FORM 2
THE PATENTS ACT 1970
[39 OF 1970]
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10; Rule 13]
TITLE: “NEUTRAL POWER FACTOR COMPENSATOR CIRCUIT AND OPERATING METHOD THEREOF”
Name and Address of the Applicant:
CTR MANUFACTURING INDUSTRIES LIMITED, Nagar Road, Pune 411 014,
Maharashtra
Nationality: India
The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD
[001] The present subject matter is generally related to the field of electrical systems, more particularly, but not exclusively, to a method and compensator circuit for correcting power factor in a 3-phase electrical system.
BACKGROUND
[002] In electrical systems, power factor is a critical parameter that indicates ratio of active power absorbed by a load to apparent power in a system. Unity power factor is desirable for better economic and technical operation of the electrical system. A power factor less than value 1 indicates voltage waveform and current waveform are out-of-phase leading to power losses in the system. Hence, it is important that the power factor of the electrical system is corrected or compensated to value close to 1. Most of the power factor correction systems designed and installed are suitable for balanced loads, which includes majorly industries. There are no power factor correction systems designed to correct the power factor for imbalanced loads like lightings, air conditioners, single phase motors and electronics control systems where the imbalanced loads are dominantly higher than 10%. As the imbalanced load dominates, power factor correction becomes more complicated. In such situations, power factor correction is a big challenge to maintain above value 0.96.
[003] The information disclosed in this background of the disclosure section is for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
SUMMARY
[004] There is a need for power factor compensator system or circuit that maintains power factor close to value 1 in most imbalanced and critical load setup.
[005] In an embodiment, the present disclosure may relate to a Neutral Power Factor Compensator (NPFC) circuit for a 3-phase electrical system. The NPFC circuit may include a controller communicatively coupled to an individual phase of the 3-phase electrical system,

wherein the controller is configured to receive AC power from the individual phase of the 3-phase electrical system to measure a current power factor of the individual phase with respect to neutral, determine a reactive AC power required to take the current power factor to unity for the individual phase when the current power factor of the individual phase is below a threshold value, produce a switching signal based on the reactive AC power determined for the individual phase; a switching module communicatively coupled the controller, wherein the switching module is configured to operate at least one thyristor switch based on the switching signal received from the controller; and at least one of a single-phase capacitor bank and a reactor communicatively coupled to the switching module, for the individual phase, wherein the at least one of the single-phase capacitor bank and the reactor is configured to supply the reactive AC power to the individual phase of the 3-phase electrical system for correcting the current power factor based on the switching signal. The NPFC circuit is connected between neutral of the 3-phase electrical system and the individual phase of the 3-phase electrical system.
[006] In an embodiment, the present disclosure may relate to a method for correcting power factor in a 3-phase electrical system. The method may include receiving AC power from an individual phase of the 3-phase electrical system to measure a current power factor of the individual phase with respect to neutral, determining a reactive AC power required to take the current power factor to unity for the individual phase when the current power factor of the individual phase is below a threshold value, producing a switching signal based on the reactive AC power determined for the individual phase, and operating at least one thyristor switch based on the switching signal received from the controller to supply the reactive AC power to the individual phase of the 3-phase electrical system from at least one of a single-phase capacitor bank and a reactor for correcting the current power factor. The NPFC circuit is connected between neutral of the 3-phase electrical system and the individual phase of the 3-phase electrical system.
[007] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[008] The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and together with the description, serve to explain the disclosed principles. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described below, by way of example only, and with reference to the accompanying figures.
[009] FIG. 1 illustrates a NPFC circuit for a 3-phase electrical system in accordance with an exemplary embodiment of the present disclosure.
[010] FIG. 2 shows a detailed block diagram of a NPFC circuit in accordance with some embodiments of the present disclosure.
[011] FIG. 3 illustrates a flowchart showing a method for correcting power factor in a 3-phase electrical system in accordance with exemplary embodiments of the present disclosure.
[012] FIGS. 4a - 4c illustrate represents KVAR compensated by a NPFC circuit in accordance with exemplary embodiments of the present disclosure.
[013] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flowcharts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.
DETAILED DESCRIPTION
[014] In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[015] While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.
[016] The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or method.
[017] In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.
[018] FIG. 1 illustrates a NPFC circuit for a 3-phase electrical system in accordance with an exemplary embodiment of the present disclosure.
[019] As shown in the FIG. 1, the 3-phase electrical system may include 3 phases represented as Red (R) 101, Yellow (Y) 103 and Blue (B) 105 connected to a common junction called neutral (N) 125. This configuration may be referred as star connection. Each phase of the 3-phase electrical system may be connected in series with a controller, a switching module and a single-phase capacitor bank. The controller, the switching module and the single-phase capacitor bank connected in series to each phase of the 3-phase electrical system together form a Neutral Power Factor Compensator (NPFC) circuit. The NPFC circuit may, also, be referred as reactive power compensator or power factor corrector. The NPFC circuit may be connected between neutral N 125 of the 3-phase electrical system and the individual phase of the 3-phase

