New Modeling and Improved Current Control Strategy to Eliminate the Impact of Synchronization Method and Parks Transformation for Grid-connected Four-leg PWM Inverter

The synchronization method’s ability is one of the fundamental guarantees for the stability and accuracy of injected current control for grid-connected converter-based distribution resources. These synchronization methods, such as phase locked loop (PLL), are generally based on Park transformation and grid voltage regulation, which may affect an unstable phenomenon under distortion and unbalanced grid voltage conditions and result in more computational complexity. In this present paper, analogous to the traditional voltage-oriented control strategy (VOC) in the synchronous rotating frame (dq0-frame) based on PLL and Parks transformation, an improved voltage-oriented control strategy (IVOC) without synchronization methods and Parks transformation is proposed for grid-connected four-leg inverters (GC-FLVSI) to achieve accurate current control with high-quality performance in the dq0-frame. This proposed strategy is not only used for controlling the GC-FLVSI but also to provide the module of GC-FLVSI in the dq0-frame based on the instantaneous active and reactive powers theory (DPC). The proposed IVOC strategy has the same properties and identical performance as the traditional VOC when the grid phase angle is correctly detected by any synchronization method, with the advantages of both traditional DPC and VOC at the same time. In order to validate the superiority and excellent dynamic and steady-state performances of the proposed IVOC strategy in comparison with the traditional VOC strategy, some simulation scenarios using MATLAB/Simulink under different operations and grid conditions have been performed and presented.