Study on dynamic energy dispatch strategy of energy storage in PV-diesel-energy storage microgrid system
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A dynamic energy dispatch strategy based on frequency bias is presented for the photovoltaic-diesel-energy storage microgrid, which aims at frequency fluctuation caused by the sudden change of load and the characteristic of photovoltaic microsource. According to the frequency bias forming principle of diesel generator and the demand for steady operation and power quality of microgrid, a three-stage dynamic energy dispatch strategy based on proportional-derivative (PD) preceding is achieved, which overcomes the shortcoming of PD strategy. This modified strategy is implemented in the established microgrid system, and two pairs of contrast experiments are made to verify the suppression effect of system frequency fluctuation. The experiments have proved that this strategy for dynamic energy dispatching can mitigate the frequency fluctuation caused by photovoltaic microsource and load sudden change to some extent, thus it is a feasible solution to improving power quality and stability of microgrid.Keywords:
Microgrid
Diesel generator
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This paper presents a method to enhance the stabilizing performance of a microgrid using an energy storage system (ESS) with under frequency (UF) relay. A microgrid is considered as a small-scale power grid that involves generation, distribution and energy storage systems operating independently from the main grid. Typically, a microgrid uses renewable energy to produce electricity as a main source. Due to the uncertain generation of power from renewable supply in a microgrid, the controlling of power balance between supply and demand of a microgrid is difficult in the islanded operation mode. When a microgrid is subjected to a large disturbance, the frequency of a microgrid may change rapidly due to the low inertia present in a microgrid. It is essential to maintain the frequency of a microgrid within acceptable ranges, particularly in islanded mode. Therefore, utilizing an ESS with UF relay gives benefits in maintaining and stabilizing the frequency effectively. In this paper, a system identification technique is applied to a microgrid to formulate a mathematical model systematically. Then, with the obtained identified model, the robust controller of an ESS can be designed by using H-infinity loop shaping procedure (HLSP). The application of such ESS with the appropriate load shedding by UF relay is also proposed. The proposed study system is implemented on DIgSILENT PowerFactory and MATLAB software. The obtained simulation results demonstrate that the stabilizing performance of frequency in a microgrid is more effective in terms of smaller frequency deviations, faster responses and minimum load shedding when collaborative ESS control and appropriate load shedding with UF relay are used.
Microgrid
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As for the control of microgrid, this paper studied multi control strategy of microgrid based on the nonlinear prime dual method. Objective function of the model is minimization of micro sources' cost and cost of purchased power from grid when microgrid is connected to grid while satisfying a series of constraints. Minimization of load shed is the objective function when microgrid is isolated when keeps load as much as possible and ensures the stable of voltage and frequency. Simulation is done with a distributed system. Results indicate that proposed method can ensure the stability of microgrid when it is connected to or isolated from grid. (6 pages)
Microgrid
Minification
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When problems such as line fault, breakdown of a substation or a generator, etc. arise on the grid, the Microgrid is designed to be separated or isolated from the grid. Most existing DGs(Distributed Generators) in distribution system use rotating machine. However, new DGs such as micro gas turbine, fuel cell, photo voltaic, wind turbine, etc. will be interfaced with the Microgrid through an inverter. So the Microgrid may have very lower inertia than the conventional distribution system. By the way, the rate of change of frequency depends on the inertia of the power system. Moreover, frequency has a strong coupling with active power in power system. Because the frequency of the Microgrid may change rapidly and largely during transient, appropriate and fast control strategy is needed for stable operation of the Microgrid. Therefore, this paper presents a power balancing strategy in Microgrid during transient. Despite of strong power or frequency excursions, power balancing in the Microgrid can be maintained.
Microgrid
Transient (computer programming)
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The analysis of control strategies developed for a microgrid control structure is presented in this paper, when it is integrated with renewable energy source. Due to weather conditions, the microgrid system with renewables is presented with unavoidable input power perturbation, produced by the renewable energy. This perturbation causes an imbalance in the power system between the energy produced and consumed, as well as creating frequency fluctuations in the output voltage. Different methods of energy management are employed in the microgrid, in order to stabilise the system. A control strategy for the load management have been developed and analysed through MATLAB/Simulink simulation. The simulation results justify the stability of the microgrid operation under irregularities of the input voltage. The flow chart transition method based on graphical transition state is employed to maintain the output voltage of the microgrid; this was attained by switching ON and OFF certain noncritical loads upon considering the available input power.
