A high-voltage direct current (HVDC) generation system using unidirectional voltage generators

Abstract

The present invention discloses a High-Voltage Direct Current (HVDC) generation system designed for efficient and cost-effective HVDC generation. The system comprises a prime mover (102), a flat-top alternating-current voltage generator (exciter) (110), and two unidirectional voltage generators (UVG-1 & UVG-2) (120 & 130), all mounted on a common shaft (104) to ensure synchronization. The prime mover (102) provides rotational motion, while a DC supply excites the field coil of the exciter (110), generating flat-top AC voltages in rotor windings-1 & 2 (116) with a 90° phase shift are supplied to the rotor coils of UVG-1 and UVG-2, which produce alternating rotating magnetic fields. These fields induce unidirectional voltages with a 180° phase shift in the stator windings (124 & 134) of UVG-1 and UVG-2, which are then connected in series to generate constant HVDC output. This innovation eliminates the need for commutation, rectification and filters, reducing the costs and harmonic issues. It offers versatility in connecting to existing HVDC-links, enhances power-transmission capacity.

Description

[0001] FORM 2 PATENTS ACT, 1970 (39 of 1970) &

[0002] The Patents Rules, 2003

[0003] COMPLETE SPECIFICATION (See section 10 and rule 13)

[0004] 1. TITLE OF THE INVENTION

[0005] “A HIGH-VOLTAGE DIRECT CURRENT (HVDC) GENERATION SYSTEM USING UNIDIRECTIONAL VOLTAGE GENERATORS”

[0006] 2. APPLICANTS a. Name : VEERABHADRA ELITE ELECTRODYNAMIC

[0007] SOLUTIONS LLP b. Nationality : INDIAN c. Address : Plot No 149, Door No 202, Venkat Classic

[0008] Apartments, Road No 4, KTR colony, Nizampet, Medchai- Malkajgiri, Telangana- 500090.

[0009] 3. PREAMBLE TO THE DESCRIPTION

[0010] COMPLETE

[0011] The following specification particularly describes the invention and the manner in which it is to be performed. 4. DESCRIPTION

[0012] Technical Field of the invention

[0013] The present invention generally relates to electrical engineering and power generation. More particularly, relates to the field of high-voltage direct current (HVDC) generation systems without commutation and rectification, where the efficient and cost-effective production of HVDC is critical for long and short distance electrical power transmission and interconnection between similar power plants or supplying power to HVDC links.

[0014] Background of the invention

[0015] High-voltage direct current (HVDC) systems have been pivotal in the field of electrical power transmission, especially for long-distance transmission and interconnecting different power grids. The ability of HVDC systems to reduce energy loss during transmission over large distances has made them a reliable solution for utilities, particularly in areas where alternating current (AC) transmission would be inefficient or infeasible. However, despite the substantial benefits of HVDC technology, the conventional systems used for converting High Voltage AC to HVDC are burdened by significant drawbacks, ranging from high capital costs to operational complexity and limited scalability. These challenges have spurred the need for an innovative approach to HVDC power generation that can address the inherent limitations of existing systems while providing a more efficient, cost-effective, and adaptable solution for modern power grids.

[0016] Traditional HVDC systems rely on complex components such as rectifiers, transformers, and inverters, which play crucial roles in the conversion of alternating current (AC) into direct current (DC) and vice versa. However, these conversion technologies come with several disadvantages. The process of converting AC to DC, for example, requires rectifiers, which are expensive and difficult to maintain. Rectifiers, typically built with phase- shifting transformers, power electronic devices like thyristors / valves / diodes, Filters, DC reactors are subject to the immense electrical stresses they endure during operation. The constant need for maintenance, repairs, and eventual replacement of these components increases the long-term operational costs and reduces system reliability. Furthermore, these devices are large, bulky, and costly to manufacture, resulting in high initial capital costs for HVDC installations. Additionally, the complexity of rectifiers and their control mechanisms often leads to operational inefficiencies, increasing the risk of system failures and adding complexity to the overall management of the HVDC system.

[0017] One of the most significant challenges in conventional HVDC systems is the need for phase- shifting transformers. These transformers are required to modify the phase angle of the AC power to facilitate its conversion to DC and vice versa. However, these transformers are costly and require significant physical space. They introduce additional complexity and maintenance challenges. As power demand increases and grid interconnections grow, the need to expand the system becomes more difficult. Phase-shifting transformers limit the flexibility of the HVDC system, as adding or modifying the system often requires additional, costly infrastructure changes.

[0018] Another critical issue associated with traditional HVDC systems is the generation of harmonics. Harmonics are unwanted high-frequency voltages or currents that arise when power electronic devices such as rectifiers and inverters interact with the grid. These harmonics distort the quality of the power being transmitted, potentially leading to interference with sensitive electrical equipment and grid instability. To counter this, additional filtering equipment is required, which further adds to the complexity and cost of the system. These filters, while effective at reducing harmonic distortion, also introduce additional losses into the system and can be costly to install, operate, and maintain. Harmonics also lead to inefficiencies in the overall transmission system, reducing the energy efficiency of the HVDC network and further escalating operating expenses. While HVDC technology has advanced over the years, these challenges persist, making it increasingly difficult to scale traditional HVDC systems to meet the growing demand for efficient power transmission. The need for high-voltage power transmission that is both efficient and scalable is growing, as global energy demands increase and as new power generation sources, including renewable energy, are integrated into the grid. As HVDC systems are crucial for connecting renewable energy sources to the grid over long distances, particularly in offshore wind farms and solar arrays, it becomes even more critical to develop solutions that eliminate the need for complex and costly conversion technologies. Scaling conventional HVDC systems typically requires adding more rectifiers and transformers, which complicates the design, increases costs, and limits the system’s ability to meet future demands.

