Electrical power system and method for single-phase traction load supply by balancing three-phase power source

Abstract

The invention relates to an electrical power system (100) and method for supplying single-phase traction loads (109) by balancing a three-phase power source (106). The system (100) comprises a multi-winding three-phase transformer (102), a power electronics converter (103), a coupling element (104), an isolation transformer (105), voltage sensors (107), current sensors (108), and a controller (700). The converter (103), connected in parallel with single-phase loads (109), redistributes active power among secondary phases to ensure balanced current draw. The coupling element (104), implemented as an inductor, LC, LCL, or TCLC module, enables reactive power support and harmonic mitigation. Vector-group configuration of transformer windings (111-113, 115- 117) is selected to optimize converter control and phase angle alignment. The controller (700) dynamically regulates converter switching to maintain balanced operation, unity power factor, and improved power quality. Offering a cost- effective alternative to special transformer based traction substation for high- power single-phase applications.

Description

[0001] TITLE

[0002] Electrical power system and method for single-phase traction load supply by balancing three-phase power source

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to the field of electrical engineering, particularly to the application of power electronics in optimizing power systems and improving power quality for single-phase traction load applications. It discloses an electrical power system and method for supplying single-phase traction loads by balancing a three-phase power source through coordinated control of transformers and power electronic converters. The invention is applicable to railway traction substations, industrial plants, and utility systems where large single-phase loads cause supply unbalance. By integrating standard multi-winding transformers with intelligent converter-based control, the system manages active power flow among phases, supports reactive power, and compensates harmonics, ensuring balanced operation and unity power factor. This approach eliminates the need for costly special transformers, enhances overall power quality, improves system efficiency, and significantly reduces capital and maintenance costs.

[0005] BACKGROUND OF THE INVENTION

[0006] Electrical power supply systems are designed to deliver electrical energy from generating stations to various categories of loads. For industrial and transportation applications such as railway traction systems, the connected loads are typically large, operating in the megawatt range, and exhibit high variability due to the dynamic nature of their operational cycles. These characteristics cause frequent fluctuations in load magnitude and power factor, which directly influence the stability and balance of the power supply system.

[0007] A fundamental peculiarity of traction loads is that they are predominantly single-phase in nature, while the upstream supply grid operates as a three-phase system. In general, when a single-phase load is connected on a three-phase network, it draws unbalanced current from the supply. Such unbalanced operation results in (i) unequal loading of the three phases, (ii) neutral voltage displacement,(iii) increased losses in transmission and transformer windings and (iv) adverse impacts on voltage regulation and power quality. These effects are particularly severe in traction substations where large, rapidly varying single-phase loads are connected, leading to unbalanced power flow and poor utilization of the generating and transmission capacity.

[0008] To mitigate unbalance, several transformer connection schemes and power supply configurations as discussed below have been historically employed in traction systems.

[0009] (i) Phase Rotation Technique:

[0010] Single-phase transformers are connected between two phases of a three-phase supply in a substation, while the neighboring substation is connected to a different phase pair. Over long distances, this alternation distributes loading approximately evenly among the three phases, thereby maintaining average balance across the grid over time.

[0011] (ii) Special Transformer Configurations:

[0012] Various special transformer connections such as Scott, V-V, Le-Blanc, Woodbridge, YnVd, Yd, and Multi-Purpose Balance Transformer (MPBT) have been developed to convert a three-phase input into two or more single-phase outputs. These configurations are typically used to feed the UP and DOWN traction lines from a single traction substation.

[0013] Although these special transformers enable partial or complete balancing of the three-phase supply, they suffer from several limitations. Balanced operation is achieved only when the two secondary single-phase loads (e.g., UP and DOWN lines) are equally loaded which is an ideal condition rarely met in practice. Unequal loading introduces neutral current and voltage unbalance that cannot be completely compensated by passive transformer configurations. Special transformers are custom-designed for traction substations, leading to high manufacturing and installation costs. These arrangements do not support reactive power demand and address the harmonics issues introduced by modem traction converters and drives.

[0014] With the increasing use of power-electronic traction drives, the systemexperiences not only load unbalance and reactive power demand but also harmonic distortion. Therefore, there is a pressing need for a cost-effective and flexible solution that employs standard multi-winding transformers rather than special designs, integrates power-electronic converters for dynamic control of active and reactive power flow, achieves balanced three-phase operation even under unequal single-phase loading, and enhances power quality by mitigating harmonics and maintaining unity power factor.

[0015] DESCRIPTION OF THE RELATED ART

[0016] Electric railway traction systems commonly draw large, time-varying single-phase power from an upstream three-phase grid, which introduces negativesequence currents, voltage unbalance, power-factor deterioration, and harmonics. Historically, railways mitigated unbalance using special transformer connections e.g., Scott, V / V. Le-Blanc, Woodbridge, YnVd / Yd to derive two single-phase outputs (UP / DOWN lines) from a three-phase source; these schemes balance satisfactorily only when the two single-phase loads are equal, which is seldom true in practice, leaving current unbalance and power-quality issues unaddressed (Firat et al., “A comparative study of different transformer connections for railway power supply-mitigation of voltage unbalance f in 10th International Conference on Advances in Power System Control, Operation Management (APSCOM 2015), Hong Kong, 2015, pp. 1-6). Comparative studies document that while such windings can reduce unbalance, they do not solve asymmetry or harmonic pollution inherent to modem traction drives (H. Yu et al., "Research on the selection of railway traction transformer f in 2010 Conference Proceedings IPEC. IEEE, 2010, pp. 677-681). In response, power-electronics-based compensators emerged. The Railway Static / Power Conditioner (RPC) often implemented as a back-to-back converter with a DC link, actively injecting compensating currents to balance phase power, correct power factor, and suppress harmonics in traction power-supply systems. Control and implementation results show that RPCs can substantially mitigate unbalance and improve supply-side power quality under unequal singlephase loading (S. Hu et al., “A balance transformer-integrated RPFC for railwaypower system PQ improvement with low-design capacity,” IEEE Transactions on Industrial Electronics, vol. 65, no. 4, pp. 2925-2934, April 2018), (Patent Document: W02016030212A1). Similarly, the power-electronics compensators based Co-Phase (COP) systems addresses similar power quality issues for highspeed railway technology (Ning-Yi Dai et al., “Modelling and control of a railway power conditioner in co-phase traction power system under partial compensation,” IET Power Electronics, vol. 7, no. 5, pp. 1044-1054, 2014), (Patent document: CN 113904565 A), (Patent Document: DE 102008012325A1). COP systems supply power to a single section of the catenary supply system thus reducing the neutral sections, whereas RPC system supplies power to two sections of the catenary supply system. Alternative or complementary approaches include STATCOM-based compensation or hybrid methods (e.g., SVC and active filtering) aimed at reducing compensator rating and losses while addressing reactive power and harmonics, particularly for Scott or NiN transformer-fed railways (Luis A. M. Barros et al., “STATCOM Evaluation in Electrified Railway Using V / V and Scott Power Transformers,” Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, Vol. 315, Springer, Cham), (M. Habibolahzadeh et al., “Hybrid SVC-HPQC scheme with partial compensation technique in co-phase electric railway system,” in 201927th Iranian Conference on Electrical Engineering (ICEE), Yazd, Iran, 2019, pp. 679-684). Theoretical principles based methods are also used to address the power quality issue of unbalance in a three-phase supply based systems supplying power to single-phase loads (Patent Document: DE19828404C1). More recent COP / RPC architectures synthesize or re-balance single-phase feeder power from the three-phase grid using modular multilevel converters (MMC) which improves the energy conversion efficiency and fault-tolerant ability of power conversion systems; these works demonstrate effective active-power reallocation among phases with concomitant reactive and harmonic compensation (D. Ronanki and S. S.Williamson, “Modular multilevel converters for transportation electrification: Challenges and opportunities,” IEEE Transactions on Transportation Electrification, vol. 4, no. 2,pp. 399-407, 2018), (P. Guo et al., "Analysis and control of modular multilevel converter with split energy storage for railway traction power conditioner f IEEE Transactions on Power Electronics, vol. 35, no. 2, pp. 1239-1255, 2020).

