1. Evolving Trends in Power Converters for Accelerators Speaker: Anirban De Accelerator Technology Group

2. Focus will be evolution in… Pulse Step Modulation Technique in Converters DSP based Controller for Power Converters Optical Fibre and Optoelectronics Applications

3. Accelerators Labs… 1870 Crookes tube 1931 Lawrence’s 13cm Cyclotron Present LHC …a Paradise for Power Converters

4. from the perspective of a Power Converter Technologist… Accelerator High Current Magnet Systems High Voltage Electrode Systems High Power Amplifier Systems

5. Illustration with a Cyclotron Injection System – Introducing the ionized beam to the central region Magnet System – Confinement of accelerated beam RF System – Beam acceleration Extraction System – Taking out the energetic beam to be used for experiments

6. What is so Critical about them? Why do we require Power Converters? Requirement: Accelerators require DC Power Sources of varied ratings – Not conventional AC power Two illustrations –K-500 SCC Beam Stability requires 1000A DC Main Magnet current not fluctuating by greater than 10 parts per million = 10mA –The Deflector Power Supply is designed for -100kV output with fluctuation < 0.005% = 5V only

7. The precision aspect was initially addressed by Linear Power Supply (LPS) Illustration: A Constant Voltage DC Regulated Power Supply AC to DC Conversion Input AC Filter Feedback & Control to Load Regulator AC to DC Conversion Input AC Filter to Load Feedback & Control Regulator Schematic Simplified Principle of regulation: dissipating excess power in the regulator

8. Merits of LPS Extremely Precise (clean) Output Voltage/Current achieved Excellent transient response Simple Mild high frequency interference due to rectifier switches Inexpensive

9. Disadvantages of LPS Continous dissipation of excess power in series regulator – Very poor efficiency < 50% Rectifier introduced multiples (1x, 2x, 6x, 12x, 24x only) of power line frequency (50/60Hz) – Cut-off frequency for a LC filter =, requires large L &/or C Input transformer supplying output power + losses, operates at 50/60 Hz – Bulky

10. Introduction of Switching Mode Power Supply (SMPS) Regulation achieved by changing duty ratio of switching

11. Merits of SMPS Loss is only during switching – Efficiency is higher Attenuation of harmonics in the range of (tens of kHz) – Filter size considerably diminishes than its LPS counterpart Output transformer operates at switching frequency – Lighter ferrite core transformer Portability increases due to decrease in size

12. Disadvantages of SMPS Increased complexity of control Increased EMI/RFI Expensive

13. Disadvantage of Topology SMPS output stage always consists of a LC These devices store energy in the form of 0.5LI 2 and 0.5CV 2 So a high voltage output at hundreds of kilovolts will force the output capacitor to store energy ~ 100s of joules In case of an internal arc in the load end, this energy will be deposited to the load, causing irreparable damage to it

14. Accelerator required Higher Power RF Amplifiers of increasing efficiency Klystron and Inductive Output Tube (IOT) was introduced – This required HV Power Supplies The voltage boosting was now not a problem – But the protection against internal tube arcing imposes a stiff criteria on response time of the crowbar

15. Solution Increase frequency to decrease capacitor value Problem Increased switching loss due to increase in frequency – Recovery time of switches becomes a constraint Inductor core fabrication at such high frequency becomes costlier Increased effect of ESL of capacitors

16. Pulse Step Modulation: A Novelty Though resonant converters, ZVS/ZCS switching were being explored but for higher voltages a novel solution came by adopting PSM Introduced by Thomson & Multimedia, Switzerland during 1980s as solid-state replacement for audio modulators in radio broadcast transmitters

17. PSM Illustration with 4 Modules Rectifier + filter of each Switched Module outputs V dc Only a single power electronic switch (IGBT) / module The modules are series connected a power diode Each module switch at the same frequency, f = 1/T Each module switching is phase shifted by T/N

18. PSM Illustration….contd Duty Cycle = 62.5%

20. PSM Illustration….contd Duty Cycle = 75%

21. PSM Illustration: Observations Compared to a single SMPS, for the same output voltage PSM output ripple magnitude is limited to V dc /N and in some cases even vanishes ideally f↑ → C↓ → lower stored energy → crowbarless operation → easier protection just by cutting off gate drive Though output frequency is Nf, each power switch is subjected to frequency f only, so no requirement of faster switches