electrical system. For instance, as shown in FIG. 1, for phase R 101, the controller 107, the switching module 113 and the single-phase capacitor bank 119 may form the NPFC circuit. Analogously, for phase Y 103, the controller 109, the switching module 115 and the single-phase capacitor bank 121 may form the NPFC circuit and for phase B 105, the controller 111, the switching module 117 and the single-phase capacitor bank 123 may form the NPFC circuit. In this case, the NPFC circuit may continuously monitor and correct power factor by injecting required leading reactive AC power through neutral N and respective individual phase in order to maintain the target power factor close to 1 (e.g. 0.999). In another embodiment, the NPFC circuit may comprise a controller, a switching module and a reactor (or an inductor). In this embodiment, the reactor (or the inductor) may be present in place of a single-phase capacitor bank and may be communicatively coupled to the switching module. In this case, the NPFC circuit may continuously monitor and correct power factor by injecting required lagging reactive AC power through neutral N and respective individual phase in order to maintain the target power factor close to 1 (e.g. 0.999). In yet another embodiment, the NPFC circuit may comprise a controller, a switching module, a single-phase capacitor bank and a reactor (or an inductor) combination. In this embodiment, the single-phase capacitor bank and the reactor (or the inductor) are connected in parallel such that the single-phase capacitor bank or the reactor (or the inductor) or a combination of the single-phase capacitor bank and the reactor (or the inductor) is selected. In this case, the NPFC circuit may continuously monitor and correct power factor by injecting required leading or lagging reactive AC power through neutral N and respective individual phase in order to maintain the target power factor above close to 1 (e.g. 0.999).
[020] For sake of explanation, the NPFC circuit may be explained with respect to the individual phase R 101 and the N 125 of the 3-phase electrical system. The controller 107 may be communicatively coupled to the individual phase R 101 of the 3-phase electrical system. The controller 107 may receive AC power from the individual phase R 101 of the 3-phase electrical system to measure a current power factor of the individual phase R 101 with respect to N 125. Subsequently, the controller 107 may determine a reactive AC power required to take the current power factor close to unity for the individual phase R 101 when the current power factor of the individual phase is below a threshold value. The threshold value may be set by the manufacturer of the NPFC circuit. Based on the reactive AC power determined for the individual phase R 101, the controller 107 may produce a switching signal. The switching module 113 may be communicatively coupled to the controller 107 and may operate at least

one thyristor switch based on the switching signal received from the controller 107. In the FIG. 1, the switching module 113 is shown to comprise two thyristor switches connected in parallel to each other in the individual phase R 101 of the 3-phase electrical system. In one embodiment, the switching module 113 may comprise more than two or multiple thyristor switches in the individual phase R 101 of the 3-phase electrical system to match required Kilo Volt Ampere Reactive (KVAR) value. The single-phase capacitor bank 119 may be communicatively coupled to the switching module 113 and may supply the reactive AC power to the individual phase R 101 of the 3-phase electrical system for correcting the current power factor based on the switching signal. Analogously, the above explanation is applicable for the NPFC circuit connected to the individual phase Y 103 and the individual phase B 105 of the of the 3-phase electrical system. In one embodiment, the response time i.e. time taken to receive AC power from the individual phase of the 3-phase electrical system to supply the reactive AC power to the individual phase of the 3-phase electrical system for correcting the current power factor is less than 40 milliseconds.
[021] FIG. 2 shows a detailed block diagram of a NPFC circuit in accordance with some embodiments of the present disclosure.
[022] The NPFC circuit 201, as described above, may include one or more modules 203 comprising, but are not limited to, a controller module 205, a switching module 207, a single-phase capacitor bank 209 and a reactor module 211. The one or more modules 203 may, also, include other modules 213 to perform various miscellaneous functionalities of the NPFC circuit 201.
[023] In the embodiment, the one or more modules 203 may be implemented as dedicated hardware units. As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a Field-Programmable Gate Arrays (FPGA), Programmable System-on-Chip (PSoC), a combinational logic circuit, and/or other suitable components that provide the described functionality. The said modules 203 when configured with the functionality defined in the present disclosure will result in a novel hardware.
[024] The controller module 205 may, also, be referred as the controller 107, the controller 109 or the controller 111 shown in the FIG. 1. The controller module 205 may be communicatively coupled to an individual phase of the 3-phase electrical system. The