[0017] Early patent literature focuses on transformer designed for balancing of unbalanced single-phase loads (e.g., multi-secondary or current-balancing transformer arrangements), whereas later filings disclose railway power conditioners tailored for co-phase supply that dynamically exchange real and reactive power between phases to achieve balance (Patent document: US5557249A). Despite these advances, much of the prior art either (i) relies on bespoke traction substation transformers (raising capex and limiting configurability), or (ii) integrates power electronics on top of special transformer schemes, rather than replacing them with standard, multi -winding transformers plus coupling elements and converters that flexibly manage active-power transfer among secondary phases, provide reactive support (e.g., via DC-link / coupling networks), and perform harmonic compensation all while drawing balanced three-phase power at (or near) unity power factor under unequal single-phase loading.

[0018] OBJECT OF THE INVENTION

[0019] The principal object of the present invention is to provide an electrical power system and method for optimizing single-phase traction load supply by integrating standard power transformers with power electronic converters and coupling elements to achieve balanced three-phase operation, enhanced power quality, and reduced system cost.

[0020] Further object of present invention is to manage the flow of active power among the secondary phases of a three-phase transformer such that each phase draws equal power from the source even under unequal single-phase loading conditions.

[0021] Further object of present invention is to provide reactive power support for single-phase traction loads by dynamically controlling converter operation or coupling elements such as inductors or TCLC modules.

[0022] Further object of present invention is to compensate harmonics produced bynon-linear traction loads using converter-based control algorithms.

[0023] Further object of present invention is to ensure that the system maintains balanced power draw from the three-phase grid and operates at or near unity power factor.

[0024] Further object of present invention is to employ standard multi-winding transformers instead of specialized transformers, thereby simplifying design, standardizing hardware, and reducing overall capital cost.

[0025] Further object of present invention is to utilize the DC-link capacitors of the converter as reactive power reservoirs, thus improving dynamic power factor correction capability and system efficiency.

[0026] Further object of present invention is to enable modular and scalable implementation suitable for high-capacity traction substations, industrial feeders, and distributed single-phase load centers.

[0027] Further object of present invention is to provide a power supply to two or more single-phase loads at different phase-displacement angles or a single-phase load at a particular phase-displacement angle.

[0028] Further object of present invention is to ensure that the system continues to supply power to the single-phase loads even under failure of power electronics converter or the controller which controls the converter.

[0029] Existing traction power supply systems are suffering from chronic issues of power unbalance, reactive power deficiency, and harmonic distortion due to large single-phase loads connected to a three-phase grid. Conventional methods such as phase rotation techniques or special transformer configurations (Scott, V-V, Le-Blanc, etc.) only achieve partial or static balancing and depend heavily on load equality across feeder lines. These arrangements fail to adapt dynamically to load variations and do not address harmonic contamination caused by modem power-electronic traction drives. Moreover, the need for custom-designed traction substation transformers at substation increases capital cost and complicates maintenance.

[0030] The present invention departs from conventional practice by replacingspecial traction substation transformers with standardized multi-winding three-phase transformers integrated with power-electronic converters and coupling elements that actively manage real and reactive power distribution. Unlike known Railway Power Conditioner or co-phase systems that rely on custom transformers or isolated converter stations, the proposed system directly connects on the secondary side of a standard transformer and dynamically redistributes power between phases through converter control, ensuring real-time balance and unity power factor. Additionally, by employing TCLC modules or equivalent coupling elements, the invention provides localized reactive power compensation and harmonic filtering without requiring high converter ratings. This approach offers a compact, cost-efficient, and scalable solution that simultaneously addresses active power balancing, reactive support, and harmonic mitigation problems that existing art typically handles through multiple, independently controlled systems.

[0031] SUMMARY OF THE INVENTION

[0032] The present invention provides an electrical power system and method for supplying single-phase traction loads while maintaining balance in a three-phase power source. The invention replaces the use of special traction substation transformers in conventional substations with a standard three-phase multi-winding transformer integrated with a power electronics converter and a coupling element, optionally connected through an isolation transformer. The system is designed to perform three primary functions; (i) managing the flow of active power among transformer secondary phases, (ii) providing reactive-power support, and (iii) compensating harmonics generated by the load thereby achieving balanced three-phase operation and improved power quality.

[0033] The power electronics converter, configured as a three-leg or four-leg, four-wire voltage-source converter, is connected in parallel with single-phase loads on the secondary side of the transformer. Each leg of the converter is connected to a separate secondary phase and to the neutral conductor. A coupling element, implemented as an inductor, EC series circuit, LCL network, or TCLC module, links the converter to the transformer or to the isolation transformer as required bythe system voltage, isolation, and performance considerations. The TCLC module provides dynamic reactive-power compensation by generating reactance of opposite polarity to that of the load, thereby reducing converter rating and enhancing efficiency.

[0034] Voltage and current sensors monitor the system variables, while a controller processes the sensed data to compute reference compensating currents and generate switching signals for the converter. The control algorithm continuously redistributes active power among the phases, maintains reactive-power balance, and suppresses harmonics so that each transformer phase draws an equal magnitude current from the source. The system operates at or near unity power factor, ensuring efficient utilization of the grid and improved voltage regulation.

