Planning of Distributed Energy Storage Systems in μGrids Accounting for Voltage Dips

Abstract

This paper deals with the optimal planning of the electrical energy storage systems in the microgrids aimed at cost minimization. The optimization accounts for the compensation of the voltage dips performed by the energy storage systems. A multi-step procedure, at the first step, identifies a set of candidate buses where the installation of a storage device produces the maximum benefit in terms of dip compensation; then, the life cycle costs in correspondence of different alternatives in terms of size and location of the storage systems are evaluated by considering an optimized use of the energy storage systems. The simulations on a medium voltage microgrid allowed validating the effectiveness of the proposed procedure.

A Closed-form Expression to Estimate the Uncertainty of THD Starting from the LPIT Accuracy Class

“…The reader must be aware that Equations (21) and (22) are estimates of the THD distribution parameters that are valid under the assumption made in this section. In what follows, the validity of such expressions is numerically proven using several case studies.…”

“…To this purpose, the case study introduced in Section 3 has been applied with some modifications: (i) the uncertainty associated to the harmonic has been kept as defined in Table 2 for each accuracy class; (ii) the amplitude of each single harmonic has been fixed to 5%, 2%, and 0.5% of the 50 Hz component, resulting in three different group of tests. Then, 1 million trials have been run to compare the reference values with those obtained applying (21) and (22). Results are collected in Tables 7-9, for the cases at 5%, 2%, and 0.5%, respectively.…”

“…Turning to the effects of PQ on the network, it is well documented that a low level of PQ may compromise the operation of the network and of its assets. For example, voltage dips effects have been discussed for wind turbines and storage systems in [20] and [21], respectively. In [22][23][24][25][26], techniques to mitigate the effects of harmonics and to improve PQ for converters/inverters have been presented.…”

“…It contains, for the three signals and for each accuracy class (AC), the mean value, variance, and standard deviation of THD, estimated by the closed-form expression (µ THD_e , σ 2 THD_e , and σ THD_e ) and the reference provided by the MC simulations (µ THD_c , σ 2 THD_c , and σ THD_c ). Before assessing the results, in Table 3 and in the following the standard deviations σ THD_c and σ THD_e are written with two significant digits to highlight the really small difference (if any) between the references and the results of Equations (21) and (22). Of course, the proper way of representing a standard deviation would have been with one significant digit.…”

“…A final comment on Table 3 is that the effectiveness of Equations (21) and 22is not affected by the harmonic content of the signal.…”