Patent Publication Number: US-2021188097-A1

Title: Power system and associated system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 15/643,537, which was filed on Jul. 7, 2017. The entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     Embodiments of the invention relate to power systems and associated methods. 
     Discussion of Art 
     Vehicles may provide power to one or more unpowered trailers, such as, coaches, passenger cars, or carriages. Particularly, the vehicles may supply power to traction motors and non-propulsion electric loads. Power supplied to the traction motors may aid in providing motive force. The non-propulsion loads may include heaters, ventilators, radial fans, coolers, lights, electric circuits for personal use, air conditioners, and the like. The power provided to the non-propulsion electric loads may be referred to as a head end power, hotel load, auxiliary load, and the like. 
     For certain applications, a plurality of vehicles, may be logically and/or mechanically coupled together. Using rail vehicles as an example, a group of coupled rail vehicles may be referred to as a train and multiple powered units may be referred as a consist. If an exemplary vehicle is a locomotive, there may be both powered and unpowered units, and even multiple powered units, that are employed to form a train. In such a case, one vehicle provides head end power to the non-propulsion electric loads and/or traction motors, while the other powered vehicles provide power only to traction motors. 
     A practical constraint for suppling power in related circumstances is that an increase in power rating of power electronic components, such as inverters, may result in an increase in weight of the corresponding vehicle. A heavier vehicle may not be practical or required. It may be desirable to have a power system and an associated system that differ from those that are currently available. 
     SUMMARY 
     In accordance with one embodiment of the present invention, a power system is disclosed. The power system includes a first power generating unit. The first power generating unit includes a first power converting subunit and a first control unit coupled to the first power converting subunit, where the first control unit is configured to regulate a voltage of the first power generating unit. The power system further includes a second power generating unit coupled to the first power generating unit and a load, where the second power generating unit includes a second power converting subunit and a second control unit coupled to the second power converting subunit, wherein the second control unit is configured to control a current of the second power generating unit to share a quantity of electrical output current flowing through the load among the first and second power generating units. 
     In accordance with another embodiment of the present invention, a method of operating a power system is disclosed. The method includes regulating a voltage of a first power generating unit, using a first control unit of the first power generating unit, where a second power generating unit is coupled to the first power generating unit and a load, where the first power generating unit further comprises a first power converting subunit coupled to the first control unit, and where the second power generating unit comprises a second power converting subunit coupled to a second control unit. Further, the method includes controlling a current of the second power generating unit to share a quantity of electrical output current flowing through the load among the first and second power generating units, using the second control unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter described herein will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below: 
         FIG. 1  is a block diagram of a power system in accordance with certain embodiments of the invention; 
         FIG. 2  is a detailed diagrammatical representation of one phase of a power system in accordance with the embodiment of  FIG. 1 ; and 
         FIG. 3  is a detailed diagrammatical representation of a power system, in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     As will be described in detail hereinafter, various embodiments of an exemplary power system and a method of operating the power system are disclosed. The exemplary embodiments disclose parallel operation of power converting subunit of each of the plurality of power generating units of the power system. Each of the plurality of power converting subunit provides electric power to a load. In particular, each of the plurality of power generating units provide a head end power to the load. 
     Turning now to the drawings and by way of example in  FIG. 1 , a block diagram of a power system  100  in accordance with certain embodiments of the present invention is shown. The exemplary power system  100  may be employed for stationary applications such as uninterruptible power supply based system and mobile applications such as trains, platooned vehicles, and the like. 
     The terms “train”, “platoon” and “consist” as used herein, refer to a plurality of vehicles operatively coupled to one another and/or to a plurality of unpowered vehicles. Powered vehicles include those vehicles that have devices for self-propulsion. Suitable examples may include aircraft, marine vessels, locomotives, on-road trucks, off-road vehicles, mining and industrial equipment, and the like. The self-propelled vehicles may further have one or more power sources to effectuate the propulsion (although others may work by wireless power transfer, catenary lines, and the like). In some applications, such as energy tenders, the vehicle may include a power source but not a means for propulsion that is on the vehicle. In certain other applications, a power source may be a stationary power source (or near stationary in that the power source is primarily intended for operation without moving). Unpowered vehicles are referred to those vehicles that do not include means for propulsion and further do not include own power sources for providing tractive effort. The term “auxiliary load”, as used herein, refers to non-propulsion electrical loads placed on a power system. Suitable non-propulsion loads include heating loads, ventilating loads, radial fans, cooling loads, lighting loads, electric circuits for personal use, and the like. The power provided to the non-propulsion loads may be referred to as head end power. 
