A cascaded 24-pulse converter topology

Abstract

The present invention relates to the field of power electronics technology, and specifically to a cascaded 24-pulse converter topology, including a dual Y pulse generator, a phase-shifting transformer group, a four-quadrant 24-pulse converter group and a resistive-inductive load, wherein the dual Y pulse generator is connected to one end of the phase-shifting transformer group, the other end of the phase-shifting transformer is connected to one end of the four-quadrant 24-pulse converter group, and the other end of the four-quadrant 24-pulse converter group is connected to the resistive-inductive load. The device can effectively suppress circulating current, eliminate the need for an external circulating current reactor, save costs, and reduce volume. Once a converter fault occurs and the circulating current is out of control, it will only affect the converter connected in parallel with the fault converter, and will not affect the remaining converters, thereby protecting the other converters to the maximum extent; four-quadrant operation can be achieved; the connection method between the transformer and the converter makes the grid side and the transformer load balanced, the transformer load is small, and the circulating current will not flow through the two secondary sides of the same transformer at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a cascaded 24-pulse converter topology. Background Art

[0002] HL-2M is my country's magnetic confinement nuclear fusion tokamak device. In the tokamak device, plasma control is a very important task. Every plasma discharge and in-depth physical experiment needs to be based on plasma control. Plasma is the fourth state of matter different from solid, liquid and gas. When conducting physical experiments, plasma will move rapidly up or down in the vertical direction. In order to prevent the plasma from disappearing due to hitting the wall, active feedback is required to control it, generate a magnetic field in the horizontal direction to control the vertical displacement of the plasma, so that the plasma can be stabilized in the horizontal direction to ensure the smooth progress of the physical experiment.

[0003] The main task of the cascaded four-quadrant 24-pulse converter topology proposed in the present invention is to solve the vertical instability control of plasma. The power supply responds quickly when the coil current needs to change positively or negatively, and outputs the required current in time.

[0004] In the prior art, 12-pulse converters, 24-pulse converters and H-bridge cascades can be used as fast-control power supply topologies, but the shortcomings of the 12-pulse converter are: low output frequency, high harmonic content, and the actual capacity of the transformer is too large, resulting in a huge transformer volume. The shortcomings of the conventional 24-pulse converter are: most conventional 24-pulse converters use parallel 24-pulse converters, and the output voltage is not high enough. Due to the single voltage source power supply and four converters in parallel, the circulating current value will be very large. In order to suppress the circulating current, a large-capacity circulating current reactor needs to be added, which is not only costly but also large in size. The shortcomings of the H-bridge cascade are: the structure requires multiple H-bridge modules to be connected in series and parallel, the topology is relatively complex, resulting in high cost, more output levels, larger ripples, and relatively complex control. Summary of the invention

[0005] The purpose of the present invention is to provide a cascaded 24-pulse converter topology to effectively increase the output frequency, which is twice that of the 12-pulse converter; reduce the harmonic content, the higher the pulse number, the lower the harmonic content; and achieve stepless voltage regulation, small voltage pulsation, smoother output voltage, adjustable power factor, and small ripple. At the same time, the four-quadrant 24-pulse converter can meet the total harmonic distortion (THD) △THD<5% requirement of IEEE Standard 519 1992.

[0006] The technical solution of the present invention is as follows:

[0007] A cascaded 24-pulse converter topology includes a dual Y pulse generator 1, a phase-shifting transformer group, a four-quadrant 24-pulse converter group and a resistive-inductive load 14, wherein the dual Y pulse generator 1 is connected to one end of the phase-shifting transformer group, the other end of the phase-shifting transformer is connected to one end of the four-quadrant 24-pulse converter group, and the other end of the four-quadrant 24-pulse converter group is connected to the resistive-inductive load 14;

[0008] The phase-shifting transformer group includes a three-phase double-winding transformer A2, a three-phase double-winding transformer B3, a three-phase double-winding transformer C4, and a three-phase double-winding transformer D5;

[0009] The four-quadrant 24-pulse converter group includes two converter groups, the positive group includes positive converter A6, positive converter B8, positive converter C10, and positive converter D12, and the negative group includes negative converter A7, negative converter B9, negative converter C11, and negative converter D13.

