36-pulse dual body rectifier transformer for medium voltage variable frequency drive

Abstract

The application discloses a 36-pulse double-body rectifier transformer for medium-voltage variable frequency speed regulation, and belongs to the technical field of transformer manufacturing, which comprises a first high-voltage winding connected in a triangle and a second high-voltage winding connected in a star, the corresponding secondary side of the first high-voltage winding comprises three groups of low-voltage windings, and the corresponding secondary side of the second high-voltage winding comprises three groups of low-voltage windings; six groups of low-voltage windings are connected with six sets of three-phase rectifier bridges respectively, the six sets of three-phase rectifier bridges are combined according to phases to form three groups of DC parallel branches, and each group of DC parallel branches is connected with an independent inverter load; the application greatly reduces the number of turns of the winding of the phase-shifting part, reduces the amount of copper material of the winding, reduces material consumption, and controls the manufacturing cost of the transformer.

Description

Technical Field

[0001] This invention belongs to the field of transformer manufacturing technology, and in particular relates to a 36-pulse dual-body rectifier transformer for medium-voltage variable frequency speed regulation. Background Technology

[0002] Medium-voltage frequency converters are core infrastructure equipment for industrial energy conservation, intelligent manufacturing, and new power systems, with long-term rigid demand and strong growth certainty. The multi-pulse technology of medium-voltage frequency converters, through phase-shifting rectifier transformers, allows multiple sets of 6-pulse three-phase rectifier bridges to stagger and superimpose their phases, suppressing input harmonics and improving the power factor at the source. This is the most mainstream grid-side harmonic mitigation solution for medium-voltage high-power frequency converters (three-level, NPC, flying capacitor, etc. topologies). The primary side is connected to the grid, and the secondary side is divided into m independent three-phase windings. Each winding is phase-shifted at a fixed angle (phase difference = 60° / m), driving a set of 6-pulse rectifier bridges. The DC side is connected in series / parallel and superimposed, with a total pulse count P = 6 × m (m = 2, then 12 pulses; m = 3, then 18 pulses; m = 4, then 24 pulses; m = 6, then 36 pulses).

[0003] Traditional 36-pulse dual-body rectifier transformers typically employ phase-shifting methods such as... Figure 1 As shown, the high-voltage windings of the first transformer body are A1X, B1Y, and C1Z; the three low-voltage windings are a1x, b1y, and c1z; a2x, b2y, and c2z; and a3x, b3y, and c3z. Each low-voltage winding consists of a phase-shifting winding and a basic winding, with shift angles of 5°, 15°, and 25°, respectively. The high-voltage windings of the second transformer body are A2X, B2Y, and C2Z; the three low-voltage windings are a4x, b4y, and c4z; a5x, b5y, and c5z; and a6x, b6y, and c6z, with shift angles of -5°, -15°, and -25°, respectively. The two high-voltage windings are connected in the same way, either D-connected or Y-connected. The vector diagram is shown below. Figure 2 As shown, the angle difference between a1x, a2x, a3x, a4x, a5x, and a6x is 10°, representing a 36-pulse waveform; the working topology diagram is as follows. Figure 3 As shown, six rectifiers are connected in parallel to operate as a single load. If the load is a medium-voltage frequency converter, the traditional direction-shifting rectification method is also used, and its working principle is as follows: Figure 4 The formula has the following problems: 1. When a rectifier transformer powers a frequency converter load, it differs from a regular load. The rectifier transformer actually powers three rectifier bridges, each supporting an independent load—one of the U, V, or W phases of the frequency converter power supply. Each rectifier bridge operates at 12 pulses, and the three bridges combine to produce a 36-pulse output. Figure 4In the design, taking the first group as an example, one shift angle is -25° and the other is +5°. Assuming the required equivalent secondary turns are 100 turns, calculations show that when the shift angle is 25°, the number of turns in the shift winding is 49 and the number of turns in the basic winding is 17. When the shift angle is 5°, the number of turns in the shift winding is 10 and the number of turns in the basic winding is 85. The difference in the number of turns in the shift winding and the basic winding between the two groups of coils is very large, resulting in a large difference in the axial and radial dimensions of the coils. It is difficult to ensure that the impedance of each low-voltage winding to the high voltage is consistent. When the two groups of rectifier bridges work in parallel, the circulating current is large, the commutation impedance difference is large, the equipment has low anti-interference capability, and the operating conditions are poor.

[0004] 2. Transformer material consumption is directly proportional to the shift angle; a larger shift angle results in greater material consumption and higher transformer load losses. The traditional scheme, with a maximum shift angle of 25°, further increases load losses. Summary of the Invention

[0005] Purpose of the invention: In view of the problems existing in the prior art, the present invention provides a 36-pulse dual-body rectifier transformer for medium-voltage variable frequency speed regulation.

[0006] Technical Solution: This invention discloses a 36-pulse dual-body rectifier transformer for medium-voltage variable frequency speed regulation, comprising a delta-connected first high-voltage winding and a star-connected second high-voltage winding. The secondary side of the first high-voltage winding includes three sets of low-voltage windings, and the secondary side of the second high-voltage winding also includes three sets of low-voltage windings. The six sets of low-voltage windings are respectively connected to six sets of three-phase rectifier bridges. The six sets of three-phase rectifier bridges are combined according to phase to form three sets of DC parallel branches, and each set of DC parallel branches is connected to an independent inverter load.

[0007] Furthermore, the first high-voltage winding includes three sets of delta-connected high-voltage windings A1X, B1Y, and C1Z, and the second high-voltage winding includes three sets of star-connected high-voltage windings A2X, B2Y, and C2Z; the secondary side corresponding to the first high-voltage winding includes the first set of low-voltage windings a1x, b1y, and c1z, the second set of low-voltage windings a2x, b2y, and c2z, and the third set of low-voltage windings a3x, b3y, and c3z;

[0008] The secondary side corresponding to the second high-voltage winding includes the fourth low-voltage winding a4x, b4y, c4z, the fifth low-voltage winding a5x, b5y, c5z, and the sixth low-voltage winding a6x, b6y, c6z.

[0009] The first set of low-voltage windings and the fourth set of low-voltage windings are respectively connected to the corresponding three-phase rectifier bridges. The outputs of the two sets of three-phase rectifier bridges are connected in parallel and then connected to an independent inverter load.

[0010] The second low-voltage winding and the fifth low-voltage winding are respectively connected to the corresponding three-phase rectifier bridges. The outputs of the two sets of three-phase rectifier bridges are connected in parallel and then connected to an independent inverter load.

[0011] The third and sixth low-voltage windings are respectively connected to the corresponding three-phase rectifier bridges. The outputs of the two sets of three-phase rectifier bridges are connected in parallel to the independent inverter load.

[0012] Furthermore, the first set of low-voltage windings includes a shifting winding. , , and basic winding , , ; and The connection forms the low-voltage winding a1x. and The connection forms the low-voltage winding b1y. and The connection forms the low-voltage winding c1z;

[0013] The three basic windings are connected by a sequential delta connection.

[0014] The structures of the fourth, third, and sixth low-voltage windings are the same as those of the first low-voltage winding.

[0015] Furthermore, the second low-voltage winding includes three basic windings, which are connected by a sequential delta connection. The fifth low-voltage winding has the same structure as the second low-voltage winding.

[0016] Furthermore, the phase shift angles of the first to the sixth low-voltage windings are -10°, 0°, +10°, -10°, 0°, and +10°, respectively.

[0017] Beneficial effects: This invention utilizes the inherent phase difference between the high-voltage windings of two transformers, which are connected in a delta and star configuration respectively, to share the overall phase shifting task. This effectively reduces the phase shift angle that the low-voltage side's extended phase-shifting winding needs to bear. In this solution, the maximum phase shift angle of the low-voltage winding is only 10°, and a low-voltage winding that does not require phase shifting is also provided. This significantly reduces the number of winding turns in the extended phase-shifting section, reduces the amount of copper used in the windings, reduces material consumption, and controls transformer manufacturing costs. Attached Figure Description

[0018] Figure 1 This is a structural diagram of a traditional 36-pulse dual-body rectifier transformer;

[0019] Figure 2 This is a vector diagram of a traditional 36-pulse dual-body rectifier transformer structure;

[0020] Figure 3 This is the working topology diagram of a traditional 36-pulse dual-body rectifier transformer structure;

[0021] Figure 4 This is the working topology diagram of an inverter load connected to a traditional 36-pulse dual-body rectifier transformer structure.

[0022] Figure 5 This is a structural diagram of the 36-pulse dual-body rectifier transformer of the present invention;

[0023] Figure 6 This is a working topology diagram of the 36-pulse dual-body rectifier transformer structure of the present invention;

[0024] Figure 7 This is a vector diagram of the 36-pulse dual-body rectifier transformer structure of the present invention. Detailed Implementation

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0026] like Figure 5 As shown, the present invention includes a first high-voltage winding A1X, B1Y, C1Z connected in a delta configuration (D-connection) and a second high-voltage winding A2X, B2Y, C2Z connected in a star configuration (Y-connection). The secondary side of the first high-voltage winding includes three sets of low-voltage windings: a first set of low-voltage windings: a1x, b1y, c1z; a second set of low-voltage windings: a2x, b2y, c2z; and a third set of low-voltage windings: a3x, b3y, c3z. a1x includes a shifting winding. and basic winding b1y includes a directional winding. and basic winding c1z includes a directional winding. and basic winding a2x includes the basic winding. b2y includes basic windings The C2Z includes the basic winding. a3x includes a directional winding. and basic winding b3y includes a directional winding. and basic winding The c3z includes a directional winding. and basic winding The three basic windings in each group are connected in a sequential triangle configuration.

[0027] The secondary side of the second high-voltage winding includes three sets of low-voltage windings. These three sets of low-voltage windings include: a fourth set (a4x, b4y, c4z); a fifth set (a5x, b5y, c5z); and a sixth set (a6x, b6y, c6z). A4x includes a shifting winding. and basic winding b4y includes a directional winding. and basic winding The c4z includes a directional winding. and basic winding The a5x includes the basic winding. b5y includes the basic winding. The C5Z includes the basic winding. a6x includes a directional winding. and basic winding b6y includes a directional winding. and basic winding The c6z includes a directional winding. and basic winding The three basic windings in each group are connected in a sequential triangle configuration.

[0028] Figure 5 In the diagram, Dd2(-20) indicates that the secondary voltage lags the primary voltage by -20°; Dd0(0) indicates that the secondary voltage is in phase with the primary voltage; Dd2(20) indicates that the secondary voltage lags the primary voltage by 20°; D indicates that the primary side adopts a delta connection, d indicates that the secondary side adopts a delta connection, and Y indicates that the primary side adopts a star connection. Because the primary side adopts a star connection and the secondary side adopts a delta connection, the secondary voltage leads the high-voltage side by 30°. (-20) is an additional lag of 20° electrical angle generated by the extension winding. The output voltage of this secondary winding leads the high-voltage primary voltage by 10°. With the two sets of secondary windings Yd11(0) and Yd11(+20), the three sets of secondary windings are 20° apart in phase, and finally form a 36-pulse rectified input to suppress grid-side harmonics.

[0029] The phase shift angles of the first to the sixth low-voltage windings are -10°, 0°, +10°, -10°, 0°, and +10°, respectively.

[0030] like Figure 6 As shown, each low-voltage winding is connected to a three-phase rectifier bridge, the outputs of the two corresponding rectifier bridges are connected in parallel, and then an independent inverter is connected.

[0031] This invention fully utilizes the inherent 30° phase difference between the high-voltage windings of two transformers, which are connected in a D (delta) and Y (star) configuration respectively, to share the overall phase shifting task. This effectively reduces the phase shift angle that the low-voltage side's extended phase-shifting winding needs to bear. In this solution, the maximum phase shift angle of the low-voltage winding is only 10°, and a low-voltage winding that does not require phase shifting is also included. This significantly reduces the number of winding turns in the extended phase-shifting section, lowers the amount of copper used in the windings, reduces material consumption, and controls transformer manufacturing costs.

[0032] Among them, the phase shift angles of the low-voltage windings a1x, b1y, c1z, a3x, b3y, c3z, a4x, b4y, c4z, and a6x, b6y, c6z are the same, meaning that the number of turns in the extended phase-shifting windings of the above windings is completely consistent with the number of turns in the basic working windings. The identical winding turn structure ensures that the axial and radial dimensions of this part of the coil remain consistent; the consistent coil geometry ensures that the short-circuit impedance of the above low-voltage windings is basically the same relative to the corresponding high-voltage windings, and the DC resistance of the windings also tends to be consistent, resulting in basically equal resistance losses for each winding during operation.

[0033] The electrical parameters of the two low-voltage windings in the same inverter unit power supply group are small, the input voltage amplitude and output DC characteristics of each rectifier bridge are consistent, and there will be no problems of circulating current or uneven load distribution when multiple rectifier bridges are connected in parallel. This effectively reduces the unbalanced losses between windings, improves the stability of DC bus voltage, and thus facilitates the stable and reliable operation of the entire frequency conversion system.

[0034] Figure 7 and Figure 3 The numbers 1-6 in the diagram represent the corresponding winding numbers, and a, b, and c represent the three-phase output terminals. Figure 7 Although the angle difference between a6 and a5, and between a3 and a1, is 20°, the variable frequency speed control uses a1 and a4 (30° difference, 12 pulses), a2 and a5 (30° difference, 12 pulses), and a3 and a4 (30° difference, 12 pulses) to supply power to the U, V, and W phases of the load motor, respectively, forming an equivalent 36 pulses. This differs from the parallel operation of six low-voltage systems in electrochemical or electrolytic systems, which requires an angle difference of 10°. The structure of this invention saves material consumption, simplifies the manufacturing process, and meets the 36-pulse requirement of medium-voltage frequency converters, reducing the harmonic content injected into the power grid. While the rectifier side of this invention is not strictly 36 pulses, it achieves an equivalent 36-pulse harmonic suppression effect externally by grouping and pairing the inverter side to the motor inverter load.

[0035] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. A 36-pulse dual-body rectifier transformer for medium-voltage variable frequency speed regulation, characterized in that, It includes a first high-voltage winding connected in a delta configuration and a second high-voltage winding connected in a star configuration. The secondary side of the first high-voltage winding includes three sets of low-voltage windings, and the secondary side of the second high-voltage winding also includes three sets of low-voltage windings. The six sets of low-voltage windings are respectively connected to six sets of three-phase rectifier bridges. The six sets of three-phase rectifier bridges are combined according to phase to form three sets of DC parallel branches. Each set of DC parallel branches is connected to an independent inverter load.

2. The 36-pulse dual-body rectifier transformer for medium-voltage variable frequency speed regulation according to claim 1, characterized in that, The first high-voltage winding includes three sets of delta-connected high-voltage windings A1X, B1Y, and C1Z; the second high-voltage winding includes three sets of star-connected high-voltage windings A2X, B2Y, and C2Z; the secondary side corresponding to the first high-voltage winding includes the first set of low-voltage windings a1x, b1y, and c1z, the second set of low-voltage windings a2x, b2y, and c2z, and the third set of low-voltage windings a3x, b3y, and c3z. The secondary side corresponding to the second high-voltage winding includes the fourth low-voltage winding a4x, b4y, c4z, the fifth low-voltage winding a5x, b5y, c5z, and the sixth low-voltage winding a6x, b6y, c6z. The first set of low-voltage windings and the fourth set of low-voltage windings are respectively connected to the corresponding three-phase rectifier bridges. The outputs of the two sets of three-phase rectifier bridges are connected in parallel and then connected to an independent inverter load. The second low-voltage winding and the fifth low-voltage winding are respectively connected to the corresponding three-phase rectifier bridges. The outputs of the two sets of three-phase rectifier bridges are connected in parallel and then connected to an independent inverter load. The third and sixth low-voltage windings are respectively connected to the corresponding three-phase rectifier bridges. The outputs of the two sets of three-phase rectifier bridges are connected in parallel to the independent inverter load.

3. The 36-pulse dual-body rectifier transformer for medium-voltage variable frequency speed regulation according to claim 2, characterized in that, The first group of low-voltage windings includes the shifting winding. , , and basic winding , , ; and The connection forms the low-voltage winding a1x. and The connection forms the low-voltage winding b1y. and The connection forms the low-voltage winding c1z; The three basic windings are connected by a sequential delta connection. The structures of the fourth, third, and sixth low-voltage windings are the same as those of the first low-voltage winding.

4. The 36-pulse dual-body rectifier transformer for medium-voltage variable frequency speed regulation according to claim 2, characterized in that, The second low-voltage winding consists of three basic windings, which are connected by a sequential delta connection. The fifth low-voltage winding has the same structure as the second low-voltage winding.

5. The 36-pulse dual-body rectifier transformer for medium-voltage variable frequency speed regulation according to claim 2, characterized in that, The phase shift angles of the first to the sixth low-voltage windings are -10°, 0°, +10°, -10°, 0°, and +10°, respectively.

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