A high voltage direct current converter and an accelerated commutation method thereof

Abstract

This invention proposes a high-voltage direct current (HVDC) converter and its accelerated commutation method. It involves modifying each arm of an existing conventional HVDC converter by adding arm-coupled reactors or replacing existing anode reactors with arm-coupled reactors. The implementation is very simple, straightforward, and low-cost. The beneficial effects of this invention are: by configuring arm-coupled reactors with a certain value, the commutation process is accelerated, the commutation overlap angle is reduced, thereby expanding the operating range of the HVDC converter, increasing the transmittable power, and reducing power loss; it can even rely on the commutation voltage created by the arm-coupled reactors to perform voltage compensation when the AC voltage unexpectedly drops, thereby suppressing commutation failure. In HVDC transmission applications, this invention exhibits excellent economic efficiency and reliability, enhancing its contribution to the national economy.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and specifically relates to a high-voltage DC converter and its accelerated switching method. Background Technology

[0002] High Voltage Direct Current (HVDC) transmission technology is widely used worldwide due to its advantages such as large transmission capacity, low loss, and high reliability. Current conventional HVDC converters utilize a three-phase bridge with six arms composed of thyristors as the basic unit for AC-DC conversion. During operation, current commutates between the six thyristor arms. Each arm, in addition to the thyristor valve string, contains an anode reactor to limit the rate of current change, thus ensuring the safety and reliability of the thyristor devices. Commutation occurs between the arms. However, the existing arm commutation process is slow, lengthy, and results in significant power loss, which is detrimental to the performance optimization of HVDC converters. Summary of the Invention

[0003] To address the aforementioned problems, this invention proposes a high-voltage direct current converter in which coupled bridge arm reactors are connected in the bridge arm.

[0004] The present invention also protects the circuit of the high voltage DC converter: the converter circuit includes a first bridge arm and a third bridge arm connected in series, and a second bridge arm is connected in parallel on the first bridge arm;

[0005] Coupled bridge arm reactors are installed in the first bridge arm, the second bridge arm, and the third bridge arm. The coupled bridge arm reactors on the first bridge arm and the second bridge arm are coupled to each other.

[0006] Specifically, both the first and second bridge arms include a series of thyristor valve strings and a turn-off valve string connected in series, and the coupling bridge arm reactor is connected to the cathode side of the thyristor valve string.

[0007] Specifically, the third bridge arm includes a thyristor valve string and a turn-off valve string connected in series, and the coupling bridge arm reactor of the third bridge arm is connected to the anode side of the turn-off valve string.

[0008] Specifically, the shut-off valve string includes one or more of the following power electronic devices: IGCT, GTO, IGBT, and IEGT.

[0009] Specifically, the first bridge arm, the second bridge arm, and the third bridge arm all include thyristor valve strings. The coupling bridge arm reactors of the first and second bridge arms are connected to the cathode side of the thyristor valve strings, and the coupling bridge arm reactor of the third bridge arm is connected to the anode side of the thyristor valve strings.

[0010] Specifically, the first bridge arm, the second bridge arm, and the third bridge arm each include a shut-off valve string. The coupling bridge arm reactors of the first and second bridge arms are connected to the cathode side of the shut-off valve string, and the coupling bridge arm reactor of the third bridge arm is connected to the anode side of the shut-off valve string.

[0011] The present invention also provides an accelerated switching method for a high-voltage direct current converter, which uses the high-voltage direct current converter protected by the present invention.

[0012] The high-voltage direct current converter of the present invention can be implemented by modifying each arm of an existing conventional high-voltage direct current converter by adding arm coupling reactors or replacing the existing anode reactors with arm coupling reactors. This is very simple, easy, and low-cost, yet achieves the following beneficial effects: by configuring arm coupling reactors of a certain value, the arm commutation process is accelerated, the commutation overlap angle is reduced, thereby expanding the operating range of the high-voltage direct current converter, increasing the transmittable power, and reducing power loss; it can even rely on the commutation voltage created by the arm coupling reactors to perform voltage compensation when the AC voltage unexpectedly drops, thereby suppressing commutation failure. In high-voltage direct current (HVDC) transmission applications, it has excellent economic efficiency and reliability, enhancing its contribution to the national economy.

[0013] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 A schematic diagram of the topology of a high-voltage DC converter with accelerated commutation according to an embodiment of the present invention is shown;

[0016] Figure 2 A simplified circuit diagram of the bridge arm commutation of a high-voltage DC converter in an embodiment of the present invention is shown. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] In high-voltage direct current (HVDC) transmission, the commutation process, including the commutation overlap angle, must be considered in the HVDC converter's control method to ensure that commutation between each bridge arm is completed each time. Theoretically, the smaller the commutation overlap angle, the wider the operating range of the HVDC converter, the greater the power it can transmit, and the lower the power loss.

