Digital Signal Processing and Generation for a DC Current Transformer for Particle Accelerators...
-
Upload
anis-grant -
Category
Documents
-
view
222 -
download
8
Transcript of Digital Signal Processing and Generation for a DC Current Transformer for Particle Accelerators...
Digital Signal Processing and Generation for a DC Current
Transformer for Particle Accelerators
Silvia Zorzetti
Contents Introduction
Fermilab Direct-current current transformer principles
Direct Current Current Transformer (DCCT) Simulink Model Specifications and Parameters Hardware Digital implementation Open loop test Closed loop test
Introduction This activity was supported and
accomplished at Fermilab, in the Instrumentation Department of the Accelerator Division
• Main Injector (MI)
• Rapid cycling synchrotron
• 150 GeV as Injector for the Tevatron
• High intensity protons for fixed target and neutrino physics
• Recycler
• Permanent Magnetics
• 8 GeV
• Antiproton cooling before the injection into the Tevatron
• Proton storage
• Tevatron
• Superconducting synchrotron
• 980 GeV
Circular Accelerators at Fermilab
Different types of DCCTs at FNAL An analog, homebrew version was developed
at FNAL in the 80’s. Installed in all the machines, except for the Recycler Bandwidth: 2 MHz
A commercial DCCT, designed by K. Unser (Bergoz) Entire system, i.e. pickup, electronics, cables, etc. Only DC signal detection (narrow band). In 2004 the system failed due to an asymmetry of
permeability between the toroids. Temporary replaced with another commercial DCCT
from Bergoz, will finally be replaced by the “digital” DCCT that is now under development.
DCCT Introduction The DCCT is a diagnostics instrument, used to
observe the beam current. Detection of DC and low frequency components of
the beam current Non-Distructive instrument For the detection of high frequency components
the classical AC transformer is used.
Principle of Operation - AC Transformer The classical AC transformer can be used to
identify the high frequency components of the beam current
Principle of Operation of the DCCT – Single Toroid The modulator winding drives the toroid into
saturation. The total magnetic flux is shifted
proportionally to the DC current The measured DC current is proportional to
the amplitude of the 2nd harmonic detected by the detector winding
Principle of Operation of the DCCT – Double Toroids
Principle of Operation of the DCCT – Double Toroids
Complete System
Beam DCCT
Modulator 400Hz
digitally supplied
Second Harmonic detector AM
demodulator on FPGA
AC Transformer Sum and
Feedback Output
Second Harmonic Detector
Input: The input signal can be viewed as a low frequency signal modulated (in amplitude) with 800Hz
Second Harmonic Detector
CIC1: Perform the first decimation of the signal sampling frequency From 62.5MHz to 500kHz
Second Harmonic Detector
NCO: Supplies in-phase and quadrature-phase signals of same
amplitude and frequency (800Hz), for downconversion to baseband
Second Harmonic Detector
CIC2: Performs a second decimation of the sampling frequency, allows a more efficient FIR filter From 500kHz to 2kHz
Second Harmonic Detector
FIR: Defines the overall system bandwidth at baseband DC to 100Hz
Second Harmonic Detector
Some mathematics to format the signal, and adjust gain and phase There is no phase detector required, because the signal is
sufficiently slow, thus a signum detector is implemented.
DCCT Model Analytic study of the DCCT functionality Simulink Model of the complete system
(AC+DC) Toroids behaviour simulation Filter Design Feedback
Simulink Model
Simulink Model – Flux at Ib=0 (a.u.)
Simulink Model – Output Voltage at Ib=0
Simulink Model – Flux at Ib=1 (a.u.)
Simulink Model – Voltage Output at Ib=1
Simulink Model – AC + DC Closed Loop
Required Specifications and Parameters Number of turns per winding Current and Voltage to saturate the toroids DCCT Bandwidth AC Bandwidth
Parameter Space Toroids Saturation
Isat<3A , Vsat=36V, Nm=22
AC and DC Sensor windings BDC=100Hz BAC=1MHz Ns_DC=100 Ns_AC=200
Test Setup for Toroid Measurements
Output Voltage from the pick-up windings of the toroids
There is a mismatch between the voltage outputs from the two toroids. Poor matching of the core material
Complete System
VHDL Implementation – CIC
0 kM
fkf s
k
M: Differential Delay ρ: Decimation factor N: Filter Order A: Gain Notch at:
NMA )(
CIC Filter – VHDL Model
The firmware is synchronized with a single clock Integration Section Comb Section Gain Number of bits: )(log)(log 22 MNBB inout
Filters – Test Setup
VHDL Implementation and Test– CIC1
fs=62.5MHz,
fd=500kHz,
M=1 ρ=125 N=2
f1=500kHz A= 15625
VHDL Implementation and Test– CIC2
fs=500kHz,
fd=2kHz,
M=2 ρ=250 N=2
f1=1kHz A= 250000
VHDL Implementation and Test– FIR
bi: filter coefficients N: filter order (127)
FIR Filter- VHDL Model
The firmware is synchronized with a single clock Counter ROM Serial Function Number of bits
VHDL Implementation and Test- FIR
fs=2kHz,
fc=100Hz,
N=127
VHDL Impelementation and Test – AM Demodulator
With a waveform generator a low frequency signal, modulated at 800Hz is generated and digitized by the ADC
The resulting output signal is observed on an oscilloscope, connected to the DAC.
VHDL Implementation and Test- Demodulator
Input: Output:
t)fm(t)cos(2 0
)m(t
Open Loop Test Measurement Setup
DC Dectector - Output signalBefore the Transition Board - Ib=0.4A
The signal is supplied by the DCCT DC Sense
Before the transition board
There are both odd and even harmonics
DC Detector - Output Signal After the Transition Board - Ib=0.4A
The signal is supplied by the DCCT DC Sense
Passed by the Transition Board
Has only the 2nd harmonic (800 Hz), the 1st harmonic is suppressed.
Open Loop Result
Closed Loop Test Measurement Setup
Closed Loop Results
Conclusions At this stage a preliminary implementation
and test of the DCCT has been successfully realized. P control τ=0.05s Resolution 0.01A
Next steps Implementation of the AC section Faster loop control
Thank you for your attention
Silvia Zorzetti
Backup Slides
Silvia Zorzetti