Energy Storage System (ESS) for Compensating Unbalanced Multi-microgrids Using Modified Reverse Droop Control (original) (raw)
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Improving Power Quality and Power Sharing in Unbalanced Multi-Microgrids Using Energy Storage System
2021 IEEE Applied Power Electronics Conference and Exposition (APEC), 2021
The integration of single-phase distributed generations (DG) and unbalanced loads to three-phase DGs brings challenges to the operating system of the microgrids (MGs). These challenges include unbalanced voltage and unequal power flow at the point of common coupling (PCC) of the MGs. The aim of this paper is to develop an Energy Storage System (ESS) with multi-function control for islanded multi-microgrids (MMG) consisting of single and three PV-DGs to enhance its power quality and power sharing of the MMGs. The proposed multifunction control consists of a reactive power compensation (RPC), a PCC power balance regulator (PBR) and a reactive power sharing algorithm (RPSA). The RPC and the PBR improve the three-phase PCC voltage and power unbalance of the MMG and the RPSA regulates the reactive power sharing among the MMGs. The proposed strategy is experimentally validated on the Opal-RT OP5600 real-time simulator. The voltage unbalance factor (VUF) at the PCC is reduced from 4.3 percent to 0.03 percent, while the three phase and the single phase reactive powers are shared proportionally between different rated DGs.
Phase unbalance mitigation by three-phase damping voltage-based droop controllers in microgrids
Electric Power Systems Research, 2015
Microgrids aggregate grid assets in geographically confined areas, allowing them to locally tackle grid issues and capture the value of their aggregated flexibility by bringing intelligence in the grid in a bottomup approach. For the control of distributed generation units in single-phase islanded microgrids, the voltage-based droop (VBD) control strategy has already been developed. The VBD strategy can also be used in grid-connected microgrids, which makes a transition between both modes possible. Phase unbalance is a significant issue in three-phase microgrids and will become more pressing with increasing penetration of single-phase renewables. Therefore, the effect of several traditional control strategies for three-phase distributed generation units to phase unbalance is discussed. Subsequently, in this paper, a new control strategy is presented which extends the basic VBD control strategy so it can be used as a three-phase controller which at the same time mitigates unbalance in islanded and grid-connected microgrids, i.e., the three-phase damping VBD control. It is concluded that the presented three-phase damping VBD control method mitigates unbalance, allows the DG units to share the unbalanced currents, and is able to operate both in grid-connected and islanded systems.
Applicability of Droop Regulation Technique in Microgrid - A Survey
Engineering Journal, 2014
Currently, the worth of power generation on the basis of renewable sources is rapidly growing. Correspondingly the microgrids and the DG units are impressed the researchers for their peculiar features. Power sharing is the major concern when various DGs are connected to the microgrid via power electronic converters. It is mandatory to achieve an appropriate power sharing when the manifold DGs are activated in parallel. For that, the two ultimate quantities-power angle δ and voltage magnitude V are regulated to acquire the real and reactive power sharing correspondingly. Many innovative control techniques have been used for load sharing. The most common method of local load sharing is the droop characteristics. Subsequently, there is a swift momentum in the advancement of researchers to meet the challenges of the droop control techniques in the power sharing concerns, an extensive literature review on active and reactive power sharing, voltage and frequency control in microgrid has been emphasized. The various conventional and modified droop control techniques/strategies that relates to power sharing issues have been highlighted in this work.
Voltage Imbalance Compensation for Droop-Controlled Inverters in Islanded Microgrid
2017
In this paper, a new control strategy is proposed for implementation in low-voltage microgrids with balanced/ unbalanced load circumstances. The proposed scheme contains, the power droop controllers, inner voltage and current loops, the virtual impedance loop, the voltage imbalance compensation. The proposed strategy balances the voltage of the single-phase critical loads by compensating the imbalanced voltage drop on the feeders. In addition, this strategy has also shown to be capable of restoring critical loads' voltage to nominal values. This method also shares the real and reactive load accurately between DG units, based on their capacity. The simulation results in MATLAB /SIMULINK environment show the efficiency of the proposed approach in improving power sharing among DG units and decreasing voltage imbalance
2013
For islanded microgrids, droop-based control concepts have been developed both in single and three-phase variants. The three-phase controllers often assume a balanced network; hence, unbalance sharing and/or mitigation remains a challenging issue. Therefore, in this paper, unbalance is considered in a three-phase islanded microgrid in which the distributed generation (DG) units are operated by the voltage-based droop (VBD) control. For this purpose, the VBD control, which has been developed for single-phase systems, is extended for a three-phase application and an additional control loop is added for unbalance mitigation and sharing. The method is based on an unbalance mitigation scheme by DG units in grid-connected systems, which is altered for usage in grid-forming DG units with droop control. The reaction of the DG units to unbalance is determined by the main parameter of the additional control loop, viz., the distortion damping resistance, Rd. The effect of Rd on the unbalance mitigation is studied in this paper, i.e., dependent on Rd, the DG units can be resistive for unbalance (RU) or they can contribute in the weakest phase (CW). The paper shows that the RU method decreases the line losses in the system and achieves better power equalization between the DG unit’s phases. However, it leads to a larger voltage unbalance near the loads. The CW method leads to a more uneven power between the DG unit’s phases and larger line losses, but a better voltage quality near the load. However, it can negatively affect the stability of the system. In microgrids with multiple DG units, the distortion damping resistance is set such that the unbalanced load can be shared between multiple DG units in an actively controlled manner rather than being determined by the microgrid configuration solely. The unit with the lowest distortion damping resistance provides relatively more of the unbalanced currents.
