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Experimental Advanced Superconducting Tokamak (EAST), a National Mage project of Science Research of China, is a very important fusion experiment facility. The ability of magnetic confinement to plasma can be improved by elongating plasma cross section in EAST. However, elongated plasma has vertical displacement instability; without control, plasma will dash against a wall of vacuum vessel and disrupt, which will cause failure of plasma discharge. Therefore, a feedback control system is needed to restrain plasma vertical displacement. Fast control power supply excites active feedback coils, which produces magnetic field to control plasma's displacement. With the development of EAST, the power supply needs to keep on enhancing the ability of fast response and output current. The structure and control method of the new power supply are introduced in this paper. The technique of carrier-wave phase-shift pulsewidth modulation is applied to raise equal switch frequency of converter and improve performance of output wave. The analysis of harmonic and the simulation are carried out, the validity of the proposed scheme and control strategy are confirmed by experiments, and the power supply system can supply large current and has the ability of fast response.