Tandem diode rectification topological structure

Abstract

The invention discloses a series diode rectification topological structure which comprises more than two six-pulse converter valves which are connected in series, each six-pulse converter valve is a three-phase bridge type rectification circuit formed by six diodes, the input end of each six-pulse converter valve is connected to an alternating current system, and after all the six-pulse converter valves are connected in series, the input end of each six-pulse converter valve is connected to the alternating current system. Positive and negative output ends are respectively connected to a DC line, and a current-limiting reactor is connected in series between every two six-pulse converter valves connected in series. A plurality of six-pulse converter valves are connected in series, and the reactor is adopted to ensure the normal operation of the system, so that the direct current side voltage is improved, the higher direct current side voltage is obtained by adopting the lower alternating current voltage, the volume and weight increase caused by the use of an alternating current transformer is avoided, and the equipment cost is also saved. The technical problem that a diode rectifier topological structure adopted by an existing offshore wind power sending scheme needs to be connected into a transformer, and consequently the size and the weight are too large is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a series diode rectifier topology structure. Background Art

[0002] Offshore wind power primarily utilizes AC transmission in nearshore areas and DC transmission in offshore areas, with individual projects boasting capacities of approximately one million kilowatts. With nearshore offshore wind power development reaching its peak, deep-sea offshore wind power is the focus of future offshore wind power development. AC transmission solutions are insufficient for large-scale deep-sea offshore wind power development, while traditional DC transmission solutions struggle to meet the economic demands of large-scale offshore wind power development. Therefore, it is necessary to explore new, low-cost transmission solutions to provide new technological options for deep-sea offshore wind power development.

[0003] To adapt to various application scenarios and reduce transmission project costs, existing technologies have proposed a variety of transmission solutions with different characteristics, including the use of unidirectional current-type uncontrolled rectifier converters based on diode elements at the transmission end, DC fan aggregation and boost transmission, low-frequency output, etc. The use of unidirectional current-type uncontrolled rectifier converters based on diode elements helps to achieve lightweight and miniaturization. Usually, in order to reduce the harmonics of the diode, a twelve-pulse form is adopted. The structure of the twelve-pulse rectifier based on diodes is as follows: Figure 1 As shown, YY and YD connection transformers must be used. The structure of the six-pulse rectifier based on diodes is as follows Figure 2 As shown, when the AC side is connected to a low-voltage system, a transformer is still required to increase the AC voltage on the DC side. Whether using the existing twelve-pulse rectifier structure or the six-pulse rectifier structure, the presence of the transformer still results in excessive size and weight for small-capacity diode systems. Summary of the Invention

[0004] The present invention provides a series diode rectifier topology structure, which is used to solve the technical problem that the diode rectifier topology structure adopted in the existing offshore wind power transmission solution needs to be connected to a transformer, resulting in excessive volume and weight.

[0005] In view of this, the present invention provides a series diode rectifier topology structure, comprising two or more six-pulsation converter valves connected in series;

[0006] The six-pulsation converter valve is a three-phase bridge rectifier circuit composed of six diodes;

[0007] The input end of each six-pulsation converter valve is connected to the AC system. After all six-pulsation converter valves are connected in series, the positive and negative output ends are connected to the DC line respectively.

[0008] A current-limiting reactor is connected in series between every two six-pulsation converter valves.

[0009] Optionally, the inductance value of the current limiting reactor is:

[0010]

[0011] Where, L is the inductance of the current limiting reactor, is the effective value of the AC system line voltage, is the fundamental angular frequency, is the rated current of the six-pulsation converter valve.

[0012] Optionally, it also includes a wave blocking capacitor and a damping resistor;

[0013] The surge-blocking capacitor is connected in parallel with the current-limiting reactor, and the damping resistor is connected in parallel with the surge-blocking capacitor.

[0014] Optionally, the capacitance value of the wave blocking capacitor is:

[0015]

[0016] Where C is the capacitance of the surge-blocking capacitor, and f is the rated power of the AC system.

[0017] Optionally, the wave-blocking capacitor is a 300 Hz wave-blocking capacitor.

[0018] Optionally, the damping resistor has a resistance value of:

[0019]

[0020] Where R is the resistance value of the damping resistor, is the harmonic coefficient, is the permissible coefficient of harmonic current, is the power frequency shunt coefficient, is the angular frequency change.

[0021] Optionally, the harmonic coefficient has a value of 0.2 to 0.4.

