Abstract
A disturbance observer (DOB)-based control for a digital low-level radio-frequency (LLRF) system in a compact energy recovery linac (cERL) at KEK has been developed. The motivation for this control approach is to compensate for or suppress the disturbance signal in the rf system such as beam loading, power supply ripples, and microphonics. Disturbance signals in specified frequency ranges were observed and reconstructed accurately in the field-programmable gate array and were then removed in the feedforward model in real time. The key component in this DOB controller is a disturbance observer, which includes the inverse mathematical model of the rf plant. In this paper, we have designed a DOB control-based approach in order to improve the LLRF system performance in disturbance rejection. We have confirmed this approach in the cERL beam commissioning.
Highlights
In KEK, a compact energy recovery linac, which is a test facility for future 3 GeV ERL accelerators, was constructed [1,2]
We may need modern system identification for a complex system model that includes high-order dynamic behavior. Disturbances such as microphonics, power-supply ripples, and beam loading often exist in level radio-frequency (LLRF) systems
An application of a disturbance observer-based control for superconducting radio-frequency (SCRF) cavity regulation is presented in this paper
Summary
In KEK, a compact energy recovery linac (cERL), which is a test facility for future 3 GeV ERL accelerators, was constructed [1,2]. Owing to the existence of the loop delay, the FB gains cannot be increased beyond certain limits In view of this situation, a disturbance observer-based (DOB) control is a promising approach for suppressing the disturbances [9,10,11,12,13,14,15,16,17,18,19,20]. In the cERL beam commissioning, we have successfully suppressed disturbances such as the 300 Hz power supply ripples, the 1 mA, 1.6 ms beam loading, and the microphonics by applying this proposed DOB approach. This paper focuses on the principle, design, and implementation of the DOB control approach mentioned above The improvement of this DOB-based application at cERL in terms of regulation performance is presented as well.
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