Abstract
Compared with the three-phase, two-split-capacitor active power filter (3P2C-APF), the three-phase, four-leg active power filter (3P4L-APF) has been widely used in three-phase, four-wire grid utility for power quality control due to its numerous advantages, such as higher current output capability, particularly in phase N, lower current and easier voltage control on the DC-side. However, designing the grid-connecting interface, which is between the voltage source converter (VSC) and grid utility, is rather difficult due to the higher requirement for current ripple filtering in phase N, cross-coupling in four phases and lack of relevant design methodology and specification. In this paper, a four-branch LCL-type (4B-LCL) grid-connecting interface is proposed for 3P4L-APF, which features better current ripple filtering performance without decreasing the current output capability in all phases. First, this paper describes the mathematical models of 4B-LCL in the fully-complex-vector form from the zero and non-zero sequence perspective, resulting in two independent and uniform equivalent circuits without cross coupling terms. Then, the 4B-LCL parameter design method based on the most comprehensive performance index is proposed, including three main stages as the specification: performance index requirement determination, fulfillment of that requirement, and verification. Finally, the validity and effectiveness of the proposed design are proven by the simulated and experimental results of a 3P4L-APF with 4B-LCL.
Highlights
Active power filters (APFs) can be classified into two types according to their grid connection mode: three-phase three-wire (3P3W) and three-phase four-wire (3P4W)
The power circuit of an APF consists of two main parts: a voltage source converter (VSC) and a grid-connecting interface
Based on an analysis via mathematical models for decoupling and the most comprehensive performance indexes in the proposed impedance perspective, this paper has proposed a four-branch
Summary
Active power filters (APFs) can be classified into two types according to their grid connection mode: three-phase three-wire (3P3W) and three-phase four-wire (3P4W). The former can only control power quality problems in phase A, B, and C, whereas the latter can in phase N. Because the low-voltage distribution system is commonly a 3P4W power system along with numerous unbalanced or single-phase harmonic loads, the 3P4W-APF has been more widely utilized in practical applications [1,2,3,4,5,6].
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