2008 - A PC-based Hardware-In-the-Loop Simulator for the Integration Testing of Modern Train and Ship Propulsion Systems.pdf

8/12/2019 2008 - A PC-based Hardware-In-the-Loop Simulator for the Integration Testing of Modern Train and Ship Propulsion

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A PC-based Hardware-In-the-Loop Simulatorfor the Integration Testing of

Modern Train and Ship Propulsion SystemsChristian Dufour, Guillaume Dumur, Jean-Nicolas Paquin, Jean Blanger

Opal-RT Technologies, 1751 Richardson, suite 2525, Montreal, Canada

Abstract - Today, the development and integration of train and ship controllers is a more difficult task than ever.Emergence of high-power switching devices has enabled thedevelopment of new solutions with improved controllabilityand efficiency. It has also increased the necessity for morestringent test and integration capabilities since these newtopologies come with less design experience on the part of the system designers. To address this issue, a real-timesimulator can be a very useful tool to test, validate andintegrate the various subsystems of modern rail vehicledevices. This paper presents such a real-time simulator,based on commercial-off-the-shelf PC technology, suitablefor the simulation of train and ship propulsion devices.

The requirements for rail/water vehicle test andintegration reaches several levels on the control hierarchyfrom low-level power electronic converters used forpropulsion and auxiliary systems to high-level supervisorycontrols. This paper places great emphasis on the real-timesimulation of several high-power drives used for train andship propulsion, including a multi-induction machine drive,

a three-level GTO - PMSM drive and a high-powerthyristor-based converter - synchronous machine drive. Allmodels are designed first with the SimPowerSystemsblockset and then automatically compiled and run oncommercial PCs under RT-LAB. Interfaces to I/O are alsomade at the Simulink model level without any low-levelcoding required by the user. Supervisory control integrationand testing can also be made using the RT-LAB real-timesimulator.

The other objective of this paper is to demonstrate thatHIL testing of complex drives, such as the those found ontrains, can be done using commercial-off-the-shelf (COTS)software and hardware and model-based design techniquesthat only require high-level system models suitable for

system specifications down to controller test and finalsystem integration.

I. I NTRODUCTION

The integration, test and verification of modern trainand ship systems represent a serious challenge. Currently,

because of the risks involved, it is not conceivable tointegrate these kinds of systems with direct subsysteminterconnection.

Modern design approaches mitigate these risks throughthe extensive use of technologies like Hardware-In-the-Loop (HIL) simulation. HIL simulation technologiesenable more gradual integration, while diminishing therisk and costs of such projects. Also, more elaborate testcoverage can be conducted than is possible using analog

prototypes because of the safety operational limits of realdevices.

Model-based design is an approach that puts the systemmodel at the center of the design process[7]. With thisapproach, the specification, controller prototype design,coding and integration tests are based on a set of referencemodels. At the integration stage, this approach makesextensive use of HIL simulators, with a number of objectives that are directly related to the control hierarchyof the complete train system. The control hierarchy of atrain system is given in Figure 1.

Figure 1 Train control hierarchy

A. Individual Train Actuators and Circuits ControllersTests:

The first stage of HIL controller test is to individuallyverify the controllers. At this stage, a detailed model of thesubsystem is used to which the controller under test isattached, while a simplified model is made of the rest of the system. Two types of tests are then conducted:

1) Open-loop tests: this kind of test is used to verifythe functionality of the I/O of the controller by simpleexcitation/monitoring of the I/Os. It is also used to verifythe behavior of the controller in case of short-circuit of theI/Os. In this last case, the controller should detect suchconditions and output proper code to the supervisorycontroller.

2) Closed-loop tests: controller behavior is testedfor its control action on the power devices. The controller is connected to the HIL-simulated power devices in theexact same manner as the real device (IGBT gate signals,current sensors, etc.) For example, the

acceleration/deceleration behavior of the inductiontraction units [4] can be tested with a simplified DC-link model.

978-1-4244-1668-4/08/$25.00 2008 IEEE


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B. Multi-subsystem Integration Tests:The different subsystems (generation, propulsion,

auxiliary) are electrically connected and may thereforeinteract with each other. Consequently, the next stage oftest/integration is to verify the functionality of thecontrollers with all system interactions. Basic Supervisory

control law can be tested at this stage. The scalability ofthe simulator is very important in this regard[8].

