Voltage Source Converter Control Under Unbalanced Grid Voltage

Abstract

The conventional control of the voltage source converter (VSC) assumes that the input voltage is balanced. However, unbalanced voltage is a phenomenon that occurs frequently in actual industrial sites. If the grid voltage is unbalanced, THD increases due to voltage negative component, and low harmonic components appear in DC-link voltage, which adversely affects the performance of the converter. Therefore, the purpose of this study is to propose an efficient control method that can solve the problem of the AC-DC converter due to the unbalance of grid voltage. A Multivariable State-Feedback (MSF) current controller is proposed to improve the performance of the VSC under grid voltage disturbances. The control process is carried out by adjusting the extracted positive and negative components of the grid d and q-axis currents. To minimize the DC-link voltage ripple, the reference negative grid currents are obtained from the DC-link voltage controller. However, if the target is to eliminate the imbalance of the grid current, the reference negative currents are set to zero. The experimental results are discussed to validate the proposed controller. The results show that the new MSF controller reduced the DC-link ripple and provides a fast dynamic response during unbalanced grid voltage.