II. HYBRID TEST TRAIN A.

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1 Drive control of the traction inverter installed on the fuel cells and lithium-ion hybrid test train. T. Furuya, K. Ogawa, T. Yamamoto, S. Nagaishi, H. Hasegawa Raiway Technical Research Institute, Tokyo, Japan ABSTRACT Main target of this research is developing of a simple hybrid power control method for existing trains. This paper describes the design, contruction and testing of the drive control method for the autonomous-decentralized hybrid test train equipped with proton-exchange-membrane-type fuel cells (PEMFC) system and lithium-ion battery system(li-batt). The main object of this research is to estimate operation status of power sources from the input voltage of the traction inverter and to control the maximum traction electric power based on this estimation result. I. INTRODUCTION Fuel cell is known as a power supply that is very clean and high efficiency. PEMFC is useful for train application because it works at low temperature. RTRI has been developing the fuel cell-powered railway car (FC-Car) with the 100-kW-class PEMFC system (FC) to clear some problems of energy and emissions in non-electrified sections from FY2001. In FY2005, RTRI succeeded in the running test by applying that PEMFC system to only the traction power; auxiliary power was taken from a catenary system because the voltage and the power of PEMFC system ware insufficient. In FY 2008, RTRI installed the lithium-ion battery system (Li -Batt) and the DC-DC up-and-down converter (Li -Ch) for power management of the hybrid system which consist of FC and Li-Batt. This enables the use of regenerative energy in the operation of the test train in non-electrified section, and it brings improvement of the energy efficiency and the fuel consumption rate of PEMFC system. This paper proposes the drive control method for the traction inverter installed the autonomous-decentralized hybrid test train equipped with FC and Li-Batt, and discusses its working principles. The control system of the traction inverter estimates the operation status of power sources from only the DC input voltage. The proposal system controls the maximum traction power based on this estimation result. Therefore, the proposal system works without control signal lines for checking of power sources. This brings a simpler composition of hybrid system relative to a centralized one. Through running tests, we verified the validity of the proposal control method and confirmed it s the effectiveness in preventing overload operation and in changing operation status of power sources. II. HYBRID TEST TRAIN A. Overview The hybrid test train has the 100-kW-class FC and the 36-kWh Li-Batt as onboard power sources. Fig.1 shows the appearance of the hybrid test train, and Table 1 shows its specifications. The train set consists of two cars. One is the FC-Car: motive car which has one motive bogie with two induction type main traction motors (MM). It has the FC system, the DC-DC up converter (FC-Ch), the traction

2 inverter for MM, and the auxiliary inverter. The other is a trailer car. It has the Li-Batt and the Li-Ch. Another driving inverter for commonly use is installed on this car. The total weight is 70 tons and most of test equipments of hybrid system are installed on board. B. Autonomous-decentralized system The hybrid control system has mainly two functions: sharing of power and protecting of equipments. The hybrid system commonly used in automobiles has centralized power control system. In this system, central control unit (CCU) sends command in all times. When some equipment has trouble, a CCU sends control signals to other equipments to prevent chain troubles. It is very useful for controlling fixed hybrid system because it manages all electric power and checks the condition of equipments. In case of the hybrid test train equipped with the FC and the Li-Batt, the main circuit isn t fixed yet. It will change by the running test condition and fixing control themes for the traction inverter. When a centralized power control system is applied to this test train, a CCU has to change the control mode along with the configuration of the main circuit. It will need a communication line, like control area network (CAN), to control all equipments for hybrid system. In protecting, each one of equipments has to check control signal for preventing chain troubles. That is means an each one also has to change the control mode along with a control signal from a CCU by complex communication line. Fig. 1. The hybrid test train. TABLE I SPECIFICATION OF THE HYBRID TEST TRAIN On the other hand, when an autonomous-decentralized system applied to flexible hybrid power supply system, it has some advantages as following. Each one of hybrid system need less changeable control mode for main circuit arrangement and it doesn t need complex communication lines for protection coordination. In addition, there are some kinds of communication system for commercial train in Japan, like TIMS and TICS, and about a half of existing trains haven t such communication system. So, it brings the reduction of initial cost for adding hybrid system to existing train. Likewise, it brings shortening the developing time, and the flexibility of adjusting control parameters of these Item Power system Fuel cell system Power converter for fuel cells Batteries Value Fuel cells and Li-ion batteries hybrid / Overhead wire (DC 1,500 V ) PEMFC, 150 kw (rated including auxiliary power) DC-DC up converter, 800 V to 1,500 V(baseline), 600 kva Li-ion type, 60 Ah, 600 V, 600 A Power converter DC-DC up-and-down converter, 600 V for batteries Main traction motor Hydrogen cylinder system to 1,500 V(baseline), 360 kw Three-phase induction motor, 95 kwx2 Type III, 35 MPa, 0.720m 3

