WO2016206547A1

WO2016206547A1 - Hybrid direct current transmission system

Info

Publication number: WO2016206547A1
Application number: PCT/CN2016/085610
Authority: WO
Inventors: 刘欣和; 吴金龙; 王先为; 张�浩; 张军; 行登江
Original assignee: 许继电气股份有限公司; 西安许继电力电子技术有限公司; 国家电网公司
Priority date: 2015-06-26
Filing date: 2016-06-13
Publication date: 2016-12-29
Also published as: CN104967141B; CN104967141A

Abstract

A hybrid direct current transmission system. The hybrid direct current transmission system is of a bipolar structure, comprising a positive convertor transformer (T1) and a positive converter (LCC), as well as a negative convertor transformer (T2) and a negative converter (MMC). In the bipolar structure, the converter on one pole is an MMC converter consisting of an MMC sub-module, and the other pole is an LCC converter system consisting of at least one LCC. The hybrid direct current transmission system has features of the mature technology and low costs of the LCC-HVDC, and also has advantages of no commutation failure, flexible control, and strong extension performance of the VSC-HVDC.

Description

Hybrid direct current transmission system

Technical field

The invention relates to a high voltage direct current transmission technology, in particular to a hybrid direct current transmission system.

Background technique

With the development of power science and technology, the technology of the traditional direct current transmission system (LCC-HVDC, Line Commutated Converter based High Voltage Direct Current) is very mature. The LCC-HVDC system has been widely used in submarine cable power transmission, large-capacity long-distance transmission, and asynchronous grid back-to-back interconnection. However, the LCC-HVDC system has the failure of the inverter station to commutate, the power supply to the weak AC system, and the need to consume a large amount of reactive power during operation, which restricts its development to a certain extent.

In recent years, VSC-HVDC (Voltage Source Converter Based High Voltage Direct Current) based on fully-controlled power electronic devices can independently control active reactive power and have no commutation failure. Many advantages such as power supply for passive islands are favored by academia and industry. As one of the VSC-HVDC topologies, the modular multilevel converter high voltage direct current (MMC-HVDC, Modular Multilevel Converter) has all the advantages of VSC-HVDC. At the same time, due to the characteristics of the MMC topology, the MMC-HVDC system also has the advantages of low switching frequency, low switching loss, no need for an AC filter bank and strong scalability, which makes it suitable for high DC voltage and high power transmission. occasion. However, the MMC-HVDC system is expensive and cannot effectively deal with DC faults, but it restricts its application in long-distance high-power transmission.

In view of the above shortcomings of the prior art, hybrid direct current transmission technology has become a new research hotspot. Hybrid DC transmission technology combines the mature and low cost of traditional LCC-HVDC technology. VSC-HVDC has no commutation failure, flexible control, and strong performance. It can effectively improve the commutation failure of the conventional DC transmission receiving end while satisfying the system transmission. The flexible DC is not equivalent to the conventional DC. Under the current situation of transmission capacity, it is an optimal configuration scheme with high technical economy. However, as a new technology, the hybrid DC transmission technology is still in the initial stage of research in the world. The research on hybrid DC transmission technology in China has also started late. Currently, there is no effective hybrid DC transmission in the prior art. The system achieves the above advantages.

Summary of the invention

In order to solve the above technical problem, the embodiment of the present invention provides a hybrid direct current transmission system, which has the advantages of mature technology and low cost of LCC-HVDC, non-commutation failure of VSC-HVDC, flexible control, and strong performance. .

A hybrid DC power transmission system provided by an embodiment of the present invention has a bipolar structure, including a positive current converter transformer and a positive current converter, a negative current converter transformer, and a negative current converter. In the bipolar structure, one of the two poles is commutated. The device is an MMC converter composed of MMC sub-modules, and the other is an LCC inverter system consisting of at least one LCC.

In the embodiment of the present invention, each bridge arm in the MMC is composed of a half bridge module and a full bridge submodule; or a cascade bridge module, a full bridge submodule, and a hybrid dual submodule.

In the embodiment of the present invention, the hybrid dual sub-module includes four power modules: T1, T2, T3, T4 and two capacitors: C1, C2; the anode of the T1 is connected to the anode of the T4, and the cathode of the T2 Connecting the cathode of T3, the cathode of T1 is connected to the anode of the T2, the cathode of the T4 is connected to the anode of the T3 through the capacitor C2, and the connection point of the T1 and T4 is connected to the T2 and T3 The capacitor C1 is connected between the points, and the connection point of the T1 and T2 is one port of the hybrid dual sub-module, and the connection point of the C2 and T4 is another port of the hybrid dual sub-module.

