Control strategy optimization for energy efficiency and harmonic mitigation in multi-series converters

Abstract

To provide electrical power for the Research System of Superconducting Magnets (RSSMs) including the background field superconducting magnet and the tested superconducting objects, the high power phase-controlled converter will be used to develop the power supply system. However, because of its inner nonlinear feature, the current harmonics and the reactive power are injected into the AC power supply system. To improve the quality of the power supply system for RSSMs, an improved synchronous control strategy is suggested for the superconducting magnet power supply system, which comprises four series-connected six-pulse converters fed by a phase-shifting transformer, respectively. According to the proposed control strategy, the basic unit is two 12-pulse converters and the control method will be changed in terms of load fluctuations which are represented by the per unit value of converter output voltage. As a result, harmonic is greatly reduced but the power factor is also high.

Preliminary design of high power magnet converter for CRAFT

“…Each thyristor has an external series fast fuse for short circuit protection and an external paralleled snubber for overvoltage protection. The thyristor, fast fuse and snubber are the key devices of the converter that parameters and types are needed to be determined [12][13][14]. According to the design requirements, the thyristor junction temperature must be lower than 125 °C and the thyristor thermal accumulation is lower than the allowable value during the downstream short circuit of DC reactor, the fast fuse must be melted during the bridge short circuit and must not be melt during the downstream short circuit of the DC reactor, the snubber consisting of resistor and capacitor is needed to reduce the commutation over-voltage to be lower than half max repetitive peak forward voltage of thyristor.…”