     In the illustrated embodiment, the power system  100  includes a first power generating unit  102  and a second power generating unit  104  coupled to each other. In particular, the second power generating unit  104  is coupled to the first power generating unit  102  and to a load  106 . More particularly, the first power generating unit  102  is coupled to the load  106  via the second power generating unit  104 . In the illustrated embodiment, the first power generating unit  102  is a first vehicle and the second power generating unit  104  is a second vehicle. In one embodiment, the first vehicle and the second vehicle is a locomotive. In this embodiment, the load  106  is a train load. In the one embodiment, the power system  100  is a locomotive power system. It should be noted herein that the terms “first power generating unit” and “first vehicle,” may be used interchangeably for the reference numeral  102 . Similarly, the terms “second power generating unit” and “second vehicle,” may be used interchangeably for the reference numeral  104 . 
     The first and second vehicles  102 ,  104  are coupled to each other and the load  106  using a head end power (HEP) train line  108 . The HEP train line  108  is disposed extending through the first and second vehicles  102 ,  104  and coupled to the load  106 . The term “HEP train line,” as used herein, refers to a common electrical line which is used to couple electrical components of different vehicles. Although  FIG. 1  shows only two vehicles, the number of vehicles of the power system  100  may vary depending on the application. 
     In one embodiment, the first vehicle  102  operates as a lead vehicle and the second vehicle  104  operates as a trail vehicle. Further, in one embodiment, the first vehicle  102  and the second vehicle  104  operate at a same frequency. In some other embodiments, the first vehicle operates as a trail vehicle and the second vehicle operates as a lead vehicle. 
     Reference numerals  107 ,  109  represent two ends respectively of the first vehicle  102  with reference to the HEP train line  108 . Further, reference numerals  110  and  112  represent two ends respectively of the second vehicle  104  with reference to the HEP train line  108 . In the illustrated embodiment, where the first vehicle  102  is the lead vehicle and the second vehicle  104  is the trail vehicle, the end  109  of first vehicle  102  is coupled to the end  110  of the second vehicle  104 . Furthermore, the end  112  of the second vehicle  104  is coupled to a load  106 . Particularly, the first and second vehicles  102 ,  104  are coupled to the load  106  in such a manner that the combination of the first and second vehicles  102 ,  104  may provide power to the load  106 . 
     A portion of the HEP train line  108  extending between the end  109  of the first vehicle  102  and the end  110  of the second vehicle  104  has an inductance represented by numeral  113 . This portion of the HEP train line may be referred to as a HEP interconnecting train line  114 . The value of the inductance  113  is dependent on the geometry of the HEP interconnecting train line  114 , such as but not limited to, length, radius, and the like of the HEP interconnecting train line  114 . 
     Further, the first vehicle  102  includes a first power converting subunit  115 . In the illustrated embodiment, the first power converting subunit  115  includes first inverters  116 ,  118 . The second vehicle  104  includes a second power converting subunit  117 . The second power converting subunit  117  includes second inverters  120 ,  122 . In an alternative embodiment, each of the first power converting subunit  115  and the second power converting subunit  117  includes an alternator. Further, although each of the vehicles  102 ,  104  includes only two inverters, in other embodiments, number of inverters of each of the vehicles may vary depending on the application. 
     Each of the first and second inverters  116 ,  118 ,  120 ,  122  includes a plurality of switches (not shown in  FIG. 1 ). In such an embodiment, each of the plurality of switches may be a semiconductor switch. In one embodiment, the semiconductor switch includes an insulated gate bipolar transistor, a metal oxide semiconductor field effect transistor, a field-effect transistor, an injection enhanced gate transistor, an integrated gate commutated thyristor, or the like. In another embodiment, the semiconductor switch includes a gallium nitride based switch, a silicon carbide based switch, a gallium arsenide based switch, or the like. 
     The first inverters  116 ,  118  are coupled to corresponding first control units  124 ,  126 . The second inverters  120 ,  122  are coupled to corresponding second control units  128 ,  130 . The operation of the first inverters  116  and  118  are controlled by the first control units  124 ,  126  respectively. Further, the operation of the second inverters  120  and  122  are controlled by the second control units  128 ,  130 , respectively. The term “operation of the inverter,” as used herein, specifically refers to operation of the switches of each of the first and second inverters  116 ,  118 ,  120 ,  122  to generate a desired output. The desired output may be a desired value of a voltage or a current. 
     The first control units  124 ,  126  of the first vehicle  102  are communicatively coupled to each other. Similarly, second control units  128 ,  130  of the second vehicle  104  are communicatively coupled to each other. In certain embodiments, each of the first and second control units  124 ,  126 ,  128 ,  130  includes one or more processors (not shown in  FIG. 1 ). The processors perform the functions of the control units  124 ,  126 ,  128 ,  130 . As used herein, the term “control unit” may refer to integrated circuits included in a computer, a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), a specification specific integrated circuit, specification-specific processor, digital signal processors (DSPs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and/or any other programmable circuits. 
     Additionally, the first vehicle  102  includes first sensors  132  disposed at corresponding first locations  134 . The first sensors  132  are used to measure current or voltage corresponding to the first locations  134 . The second vehicle  104  includes second sensors  136  disposed at corresponding second locations  138 . The second sensors  136  are used to measure current or voltage corresponding to the second locations  138 . The terms “first and second locations,” as used herein, refers to locations of electrical nodes. 
     The first sensors  132  are coupled to the first control units  124 ,  126 . Further, the second sensors  136  are coupled to the second control units  128 ,  130 . The first and second sensors  132 ,  136  may include voltage sensors and current sensors. In one embodiment, at least one of the second sensors  136  measure a quantity of electrical output current flowing through the load  106 . 