In the embodiment of the invention, the power module is an insulated gate bipolar transistor (IGBT, An Insulated Gate Bipolar Transistor module, the anode of the power module is a collector of the IGBT module, and the cathode of the power module is an emitter of the IGBT module.

In the embodiment of the present invention, the hybrid DC power transmission system further includes a reactive power compensation device, and the reactive power compensation device is connected to the AC power grid.

In the embodiment of the present invention, the reactive power compensation device is one of the following: a parallel capacitor, a shunt reactor, a static reactive power compensation device, and a camera.

In the embodiment of the present invention, the hybrid DC power transmission system further includes an AC filter device, and the AC filter device is connected to the AC power grid.

In the embodiment of the invention, the AC filtering device is composed of an AC filter bank.

In the embodiment of the present invention, the reactive power compensation device and the AC filter bank and the MMC provide reactive power compensation for the LCC.

The technical solution of the embodiment of the invention provides a novel hybrid DC transmission system, which not only has a simple and reliable structure, but also combines the respective advantages of the LCC and the MMC and overcomes their respective shortcomings: using the active and reactive independent adjustment capability of the MMC to Adjust the AC voltage, thereby increasing the maximum transmission active power capability of the LCC and reducing the possibility of its commutation failure; and the MMC can access various types of sub-modules according to actual needs, the control is more flexible and variable, and the DC side fails. When the DC output of the DC terminal can be controlled, the shortcoming of the normal MMC can not effectively deal with the DC fault.

DRAWINGS

1 is a schematic structural view of a hybrid DC power transmission system according to an embodiment of the present invention;

2 is a schematic top view showing a topology of a power grid commutator (LCC) according to an embodiment of the present invention;

3 is a topological structural diagram of a module hybrid modular multilevel converter MMC according to an embodiment of the present invention;

4 is a schematic diagram of a topology structure of a half bridge submodule according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a topology structure of a full bridge submodule according to an embodiment of the present invention; FIG.

6 is a schematic diagram of a topology structure of a hybrid dual sub-module according to an embodiment of the present invention;

7-1 is a schematic diagram of a first working state in a normal working mode of a hybrid dual sub-module according to an embodiment of the present invention;

7-2 is a schematic diagram of a second working state in a normal working mode of a hybrid dual sub-module according to an embodiment of the present invention;

7-3 is a schematic diagram of a third working state in a normal working mode of a hybrid dual sub-module according to an embodiment of the present invention;

7-4 is a fourth working state diagram of a hybrid dual sub-module in a normal working mode according to an embodiment of the present invention;

8-1 is a schematic diagram of one of the working states of the hybrid dual sub-module in the latching mode according to the embodiment of the present invention;

FIG. 8-2 is a schematic diagram of another working state in the interlocking mode of the hybrid dual sub-module according to the embodiment of the present invention.

detailed description

The present invention will be further described in detail below with reference to the accompanying drawings.

Example 1

As shown in FIG. 1, the hybrid DC transmission system includes a power grid commutating converter (LCC), a modular multilevel converter (MMC), a converter transformer, an alternating current filter bank (ACF), and an alternating current reactive power compensation system. Device group, DC smoothing reactor, DC filter (DCF). The LCC and MMC form a bipolar structure, and an AC filter bank (ACF) and an AC reactive power compensation device are also connected to the AC grid.

The AC reactive power compensation device can be a parallel capacitor, or one of a shunt reactor, a static reactive power compensation device, and a camera. It cooperates with an AC filter bank (ACF) and an MMC to provide reactive power compensation for the LCC. .

A DC filter (DCF) is connected between the two DC terminals of the grid commutating converter, and the DC negative terminal of the grid commutating converter is connected to the DC positive terminal of the modular multilevel converter, and the connection point is A switch is connected in series between the DC negative terminal of the grid commutated converter and the DC positive terminal of the modular multilevel converter, and the contact is grounded through a switch (MRTB). The DC positive terminal of the grid commutating converter is the DC positive terminal of the hybrid DC transmission system, and the DC cathode terminal of the modular multilevel converter is the DC cathode terminal of the hybrid DC transmission system, the hybrid DC transmission system A DC smoothing reactor is connected in series on both DC positive and negative lines.

The most basic LCC is a three-phase bridge circuit based on a semi-controlled thyristor, but the LCC can be a 6-pulse converter composed of 6 bridge arms, or it can be a 6-pulse converter. The 12-pulse wave converter can also be a multi-pulse converter composed of a plurality of 6-pulse converters. As shown in Fig. 2, an embodiment of LCC is given. That is to say, the LCC can be a basic three-phase bridge circuit or a combination of a plurality of three-phase bridge circuits.

