Ac to DC converter system with reduced transformer windings

Abstract

The AC to DC converter system (100) revolutionizes Variable Frequency Drives (VFDs) by introducing a cost-effective and efficient design. Harnessing a rotating magnetic field strategically induces electro motive force in secondary windings (110), generating a flat-top AC voltage waveform. This inventive approach eliminates the need for numerous secondary windings (110) in the phase shift transformer, significantly cutting costs and simplifying the system architecture. The transformer, mimicking a locked-wound rotor induction motor, ensures a compact footprint. A bridge rectifier (104) enhances the system's stability, providing a reliable DC output with an extended conduction period. The system's scalability accommodates diverse power ratings, making it versatile for high-power rectifiers, VFDs, DC chargers and HVDC transmission systems. Notably, it excels in mitigating harmonics and reducing power diodes required for higher pulse rectifiers, offering a dependable and cost-efficient alternative for various power system applications.

Description

[0001]FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & The Patents Rules, 2003 COMPLETE SPECIFICATION (See section 10 and rule 13) 1. TITLE OF THE INVENTION “AC TO DC CONVERTER SYSTEM WITH REDUCED TRANSFORMER WINDINGS” 2. APPLICANTS a) Name : VEERABHADRA ELITE ELECTRODYNAMIC SOLUTIONS LLP b) Nationality : INDIAN c) Address : Plot No 149, Door No 202, Venkat Classic Apartments, Road No 4, KTR colony, Nizampet, Medchal - Malkajgiri, telangana- 500090. 3. PREAMBLE TO THE DESCRIPTION COMPLETE The following specification particularly describes the invention and the manner in which it is to be performed. 4. DESCRIPTION Technical Field of the invention The present invention generally relates to the field of power electronics. More particularly, relates to an improved AC to DC converter system designed to reduce the number of transformer windings and enhance efficiency. Background of the invention The field of power electronics has witnessed remarkable progress, particularly in the realm of converting Alternating Current (AC) to Direct Current (DC). Traditional Variable Frequency Drives (VFDs) have long relied on AC to DC converters featuring various pulse configurations, typically 6, 12, 18, 24, or 36 pulses, to regulate the speed of electric motors. While these conventional systems effectively serve their purpose, they come with inherent drawbacks that the present invention seeks to redress. A fundamental limitation of traditional VFDs lies in their dependence on power electronic devices, power diodes employed for AC to DC rectification and switching devices like IGBTs (Insulated Gated Bipolar Transistors) employed to generate variable frequencies. The higher the number of pulses rectifier utilized, the lower the harmonics introduced in the system and vice versa. The higher the pulses, the higher the requirement of secondary windings of the phase shift transformer and more power diodes. Despite affording precise control over the power circuit, these devices contribute to an escalation in the overall cost of the converter system. Moreover, the introduction of power electronics into the equation gives rise to harmonics, an undesirable factor in power systems networks. This can lead to potential issues such as increased losses and interference with other equipment, undermining the overall efficiency of the system. The conventional approach also incorporates the use of a Phase Shift Transformer (VFD transformer or isolation transformer) with a variable number of secondary windings contingent on the pulse configuration. As the pulse configuration escalates, so does the count of secondary windings, resulting in augmented costs and a larger physical footprint. The necessity for additional filter circuits to mitigate harmonics further compounds the complexity and cost of the system. Recognizing these challenges as opportunities for improvement, the inventor embarked on developing an innovative AC to DC converter system designed to surmount the limitations of traditional designs. The primary objectives guiding this endeavor were to curtail the overall cost of the converter system, minimize its footprint, and decrease the generation of harmonics. The proposed solution involves a departure from the reliance on conventional power electronic devices for commutation. Instead, the inventive system leverages a streamlined transformer design, reminiscent of a locked-wound rotor induction motor, to achieve the desired AC to DC conversion. This departure from traditional power electronics not only reduces costs but also mitigates the generation of harmonics, marking a significant advancement in the field. A key feature of the invention is its strategic reduction in the number of secondary windings in the Phase Shift Transformer. By limiting the count to 2 to 4 windings, each producing a flat-top AC voltage waveform, the