[0022] Optionally, the permissible harmonic current coefficient is set to a value between 0.05 and 0.1.

[0023] Optionally, the power frequency shunt coefficient is set to a value of 1.5 to 2.

[0024] Optionally, a lightning arrester is further included, and the lightning arrester is connected in parallel with the damping resistor.

[0025] From the above technical solutions, it can be seen that the series diode rectifier topology provided by the present invention has the following advantages:

[0026] The series diode rectifier topology provided by the present invention includes two or more six-pulse converter valves connected in series. The six-pulse converter valves are three-phase bridge rectifier circuits composed of six diodes. The input of each six-pulse converter valve is connected to the AC system. After all six-pulse converter valves are connected in series, the positive and negative output terminals are connected to the DC line respectively. A current-limiting reactor is connected in series between every two six-pulse converter valves in series. The series connection of multiple six-pulse converter valves and the use of current-limiting reactors ensure the normal operation of the system, increase the DC side voltage, and achieve a higher DC side voltage using a lower AC voltage. This avoids the increased size and weight caused by the use of an AC transformer, saving equipment costs. This solves the technical problem of the diode rectifier topology used in existing offshore wind power transmission solutions, which requires the connection of a transformer, resulting in excessive size and weight.

[0027] At the same time, the series diode rectifier topology provided by the present invention optimizes the circuit structure of the current limiting reactor part. A wave-blocking capacitor is connected in parallel to the current limiting reactor for wave blocking, a damping resistor is connected in parallel for improving the quality factor of the system, and a lightning arrester is connected in parallel for limiting the voltage between the terminals of the current limiting reactor under transient conditions, thereby reducing equipment costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 Schematic diagram of the structure of an existing diode-based twelve-pulse rectifier;

[0030] Figure 2 Schematic diagram of the structure of an existing diode-based six-pulse rectifier;

[0031] Figure 3 A wiring diagram of a series diode rectifier topology structure provided in an embodiment of the present invention;

[0032] Figure 4 A schematic diagram of the connection of a current-limiting reactor connected in series between six pulsating converter valves provided in an embodiment of the present invention;

[0033] Figure 5 This is a schematic diagram of the circuit structure of the current-limiting reactor provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0035] For easier understanding, see Figure 3 and Figure 4 , the present invention provides an embodiment of a series diode rectifier topology structure, comprising two or more six-pulsation converter valves connected in series;

[0036] The six-pulsation converter valve is a three-phase bridge rectifier circuit composed of six diodes;

[0037] The input end of each six-pulsation converter valve is connected to the AC system. After all six-pulsation converter valves are connected in series, the positive and negative output ends are connected to the DC line respectively.

[0038] A current-limiting reactor is connected in series between every two six-pulsation converter valves.

[0039] It should be noted that in the embodiment of the present invention, two or more six-pulse converter valves are connected in series, with the input of each six-pulse converter valve connected to the AC system. After all six-pulse converter valves are connected in series, the positive and negative output terminals are connected to the DC line respectively, and a current-limiting reactor is connected in series between every two six-pulse converter valves in series. The DC voltage expression of the series-connected six-pulse converter valves is:

[0040]

[0041] in, is the DC voltage of the six-pulsation converter valve in series, n is the number of six-pulsation converter valves, is the effective value of the AC system line voltage.

[0042] Based on the above six-pulse converter valve series structure, the DC side voltage can be increased, that is, a lower AC voltage can be used to achieve a higher DC side voltage, but a current limiting reactor must be used, such as Figure 4 As shown, the black diodes (i.e., D1, D4, D7, and D10) are conducting during operation. When diodes D4 and D7 conduct, phases B and A short-circuit, causing the six-pulse converter valve and AC system to experience high short-circuit currents. Therefore, current-limiting reactors are required to limit the short-circuit current and ensure normal system operation.

[0043] The six-pulse converter valve can also be a three-phase bridge rectifier circuit composed of six thyristors or IGBTs, but the volume and weight of the three-phase bridge rectifier circuit composed of six thyristors or IGBTs exceed the three-phase bridge rectifier circuit composed of six diodes.