[0019] In light of these challenges, there is a growing need for a more efficient, cost- effective, and flexible HVDC generation system. Conventional systems, while effective in some applications, are not well-suited to meet the demands of modem power grids, which require systems that are both highly scalable and able to integrate seamlessly with existing infrastructure. The innovation proposed in this invention seeks to address these issues by introducing a scalable system that eliminates the need for phase- shifting transformers and rectifiers. This innovative approach leverages unidirectional voltage generators that directly produce unidirectional voltage waveforms from a flat-top alternating current (AC) voltage generator (acts as an exciter to the unidirectional voltage generators). By cascading these generators in series, the system can generate high-voltage direct current (HVDC) output without the need for complex power conversion devices. This eliminates the need for additional filtering devices to manage harmonics and improves the overall efficiency of the system. Moreover, the design is scalable, making it easier to adapt to growing power demands without the need for significant infrastructure changes.

[0020] The need for such an innovation is dire. As the world transitions towards more sustainable energy sources, including renewable energy like wind and solar, the requirement for efficient, long-distance power transmission systems becomes even more pressing. Renewable energy sources are often located in remote areas far from population centres, necessitating the development of advanced HVDC transmission systems that can efficiently deliver power across vast distances with minimal loss. Traditional HVDC systems, while capable of addressing these needs to some extent, do so at high cost and with limited scalability. As power demands continue to rise, the traditional systems become less viable, and there is a clear need for new solutions that can support both high-voltage transmission and integration with renewable energy sources.

[0021] Brief Summary of the invention

[0022] The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure, and it does not identify key / critical elements of the invention or delineate the scope of the invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

[0023] The primary object of the present invention is to provide an efficient and cost- effective solution for the generation of high-voltage direct current (HVDC), particularly for long-distance electrical power transmission and interconnection between similar power plants or supplying power to HVDC links. The invention aims to simplify the design and operational aspects of traditional HVDC systems, addressing the need for higher efficiency, lower costs, and easier integration with existing infrastructure.

[0024] Another significant object of the invention is to eliminate the need for complex and costly conversion technologies in HVDC transmission systems. Conventional HVDC systems typically rely on rectifiers, phase-shift transformers, and other power electronic devices for AC to DC conversion, which are expensive, bulky, and require significant maintenance. This invention addresses the challenges posed by these devices by utilizing unidirectional voltage generators (UVGs) that directly generate DC voltage waveforms, eliminating the need for rectifiers and phase-shifting transformers.

[0025] A further object of the invention is to provide a scalable and adaptable HVDC generation system that can generate high-voltage DC output voltages of 500kV and above. The invention introduces a system capable of cascading multiple unidirectional voltage generators in series, allowing for the generation of higher voltage levels while maintaining synchronization across the system. This scalability is critical for adapting the HVDC system to meet growing power demands without the need for additional complex devices or major infrastructure changes.

[0026] Yet another object of the invention is to offer a system that provides enhanced flexibility and controllability of DC voltages, enabling seamless integration with existing HVDC links and enhancing the overall power transmission capacity. This system also addresses the harmonic distortion challenges typically encountered in conventional HVDC systems, providing a solution that reduces the need for filtering equipment, improving overall system efficiency.

[0027] Finally, the invention seeks to provide an improved solution for HVDC generation and HVDC power transmission that is simple to operate, reduces operational costs, and simplifies the design and maintenance process. The system eliminates the reliance on complex power electronic devices like rectifiers and transformers, offering a more robust and cost-effective solution to modern power transmission needs.

[0028] The present invention provides a high-voltage direct current (HVDC) generation system that eliminates the need for traditional conversion technologies, offering a simplified design and significantly reduced operational costs. The system is designed to generate high-voltage direct current (HVDC) for long-distance power transmission and interconnection between power plants or HVDC links, addressing the challenges of conventional HVDC systems while enhancing scalability, flexibility, and efficiency.

[0029] The system comprises a prime mover configured to provide rotational motion (mechanical energy) to the entire system. This prime mover drives a flat-top alternating current (AC) voltage generator (exciter) whose magnetic pole coils are excited by external DC supply and produces trapezoidal or flat-top alternating current voltage waveforms. These AC voltage waveforms are generated in rotor windings, leading to a 90-degree phase shift between the rotor windings. These generated flat-top voltages are further exciting the unidirectional voltage generator rotor windings produce flat-top alternating magnetic fields.

