Asymmetrical 24-pulse autotransformer rectifier unit for turbine electric propulsion, and related 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. Further, 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 the AC / DC converter should be improved.

[0004] A certain conventional system relies on a hexagonal winding configuration to establish 12 AC phases that are converted to a DC voltage (24 - pulse rectification is possible). However, in such a conventional system, triple - n harmonics are likely to occur and there are limitations for use in aerospace industry applications. Triple - n 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 triple - n harmonic currents causes problems such as voltage inequality and excessive power dissipation. To mitigate triple - n harmonics, typically, it is necessary to add windings or increase the core size, resulting in increased weight and decreased efficiency. On the other hand, in the configuration of a conventional single - winding transformer that requires eight windings per phase, nine windings per phase are required to mitigate triple - n harmonics. In a conventional single - winding transformer, additional windings per phase are required to form a delta winding dedicated to triple - n harmonic mitigation and provide a low - impedance path for triple - n harmonic currents.

[0005] Other conventional designs, based on delta-wound symmetric autotransformers, supply 12 output phases from 3 input phases to multiple bridge rectifiers, enabling 24-pulse AC / DC conversion. In the delta-wound symmetric approach, the phases are designed to have uniform amplitude and fading with respect to the neutral point. The delta-wound symmetric approach achieves low current distortion due to its inherent triplene harmonic relaxation, but requires the addition of inter-phase transformers. Inter-phase transformers require autotransformers to handle all the power supplied to the load, resulting in weight and efficiency penalties compared to asymmetric power handling techniques. As a result, symmetric solutions are heavier and less efficient than acceptable weight and efficiency for aerospace applications.

[0006] In short, the conventional approaches described above suffer from one or more of the following drawbacks: a complex assembly process requiring eight or more windings per core leg, high weight, and low efficiency, lack of inherent triplene harmonic relaxation. On the other hand, AC / DC converters with fewer than 24 pulses, such as the 18-pulse and 12-pulse ATRUs common in modern aerospace applications, are lightweight, highly efficient, and possess inherent triplene harmonic relaxation. However, these 18-pulse and 12-pulse ATRUs cannot provide the high power quality and low current distortion (total harmonic distortion or THDi < 5%) offered by 24-pulse conversion. Therefore, there is a need for AC / DC converter systems and methods that can provide 24-pulse conversion and triplene harmonic relaxation with acceptable weight and operating efficiency to meet the needs of aerospace applications. [Overview of the project]

[0007] This summary is provided to simplify and introduce the selection of concepts that will be further described in the following "Detailed Description." This summary is not intended to identify the main 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 present invention makes it possible to convert a three-phase AC voltage into a DC voltage with an amplitude approximately 2.35 times that of the average input phase-neutral point RMS voltage. For example, this technology enables a nominal 540-volt DC output from a 230-volt AC input, which is commonly used in modern aerospace power systems. The output voltage is proportional to the input voltage.

[0009] The present invention combines an autotransformer and a rectifier to form a 24-pulse auto-transformer rectifier unit (ATRU). To provide three of the twelve phases required for 24-pulse rectification, three input phases can be directly supplied to three nodes of a bridge rectifier. The power path formed by directly connecting the three input phases to the bridge rectifier handles the majority of the power processed by the ATRU (e.g., approximately two-thirds or 66% of the power). This power path allows for a significant reduction in the size of the autotransformer. The autotransformer consists of three coils forming a delta configuration. The three input phases are also supplied to the delta coil of the autotransformer.

[0010] Each coil contains multiple series windings. Each of the three coils in a delta autotransformer may contain four series windings and three compensatory windings forming the sides of the delta. The nine compensatory windings together provide nine output points with appropriate amplitude and phasing for the three input phases for the combined 24-pulse operation (nine phases from the compensatory windings and three phases from the input phases). These 12 phases are directly rectified into 24 pulses by a bridge rectifier, eliminating the need for additional interphase transformers (IPTs) commonly used in conventional known systems.

[0011] In one embodiment, the system includes an asymmetric autotransformer having: a first coil, a second coil, and a third coil of a delta winding (each coil being excited in its corresponding input phase); a first plurality of compensating windings coupled to the first coil; a second plurality of compensating windings coupled to the second coil; and a third plurality of compensating windings coupled to the third coil. The system also includes a bridge rectifier having a plurality of rectifiers coupled to each of the individual compensating windings, wherein the phases of the individual compensating windings are asymmetrical such that the individual phase voltages are controlled with respect to the inverse input phase, and the voltages are unbalanced with respect to the neutral point.