system substantially reduces voltage ripples in the secondary voltage. This reduction in ripples contributes to a more stable DC output, obviating the need for extensive filtering circuits and further streamlining the system. The innovative design also addresses the scalability of the converter system, allowing for adaptation to various power ratings and applications in high-power rectifiers, VFDs at different voltage levels, and DC chargers for electrical vehicles. This scalability enhances the versatility of the invention, making it suitable for a broad spectrum of power distribution scenarios. The inventive AC to DC converter system represents a paradigm shift in the field of power electronics. By challenging the reliance on traditional power electronic devices and introducing a streamlined transformer design, the invention achieves the dual goals of cost reduction and harmonics mitigation. The strategic reduction in secondary windings further enhances the stability of the DC output. This groundbreaking solution is poised to redefine the landscape of AC to DC conversion, offering a more efficient and cost-effective alternative to traditional designs. Brief Summary of the Invention The invention addresses crucial challenges in the field of power electronics, specifically the conversion of Alternating Current (AC) to Direct Current (DC) in Variable Frequency Drives (VFDs). Traditional VFDs rely on AC to DC converters with multiple pulse configurations, leading to increased costs. The present invention aims to overcome these limitations by streamlining the AC to DC conversion process. One primary objective is cost reduction. By minimizing the number of secondary windings in the phase shift transformer, the invention significantly cuts material costs and simplifies construction. Traditional designs often rely on power electronic devices power diodes, Insulated Gate Bipolar Transistors (IGBTs), contributing to overall system cost. The new approach minimizes secondary windings of phase shift transformer, also minimizes the power diodes required for rectifiers with 12 pulse and above, leading to substantial cost savings. Harmonics mitigation is another critical goal. Traditional VFDs generate harmonics, causing issues such as increased losses and interference with other equipment. The present invention strategically distributes secondary windings and employs a rotating magnetic field to induce a flat-top AC voltage waveform. This innovative approach minimizes harmonics in the power system, enhancing overall electrical supply quality and reliability. Efficiency improvement is a key aspect of the invention. By minimizing reliance on power electronics for AC to DC rectification, the system aims to enhance the efficiency of AC to DC conversion. This contributes to a more stable and reliable DC output voltage. A distinctive feature is the intentional reduction in the number of secondary windings in the phase shift transformer. This departure from conventional designs streamlines the system, leading to cost-effectiveness and simplified construction. The invention distributes the primary windings for generating a rotating magnetic field in core / space and strategically distributed secondary windings to induce a flat-top AC voltage waveform in secondary windings, significantly reducing ripples in the DC output. The streamlined transformer design is noteworthy. Resembling a locked-wound rotor induction motor, it eliminates complexities associated with traditional phase shift transformers. This design reduces the number of secondary windings, resulting in lowered transformer costs and simplified system architecture. The system's adaptability to various voltage levels ensures versatility and applicability in diverse power distribution scenarios. This adaptability enhances the system's usability in different environments, making it suitable for a range of power system applications. At the core of the invention is the utilization of a rotating magnetic field to induce electromotive force (emf) in a carefully distributed set of secondary windings. This innovative approach eliminates the need for numerous secondary windings and contributes to induce of a flat-top AC voltage waveform. The reduction in secondary windings directly translates to reduced material costs and simplified construction, leading to a substantial reduction in the overall cost of the AC to DC conversion system. The streamlined transformer design and strategic distribution of secondary windings result in a more compact physical footprint, contributing to overall system efficiency. By minimizing harmonics in the power system, the inventive system enhances the quality and reliability of the electrical supply, leading to improved system performance. The reduction in reliance on power electronics and the elimination of unnecessary secondary windings contribute to an overall improvement in the efficiency of AC to DC conversion, ensuring a more stable and