Chapter 6: Real-Time Digital Time-Varying Harmonics Modeling and Simulation Techniques

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Chapter 6 Real-Time Digital Time-Varying
Harmonics Modeling and Simulation Techniques

• Contributors L-F. Pak, V. Dinavahi, G. Chang,
  M. Steurer, S. Suryanarayanan, P. Ribeiro

Organized by Task Force on Harmonics Modeling
Simulation Adapted and Presented by Paulo F
Ribeiro AMSC May 28-29, 2008
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Need for Sophisticated Tools for Power Quality
(PQ) Studies

• Proliferation of nonlinear and time-varying
  loads has led to significant power quality
  concerns.
• Traditionally, time-varying harmonics were
  studies using statistical and probabilistic
  methods for periodic harmonics.
• Cannot describe random characteristics
• Cannot capture the reality of physical
  phenomena.
• A time-dependent spectrum is needed to compute
  the local power-frequency distribution at each
  instant.
• Significant advances in equipment for PQ
  monitoring,
• waveform generation, disturbance detection, and
  mitigation.
• Digital signal processing is widely used.
• Sophisticated power electronic controllers are
  used for PQ mitigation.
• Need for testing and validation of such
  equipment.
• Real-time digital simulation as an advanced
  tool for PQ analysis and mitigation.

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Real-Time Harmonic Modeling and Simulation
Techniques

• Wave Digital Filters
• Discrete Wavelet Transform
• Real-Time Electromagnetic Transient Network
  Solution
• Real-Time Digital Simulators
• RTDS
• PC-Cluster Based Simulators
• HYPERSIM
• DSPACE

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Wave Digital Filters

• Digital Signal Processing tool that transforms
  analog networks into topologically equivalent
  digital filters
• Synthesis is based on wave network
  characterization
• Designed to attain low-sensitivity structures
  to quantization errors in digital filter
  coefficients
• Powerful technique for simulating power system
  harmonics and transients

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Discrete Wavelet Transform

• Time-Frequency representation of time varying
  signals.
• Wavelet analysis starts by adopting a prototype
  function. Time Analysis is done with a
  contracted high-frequency prototype. Frequency
  analysis is done using a dilated low- frequency
  prototype.
• Operator representation theory is used to model
  electrical componenets in discrete wavelet
  domain

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PC-Cluster Based Real-Time Digital Simulator

• Real-Time eXperimental LABoratory (RTX-LAB) at
  the University of Alberta.

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Features of the RTX-LAB Simulator

• Fully Flexible and scalable
• Fast FPGA based analog and digital I/O and high
  intra-node communication speed
• Varity of synchronization options
• Compatible with MATLAB/SIMULINK and other
  programming languages

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Hardware Architecture of the RTX-LAB Simulator

• Two types of computers- Targets and Hosts
• Targets are dual CPU based 3.0 GHZ Xeon, work as
  the main simulation engine and facilitates FPGA
  based I/Os
• Hosts are 3.00 GHZ Pentium IV, used for model
  development, compilation and loading of the model
  to the cluster

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Software Architecture of the RTX-LAB Simulator

• Target OS- RedHawk Linux
• Host OS- Windows XP
• Model Development-
• MATLAB/SIMULINK
• Other programming Languages C, C

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Communication Links in the RTX-LAB Simulator

• InfiniBand Link
• Maximum Throughput- 10Gbps
• Shared Memory
• bus speed 2.67Gbps
• Signal Wire Link
• Data Transfer rate-1.2Gbps
• Gigabit Ethernet link
• Transfer Rate- Up to 1Gbps

• I/O signals from real-hardware are connected
  through FPGA based I/Os
• Xilinx Virtex-II Pro is used
• 100 MHZ operation speed

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Subsystems and Synchronization in the RTX-LAB
Simulator
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Case Study 1 Time-Varying Harmonic Analysis on
the RTX-LAB Real-Time Digital Simulator
Single-line Diagram of the Arc Furnace
Installation
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Case Study 1 Time-Varying Harmonic Analysis on
the RTX-LAB Real-Time Digital Simulator
Schematic of the Arc Furnace Model
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Case Study 1 Time-Varying Harmonic Analysis on
the RTX-LAB Real-Time Digital Simulator
Voltage and Current for the Arc Furnace
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Case Study 1 Time-Varying Harmonic Analysis on
the RTX-LAB Real-Time Digital Simulator
Voltage at the Primary Winding of the MV/LV
Transformer
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Case Study 1 Time-Varying Harmonic Analysis on
the RTX-LAB Real-Time Digital Simulator
Current in the Primary Winding of the MV/LV
Transformer
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RTDS at CAPS

• Provides time domain solution in real time with
  typical time step sizes around 50 µs using the
  Dommel (EMTP) algorithm
• Features dual time step (lt2 µs) capability for PE
  simulations
• Allows up to 54 electrical nodes per rack, but
  subsystems can be connected through cross-rack
  elements (transmission lines, etc.)
• Large library of power system and control
  component models (like EMTDC)
• gt 350 parallel DSPs
• gt 2500 analog outputs and over 200 digital inputs
  and outputs

RPC Network Solution IRC Inter-rack
Communication
WIF Workstation Interface 3PC Controls,
system dynamics
GPC Network solution, fast-switching converters
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14 Rack RTDS Installation at CAPS

• Largest RT simulator installation in any
  university worldwide
• Systems of up to 250 three-phase buses
• Sufficient high-speed I/O to enable realistic HIL
  and PHIL experiments

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(Controller) hardware in loop (HIL) and power
hardware in loop PHIL
Simulated rest of system
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Case Study 2 Power Quality Sensitivity Study of
a Controller on the RTDS
Schematic of the Industrial Distribution System
and Rectifier Load
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Case Study 2 Power Quality Sensitivity Study of
a Controller on the RTDS
Single-phase Voltage Sag (40 reduction, no phase
shift) and its Impact on Rectifier DC Output
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Case Study 2 Power Quality Sensitivity Study of
a Controller on the RTDS
Phase-Shifted Single-phase Voltage Sag (40
reduction) and its Impact on Rectifier DC Output
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Case Study 3 Harmonic Distortion on the
RTDSShipboard Power System
Voltage (kV)
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Case Study 4 A HIL Simulation for Studying the
Transient Behavior of Wind DG
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Case Study 4 A HIL Simulation for Studying the
Transient Behavior of Wind DG
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Conclusions

• With rising number of time-varying and nonlinear
  loads sophisticated harmonics modeling and
  simulation tools are needed.
• A combination of fast topological methods and
  powerful real-time simulators can overcome
  limitations of off-line simulation tools.
• A general review of current off-line harmonic
  modeling and simulation tools is presented.
• Currently available real-time simulation
  techniques are discussed.
• Two real-time case studies arc furnace modeling
  and power quality sensitivity of a controller,
  are presented.