IEEE Vehicle Power and Propulsion Conference (VPPC), September 3-5, 2008, Harbin, China

978-1-4244-1849-7/08/$25.00○C 2008 IEEE

7 +1500V1 6GND15GND4+1500V

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Figure 2. Traction transformers and 12 pulse rectifiers

Modeling and Simulation of the 1500V Metro Supply Network and Vehicles

ZHANG Yi-cheng*, WU Lu-lu*, WANG Bo*, LIANG Hai-quan* *Control and Science Engineering, College of Electronics & Information Engineering, Tongji University, Shanghai,

China. wll0412@126.com

Abstract—In order to utilize braking energy of metro vehicles at high recovery efficiency, it is necessary to research the metro supply network and metro vehicles. The simplified models of the metro supply network and vehicles are presented based on Simulink/SimPowerSystem via external characteristics. And the detail of some important modules are described in this paper. Meanwhile the character of the metro supply network, the accelerating and braking characteristics of the vehicles are given via simulation. Finally, the control strategy of the energy recovery system (ERS) is generalized. The simulation results are very similar to the data that the metro company offers. And the control strategy can drive the energy recovery system works well at high recovery efficiency.

Keywords—Metro Supply Network; Metro Vehicles; Energy Recovery System

I. INTRODUCTION The recovering of the braking energy is potential,

especially for city buses and metro vehicles, which need to start and brake frequently. Considering energy saving, variable ways for metro system are presented, such as the hydraulic way, flywheel and the electrochemical ways [1~3]. For the complex of the metro system, it is important to research the metro supply system and its vehicles in order to utilize braking energy at high recovery ratio. In recent years, some work has been done for middle and low voltage (600V and 750V) metro supply network, but less has been done for high voltage (DC 1500V) metro supply network.

This paper presents the models of the DC 1500V metro supply network and vehicles based on Simulink/SimPowerSystem via external characteristics, whose simulation results are very similar to voltage and current waveforms measured online. And the energy of the vehicles that can be recovered is also calculated via Simulink. The character of the metro supply network, the accelerating and braking characters of the vehicles are given in the form of simulation results. Moreover, the control strategy of the energy recovery system is generalized, which is helpful to drive it at high recovery efficiency.

II. THE MODEL OF POWER SUPPLY NETWORK Taking the Shanghai Metro Line No. 1 Engineering as

example, we present the models of the DC 1500V metro supply network and vehicles based on Simulink/SimPowerSystem via external characteristics, and the structure of the supply network is shown in Fig.1 [4]. Centralized power supply is adopted for the power

supply system of Shanghai Line No. 1. The high voltage power supply comes from Shanghai power network with centralized form. It is composed of two AC 110kV Main Stations, and several AC 33kV Traction and AC 10kV Lighting Substations. The DC 1500V Contact Network is supported by the AC 33kV Traction Substations which convert AC 33kV to DC 1500V.

In order to make the simulation more efficient, some parts of power supply network will be simplified, and the AC 33kV Traction Substations is modeled in detail, as shown in Fig. 2. There are two traction transformers and

AC 110kV City Power System

110KV/33KV Main

Station 1 Main

Station 2

DC 1500V Contact Network

AC 10kV

AC 33kV AC 33kV AC 33kV

- - - - - - - - - - - - - -

- - - - - - - - - - - - - -

Figure 1. Power supply network of Shanghai Metro Line No. 1

IEEE Vehicle Power and Propulsion Conference (VPPC), September 3-5, 2008, Harbin, China

1a*Rate Limiter Max a

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Figure 4. The model of acceleration

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Figure 3. The model of single vehicle dynamics

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Figure 5. The model of power calculation

two 12 pulse rectifiers in one Traction Substation, if the phase of one transformer is +15° and the other is -15°, it will be a 24 pulse rectifier as a whole [5].

