Time-Varying Amplitude-Frequency Characteristics Analysis of VSC Internal Voltage Under Grid Fault

As the voltage source converters (VSCs) are widely used as the important interface between the new energy applications and the power systems, the transient characteristics of VSC have great influence on the operation of the modern power systems. In this paper, internal voltage concept is introduced to represent the external characteristics of VSC. The amplitude/frequency characteristics of VSC internal voltage under non-severe grid fault and severe grid fault are analyzed and compared. The results show that under non-severe grid fault, the amplitude/frequency characteristics of VSC internal voltage are periodic time-varying. And the amplitude and frequency are the linear combination of modes of the close-loop system, while in severe grid fault, the characteristics of amplitude and frequency are aperiodic time-varying and are decided by the modes and the nonlinear elements. The results and conclusion are validated in Matlab/Simulink.