Abstract
Voltage sags have become a major power quality issue encountered by industries in recent years. Industrial manufacturing equipments are very sensitive to the power quality issues. Any voltage sag event in the power distribution system could cause under-voltage fault in sensitive loads and inflict significant losses with production process interruption. The voltage sag compensator, based on the transformer-coupled series-connected voltage source inverter, is among the most cost-effective solution to protect sensitive loads. Many voltage sag compensators adopt open-loop control strategies to increase the response speed for the sag compensation. But the L-C filter installed at the output of the voltage source inverter could introduce oscillations in transient, and the voltage disturbance could appear due to varied load conditions. In addition, the coupling components could appear due to coordinate transform for simplified operation process. It is unclear how errors can affect the performance of the voltage sag compensation. A close-loop control scheme is designed in this thesis to accomplish active damping without using any damping resistors. The entire controller is implemented in the synchronous reference frame, and all the cross-coupling terms under the synchronous reference frame are identified and de-coupled in the controller. Detailed explanations of the proposed close-loop control scheme are presented, and the effectiveness of the proposed scheme is verified by simulation and laboratory test results.