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Description
LLRF systems typically employ the classical PI control algorithm to maintain constant cavity voltage and phase. The performance of PI control depends on the design and optimization of the proportional (kp) and integral (ki) parameters; therefore, accurate modeling of the closed-loop path is of great importance. Loop delay is a critical parameter of the closed-loop system, as it determines the ultimate limit of the closed-loop bandwidth. The common method for measuring delay is to compare the time difference between a step input and the corresponding step output; however, this approach struggles to cover the entire loop and inevitably includes the cavity's step rise time, leading to inaccurate loop delay measurements. This paper adopts the Self-Excited Loop (SEL) control technique to identify the loop delay, based on the relationship among the SEL resonant frequency, loop phase shift, and loop delay. The loop delay identification is tested on the buncher of the Dalian Advanced Light Source (DALS). The obtained results are then used to design the PI parameters for the buncher's closed-loop control. Finally, the amplitude and phase noise of the buncher under open-loop and closed-loop conditions are compared using these PI parameters.
| Abstract Classification | System Identification |
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