[0030] At the core of the innovation, the system utilizes unidirectional voltage generators (UVGs) to directly generate unidirectional DC voltage waveforms from the flattop alternating magnetic field. The first unidirectional voltage generator (UVG-1) is excited by rotor winding- 1 of the flat-top AC voltage generator, while the second unidirectional voltage generator (UVG-2) is excited by rotor winding-2. These unidirectional voltage generators produce unidirectional voltage waveforms such as segment wise (piecewise) linear waveforms (triangular, trapezoidal, flattop, stepped, etc.,), depending on the rotor and stator design. This direct generation of DC voltage is a key aspect of the present invention, as it eliminates the need for complex rectifiers and phase- shifting transformers that are typically used in traditional HVDC systems.

[0031] The unidirectional voltage generators are designed to operate with rotating magnetic poles and field coil arrangement that ensures the induction of unidirectional voltage in the stator coils. This design not only improves the efficiency of the system but also reduces the number of components required, which ultimately leads to lower capital costs and simplified maintenance. Moreover, these unidirectional voltage generators are capable of scaling the system to generate HVDC voltages of 500kV and above by cascading multiple stages of UVGs in series. Each stage of the UVGs is synchronized through the common shaft that connects the entire system, ensuring uniform speed and maintaining the desired phase shifts between each stage.

[0032] The scalability of the system is one of its most important features. As power demands grow, the system can easily be expanded by adding additional stages of UVGs in series, each synchronized with the common shaft. This modular design allows the HVDC system to generate higher voltages efficiently, supporting the needs of large-scale power transmission without requiring major changes to the system infrastructure. By avoiding the addition of bulky components such as rectifiers and transformers, the system simplifies the design and reduces overall installation and maintenance costs.

[0033] The system's ability to generate stable HVDC output voltage is another key advantage of the present invention. By connecting the unidirectional voltage generators in series with precise phase shifts, the system produces a constant high- voltage DC output without the need for complex power electronic devices. This continuous and stable HVDC output is essential for high-voltage transmission over long distances and ensures that the system can integrate easily with existing HVDC links, enhancing power transmission capacity and improving grid stability.

[0034] An important aspect of the invention is the elimination of the need for additional filtering equipment to manage harmonic distortion. In conventional HVDC systems, rectifiers and other power electronic devices generate harmonics that can degrade power quality. These harmonics require the use of filtering equipment to reduce their impact on the system, which adds to the complexity and cost of the system. The unidirectional voltage generators in the present invention reduce harmonic generation, thereby improving power quality and eliminating the need for additional filtering devices.

[0035] The flexibility and controllability of the system are enhanced by its design, which allows for seamless integration with existing HVDC links. This enables the system to handle varying power loads and adjust to grid conditions more efficiently than traditional HVDC systems. Furthermore, the modular nature of the system allows it to be adapted for different applications, from long-distance power transmission to interconnection between different grids, making it a highly versatile solution for modem electrical grids.

[0036] Another notable feature of the present invention is its reduced operational costs. By eliminating the need for complex power conversion devices and minimizing the number of components in the system, the invention significantly lowers the capital costs, operational and maintenance costs compared to traditional HVDC systems. The system's simpler design reduces the risk of component failure, improves system reliability, and ensures long-term cost savings.

[0037] In summary, the invention provides a highly efficient, scalable, and cost-effective HVDC generation system that eliminates the need for traditional conversion technologies like rectifiers, transformers and filters. By using unidirectional voltage generators that directly generates unidirectional voltages thereby stable DC output, the system improves overall efficiency, reduces system complexity, and offers enhanced flexibility for modem power grids. The invention addresses the growing need for high-voltage power transmission systems that are adaptable, easy to integrate, and capable of supporting the increasing energy demands of the future.

[0038] 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.

[0039] Brief Description of the Drawings

[0040] 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. 1 illustrates the block diagram of HVDC generation system using unidirectional voltage generators (100), in accordance with an exemplary embodiment of the present invention;

[0041] Fig. 2 illustrates the detailed block diagram of HVDC generation system using unidirectional voltage generators (100), in accordance with an exemplary embodiment of the present invention;

[0042] Fig. 3a illustrates the general arrangement of flat-top alternating current voltage generator (110) using salient pole type stator, in accordance with an exemplary embodiment of the present invention;

[0043] Fig. 3b illustrates the general arrangement of flat-top alternating current voltage generator (110) using non-salient pole type (cylindrical type) stator, in accordance with an exemplary embodiment of the present invention;

[0044] Fig. 4a illustrates the general arrangement of unidirectional voltage generator- 1 (UVG-1) (120) with salient pole type rotor, in accordance with an exemplary embodiment of the present invention;

[0045] Fig. 4b illustrates the generated magnetic flux in unidirectional voltage generator-2 (UVG-2) (130) with salient pole type rotor, in accordance with an exemplary embodiment of the present invention;

[0046] Fig. 5a & 5b illustrates the general arrangement of unidirectional voltage generator-1 (UVG-1) (120) & unidirectional voltage generator-2 (UVG-2) (130) with cylindrical type rotor, in accordance with an exemplary embodiment of the present invention;

[0047] Fig. 6a illustrates the connection diagram of UVG-1 & UVG-2, in accordance with an exemplary embodiment of the present invention; Fig. 6b illustrates the connection diagram of UVG-1 & UVG-2, in accordance with an exemplary embodiment of the present invention;

