CA2025592A1 - Excitation and power control system for locomotives - Google Patents

Abstract

An excitation and power control system for a diesel engine-generator unit of a locomotive including a programable logic controller for processing input signals received from a throttle lever switches module, a load regulator module, a wheel slip transductor module and a performance control module, and generates output signals which control an engine speed governor and a sensor module. The load regulator module is controlled by the engine speed governor according to a set throttle lever position and generating a signal representative of a required power output and the performance control module processes a feedback current and voltage signals from a main generator, representative of a measured power output signal. The sensor module controls the excitation current of said main generator, and a wheel slip transductor module is provided for detecting wheel slip condition, wherein the excitation current to said main generator is a function of difference between the required power output signal and the measured power output signal. A traction motor is located on a locomotive axle.

Description

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This invention relates generally to an excitation and power control system using a programmable logic controller (P.L.C. ) for monitoring the engine-generator unit in locomotives. More specifically the invention relates to the monitoring of input signais which are commonly controlled in a locomotive during travel, determining the locomotive engine performance, using this information to control the excitation current to the main generator and storing, for a desired period of time, the accumulated information respecting such signals.
The excitation and power control system of the present invention is not limited in its use to a particular locomotive manufacturer or model. This system can be adapted to substantially all diesel electric locomotives and offers the option of standardization of control systems and of maintenance personnel training. Furthermore, the system can be easily expanded while maintaining use of the original equipment.
An engine-generator unit includes a diesel engine having fuel injectors and an engine speed governor and a main electric generator connected to the engine. The speed and power output of the engine are controlled by an engine speed governor through the fuel delivery rate. The output power control is effected by the field excitation level. The generator drives the traction motors, located on locomotive axles. The number of thè motors may vary. In a six axle locomotive generally six such traction motors are used.
There are various types of locomotive excitation and power systems presently in use. The engine speed is set by the throttle lever position on the control stand. The fuel supply is controlled based on the measured speed and throttle lever setting. Mechanical linkages within the engine control fuel and air consumption and output power. In some known types of locomotives, a signal, representative of throttle position, is sent to a throttle module, (an electronic board) which provides a reference voltage based on that throttle ,~: -. - ,... ...
:, ~ t~ 3, .~ ?, position. This reference signal is processed in accordance with information such as the presence of wheel slip condit~on, engine speed and the condition of the trail. A load regulator, based on mechanical input from the engine, further conditions the reference voltage (e.g. by reducing it, should the engine speed (rpm) exceed its setting). The throttle module also provides a stabilized control voltage (68 V) to a sensor module. A performance control module takes both voltage and current readings from the main generator and processes them to provide a power control feedback signal.
By comparing the reference control signal with the power control feedback signal from the performance control module, ` the control voltage enables or disables a sensing module to send control (gating) pulses to electronic switches (SCR) which provide an excitation current to the main generator.
The main generator converts the mechanical power into electrical power for the traction motors, located on the ` locomotive axles.
In such a prior art system as heretofore described, a proper correlation between fuel delivery rate and engine speed is often not accomplished for the transitions between power settings and load variations. In addition, the system response to the transitions in power demand (as when the track, terrain, temperature or fuel quality change) may produce a response in field excitation of the generator which is opposite in sense to the operator command.
` Some of the prior art excitation and power control ; systems for locomotives have replaced parts of the classical system with microprocessors with a view to improving upon conventional engine-generator control. For example, in the invention of US Patent No. 4,498,016 (Walter Earleson et al) ;` the conventional engine speed governor was replaced with a ` microprocessor for fuel delivery, speed error control and monitoring.
Although the prior art developments heretofore discussed and particularly U.S. Patent No. 4,489,016 aforesaid .