[0012] In one embodiment, each of the multiple correction windings includes three individual windings. In another embodiment, the tap positions of each of the multiple correction windings separate each corresponding coil of the delta winding into four segments.

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

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

[0015] In one embodiment, a method for designing an autotransformer having a first coil, a second coil, and a third coil of a delta winding includes the following: Steps include selecting the number of turns for the first, second, and third coils of a delta winding; selecting three tap positions for a compensatory winding along each of the first, second, and third coils of the delta winding (these tap positions divide each of the first, second, and third coils into four segments); and constructing a vector diagram of the transformer using equilateral triangles with leg lengths proportional to the number of turns between the input phases of the three-phase input (each side of the triangle represents a complete coil of the delta winding). The method also includes the step 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 of the coil wound around the correction winding and the number of turns of the correction winding, and each of the first plurality of vectors is parallel to one of the sides of the triangle. The method also includes the steps of determining the turns ratio of each correction winding based on the lengths of the corresponding vectors 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 embodiment, the method also includes the step of determining the output phase of an autotransformer by the following steps: drawing a vector of a second plurality of vectors from the end of each corrected winding vector to the opposite vertex of the equilateral triangle; and determining the output phase of each corrected winding by the length of the corresponding vector of the second plurality of vectors.

[0017] In one embodiment, 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 other embodiments, the output voltage of an autotransformer is controlled as a phase-to-phase voltage and not as a phase-to-neutral point voltage.

[0019] In one embodiment, adjacent bridge rectifier conduction pairs are spaced approximately 15 degrees apart.

[0020] In one embodiment, the four segments along each individual coil 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 a segment or correction winding divided by the total number of turns of the coil of the delta winding.

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

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

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

[0024] In another aspect, four segments along each coil 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 each coil 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 each coil 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 each coil 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 can be better understood by referring to the following detailed description in conjunction with the accompanying drawings.

[0029] [Figure 1A] Figure 1A is a diagram showing an ATRU according to an embodiment of the technology of the present invention. [Figure 1B] Figure 1B is a diagram showing an ATRU according to an embodiment of the technology of the present invention. [Figure 2] Figure 2 is a diagram showing the windings of a delta-wound single-winding transformer according to an embodiment of the technology of the present invention. [Figure 3] Figure 3 is a diagram showing the topology diagram of a delta-wound single-winding transformer for the single-winding transformer of Figure 2. [Figure 4] Figure 4 is a diagram showing a delta-wound single-winding transformer according to an embodiment of the technology of the present invention. [Figure 5] Figure 5 is a diagram showing the topology diagram of a delta-wound single-winding transformer according to an embodiment of the technology of the present invention. [Figure 6] Figure 6 is a diagram showing the topology diagram of a delta-wound single-winding transformer according to an embodiment of the technology of the present invention. [Figure 7] Figure 7 is a diagram showing the topology diagram of a delta-wound single-winding transformer according to an embodiment of the technology of the present invention. [Figure 8] Figure 8 is a diagram showing the topology diagram of a delta-wound single-winding transformer according to an embodiment of the technology of the present invention. [Figure 9] Figure 9 is a diagram showing the topology diagram of a delta-wound single-winding transformer according to an embodiment of the technology of the present invention. [Figure 10] Figure 10 is a diagram showing the topology diagram of a delta-wound single-winding transformer according to an embodiment of the technology of the present invention. [Figure 11] Figure 11 is a diagram showing the topology diagram of a delta-wound single-winding transformer according to an embodiment of the technology of the present invention. [Figure 12] Figure 12 is a flowchart of a design method for a 24-pulse asymmetric ATRU according to an embodiment of the technology of the present invention. [Figure 13] Figure 13 is a graph simulating the three-phase input current waveform of a 24-pulse asymmetric ATRU using the ideal single-winding transformer of the topology depicted in Figure 3. [Figure 14]Figure 14 is a graph simulating the rectifier bridge current of a 24-pulse asymmetric ATRU using an ideal autotransformer with the topology shown in Figure 3. [Figure 15] Figure 15 is a graph simulating the A-phase input voltage and current of a 24-pulse asymmetric ATRU using an ideal autotransformer with the topology shown in Figure 3. [Figure 16] Figure 16 is a graph of an actual three-phase input current waveform according to one embodiment of the present invention. Detailed description

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

[0031] Commercial aircraft continue to evolve towards more electric aircraft (MEA), characterized by an increase in electrical content instead of hydraulic and pneumatic systems. Recent advances in power electronics and high-density electric motors, along with ongoing pressure to reduce operating costs, ensure this trend continues. Furthermore, electric propulsion in aircraft is transitioning to hybrid electric, turbo-electric, and even all-electric powertrains. Under one scenario, the transition to electric propulsion is expected to increase the power demand of electrical systems by more than 40 times.

