TUP062

Development of iterative learning and disturbance observer-based
low-level radio-frequency control system for international linear collider
F. QIU#,a),b), T. MATSUMOTOa),b), S. MICHIZONOa),b), T. MIURAa),b), N. LIUb) AND S. B.WIBOWOb)a) KEK (High Energy Accelerator Research Organization), Tsukuba 305-0801, Japanb) SOKENDAI (The Graduate University for Advanced Studies), Tsukuba, Japan

Abstract
This paper shows the development of a iterative learning control (ILC) combined with a disturbance observer (DOB)-based control for the digital
low-level radio-frequency (LLRF) system of international linear collider (ILC) project. The motivation of this study is to compensate for therepetitive (or predictable) and unpredictable disturbances in the radio-frequency (RF) system such as beam loading, Lorentz force detuning (LFD)
and microphonics. Results in a cavity simulator-based test bench demonstrate the possibility of the presented control approach. We have a plan tofurther generalize this approach to LLRF systems at superconducting test facility (STF) and future ILC project.

Introduction

DOB control• ILC project: 1.3 GHz Superconducting (SC) cavity, pulse mode operation,
400 RF stations, 10 MW multi-beam klystron (MBK).

• Disturbance observer-based (DOB) control: estimate
the disturbances at first and remove it.
-1n• LLRF system: Stabilize the RF field in the RF cavity with PI (or P) feedback
control in the presence of disturbances.

• Model-based method (inverse model G is needed).

• Disturbances source: Repetitive error (beam-loading, Lorentz force
detuning), and unpredictable error (microphonics).

• Effective in both repetitive and unpredictable errors.

-1n• QDOB is the Q-filter to make the QDOB G realizable.

-1ˆéd = QDOB ë(e + d ) GpGn - e ùû

Master Oscillator
I/Q modulator

RFDAC

Baseband IQFPGAecPre-amplifier

DAC

Fil

QDOB ( s )
Epics
IOC

LLRF
systemQDOB ( s ) Gn-1 ( s )d̂IIR filter

gate

Figure 3: DOB control with Q-filter.

RFSource

Rotation
I component

PS ripples

Q component

Power
SupplyI/Q detection
ADC

ADC

ADC

ADC

ADC

Pf (IF)Pr (IF)

Combined controller (P+DOB+ILC)

Pf (RF)

Ethernet

Pr (RF)

Pick-up n (IF)Clockdistribution

Pick-up 2 (IF)Pick-up 2 (RF)

Pick-up 1 (RF)LFD effects

Cavity #1e(k )Crymodulef (k )Microphonics
Water cooling

SWKP

ue (k )c (k )

Vaccum system

DOB Ctrl.

Figure 1: Schematic of the LLRF system and the typical disturbance sources.

u ILC(k )j +1
FFr (k )

...

Beam

Cryogenic system

QILC ( z )ILC Algorithm

Pick-up n (RF)

Cavity #2

BeamL

ej (k )

Local (LO)u ILC(k )jLearning

MemorywaveguideIntermediate Frequency (IF)...

Inv + Fil

MemorySet I/Q

Vector-sum ( Σ )RF

Gp ( s )FF I/QPI controlclockdd̂ ( k )SW

Gp- sTdedisturbancez-Lf (k )QDOB ( z )-QDOB ( z ) Gn-1 ( z )ILC algorithm• Iterative learning control (ILC): Using the error information of last pulse toimprove control signal of the current pulse.

Figure 4: Combined control algorithm including P control, ILC
algorithm and DOB control.

u j +1 ( k ) = QILC éëu j ( k ) + L ( e j ( k ) ) ùûExperiments on cavity simulator• The subscript “ j ” is iteration index, “ k ” is the time index.
• u j : Control signal, e j : Error signal.

• Simulators of beam-loading, Lorentz force detuning
and microphonics, pulse mode operation.

• QILC : Q-filter, L： Learning function.

• “P+DOB+ILC” is valid for all of these disturbances.

• Valid for the repetitive disturbances in a pulse mode machine, incapable ofunpredictable disturbances.
u j (k )Controlu0 ( k )0u1 ( k )1u j (k )jj+1ju j +1 ( k )IterationGPkSample∑

e0 ( k )e1 ( k )kSampleej (k )

LOutputj+1

y j +1 ( k )01jQILCd∑Errorej (k )

kj+1

ke j +1 ( k )∑rjIteration

Figure 2: Learning process of ILC algorithm

Figure 5: Comparison of P control (blue), “P+DOB” control (black),“P+ILC” control (green) and “P+DOB+ILC” control.