1. Title Intelligent Power Management System Interim Report July 30, 1997 Table of Contents 1. Title Intelligent Power Management System ................................ .............................................................1 2. Abstract................................ ........................................................................................................................3 3. Introduction................................ .................................................................................................................3 3.1 High Speed Rail Transportation................................ ............................................................................3 3.2 Locomotive Propulsion Options................................ ............................................................................4 3.3 Flywheel Energy Storage ................................ .......................................................................................5 3.4 High Speed Rail Corridors............................... . .....................................................................................5 3.5 High Speed Train Set ............................... . .............................................................................................6 4. Possible Optimizations ................................ ................................................................................................7 4.1 Prime Mover/Flywheel Sizing ................................ ...............................................................................7 4.2 Energy/Fuel Efficiency ................................ ..........................................................................................8 4.3 Flywheel Use ................................ .........................................................................................................8 5. Simulation ................................ ....................................................................................................................9 5.1 Model Description................................ .................................................................................................9 5.2 Results ................................ .................................................................................................................12 6. Demonstration................................ ............................................................................................................14 6.1 Discussion................................ ............................................................................................................14 6.2 Computer Controls................................ ...............................................................................................14 6.2.1 Philosophy of Control Communications ................................ .......................................................14 6.2.2 Analysis of Networked Control and Instrumentation ................................ ....................................15 6.2.3 Review of Network Technology ................................ ...................................................................20 6.2.4 Description of CAN Technology................................ ..................................................................22 6.2.5 Energy Management Organization ................................ ................................................................23 6.2.6 Information Communications ................................ .......................................................................26 6.2.7 Observations on the Energy Management Code ................................ ...........................................30 6.2.8 Route Simulator and Track Load Simulator Processor................................ .................................31 6.2.9 Network Communications Results ................................ ................................................................32 6.3 Power Control................................ ......................................................................................................34 6.3.1 AC Drives................................ .....................................................................................................34 6.3.2 Power Train................................ ..................................................................................................36 6.3.3 Load Simulator................................ .............................................................................................40 6.4 Demonstration Results ................................ .........................................................................................40 7. Conclusion ................................ .................................................................................................................40 8. Recommendations ................................ ......................................................................................................41 9. Appendices................................ ................................................................................................................42 10. Bibliography................................ ............................................................................................................42 Table of Figures Figure 1. Route Speed Limit Profile................................ ................................................................................6 Figure 2. Locomotive Power Train................................ ..................................................................................7 Figure 3. Block diagram of train simulation ................................ ....................................................................9 Figure 4. Propulsion Model................................ ...........................................................................................10 Figure 5. Block diagram of the Locomotive Simulation Model................................. ....................................11 Figure 6. Block diagram of the Speed Control Model ............................... . ...................................................11 Figure 7. Commanded Speed Compared to Track Speed Limit................................ .....................................12 Figure 8. Actual Velocity Compared to Track Speed Limit ................................ ..........................................13 Figure 9. Net Power To Traction Motors............................... . ......................................................................13 Figure 10. Information relation diagram for distributed networked control. ................................ .................23 1 Figure 11. Demonstration train system control and instrumentation block diagram. ................................ .....24 Figure 12. Energy management control LabVIEW display panel ................................ ..................................25 Figure 13. CAN message format ................................ ....................................................................................26 Figure 14. RTOS flow diagram ................................ .....................................................................................27 Figure 15. Demonstration train network with J1939 message routing. ................................ ..........................29 Figure 16. Track load simulator functional block diagram................................ ............................................32 Figure 17. Message timing for normal operations ................................ .........................................................33 Figure 18. Message timing for no response from Flywheel #2. ................................ .....................................34 Figure 19. CAN status update message. ................................ .........................................................................34 Figure 20. CAN status message update with no response from Flywheel #2 unit. ................................ .........34 Figure 21. VSI Schematic ................................ ..............................................................................................35 Figure 22. Schematic of phase "A" of a 3-phase VSI ................................ ....................................................35 Figure 23. Train energy control block diagram................................. ............................................................37 Figure 24. Open circuit terminal voltage as a function of field current. ................................ ........................39 Figure 25. DC bus voltage control MATLAB simulation model. ................................ ..................................40 Table of Tables Table I.Comparison of control network technologies................................ ....................................................20 Table II. Evaluation matrix for selecting network technology. ................................ ......................................21 Table III. Master to PC data format. ................................ ..............................................................................28 Table IV. PC to master data format................................ ...............................................................................28 Table V. Network message data formats. ................................ ......................................................................29 Table VI. Synchronous generator open circuit test results................................. ............................................38 2 2. Abstract The preliminary report on the investigation of Intelligent Power Management Systems addresses energy management issues for high speed trains that have renewable energy sources on board. The design issues that dictate the viability of flywheel energy storage on trains are the transfer capability of electronic converters, the magnitude of both prime mover and flywheel energy storage capacity, and the number of flywheels that e nergy storage is to be distributed among. This report discusses the simulation of trains to determine power ratings for both prime mover as well as flywheel sizing for trip time management and energy conserv ation. The report considers the computational control needed for efficient and effective management of this train system. A distributed networked control system is compared to a single central computer that is direct wired with instrumentation and control effectors. Issues of reliability and cost, both installation and maintenance are discussed. Bench mark requirements for processor and network performance and cost allow the identific ation of classes of network technology suitable for critical train controls. For the final report, the hardware and software used in the demonstration system will be described in sufficient detail to allow the reader to reproduce an identical system. The description in this report includes discussions of power electronics, user interfaces with computer controls and network management schemes, and performance analysis of these systems. 3. Introduction The US Federal Railroad Administration has been pursuing the idea of using l ocomotives with an on-board prime mover for high speed rail applications. Such transpo rtation systems would not require the added cost of rail electrification. Gas turbines are preferred over diesel engines as prime movers for high speed rail in order to save weight. However, electric traction motors are still preferred over fluid turbine drives. This report presents preliminary results from a study of the possibility of adding flywheel energy storage to a high speed locomotive. The flywheels are charged whenever the locomotive is in regenerative braking mode and whenever the prime mover is pr oducing more power than is needed to maintain the desired track speed yet operating in the optimal performance power range. The chief benefits to such a scheme are: 1) decreased trip time, 2) better acceleration at high speeds, 3) reduced prime mover power rating and weight, 4) reduced rail bed cost, and 5) improved fuel efficiency. 