C. Main Supervisory Control Tests:The main supervisory control algorithm is tested at this

stage. This includes testing in normal conditions with ahuman operator command (start and accelerate, stoppingthe train) and in abnormal conditions (communication busfault or electric fault).

D. User Control Tests:The real-time simulator can be used to verify the

overall conductibility of the train by a human operator, in

normal and faulty modes, as well as for operator training.At this point, the user graphical interface becomesimportant because the human operators I/Os are mainlytheir eyes and hands.

II. C HALLENGES AND SOLUTIONS IN R EAL -TIMESIMULATION OF COMPLEX ELECTRIC DRIVES

There are several challenges to achieve real-timesimulation of large electric drives. The global challenge isto obtain good accuracy using fixed time step solvers andmethods. Furthermore, the calculation time of all timesteps must always be kept under a prescribed value to

enable HIL interface of the simulator with externalequipment or controllers. The last challenge consists offinding the right simulation platform.

Challenge 1) Keeping the accuracy of simulation withhigh-frequency power converter.

Given that the simulator is a sampled system, theaccuracy of simulation of high-frequency PWM invertermay be compromised if the ratio of simulator samplingfrequency to the PWM frequency is too low.Interpolation-capable inverter models are the solution tothis problem. These inverter models are part of theRTeDRIVE[5] package from Opal-RT Technologies. Thischallenge notably exists in the Three-Level GTO-InverterPMSM Drive of section IV.A.

Challenge 2) Keeping the calculation time of all timesteps almost constant to achieve HIL.

The SimPowerSystems default solver takes more timeto iterate whenever a switch changes position because itrecalculates circuit mode on-line. The ARTEMIS plug-infor SimPowerSystems makes pre-computation of allsystem state-space matrices in advance to solve this

problemChallenge 3) Keeping the calculation time of large

systems relatively low. Power systems are typicallysimulated with a time step objective typically near 25-50

s. This objective may be difficult to reach for largenetworks or drives (a bigger system implies bigger set of

equations to solve). The ARTEMIS[5] package providesnice solutions to this problem with distributed parameterline and stublines models that enable the decoupling of theunderlying system equations.

The stubline model is particularly interesting in electricdrives. The stubline is the equivalent of a distributed

parameter line with an exact 1-time step propagation delayand a fully tunable inductance value[2]. It can effectivelyreplace inductances and provide decoupling of the systemequations. The stubline can be used to model transformerleakage inductance (section IV.A) or current converterchokes (section IV.B) and increases simulation speed bysplitting the system equations into 2 parts.

III. HIL S IMULATION PLATFORM (RT-LAB).

RT-LAB is the real-time simulation software fromOpal-RT Technologies. RT-LAB runs almost entirely oncommercial-off-the-shelf hardware. The only exception,

because of the extreme I/O requirements for electric drivesand system applications, is the Opal-RT FPGA-based I/Ocard. RT-LAB supports distributed simulation throughshared memory with 2/4/8/16-CPU (including multi-coreCPU technology), AMD- or Intel-based systems, orthrough PC clusters with InfiniBand or FireWirecommunication links[8].

The RT-LAB real-time operating system, running onthe actual simulation targets, is either QNX from QNXSoftware System Corp. or RedHawk-Linux fromConcurrent Computer Corp.

Most commercial I/O cards are supported with RT-LAB, including cards from Acromag, DDC, Kontron,

Measurement Computing, National Instruments, Quanser,RTD, Sensoray, and Softing. However, Opal-RT FPGAcards are preferred for electrical applications because suchapplications have unusually high switching frequencies.Opal-RT FPGA I/O cards feature 10-ns digital I/O, 1-microsecond D/A converters, and 2-microsecond A/Dconverters with integrated signal conditioning. XSGsupport enables users to fully customize I/Os for Opal-RTFPGA cards using the standard Simulink diagram editor.

