Asymmetric 24-pulse autotransformer rectifier unit for turboelectric propulsion, and associated systems and methods

Abstract

To provide an asymmetric AC / DC autotransformer for turboelectric propulsion and an associated system and method.SOLUTION: An asymmetric AC / DC autotransformer comprises: a first coil, a second coil, and a third coil of a delta winding (each coil is energized at its corresponding input phase); and a first plurality of correction windings coupled to the first coil; a second plurality of correction windings coupled to the second coil; and a third plurality of correction windings coupled to the third coil. A bridge rectifier having a plurality of rectifiers is coupled to each of individual correction windings. Phases of the individual correction windings are asymmetric such that individual phase voltages are controlled relative to reverse input phases. Voltages are unbalanced relative to a neutral point.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] Cross - reference to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 874,782, filed Jul. 16, 2019, the entire disclosure of which is incorporated herein by reference.

[0003] Modern aircraft are increasingly using electricity for the actuators they carry. Furthermore, a completely new category of electrically - driven aircraft engines is being developed. As a result, for the structure of electric aircraft, the power quality of AC / DC converters should be improved.

[0004] A certain conventional system relies on a hexagonal winding configuration and establishes 12 AC phases that are converted to DC voltage (24 - pulse rectification is possible). However, in such a conventional system, triplen harmonics are likely to occur, and there are limitations in use for aerospace industry applications. Triplen harmonics are odd harmonics that become co - phasal in a three - phase system. Such harmonics are the third harmonic, the ninth harmonic, the fifteenth harmonic, etc. Since these harmonics are co - phasal, they are not canceled out in a three - phase system, and a return path or a delta loop is required to circulate them. If these are not provided, the presence of triplen harmonic currents causes problems such as voltage inequality and excessive power dissipation. To mitigate triplen harmonics, typically, it is necessary to add windings or increase the core size, resulting in an increase in weight and a decrease in efficiency. On the other hand, in the configuration of a conventional single - winding transformer that requires 8 windings per phase, 9 windings per phase are required to mitigate triplen harmonics. In a conventional single - winding transformer, additional windings per phase are required to form a delta winding dedicated to triplen harmonic mitigation and provide a low - impedance path for triplen harmonic currents.

[0005] In other conventional designs, based on a delta-wound symmetrical single-winding transformer, 12 output phases are supplied from three input phases to a plurality of bridge rectifiers to enable 24-pulse AC / DC conversion. In the delta-wound symmetrical approach, the phases are designed to have uniform amplitude and phasing with respect to the neutral point. The delta-wound symmetrical approach achieves low current distortion through inherent triple harmonic mitigation, but it is necessary to add an interphase transformer. The interphase transformer requires a single-winding transformer that processes all the power supplied to the load, which results in a penalty in terms of weight and efficiency compared to asymmetrical power processing techniques. As a result, the symmetrical solution has increased weight and decreased efficiency compared to the acceptable weight and efficiency for aerospace industry applications.

[0006] In short, the above conventional approach suffers from one or more of the following drawbacks: namely, no inherent triple harmonic mitigation, a complex assembly process requiring more than eight windings per core leg, high weight, and low efficiency. On the other hand, there are AC / DC converters that provide less than 24 pulses, such as 18-pulse and 12-pulse ATRUs commonly used in modern aerospace industry applications, which are lightweight, highly efficient, and have inherent triple harmonic mitigation. However, these 18-pulse and 12-pulse ATRUs cannot provide the high power quality and low current distortion (total harmonic distortion or THDi < 5%) provided by 24-pulse conversion. Therefore, there is a need for a system and method for an AC / DC converter that can provide 24-pulse conversion and triple harmonic mitigation with acceptable weight and operating efficiency to meet the needs of aerospace industry applications. SUMMARY OF THE INVENTION

[0007] This summary is provided to introduce a selection of concepts that are further described below in the "Detailed Description". This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0008] The technology of the present invention enables conversion from a three-phase AC voltage to a DC voltage with an amplitude approximately 2.35 times the amplitude of the average input phase-neutral RMS voltage. For example, in this technology, a nominal 540-volt DC output is achieved from a 230-volt AC input commonly used in modern aerospace industry power systems. The output voltage is proportional to the input voltage.

[0009] The technology of the present invention combines a single-winding transformer and a rectifier to form a 24-pulse single-winding transformer rectifier unit (Auto-Transformer Rectifier Unit, ATRU). To provide three of the twelve phases required for 24-pulse rectification, the three input phases can be directly supplied to the three nodes of the bridge rectifier. The power path formed by directly connecting the three input phases to the bridge rectifier processes most of the power (e.g., about two-thirds or about 66% of the power) processed by the ATRU. This power path makes it possible to significantly reduce the size of the single-winding transformer. The single-winding transformer is composed of three coils that form a delta configuration. Also, the three input phases are supplied to the delta coils of the single-winding transformer.