3.1 High Speed Rail Transportation Rail has long been a transportation option for both passengers and freight. Early locomotives were based on a steam boiler fired by either wood or coal. The steam pre ssure was used to turn the drive wheels. These were eventually replaced with the dieselelectric locomotives commonly used in North America today. The diesel-electric loc o- 3 motive consists of a diesel engine that is the prime mover for a synchronous generator. Most modern locomotives have a 3 to 5000 HP synchronous generator, with the output rectified by a diode rectifier. The resulting DC bus then supplies the DC traction motors. A locomotive is a small (roughly 4 MW) power system on wheels. Most of the rail traffic in North America consists of freight trains, which tend to be long, heavy and slow. There is also some passenger travel in the form of light and commuter rail systems around urban areas and some government controlled long distance travel along lines owned by the freight railroad. Nearly all of these passenger systems are constrained by the civil speed limits which, for US rail lines, is 78 miles per hour. The chief exception to this rule is the Northeast Corridor, where 120 mile per hour travel is allowed on limited access sections of track. High speed rail transportation is getting increased attention as a possible altern ative to air travel for business travel between cities that are between 150 and 400 miles apart. The chief objective is to provide transportation between cities that are far enough apart to discourage automobile travel and too close together for air travel to be efficient, generally in the range of 150 to 400 miles. Rail service would avoid the congestion and delays often present at major airports, and by reducing the traffic at the airports also r elieve some of the congestion. Fast, efficient high speed rail systems already exist in Europe and Japan. Exa mples would be the TGV in France and the TransRapid in Germany where trains often e xceed 150 miles per hour. The European rail infrastructure is designed around all-electric locomotives, where the electric power to run the traction motors is provided through a pantograph and catenary supplied from an electric power distribution grid. These loc omotives are typically referred to as all-electric locomotives. However, the catenary and utility interface infrastructure required for all-electric locomotives is not economically feasible in the US as studies in Florida, Texas, California, the upper Midwest, and the P acific Northwest have all shown. However, there is a project in Florida that is still moving ahead 1. Therefore, studies are being conducted on high speed locomotives with on-board prime movers that drive synchronous generators. These locomotives are typically referred to as non-electric locomotives even though they use a small on-board autonomous electric power system. 3.2 Locomotive Propulsion Options The typical North American locomotive is a small electric power system. A diesel engine powers a synchronous generator. The output of the generator is immediately rect ified to DC by diode rectifiers. This DC bus supplies DC traction motors which have s eries excitation for high torque production at low speeds, ideal for freight operation. Each of these motors is capable of regenerating when the train is braking, with the energy di ssipated by a braking resistor bank. The traditional diesel electric design has several drawbacks for high speed rail a pplications. Foremost among these is the size and weight of the diesel engine, which e ffectively limits the top speeds attainable for a diesel locomotive. Gas turbines engines are considered to be a better option for a lightweight prime mover for high speed rail. Gas turbines have been considered for both mechanical drive systems and for electric drive systems. 4 DC traction motors have significant drawbacks. The tractive effort applied to the rails is limited by the axle with the poorest adhesion between its wheels and the rails. Once that axle starts to slip, all of the drive axles must be throttled back to require a zero slip condition. Typically, this is the front axle on the lead locomotive, since it will be seeing the wettest, dirtiest rails and is thus most likely to slip. Significant improvements in locomotive performance can be made by utilizing i nduction motors driven by inverters in place of DC traction motors. A system with a single inverter per traction motor allows for individual adhesion control for each axle, signif icantly improving the efficiency in getting the power to the rail. In addition, the largest DC motor that will fit on a locomotive is roughly 1000HP. However, a higher horse power induction motor will fit in the same space since it does not require space for the comm utator. There has also been a significant move towards ac propulsion for freight locom otives as well. 3.3 Flywheel Energy Storage The idea of storing energy in the form of kinetic energy in a rotating inertia has been known for centuries. Modern flywheels can be operated as part of a rotating electric machine and have the ability to compete with conventional electrochemical batteries 2,3. A key objective of the energy storage system is to maximize the energy density of the storage system. The amount of kinetic energy stored in a rotating mass is directly pr oportional to its moment of inertia and to its rotational speed squared. Therefore, it is much more effective to increase the rotational velocity, rather than making a heavier flywheel with a larger diameter. Many flywheel energy storage systems are designed to rotate at speeds above 50,000 RPM, and most have a goal of exceeding 100,000 RPM. In order to incorporate these high rotational velocities with an interface to an electric power system the flywheel is driven by a power electronic drive. The mechanical strength of the rotating assembly determines the peak energy storage, but the converter will determine how fast the flywheel can be charged or discharged; i.e., the maximum power transfer rate. The flywheel can be used in transportation applications to store energy when the locomotive is resistive braking. This energy can then be used to accelerate the locom otive. So the inverter rating will need to be based on the peak energy transfer rate desired for braking and acceleration. Another concern with flywheels for transportation is how the rotating mass of the flywheel effects the handling of the vehicle. This problem can be solved for high speed rail applications by having many small counter-rotating flywheels on a locomotive. 