IV. TRAIN AND SHIP PROPULSION DEVICES

In this section, we give examples of common train andship propulsion drive configurations for which low-level

power electronic controls are to be tested. The first modelis a four-induction machine traction unit that can be driven

by either an on-board synchronous generator or AC-single phase catenary system. A high-power three-level GTO- based PMSM drive is shown next. The dual-voltage DC-link of the drive is made of a 12-pulse rectifier connectedto the grid by a three-phase three-winding transformer.The last drive is a very-high power current converter madeof back-to-back thyristor converters (12-pulse rectificationand 6-pulse inversion). The converter drives asynchronous machine. Except for the catenaries powerfeeds, all topologies can be studies in the context of eithertrain or train studies. In some cases, the generator model isreplaced by a simple 3-phase source. The description ofthe various systems is given next:


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A. High-Power Three-level GTO-Based PMSM Drive Propulsion SystemThis type of system involves a power converter feed

from a 20-kV three-phase power system which istransformed to lower voltage by 3-winding transformers.A 12-pulse thyristor rectifier is then used to control the

DC-link voltages. From the bipolar DC-bus, a three-levelneutral-clamped GTO inverter drives a permanent magnetsynchronous machine. The machine is rated at 1 MVAwith magnet flux of 2.5 Weber.

Figure 2 Three-level GTO inverter motor drive

Figure 3 shows the PMSM motor terminal voltages,currents, electric torque and speed during the drive start-up from zero speed to 4 Hz rotation frequency. Figure 4shows the DC-link voltage and transformer secondarycurrents during the start-up. A system engineer mightwant to investigate a method to reduce the DC-link voltage oscillations during the acceleration phase of thetest.

Interpolation method requirements of the RTeDRIVE package for the accurate simulation of the PMSM drivecan be seen in Figure 5. For the test, the PWM frequencyof the drive is 1 kHz, no dead time is applied and thesampling frequency of the model is 40 kHz (Ts=25 s).For the purpose of the test, interpolation is disabled duringthe simulation. On Figure 5, one can clearly observe theincreased distortion in the current and torque values wheninterpolation is disabled.

Figure 3 PMSM motor voltages, currents, electric torque and speed

Figure 4 DC-link voltage and transformer currents.

Figure 5 Effect of interpolation on the PMSM Drive accuracy

B. Very-High-Power C urrent C onverter S ystemThis type of propulsion system involves a direct AC-

AC converter based on thyristor switching devices. Froman AC primary feed, a step-down transformer feeds a 12-

pulse thyristor rectifier. The thyristor rectifier is connectedto a 6-pulse inverter through a simple smoothing reactor.The inverter drives a synchronous machine used for

propulsion.This type of drive can handle more power than its IGBT

or GTO counterparts. It is however more difficult tocontrol. For example, special techniques must be used todrive a motor at very low speed because the back-EMF isnot sufficient to enable inverter thyristor commutation.

A test has been made on this model which consisted ofrising the commanded DC-link current from a steady-statevalue of 0.5 pu to 0.8 pu. For the test, the SM machineworks at a fixed speed of 50 Hz and a constant fieldexcitation voltage is applied to the machine. Testing thisdevice in constant speed mode is something rather difficult with real devices (requiring a test bench), but isvery easy to achieve in simulation. It enables theverification of torque and current controls. The result of the test is shown in Figure 7. The test shows that thesystem takes less than 0.1 sec to reach the commandedcurrent.


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Figure 6 Thyristor-based current converter SM propulsion system

Figure 7 Current converter response to a commanded current step

C. Diesel-based P ower G eneration S ystem

Synchronous machine

Exciter armature

DieselEngine

Diode rectifiersBreakers

Fieldwinding

+V1

-V1

+V2

-V2

Actuator

Diesel Power Generation System

Figure 8 Diesel-based power generation systems

This system is composed of a diesel-engine-drivenalternator connected to two 6-pulses diode rectifiers. Thediode rectifiers produce 2 DC-link voltages. The alternator

field winding is fed with the rectified voltage of anarmature voltage induced by an external DC-winding.This approach avoids slip rings as the rectification circuit

is physically inside the alternator rotor. The system is protected by several breakers that control the alternator connection to the DC-links.

D. Catenary-based P ower G eneration S ystemsFor externally powered train from an AC-catenary, this

circuit uses two active-front end rectifiers to generate the2 DC-link voltages. Breakers control the connections of the IGBTs to the catenarys transformer.