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have attempted to provide a system with wheel slip detection means and to implement engine control for low speed (throttle positions O or 1), the systems proposed do not integrate the overall locomotive operations.
It is an object of the present invention to provide an excitation and power control system for the diesel engine-generator unit of locomotives, wherein by the use of a programmable logic controller, the fuel delivery to the engine is controlled by continuously monitoring the actual and the desired (set) speed and the actual fuel delivery rate and : accordingly correcting the excitation field to the generator.
The speed control, wheel slip control, traction motor ~` overload, dynamic brake and fan control functions are ; implemented by the use of programmable logic controller.
Another object of the present invention is to provide an excitation and power control system which, by use of a programmable logic controller, will substantially replace switches and relays with electronic elements. Thus, the control signals become logic (binary) electric signals. Large multiple path relays and switches have been either removed entirely or replaced with simple switches. On one application ~ of the present invention forty-one relays, three time relays, `~i and sixteen electronic modules were replaced by the programmer logic controller of the present invention. With cost considerations being approximately equal, there are many advantages for the proposed control system such as:
~' (a) the monitoring of locomotive parameters (i.e.
the input signals and the signals that are commonly controlled ~ during the travel);
`~ 30 (b) increase in the safety control means by the use of software instead of electrical and electro-mechanical connections and devices and by the adaptation of special purpose electronics;
(c) improved engine fuel efficiency obtained by the monitoring of travel conditions such as speed, track-load and by implementing the auto shut down/auto start functions;

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., (d) miniaturization of the locomotive controls.
Another object of the present invention is to provide an excitation and power control system which is not limited in its use to a particular locomotive manufacturer or model. The present invention can be adapted to substantially all diesel electric locomotives thus opening the option of standardizing and the possibility of readily expanding the system while using original equipment.
A further object of this invention is to provide the locomotive with an event recording system. A programmer logic controller of the present invention can monitor and record up to 1024 inputs and outputs compared to the 8 channels which can be recorded in systems in actual use. The information may be stoxed in either the PLC (in registers), or an external hard disk or may be communicated through a modem to a remotely located mainframe computer. The recorded information also contains the alarms, the failures and other such details so that the maintenance personnel could readily determine what problems the locomotive has before it arrives for repair.
It is a further object of the present invention to monitor the in and out periods of engine cooling fans so that all fans will have the same number of working hours, replacing the actual set sequence which does not utilize all fans for the same amount of time.
According to one aspect of the present invention an excitation and power control system for a diesel engine-generator unit of a locomotive comprises:
a programable logic controller for processing input signals received from a throttle lever switches module, a load regulator module, a wheel slip transductor module and a performance control module, and generates output signals which control an engine speed governor and a sensor module: said load regulator module, controlled by said engine speed ` governor according to a set throttle lever position and generating a signal representative of a required power output;
said performance control module for processing a feedback .

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current and voltage signals from a main generator, representative of a measured power output signal; said ~ensor module for controlling the excitation current of said main generator; a wheel slip transductor module for detecting wheel slip condition, wherein the excitation current to said main i generator is a function of difference between said required power output signal and said measured power output signal and at least a traction motor located on a locomotive axle.
These and other features and advantages of the invention will be better understood from the following description with reference to the accompanying drawings wherein:
Figure 1 illustrates a block diagram of the excitation and power control system for a prior art locomotive;
Figure 2 illustrates a block diagram of the ` excitation and power control system for a locomotive according to the present invention;
Figure 3a is a flow chart for the engine speed control of the present invention;
Figure 3b is a flow chart for the wheel slip control of the present invention;
Figure 3c is a flow chart for the traction motor overload control of the present invention;
Figure 3d is a flow chart for the dynamic brake control of the present invention;
Figure 3e is a flow chart for the fan control of ~ the present invention.
`~ A block diagram of the excitation and power control ` 30 system in actual use is embodied in Figure 1 and will be ^~ further described in order to provide a general description ` of typical modules and assemblies used in the system. In this diagram, electrical power and electrical control signals are illustrated by solid lines, while mechanical and hydraulic connections are illustrated by broken lines. The voltage reference regulator, located in the throttle (TH~ module 2, .
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:, and the throttle lever switches 1 receive a 74V dc input from an auxiliary generator. This signal is used to energize the throttle response relays located in the throttle response circuit of the TH module 2. The throttle response circuit generates an output reference signal according to the set throttle position. The voltage reference regulator output is a stabilized 68 V dc level which is applied to the throttle response circuit and to the sensor bypass (SB) module 9. The reference signal from the throttle response circuit is applied to load regulator (LR) module 5, through the rate control (RC) module 3. This module limits the rate of change as the throttle position is changed. A fast and smooth increase or decrease in the reference signal is obtained. The reference signal generated by LR module 5 is applied to the sensor bypass (SB) module 9 as an input for the excitation and power control loop comprising of SB module 9, the generator excitation (GX) current regulator module 6, the generator voltage (GV) regulator module 7, sensor (SE) module 10, silicon controlled rectifier (SCR) 11, main generator 12, current transformer 19, generator potential transformer (GPT) ~`~ 20, and performance (PF) control module 8. Excitation to the main generator is determined by this reference signal from ~`` load regulator 5.
~ The load regulator 5 wiper arm position is ; 25 controlled by engine speed governor 14 so that the load on the diesel engine (as well as engine rotation speed) is determined by throttle position. The SB module 9 compares input reference signal with feedback signals which are proportional to main generator 12 output signals.
~` 30 Main generator 12 output signal is sensed by the current transformer 19 and potential transformer 20. The , current transformer 19 feedback signal is proportional to the main generator output current. The potential transformer 20 feedback signal is proportional to the main generator output voltage. The current feedback and the voltage feedback signals are combined by tho performance modulo 8 to provide , ~, .