III. THE MODEL OF METRO VEHICLES A unique characteristic of metro vehicles is that the

loads are not stationery. The implication is twofold. First, metro vehicles in service are constantly moving along both tracks, hence their locations and the resulting electric network configuration are changing all the time. Second, DC power demand of a metro vehicles can have drastic changes in a matter of seconds [6]. This factors will be considered in this paper and reflected in simulation results.

Although, there are two kinds of metro vehicles running in Shanghai Metro Line, DC motor vehicles and AC motor vehicles, the dynamic of metro vehicles can still be accurately described by the following basic equations [6]:

( ) ( ) ( ) ( ) )()( xTVTTExCxGVTVTTEdtdVM

Vdtdx

RRRARRE −−=−−−−=

=

(1) Here, x : vehicle position, V : vehicle speed, EM :

vehicle equivalent mass, TE : tractive effort, ( )VTRR : Rolling and bearing friction resistance, ( )VTRA : aerodynamic resistance, ( )xG : grade resistance, ( )xC : curvature resistance. ( ) ( ) ( )VTVTVT RARRR += ,

( ) ( ) ( )xCxGxTR += . Equation (1) means the acceleration force of a vehicle is

the traction force, or tractive effort ( TE ), minus the total resistance. Note that the equivalent mass is that the vehicle mass plus the rotational inertial effect. Generally, the characteristics of propulsion system are usually specified by manufacturers as groups of curves for various speed and line voltage values.

The resistance force can be divided into two groups. Rolling resistance, which represents the friction and bearing resistance, and aerodynamic resistance force are both functions of speed, V . On the other hand, both grade and curvature resistance depend on the track location, hence is a function of vehicle position, x . In order to simplify the calculation here, we use ( )xTR to indicated resistance force that is function of vehicle position, and

( )VTR to indicated resistance force that is function of speed.

While Equation (1) is simple in form, it is not easy to solve when it comes to integration. First, maximum TE a vehicle propulsion system can produce is affected by both vehicle speed and line voltage. Yet to include the effects

in simulation we must couple vehicle performance simulation with power supply network. In order to conquer the problems, we use Simulink/SimPowerSystem to construct the model of single vehicle dynamics, as shown in Fig. 3.

Here, we use desired speed vs time profile as the input variable, and the “Acceleration” module produce the desired acceleration *a , as shown in Fig. 4.

According to the desired *a and the characteristic of

propulsion system, which is coupled with the vehicle speed V and supply network voltage U , the TE will be calculated. Using (1), (2) and (3) [6], real time variables x , V , acta _ , ( )xTR , ( )VTR can be calculated.

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( ) )()1000

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3600(00156.027.2[ 2 NMVVT ER ×××+= (3)

Since the real time TE and V is given, then P that vehicles need can be calculated using (4).

VTEP ⋅⋅= μ (4) Here, μ is tractive efficiency, and can be given by the

manufacturer. In order to simulate the variable power source, we construct a controlled current source with a voltage feedback as the power source, and use a controlled voltage source to simulate the line voltage drop. Because the x is changing, the line voltage drop is changing with the variable line resistance and variable tractive current.

IEEE Vehicle Power and Propulsion Conference (VPPC), September 3-5, 2008, Harbin, China

4V2

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Figure 6. The model of ERS

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Figure 7. The model of DC 1500V metro supply network and vehicles

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Figure 8. The performances of metro vehicles without ERS

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Figure 9. The performances of metro vehicles with ERS

IV. THE MODEL OF THE ENERGY ECOVERY SYSTEM In order to evaluate control rules made for ERS, there is

need to build the model of the energy recovery system. A kind of topology derivation of Buck and Boost is adopted here, as shown in Fig. 6. When ERS returns energy to the

metro supply network, it works in Boost mode, with IGBT turn-off and IGBT1 working. And when ERS stores energy to the supercapacitor bank, it works in Buck mode, with IGBT working and IGBT1 turn-off.