     In one embodiment, the first inverters  116 ,  118  are controlled by the first control units  124 ,  126 , respectively, based on output of the first sensors  132 . Further, the second inverters  120 ,  122  are controlled by the second control units  128  and  130 , respectively, based on output of the second sensors  136 . In one specific embodiment, the second inverters  120 ,  122  are controlled by the second control units  128  and  130 , respectively, based on the quantity of the electrical output current flowing through the load  106  measured by at least one second sensor  136 . 
     In the illustrated embodiment where the first vehicle  102  is the lead vehicle, the first inverter  116  regulates a corresponding output voltage. Further, the first inverter  118  and second inverters  120 ,  122  regulate a corresponding output current. In one specific embodiment, the second inverters  120 ,  122  are controlled by the second control units  128  and  130 , respectively, based on the measured quantity of the electrical output current flowing through the load  106  such that the second inverters  120  and  122  provide about 50% of the total current required by the load  106 . Hence, the first inverters  116 ,  118  need to provide the remaining 50% of the total current required by the load  106 . Particularly, the quantity of electrical output current flowing through the load  106  is shared among the first and second inverters  116 ,  118 ,  120 ,  122  of the first and second vehicles  102 ,  104 . More particularly, the head end power to be provided to the load  106  is shared among the first and second inverters  116 ,  118 ,  120 ,  122  of the first and second vehicles  102 ,  104 . 
     In one embodiment, the quantity of the electrical output current flowing through the load  106  is equally shared among the first and second inverters  116 ,  118 ,  120 ,  122  of the first and second vehicles  102 ,  104 . In another embodiment, the quantity of the electrical output current flowing through the load  106  is shared unequally among the first and second inverters  116 ,  118 ,  120 ,  122  of the first and second vehicles  102 ,  104 . In a specific embodiment, the quantity of the electrical output current flowing through the load  106  is shared among the first and second inverters  116 ,  118 ,  120 ,  122  of the first and second vehicles  102 ,  104  without any communication between the first and second vehicles  102 ,  104 . In another embodiment, there may be intra-vehicle communication, and/or there may be communication between the first and second vehicles  102 ,  104  and an offboard location that relays such information back to the first and second vehicles  102 ,  104 . The method of sharing of the power provided to the load  106  is explained in greater detail below with reference to subsequent figures. 
     Additionally, with reference to the first vehicle  102 , the first control units  124 ,  126  control pulse width modulation of the first inverters  116 ,  118  respectively, using corresponding carrier waves. Similarly, with reference to the second vehicle  104 , the second control units  128 ,  130  control pulse width modulation of the second inverters  120 ,  122 , respectively using corresponding carrier waves. The carrier waves used for pulse width modulation of the first inverters  116 ,  118  and the carrier waves used for pulse width modulation of the second inverters  120 ,  122  are not mutually synchronized due to lack of communication between the first and second vehicles  102 ,  104 . As a result, a high frequency circulating harmonic current may flow between the first vehicle  102  and the second vehicle  104 . It should be noted herein that the terms ‘high frequency harmonic current’ and ‘high frequency circulating harmonic current’ may be used interchangeably. The frequency of the circulating harmonic current is dependent on a switching frequency of the switches of the first and second inverters  116 ,  118 ,  120 ,  122 . In one embodiment, the frequency of the circulating harmonic current may be a harmonic component of the switching frequency of the switches of the first and second inverters  116 ,  118 ,  120 ,  122 . 
     In one embodiment, the carrier waves used for pulse width modulation of the first inverters  116 ,  118  and carrier waves used for pulse width modulation of the second inverters  120 ,  122  are mutually synchronized by changing time-period of at least one switching cycle of the carrier waves used for pulse width modulation of the second inverters  120 ,  122  based on measurement of a high frequency circulating harmonic current. To state differently, the carrier waves corresponding to the first vehicle  102  is synchronized with the carrier waves corresponding to the second vehicle  104  by changing time-period of at least one switching cycle of the carrier waves of the second vehicle  104  based on the measured high frequency harmonic circulating current. In one embodiment, if the time period of one switching cycle of the carrier waves used for pulse width modulation of the second inverters  120 ,  122  is represented by Ts, the time period of at least one switching cycle of the carrier waves used for pulse width modulation of the second inverters  120 ,  122  is changed from Ts to Ts+ΔTs. In another embodiment, the time period of at least one switching cycle of the carrier waves used for pulse width modulation of the second inverters  120 ,  122  is changed from Ts to Ts−ΔTs Subsequent to change of time period for one or more switching cycles of the carrier waves used for pulse width modulation of the second inverters  120 ,  122 , the carrier waves used for pulse width modulation of the first inverters  116 ,  118  and carrier waves used for pulse width modulation of the second inverters  120 ,  122  are mutually synchronized. 
     The term “synchronization of carrier waves” as used herein, refers to alignment of carrier waves of inverters of one vehicle with carrier waves of inverters of other vehicles. In the illustrated embodiment, carrier waves corresponding to the first vehicle  102  are synchronized with carrier waves corresponding to the second vehicle  104 . The synchronizing of carrier waves aids in limiting any high frequency circulating harmonic current between capacitors (not shown in  FIG. 1 ) of the first and second vehicles  102 ,  104 . Accordingly, the high frequency harmonic current circulating between the first and the second vehicles is reduced to less than or equal to a threshold value. In the illustrated embodiment, no communication is required between the first vehicle  102  and the second vehicle  104 . 
