An active protection method based on superimposed phase currents for active distribution systems.

• Proposing an active control strategy. An active control strategy is achieved by setting different reference values of the filter inductor current of each DG when the fault intensity of the active distribution system changes. • Analysis of the effect of the active control strategy on the faulty feature. A detailed fault theory analysis is conducted by considering the active control strategy. It presents how the active control strategy influences the faulty feature. • Proposing a protection criterion based on fundamental phase angle difference. With the help of the active control strategy, this criterion can simplify the calculation procedure and coordination among different relays. To enhance the fault current amplitude of active distribution systems during the weak fault period and decrease the influence of the measurement equipment noise, this paper proposes an active protection method based on superimposed phase currents for active distribution systems. This method is shown as follows. First, the reference value of the filter inductor current of each distributed generator (DG) is set as different values when the fault intensity of the active distribution system changes. Second, the superimposed phase current in each relay is obtained by subtracting each sample of phase current from its corresponding sample of phase current in the previous cycle. Third, the fundamental phase angle of the superimposed phase current is extracted. This is because the fundamental current component of the superimposed current cannot be affected by the active control strategy, which is proved in this paper in detail. Meanwhile, the feature direction is built by fundamental phase angles at both ends of the line to detect faulty zone. Finally, the proposed protection method has been validated in a modified IEEE 13-bus test system, and the test results prove the effectiveness of the proposed active protection method that can enhance the faulty feature to detect faults. [ABSTRACT FROM AUTHOR]