3 equipments to change power control method. So, the autonomous-decentralized control system is used to the FC and the Li-Batt hybrid train system. C. Traction inverter Fig.2 shows the traction inverter, and Table 2 shows its specifications. The hardware components of the traction inverter are the same one of common commuter trains, but the control system is specialized. It has a developmental setting for user to modify a source program written in C language. So, it is useful to add new control functions and to change control parameters. Then, this traction inverter works in widely input voltage range from 500 to 1,850 V by changing threshold levels of low and high input voltage protection. These features bring the reduction of modifying cost and shortening the developing time of a power control method for the autonomous-decentralized hybrid system. A single onboard digital signal processor (DSP) controls all function of the traction inverter. It has two kinds of interrupt processing: one is used for traction motor control, and the other is used for sequence control. A sequence control evaluates the status of main circuit contactors and driving reference commands from cab, they are sent as digital signals at DC 100 volts. Fig. 2. The traction inverter. TABLE II SPECIFICATION OF THE TRACTION INVERTER Item Value Input voltage range DC 500 to 1,850 V Voltage source, Type 3.3 kv-800 A, two-level IGBT 1,000 Hz, Switching frequency asynchronous 225 MHz, Control DSP 256 kb RAM (TI C6713) Control cycle 500 μs D. Power Flows The main circuit configuration of the hybrid test train is shown in Fig.3. There are two switch boxes for changing power sources from an external power source namely catenary system, or onboard. One is for the traction inverter, another is for the auxiliary inverter. Because of the FC is insufficient for supplying electric power to both traction power and auxiliary power, the auxiliary power is supplied by way of pantograph when the traction power is supplied from only the FC. The FC voltage changes widely from 600 to 900 volts according to the output current. Switch box DC-Bus pantograph Signal line Auxiliary Air Inverter Conditioner Etc. FC-Ch Li-Ch (up conv.) (up-and-down conv.) Traction FC Li-Batt Inverter (PEMFC system) (Li-ion batteries) Induction Motor IM IM Fig. 3. Main circuit Configuration of the hybrid test train.

