared with the traditional microgrid, a smart transformer (ST)-based microgrid shows advantages in terms of higher efficiency, increased hosting capacity, and enhanced reliability. However, this novel microgrid presents challenges because of the complex resonances within the system and the interactions between ST and power converter-based distributed energy resources (DERs). Both the ST and DERs...
This work presents the development and implementation of four control configurations for photovoltaic inverter. These configurations are: Proportional Integral plus Resonant controller, Proportional Integral plus Repetitive controller, Proportional Integral-Proportional plus Resonant Controller and Two Degrees of Freedom plus Repetitive control with the aim of reducing the Total Harmonic Distortion...
Islanded DC microgrid architecture and control have become popular recently. One of the main control architectures is the DC bus voltage following type, where a main generator controls the DC bus voltage and the others follow the bus voltage and the power commands. Conventionally, the power regulation in the following generators is often employed with the droop control method. The main problem of...
In an autonomous microgrid without connection to the interconnected grid to support the frequency and voltage, it is more complex to control and manage. Thus in order to investigate the dynamic stability of the medium-voltage (MV) microgrid in Dongao Island, a detailed small-signal state-space model of the autonomous MV mixed-source microgrid containing diesel generator set (DGS), grid-supporting...
Multiphase energy conversion systems have been recently proposed to achieve simple fault-tolerant operation with no extra hardware. When such multiphase systems are connected to the grid, efficiency is maximized by operating the system in a balanced manner with an equal distribution of the power among phases. However, the situation differs when the multiphase system is connected to different microgrids...
With the increasing penetration of renewable energy, microgrids (MGs) have gained a great attention over the past decade. However, a sudden cut out of the MGs due to grid fault may lead to adverse effects to the grid. As a consequence, reactive power injection provided by MGs is preferred since it can make the MG a contributor in smooth ride through the faults. In this paper, a reactive power support...
As a type of Cyber-Physical Systems (CPSs), Smart Grid has been adding more communication and control capabilities to improve power efficiency and availability. Especially, more and more distributed control algorithms have been developed for Smart Grids because of their flexibility and robustness. In order to deploy them in real electric power systems, distributed control algorithms must be tested,...
To ensure stable and optimal operation of DC microgrid, a three-level based hierarchical control strategy is proposed which consists of primary, secondary and tertiary controls. Usually, the primary control is performed locally without communication, the higher levels, however, can be either centralized or distributed. Considering the risks brought by centralized control, such as surviving central...
This paper develops selective strategies for Neutral Point Clamped Multilevel Inverter (NPC) in a microgrid application with load current decomposition based on Synchronous Reference Frame (DQ) method. The 3-level NPC inverter is investigated as widely used topology for medium and high power applications. In addition to the current injection into the grid, the 3-level NPC DG inverter is also being...
Integration of renewable energy sources (RES) into the ac grid is growing very rapidly to meet the high and reliable load demand. The penetration of this growing microgrid structures within the distribution network are leading to several challenging power quality issues. It is mandatory to maintain the voltage and frequency within the prescribed limits at the local bus under any condition of the renewable...
Battery energy storage systems (BESSs) have been widely used to minimize wind power fluctuations in microgrids. BESSs control systems are usually based on vector-controlled techniques with inner current control loops and outer control loops. Owing to the complexity of a control system, it is difficult to apply additional functions such as predicting wind power. This paper presents a detailed description...
Smart meters are the cornerstone in the new conception of the electrical network or Smart Grid (SG), providing detailed information about users' energy consumption and allowing the suppliers to remotely collect data for billing. Nevertheless, their features are not only useful for the energy suppliers, but they can also play a big role in the control of the Microgrid since the recorded power and energy...
Frequency-based energy management strategies have been proposed for stand-alone systems with either centralized or distributed energy storage. This paper proposes a methodology for the design of the control parameters which ensures stability in both type of systems. As a result, the inverter manufacturer can implement one sole strategy, regardless of whether the expected stand-alone system is centralized...
Harmonic power sharing is important in islanded microgrid due to the presence of excessive nonlinear loads in distribution network. The lack of effective harmonic power sharing techniques may lead to overloading of certain distributed generation (DG) units. The concept of variable negative virtual harmonic impedance to share non-linear load in an islanded microgrid has been proposed recently. This...
In this paper, an optimal power flow problem is formulated in order to minimize the total operation cost by considering real-time pricing in DC microgrids. Each generation resource in the system, including the utility grid, is modeled in terms of operation cost, which combines the cost-efficiency of the system with the demand response requirements of the utility. By considering the primary (local)...
Rapid development of Distributed Energy Resources (DERs) and DC-powered loads entails the possibility of DC micro-grids to revenge conventional AC distribution networks. In addition, a continuous evolution of the power electronic technology allowing the highest possible power of DER production also makes the DC micro-grids more feasible in the near future. Although energy efficiency and steady state...
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