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The SSRF Elliptically Polarized Undulator (EPU) has been in operation for about three years. The feed-forward control algorithm of correction coil power supply (CCPS) is implemented in the Input and Output Controller (IOC) based on VME. The correction current responds not fast enough to gap movement, mainly because the communication between IOC and digital CCPS taking up much time. This paper introduces one new feed-forward design, that is ,on the one hand, the CCPS current responds to both gap movement and shift movement according to 2D Look-up Table(LUT) by linear interpolation method. On the other hand, feed-forward control algorithm is carried out in the EPU controller, and the CCPS with fast control response is directly controlled by PLC through analog interface. Thus, the correction current respond well to gap and shift movement owing to leaving out communication time.
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