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CICSyN 2010 Liverpool 28 July 2010

Computational Challenges in the Simulation of Modern Electrical Power Systems Roy Crosbie California State University, Chico. CICSyN 2010 Liverpool 28 July 2010. Acknowledgements.

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CICSyN 2010 Liverpool 28 July 2010

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  1. Computational Challenges in the Simulation of Modern Electrical Power SystemsRoy CrosbieCalifornia State University, Chico CICSyN 2010 Liverpool 28 July 2010

  2. Acknowledgements The research described in this presentation is based on the work of a research team at the McLeod Institute of Simulation Sciences at California State University, Chico, USA. Team Members Richard Bednar, Professor Emeritus Roy Crosbie, Professor Emeritus and Institute Director Nari Hingorani, Visiting Research Professor Dale Word, Associate Professor, Electrical & Computer Engineering John Zenor, Professor Emeritus Financial support by the US Office of Naval Research is gratefully acknowledged CICSyN, Liverpool, 28 July 2010

  3. Conference Themes Computational Intelligence > System Modeling & Simulation Communication Systems> Real-time Simulation & Control Networks> Distributed Power System Control CICSyN, Liverpool, 28 July 2010

  4. Traditional Approach toSimulation of Power Systems • Steady State Load Flow Studies • Dynamic Simulation of Transient Behavior • Seminal Analysis by Dommel • Nodal Circuit Analysis + Implicit Trapezoidal Integration • Non-linearities require iterative procedures • Electromagnetic Transients Program (EMTP) • 50 microsecond maximum integration steps CICSyN, Liverpool, 28 July 2010

  5. Modern Power Systems • Much greater use of power converters (ac to dc & dc to ac) • High-voltage d.c. transmission • Renewable energy generation (solar, wind etc.) • Independent power systems for ships etc. CICSyN, Liverpool, 28 July 2010

  6. 23 ODEs, 12 switches, 2 PWM controllers with sine/triangle comparison PI control plus power calculations 6-pulse Back-to-Back Converter System CICSyN, Liverpool, 28 July 2010

  7. Distributed Energy System (Adel Ghandakly) WTPEC Wind Turbine Unit Integration System Monitoring & Control PowerGrid Booster Rectifier Unit Inverter Rectifier Unit Photo Voltaic Unit DSPEC PVPEC Battery Storage Unit BSPEC Load

  8. Power System for Electric Ship Questions? CICSyN, Liverpool, 28 July 2010

  9. High-Speed Real-Time Simulation Why Real-Time? Simulation running at true speed allows connection to real hardware Hardware can be tested in absence of real system Plant operators, pilots etc. can be trained under realistic conditions Why High-Speed? For many systems frame times can be tens of milliseconds or longer Systems with fast dynamics or rapid switching need shorter frames Power electronic systems often need microsecond frame times CICSyN, Liverpool, 28 July 2010

  10. Choice of Technology Many real-time simulations use a real-time version of Linux running on a high-performance PC Operating system jitter (of the order of 10 μS) limits minimum frame time Higher-performance is possible from systems with Pentium or PowerPC based processors but only with custom designs Initial solution: arrays of digital signal processors inserted in PCI bus of conventional PC with Windows OS running on host – off-the-shelf components; no problems with OS jitter CICSyN, Liverpool, 28 July 2010

  11. TS201 Board Architecture CICSyN, Liverpool, 28 July 2010

  12. DSP Issues • Scheduling Processor Tasks • Equalizing processor execution times • Minimise inter-processor data transfers • Internal Data Transfer • Common memory vs. link ports • External Data Transfer • Digital and analog outputs and inputs • Code efficiency • Hand-coding vs compiler efficiency • Identify efficient HLL code sequences CICSyN, Liverpool, 28 July 2010

  13. Software Issues • Choice of numerical integration algorithm • Euler vs Runge-Kutta vs implicit trapezoidal vs state-transition methods • Analyse and monitor accuracy and stability of numerical integration • Combine differential equations with integration algorithm before coding • Minimize total mathematical operations • Hand coding vs optimizing compiler • Hand coding may be needed if compiler can’t exploit processor architecture • Use HLL constructs that produce more efficient code CICSyN, Liverpool, 28 July 2010

  14. Real-Time Simulation with FPGA • FPGA offers competitive alternative to DSP; shorter frame times • Can be programmed using Simulink blockset, VHDL, M-code • Full 6-pulse model ported to larger FPGA • Soft processor used for slow Ethernet interface • Direct programmed high-speed Ethernet interface CICSyN, Liverpool, 28 July 2010

  15. ML506 Board CICSyN, Liverpool, 28 July 2010

  16. FPGA Performance vs DSP CICSyN, Liverpool, 28 July 2010

  17. FPGA Based Performance vs DSP CICSyN, Liverpool, 28 July 2010

  18. The Need for Multi-RateReal-Time Simulation • CSU, Chico developed HSRT simulations with frame rates up to 2 MHz (500 nS frame times) • These frame rates are needed for power electronic components but not for slower system components such as motors, mechanical components, thermal effects etc. • Multi-rate real-time simulations simulate different subsystems at different frame-rates on different simulation platforms. • The slower components are simulated in real-time using a commercial RTOS, often with Simulink support, for faster, cheaper model development. • Multi-rate also improves performance of non real-time simulations. • Multi-rate raises questions of stability and accuracy. CICSyN, Liverpool, 28 July 2010

  19. Multi-Rate Example: Unmanned Underwater Vehicle CICSyN, Liverpool, 28 July 2010 19

  20. Multi-Rate Results • Multi-Rate Configuration • Converter, Switch Controller 2 µsec • Feedback Controller 800 µsec • Motor/Propeller 50-100 µsec • Battery, Ship .1 sec • Graphics .1 sec • Multi-Rate Performance on 2.16 GHz Mac Running Windows XP • All components at 2 µsec: .001x real time • Multi-rate, Motor/Propeller 50 µsec 1.2x real-time • Multi-rate, Motor/Propeller 100µsec 2.0x real-time CICSyN, Liverpool, 28 July 2010 20

  21. UUV Effects of MultirateShip at .1sec vs .001 sec (Identical Plots) CICSyN, Liverpool, 28 July 2010 21

  22. UUV VTB 3D Model Output CICSyN, Liverpool, 28 July 2010 22

  23. Power System Control Hierarchical control combines local controllers at stations and system wide control at control centers As more and more raw data is being sent from stations to control centers communication channels are overloaded On-line real-time simulators at stations can reduce data volume through processing of raw data This can facilitate more rapid detection of critical behavior and more rapid action to minimize its effect CICSyN, Liverpool, 28 July 2010

  24. Regional Control Center Power System Communication Local Station Local Station Local Station CICSyN, Liverpool, 28 July 2010

  25. Power System ControlNetwork CICSyN, Liverpool, 28 July 2010

  26. Acknowledgement The following material is based on: Power System Stability: New Opportunities for Control By Anjan Bose Chapter in Stability and Control of Dynamical Systems and Applications, Derong Liu and Panos J. Antsakliseds http://gridstat.eecs.wsu.edu/Bose-GridComms-Overview-Chapter.pdf CICSyN, Liverpool, 28 July 2010

  27. Power System Networks: Stability CICSyN, Liverpool, 28 July 2010 Power system networks in North America & Europe are the world’s’ largest man-made interconnected networks All the rotating generators in one network rotate synchronously Any large disturbance (e.g. equipment short circuit) can make the power system unstable.

  28. Power System Networks: Control Control uses a combination of isolating switches, continuous control of voltage and power, and power-electronic switch-based control. These controls are all local (equipment/control in same substation) Regional and system-wide control is mainly limited to adjusting generation levels to adjust to slowly changing power loads CICSyN, Liverpool, 28 July 2010

  29. Power System Networks: Communication • System-wide control needs communication between contol centre and substations (microwave, telephone lines, increasing use of optical fibre) • Lower costs, increasing bandwidth, GPS time synchronization, improved power electronics offer opportunities for fast distributed controls • Increasing amount of data gathered at substations at mS rates is too voluminous for real-time transmission and control. OK for later study. CICSyN, Liverpool, 28 July 2010

  30. Power System Networks:New Technologies • Faster, cheaper computers • Embedded in equipment • Provide intelligence in the control loops • Low-cost broadband communications • Greater volume of real-time data • Possibilities for decentralizing control • Better power electronic controls • FACTS – Flexible AC Transmission Systems CICSyN, Liverpool, 28 July 2010

  31. Future Research The Goal Automatic global control for system-wide transient stability. The Need Computation to analyze the situation and compute necessary control actions, has to match the time-frame of current protection schemes (milliseconds). “Whether this is possible with today’s technology is unknown. However, the goal is to determine what kind of communication-computation structure is needed to make this feasible.” (Bose) CICSyN, Liverpool, 28 July 2010

  32. Conclusion Modern electric power systems provide research opportunities that synthesize the conference themes: computational intelligence, communication systems and networks CICSyN, Liverpool, 28 July 2010

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