     Although in the illustrated embodiment of  FIG. 1  only two vehicles  102 ,  104  are disclosed, in other embodiments, the number of vehicles may vary depending on the application. Furthermore, although the embodiment of  FIG. 1  discloses a single phase, in other embodiments, the power system may include a plurality of phases. Further, although power system  100  of  FIG. 1  discloses only the first and second inverters  116 ,  118 ,  120 ,  122  which provide head end power to the load  106 , use of additional auxiliary converters and traction converters are also envisioned. 
     Referring now to  FIG. 2 , a detailed diagrammatical representation of one phase of the power system  100  in accordance with certain embodiments of the present invention is depicted. In one embodiment, the power system  100  is a locomotive power system. 
     The power system  100  includes the first and second vehicles  102 ,  104 . The first vehicle  102  includes the first inverters  116 ,  118  coupled in parallel to each other. Further, the second vehicle  104  includes the second inverters  120 ,  122  coupled in parallel to each other. For the ease of illustration, the first inverters  116 ,  118  and the second inverters  120 ,  122  are represented using a single switch  201 . Within the first vehicle  102 , each of the first inverters  116 ,  118  generate at least one of an output voltage and an output current. Further, within the second vehicle  104 , each of the second inverters  120 ,  122  generate at least one of an output voltage and an output current. 
     Reference numeral  202  represents an output end of the first inverter  116 . Further, the reference numeral  204  represents an output end of the first inverter  118 . Reference numeral  206  represents an output end of the second inverter  120  and reference numeral  208  represents an output end of the second inverter  122 . In one embodiment, each of the output ends  202 ,  204 ,  206 ,  208  includes three AC phase terminals. 
     Further, the first vehicle  102  includes a first inductor  210 . The first inductor  210  is coupled to the output end  202  of the first inverter  116 . Additionally, the first vehicle  102  includes another first inductor  212 . The first inductor  212  is coupled to the output end  204  of the first inverter  118 . The second vehicle  104  includes a first inductor  214 . The first inductor  214  is coupled to the output end  206  of the second inverter  120 . Additionally, the second vehicle  104  includes another first inductor  216 . The first inductor  216  is coupled to the output end  208  of the second inverter  122 . 
     Additionally, the first vehicle  102  includes a first capacitor  218 . The first capacitor  218  is coupled to the output ends  202 ,  204  of the first inverters  116 ,  118 . Further, the first capacitor  218  is coupled to the first inductors  210 ,  212 . The first inductors  210 ,  212  and with first capacitor  218  is referred to as a first filter. Similarly, the second vehicle  104  includes a second capacitor  220 . The second capacitor  220  is coupled to the output ends  206 ,  208  of the second inverters  120 ,  122 . Further, the second capacitor  220  is coupled to the first inductors  214 ,  216 . The first inductors  214 ,  216  and the second capacitor  220  forms a second filter. 
     Additionally, a resonant circuit  221  is formed between the first and second vehicles  102 ,  104 . In particular, the resonant circuit  221  is formed by coupling the first capacitor  218  to the second capacitor  220  via the HEP interconnecting train line  114  having the inductance  113 . 
     The resonant circuit  221  provides a low impedance path to harmonics of the switching frequency when the value of a resonant frequency is substantially same as a value of the switching frequency of switches  201  of the first or second inverters  116 ,  118 ,  120 ,  122  and corresponding harmonics of the switching frequency. As a result, the high frequency circulating harmonic current flows between the capacitors  218 ,  220  of the first and second vehicles  102 ,  104 . In such a scenario, the impedance of the resonant circuit  221  is modified by adding/removing capacitors/inductors from the resonant circuit  221  to shift the resonant frequency from the switching frequency of switches  201  of the first or second inverters  116 ,  118 ,  120 ,  122 . Accordingly, the high frequency circulating harmonic current flowing between the capacitors  218 ,  220  of the first and second vehicles  102 ,  104  is limited. 
     In illustrated embodiment, the first vehicle  102  includes a current limiting device such as a second inductor  222 . Further, the second vehicle  104  includes a current limiting device such as another second inductor  224 . The second inductors  222 ,  224  are coupled in series to the resonant circuit  221 . The coupling of the second inductors  222 ,  224  in series to the resonant circuit  221  shifts resonant frequency from a switching frequency of the switches  201  of the first or second inverters  116 ,  118 ,  120 ,  122  and corresponding harmonics of the switching frequency, thereby limiting flow of high frequency circulating harmonic current between the first and second vehicles  102 ,  104 . 
     In another embodiment, at least one capacitor of the first and second capacitors  218 ,  220  is decoupled from the resonant circuit  221 , using a switch  223 . Accordingly, the resonant circuit  221  is eliminated. 
     In yet another embodiment, in order to limit the high frequency circulating harmonic current, a synchronizing line  226  (for example, a communication line) is used to couple the first control units  124 ,  126  to the second control units  128 ,  130 . The use of the synchronizing line  226  enables to synchronize the carrier waves corresponding to the first vehicle  102  to the carrier waves corresponding to the second vehicle  104 . As a result, the high frequency circulating harmonic current is minimized. The synchronizing line  226  and the HEP interconnecting train line  114  may be referred to as a common bus. 
     In one embodiment, if the synchronizing line  226  is used, the value of inductance of the second inductors  222 ,  224  is negligible. In another embodiment, if the synchronizing line  226  is used, the second inductors  222 ,  224  may not be employed. Thus, the cost and footprint of the second inductors  222 ,  224  may be reduced/avoided. In one embodiment, if the synchronizing line  226  is not used, value of inductance of the second inductors  222 ,  224  is high. In another embodiment, if the capacitors  218 ,  220  are decoupled from the resonant circuit  221 , the synchronizing line  226  may not be employed. In yet another embodiment, if the carrier waves corresponding to the first vehicle  102  is synchronized with the carrier waves corresponding to the second vehicle  104  by changing time-period of at least one switching cycle of the carrier waves of the second vehicle  104  based on the measured high frequency harmonic circulating current, the value of inductance of the second inductors  222 ,  224  is negligible. In such an embodiment, the use of a synchronizing line  226  is avoided. 