3.4 High Speed Rail Corridors Ideally the high speed rail train sets will operate on a dedicated route where they won't have to be scheduled around freight trains. However, this does not mean that the train simply accelerates to 120 MPH and stays at that speed until the next stop. A typical route, such as the Northeast Corridor or the Empire Corridor in New York will have a wide range of speed limits as shown in Figure 1. Each track section has speed limits d etermined by factors such as track curvature, grade crossings, slope, condition of track, and 5 the area the track is passing through. Therefore, the train will vary its speed as it covers the route. Figure 1. Route Speed Limit Profile 3.5 High Speed Train Set The high speed locomotive being studied for simulation purposes consists of a gas turbine engine for the prime mover that powers a synchronous alternator which in turn feeds rectifier to produce a DC bus, as shown in Figure 2. The DC bus connects the prime mover to four traction inverters which drive induction traction motors. These motor drives are capable of regenerative braking operation. The DC bus also supplies multiple flywheel inverters, which can transfer power between the DC bus and the flywheel. A braking resistor is still needed on the DC bus for cases where the braking energy transfer rate exceeds the capacity of the flywheel inverters and for emergency braking. The train being studied has two locomotives, each rated at about 4000 HP, and six pa ssenger cars. 6 Figure 2. Locomotive Power Train 4. Possible Optimizations There are several areas where performance of a high speed train that can be opt mized. The possible areas that can be optimized are total trip time and energy consum tion over the course of the route. Further options become available when flywheels are added to the locomotive, especially in a system that utilizes 30 to 40 small flywheels. The decision to use many versus a few flywheels depends upon the state of flywheel co struction technology as well as the efficiency of scale. Inherent limitations of flywheels point to the conclusion that, from an energy management for optimization perspective, many smaller flywheels have a distinct advantage. This issue is discussed in greater d tail in the following sections. ip- n- e- 4.1 Prime Mover/Flywheel Sizing The addition of the flywheels provides several areas where the performance of a high speed rail locomotive can be optimized. The first is in the power rating of the prime mover, which in this case is a gas turbine. Since gas turbines have a relatively narrow o perating band for peak operational efficiency, the flywheel can be used to level the loading on the turbine to keep it in its most efficient state. However, the addition of the flywheel provides the possibility for even greater savings. The flywheels can be charged any time the power demanded to keep the train at the desired speed is below the optimal output level of the gas turbine. This condition will occur when slowing for stops, slowing for curves, going downhill, and so on. The energy in the flywheels can be used to accelerate the locomotive to the desired speed more quickly. One of the limitations for the high speed rail locomotive is its ability to accele rate quickly when it is already running at high speeds, since it is already near the power limits of the prime mover, so there is little excess power for acceleration. The flywheels can supplement the prime mover in these cases, allowing the train to acquire the legal speed more quickly and hence maintain time schedules. Taking this a step further, the flywheels could provide some if not all of the additional energy needed to accelerate at the higher speeds, allowing a somewhat smaller prime mover, one that is
7 sized to just maintain the train at a set maximum speed. The flywheels can allow it to a ccelerate around this maximum or even exceed it for a short time. 4.2 Energy/Fuel Efficiency Another area where the flywheels will have a significant impact is in the area of optimizing the energy/fuel needs over the length the route. The rate of acceleration / d eceleration between the differing speed limits along the route can be programmed to obtain optimum fuel efficiency. Use of the flywheels to capture energy from braking improve upon this further. However, the control scheme for the locomotive needs to be able to adjust as the train progresses down the route to adapt to any changes from the original plan. If the train is behind schedule, the goal will be to get to the next stop on time, or with minimal delay. In this case fuel efficiency is secondary to time, since many transit systems may be ec onomically penalized from reduced ridership by adverse passenger attitude for late arr ivals. 4.3 Flywheel Use In a locomotive with 30 to 40 small flywheels it will also be possible to choose how many flywheels to use at a given time and which ones might be best to charge. Fl ywheels generally work best as energy storage devices when they are spinning above roughly 50% of maximum rated speed. Since there are some rotational losses with fl ywheels at present, especially in the bearings, there are some steady-state losses present in the system. In addition, the power converters interfacing the flywheel to the DC bus will also experience losses. Therefore, there are cases where a relatively small amount of energy is available to be stored in or retrieved from the flywheels thus allowing optimal sizing the flywheel storage system on the fly. It may be more efficient to only activate a few of the flywheel inverters instead of all of them. The route that the train will follow is known in advance, including speed limits, curve information, and grade information. Thus it is possible to manage the energy budget for the flywheels and choose which ones are dischar ging/charging at any moment. For some routes it may even be possible to have several flywheels per inverter rather than one flywheel per inverter. The inverters are the dominant expense in the fl ywheel system, so using one larger inverter rather than several small ones may be ec onomically feasible. This inverter would then multiplex the flywheels in these cases. 8 5. Simulation The simulation discussed the computer modeling of a specified train scenario. The purpose of such a model is investigate performance sensitivities to independent var iables such as track speed profile, passenger load, size of prime mover, amount of storage capability, and losses. Individual components used in this simulation have been scrut inized in published work to validate the results of the system model. Although only the general details are presented in this interim report, a description of the simulation and the models used will be included in the final report. 5.1 Model Description A software simulation was developed in MATLAB to model the locomotive pr opulsion system as it travels the length of the route. The objective of this simulation is to develop a basis for performing the design and control optimizations described in the pr evious section. Therefore, the models for the power converters and the rotating machines represent input/output energy flow. The system energy flow is driven by the power r equirements of the traction inverters, which are driving the motors to run the locomotive at the desired speed. The simulation consists of several modules, as shown in Figure 3. Additional details of these models are provided in Figure 4 through Figure 6 and in the following discussion.
