RT-LAB Real Time Simulation of Electric Drives and Systems

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					INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR 721302, DECEMBER 21-23, 2005                                                              1

                             RT-LAB Real Time Simulation
                             of Electric Drives and Systems
                                 C. Dufour, S. Abourida, Girish Nanjundaiah, Jean Bélanger

                                                                         step solvers to achieve convergence and/or accuracy.
   Abstract-- This paper presents the RT-LAB Electrical Drive               The last difficulty comes from the use of power electronic
Simulator technology along with practical applications. The RT-          switching devices running at high commutation frequencies.
LAB simulation software enables the parallel simulation of an            Emulating an IGBT motor inverter requires sub-microsecond
electrical circuit on clusters of PC running QNX or RT-Linux
                                                                         precision on the firing time. This is problematic in HIL
operating systems at sample time below 10 us. Using standard
Simulink models including SimPowerSystems models, RT-LAB                 simulation where current hardware can barely simulate the
build computation and communication tasks necessary to                   system at a 10 us time step. For power drive simulation, even
effectively make parallel simulation of electrical systems with          such a small time step requires special solvers and
low cost off-the-shelf PC technology. To accommodate the high            interpolation techniques to ensure accurate results.
bandwidth of electrical systems, the RT-LAB Electrical Drive                This paper introduces the RT-LAB Electric Engineering
Simulator comes with special Simulink-based modeling tools,
                                                                         simulator. The paper describes the hardware and software
namely ARTEMIS and RT-Events that permits real-time
simulation of electrical systems at practical time step of 10 us         solutions used with some example applications for HIL
but with sub-us equivalent precision through the use of                  simulation of electrical systems and drives.
interpolation techniques.                                                   The RT-LAB Electric Engineering simulator has been
                                                                         demonstrated to run real-time applications such as fuel cell
  Index Terms-- Hardware-In-the-Loop simulation, Motor                   hybrid vehicle[2][3][4][5], industrial PMSM drives[7], wind-
Drives, Power Electronics, Real-Time Simulation.                         turbine systems[8][9], off-highway vehicle induction motor
                                                                         drives[10],     power      system     48-pulse     STATCOM
                        I.   INTRODUCTION                                simulation[15] and even advanced topologies like matrix

A     utomatic code generation software such as Real-Time
      Workshop and Autocode has made it possible to build
very powerful real-time simulators like RT-LAB without

                                                                                   II. THE RT-LAB REAL-TIME SIMULATOR
writing any code by hand. An engineer can now go directly                   The RT-LAB simulator is designed to make the real-time
from a Simulink or SystemBuild simulation to hardware                    simulation of Simulink or SystemBuild models on clusters of
implementation with minimal debugging time. Since the                    standard Pentium-based multi-CPU PC.
introduction of real-time simulation, two major applications
have emerged: rapid prototyping of controllers and                       A. Hardware description
Hardware-in-the-Loop (HIL) testing of production-line                       Parallel simulation based on shared-memory multi-CPU
controllers. In rapid prototyping, a controller is first modeled         PCs is the most commonly used methods for real-time
in Simulink and the model is then compiled to run on a                   simulation in RT-LAB. With this configuration, one CPU can
specified target system allowing testing of the controller               hold the plant model and I/O interface while the other CPU
algorithm against a real plant. In HIL simulation testing of             can hold numerical version of the controllers for example
production-line controllers, the actual controller is tested                 Another method involves transmitting data between CPUs
against a simulated plant model running in the real-time                 on separate PC through external communication links. To
simulator.                                                               achieve this, RT-LAB uses a standard FireWire link or
      While controller rapid-prototyping is a well-established           FPGA-based communication link called SignalWire™
technique, the HIL plant simulation technique is more                    capable to deliver up to 1.25 Gbit/s transfer rates, with a
difficult to realize for electrical systems for several reasons.         latency of 200 ns or recently implemented InfiniBand
For example, electrical systems usually have a lot of working            switching fabric. With SignalWire or InfiniBand links, one
modes caused by switches. Electrical systems also tend to be             can run distributed simulations on PC-cluster at cycle times
“stiff” by nature, requiring very small time steps or variable-          of less than 10 us without data overruns.
                                                                            The same FPGA board implements useful functionalities
The authors are with Opal-RT Technologies, 1751 Richardson suite 2525,   for hardware-in-the-loop testing of electrical systems. The
Montreal, Quebec, Canada, H3K 1G6.                                       RT-LAB platform is configured to be used with a supplied
They can be contacted by email at {christian.dufour, simon.abouriba,
girish}@                                                     library of Simulink blocks that allow the user to implement
2                                                                                          NATIONAL POWER ELECTRONICS CONFERENCE, NPEC 2005