     Additionally, the first and second vehicles  102 ,  104  include first and second converter breakers  228 ,  230  respectively. Further, the first vehicle  102  includes first switches/breakers  232 ,  234  and the second vehicle  104  includes second switches/breakers  236 ,  238 . The first and second converter breakers  228 ,  230  and the first and second switches/breakers  232 ,  234 ,  236 ,  238  enable to establish or terminate an electrical connection between the first and second vehicles  102 ,  104 . Additionally, the first and second converter breakers  228 ,  230  and the first and second switches/breakers  232 ,  234 ,  236 ,  238  enable to establish or terminate an electrical connection between the first and second vehicles  102 ,  104  and the load  106 . 
     In the illustrated embodiment, the first locations of the first sensors  132  are represented by reference numerals  240 ,  242 ,  244 ,  246 ,  248 ,  250 ,  252 . The reference numeral  240  represents a location of the output end  202  of the first inverter  116  and the reference numeral  242  represents a location of the output end  204  of the first inverter  118 . Specifically, the first locations  240 ,  242  may be referred to as first inverter output locations. Further, the reference numeral  244  represents a location proximate to the first capacitor  218  of the first vehicle  102 . Specifically, the first location  244  may be referred to as a first capacitor location. The reference numerals  246 ,  248  are representative of locations proximate to the first converter breaker  228 . In particular, the reference numeral  246  represents a location proximate to the first converter breaker  228  and towards first inverters  116 ,  118 . The reference numeral  248  represents a location proximate to the first converter breaker  228  and towards the HEP train line  108 . Specifically, the first locations  246 ,  248  may be referred to as first converter breaker locations. The reference numerals  250 ,  252  represent two locations along the HEP train line  108 . Specifically, the first locations  250 ,  252  may be referred to as first train line locations. 
     Within the first vehicle  102 , first sensors  132  are disposed at the first locations  240 ,  242 ,  244 ,  246 ,  248 ,  250 ,  252 . The first sensors  132  include first current sensors  132   a  and first voltage sensors  132   b.  Particularly, the first current sensors  132   a  are disposed at the first locations  240 ,  242 ,  246 ,  250 ,  252 . Further, the first voltage sensors  132   b  are disposed at the first locations  244 ,  248 . 
     Second locations of the second sensors  136  are represented by reference numerals  258 ,  260 ,  262 ,  264 ,  266 ,  268 , and  270 . The reference numeral  258  represents a location at the output end  206  of the second inverter  120  and the reference numeral  260  represents a location of the output end  208  of the second inverter  122 . Specifically, the second locations  258 ,  260  may be referred to as second inverter output locations. Further, the reference numeral  262  represents a location proximate to the second capacitor  220 . Specifically, the second location  262  may be referred to as a second capacitor location. The reference numerals  264 ,  266  are representative of locations proximate to the second converter breaker  230 . In particular, the reference numeral  264  represents a location proximate to the second converter breaker  230  and towards second inverters  120 ,  122 . Further, the reference numeral  266  represents a location proximate to the second converter breaker  230  and towards the HEP train line  108 . Specifically, the second locations  264 ,  266  may be referred to as second converter breaker locations. The reference numerals  268 ,  270  represent two locations respectively along the HEP train line  108 . Specifically, the second locations  268 ,  270  may be referred to as second train line locations. 
     Within the second vehicle  104 , the second sensors  136  are disposed at the second locations  258 ,  260 ,  262 ,  264 ,  266 ,  268 , and  270 . The second sensors  136  include second current sensors  136   a  and second voltage sensors  136   b.  The second current sensors  136   a  are disposed at the second locations  258 ,  260 ,  264 ,  268 ,  270 . Further, the second voltage sensors  136   b  are disposed at the second locations  262 ,  266 . 
     The first current and voltage sensors  132   a,    132   b  of the first vehicle  102  are coupled to the first control units  124 ,  126 . Further, the second current and voltage sensors  136   a,    136   b  of the second vehicle  104  are coupled to the second control units  128 ,  130 . The current and voltage measurement by the first current and voltage sensors  254 ,  256 , of the first vehicle  102  is not communicated to the second vehicle  104  and vice versa. 
     As noted with respect to  FIG. 1 , the operation of the first inverters  116 ,  118  is controlled by the first control units  124 ,  126 . Further, the operation of the second inverters  120  and  122  is controlled by the second control units  128 ,  130 . 
     Additionally, the first and second control units  124 ,  126 ,  128 ,  130  facilitates to establish an electrical connection between the first vehicle  102  and the second vehicle  104 . When the operation of the power system  100  is initiated, the first converter breaker  228  is in a closed state and the first switch/breaker  234  is in a closed state. Further, the second switches/breakers  236 ,  238  are in a closed state, and the second converter breaker  230  is in an open state. In accordance with the illustrated embodiment, only the first vehicle  102  is used to provide electric power to the load  106 . 
     After a predetermined time duration, for example, 0.5 seconds, in one embodiment, the second vehicle  104  also starts providing electric power to the load  106 . In particular, the electric power provided to the load  106  is shared by the first and second vehicles  102 ,  104 . Such sharing of the electric power by the first and second vehicles  102 ,  104  is possible only if the first and second vehicles  102 ,  104  are electrically coupled to each other and to the load  106 . In particular, the second converter breaker  230  needs to be in a closed state for electrically coupling the first and second vehicles  102 ,  104  to each other and to the load  106 . 