F l y w h e e l E n e r g S t o r a g e C a p a P ir c M F l y w h e e l P o w e y to yp u l s i Eo nn e r g y ro d e l C o n s u m e d T T R D r i o a i p m e u t e t a C o m m E f f i c i e S pc ey n C o n t r o l M o d e l a n e d d e d S p e e d C o n t r o l M o d e l T r a c t i v e E f f o r t L o c o m o t i v e M o d e l S p e e d S p e e d P o s i t i o n R o u t e D a t a Figure 3. Block diagram of train simulation The propulsion model shown in Figure 4 uses information energy conversion processes and the commanded torque to the motors to compute the energy efficiency of the locomotive. This propulsion module has power efficiency models for the alternator, rectifier, inverters, traction motors and other components. Each block described in Figure 4 represents the losses associated with that particular conversion process. Many of these loss components have already been quantified in other areas, especially for diesel loc omotives 4. The rotor angular velocity input is obtained from the Locomotive model and Speed 9 the commanded torque input from the Speed Control model, both of which are discussed below. The FOC (field oriented control) model is used to simulate the efficiency of the torque energy conversion to train mass - velocity energy of the induction traction motors . Each traction motor is assumed to operate under identical conditions. The outputs are the power input of the generator required to maintain the train speed and the efficiency of the system. The generator uses a load follower regulator, producing the necessary energy demanded by the system to maintain the DC Bus voltage constant.
T r a c t i o n M o t o r V e l o c i t y I M V S I f r o m ( F O C ) L o c o m o t i v e S i m u l a t i o n M o d e l T o r q u e f r o m S p e e d C o n t r o l M o d e l D C B U S I n p u t R e c t i f i G re n e r a tP oo r w e r e & E f f i c i e n c y Figure 4. Propulsion Model The locomotive model ustrated in Figure 5, takes the tractive ffort (real ill e power) command from he speed control m t odule nd combines it with route data to ea d termine where the train is on the route and to output that position and speed and acceleration to the other modules. The acce leration o the train is computed from he tractive ef t f fort force operating against the mass of the train. The train velocity and the position along t b b the track is obtained from he two integrators. The velocity is fed ack y a function fo 5 d ording to the Davis equations. The train rag which calculates the drag resistance acc tput s used to generate the resistance generated from he track grade a curi t nd position ou vature. The grade nd curvature re obtained from a lookup table in the track file. The a a b input ot this model s ia power command generated y a proportional plus integral (P-I) controller common to classical linear sy stems control theory. The output from he locomotive simulation model are train acceleration, train v t elocity, and sition f o train along the track. The velocity is fed ack to the Speed po the b Control odel for closed loop speed control as well as the propulsion model for effim tain t ciency calculations. The position is used to ob the desired train speed from he track profile database, which will be a fed b to the Speed Control m lso ack odel. The c urve a d n t p grade resistance is determined from his position and the track rofile database. Losses associated with the track and train resistance re aincluded in efficiency computations. p i e h The track rofile database does not nclude levation changes and ence there is no energy storage as a function of train position. 10 G r a d e + + - C u r v e D r a g T o P o s i tE i f of n c i e n c y i C o n t r o l S p e eM o d e l d 1 / M a s s 1 / s 1 / s +
T r a c t i v eA c c e l e r a t S op ne e d i E f f o r t S p e e d F r o m S p eT eo d S p e eT do C o n t r o l M o d e r o l C oo nd t e r l o l M o d e l C o n t l M a n d P r o p u l s i o n M o d e l Figure 5. Block diagram of the Locomotive Simulation Model. The speed control m determines the tractive ffort command eeded for the odel e n train to run at he requested speed as pecified y the train poition and the track rofile t s b s p database. The ontrol algorithm si a ombination fo ule-based control as well as linear c c r proportional plus integral control. A block diagram for the speed control m odel i s s hown in Figure 6. The two limiters control het trains acceleration for passenger comfort and safety.
