Continuous Characterization and Closed Loop Control of the Linear Traveling-Wave Flux Pump With Asymmetric Waveforms

This paper experimentally investigates the characteristics of the linear traveling-wave flux pump by varying the rise-time to fall-time duty ratio, DC offset, and amplitude of triangular magnetization waveforms continuously over time and observing the generated current in the high-temperature superconductor (HTS) magnet. From the experimental results, the asymmetric triangle waveform is observed to have a certain rise-time duty cycle between 15% and 17% that maximizes the generated current and a threshold magnitude of 0.625 A below which no flux pumping is achieved. The results also confirm the ability of the magnitude and duty ratio of the asymmetric triangle waveform to alter the magnitude and direction of the generated current, respectively. Using these properties, a closed-loop control system is implemented in which the magnetization wave amplitude is the scaled difference between a demand current and the actual HTS current, and the duty ratio of the waveform is 1:9 or 9:1 based on the sign of the difference.