     The first vehicle  102  needs to be synchronized with the second vehicle  104  before establishing the electrical connection between the first vehicle  102  and the second vehicle  104 . Particularly, a voltage V abc_CapT  needs to be synchronized with a voltage V abc_LdT . More particularly, a phase and a magnitude of the voltage V abc_CapT  needs to be synchronized with a phase and a magnitude of the voltage of the voltage V abc_LdT . The voltage V abc_LdT  may be referred to as a first voltage and the voltage V abc_CapT  may be referred to as a second voltage. The voltage V abc_LdT  may be referred to as a quantity of output voltage of the vehicle  102 . The voltage V abc_CapT  may be referred to as a voltage of the second capacitor  220 . In one embodiment, the voltage V abc_CapT  is measured using the second voltage sensor  136   b  disposed at the second capacitor location  262  of the second vehicle  104 . Further, the voltage V abc_LdT  is measured using the second voltage sensor  136   b  disposed at the second converter breaker location  266  of the second vehicle  104 . 
     Further, a phase lock loop is employed to lock a phase and a magnitude of the voltage V abc_CapT  with a phase and a magnitude of the voltage V abc_LdT . When the phase and the magnitude of the voltage V abc_CapT  is locked with the phase and the magnitude of the voltage V abc_LdT , the voltage V abc_CapT  is synchronized with the voltage V abc_LdT . The locking of the phase and magnitude of the voltage V abc_CapT  with the phase and magnitude of the voltage V abc_LdT  refers to a condition when the phase and the magnitude of the voltage V abc_CapT  is same as the phase and the magnitude of V abc_LdT . When the voltage V abc_CapT  is synchronized with the voltage V abc_LdT , the second converter breaker  230  is closed. Accordingly, the vehicle  102  is electrically coupled to the vehicle  104 . In one embodiment, when the first and the second vehicles  102 ,  104  are synchronized, both the first and second vehicles  102 ,  104  share electric power provided to the load  106 . In another embodiment, even after synchronization of the first and the second vehicles  102 ,  104 , only the first vehicle  102  provides electric power to the load  106  and the second vehicle  104  provides electric power to the load  106  only if the total electric power to be provided to the load  106  is above a determined value of electric power. 
     In addition, the first and second control units  124 ,  126 ,  128 ,  130  of the corresponding first and second vehicles  102 ,  104  input a plurality of operational parameters corresponding to each of the first and second vehicles  102 ,  104 . The plurality of operational parameters includes an assigned lead position of a vehicle, an assigned trail position of a vehicle, number of inverters in each of the vehicles, an assigned position of each inverter among inverters of each of the vehicles, and number of vehicles. 
     In one embodiment, operational parameters such as but not limited to an assigned lead position or a trail position of the first vehicle  102 , number of inverters in the first vehicle  102 , assigned position of each inverter of the first vehicle  102 , and number of vehicles are input to the first control units  124 ,  126 . Similarly, operational parameters such as but not limited to an assigned lead position or an assigned trail position of the second vehicle  104 , number of inverters in the second vehicle  104 , assigned position of each inverter of the second vehicle  104 , and number of vehicles are input to the second control units  128 ,  130 . In one embodiment, the trail vehicle may be coupled to the load  106  and the head end power to be provided to the load  106  is provided by a combination of the lead vehicle and the trail vehicle. 
     It should be noted herein that a vehicle which is assigned the lead position operates as a lead vehicle. For example, for an integer value k, where k=1 is assigned corresponding to a vehicle which is assigned a lead position. The vehicles which are assigned trail positions operate as trail vehicles. For example, for an integer value k, where k≥2 is assigned corresponding to the vehicles which are assigned the trail position. For example, if the first vehicle  102  is assumed to operate as a lead vehicle and the second vehicle  104  operates as a trail vehicle, an integer value  1  is assigned to the first vehicle  102  and an integer value  2  is assigned to the second vehicle  104 . 
     The term “assigned position of each inverter,” as used herein, refers to a functionality of an inverter. The functionality of the inverter is characterized by whether an inverter controls current or voltage. In another embodiment, the functionality of inverter is characterized by whether an inverter is a master inverter or a slave inverter. In one embodiment, the first and second inverters  116 ,  120  operate as master inverters and the first and second inverters  118 ,  122  operate as slave inverters. Further, in one embodiment the first inverter  116  controls output voltage and the first inverter  118  and the second inverters  120 ,  122  control output current. 
     For example, the first control unit  124  regulates voltage of the first capacitor  218  of the vehicle  102  to a predefined value, using the first inverter  116 , where the first inverter  116  operates as the master inverter. Further, the first control unit  126  controls a current generated by the first inverter  118  of the first vehicle  102 . 
     Further, in an embodiment, where both the first and second vehicles provide power to the load  106 , the second control units  128 ,  130  control operation of the second inverters  120 ,  122  of the second vehicle  104  based on a current I abc_LdT2  measured by the second current sensor  130   a  at the second train line location  270 . The current I abc_LdT2  is a measure of the quantity of the electrical output current flowing through the load  106 . The measured current I abc_LdT2  and voltage V abc_CapT  are input to the second control units  128 ,  130 . The current flowing through the second capacitor  220  is determined by the second control units  128 ,  130  based on the voltage V abc_CapT  of the second capacitor  220  and a value of capacitance of the second capacitor  220 . The second inverters  120 ,  122  are controlled based on the measured current I abc_LdT2  and voltage V abc_CapT , such that each of the second inverters  120 ,  122  generate a current which is a sum of half of the current flowing through the second capacitor  220  and one fourth of the measured current I abc_LdT2 . Accordingly, the second inverters  120 ,  122  together provide a current having a value of about 
     
