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

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 focuses on the demonstration of multistability phenomenon in radial distribution systems with reversed power flow where multiple stable equilibria coexist for 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 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 also be used for characterization of the solution branches via a novel approach, so-called the admittance homotopy power flow method.