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During the operation of Tokamak power system, a large number of low frequency harmonic currents with complex spectrum will be generated. Low-frequency resonance suppressor is an effective solution to suppress this low-frequency harmonic currents. The low-frequency harmonic suppression theory of low-frequency resonance suppressor is analyzed in this paper. Meanwhile, the state space equation of three-phase four-wire neutral-point-clamped rectifier is established in the LFRS. According to the mathematical model, the double closed-loop and zero sequence current control strategies are proposed to improve power factor operation on AC side and neutral point potential balance control on DC side of three-phase four-wire converter. The results show the correctness of the theoretical analysis and provide a technical reference for suppression of low-frequency harmonics of other Tokamak devices.

The excellent performance of synchronous phase locked technology is the basis of improving the power quality of Experimental Advanced Superconducting Tokamak (EAST) power system. The conventional synchronous reference frame phase-locked loop (SRF-PLL) with low pass filter (LPF) has a poor filter capacity for the 2nd harmonic component as the fundamental frequency fluctuation due to the high-power, high-parameter operation of the EAST. To improve accuracy of the phase estimation, adaptive notch filter (ANF) will be introduced into the LSRF-PLL to reject the disturbance of 2nd harmonic component, which can adaptively track the fluctuation of fundamental frequency with least mean square (LMS) algorithm. A novel composite algorithm of LPF and ANF SRF-PLL (LASRF-PLL) is presented to suppress the disturbance of the frequency fluctuation and harmonic pollution. At the last, the performance of the proposed LASRF-PLL is finally validated by simulation results of MATLAB software.

Tokamak power supply system generates non-stationary harmonics which tend to exhibit high power, complex spectrum and drastic change. Although the hybrid active power filter (HAPF) can effectively exclude those non-characteristic harmonics, especially in the low-frequency spectrum, it is intricate to consider low-frequency harmonic extraction, correction, overall filtering performance and stability of the system at the same time. To ensure that HAPF can adapt to complex Tokamak power supply, the mathematical function of the whole power supply system is established in this paper, and the coordinated control method containing low-frequency harmonic detection, stability correction and filtering effect analysis is proposed. The effectiveness of the control method in the whole system is simulated by PSCAD/EMTDC, and the detection method has been debugged on the DSP.

Aiming at the problem that the low-order harmonics generated by EAST poloidal field power supply is difficult to control, a new method combining active filter and passive filter is proposed. The topological structure and filtering principle of the low frequency suppression hybrid active power filter are described in detail. A three-level space voltage vector modulation algorithm for reducing the voltage fluctuation at the DC side midpoint is introduced, and the method for calculating the basic vector time is given. Combined with the algorithm, the output filter of the hybrid active power filter is simulated, and the feasibility of the low frequency suppression scheme and the effectiveness of the output filter design are verified.

The low-frequency resonance suppressor effectively reduce the low-order harmonics and resonance amplification generated by the EAST poloidal field power system during the operation. This article takes the control parameters of the three-level neutral-point clamp rectifier in the low-frequency resonance suppression device as the research object to reduce the steady-state delay of the system and to ensure the stability of the DC side voltage balance. The system model of the three-level midpoint clamp rectifier in d q rotating coordinate system is constructed to study the effect of various control parameters on the stability of the rectifier system. Furthermore, combined with variation regularity of system eigenvalue, the control parameters of the rectifier are optimized, and the anti-interference ability, dynamic performance and robustness of rectifier system are improved. Finally, the correctness and effectiveness of the control parameters optimization are verified through RT-LAB simulation.

During the operation of the nuclear fusion experiment device EAST (Experimental Advanced Superconducting Tokamak), low-frequency harmonic current with high amplitude was further resonantly amplified by the capacitive impedance in the poloidal field power supply system, which is endangering the reliable operation and power system of EAST device. A low-frequency harmonic resonance scheme is proposed in this paper to repress low-order harmonics generated by EAST poloidal field power supply. The low-frequency resonance suppressor (LFRS) based on hybrid active filter can effectively restrain the low-order harmonic current and its resonance amplification. The low-frequency harmonic suppression principle of LFRS is analyzed and the control equation of LFRS is established. Meanwhile, an active damping strategy is designed to control the resonance peak of the LCL filter and improve the overall stability of the LFRS. The results show the correctness of the theoretical analysis and provide a technical reference for suppression of low-frequency harmonics in other Tokamak devices.