Qian, Peng and Ma, Xiandong and Liu, Guohai and Chen, Zhaoling (2018) Reducing neutral-point voltage fluctuation in NPC three-level active power filters. Electrical Engineering, 100 (2). pp. 721-732. ISSN 0948-7921
Lancaster_electrical_engineering_revised_ELEN_D_16_00971.pdf - Accepted Version
Available under License Creative Commons Attribution-NonCommercial.
Download (781kB)
Abstract
Shunt active power filters (SAPFs) have been widely used to improve power quality of the grid by mitigating harmonics injected from nonlinear loads. This paper presents a new method for improving the performance of SAPFs using neutral-point-clamped (NPC) three-level inverters. NPC three-level inverters often suffer excessive voltage fluctuations at the neutral-point of DC-link capacitors, which may damage switching devices and cause additional high harmonic distortion of the output voltage. In order to solve the problem, two compensating schemes are proposed to restrict voltage fluctuation in the inverters. The first is voltage dependent, adopting a voltage compensation method, while the second is current dependent, using a current compensation method. The paper describes the respective circuit architectures and principles of operation. Corresponding models are mathematically formulated and evaluated under typical balanced and unbalanced working load conditions. The results show that both schemes are able to alleviate considerably voltage oscillations and hence harmonic distortions, and the current-compensated NPC inverter outperforms the voltage-compensated NPC inverter. Consequently, it is shown that the proposed approaches are effective and feasible for improving power quality of the grid when connected to nonlinear loads.