reliable DC output voltage. The inherent adaptability of the system to various voltage levels enhances its versatility and applicability in diverse power distribution scenarios. The transformer design, resembling a locked-wound rotor induction motor, marks a departure from traditional approaches. This innovative design reduces complexities, lowers transformer costs, and simplifies the overall system architecture. Since, there are no moving parts and based on the rating the AC to flat-top AC voltage waveform converter can be housed in an insulating oil tank for better insulation and cooling purposes. The system proves ideal for high-power rectifiers where a stable DC output is critical. Its scalability and efficiency make it suitable for Variable Frequency Drives (VFDs) operating at both medium and low voltages. Additionally, the invention extends to applications in DC chargers for electrical vehicles. Moreover, the system also proves ideal for EHV (Extra High Voltages) AC to HVDC conversion. In summary, the invention stands as a comprehensive and innovative solution, poised to reshape the landscape of AC to DC conversion systems, offering a harmonics-free, cost-effective, and efficient alternative for diverse power system applications. Further objects, features, and advantages of the invention will be readily apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings. Brief Description of the Drawings The invention will be further understood from the following detailed description of a preferred embodiment taken in conjunction with an appended drawing, in which: Fig. 1a illustrates AC to DC Converter system with reduced transformer windings (100), in accordance with an exemplary embodiment of the present invention; Fig. 1b illustrates multi-stage AC to DC Converter system with reduced transformer windings (100), through which Extra High Voltages Alternating Current (EHV AC) can be converted into High Voltage Direct Current (HVDC), in accordance with an exemplary embodiment of the present invention; Fig. 2a & 2b illustrates the prior art circuit diagram and output waveform of 6-PULSE VFD with VSI & MOTOR, in accordance with an exemplary embodiment of the present invention; Fig. 3a & 3b illustrates the prior art circuit diagram and output waveform of 12-PULSE VFD with VSI & MOTOR, in accordance with an exemplary embodiment of the present invention; Fig. 4a, 4b & 4c illustrates the three different types of construction of AC to flat-top alternating current voltage converters (102) which replaces traditional phase shift transformer, in accordance with an exemplary embodiment of the present invention; Fig.5a illustrates the primary windings (108) (R, Y, B Phase windings) location and magnetic flux produced by each phase winding, in accordance with an exemplary embodiment of the present invention; Fig.5b illustrates the primary windings (108) (R, Y, B Phase windings) currents have phase shift of 1200electrical as per 3 Phase input supply, in accordance with an exemplary embodiment of the present invention; Fig.6a illustrates the rotating magnetic field produced by the primary windings (108) in the space at different angles, in accordance with an exemplary embodiment of the present invention; Fig.6b illustrates the rotating magnetic field produced by the primary windings (108) in the space at wt-θ = 00(360o) electrical, in accordance with an exemplary embodiment of the present invention; Fig. 7 illustrates the rotating magnetic field produced by the primary windings (108) in the space at wt-θ = 00, 450, 900, 1350electrical, in accordance with an exemplary embodiment of the present invention; Fig. 8 illustrates the rotating magnetic field produced by the primary windings (108) in the space at wt-θ = 1800, 2250, 2700, 3150electrical, in accordance with an exemplary embodiment of the present invention; Fig. 9 illustrates the circuit diagram of AC to DC Converter System (100) with four secondary windings, in accordance with an exemplary embodiment of the present invention; Fig. 10 & 11 illustrates the output voltages of secondary windings (110) - 1, 2 and windings-3 and 4, in accordance with an exemplary embodiment of the present invention; Fig. 12 illustrates the rectified output voltages of secondary windings (110) - 1, 2 and windings-3 and 4, and final DC output voltage of the AC to DC Converter System, in accordance with an exemplary embodiment of the present invention; Fig.13 illustrates the circuit diagram of AC to DC Converter System (100) with two secondary windings, in accordance with an exemplary embodiment of the present invention; Fig. 14 illustrates the output voltages of secondary windings (110) - 1 and 2, in accordance with an exemplary embodiment of the present invention; Fig. 15 illustrates the rectified output voltages of secondary windings (110) -1 and 2 and final DC output voltage of the AC to DC Converter System, in accordance with an exemplary embodiment of the present invention. Fig.16 illustrates