[0010] Each coil includes a plurality of series windings. Each of the three coils of the delta-wound single-winding transformer may include four series windings forming the sides of the delta and three correction windings. The nine correction windings together provide nine output points with appropriate amplitudes and phasings for the three input phases for the combined 24-pulse operation (nine phases from the correction windings and three phases from the input phases). These twelve phases are directly rectified to 24 pulses by the bridge rectifier, eliminating the need to add interphase transformers (IPTs) commonly used in conventional known systems.

[0011] In one embodiment, the system includes an asymmetrical single-winding transformer having the following: a first coil, a second coil, and a third coil of a delta winding (each coil is excited by this corresponding input phase), a first plurality of correction windings coupled to the first coil, a second plurality of correction windings coupled to the second coil, and a third plurality of correction windings coupled to the third coil. Also, the system includes a bridge rectifier having a plurality of rectifiers coupled to each respective correction winding, wherein the phases of the respective correction windings are asymmetrical such that the individual phase voltages are controlled with respect to the reverse input phase, and the voltages are unbalanced with respect to the neutral point.

[0012] In one aspect, each plurality of correction windings includes three individual windings. In another aspect, the tap position of each plurality of correction windings separates each corresponding coil of the delta winding into four segments.

[0013] In one aspect, the bridge rectifier receives 12 AC phases at the input of this corresponding diode, and the bridge rectifier outputs a DC voltage. In another aspect, the bridge rectifier includes the following: a main rectifier configured to rectify the AC voltage of the input phase, and a secondary rectifier configured to rectify the AC voltage of the correction winding. In one aspect, the main rectifier supplies approximately 66% of the DC power, and the secondary rectifier supplies approximately 34% of the DC power.

[0014] In one aspect, the delta winding constitutes a low-impedance path for triple harmonics. In another aspect, in the bridge rectifier, the individual phase voltages are offset by approximately 15 degrees from one phase to the next adjacent phase.

[0015] In one embodiment, a design method of a single-winding transformer having a first coil, a second coil, and a third coil of a delta winding includes the following. Steps of selecting the number of turns of the first coil, the second coil, and the third coil of the delta winding; steps of selecting three tap positions for the correction winding along each of the first coil, the second coil, and the third coil of the delta winding (the tap positions divide each of the first coil, the second coil, and the third coil into four segments); steps of constructing a vector diagram of a transformer using an equilateral triangle having leg lengths proportional to the number of turns between the input phases of a three-phase input (each side of the triangle represents a complete coil of the delta winding). Also, the method includes steps of drawing lines representing individual correction windings from each tap position along the first coil, the second coil, and the third coil of the delta winding. Each line is represented as a vector of a first plurality of vectors having a length proportional to the phase corresponding to the phase of the coil wound by the correction winding and the number of turns of the correction winding, and each vector of the first plurality of vectors is parallel to one of the sides of the triangle. Also, the method includes steps of determining the turns ratio of each correction winding according to the length of the corresponding vector of the first plurality of vectors, and determining the number of turns of each correction winding as the product of the turns ratio and the number of turns of the complete coil of the delta winding.

[0016] In one aspect, the method also includes steps of determining the output phase of a single-winding transformer by the following steps. Steps of drawing vectors of a second plurality of vectors from the end of each correction winding vector to the opposite vertex of the equilateral triangle, and determining the output phase of the individual correction winding according to the length of the corresponding vector of the second plurality of vectors.

[0017] In one aspect, the output phase of each correction winding is proportional to the amplitude of the corresponding output phase with respect to the phase represented by the opposite vertex of the triangle.

[0018] In another aspect, the output voltage of a single-winding transformer is controlled as an inter-phase voltage and not as a phase-neutral voltage.

[0019] In one aspect, adjacent bridge rectifier conduction pairs can be spaced approximately 15 degrees apart.

[0020] In one aspect, four segments along the individual coils of the delta winding have turns ratios of N1 = 0.17, N2 = 0.24, N3 = 0.42, and N4 = 0.17, and the individual correction windings have turns ratios of N5 = 0.13, N6 = 0.13, and N7 = 0.18, where the turns ratio is defined as the number of turns of the segment or correction winding divided by the total number of turns of the coil of the delta winding.

[0021] In another aspect, four segments along the individual coils of the delta winding have turns ratios of N1 = 0.17, N2 = 0.42, N3 = 0.11, and N4 = 0.30, and the individual correction windings have turns ratios of N5 = 0.18, N6 = 0.13, and N7 = 0.13, where the turns ratio is defined as the number of turns of the segment or correction winding divided by the total number of turns of the coil of the delta winding.