the DIO, event capture, event generation, and PWM I/O                                control effect that rises when the machine is required to
capabilities, all with 10 ns resolution, in the real-time model                      accelerates and goes negative when the machine is
without coding.                                                                      commanded to decelerate. One can notice that noise levels
   Recently, Opal-RT has introduced the capability to                                are much higher when the interpolation capability of Time
implement models directly in FPGA using the XILINX                                   Stamped Bridges is disabled. This noise indicates that IGBT
System Generator tools enabling the generation of FPGA                               switching phenomenon are not well simulated when real-time
code directly from SIMULINK block diagrams. A power                                  interpolation is not used.
electronic IGBT DC-AC motor drive system has already been                               A real-time simulator running this model has been
implemented with a model update time of 200 nanos. This                              successfully commissioned by Opal-RT for Mitsubishi
new technology will however not be discussed in this paper.                          Electric Co. of Japan in August 2004[7]. The model is
                                                                                     connected to a real external vector controller with a sampling
B. RT-LAB software toolboxes
                                                                                     rate of 55 us. The external controller reads the motor currents
The RT-LAB real-time simulator comes with a suite of                                 and the quadrature encoder signals from the simulator and
numerical solvers (ARTEMIS) and power systems models                                 feeds the simulator with the 6 IGBT gate signals. The
(Time Stamped Bridges). ARTEMIS is an add-on the
                                                                                     complete model run in this HIL mode at a sample time of 10
SimPowerSystems blockset that enables hard real-time
                                                                                     us for the CPU simulating the inverter and 80 us for the CPU
simulation. It has also built-in option for interpolation in
                                                                                     running the AC-side of the model.
current-commutated drives (diode, thyristors) [12][13] and
comes with specials models for real-time simulation like
Decoupling Distributed Parameters Lines to simulate power
systems on several CPUs. Time-Stamped Bridges (TSB)
[8][14] are interpolation-capable IGBT/MOSFET/GTO
models optimized for real-time simulation.

                         SIDE DIODE RECTIFIER
   The circuit of Fig. 1 represents a permanent magnet motor
drive fed by a 3-phase diode rectifier. The model runs under
RT-LAB on a 2.8 GHz dual-Xeon PC at sample times of 10
micros for the motor inverter and 80 micros for the diode
rectifier. The diode rectifier uses the ARTEMIS blockset,
from Opal-RT, to precompute all modes of the rectifier, thus
removing SimPowerSystems mode computation from the
real-time loop. A Time Stamped Bridge (TSB), from the RT-                                   Fig. 2. Controller Vq Iq values and motor currents with TSB

Drive blockset from Opal-RT, models the IGBT Bridge is
used to accurately compute the voltage-time application time
to the motor model. This is important because if the model
where to sample the IGBT gate signals at 10 micros without
special care, important error would occur in the motor fluxes
computation with the PWM carrier set at 9 kHz (~110 us
period, ~10 time the simulation time step).
          CPU 1: (Ts= 80 us)                CPU 2: (Ts= 10 us)

    3-phase        diode                            permanent
     source       rectifier                        magnet motor Tload

                    x6               x6

                                          IGBT                       Quadrature
                         (Fpwm =9 kHz)    pulses                   encoder signals

                                                                                          Fig. 3. Controller Vq Iq values and motor currents without TSB
                    External controller (sampling rate =55 µs)