[0035] By employing conventional transformer designs configurable in delta or star connections and adaptable vector-group arrangements as per international standards, the invention provides flexibility for diverse voltage levels and grounding schemes. The modular configuration allows deployment in traction substations, industrial feeders, and other installations involving high-capacity single-phase loads. Integration of standard transformers with intelligent converter control significantly reduces capital cost, simplifies maintenance, and delivers enhanced power quality through balanced, stable, and efficient operation of the electrical power system.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] An illustrative embodiment of the present invention is diagrammatically shown on the drawing.

[0038] FIG. 1 shows an electrical power system for optimizing power supply to singlephase traction loads by balancing three-phase power source as per present invention.

[0039] FIG. 1-A shows the electrical power system (100) and the controller (700) exchanging the measurement and control signals.

[0040] FIG. 1-B shows the electrical power system (600) which can operate in isolation when the power electronics converter (103) or the controller (700) fails to operate.FIG. 1-C shows the flow-chart of the process of the controller (700).

[0041] FIG. 2 shows various combinations of the windings on primary side and secondary side of the conventional three-phase multi-winding transformer.

[0042] FIG. 3 shows some of the available power electronics converter configurations. FIG. 4 shows four different types of the coupling elements (104).

[0043] FIG. 5 shows an isolation transformer (105).

[0044] FIG. 6 shows results depicting balancing operation starting from 0.4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF) for the electrical power system (100) as per example 2.

[0045] FIG. 7 shows results of balancing operation starting from 0.4 s and under dynamic load change at 4 s: (a) converter DC link voltage with reference DC link voltage (b) voltage across capacitor C 1 and C2 of the converter for the electrical power system (100) as per example 2.

[0046] FIG. 8 shows results of load current with load changing dynamically at 4 s: (a) Phase-a (116) (b) Phase-b (117) for the electrical power system (100) as per example 2.

[0047] FIG. 9 shows results depicting balancing operation with load changing dynamically at 4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF) for the electrical power system (100) as per example 2.

[0048] FIG. 10 shows results depicting balancing operation starting from 0.4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF) for the electrical power system (100) as per example 3.

[0049] FIG. 11 shows results of balancing operation starting from 0.4 s and under dynamic load change at 4 s: (a) converter DC link voltage with reference DC link voltage (b) voltage across capacitor C 1 and C2 of the converter for the electrical power system (100) as per example 3.

[0050] FIG. 12 shows results of load current with load changing dynamically at 4 s: (a) Phase-a (116) (b) Phase-b (117) for the electrical power system (100) as per example 3.FIG. 13 shows results depicting balancing operation with load changing dynamically at 4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF) for the electrical power system (100) as per example 3.

[0051] FIG. 14 shows results depicting balancing operation starting from 0.4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF) for the electrical power system (100) as per example 4.

[0052] FIG. 15 shows results of balancing operation starting from 0.4 s and under dynamic load change at 4 s: converter DC link voltage with reference DC link voltage for the electrical power system (100) as per example 4.

[0053] FIG. 16 shows results of load current with load changing dynamically at 4 s: (a) Phase-a (116) (b) Phase-b (117) for the electrical power system (100) as per example 4.

[0054] FIG. 17 shows results depicting balancing operation with load changing dynamically at 4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF) for the electrical power system (100) as per example 4.

[0055] List of designations / reference numbers in figure

[0056] 100. an electrical power system

[0057] 101. neutral conductor

[0058] 102. a three-phase multi -winding conventional transformer

[0059] 103. a power electronics converter

[0060] 104. a coupling element

[0061] 105. an isolation transformer

[0062] 106. a three-phase power supply

[0063] 107. a voltage sensor

[0064] 108. a current sensor

[0065] 109. a single-phase traction load

[0066] 110. a primary side of a three-phase multi -winding conventional transformer ( 102) 111. a winding on a primary side ( 110)

[0067] 112. a winding on a primary side ( 110)

[0068] 113. a winding on a primary side ( 110)114. a secondary side of a three-phase multi -winding conventional transformer (102)

[0069] 115. a winding on a secondary side ( 114)

[0070] 116. a winding on a secondary side ( 114)

[0071] 117. a winding on a secondary side ( 114)

[0072] 118. a section (UP line) of a catenary system

[0073] 119. a section (DOWN line) of a catenary system

[0074] 120. a circuit breaker

[0075] 121. a circuit maker

[0076] 122. a neutral section on a catenary system

[0077] 201. a star-star configuration of transformer ( 102)

[0078] 202. a delta-star configuration of transformer ( 102)

[0079] 203. a star-delta configuration of transformer ( 102)

[0080] 204. a delta-delta configuration of transformer ( 102)

[0081] 301. a four-leg, four-wire voltage source converter

[0082] 302. a four-leg, four-wire neutral-point clamped voltage source converter 303. a three-leg, four-wire voltage source convertor

[0083] 304. a modular multilevel voltage source converter

[0084] 401. an inductor

[0085] 402. an inductor-capacitor series connection

[0086] 403. an inductor-capacitor-inductor connection

[0087] 404. a TCLC module

[0088] 600. an electrical power system without compensating system

[0089] 700. a controller

[0090] DETAILED DESCRIPTION OF THE INVENTION

[0091] The electrical power system (100) as per present invention is designed to perform following three tasks: (i) managing the flow of active power between the three secondary phases of transformer, (ii) to support the reactive power of loads, and (iii) to compensate harmonics produced by the load.

