Robust Stability Analysis of LCL Filter Based Synchronverter Under Different Grid Conditions

Abstract

Synchronverters have gained interest due to their capability of emulating synchronous machines (SMs), offering self-synchronization to the grid. Despite the simplicity of the control structure, the adoption of an LCL-filter makes the overall model complex again, posing questions regarding the tuning of the synchronverter and its robustness. The multi-inputs multioutputs (MIMO) formulation of the problem requires multivariable analysis. In this paper, the effects of control parameter and grid conditions on the stability of the system are investigated by means of structured singular values (SSV or µ-analysis). A stepby-step design procedure for the control is introduced based on a linearized small-signal model of the system. Then the design repercussions on the stability performance are evaluated through the performed robustness analysis. The developed linearized model is validated against time-domain simulations and laboratory experiments. These have been carried out using a power hardware-in-the-loop (PHIL) test bench, which allows to test the synchronverter under different grid conditions. As a conclusion the paper offers a simple guide to tune synchronverters but also a theoretical solid framework to assess the robustness of the adopted design. Index Terms-Synchronverter robust stability analysis, µanalysis, synchronverter design, power hardware-in-the-loop tests.

Design of passive power filters for battery energy storage system in grid connected and islanded modes

“…Research results reported in [13,24] shows that these limits depend on the control strategy. Indeed control methods can be mainly grouped in two major classes, namely control system with inverter-side current feedback (ICF) and with grid current feedback (GCF).…”

“…At high frequencies, Bode diagram of h(s) shows no impact of the load resistance on the magnitude of the filter output current. So the transfer function between the LCL filter output and input current (I fi and I i respectively) especially at high frequencies can be approximate by (13).…”

“…This current I fi HF is resonant at the frequency is given by (18) The resonance frequency depends on L g grid inductance which is related to grid conditions: weak or strong grid. The effect of this inductance on filter design has been investigated and reported in several works, like [11][12][13]28], where authors have also proposed a control that takes into account grid state variation.…”

“…The resonance frequency should meet border conditions expressed in (20) to avoid unexpected resonance problems [13].…”

“…In addition, as LCL filter presents an inherent resonance, proper design is of prime importance to avoid any system instability [11]. Grid impedance variation and its impact on stability system is another issue to be challenged for LCL design [12,13].…”