4 The FC-Ch runs under constant current (CC) mode in hybrid power supply mode. It receives a reference output current command from the Li-Ch. If it becomes under a threshold value, the FC-Ch changes automatically from CC mode to constant voltage (CV) mode for keeping DC-Bus voltage to work auxiliary systems. Of course, the FC system cannot be connected to the catenary system directly. The Li-Batt is effective as the onboard energy storage device because it has such advantages as high power density and low internal resistance. The Li-Ch is connected to the Li-Batt through some electromagnetic contactors. It works constantly in CV mode, and keeps DC-Bus voltage of around 1,500 volts in operation. Then, it controls the power supply capability of the hybrid system, and exchanges control signals with other onboard power sources. Thus, all power converters connected with DC-Bus have same dielectric strength voltage as for DC 1,500 volts electrified sections. The Li-Ch is connected directly to the traction inverter, so the Li-Batt charges from overhead wire or the FC with the FC-Ch by the switch box for the traction inverter. In addition, the Li-Ch sends a reference output current command to the FC-Ch according to the state of charge (SOC) of the Li-Batt to keep the total onboard power into a settled range. But, the traction and the auxiliary inverter are not controlled by this energy management system of the hybrid test train. They don t receive such reference commands from Li-Ch, so they work regardless of the operation status of the Li-Ch in catenary feeding. E. Protect operation for battery failure In the autonomous-decentralized power control system, the protect coordination of equipments that are connected to the main circuit is very important. If it doesn t work well, each one of those equipments will be broken and some troubles will occur in protect operation of others. The traction inverter sends its failure signals to the Li-Ch and receives sub-signal for checking battery hardware failure like overcharge or over discharge, to prevent its overload operation. By cutting out these signals, the traction inverter reduces the traction power to less than 100 kilowatts correspond to the maximum output power of FC. Fig. 4 shows an example of battery failure. representation 1 for normal, and 0 for battery hardware failure. As the power flag value moves from 1 to drive-ref changes from 4 to 2. 0, the This drive-ref value is an internal reference command of an inverter control system. While sub-signals are cut off from the Li-Ch, the drive-ref value is always less than 2 regardless of driver s operation. Through a drive-ref limitation, the traction inverter reduces the traction The signal status is shown by a power flag Fig. 4. Example of the results of battery failure.

5 power. This function is very important for preventing chain failure in the hybrid system. III. STATE ESTIMATION OF POWER SOURCES It is difficult to find out the FC s operation status and the SOC of the Li-Batt for the traction inverter, because that inverter (shown in Fig.2) has no signal line to check them. In addition, the maximum traction power will change by the kind of the power sources and the total onboard power of hybrid system. But for the autonomous-decentralized system, the development of a traction power control without using control signal line is needed. Most of series hybrid systems adapts a certain constant value for the output voltage of power sources [3][4]. In some centralized power control systems of that used in automobiles control the DC output voltage of onboard power sources according to the power of traction motor to reduce switching loss of inverter [5]. However, it is difficult to find out the status of power sources without a signal line in every hybrid system. One of the solutions to this issue, the output voltage range of the onboard power sources have to be set at different values. This has to be led to find out the power sources for the traction inverter to check its input voltage range. It is a major feature of the hybrid test train. Table 3 shows the relationships between the input voltage range and the operation status of power sources. Case 1 involves direct FC feeding, which is the configuration used in validation experiments of the FC load-following capability. In this case, only the FC-Car is used for running test for fluctuating load operation, and the auxiliary inverter fed by the catenary system with pantograph. Case 2 involves power feeding from the FC with the FC-Ch. In this case, the traction inverter cares little for the voltage drop according to the traction power. Both traction and auxiliary electric power are administered through the FC-Ch. In both case 1 and case 2, the maximum traction electric power is set at the values under 100 kw at all times. Case 3 involves power feeding from TABLE III the Li-Batt with the Times New Roman Type Sizes and Styles Li-Ch. In this case, Power sources the maximum traction Input voltage FC Li-Batt Max. traction Status Fuel Pantograph electric power is set at range with with power Cells the values under 360 FC-Ch Li-Ch kw. Both traction and auxiliary electric power are administrated through the Li-Ch. Case 3 has an input voltage range Case V 100 kw Case 2 1,200 1,380 V 100 kw Case 3 1,420 1,580 V 360 kw Case 4 1,200 1,580 V *410 kw Case 5 1,600 1,850 V *480 kw * set to 360 kw by using two induction motor drives. Enable, Disable, Both

