Abstract. 1 Introduction

Transcription

1 Analysis and CAD of electric vehicle power electronic converters as a source of electromagnetic disturbances W. Zajac" & A. Szelag^ "Department of Electrical Engineering, Cracow University of Technology, Cracow, Warszawska St 24, Poland ^Institute of Electrical Machines, Warsaw University of Technology, Warsaw, PL Politechniki 1, Poland Abstract The problem of disturbances caused by the converters of an electric traction vehicle is discussed in this paper. As there have been projects to introduce new types of rolling stock in a suburban railway line in Silesia (the south-western part of Poland), some introductory analyses have been done in order to estimate the electromagnetic disturbances which could be caused by the vehicles' converters. As a type of rolling stock, supplied by a 3 kv DC traction system, a multiple unit with a.c. motors and a voltage inverter have been taken into consideration. Specialized software for the simulation of the power electronic and electrical machines PC-NAP have been used. A complex model of the system has been worked out which includes:power utility system, DC traction substation 12-pulse rectifiers, traction contact line, vehicle input filters,power electronic converters and asynchronous traction motors. The parameters of the subsystems were calculated according to the measurements carried out by the authors or were taken as specified by manufacturers. The results of analyses and simulations are presented and discussed 1 Introduction When a new type of rolling stock is to be put into service on an electrified railway line, a compatibility study of the effects of the high power electronic equipment and the feeding system on the signalling and communication

2 396 Railway Operations systems must he undertaken. These problems have been under consideration for many years [ 3,7,8], but quick progress in power electronics and sophisticated controls create new aspects which should be thoroughly investigated. Due to the complexity of the phenomena and the mutual coupling between the supply system, contact line and the electric traction vehicle, the simulation methods are not only inexpensive and easy but in some circumstances the only solutions when an early stage study of the new railway lines are carried out. A computer aided analysis of the inverter drive with a.c. motors of the traction unit EW61T, which was planned to be put into service on a newly designed suburban electrified railway line in Silesia (Poland), is presented in the paper. The simulation model, implemented in PC-NAP (a simulator for analysis and synthesis of electronic circuits), is composed of sub-models of: a power utility system, a DC rectifier substation, an overhead contact line and power electronic equipment of the traction vehicle with a.c. motors. The focus was placed on the validity of the parameters of the elements, as they have a great influence in the case of a compatibility study; contact line parameters have been taken from measurements [ 4 ]. 2 Silesian Regional Railway system project The 3 kv DC Silesian Regional Railway was planned to be built and to operate as a passenger suburban line in the densely populated region of Silesia (Poland). The 46 km double track was designed to be supplied by seven traction substations, each of them equipped with two twelve-pulse rectifiers, feeding by fourteen AC MV lines connected to eight ESB bulk common connection points. The distance between the traction substations varies from 6.95 to 13.3 km and traction units are to be energized from overhead copper catenary composed of 20()mm Cu contact wire and 120mm messenger wire. In the first stage of the project traction units with choppers and DC motors have been taken into account. At the next stage, a new generation of EW61T units with a.c. motors were proposed to be used. Articulated trains composed of two three-coach 0.8MW units are to be put into service with five minute headways reaching an average speed 40km/h. The power circuit of the EW61T unit is designed as a VSI with step-down 600Hz chopper and two filters: the input filter and the inverter filter. 3 Signalling and train control systems The signalling project undertaken for Silesian Regional Railway (SRR) took into consideration: - basic layer equipment, which should ensure train movement control with safety measures, i.e. local traffic control, automatic block system, automatic control of train sequence;

