New progress in low frequency harmonic detection and suppression of plasma
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The Plasma Power Supply and Control Engineering Laboratory recently published a groundbreaking study in the *International Journal of Energy Research*, titled *"A New Hybrid Filter Based on Differential Current Control Method for Low-Order Harmonic Suppression in Tokamak Power Systems"* (DOI: 10.1002/er.3829). This paper presents a comprehensive overview of recent advancements in detecting and suppressing low-frequency harmonics, offering new insights into improving power system quality.
With the increasing use of non-linear loads, harmonic pollution has become a growing concern in power grids, leading to deteriorated power quality and higher technical demands for harmonic control. In particular, low-frequency harmonics are a common issue in AC speed control systems that rely on frequency converters. As the power supply capacity of Tokamak devices continues to grow, the problem of low-frequency harmonics is expected to become more severe, with potentially greater impacts on system stability.
Current methods for detecting low-frequency harmonics include DFT (or FFT) window interpolation algorithms and Prony-based techniques. However, interharmonics are often volatile and random, making accurate detection challenging. Standards such as IEC61000-4-7 and GB/T24337-2009 emphasize the need for stable and real-time detection, typically defining a measurement window of 10 fundamental frequency periods (i.e., 200 ms), with a spectral line spacing of 5 Hz.
Despite these approaches, traditional DFT-based methods often fail under real-world conditions, while Prony and its extensions, though more advanced, require complex matrix operations and precise signal sequencing. These limitations make them unsuitable for broadband multi-frequency signals, reducing their real-time performance and stability. Additionally, Prony-based algorithms are highly sensitive to noise, resulting in significant errors during practical implementation.
To address these challenges, the research team developed a novel hybrid approach based on a multi-reference composite vector control algorithm. This strategy optimizes control mechanisms and enables the implementation of a low-voltage active filter through resonant injection. The proposed solution provides valuable technical and engineering references for applications at voltage levels of 10kV and above.
The study was supported by the EAST team and collaborators, and it was funded by the National Natural Science Foundation of China. This research marks an important step forward in the field of power system harmonics suppression, especially for high-energy physics applications like Tokamak devices.
(Sources: Chinese Academy of Sciences, Baidu Encyclopedia, State Intellectual Property Office)