[0092] As shown in FIG. 1, an electrical power system (100) as per presentinvention comprises of a three-phase multi-winding conventional transformer (102), a power electronics converter (103), a coupling element (104), an isolation transformer (105), current sensors (108), voltage sensors (107) and a controller (700). The conventional transformer (102) is a multi -winding transformer having three -windings (111-113) on a primary side (110) and three-windings (115-117) on a secondary-side (114). The windings (111-113, 115-117) on the primary and secondary side (110, 114) respectively can be connected in either delta or star configuration. The transformer windings (111-113, 115-117) of the primary and secondary side (110, 114) respectively may further be connected in various vector-group configurations as per the IEC (i.e. IEC 60050) or equivalent international standard. The various possible combinations for the windings are shown in FIG. 2. FIG. 2(a) shows star-star configuration (201) of the windings (111-113) and the windings (115-117) on the primary and secondary side (110, 114) respectively. FIG. 2(b) shows delta-star configuration (202) of the windings (111-113) and the windings (115-117) on the primary and secondary side (110, 114) respectively. FIG. 2(c) shows star-delta configuration (203) of the windings (111-113) and the windings (115-117) on the primary and secondary side (110, 114) respectively. FIG. 2(d) shows delta-delta configuration (204) of the windings (111-113) and the windings (115-117) on the primary and secondary side (110, 114) respectively. The selection of transformer vector-group configuration directly influences the control strategy and reference current generation for the power electronics converter (103), as it governs the phase relationship between the three-phase primary (110) and secondary (114) voltages. In a delta-star configuration, the delta-connected primary provides a closed path for circulating zero-sequence and triplen harmonics, preventing their transmission to the grid and allowing the converter (103) to reference a clean, balanced secondary voltage waveform. The 30° phase shift introduced by the delta-star vector group must be accounted for in the converter’s control algorithm to correctly align the reference compensating currents with the actual load currents and voltages. Conversely, in a star-delta configuration, the star-connected primary allows neutral referencing for current measurement and control,while the delta secondary isolates converter-side harmonics from the source and provides inherent load balancing through internal circulating currents. In such a case, the converter control algorithm must adjust the phase reference by -30° and calculate the active and reactive power components accordingly to ensure correct power exchange among phases. When both windings are star-connected (i.e. starstar), the converter operates with zero phase displacement, simplifying synchronization but requiring careful management of third-harmonic and zerosequence components through modulation strategy. Hence, the vector-group configuration determines the mathematical transformation used within the controller (700) for coordinate conversion, reference current synthesis, and switching signal generation. The controller (700) is an electronic control unit designed to acquire system measurements, execute control computations, and generate control outputs to regulate the operation of the electrical power system (100). The controller (700) includes one or more processing devices such as a microcontroller, a digital signal processor, an application-specific processor, or a general-purpose processor, arranged to execute stored program instructions at a speed sufficient for real-time control. The controller (700) further includes one or more memory devices, such as non-volatile memory including flash memory and volatile memory including Static Random-Access Memory (SRAM) and / or Pseudo-Static Random-Access Memory (PSRAM), for storing executable code, control parameters, calibration data, and sampled measurement data. In one embodiment, the controller (700) includes signal -conditioning and conversion circuitry comprising analog-to-digital converters for digitizing analog sensor signals and, where required, digital-to-analog converters for generating analog reference or command signals. The controller (700) also includes one or more communication and interface modules for coupling to external devices, including a human-machine interface and / or display device, supervisory control systems, and protection or monitoring equipment. Input and output capability is provided through analog input and output channels, and digital input and output channels, enabling exchange of signals with the sensors (107, 108), converter gate-drive or switchingcontrol circuitry, interlocks, protection devices, and other subsystems associated with the electrical power system. Proper vector-group selection and algorithmic compensation ensure that the converter (103) maintains accurate phase alignment, effective active power redistribution, and harmonic mitigation, thereby sustaining balanced three-phase operation and unity power factor in the electrical power system (100).

[0093] As shown in FIG. 1, the primary side (110) of the transformer is connected to a three-phase power supply (106) and the secondary side (114) of the transformer (102) is connected to the single-phase loads (109). Two single-phase loads (109) are connected to two different phases (i.e. windings (116, 117) on the secondary side (114) of the transformer (102), that is, each phase has a single-phase load. The single-phase load (109) may be a linear load or a non-linear load or a combination of both. The power rating of these single-phase loads (109) may be 2 - 25 MVA. The electrical power system (100) and the method as per present invention may be more effectively utilized for but not limited to high power rating loads, which may be in kilo Volt-Ampere (kVA) and mega Volt-Ampere (MVA). As shown in FIG.

[0094] 1, the power electronics converter (103) is connected on the secondary side (114) of the transformer (102) in parallel to the single-phase loads (109). Each leg of the power electronic converter (103) is connected to different phases (115-117) of the secondary side (114) of the transformer (102). The fourth leg of the power electronic converter (103) is connected to the neutral conductor (101), the return conductor of the load. The power electronics converter (103) may be any device capable of controlling the flow of power bi-directionally or uni -directionally. It may consist of controlled or un-controlled semiconductor switches for its operation. FIG. 3 shows some of the available power electronics converter (103) configurations like (301-304). A coupling element (104) is used to connect the power electronics converter (103) to the isolation transformer (105) or directly to the secondary transformer (102), as per the requirement of the electrical power system (100) depending upon design criteria such as voltage level, isolation necessity, harmonic performance, converter insulation rating, and intendedcompensation function. In high-voltage or sensitive installations, isolation transformer (105) provides galvanic isolation and filtering benefits, whereas in compact or low-voltage systems, direct coupling minimizes losses and hardware cost. This flexibility allows the same power-balancing principle to be implemented across diverse system scales and operational environments. An inductor (401) or a series connection of inductor-capacitor (402) or an inductor-capacitor-inductor connection (403) or a TCLC module (404) as shown in FIG. 4 may be used as a coupling element to connect legs of the power electronic converter (103) to the point of common coupling. The coupling element (104) may be a device that can limit the rate of change of current or voltage as per the requirement of the electrical power system (100). A TCLC module (404), a type of the coupling element (104) consists of an inductor in series with a parallel combination of a capacitor and a thyristor controlled inductor. Four different types of the coupling elements (104) are shown in FIG. 4. A capacitor or a string of capacitor may be connected across the legs of the power electronics converter (103) as shown in FIG. 3. The voltage of each secondary phase, and capacitor connected across the power electronic converter (103) is measured using individual voltage sensors (107). The load currents and currents of each leg of the power electronic converter (103) are measured using the individual current sensors (108). The controller (700) receives data from the voltage and current sensors (107, 108) and controls functioning of the power electronic convertor (103) by sending control signals as shown in FIG. 1-A, by implementing methods steps as explained as a part of this description. The FIG.

[0095] 1-B, shows the electrical power supply system (600) without the power electronics converter (103) and the coupling element (104) and the isolation transformer (105), depicting the failure of any or all of (103), (104), (105), (700). FIG. 1-C, shows the flow-chart of the process which the controller (700) follows during the normal operation the system (100) for balancing the system and operating it at or near unity power factor with harmonics current mitigation.

[0096] The electrical power system (100) may perform any or all the tasks (i)-(iii) listed above as per the requirement. The first and third task is performed by thepower electronic converter (103) and the second task is dependent on the type of the coupling element (104). If the coupling element (104) used is an inductor (401) or the series combination of inductor-capacitor (402) or a series parallel combination of inductor-capacitor-inductor (403) then, the power electronic converter (103) performs the task of load reactive power compensation. If the TCLC module (404) is used as the coupling element (104) then, the TCLC module (404) compensate the load reactive power. The power electronic converter (103) is operated such that all three phases of the transformer (102) draw the same magnitude of current. The control algorithm calculates the reference power, required to be drawn or supplied by each leg of the power electronic converter (103) based on the total power consumed by both the single-phase loads (109). Based on the calculated reference compensating power, reference compensating currents are calculated. When TCLC modules are connected, the reactive power compensation of the single-phase loads (109) is achieved by producing reactive impedance of same magnitude but opposite polarity in the series connected TCLC modules. That is, if the single-phase loads (109) is having inductive impedance, then TCLC module produces a capacitive impedance across its terminal of the same magnitude, and vice versa. When reactive power compensation is managed by the TCLC modules, the power rating of the power electronic converter (103) reduces. Also, the power flow between the phases of the power electronic converter (103) would only be active power flow. When the compensating system compensates as per the requirement, the process is called the balancing operation, under which balanced power is drawn from the source ( 106) at unity power factor. When the compensating system does not operate and no compensation is performed, the process is called the non-balancing operation, under which unbalanced power is drawn from the source (106) at non-unity power factor.