s~ :1 a power control feedback signal. In some embodiments, a performance control feedback signal is obtained by combining the voltage feedback signal from a second potential transformer, with the current feedback signal~ The power - 5 control feedback signal is smaller than the performance - control feedback signal during low current-high voltage driving, and the performance control feedback signal is smaller than the power control feedback signal during low voltage high current operation. The two signals are applied to the sensor bypass module 9. The SB module 9 compares the reference signal from the load regulator 5 with the feedback signals from the performance module 8. Whenever the value of the reference signal is larger than the instantaneous value of either one of the feedback signals, transistor Ql of the sensor bypass module 9 is biased forward. The control signal is applied thus to the sensor module 10, through the generator excitation current regulator module 6 and the generator ; voltage regulator module 7. These two modules pass the control signal as long as the main generator output voltage ; 20 and excitation current remain below the maximum safe value and transistor Ql is forward biased. The GX module 6 blocks the control signal if the generator excitation current rises ` above a safe value. The GV module 7 blocks the control signal if the generator output voltage rises above a safe value. The control signal (e.g. 68 volts) is applied to sensor module 10 which in response generates the gating pulses for silicon controlled rectifier assembly SCR 11. The SCR 11 is forward biased during each positive alternation of output voltage from D14 alternator so that a pulse of a proper magnitude applied to its gate will turn on the SCR diode, for a period as long ; as the SCR is forward biased. Excitation to the main generator 12 from the D14 alternator is controlled by the gating pulses which determine the SRC's conduction interval.
When the gating pulses are applied to SRC 11, excitation and main generator output increase until the instantaneous difference between the reference and the feedback signals is ....

- large enough to maintain the gating pulses generated by sensor modules.
Figure 2 illustrates the block diagram of the control of the present invention. On this figure the same ; 5 parts are represented by the same reference numerals as in Figure 1.
The improvement introduced by the method of this invention consists in eliminating the TH, the RC, the WS, the SB, the GV and the GX modules conventionally used for excitation control. The throttle lever switches 1 generate, in the new arrangement, the input signals for a programable logic control (PLC) 15. This unit energizes the appropriate valves in the engine speed governor 14 and sets the engine speed (rpm) levels. The PLC effects the logic control, the recording functions, the device protection, supervises the fan and thermostat cycling and the communication with a display ~` for maintenance. The mechanical feedback systems remain unchanged.
` In the present invention the fuel delivery is ` 20 controlled by a conventional governor and load regulator interfaced with the new control system. As an illustrative example, once the control system acknowledges that the governor operate in a specified throttle position, the governor, as for the conventional systems, will control the ~` 25 engine speed and fuel delivery. The system will then take a further reading from the load regulator to determine engine ~ performance and will use this information to control `~ excitation current to the main generator.
` Power dips and overruns are corrected by modulating the excitation current and making this a function of the difference between power output required and power output measured. This control is obtained with a closed loop control system which can measure and react in "real time" (less than 20 milliseconds).
The feedback signals are received from the performance control module 8 as it is being done by SB module :,~
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,?, 9 according to the block diagram of Figure 1. A constant voltage (typically 10 V) is applied to the load regulator 5 to monitor the engine response. This voltage level of +lOV
is used as a lower limit for the load regulator, when the throttle takes low positions (O or 1). This feature of the invention was designed because accessory items, such as locomotive lights, compressors and the like, which are either in or out and are easily detectable in the low throttle positions by the system, will consequently be processed as changes in the load, which is undesirable. The +lOV voltage will invalidate the control loop at low speed. The feedback from the load regulator 5 will be conditioned mathematically within the programmable logic controller 15 based on throttle setting. This conditioned feedback will be compared to the performance control module feedback. When LR feedback signal is higher than the performance module feedback signal, a signal proportional to the difference is applied to the SE
module 10 to close the excitation control loop. The wheel slip transducers 16 are used by PLC 15 to sense wheel slip conditions and their severity. The PLC elaborates an appropriate system response.
There are two types of input signals to programmable logic controller, these being digital and analog signals.
Digital signals take the value of O volts (logic "O") or 74 volts (logic "1"). These signals constantly indicate to the logic unit what contractor, switch or train line wire is powered. These contactors and switches identified by numerals 10001-10080 in the program are:
contactors for series parallel connection of traction motors, trunk sand switch which notifies the reader if the engineer is calling for a sand generator field switch; a motor brake switch-gear which reports whether the braking position is on or off; switches for high temperature, emergency fuel cut-off switches etc. The program stored in programmable logic controller memory monitors all the inputs, makes the logical .