[0022] In another aspect, four segments along the individual coils of the delta winding have turns ratios of N1 = 0.30, N2 = 0.11, N3 = 0.29, and N4 = 0.30, and the individual correction windings have turns ratios of N5 = 0.13, N6 = 0.18, and N7 = 0.13, where the turns ratio is defined as the number of turns of the segment or correction winding divided by the total number of turns of the coil of the delta winding.

[0023] In another aspect, four segments along the individual coils of the delta winding have turns ratios of N1 = 0.17, N2 = 0.24, N3 = 0.29, and N4 = 0.30, and the individual correction windings have turns ratios of N5 = 0.13, N6 = 0.18, and N7 = 0.13, where the turns ratio is defined as the number of turns of the segment or correction winding divided by the total number of turns of the coil of the delta winding.

[0024] In another aspect, four segments along the individual coils of the delta winding have turn ratios of N1 = 0.30, N2 = 0.29, N3 = 0.24, and N4 = 0.17, and the individual correction windings have turn ratios of N5 = 0.13, N6 = 0.18, and N7 = 0.13, where the turn ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coils of the delta winding.

[0025] In another aspect, four segments along the individual coils of the delta winding have turn ratios of N1 = 0.30, N2 = 0.29, N3 = 0.11, and N4 = 0.30, and the individual correction windings have turn ratios of N5 = 0.13, N6 = 0.18, and N7 = 0.13, where the turn ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coils of the delta winding.

[0026] In another aspect, four segments along the individual coils of the delta winding have turn ratios of N1 = 0.30, N2 = 0.11, N3 = 0.42, and N4 = 0.17, and the individual correction windings have turn ratios of N5 = 0.13, N6 = 0.13, and N7 = 0.18, where the turn ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coils of the delta winding.

[0027] In another aspect, four segments along the individual coils of the delta winding have turn ratios of N1 = 0.17, N2 = 0.42, N3 = 0.24, and N4 = 0.17, and the individual correction windings have turn ratios of N5 = 0.18, N6 = 0.13, and N7 = 0.13, where the turn ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coils of the delta winding.

Brief Description of the Drawings

[0028] The foregoing aspects and attendant advantages of the technology of the present invention will become more readily understood as the same becomes better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings.

[0029]

Figure 1A

Figure 1B

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[0030] Although the exemplary embodiments have been illustrated and described, it should be understood that various changes can be made to the exemplary embodiments without departing from the spirit and scope of the present invention.

[0031] Commercial aircraft are continuing to evolve towards more electric aircraft (MEA). This is characterized by an increase in electrical content instead of hydraulic and pneumatic systems. Recent advancements in the fields of power electronics and high-density electric motors, along with the continuous pressure to reduce operating costs, ensure that this trend continues. Furthermore, aircraft electric propulsion is shifting towards hybrid electric, turbo-electric, and even all-electric power trains. Under one scenario, the shift to electric propulsion is expected to increase the power demand of the electrical system by more than 40 times.

[0032] However, conventional power conversion technologies are currently unable to meet the needs of turbine electric propulsion. For example, while conventional ATRUs have relatively high power conversion efficiency and reliability, conventional ATRU technologies must make significant trade - offs between weight and power quality. In some prior arts, it is possible to achieve total current harmonic distortion (THDi) of less than 5%, but a 24 - or 30 - pulse design is required. In a conventional 24 - pulse design, there is a weight penalty of approximately 50% compared to industry - leading 12 - or 18 - pulse (generating 7 - 13% THDi) solutions. This causes an important trade - off between weight and power quality for aircraft system designers. Most existing MEAs have preferred to reduce weight at the expense of power quality for applications in the 10 - 100 kW range.

[0033] However, when the power demand of the ATRU exceeds 100 kW, sacrificing power quality becomes much more difficult. The increased line impedance at harmonic frequencies causes excessive current harmonics to significantly distort the waveform of the AC distribution system. This causes various adverse effects, including increased conducted interference problems to other devices on the AC bus, low power factor (resulting in an oversized generator for delivering apparent power rather than real power and excessive heating in the distribution system), excessive radiated magnetic fields, excessive heating of generators and motors, and increased wear and acoustic noise of rotating devices (due to harmonic torque).

[0034] The above - mentioned drawbacks of the prior art can be overcome by a 24 - pulse ATRU based on asymmetric power processing according to the present technology. In some embodiments, the 24 - pulse ATRU according to the present invention's technology achieves an efficiency of over 98%, THDi of less than 5%, and a power - to - weight ratio of over 5 kW per kg. In the asymmetric single - winding transformer of the present invention, the output voltage is unbalanced with respect to the neutral point.

