Control and stability of microgrid during transient states (original) (raw)
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Islanding Detection and Enhancement of Microgrid Performance
IEEE Systems Journal, 2017
Nowadays, renewable energy sources (RES) are widely used in the distribution system. Despite the advantages of RES in the system, they also introduce some problems such as unintentional islanding, protection concerns, reverse power flow, etc. Due to the unpredictable faults or scheduled maintenance plans, a distribution system can be sectionalized into several islands provided that enough dispersed generation units are available. Thus, distribution systems should be capable of detecting islanding condition for smooth transition to an islanded mode. As a first step, an islanding detection method (IDM) is proposed in this paper to detect the islanding phenomenon in a distribution system. The proposed method is a hybrid IDM which consists of a remote detection method and a passive method. In the next step, an adaptive control strategy is proposed to ensure stable operation of islanded subsections. The proposed method utilizes error rates of system parameter such as voltage and power to readjust generator controllers and maintain the system stability. The proposed IDM and adaptive controller are implemented on a generic distribution network using EMTDC/PSCAD software. Results have shown that the hybrid detection method is capable of detecting the islanding in the presence multiple distributed generation units. Moreover, the proposed IDM is not affected by load/generation changes. Results also showed a smooth transition from grid-connected mode to autonomous operation mode. Furthermore, the proposed adaptive control strategy maintains stable operation of the island when fault occurs in the island.
Dynamic modeling of microgrid for grid connected and intentional islanding operation
2012 International Conference on Advances in Power Conversion and Energy Technologies (APCET), 2012
Microgrid is defined as the cluster of multiple distributed generators (DGs) such as renewable energy sources that supply electrical energy. The connection of microgrid is in parallel with the main grid. When microgrid is isolated from remainder of the utility system, it is said to be in intentional islanding mode. In this mode, DG inverter system operates in voltage control mode to provide constant voltage to the local load. During grid connected mode, the Microgrid operates in constant current control mode to supply preset power to the main grid. The main contribution of this paper is summarized as 1) Design of a network based control scheme for inverter based sources, which provides proper current control during grid connected mode and voltage control during islanding mode. 2) Development of an algorithm for intentional islanding detection and synchronization controller required during grid reconnection. 3) Dynamic modeling and simulation are conducted to show system behavior under proposed method using SIMULINK. From the simulation results using Simulink dynamic models, it can be shown that these controllers provide the microgrid with a deterministic and reliable connection to the grid.
Auto Synchronization of Microgrid with Main Grid After Islanding Operation - a Review
International Journal of Advance Engineering and Research Development, 2015
This paper provides a review of research concerning thesynchronization technique for microgrid reclosing after islanding operation. It offers a brief review on some of the published work on control for grid connected and intentional islanding operations of microgrid. The future electric grid concept will cover some small parts to be disconnected and work in an autonomous way isolated from the main utility. Control of microgridscomposed by the couple distributed sources-local loadswith the competence of operating in grid-connected and island mode is a trending research area. The presence of an efficient algori thm for synchronizing the microgrid with the main grid every time the reclosure is allowed is crucial for assuring a safe operation.DG units are significantly and conceptually very different from conventional power system in terms of load characteristics, power quality constraints, market participation strategies and the control and operational strategies.
Recently, with increasing penetration of distributed generations (DGs) in electricity networks, Microgrids (MGs) have been created. These MGs can operate in grid connected or islanded mode. Islanded operation of a MG has its own challenging issues. The main issue in off-grid operation is voltage and frequency control of MG. Energy storage system (ESS) can play an effective role in this situation. In this paper, battery energy storage system (BESS) is used to improve the control of voltage and frequency in off-grid mode. An appropriate control strategy for BESS is defined and used in order to regulate the voltage and frequency of an islanded MG. To show the effectiveness and accuracy of the proposed method, the proposed strategy is applied to CIGRE benchmark MG in MATLAB/Simulink. Different events such as islanding and load switching for static load and dynamic load (induction motor) are investigated with and without BESS and its control strategy.