decision based on their value and responds by either energizing or de-energizing the logic outputs.
Another category of input signals is the analog signals. These signals are variable and are calibrated by passing through a transducer or a voltage divider be~ore entering the programmer logic controller, in order to achieve the required level. The analog inputs are changed to either signals in the range of O-lOV or 4-20 mA. These signals represent dynamic brake lever position, main generator voltage, main generator current, grid current, speed, wheel slip bridge current (representative of a detected wheel slip condition) and wheel slip transducer current. The programmable logic controller compares the inputs to a registered information representing optimum travel parameters ` 15 in order to generate output control signals based on ; programming.
The output signals of the programmer logic controller can be classified into two categories - the real and the internal outputs.
The real outputs drive either contactors, lights, switch-gear or switches. These components are used on locomotives today. According to this invention, they are driven using software generated signals which replace relays and electro-mechanical modules. Some of the components which `~ 25 may be replaced by software according to the present invention are sanding, throttling, wheel slip, extended braking, excitation limit, generator voltage and generator excitation modules.
~` The second category of outputs is internal outputs `~` 30 used for PLC internal control logic.
; The information concerning the locomotive travel is recorded and stored. It is accessible to the engineer or to the maintenance personnel with a display. The s t o r e d information includes the power consumption, the time when throttle portion has changed, dynamic bra~ing ti=e, etc.

