Islanding Detection Time Calculation for Constraint Characterization in DC Microgrid

Detection time is the core indicator of the islanding detection method with positive feedback power disturbance (PFPD) for dc microgrid, which determines the speed and effectiveness of the detection. However, the PFPD-based system presents high-order characteristics due to the employment of a high-pass filter, making it hard to analyze in the time domain. The existing studies rely on the frequency domain to indirectly constrain the range of positive feedback parameters, which may make the detection speed cannot be designed accurately and even lead to detection failure. In this letter, the equivalent control model of the distributed generator is developed to reveal the limitation of the conventional frequency domain-based parameter design method. Then, the dynamics model of the voltage at the point of common coupling is analyzed and simplified to describe the time domain oscillation trajectory triggered by the islanding event. Furthermore, a detection time calculation method based on voltage envelope is proposed to constrain the islanding detection parameters, and its effectiveness and advantages are validated by experiments. This method quantitatively and intuitively characterizes the constraints of detection time on positive feedback parameters, and it provides good insight into the detection control optimization and detection speed improvement.