Abstract
During excitation and demagnetization phase for the superconducting magnet, in dual-active-bridge (DAB) converter based power supply, a dc bias may occur in high-frequency transformer and thus lead to the faults. In this paper, an improved transient extend-phase-shift (TEPS) control strategy is proposed to suppress the dc bias without any additional hardware. Unlike the traditional extend-phase-shift (EPS) strategy, the voltages of the transformer are asymmetrical for half a period after changing phase-shift and then remain symmetrical. This makes it take half a switching period for the current of transformer to reach the steady state, and then eliminates the dc bias. The experiment verifies the performance on dc bias suppression. This method provides a good theoretical and experimental basis for the EPS DAB DC-DC converter to realize the optimal control for excitation and demagnetization system in high-field superconducting magnet power supply (SMPS).
Highlights
With the development of life and material science, there is an increasing demand for imagining tools with high magnet field such as high-field Magnetic Resonance Imaging (MRI) and high-field Nuclear Magnetic Resonance (NMR)
This paper is organized as follows: 1) the power transmission and steady characteristics are analyzed in order to conclude the change mode of inner and outer PS ratio; 2) the transient dc bias is explained with the PS ratio changing; 3) the improvement transient control strategy method is proposed to suppress dc bias; 4) the engineering implementation and dynamic analysis are presented; 5) the comparison test is given to verify the analysis and conclusion
As the HF isolated TF iTdc is not steady current when changing the PS ratio due to symmetrical voltages, a dc bias may occur with traditional EPS control strategy, and could lead to faults
Summary
With the development of life and material science, there is an increasing demand for imagining tools with high magnet field such as high-field Magnetic Resonance Imaging (MRI) and high-field Nuclear Magnetic Resonance (NMR). A power supply based on DAB converter is designed and developed This paper is organized as follows: 1) the power transmission and steady characteristics are analyzed in order to conclude the change mode of inner and outer PS ratio; 2) the transient dc bias is explained with the PS ratio changing; 3) the improvement transient control strategy method is proposed to suppress dc bias; 4) the engineering implementation and dynamic analysis are presented; 5) the comparison test is given to verify the analysis and conclusion. We just analyze the steady characteristic and power transmission of EPS control strategy in the forward power flow. According to the principle of current iL positive and negative symmetry, those are listed in formula (2) in half a switching period
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