multi-stage AC to DC Converter System (100), in accordance with an exemplary embodiment of the present invention. Detailed Description of the invention It is to be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The present disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. In addition, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including”, “comprising” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Further, the use of terms “first”, “second”, and “third”, and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. According to an exemplary embodiment of the present invention, an AC to DC converter system is disclosed. The system comprises three primary windings distributed uniformly to generate a rotating magnetic field. It also includes secondary windings strategically positioned to intersect with the rotating magnetic field, inducing a flat-top AC voltage waveform. In accordance with an exemplary embodiment of the present invention, the system comprises an AC to flat-top AC voltage waveform converter in place of traditional phase shift transformer with a design resembling a locked-wound rotor induction motor for simplified construction. It also includes a rectifier converting flat-top AC voltages to unidirectional voltages from secondary windings. The conduction period of each secondary winding configuration is 90 electrical degrees. To extend the conduction period of each secondary winding to 180 electrical degrees a bridge rectifier is employed thereby minimizing the secondary windings to two windings for a stable and reliable DC output voltage. It further reduces the cost of the converter system. The system consists a maximum of four secondary windings comparative to traditional phase shift transformer. According to an exemplary embodiment of the present invention, the converter system, wherein the rotating magnetic field considered a non-uniform distribution (0.9 to 1.5 times of flux) with up to 60% non-uniformity in the core / space as a worst-case scenario. If the rotating magnetic flux is closer to uniformity in the core / space results better the induction of flat-top AC voltage waveform in the secondary windings. The converter system features a streamlined transformer design that reduces the number of secondary windings, resulting in lowered transformer costs and simplification of the overall system design. In accordance with an exemplary embodiment of the present invention, the converter system is adaptable to various voltage levels, providing flexibility for implementation in diverse power distribution scenarios. According to an exemplary embodiment of the present invention, the system is designed to mitigate harmonics in the power system, thereby enhancing the quality and reliability of the electrical supply. The system comprises a means for scalability to various power ratings, facilitating applications in high-power rectifiers, Variable Frequency Drives (VFDs) at different voltage levels, and DC chargers for electrical vehicles. According to an exemplary embodiment of the present invention, the system is designed to mitigate the HVDC transmission systems. A multi-stage AC to DC Converter system with reduced transformer windings, through which an Extra High Voltages Alternating Current (EHV AC) can be converted into High Voltage Direct Current (HVDC). According to an exemplary embodiment of the present invention, the system is designed to mitigate harmonics in the power system, thereby enhancing the quality and reliability of the electrical supply. The streamlined transformer design reduces the number of secondary windings, resulting in lowered transformer costs and simplification of the overall system design. In accordance with an exemplary embodiment of the present invention, the system is adaptable to various voltage levels, providing flexibility for implementation in diverse power distribution scenarios. According to an exemplary embodiment of the present invention, the transformer construction resembles a locked-wound rotor induction motor without moving parts. The increased conduction period of secondary windings contributes to a stable DC output voltage, minimizing the need for extensive filtering circuits. According to an exemplary embodiment of the present invention, the rotating magnetic field's uniform distribution enhances flat-top alternating current voltage waveform generation, reducing voltage ripples in the DC output. In accordance with an exemplary embodiment of the present invention, a method of utilizing the AC to DC converter system is disclosed. The method comprises steps of: ^ employing an AC to flat-top AC voltage waveform converter in place of traditional phase shift transformer with a design resembling a locked-wound rotor induction motor for simplified construction; ^ distributing the primary windings uniformly to generate a rotating magnetic field; ^ strategically positioning secondary windings to intersect with the rotating magnetic