[0097] Steps for working of the electrical power system (100) as per present invention includes:

[0098] Step 1: Read current and voltage values from the voltage sensor (107) and the current sensors (108) and condition the signals for further processing.Step 2: Calculate each single-phase load’s (109) active power, each single-phase load’s (109) reactive power, each single-phase load (109) current’s harmonic content from values obtained in Step 1.

[0099] Step 3: Calculate total active power requirement of all the single-phase loads (109), total reactive power requirement of all the single-phase loads (109) and total harmonic content in the single-phase loads (109) from values obtained in Step 2. Step 4: Calculate power to be drawn from each secondary phase of the transformer (102) for balanced electrical power system (100) operation, from values obtained in Step 3.

[0100] Step5: Calculate power to be drawn or supplied by each phase of the power electronic converter (103) from values obtained in Step 2 and Step 4.

[0101] Step 6: Calculate required compensating reactive power from values obtained in Step 2.

[0102] Step 7: Calculate compensating harmonic current from values obtained in Step 2 and Step 3.

[0103] Step 8: From the values obtained in Step 5-7, calculate the required current for each phase of the power electronic converter (103).

[0104] Step 9: Compare the instantaneous values of the power electronic converter (103) currents calculated in Step 8 and instantaneous values of the power electronics converter (103) currents obtained from the current sensors (108) in Step 1 to calculate the switching instances of the switching signals for controlling the controlled switches of the power electronic converter (103).

[0105] Step 10: Send the switching signals calculated in Step 9 to the power electronic converter (103) to control its controlled switches individually.

[0106] Step 11 : Go to Step 1.

[0107] Broad workable range of the various system components involved in the present invention is shown in following Table 1, but it may be implemented with the values of parameters not covered by range.

[0108] Table 1

[0109] PARAMETERS VALUESGRID SUPPLY VOLTAGE, vLL66-220 kV CATENARY SUPPLY VOLTAGE, vL20-30 kV TRACTION TRANSFORMER 220 / 25 kV, 30-100 MVA COUPLING INDUCTOR, L 5-250 mH

[0110] DC LINK CAPACITOR, CDC2500-10000 jxF DC LINK VOLTAGE, VDC30-90 kV

[0111] TCLC CAPACITOR, CPF10-500 jxF TCLC INDUCTOR, LPP100-500 mH INDUCTIVE LOADS 2 -25 MVA

[0112] BEST METHOD OF PERFORMING THE INVENTION

[0113] Implementation of the power supply system (100) and the method as per the present invention is illustrated with the help of following examples.

[0114] Example 1

[0115] The power supply system (100) and the method as per the present invention is implemented for a railway electrical traction substation system. This system is assumed to be similar to FIG. 1. For the secondary windings of the three-phase transformer (102) shown in FIG. 1, 1st, 2ndand 3rdphase is named as phase (116), phase-6 (117) and phase-c (115). The phase-a (116) is connected to the UP line (118) of the catenary system supplied by the railway electrical traction substation system and phase -b (117) is connected to the DOWN line (119) of the catenary system supplied by the railway electrical traction substation system. For an example, the load on phase-a (116) has active power requirement of 10 MW and the load on phase-6 (117) has active power requirement of 5 MW, thus the total load active power required is 15 MW. So, each phase (111-113) of the primary side (110) of the three-phase multi-winding conventional transformer (102) should draw 5 MW from the source (106) to balance the power supply system (100). In order to fulfill the load requirement of active power, the power electronic converter (103) should draw 5 MW from phase-c (115) and supply the same to phase-a (116) at the point of common coupling, that is, the point at which the single-phase load (109) and the power electronic converter (103) is connected using the coupling element (104) and / or the isolation transformer (105) to each of the respective phases on thesecondary side (114) ofthe three-phase multi-winding transformer (102). No power should be drawn or supplied from phase-6 (117) by the power electronic converter (103) as load on phase-6 (117) itself is 5 MW. When the power electronic converter (103) controls the flow of active power in this manner than the power drawn from each phase of the conventional three-phase multi-winding transformer (102) is 5 MW each. Further, the load on phase -a (116) has reactive power requirement of 6.2 MV Ar and the load on phase-6 (117) has reactive power requirement of 3.1 MV Ar. In order to fulfill the load requirement of reactive power, the power electronic converter (103) should support the system with reactive power support of 6.2 MV Ar to phase-a (116) and 3.1 MV Ar to phase-6 (117) at the point of common coupling. When the power electronic converter (103) supports the reactive power requirement in this manner then no reactive power is drawn from the source (106) via the conventional three-phase multi-winding transformer (102). Thus, only active power is drawn by the conventional three-phase multi -winding transformer (102) from the source (106), and it is balanced and drawn at unity power factor.

[0116] Further, Examples 2-4 illustrate a simulation study for a system (106) with different power supply voltage, different transformer (102) configurations, different power electronics converter (103) configurations, different coupling element (104) and different ratings of load connected to phase -« (116) and phase-6 (117), which are as mentioned in respective Tables 2-4. The load ratings of the load are also changed dynamically during the simulation process to show the dynamic stability of the system.

[0117] Example 2

[0118] In this illustration, the transformer (102) is configured in star-star configuration (201), power electronics converter (103) is configured as three-leg, four-wire voltage source convertor (303), the coupling element (104) used is a TCLC module (404). The source (106) parameters and the load parameters are mentioned in Table 2.

[0119] Table 2

[0120] Power supply voltage 220 kV line-to-line voltagemaximum load on the system (100) 17.65 MV Ar

[0121] minimum load on the system (100) 11.76 MV Ar

[0122] maximum load on the single phase 11.76 MV Ar

[0123] minimum load on the single phase 2.95 MVAr configuration of the windings (111-113) and

[0124] the windings (115-117) of the primary side

[0125] (110) and the secondary side (114) three- star-star configuration (201) phase multi-winding conventional transformer

[0126] (102)

[0127] power electronics converter (103) three-leg, four-wire voltage source convertor configuration (303)

[0128] the coupling element (104) a TCLC module (404)

[0129] FIG. 6-9 shows results depicting system voltages, currents and other parameters for the electrical power system (100) with specification as per Table 2.