[0032] However, conventional power conversion technologies currently cannot meet the needs of turbine-electric propulsion. For example, conventional ATRUs offer relatively high power conversion efficiency and reliability, but conventional ATRU technologies require a significant trade-off between weight and power quality. Some conventional technologies can achieve a total current harmonic distortion (THDi) of less than 5%, but require a 24 or 30-pulse design. A conventional 24-pulse design results in approximately a 50% weight penalty compared to industry-leading 12 or 18-pulse solutions (which produce 7-13% THDi). This presents a significant 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 10-100kW applications.

[0033] However, when the ATRU's power demand exceeds 100kW, sacrificing power quality becomes far more difficult. Due to the increased line impedance at harmonic frequencies, excess current harmonics significantly distort the waveform of the AC distribution system. This leads to a variety of adverse effects, including increased conduction interference problems to other equipment on the AC bus, a low power factor (resulting in excessively large generators and overheating in the distribution system to deliver apparent power rather than actual power), excessive radiated magnetic fields, overheating of generators and motors, and increased wear and acoustic noise in rotating devices (due to harmonic torque).

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

[0035] In some embodiments, an asymmetric 24-pulse ATRU is a power converter that first converts a 3-phase AC input to 12-phase AC and then to a DC output via a 24-pulse rectifier bridge for power factor correction and harmonic current cancellation. In some embodiments, the asymmetric approach requires the 3-phase AC input to be passed directly to the rectifier bridge and simultaneously to an autotransformer. The autotransformer generates an additional 9 phases, which are also supplied to the rectifier bridge, for a total of 12 phases. This allows for a significant reduction in weight and power dissipation, as the autotransformer handles only about one-third of the power delivered to the ATRU output, achieving the harmonic current cancellation necessary to minimize harmonic distortion in the input current and maximize the power factor. Furthermore, the autotransformer includes a delta embodied in its winding configuration, resulting in inherent triplene harmonic mitigation. In the present invention, the autotransformer winding uses a delta configuration, which handles the main power and acts as a low-impedance path for triplene harmonic currents. Conventional autotransformers with a hexagonal winding configuration do not provide a low-impedance path for triplen harmonic currents, and consequently require an additional delta winding (usually a five-legged core) to perform this function. In some embodiments, the autotransformer includes three core legs, each having one coil (e.g., coils A, B, or C) wound around the core leg. Each coil has only seven different windings, facilitating a reduction in assembly complexity and cost.

[0036] Figure 1A shows an ATRU 1000 according to one embodiment of the present invention. On the input side, a three-phase 230-volt AC power 100 is supplied to an autotransformer 300. In a typical embodiment described later, the autotransformer converts the three-phase input (A, B, C) into nine auxiliary phases (1-9) and supplies them to a secondary rectifier circuit 400, providing 18 of the 24 pulses required for 24-pulse operation. The three-phase input is also supplied directly to a main rectifier circuit 200, supplying the remaining three phases and six pulses for 24-pulse operation. The rectifier circuits 200 and 400 may include a diode arrangement that rectifies the input AC voltage to a DC voltage. With the autotransformer of the present invention, the ATRU outputs a high-quality 540-volt DC while maintaining a 24-pulse input waveform with a high power factor and low harmonic content.

[0037] Direct feedthrough of the three input phases to the main rectifier circuit 200 allows a large portion of the power processed by the ATRU (e.g., about 66%) to bypass the autotransformer 300. As a result, significant reductions in size, weight, and dissipation can be achieved in the autotransformer 300. The 66% to 34% power distribution is merely 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. In general, the reduction in power in the autotransformer 300 also reduces the weight and size of the autotransformer.