Microgrid
Energy management system
State of charge
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Microgrid
Islanding
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Microgrid
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Frequency is the key indicator for island microgrid, but it can be affected by the renewable energy fluctuation and the load variation. The robust coordinated control strategy is proposed for the photovoltaic (PV) -diesel-battery isolated microgrid. Based on different frequency deviation ranges, PV systems and diesel generator (DG) systems are prioritized for frequency regulation. When the frequency deviation exceeds the set frequency threshold, the battery system begins to response quickly. Furthermore, the sliding mode (SM) load frequency control (LFC) is designed to improve the dynamic characteristics of the coordinated strategy and restrain the randomness and volatility of the source and load. The results of Matlab/Simulink prove that the proposed coordinated strategy can make full use of renewable energy and improve the frequency quality.
Microgrid
Diesel generator
Frequency deviation
Frequency Regulation
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Remote microgrids with battery energy storage systems (BESSs), diesel generators, and renewable energy sources (RESs) have recently received significant attention because of their improved power quality and remarkable capability of continuous power supply to loads. In this paper, a new proportional control method is proposed using frequency-bus-signaling to achieve real-time power balance continuously under an abnormal condition of short-term power shortage in a remote microgrid. Specifically, in the proposed method, the frequency generated by the grid-forming BESS is used as a global signal and, based on the signal, a diesel generator is then controlled indirectly. The frequency is controlled to be proportional to the AC voltage deviation of the grid-forming BESS to detect sudden power shortages and share active power with other generators. Unlike a conventional constant-voltage constant-frequency (CVCF) control method, the proposed method can be widely applied to optimise the use of distributed energy resources (DERs), while maintaining microgrid voltages within an allowable range, particularly when active power balance cannot be achieved only using CVCF control. For case studies, a comprehensive model of an isolated microgrid is developed using real data. Simulation results are obtained using MATLAB/Simulink to verify the effectiveness of the proposed method in improving primary active power control in the microgrid.
Microgrid
Diesel generator
Frequency deviation
Power Balance
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Microgrid is an effective approach to solve the grid-connection of distributed generations,and the hybrid microgrid composed of wind farm,photovoltaic generation and energy storage system possesses the feature that the clean energy can be fully utilized and its operation is reliable.The smooth switching between grid-connected operation mode and islanded operation mode of microgrid is an important measure to ensure the secure and reliable operation of microgrid.For this reason,a synthetical control strategy integrating new type of master-slave control with peer-to-peer control is adopted to control the operation mode transition between grid-connected operation mode and islanded operation mode of microgrid.A model of microgrid composed of complementary wind farm,photovoltaic generation and energy storage system is constructed on DigSILENT/PowerFactory platform,and the feasibility of the proposed control strategy is verified by simulation results.Besides,simulation results also show that the improved control strategy can ensure power balance of microgrid before and after the switching and keep the voltage of the bus connected with microgrid and frequency of the microgrid within the allowed range.
Microgrid
Mode (computer interface)
Grid connection
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Based on the characteristics of electric vehicles (EVs), this paper establishes the load models of EVs under the autonomous charging mode and the coordinated charging and discharging mode. Integrating the EVs into a microgrid system which includes wind turbines (WTs), photovoltaic arrays (PVs), diesel engines (DEs), fuel cells (FCs) and a storage battery (BS), this paper establishes multi-objective economic dispatch models of a microgrid, including the lowest operating cost, the least carbon dioxide emissions, and the lowest pollutant treatment cost. After converting the multi-objective functions to a single objective function by using the judgment matrix method, we analyze the dynamic economic dispatch of the microgrid system including vehicle-to-grid (V2G) with an improved particle swarm optimization algorithm under different operation control strategies. With the example system, the proposed models and strategies are verified and analyzed. Simulation results show that the microgrid system with EVs under the coordinated charging and discharging mode has better operation economics than the autonomous charging mode. Meanwhile, the greater the load fluctuation is, the higher the operating cost of the microgrid system is.
Microgrid
Economic Dispatch
Mode (computer interface)
Diesel generator
Operating cost
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