[0048] Fig. 7a & 7b illustrates the output voltage waveforms of trapezoidal / flat-top alternating current voltage generator (exciter) winding- 1 & 2, in accordance with an exemplary embodiment of the present invention;

[0049] Fig. 8 illustrates the output voltage waveforms (triangular waveforms) of unidirectional voltage generator- 1 & 2 and combination of UVG-1 & UVG-2, in accordance with an exemplary embodiment of the present invention;

[0050] Fig. 9 illustrates the output voltage waveforms (trapezoidal waveforms) of unidirectional voltage generator- 1 & 2 and combination of UVG-1 & UVG-2, in accordance with an exemplary embodiment of the present invention;

[0051] Fig. 10a illustrates the block diagram of single shaft n-stage HVDC generation system for 500kV & above, in accordance with an exemplary embodiment of the present invention;

[0052] Fig. 10b illustrates the block diagram of n-stage HVDC generation system for 500kV & above, in accordance with an exemplary embodiment of the present invention.

[0053] Detailed Description of the invention

[0054] 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.

[0055] The present invention provides a high-voltage direct current (HVDC) generation system designed to overcome the limitations of traditional HVDC technologies. The system is simplified, efficient, and scalable, eliminating the need for complex conversion technologies like rectifiers, phase- shifting transformers, filters. This allows for the direct generation of high-voltage DC power suitable for longdistance transmission and interconnection with other power plants.

[0056] The HVDC generation system comprises key components working in harmony to convert mechanical energy into high-voltage direct current (HVDC) output. These components include a prime mover, a flat-top alternating current (AC) voltage generator (exciter), and unidirectional voltage generators. The prime mover initiates and sustains the rotational motion needed for the entire system. The mechanical energy from the prime mover drives the flat-top AC voltage generator (exciter), which, with the aid of a direct current (DC) supply, generates trapezoidal or flat-top AC voltage waveforms in the rotor windings. These AC waveforms are subsequently used to generate unidirectional DC voltage in unidirectional voltage generators.

[0057] The unidirectional voltage generators are the heart of the system. They utilize the AC voltage from the flat-top generator to produce alternating magnetic fluxes within their rotors. The unidirectional voltage generators are designed to generate DC voltages in a manner that eliminates the need for commutators or rectifiers. The unidirectional voltage is then harnessed and connected in series or parallel, forming a constant high-voltage DC output. The system is scalable, allowing for multiple unidirectional voltage generators to be connected in series with precise phase shifts, enabling the generation of high-voltage DC outputs of 500kV and above.

[0058] This innovative design allows for a compact and cost-effective HVDC system that is more adaptable and flexible than conventional systems, meeting the increasing demand for long-distance, high-voltage power transmission without the complexity of traditional AC to DC power conversion methods.

[0059] The prime mover in the system is responsible for rotational mechanical energy, which is then used to drive the flat-top alternating current (AC) voltage generator and unidirectional voltage generators. The prime mover can be an electric motor (either AC or DC), capable of converting electrical energy into rotational mechanical energy. This mechanical energy is transferred to the rotor of the flattop AC voltage generator (exciter) and unidirectional voltage generators.

[0060] The flat-top AC voltage generator operates with a field coil that is powered by a DC supply. This exciter is configured to produce trapezoidal or flat-top AC voltages within the rotor windings. The waveform produced in the rotor is essential for the subsequent stages of the HVDC generation process, ensuring that the correct characteristics are achieved to maintain stable and efficient high- voltage DC output.

[0061] The unidirectional voltage generators (UVG-1 and UVG-2) receive the AC voltage generated by the flat-top generator (exciter) and convert it into unidirectional voltage waveforms. These generators (UVG-1 and UVG-2) utilize the alternating magnetic flux produced by the AC voltage to induce a consistent unidirectional electromotive force (emf) in the stator coils. The design of the unidirectional voltage generators ensures that the generated voltage is always in one direction (unidirectional), thus eliminating the need for rectification or commutator systems. The unidirectional voltage generators are designed to produce waveforms such as segment-wise (piecewise) linear waveforms (triangular, trapezoidal, flat-top, stepped, etc.,). The voltage generated by each UVG consists of a specific phaseshift with the other, allowing the system to connect multiple stages in series to achieve the desired high-voltage output. By connecting the unidirectional voltage generators in series, the system maintains a constant DC output voltage, which can be adjusted to meet the requirements of long-distance power transmission.

[0062] A key feature of the system is its scalability. The system can easily be expanded to generate higher voltage levels by connecting multiple stages of unidirectional voltage generators in series. Each stage is synchronized via a common shaft, ensuring that the voltage outputs are consistent and with specific phase- shift depending on the shape of voltage waveform generated by the unidirectional voltage generators, which is crucial for the stable operation of the HVDC system. This scalability allows the system to generate HVDC outputs of 500kV and above, making it suitable for large-scale power transmission applications.

[0063] The scalability of the system is critical in applications that require high-voltage DC transmission, such as connecting offshore wind farms to the grid or interconnecting power plants over vast distances. The ability to scale the system without needing additional complex devices, such as transformers or rectifiers, makes it a cost-effective and efficient solution for modern power grids.