field, inducing a flat-top AC voltage waveform; ^ utilizing a rectifier to convert flat-top AC voltages induced in the 4 secondary windings to unidirectional voltage waveforms, the conduction period of each winding is 90 electrical degrees for achieving a stable and reliable DC output voltage; ^ or utilizing a bridge rectifier in place of ordinary rectifier and increasing the conduction period of each secondary winding to 180 electrical degrees thereby reducing the secondary windings to two windings for achieving a more stable and reliable DC output voltage; ^ adjusting the converter system to accommodate various voltage levels for implementation in diverse power distribution scenarios. Now referring to Figs., Fig. 1a illustrates AC to DC Converter system with reduced transformer windings (100). Fig. 1b illustrates multi-stage AC to DC Converter system with reduced transformer windings (100). Cascading ‘n’ number of stages which converts an Extra High Voltages Alternating Current (EHV AC system) to High Voltage Direct Current (HVDC). Fig’s 2-3, illustrate (prior art) traditional 6-Pulse and 12-Pulse VFDs that utilize AC to DC converters with 6 and 12 pulses to control the voltage ripples in the DC link voltage (Vdc). The secondary windings required for traditional VFDs range from 2 per phase (6 Nos.), 3 per phase (9 Nos.), 4 per phase (12 Nos.) & 6 per phase (18 Nos.) for 12, 18, 24 & 36 pulse VFDs respectively, leading to increased transformer costs. The higher number of secondary windings is associated with the phase shift transformer (isolation transformer / VFD transformer), contributing to higher costs and potentially larger physical size. The present invention addresses the issue of increased transformer costs by reducing the number of secondary windings in the phase shift transformer to 2 to 4 windings. Each winding induces a flat-top AC voltage waveform from the rotating magnetic field, helping reduce ripples in the secondary voltage of the phase shift transformer. The reduction in voltage ripples contributes to a more stable DC output, reducing the need for extensive filtering circuits. Overall, the present invention aims to achieve a more efficient and cost-effective alternative to traditional VFD designs by lowering transformer costs, reducing footprint, weight, and reliance on extensive filtering. Fig. 4a, 4b & 4c illustrate AC voltage to Flat-top alternating current waveform converter (102) (which is a replacement of traditional phase shift transformer) with a yoke (106) to allow a magnetic path in the system. Three primary windings (108) (with R-Y-B phase sequence), also called the outer windings, are spaced 120 degrees apart to produce a rotating magnetic field. Four numbers of secondary windings (110), also called inner windings, induces a flat-top alternating current voltage waveform from the rotating magnetic field. The core / space (112) provides path for the magnetic flux. The secondary windings (110) are spaced electrically 90 degrees apart. These secondary windings (110) are meticulously spaced to produce a flat-top alternating current voltage waveform. The insulator (116) provides electrical isolation between primary windings (108) and secondary windings (110). All the slots will be insulated accordingly. Base frame (114) provides mechanical supports for yoke (106). The three different types of construction of AC to flat-top alternating current voltage converters (102) have yoke (106) and core (112) that can be separated for winding purposes. Once the windings are wound, they can be replaced to their original position. Type-3 construction resembles an induction motor; however, the rotor must be locked to avoid any movement. Air gap (118) provides insulation between primary (108) and secondary windings (110). Fig.5a illustrates the primary windings (108) (R, Y, B Phase windings) location and magnetic flux produced by each phase winding; these windings are spaced 120 degrees electrically to produce rotating magnetic flux in core / space (112). Fig. 5b illustrates the primary winding (108) (R, Y, B Phase winding) currents produced by the three-phase supply with a phase shift of 120 degrees electrically, as per the phase sequence of the source. The R, Y, B phases currents for balanced conditions have instantaneous currents: IR = Im Cos wt IY = Im Cos (wt - 1200) IB= ImCos (wt - 2400) Where, Im is the maximum value of current w = angular velocity of supply = 2πf f = Frequency of power supply in Hz (50 or 60) t = time in Seconds R-Phase primary winding has the following Magneto Motive Force (m.m.f.) FR(θ) = FmCos θRWhere, θR= θ, space angle of R-phase primary winding Since, Fm = N1I and it is the maximum m.m.f value, then, m.m.f. of R-Phase primary winding: FR(θ) = N1IRCos θ = FmCos wt. Cos θ Since, IR=ImCos wt Where, N1 is the number of turns in R-phase primary winding. IRis the instantaneous value of the current in R-phase primary winding. as well. Similarly, the m.m.f. contributions from Y-phase & B-phase primary windings are: Since, R, Y, B Phases are spaced 1200apart, Y phase lags by 1200to R-phase i.e, θY= θ - 1200similarly, B phase lags by 1200to Y-phase i.e, θB= θY- 1200= θ - 2400FY = Fm Cos (wt - 120°). Cos θY = Fm Cos (wt - 120°). Cos (θ-120°) FB = Fm Cos (wt - 240°). Cos θB = Fm Cos (wt + 120°). Cos (θ-240°) FTOTAL= FR+ FY+ FB= Fm Cos wt Cos θ + Fm Cos (wt - 120°). Cos (θ-120°) + Fm Cos (wt + 120°).Cos (θ-240°) FTOTAL = 0.5 Fm [Cos (wt + θ) + Cos (wt - θ)] + 0.5 Fm [Cos (wt + θ - 2400) + Cos (wt - θ)] + 0.5 Fm [Cos (wt + θ - 4800) + Cos (wt - θ)] Adding 2nd half of each term in above equation =1.5 Fm Cos (wt - θ) Adding 1st half of each term in above equation =0.5 FM {Cos (wt + θ) + Cos (wt + θ - 2400) +Cos (wt + θ - 4800)} =0.5 FM {Cos (wt + θ) + 2 Cos (wt + θ - 3600) x Cos (120°)} =0.5 FM{Cos (wt + θ) + 2 [Cos (wt + θ)] x (-0.5)} =0.5 FM {Cos (wt + θ) - Cos (wt + θ)} = 0 FTOTAL = 1.5 FM Cos (wt + θ) Therefore, FTOTAL = 1.5 Fm Cos (wt - θ), which is a rotating m.m.f in the core / space. Since, flux = N1I / Reluctance of magnetic path. Hence the flux developed in the space is rotating with an angular velocity 'w'. The magnitude of instantaneous flux (Φ) and direction can be identified with respect to time and space angle of winding θ. Fig.6a illustrates the sinusoidal or rotational flux in core / space in accordance with an exemplary embodiment of the present invention. The rotational flux in space is defined as a constant unit magnitude rotating magnetic field (Φ) in space. Fig.6b illustrates the rotating flux (Φ) developed in core / space in accordance with an exemplary embodiment of the present invention. The rotating magnetic flux developed in core / space is considered as non-uniform field strength (0.9 to 1.5 times), considering the reluctance of the magnetic path as a worst-case scenario. The better the uniform rotating magnetic field in core / space, the better the flat-top alternating current voltage waveform induction, in accordance with an exemplary embodiment of the present invention. Figs. 7 and 8 illustrate the rotating magnetic field produced by the primary windings in space at wt-θ = 00, 450, 900, 1350, 1800, 2250, 2700, 3150electrically in accordance with an exemplary embodiment of the present invention. The primary windings in space can understand that the generated magnetic field is rotating the space with respect to time. Fig. 9 illustrates the circuit diagram of the AC to DC converter system (100) with four secondary windings (110). Primary windings (108) are connected in the form of a delta, and these R, Y, B Phase windings' location and magnetic flux produced by each phase winding are spaced 120 degrees electrically to produce rotating magnetic flux in core / space. The primary windings (108) and secondary windings (110) are magnetically coupled in such a way that they induce flat-top alternating current voltage waveforms in secondary windings (110). The induced electro motive force (emf) in the secondary windings (110) is given by the below formula: Induce emf (voltage) in secondary windings = - ∑ [ N2(dΦ / dt) ] in volts Where, N2= Number of Secondary windings linked with rotating flux at the instant of the time (dΦ / dt) = Rate of change of flux with respect to time Since the flux distribution considered in the core is non-uniform as a worst-case scenario due to the variation of reluctance of magnetic flux paths. The higher the uniformity flux in the core results, the better the flat-top AC voltage waveform induced in AC to DC flat-top AC voltage waveform converter (102). Figs.10 and 11 illustrate the induced emf (voltages) in the secondary windings (110) 1, 2, and windings 3, and 4 in accordance with an exemplary embodiment of the present invention. The voltages induced in the secondary windings (110) is rectified by a rectifier (104) further to produce unidirectional voltages in the output. Fig. 12 illustrates the rectified output voltages from rectifier (104) of secondary windings (110) 1, 2, and windings 3, and 4, and the final output voltage of the AC to DC converter system (100), wherein the final output is a pure DC Voltage with very minimum ripple. The mathematical model is developed and verified, considering the rotating flux developed in space is non-uniform field strength (0.9 to 1.5 times) due to different reluctances of the magnetic paths as a worst-case scenario, refer fig.6b. The higher the uniform magnetic field strength in the core / space the better the flat-top alternating current voltage waveform generation. Based on the mathematical model developed, the output DC voltage ripples are less than 0.6V for 460V DC output. These results can be scalable up to 33kV VFD. The voltage ripples can be minimized to a few volts even for 33kV VFDs by carefully locating / placing and sizing the secondary windings. The DC output voltage developed is better than traditional 36-pulse VFD converters. Fig. 13 illustrates the circuit diagram of the AC to DC Converter