Virtual Impedances Optimization to Enhance Microgrid Small-Signal Stability and Reactive Power Sharing

Matti Lehtonen,Shamsodin Taheri,Edris Pouresmaeil,S Sajjad Seyedalipour,Bahram Pournazarian

doi:10.1109/access.2020.3013031

Matti Lehtonen, Shamsodin Taheri + Show 3 more

Open Access

https://doi.org/10.1109/access.2020.3013031

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Abstract

Microgrid instability poses critical issues to the power delivery following a load change or a tripping event. In island operating mode lack of grid intensifies this challenge. This study aims at controlling several converter-based distributed generations (DG) sharing the power in an island microgrid (MG). At first, the microgrid model including virtual impedances and phase-locked loop (PLL) is introduced. Afterwards a novel small-signal stability analysis for island microgrids is proposed. Finally, an optimization algorithm based on particle swarm optimization (PSO) is proposed to design the virtual impedances. The optimization algorithm analyzes all possible operating points and aims at maximizing the microgrid stability index while keeping the reactive power mismatches at minimum level. The fractional objective function facilitates reaching at these objectives simultaneously. The proposed optimization algorithm is implemented in two separate case-studies and the corresponding virtual impedances are drawn in any microgrid. On the other hand, The voltage drops are checked as a condition in the optimization process. The results drawn from two separate case-studies verify that the proposed algorithm effectively maximizes the microgrid stability index and minimizes the reactive power mismatches.

Highlights

The worldwide concern over greenhouse gas emissions and future energy resources has motivated the energy sectors towards renewable energy sources (RES)
Afterwards, a particle swarm optimization (PSO)-based optimization method is introduced which determines the virtual impedances for the converters in the MG based on the MG small-signal stability analysis and reactive power exchanges in a MG
It analyzes the small-signal stability in all different operating points to insure the microgrid stability while applying the virtual impedances

Summary

Introduction

The worldwide concern over greenhouse gas emissions and future energy resources has motivated the energy sectors towards renewable energy sources (RES). Microgrids (MGs) are critical building blocks of future power systems which facilitate the integration of RES into traditional power systems. MGs pose imperative challenges to power systems, such as the complexity of control and stability, lack of intrinsic inertia, a higher number of generating units and intermittency of prime movers. Similar to control fundamentals of traditional power systems including multiple generators [1], droop control has been deployed in MGs to imitate the power sharing regime of the machine-based power systems [2]. Active and reactive power sharing coupling in complex MGs was reported causing non-accurate power sharing [3]

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