CN102969708A - Interline power flow controller based on modular multi-level converter structure - Google Patents

Abstract

The invention relates to an interline power flow controller based on a modular multi-level converter structure. The interline power flow controller comprises a static synchronous compensator (1) and a static synchronous series compensator (2), the static synchronous compensator (1) comprises a converter (7) and a parallel transformer (8), the static synchronous series compensator (2) comprises a converter (9) and a series transformer (10), the converter (7) is connected into a power transmission line I in parallel through the parallel transformer (8), the converter (9) is connected in a power transmission line II in series through the series transformer (10), a unified power flow controller comprises a by-pass switch (4), and the by-pass switch (4) is connected with the series transformer (10) in parallel. The interline power flow controller avoids the technical difficulty of device series connection, facilitates split-phase control and modular design, can bypass a trouble unit through the redundancy technology, improves operational reliability of a device, and is low in device switching frequency and small in device operation loss.

Description

A Line-to-Line Power Flow Controller Based on Modular Multilevel Converter Structure

technical field

The invention relates to an inter-line power flow controller in the field of flexible AC power transmission, in particular to an inter-line power flow controller based on a modular multilevel converter structure.

Background technique

The inter-line power flow controller (IPFC) is the latest development of power electronics technology and modern control technology to achieve flexible and fast control of the parameters and network structure of the AC multi-line transmission system. Its characteristic is that its flexibility can adapt to the requirements of complex systems for a series of compensation and power flow control. It can complete independent comprehensive compensation of a single line, and can also carry out active power transmission among multiple lines.

The IPFC device can be regarded as a static synchronous compensator (STATCOM) device and a static synchronous series compensator (SSSC) device connected in parallel on the DC side, which can simultaneously and quickly and independently control the active power and reactive power in different lines. Power, so that IPFC has a four-quadrant operation function that STATCOM and SSSC devices do not have.

The main circuit topology of the IPFC device adopts the parallel connection method of two voltage source converters (VSC) on the DC side. One of the converters is connected directly or through a transformer in parallel with a line in the system, and the other converter is connected in parallel through the AC side. The transformer is connected in series with another line in the system. Each voltage source converter usually adopts a two-level or three-level three-phase voltage source converter structure.

In large-capacity IPFC, the voltage source converter usually adopts the way of turning off power electronic devices (typical devices such as insulated gate bipolar transistor IGBT) in series to improve the withstand voltage capability of the device. The technical difficulties of IGBT series connection with turn-off devices are mainly manifested in: affected by technology monopoly, it is difficult to purchase IGBT devices with their own short-circuit current limiting characteristics, and the theoretical research on IGBT series voltage equalization control technology is not deep enough. In order to reduce the output harmonics of the device, a higher switching frequency is required, so the operating loss of the device is relatively large, which limits the application of large-capacity IPFC.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention provides an inter-line power flow controller based on a modular multilevel converter structure. The inter-line power flow controller avoids the technical difficulties of connecting devices in series, and has the following characteristics: it is convenient for phase separation Control and modular design; faulty units can be bypassed through redundancy technology to improve device operation reliability; and the device switching frequency is low, and the device operation loss is small.

The object of the present invention is to adopt following technical scheme to realize:

An interline power flow controller based on a modular multilevel converter structure, the improvement of which is that the interline power flow controller includes a static synchronous compensator 1 and a static synchronous series compensator 2;

The static synchronous compensator 1 includes a converter 7 and a shunt transformer 8;

The static synchronous series compensator 2 includes a converter 9 and a series transformer 10;

The converter 7 is connected in parallel to the transmission line I through a parallel transformer 8; the converter 9 is connected in series to the transmission line II through a series transformer 10;

The unified power flow controller includes a bypass switch 4; the bypass switch 4 is connected in parallel with the series transformer 10.

Wherein, a support capacitor 3 is provided between the STATS compensator 1 and the STATS series compensator 2; the support capacitor 3 is connected in parallel with the STATS 1 and the STATS series compensator 2 respectively .

Wherein, the static synchronous compensator 1 includes a starting circuit 5; the starting circuit 5 is connected to the secondary side of the parallel transformer 8, and the primary side of the parallel transformer 8 is connected to the transmission line I in parallel.

Wherein, the starting circuit 5 includes a resistor and a switch connected in parallel.

Wherein, the static synchronous series compensator 2 includes a start-up circuit 6 ; one end of the start-up circuit 6 is connected to the converter 9 ; the other end of the start-up circuit 6 is connected to the series transformer 10 .

