Benchmarking of Stability and Robustness Against Grid Impedance Variation for <italic>LCL</italic> -Filtered Grid-Interfacing Inverters

Abstract

This paper comprehensively analyzes the stability of a grid-interfacing inverter with LCL-filter in the discrete domain, where the LCL-filter, along with the controller, are modeled in a polar coordinate. System open-loop and closed-loop poles are analytically studied and expressed in the z-domain.Through the poles movement and distribution analysis, the relationship between system stability and the ratio of resonance frequency over sampling frequency is mathematically revealed and calculated as well as the system control gain limit. Moreover, this paper demonstrates that grid-voltage feedforward regulator would significantly alter the inverter stability in a weak power system. By means of Jury stability criterion, the stability status under different filter resonance frequency is given. The selection of resonance frequency and filter parameters makes a considerable difference on system behavior. Finally, to improve the robustness against grid inductance variation, a conservative design recommendation of filter parameters and control gain is given. Through the tests on a laboratory-scale prototype, the theoretical analysis is validated by experimental results.

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

“…The expression of h(s), derived from (12) and 13is presented by (14) Relation (14) shows that the attenuation of the output filter current compared to the input filter current depends on grid side inductance L f2 and not on the converter side inductance. This relation expresses the main constraint for grid-side inductance design.…”

“…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.…”

“…In the traditional design of the LCL Filter method as developed in [11][12][13][14][15][16][17], the grid connected mode is usually adopted since the filters are sized to protect the grid against harmonics. For this reason the traditional design methods of the LCL filter present good performances and meet the grid code requirements in terms of harmonic injections and THDs.…”

“…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].…”

Low-Loss Active Grid Impedance Cancellation in Grid-Connected Inverters with LCL Filter

“…A well-known method is to utilize the PCC voltage feedforward control to ease such dynamic interaction between inverters and the grid and improve the power quality of the inverter. However, it has been proven that the unit PCC voltage feedforward control method weakens the inverter stability due to the effect of digital delay [29]. Therefore, the PCC voltage feedforward control method with reduced digital delay is studied to cancel the negative real part of the inverter output admittance according to passivity-based stability approach [30].…”