[0130] FIG. 6 shows results depicting balancing operation starting from 0.4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF); FIG. 6 shows the transition of the system (100) from the non-balancing operation to balancing operation. The transition happens at 0.4 s. FIG. 6(a) shows the phase voltages of power supply(106), the voltage of the three phases are termed as vA, vB, vc. The RMS (root-mean-square) value of these voltages is -127 kV. FIG. 6(b) shows the currents drawn from the power supply(106), these currents are termed as iA, iB, icand has RMS values as 89.3 A, 45.5 A, 0 A, respectively under non-balancing operation until 0.4 s. Thereafter, with the balancing operation starting at 0.4 s, the currents iA, iB, ichas RMS values of 40.7 A, 40.4 A, 40.9 A, respectively. As observed, the currents’ magnitude are unbalanced before balancing operation, and post balancing operation at 0.4 s, the current magnitudes are balanced. The current unbalance factor (CUF) is shown in FIG. 6(c), which shows the extent of current unbalance in supply currents in terms of percentage. The CUF reduces from 56.6% under non-balancing operation to 1.5% under balancing operation.

[0131] FIG. 7 shows results depicting balancing operation starting from 0.4 s and under dynamic load change at 4 s: (a) converter DC link voltage with reference DClink voltage (b) voltage across capacitor C 1 and C2 of the converter; FIG. 7 shows the voltages of the DC link of the power electronics converter (103) and the individual capacitors connected on the DC link. It shows voltages during the starting of balancing operation from 0.4 s, and during the dynamic load change at 4 s. From FIG. 7(a), it is observed that the control algorithm is able to maintain the DC link voltage vDCnear the reference DC link voltage vref of 80 kV. From FIG.

[0132] 7(b), it is observed that the individual capacitor voltages vDC1, vDC2are also maintained near their reference capacitor voltage vref of 40 kV during the balancing operation.

[0133] FIG. 8 shows results depicting load current with load changing dynamically at 4 s: (a) Phase-a (116) (b) Phase-b (117); FIG. 8 shows the current of singe-phase traction loads (109) connected to winding on the secondary side (114) of transformer (102). It shows the transition of the system (100) from one loading condition to another loading condition, the dynamic load change in the system, at 4 s the load on each of the winding (116, 117) on the secondary side (114) changes dynamically. Initially, a load of 11.76 MV Ar drawing 470 A is connected to winding (116) and another load of 5.88 MV Ar drawing 230 A is connected to winding (117) of transformer (102), the current of each of these load is termed as tLaand iLb, respectively. At 4s, the load on winding (116) is changed to 2.95 MV Ar, drawing 117 A, and the load on winding (117) is changed to 8.82 MVAr, drawing 352 A. FIG. 8(a) shows iLacurrent and FIG. 8(b) shows iLb current. As observed in both the figures, the load currents remains stable and covers broad range of loading in terms of load rating.

[0134] FIG. 9 shows results depicting balancing operation with load changing dynamically at 4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF) FIG. 9 shows the transition of the system (100) from one loading condition to another loading condition, that is, there is a dynamic load change in the system on both phases (116) and (117). FIG. 9(a) shows the phase voltages of power supply(106), the voltage of the three phases are termed as vA, vB, vc. The RMS (root-mean-square) value of these voltages is -127 kV. FIG. 9(b) shows thecurrents drawn from the power supply(106), these currents are termed as iA, iB, icand has RMS values as 40 A, 42 A, 40.7 A, respectively under initial load condition until 4 s. Thereafter, with the dynamic load change at 4 s, the currents iA, iB, ichas RMS values of 25.6 A, 27.3 A, 27.6 A, respectively. As observed, the currents’ magnitude are balanced under both loading conditions to a satisfactory level. The current unbalance factor (CUF) is shown in FIG. 9(c), which shows the extent of current unbalance in supply currents in terms ofpercentage. The CUF is 1.5%under for first load condition and 2.2% under the second load condition during balancing operation.

[0135] Example 3

[0136] In this illustration, the transformer (102) is configured in star-star configuration (201), power electronics converter (103) is configured as three-leg, four-wire voltage source convertor (303), the coupling element (104) used is an inductor module (401). The source (106) parameters and the load parameters are mentioned in Table 3.

[0137] Table 3

[0138] grid voltage 220 kVline-to-line voltage maximum load on the system (100) 17.65 MV Ar

[0139] minimum load on the system (100) 11.76 MV Ar

[0140] maximum load on the single phase 11.76 MV Ar

[0141] minimum load on the single phase 2.95 MVAr configuration of the windings (111-113) and

[0142] the windings (115-117) of the primary side

[0143] (110) and the secondary side (114) three- star-star configuration (201) phase multi-winding conventional transformer

[0144] (102)

[0145] power electronics converter (103) three-leg, four-wire voltage source convertor configuration (303)

[0146] the coupling element (104) an inductor (401)

[0147] FIG. 10-13 shows results depicting system voltages, currents and other parameters for the electrical power system (100) with specification as per Table 3.FIG. 10 shows results depicting balancing operation starting from 0.4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF); FIG. 10 shows the transition of the system (100) from the non-balancing operation to balancing operation. The transition happens at 0.4 s. FIG. 10(a) shows the phase voltages of power supply(106), the voltage of the three phases are termed as vA, vB,vc. The RMS (root-mean-square) value of these voltages is -127 kV. FIG.

[0148] 10(b) shows the currents drawn from the power supply(106), these currents are termed as iA, iB, icand has RMS values as 89.3 A, 45.5 A, 0 A, respectively under non-balancing operation until 0.4 s. Thereafter, with the balancing operation starting at 0.4 s, the currents iA, iB, ichas RMS values of 43.2 A, 43.5 A, 42 A, respectively. As observed, the currents’ magnitude are unbalanced before balancing operation, and post balancing operation at 0.4 s, the current magnitudes are balanced. The current unbalance factor (CUF) is shown in FIG. 10(c), which shows the extent of current unbalance in supply currents in terms of percentage. The CUF reduces from 56.6% under non-balancing operation to 1.1% under balancing operation.

[0149] FIG. 11 shows results depicting balancing operation starting from 0.4 s and under dynamic load change at 4 s: (a) converter DC link voltage with reference DC link voltage (b) voltage across capacitor Cl and C2 of the converter; FIG. 11 shows the voltages of the DC link of the power electronics converter (103) and the individual capacitors connected on the DC link. It shows voltages during the starting of balancing operation from 0.4 s, and during the dynamic load change at 4 s. From FIG. 11(a), it is observed that the control algorithm is able to maintain the DC link voltage vDCnear the reference DC link voltage vref of 90 kV. From FIG.

[0150] 11(b), it is observed that the individual capacitor voltages vDC1, vDC2are also maintained near their reference capacitor voltage vrej- of 45 kV during the balancing operation.

