Research On Energy Management Operation Optimum Of Micro Grid

In recent years, the participation of Renewable Energy Sources (RESs) in the forms of Wind Turbines (WTs), Photovoltaic (PVs), Fuel Cells (FC), Micro Turbines (MT), etc has resulted in more reliable and efficient operations with better power quality and flexibility especially in distribution systems. Firstly, as micro grid is connected to power system, the structure of distribution system is transformed from the traditional single power supply radial structure to multi-source power mesh structure. Safe operation of the grid will be affected by bi-directional power flow, therefore in order to improve the stability and security of the micro grid, it is necessary to reconsider the micro grid protection strategy, while the fault is removed by Relay protection action, on the other hand, the reliability of the system will be inevitably influenced, therefore, the output power of micro sources need to be controlled without removing the fault control, that is to control output power of micro power sources dynamically. Secondly, From that perspective to make full use of new energy, micro power generator should have priority, as to the problem of ratio balance between new energy and power grid energy, in principle, the power is provided by micro grid under the condition of the output is enough, However, considering the uncertainty of the power from the micro power resources, the ratio of power provided by new energy resources need to be limited, then the control problem of micro power output power required to be researched. Finally, Characteristics of micro resources are different, how to coordinate the reasonable distribution of the power between each micro power source and power grid, is the key to ensure the power quality. And in order to meet the customer’s needs and realize uninterrupted power supply, the energy of the whole micro power grid need to be managed and optimized, how to realize comprehensive analysis and control of the whole micro power grid by controlling coordinately power supply and load is the key problem. Therefore, relying on Liaoning key laboratory micro grid technology innovation platform in Shenyang institute of engineering,the following aspects are researched aiming at above problems:1. Operating characteristics of micro grid resources and energy storage system are analyzed and equivalent models are established.The key point is to analysis the characteristic of the permanent magnet direct drive synchronous generator. The equivalent models have been developed by adapting different aggregation criteria and had been applied to other technologies. The responses of three aggregated models are evaluated consisting of variable speed permanent magnet synchronous generator wind turbines when wind fluctuations or grid disturbances occur. The results show that the three aggregated models provide very similar results to the detailed model, both in the evolution of active power when fluctuations in wind speed occur. The aggregated model with an approximate mechanical torque offers excellent results. This part lay the foundation for the study of micro power grid of dynamic characteristic of the micro power supply and micro power grid interconnection main protection strategy, micro grid energy management and power control.2. The influence of the micro grid on the protection is analyzed, a novel protection principle based on phase comparison for micro grid is proposed.The protection scheme is used to protect the main lines from fault occurrences. By comparing both sides phase relationship of the current of the fault line, Phase current phase comparison longitudinal differential protection is applied to micro grid. The protection scheme based on the communication network is simple, reliable small amount of calculation and is suitable for more complex micro grid, can be in micro grid parallel operation and planning isolated operation, protection principle is simple and reliable, Various operation condition at the time of the micro grid is connected is simulated, the results show that the proposed micro grid main protection method has higher sensitivity and conforms to the requirements of the development of micro power grid3. In view of fluctuation of output power of DG, presents novel methods to smooth the output power.Hybrid Storage Systems (HSSs) is used for smoothing the output power of wind units, HSS consists of a lead-acid battery and an Electric Double-Layer Capacitor (EDLC),Proposed control scheme applies mode switching strategy,in which different operation modes are carefully designed under different HSS status. Performance of the proposed control method is investigated using simulations in MATLAB-Simulink. Results show robustness and effectiveness of the proposed control method.In view of fluctuation of output power of PV But also investigated the solar PV impacts and proposed a charging/discharging control strategy is developed taking into account the current state of charge (SoC) of the storage and the intended length of charging/discharging period to effectively utilize the available capacity of the storage. The storage is used to consume surplus solar PV power locally during PV peak, and the stored energy is utilized in the evening for the peak-load support. The proposed PV impact mitigation strategy is tested on the micro grid proposed in paper and the result shows that it can also mitigate the impact of sudden changes in PV output, due to unstable weather conditions, by putting the storage into a short-term discharge mode.4. In order to control power flow between power grid and micro grid, an optimal power flow controller for a utility connected micro grid based on a real time self-tuning method is presented.The controller scheme is composed of an inner current control loop and an outer power control loop based on a synchronous reference frame and the conventional PI regulators. FA is an intelligent searching algorithm that is applied for real-time self-tuning of the power control parameters. The results show that the proposed controller offers an excellent response and proves the validity of the proposed strategy.5. An advanced EMS in the typical MG working in grid connected mode is introduced.The developed EMS is able to determine the optimal operating strategies that minimize the energy costs, pollutant emissions, and hence maximizing the output of the available renewable energy resources. The established EMS is formulated as a nonlinear optimization model with different equality and inequality constraints for proper solution The performance of AMFA is compared with other commonly used algorithm such as FA (Fired algorithms) to clarify the efficient and robustness of AMFA solver.