[0064] By using unidirectional voltage generators to directly generate DC voltage from alternating magnetic fields, the system eliminates the need for conventional conversion technologies like rectifiers, transformers, and phase-shifting transformers. These conventional devices are typically used in HVDC systems to convert AC to DC and vice versa, but they add complexity, cost, and maintenance requirements to the system.

[0065] The design of the unidirectional voltage generators allows for the direct generation of stable, high-voltage DC power, without the need for commutators or rectifiers. This simplification reduces the number of components in the system, resulting in lower capital and operational costs. Additionally, the absence of rectifiers and phase-shifting transformers leads to fewer points of failure, improving the overall reliability and efficiency of the system.

[0066] Traditional HVDC systems often suffer from harmonic distortion due to the nonlinear behaviour of rectifiers and other power electronic devices. The proposed system addresses this issue by generating stable, unidirectional voltage waveforms directly from the flat- top alternating magnetic fields. The unidirectional voltage generators produce clean DC power without the harmonic distortion typically associated with conventional HVDC systems. This reduces the need for external filtering devices, improving power quality and system efficiency.

[0067] The system is designed to be flexible and easily integrated with existing HVDC links and power grids through HVDC links. The modular design of the system allows it to be adapted for a wide range of applications, from small-scale installations to large-scale transmission networks. The ability to seamlessly integrate with existing infrastructure makes it a versatile solution for modern electrical grids, which are increasingly incorporating renewable energy sources and require reliable and efficient power transmission.

[0068] The following figures illustrate various aspects of the HVDC generation system and its components, as described in the exemplary embodiment of the present invention:

[0069] Fig. 1 illustrates the block diagram of the HVDC generation system using unidirectional voltage generators (100). The system comprises a prime mover (102), a flat- top alternating current voltage generator (exciter) (110), a unidirectional voltage generator- 1 (UVG-1) (120), a unidirectional voltage generator-2 (UVG-2) (130), and a common shaft (104). The prime mover (102) generates rotational motion, which is then transmitted to the flat-top alternating current voltage generator (110) through the common shaft (104). This exciter (110) is powered by a DC supply (106) to produce trapezoidal or flat-top AC voltages in rotor windings-1 & 2 (116), responsible for flux reversal in every 180 degrees of rotation in the unidirectional voltage generators (120, 130). The generated AC voltages are fed into the field coils (126 & 136) of UVG-1 (120) and UVG-2 (130) respectively to produce alternating magnetic fluxes, which generate unidirectional voltage waveforms such as segment wise (piecewise) linear waveforms (triangular, trapezoidal, flat-top, stepped, etc.,) with the appropriate phase shift. The flux reversal ensures the generation of unidirectional voltages in the UVG-1 (120) & UVG-2 (130). All components, including the prime mover (102), flat-top alternating current voltage generator (exciter) (110), and unidirectional voltage generators (120, 130), are connected to the same shaft (104) to ensure synchronization and eliminate the need for slip rings. These unidirectional voltages are then connected in series within the HVDC generation system using unidirectional voltage generators (100), resulting in a constant high voltage direct current (HVDC) output (200). If the waveform other than triangular or trapezoidal or combination of these two used in the UVGs, multiple stages of the HVDC generation system are connected in series with the necessary phase shifts among each UVG or (stage), ensuring the generation of a constant HVDC voltage output and facilitating the generation of higher HVDC voltages. Small change in windings or compensating windings in UVGs are envisaged if there are minor ripples encountered due to magnetic properties change in of UVGs. This innovation eliminates the need for additional AC to DC conversion technologies, making it advantageous for HVDC transmission, feeding HVDC links, and interconnecting similar power plants.

[0070] Fig. 2 illustrates the general arrangement of the HVDC generation system. The flat- top alternating current voltage generator (110) comprises a yoke (112) and salient poles (114P), which form the magnetic path, and an excitation coil (114) that initiates the magnetic field. The rotor windings-1 & 2 (116) induce flat-top alternating current voltages in response to the rate of change of the magnetic field, in accordance with Faraday’s Laws of Electromagnetic Induction. The rotor magnetic core (118) enhances the magnetic properties. The unidirectional voltage generator- 1 (UVG-1) (120) includes a yoke (122) for the magnetic path, a stator coil (124) for inducing unidirectional voltage, and a rotor coil (126) for producing a flat-top alternating magnetic field or trapezoidal magnetic field, which is a critical element in the system.