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

[0039] Figure 2 shows the windings of a delta autotransformer according to one embodiment of the present invention. The illustrated delta autotransformer includes three input points PA, PB, and PC for a 230-volt AC, three-phase input, and 12 output taps (T1 to T12) for 12 output phases (three main phases and nine auxiliary phases of the autotransformer). The topology orientation is illustrative, and different topologies may be applied in different embodiments.

[0040] The turns ratios of each winding in the illustrated embodiment are shown adjacent to the winding. For example, the series windings along coil C corresponding to N1, N2, N3, and N4 have turns ratios of 0.17, 0.24, 0.42, and 0.17, respectively. The compensatory 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 for coils A and B is equal to the number of turns of coil C.

[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 autotransformer, different parasitic elements, and 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 autotransformer core. Examples of turns for the autotransformer embodiment illustrated in Figure 2 are shown in Tables 1 and 2 below.

[0042] Table 1 shows sample turns ratios for autotransformers with 139 turns along each of coils A, B, and C. For example, segment N1 contains 24 turns, while segment N2 contains 33 turns. Similarly, secondary winding N6 contains 18 turns, while secondary winding N7 contains 25 turns. The ratio of these turns to the number of turns in each individual coil (139 turns in the illustrated example) is shown in the "Turns Ratio" column.

[0043] [Table 1]

[0044] Table 2 shows the voltage amplitude ("Amplitude" column) and phase ("Phase" column) of the autotransformer shown in Figure 2 (practical corrections are implemented in the turns ratio to compensate for parasitic effects including winding impedance and leakage inductance). Generally, the voltage difference between corresponding tap pairs ("Amplitude" column) is nearly constant. The phase difference in the "Phase Delta" column is also nearly constant, corresponding to 15° intervals from one conducted pair to the next in a bridge rectifier.

[0045] In the autotransformer according to embodiments of the present invention, the compensating winding phase voltage is controlled as the inter-phase voltage relative to the reverse input phase voltage, forming balanced bridge rectifier conduction pairs at nominal 15-degree intervals. This differs from the conventional symmetrical autotransformer design approach, which aims to achieve balance between the phase and neutral point compensating winding voltages. For example, referring to the autotransformer in Figure 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 contains the nominal voltage amplitudes and phases for all bridge rectifier conduction pairs of the autotransformer in Figure 2. The bridge rectifier conduction pairs consist of two phases supplied to the bridge rectifier and conduct to each other at a consistent point within each complete electrical cycle. In the case of the autotransformer according to embodiments of the present invention, each conduction pair conducts twice per complete electrical cycle, once for each polarity. For example, this shows that the voltage (A phase - T8) in Table 2 has a phase difference of -14.97 degrees, and the voltage (T8 - A phase) in Table 2 has a phase difference of -194.97 degrees, and a phase difference of 180 degrees indicates that the voltage polarity is reversed.

[0046] [Table 2]

[0047] Figure 3 shows the topology diagram of a delta autotransformer for the autotransformer in 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 also inserted between C and A and between A and B, but are not labeled in the figure to reduce confusion.

[0048] A sampling method for determining the phase-to-phase voltage of an asymmetric autotransformer is described below. The sampling method involves drawing vectors from the ends of each compensating 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 autotransformer. 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 the neutral point, as in a symmetric autotransformer). This phase-to-phase voltage is presented to the bridge rectifier as a conducted pair, as shown in Table 2. By designing the output voltage and phase angle of the autotransformer to be balanced with respect to the inverse input phase rather than the neutral point voltage, a large portion of the processed power can bypass the autotransformer without compromising power quality, thus eliminating the phase-to-phase transformer. In some embodiments, triplene harmonic relaxation is ensured by a main delta winding formed by an N1-N4 winding ratio, which provides a suitable winding configuration for triplene harmonic relaxation.

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

[0050] [Table 3]

[0051] Figure 12 illustrates a sample method for determining the phase-to-phase voltage of an asymmetric autotransformer. In particular, the illustrated method outlines a design process for selecting turns ratio for appropriate output phase amplitude and spacing for asymmetric 24-pulse operation. In different embodiments, the illustrated method may include additional steps, or other steps not shown in the flowchart.

[0052] This method can be initiated in block 510. In block 515, the number of interphase turns is selected to maintain an acceptable magnetic flux density for the selected core, operating frequency, and operating voltage.

[0053] In block 520, the vector diagram of the transformer is constructed using equilateral triangles 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, Figures 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 correction winding.