[0151] FIG. 12 shows results depicting load current with load changing dynamically at 4 s: (a) Phase-a (116) (b) Phase-b (117); FIG. 12 shows the current of singe-phase traction loads (109) connected to winding on the secondary side(114) of transformer (102). It shows the transition of the system (100) from one loading condition to another loading condition, the dynamic load change in the system, at 4 s the load on each of the winding (116, 117) on the secondary side (114) changes dynamically. Initially, a load of 11.76 MV Ar drawing 470 A is connected to winding (116) and another load of 5.88 MVAr drawing 235 A is connected to winding (117) of transformer (102), the current of each of these load is termed as iBaand iLb, respectively. At 4s, the load on winding (116) is changed to 8.82 MVAr drawing 352 A and on winding (117) the load is changed to 2.95 MVAr drawing 117 A. FIG. 8(a) shows iLacurrent and FIG. 8(b) shows iLbcurrent. As observed in both the figures, the load currents remains stable and covers broad range of loading in terms of load rating.

[0152] FIG. 13 shows results depicting balancing operation with load changing dynamically at 4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF); FIG. 13 shows the transition of the system (100) from one loading condition to another loading condition, that is, there is a dynamic load change in the system on both phases (116) and (117). FIG. 10(a) shows the phase voltages of power supply(106), the voltage of the three phases are termed as vA, vB, vc. The RMS (root-mean-square) value of these voltages is -127 kV. FIG. 13(b) shows the currents drawn from the power supply(106), these currents are termed as iA, iB, icand has RMS values as 42 A, 40.4 A, 41.5 A, respectively under initial load condition until 4 s. Thereafter, with the dynamic load change at 4 s, the currents G, i-B> ic has RMS values of 29 A, 28.6 A, 28.3 A, respectively. As observed, the currents’ magnitude are balanced under both loading conditions to a satisfactory level. The current unbalance factor (CUF) is shown in FIG. 13(c), which shows the extent of current unbalance in supply currents in terms of percentage. The CUF is 1.4% under for first load condition and 0.76% under the second load condition during balancing operation.

[0153] Example 4

[0154] In this illustration, the transformer (102) is configured in star-star configuration (202), power electronics converter (103) is configured as four-leg,four-wire voltage source convertor (301), the coupling element (104) used is an inductor module (401). The source (106) parameters and the load parameters are mentioned in Table 4.

[0155] Table 4

[0156] grid voltage 110 kVline-to-line voltage maximum load on the system (100) 29.18 MV Ar

[0157] minimum load on the system (100) 20.42 MV Ar

[0158] maximum load on the single phase 23.34 MV Ar

[0159] minimum load on the single phase 2.95 MVAr configuration of the windings (111-113) and

[0160] the windings (115-117) of the primary side

[0161] (110) and the secondary side (114) three- delta-star configuration (202) phase multi-winding conventional transformer

[0162] (102)

[0163] power electronics converter (103) four-leg, four-wire voltage source converter configuration (301)

[0164] the coupling element (104) an inductor (401)

[0165] FIG. 14-17 shows results depicting system voltages, currents and other parameters for the electrical power system (100) with specification as per Table 4.

[0166] FIG. 14 shows results depicting balancing operation starting from 0.4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF); FIG. 14 shows the transition of the system (100) from the non-balancing operation to balancing operation. The transition happens at 0.4 s. FIG. 14(a) shows the phase voltages of power supply(106), the voltage of the three phases are termed as vA, VB, VC. The RMS (root-mean-square) value of these voltages is -63.6 kV. FIG.

[0167] 14(b) shows the currents drawn from the power supply(106), these currents are termed as iA, iB, ic and has RMS values as 225 A, 51 A, 199 A, respectively under non-balancing operation until 0.4 s. Thereafter, with the balancing operation starting at 0.4 s, the currents iA, iB, ic has RMS values of 140 A, 137 A, 140 A, respectively. As observed, the currents’ magnitude are unbalanced before balancing operation, and post balancing operation at 0.4 s, the current magnitudes arebalanced. The current unbalance factor (CUF) is shown in FIG. 14(c), which shows the extent of current unbalance in supply currents in terms of percentage. The CUF reduces from 70% under non-balancing operation to 1.7% under balancing operation.

[0168] FIG. 15 shows results depicting balancing operation starting from 0.4 s and under dynamic load change at 4 s: converter DC link voltage with reference DC link voltage; FIG. 15 shows the voltages of the DC link of the power electronics converter (103). It shows voltages during the starting of balancing operation from 0.4 s, and during the dynamic load change at 4 s. It is observed that the control algorithm is able to maintain the DC link voltage vDCnear the reference DC link voltage vref of 90 kV.

[0169] FIG. 16 shows results depicting load current with load changing dynamically at 4 s: (a) Phase-a (116) (b) Phase-b (117); FIG. 16 shows the current of singe-phase traction loads (109) connected to winding on the secondary side (114) of transformer (102). It shows the transition of the system (100) from one loading condition to another loading condition, the dynamic load change in the system, at 4 s the load on each of the winding (116, 117) on the secondary side (114) changes dynamically. Initially, a load of 23.34 MV Ar drawing 938 A is connected to winding (116) and another load of 5.88 MVAr drawing 234 A is connected to winding (117) of transformer (102), the current of each of these load is termed as ibaand iLb, respectively. At 4s, the load on winding (116) is changed to 2.95 MVAr drawing 117 A and on winding (117) the load is changed to 17.5 MVAr drawing 704 A. FIG. 16(a) shows iLacurrent and FIG. 16(b) shows iLbcurrent. As observed in both the figures, the load currents remains stable and covers broad range of loading in terms of load rating.

[0170] FIG. 17 shows results depicting balancing operation with load changing dynamically at 4 s: (a) Grid Voltages (b) Grid Currents (c) Current Unbalance Factor (CUF); FIG. 17 shows the transition of the system (100) from one loading condition to another loading condition, that is, there is a dynamic load change in the system on both phases (116) and (117). FIG. 17(a) shows the phase voltages ofpower supply(106), the voltage of the three phases are termed as vA, vB, vc. The RMS (root-mean-square) value of these voltages is -63.6 kV. FIG. 17(b) shows the currents drawn from the power supply(106), these currents are termed as iA, iB, icand has RMS values as 134.5 A, 133 A, 136 A, respectively under initial load condition until 4 s. Thereafter, with the dynamic load change at 4 s, the currents G, ft> ft has RMS values of 90.3 A, 90.5 A, 89.8 A, respectively. As observed, the currents’ magnitude are balanced under both loading conditions to a satisfactory level. The current unbalance factor (CUF) is shown in FIG. 17(c), which shows the extent of current unbalance in supply currents in terms of percentage. The CUF is 1.1% under for first load condition and 0.89% under the second load condition during balancing operation.

