Abstract
Inductive-capacitive-inductive (LCL)-type line filters are widely used in grid-connected voltage source inverters (VSIs), since they can provide substantially improved attenuation of switching harmonics in currents injected into the grid with lower cost, weight and power losses than their L-type counterparts. However, the inclusion of third order LCL network complicates the current control design regarding the system stability issues because of an inherent resonance peak which appears in the open-loop transfer function of the inverter control system near the control stability boundary. To avoid passive (resistive) resonance damping solutions, due to their additional power losses, active damping (AD) techniques are often applied with proper control algorithms in order to damp the LCL filter resonance and stabilize the system. Among these techniques, the capacitor current feedback (CCF) AD has attracted considerable attention due to its effective damping performance and simple implementation. This paper thus presents a state-of-the-art review of resonance and stability characteristics of CCF-based AD approaches for a digitally-controlled LCL filter-based grid-connected inverter taking into account the effect of computation and pulse width modulation (PWM) delays along with a detailed analysis on proper design and implementation.
Highlights
Due to the increasing emergence of power electronics-interfaced distributed generation (DG)units in modern power distribution systems, control of interfacing inverters has become a very important issue and a flexible and outstanding opportunity for robust integration of renewable energy resources-based DG units with high sustainability, as well as for overcoming the various power quality problems [1,2,3,4].In low-power applications with high switching frequency, a single inductor L is usually installed in series with the inverter output port in order to attenuate the switching harmonics of the inverter output currents
To overcome (LCL) filter is preferred to its conventional L-type counterpart due to the high attenuation of the these limitations and improve the grid current quality, the inductive-capacitive-inductive (LCL) filter is converter switching ripples and harmonics that can provide even in high-power conversion systems preferred to its conventional L-type counterpart due to the high attenuation of the converter switching with low switching frequency, of in overall size and cost of systems the filter, decrease of the filter ripples and harmonics that canreduction provide even high-power conversion with low switching power losses reduction and better dynamic
It may lead to greater susceptibility to interference risks and the lower harmonic impedance introduced to the grid [8,9,19,20,21,22,23]
Summary
Due to the increasing emergence of power electronics-interfaced distributed generation (DG). It may lead to greater susceptibility to interference risks and the lower harmonic impedance introduced to the grid [8,9,19,20,21,22,23] As a result, this third-order passive filter brings some resonance hazards at the frequency response, which reduce the efficiency and performance of the inverter system and in the worst case even leads to closed-loop system instability. The single-loop grid-side current control strategy is analyzed in the discrete-time domain, when computation and PWM delays are considered This leads to the identification of two distinct LCL filter resonant frequency regions [23,26,27], which determined when AD is needed for these systems in order to damp the resonance and retain the system stability
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