System (100) with two secondary windings (110). The primary windings (108) are connected in the form of a delta. These three primary windings' (108) location and magnetic flux produced by each phase winding are spaced 120 degrees electrically to produce rotating magnetic flux in space. The primary (108) and secondary windings (110) are magnetically coupled in such a way that they induce flat-top alternating current voltage waveforms in secondary windings (110). This system reduces the requirement for more secondary windings (110) in the phase shift transformer, thereby reducing its cost. The induced emfs are further rectified by employing bridge rectifiers (104) to increase the conduction period of each secondary windings (110) to 180 electrical degrees, which provide faithful pure DC output. Fig. 14 illustrates the induced voltages of secondary windings-1 and 2 (110) the induced voltages are rectified further with a bridge rectifier (104) and produce unidirectional voltages in the output. Fig. 15 illustrates the rectified output voltages of secondary windings-1 and 2 (110) and the final output voltage of the AC to DC converter system (100). The final output is a pure DC Voltage with very minimum ripple. The mathematical model developed and verified considering the rotating flux developed in space is non-uniform field strength (0.9 to 1.5 times) and due to different reluctances of magnetic paths as a worst-case scenario, refer fig. 6b. The higher the uniform magnetic field strength in core / space the better the flat-top alternating current voltage waveform generation. Based on the mathematical model developed, the output DC voltage ripples are less than 0.6V for 460V DC output. These results can be scalable up to 33kV VFD. The voltage ripples can be minimized to a few volts even for 33kV VFDs by carefully locating / placing and sizing the secondary windings (110). The DC voltage output developed is better than traditional 36-pulse VFD converters. Fig. 16 illustrates the multi-stage AC to DC converter system (100) with reduced transformer windings cascaded for converting Extra High Voltage AC (400kV AC and above) to HVDC (500kV DC and above), which is useful for HVDC power transmission. Since, there are no moving parts and by taking care the necessary insulation of each system, a EHV AC supply can be connected to n-stages in series and the DC output of each stage can be connected in series to get the required HVDC output. This facilitates to convert Extra High Voltages AC to High Voltage DC, which has great advantages than the traditional HVDC transmission system. The AC to DC converter system proposed in this invention introduces a range of compelling advantages that position it as a notable innovation in power conversion technology. A primary benefit lies in Cost Reduction as the streamlined transformer design and reduced number of secondary windings significantly cut down on transformer costs. This economic efficiency enhances the appeal of the system, making it a financially prudent alternative. Moreover, the construction of the system, resembling a locked-wound rotor induction motor, not only simplifies the overall design but also leads to a potentially smaller physical footprint. This feature is particularly advantageous in applications where space considerations are critical. The system addresses the issue of harmonics in the power system, contributing to Harmonics Mitigation and thereby improving power quality and enhancing the reliability of the electrical supply. This capability makes the system a valuable asset in environments where harmonics must be carefully managed. Additionally, by extending the conduction period of each secondary winding and inducing a flat-top AC voltage waveform, the system achieves Efficiency Improvement. It reduces voltage ripples in the DC output, leading to a more stable DC output and minimizing the need for extensive filtering circuits. In terms of Applications, the AC to DC converter system is versatile and finds utility in various high-power scenarios. It is well-suited for deployment in High-Power Rectifiers in industrial settings, offering a reliable and efficient solution for power conversion. Its adaptability to different voltage levels makes it suitable for Variable Frequency Drives (VFDs) at both medium and low voltages, catering to a wide range of industrial applications. The system's scalability extends to applications such as DC Chargers for Electrical Vehicles, contributing to the development of efficient charging infrastructure. This system can be efficiently utilized for HVDC transmission system for converting AC to DC. The system's versatility in adapting to different power ratings and voltages underscores its broad applicability across diverse power system requirements. Overall, the AC to DC converter system stands out as a cost-effective, space-efficient, and harmonics-mitigating solution, poised to make a meaningful impact in high-power scenarios.

