A novel second harmonic disturbance suppression method for islanded hybrid AC/DC microgrid clusters under asymmetric AC side fault

In this paper, a novel second harmonic disturbance suppression method for islanded hybrid AC/DC microgrid clusters under asymmetric AC side fault is proposed. Firstly, The second harmonic disturbance characteristic analysis of common bus voltage under asymmetric AC side fault is given. Based on that, this paper elaborates the influence of the second harmonic disturbance of common voltage on the transmission power of bi-directional DC/DC converters (BDC) and bi-directional DC/AC converters (BAC) with normalized droop control at length. Secondly, the second harmonic disturbance suppression methods of BDC and BAC based on linear active disturbance rejection control (LADRC) are proposed, and total disturbance of BDC and BAC are defined which contain the second harmonic disturbance of common bus voltage. Then, second-order linear extended state observers (LESO) are designed to observe the total disturbance in real time. Next, we introduce the observer state variables into the normalized droop control of BDC and BAC to eliminate the second harmonic disturbance caused by common bus voltage. Finally, the results of Hardware-In-Loop tests verify the correctness and effectiveness of the proposed control method. • The second harmonic disturbance characteristic analysis of common bus is given. • The influence of the harmonic disturbance on the power of BDC and BAC is elaborated. • The disturbance of common bus voltage, power of BDC/BAC/ES/load is eliminated. • The AC bus frequency, DC bus voltage can be well controlled by the LADRC.