An Integrated Design Approach for LCL-Type Inverter to Improve Its Adaptation in Weak Grid

Abstract

To improve the robustness of grid-connected inverter against grid impedance in a weak grid an integrated design method of LCL-filter parameters and controller parameters is proposed. In the method the inherent relation of LCL-filter parameters and controller parameters is taken into consideration to realize their optimized match. A parameter normalization scheme is also developed to facilitate the system stability and robustness analysis. Based on the method all normalization parameters can be designed succinctly according to the required stability and robustness. Additionally, the LCL parameter and controller parameter can be achieved immediately by restoring normalization parameters. The proposed design method can guarantee the inverter stability and robustness simultaneously without needing any compensation network, additional hardware, or the complicated iterative computations which cannot be avoided for the conventional inverter design method. Simulation and experiment results have validated the superiority of the proposed inverter design method.

Magnetic integrated LLCL filter with resonant frequency above Nyquist frequency

“…Moreover, the LCL filter has a dominant switching harmonic of 0.57%, which is expected since the LCL does not have a trap in the dominant switching frequency. On the other hand, the LLCL filter performs better in the dominant switching fre-FIGURE 9 Simulation results of the grid-tied inverter with LLCL filter (a) Simulation waveforms, (b) i g spectrum quency than the LCL filter but has the largest size among all the selected filters. The total volume of cores for the filters' inductors is calculated based on the area-product method [70].…”

“…It is worth mentioning that M ig and M gi are equal and thus can be referred to as M ig . Based on (8) and (9), it is noted that the two inductors are coupling with each other. According to (8), V i and V g can finally be described as:…”

“…According to (9), the magnetic resistances determine the self and mutual inductances, which can be obtained as:…”

“…In order to address the first issue, various modified configurations of LCL filters have been presented [4][5][6][7][8][9][10][11][12][13][14][15][16]. These modified filters have additional components such as resonant LC traps connected in series or parallel, which are resonated at the switching frequency and its multiples to bypass or block the selected harmonics by these LC traps.…”

Enhancing power quality of high‐speed railway traction converters by fully integrated T‐LCL filter

“…Typically, the traction transformer (TT) leakage inductance has been used as the inductance of the grid-side converter for maximizing the utilization of the iron core while also meeting the criteria for compact size and low weight in HST equipment [11]. In [12][13][14][15][16][17][18][19][20][21][22][23], various configurations of LCLmodified filters have been presented. Many of these filters have additional LC traps, resonant tanks in series or parallel, resonated at the switching frequencies and their multiples, which allows bypassing or blocking specified harmonics via those traps.…”