| With the development of distributed power supply technology, a large number of new energy distributed power supplies have connected to the power grid. But the traditional grid technology of distributed power supply is relatively backward,which adopting the voltage phase lock loop or maximum power tracking methods. The power that uses these traditional methods into the grid is probably useless. The unidirectional power flow and high frequency characteristics of distributed power system, lead to lack of the inertia of grid which the penetration level of distributed power is higher or the synchronous generator is missing.Eventually it leads to the grid difficulty to resist the high frequency interference in the power system, which tending to degrade system’s stability.In this paper, basing on full understanding to the principle of synchronous generator connected to the grid, the process of inverter equivalent to synchronous generator is known. I focus on the research of the electromechanical equation of the virtual synchronous generator(Virtual Synchronous Generator,VSG) and analyzes the the concrete realization method of engineering practice. Rendering algorithm realization block diagram and the modeling effectiveness and feasibility is verified by means of simulation. And then I have designed a kind of pre-grid control unit through regulating the output voltage phase of the inverter by changing the mechanical power which is the input of virtual synchronous generator, and it can achieve the fast and smooth grid connected without the condition of electrical isolation.Charging and discharging characteristics of lead-acid battery are studied. The modeling methods of battery cells are determined. Suitable bidirectional DC-DC circuit topology for the realization of the between DC side of the inverter and the storage battery’s two-way fast power flow are selected. In order to fully consider the characteristics of battery energy storage system and the factors of charging and discharging depth influencing the life of lead-acid battery, this article makes every effort to design a kind of control strategy, which can not only ensure the effective control of the power grid frequency and voltage,but protect the battery effectively, so it can meet the economic requirement. In order to more fully explain the superiority of the control strategy, I establish the life loss model of battery and quantify the battery service life’s consumption.In this paper, a kind of improved droop coefficient p-f controller is designed by improving the traditional p-f droop controller of virtual synchronous generator(VSG). In the process of virtual synchronous generator system grid connected operation, it can change the droop coefficient of p-f controller dynamically and control system output power indirectly with real-time battery’s state of charge(SOC) and working conditions as the input. And in some special situations, such as over-charge or over-discharge of the battery, the new control strategy will adjust the system output, and then prevent the situation of over-charge or over-discharge from happening effectively. The storage energy of DC side and the inverter side are combined effectively with the fully consideration of the design of accumulator side energy storage system. Instead of the related research about traditional virtual synchronous generator which the DC side is ignored or ideal, the whole system has strong applicability and it is very conducive to the realization of engineering.On the basis of the above work,the article has used Matlab/Simulink system simulation tool to construct the simulation model of the virtual synchronous generator grid connected system. The performance of each part of the system is validated. The simulation result shows that it can participate in the intelligent control of voltage and frequency of the micro grid effectively in the premise of economic operation. |
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