Improved Virtual Vector Control of Single-Phase Inverter Based on Unified Model

A unified model is established for virtual vector control schemes of current-regulated single-phase inverters. Based on this model, it is proved that the cross-coupling interaction between the real and virtual orthogonal axes may induce dc positive feedback and destabilize the system. Therefore, a stability criterion is identified to reveal the special characteristics of the virtual vector control system and provide guidelines for the controller design. It is further explicated that the stability issue imposes an extra limitation on the controller parameters so that they may not be sufficiently optimized. To solve this problem, a family of improved control methods is proposed by inserting a high-pass filter in the virtual signal generation stage so that the corresponding dc gain is changed to zero to eliminate the dc positive feedback. As a result, both the steady-state and transient responses can be significantly enhanced. A comprehensive design procedure is provided for the proposed method and the results are compared with conventional solutions, both theoretically and experimentally, to verify the advantages of the improved strategy.