[0019] The purpose of this invention is to propose a high-voltage direct current converter that can accelerate commutation. Essentially, it utilizes coupled reactance to create additional voltage. Compared with current conventional high-voltage direct current converters, it can accelerate the commutation process between bridge arms, reduce commutation time, and reduce commutation overlap angle, thereby expanding the control operating range of the high-voltage direct current converter and increasing the transmittable power. It has excellent economy and reliability in application.

[0020] This invention proposes a high-voltage DC converter that can accelerate commutation. Figure 1 A schematic diagram of the topology of a high-voltage DC converter with accelerated commutation according to an embodiment of the present invention is shown. Figure 1 In the diagram, P represents the DC positive terminal, N represents the DC negative terminal, and ABC represents three-phase AC. Each bridge arm contains a coupling bridge arm reactor. Bridge arms Ap, Bp, and Cp are all located near the DC positive terminal and are connected to the DC positive terminal through the coupling bridge arm reactor. Bridge arms An, Bn, and Cn are all located near the DC negative terminal and are connected to the DC negative terminal through the coupling bridge arm reactor.

[0021] The reactors contained in bridge arms Ap, Bp, and Cp are coupled to each other, and the reactors contained in bridge arms An, Bn, and Cn are coupled to each other.

[0022] Figure 1 In the bridge arm, both bridge arms Ap and An include thyristor valve strings and turn-off transistor valve strings. Bridge arm Ap is connected in series with bridge arm An. The coupling bridge arm reactor is connected to the positive DC terminal, and its other end is connected to the cathode of the thyristor valve string. The thyristors (S1, S2...S... k ) and turn-off tubes (Q1, Q2...Q mThe ratio of the two can be 0%-100% for each other. The anode of the last thyristor in series is connected to the cathode of the first turn-off tube in series. The anode of the turn-off tube valve string of bridge arm Ap is connected to the three-phase AC connection point. The cathode of the thyristor valve string of bridge arm An is connected to the three-phase AC connection point. The anode of the thyristor valve string of bridge arm An is connected to the cathode of the turn-off tube valve string. The anode of the turn-off tube valve string of bridge arm An is connected to the coupling bridge arm reactor. The other end of the coupling bridge arm reactor is connected to the DC negative terminal.

[0023] Specifically, the turn-off valve string can be composed of one or more of the following power electronic devices with bidirectional voltage bearing and turn-off capability: IGCT (Integrated Gate-Commutated Thyristor), GTO (Gate-Turn-Off Thyristor), IGBT (Insulated Gate Bipolar Transistor), or IEGT (Injection Enhanced Gate Transistor). Alternatively, it can be composed of a series combination of IGCT, GTO, IGBT, or IEGT devices without bidirectional voltage bearing capability and a diode.

[0024] In each bridge arm, the thyristor valve string and the turn-off valve string can exist alone or not at all, or the thyristor valve string and the turn-off valve string can exist simultaneously, with each of them having a ratio of 0% to 100%, and the sum being 100%.

[0025] This invention also provides an accelerated switching method for a high-voltage direct current converter, using the high-voltage direct current converter described in this invention.

[0026] The working principle of the new converter is also explained in this embodiment of the invention. Figure 2 A simplified circuit diagram of the bridge arm commutation of a high-voltage DC converter in an embodiment of the present invention is shown. During bridge arm commutation, Figure 2 In the diagram, Ap, Bp, and Cn are the bridge arms used in the analysis example, Id is the DC current, and Ia, Ib, and Ic are the AC currents. COMMUTATION For the commutation current, L Y Lc is the coupling reactance of the bridge arm, and Lc is the original anode reactance of the bridge arm. The commutation power of the bridge arm comes from the AC electromotive force U. AB The electromotive force forces current to commutate between bridge arms Ap and Bp. During commutation, the coupling reactance L increases due to the current changes in Ia and Ib. Y An induced voltage will be generated, and the direction of the induced voltage is perpendicular to that of bridge arm Ap to bridge arm Bp. The induced voltage will be superimposed on the AC electromotive force U.AB Increasing the commutation voltage accelerates the commutation process and reduces the commutation overlap angle.

[0027] Specifically, initially, the current Ia is the rated current Id, the current Ib is 0, and Ic is also the rated current Id. After commutation begins, Ia gradually decreases, Ib gradually increases, and Ic remains constant at the rated current Id. During the commutation process, the sum of the values ​​of Ia and Ib equals the rated current Id. At the end of the commutation, the current Ia is 0, and the current Ib is the rated current Id.

[0028] In the specific commutation process, embodiments of the present invention modify each arm of an existing conventional HVDC converter by adding an arm-coupling reactor or replacing the existing anode reactor with an arm-coupling reactor. The anode reactor is also identified as the reactor shown in the figure. However, in existing conventional HVDC converters, the anode reactor only serves a current-limiting function and has no corresponding terminal; the reactors between each arm do not have coupling. The purpose of this invention is to create coupling between the reactors, enabling them to couple out the commutation voltage and accelerate the commutation process.