The topology of the MMC is shown in Figure 2. The MMC consists of three-phase six-bridge arms. Each bridge arm is composed of a half-bridge topology sub-module and a full-bridge topology sub-module in a one-to-one ratio. The bridge arm is also connected in series with the bridge arm reactor L. On the AC side of the MMC, the same AC grid system as the LCC is connected to the AC side of the three-phase bridge circuit of the MMC through a converter transformer and a soft-start resistor.

The half bridge submodule and the full bridge submodule in the MMC are based on a fully controlled power electronic device such as an IGBT, and the topology thereof is shown in FIGS. 3 and 4.

When the hybrid DC transmission system is working, the LCC and the MMC are simultaneously connected to an AC system to form a hybrid multi-infeed DC transmission system. When the system is running, it can fully utilize the active and reactive power independent adjustment capability of the MMC system, effectively adjust the AC bus voltage, increase the maximum transmission active power capability of the LCC system, reduce the transient overvoltage of the LCC system, and also reduce the LCC. Inverter commutation failure may be possible. When the DC side fails, the LCC system can overcome the DC fault by adjusting the trigger phase angle. The MMC system can realize the DC voltage control on the DC side by controlling the full bridge submodule, thereby effectively overcoming the DC fault.

Of course, the topology of the hybrid DC power transmission system of the present invention is not limited to the above embodiment. For example, by properly matching the AC filter bank (ACF) and supporting the reactive power of the AC system with the MMC, the reactive power compensation device is cancelled.

In the above embodiment, the DC negative terminal of the grid commutated inverter is connected to the DC positive terminal of the modular multilevel converter and grounded, and the DC positive terminal of the grid commutated converter is the DC of the hybrid DC transmission system. At the extreme end, the DC negative terminal of the modular multilevel converter is the DC negative terminal of the hybrid DC transmission system; as another embodiment, the positions of the LCC and the MMC can be exchanged, and the DC positive terminal of the grid commutation converter Connected to the DC negative terminal of the modular multilevel converter and grounded, the DC positive terminal of the modular multilevel converter is the DC positive terminal of the hybrid DC transmission system, and the DC negative terminal of the grid commutated converter It is the DC negative terminal of the hybrid DC transmission system.

In the above embodiment, the MMC includes a half bridge submodule and a full bridge submodule, and the ratio of the two in each bridge arm is 1:1. As another embodiment, the configuration ratio of the half bridge submodule and the full bridge submodule It can be set according to the actual situation. It is also possible to change the full bridge submodule to a clamped dual submodule depending on the situation.

Example 2

The difference between this embodiment and the embodiment 1 is that in the MMC in this embodiment, at least one submodule of each bridge arm is a hybrid dual submodule. As shown in FIG. 6, the hybrid dual sub-module includes four IGBT modules: T1, T2, T3, T4 and two capacitors: C1, C2, the collector of T1 is connected to the collector of T4, and the emitter of T2 is connected to the emission of T3. The emitter of T1 is connected to the collector of T2, the emitter of T4 is connected to the collector of T3 through capacitor C2, the connection point of T1 and T4 is connected with the connection point of T2 and T3, and the connection point of T1 and T2 is connected. For one port of the hybrid dual submodule, the connection point of C2 and T4 is the other port of the hybrid dual submodule. All the IGBTs (T1, T2, T3, T4) in the hybrid dual sub-module are connected in parallel with the freewheeling diode. The bases of T1, T2, T3 and T4 respectively receive the control signals provided by the external device.

The hybrid dual submodule has two operating modes, normal operating mode and blocking mode. In normal operation In row mode, only one IGBT can be turned on between T1 and T2. In order to prevent capacitor C1 from short-circuiting, T1 and T2 cannot be turned on at the same time; at most one IGBT can be turned on between T3 and T4.

The hybrid dual submodule has four operating states in the normal operating mode, and the four operating states in the normal operating mode are shown in Figures 7-1 to 7-4. (1) The current flow when T1 and T3 are turned on. (2) is the current flow when T1 and T4 are turned on, (3) is the current flow when T2 and T3 are turned on, and (4) is the current flow when T2 and T4 are turned on. As shown in Table 1, when T1 and T3 are turned on, the port output voltage is two capacitor voltages; when T1 and T4 are turned on, the port output voltage is zero; when T2 and T3 are turned on, the port output voltage is Capacitor C2 voltage; when T2 and T4 are turned on, the port output voltage is the reverse voltage of the capacitor C1, that is, the output negative voltage. The current direction does not affect the port output voltage. In Table 1, Usm represents the submodule port output voltage.