controller module 205 may comprise of at least relays and Programmable Logic Controller (PLC) or a microcontroller or a microprocessor or a control logic circuit. The controller module may be, but not limited to, a single phase intelligent reactive power (power factor) controller of 8 stage, 12 stage or 16 stage. The controller module 205 may receive AC power from the individual phase of the 3-phase electrical system to measure a current power factor of the individual phase with respect to N 125. The controller module 205 may determine a reactive AC power required to take the current power factor to unity for the individual phase when the current power factor of the individual phase is below a threshold value. The controller module 205 may produce a switching signal based on the reactive AC power determined for the individual phase.
[025] In detail, the controller module 205 may receive AC power from the individual phase of the 3-phase electrical system at a predefined interval of time. The predefined interval of time may be fixed by the manufacturer of the NPFC circuit. In one embodiment, the controller module 205 may keep monitoring AC power continuously instead of receiving the AC power at a predefined interval of time. On receiving the AC power from the individual phase, the controller module 205 may determine the power factor of the received AC power and may compare the determined power factor with the threshold value. The threshold value may be set by the manufacturer of the NPFC circuit. The threshold value may be normally set to value 1 and may be changed wherever needed by the manufacturer. When the determined power factor is less than or below the threshold value, the controller module 205 may determine a reactive AC power required to take the determined (current) power factor to unity for the individual phase. Based on the determined reactive AC power, the controller module 205 may produce a switching signal for the individual phase. When the determined power factor greater than or equal to the threshold value, the controller module 205 may not determine a reactive AC power and consequently, may not produce a switching signal for the individual phase. For example, suppose the threshold value for the power factor is set to 0.98 for an individual phase. When the power factor determined by the controller module 205 for an individual phase is 0.95, the controller module 205 may determine a reactive AC power required to take the determined (current) power factor to unity for the individual phase. Based on the determined reactive AC power, the controller module 205 may produce a switching signal for the individual phase. When the power factor determined by the controller module 205 for an individual phase is 0.99, the controller module 205 may not determine a reactive AC power and consequently, may

not produce a switching signal for the individual phase. The output of the controller module 205 i.e. the switching signal may be sent to the switching module 207.
[026] The switching module 207 may be communicatively coupled to the controller module 205. The switching module 207 (the switching module 113, the switching module 115 or the switching module 117 shown in the FIG. 1) may, also, be referred as soft switching module or thyristor switching module. In one embodiment, the switching module 207 may comprise at least one thyristor switch i.e. the switching module 207 may comprise two or more thyristor switches in each phase of the 3-phase electrical system to match required KVAR value. In one embodiment, the thyristor switches may be arranged in parallel to each other but in opposite direction, as shown in references 113, 115 and 117 of the FIG. 1. The switching module 207 may operate at least one thyristor switch based on the switching signal received from the controller module 205. The current rating of the at least one thyristor switch may be 4 to 5 times of each capacitor rating in the single-phase capacitor bank. This approach prevents any possibility of the NPFC circuit 201 failure and consequently, prevents failure of the individual phase of the 3-phase electrical system. In one embodiment, the thyristors rated for 1600 PIV may be used for 240 V power supply.
[027] The single-phase capacitor bank 209 may be communicatively coupled to the switching module 207 for the individual phase of the 3-phase electrical system. The single-phase capacitor bank 209 may, also, be referred as the single-phase capacitor bank 119, the single-phase capacitor bank 121 or the single-phase capacitor bank 123 shown in the FIG. 1. The single-phase capacitor bank 209 may supply the reactive AC power to the individual phase of the 3-phase electrical system for correcting the current power factor based on the switching signal. The single-phase capacitor bank 209 may comprise of a plurality of capacitors. The plurality of capacitors included in the single-phase capacitor bank 209 may be, but not limited to, 440V single-phase capacitors. These capacitors may be connected in series connection or in parallel connection or in a combination of series and parallel connection depending on the type of application. The capacitors may be available and operated in multiple stages and multiple steps. For example, the capacitor stages may be 0.10, 0.25, 0.50, 1.0, 2.0, 3.0, 4.0, 5.0 KVAR. Suppose the individual phase R 101 has a power factor of value 0.995, the individual phase Y 103 has a power factor of value 0.992 and the individual phase B 105 has a power factor of value 1.00, the required KVAR may be 7.8 KVAR in the individual phase R 101, 14.2 KVAR in the individual phase Y 103 and 0 KVAR in the individual phase B 105 to improve