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

[0055] In block 530, vectors are drawn from the end of each corrected winding vector to the opposite vertex of an equilateral triangle. These vectors represent the output phases of the autotransformer. 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. A vector can be drawn from each output tap to the neutral point, which accurately represents the output phase voltage relative to the neutral point; however, due to the nature of the asymmetric design, the voltages from these phases to the neutral point will be non-uniform. Controlling the phase-to-phase voltage, rather than the phase-to-neutral voltage, is the difference between the asymmetric and symmetric design approaches.

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

[0057] In block 540, the number of turns for the autotransformer series winding and the correction winding are set based on the final length of each series winding segment in the transformer vector diagram and the correction winding vector. This method may end in block 545.

[0058] Figure 4 shows a delta-wound autotransformer according to one embodiment 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 secondary windings (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 main rectifier circuits / secondary rectifier circuits 200 and 400.

[0059] Figures 5 to 11 show topology diagrams of delta-wound autotransformers according to embodiments of the present invention. For the embodiments shown in Figures 5 to 11, the number of turns and turns ratio are shown in Table 4 below. In different embodiments, these number of turns and turns ratio are determined using the method shown in Figure 12.

[0060] [Table 4]

[0061] Figures 13 to 15 are graphs simulating the current waveform of a 24-pulse asymmetric ATRU using an ideal autotransformer with the topology shown in Figure 3. Since non-ideal characteristics such as leakage inductance and winding resistance are ignored, this simulated asymmetric ATRU is referred to as "ideal". Figure 16 is a graph of an actual three-phase input current waveform according to one embodiment of the present invention. In each of these graphs, the horizontal axis represents elapsed time, and the vertical axis represents current (amperes).

[0062] In particular, Figure 13 is a graph simulating the three-phase input current waveform of a 24-pulse asymmetric ATRU using an ideal autotransformer with the topology shown in Figure 3. An ideal autotransformer without leakage inductance or winding resistance exhibits a stepped current waveform that approximates a sine wave with 24 "steps" or "pulses" when inputting a sinusoidal voltage. This is a result of the conducted pairs of the bridge rectifier switching every 15 degrees. By adding leakage inductance and winding resistance, the waveform is smoothed and eventually becomes almost a sine wave (see Figure 16 below).

[0063] Figure 14 is a graph simulating the rectifier bridge current of a 24-pulse asymmetric ATRU during one complete electrical cycle at 400 Hz. In Figure 14, the 15-degree spacing of the bridge rectifier conduction pairs can be observed. Here, it can be seen that each conduction pair conducts for a time slightly over 100 microseconds, i.e., an electrical angle of approximately 15 degrees in a given 400 Hz cycle with a period of 2.5 ms. Furthermore, in Figure 14 and Table 2, it can be seen that each input phase connection to the bridge rectifier conducts current for 5 consecutive pulses, while each compensating winding conducts current for only 1 pulse in a given half-cycle. This indicates that the majority of the power is handled by the ATRU, bypassing the autotransformer, thereby enabling improved efficiency and reduced weight.

[0064] Figure 15 is a graph simulating the A-phase input voltage and current of a 24-pulse asymmetric ATRU using an ideal autotransformer of the topology depicted in Figure 3. Figure 16 is a graph of the actual three-phase input current waveform according to one embodiment of the present invention. In the embodiment illustrated in Figure 16, the actual current waveform is smoother than the ideal input current waveform shown in Figure 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 be kept as small as possible. As seen in Figures 14 and 15, pulse currents with large amplitude and short duration flow through the compensating winding. If the leakage inductance is too large, these pulse currents may not be able to reach their maximum amplitude, and the 24-pulse operation may degrade, reducing the number of effective pulses and bringing the performance of the 24-pulse ATRU closer to that of an 18 or 12-pulse solution.

[0065] Many embodiments of the techniques described above can take the form of computer-executable instructions or controller-executable instructions, which include routines executed by a programmable computer or controller. Those skilled in the art will understand that the techniques may be implemented in computer / controller systems other than those shown and described above. The techniques may be embodied in special-purpose computers, controllers, or data processors that are specifically programmed, configured, or constructed to execute one or more of the computer-executable instructions described above. Accordingly, the terms “computer” and “controller” as commonly used herein refer to any data processing device and may include Internet electrical appliances and handheld devices (including palmtop computers, wearable computers, cellular phones or mobile phones, multiprocessor systems, processor-based home appliances or programmable home appliances, network computers, minicomputers, etc.).