F E f C M r o f i c o n t o d m i e n c y r o l e l T o L o c o m a t i v e S i m u l a t i o n M o d e l S p e e d C o m m a n d T r a c t i v e E f f o r t
D e l t a P o w e r L i m i t e r P I P o w e r L i m i t e T o r q u e r d a / d t T o S p e e d f r L o c S i m M o o o u d P r o p u l s i o n M o d e l A c c e l e r a t i o n r c m o o o u d m m o t i v e l a t i o n e l T r a c t i o n m o t o r V e l o c i t y F r L o c S i m M o o o u d m m o t i v e l a t i o n e l m F m o t i v e l a t i o n L o S i e l M Figure 6. Block diagram of the Speed Control Model 11 5.2 Results The results of software simulation can be used to aid in the design of the locom otive itself. The required power rating for the prime mover can be determined, as well as both energy storage capacity for the flywheels and the power rating for the inverters tran sferring energy into and out of the flywheels. Once this task has been completed, the simulation is next used to finalize the overall control scheme for the locomotive system. Figure 7 through Figure 9 show some initial results from the software simulation. Figure 7 shows the speed set point for the locomotive as compared to the speed limit. The speed setting needs to plan ahead to make sure the speed is always at or under the speed limit. Figure 8 compares the actual locomotive speed on a section of track to the speed limit on that section. The speed must always be less than the speed limit on a section of track, r equiring the train to slow before it reaches it. The fundamental objectives is to determine the most energy and time efficient profile for accelerating and decelerating. The contribution of the energy storage provides many additional degrees of freedom in this optimization. Figure 9 shows the total power delivered to the traction motors as the train moves down its route. Notice that there are a few high peaks and there are also areas where the net power is negative due to regener ative braking. The flywheel energy storage could provide the power needed to meet those peaks, allowing a smaller prime mover to be used to meet the "base load." More detailed results will be presented in a future paper after the completion of the pro ject.
140 120 100 Velocity (mph) 80 60 40 20 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Track Positio n (miles) track limit com and m Figure 7. Commanded Speed Compared to Track Speed Limit 12 140 120 100 Velocity (mph) 80 60 40 20 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Track Positio n (miles) velocity track limit Figure 8. Actual Velocity Compared to Track Speed Limit
10000 8000 6000 4000 Power (hp) 2000 0 -2000 -4000 -6000 -8000 -10000 Track Positio n (miles) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Figure 9. Net Power To Traction Motors 13 6. Demonstration At the time of this interim report, the demonstration system is still under co nstruction at the University of Idaho, in Moscow Idaho. The final phase to be completed is the integration of the flywheels into the rest of the system. All other major components have been tested and integrated at this time. 6.1 Discussion The demonstration system will be presented in three parts; the computer controls, the power conversion electronics and machinery, and the performance results. Discu ssions of the computer controls all include the analysis of networked controls as compared to conventional direct wired controls, a review of control network technologies and the criteria for selecting a control ne twork technology. 6.2 Computer Controls 6.2.1 Philosophy of Control Communications The locomotion controls regulate the train speed. This is accomplished by tran sferring power from the prime mover, whether that diesel, turbine or catenary to kinetic energy manifested as train mass multiplied by the square of train velocity. Classically, trains decrease speed by transferring the kinetic energy into heat either with friction brakes or dynamic braking. Renewable energy system on board allow prime mover peaking or reco very of energy usually lost as heat when the train is decelerating. Control wiring, generally speaking, connects the origin of decisions to the point of decision implementation. Instrumentation wiring brings the measurement of state back to the point of analysis and decision generation. Hence, the network implementation would in the strictest sense merely replace point to point control and instrumentation wires. The control scheme assumes the following design philosophies: 1. High speed equipment and personnel protection controls are independent of the energy management controls. 2. The level of system reliability for proposed systems must be equivalent to or better than conventional controls 3. All control equipment (conventional and proposed) has been pre-qualified for equal or better reliability specifications. Hence any new electronics is a ssumed to have comparable reliability in so much as the degree of complexity is comparable. 4. A bandwidth maximum of 1Khz is needed for any control and instrumentation signals. Using networked distributed control for the demonstration revealed two important conclusions; considering the total amount of computer and control electronics needed for the system, the network technology contributes minimal additional electronics and hence no cost advantage is held by either direct control wiring or networked control. The first conclusion is based upon the available of high performance microprocessors with the 14 network electronics packaged together. The second conclusion arises from the minimal amount of control and instrumentation needed to achieve the necessary degree of control. The incremental cost for equipment to control and monitor flywheels or some other renewable energy source will be a very small percentage of the total installed cost of such a system. The exception to this claim is if many (more than 10) flywheels are used in a single train system. One may then desire that each flywheel energy storage unit be individually controlled. This would then have some impact on the complexity of the control wiring. The UI demonstration control scheme presently uses three or less signals per power device. For example, each traction motor and flywheel requires one control signal and two instrumentation signals for inverter management for traction motors and flywheels. Controlling the power plant requires one control signal and two instrument ation signals. The number of controls required for dynamic braking is determined by the amount of brake control. 