[0035] In some embodiments, the asymmetric 24-pulse ATRU is a power converter that first converts a three-phase AC input to a 12-phase AC for power factor correction and harmonic current cancellation and then to a DC output via a 24-pulse rectifier bridge. In some embodiments, the asymmetric approach requires that the three-phase AC input be fed directly to the rectifier bridge and at the same time to a single-winding transformer. The single-winding transformer generates an additional nine phases, which are also fed to the rectifier bridge, resulting in a total of 12 phases. Thereby, the single-winding transformer only processes about one-third of the power delivered to the ATRU output, minimizing the harmonic distortion of the input current and realizing the harmonic current cancellation necessary to maximize the power factor, making it possible to significantly reduce the weight and power dissipation. Further, the single-winding transformer includes a delta embodied in this winding configuration, resulting in inherent triple harmonic mitigation. In the technology of the present invention, the windings of the single-winding transformer use a delta configuration, which processes the main power and functions as a low-impedance path for triple harmonic currents. Conventional single-winding transformers with a hexagonal winding configuration do not provide a low-impedance path for triple harmonic currents and as a result require an additional delta winding (usually a five-leg core) to perform this function. In some embodiments, the single-winding transformer includes three core legs, each having one coil (e.g., coil A, B, or C) wound around the core leg. Each coil has only seven different windings, facilitating the reduction of assembly complexity and cost.

[0036] Figure 1A is a diagram showing the ATRU1000 according to an embodiment of the technology of the present invention. On the input side, three-phase 230-volt AC power 100 is supplied to the single-winding transformer 300. In a typical embodiment described later, the single-winding transformer converts three-phase input (A, B, C) into nine auxiliary phases (1 to 9), supplies them to the secondary rectifier circuit 400, and provides 18 out of the total 24 pulses required for 24-pulse operation. Also, the three-phase input is directly supplied to the main rectifier circuit 200 as well, supplying the remaining three phases and six pulses for 24-pulse operation. The rectifier circuits 200 and 400 can include an arrangement of diodes that rectify the input AC voltage into a DC voltage. With the single-winding transformer of the technology of the present invention, the ATRU outputs high-quality 540-volt DC while maintaining a 24-pulse input waveform with a high power factor and a low harmonic content.

[0037] Due to the direct feed-through of the three input phases to the main rectifier circuit 200, most of the power (e.g., about 66%) processed by the ATRU can bypass the single-winding transformer 300. As a result, in the single-winding transformer 300, a significant reduction in size, weight, and dissipation can be achieved. The power distribution of 66% to 34% is only an exemplary embodiment, and in other embodiments, different power ratios may be achieved in the main rectifier circuit 200 and the secondary rectifier circuit 400. Also, generally, the reduction in power in the single-winding transformer 300 also reduces the weight and size of the single-winding transformer.

[0038] Also, Figure 1B is a diagram showing the ATRU according to an embodiment of the technology of the present invention. The three-phase input is supplied to the single-winding transformer 300 through the input filter 150. In the illustrated embodiment, the 12 output phases (three main phases A, B, C and nine auxiliary phases 1 to 9, collectively "output phase 310") are coupled to a common rectifier circuit that rectifies 12 phases into 24 pulses. The resulting pulses may be supplied through the output electromagnetic interference (EMI) filter 410. The illustrated ATRU converts a 230-volt AC input into a 540-volt DC output.

[0039] Figure 2 is a diagram showing the windings of a delta-wound single-winding transformer according to an embodiment of the present invention. The illustrated delta-wound single-winding transformer includes three input points PA, PB, and PC for 230 VAC, three-phase input, and twelve output taps (T1 to T12) for twelve output phases (three main phases and nine auxiliary phases of the single-winding transformer). The topology orientation is exemplary, and different topologies may be applied in different embodiments.

[0040] The turns ratio of each winding in the illustrated embodiment is shown adjacent to the winding. For example, the series windings along the C coil corresponding to N1, N2, N3, and N4 have turns ratios of 0.17, 0.24, 0.42, and 0.17, respectively. The correction windings corresponding to N5, N6, and N7 have turns ratios of 0.13, 0.13, and 0.18, respectively. The number of turns of the windings of the A coil and the B coil is equal to the number of turns of the C coil.

[0041] The turns ratio of a given winding is defined as the ratio of the number of turns of the winding to the total number of turns between each input phase. In some embodiments, the optimal turns ratio may vary depending on the structure of the single-winding transformer, different parasitics, and the use case, so the illustrated turns ratio may be an approximation. As a result, the actual number of turns implemented may vary depending on the selected single-winding transformer core. Examples of the number of turns of the embodiment of the single-winding transformer illustrated in Figure 2 are shown in Table 1 and Table 2 below.

