New progress in low frequency harmonic detection and suppression of plasma

[ China Instrument Network Instrument Development ] Recently, the Plasma Power Supply and Control Engineering Laboratory published in the International Journal of Energy Research, "International Journal of Energy Research" entitled "A new hybrid filter based on differential current control method for low-order harmonic The research paper on suppression in Tokamak power system (DOI: 10.1002/er.3829) systematically describes the research progress in low-frequency harmonic detection and suppression.

In recent years, with the use of a large number of non-linear loads, the harmonic pollution of the power grid has become increasingly serious, the power quality of the power grid has deteriorated, and the technical requirements for the harmonic processing of power systems have become higher and higher. Low-frequency harmonics are a common problem in AC speed control systems composed of frequency converters. With the substantial increase in the power supply of the Tokamak device in the future, the low-frequency harmonic problem will become more prominent and the impact will be even worse.

For the detection of low-frequency harmonics in power systems, the currently available solutions include DFT (or FFT) based window interpolation algorithm and Prony and its extension algorithm. The interharmonics in the power system are characterized by volatility and randomness. At the same time, IEC61000-4-7 and GB/T24337-2009 are based on the stability and real-time consideration of inter-harmonic detection. The window DFT spectrum analysis method performs the measurement of interharmonics and defines the measurement time window as 10 fundamental frequency periods (ie, 200 ms), and the spectral line spacing on the spectrum is 5 Hz.

However, under the IEC framework, the detection algorithm based on DFT spectrum analysis basically fails, and Prony and its extended algorithm (extended Prony method) are based on the method of modern spectrum estimation, which is theoretically free of frequency when detecting low frequency and ultra low frequency components. The resolution is limited, but large matrix operations must be performed. It is also necessary to accurately sequence the signals. The signals of the broadband multi-frequency of the grid cannot be directly detected, which affects the real-time and stability of the algorithm. At the same time, Prony-based algorithms are very sensitive to system noise, and the errors in actual detection are large. Therefore, the prior art has many shortcomings in detecting the ultra-low frequency harmonics.

After a large number of data analysis and program investigation, the research group proposed a new hybrid scheme based on multi-reference composite vector control algorithm, which optimized the control strategy and implemented the low-voltage active filter by means of resonant injection. Technical and engineering references are available for applications at voltage levels of 10kV and above.

The study received strong support from the EAST team and collaborators and was funded by the National Natural Science Foundation.

(Source: Chinese Academy of Sciences, Baidu Encyclopedia, State Intellectual Property Office)