Table 1

According to the normal working mode of the hybrid dual sub-module, the sub-module can output four kinds of voltages, which are twice the capacitance voltage, the capacitor voltage, the zero voltage and the negative capacitance voltage. This sub-module can replace the two half-bridge modules to output 2 times the capacitor voltage, and has the negative voltage characteristic of the full bridge sub-module, which can improve the DC voltage utilization and increase the system capacity.

The hybrid dual submodule has two operating states in the blocking mode, and the two operating states in the blocking mode are shown in Figures 8-1 and 8-2. In the latched state, all IGBTs are in the off state. When the forward current flows (the current direction is from A to B), the port output voltage is two capacitor voltages; when the negative current flows, the port output voltage is the negative voltage of the capacitor C1, that is, opposite to the current The voltage to the direction.

Mixing the two capacitors inside the dual sub-module, you can properly configure the two capacitor voltages to different values as needed. In this mode, the application range of the MMC can be effectively extended. For example, two capacitor voltages in the submodule are reasonably configured to achieve the MMC to improve the modulation degree and the STATCOM operation fault traversing capability.

In addition, the submodules in the MMC may all be the hybrid dual submodules, or the following cases: the bridge arm in the MMC is composed of a hybrid submodule and one or more existing submodules (half bridge submodules, all The bridge module and the clamped double sub-module are cascaded. Then, the MMC is a hybrid MMC inverter. The hybrid MMC converter has a wide range of applications when it is expanded according to actual conditions, such as improving the modulation degree and having the STATCOM operation fault traversing capability and saving system hardware cost.

In the above embodiment, the power module is an IGBT module. As another embodiment, the power module may be other fully controlled devices.

Specific embodiments have been given above, but the invention is not limited to the described embodiments. The basic idea of the present invention lies in the above basic scheme, and it is not necessary for the person skilled in the art to design various modified models, formulas and parameters according to the teachings of the present invention. Variations, modifications, alterations and variations of the embodiments may be made without departing from the spirit and scope of the invention.

Industrial applicability

The technical solution of the embodiment of the invention not only has a simple and reliable structure, but also combines the respective advantages of the LCC and the MMC and overcomes the respective disadvantages: the active voltage and reactive independent adjustment capability of the MMC is used to adjust the AC voltage, thereby increasing the maximum transmission active power of the LCC. Power capability and reduce the possibility of its commutation failure; and MMC can access various types of sub-modules according to actual needs, the control is more flexible and variable, and the DC-side output zero voltage can be controlled when the DC side fails. Overcoming the shortcomings of ordinary MMC can not effectively deal with DC faults.

Claims

A hybrid direct current transmission system, the hybrid direct current transmission system is a bipolar structure, comprising a positive current converter transformer and a positive current converter, a negative current converter transformer and a negative current converter, wherein one of the bipolar structures is commutated The device is an MMC converter consisting of a modular multilevel converter MMC sub-module, and the other is an LCC converter system consisting essentially of at least one grid commutating converter LCC.
The hybrid DC power transmission system according to claim 1, wherein each of the MMCs is constituted by a cascade of a half bridge submodule and a full bridge submodule; or, by a half bridge submodule, a full bridge submodule, and Hybrid twin sub-modules are cascaded.
The hybrid DC power transmission system according to claim 2, wherein said hybrid dual sub-module comprises four power modules: T1, T2, T3, T4 and two capacitors: C1, C2; said anode of said T1 is connected to said T4 The cathode of the T2 is connected to the cathode of T3, the cathode of the T1 is connected to the anode of the T2, and the cathode of the T4 is connected to the anode of the T3 through the capacitor C2, the connection point of the T1 and the T4 Connecting the capacitor C1 to the connection point of the T2 and T3, the connection point of the T1 and T2 is a port of the hybrid dual sub-module, and the connection point of the C2 and T4 is the mixed dual sub-module Another port.
The hybrid DC power transmission system according to claim 3, wherein the power module is an insulated gate bipolar transistor IGBT module, an anode of the power module is a collector of an IGBT module, and a cathode of the power module is an IGBT module. The emitter.
The hybrid direct current transmission system according to claim 1, wherein said hybrid direct current transmission system further comprises a reactive power compensation device, said reactive power compensation device being connected to the alternating current grid.
The hybrid DC power transmission system according to claim 5, wherein the reactive power compensation device is one of the following: a parallel capacitor, a shunt reactor, a static var compensator, and a camera.
A hybrid direct current transmission system according to claim 5, wherein said hybrid direct current transmission system further comprises an alternating current filtering means, said alternating current filtering means being connected to the alternating current grid.
The hybrid DC power transmission system according to claim 7, wherein said AC filter package The set consists of an AC filter bank.
The hybrid DC power transmission system according to claim 8, wherein said reactive power compensation device and said AC filter bank and MMC provide reactive power compensation for said LCC.