An active power flow control method for spot network

Abstract

Spot network, as a special low voltage secondary network, has very high supply reliability and it is beneficial for integrating Distributed Energy Resources (DERs). In the conventional spot network, all the feeders are the sole power source and provide unidirectional power to the secondary network. The equipped network protector prevents the power flow from the network to the feeder, in order to protect the feeder transformer against upstream fault. If the power among all the feeders is not balanced especially with relatively light load and amounts DERs, some of them will operate with reverse power frequently. That will result in mis-tripping of the equipped network protector. This article analyzes the relationship between the feeder power, source voltage, source impedance and the load. Theoretically the condition of reverse power is deduced. Then, a power flow control model to balance the feeder power in spot network based on Unified Power Flow Controller (UPFC) is presented. It can control the feeder power by the series compensating voltage at the secondary bus-bar. It can eliminate the reverse power and meet the demand of network protector stable operation. Meanwhile, an active voltage control method for secondary bus-bar during the re-closing procedure is also proposed, which can enhance the success rate of re-closing. Finally, a UPFC based simulation and experimental system is developed and the effectiveness of the presented control method is proved.