Harmonic current emission of photovoltaic (PV) systems is a well-known problem. However, its quantitative characterisation, which requires the compilation and use of abundant statistical data, had never been satisfactorily dealt with. This paper discusses the multifaceted statistical characterisation of these emissions in a large PV plant. The topics addressed are harmonic current magnitude and its phase angle in relation to PV power output level and background harmonic voltages. Harmonic current emission in PV systems should be recorded during any single 1-week period throughout a full year. Because power quality metres are expensive, it is more economical to measure this type of emission with simple, cost-effective equipment. This paper thus presents a new assessment method for harmonic emission based on PV power output level, which is the main parameter affecting the emission, and which is easily monitored by most PV inverters. This new method uses statistical data to define a dependence model for the PV power output of PV harmonic current emissions. Such a model is rarely provided by PV inverter manufacturers. However, the simpler dependence model required for this method can be obtained by inexpensive power quality metres. This new method also produces accurate results at low process costs. Copyright © 2013 John Wiley & Sons, Ltd.

This paper deals with the optimal reconfiguration problem of DC distribution networks by proposing a new mixed-integer nonlinear programming (MINLP) formulation. This MINLP model focuses on minimising the power losses in the distribution lines by reformulating the classical power balance equations through a branch-to-node incidence matrix. The general algebraic modelling system (GAMS) is chosen as a solution tool, showing in tutorial form the implementation of the proposed MINLP model in a 6-nodes test feeder with 10 candidate lines. The validation of the MINLP formulation is performed in two classical 10-nodes DC test feeders. These are typically used for power flow and optimal power flow analyses. Numerical results demonstrate that power losses are reduced by about $16\%$ when the optimal reconfiguration plan is found. The numerical validations are made in the GAMS software licensed by Universidad Tecnológica de Bolívar.

This paper analyzes the power flow solution in bipolar direct current networks with radial structures considering multiple monopolar and bipolar constant power loads. The electrical configuration of the bipolar DC grid considers that the reference pole is non-grounded along the feeder, which produces important neutral currents and voltage imbalances along the DC grid. The power flow problem is formulated through the triangular-based representation of the grid topology, which generates a recursive formulation that allows determining the voltage values in the demand nodes through an iterative procedure. The linear convergence of the triangular-based power flow method is tested through multiple load variations with respect to the nominal grid operative condition. Numerical results in the 21- and the 85-bus grids reveal the relevant variations in the voltage profiles and total grid power losses when the neutral cable is solidly grounded or not.