[0071] According to Faraday’s Laws of Electromagnetic Induction, the stator winding (124) generates unidirectional voltage. Since the flux reverses every half cycle (or 180 degrees of rotation of the rotor), the flux direction with respect to the stator coils always remains in one direction (positive), ensuring that the generated voltage in the stator coil is always positive (unidirectional in nature). The stator and rotor windings and their design are meticulously designed such that the generated voltages will be segment-wise (piecewise) linear waveforms (triangular, trapezoidal, flat-top, stepped, etc.,). The unidirectional voltages eliminate the requirement for commutator and rectification units. The magnetic pole (128) and the stator windings (124) contribute to the overall generation process. Similarly, unidirectional voltage generator-2 (UVG-2) (130) has a yoke (132), a stator coil (134), and a rotor coil (136). These components collectively facilitate the generation of unidirectional voltages waveforms of segment-wise (piecewise) linear waveforms (triangular, trapezoidal, flat-top, stepped, etc.,)., contributing to the HVDC system's functionality. These UVG-1 (120) & UVG-2 (130) are connected in series to produce a constant HVDC output voltage (200) without the need for commutation or rectification units. In the case of triangular or trapezoidal or combination of these two voltage waveforms, only two units are required to produce a constant HVDC voltage output (series connection for triangular and parallel connection for trapezoidal / flat-top voltage waveforms). In the case of other waveforms, multiple UVGs with specific phase shifts are connected in series to generate the constant HVDC voltage output. The number of UVGs and phase shifts required depends on the stator and rotor design.

[0072] Fig. 3a illustrates the general arrangement of the flat-top alternating current voltage generator (exciter) (110) with a salient pole-type stator. The yoke (112) and salient poles (114P) form a magnetic path, facilitating the magnetic flux necessary for power generation. The excitation coil (114) initiates the magnetic field with a DC voltage input, and as the rotor coil (116) within the rotating component interacts with this field, it induces a trapezoidal or flat-top AC voltage waveform, in accordance with Faraday’s Laws of Electromagnetic Induction. The magnetic core (118) enhances the efficiency of the generator by concentrating and guiding the magnetic flux. This exciter serves as a fundamental component in the HVDC system, producing the necessary alternating flux in the UVGs for the conversion of mechanical energy from the prime mover (102) into the desired high-voltage direct current (HVDC) voltage output.

[0073] An alternating voltage supplied to a rotor winding produces alternating magnetic field in the rotor poles as the rotor rotates 180 degrees and the alternating flux also reverses it direction, hence the flux direction in the generator / space is always unidirectional with respect to stator windings and produces unidirectional voltage in the stator windings.

[0074] Fig. 3b illustrates the general arrangement of the flat-top alternating current voltage generator (exciter) (110) with a non- salient pole-type (cylindrical type) stator. The configuration is similar to the one shown in Fig. 3a, but with a cylindrical stator. The yoke (112) forms a magnetic path, facilitating the magnetic flux necessary for power generation. The excitation coil (114) initiates the magnetic field with a DC voltage input, and as the rotor coil (116) within the rotating component interacts with this field, it induces a trapezoidal or flat-top AC voltage waveform, in accordance with Faraday’s Laws of Electromagnetic Induction. The magnetic core (118) enhances the efficiency of the generator by concentrating and guiding the magnetic flux. This exciter serves as a fundamental component in the HVDC system, producing the necessary alternating flux in the UVGs for the conversion of mechanical energy from the prime mover (102) into the desired high-voltage direct current (HVDC) voltage output.

[0075] Fig. 4a illustrates the general arrangement of unidirectional voltage generator- 1 (UVG-1) (120) with a salient pole-type rotor. The yoke (122) forms a magnetic path, guiding the magnetic flux. The rotor coil (126) is fed from rotor winding- 1 (116) of the flat-top AC voltage generator (110), producing a trapezoidal or flattop alternating magnetic flux in UVG-1. The stator coil / winding (124), a stationary winding, interacts with the flat-top rotating magnetic field produced by the rotor coil (126) to generate a unidirectional voltage waveform. The design ensures a consistent direction of the induced electromotive force. The rotating magnetic pole (128) with trapczoidal / flat-top alternating flux ensures that the flux linkages with the stator windings is always in one direction, inducing unidirectional voltage in the stator winding (124). This process is essential for the overall HVDC generation system to ensure the reliable generation of high-voltage direct current (HVDC) voltage output.

[0076] Fig. 4b illustrates the general arrangement and magnetic flux distribution of unidirectional voltage generator-2 (UVG-2) (130) with a salient pole-type rotor. The configuration is similar to UVG-1, but this generator is fed from rotor winding-2 (116) of the flat-top AC voltage generator (110), producing a trapezoidal or flat-top alternating magnetic flux in UVG-2. The stator coil / winding (134), a stationary winding, interacts with the flat-top rotating magnetic field produced by the rotor coil (136) to generate a unidirectional voltage waveform. The design ensures that the induced electromotive force is always in one direction, contributing to the overall HVDC generation system and ensuring the reliable generation of high-voltage direct current (HVDC) voltage output.

[0077] Fig. 5a illustrates the general arrangement of unidirectional voltage generator- 1 (UVG-1) (120) with a non-salient pole-type rotor. The configuration is similar to UVG-1 in Fig. 4a, but this generator uses a non-salient pole rotor to guide the magnetic flux. The rotor coil (126) is fed from rotor winding-1 (116) of the flattop AC voltage generator (110), producing a trapezoidal or flat-top alternating magnetic flux in UVG-1. The stator coil / winding (124), a stationary winding, interacts with the rotating magnetic field to generate a unidirectional voltage waveform. The design ensures the consistent direction of the induced electromotive force, contributing to the overall system's ability to generate high- voltage direct current (HVDC) voltage output. Fig. 5b illustrates the general arrangement of unidirectional voltage generator-2 (UVG-2) (130) with a non-salient pole-type rotor. The rotor is fed from rotor winding-2 (116) of the flat-top AC voltage generator (110), producing a trapezoidal or flat-top alternating magnetic flux in UVG-2. The stator coil / winding (134), a stationary winding, interacts with the rotating magnetic field produced by the rotor coil (136) to generate a unidirectional voltage waveform. The design ensures that the induced electromotive force flows consistently in one direction, contributing to the system's ability to generate a stable high-voltage direct current (HVDC) voltage output.