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The alarm signals are also recorded and stored They acknowledge a faulty condition of the engine such as hot engine, low oil pressure, low water level, overspeed, fan failure, motor brake failure, contactor failure, etc All alarms are displayed as an alarm condition, i e they are ; listed on the display with the time and date of occurrence In one embodiment, the traction motor voltage and the current are monitored to detect if a difference over 10%
in the values of current and voltage appears When such a situation is detected it is recorded also as an alarm condition. These records are of a great help for maintenance personnel who can diagnose a possible motor failure (e.g.
faulty brushes or insulation breakdown) before a consequent major failure.
The block diagram of Figure 2 will be best understood when considered in conjunction with the flow diagrams of Figure 3a - 3e showing the implementation of the functions of the present invention.
`` Figure 3a illustrates how the engine speed is changed according to the position of the throttle. Speed is a parameter in a performance equation where maximum track adhesion is obtained through precision control of excitation current. The excitation current is reduced or removed in overspeed situations.
On a six axle locomotive, traction motors operation can assume one of two configurations. When starting up and at low speeds, traction motors operate as three independent (parallel) sets of two traction motors electrically connected `~` in series. This mode of operation is known as series-parallel ` 30 and it is set up to take place during the high current-low ~ voltage operation of the generator. At high speeds, these `~ same traction motors are all connected in parallel across the generator output. This takes place during the low current-high voltage operation of the generator. The change from series-parallel operation to parallel operation is known as forward transition operation. This happens when the main ; generator voltage exceeds a preset limit and the current drops below a preset limit. During forward transition, the traction motors are disconnected and reconnected through an automated procedure. If the engine-generator set is not preconditioned before this happens, the instant change from a load to no load condition will result in an instant uncontrollable increase in engine RPM. This presents a high probability of engine and/or generator damage. Additionally, the generator field needs time to decay so that contactors are opened and reconnected under "no load" conditions. Braking or closing contactors under load is undesirable being highly destructive under certain conditions. The transition point is set by P.L.C. based on the speed value. Should one of traction motors fail, the system will automatically switch back to the voltage and current control board on throttle position.
The program checks if the throttle position has changed. If the throttle position has not changed, the coil for that internal throttle position control stays energized.
If the throttle setting has changed, an internal function n takes a new value according to the new setting. This function is a four variable function (current, voltage, rotational speed of the engine and value of excitation). If the new setting requires an increased/decreased rotational speed of the engine, this new corresponding value is read and the value of excitation is accordingly increased/decreased in steps, until the actual excitation value becomes equal to the excitation value corresponding to the set throttle position.
The new set of parameters is stored in the four fields of the function n replacing the old values. These new values will be considered the reference value for the next changes in the throttle position.
Figure 3b shows a flow chart for the program controlling the wheel slip. Three preset values of slip control signals (namely STAGE1, STAGE2, STAGE3) represent ~` 35 threshold values for different severity levels IVALl , IVAL2, IVAL3. The control system of the present invention -.
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incorporates different responses to those three levels o~
wheel slip. If the detected wheel slip condition belongs to the first stage (i.e. is moderate), sand is applied to ra~l~
When the wheel slip condition is more severe and it belongs 5 to a second stage (i.e. is sharp) the excitation current i5 reduced and sand is applied to rails. In the situation when the wheel slip condition belongs to the third level, in addition to sand and excitation reduction, the "Over Ride Solenoid" on engine speed governor is energized (this drives 10 load regulator position to minimum). In the situation where the wheel slip condition surpasses the third level (i.e.
; surpasses the admissible level), excitation is removed and an annunciation device is activated.
" The threshold values can be changed as desired 15 depending on the locomotive model or other factors that are taken into consideration. A wheel slip condition at high speed is much more serious than wheel slip on a locomotive ; ~ust starting to pull a load. This system utilizes locomotive track speed as a factor in their response to wheel slip 20 detection. As shown in the flow chart of Figure 3b the signals from the wheel slip transductor 16 are continuously monitored. The difference between two successive values ~` (IDIFF) is compared with the threshold values in order to determine the level of severity of wheel slip conditions and 25 accordingly, the above described steps are followed. The HP
signal representative of the motor power is checked in order ~`~ to determine if it is a high or low speed wheel slip. For ;` various levels of wheel slip conditions, the signal HP is reduced or increased to the set point value, which corresponds 30 to the throttle position.
Figure 3c shows the functioning of the traction motor overload condition control. The current values are read every second and are compared with four preset threshold values in order to determine three intervals for the degree "3S of motor load. The values for this embodiment are 4300A, 4400A, 4800A and 6000A. A counter is increased with 6, 2 or :.
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1, depending upon the interval in which the read value (AMPS) belongs, up to a limit of 1800. When the counter limit is reached, according to the time interval in which the limit wa~
reached, an overload condition is detected and its severity is evaluated. As a result, the maxim current set limit is decreased for a period of time (SEC-VAL). After this time the cycle is restarted with the initial values for the current and voltage values.
Figure 3d is a flow chart of the dynamic brake control. Dynamic braking consists in the use of traction motors to slow down the locomotive in place of the traditional mechanical brake shoes. This is done by electrically positioning the traction motors across a bank of resistors (grid resistors) which provide a load. The traction motor output is a function of the value of these resistors and the excitation current provided by the main generator. The excitation current is a function of the position of the variable brake lever controlled by the operator. Where the resistance of the resistors is variable, track speed also becomes part of the function which determines the braking force. Main generator excitation also needs to be controlled so that the maximum current allowable through the resistors is not exceeded.
Dynamic brake starts by checking if the conditions which validate this control are met. Dynamic brake lock-out signal, invalidating the dynamic brake control may be activated manually by use of a switch or automatically by the `~ PLC in the case of a problem. It is reset manually. When ~ braking operations is initiated the voltage on the braking `~ 30 rheostat on the locomotive control stand will change its value between O and 68V, according to the lever position. (variable GRID SET in the flow chart). This range is translated in this embodiment in a range of current between 0 and 700A (in fact the voltages under 10V are translated in a OA current and the voltage over 53V are treated as asking for full 700A). The set value of the current is read and the generator field is :`
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modified to a value according to the brake lever position.
This value is limited to 700A and the wheel slip condition is controlled. Should the measured voltage surpass 550V, for safety reasons the faulted condition is acknowledged and the dynamic braking is locked-out (by lock-out signal~. Depending on the range of the braking, extended range dynamic brake contactors (expressed by variable CONTACTOR (p) in the flow chart of which there can be two or three depending on the application) short out a section of the grid resistors in order to maintain a high braking current for speeds less than 18 mph, so that the braking action can be maintained at slow speeds. The PLC keeps the dynamic current between 550A and 700A. If current drops below 550A, an extended range condition will be energized. If the speed increases and the current tends to overpass the admissible limit of 700A, a contractor will be de-energized. During the dynamic braking the high voltage ground condition and the dynamic braking fan operation are checked and should the tests results be unsatisfactory, the dynamic braking is interrupted by lock-out signal. These fans cool the grid resistors and if they ; are not operational, the PLC will interrupt the braking in order to save the grids from melting. In order to prevent a false warning which may occur occasionally when fan can not be started, the control voltage becomes a logic condition for the lock-out function. When the unit is in self load, (i.e.
loading of the main generator takes place through dynamic brake grids) the lock-out signal is conditioned by a level of at least 75V. During dynamic braking the control voltage " must be greater than 10V.
Figure 3e is a flow chart of the fan and thermostat controls. On this flow chart, THERM (N) represents the state of the thermostat number N and the FAN(M) represents the state of the fan number M. These variables have as many fields as many thermostats or fans are present in the system. A "O"
value represents the "off" setting and a "1" value for these variables represents the "on" setting of a thermostat or a fan .