22. PSM: Regulation Among the several philosophies that has evolved – Output regulation may be achieved by PWM modulation of all the modules at once – If MV dc is the required output (M-1) modules are kept ON continuously → Coarse modulation M th module is PWM controlled → Fine modulation – Several other techniques evolving from standard SMPS control philosophies PSM : Added advantage Inherent modularity helps in generalized design, faster production and efficient maintenance Provision of extra modules increases redundancy and decreases downtime Application became more robust

23. Implementation of control strategy in evolving Converters: A new challenge LPS Simple SMPS PSM type units Control Complexity

24. SMPS and PSM: an interesting difference with LPS In LPS, regulated output is an amplified version of the control output – Actual output linearly corresponds to bias at base-emitter junction of the regulating transistor In SMPS and PSM, regulated output is average determined by frequency and duty ratio of actual control output (ON/OFF type) – while gate of MOSFET / IGBT are switched ON and OFF the actual output depends on the relative period of ON and OFF or on the relative variation of one period with the next

25. How this may help? As the actuator signal to the power switches are binary type, a digital circuitry can be used to generate the firing pulses In that case, the logic of the firing can be computed by a microcomputer Additional support required from digital data acquisition circuits

26. Migration from Analog to Digital Govering Differential Equation Bilinear Transformed Difference Equation Present Instance Past Instance Derived from R, C & sample time Multiply and Sum/Accumulate (MAC) Data Storage (Memory) Data Conversion & Acquisition ( Fast ADC) How to Compute? (Fast & Efficient Digital Processor) Digital Realization

27. ADC Requirement: Data Acquisition Slower SamplingFaster Sampling High freq components missed in slower sampling Data Acquisition rate to be chosen so as not to miss the Highest Frequency Component of the Data @ Nyquist Rate

28. ADC: Resolution Bits ↑ → Resolution ↑ → Conversion Time ↑ →Speed ↓

29. ADC: Architecture Optimization between resolution, speed, cost 1921 Electo-opto-mechanical 5-bit Flash type 1954 Vacuum Tube system 11-bit 50ksps SAR type 1969 Semiconductor based 12-bit 10  s SAR ADC 1977 Integrated Circuits Hybrid ADC Now ADCs are integrated inside controller chips 16-bit, 18-bit, 24-bit sigma-delta, pipeline, time-interleaved, time-stretched, 12.5MSPS Microcontroller with ADC integrated

30. Evolution of Processor Technology Harvard architecture Modified Harvard & Super Harvard architecture Von Neumann architecture

31. Evolution of Digital Controller Technology to match Power Converter Requirement 8-, 16-bit  C 32-bit Digital Signal Controllers Multiprocessor DSPs Fixed Point ProcessorsFloating Point Processors 30MHz Clock150MHz Clock, single cycle instruction 16 bit Timer32 bit Timer 32 x 32 MAC, 16 x 16 Dual MAC 4 PWM channels16 PWM channels18 PWM channels Processing Power Processing Precision Processing Speed / BW Switching Power Modules Duty Cycle Precision

32. Control complexity addressed by Switching to Digital control Advantages Flexibility: Easy to configure & reconfigure by firmware Static Operation: Less prone to ageing & environmental influences. Scaling: Programme can scale to the limits of memory & storage space. Adaptive: Firmware can be made self-tuning with time. Non-linear control: Easier implementation of non-linear control algorithm. Cheap.

33. Next challenge Output @ kV → MV Regulation @ 3.3V → 1.8V Control Room Supervision @ communication level How to bridge/isolate this huge gap? Transformers can isolate AC but how to isolate DC signals that are more abundant? Solution in Optoelectronics & Fibre Optic technology

34. Basic Requirement Power Electronic Switch Mains Output Feedback Regulation and Control Isolation Field Isolation Control Room Supervision

35. Optocoupler A light source (LED) that converts input electrical signal to light Output photosensor detects the incoming light and modulates the electrical current flowing through it Electrical i/p Light Electrical o/p Linearity Problem!

