1,425 research outputs found
Optimal Power Flow with Step-Voltage Regulators in Multi-Phase Distribution Networks
This paper develops a branch-flow based optimal power flow (OPF) problem for
multi-phase distribution networks that allows for tap selection of wye,
closed-delta, and open-delta step-voltage regulators (SVRs). SVRs are assumed
ideal and their taps are represented by continuous decision variables. To
tackle the non-linearity, the branch-flow semidefinite programming framework of
traditional OPF is expanded to accommodate SVR edges. Three types of
non-convexity are addressed: (a) rank-1 constraints on non-SVR edges, (b)
nonlinear equality constraints on SVR power flows and taps, and (c) trilinear
equalities on SVR voltages and taps. Leveraging a practical phase-separation
assumption on the SVR secondary voltage, novel McCormick relaxations are
provided for (c) and certain rank-1 constraints of (a), while dropping the
rest. A linear relaxation based on conservation of power is used in place of
(b). Numerical simulations on standard distribution test feeders corroborate
the merits of the proposed convex formulation.Comment: This manuscript has been submitted to IEEE Transactions on Power
System
Real-Time Local Volt/VAR Control Under External Disturbances with High PV Penetration
Volt/var control (VVC) of smart PV inverter is becoming one of the most
popular solutions to address the voltage challenges associated with high PV
penetration. This work focuses on the local droop VVC recommended by the grid
integration standards IEEE1547, rule21 and addresses their major challenges
i.e. appropriate parameters selection under changing conditions, and the
control being vulnerable to instability (or voltage oscillations) and
significant steady state error (SSE). This is achieved by proposing a two-layer
local real-time adaptive VVC that has two major features i.e. a) it is able to
ensure both low SSE and control stability simultaneously without compromising
either, and b) it dynamically adapts its parameters to ensure good performance
in a wide range of external disturbances such as sudden cloud cover, cloud
intermittency, and substation voltage changes. A theoretical analysis and
convergence proof of the proposed control is also discussed. The proposed
control is implementation friendly as it fits well within the integration
standard framework and depends only on the local bus information. The
performance is compared with the existing droop VVC methods in several
scenarios on a large unbalanced 3-phase feeder with detailed secondary side
modeling.Comment: IEEE Transactions on Smart Grid, 201
NOVEL OPTIMAL COORDINATED VOLTAGE CONTROL FOR DISTRIBUTION NETWORKS USING DIFFERENTIAL EVOLUTION TECHNIQUE
This paper investigates a Distributed Generators (DG) connected to distribution networks offer multiple benefits for power networks and environments in the case of renewable sources. Nevertheless, if there is not an appropriate planning and control strategy, several issues, such as voltage rise problems and increased power losses, may happen. In order to overcome such disadvantages, in this paper, a coordinated voltage control method for distribution networks with multiple distributed generators is proposed. This method is based on a differential evolution DE approach to obtain the optimal setting points for each control component. Furthermore this proposed method considers both of time-varying load demand and production, leading to not only an improvement in the voltage profile but also to optimally minimize the active power loss
Improving the Performance of Low Voltage Networks by an Optimized Unbalance Operation of Three-Phase Distributed Generators
This work focuses on using the full potential of PV inverters in order to improve the efficiency of low voltage networks. More specifically, the independent per-phase control capability of PV three-phase four-wire inverters, which are able to inject different active and reactive powers in each phase, in order to reduce the system phase unbalance is considered. This new operational procedure is analyzed by raising an optimization problem which uses a very accurate modelling of European low voltage networks. The paper includes a comprehensive quantitative comparison of the proposed strategy with two state-of-the-art methodologies to highlight the obtained benefits. The achieved results evidence that the proposed independent per-phase control of three-phase PV inverters improves considerably the network performance contributing to increase the penetration of renewable energy sources.Ministerio de Economía y Competitividad ENE2017-84813-R, ENE2014-54115-
Voltage and Reactive Power Control in Islanded Microgrids
Previous studies put on view lots of advantages and concerns for islanded microgrids (IMGs), whether it is initiated for emergency, intentionally planned or permanent island system purposes. From the concerns that have not been addressed yet, such as: 1) The ability of the distributed generation (DG) units to maintain equal reactive power sharing in a distribution system; 2) The ability of the DG units to maintain acceptable voltage boundary in the entire IMG; 3) The functionality of the existing voltage and reactive power (Volt/Var) DG, this thesis analyzes the complexity of voltage regulations in droop-controlled IMGs. A new multi-agent algorithm is proposed to satisfy the reactive power sharing and the voltage regulation requirements of IMGs. Also, the operation conflicts between DG units and Volt/Var controllers, such as shunt capacitors (SCs) and load-ratio control transformer (LRT) during the IMG mode of operation, are investigated in this thesis. Further, a new local control scheme for SCs and LRTs has been proposed to mitigate their operational challenges in IMGs
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