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respectively. The variable OFFTEMP and ONTEMP represent the respective switch setting for thermostats variables N_T_O and N_F_O represent the number of thermostats or fans which are "on" and #THERM represents the total number of fans ~or thermostats). As can be seen from the flow chart, the fans are started sequentially and accordingly, the counters N_T_O
and N_F_O count the number of thermostats and fans which are ` "on".
In order to reduce the fuel consumption, the autostart and auto shutdown of the units is used. The units are off for a period of time, their temperature and air i pressure is monitored and when the operating range for these parameters is reached, the unit auto starts. This monitoring is effected by thermocycle in engine water, ambient air, oil and main reservoir air pressure. While only certain embodiments of the present invention have been described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as claimed in the following claims.

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An excitation and power control system for a diesel engine-generator unit of a locomotive comprising:
(a) a programable logic controller for processing input signals received from a throttle lever switches module, a load regulator module, a wheel slip transductor module and a performance control module, and generates output signals which control an engine speed governor and a sensor module, (b) said load regulator module, controlled by said engine speed governor according to a set throttle lever position and generating a signal representative of a required power output, (c) said performance control module for processing a feedback current and voltage signals from a main generator, representative of a measured power output signal, (d) said sensor module for controlling the excitation current of said main generator, (e) a wheel slip transductor module for detecting wheel slip condition, wherein the excitation current to said main generator is a function of difference between said required power output signal and said measured power output signal, (f) at least a traction motor located on a locomotive axle.

2. A system as claimed in claim 1 wherein said programmable logic controller monitors said locomotive track speed by: continuously reading a speed set value for said set throttle lever position, which corresponds to a set current voltage and excitation signals for the main generator, comparing the set values accordingly to an actual speed, current voltage and excitation signals, and, accordingly adjusting said actual excitation signal value to said set excitation signal.

3. A system as claimed in claim 1 wherein said programmable logic controller is capable of detecting three stages of severity levels for a wheel slip condition and capable of distinctly correcting said wheel slip condition according to the detected severity level.

4. A system as claimed in claims 1 or 2 wherein said programmable logic controller is capable of detecting a traction motor overload situation by measuring an actual current value, including said current value into three overload severity ranges and distinctly correcting said overload condition according to the detected severity level range.

5. A system as claimed in claims 1 or 2 wherein said programmable logic controller compares said main generator voltage and current signals to a threshold voltage and current values and further based on said set throttle level position connects across said at least a traction motor a bank of grid resistors for obtaining a dynamic braking of the locomotive, and wherein said dynamic braking is locked-out in the cases of exceeding said voltage threshold value, a high voltage-ground short-circuit or a malfunctioning of a grid cooling fan.

6. A system as claimed in claims 1 or 2 wherein said programmable logic controller monitors engine cooling fans in order to obtain a substantially equal working interval for said cooling fans.

7. A system as claimed in claims 1 or 2 wherein said programmable logic controller set and monitors the system thermocuples state for obtaining auto-start and auto-shutdown function.