Improved secondary control for optimal total harmonic distortion compensation of parallel connected DGs in islanded microgrids

Abstract

This study proposes a two-layer hierarchical control to actualize optimal total harmonic distortion (THD) compensation in different buses of parallel-connected inverters in islanded microgrids which had not been studied so far. The proposed secondary layer is used to realize THD compensation of sensitive load bus (SLB) and make distributed generators (DGs) distribute the compensating efforts between them according to their rated capacity. It is noteworthy that improving THD at the SLB can lead to an increase in THD at local buses and/or DG terminals. Although the THD limitations of these buses are not as strict as the THD limitation of SLB, it is necessary to control them within their allowed range. This important problem is not well studied in the literature. A novel complementary part is designed and added to the secondary control to tune the compensation portion of each DG while the THD limitations in DG terminals and local buses are considered. The proposed method actualizes a multi-level voltage quality control in multi-bus islanded microgrids with parallel DGs through a simple yet effective solution. Furthermore, considering the DGs peak current limitation is added to the controller and a method for calculating this peak value is proposed.

Strategies for Controlling Microgrid Networks with Energy Storage Systems: A Review

“…A further secondary centralized control objective has been accomplished by M.H. Andishgar et al [52], in which a…”

Control method for improvement of power quality in single interlinking converter hybrid AC‐DC microgrids

“…The decentralised control method employs sources droop characteristics to achieve power sharing in the islanded operation mode [8, 10].…”

“…m ac,i is calculated as the ratio of the intended frequency variation range in the AC MG to the rated source active power and n ac,i is calculated as the ratio of intended voltage variation range in the AC MG to the rated source reactive power. This results in active and reactive power sharing between AC sources, in accordance with the rated sources power [8, 10]. It is supposed that the lines of the AC MG are dominantly inductive.…”

Cascaded controller for a standalone microgrid‐connected inverter based on triple‐action controller and particle swarm optimisation

“…In a MG, each inverter will have an external power loop, also called autonomous control, based on the droop control technique [38,39], whose purpose is to share active and reactive power among DG units and to improve the system performance. The droop function can be expressed as follows:…”

“…These variables are THD, voltage error, rate of change of voltage error, and mean square error (MSE) of voltage. PSO evaluates the minimum fitness function (F) respecting the constraints where the THD and the error voltage must not exceed 5% [38,40]. Several fitness functions were tested keeping the same restrictions/constraints mentioned, while the best results were recorded for the function (F) in (12).…”