=

2~

Catenary

Pento

=

2~

+V1

-V1

+V2

-V2

Catenary-fed power generation system

Figure 9 Caterany-based power generation system

E. Four Induction Motor Traction S ystemThis system is composed of 4 induction motors, two on

each DC-link, driven by IGBT inverters. Each DC-linkalso has a chopper to control overvoltages and anadditional inverter to feed the auxiliary systems. Thechallenges of conducting real-time simulation of inductionmotor drives are described in [2], especially with regards

to the correct simulation of high-frequency PWMtypically found in these applications. This type of tractionsystem can be connected to either a Diesel-based powergeneration system or catenary-based power generationsystems.

+V2

-V2

=

3~

=

3~

=

1~

=

1~

AUXsystem

=

1~

=

1~ 3~

=

3~

=

Chopper

Chopper

Tractioninduction motors

IM 1 IM 2

IM 3 IM 4

+V1

-V1

-V1

-V2

+Vx1

+Vx2

Traction system

Figure 10 Induction machine traction system

1) Validation against EMTP-RV S imulation

In this sub-section, we compare the simulation resultsof SimPowerSystems and RTeDRIVE inverter modelsagainst a well-known reference, EMTP-RV. The model

under test is a simple induction machine driven by anIGBT-inverter. The machine is driven in open loop from aDC voltage source of 700V and the inverter is modulated


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at 60 Hz with PWM (Carrier frequency: 4kHz, modulationindex: 0.5). In particular, the use of ARTEMIS enables theinduction machine equations to be simulated with theHeun 2 nd order solver (ode2 Simulink solver).

The TCN consist of two simple serial buses at the physical level. Therefore, implementation on a real-timesimulator should not be difficult.Figure 11 Comparison between EMTP and SPS of mechanical speed,

electromagnetic torque and stator current (phase A)

The RTeDRIVE interpolation-capable inverter is usedin the SimPowerSystems simulation. Tests have been

performed at different time-steps, 1 s and 25 s for each package. Open-loop control of the induction machine was preferred only for the sake of simplicity[6].

Figure 11 shows results on the mechanical speed, on theelectromagnetic torque and on stator currents for the testrespectively. Results are exactly the same between EMTP-RV @ 1 s and SimPowerSystems @ 25 s.

V. S UPERVISORY SYSTEM AND HUMAN OPERATOR

The supervisory system test can be conducted byinterconnecting various low-level electronic controlsystems together with a real-time model of the supervisorycontroller. The modularity of the RT-LAB simulator can

be exploited in this manner. Supervisory controls can beimplemented on a separate simulator and interfaced, in aasynchronous way, with the real communication protocolused on actual train like TCN[9]. The TCN is a datacommunication network intended to connect

programmable electronic equipment on-board rail vehiclesfor the support of traction and vehicle control, remotediagnosis and maintenance, and other auxiliary systems.The TCN regroups two types of buses: the MultifunctionVehicle Bus (MVB), which interconnects devices within avehicle, and the Wire Train Bus (WTB), whichinterconnects the vehicles in trains of variablecomposition. It is the equivalent of the CAN bus inautomobiles.

The human-machine interface is very important when itcomes to including the human factor in controllabilitytests. At this stage, the real-time simulation of the trainsystem in RT-LAB can greatly benefit from the TestDrivegraphical interface from Opal-RT. TestDrive is aLabVIEW-based interface to control and monitor real-time simulations, and only requires the LabVIEW runtimeengine. For monitoring real-time simulations, the interfacehas some advantages over standard Simulink: its interface

enables easy, point-and-click dynamic selection of signalsto view, synchronous display of data on triggered events(like faults) and has built-in Python-based scriptingcapability. Figure 12 and Figure 13 show a possiblehuman interface for the testing of train traction devicesunder fault conditions.

Figure 12 Main user control panel Figure 13 Fault and test control panel


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VI. R EAL -TIME PERFORMANCE

The various models presented in this paper wheresimulated on various RT-LAB real-time simulatorconfigurations. The results are shown in TABLE 1.

TABLE I. R EAL -TIME PERFORMANCE ON 2.3 GH Z MULTI -CORE PCS.

ModelSample

time in sConfiguration

Diesel-based powergeneration system + FourInduction Motor Tractionsystem

55

2 PC (4 coreeach) w/FireWire

connectionI/Os: 64 TSDI,64 TSDO, 32

AO6 cores used.

