A DC-Offset Reduced Grid-Voltage Sensorless Model Predictive Control Strategy for Grid-Tied Inverters With a Two-Stage Optimal Voltage Vector Searching Method

Grid-voltage sensorless model predictive control (MPC) strategies for grid-tied inverters (GTIs) have been studied frequently in recent years. However, the effects of dc-offset are not well addressed, and the current ripples are quite large as only one voltage vector (VV) is applied per control period. To solve these problems, a dc-offset reduced grid-voltage sensorless MPC strategy for GTIs with a two-stage optimal VV searching method is proposed. First, a new grid-voltage observer is proposed to reduce the effects of dc-offset. Second, by analyzing the proposed observer, it is found that the introduced intermediate variable can be used to estimate the dc-offset contained in the sampled grid current. Thus, the effects of dc-offset on the current control can be compensated accordingly. Third, to reduce the current ripples, a new two-stage optimal VV searching method is proposed on the basis of a detailed theoretical analysis. The novelty of this method is that it searches the phase and amplitude of the optimal VV in two independent stages, which reduces the number of VV that required to be evaluated online obviously. Finally, comparative experimental studies verify the effectiveness of the proposed methods in this article.