             Fig. 1. PMSM drive with AC-side diode rectifier                              IV. FUEL CELL HYBRID ELECTRIC VEHICLE DRIVE
                                                                                       The circuit of Fig. 4 represents a fuel cell hybrid electrical
  Simulation results of the drive are shown in Fig. 2 and Fig.                       vehicle drive system composed of a battery, a fuel cell, a DC-
3 using an internal Simulink controller. For this case, the                          DC converter and PMSM motor drive [2][3][4][5]. The
speed command is varied in a square wave (10 Hz) fashion                             Proton Exchange Membrane (PEM) fuel cell model used in
between 3000 and 600 rpm. Both figure show the Iq torque
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR 721302, DECEMBER 21-23, 2005                                                                                                                                                3

this study, developed by Emmeskay Inc, is a commercially                                       preserved with the time stamped bridge while the
available control oriented model developed in the                                              uncompensated bridge causes the characteristic to have
MATLAB/Simulink environment. This is a dynamic model                                           discontinuities. It is clear that a simulator without real-time
and simulates the following thermo-electro-chemical                                            interpolation capability cannot be used to test prototype and
phenomena occurring in the fuel cell: diffusion of gaseous                                     production electronic controller in real-time
reactants to the reaction sites, electrochemical reactions,                                       The model runs under RT-LAB on a 2.8 GHz dual-Xeon
combustion product diffusion from reaction sites and heat                                      PC at sample times of 10 us. With 6 Time Stamped digital
generation.                                                                                    inputs and 5 analog outputs, the sample time rises to 17
In this system, the DC-DC converter controls the power                                         micros. The same model can executed in less than 10 micos
sharing between the battery and the fuel cell. The use of Time                                 with IOs using AMD OPTERON dual-core processors.
Stamped Bridge is mandatory to obtain accurate simulation
of the DC-DC converter because it’s chopping frequency (10                                             V. OTHER RT-LAB DRIVE SIMULATION EXAMPLES
kHz) represent only 1/10 the period of the 10 us model
sample time. Errors on IGBT gate sampling can lead to                                          A. Nine-level inverter with 13-winding three-phase
uncontrollability in the real-time simulator. To show this                                     transformer
point, the duty-cycle of the DC-DC converter has been                                             The nine-level inverter with 13-winding three-phase
scanned and the resulting inductance currents plotted in Fig.                                  transformer depicted in Fig. 6 is a high-power ultra-low
5. The figure shows that the use of Time Stamped Bridges to                                    harmonic generating inverter drive. By feeding the DC-stage
simulate the DC-DC converter with a 10 us time step (curve                                     from winding with different phases, the injected harmonics
b) produces a smooth and accurate response                                                     are minimized at the primary. Nine-level inverter also
                                                                                               provides low harmonics at the load. Time Stamped Bridges
                  10 kHz DC-DC converters            10 kHz PWM inverter                       are used to model the inverter part while a special decoupling
                                                                                               transformer models of ARTEMIS permits full mode

                           550 uH

                                                                                               precomputation of this model and achieve real-time
                                                                                               simulation at 75 us time step on a dual Xeon 2.4 GHz
                                                                              PMSM vehicle
                                                                              traction drive
                                                                                 80 kW          CPU1: 75 us                                                           CPU2: 75 us
                 Battery circuit                            Fuel cell stack
                  240 - 380 V                                240 - 400 V                                                                                                                       9 -level GTO
                                                                                                                  Phase A transformer
                                                                                                                                           Diode rectifiers                                   bridge inverter
                                                                                                                     (6 windings)

                                                                                                                                                                                                 Phase A of Load
                                                                                                                                   920 V
                                                                                                                                                              54 mF
                                                                                                                             +30 degree

                                                                                                                                  920 V                                                                    R-L load
                                                                                                 Network                                                      54 mF
                                                                                                               3000 V
                                                                                                                              +15 degree
     Fig. 4. Fuel cell hybrid electric vehicle drive circuit with numerical                      3000V L-L                        920 V
                                                                                                                                                              54 mF
                        controllers and task separation (below)
                                                                                                                               0 degree
that perfectly matches the reference results obtained with a
                                                                                                                                   920 V
very low time-step value of 1 us (r). The response has an                                                                                                     54 mF

unacceptable staircase shape when the time stamps are                                                                         -15 degree

deactivated, even at 1 us (c & g).                                                                                                                                       neutral point
                                                                                                               Phase B transformers                                             9-level GTO
                                                                                                                     -rectifier                                       phase B       bridge

