Stability Improvement of Distributed Power Generation Systems with an LCL-Filter Using Gain Scheduling Based on Grid Impedance Estimations

Abstract

This paper proposes a gain scheduling method that improves the stability of grid-connected systems employing an LCL-filter. The method adjusts the current controller gain through an estimation of the grid impedance in order to reduce the resonance that occurs when using an LCL-filter to reduce switching harmonics. An LCL-filter typically has a frequency spectrum with a resonance peak. A change of the grid-impedance results in a change to the resonant frequency. Therefore an LCL-filter needs a damping method that is applicable when changing the grid impedance for stable system control. The proposed method instantaneously estimates the grid impedance and observes the resonant frequency at the same time. Consequently, the proposed method adjusts the current controller gain using a gain scheduling method in order to guarantee current controller stability when a change in the resonant frequency occurs. The effectiveness of the proposed method has been verified by simulations and experimental results.

Design of an LCL-Filter for Space Vector PWM in a Grid-Connected System

“…이러한 계통의 손상 방지를 위해 계통 전류의 고조 파 성분은 통상 IEEE-519, IEEE-1547 과 같은 규정을 준수하여야 한다 [2] . [3] . 이러한 3상 계통 연계 인버터의 SVPWM을 위한 LCL-필터 설계 …”

Review of Local Network Impedance Estimation Techniques

“…Other authors are motivated by LCL-filter resonances, a phenomenon which is difficult to mitigate in variable impedance networks [43]- [47]. It is demonstrated in [48] that network impedance estimation could help avoid filter resonance issues by retuning the current controller appropriately. [49] also utilises impedance estimations to improve stability of an LCL-filter interfaced converter by adapting the phaselocked loop (PLL) tuning accordingly.…”

Active Damping for Wind Power Systems with LCL Filters Using a DFT

“…When it is properly designed, an LCL filter is more appropriate and economical than L or LC filters, because its filter performance is better than that of L or LC filters under the same inductance conditions [5]. However, in the design of wind power systems, the LCL filter has a resonance problem [6], [7]. To reduce this resonance problem, this paper presents an active damping algorithm using a Discrete Fourier Transform (DFT).…”