High accuracy and high stability magnet power supply by four-phase buck type DC/DC converter

Linear accelerator and Beam Transfer Line magnet power supply (MPS) in Pohang Accelerator Laboratory have been upgraded from convention scheme to switching scheme for the stable beam injection and the 4^th generation light source research. New MPS consists of two-main power board (MPB), which are regulator, CPU and control power boards. The size of each board is only 100 mm times 240 mm. The MPB consists of full-bridge scheme switch. The functions of the one MPB are that they operate as two parallel buck (PB) DC/DC converter. Switching frequency is 42 kHz at MPB. Two-MPB is operated as synchronous four-PB DC/DC converter. Input and output of the MPS are 3p 35V_ac and 80A_dc/50V_dc, respectively. Its resolution and stability are 16-bit and <20 ppm, respectively. To eliminate generated switching noise from main switch, specially designed 2-stage LC output filter is adopted in output station. The 1^st-stage filter is included in the MPB. The 2^nd-stage filter is located in output stage of MPB as separated PCB. High accuracy CT for sensing of output current is located in the summing stage of synchronous four-PB type DC/DC converter. This paper describes the design concept and performance of the MPS with four-phase buck type DC/DC converter.