3 Railway Operations intermediate layer: remote control of route setting and remote control of the supply system; - superordinated layencomputer-based centralized traffic control, automatic passenger information system and automatic guidance of trains. The designed traction units are to incorporate automatic control of train sequence. This is a train protective system which is to limit the speeds of trains when a track block appears. Information is sent to the driver about the state of the automatic block system and station semaphore signals; the system controls the driver's work. There were some alternative designs for the trains' protective systems proposed: digital system of sending information track-totrain and automatic control of speed systems. The first one worked out for Polish National Rail (PKP) is to be used with signals transmission via rails (operating frequency 2.2kHz). Other operating frequencies of the signalling system are: 1866, 2179, 2480 and 2790 Hz. All these frequencies are in a frequency band of disturbances caused by the thyristor rolling stock planned for operation on the SRR line. So this part of the signalling and communication equipment is mostly subject to the source of disturbance which have direct connection to the track, mainly when the disturbances are conductively coupled in track (i.e. drive generated harmonics and main frequencies harmonics generated by the DC substation/the main sources of harmonics are the unit's drive chopper with inverter and the rectifier of DC substation. The amplitudes of harmonics depend on the duty cycle of the traction vehicle and the parameters of its filters, the contact line (i.e. distance between the vehicle and the substation) and the traction substation. These parameters vary with frequency. When the traction vehicle as a source of disturbances on track circuits is analyzed the frequency-dependent characteristics of elements of the system within the signalling frequency band are to be taken into account [31. 4 Permitted level of disturbances Signalling and communication circuits, especially those which belong to the basic layer are to fulfill special requirements in order to be immune to the interference. This means, that low-power track circuits or voltage type receivers are excluded from use in the system. Conductive disturbances are of the current type and limits of amplitudes and time of their occurrence for the band of signalling frequency are specified (Table 1) for the types of track circuits planned to be installed on the SRR line. For the time of duration in the range of 50 to ms, the permitted level of harmonics' amplitudes is 25% higher than shown in Table 1.

4 398 Railway Operations Table 1 Maximum permitted line currents in signalling circuits type of circuit OIS-2 ZLB-DT OTS-2-ZLB-DT OTS-2-ZLB-ZP OTS-2-ZLB-ZP OTS-2-ZLB OTS-2-ZLB OTL-21-a ZLB OTL-2f-a-ZLB OTS-2-SOT-1 OTS-2-SOT-1 frquency band \] \7.} and and and and ,15(H)-K>00, , , , , , , , , , maximum permitted RMS line current in signalling bands [maj time to trip [msj 5 Simulation experiments The objective of the study was to check the compatibility of the designed rolling stock and the signalling circuits on the SRR and the simulation model of the whole analyzed system has been worked out. The technique of modelling and simulation as a tool for analysis of electromagnetic compatibility between electric traction systems and signalling systems have been widely used and is well reported [3,8]. Due to the complexity of the system, different models and software were applied with different stages of simplification. A CH. LF2 INV A I I -p T M^L_LJ i PUS TS OC(six 1-km sections) TD Figure 1: The scheme of the electric traction system

5 Railway Operations 399 For the purposes of this study the whole object-oriented model of the system, composed of the following subsystems have been set together. Power utility system model (PUS) The power utility system is represented as a three-phase medium voltage source with short-circuit inductance (Lse) and a overhead line inductance (Lt)(Figure 1). Traction substation model (TS) A model of a 2.5M W twelve-pulse diode rectifier substation is composed of a model of a three-phase three-winding transformer and a rectifier model with output filter, which has a choke (Lpo=1.8mH), a twelfth harmonic contour (Lpi = 1.17mH, Cpi = 60microF), a twenty-fourth harmonic contour (Lp2=0.44mH,Cp2=50microF) and an aperiodic filter (Cp3=HX)microF). Overhead catenary model (OC) The overhead catenary is represented as a pi-scheme with C% (parallel) and U,Rs (series) unitary parameters (Figure 1), which are frequency dependent and have been obtained from measurements made by the authors [ 4 ]. The measured values of parameters are for the range of the frequencies presented in Table 2. Table 2 Frequency dependence of contact line parameters frequency [I Iz] R [ohm/km] C [nf/km] L [mil/km Traction drive model (TD) The model of a traction unit drive includes: an input filter (Lfi=2mH, Cn=2mF), a 600 Hz step-down chopper (CH), a inverter filter (Lf2=5mH, Crz=5mF), a VSI GTO model (INV) with snubber circuits and simplified models of four 210 kw a.c. squirrel cage motors with all values referred to the machine stator side [ 2]. As a simulation tool the PC-NAP program for analysis and synthesis of electric circuits have been used. Using the complex model of the system, the analysis of the input current of the traction unit as a source of disturbances in track circuits has been performed. The emphasis has been placed on preparing accurate models of the whole system and taking into account the mutual interaction of the subsystems. The steady-states of the traction-duty