Claims

5. CLAIMS I / We Claim:

1. An AC to DC converter system (100), comprising: a transformer with a design resembling a locked-wound rotor induction motor for simplified construction; a primary windings (108) distributed uniformly to generate a rotating magnetic field; secondary windings (110) strategically positioned to intersect with the rotating magnetic field, inducing a flat-top AC voltage waveform; a rectifier (104) for converting flat-top AC voltage from secondary windings (110) with a conduction period of 90 electrical degrees for a stable and reliable DC output voltage; a bridge rectifier (104) converting flat-top AC voltages from secondary windings; extension of the conduction period of each secondary winding (110) to 180 electrical degrees for a stable and reliable DC output voltage; Characterized in that, the converter system (100) wherein the rotating magnetic field considering that exhibits a non-uniform distribution (0.9 to 1.5 times of flux) with up to 60% non-uniformity in core / space (112) due to variation of reluctances in the magnetic paths; the converter system features a streamlined transformer design that reduces the number of secondary windings (110), resulting in lowered transformer costs and simplification of the overall system design; and the AC to DC converter system (100) is adaptable to various voltage levels, providing flexibility for implementation in diverse power distribution scenarios.

2. The AC to DC converter system (100) as claimed in claim 1, wherein the systemis designed to mitigate harmonics in the power system, thereby enhancing the quality and reliability of the electrical supply.

3. The AC to DC converter system (100) as claimed in claim 1, comprises a means for scalability to various power ratings, facilitating applications in high-power rectifiers, Variable Frequency Drives (VFDs) at different voltage levels, DC chargers for electrical vehicles and HVDC transmission systems.

4. The AC to DC converter system (100) as claimed in claim 1, wherein the system is designed to mitigate harmonics in the power system, thereby enhancing the quality and reliability of the electrical supply.

5. The AC to DC converter system (100) as claimed in claim 1, wherein the streamlined transformer design reduces the number of secondary windings (110), resulting in lowered transformer costs and simplification of the overall system design.

6. The AC to DC converter system (100) as claimed in claim 1, wherein the system is adaptable to various voltage levels, providing flexibility for implementation in diverse power distribution scenarios.

7. The AC to DC converter system (100) as claimed in claim 1, wherein the transformer construction is similar to a locked-wound rotor induction motor without moving parts.

8. The AC to DC converter system (100) as claimed in claim 1, wherein the reduction in secondary windings (110) contributes to a stable DC output voltage, minimizing the need for extensive filtering circuits.

9. The AC to DC converter system (100) as claimed in claim 1, wherein the rotating magnetic field's non-uniform distribution also can produce flat-top alternating current voltage waveform generation, reducing voltage ripples in the DC output. The higher the uniformity of the rotating magnetic field, the better the flat-top alternating current voltage waveform generation.

10. A method of utilizing the AC to DC converter system (100) as claimed in claim 1, comprising the steps of: employing an AC to flat-top AC voltage waveform converter (102) in place of traditional phase shift transformer with a design resembling a locked-wound rotor induction motor for simplified construction; distributing the primary windings (108) uniformly to generate a rotating magnetic field; strategically positioning secondary windings to intersect with the rotating magnetic field, inducing a flat-top AC voltage waveform; utilizing a rectifier (104) to convert flat-top AC voltages induced in the 4 secondary windings (110) to unidirectional voltage waveforms, the conduction period of each winding is 90 electrical degrees for achieving a stable and reliable DC output voltage; or utilizing a bridge rectifier (104) in place of ordinary rectifier and increasing the conduction period of each secondary winding to 180 electrical degrees thereby reducing the secondary windings (110) to two windings for achieving a more stable and reliable DC output voltage; adjusting the AC to DC converter system (100) to accommodate various voltage levels for implementation in diverse power distribution scenarios.

6. DATE AND SIGNATURE Dated this 03rdday of January 2024 Signature3124 Agent for Applicant.

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