[0044] The series diode rectifier topology provided by the present invention includes two or more six-pulse converter valves connected in series. The six-pulse converter valves are three-phase bridge rectifier circuits composed of six diodes. The input of each six-pulse converter valve is connected to the AC system. After all six-pulse converter valves are connected in series, the positive and negative output terminals are connected to the DC line respectively. A current-limiting reactor is connected in series between every two six-pulse converter valves in series. The series connection of multiple six-pulse converter valves and the use of current-limiting reactors ensure the normal operation of the system, increase the DC side voltage, and achieve a higher DC side voltage using a lower AC voltage. This avoids the increased size and weight caused by the use of an AC transformer, saving equipment costs. This solves the technical problem of the diode rectifier topology used in existing offshore wind power transmission solutions, which requires the connection of a transformer, resulting in excessive size and weight.

[0045] In one embodiment, the inductance of the current limiting reactor is:

[0046]

[0047] Where, L is the inductance of the current limiting reactor, is the effective value of the AC system line voltage, is the fundamental angular frequency, is the rated current of the six-pulsation converter valve.

[0048] In one embodiment, when a 6-pulse diode commutation valve is in operation, the system will generate 6-fold frequency harmonics, which will cause the harmonics of the connected system to exceed the standard. In the prior art, an AC filter is usually added on the AC side to achieve filtering. However, the added filter on the AC side is large in size and weight, and the cost is relatively high. To solve this problem, Figure 5 As shown, in the embodiment of the present invention, a wave-blocking capacitor can be connected in parallel with the current-limiting reactor, and a damping resistor can be connected in parallel with the wave-blocking capacitor. The wave-blocking capacitor is a 300Hz wave-blocking capacitor used for 300Hz wave blocking. The capacitance value of the wave-blocking capacitor is:

[0049]

[0050] Where C is the capacitance of the surge-blocking capacitor, and f is the rated power of the AC system.

[0051] Damping resistors are used to improve the quality factor of the system. The resistance value of the damping resistor is:

[0052]

[0053] Where R is the resistance value of the damping resistor, is the harmonic coefficient, is the permissible coefficient of harmonic current, is the power frequency shunt coefficient, is the change in angular frequency. Harmonic coefficient The value is 0.2~0.4. Harmonic current allowable coefficient The value is 0.05~0.1. Power frequency shunt coefficient The value is 1.5~2.

[0054] In one embodiment, a lightning arrester is connected in parallel to the damping resistor. The lightning arrester is used to limit the voltage between the terminals of the current-limiting reactor in a transient state, thereby reducing equipment costs.

[0055] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A series diode rectifier topology, characterized in that: including two or more six-pulsation converter valves connected in series; The six-pulsation converter valve is a three-phase bridge rectifier circuit composed of six diodes; The input end of each six-pulsation converter valve is connected to the AC system. After all six-pulsation converter valves are connected in series, the positive and negative output ends are connected to the DC line respectively. A current-limiting reactor is connected in series between every two six-pulsation converter valves.

2. The series diode rectifier topology structure according to claim 1, characterized in that: The inductance of the current limiting reactor is: Where, L is the inductance of the current limiting reactor, is the effective value of the AC system line voltage, is the fundamental angular frequency, is the rated current of the six-pulsation converter valve.

3. The series diode rectifier topology structure according to claim 2, characterized in that: It also includes wave-blocking capacitors and damping resistors; The surge-blocking capacitor is connected in parallel with the current-limiting reactor, and the damping resistor is connected in parallel with the surge-blocking capacitor.

4. The series diode rectifier topology structure according to claim 3, characterized in that: The capacitance value of the wave blocking capacitor is: Where C is the capacitance of the surge-blocking capacitor, and f is the rated power of the AC system.

5. The series diode rectifier topology structure according to claim 3, characterized in that: The wave blocking capacitor is a 300Hz wave blocking capacitor.

6. The series diode rectifier topology structure according to claim 3, characterized in that: The resistance value of the damping resistor is: Where R is the resistance value of the damping resistor, is the harmonic coefficient, is the permissible coefficient of harmonic current, is the power frequency shunt coefficient, is the angular frequency change.

7. The series diode rectifier topology structure according to claim 6, characterized in that: The harmonic coefficient value is 0.2~0.

4.

8. The series diode rectifier topology structure according to claim 6, characterized in that: The permissible harmonic current coefficient is 0.05~0.

1.

9. The series diode rectifier topology structure according to claim 6, characterized in that: The value of the power frequency shunt coefficient is 1.5~2.

10. The series diode rectifier topology structure according to claim 3, characterized in that: A lightning arrester is also included, which is connected in parallel with a damping resistor.

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