General Small-Signal Modeling and Parameter Optimization of the Soft Normally-Open Point Connected to the Distribution Network

The soft normally-open point (SNOP) is a multi-terminal power electronic device installed between two or more feeders in the low and medium voltage distribution network, which can adjust the active power and reactive power between the feeders. A small-signal model of SNOP connected to the distribution network is established. The model includes the linearization equations of the AC system, voltage source converter, control system and internal DC system. State space is used to describe the small-signal model. The state matrix of SNOP is derived, which is not limited by the strength of AC system and the number of terminals. The objective function of control parameter optimization is established according to the characteristic roots of the state matrix. Taking a three-terminal system as an example, the characteristic roots of the state matrix are calculated and the stability of the system can be judged. The accuracy of the model is verified by the comparison of the electromagnetic transient model and the small-signal model, and the parameter optimization method is verified by the time domain simulation.