Novel Differential Current Control Strategy Based on a Modified Three-Level SVPWM for Two Parallel-Connected Inverters

Recently, parallel inverters have been investigated to provide multilevel characteristics besides their advantage to increase the power system capacity, reliability, and efficiency. However, the issue of differential currents imbalance remains a challenge in parallel inverter operation. The distribution of switching vectors of the resulting multilevel topology has a certain degree of self-differential current balancing properties. Nevertheless, the method alone is not sufficient to maintain balanced differential current in practical applications. This paper proposes a closed-loop differential current control method by introducing a control variable adjusting the dwell time of the selected switching vectors and thus maintaining the differential currents balanced without affecting the overall system performance. The control strategy, including distribution of switching sequence, selection of adjusted switching vectors, and calculation of adjusting times are described and analyzed in detail in this paper. Finally, experimental results confirm the performance and effectiveness of the proposed method.