Abstract
This study proposes an advanced control scheme for the interlinking inverters of the hybrid AC/DC microgrids, which facilitates a seamless transition between grid-connected and stand-alone/islanding modes for the microgrid. Due to a nonlinear relationship between the terminal voltages of the voltage-source inverter (VSI) interfacing through inductor–capacitor (LC) filters with the grid voltages and currents, a feedback linearization technique (FLT) is employed to control the interlinking VSI under both grid-connected and islanding operations. The FLT-based current controllers are applied in the grid-connected mode, in which they adjust the power exchange between the DC and AC subgrids and mitigate the distortion of the grid currents produced by nonlinear loads. Under the stand-alone operation, the AC bus voltages are directly regulated by the FLT-voltage controllers of the interlinking VSI. In order to reduce the inrush currents and voltage overshot at the instant of mode switching, the FLT-based controllers are performed all the time regardless of the operating modes, where the voltage references for the VSI are not changed abruptly. The control performance of the VSI is highly satisfactory with low-transient overshoot values of the voltages and currents and low total harmonic distortion (THD) values of the grid currents and AC bus voltages are about 3.5% and 2.7%, respectively, under the nonlinear load condition. The validity of the new control strategy is verified by the simulation work, which investigates the operation of a hybrid AC/DC microgrid.
Highlights
Faculty of Engineering Technology and Science, Higher Colleges of Technology, Department of Electrical and Electronics Engineering, Ho Chi Minh City University of Food Industry, 140 Le Trong Tan, Ho Chi Minh City 760310, Vietnam
PSIM simulation tests on the hybrid AC/DC microgrid with two-level voltage-source inverter (VSI) were carried out to verify the feasibility of the proposed algorithm
In order to prove the effectiveness of the suggested control method, simulation tests for a 15-kW microgrid presented in Figure 1 by PSIM software were performed
Summary
With the requirement and utilization of both AC and DC electrical powers from the load and generation sides, a type of microgrid based on both DC and AC busbars called hybrid microgrid is an efficient solution, which has been paid remarkable attention in the past few years [1,2,3,4,5,6]. The cascaded control structure based on PI and PR requires considerable tuning, which is a time-consuming process to achieve a satisfactory control performance [20,21] Another issue for the interlinking inverter of the microgrid is that the mode changing between the on-grid and off-grid operations may lead to the voltage surge across the critical loads or inrush current flowing to the grid. The interlinking inverter is utilized to provide an active filter operation mode, which eliminates the distorted currents generated from nonlinear loads before injecting them into the grid For this mode, the FLT-based controllers for the phase currents of the inverter expressed in the SRF are applied. PSIM simulation tests on the hybrid AC/DC microgrid with two-level VSI were carried out to verify the feasibility of the proposed algorithm
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