36. Linearity Problem solved to some extent Photo-compensation networks inside IC gave linearity ~ 0.01%

37. Advantages if we go Digital High Current Transfer Ratio ~100% to 600% (in photo-darlington configuration / integrated driver systems) allowed its use in efficient Digital Data Transfer Voltage withstand capability ~ 10kV to 50kV and surge capability of 10kV/  s allowed extensive use in HV units Response time ~ nsec (fastest being PIN photodiode in photoconductive mode) helped in high speed applications

38. Optical fibre Light Input Light output Optical guide following the principle of total internal reflection to contain the light beam

39. Compared to electrical communication, optical communication provides advantages like… Less Signal Attenuation EMI/RFI Immunity Simple and Cheaper High Data Rate Higher Availability Complete Galvanic Isolation Higher BW Low PowerLightweight

40. Application philosophy Convert the electrical signal to optical signal by LEDs Transmit the light signal through optical link Revert back to electrical signal using optical sensors

41. Implementation Power Electronic Switch Mains Output Feedback Regulation and Control Isolation Field Isolation Control Room Supervision Linear Optocouplers Switching Optocouplers and/or Optical fibre links Optical fibre links terminated by Optocouplers

42. Summary of Evolution Power Converter Electrical Engineering Power Electronics Analog Instrumentati on Digital Control Optical Fibre Communicati on Optoelectroni cs

43. Activities of Accelerator Technology Group in These Fields Digital Controller based Dynamic Voltage Restorer (both single & three phase) for Sag Mitigation in SMES Project 1-  DVR 3-  DVR MainsLoad

44. Activities of Accelerator Technology Group in These Fields 50 x 800V, 5A PSM based Power Converter (200kW) for IOT of SCRF Linac Cavity Project

45. Activities of Accelerator Technology Group in These Fields Optical Fiber based ~1  s Crowbar Unit with Fast Acting MOSFET for High Voltage Power Supply Response Trigger

46. References http://www.wikipedia.org/ http://www.nobelprize.org Anirban De, “Power Supplies for Different Systems at VECC and their safety” http://www.kepcopower.com/fowler.htm http://www.powerqualityworld.com/2011/07/switched-mode-power-supply-smps.html http://www.engineersgarage.com/articles/smps-switched-mode-power-supply?page=2 P.J. Patel, D. P. Thakkar, L.N. Gupta, V. B. Patel, V. Tripathi, N.P.Singh and U.K. Baruah, “A Regulated Power Supply for Accelerator Driven System” http://pemclab.cn.nctu.edu.tw/peclub/w3cnotes/cn06.%E9%9B%BB%E5%8A%9B%E9%9B%BB%E5%AD%90%E7%B0%A1%E4%BB%8B/html/cn06.ht m http://pemclab.cn.nctu.edu.tw/peclub/w3cnotes/cn06.%E9%9B%BB%E5%8A%9B%E9%9B%BB%E5%AD%90%E7%B0%A1%E4%BB%8B/html/cn06.ht m J. Alex, M. Bader, J. Troxler, Thomson Broadcast & Multimedia, Turgi, Switzerland, “A NEW KLYSTRON MODULATOR FOR XFEL BASED ON PSM TECHNOLOGY”, Proceedings of PAC07, Albuquerque, New Mexico, USA Paul Scherrer Institut, “Modern and Crowbarless HVPS”, Fourth CW and High Average Power RF Workshop / May 2006 / W. Tron http://www.maxim-ic.com/app-notes/index.mvp/id/733 http://www.technologyuk.net/computing/software_development/programming_languages.shtml http://andrewharvey4.wordpress.com/2009/03/13/comp2121-wk01/ http://www.beis.de/Elektronik/DeltaSigma/DeltaSigma.html http://www.ni.com/white-paper/9078/en http://www.ti.com/product/msp430afe253 Anirban De, “Design of a Generalized and Modular Architecture for Embedded Controller for Power Supplies”, SACET09 http://www.digikey.com/us/en/techzone/lighting/resources/articles/adding-intelligence-and-flexibility.html http://computer.howstuffworks.com/fiber-optic4.htm Mohammad Towhidul Islam, “Fundamentals of Optical Fiber Systems”, North South University http://www.analog.com/library/analogDialogue/archives/39-06/Chapter%201%20Data%20Converter%20History%20F.pdf Acknowledgements Organizers, UFCYC12, Kum. Santwana Kumari, Shri M.L.V. Krishnan, Shri Samit Bandyopadhyay, Shri S.K. Thakur, Shri Subimal Saha Thank You Very Much