Voltage Ripple Suppression Strategy of DC Bus in AC-DC Hybrid Microgrid Based on Bidirectional Interface Converter

Abstract

In AC-DC hybrid microgrid, the instantaneous power fluctuation of interface converter caused by the unbalance of AC voltage leads to the double frequency fluctuation of DC voltage, which affects the normal operation of hybrid microgrid. Aiming at the above problems, the mathematical model of bidirectional interface converter in an αβ coordinate system is established, and the transmission characteristics of double frequency power of AC and DC subnets are analyzed under unbalanced conditions. On this basis, the bidirectional Buck/Boost fluctuating power compensation circuit is introduced into the DC side of bidirectional interface converter. The unified control strategy of AC unbalance voltage and DC double frequency pulsation voltage based on improved bidirectional interface converter is designed in detail. The voltage ripple on the DC bus can be transferred to the additional capacitor, which can vary over a wide range. In addition, the average voltage of the additional capacitance can be controlled to be lower or higher than the DC bus voltage, which provides the possibility to further reduce the additional capacitance and the capacitance capacity of the DC bus. Therefore, the bidirectional interface converter can compensate both the AC unbalance voltage and the DC double frequency pulsation voltage with its own power margin under the condition of small DC bus capacitance. Simulation results show the effectiveness of the proposed control strategy.