[0010] The primary side phase shift of three-phase double-winding transformer 2 is +7.5°, and the secondary side is in delta connection and star connection respectively; the primary side phase shift of three-phase double-winding transformer 3 is -7.5°, and the secondary side is in delta connection and star connection respectively; the primary side phase shift of three-phase double-winding transformer 4 is +7.5°, and the secondary side is in delta connection and star connection respectively; the primary side phase shift of three-phase double-winding transformer 5 is -7.5°, and the secondary side is in delta connection and star connection respectively.

[0011] The incoming line voltages of the three-phase double-winding transformer A2 and the three-phase double-winding transformer C4 differ by 30°, and the incoming line voltages of the three-phase double-winding transformer B3 and the three-phase double-winding transformer D5 differ by 30°; the incoming line voltages of the three-phase double-winding transformer A2 and the three-phase double-winding transformer D5 are in phase, and the incoming line voltages of the three-phase double-winding transformer B3 and the three-phase double-winding transformer C4 are in phase.

[0012] The triangle secondary side of the three-phase dual-winding transformer A2 is connected to the positive group converter A6, and the star secondary side is connected to the negative group converter B9; the triangle secondary side of the three-phase dual-winding transformer B3 is connected to the negative group converter C11, and the star secondary side is connected to the positive group converter D12; the triangle secondary side of the three-phase dual-winding transformer C4 is connected to the positive group converter B8, and the star secondary side is connected to the negative group converter A7; the triangle secondary side of the three-phase dual-winding transformer D5 is connected to the negative group converter D13, and the star secondary side is connected to the positive group converter C10.

[0013] The positive group converter A6 is connected in reverse parallel with the negative group converter A7; the positive group converter B8 is connected in reverse parallel with the negative group converter B9; the positive group converter C10 is connected in reverse parallel with the negative group converter C11; the positive group converter D12 is connected in reverse parallel with the negative group converter D13.

[0014] Positive group converter A6, positive group converter B8, positive group converter C10, and positive group converter D12 are connected in series, and negative group converter A7, negative group converter B9, negative group converter C11, and negative group converter D13 are connected in series;

[0015] The positive output of the positive group current transformer A6 is connected to the positive input of the resistive-inductive load 14 , and the negative output of the positive group current transformer D12 is connected to the negative input of the resistive-inductive load 14 .

[0016] The three-phase double-winding transformers are all step-down transformers with a transformation ratio of 3000 / 476. The high voltage output by the generator is stepped down and sent to the converter.

[0017] The converters are all three-phase full-bridge rectifier structures, and the devices are thyristors.

[0018] The beneficial effects of the present invention are:

[0019] Two groups of Y generators staggered 30° are used for power supply. Due to the large impedance of the generator, the circulating current can be effectively suppressed, eliminating the need for external circulating current reactors, saving costs and reducing size.

[0020] Since the positive and negative groups of converters are connected in parallel and then in series, once a converter fault occurs and the loop is out of control, it will only affect the converter connected in parallel with the faulty converter, but will have no effect on the remaining converters, thus protecting the other converters to the maximum extent.

[0021] Since the positive and negative converter groups work together, four-quadrant operation can be achieved.

[0022] The connection method between the transformer and the converter makes the grid side and the transformer load balanced, the transformer load is small, and the circulating current does not flow through the two secondary sides of the same transformer at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of the specific structure of a cascaded four-quadrant 24-pulse converter topology of the present invention;

[0024] Figure 2 Based Figure 2 It is the waveform of output current and given current.

[0025] Figure 1 Among them, 1. Double Y pulse generator, 2. Three-phase double-winding transformer A, 3. Three-phase double-winding transformer B, 4. Three-phase double-winding transformer C, 5. Three-phase double-winding transformer D, 6. Positive group converter A, 8. Positive group converter B, 10. Positive group converter C, 12. Positive group converter D, 7. Negative group converter A, 9. Negative group converter B, 11. Negative group converter C, 13. Negative group converter D, 14. Resistive and inductive load. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] A cascaded 24-pulse converter topology includes a dual Y-pulse generator 1, a phase-shifting transformer group, a four-quadrant 24-pulse converter group and a resistive-inductive load 14. The dual Y-pulse generator 1 is connected to one end of the phase-shifting transformer group, the other end of the phase-shifting transformer is connected to one end of the four-quadrant 24-pulse converter group, and the other end of the four-quadrant 24-pulse converter group is connected to the resistive-inductive load 14.