[0078] Fig. 6a illustrates the connection diagram for unidirectional voltage generator- 1 (UVG-1) and unidirectional voltage generator-2 (UVG-2) within the HVDC generation system. The electrical outputs of UVG-1 and UVG-2 are connected in series for triangular voltage waveforms to ensure that their voltages contribute to the overall HVDC output. This series connection ensures that the voltages are combined to provide a stable and constant HVDC output.

[0079] Fig. 6b illustrates the connection diagram for unidirectional voltage generator- 1 (UVG-1) and unidirectional voltage generator-2 (UVG-2) within the HVDC generation system. The electrical outputs of UVG-1 and UVG-2 are connected in parallel for trapezoidal / flat-top voltage waveforms to ensure that their voltages contribute to the overall HVDC output. This series connection ensures that the voltages are combined to provide a stable and constant HVDC output.

[0080] Fig. 7a & 7b illustrates the mathematical model of trapezoidal / flat-top AC voltage waveforms (140A & MOB) from winding- 1 and winding-2 in the flat- top alternating current voltage generator (exciter). The output voltage waveforms are graphically represented, and the shape of these waveforms is crucial for the functioning of the HVDC generation system. The phase relationship between winding- 1 and winding-2 is important for the subsequent stages of the HVDC generation process. This phase relationship is essential for combining the unidirectional voltages generated by UVG-1 and UVG-2 to produce a stable DC output.

[0081] Fig. 8 illustrates the mathematical model of triangular voltage waveforms (170 & 180) of UVG-1 and UVG-2 respectively as they vary over time. This graphical representation demonstrates the shape and characteristics of the generated voltages, ensuring that the induced electromotive force in the stator windings remains consistently in one direction. The phase relationship between UVG-1 and UVG-2 outputs is crucial for achieving a stable and unidirectional high-voltage direct current (HVDC) output. The output voltages of UVG-1 (170) and output voltages of UVG-2 (180), and their combination is the final HVDC voltage output (200) are shown. These two voltages are connected in series.

[0082] Fig. 9 illustrates the mathematical model of final high-voltage direct current (HVDC) output generated by the system, combining the outputs from UVG-1 (120) and UVG-2 (130) with precise phase synchronization. The waveform demonstrates a smooth, stable DC output (200) devoid of ripple or harmonic distortions, achieved through the unique design of unidirectional voltage generators and the synchronized operation of the common shaft. The figure highlights the efficiency of the system in generating clean, high-quality DC power, eliminating the need for external filtering devices, and making it suitable for reliable long-distance power transmission.

[0083] Fig. 10a illustrates a block diagram of a single-shaft HVDC system where multiple stages of UVGs (120,130...) are connected in series to generate voltages exceeding 500kV. The common shaft (104) connects the prime mover, flat-top AC voltage generator (110) (exciter), and UVGs, ensuring uniform rotation, synchronized phase shifts, and precise alignment of alternating and unidirectional magnetic fluxes. Electrical isolated shaft couplings (220) are depicted, providing mechanical continuity while maintaining electrical isolation for safe high-voltage operations. The modular arrangement supports the addition of UVG stages, making the system scalable to meet increasing power demands while reducing complexity and cost.

[0084] Fig. 10b illustrates the n-stage configuration of the HVDC system, where multiple UVGs (120,130...) are cascaded to achieve high-voltage outputs with modular scalability. Each stage is electrically isolated (220), as illustrated, to handle increasing voltage levels safely and reliably. The diagram highlights the connection of stages via isolated couplings and the common synchronization mechanism, ensuring uniform rotational speeds and phase alignment across stages. The scalable architecture supports voltages above 500kV, enabling seamless integration into existing HVDC grids and renewable energy installations, while offering a cost-effective and flexible solution for large-scale transmission networks.