2016 IEEE Power and Energy Society General Meeting (PESGM), 2016
A distributed secondary voltage controller is designed for droop-controlled microgrids in power distribution networks to improve power quality. Microgrids are typically managed by the droop control mechanism that ensures stability but does not guarantee power quality of voltage magnitude. To solve this power quality problem, the proposed distributed secondary voltage controller maintains a constant voltage at a microgrid's point of common coupling (PCC) using only local measurements. With the voltage regulation capability, a microgrid can be used to improve power quality so that greatly promote the microgrid's value to power system daily operations. The improved voltage regulation in a power network is demonstrated through simulation tests of a modified IEEE 37-node test feeder. Furthermore, this secondary voltage controller is compatible with existing voltage control devices, such as tap-changing transformers that automatically regulate voltage.
2014
This paper presents the coordinated control of distributed energy storage systems in dc microgrids. In order to balance the state-of-charge (SoC) of each energy storage unit (ESU), an SoC-based adaptive droop control method is proposed. In this decentralized control method, the droop coefficient is inversely proportional to the nth order of SoC. By using a SoC-based droop method, the ESUs with higher SoC deliver more power, whereas the ones with lower SoC deliver less power. Therefore, the energy stored in the ESU with higher SoC decreases faster than that with lower SoC. The SoC difference between each ESU gradually becomes smaller, and finally, the load power is equally shared between the distributed ESUs. Meanwhile, the load sharing speed can be adjusted by changing the exponent of SoC in the adaptive droop control. The model of the SoC-based adaptive droop control system is established, and the system stability is thereby analyzed by using this model. Simulation and experimental results from a 2 × 2.2 kW parallel converter system are presented in order to validate the proposed approach.
Protection and Control of Modern Power Systems, 2019
Recently microgrids have drawn a potential attraction by fulfilling the environmental demands and the increasing energy demands of the end-users. It is necessary to focus on various protection and control aspects of a microgrid. During the transition between the grid-following and grid-forming modes, the voltage and the frequency instability due to the power mismatch condition becomes the major point of concern. Therefore, the paper executes a frequency-active power and voltage-reactive power drooping control strategy for the precise power-sharing among the distributed power generators. Furthermore, to handle the power deficit scenarios and to maintain the system stability, a system independent and priority-based adaptive three-stage load shedding strategy is proposed. The sensitivity of the strategy depends on the system inertia and is computed according to the varying absolute rate-of-change-of-frequency. The strategy incorporates the operation of battery storage system and distri...
IEEE Transactions on Smart Grid, 2000
The concept of microgrid hierarchical control is presented recently. In this paper, a hierarchical scheme is proposed which includes primary and secondary control levels. The primary level comprises distributed generators (DGs) local controllers. The local controllers mainly consist of power, voltage and current controllers, and virtual impedance control loop. The central secondary controller is designed to manage the compensation of voltage unbalance at the point of common coupling (PCC) in an islanded microgrid. Unbalance compensation is achieved by sending proper control signals to the DGs local controllers. The design procedure of the control system is discussed in detail and the simulation results are presented. The results show the effectiveness of the proposed control structure in compensating the voltage unbalance.
A direct voltage unbalance compensation strategy for islanded microgrids
2015 IEEE Applied Power Electronics Conference and Exposition (APEC), 2015
In this paper, a control strategy with low bandwidth communications for paralleled three-phase inverters is proposed to achieve satisfactory voltage unbalance compensation. The proposed control algorithm mainly consists of voltage/current inner loop controllers, a droop controller, a selective virtual impedance loop, and an unbalance compensator. The inner loop controllers are based on the stationary reference frame to better mitigate the voltage distortion under nonlinear loads. Droop control and selective virtual impedance loop achieve accurate current-sharing when supplying both linear and nonlinear loads. Moreover, by adjusting voltage references according to the amplitude of the negative sequence voltage, the unbalance factor, which is mainly caused by single phase generators/loads, can be mitigated to an extremely low value. Finally, an AC microgrid which includes three three-phase three-leg inverters was tested in order to validate the proposed control strategy.