the power factor of each phase to unity. Based on the determined (or required) KVAR for each phase, the controller module 205 in each individual phase may give a switching signal to the respective switching module 207 which in turn may switch capacitors in the single-phase capacitor bank 209 (as shown below) to correct the power factor to unity.
[028] For individual phase R 101: 5 KVAR + 2 KVAR + 0.5 KVAR + 0.10 KVAR + 0.10 KVAR + 0.10 KVAR (= 7.8 KVAR)
[029] For individual phase Y 103: 5 KVAR + 5 KVAR + 4 KVAR + 0.10 KVAR + 0.10 KVAR (= 14.2 KVAR)
[030] For individual phase B 105: 0 KVAR.
[031] In case the power factor correction requirement (i.e. the required KVAR changes), the capacitors in the single-phase capacitor bank 209 may be switched on and off according to the switching signal from the controller module 205 and the switching module 207.
[032] The reactor module 211 may comprise of a reactor (or inductor). The reactor module 211 may be communicatively coupled to the switching module 207. The NPFC circuit 201 may comprise the controller module 205, the switching module 207 and the reactor module 211. In this case, the reactor (or the inductor) may be present in place of the single-phase capacitor bank 209 and may be communicatively coupled to the switching module 207. Furthermore, the NPFC circuit 201 may continuously monitor and correct power factor by injecting required lagging reactive AC power through neutral N 125 and respective individual phase in order to maintain the target power factor above 0.999 (i.e. close to 1). The NPFC circuit 201 may, also, comprise the controller module 205, the switching module 207, the single-phase capacitor bank 209 and the reactor module 211. In this case, the single-phase capacitor bank 209 and the reactor module 211 may connected in parallel such that either the single-phase capacitor bank 209 or the reactor module 211 may selected. Furthermore, the NPFC circuit 201 may continuously monitor and correct power factor by injecting required leading or lagging reactive AC power through neutral N 125 and respective individual phase in order to maintain the target power factor above 0.999 (i.e. close to 1).

[033] The NPFC circuits (or models) 201 of the present disclosure may be, but not limited to, available with AC continuous current in three phases (R 101, Y 103 and B 105) and neutral N 125 from 6 Amp to 600 Amp with standard ratings of 6, 9, 12, 15, 21, 27, 36, 45, 60, 75, 90, 120, 150, 180, 225, 270. 300, 400, 500 and 600 KVAR.
[034] FIG. 3 illustrates a flowchart showing a method for correcting power factor in a 3-phase electrical system in accordance with exemplary embodiments of the present disclosure.
[035] As illustrated in the FIG. 3, the method 300 includes one or more blocks for correcting power factor in a 3-phase electrical system. The method 300 may be described in the general context of computer executable instructions. Generally, computer executable instructions can include routines, programs, objects, components, data structures, procedures, modules, and functions, which perform particular functions or implement particular abstract data types.
[036] The order in which the method 300 is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method. Additionally, individual blocks may be deleted from the methods without departing from the scope of the subject matter described herein. Furthermore, the method can be implemented in any suitable hardware, software, firmware, or combination thereof.
[037] At block 301, the controller (or the controller module) 205 of the NPFC circuit 201 may receive AC power from an individual phase of a 3-phase electrical system to measure a current power factor of the individual phase with respect to neutral. The NPFC circuit may be connected between neutral of the 3-phase electrical system and the individual phase of the 3-phase electrical system.
[038] At block 303, the controller (or the controller module) 205 of the NPFC circuit 201 may determine a reactive AC power required to take the current power factor to unity for the individual phase when the current power factor of the individual phase is below a threshold value.
[039] At block 305, the controller (or the controller module) 205 of the NPFC circuit 201 may produce a switching signal based on the reactive AC power determined for the individual phase.

