Three-loop control scheme for high tracking precision magnet power supply used in rapid cycling synchrotron

In Rapid Cycling Synchrotron, very high tracking precision and stability is required for the magnet power supply, while the load is high order resonant network and the parameters of resonant network vary to some extent. In this paper, a three loop digital controller is studied for this application. The inner loop is the filter inductor current feedback, which aims to realize the current sharing between four choppers. The middle loop is the filter capacitor voltage close loop, which is designed to meliorate the characteristics of the plant. To improve the tracking precision, the cascaded PI+PR controller was applied to the outer magnet current loop. Meanwhile, the cascaded PI+PR controller can effectively improve the parameter-disturbance rejection capability. The proposed controller was verified in a high power Rapid Cycling Synchrotron magnet power supply. Experimental results show that the proposed controller achieves nearly 0.1% tracking precision for the DC biased 25 Hz sinusoidal references.