                                                                                                                Phase C transformers-                                           9-level GTO
                                                                                                                      rectifiers                                      phase C bridge

                                                                                                              Fig. 6. Nine-level inverter with feeding transformer

                                                                                               B. Parallel bridge induction motor drive

Fig. 5. DC-DC converter inductance current characteristic with regards to the
                             usage of interpolation
  The results demonstrate that the small-signal linearity is
4                                                                                                                                     NATIONAL POWER ELECTRONICS CONFERENCE, NPEC 2005

     Real-time                                      IGBT inverters
                                                                                                                             demonstrated its capability to make real-time simulation of
     simulator        DC-Link model                                           transformer                                    motor drives.
            +                                                                                                                   The paper has also explained the special simulation tools
       Vdc                                                                                          Induction
    (set point)                                                                                       Motor                  developed by Opal-RT to enable real-time simulation like
                                                               6                                                             RT-Events and ARTEMIS. All the studied case had some
                                                                                                                             high frequency power converter built-in and it has been

                                                                                                    encoder signals
                                                                                                                             demonstrated that the use of interpolation technique was

                                                                                   Motor currents
                                     Chopper gate

                                                                                                    Motor speed
                                                           IGBT bridge
                                                           gate pulses
                                                                                                                             mandatory to obtain accurate results.

                                                                                                                                The RT-Events blockset and especially the Time-Stamped
                                                                                                                             Bridges models were demonstrated to provide for the
                                                External Controller
                                                                                                                             necessary accuracy to make the real-time simulation of power
                                                                                                                             systems with 2-10 kHz PWM inverters in the 10 to 50 us
                  Fig. 7. Parallel inverter induction motor drive                                                            time step range.