6 400 Railway Operations cycle of the vehicle have been investigated. Due to complexity of the models, the calculations some seconds of operation of the system took some hours when a compatible PC486/66MHz was used. For FFT analysis of the vehicle's current the 100ms 'window' has been taken. This allowed a calculation of the amplitudes both low and high order harmonics. Silesia is the most industrialized region in Poland, with mines and steel factories when arc furnaces work. These kinds of unstable loads may cause significant harmonic distortion and asymmetry. In order to take into account different conditions of the operation of the vehicle the simulation experiments have been carried out for a set of parameters, and exemplary results of simulations are presented in Figure 2 and Figure 3, the list of major symbols used: I _ distance between the vehicle and the DC substation, fi- inverter operating frequency, rch- chopper on ratio, a% - percentage of asymmetry in PUS voltage 3.1KV -i 3.1KV I 3. OKV 3.2KV o v501 J -i 3. 3.OKV v OKV AWMWWWVWWWWWW 3. OKV -} I 2.8KV 360A D Vl 360A vl 340A-L-- 660ms -I 700ms 340A-L 660ms i lz i Iz ti me time H 700ms symmetric voltage PUS asymmetric PUS voltage,a%= 1 % l=3km, fi=70hz, rch=0.66 Figure 2: Waveforms of: v501 - voltage at DC busbars of TS, vl - voltage at the pantograph of the traction unit, ilz- traction unit's current

7 Railway Operations a.) symmetric PUS voltage e.) symmetric PUS voltage b.) asymmetry, a% = 1 o mo 200 f.) asymmetry, a% = c.) symmetric PUS voltage g.) symmetric PUS voltage E 03 10'* Frequency x 10 (Hz] d.) asymmetry, a% = fi=50hz,nch=0.5 l=3km Frequency x 10 [Hz] h.) asymmetry, a% = l fi=70hz,nch=0.66 Figure 3: The frequency content of the traction unit's current

8 402 Railway Operations 6 Conclusions The presented model of the whole traction system and its implementation with the PC-NAP simulator permits the analysis of the mutual coupling between the elements of the traction system and the influence of the traction vehicle as a source of disturbances on track circuits. The precise representation of the frequency dependence of the parameters of the system during time domain analysis is a significant factor in the accuracy of the model. When elements of the analyzed system are operating at different frequencies, the 'window' for FFT analysis should be so wide, that not only high order harmonics, but subharmonics as well can be calculated. This is especially important when the compatibility of low frequency track circuits are investigated. From the simulation of the designed 0.8 M W traction unit EW6 IT with a.c. motors it was determined that the spectrum of the vehicle current depends on the distance between the substation and the mode of operation of the vehicle's drive. The asymmetry in the power network supplying traction substations results in the occurrence of uncharacteristic low frequency harmonics. Resonances between the traction substation, its DC side filter, contact line and the filter of the vehicle may result as well in increasing certain harmonics. All these facts may cause the necessity of installing a new type of filter onto the vehicle or choosing the track circuits with an operating frequency outside the band of the vehicle's current interference. 7 References 1. Bialon, ^Settlement of permissible level of disturbances caused by traction current in PKP track circuits, (in Polish), Railway Research Institute Work 392/20, Warsaw, Bose, B.K.Power electronics and AC drives. Prentice-Hall, New Jersey Coles, P.C, Fracchia, M., Hill, R.J., Pozzobon, P.&Szelag, ^.Identification of catenary harmonic in 3 kv DC railway traction system. MELECON'94, Antalaya, Turkey IV, Malisz,K., PrusakJ.&Za)ac,W. Measurements of unitaryparameters of 3kV overhead catenary. International Conference Transsystem, Warsaw, Setting methods for protection of low-power circuits from electric traction disturbances on Silesian Regional Railway. Polish Ministry of High Education Grant CPBR Pieczarka, M. & Zajac, W. Electric traction interfering on telecommunication lines; system parameters and effect in overhead catenary. Scientific Journal of Cracow University of Technology No 54, ORE Reports DT 73, Utrecht Taufiq,J.A., Goodman,C.J &Mellitt, B. Railway signalling compatibility of inverter fed induction motor drives for rapid transit. IEE Proc. B, Vol. 133, No2, March 1986, pp