6.2.2 Analysis of Networked Control and Instrumentation This analysis focuses on the comparison of distributed network controls and co nventional direct wired controls which use a single central computer. The comparison is based upon functional capability, reliability, and cost. The discussion is intended to pr ovide a procedure for selecting control technologies. Based upon the importance of key issues, the same procedure may result in selecting different but still viable technologies. The network will be limited to supporting only those controls suggested by the simulation and those actually needed for the speed control and energy management. Fault protection controls and regulatory instrumentation are not included in this analysis as the investig ators are convinced that those systems should be kept entirely separate and autonomous for reliability and security. 6.2.2.1 Communications Reliability Three aspects of component reliability are considered: intrinsic failure rate, o perational failure rate, factors that accelerate intrinsic failure rates. Intrinsic failure rates are manufactured into devices and systems and are independent of operations. Oper ational failure rates can be determined by decisions that place the equipment in abnormal operating conditions. But more often, ordinary use only increases the probability that components will be exposed to a failure rate accelerator. The three dominate accelerating factors are heat, electrical stress, and interference. Heat may be either self generated or ambient. Elevated ambient heat is generally caused by inadequate engineering or the failure of another component or system. Electrical stress is either sustained or transient. Sustained electrical stress is either caused by poor engineering or a failure of another component or system which perpetuates a sustained over or under voltage situation. Voltage transients are generally initiated by a high rate of change of inductor current caused by switching contactors or other electro-magnetic ci rcuit. Voltage transient are capacitatively coupled into neighboring circuits Current transients are generally caused by switch voltage into uncharged capacitors and are i nductively coupled into neighboring circuit. Either voltage or current transients can cause equipment failures, but more often these transients generate interference on instrumentation signals. Interference is usually 15 thought of as an intrusion that degrades the quality of information. The results of which can be failure of a system not because of any component failure but because the proces sing of the corrupted information yielded an erroneous result perpetuating an incorrect a ction. System engineering is challenged with two design goals; choose components and systems with low intrinsic failure rates and integrate them into a system with the lowest probability of exposure to a failure rate accelerator. Assuming that the first goal is a lready achieved, we look at networked controls to strive for improvement in the second. In order of ranked importance, each method of control communications is analyzed from the perspectives of; 1. reliability, 2. cost, and 3. adaptability to future modifications. Rel iability assessment is performed on system differences recognizing that either networked or direct point to point control wiring requires common computers, instrumentation and control equipment. This wiring to achieve the necessary communications is next di scussed to illustrate where improvements are obtainable. 6.2.2.1.1 Reliability of Conductors and Terminating Hardware Conductors and connecting hardware are considered because these devices have low reliability and high cost. They are required for both direct wired control as well as networked control but the manner in which they are used can significantly affect reliabi lity. These issues are discussed in the following paragraphs. The chief cause of insulated conductor failures is insulation breakdown. The rel iability of conductors is therefore inversely dependent on the electric potential stress caused by the circuit voltage. The reliability of connectors that terminate the control ci rcuits is inversely dependent upon heat. One source of this heat is the I 2R losses in the terminating device. The reliability of both conductors and terminating devices have an inverse time dependency as well that is separate from the probability random failures. Circuits that operate continuously have higher failure rates than those operated intermi ttently. Being physical devices, the reliability of terminating devices are also inversely affected by the number of connecting and disconnecting operations due to mechanical wear. Three classifications of control circuits are investigated: low power, medium power and high power. Low power circuits refer to signals that operate under 10 watts at voltages less than 100 volts AC or DC and currents less that 1 amp AC or DC. Medium power circuits operate between 10 watts and 100 watts with voltages less than 500 volts AC or DC and less that 10 amps AC or DC. High power circuits operate above 100 watts at voltages greater than 500 volts AC or DC or currents in excess of 10 amps. Low power circuits can use multi-conductor bundled cable and are within the c apability of standard low and medium power semiconductor devices. Heat generated in the control of low power circuits is