[0028] The phase-shifting transformer group includes three-phase double-winding transformer A2, three-phase double-winding transformer B3, three-phase double-winding transformer C4, and three-phase double-winding transformer D5. The above three-phase double-winding transformers are all step-down transformers with a transformation ratio of 3000 / 476. They step down the high voltage output by the generator and send it to the converter.

[0029] The primary side phase shift of three-phase double-winding transformer 2 is +7.5°, and the secondary side is in delta connection and star connection respectively; the primary side phase shift of three-phase double-winding transformer 3 is -7.5°, and the secondary side is in delta connection and star connection respectively; the primary side phase shift of three-phase double-winding transformer 4 is +7.5°, and the secondary side is in delta connection and star connection respectively; the primary side phase shift of three-phase double-winding transformer 5 is -7.5°, and the secondary side is in delta connection and star connection respectively.

[0030] The incoming line voltages of the three-phase double-winding transformer A2 and the three-phase double-winding transformer C4 differ by 30°, and the incoming line voltages of the three-phase double-winding transformer B3 and the three-phase double-winding transformer D5 differ by 30°; the incoming line voltages of the three-phase double-winding transformer A2 and the three-phase double-winding transformer D5 are in phase, and the incoming line voltages of the three-phase double-winding transformer B3 and the three-phase double-winding transformer C4 are in phase.

[0031] The four-quadrant 24-pulse converter group includes two converter groups, the positive group includes positive converter A6, positive converter B8, positive converter C10, and positive converter D12, and the negative group includes negative converter A7, negative converter B9, negative converter C11, and negative converter D13.

[0032] The above converters are all three-phase full-bridge rectifier structures, and the devices used are thyristors.

[0033] The triangle secondary side of the three-phase dual-winding transformer A2 is connected to the positive group converter A6, and the star secondary side is connected to the negative group converter B9; the triangle secondary side of the three-phase dual-winding transformer B3 is connected to the negative group converter C11, and the star secondary side is connected to the positive group converter D12; the triangle secondary side of the three-phase dual-winding transformer C4 is connected to the positive group converter B8, and the star secondary side is connected to the negative group converter A7; the triangle secondary side of the three-phase dual-winding transformer D5 is connected to the negative group converter D13, and the star secondary side is connected to the positive group converter C10.

[0034] The positive group converter A6 is connected in reverse parallel with the negative group converter A7; the positive group converter B8 is connected in reverse parallel with the negative group converter B9; the positive group converter C10 is connected in reverse parallel with the negative group converter C11; the positive group converter D12 is connected in reverse parallel with the negative group converter D13.

[0035] Positive group converter A6, positive group converter B8, positive group converter C10, and positive group converter D12 are connected in series, and negative group converter A7, negative group converter B9, negative group converter C11, and negative group converter D13 are connected in series.

[0036] The positive output of the positive group current transformer A6 is connected to the positive input of the resistive-inductive load 14 , and the negative output of the positive group current transformer D12 is connected to the negative input of the resistive-inductive load 14 .

[0037] The working mode is that when the current is positive, only the positive group of current transformers A6, B8, C10 and D12 are put into operation; when the current is negative, only the negative group of current transformers A7, B9, C11 and D13 are put into operation; when the current is about to cross zero, the positive group of current transformers A6, 8B, C10 and D12 and the negative group of current transformers A7, B9, C11 and D13 are put into operation at the same time, and the logic belt circulation operation mode is adopted to realize four-quadrant operation.

[0038] When the positive group converter A6, the positive group converter B8, the positive group converter C10, the positive group converter D12 or the negative group converter A7, the negative group converter B9, the negative group converter C11, and the negative group converter D13 work alone, all four transformers are put into operation, so the grid side and the transformer load are balanced, and the load on each transformer is small.

[0039] When the positive group converter A6, the positive group converter B8, the positive group converter C10, the positive group converter D12 and the negative group converter A7, the negative group converter B9, the negative group converter C11, and the negative group converter D13 are working at the same time, that is, when there is circulating current, the circulating current will not flow through the two secondary sides of the same transformer at the same time. The circulating current will only flow through two converters at the same time, and the circulating current will not flow through the same Y of the generator.

