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Voltage multi-stability in distribution grids with power flow reversal

High levels of penetration of distributed generation and aggressive reactive power compensation with modern power electronics may result in the reversal of active and reactive power flows in future distribution grids. The voltage stability of these operating conditions may be very different from the more traditional power consumption regime. We study the stability characteristics of distribution networks with reversed power flow. After introducing a universal algebraic approach to characterize all the solutions of the power flow equations, we show that new solutions appear in the reversed power flow regime even in the simplest three bus systems. We show that the some of these solutions are stable and the system may exhibit a phenomenon of multistability, where multiple stable equilibria co-exist at the given set of parameters, and the system may converge to an undesirable equilibrium after a disturbance. These predictions are validated with dynamic simulations of two different systems. Under certain conditions the new states are viable and may be characterized by relatively high voltages. Possible approaches towards reactive power/voltage regulation as well as permissible distributed generation capacity in future power systems are proposed and discussed in the end of the paper.