   A critical aspect of the parallel bridge induction motor                                                                                              VI. REFERENCES
drive of Fig. 7 is the individual firing delay between parallel                                                              [1]    RT-LAB 7.2, Opal-RT Technologies inc. 1751 Richardson, bureau
IGBT, which can cause huge current spikes in the PMSM                                                                               2525, Montreal Qc H3K 1G6
                                                                                                                             [2]    C. Dufour, J. Bélanger, T. Ishikawa, K. Uemura, “Advances in Real-
drive with AC-side diode rectifier.                                                                                                 Time Simulation of Fuel Cell Hybrid Electric Vehicles”, Proceedings
                                                                                                                                    of 21st Electric Vehicle Symposium (EVS-21), Monte Carlo, Monaco,
  C. Matrix converter drive                                                                                                         April 2-6 2005
   Recent years have seen renewed interest on matrix                                                                         [3]    T. Matsumoto, N. Watanabe, H. Sugiura, T. Ishikawa, “Development of
                                                                                                                                    Fuel-Cell Hybrid Vehicle”, The 18th International Electric Vehicle
converter based drives. Fig. 8 depicts such a drive                                                                                 Symposium, Berlin, 2001
configuration. It is composed of 18 IGBTs, MCTs or Reverse                                                                   [4]    T. Ishikawa, S. Hamaguchi, T. Shimizu, T. Yano, S. Sasaki, K. Kato,
Blocking IGBTs (RB-IGBTs), grouped in pairs in series-                                                                              M. Ando, H. Yoshida “ Development of Next Generation Fuel-cell
                                                                                                                                    Hybrid System”, Proceedings of 2004 SAE International Conference
parallel configuration with diodes (except in the case of RB-
                                                                                                                             [5]    C. Dufour, T. K. Das, S. Akella,”Real Time Simulation of Proton
IGBT). An input filter and voltage clamp circuit complete the                                                                       Exchange Membrane Fuel Cell Hybrid Vehicle”, Proceedings of the
circuit. This drive topology has some interesting                                                                                   2005 Global Powertrain Congress (GPC-05), Sept. 27-29, 2003, Ann
characteristics of it own. It has intrinsic power regeneration                                                                      Harbor, MI, USA.
                                                                                                                             [6]    C. Dufour, S. Abourida, J. Belanger, “Real-Time Simulation of Hybrid
capability.    It can have smaller mounting place than                                                                              Electric Vehicle Traction Drives”, Proceedings of the 2003 Global
conventional AC-AC converters because braking resistor or                                                                           Powertrain Congress (GPC-03), Sept. 23-25, 2003, Ann Harbor, MI,
large electrolytic capacitor are not necessary. It has low total                                                                    USA.
                                                                                                                             [7]    M. Harakawa, H. Yamasaki, T. Nagano, S. Abourida, C. Dufour and J.
harmonics of input current with high efficiency and power                                                                           Bélanger, “Real-Time Simulation of a Complete PMSM Drive at 10 us
factor. Because the matrix converter drive also has no large                                                                        Time Step”, Proceedings of the 2005 International Power Electronics
DC-bus capacitor (usually electrolytic) so it has longer                                                                            Conference (IPEC 2005) – Niigata, Japan.
                                                                                                                             [8]    C. Dufour, J. Bélanger, “A Real-Time Simulator for Doubly Fed
lifetime and is more reliable.                                                                                                      Induction Generator based Wind Turbine Applications”, Proceedings of
       Input filter                                                                                                                 IEEE 35th Power Electronics Specialists Conference (PESC 2004),
                                                     Matrix converter
                                                                                                                                    Aachen, Germany, June 20-25, 2004
                                 a                                                                                           [9]    C. Dufour, J. Bélanger, “Real-Time Simulation of Doubly Fed
                                                                                                                                    Induction Generator for Wind Turbine Applications” Proceedings of
                                                                                                                      Sawn          the 11th International Power Electronics and Motion Control
                                 b                                                                                                  Conference (EPE-PEMC 2004), Sept. 2-4 2004, Riga, Latvia
                                                     off                                                              Sawp   [10]   C. Dufour, S. Abourida, J. Bélanger, “Real-Time Simulation of
                                                                                                                                    Electrical Vehicle Motor Drives on a PC Cluster”, Proceedings of the
                                                                                                                                    10th European Conference on Power Electronics and Applications
                                                                                                      Bi-directional                (EPE-2003), Toulouse, Sept. 2-4, 2003.
                                                     u                   v       w                        switch             [11]   C. Dufour, L. Wei, T. A. Lipo, ”Real-Time Simulation of Matrix
                                                                                                                                    Converter Drives”, Proceedings of the 11th European Conference on
                                                      iu                 iv       iw                                                Power Electronics and Applications (EPE-2005), Dresden, Sept. 11-14,
                             Clamp                                                                                                  2005
                             circuit                                          Inductive                                      [12]   C. Dufour, J. Bélanger, S.Abourida, “Accurate Simulation of a 6-pulse
                                                                                load                                                Inverter with Real Time Event Compensation in ARTEMIS”,
       Power grid                                                                                                                   Proceedings of the 7th International Conference on Modeling and
                                                                                                                                    Simulation of Electrical Machine, Converters and Systems,
                              Fig. 8. Matrix converter drive                                                                        (ELECTRIMACS 2002), Montreal, Canada, August 2002
  Opal-RT has recently developed a matrix converter model                                                                    [13]   C. Dufour, J. Bélanger, “Discrete Time Compensation of Switching
with interpolation capability designed for real-time                                                                                Events for Accurate Real-Time Simulation of Power Systems”,
                                                                                                                                    Proceedings of the 27th IEEE Industrial Electronics Society Conference
simulation of matrix converter drives[11].                                                                                          (IECON'01), Nov 29-Dec 2 2001, Denver, Colorado, USA
                                                                                                                             [14]   C. Dufour, J. Bélanger, S.Abourida, “Real-Time Simulation of Onboard
                                          CONCLUSION                                                                                Generation and Distribution Power Systems”, Proceedings of the 8th
                                                                                                                                    International Conference on Modeling and Simulation of electrical
    This paper has presented the RT-LAB simulator and

     Machine, Converters and Systems, (ELECTRIMACS 2005), April 17-
     20, 2005, Hammamet, Tunisia
[15] C. Dufour, J. Bélanger, “Real-time Simulation of a 48-Pulse GTO
     STATCOM Compensated Power System on a Dual-Xeon PC using RT-
     LAB”, Proceedings of the 6th International Conference on Power
     Systems Transients (IPST-05), June 19-23, 2005, Montréal, QC,