High Power Three-levelGTO-Based PMSM DrivePropulsion System

26

2 cores used.IOs: 12 TSDI,12TSDO, 16AI, 16 AO

Very-High-Power currentconverter propulsion system 15

2 cores used.IOs: none

All the timing given represents the minimum time stepachievable without overruns. An overrun means that theactual time taken to compute one (1) iteration is largerthan the simulator time step.

In all cases, the model controllers are simulated withthe electric apparatus. When the simulator is connected inHIL mode with an external controller, the internalcontrollers are no longer required and therefore thesimulation speed can be increased in this case.

For testing purposes, it is very convenient to havesimulated controllers. With the internal controllers

running, it is possible to test the I/O by implementingloopback tests, where the IGBT gate signals (for example)are sent to Digital Output then immediately read back byDigital Inputs and fed to the model. Configurations withI/Os make use of this approach. The TSDI acronym is forTime Stamped Digital Input, meaning that the digitalinput value is measured with a high accuracy clock (100MHz) by the FPGA-based I/O. The resulting TimeStamp[3] is used by the RTeDRIVE inverter model forinterpolation purposes.

CONCLUSION

In this paper, we have presented a real-time simulatorcapable of conducting real-time simulation of complextrain and ship propulsion devices. Real-time simulation ofan AC-fed three-level neutral-clamped GTO PMSM driveand a high power thyristor current converter-basedsynchronous machine drive were demonstrated with real-time simulation results. A third model, a diesel-powerdrive generation system with a four-induction motor drivewas validated against EMTP validation.

The simulator is also suitable for higher-level controlhierarchy. For these controllers, the simulator speed ismuch less critical but the human interface becomes moreimportant. The TestDrive interface, which is based on theLabView runtime engine, provides a powerful tool for

building efficient human interfaces.

R EFERENCES

[1] I. Boldea, S.A. Nasar, Electric Drives, CRC Press,ISBN: 0-8493-2521-8

[2] H.W. Dommel (Editor), EMTP Theory Book 2 nd edition,MicroTran Power Analysis Corporation, May 1992.

[3] P. Terwiesch, T. Keller, E. Scheiben, Rail Vehicle ControlSystem Integration Testing Using Digital Hardware-in-the-LoopSimulation, IEEE Trans. On Control Systems Technology, Vol.7, No. 3, May 1999.

[4] C. Dufour, S. Abourida, J. Blanger, Real-Time Simulation ofElectrical Vehicle Motor Drives on a PC Cluster, Proceedings ofthe 10th European Conference on Power Electronics andApplications (EPE-2003), Toulouse, Sept. 2-4, 2003.

[5] C. Dufour, S. Abourida, J. Blanger,V. Lapointe, InfiniBand-Based Real-Time Simulation of HVDC, STATCOM, and SVCDevices with Commercial-Off-The-Shelf PCs and FPGAs, 32nd

Annual Conference of the IEEE Industrial Electronics Society(IECON-06), Paris, France, November 7-10, 2006[6] M. Ouhrouche, R. Beguenane, A., Trzynadlowski, J.S. Thongam

and M., Dube-Dallaire, PC-Cluster Based Fully Digital Real-Time Simulation of a Field-Oriented Speed Controller for anInduction Motor, International Journal of Modelling andSimulation, Vol.26, No.3, 2006, pp. 219-228.

[7] S. Abourida, C. Dufour, J. Blanger, Real-Time and Hardware-In-The-Loop Simulation of Electric Drives and Power Electronics:Process, problems and solutions, Proceedings of the InternationalPower Electronics Conference (IPEC-Niigata 2005), Niigata,Japan, 2005

[8] L.-F. Pak, O. Faruque, X. Nie, V. Dinavahi, A Versatile Cluster-Based Real-Time Digital Simulator for Power EngineeringResearch, IEEE Transactions on Power Systems, Vol. 21, No. 2,

pp. 455-465, May 2006.

[9] Juan Carlos Moreno, Eduardo Jess Laloya and Jess Navarro,Line Redundancy in MVB-TCN Devices: A Control UnitDesign, IEEE MELECON 2006, May 16-19, Benalmdena(Mlaga), Spain, pp. 789-794

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2008 - A PC-based Hardware-In-the-Loop Simulator for the Integration Testing of Modern Train and Ship Propulsion Systems.pdf