[0066] From the foregoing, it will be understood that while specific embodiments of the Art have been described herein for illustrative purposes, various modifications are possible without departing from this disclosure. Furthermore, while various advantages and features related to specific embodiments have been described above in the context of those embodiments, other embodiments may also exhibit such advantages and / or features, and not all embodiments are required to exhibit such advantages and / or features in order to fall within the scope of the Art. Where a method is described, the method may include more, fewer, or other steps. Furthermore, the steps may be performed in any suitable order. Thus, this disclosure may encompass other embodiments not expressly shown or described herein. In the context of this disclosure, the term “about” means ±5% of a given value.

[0067] For the purposes of this disclosure, a list of two or more elements in the form of, for example, “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 further includes all similar sortings if any other quantity of elements is listed.

Claims

1. It is a system, It comprises an asymmetric autotransformer and a bridge rectifier, The aforementioned asymmetric autotransformer comprises a three-phase delta winding, three correction windings of the first group, three correction windings of the second group, and three correction windings of the third group. The three-phase delta winding has three input points configured to receive a three-phase AC input voltage, and comprises three core legs and three coils. Each of the three core legs provides one side of the three-phase delta winding, and defines three input points at the interconnection of each of the three core legs, each including a first core leg, a second core leg, and a third core leg. Each of the three coils is wound around one of the three core legs, and each coil defines three tap positions between each of the three input points of the three-phase delta winding. Each of the aforementioned tap positions provides a different phase from there. Furthermore, each of the three coils is excited by the three-phase AC input voltage applied to the three input points. The three correction windings of the first group are each connected to one of the three tap positions of the first group of the first core legs, each providing an asymmetric phase output voltage of the first group having a different phase. The three correction windings of the second group are each connected to one of the three tap positions of the second group of the second core legs, each providing an asymmetric phase output voltage of the second group having a different phase. The three correction windings of the third group are each connected to one of the three tap positions of the third group of the third core legs, each providing an asymmetric phase output voltage of the third group having a different phase. Each of the first, second, and third groups of correction windings provides a total of nine asymmetric phase output voltages, each having a different phase. The asymmetric phase output voltages from each of the first, second, and third group correction windings are unbalanced with respect to the neutral point voltage. The asymmetric phase output voltages of the first, second, and third groups of correction windings are controlled according to the inverse phase of the three-phase AC input voltage applied to the input point of the three-phase delta winding. The aforementioned bridge rectifier comprises a plurality of rectifiers, Each pair of rectifiers in the first group is coupled to one of the nine asymmetrical phase output voltages from the first, second, and third group correction windings, providing 18 pulses of the 24 pulse rectified DC output voltage. Each pair of rectifiers in the second group is coupled to the three input points of the three-phase delta winding, providing six pulses of the 24 pulse rectified DC output voltage in response to the three-phase AC input voltage, in a system.

2. The system according to claim 1, The first, second, and third group correction windings each comprise three individual coils in a system.

3. The system according to claim 2, The tap position is a system that divides the corresponding coil of the three coils of the three-phase delta winding into four segments.

4. The system according to claim 3, The bridge rectifier receives the nine asymmetric phase output voltages as AC voltages at the input of the corresponding diode, The aforementioned bridge rectifier is a system that outputs a DC voltage.

5. The system according to claim 1, The aforementioned bridge rectifier is, A main rectifier configured to rectify the three-phase AC input voltage to the three-phase delta winding and provide six pulses of the 24-pulse rectified DC output voltage, A system comprising: a secondary rectifier configured to rectify the AC voltages of the first, second, and third groups of correction windings and to provide 18 pulses of the 24 pulse rectified DC output voltage.

6. The system according to claim 5, The aforementioned main rectifier supplies approximately 66% of the DC power when AC / DC conversion is performed. The system wherein the secondary rectifier supplies approximately 34% of the DC power during the AC / DC conversion.

7. The system according to claim 1, A system in which the three-phase delta winding provides a low-impedance path that mitigates triplen harmonic currents.

8. The system according to claim 1, In the bridge rectifier system, the offset between the asymmetric phase output voltages provided from each of the tap positions of the first, second, and third groups of correction windings is approximately 15 degrees each.

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