Research On Key Technologies Of Low-Frequency Resonance Suppression For Hybrid Filtering Device

The power supply system of fusion device converts AC power to a controllable DC voltage/current to realize plasma generation,heating and the control of plasma current,position and shape.With the increasing of Tokamak power and the complexity of the operating mode,a lot of harmonic has been generated during the operation of the AC/DC converter.Most of the characteristic hannonichas been suppressed below the standardby reactive power compensation&harmonic filter(RPC&HF).However,the non-characteristic hannonicssuch as low-order harmonics and inter-harmonics,which are often ignored in the past,have become increasingly harmful to the system.For example,during the operation of EAST device in recent years,the second-order harmonic was observed,and amplified by low-frequency oscillation between grid and reactive power compensation device.Aiming at the phenomenon of low-frequency oscillation in fusion power system,a hybrid filtering solution is proposed for resonance suppression in this paper.Additionally,the topology structure is analyzed in detail,the control strategy is deeply studied and the testing platform is developed.The feasibility of the solution provides an application reference in fusion project.The main innovations and research acitivitesare as follows:(1)Various possible methods of passive injection of active power filter(APF)are analyzed in detail.The most suitable hybrid solution based on mechanism of the resonant amplification of low-order harmonicsis extracted after comprehensive consideration of system stability,feasibility and economy.The proposed hybrid filtercan effectivelysupress the resonance of passive filters,and breakthrough the limit of high-voltage application of APF.(2)By analyzing the mathematical model functions of different control strategies,a new type of control strategy based ona compound multi-target andmulti-referencevector is proposed.This control strategy optimizes the voltage and current tracking method of the entire system,which greatly enhances the robustness of the system.(3)The applicability of traditional harmonic detection methods is deeply studied,and the shortcomings of those methods based on Fourier transform principle,coordinate space vector transformation or other adaptive algorithms are pointed out.Combined with the principle of improved finite impulse response(FIR)digital filter and proportional-resonant(PR)controller,a comprehensive harmonic detection algorithm with high precision and fast response is proposed.(4)Following the impedance frequency characteristics of the fusion power supply system in low-order band,an experimental platform of hybrid filter for resonant suppression is designed,and the effectiveness of the proposed topology,control strategy and detection method is validated.The experiments provide important applicationreference for the fusion application.