easily mitigated and has little effect on reliability. Electrical transients generated during control operations can be easily managed by co mmercial and industrial grade semiconductor devices. Control of low power controls are suitable for direct computer control with reasonable attention to engineering design. Medium power circuits require special transient protection and heat management. Devices are more expensive and greater engineering expertise is needed or reliability will 16 be significantly impaired. For direct computer control of medium power circuits, signif icant attention for engineering design is required. High power control circuits are not suitable for direct computer control. In train control environments, these controls generate high energy RFI and EMI noises which are difficult to contain. The longer the control circuits the more severe the noise problems. Usually a low or medium power control circuit interfaces computers to high power ci rcuits. 6.2.2.1.2 Signal Reliability For a given control system with a fixed number of points of control and instr umentation, the number of conductors and terminating devices are only slightly more for networked control wired systems. However the length of medium power circuits can be significantly reduced by being replaced with low power circuits. This reduces the pro bability of EMI and RFI interference which inherently improves reliability. Networked control wiring can offer significant advantages in validating inform ation. If the network is engineered with the expectation of periodical communications, the lack of communication contains information of failure. Corrupted data is detected with a highly level of confidence using error detection codes. Direct wiring offers little or no opportunity to qualify information particularly if the noise is indistinguishable from valid signals. For example, a digital signal can be re presented by zero volts which indicates a logic zero, and the presence of a voltage above a fixed threshold. A receiver cannot distinguish the zero volts sent as a valid control signal from zero volts due to an open circuit. Analog signals have a degree of signal qualific ation if the zero point is excluded from the range of valid data. Such is the case for 4-20 mA constant current analog circuits. However, if interference added or subtracted current from the signal such that the resultant current is in the valid range, the signal error is i ndistinguishable from an uncorrupted signal. Another means of discriminating information from noise is by frequency domain filtering. The information must be characterized to determine the signal's center fr equency and bandwidth as well as required signal to noise ratio. The circuit must then be characterized to determine the noise magnitude and bandwidth. The type and degree of filtering may be determined if sufficient frequency separation exists between the info rmation signal and noise. This filtering may be analog, digital or a combination of both to achieve the desired signal to noise ratio. If filtering cannot provide the necessary signal to noise ratio, the circuit will have to be modified to reduce the amplitude of the interfe ring noise. 6.2.2.2 Cost Conventional train control wiring schemes will be used as the base case. Only the network data electronics will be considered since one of the assumptions is that the amount of control electronics will be approximately the same for either direct wire or networked controls. The incremental cost of the additional network management ele ctronics will be considered. 17 6.2.2.2.1 Installation Cost 6.2.2.2.1.1 Cables No specialized proprietary equipment is necessary for terminating the network cable. Since no particular handling care is required to install network cable, the cost of doing so is strictly a function of the number of cables. To achieve proper impedance matching electrical termination, CAN networks use a linear configuration rather than a star or ring configuration. Termination connecting devices may be simple and inexpensive as quick disconnect connectors are not required since the network connection would only be br oken for repairs. 6.2.2.2.1.2 Data Communications Electronics The cost of CAN electronics is less than $50 per node. This electronics can be a sep arate IC such as the Intel 82527 CAN controller or the 80196CA processor which int egrates the 82527 functionality on the silicon of an Intel 80C196KR type processor. The processor and data communications electronics will need to be packaged in conformance with conventional electronics. Usually all electronics are specified for industrial te mperature range operation. ESD protection is also required on all interfaces to wires ou tside the computing environment. 6.2.2.2.2 Maintenance Cost Maintenance of networked controls will require sophisticated test equipment and very knowledgeable technicians. This is in contrast to electronic digital multimeters (DMM) and analog oscilloscopes which may be the only test equipment required for direct wired controls. Such additional equipment to support networked controls may include network analyzers, digital storage oscilloscopes, and CAN protocol analyzers. The cost of this equipment may exceed $25,000. The larger problem that faces the rail industry is to identify technicians who have the knowledge and aptitude to use the sophisticated equi pment and to interpret the results to locate failures quickly and economically. 6.2.2.2.2.1 Cables Since the signals used on the CAN twisted pair cable constitute them as low power circuits, an improved cable and connector reliability can be expected. If the data rates are pushed to 1M baud, specialized network analyzers as discussed above maybe required to characterize the cable necessary to pin point physically damaged cable. 6.2.2.2.2.2 Data Communications Electronics Field repair of electronics is usually at the board level replacement. Shop maint enance will be lim