[040] At block 307, the switching module 207 of the NPFC circuit 201 may operate at least one thyristor switch based on the switching signal received from the controller (or the controller module) 205 to supply the reactive AC power to the individual phase of the 3-phase electrical system from at least one of a single-phase capacitor bank 209 and a reactor module 211 for correcting the current power factor. The current rating of the at least one thyristor switch is 4 to 5 times of each capacitor rating in the single-phase capacitor bank.
[041] The NPFC circuit may be individually and communicatively coupled to each phase of the 3-phase electrical system.
[042] The reactor module 211 may be connected in parallel to the single-phase capacitor bank 209.
[043] FIGS. 4a - 4c illustrate represents KVAR compensated by a NPFC circuit in accordance with exemplary embodiments of the present disclosure.
[044] FIGS. 4a, 4b and 4c demonstrate operational example of the NPFC circuit 201. In FIGS. 4a, 4b and 4c, the NPFC circuit 201 corrects power factor in a 3-phase electrical system at different instance of time. For example, in FIG. 4a, the NPFC circuit 201 maintains a power factor of 1 for the 3-phases L1, L2 and L3 by producing compensating reactive power of 0.1 KVAR for L1 phase, 1.3 KVAR for L2 phase and 1.6 KVAR for L3 phase at 12:41:37 hours. In FIG. 4b, the NPFC circuit 201 maintains a power factor of 0.98 (i.e. close to 1) for the 3-phases L1, L2 and L3 by producing compensating reactive power of 0.0 KVAR for L1 phase, 1.2 KVAR for L2 phase and 1.1 KVAR for L3 phase at 10:53:26 hours. In FIG. 4c, the NPFC circuit 201 maintains a power factor of 1 for the 3-phases L1, L2 and L3 by producing compensating reactive power of 0.0 KVAR for L1 phase, 1.4 KVAR for L2 phase and 1.7 KVAR for L3 phase at 12:41:49 hours.
[045] Some of the advantages of the present disclosure are listed below.
[046] The present disclosure maintains power factor of value close to value 1 e.g. 0.999 in most imbalanced and critical load setup like hotels, hospitals, commercial buildings, offices,

educational institutes, large residential buildings and industries where power factor and optimizing Kilo Volt Ampere Hours (KVAH) is a challenge.
[047] The present disclosure provides solution to eliminate power factor penalty and allows qualification for power factor incentive in electricity billing where power factor incentive-based tariff is in force. Since reduction in KVAH consumption almost equal to KWH, the present disclosure helps in direct savings in electricity bills.
[048] The NPFC circuit of the present disclosure produces low losses and has no maintenance cost as compared to other imbalanced load power factor correction options available like Active Filter, where equipment cycle operational losses are in multiples of their capital cost.
[049] The NPFC circuit of the present disclosure provides a perfect solution to be installed for low rating unit. Furthermore, the NPFC circuit of the present disclosure works as a top-up and master power factor compensator with the Automatic Power Factor Controllers (APFC)/Real-Time Power Factor Correction (RTPFC) and fine tunes the power factor at micro-level.
[050] IGBT based Active Harmonic Filter is highly sensitive and costly equipment and has a very high maintenance cost, thus, not affordable for smaller installations. Furthermore, the IGBT based Active Harmonic Filter has very high self-consumption losses at 3% of the total capacity. In contrast, the NPFC circuit of the present disclosure overcomes the above-mentioned disadvantages.
[051] One or more computer-readable storage media may be utilized in implementing embodiments consistent with the present disclosure. A computer-readable storage medium refers to any type of physical memory on which information or data readable by a processor may be stored. Thus, a computer-readable storage medium may store instructions for execution by one or more processors, including instructions for causing the processor(s) to perform steps or stages consistent with the embodiments described herein. The term “computer-readable medium” should be understood to include tangible items and exclude carrier waves and transient signals, i.e., be non-transitory. Examples include Random Access Memory (RAM), Read-Only Memory (ROM), volatile memory, non-volatile memory, hard drives, CD ROMs, DVDs, flash drives, disks, and any other known physical storage media.

