A New LPF-Based Grid Frequency Estimation for the SOGI Filter with Improved Harmonic Rejection

Abstract

This paper proposes a new method for the estimation of the grid voltage frequency using a low-pass filter (LPF) approach. The estimated frequency is used to tune a second order generalized integrator (SOGI) filter commonly used for grid monitoring purposes and applications requiring parameter estimation from the grid. A first-order LPF is used first for the estimation that behaves identically to the reported normalized SOGI-FLL. A second-order LPF is proposed instead to overcome this circumstance. The behavior of this approach is dynamically analyzed and a linearized model useful for design purposes is derived. The behavior of the proposed system is checked with simulations, showing that the model matches well with the real system and has a smoother transient response to step frequency perturbations and also a better rejection to harmonic distortion than previous approaches.

SOGI-FLL Grid Frequency Monitoring with an Error-Based Algorithm for a Better Response in Face of Voltage Sag and Swell Faults

“…Several approaches can be found in literature for achieving the grid parameters [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. Among them, the SOGI-FLL had become popular due to its simplicity of implementation and low computational needs.…”

“…Among them, the SOGI-FLL had become popular due to its simplicity of implementation and low computational needs. The SOGI-FLL has been widely analyzed and behaves well under grid normal conditions and even considering harmonic distortion [20,[23][24][25][26]30,33]. The SOGI can be seen as a second-order Band-Pass Filter (BPF), coupled to the FLL, which is in charge of tuning the SOGI with the grid frequency [23].…”

Three‐phase four‐wire shunt active power filter based on the SOGI filter and Lyapunov function for DC bus control

“…14 Furthermore, the classic LPF employed in PQ theory introduces a time delay and does not perfectly extract the fundamental components from the load currents at the pulsation w = 2.𝜋.𝑓 (phase shift problem), which slows the dynamic response. Several works have used the second-order generalized integrator (SOGI) filter to filter the distorted voltage and to generate orthogonal voltage components for each of the three phases, [15][16][17][18] but in this work, to overcome the inherent limitations of LPF, we consider the use of the SOGI filter as a replacement for the LPF, except that it is applied directly to the line currents and not to the PQ com-FIGURE 2 Simplified block diagram of a shunt active power filter (SAPF) highlighting the contributions of this work (in shaded gray). LP, low pass; PI, proportional-integral; SOGI, second-order generalized integrator; THD, total harmonic distortion ponents because the SOGI filter extracts only the fundamental component of any input signal without DC offset and phase shift, unlike LPF.…”