6 different from case 2, in order to allow its use of regenerative brake. Case 4 involves FC and Li-Batt hybrid feeding. In this case, the maximum value has to be limited to the sum of the two, i.e., 410 kw. Case 5 involves feeding from an overhead wire, in the same way as the usual electrical train. In this case, the maximum value has to be limited to the rated capacity of the traction inverter, i.e., 480 kw, and Li-Ch can be charged from overhead wire. In the hybrid test train, there are no priorities in all cases. Each case has equivalent chance for traction and auxiliary power sources, only depends on targets of researches. Thus, in this test train, power sources and the maximum traction power are changed by test contents. This estimation method brings to the operation status of power sources without control signal before the beginning of the running. IV. LOAD POWER ADJUSTMENT A. Overview of traction control Fig 5 shows a commonly cab of in Japan. There is each handle for powering and braking, and it has some steps called notches. In Japan, notches are commonly used in commercial train. Unlike the flexible operation system that is used to cars, the train driver selects only fixed patterns by notch. Every notch for powering is set to a different reference torque pattern. Fig 6 shows an example of the torque patterns selected using these notches. Almost all commuter trains have five notches in Japan. In addition, punctual driving is very important. If the driver selects a lower notch than that required, the train will be delayed. Therefore, it might be necessary to select a higher notch to ensure punctuality regardless of an overload operation. Taking into consideration of these matters, the lifetime of the FC and the Li-Batt will drastically degrade by Fig. 5. Commonly cab in Japan. frequent overload operation in the hybrid system using few control or communication lines between power sources and the traction inverter. Thus, it is effective to control the maximum traction power for preventing these situations. Fig 7 shows the main traction motor (MM) control strategy of the hybrid test train. The main control method for MM is generic vector control, which has light load adjustment for regenerative braking and damping adjustment control for DC bus Fig. 6. Example of torque patterns selected using notches

7 CB Input filter FC-Ch FC sys Li-Ch Li-Batt v dc v inv Traction Inverter IM IM PG PG cnt r 3/dq drive_ref v dc r Status Estimator Anti slip Controller k vdc k slip Max Power Generator k inv Reference Generator I d * I q * I q I d Slip-freq Vector Control s * 1 * 1 v d * v q * dq/3 PWM v inv r voltage. These are the common functions of railway traction control. In addition, an anti-slip control is widely used for commercial train. The control system of hybrid test train also has an anti-slip controller that consists of an acceleration detector (Ac-D) and a continuous slipping detector (Cs-D). Fig. 8 shows the block diagram for anti-slip control system. The motor s average speed is calculated from pulse generators (PG) on the MM, and acceleration is calculated from the value obtained. When the Ac-D detects slipping, it reduces the internal parameter according to the set pattern. The Cs-D calculates the estimated motor speed from the Drive-ref, and if it detects continuous slipping, it reduces another internal parameter drastically. Then, the anti-slip controller outputs an adjusting parameter ksip to the reference command generator using the internal parameters of both Ac-D and Cs-D. Fig 9 shows the results of power assist with the FC. If the SOC falls below the relevant threshold, the Fig. 7. Control strategy for the main traction motor r drive_ref d dt Acceleration Estimator Detection speed generator Acceleration Detector Pattern Generator 1 Pattern Generator 2 Continuous slipping Detector Gain Generator Fig. 8. Block diagram for anti-slip control system Fig. 9. Test result of power assist in hybrid feeding. k slip

