A Non-Iterative Design Method for Output LCL Filter With RC Damping in Grid-Connected Inverters
Bishal Mondal, Arun Karuppaswamy B
Abstract
A novel noniterative component selection procedure is proposed for the RC-damped LCL filter used in grid-connected inverter applications. While the primary objective of the filter is to effectively attenuate the switching frequency components of the inverter current, several other desirable constraints make the selection process challenging. Eight such constraints are identified from the existing literature for the design. Traditionally, the damping resistor (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{d}$</tex-math></inline-formula>) is considered after selecting the LCL parameters, leading to iterations as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{d}$</tex-math></inline-formula> reduces the high-frequency attenuation capability. The proposed method eliminates such iterations by incorporating <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{d}$</tex-math></inline-formula> at an earlier stage of the design, utilizing the grid-side inductance factor (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\alpha}$</tex-math></inline-formula>). The factor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\alpha}$</tex-math></inline-formula> allows a wide range of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{d}$</tex-math></inline-formula>. An analytical approach is proposed for choosing a value of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}_{d}$</tex-math></inline-formula> that makes the shunt branch highly effective at the resonance frequency, which helps minimize the filter's quality factor. Additionally, most literature employs equal values for the shunt branch capacitors. However, this article leverages the capacitor split factor (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{n}$</tex-math></inline-formula>) as an additional degree of freedom. An appropriate choice of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{n}$</tex-math></inline-formula> is used to meet multiple desirable constraints, including achieving a critically flat resonance peak. Finally, the designed filter is shown to ensure better stability of the current controller under weak grid conditions.