       
         
           
             
               
                 I 
                 
                   
                     abc 
                      
                     _ 
                      
                     LdT 
                   
                    
                   
                       
                   
                    
                   2 
                 
               
               2 
             
             . 
           
         
       
     
     The first vehicle  102  needs to provide about a current having a value of 
     
       
         
           
             
               
                 I 
                 
                   
                     abc 
                      
                     _ 
                      
                     LdT 
                   
                    
                   
                       
                   
                    
                   2 
                 
               
               2 
             
             . 
           
         
       
     
     since, the second inverters  120 ,  122  together provide a current having a value of about 
     
       
         
           
             
               
                 I 
                 
                   
                     abc 
                      
                     _ 
                      
                     LdT 
                   
                    
                   
                       
                   
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                   2 
                 
               
               2 
             
             . 
           
         
       
     
     Thus, a quantity of output current of the first vehicle  102  at the first train line location  252 , is 
     
       
         
           
             
               
                 I 
                 
                   
                     abc 
                      
                     _ 
                      
                     LdT 
                   
                    
                   
                       
                   
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                   2 
                 
               
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             . 
           
         
       
     
     In the illustrated embodiment, a voltage V abc_CapL  is measured using the first voltage sensor  132   b.  The voltage V abc_CapL  may be referred to as the voltage of the first capacitor  218 . The current I abc_LdL2  and the voltage V abc_CapL  are input to the first control units  124 ,  126 . The current flowing through the first capacitor  218  is determined by the first control units  124 ,  126 , based on the voltage V abc_CapL  and the value of capacitance of the first capacitor  218 . 
     The first inverter  118  is controlled by the first control unit  126  based on the current I abc_LdL2  and the voltage V abc_CapL  such that the current generated by the first inverter  118  is a sum of half of the value of current flowing through the first capacitor  218  and the current 
     
       
         
           
             
               
                 I 
                 
                   
                     abc 
                      
                     _ 
                      
                     LdL 
                   
                    
                   
                       
                   
                    
                   2 
                 
               
               2 
             
             . 
           
         
       
     
     Accordingly, the first inverter  116  needs to provide a current which is a sum of half of the value of current flowing through first capacitor  218  and the current 
     
       
         
           
             
               
                 I 
                 
                   
                     abc 
                      
                     _ 
                      
                     LdL 
                   
                    
                   
                       
                   
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                   2 
                 
               
               2 
             
             . 
           
         
       
     
     Hence, the current I abc_LdL2  is shared among the first inverters  116 ,  118 . Further, the current flowing through the first capacitor  218  is shared among the first inverters  116 ,  118 . 
     As a result, the first inverters  116 ,  118  of the first vehicles  102  and the second inverters  120 ,  122  of the second vehicle  104  equally share the quantity of output electrical current provided to the load  106 . In another embodiment, the first inverters  116 ,  118  of the first vehicles  102  and the second inverters  120 ,  122  of the second vehicle  104  unequally share the quantity of output electrical current provided to the load  106 . 
       FIG. 3  is a detailed diagrammatical representation of a power system  300  in accordance with an exemplary embodiment of the present invention. In the illustrated embodiment, the power system  300  includes ‘m’ vehicles, where each vehicle includes ‘n’ inverters, where m and n are integer values and m&gt;1 and n≥1. In particular, current provided to a load  302  is shared by ‘n’ inverters corresponding to each of the ‘m’ vehicles. 
     For the ease of representation, in the illustrated embodiment, only the first vehicle, the second vehicle, and the m th  vehicle are represented. The first, second, and m th  vehicles are represented by reference numerals  304 ,  306 ,  308  respectively. In the illustrated embodiment, the first vehicle  304  is a lead vehicle and the second and m th  vehicles  306 ,  308  are trail vehicles. For an integer value k, where k≥1 is assigned to the corresponding vehicle based on the assigned lead or trail position of the corresponding vehicle. For example, an integer value  1  is assigned to the first vehicle  304 , an integer value  2  is assigned to the second vehicle  306 . 
     Further, for ease of illustration, within each of the vehicles, only the first inverter, the second inverter, and the n th  inverter are depicted. The first, second, and n th  inverters of the first vehicle  304  are represented by reference numerals  310 ,  312 ,  314  respectively. The first, second, and n th  inverters of the second vehicle  306  are represented by reference numerals  316 ,  318 ,  320  respectively. Additionally, the first, second, and n th  inverters of the m th  vehicle  308  are represented by reference numerals  322 ,  324 ,  326  respectively. Each of the vehicles  304 ,  306 ,  308  includes a capacitor represented by reference numerals  328 ,  330 ,  332 , respectively. 
     A quantity of electrical output current of the vehicle  304  is represented as I 1 . Further, current flowing through the capacitor  328  is represented as x. Accordingly, current generated by each inverter of the vehicle  304  is represented by the relation: 
     
       
         
           
             
               
                 
                   
                     
                       I 
                       1 
                     
                     
                       
                         
                           
                             ( 
                             
                               assigned 
                                
                               
                                   
                               
                                
                               integer 
                                
                               
                                   
                               
                                
                               value 
                                
                               
                                   
                               
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                               of 
                                
                               
                                   
                               
                                
                               vehicle 
                                
                               
                                   
                               
                                
                               304 
                               × 
                             
                           
                         
                       
                       
                         
                           
                             
                               number 
                                
                               
                                   
                               
                                
                               of 
                                
                               
                                   
                               
                                
                               inverters 
                                
                               
                                   
                               
                                
                               in 
                                
                               
                                   
                               
                                
                               the 
                                
                               
                                   
                               
                                
                               vehicle 
                                
                               
                                   
                               
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                               304 
                             
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                             number 
                              
                             
                                 
                             
                              
                             of 
                              
                             
                                 
                             
                              
                             inverters 
                           
                         
                       
                       
                         
                           
                             in 
                              
                             
                                 
                             
                              
                             the 
                              
                             
                                 
                             
                              
                             vehicle 
                              
                             
                                 
                             
                              
                             304 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     A quantity of electrical output current of the vehicle  306  is represented as I 2 . Further, current flowing through the capacitor  330  is represented as y. Accordingly, current generated by each inverter of the vehicle  306  is represented by relation (2). 
     
