.. computational challenges in the simulation of modern...

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Computational Challenges in the Computational Challenges in the Simulation of Modern Electrical Simulation of Modern Electrical

Power SystemsPower Systems

Roy CrosbieRoy CrosbieCalifornia State University, ChicoCalifornia State University, Chico

CICSyN 2010Liverpool

28 July 2010

____________________ .. ________________________________________ .. ____________________ 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 EmeritusRoy Crosbie, Professor Emeritus and Institute DirectorNari Hingorani, Visiting Research ProfessorDale Word, Associate Professor, Electrical & Computer EngineeringJohn Zenor, Professor Emeritus

Financial support by the US Office of Naval Research is gratefully acknowledged

2CICSyN, Liverpool, 28 July 2010

____________________ .. ________________________________________ .. ____________________ Conference ThemesConference Themes

• Computational Intelligence > System Modeling & Simulation

• Communication Systems> Real-time Simulation & Control

• Networks> Distributed Power System Control

CICSyN, Liverpool, 28 July 20103

____________________ .. ________________________________________ .. ____________________ Traditional Approach to

Simulation of Power Systems

A. Steady State Load Flow Studies

B. 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


____________________ .. ________________________________________ .. ____________________ Modern Power SystemsModern 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.


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23 ODEs, 12 switches, 2 PWM controllers with sine/triangle comparison PI control plus power calculations

6-pulse Back-to-Back 6-pulse Back-to-Back Converter SystemConverter System

6


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Distributed Energy System Distributed Energy System (Adel Ghandakly)(Adel Ghandakly)

Booster RectifierUnitBooster RectifierUnit

InverterRectifierUnit

InverterRectifierUnit

Battery Storage UnitBattery Storage Unit

PowerGridPowerGrid

LoadLoad

Photo Voltaic UnitPhoto Voltaic Unit

Wind Turbine UnitWind Turbine Unit

DSPECDSPEC

Integration System Monitoring & Control

WTPECWTPEC

PVPECPVPEC

BSPECBSPEC

____________________ .. ________________________________________ .. ____________________ Power System for Electric ShipPower System for Electric Ship

Questions?

8


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High-Speed Real-Time Real-Time SimulationSimulation

Why Real-Time?Simulation running at true speed allows connection to real hardwareHardware can be tested in absence of real systemPlant operators, pilots etc. can be trained under realistic conditions

Why High-Speed?For many systems frame times can be tens of milliseconds or longerSystems with fast dynamics or rapid switching need shorter frames Power electronic systems often need microsecond frame times


____________________ .. ________________________________________ .. ____________________ Choice of TechnologyChoice 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


____________________ .. ________________________________________ .. ____________________ TS201 Board ArchitectureTS201 Board Architecture


____________________ .. ________________________________________ .. ____________________ DSP IssuesDSP 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


____________________ .. ________________________________________ .. ____________________ Software IssuesSoftware 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


____________________ .. ________________________________________ .. ____________________ Real-Time Simulation with FPGAReal-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


____________________ .. ________________________________________ .. ____________________ ML506 BoardML506 Board


____________________ .. ________________________________________ .. ____________________ FPGA Performance vs DSPFPGA Performance vs DSP

Model/Platform Minimum Frame Time

Processor Clock Rate

6 Pulse BTB - Hammerhead Board, 23 ODEs

16 µs AD 21160 DSP 80Mhz

6 Pulse BTB - TigerSharc Board, 23 ODEs

3.85µs AD TS101 DSP 250Mhz





6 Pulse BTB - Xilinx ML506 Board, Virtex 5, 23 ODEs

450nS Virtex 5 FPGA 100Mhz


____________________ .. ________________________________________ .. ____________________ FPGA Based Performance vs DSPFPGA Based Performance vs DSP

Communications

Controller

Converter Left

0.398 1.622 Main Communicator Loop

1.630 Main Controller Loop

1.506 Main Converter Right Loop

1.406 Main Converter Left Loop

1.869

1.8781.757

1.7901.669

Step Size2.02us

Step Time Begins

Main Communicator Loop Begins

0.239

0.251

0.263

Start Signals Sent by Communicator

Main Controller

Loop Begins

End Signals Sent to Communicator

End Signal Received by

Communicator

Communicator Ends

Converter Right

1.990

0.121 is used to send and receive handshaking variables between that processor and the communicator.

Interrupt Handler

Main Converter Right Loop

Begins

Main Converter Left Loop Begins

This is the delay between when a new simulation frame begins and when the processor is sent handshaking variables.

0.118

0.130

0.142

.230 Converter Left Loop

Setup TimeTBDFPGA


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The Need for The Need for Multi-RateMulti-RateReal-Time SimulationReal-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.18


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Multi-Rate Example: Multi-Rate Example: Unmanned Underwater VehicleUnmanned Underwater Vehicle

19

Converter

Controller

VTB BatteryModel

Controller/Converter Model(CSU Chico)

VTB Synchronous,Permanent Magnet Motor

Model

UUV Physical Model(Glasgow)

Vehicle Control Inputs

VTB Multi-Rate Solver (USC)

Low Rate High Rate Medium Rate Low rate


____________________ .. ________________________________________ .. ____________________ Multi-Rate ResultsMulti-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


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UUV Effects of Multirate UUV Effects of Multirate Ship at .1sec vs .001 sec (Identical Plots)Ship at .1sec vs .001 sec (Identical Plots)


____________________ .. ________________________________________ .. ____________________ UUV VTB 3D Model OutputUUV VTB 3D Model Output


____________________ .. ________________________________________ .. ____________________ Power System ControlPower 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


____________________ .. ________________________________________ .. ____________________ Power System CommunicationPower System Communication

Regional Control Center

Local Station

Local Station

Local Station

CICSyN, Liverpool, 28 July 2010 24

____________________ .. ________________________________________ .. ____________________ Power System ControlNetworkPower System ControlNetwork


____________________ .. ________________________________________ .. ____________________ AcknowledgementAcknowledgement

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. Antsaklis eds

http://gridstat.eecs.wsu.edu/Bose-GridComms-Overview-Chapter.pdf


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• 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.


Power System Networks: Power System Networks: StabilityStability

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Power System Networks: Power System Networks: ControlControl

• 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


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Power System Networks: Power System Networks: CommunicationCommunication

• 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.


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Power System Networks:Power System Networks:New Technologies 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


____________________ .. ________________________________________ .. ____________________ Future ResearchFuture Research

The GoalAutomatic global control for system-wide transient stability.

The NeedComputation 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)


____________________ .. ________________________________________ .. ____________________ ConclusionConclusion

Modern electric power systems provide research opportunities that synthesize the conference themes: computational intelligence, communication systems and networks


.. computational challenges in the simulation of modern...

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____________________.. ____________________ computational challenges in the simulation of modern...

.. computational challenges in the simulation of modern...