Voltage Multistability and Pulse Emergency Control for Distribution System with Power Flow Reversal

TL;DR

This paper investigates voltage multistability in distribution systems with power flow reversal, demonstrating how multiple stable states can cause system transitions and proposing a pulse emergency control to restore normal operation without power interruption.

Contribution

It introduces a novel pulse emergency control strategy for reversed flow distribution systems and a new admittance homotopy power flow method for system characterization.

Findings

Multistability occurs in reversed flow distribution systems.

Pulse emergency control effectively restores normal voltage levels.

Dynamic simulations validate the proposed control strategy.

Abstract

High levels of penetration of distributed generation and aggressive reactive power compensation may result in the reversal of power flows in future distribution grids. The voltage stability of these operating conditions may be very different from the more traditional power consumption regime. This paper focused on demonstration of multistability phenomenon in radial distribution systems with reversed power flow, where multiple stable equilibria co-exist at the given set of parameters. The system may experience transitions between different equilibria after being subjected to disturbances such as short-term losses of distributed generation or transient faults. Convergence to an undesirable equilibrium places the system in an emergency or \textit{in extremis} state. Traditional emergency control schemes are not capable of restoring the system if it gets entrapped in one of the low voltage equilibria. Moreover, undervoltage load shedding may have a reverse action on the system and can induce voltage collapse. We propose a novel pulse emergency control strategy that restores the system to the normal state without any interruption of power delivery. The results are validated with dynamic simulations of IEEE $13$-bus feeder performed with SystemModeler software. The dynamic models can be also used for characterization of the solution branches via a novel approach so-called the admittance homotopy power flow method.