[0042] Table 1 shows samples of the turns ratios of a single-winding transformer having 139 turns along each of the A, B, and C coils. For example, the N1 segment includes 24 turns, while the N2 segment includes 33 turns. Similarly, the secondary winding N6 includes 18 turns, while the secondary winding N7 includes 25 turns. The ratios of these numbers of turns with respect to the number of turns of each individual coil (139 turns in the illustrated example) are shown in the "Turns Ratio" column.

[0043]

Table 1

[0044] Table 2 shows the voltage amplitude ("Amplitude" column) and phase ("Phase" column) of the single-winding transformer shown in FIG. 2 (practical corrections to the turns ratio are implemented to compensate for parasitics including winding impedance and leakage inductance). Generally, the voltage difference between corresponding tap pairs ("Amplitude" column) is approximately constant. The phase difference in the "Phase Delta" column is also approximately constant, corresponding in 15° increments from one conduction pair of one bridge rectifier to the next conduction pair.

[0045] In a single-winding transformer according to an embodiment of the present invention's technology, the corrected winding phase voltage is controlled as the line voltage with respect to the reverse input phase voltage, forming balanced bridge rectifier conduction pairs at nominal 15-degree intervals. This is different from the conventional design approach of a symmetric single-winding transformer, which aims to achieve balance between the phase and neutral point corrected winding voltages. For example, referring to the single-winding transformer in FIG. 2 and the values in Table 2, tap T4 is paired with phase B to represent the relative voltage and phase amplitude. As another example, tap T12 is paired with phase C to represent the relative voltage and phase amplitude. Table 2 includes the amplitude and phase of the nominal voltages of all bridge rectifier conduction pairs of the single-winding transformer in FIG. 2. The conduction pairs of the bridge rectifier are composed of two phases supplied to the bridge rectifier and conduct with each other at a consistent point within each complete electrical cycle. In the case of a single-winding transformer according to an embodiment of the present invention's technology, each conduction pair will conduct twice per polarity per complete electrical cycle, i.e., a total of two times. As an example, this means that the voltage in Table 2 (phase A - T8) has a phase of -14.97 degrees, and the voltage in Table 2 (T8 - phase A) has a phase of -194.97 degrees, and the 180-degree phase difference indicates that the voltage polarities are opposite.

[0046]

Table 2

[0047] Figure 3 shows a topology diagram of a delta-wound single-winding transformer for the single-winding transformer of Figure 2. The delta configuration includes three input points A, B, and C for a three-phase AC input. Each side of the delta has four series windings. Moving clockwise from B to C, series windings N4, N3, N2, and N1 are inserted between B and C. Similarly, windings are inserted between C and A and between A and B, but they are not labeled in the figure to reduce confusion.

[0048] A sample method for determining the phase voltages of an asymmetric single-winding transformer is described below. The sample method includes the step of drawing vectors from the ends of each correction winding (e.g., taps T6, T7) to the opposite vertex of an equilateral triangle (e.g., the vertex where phase windings B and C intersect). These vectors represent the output phases of the single-winding transformer. The length of each vector is proportional to the amplitude of the corresponding output phase with respect to the phase represented by the opposite vertex of the triangle (not relative to a neutral point as in a symmetric single-winding transformer). This phase voltage is presented to a bridge rectifier as a conduction pair as shown in Table 2. By designing the output voltage and phase angle of the single-winding transformer to balance with respect to the reverse input phase rather than the neutral point voltage, most of the processed power can bypass the single-winding transformer without degrading power quality, and the phase transformer can be eliminated. In some embodiments, triple harmonic mitigation is ensured by the main delta winding formed by the N1-N4 winding ratio, which provides an appropriate winding configuration for triple harmonic mitigation.

[0049] As described above, the desired phase shift of the output phase of the single-winding transformer is obtained from a correction winding tapped at a selected position between the series windings that cross the input phase and provide the output at T2, T3, T4, T6, T7, T8, T10, T11, and T12. The coil around which the correction winding is wound and the winding polarity of the correction winding determine the direction of the phase shift that the correction winding imparts to the output phase. The turns ratio of each correction winding and the tap position of the correction winding between the series windings determine the final phase angle and amplitude of the output phase. The amplitudes and phases of these output phases are illustrated by the dotted lines in FIG. 3. In the case of a 24-pulse mode, an interval of nominally 15 degrees is desirable between adjacent phases. As explained above, the actual amplitude of the output phase will depend on the structure of the single-winding transformer, parasitics (e.g., leakage inductance), and the use case (e.g., power supply and load impedance). For the embodiment illustrated in FIG. 3, the number of turns and turns ratios are shown in Table 3 below.