8 generated FC output increases to assist traction power. In this case, the FC-Ch maintains a power level over 35 kw in powering. Fig 10 shows comparative results for anti-slip control derived from the hybrid power supply. In both dry and wet conditions, the average acceleration is almost the same, and FC and Li-Batt hybrid system sufficiently follows the load change of the traction inverter. Accordingly, the proposed anti-slip method offers an adequate level of performance. B. Maximum electrical power control Load power adjustment and limitation are well-known methods in train control. But almost all applications consist of multi-power sources have selecting switches. They are used to clearly change control methods and parameters of power sources and load equipments. The proposal autonomous-decentralized control method uses only the estimation results shown in Table 3. It brings load power adjustment and limitation functions without selecting switches. When the driver prepares for running, the MM controller checks the input voltage. Then, the controller estimates the operation status of the power sources for each case from case 1 to case 5 shown in table 3, and set the default maximum electrical power. After that, the main circuit contactors for traction inverter are closed for starting of car. The state estimator always outputs kvdc to limit the maximum traction power, and it is reset when the main contactors are opened. The state estimator also set the internal parameter in order to permit or not the use of regenerative brake. (a) Dry condition (b) Wet condition Fig. 10. Comparative results for anti-slip control C. Online power control The SOC of the Li-Batt may drop to around the low limit level during the driving operation. At that time, electrical power from the Li-Batt may be sufficient as traction electrical power. In such cases, the

9 maximum electrical power control method can t prevent overloading. For this reason, another power control function must be added. Fig. 11 is a block diagram showing the Max Power Generator for the online power control. The Li-Ch has limits of both current and voltage for the Li-Batt to prevent breakdown of it. And the Li-Ch also has control functions that work in CV mode. Accordingly, the output voltage would drop in overload operation by CV control gains of these functions. In this way, a traction inverter can judge overloading during the driving operation and the maximum power generator outputs kinv to adjust the traction power. Fig. 12 shows the test results of drive_ref online power control. In this test, the current limits of the Li-Ch are changed about a half of those commonly used to make the input voltage drop dominantly. The torque current reference command decreases along with reductions in an input voltage like in area A. Then, an input voltage becomes normal again as kinv gradually rises. In this case, the torque reference command is controlled at 20% k vdc of the default value by the maximum power generator. Limit Generator This method achieves the avoidance of overload operation during driving. If the DC-bus voltage falls to 900 V, the auxiliary inverter stops at the same time to prevent the breakdown of auxiliary equipments. So, the proposed method is useful for protect coordination of the hybrid test train. v inv Gain Generator k inv Fig. 11. Block diagram for the Max Power Generator Fig. 12. Test result of an online power control. V. CONCLUSIONS The hybrid control system has mainly two functions: sharing of power and protecting of equipments. The centralized power control system is very useful for controlling fixed hybrid system, but it will have complex control system if it is applied to unfix hybrid system or existing train. This paper reports on the development of drive control method which is based on the autonomous-decentralized control for a hybrid train system. The proposed method has a state estimator and the maximum traction power controller to prevent overload operation. It uses few control signal lines to estimate the operation status of power sources by the input voltage range. It brings advantages for sharing of power and protecting of equipments by the flexibility of adjusting control

10 parameters of hybrid system. By applying this online power control method, the traction inverter prevents overload operation of onboard power sources. This method extends the lifetimes of onboard power sources, like FC and Li-Batt, and achieves a flexible power flow between a main traction system and auxiliary one. The results of tests including state estimation and online power controls validated the usefulness and compatibility of the proposed control system. REFERENCES [1] T. Yoneyama, K. Ogawa, T. Furuya, K. Kondo, and T. Yamamoto, Specifications and schedule of a fuel cell test railway vehicle, World congress on railway research. Montreal, IP3.6, June [2] K. Ogawa, T. Yamamoto, and T. Yoneyama, Energy efficiency and fuel consumption of fuel cells powered test railway vehicle, World congress on railway research. Seoul, PS.2.26, May [3] H. Girard, J. Oostra, and J. Neubauer, Hybrid shunter locomotive, World congress on railway research. Seoul, R , May [4] T. Kawaji, S. Nishikawa, A. Okazaki, S. Araki, and M. Sasaki, Development of Hybrid Commercial Vehicle with EDLC, The 22nd international battery, hybrid and fuel cell electric vehicle symposium & exposition.yokohama, pp , October [5] M. Kamiya, Development of traction drive motors for the toyota hybrid system, International Power Electronics Conference. Niigata, pp , April 2005.