DC Voltage Regulation Strategy Research In Wind Turbine/Energy Storage DC Micro-grid

With the extensive application of renewable energy, DC micro-grid has attracted more and more attention with its advantages of lower cost and improved efficiency. The DC voltage can be used to measure the stability of the DC micro-grid. In order to maintain the stability of the DC voltage, the coordination control of multiple micro sources is needed. The real time coordinated operation control scheme of the DC micro-grid, typically adopts the Master slave control centralized control, the point-to-point control and hierarchical control. However,there are some defects in these three methods. It is necessary to propose a reasonable method for the micro-grid real-time control. The stability of the DC voltage is the precondition for the economic dispatch which builds the economic mathematical models and optimizes the DC micro-grid with multiple algorithms. The closed-loop regulation of the DC voltage which includes operation control and economic dispatch needs to be further studied.In this paper, a novel closed-loop DC voltage regulation strategy of DC micro-grid based on wind turbine-energy storage system is proposed. This new strategy takes both economic dispatch and operation control into account. The main work and achievements of this paper are as follows:(1) This paper introduces the units of DC micro grid and the control method of the converters.(2) A closed loop control method for DC voltage is presented in the case of ignoring the line impedance in the DC micro-grid. This method includes tertiary,secondary and primary control. The tertiary control is in charge of economical dispatch. The primary control and secondary control are real time operation control.For the primary control, voltage fluctuations caused by small load power fluctuations are adjusted by all the main voltage regulation units according to their respective Droop characteristics. And the primary control regulation is a differential regulation of the DC voltage. The secondary control is carried out by the selected voltage regulation units mainly for the voltage fluctuations caused by larger load power fluctuations. And the secondary control can meet the requirements of non-error regulation as it adopts PI control method. In summary, the closed-loop DC voltage regulation is achieved by the proposed strategy. Finally, with an actual wind turbine/energy storage DC Micro-Grid, the validity and effectiveness of the proposed strategy is verified by the MATLAB simulation results.(3) In the case of the line impedance cannot be ignored, a new closed-loop control method of DC voltage is proposed, which also consists of tertiary, secondaryand primary control. The third voltage regulation is the same(2). And the secondary voltage regulation uses distributed control method. In this method the adjustment tasks are carried out by several corresponding converters at the bottom instead of by the traditional secondary central controller in order to reduce the dependence on the central controller. The primary voltage regulation also uses the droop control method. This method can ensure the reasonable distribution of load between converters and the quality of the power quality. And because there is no central controller, the reliability of the system is increased. Finally, with an actual wind turbine/energy storage DC Micro-Grid, the validity and effectiveness of the proposed strategy is verified by the MATLAB simulation results.