[0050]

Table 3

[0051] FIG. 12 illustrates a sample method for determining the phase voltage between phases of an asymmetric single-winding transformer. In particular, the method illustrated shows an overview of the design process for selecting the turns ratio for appropriate amplitudes and intervals of the output phases for asymmetric 24-pulse operation. In different embodiments, the method illustrated may include additional steps and may include other steps not shown in the flowchart.

[0052] This method can start at block 510. At block 515, for the selected core, operating frequency, and operating voltage, the phase-to-phase turns are selected to maintain an acceptable magnetic flux density.

[0053] In block 520, a vector diagram of the transformer is constructed using an equilateral triangle with leg lengths proportional to the number of turns between phases. Each side of the triangle represents a complete delta winding and consists of four segments between each pair of vertices of the triangle (see, for example, FIGS. 2 and 3). Each segment represents a series winding and has a length proportional to the number of turns of the corresponding series winding. The three points between the vertices of each leg where the segments intersect represent the tap positions of the corrective windings.

[0054] In block 525, a line representing the corrective winding is drawn from each tap position between the vertices of the triangle. Each line is a vector having a phase corresponding to the phase in which the corrective winding is wound and a length proportional to the number of turns of the corrective winding. Each vector is parallel to one side of the triangle. The turns ratio of each corrective winding corresponds to the number of turns of the corrective winding divided by the number of turns of the complete delta winding. This is illustrated in the vector diagram of the transformer as the length of the corrective winding vector relative to the length of the complete leg of the equilateral triangle.

[0055] In block 530, vectors are drawn from the ends of each corrective winding vector to the opposite vertex of the equilateral triangle. These vectors represent the output phases of the single-turn transformers. The length of each vector is proportional to the amplitude of the corresponding output phase relative to the phase represented by the opposite vertex of the triangle. Vectors can be drawn from each output tap to the neutral point, which accurately indicates the output phase voltage relative to the neutral point, but due to the nature of the asymmetric design, the voltages from these phases to the neutral point are non-uniform. Controlling the phase-to-phase voltage rather than the voltage between the phase and the neutral point is the difference between the asymmetric design approach and the symmetric design approach.

[0056] In block 535, the delta segment lengths are optimized and the tap positions are adjusted while keeping the total delta length constant. In some embodiments, the corrective winding vector length is adjusted until the output phase vector lengths are approximately equal to the length of each side of the equilateral triangle, and all vectors originating from each vertex of the triangle maintain a phase separation of approximately 15 degrees. Examples of vector diagrams of complete transformers fabricated using this method are shown in FIGS. 3 and 5 - 11.

[0057] In block 540, the number of turns of the single-winding transformer series winding and the correction winding is set based on the segments of each series winding in the transformer vector diagram and the final length of the correction winding vector. This method may end in block 545.

[0058] FIG. 4 is a diagram showing a delta-wound single-winding transformer according to an embodiment of the technology of the present invention. In some embodiments, coils A, B, and C are housed in their respective housings 110, 120, and 130. Output ports 1 to 9 are connected to their respective coils via a secondary winding (for example, secondary windings N6 and N7 connected to coil A). During operation, the free ends of wires A, B, C, and 1 to 9 are connected to the main rectifier circuit / secondary rectifier circuit 200, 400.

[0059] FIGS. 5 to 11 show topology diagrams of a delta-wound single-winding transformer according to embodiments of the technology of the present invention. For the embodiments illustrated in FIGS. 5 to 11, the number of turns and the turn ratio are shown in Table 4 below. In different embodiments, these number of turns and turn ratio are determined using the method illustrated in FIG. 12.

[0060]

Table 4

[0061] FIGS. 13 to 15 are graphs simulating the current waveforms of a 24-pulse asymmetric ATRU using the ideal single-winding transformer of the topology depicted in FIG. 3. Since non-ideal characteristics such as leakage inductance and winding resistance are ignored, this simulated asymmetric ATRU is called "ideal". FIG. 16 is a graph of the actual three-phase input current waveform according to an embodiment of the technology of the present invention. In each of these graphs, the horizontal axis represents the elapsed time. The vertical axis represents the current (ampere).

[0062] In particular, FIG. 13 is a graph simulating the three-phase input current waveforms of a 24-pulse asymmetric ATRU using the ideal single-winding transformer of the topology depicted in FIG. 3. An ideal single-winding transformer without leakage inductance or winding resistance shows a stepped current waveform approximating a sine wave with 24 "steps" or "pulses" for a sine wave voltage input. This is the result of the conduction pairs of the bridge rectifier switching every 15 degrees. By adding leakage inductance and winding resistance, the waveform is smoothed and ultimately becomes approximately a sine wave (see FIG. 16 below).