Claims

5. CLAIMSWe Claim1. A high-voltage direct current (HVDC) generation system, comprising: a prime mover (102) configured to provide rotational motion to the system; a flat-top alternating current (AC) voltage generator (exciter) (110), comprising: rotor windings- 1 & 2 (116); a stator coil (114) excited by a DC supply to generate flat-top AC voltages in the rotor windings, producing trapezoidal or flat-top alternating current voltage waveforms with a 90° phase shift between rotor windings- 1 and rotor windings -2 (116); a first unidirectional voltage generator (UVG-1) (120), comprising: a rotor coil (126) excited by rotor winding-1 (116) of the flattop AC voltage generator (exciter); a rotor coil (126) excited by the flat- top alternating voltage produces an alternating flux in the UVG-1, since the rotor is rotating with alternating flux ensure the flux linkages with respect to stator is always in one direction hence it produces unidirectional voltage in stator winding (124). a stator coil (124) generating a unidirectional voltage waveform selected from segment-wise linear waveforms (triangular, trapezoidal, flat-top, stepped, etc.,) induced by the alternating rotating magnetic field produced by rotor winding- 1; a magnetic poles with alternating magnetic field rotation and field coils and stator windings design ensuring unidirectional flux to induce unidirectional voltage of desired waveform in the stator coil; a second unidirectional voltage generator (UVG-2) (130), comprising: a rotor coil (136) excited by rotor winding-2 (116) of the flattop AC voltage generator (exciter);a rotor coil (136) excited by the flat- top alternating voltage produces an alternating flux in the UVG-2, since the rotor is rotating with alternating flux ensure the flux linkages with respect to stator is always in one direction hence it produces unidirectional voltage in stator winding (134). a stator coil (134) generating a unidirectional voltage waveform selected from segment-wise linear waveforms (triangular, trapezoidal, flat-top, stepped, etc.,) induced by the alternating rotating magnetic field produced by rotor winding-2; a magnetic poles with alternating magnetic field rotation and field coils and stator windings design ensuring unidirectional flux to induce unidirectional voltage of desired waveform in the stator coil; a common shaft (104) connecting the prime mover, flat-top AC voltage generator, and both UVGs (120, 130) for synchronization, maintaining the same speed and desired phase shifts at all times; wherein, the system utilizes the unidirectional voltage generators (UVG-1 & UVG-2) to generate unidirectional voltage waveforms directly from the flat-top alternating magnetic fields; the system is scalable and generating HVDC voltages of 500kV and above by cascading multiple-stages / multiple unidirectional voltage generators (UVGs) in series, with each stage synchronized via the common shaft (104), ensuring uniform speed and precise phase shifts, thus facilitating the generation of high-voltage DC output (200); the system ensures stable HVDC output voltage by connecting the unidirectional voltage generators (UVG-1 & UVG-2) in series with appropriate phase shifts, enabling efficient high-voltage transmission; the system provides enhanced flexibility and controllability by enabling seamless integration with existing HVDC links, enhancing power transmission capacity and minimizing harmonic disturbances, for modern electrical grids.

2. The system as claimed in claim 1, wherein the flat-top alternating current voltage generator (110) is configured to generate trapezoidal or flat-top alternating current waveforms in rotor windings- 1 and rotor windings-2 (116) with a 90° phase shift between them, thus producing alternating rotating magnetic fluxes in the unidirectional voltage generators (UVG-1 & UVG-2) to produce stable unidirectional voltage waveforms.

3. The system as claimed in claim 1, wherein the unidirectional voltage generators (UVG-1 & UVG-2) are each designed to produce unidirectional voltage waveforms selected from a group consisting of segment wise linear waveforms (triangular, trapezoidal, flat-top, stepped, etc.,) wherein the specific waveform is determined by the rotor and stator coil design in each unidirectional voltage generator.

4. An alternating voltage supplied to a rotor winding produces alternating magnetic field in the rotor poles as the rotor rotates 180 degrees and the alternating flux also reverses it direction, hence the flux direction in the generator / space is always unidirectional with respect to stator windings and produces unidirectional voltage in the stator windings.

5. The system as claimed in claim 1, wherein the unidirectional voltage generators (UVG-1 & UVG-2) are connected in series with a specific phase shift between each generator, ensuring that the output voltage remains constant and that the series connection produces a stable high-voltage direct current (HVDC) output.

6. The system as claimed in claim 1, wherein the system is configured to allow for cascading multiple stages of unidirectional voltage generators (UVGs), with each stage being synchronized via the common shaft (104) to maintain the same rotational speed and phase shifts across all stages, enabling scalable generation of HVDC voltages of 500kV and above.

7. The system as claimed in claim 1, wherein the common shaft (104) is coupled to a suitable electrical isolator system to maintain electrical isolation between different stages of the HVDC generation system, ensuring safe operation at high-voltage levels.

8. The system as claimed in claim 1, wherein the flat-top AC voltage generator (110) is a salient-pole type generator, configured to produce trapezoidal or flattop waveforms in the rotor windings, which are crucial for inducing the desired alternating magnetic flux in the unidirectional voltage generators (UVG-1 & UVG-2).

9. The system as claimed in claim 1, wherein the prime mover (102) is an electric motor, and further wherein the electric motor is configured to provide a constant rotational speed and torque, ensuring continuous and efficient operation of the HVDC generation system.

10. The system as claimed in claim 1, wherein the system is designed to operate with zero harmonic distortion, achieved by the precise design of the unidirectional voltage generators (UVG-1 & UVG-2) and their respective phase shift control, which eliminates the need for complex filtering systems commonly used in traditional HVDC systems.

11. The system as claimed in claim 1, wherein each unidirectional voltage generator (UVG-1 & UVG-2) employs a magnetic pole and field coil design specifically tailored to produce a stable and consistent unidirectional voltage waveform, minimizing any fluctuation in the output and ensuring a smooth HVDC voltage generation.

Images