• Energy Research

Abstract In this paper the optimal operation scheduling of a microgrid laboratory system consisting of a wind turbine, a solar unit, a fuel cell and two storage battery banks is formulated as an optimization problem. The proposed optimization algorithm considers the minimization of active power losses. Due to this type of variable, the problem is formulated as a Mixed-Integer Quadratic Programming model (MIQP) and solved by a deterministic optimization technique implemented in General Algebraic Modeling System (GAMS). This algorithm has been used as Virtual Power Producer (VPP) software to operate the generation units and storage system, assuring a global functioning of all equipment efficiently, taking into account the maintenance, operation and the generation measurement and control considering all involved costs. The VPP software has been implemented in a mini Supervisory Control and Data Acquisition (SCADA) system and controls the microgrid laboratory via Programmable Logic Controllers (PLC) devices. The application of this methodology to a real case study of the laboratory equipment demonstrates the effectiveness of this method for solving the optimal dispatch and online control of a microgrid, encouraging the application of this methodology for larger power systems.

Application of a simplified PV model to large-scale PV installations neglects the current distortion, potential rise and losses in the system as consequence of the capacitive coupling inside the dc electric circuit. These capacitive couplings represent a leakage impedance loop for the capacitive currents imposed by the high frequency switching performance of power converters. This paper proposes a suitable method to reproduce these harmonic currents injected not only into the grid, but also into the dc circuit of the PV installation. The capacitive coupling proposed of PV modules with ground is modeled as a parallel resistance and capacitor arrangement which leads to an accurate approximation to the real operation response of the PV installation. Results obtained are compared with those of simplified models of PV installations used in literature. An experimental validation of the proposed model was performed with field measurements obtained from an existing 1 MW PV installation. Simulation results are presented together with solutions based on the proposed model to minimize the capacitive ground current in this PV installation for meeting typical power quality regulations concerning to the harmonic distortion and safety conditions and to optimize the efficiency of the installation.

The trends of the actual distribution networks are moving toward a high penetration of distributed generation and power electronics converters. These technologies modify contribution-to-fault current magnitudes and raise concern about new protection parameters settings to accurately detect faults on distribution networks. This paper proposes a differential phase jump pilot scheme to detect faulted branches in distribution networks. The aim of the proposed scheme is to provide an efficient algorithm with functions of fault detection and isolation, which are part of the self-healing functions used for smart grids. The proposed scheme is based on the current phase jump measured in each node with fault inception. Then, by comparing the phase jump obtained with the prefault conditions and rate changes, it determines the fault direction enabling a trip signal to the corresponding nodes to isolate the branch under fault. A distribution network has been modeled in PSCAD/EMTDC program to verify the proposed algorithm, taking into account distributed generation provided by both wind turbines (doubly fed induction generator and permanent magnet generator with full converter) and solar photovoltaic installations. The behavior of the current phase jump has been studied for both generation and load nodes. This algorithm is not affected by the magnitude of current and voltage and has been tested varying fault location and resistance along the modeled distribution network.

Abstract Distributed Generation (DG) systems using power-electronics-based grid interfaces magnify the problem of ground capacitive couplings in modern distribution networks. The application of simplified models to DG installations neglects the current distortion, potential rise, and losses in the system as consequence of the capacitive coupling within the installation. These capacitive couplings represent a leakage impedance loop for the capacitive currents imposed by the high-frequency switching of power converters. This paper proposes a suitable method to reproduce this DG harmonic current injection into the distribution network. The capacitive coupling proposed for DG installation with ground is modeled as a parallel resistance and capacitor arrangement, and leads to an accurate approximation to the real operation response of the DG networks. Simulation results are presented together with solutions based on the proposed model to minimize the capacitive ground current in DG networks. Objectives include for meeting typical power quality regulations concerning harmonic distortion, improving safety, and optimizing the efficiency of the installation.