Time-Domain Stability Analysis and Improvement of Two-Stage Three-Phase Off-Grid Inverter

Two-stage three-phase off-grid inverter could be connected to photovoltaic systems devices to provide reliable power supply for critical loads. However, this system has stability problems under disturbance. In this paper, a time-domain model of the two-stage three-phase off-grid inverter is first established, and based on the time-domain model, the stability of this two-stage three-phase inverter is analyzed based on Floquet theory, and further verified by simulation. To further improve the robustness and extend the stability region of two-stage three-phase off-grid inverters, a time-domain stability improvement method is proposed based on the time-domain stability criterion and eigenvalue sensitivity theory, as well as a new stability control strategy with additional inductor current feedback is obtained by using the proposed stability improvement method. Following, the correctness and effectiveness of the proposed control strategy are proved by comparing the stable region between the inverter with traditional PI control and the proposed control strategy. Finally, the conclusions are drawn. This paper provides a fast way to accurate analyze the stability of two-stage three-phase off-grid inverters and a easy way to improve the stability of two-stage three-phase off-grid inverter according to the real application requirements.