[0040] There are only two types of three-phase double-winding transformer A2, three-phase double-winding transformer B3, three-phase double-winding transformer C4 and three-phase double-winding transformer D5, i.e., primary side phase shift ±7.5°, which reduces the cost.

[0041] When the current waveform needs to change according to a given value, a negative feedback module is added to the circuit. The output current has good followability and a response speed of several hundred amperes per millisecond. Figure 2As shown in the figure, it can be seen that the output current is almost completely consistent with the given current, and has good tracking performance. At the same time, the current can be smoothly zero-crossed.

Claims

1. A cascaded 24-pulse converter topology, comprising a dual Y-pulse generator (1), a phase-shifting transformer group, a four-quadrant 24-pulse converter group and a resistive-inductive load (14), wherein the dual Y-pulse generator (1) is connected to one end of the phase-shifting transformer group, the other end of the phase-shifting transformer is connected to one end of the four-quadrant 24-pulse converter group, and the other end of the four-quadrant 24-pulse converter group is connected to the resistive-inductive load (14); Features: The phase-shifting transformer group includes a three-phase double-winding transformer A (2), a three-phase double-winding transformer B (3), a three-phase double-winding transformer C (4), and a three-phase double-winding transformer D (5); The four-quadrant 24-pulse converter group includes two converter groups, the positive group includes a positive converter group A (6), a positive converter group B (8), a positive converter group C (10), and a positive converter group D (12), and the negative group includes a negative converter group A (7), a negative converter group B (9), a negative converter group C (11), and a negative converter group D (13); The primary phase of the three-phase double-winding transformer A (2) is +7.5°, and the secondary is connected in a delta connection and a star connection respectively; the primary phase of the three-phase double-winding transformer B (3) is -7.5°, and the secondary is connected in a delta connection and a star connection respectively; the primary phase of the three-phase double-winding transformer C (4) is +7.5°, and the secondary is connected in a delta connection and a star connection respectively; the primary phase of the three-phase double-winding transformer D (5) is -7.5°, and the secondary is connected in a delta connection and a star connection respectively; The line voltages of the three-phase double-winding transformer A (2) and the three-phase double-winding transformer C (4) differ by 30°, and the line voltages of the three-phase double-winding transformer B (3) and the three-phase double-winding transformer D (5) differ by 30°; the line voltages of the three-phase double-winding transformer A (2) and the three-phase double-winding transformer D (5) are in phase, and the line voltages of the three-phase double-winding transformer B (3) and the three-phase double-winding transformer C (4) are in phase; The triangle secondary side of the three-phase double-winding transformer A (2) is connected to the positive group converter A (6), and the star secondary side is connected to the negative group converter B (9); The triangle secondary side of the three-phase double-winding transformer B (3) is connected to the negative group converter C (11), and the star secondary side is connected to the positive group converter D (12); the triangle secondary side of the three-phase double-winding transformer C (4) is connected to the positive group converter B (8), and the star secondary side is connected to the negative group converter A (7); the triangle secondary side of the three-phase double-winding transformer D (5) is connected to the negative group converter D (13), and the star secondary side is connected to the positive group converter C (10); The positive group converter A (6) and the negative group converter A (7) are connected in reverse parallel; the positive group converter B (8) and the negative group converter B (9) are connected in reverse parallel; the positive group converter C (10) and the negative group converter C (11) are connected in reverse parallel; the positive group converter D (12) and the negative group converter D (13) are connected in reverse parallel; A positive group converter A (6), a positive group converter B (8), a positive group converter C (10), and a positive group converter D (12) are connected in series, and a negative group converter A (7), a negative group converter B (9), a negative group converter C (11), and a negative group converter D (13) are connected in series; The positive output of the positive group converter A (6) is connected to the positive input of the resistive-inductive load (14), and the negative output of the positive group converter D (12) is connected to the negative input of the resistive-inductive load (14).

2. A cascaded 24-pulse converter topology as claimed in claim 1, characterized in that: The three-phase double-winding transformers are all step-down transformers with a transformation ratio of 3000 / 476. The high voltage output by the generator is stepped down and sent to the converter.

3. A cascaded 24-pulse converter topology as claimed in claim 1, characterized in that: The converters are all three-phase full-bridge rectifier structures, and the devices are thyristors.

4. A cascaded 24-pulse converter topology as claimed in claim 1, characterized in that: A negative feedback module is added to the circuit.

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