The left side of the main circuit is high voltage, and the right side of it is lower voltage. An important problem should be noted that if the left side voltage drops off, a large of current out of control will flow from the right to the left. So a rapid protection equipment should be used to cut off the fault current.

V. SIMULATION Now, the whole system can be constructed and is

shown in Fig. 7. Giving the desired speed curve, we can calculate the other performance of the metro vehicles as shown in Fig. 8.

It shows that the vehicle starts at 0s, accelerates until 20s, keeps speed at 55km/s from 20s to 60s, and braking from 60s to 88s. When the vehicle starts, the network voltage drops off to about 1500V, and the voltage raises when it brakes. Because of the effect of the braking resistance, the network voltage is kept under 1800V, or it will be higher than 1800V and makes harm to the other

metro equipments. Meanwhile, a lot of energy is wasted on the braking resistance. In order to save the energy, the energy recovery system is adopted to storage the regenerative braking energy of vehicles. And its control rule is shown below:

1) When the metro vehicle is starting ( VU 1600< ), ERS returns energy to the metro supply network.

2) When the metro vehicle is braking ( VU 1750> ), ERS recovers energy to the supercapacitor bank.

3) When there is short-circuit fault occur ( VU 1200< ), ERS will shut down immediately and never work again.

4) Generally, there is about half energy stored in the supercapacitor bank, because we don’t know whether ERS will work in recovery or return mode at first.

According to the control rules, we add ERS to the metro supply network, and get the new simulation results, as shown in Fig. 9. From the simulation results, we can conclude that the voltage peak of the metro supply network with ERS is smaller than that of the metro supply network without ERS. And Traction Substation offers less

IEEE Vehicle Power and Propulsion Conference (VPPC), September 3-5, 2008, Harbin, China

tractive current in Fig. 9. than in Fig. 8. Meanwhile, the performance of the metro vehicles is not affected.

It should be noted that the energy quantity that can be recovered depends on the capacity of ESR. Here, the peak power of ESR is about 1Mw, and maximum current of ESR is about 500A. And according to the control strategy here, it can save about half of dissipated energy on the braking resistance and it can drive the ESR to work at full power and high conversion efficiency. To save more braking energy, more supercapacitors and higher power of bi-directional DC/DC converter are needed, and the costs are increased. So two aspects of factors should be considered and balanced.

VI. CONCLUDTION This paper presents the models of the DC 1500V metro

supply network and vehicles based on Simulink/SimPowerSystem via external characteristics. The character of the metro supply network, the accelerating and braking characters of the vehicles are described here. Compared with the data that the metro company offers, the simulation results are verified. And the control strategy presented can drive the energy

recovery system works at high conversion efficiency. The next work is to take account into more distribution parameters and make the control strategy work well under fault operating mode.

REFERENCES [1] Steiner M, Scholten J. “Energy storage on board of DC fed

railway vehicles”. Power Electronics Specialists Conference, 2004. PESC 04. 2004 IEEE 35th Annual. Vol 1, 20–25 June 2004, pp. 666–671.

[2] Sleiner M, Schollen J. “Energy Storage on board of Railway Vehicles”. Power Electronics and Applications, 2005 European Conference on. Sept 2005.

[3] Engel B. “The Innovative traction system with the flywheel of the LIREX”. WCRR, Koln 2001.

[4] Science and Technology Committee of Shanghai Municipal Construction Commission. “METRO LINE NO. 1”. Shanghai Science and Technology Publishers. 2002.

[5] Science and Technology Committee of Shanghai Municipal Construction Commission. “METRO LINE NO. 2”. Shanghai Science and Technology Publishers. 2002.

[6] Bih–Yuan Ku, Jang, J. S. R. Shang–Lin Ho. “A Modulized Train Performance Simulator for Rapid Transit DC Analysis”. Railroad Conference, 2000. Proceedings of the 2000 ASME/IEEE Joint. pp. 213–219, 2000.