[0063] FIG. 14 is a graph simulating the rectifier bridge current of a 24-pulse asymmetric ATRU during one complete electrical cycle at 400 Hz. In FIG. 14, the 15-degree intervals of the bridge rectifier conduction pairs can be confirmed. Here, it can be confirmed that each conduction pair conducts at an electrical angle of approximately 15 degrees of a given 400 Hz cycle, for a time slightly exceeding 100 microseconds, i.e., with a period of 2.5 ms. Further, in FIG. 14 and Table 2, it can be confirmed that each input phase connection to the bridge rectifier conducts current continuously for 5 pulses, while each corrective winding conducts current for only 1 pulse in a given half-cycle. This indicates that most of the power bypasses the single-winding transformer and is processed by the ATRU, thereby enabling efficiency improvement and weight reduction.

[0064] FIG. 15 is a graph simulating the A-phase input voltage and current of a 24-pulse asymmetric ATRU using the ideal single-winding transformer of the topology depicted in FIG. 3. And FIG. 16 is a graph of the actual three-phase input current waveform according to an embodiment of the technology of the present invention. In the embodiment illustrated in FIG. 16, the actual current waveform is smoother than the ideal input current waveform shown in FIG. 13 (indicating lower harmonic distortion). This is because the presence of a small amount of leakage inductance serves to smooth the input current waveform. However, generally, the leakage inductance should generally be kept as small as possible. As seen in FIGS. 14 and 15, a pulsed current with a large amplitude and a short duration flows through the correction winding. If the leakage inductance is allowed to be too large, these pulsed currents cannot reach their maximum amplitudes, and the 24-pulse operation may deteriorate such that the effective number of pulses decreases and the performance of the 24-pulse ATRU approaches that of an 18- or 12-pulse solution.

[0065] Many embodiments of the technology described above can take the form of computer-executable instructions or controller-executable instructions, including routines executed by a programmable computer or controller. Those skilled in the relevant technical fields will understand that the technology can be implemented on computer / controller systems other than those shown and described above. The technology can be embodied in a special-purpose computer, controller, or data processor, which is specifically programmed, configured, or constructed to execute one or more of the computer-executable instructions described above. Thus, the terms "computer" and "controller" as commonly used herein refer to any data processing device and can include Internet appliances and handheld devices (including palm-top computers, wearable computers, cellular phones or mobile phones, multiprocessor systems, processor-based home appliances or programmable home appliances, network computers, minicomputers, etc.).

[0066] As described above, certain embodiments of the present technology have been described herein for the purpose of illustration, but it will be understood that various changes can be made without departing from the present disclosure. Further, although various advantages and features associated with specific embodiments have been described above in the context of these embodiments, other embodiments may exhibit such advantages and / or features, and not all embodiments necessarily exhibit such advantages and / or features in order to fall within the scope of the present technology. When a method is described, the method can include more, fewer, or other steps. Further, the steps may be performed in any suitable order. Accordingly, the present disclosure can encompass other embodiments not explicitly shown or described herein. In the context of the present disclosure, the term "about" means ±5% of a given value.

[0067] For the purposes of the present disclosure, for example, a list of two or more elements in the form "at least one of A, B, and C" is intended to mean (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C), and when any other number of elements are listed, all similar permutations are further included.

Claims

1. 1. A system comprising: An asymmetrical autotransformer and a bridge rectifier are provided. The transformer comprises: First to third coils of a delta winding are excited by corresponding input phases; a first plurality of correction windings coupled to the first coil; a second plurality of correction windings coupled to the second coil; a third plurality of correction windings coupled to the third coil; the bridge rectifier having a plurality of rectifiers coupled to respective respective compensation windings; The system wherein the phases of the individual correction windings are asymmetric such that the individual phase voltages are controlled relative to the inverse input phase and the voltages are unbalanced relative to the neutral point.

2. The system of claim 1 , wherein each of the plurality of correction windings includes three individual windings.

3. 3. The system of claim 2, wherein the tap positions of each of the plurality of correction windings separate each corresponding coil of the delta winding into four segments.

4. 4. The system of claim 3, wherein the bridge rectifier receives twelve AC phases at inputs of corresponding diodes, the bridge rectifier outputting a DC voltage.

5. The bridge rectifier comprises: a main rectifier configured to rectify the AC voltage of the input phase; and a secondary rectifier configured to rectify the AC voltage of the correction winding.

6. 6. The system of claim 5, wherein the main rectifier provides approximately 66% of the DC power and the secondary rectifier provides approximately 34% of the DC power.

7. 2. The system of claim 1, wherein the delta winding provides a low impedance path for triplet harmonics.