[052] The terms “an embodiment”, “embodiment”, “embodiments”, “the embodiment”, “the embodiments”, “one or more embodiments”, “some embodiments”, and “one embodiment” mean “one or more (but not all) embodiments of the invention(s)” unless expressly specified otherwise.
[053] The terms “including”, “comprising”, “having” and variations thereof mean “including but not limited to”, unless expressly specified otherwise.
[054] The enumerated listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise.
[055] The terms “a”, “an” and “the” mean “one or more”, unless expressly specified otherwise.
[056] A description of an embodiment with several components in communication with each other does not imply that all such components are required. On the contrary, a variety of optional components are described to illustrate the wide variety of possible embodiments of the invention.
[057] When a single device or article is described herein, it will be readily apparent that more than one device/article (whether or not they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether or not they cooperate), it will be readily apparent that a single device/article may be used in place of the more than one device or article or a different number of devices/articles may be used instead of the shown number of devices or programs. The functionality and/or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality/features. Thus, other embodiments of the invention need not include the device itself.
[058] The illustrated operations of FIG. 3 show certain events occurring in a certain order. In alternative embodiments, certain operations may be performed in a different order, modified or removed. Moreover, steps may be added to the above described logic and still conform to the described embodiments. Further, operations described herein may occur sequentially or certain

operations may be processed in parallel. Yet further, operations may be performed by a single processing unit or by distributed processing units.
[059] Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based here on. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.
[060] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims.

Reference number Description
101 R (Red) of a 3-phase electrical system
103 Y (Yellow) of a 3-phase electrical system
105 B (Blue) of a 3-phase electrical system
107, 109, 111 Controller
113, 115, 117 Thyristor switches
119, 121, 123 Single-phase capacitor banks
125 N (Neutral) of a 3-phase electrical system
201 NPFC circuit
203 Modules
205 Controller module
207 Switching module
209 Single-phase capacitor bank
211 Reactor module
213 Other modules

We claim:
1. A Neutral Power Factor Compensator (NPFC) circuit for a 3-phase electrical system,
the NPFC circuit comprising:
a controller communicatively coupled to an individual phase of the 3-phase electrical system, wherein the controller is configured to:
receive AC power from the individual phase of the 3-phase electrical
system to measure a current power factor of the individual phase with respect to neutral;
determine a reactive AC power required to take the current power factor to unity
for the individual phase when the current power factor of the individual phase is below a
threshold value;
produce a switching signal based on the reactive AC power determined for the individual phase;
a switching module communicatively coupled to the controller, wherein the switching module is configured to:
operate at least one thyristor switch based on the switching signal received from the controller; and
at least one of a single-phase capacitor bank and a reactor communicatively coupled to the switching module, for the individual phase, wherein the at least one of the single-phase capacitor bank and the reactor is configured to:
supply the reactive AC power to the individual phase of the 3-phase electrical system for correcting the current power factor based on the switching signal, wherein the NPFC circuit is connected between neutral of the 3-phase electrical system and the individual phase of the 3-phase electrical system.
2. The circuit as claimed in claim 1, wherein the NPFC circuit is individually and communicatively coupled to each phase of the 3-phase electrical system.
3. The circuit as claimed in claim 1, wherein current rating of the at least one thyristor switch is 4 to 5 times of each capacitor rating in the single-phase capacitor bank.
4. The circuit as claimed in claim 1, wherein the reactor is connected in parallel to the single-phase capacitor bank.

5. A method for correcting power factor in a 3-phase electrical system, the method
comprising:
receiving, by a controller of a Neutral Power Factor Compensator (NPFC) circuit, AC power from an individual phase of the 3-phase electrical system to measure a current power factor of the individual phase with respect to neutral;
determining, by the controller of the NPFC circuit, a reactive AC power required to take the current power factor to unity for the individual phase when the current power factor of the individual phase is below a threshold value;
producing, by the controller of the NPFC circuit, a switching signal based on the reactive AC power determined for the individual phase; and
operating, by a switching module of the NPFC circuit, at least one thyristor switch based on the switching signal received from the controller to supply the reactive AC power to the individual phase of the 3-phase electrical system from at least one of a single-phase capacitor bank and a reactor for correcting the current power factor,
wherein the NPFC circuit is connected between neutral of the 3-phase electrical system and the individual phase of the 3-phase electrical system.
6. The method as claimed in claim 5, wherein the NPFC circuit is individually and communicatively coupled to each phase of the 3-phase electrical system.
7. The method as claimed in claim 5, wherein current rating of the at least one thyristor switch is 4 to 5 times of each capacitor rating in the single-phase capacitor bank.
8. The method as claimed in claim 5, wherein the reactor is connected in parallel to the single-phase capacitor bank.