Operation and control of micro sources in Island mode of a Microgrid
2014
In the country like India where population is increasing at a rapid rate the electrical power demand has become a great problem. Unfortunately the conventional energy resources are limited, cause greenhouse emissions and are expected to increase in costs due to an increase in the demand. Recently, the new concept of MicroGrid has been emerging on distribution network for integration of micro generation in low voltage network and to increase the reliability of supply. A microgrid is a cluster of micro generators, loads, storage devices, control devices and a low voltage distribution network functioning in a coordinated manner. The microgrid can operate in two different modes: interconnected or emergency. In first mode the microgrid is connected with the conventional low voltage distribution network for importing or exporting electricity. In emergency mode the microgrid is isolated (islanded) with the help of control devices from the distribution network and uses local micro-generator...
A synchronization technique for microgrid reclosing after islanding operation
IECON 2012 - 38th Annual Conference on IEEE Industrial Electronics Society, 2012
The future electric grid concept will cover some small parts to be disconnected and work in an autonomous way isolated from the main utility. Control of microgridscomposed by the couple distributed sources-local loads -with the competence of operating in grid-connected and island mode is a trending research area. The presence of an efficient algorithm for synchronizing the microgrid with the main grid every time the recIosure is allowed is crucial for assuring a safe operation. The synchronization system presented in this work is compounded by two elements: Dual Second Order Generalized Integrator (DSOGI) and stationary reference frames phase locked loop (SRF-PLL). Besides, the voltage control of the microgrid plays a great role in the synchronization system performance.
Control of Transient Power during Unintentional Islanding of Microgrids
IEEE Transactions on Power Electronics, 2014
In 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 gridconnected mode. But in stand-alone mode they all need their power set-points to be adjusted according to their power ratings.
Survey on microgrids: Unplanned islanding and related inverter control techniques
Renewable Energy, 2011
Nowadays, the importance of electrical generation based on renewable energies is increasing, due to its low emissions of greenhouse gases. At the same time, Distributed Generation and Microgrids (MG) are becoming an important research line because of their peculiar characteristics. MGs are composed of small power sources which can be renewable, placed near customer sites. Moreover, they have the inherent property of islanding: the disconnection of either the MG from the main grid or a portion of a MG from the rest of the MG. There are two kinds of islanding: intentional or planned (for maintenance purposes), and unintentional or unplanned. The latter is mainly due to disturbances and it is used to avoid damages in sources and loads. It is the most critical case because it must be detected as soon as possible to activate all the control systems which allow continuing the energy production and distribution despite the disconnection. In islanding, it is crucial to ensure the power and the electrical signal quality. In grid-connected mode, the inverters use the electrical signal of the main grid as reference. Once in islanding, the main grid reference is lost and new control techniques for the inverters are needed in order to obtain the correct values of voltage magnitude and frequency in the MG. The main objective of this paper is to make a survey on MGs focussed on two important features: unplanned islanding and control of inverters in that scenario. The idea is to present the basic architectures and regulation techniques of MGs and to study the islanding behaviour, mainly the different detection techniques and the inverters' control once islanded.
A Novel Approach to Control the Frequency and Voltage of Microgrids in Islanding Operation
International Journal of Engineering and Technology, 2012
In this paper, electrical parameters of a microgrid containing distributed generation wind and fuel cell units are controlled in islanding mode operation. Islanding operation refers to isolation of a part of power system including distributed generation from the grid having continuous and independent operation. This has negative impacts on the isolated network including voltage and frequency dependence on load. These impacts and their solutions are studied in this paper. A proper controller using power electronics converters has been proposed. In order to verify the validity of the proposed control approach, it has been implemented and simulated on a 13-bus IEEE distribution power system containing a combination of distributed generation wind and fuel cell units.
Design of Controller for Transition of Grid Connected Microgrid to Island Mode
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A microgrid is the combination of Distributed generators that interconnected with the main grid to ensure continuity in supply to the load. The operating system will be in grid-connected and the island mode. This paper presents a mathematical model of hybrid microgrid consisting of PV system, wind power generation using DFIG which are integrated to the utility grid and a PI Controller for controlling the transition from grid-connected mode to island mode and normal operation, each DG inverter sated in constant current control mode to provide preset power to the main grid. When it disconnects from the main grid each DG inverter detects and connect to voltage control mode in the islanding situation. The modeling is performed in MATLAB Simulink and results are discussed out to verify the operation of the proposed system .