Hardware in the Loop for a Power Traction System Marc-Anthony Mannah, Ahmad Haddad, Ali El-Khechen, Hussein Mahmoud Department of Electrical and Electronic Engineering, Lebanese International University
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Abstract: This paper focuses on the feasibility of a hardware in the loop ‘HIL’ based system in a power electronic environment, in particular for a power traction system. The challenge lies in demonstrating the feasibility of a real time simulator ‘RTS’ for the traction system. A power system containing a chopper, two three phase current fed inverters and induction motors is analyzed and simulated in a fixed step solver. Investigations over a particular traction system used in France and the analysis of the main I/O parameters are addressed. The purpose would be to define and underline the limitations and the requirements of real time simulations for power electronic systems. Index Terms— Hardware in the Loop, Real Time Simulation, Power Converters I. INTRODUCTION This paper discusses the real time simulation requirements and its feasibility for a power electronic system. For this purpose, a power traction system made of a chopper and two inverters is simulated (Fig. 1) and the application of Hardware in the Loop is investigated. HIL systems provide good means to analyze the performance of electrical systems in embedded and power systems and allow to easily test and implement modifications in the system [1] while reducing the cost and the time of maintenance. The principle of the HIL system is shown in Fig. 1.
Simulation Environment Power System
System under Test (Electronic card)
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Fig. 1 - HIL system for a traction power system.
II. PROCEDURE AND SIMULATION The power system described above is first simulated under Simulink Matlab using a variable step solver. Many parameters connecting the power system to the control system are investigated and analyzed such as the output current and voltage of the chopper, the output voltage of the inverter, the control signals of the semi conductor switches, etc. Since the purpose is to analyze the feasibility of HIL in power systems, only the open loop is studied and feedbacks are removed. Once the simulation in variable step solver is validated, it is modified into a fixed step solver. In order for the simulation to run correctly under the fixed step solver, the sampling period Te has to be adequately chosen [2]. Considering the inverter’s switching frequency (Fs = 1/Ts= 600 Hz)
and the triggering pulse’s width and phase shifting [3], the fixed step simulation is tested for different steps, decreased respectively: Te1 = 0.02*(Ts/6) ; Te2 = 0.01*(Ts/6) ; Te3 = 0.002*(Ts/6) ; Te4 = 0.001*(Ts/6) In order to overcome the capacity of Matlab in handling a maximum of 32 switches under fixed step solver, simulations are modified by using the software Plecs and combining both software to provide fastest and more accurate results [4]. Note that in real time, TSimulink min.=1µs, TPlecs min.= 400ns. An additional factor know by “Refine Factor” (RF) is used to increase the step under Plecs. Four different values of RF are considered and tested: RF1=1 ; RF2=2 ; RF3=10 ; RF4=25. The preliminary results obtained in [3], show that the real time simulation using the step Te3RF2 has approximately the same behavior as the actual physical system represented by the signal pv. III. SAMPLE OF THE RESULTS Fig. 2 compares between the real experimental signal ‘pv’ considered as reference and the simulated Te3RF2 signal of the virtual system for both the chopper output current Is and the inverter’s output voltage Vinv ( along with a Zoom). This sample result shows that we can easily implement a real time simulation of the power system that will provide results exactly similar to the actual signals. Hence, we are capable of reproducing virtually the power system. 700
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IV. CONCLUSION This coherence between the signals show that the virtual power system behaves exactly as the physical one. Hence, the concept of the HIL allows improving maintenance conditions and reducing costs by simply analyzing and applying modifications over the virtual systems. These modifications once validated, can then be directly implemented on the physical system. REFERENCES [1] C. Dufour et al., "A multicore pc-based simulator for the hardware-in-the-loop testing of modern train and ship traction systems," EPE-PEMC 2008, Poznan, Poland, 1-3 Sept. 2008, pp. 1475–1480. [2] Hans-Petter Halvorsen, M.Sc., “Hardware-In-The-Loop Simulation”, Telemark University College, Faculty of Technology, 2011. [3] M. A. Mannah, Real time simulation and implementation of a railway traction power system: feasibility and limits, Technical report, SNCF, 2011. [4] OPAL-RT TECHNOLOGIES, INC., “RT-LAB Professional - Real Time Digital Simulation Software”, http://www.opal-rt.com, 2013.
