Adaptive resonant current-control for active power filtering within a microgrid

Abstract

This paper presents an adaptive current-control scheme for a three-phase active-power filter (APF) for use within a microgrid. A vector-proportional-integral (VPI) controller with grid frequency tracking capabilities is used to compensate up to the 18 th harmonic in the synchronous-reference-frame. This control scheme utilizes an advanced synchronous-referenceframe phase-locked loop (SRF-PLL) to update the resonant frequency values of the current controllers to ensure the resonant frequency of the VPI remain at the optimum point regardless of changes in the grid frequency. The advanced SRF-PLL uses adaptive digital notch filters based on the adaptive lattice structure to implement an adaptive lattice SRF-PLL (ALSRF-PLL). The ALSRF-PLL is able to reject the grid voltage harmonics thus preventing the estimation of the grid frequency to be polluted, which is essential for the correct behavior of the adaptive VPI controllers. In order to validate the adaptive control structure applied to APF, experimental testing has been carried out in a 70 kVA laboratory microgrid, where a 15 kVA three phase inverter is used as the APF.

Enhancing the Frequency Adaptability of Periodic Current Controllers with a Fixed Sampling Rate for Grid-Connected Power Converters

“…Thus, feeding back the frequency estimated by an advanced PLL system [10] or frequency estimator (e.g., using Kalman filter) [13], [14] to the current controllers is a possibility to decrease the frequency sensitivity. This is much convenient for the resonant controllers [30], [31], [35], which is given as Fig. 6(a) shows the implementation of a frequency adaptive resonant controller.…”

Enhancing the frequency adaptability of periodic current controllers for grid-connected power converters

“…Thus, feeding back the frequency estimated by an advanced PLL system to the current controllers is a possibility to decrease the frequency sensitivity. This is much convenient for the resonant controllers [23]- [25], which is given as Fig. 6(a) shows the implementation of a frequency adaptive resonant controller.…”

“…either due to the PLL errors or the grid disturbances [11], [12], [22], resulting in a possibility for the feed-in current to reach the Total Harmonic Distortions (THD) limits [3]. Thus, advanced synchronizations (e.g., PLL systems) are desirable in order to ensure a reliable and satisfactory control of the grid current, and also it is essential to enhance the frequency adaptability of the periodic current controllers [13], [23]- [28].…”

Modified multifrequency resonant current controller

“…They have been applied in motor drives, 2 AC power supplies, 3 and various types of power grid connected devices 4 . In this paper, proportional‐resonant second order generalized integrator (SOGI) 5 and reduced order generalized integrator (ROGI) 4,6‐8 based AC current controllers are addressed, since they are increasingly being used, especially where devices require selective harmonic compensation 9‐13 …”

“…1 They have been applied in motor drives, 2 AC power supplies, 3 and various types of power grid connected devices. 4 In this paper, proportional-resonant second order generalized integrator (SOGI) 5 and reduced order generalized integrator (ROGI) 4,[6][7][8] based AC current controllers are addressed, since they are increasingly being used, especially where devices require selective harmonic compensation. [9][10][11][12][13] LIST OF SYMBOLS AND ABBREVIATIONS: G mf SOGI (s), novel ROGI multifrequency controller, V/V; ω cutoff , controller cutoff frequency, rad/s; h max , maximum controller harmonic term order; φ r , controller phase lag at cutoff frequency, Rad; g aw , back-propagation anti-windup controller gain, V/V; I * αβ , current reference vector, V; I αβ , current measurements vector, V; Y αβ , regulator output vector, V; Y αβL , limited regulator output vector, V; ρ, regulator output vector amplitude, V; ρ L , limited regulator output vector amplitude, V; θ, regulator output vector angle, rad; T s , sampling period, S; G VSI (s), VSI equivalent transfer function, V/V; K VSI , VSI equivalent gain, V/V; T d , VSI equivalent time delay, seconds; R, load resistance, Ω; L, load inductance, H; ω marg , controller design auxiliary frequency, rad/s; φ PM , controller phase margin, rad; G aw (z), back-propagation anti-windup transfer function, V/V; D αβ , disturbance vector, V; I * dq , current reference vector in dq reference frame, A; t r , current response rising time, seconds; t set , current response settling time, seconds; o s , current response overshoot, %.…”