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Distributed control methods generally implemented with droop control have been widely applied in the energy management of microgrids. However, the robustness and stability of distributed control has been influenced by the size and diversity of the microgrid structure and compositions. Meanwhile, centralized control has been considered lack of flexibility and expansibility. In this paper, a novel control...
This paper deals with a voltage disturbance generator output characteristics. Usually a microgrid is connected to utility grid through STS to disconnect in case of fault occurrence. The STS should be opened in case of outage, however, it may be connected in case of voltage sag occurrence. The magnitude of surge or over current through the STS is determined by the dip of the sag. The voltage disturbance...
In this paper, a positioning method of distributed power system is proposed to minimize average voltage variation of DC microgrid through voltage sensitivity. Power flow analysis is performed to derive voltage sensitivity, and droop bus is introduced to improve the accuracy of voltage sensitivity. In addition, the averaged voltage sensitivity according to the position of the distributed power system...
Energy storage systems (ESSs) are desired and widely applied for power smoothing especially in systems with renewable generation and pulsed loads. High-pass-filter (HPF) is commonly applied in those applications in which the HPF extracts the high frequency fluctuating power and uses that as the power reference for ESS. The cut-off frequency, as the critical parameter, actually decides the power/energy...
In microgrids, photovoltaic (PV) and storage are integrated as a droop-controlled ideal source, which is not practical and challenges the system efficiency. Instead, PV-storage can be allocated separately. This PV-storage independent system is more flexible and easier to optimize. But, the conventional PQ-controlled PVs rely on master voltage-controlled storage sources. In this paper, a novel operation...
In islanding microgrid, the distributed generation (DG) units should take over the microgrid and meet the power demand of loads. Due to the randomness and capacity limitation of DG units, the islanding microgrid may face overload challenge with load increasing. The islanding microgrid need massive energy storage system for power reserve or load shedding to maintain microgrid stable. However, this...
In the case of sensitive and critical load, the distributed generation (DG) should supply continuous power, even in the condition of utility outage. This paper proposes a novel seamless transfer control strategy, which based on special master and slave DGs. The master DG unit is controlled by a novel control strategy, which combines indirect current control and droop control. A part of slave DGs are...
This paper presents an FPGA-based adaptive predictive control scheme for single-phase T-type NPC inverter in applications to microgrids with high efficiency and robust performance. Predictive control is applied for current regulation to achieve fast dynamic response with low total harmonic distortion (THD). Implementation of a grid inverter with minimum inductor will result nonlinear inductance due...
The distributed generation (DG) should supply continuous power to local critical load, even in the condition of utility outage. This paper proposes a novel seamless transfer control strategy, which combines indirect current control and droop control. A microgrid structure of multi-masters and multi-slaves is also proposed, which based on the master-slave control and droop control. The master DGs are...
With the assessment of single-phase microgrids (MGs), three-phase/single-phase (TP/SP) hybrid multi-microgrids (MMGs) are emerging, provided with more complex architecture. This paper deals with the black-start problem for TP/SP MMGs in islanded mode caused by an unscheduled breakdown from the main grid. The three-phase units, such as energy storage systems (ESSs), photovoltaic (PV) systems, and loads,...
Islanded operation of microgrid is sensitive to frequency and voltage fluctuations due to lack of inertia. This makes it vulnerable to disturbances and intermittent renewable generation. Integration of energy storage devices is an effective but expensive solution to stabilize the microgrid. Electric Spring (ES) is a new power electronic based smart grid technology which can be used to provide voltage...
The nonlinear loads in microgrid not only distort the voltage but also degrade the harmonic power distribution in a conventional droop-controlled microgrid. This paper starts with analyzing the trade-off between voltage total harmonic distortion (VTHD) and harmonic sharing effectiveness. A multi-framed droop controller is proposed to improve the harmonic power sharing without deteriorating VTHD by...
In this work, load current in a multi-unit microgrid is decomposed into components. These components reflect the nature of total connected load at the point of common coupling (PCC) with the utility grid. Each unit (composed of distributed energy resources (DER), interfacing converter, and filtering elements), contributes to the total current fed by the microgrid. The current supplied by a unit is...
Power sharing performance is a critical issue of hybrid energy storage system (HESS) in autonomous DC microgrid (MG). In this paper, a novel integral droop (ID) is proposed to mimic dynamic characteristics of the capacitor by using energy storages (ESs) with quick response. The main advantage of the proposed controller is that dynamic power sharing among ESs is automatically realized in the decentralized...
Due to the challenge of energy demand, renewable energy sources are introduced to our daily life in order to satisfy the energy demand and reduce the emission of greenhouse gas. But the increasing penetration of renewable energy sources causes obvious impact on the conventional power systems especially the control strategies. In order to solve the problem, microgrid is introduced, which usually consists...
Load frequency control in an islanded microgrid is challenging due to the low system inertia and random power variations resulting from renewable energy sources and loads. The traditional droop control mechanism may become unstable under some conditions. To overcome this problem a new control algorithm is proposed in this paper. The necessary condition derived to ensure the frequency stability is...
In this paper, an adaptive integrated hybrid AC/DC microgrid module is proposed to accommodate a wide range of Distributed Renewable Energy Resources (DRERs), Distributed Energy Storage Devices (DESDs) and Distributed Demand Resources (DDRs) into the existing distribution systems. The concept and the architecture of adaptive integrated hybrid AC/DC microgrid module have been elaborately explained...
The well-known active power-frequency and reactive power-voltage amplitude droop control is widely used in the coordinated control of parallel inverters in microgrids. However, the dynamics of the conventional droop method is slow due to the low-pass filters used for power calculation purposes. Stability concerns also exist in the conventional droop method. This paper proposes a novel droop control...
The microgrid can operate in grid-connected mode and islanded mode, and the parallel operation of inverters will be involved in both modes. However, due to the differences of output characteristic among various inverters, the load power can't be shared equally. As a result, some methods without communication lines such as droop control and VSG (virtual synchronous generator) control have been proposed...
Due to different initial state of charge (SoC) of distribution energy storage system (DESS) and mismatched line impedance, the SoC of DESS is unbalanced in microgrid. The conventional P-f droop, used to obtain accuracy load sharing, cannot balance the SoC. To overcome the drawback, this paper proposes a unified SoC based droop control method with distributed communication lines. In this scheme, the...
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