Estimação de estados trifásica a quatro fios para sistemas de distribuição multiaterrados: uma abordagem considerando pseudomedidas associadas ao neutro

Abstract

Currently, there is an increasing need to monitor electrical quantities in distribution networks. However, traditional state estimation techniques cannot be directly applied to these networks due to intrinsic characteristics such as unbalanced loads, predominantly radial topology, and a limited number of meters installed along medium voltage feeders. In this complex scenario, in addition to real-time measurements, it is necessary to use supplementary information to assist in estimating the operational state of the network. Such information is referred to as pseudo-measurements and is traditionally associated with active and reactive power values obtained through historical monthly energy consumption data for each consumer. Due to the scarcity of research considering three-phase four-wire state estimation (SE) for distribution systems, this work presents a new approach to SE in multi-grounded networks. In the proposed methodology, the state variable vector consists of branch currents in rectangular coordinates, and measurements are obtained with the use of Phasor Measurement Units (PMUs) installed along radial feeders. The three-phase four-wire model is considered for network elements representing the neutral conductor and grounding impedance. An optimization problem is formulated to determine the operational state of the system based on an objective function defined by the weighted least squares concept. Pseudo-measurements related to loads are modeled by inequality constraints to compensate for the lack of real-time measurements, assuming a scenario with a scarcity of phasor meters that allow real-time monitoring. To demonstrate the effectiveness of the proposed method, simulations are conducted using the 21-bus Kersting test system and the modified 33-bus system, assuming different meter placements, load scenarios, and grounding impedances. Analyses of the impact of distributed generation on the 33-bus system are also included in the study. Additionally, the impact of increased load on neutral voltage determination and phase imbalance will be addressed to validate the effectiveness of the proposed method. A significant contribution of this work is the addition of inequalities related to the power dissipated in the neutral, aiding in the reduction of errors for all phases and allowing for the estimation of neutral-to-earth voltage (NEV) and phase imbalance, with reduced estimation errors.