8. 2. The system of claim 1, wherein in the bridge rectifier, individual phase voltages are offset by approximately 15 degrees from one phase to the next adjacent phase.

9. 1. A method for designing an autotransformer having a first coil, a second coil and a third coil of a delta winding, comprising the steps of: The method includes a turns selection step, a tap position selection step, a vector diagram construction step, a line drawing step, a turns ratio determination step, and a turns determination step; the turns selection step is a step of selecting the numbers of turns of a first coil, a second coil, and a third coil of a delta winding; the tap position selecting step comprises selecting three tap positions for a correction winding along each of a first coil, a second coil and a third coil of the delta winding, the tap positions dividing each of the first coil, the second coil and the third coil into four segments; the step of constructing a vector diagram of a transformer is a step of constructing a vector diagram of a transformer using an equilateral triangle having leg lengths proportional to the number of turns between input phases of a three-phase input, each side of the triangle representing a complete coil of the delta winding; the step of drawing lines includes drawing lines representing individual correction windings from each tap location along a first coil, a second coil and a third coil of the delta winding, each line being represented as a vector of a first plurality of vectors having a length proportional to a phase corresponding to a phase of the coil wound around the correction winding and a number of turns of the correction winding, each vector of the first plurality of vectors being parallel to one of the sides of the triangle; the turns ratio determining step determining a turns ratio of each correction winding according to the length of a corresponding vector of the first plurality of vectors; and The method, wherein the turns determining step includes determining a number of turns for each correction winding as a product of the turns ratio and a number of turns for a complete coil of the delta winding.

10. determining an output phase of the autotransformer; The step of determining an output phase comprises: drawing vectors of a second plurality of vectors from an end of each correction winding vector to an opposite vertex of the equilateral triangle; and determining the output phase of the individual correction windings according to a length of the corresponding vector of the second plurality of vectors.

11. 10. The method of claim 9, wherein the output phase of each correction winding is proportional to the amplitude of the corresponding output phase relative to the phase represented by the opposite vertex of the triangle.

12. 10. The method of claim 9, wherein the output voltage of the autotransformer is controlled as a phase-to-phase voltage and not as a phase-to-neutral voltage.

13. 10. The method of claim 9, wherein adjacent bridge rectifier conduction pairs are spaced apart by approximately 15 degrees.

14. the four segments along each coil of the delta winding have turns ratios of N1=0.17, N2=0.24, N3=0.42, and N4=0.17; the individual correction windings having turns ratios of N5=0.13, N6=0.13 and N7=0.18; 10. The method of claim 9, wherein the turns ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coil of the delta winding.

15. the four segments along each coil of the delta winding have turns ratios of N1=0.17, N2=0.42, N3=0.11, and N4=0.30; the individual correction windings having turns ratios of N5=0.18, N6=0.13 and N7=0.13; 10. The method of claim 9, wherein the turns ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coil of the delta winding.

16. the four segments along each coil of the delta winding have turns ratios of N1=0.30, N2=0.11, N3=0.29, and N4=0.30; the individual correction windings having turns ratios of N5=0.13, N6=0.18 and N7=0.13; 10. The method of claim 9, wherein the turns ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coil of the delta winding.

17. the four segments along each coil of the delta winding have turns ratios of N1=0.17, N2=0.24, N3=0.29, and N4=0.30; the individual correction windings having turns ratios of N5=0.13, N6=0.18 and N7=0.13; 10. The method of claim 9, wherein the turns ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coil of the delta winding.

18. the four segments along each coil of the delta winding have turns ratios of N1=0.30, N2=0.29, N3=0.24, and N4=0.17; the individual correction windings having turns ratios of N5=0.13, N6=0.18 and N7=0.13; 10. The method of claim 9, wherein the turns ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coil of the delta winding.

19. the four segments along each coil of the delta winding have turns ratios of N1=0.30, N2=0.29, N3=0.11, and N4=0.30; the individual correction windings having turns ratios of N5=0.13, N6=0.18 and N7=0.13; 10. The method of claim 9, wherein the turns ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coil of the delta winding.

20. the four segments along each coil of the delta winding have turns ratios of N1=0.30, N2=0.11, N3=0.42, and N4=0.17; the individual correction windings having turns ratios of N5=0.13, N6=0.13 and N7=0.18; 10. The method of claim 9, wherein the turns ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coil of the delta winding.

21. the four segments along each coil of the delta winding have turns ratios of N1=0.17, N2=0.42, N3=0.24, and N4=0.17; the individual correction windings having turns ratios of N5=0.18, N6=0.13 and N7=0.13; 10. The method of claim 9, wherein the turns ratio is defined as the number of turns of a segment or correction winding divided by the total number of turns of the coil of the delta winding.

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