Claims

CLAIMSI Claim:

1. An electrical power system (100) for single-phase traction load (109) power supply by balancing three-phase power source (106) characterized in that the said electrical power system (100) comprising:a three-phase multi -winding conventional transformer (102) having primary windings (111-113) connected to a three-phase power supply (106) and secondary windings (115-117) connected to two single-phase loads (109) or a secondary winding connected to one single-phase load;a power electronics converter (103) connected in parallel with said singlephase loads (109) of the three-phase multi-winding conventional transformer (102);a coupling element (104) operatively connecting the power electronics converter (103) to the secondary side (114) of the three-phase multi-winding conventional transformer (102) directly or through an isolation transformer (105); voltage sensors (107) configured to measure voltage of each secondary phase and of the capacitors connected across the power electronic converter (103);current sensors (108) configured to measure load currents and currents of each leg of the power electronic converter (103);circuit breaker (120) device connected in series with the phase supplying power to loads (109) and circuit maker (121) device connected across the neutral section (122); anda controller (700) operatively coupled to the voltage and current sensors (107, 108) and the power electronic converter (103) and the coupling element when required, configured to process said measurements and control the converter (103) to manage active power flow, provide reactive power support, and perform harmonic compensation, thereby ensuring balanced three-phase operation at unity power factor;whereinthe transformer (102) is a conventional three-phase transformer with windings (111-113) and windings (115-117) on the primary side (110) andsecondary side (114) respectively configurable in delta or star connection and vector-group configurations as per IEC or equivalent international standard, the power electronics converter (103) comprises controlled or uncontrolled switches, and is configured as a three-leg, four-wire voltage source convertor (303) or four-leg, four-wire voltage source converter (301) or four-leg, four-wire neutralpoint clamped voltage source converter (302), or modular multilevel voltage source converter (304) or any other power electronics converter configuration capable of performing the required tasks of the active power flow control, provide reactive power support and produce harmonics mitigating currents or voltages,the power electronics converter (103) is any device capable of controlling the flow of power bi-directionally or uni -directionally and having an energy storage element like a capacitor,the coupling element (104) is selected from an inductor (401), an inductorcapacitor series connection (402), an inductor-capacitor-inductor connection (403), or a TCLC module (404) or any element which is able to limit the rate of change of current,the isolation transformer (105) provides galvanic isolation and filtering to limit high-frequency harmonics transferred between converter (103) and transformer (102),the controller (700) compensates, if required, phase displacement introduced by the selected vector-group configuration of the transformer (102) for accurate reference current generation,the circuit breaker (120) isolates the load from the phase supply, as and when required,the circuit maker (121) connects the two sections (118, 119) of the catenary supply system, as and when required, andthe system (100) is configured for traction substations, industrial plants, or power supply networks with high single-phase load demand.

2. The electrical power system (100) as claimed in claim 1, wherein the controller (700) is configured to operate the power electronics converter (103) toensure that all secondary phases of the transformer (102) draw the same magnitude of current irrespective of unequal loading of the single-phase loads (109).

3. The electrical power system (100) as claimed in claim 1, wherein the coupling element (104) in the form of a TCLC module (404) compensates reactive power by producing reactive impedance of equal magnitude and opposite polarity to that of the single-phase load ( 109) thereby reducing converter rating requirement.

4. The electrical power system (100) as claimed in claim 1, wherein the controller (700) is configured to stabilize the DC link voltage of the capacitor or a bank of capacitors connected across legs of the power electronics converter (103).

5. The electrical power system (100) as claimed in claim 1, wherein the singlephase load (109) is a linear load or a non-linear load or a combination of both.

6. A method for single-phase traction load (109) power supply by balancing three-phase power source (106) using the said electrical power system (100), the method comprising:(a) reading voltage and current values from the voltage sensor (107) and the current sensors (108) and conditioning these signals;(b) calculating each single-phase load’s (109) active power, reactive power and current’s harmonic content from values obtained in step (a);(c) calculating total active power requirement and total reactive power requirement of all the single-phase loads (109) and total harmonic content in the single-phase loads (109) from values obtained in step (b);(d) calculating power to be drawn from each secondary phase of the transformer (102) for balanced electrical power system (100) operation, from values obtained in step (b);(e) calculating power to be drawn or supplied by each phase of the power electronic converter (103) from values obtained in step (b) and (d);(f) calculating required compensating reactive power from values obtained in step (b);(g) calculating compensating harmonic current from values obtained in step (b) and (c);(h) calculating the required current for each phase of the power electronic converter (103) from the values obtained in step (e-g);(i) calculating the switching instances of the switching signals for controlling the controlled switches of the power electronic converter (103) by comparing the instantaneous values of the power electronic converter ( 103) currents calculated in step (h) and instantaneous values of the power electronics converter (103) currents obtained from the current sensors (108) in step (a);(j) sending the switching signals calculated in step (i) to the power electronic converter (103) to control its controlled switches individually;(k) calculating the switching instances of the switching signals for controlling any other controlled device, if any, like the coupling element (404) by using the required compensating reactive power data calculated in step (f) and voltages measured in step (a);(l) sending the switching signals calculated in step (k) to the controlled switches, if any, of the coupling element (104) to control its controlled switches individually; and(m) repeating the above steps in real time for continuous balancing operation;wherein the controller (700) performs the above steps.

7. The method for single-phase traction load (109) power supply by balancing three-phase power source (106) as claimed in claim 6, wherein the active power flow between the secondary phases (114) of transformer (102) and the load (109) is controlled by the power electronics converter (103).

8. The method for single-phase traction load ( 109) power supply by balancing three-phase power source (106) as claimed in claim 6, wherein harmonic compensation is performed by generating reference harmonic currents and injecting the compensating currents via the power electronics converter (103).

9. The method for single-phase traction load (109) power supply by balancing three-phase power source (106) as claimed in claim 6, wherein reactive power support is provided by the compensating currents via the power electronics converter (103), if required.

10. The method for single-phase traction load (109) power supply by balancing three-phase power source (106) as claimed in claim 6, wherein with use of a TCLC module (404) as the coupling element (104), reactive power compensation is achieved by generating capacitive or inductive impedance depending on the nature of the single-phase load (109).

11. The method for single-phase traction load ( 109) power supply by balancing three-phase power source (106) as claimed in claim 6, wherein the balanced power drawn from each phase of the transformer (102) results in unity power factor operation at the three-phase source (106).

12. The method for single-phase traction load (109) power supply by balancing three-phase power source (106) as claimed in claim 6, wherein the system (100) provide power supply to two single-phase loads at different phase displacement angles or to only one single phase load at a particular phase displacement angle by operating the circuit breaker (120) and the circuit maker (121) as per the requirement.

13. The method for single-phase traction load ( 109) power supply by balancing three-phase power source (106) as claimed in claim 6, wherein the system (100) provides power supply even when the power electronics converter (103) or the coupling element (104) or the isolation transformer (105) or the controller (700) or the sensors (107, 108) fails to operate, with system (100) operating as system (600) in unbalanced condition, without reactive power support and harmonics mitigation.

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