       
         
           
             
               
                 
                   
                     
                       I 
                       2 
                     
                     
                       
                         
                           
                             ( 
                             
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                                
                               
                                   
                               
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                               value 
                                
                               
                                   
                               
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                               of 
                                
                               
                                   
                               
                                
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                                
                               
                                   
                               
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                               306 
                               × 
                             
                           
                         
                       
                       
                         
                           
                             number 
                              
                             
                                 
                             
                              
                             of 
                              
                             
                                 
                             
                              
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                              
                             in 
                              
                             
                                 
                             
                              
                             the 
                              
                             
                                 
                             
                              
                             vehicle 
                              
                             
                                 
                             
                              
                             306 
                           
                         
                       
                     
                   
                   + 
                   
                     y 
                     
                       
                         
                           
                             number 
                              
                             
                                 
                             
                              
                             of 
                              
                             
                                 
                             
                              
                             inverters 
                           
                         
                       
                       
                         
                           
                             in 
                              
                             
                                 
                             
                              
                             the 
                              
                             
                                 
                             
                              
                             vehicle 
                              
                             
                                 
                             
                              
                             306 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     A quantity of electrical output current of the vehicle  308  is represented as I m . Further, current through the capacitor  332  is represented as z. Accordingly, current generated by each inverter of the vehicle  308  is represented by relation (3). 
     
       
         
           
             
               
                 
                   
                     
                       I 
                       m 
                     
                     
                       
                         
                           
                             assigned 
                              
                             
                                 
                             
                              
                             integer 
                              
                             
                                 
                             
                              
                             value 
                              
                             
                                 
                             
                              
                             of 
                              
                             
                                 
                             
                              
                             vehicle 
                              
                             
                                 
                             
                              
                             308 
                             × 
                           
                         
                       
                       
                         
                           
                             number 
                              
                             
                                 
                             
                              
                             of 
                              
                             
                                 
                             
                              
                             inverters 
                              
                             
                                 
                             
                              
                             in 
                              
                             
                                 
                             
                              
                             the 
                              
                             
                                 
                             
                              
                             vehicle 
                              
                             
                                 
                             
                              
                             308 
                           
                         
                       
                     
                   
                   + 
                   
                     z 
                     
                       
                         
                           
                             number 
                              
                             
                                 
                             
                              
                             of 
                              
                             
                                 
                             
                              
                             inverters 
                           
                         
                       
                       
                         
                           
                             in 
                              
                             
                                 
                             
                              
                             the 
                              
                             
                                 
                             
                              
                             vehicle 
                              
                             
                                 
                             
                              
                             308 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     According to embodiments of the present invention, the current I m  flows through the load  302 . In one embodiment, the current I m  flowing through the load  302  is shared equally by the inverters of the first, second, third . . . and m th  vehicles. In particular, the electric power provided to the load  302  is shared equally among the inverters of the first, second, third . . . and m th  vehicles. In another embodiment, the power provided to the load  302  is shared unequally among the inverters of the first, second, third . . . and m th  vehicles. 
     Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this specification belongs. The terms “first”, “second”, and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The use of “including,” “comprising” or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect. Furthermore, terms “circuit” and “circuitry” and “controlling unit” may include either a single component or a plurality of components, which are active and/or passive and are connected or otherwise coupled together to provide the described function. In addition, the term “operatively coupled,” as used herein, includes wired coupling, wireless coupling, electrical coupling, magnetic coupling, radio communication, software based communication, or combinations thereof. 
     The exemplary process steps such as those that may be performed by the exemplary system may be implemented by suitable code on a processor-based system such as a general-purpose or special-purpose computer. It should also be noted herein that different exemplary implementations may perform some or all of the steps described herein in different orders or substantially concurrently. Furthermore, the functions may be implemented in a variety of programming languages including but not limited to C++ or Java. Such code may be stored or adapted for storage on one or more tangible, machine readable media such as on data repository chips, local or remote hard disks, optical disks (that is, CDs or DVDs), memory or other media, which may be accessed by a processor-based system to execute the stored code. The tangible media may include paper or another suitable medium upon which the instructions are printed. For instance, the instructions may be electronically captured via optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in the data repository or memory. 
     In accordance with the embodiments discussed herein, the exemplary power system having a plurality of power generating units and the method of operating the power system enables sharing electric power to be provided to the load between the plurality of power generating units of the power system. In particular, the exemplary system and method enables sharing head end power provided to the load among the power converting subunits of the plurality of power generating units of the power system. Further, the system and method uses sensors in respective power generating units to control operation of the power converting subunits of the respective power generating units. The data measured by the sensors of one power generating unit is not communicated to the other power generating unit. Accordingly, control of the power system is simpler and efficient. Further, the power rating of the power converting subunits used in the power generating units is a nominal value, since the head end power to be provided to the load is shared between the plurality of power generating units of the power system. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof.