A through-type in-phase power supply system based on cascaded multilevel converters

Abstract

A through-phase power supply system based on cascaded multilevel converters includes a power electronic converter and a transformer. This through-phase power supply system can simultaneously eliminate phase separation at the substation outlet and at the section substation, achieving full-line power supply and avoiding train speed losses. Furthermore, this system can improve the power quality of the power grid. Compared to existing through-phase power supply systems based on three-phase to single-phase converters, this system uses delta, V-shaped, and diamond-shaped cascaded multilevel converters, which allows for a reduction in converter capacity, thereby lowering costs and increasing its application value.

Description

Technical Field

[0001] This invention relates to the field of electrified railway traction power supply technology, specifically a through-type in-phase power supply system based on a cascaded multilevel converter. Background Technology

[0002] The power supply system for my country's electrified railways is a single-phase power frequency AC system. 110kV or 220kV AC power from the power grid is converted at traction substations before reaching the overhead contact line, and then supplies power to the trains via pantographs. Currently, there are some problems with electrified railways. Because trains are single-phase loads with random and fluctuating characteristics, issues such as negative sequence current and reactive power arise, leading to deteriorated power quality. Furthermore, the use of alternating phase sequence power supply for trains results in phase separation issues, which involve complex electromechanical processes and cause speed losses.

[0003] To simultaneously address power quality and phase separation issues, a phase-in-phase power supply scheme can be adopted. In traditional traction power supply systems, two power supply lines with different phases are drawn from the traction substation to power the train. However, in a phase-in-phase power supply system, only one power supply line needs to be drawn to power the train. Phase-in-phase power supply systems can be divided into compensated phase-in-phase power supply systems and through-phase phase-in-phase power supply systems. Compensated phase-in-phase power supply systems can only eliminate phase separation at the traction substation outlet, but not at the section substation; through-phase phase-in-phase power supply systems can eliminate phase separation at both the traction substation outlet and the section substation.

[0004] Traditional through-type in-phase power supply system structure based on three-phase to single-phase converter, such as Figure 6 As shown, its core component is the three-phase to single-phase converter 55. Three-phase AC power from the three-phase power grid 51 is converted to DC power by the three-phase Yd-connected traction transformer 13, then to DC power by the three-phase rectifier section of the converter 55. Finally, it is inverted to single-phase AC power by the single-phase inverter section of the converter 55, ultimately supplying power to the train. However, while it can achieve continuous, same-phase power supply, it suffers from excessively high converter capacity, leading to increased equipment costs and hindering practical applications. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a continuous in-phase power supply system based on a cascaded multilevel converter.

[0006] One of the problems to be solved by the present invention is to control the first link 34 and the second link 35 of the delta-cascaded multilevel converter 31 to make the voltage of each section of the power supply line the same, while eliminating the electrical phase separation at the traction substation outlet and the electrical phase separation at the section, so as to achieve smooth train operation without speed loss.

[0007] The second problem to be solved by the present invention is to improve the power quality of the power grid by controlling the third link 36 of the delta-cascaded multilevel converter 31, thereby suppressing the adverse effects of train operation on the power grid.

[0008] The third problem that this invention aims to solve is that the traditional through-type in-phase power supply system based on a three-phase to single-phase converter has the problem of excessively large capacity of the three-phase to single-phase converter. However, by adopting a through-type in-phase power supply system based on a delta-cascaded multilevel converter, the capacity of the converter can be reduced, thereby achieving the goal of reducing costs and being more conducive to practical applications.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A continuous in-phase power supply system based on a cascaded multilevel converter is characterized in that the structure of the power supply system is as follows: the three-phase power grid 51 is connected to the cascaded multilevel converter via the Vv-connected traction transformer 1, and the output point of the cascaded multilevel converter is connected to the contact network 54 via the first single-phase step-down transformer 8, so as to achieve the purpose of powering the train 53.

[0011] Based on the above plan,

[0012] A cascaded multilevel converter is composed of several links with identical structures connected together.

[0013] The types of cascaded multilevel converters include delta cascaded multilevel converter 31, V-shaped cascaded multilevel converter 32, and diamond cascaded multilevel converter 33;

[0014] The aforementioned link is formed by link inductor 43 connected in series with the sub-module link;

[0015] The above submodule chain is formed by cascading several chain-segment submodules with the same structure, including the first submodule 44 to the nth submodule 45;

[0016] The inductor 43 of the chain link is the head of the chain link on one side, and the nth sub-module 45 of the chain link is the tail of the chain link on one side.

[0017] The sub-modules in the above sub-module chain include two-level H-bridge sub-modules, midpoint clamping three-level H-bridge modules, and flying capacitor three-level H-bridge modules; the above sub-modules are not limited to the various H-bridge modules listed, but also include other devices or combinations of devices with the same function.

[0018] The second terminal 10 of the primary winding of the first single-phase step-down transformer is grounded, and the first filter capacitor 61 is connected in parallel between the first terminal 9 of the primary winding of the first single-phase step-down transformer and the second terminal 10 of the primary winding of the first single-phase step-down transformer.

[0019] Based on the above plan,

[0020] The delta-cascaded multilevel converter 31 includes three links: a first link 34, a second link 35, and a third link 36. The beginning and end of these three links are connected sequentially to form a triangular structure. The through-type in-phase power supply system using the delta-cascaded multilevel converter 31 is suitable for applications requiring power quality management.

[0021] The intersection point 66 of the first and third links of the delta-cascaded multilevel converter is connected to the first terminal 5 of the secondary winding of the Vv-connected traction transformer; the intersection point 67 of the second and third links of the delta-cascaded multilevel converter is connected to the third terminal 7 of the secondary winding of the Vv-connected traction transformer; and the intersection point 65 of the first and second links of the delta-cascaded multilevel converter is connected to the first terminal 9 of the primary winding of the first single-phase step-down transformer.

[0022] Based on the above plan,

[0023] The V-shaped cascaded multilevel converter 32 includes two links, namely the first link 37 and the second link 38 of the V-shaped cascaded multilevel converter; the through-type in-phase power supply system using the V-shaped cascaded multilevel converter 32 is suitable for occasions where power quality management is not required;

[0024] The head of the first link 37 of the V-shaped cascaded multilevel converter and the tail of the second link 38 of the V-shaped cascaded multilevel converter meet at the intersection point 68 of the first and second links of the V-shaped cascaded multilevel converter and are connected to the first terminal 9 of the primary winding of the first single-phase step-down transformer; the tail of the first link 37 of the V-shaped cascaded multilevel converter is connected to the first terminal 5 of the secondary winding of the Vv-connected traction transformer; the head of the second link 38 of the V-shaped cascaded multilevel converter is connected to the third terminal 7 of the secondary winding of the Vv-connected traction transformer.

[0025] Based on the above plan,

[0026] The diamond-shaped cascaded multilevel converter 33 includes four links: the first link 39, the second link 40, the third link 41, and the fourth link 42. The through-type in-phase power supply system using the diamond-shaped cascaded multilevel converter 33 is suitable for applications requiring power quality management.

[0027] The beginning and end of the four links are connected in sequence to form a rhombus structure;

[0028] The intersection point 70 of the first and third links of the aforementioned rhombic cascaded multilevel converter is connected to the first terminal 5 of the secondary winding of the Vv-connected traction transformer; the intersection point 71 of the second and fourth links of the rhombic cascaded multilevel converter is connected to the third terminal 7 of the secondary winding of the Vv-connected traction transformer; the intersection point 69 of the first and second links of the rhombic cascaded multilevel converter is connected to the first terminal 9 of the primary winding of the first single-phase step-down transformer; and the intersection point 72 of the third and fourth links of the rhombic cascaded multilevel converter is grounded.

[0029] Based on the above plan,

[0030] Through current closed-loop control, the currents of the first link 34 and the second link 35 of the delta-cascaded multilevel converter are made to be π / 2 out of phase with the voltages at their ends, thereby achieving the purpose of transmitting grid energy. The two ends of the third link 36 of the delta-cascaded multilevel converter are connected to the first terminal 5 and the third terminal 7 of the secondary winding of the Vv-connected traction transformer, respectively. Through current loop control, the current tracks the command value, thereby achieving the purpose of power quality management on the grid side.

[0031] Based on the above plan,

[0032] In the two-level H-bridge submodule, the first fully controlled power electronic switch 47 and the second fully controlled power electronic switch 48 of the two-level H-bridge submodule are connected in series; the third fully controlled power electronic switch 49 and the fourth fully controlled power electronic switch 50 of the two-level H-bridge submodule are connected in series; a DC-side capacitor 46 is connected in parallel with the above two series circuits; the connection point 73 of the first fully controlled power electronic switch 47 and the second fully controlled power electronic switch 48 of the two-level H-bridge submodule, and the connection point 74 of the third fully controlled power electronic switch 49 and the fourth fully controlled power electronic switch 50 of the two-level H-bridge submodule are led out as the AC side port of the H-bridge submodule;

[0033] In the midpoint clamping three-level H-bridge submodule, the first fully controlled power electronic switch 77, the second fully controlled power electronic switch 78, the third fully controlled power electronic switch 79, and the fourth fully controlled power electronic switch 80 are connected in series; the fifth fully controlled power electronic switch 81, the sixth fully controlled power electronic switch 82, the seventh fully controlled power electronic switch 83, and the eighth fully controlled power electronic switch 84 are connected in series. Electronic switch 84 is connected in series; the intersection of the first capacitor 75 on the DC side of the midpoint clamping three-level H-bridge module and the second capacitor 76 on the DC side of the midpoint clamping three-level H-bridge module is the midpoint 91 on the DC side of the midpoint clamping three-level H-bridge module. The branch formed by the series connection of the two capacitors is connected in parallel with the two branches formed by the series connection of the midpoint clamping three-level H-bridge modules mentioned above; the branch formed by the first clamping diode 85 and the second clamping diode 86 of the midpoint clamping three-level H-bridge module intersecting at connection point 115 and connected in series is connected at one end to the first fully controlled power electronic switch 77 and the second fully controlled power electronic switch 77 of the midpoint clamping three-level H-bridge module. The connection point 92 of the fully controlled power electronic switch 78 is connected to the connection point 93 of the third fully controlled power electronic switch 79 and the fourth fully controlled power electronic switch 80 of the mid-point clamping three-level H-bridge module; the branch formed by the third clamping diode 87 and the fourth clamping diode 88 of the mid-point clamping three-level H-bridge module, which intersect at connection point 116, is connected at one end to the connection point 94 of the fifth fully controlled power electronic switch 81 and the sixth fully controlled power electronic switch 82 of the mid-point clamping three-level H-bridge module, and at the other end to the connection point 93 of the fourth fully controlled power electronic switch 80 of the mid-point clamping three-level H-bridge module. The connection point 95 between the seventh fully controlled power electronic switch 83 and the eighth fully controlled power electronic switch 84 of the midpoint clamping three-level H-bridge module; the midpoint 91 of the DC side of the midpoint clamping three-level H-bridge module is connected to the connection point (115) and the connection point 116; the connection point 89 between the second fully controlled power electronic switch 78 of the midpoint clamping three-level H-bridge module and the third fully controlled power electronic switch 79 of the midpoint clamping three-level H-bridge module, and the connection point 90 between the sixth fully controlled power electronic switch 82 of the midpoint clamping three-level H-bridge module and the seventh fully controlled power electronic switch 83 of the midpoint clamping three-level H-bridge module are led out as the AC side port of the midpoint clamping three-level H-bridge module;

[0034] In the aforementioned flying capacitor type three-level H-bridge submodule, the first fully controlled power electronic switch 98, the second fully controlled power electronic switch 99, the third fully controlled power electronic switch 100, and the fourth fully controlled power electronic switch 101 are connected in series; the fifth fully controlled power electronic switch 102, the sixth fully controlled power electronic switch 103, and the seventh fully controlled power electronic switch 104 are connected in series. The power electronic switch 104 and the eighth fully controlled power electronic switch 105 of the flying capacitor type three-level H-bridge module are connected in series; the intersection of the first capacitor 96 and the second capacitor 97 on the DC side of the flying capacitor type three-level H-bridge module is the midpoint 110 on the DC side of the flying capacitor type three-level H-bridge module, and the branch formed by the two capacitors connected in series is connected in parallel with the two branches formed by the flying capacitor type three-level H-bridge modules connected in series; one end of the first flying capacitor 106 of the flying capacitor type three-level H-bridge module is connected to the first fully controlled power electronic switch 98 of the flying capacitor type three-level H-bridge module and One end of the second fully controlled power electronic switch 99 of the flying capacitor type three-level H-bridge module is connected to connection point 111, and the other end is connected to connection point 112 of the third fully controlled power electronic switch 100 and the fourth fully controlled power electronic switch 101 of the flying capacitor type three-level H-bridge module; one end of the second flying capacitor 107 of the flying capacitor type three-level H-bridge module is connected to connection point 113 of the fifth fully controlled power electronic switch 102 and the sixth fully controlled power electronic switch 103 of the flying capacitor type three-level H-bridge module, and the other end is connected to the flying capacitor type three-level H-bridge module... The connection point 114 between the seventh fully controlled power electronic switch 104 of the H-bridge module and the eighth fully controlled power electronic switch 105 of the flying capacitor type three-level H-bridge module; the connection point 108 between the second fully controlled power electronic switch 99 of the flying capacitor type three-level H-bridge module and the third fully controlled power electronic switch 100 of the flying capacitor type three-level H-bridge module; and the connection point 109 between the sixth fully controlled power electronic switch 103 of the flying capacitor type three-level H-bridge module and the seventh fully controlled power electronic switch 104 of the flying capacitor type three-level H-bridge module are led out as the AC side port of the flying capacitor type three-level H-bridge module.

[0035] The beneficial effects of the through-type in-phase power supply system based on a cascaded multilevel converter described in this invention are as follows:

[0036] The through-phase power supply system based on cascaded multilevel converters described in this invention can achieve through-phase power supply along the entire line, eliminating the need for phase separation at the substation outlet and at the section location, thus enabling trains to operate without speed loss. By adjusting the amplitude of the reference current in the third link 36 of the delta-cascaded multilevel converter, negative sequence current on the grid side or reactive power on the grid side can be eliminated, thereby improving the power quality of the grid. In addition, compared with the traditional through-phase power supply system based on three-phase to single-phase converters, this scheme uses delta-cascaded multilevel converters instead of traditional three-phase to single-phase converters, reducing the converter capacity, thereby lowering costs and making it more practical. Attached Figure Description

[0037] The present invention includes the following figures:

[0038] Figure 1 This is a schematic diagram of the through-type in-phase power supply system based on a delta-cascaded multilevel converter according to Embodiment 1 of the present invention;

[0039] Figure 2 This is a schematic diagram of the structure of a link in a cascaded multilevel converter based on the present invention;

[0040] Figure 3 yes Figure 2 The following is a schematic diagram of the linked submodule structure in the chain: (a) Two-level H-bridge submodule; (b) Midpoint clamping three-level H-bridge submodule; (c) Flying capacitor three-level H-bridge submodule;

[0041] Figure 4 This is a schematic diagram of the through-type in-phase power supply system based on a V-shaped cascaded multilevel converter according to Embodiment 2 of the present invention;

[0042] Figure 5 This is a schematic diagram of the through-type in-phase power supply system based on a diamond-shaped cascaded multilevel converter according to Embodiment 3 of the present invention;

[0043] Figure 6 This is a schematic diagram of a through-type in-phase power supply system based on a three-phase to single-phase converter;

[0044] Figure 7 This is the voltage and current phasor diagram of a delta-cascaded multilevel converter;

[0045] Figure 8 This is a control block diagram of a delta-cascaded multilevel converter. Figure 8 (a) is a control block diagram of the first and second links of a delta-cascaded multilevel converter. Figure 8 (b) is the control block diagram of the third link of the delta-cascaded multilevel converter;

[0046] Figure 9This is the phasor diagram of the reference current for the first and second links of a delta-cascaded multilevel converter.

[0047] Figure 10 This is a block diagram of the DC-side voltage equalization control of a delta-cascaded multilevel converter link, where... Figure 10 (a) is a block diagram of the DC-side voltage control of the third link of a delta-cascaded multilevel converter, in which... Figure 10 (b) is a block diagram of the DC-side voltage control of the first and second links of the delta-cascaded multilevel converter;

[0048] Figure 11 This is the phasor diagram corresponding to the DC-side voltage control method of the first and second links of a delta-cascaded multilevel converter.

[0049] Figure 12 This is a simulation waveform diagram of the third link of a delta-cascaded multilevel converter operating in non-power quality management mode. Figure 12 (a) shows the DC-side voltage waveforms of the first, second, and third links of the delta-cascaded multilevel converter. Figure 12 (b) shows the voltage and current waveforms output at point C of the delta-cascaded multilevel converter. Figure 12 (c) shows the voltage and current waveforms of the three-phase power grid when the delta-cascaded multilevel converter is operating. Figure 12 (d) shows the waveforms of the negative sequence current and reactive power on the grid side;

[0050] Figure 13 This is a simulation waveform diagram of the third link of a delta-cascaded multilevel converter switching from non-power quality management mode to negative sequence current elimination mode at 0.35s. Figure 13 (a) shows the DC-side voltage waveforms of the first, second, and third links of the delta-cascaded multilevel converter. Figure 1 3(b) shows the voltage and current waveforms output at point C of the delta-cascaded multilevel converter. Figure 13 (c) shows the voltage and current waveforms of the three-phase power grid when the delta-cascaded multilevel converter is operating. Figure 13 (d) shows the waveforms of the negative sequence current and reactive power on the grid side;

[0051] Figure 14 This is a simulation waveform diagram of the third link of a delta-cascaded multilevel converter switching from non-power quality management mode to reactive power compensation mode at 0.35s. Figure 14 (a) shows the DC-side voltage waveforms of the first, second, and third links of the delta-cascaded multilevel converter. Figure 14 (b) shows the voltage and current waveforms output at point C of the delta-cascaded multilevel converter. Figure 14 (c) shows the voltage and current waveforms of the three-phase power grid when the delta-cascaded multilevel converter is operating. Figure 14 (d) shows the waveforms of the negative sequence current and reactive power on the grid side.

[0052] In the diagram, 1: Vv-connected traction transformer; 2: First terminal of the primary winding of the Vv-connected traction transformer; 3: Second terminal of the primary winding of the Vv-connected traction transformer; 4: Third terminal of the primary winding of the Vv-connected traction transformer; 5: First terminal of the secondary winding of the Vv-connected traction transformer; 6: Second terminal of the secondary winding of the Vv-connected traction transformer; 7: Third terminal of the secondary winding of the Vv-connected traction transformer; 8: First single-phase step-down transformer; 9: First terminal of the primary winding of the first single-phase step-down transformer; 10: Second terminal of the primary winding of the first single-phase step-down transformer; 11: First terminal of the secondary winding of the first single-phase step-down transformer; 12: Second terminal of the secondary winding of the first single-phase step-down transformer. 13: Three-phase Yd-connected traction transformer; 14: First terminal of the primary winding of the three-phase Yd-connected traction transformer; 15: Second terminal of the primary winding of the three-phase Yd-connected traction transformer; 16: Third terminal of the primary winding of the three-phase Yd-connected traction transformer; 17: Fourth terminal of the primary winding of the three-phase Yd-connected traction transformer; 18: Fifth terminal of the primary winding of the three-phase Yd-connected traction transformer; 19: Sixth terminal of the primary winding of the three-phase Yd-connected traction transformer; 20: First terminal of the secondary winding of the three-phase Yd-connected traction transformer; 21: Second terminal of the secondary winding of the three-phase Yd-connected traction transformer; 22: Third terminal of the secondary winding of the three-phase Yd-connected traction transformer; 23: 24: Terminal 4 of the secondary winding of a three-phase Yd-connected traction transformer; 25: Terminal 5 of the secondary winding of a three-phase Yd-connected traction transformer; 26: Terminal 6 of the secondary winding of a three-phase Yd-connected traction transformer; 27: Second single-phase transformer; 28: Terminal 1 of the primary winding of a second single-phase transformer; 29: Terminal 1 of the secondary winding of a second single-phase transformer; 30: Terminal 2 of the secondary winding of a second single-phase transformer; 31: Delta-cascaded multilevel converter; 32: V-shaped cascaded multilevel converter; 33: Diamond-shaped cascaded multilevel converter; 34: First link of the delta-cascaded multilevel converter; 35: Second link of the delta-cascaded multilevel converter; 3 6: Third link of a delta-cascaded multilevel converter; 37: First link of a V-shaped cascaded multilevel converter; 38: Second link of a V-shaped cascaded multilevel converter; 39: First link of a diamond-shaped cascaded multilevel converter; 40: Second link of a diamond-shaped cascaded multilevel converter; 41: Third link of a diamond-shaped cascaded multilevel converter; 42: Fourth link of a diamond-shaped cascaded multilevel converter; 43: Link inductor; 44: First submodule of a link; 45: nth submodule of a link; 46: DC-side capacitor of a two-level H-bridge submodule; 47: First fully controlled power electronic switch of a two-level H-bridge submodule; 48: Second fully controlled power electronic switch of a two-level H-bridge submodule; 49: Third fully controlled power electronic switch of a two-level H-bridge submodule.50: Four fully controlled power electronic switches for two-level H-bridge submodules; 51: Three-phase power grid; 52: Rail; 53: Train; 54: Overhead contact network; 55: Three-phase to single-phase converter; 56: First inductor on the input side of the three-phase to single-phase converter; 57: Second inductor on the input side of the three-phase to single-phase converter; 58: Third inductor on the input side of the three-phase to single-phase converter; 59: First inductor on the output side of the three-phase to single-phase converter; 60: Second inductor on the output side of the three-phase to single-phase converter; 61: First filter capacitor; 62: Second filter capacitor; 63: Third filter capacitor; 64: Fourth filter capacitor; 65: Intersection of the first and second links of the delta-cascaded multilevel converter; 66: Intersection of the first and third links of the delta-cascaded multilevel converter. Link intersection; 67: Intersection of the second and third links of a delta-cascaded multilevel converter; 68: Intersection of the first and second links of a V-shaped cascaded multilevel converter; 69: Intersection of the first and second links of a rhombus-cascaded multilevel converter; 70: Intersection of the first and third links of a rhombus-cascaded multilevel converter; 71: Intersection of the second and fourth links of a rhombus-cascaded multilevel converter; 72: Intersection of the third and fourth links of a rhombus-cascaded multilevel converter; 73: Connection point; 74: Connection point; 75: First capacitor on the DC side of a midpoint-clamped three-level H-bridge module; 76: Second capacitor on the DC side of a midpoint-clamped three-level H-bridge module; 77: First fully controlled power electronic switch of a midpoint-clamped three-level H-bridge module. 78: Midpoint clamping type three-level H-bridge module second fully controlled power electronic switch; 79: Midpoint clamping type three-level H-bridge module third fully controlled power electronic switch; 80: Midpoint clamping type three-level H-bridge module fourth fully controlled power electronic switch; 81: Midpoint clamping type three-level H-bridge module fifth fully controlled power electronic switch; 82: Midpoint clamping type three-level H-bridge module sixth fully controlled power electronic switch; 83: Midpoint clamping type three-level H-bridge module seventh fully controlled power electronic switch; 84: Midpoint clamping type three-level H-bridge module eighth fully controlled power electronic switch; 85: Midpoint clamping type three-level H-bridge module first clamping diode; 86: Midpoint clamping type three-level H-bridge module second clamping diode; 87: Third clamping diode of the midpoint clamping type three-level H-bridge module; 88: Fourth clamping diode of the midpoint clamping type three-level H-bridge module; 89: Connection point; 90: Connection point; 91: Midpoint of the DC side of the midpoint clamping type three-level H-bridge module; 92: Connection point; 93: Connection point; 94: Connection point; 95: Connection point; 96: First capacitor on the DC side of the flying capacitor type three-level H-bridge module; 97: Second capacitor on the DC side of the flying capacitor type three-level H-bridge module; 98: First fully controlled power electronic switch of the flying capacitor type three-level H-bridge module; 99: Second fully controlled power electronic switch of the flying capacitor type three-level H-bridge module; 100: Third fully controlled power electronic switch of the flying capacitor type three-level H-bridge module;101: Fourth fully controlled power electronic switch of the flying capacitor type three-level H-bridge module; 102: Fifth fully controlled power electronic switch of the flying capacitor type three-level H-bridge module; 103: Sixth fully controlled power electronic switch of the flying capacitor type three-level H-bridge module; 104: Seventh fully controlled power electronic switch of the flying capacitor type three-level H-bridge module; 105: Eighth fully controlled power electronic switch of the flying capacitor type three-level H-bridge module; 106: First flying capacitor of the flying capacitor type three-level H-bridge module; 107: Second flying capacitor of the flying capacitor type three-level H-bridge module; 108: Connection point; 109: Connection point; 110: DC side midpoint of the flying capacitor type three-level H-bridge module; 111: Connection point; 112: Connection point; 113: Connection point; 114: Connection point; 115: Connection point; 116: Connection point; Detailed Implementation

[0053] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be emphasized that the above drawings and the following description are merely exemplary and are not intended to limit the scope of the invention or its application.

[0054] Example 1: Through-type in-phase power supply system based on delta-cascaded multilevel converter

[0055] like Figure 1 As shown:

[0056] The through-phase power supply system based on a delta-cascaded multilevel converter of the present invention includes a Vv-connected traction transformer 1, a delta-cascaded multilevel converter 31, and a first single-phase step-down transformer 8. The primary winding of the Vv-connected traction transformer 1 is connected to a three-phase power grid 51. The first terminal 2 of the primary winding of the Vv-connected traction transformer 1 is connected to phase A of the three-phase power grid 51. The second terminal 3 of the primary winding of the Vv-connected traction transformer 1 is connected to phase C of the three-phase power grid 51. The third terminal 4 of the primary winding of the Vv-connected traction transformer 1 is connected to phase B of the three-phase power grid 51. The first terminal 5 of the secondary winding of the Vv-connected traction transformer 1 is connected to the intersection point 66 of the first and third links of the delta-cascaded multilevel converter. The third terminal 7 of the secondary winding of the Vv-connected traction transformer 1 is connected to the intersection point 67 of the second and third links of the delta-cascaded multilevel converter. The second terminal 6 of the secondary winding of the Vv-connected traction transformer 1 is grounded. The first terminal 5 and the third terminal 7 of the secondary winding of the Vv-connected traction transformer are voltage output points, and the voltage phase output from the first terminal 5 leads the voltage phase output from the second terminal 7 by π / 3.

[0057] The intersection point 66 of the first and third links of the delta-cascaded multilevel converter 31, and the intersection point 67 of the second and third links of the delta-cascaded multilevel converter, are respectively connected to the first terminal 5 and the third terminal 7 of the secondary winding of the Vv-connected traction transformer. They receive electrical energy from the low-voltage winding of the Vv-connected traction transformer and transform it. The delta-cascaded multilevel converter 31 contains three links: the first link 34, the second link 35, and the third link 36. They work together to enable the delta-cascaded multilevel converter 31 to achieve energy transmission and power quality management.

[0058] Under normal circumstances, trains have a high power factor during operation, so they can be approximated as purely resistive loads. In the ideal operating condition when the load is purely resistive, the voltage and current phasors in the delta-cascaded multilevel converter are as follows: Figure 7 As shown, This is the output voltage at terminal 7 of the secondary winding of the Vv-connected traction transformer, with its phase used as the 0 reference phase. It is the output voltage of terminal 5 of the secondary winding of a three-phase Vv-connected traction transformer. and The amplitudes are the same. Phase advance The radian length is π / 3. These are the phasors of the voltages of the first, second, and third links of the delta-cascaded multilevel converter, respectively. They have the same amplitude and phases of 2π / 3, -2π / 3, and π, respectively. The point 65 (output point C) at the intersection of the first and second links of the delta-cascaded multilevel converter is the output voltage phasor of the delta-cascaded multilevel converter, and its amplitude is equal to the amplitude of the link voltage. It is twice the size of the phase, which is π / 6. The intersection point 65 (output point C) between the first and second links of the delta-cascaded multilevel converter is the output current phasor of the delta-cascaded multilevel converter, which is derived from... and The synthesized voltage has the same phase as the output voltage at output point C, which is also π / 6. These are the current phasors of the first, second, and third links of the delta-cascaded multilevel converter, respectively, with phases of π / 6, -π / 6, and π / 2. Delayed The radian length is π / 2. ahead of The radian length is π / 2, and the required output point C output current can be obtained by combining the two if and only if in this case. Lagging behind The radius is π / 2.

[0059] The first link 34 and the second link 35 of the delta-cascaded multilevel converter are energy transmission links. The end where the first link 34 and the third link 36 of the delta-cascaded multilevel converter intersect is connected to the first terminal 5 of the secondary winding of the Vv-connected traction transformer. The end where the second link 35 and the third link 36 of the delta-cascaded multilevel converter intersect is connected to the third terminal 7 of the secondary winding of the Vv-connected traction transformer. The intersection point 65 of the other ends of the first link 34 and the third link 35 of the delta-cascaded multilevel converter serves as the voltage output point of the triple delta-cascaded multilevel converter 31, and is connected to the first terminal 9 of the primary winding of the first single-phase step-down transformer 8.

[0060] The first link 34 and the second link 35 of the delta-cascaded multilevel converter are responsible for transmitting energy from the three-phase power grid. Their currents need to be controlled so that their phase differs from their voltage phase by π / 2, ensuring that the active power they absorb is zero to maintain stable DC-side capacitor voltage. The control block diagram is shown below. Figure 8 As shown in (a), the output voltage at point 65 (output point C) of the intersection of the first and second links of the delta-cascaded converter is the reference value u of the output voltage of the delta-cascaded multilevel converter. ref_CO With respect to the actual output point voltage u CO The difference is used by the voltage controller to obtain the output point command current i. ref_CO When the train is not considered as a purely resistive load, the command current at the output point is obtained by formulas (1) to (4) given later, which yield the reference current i of the first link of the delta-cascaded multilevel converter. ref_AC and the reference current i of the second link of the delta-cascaded multilevel converter ref_BC Reference current i ref_AC The phase is ωt+π / 2, and the reference current is i ref_BC The phases are ωt-π / 6, and the differences between them and their respective actual currents are obtained through a current controller. and Then, through feedforward links and u respectively s_AC and u s_BC Perform calculations, where u s_AC u is the voltage of the first link of the delta-cascaded multilevel converter. s_BCThe voltage of the second link of the delta-cascaded multilevel converter is used. Their outputs are modulated by carrier phase-shifted unipolar frequency doubling PWM to obtain trigger pulses, which control the opening and closing of the power electronic switches of the first and second links of the delta-cascaded multilevel converter.

[0061] The reference current i of the first link of the delta-cascaded multilevel converter ref_AC and the reference current i of the second link of the delta-cascaded multilevel converter ref_BC The output current i at the intersection of the first and second links of the delta-cascaded multilevel converter is the output point of the converter. ref_CO Relationship such as Figure 9 As shown, this case also takes into account the situation where the load electric locomotive is not operating ideally, making it more representative than the case of a purely resistive load. It is the output voltage phasor of the first terminal 5 of the secondary winding of the Vv-connected traction transformer. It is the output voltage phasor of the third terminal 7 of the secondary winding of the Vv-connected traction transformer, in order to The phase is used as the 0 reference phase. These are the voltage phasors of the first link, the second link, and the third link of the delta-cascaded multilevel converter, respectively. These are the current phasors of the first link and the second link of the delta-cascaded multilevel converter, respectively, with phases of -π / 6 and π / 2. The point 65 (output point C) at the intersection of the first and second links of the delta-cascaded multilevel converter is the output voltage phasor of the delta-cascaded multilevel converter, and its amplitude is equal to the amplitude of the link voltage. The phase is π / 6, and it consists of resistive voltage components. and inductive voltage component Composition. Here, it is assumed that the converter output current phasor at point C is... hysteresis phasor The radian length is θ, and the current phasor of the first link of the delta-cascaded multilevel converter is... and converter output current phasor The arc length is π / 2 + θ, and the current phasor of the second link of the delta-cascaded multilevel converter is... and the output current phasor at converter output point C The arc formed is π / 6-θ.

[0062] Depend on Figure 9 As shown, a delta-cascaded multilevel converter Current phasor of the first link of the delta-cascaded multilevel converter Current phasor of the second link of the delta-cascaded multilevel converter The amplitude and phase relationship can be expressed by mathematical formulas:

[0063]

[0064]

[0065]

[0066]

[0067] in For the first link current i of the delta-cascaded multilevel converter AC Initial phase, The initial phase of the current in the second link of the delta-cascaded multilevel converter. The initial phase of the output current at output point C of the delta-cascaded multilevel converter.

[0068] The third link 36 of the delta-cascaded multilevel converter is a power quality management link, playing a role in power quality management. Its end, which intersects with the first link 34 of the delta-cascaded multilevel converter, is connected to the first terminal 5 of the secondary winding of the Vv-connected traction transformer. Its end, which intersects with the second link 35 of the delta-cascaded multilevel converter, is connected to the third terminal 7 of the secondary winding of the Vv-connected traction transformer. The control block diagram of the third link 36 of the delta-cascaded multilevel converter is shown below. Figure 8 (b) shows the reference current i of the third link 36 of the delta-cascaded multilevel converter. ref_AB The phase is ωt+π / 6, and the difference between it and the actual current of the third link 36 of the delta-cascaded multilevel converter is obtained through a current controller. Then through the feedforward link and u s_AB Perform calculations, u s_AB The voltage of the third link of the delta-cascaded multilevel converter is used as the output. A trigger pulse is obtained through a carrier-phase-shifted unipolar frequency-doubling PWM stage, which controls the on / off switching of the power electronic switch in the third link of the delta-cascaded multilevel converter. Specifically, this control causes the current i in the third link of the delta-cascaded multilevel converter to... AB The phase of its voltage u AB The phase difference is π / 2, causing its AC side active power to be 0, thus maintaining the stability of its DC side capacitor voltage. The reference current i of the third link of the delta-cascaded multilevel converter. ref_AB The amplitude is determined by the current i of the first link of the delta-cascaded multilevel converter. AC And the second link of the delta-cascaded multilevel converter with current i of 35 BC And the operating mode of the third link of the delta cascaded multilevel converter is determined by this.

[0069] The third link 36 of the delta-cascaded multilevel converter has two power quality management modes: a negative sequence current elimination mode that can eliminate negative sequence current on the grid side and a reactive power compensation mode that can compensate reactive power on the grid side.

[0070] A through-type in-phase power supply system based on a delta-cascaded multilevel converter (DMP) has power quality management capabilities. By controlling the current amplitude of the third link of the DMP, the system can eliminate negative-sequence current on the grid side or compensate for reactive power on the grid side, i.e., operate in negative-sequence current elimination mode or reactive power compensation mode. In each operating mode, the current phasor of the third link of the DMP... Current phasor of the first link of the delta-cascaded multilevel converter and the second link of the delta-cascaded multilevel converter Different relationships need to be satisfied, and the specific relationships are derived through the following formula.

[0071] Depend on Figure 1 It can be seen that i SA i is the current flowing from phase A into the first terminal 2 of the primary winding of the Vv-connected traction transformer in the three-phase power grid 51. SB For the current flowing into the third terminal 4 of the primary winding of the Vv-connected traction transformer in phase B of the three-phase power grid 51, i SC Let k be the current flowing from phase C into the second terminal 3 of the primary winding of the Vv-connected traction transformer in the three-phase power grid 51, and let k be the turns ratio between the primary and secondary windings of the Vv-connected traction transformer. AC i is the current of the first link of the delta-cascaded multilevel converter. BC i is the current of the second link of the delta-cascaded multilevel converter. AB For the third link current of the delta-cascaded multilevel converter, i C This refers to the current at point 65 (output point C) where the first and second links of the delta-cascaded multilevel converter intersect.

[0072] according to Figure 7 The current phasors of the first, second, and third links of the delta-cascaded multilevel converter are:

[0073]

[0074] in For the first link current of the delta-cascaded multilevel converter phasor phase, For the second link current of the delta-cascaded multilevel converter Phase, For the third link current of the delta-cascaded multilevel converter phase

[0075]

[0076] The phasor of the negative sequence current in a three-phase power grid is

[0077]

[0078] in is the rotation factor.

[0079] According to formulas (5) to (7), the relationship between the amplitude of the negative sequence current of the three-phase power grid and the amplitude of the current of each link of the converter can be obtained.

[0080]

[0081] The apparent power on the grid side can be expressed as

[0082]

[0083] in These are the AC voltage phasors of phases A, B, and C on the grid side, respectively, P S Q represents the active power on the grid side. S Reactive power on the grid side

[0084]

[0085] When power quality management is not performed through the third link of a delta-cascaded multilevel converter, I AB Substituting 0 into equation (8), we obtain the corresponding negative sequence current amplitude as

[0086]

[0087] When I AB When = 0, the corresponding reactive power on the grid side is:

[0088]

[0089] Depend on Figure 4 The voltage and current phasor diagram of the converter can be obtained.

[0090]

[0091] The reactive power on the load side is

[0092]

[0093] From equations (1)(12)(13)(14), we can obtain

[0094]

[0095] Among them U SA =U SB =U SC =U S ,

[0096] When the third link of the delta-cascaded multilevel converter operates in grid-side negative sequence current elimination mode, I AB =I AC -I BC Substituting into equation (8), we obtain the corresponding negative sequence current amplitude as

[0097]

[0098] This achieves the goal of eliminating negative sequence current.

[0099] Will I AB =I AC -I BC Substitution formula (10)

[0100] At this time, the reactive power on the grid side is

[0101]

[0102] Comparing equation (17) with equation (12), we can obtain...

[0103] Q S1 =3Q S0 (18)

[0104] From the above derivation, it can be seen that when the third link of the delta-cascaded multilevel converter operates in negative sequence current elimination mode, its current reference value is I. AB =I AC -I BC The negative sequence current on the grid side is reduced to 0, and the reactive power on the grid side is 3 times that of the third link of the delta-cascaded multilevel converter when no power quality management is performed.

[0105] When the third link of the delta-cascaded multilevel converter operates in grid-side reactive power compensation mode, Substituting into equation (10), the corresponding reactive power on the grid side is obtained as follows:

[0106] Q S1 =0 (19)

[0107] This achieves the purpose of compensating for reactive power on the grid side. Substitute into equation (8).

[0108] At this time, the amplitude of the negative sequence current in the power grid is

[0109]

[0110] Comparing equation (20) with equation (11), we can obtain

[0111]

[0112] From the above derivation, it can be seen that when the third link of the delta-cascaded multilevel converter operates in reactive power compensation mode, its current reference value is: The reactive power on the grid side is reduced to 0, and the negative sequence current on the grid side is 1.5 times that of the third link of the delta-cascaded multilevel converter when no power quality management is performed.

[0113] In summary, for in-phase power supply systems based on delta-cascaded multilevel converters, considering that the electric locomotive load is not a unity power factor, the following conclusions can be drawn:

[0114] 1) When the third link of the delta-cascaded multilevel converter is not working, or when only the first and second links of the delta-cascaded multilevel converter are used in the system, reactive power and negative sequence current will inevitably exist on the grid side.

[0115] 2) When the third link of the delta-cascaded multilevel converter is used to eliminate the negative sequence current on the grid side, the reactive power on the grid side increases to 3 times the original value.

[0116] 3) When the third link of a delta-cascaded multilevel converter is used to fully compensate for the reactive power of the system, the negative sequence current component on the grid side increases to 1.5 times its original value. In this case, multiple substations can be used in coordination to eliminate the negative sequence current in the system.

[0117] Select the appropriate operating mode, and determine the actual current i of the first link of the delta-cascaded multilevel converter. AC The actual current i of the second link of the delta-cascaded multilevel converter BC The reference current of the third link of the delta-cascaded multilevel converter, i.e. the power quality management link, is calculated and controlled through a current loop.

[0118] Ideally, the current phases of the first, second, and third links of the delta-cascaded multilevel converter (DLP) are π / 2 out of phase with their respective voltage phases, resulting in zero active power and stable DC-side voltages. However, in reality, active power cannot be ideally maintained at zero, leading to variations in the DC-side voltages. Therefore, voltage equalization control using the DC-side capacitors of the links is necessary to ensure voltage balance across the three links.

[0119] The block diagram of the DC-side capacitor equalization control of the chain link is as follows: Figure 10 As shown, (a) is the control block diagram of the third link of the delta-cascaded multilevel converter, which is mentioned earlier as... Figure 8 (b) A voltage loop is added to the current loop shown in the control block diagram to control the stability of the DC-side voltage of the third link of the delta-cascaded multilevel converter. The DC-side reference voltage V of the delta-cascaded multilevel converter is... ref The actual DC-side voltage V of the third link of the delta-cascaded multilevel converter dc_AB The difference is used by the voltage controller to obtain the DC-side reference compensation current amplitude I of the third link of the delta-cascaded multilevel converter. ref_AB1 Multiplying by sin(ωt+2π / 3) yields the DC-side reference compensation current i of the third link of the delta-cascaded multilevel converter, which has the same phase as the voltage of that link. ref_AB1 This current is in phase with the reference current i of the third link current loop of the original delta-cascaded multilevel converter at ωt+π / 6. ref_AB0 Added together as the new reference current i ref_AB This allows for the application of control over the third link of the delta-cascaded multilevel converter, thereby achieving both DC-side voltage stability and power quality management.

[0120] For the first and second links of the delta-cascaded multilevel converter, there is a constraint relationship between their respective currents and the output current at output point C, making the control of their DC-side voltages relatively more complex. To achieve the goal of adding compensation current to the first and second links of the delta-cascaded multilevel converter without affecting the output current at output point C, the current i applied to the first link of the delta-cascaded multilevel converter for DC-side voltage control is... ref_AC1 The current i applied to the second link of the delta-connected multilevel converter for DC-side voltage control of the link. ref_BC1 They should satisfy the relationship of equal magnitude and opposite phase, where i ref_AC1 The positive direction is from output point A (intersection of the first and third links of the delta-cascaded multilevel converter, point 66) to output point C (intersection of the first and second links of the delta-cascaded multilevel converter, point 65). ref_BC1 The positive direction is from output point B (the intersection of the second and third links of the delta cascaded multilevel converter) to output point C (the intersection of the first and second links of the delta cascaded multilevel converter at 65°). Figure 11 This is a voltage-current phasor diagram of the DC-side voltage control of the first and second links of a delta-cascaded multilevel converter. This is the output voltage phasor of terminal 7 on the secondary winding of the Vv-connected traction transformer, with its 0 reference phase. It is the output voltage of terminal 5 of the secondary winding of the Vv-connected traction transformer. and The amplitudes are the same. Phase advance The phase is π / 3. These are the voltage phasors of the first, second, and third links of the delta-cascaded multilevel converter, respectively. They have the same amplitude and phases of 2π / 3, -2π / 3, and π, respectively. The intersection point 65 (output point C) of the first and second links of the delta-cascaded multilevel converter is the output voltage phasor of the delta-cascaded multilevel converter. The direction of line GH passing through point O is the same as the direction of the voltage phasor of the first link of the delta-cascaded multilevel converter. The direction of line EF passing through point O is the same as the direction of the voltage phasor of the second link of the delta-cascaded multilevel converter. The dashed line KL passing through point O is perpendicular to line GH, that is, perpendicular to the voltage phasor of the first link of the delta-cascaded multilevel converter. The dashed line IJ passing through point O is perpendicular to line EF, that is, perpendicular to the voltage phasor of the second link of the delta-cascaded multilevel converter. For example... Figure 11 As shown in (a), the first link of the delta-cascaded multilevel converter compensates for the current. Located in the upper left region between the dashed lines KL and IJ, the second link of the delta-cascaded multilevel converter, which is of equal size but opposite phase, compensates for the current. Located in the lower right region, in this case, both the first and second links of the delta-cascaded multilevel converter absorb active power, the DC-side voltage rises, and the compensation current of the first link of the delta-cascaded multilevel converter... Phase 2π / 3, second link compensation current of delta-cascaded multilevel converter With a phase of -π / 3, both the first and second links of the delta-cascaded multilevel converter absorb active power, and the amount of active power absorbed is the same. Consequently, their DC-side voltages also increase synchronously. For example... Figure 11 As shown in (b), the first link of the delta-cascaded multilevel converter compensates for the current. Located in the upper right region between the dashed lines KL and IJ, the second link of the delta-cascaded multilevel converter, which is of equal size but opposite phase, compensates for the current. Located in the lower left region of the sandwiched area, in this case, the first link of the delta-cascaded multilevel converter generates active power, corresponding to a decrease in DC-side voltage; the second link of the delta-cascaded multilevel converter absorbs active power, corresponding to an increase in DC-side voltage. Furthermore, when the compensation current of the first link of the delta-cascaded multilevel converter... Phase π / 6, compensation current for the second link of a delta-cascaded multilevel converter. When the phase is -5π / 6, the active power output by the first link of the delta-cascaded multilevel converter is equal to the active power absorbed by the second link of the delta-cascaded multilevel converter. The DC-side voltage of the first link of the delta-cascaded multilevel converter decreases, while the DC-side voltage of the second link of the delta-cascaded multilevel converter increases.

[0121] The DC-side voltage control block diagram of the first link and the second link of the delta-cascaded multilevel converter is shown below. Figure 10 As shown in (b), the DC-side reference voltage V of the delta-cascaded multilevel converter ref The average DC-side voltage V of the first link of the delta-cascaded multilevel converter dc_AC The average DC-side voltage V of the second link of the delta-cascaded multilevel converter dc_BC The difference between their average values ​​is used by a voltage controller to obtain the reference compensation current amplitude I for the overall DC-side voltage control of the first and second links of the delta-cascaded multilevel converter. ref10 Multiplying this amplitude by sin(ωt-π / 3) yields the reference compensation current i used for the overall DC-side voltage control of the first and second links of the delta-cascaded multilevel converter. ref10 The actual DC-side voltage V of the first link of the delta-cascaded multilevel converter dc_AC The actual DC-side voltage V of the second link of the delta-cascaded multilevel converter dc_BC The voltage difference is processed by a voltage controller to obtain the reference compensation current amplitude I used to reduce the voltage difference between the DC-side voltage of the first link of the delta-cascaded multilevel converter and the DC-side voltage of the second link of the delta-cascaded multilevel converter. ref11 Multiplying this amplitude by sin(ωt-5π / 6) yields the reference compensation current i used to reduce the voltage difference between the DC-side voltage of the first link of the delta-cascaded multilevel converter and the DC-side voltage of the second link of the delta-cascaded multilevel converter. ref11 The reference compensation current i is used for the overall DC-side voltage control of the first and second links of the delta-cascaded multilevel converter. ref10 and the reference compensation current i used to reduce the difference between the DC-side voltage of the first link of the delta-cascaded multilevel converter and the DC-side voltage of the second link of the delta-cascaded multilevel converter. ref11 The summation yields the reference compensation current i used for controlling the DC-side capacitor voltage of the first and second links of the delta-cascaded multilevel converter. ref1 The compensation current is passed through gain stages of -1 and 1 respectively to obtain the reference compensation current i used for controlling the DC-side capacitor voltage of the first link of the delta-cascaded multilevel converter. ref_AC1 and the reference compensation current i used for DC-side capacitor voltage control of the second link of the delta-cascaded multilevel converter ref_BC1These two compensation currents are respectively related to the reference current i of the first link of the original delta-cascaded multilevel converter. ref_AC0 The reference current i of the second link of the original delta-cascaded multilevel converter ref_BC0 Adding them together, we obtain the new reference current i for the first link of the delta-cascaded multilevel converter. ref_AC and the reference current i of the second link of the new delta-cascaded multilevel converter ref_BC Each link is controlled by a current loop to achieve energy transfer and DC-side voltage control.

[0122] The control of the DC-side capacitor voltage of the third link of the delta-cascaded multilevel converter and the control of the DC-side capacitor voltage of the first and second links of the delta-cascaded multilevel converter together constitute the voltage equalization control of the links of the delta-cascaded multilevel converter, thereby enabling the capacitor voltage of the three links to be balanced.

[0123] The structure of the first link, the second link, and the third link of the delta-cascaded multilevel converter is as follows: they are formed by link inductor 43 and sub-modules chained together by several sub-modules 44 and 45.

[0124] The structure of the delta-cascaded multilevel converter chain segment submodule is as follows: Figure 3 As shown in (a), it consists of a DC-side capacitor 46 and a two-level H-bridge submodule first fully controlled power electronic switch 47, a two-level H-bridge submodule second fully controlled power electronic switch 48, a two-level H-bridge submodule third fully controlled power electronic switch 49, and a two-level H-bridge submodule fourth fully controlled power electronic switch 50. The connection point 73 of the two-level H-bridge submodule first fully controlled power electronic switch 47 and the two-level H-bridge submodule second fully controlled power electronic switch 48, and the connection point 74 of the two-level H-bridge submodule third fully controlled power electronic switch 49 and the two-level H-bridge submodule fourth fully controlled power electronic switch 50 are led out as the AC side port of the link submodule.

[0125] The intersection point 65 of the first link and the second link of the delta-cascaded multilevel converter is connected to the first terminal 9 of the primary winding of the first single-phase step-down transformer 8. The second terminal 10 of the primary winding of the first single-phase step-down transformer 8 is grounded. A first filter capacitor 61 is connected in parallel between the first terminal 9 and the second terminal 10 of the primary winding of the first single-phase step-down transformer 8. The first terminal 11 of the secondary winding of the first single-phase step-down transformer is connected to the contact network 54 to supply power to the train 53. The second terminal 12 of the secondary winding of the first single-phase step-down transformer is connected to the rail 52, and the rail 52 is grounded. Ultimately, this achieves continuous power supply along the entire line, eliminating the need for phase separation at substation outlets and substation locations, and also serves to improve power quality.

[0126] The simulation waveform of the delta-cascaded multilevel converter without power quality management via a third link is shown below. Figure 12 As shown, Figure 12 (a) shows the DC-side voltage waveforms of the first, second, and third links of the delta-cascaded multilevel converter. Figure 12 (b) shows the voltage and current waveforms output at point C of the delta-cascaded multilevel converter. Figure 12 (c) shows the voltage and current waveforms of the three-phase power grid when the delta-cascaded multilevel converter is operating. Figure 1 2(d) shows the waveforms of the negative sequence current and reactive power on the grid side, indicating that the delta-cascaded multilevel converter operates stably in non-power quality management mode.

[0127] The simulation waveform of the third link of the delta-cascaded multilevel converter switching from non-power quality management mode to negative sequence current elimination mode at 0.35s is shown below. Figure 13 As shown, Figure 13 (a) shows the DC-side voltage waveforms of the first, second, and third links of the delta-cascaded multilevel converter. Figure 13 (b) shows the voltage and current waveforms output at point C of the delta-cascaded multilevel converter. Figure 13 (c) shows the voltage and current waveforms of the three-phase power grid when the delta-cascaded multilevel converter is operating. Figure 13 (d) shows the waveforms of the negative sequence current and reactive power on the grid side. It can be seen that the delta-cascaded multilevel converter can work stably when switching from the non-power quality management mode to the negative sequence current elimination mode. After the switch, the negative sequence current on the grid side drops to 0, and the reactive power on the grid side increases to 3 times the original value, which is consistent with the theoretical derivation.

[0128] The simulation waveform of the third link of the delta-cascaded multilevel converter switching from non-power quality management mode to reactive power compensation mode at 0.35s is shown below. Figure 14 As shown, Figure 14 (a) shows the DC-side voltage waveforms of the first, second, and third links of the delta-cascaded multilevel converter. Figure 14 (b) shows the voltage and current waveforms output at point C of the delta-cascaded multilevel converter. Figure 14 (c) shows the voltage and current waveforms of the three-phase power grid when the delta-cascaded multilevel converter is operating. Figure 14 (d) shows the waveforms of the negative sequence current and reactive power on the grid side. It can be seen that the delta-cascaded multilevel converter can work stably when switching from the non-power quality management mode to the reactive power compensation mode. After the switch, the reactive power on the grid side drops to 0, and the negative sequence current rate on the grid side increases to 1.5 times the original, which is consistent with the theoretical derivation.

[0129] Example 2: Through-type in-phase power supply system based on V-shaped cascaded multilevel converter

[0130] like Figure 4 As shown:

[0131] The through-type in-phase power supply system based on a V-shaped cascaded multilevel converter of the present invention is an improvement on the through-type in-phase power supply system based on a delta-shaped cascaded multilevel converter. It removes the third link 36 of the delta-shaped cascaded multilevel converter, i.e., the power management link, while the structure and connection method of other parts remain unchanged. The first link 34 of the original delta-shaped cascaded multilevel converter is changed to the first link 37 of the V-shaped cascaded multilevel converter, the second link 35 of the original delta-shaped cascaded multilevel converter is changed to the second link 38 of the V-shaped cascaded multilevel converter, and the original delta-shaped cascaded multilevel converter is changed to a V-shaped cascaded multilevel converter.

[0132] The basic control strategy and voltage equalization strategy of the V-shaped cascaded multilevel converter in the through-type in-phase power supply system based on the V-shaped cascaded multilevel converter are the same as those of the delta cascaded multilevel converter in the through-type in-phase power supply system based on the delta cascaded multilevel converter.

[0133] In a through-phase power supply system based on a V-type cascaded multilevel converter, the V-type cascaded multilevel converter does not contain a power quality management link, therefore it does not have a power quality management function and is suitable for applications with relatively ideal load conditions. Furthermore, the V-type cascaded multilevel converter contains only two power transmission links, one fewer than a delta cascaded multilevel converter. Therefore, the cost of a through-phase power supply system based on a V-type cascaded multilevel converter is lower than that based on a delta cascaded multilevel converter, and the choice can be made based on actual conditions.

[0134] Example 3: Through-type in-phase power supply system based on diamond cascaded multilevel converter

[0135] like Figure 5 As shown:

[0136] The through-type in-phase power supply system based on a rhombus cascaded multilevel converter of the present invention is an improvement on the through-type in-phase power supply system based on a delta cascaded multilevel converter. The third link 36 of the delta cascaded multilevel converter is removed, and the third link 41 and the fourth link 42 of the rhombus cascaded multilevel converter are connected. The first link 34 of the original delta cascaded multilevel converter is changed to the first link 39 of the rhombus cascaded multilevel converter, and the second link 35 of the original delta cascaded multilevel converter is changed to the second link 40 of the rhombus cascaded multilevel converter. One end of the third link 41 of the rhombus cascaded multilevel converter is connected to… One end of the fourth link 42 of the diamond-shaped cascaded multilevel converter forms an intersection point 72, which is grounded. The intersection point 70 of the first and third links of the diamond-shaped cascaded multilevel converter is connected to the first terminal 5 of the secondary winding of the three-phase Vv-connected traction transformer. The intersection point 71 of the second and fourth links of the diamond-shaped cascaded multilevel converter is connected to the third terminal 7 of the secondary winding of the three-phase Vv-connected traction transformer. The original delta-shaped cascaded multilevel converter 31 is changed to a diamond-shaped cascaded multilevel converter 33. The through-type in-phase power supply system based on the delta-shaped cascaded multilevel converter is changed to a through-type in-phase power supply system based on the diamond-shaped cascaded multilevel converter.

[0137] The control strategies for the first and second links of the rhombic cascaded multilevel converter (MLC) in a through-type in-phase power supply system based on a rhombic cascaded MLC are the same as those for the first and second links of the delta-cascaded MLC. The third and fourth links of the rhombic cascaded MLC in the same system are power quality management links, and their control strategies are similar to those for the third link of the delta-cascaded MLC. Power quality management of the power grid is achieved through the control of the third and fourth links of the rhombic cascaded MLC.

[0138] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A through-feed phase-to-phase power supply system based on a cascaded multilevel converter, characterized by The structure of the power supply system is that: three-phase power grid (51) is connected to the cascaded multilevel converter through the Vv connection type traction transformer (1), the output point of the cascaded multilevel converter is connected to the catenary (54) through the first single-phase step-down transformer (8), and the purpose of supplying power to the train (53) is achieved; the secondary side of the Vv connection type traction transformer (1) is not directly connected with the catenary (54); The cascaded multilevel converter is composed of a plurality of chain links with the same structure connected with each other; The cascaded multilevel converter is a delta connection cascaded multilevel converter (31); The delta connection cascaded multilevel converter (31) includes three chain links, which are a delta connection cascaded multilevel converter first chain link (34), a delta connection cascaded multilevel converter second chain link (35) and a delta connection cascaded multilevel converter third chain link (36), and the chain head and the chain tail of the above three chain links are connected in sequence to form a delta structure; the through-type same-phase power supply system using the delta connection cascaded multilevel converter (31) is called a through-type same-phase power supply system based on the delta connection cascaded multilevel converter, which is suitable for occasions requiring power quality management; The intersection (66) of the delta connection cascaded multilevel converter first chain link and the third chain link is connected to the first terminal (5) of the secondary side winding of the Vv connection type traction transformer; the intersection (67) of the delta connection cascaded multilevel converter second chain link and the third chain link is connected to the third terminal (7) of the secondary side winding of the Vv connection type traction transformer; and the intersection (65) of the delta connection cascaded multilevel converter first chain link and the second chain link is connected to the first terminal (9) of the primary side winding of the first single-phase step-down transformer; Through the control of the current closed loop respectively, the current of the delta connection cascaded multilevel converter first chain link (34) and the current of the delta connection cascaded multilevel converter second chain link (35) are respectively made to be π / 2 out of phase with the voltage between them, so as to achieve the purpose of transmitting the power grid energy, the two ends of the delta connection cascaded multilevel converter third chain link (36) are respectively connected to the first terminal (5) of the secondary side winding of the Vv connection type traction transformer and the third terminal (7) of the secondary side winding of the Vv connection type traction transformer, and through the control of the current loop, the current of the third chain link is made to track the command value, so as to achieve the purpose of power quality management at the power grid side.

2. The through-type same-phase power supply system based on the cascaded multilevel converter according to claim 1, characterized in that: The cascaded multilevel converter further includes a V-shaped cascaded multilevel converter (32) and a rhombic cascaded multilevel converter (33); The chain link is composed of a chain link inductor (43) and a sub-module chain in series; The sub-module chain is composed of a plurality of chain link sub-modules with the same structure cascaded, including a chain link first sub-module (44) to a chain link nth sub-module (45); One side of the chain link inductor (43) is the chain head, and one side of the chain link nth sub-module (45) is the chain tail; The chain link sub-modules in the sub-module chain include two-level H-bridge type sub-modules, neutral-point-clamped three-level H-bridge sub-modules and flying capacitor three-level H-bridge sub-modules; The first single-phase step-down transformer primary side winding second terminal (10) is grounded, and the first single-phase step-down transformer primary side winding first terminal (9) and the first single-phase step-down transformer primary side winding second terminal (10) are connected in parallel with the first filter capacitor (61).

3. The through-type phase power supply system based on the cascaded multi-level converter according to claim 2, characterized in that: The V-shaped cascaded multi-level converter (32) comprises two chain links, namely a V-shaped cascaded multi-level converter first chain link (37) and a V-shaped cascaded multi-level converter second chain link (38); the through-type phase power supply system using the V-shaped cascaded multi-level converter (32) is referred to as a through-type phase power supply system based on the V-shaped cascaded multi-level converter, which is suitable for occasions where power quality treatment is not required; The head of the V-shaped cascaded multi-level converter first chain link (37) and the tail of the V-shaped cascaded multi-level converter second chain link (38) meet at the V-shaped cascaded multi-level converter first chain link and second chain link intersection (68) and are connected to the first single-phase step-down transformer primary side winding first terminal (9); the tail of the V-shaped cascaded multi-level converter first chain link (37) is connected to the Vv connection type traction transformer secondary side winding first terminal (5); and the head of the V-shaped cascaded multi-level converter second chain link (38) is connected to the Vv connection type traction transformer secondary side winding third terminal (7).

4. The through-type phase power supply system based on the cascaded multi-level converter according to claim 2, characterized in that: The diamond-shaped cascaded multi-level converter (33) comprises four chain links, namely a diamond-shaped cascaded multi-level converter first chain link (39); a diamond-shaped cascaded multi-level converter second chain link (40); a diamond-shaped cascaded multi-level converter third chain link (41); and a diamond-shaped cascaded multi-level converter fourth chain link (42); the through-type phase power supply system using the diamond-shaped cascaded multi-level converter (33) is referred to as a through-type phase power supply system based on the diamond-shaped cascaded multi-level converter, which is suitable for occasions where power quality treatment is required; The chain link heads and chain link tails of the four chain links are sequentially connected to form a diamond structure; The diamond-shaped cascaded multi-level converter first chain link and third chain link intersection (70) is connected to the Vv connection type traction transformer secondary side winding first terminal (5); the diamond-shaped cascaded multi-level converter second chain link and fourth chain link intersection (71) is connected to the Vv connection type traction transformer secondary side winding third terminal (7); the diamond-shaped cascaded multi-level converter first chain link and second chain link intersection (69) is connected to the first single-phase step-down transformer primary side winding first terminal (9); and the diamond-shaped cascaded multi-level converter third chain link and fourth chain link intersection (72) is grounded.

5. The through-type phase power supply system based on the cascaded multi-level converter according to claim 2, characterized in that: In the two-level H-bridge sub-module, a first full-control power electronic switch (47) and a second full-control power electronic switch (48) of the two-level H-bridge sub-module are connected in series; a third full-control power electronic switch (49) and a fourth full-control power electronic switch (50) of the two-level H-bridge sub-module are connected in series; a DC side capacitor (46) is connected in parallel with the two series circuits; a connection point (73) of the first full-control power electronic switch (47) and the second full-control power electronic switch (48) and a connection point (74) of the third full-control power electronic switch (49) and the fourth full-control power electronic switch (50) are led out as an AC side port of the H-bridge sub-module; The midpoint clamping type three-level H-bridge sub-module, the midpoint clamping type three-level H-bridge sub-module first full control type power electronic switch (77), the midpoint clamping type three-level H-bridge sub-module second full control type power electronic switch (78), the midpoint clamping type three-level H-bridge sub-module third full control type power electronic switch (79) and the midpoint clamping type three-level H-bridge sub-module fourth full control type power electronic switch (80) are connected in series; the midpoint clamping type three-level H-bridge sub-module fifth full control type power electronic switch (81), the midpoint clamping type three-level H-bridge sub-module sixth full control type power electronic switch (82), the midpoint clamping type three-level H-bridge sub-module seventh full control type power electronic switch (83) and the midpoint clamping type three-level H-bridge sub-module eighth full control type power electronic switch (84) are connected in series; the intersection of the midpoint clamping type three-level H-bridge sub-module DC side first capacitor (75) and the midpoint clamping type three-level H-bridge sub-module DC side second capacitor (76) is the midpoint clamping type three-level H-bridge sub-module DC side midpoint (91), the branch formed by the two capacitors in series is connected in parallel with the two branches formed by the midpoint clamping type three-level H-bridge sub-module in series; the midpoint clamping type three-level H-bridge sub-module first clamping diode (85) and the midpoint clamping type three-level H-bridge sub-module second clamping diode (86) are connected in series and intersect at the connection point (115), one end of the branch formed by the connection is connected to the connection point (92) of the midpoint clamping type three-level H-bridge sub-module first full control type power electronic switch (77) and the midpoint clamping type three-level H-bridge sub-module second full control type power electronic switch (78), and the other end is connected to the connection point (93) of the midpoint clamping type three-level H-bridge sub-module third full control type power electronic switch (79) and the midpoint clamping type three-level H-bridge sub-module fourth full control type power electronic switch (80); the midpoint clamping type three-level H-bridge sub-module third clamping diode (87) and the midpoint clamping type three-level H-bridge sub-module fourth clamping diode (88) are connected in series and intersect at the connection point (116), one end of the branch formed by the connection is connected to the connection point (94) of the midpoint clamping type three-level H-bridge sub-module fifth full control type power electronic switch (81) and the midpoint clamping type three-level H-bridge sub-module sixth full control type power electronic switch (82), and the other end is connected to the connection point (95) of the midpoint clamping type three-level H-bridge sub-module seventh full control type power electronic switch (83) and the midpoint clamping type three-level H-bridge sub-module eighth full control type power electronic switch (84); the midpoint clamping type three-level H-bridge sub-module DC side midpoint (91) is connected with the connection point (115) and the connection point (116); the connection point (89) of the midpoint clamping type three-level H-bridge sub-module second full control type power electronic switch (78) and the midpoint clamping type three-level H-bridge sub-module third full control type power electronic switch (79) and the connection point (90) of the midpoint clamping type three-level H-bridge sub-module sixth full control type power electronic switch (82) and the midpoint clamping type three-level H-bridge sub-module seventh full control type power electronic switch (83) are led out as the midpoint clamping type three-level H-bridge sub-module AC side port; In the flying capacitor type three-level H-bridge sub-module, the flying capacitor type three-level H-bridge sub-module first full-control power electronic switch (98), the flying capacitor type three-level H-bridge sub-module second full-control power electronic switch (99), the flying capacitor type three-level H-bridge sub-module third full-control power electronic switch (100) and the flying capacitor type three-level H-bridge sub-module fourth full-control power electronic switch (101) are connected in series; the flying capacitor type three-level H-bridge sub-module fifth full-control power electronic switch (102), the flying capacitor type three-level H-bridge sub-module sixth full-control power electronic switch (103), the flying capacitor type three-level H-bridge sub-module seventh full-control power electronic switch (104) and the flying capacitor type three-level H-bridge sub-module eighth full-control power electronic switch (105) are connected in series; the intersection of the flying capacitor type three-level H-bridge sub-module DC side first capacitor (96) and the flying capacitor type three-level H-bridge sub-module DC side second capacitor (97) is the flying capacitor type three-level H-bridge sub-module DC side midpoint (110), and the branch formed by the two capacitors in series is connected in parallel with the two branches formed by the flying capacitor type three-level H-bridge sub-module in series; one end of the flying capacitor type three-level H-bridge sub-module first flying capacitor (106) is connected to the connection point (111) of the flying capacitor type three-level H-bridge sub-module first full-control power electronic switch (98) and the flying capacitor type three-level H-bridge sub-module second full-control power electronic switch (99), and the other end is connected to the connection point (112) of the flying capacitor type three-level H-bridge sub-module third full-control power electronic switch (100) and the flying capacitor type three-level H-bridge sub-module fourth full-control power electronic switch (101); one end of the flying capacitor type three-level H-bridge sub-module second flying capacitor (107) is connected to the connection point (113) of the flying capacitor type three-level H-bridge sub-module fifth full-control power electronic switch (102) and the flying capacitor type three-level H-bridge sub-module sixth full-control power electronic switch (103), and the other end is connected to the connection point (114) of the flying capacitor type three-level H-bridge sub-module seventh full-control power electronic switch (104) and the flying capacitor type three-level H-bridge sub-module eighth full-control power electronic switch (105); the connection point (108) of the flying capacitor type three-level H-bridge sub-module second full-control power electronic switch (99) and the flying capacitor type three-level H-bridge sub-module third full-control power electronic switch (100) and the connection point (109) of the flying capacitor type three-level H-bridge sub-module sixth full-control power electronic switch (103) and the flying capacitor type three-level H-bridge sub-module seventh full-control power electronic switch (104) are led out as the flying capacitor type three-level H-bridge sub-module AC side port.

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