| Summary: | 碩士 === 國立交通大學 === 電控工程研究所 === 107 === The purpose of this research is to investigate the current sharing control of parallel connected single-phase full-bridge inverters for AC microgrid. The inverters in a microgrid system can be operated in two modes, the grid-connected mode and the stand-alone mode. A big difference of these two modes of operations is whether a communication in between or not. In this research, two inverters operated in stand-alone mode are controlled by a droop control method, which achieves synchronization and load power sharing without communication in between. The current distribution can be setup to average distribution or force distribution by the current sharing commands in the droop control. Due to the uncertainties of the lengths of the transmission lines between each inverters and the load, the mismatch of the output impedance and the transmission line impedances reduces the droop control power sharing performance and increase the output current error. In order to reduce the current error in the above condition, a virtual impedance, which is between the output filter and load, is added to rematch the output impedance and transmission line impedance.This method is verified to reduce the current error effectively. In the microgrid system, multiple inverters are operated in parallel at the same time usually,and in order to verify the method and simplify the system, this thesis proposes a two-layer current sharing control scheme for parallel connected inverters with specified uncertainties of line impedances. The inner layer controller is designed to achieve a desired output impedance with specified voltage THD under nonlinear rectified load. The outer layer controller is designed to provide robust current sharing control by using virtual impedance control with specified line impedance uncertainties. The outer layer control is composed of the droop control and the virtual impedance loop. This two layer architecture realizes the sharing control and solving the transmission line impedance uncertainties. The experiment is verified by the test bench with two 90W single-phase full-bridge inverters controlled by Texas Instruments TMS320F28335 DSP.
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