[0029] This invention provides a high-voltage DC converter that can accelerate commutation, wherein the bridge arms are connected to mutually coupled bridge arm reactors.

[0030] This invention provides a high-voltage DC converter that can accelerate commutation. The converter circuit includes a first bridge arm and a third bridge arm connected in series, and a second bridge arm is connected in parallel to the first bridge arm.

[0031] Coupled bridge arm reactors are installed in the first bridge arm, the second bridge arm, and the third bridge arm. The coupled bridge arm reactors on the first bridge arm and the second bridge arm are coupled to each other.

[0032] Specifically, both the first and second bridge arms include a series of thyristor valve strings and a turn-off valve string connected in series, and the coupling bridge arm reactor is connected to the cathode side of the thyristor valve string.

[0033] Specifically, the third bridge arm includes a thyristor valve string and a turn-off valve string connected in series, and the coupling bridge arm reactor of the third bridge arm is connected to the anode side of the turn-off valve string.

[0034] Specifically, the shut-off valve string includes one or more of the following power electronic devices: IGCT, GTO, IGBT, and IEGT.

[0035] Specifically, the first bridge arm, the second bridge arm, and the third bridge arm all include thyristor valve strings. The coupling bridge arm reactors of the first and second bridge arms are connected to the cathode side of the thyristor valve strings, and the coupling bridge arm reactor of the third bridge arm is connected to the anode side of the thyristor valve strings.

[0036] Specifically, the first bridge arm, the second bridge arm, and the third bridge arm each include a shut-off valve string. The coupling bridge arm reactors of the first and second bridge arms are connected to the cathode side of the shut-off valve string, and the coupling bridge arm reactor of the third bridge arm is connected to the anode side of the shut-off valve string.

[0037] The high-voltage direct current converter of the present invention can be implemented by modifying each arm of an existing conventional high-voltage direct current converter by adding arm coupling reactors or replacing the existing anode reactors with arm coupling reactors. This is very simple, easy, and low-cost, yet achieves the following beneficial effects: by configuring arm coupling reactors of a certain value, the arm commutation process is accelerated, the commutation overlap angle is reduced, thereby expanding the operating range of the high-voltage direct current converter, increasing the transmittable power, and reducing power loss; it can even rely on the commutation voltage created by the arm coupling reactors to perform voltage compensation when the AC voltage unexpectedly drops, thereby suppressing commutation failure. In high-voltage direct current (HVDC) transmission applications, it has excellent economic efficiency and reliability, enhancing its contribution to the national economy.

[0038] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-voltage direct current converter, characterized in that, The bridge arms are connected to each other, and the coupling bridge arm reactors are coupled together. The converter circuit includes a first bridge arm and a third bridge arm connected in series, and a second bridge arm is connected in parallel to the first bridge arm. The first bridge arm, the second bridge arm, and the third bridge arm all carry alternating current. Coupled bridge arm reactors are installed in the first, second, and third bridge arms. The coupled bridge arm reactors on the first and second bridge arms are coupled to each other, and the commutation voltage is increased by inducing a voltage in the coupled bridge arm reactors, so as to accelerate commutation and reduce the commutation overlap angle.

2. The high-voltage DC converter according to claim 1, characterized in that, The first bridge arm and the second bridge arm each include a thyristor valve string and a turn-off tube valve string connected in series, and the coupling bridge arm reactor is connected to the cathode side of the thyristor valve string.

3. The high-voltage DC converter according to claim 2, characterized in that, The third bridge arm includes a thyristor valve string and a turn-off valve string connected in series, and the coupling bridge arm reactor of the third bridge arm is connected to the anode side of the turn-off valve string.

4. The high-voltage DC converter according to claim 3, characterized in that, The shut-off valve string includes one or more of the following power electronic devices: IGCT, GTO, IGBT, and IEGT.

5. The high-voltage DC converter according to claim 1, characterized in that, The first bridge arm, the second bridge arm, and the third bridge arm all include a thyristor valve string. The coupling bridge arm reactors of the first bridge arm and the second bridge arm are connected to the cathode side of the thyristor valve string, and the coupling bridge arm reactor of the third bridge arm is connected to the anode side of the thyristor valve string.

6. The high-voltage DC converter according to claim 1, characterized in that, The first bridge arm, the second bridge arm, and the third bridge arm each include a shut-off valve string. The coupling bridge arm reactors of the first and second bridge arms are connected to the cathode side of the shut-off valve string, and the coupling bridge arm reactor of the third bridge arm is connected to the anode side of the shut-off valve string.

7. A method for accelerating commutation of a high-voltage direct current converter, characterized in that, Use the high-voltage DC converter according to any one of claims 1-6.

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