Wherein, the starting circuit 6 includes a resistor and a switch connected in parallel.

Wherein, the series transformer 10 is connected to a load in series and connected to the transmission line II.

Wherein, the converter 7 is composed of three-phase six bridge arms, and each bridge arm includes a reactor and N sub-modules with the same structure; after the sub-modules of each bridge arm are cascaded, one end of the bridge arm is connected to the reactor through the reactor. The starting circuit 5 is connected; the other end is connected to one end of the cascaded submodules of the other two bridge arms to form the positive and negative bus bars of the converter 7; or

The converter 7 is composed of three-phase six bridge arms, each bridge arm includes a reactor and N submodules with the same structure; the submodules of each bridge arm are cascaded and one end is connected to the start-up circuit 5 The reactor at the other end is connected in series with the reactors of the other two bridge arms to form the positive and negative busbars of the converter 7 .

Wherein, the converter 9 is composed of 3 phases and six bridge arms, and each bridge arm includes a reactor and M submodules with the same structure; after the submodules of each bridge arm are cascaded, one end passes through the reactor and The series transformer 10 is connected; the other end is connected to one end of the cascaded sub-modules of the other two bridge arms to form the positive and negative bus bars of the converter 9, which are connected to the positive and negative bus bars of the converter 7; or

The converter 9 is composed of 3 phases and six bridge arms, and each bridge arm includes a reactor and M submodules with the same structure; after the submodules of each bridge arm are cascaded, one end is connected to the series transformer 10 connection; the other end is connected to the reactors of the other two bridge arms in series with the reactor to form the positive and negative busbars of the converter 9, which are connected to the positive and negative busbars of the converter 7.

Wherein, the sub-module is composed of a half-bridge structure and a DC capacitor connected in parallel, the half-bridge structure includes two IGBT modules connected in series, and each IGBT module includes an anti-parallel IGBT and a diode;

A sub-module bypass circuit is connected in parallel between the midpoint of the half-bridge structure and the IGBT emitter;

The DC capacitor provides power for the control circuit of the sub-module through the energy harvesting power supply.

Compared with prior art, the beneficial effect that the present invention reaches is:

1. The inter-line power flow controller based on the modular multilevel converter structure provided by the present invention can greatly increase the capacity of the device without using complex IGBT device series technology;

2. The line-to-line power flow controller based on the modular multilevel converter structure provided by the present invention can realize phase separation control;

3. The inter-line power flow controller based on the modular multilevel converter structure provided by the present invention can realize modular design;

4. The inter-line power flow controller based on the modular multi-level converter structure provided by the present invention can bypass the faulty unit through redundant technology, improve the reliability of the device operation, and avoid frequent withdrawal and investment of the device;

5. The inter-line power flow controller based on the modular multi-level converter structure provided by the present invention, in order to reduce the output harmonics, the switching frequency of the IGBT device series scheme is usually high, and the device loss is relatively large; this scheme adopts modular With multi-level technology, the switching frequency of each device is low, but it can achieve a high external equivalent switching frequency and reduce output harmonics, so the operating loss of the device is small.

Description of drawings

Fig. 1 is the basic circuit structure diagram of the inter-line power flow controller based on the modular multilevel converter structure provided by the present invention;

Fig. 2 is a structural diagram of the main circuit scheme 1 of the inter-line power flow controller based on the modular multilevel converter structure provided by the present invention;

Fig. 3 is a structural diagram of the main circuit scheme 2 of the inter-line power flow controller based on the modular multilevel converter structure provided by the present invention;

Fig. 4 is a structural diagram of a sub-module of an inter-line power flow controller based on a modular multilevel converter structure provided by the present invention.

Detailed ways

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

The basic circuit structure diagram of the inter-line power flow controller based on the modular multilevel converter structure provided by the present invention is shown in Figure 1, including a static synchronous compensator 1 and a static synchronous series compensator 2; the static synchronous compensator 1 includes A converter 7 and a parallel transformer 8; the static synchronous series compensator 2 includes a converter 9 and a series transformer 10; the converter 7 is connected in parallel to the transmission line I through a parallel transformer 8; the converter 9 is connected through a series transformer 10 are connected in series to the transmission line II.

Example 1

A switchable static compensator based on a modular multilevel converter structure provided in this embodiment is shown in Figure 2, including a static synchronous compensator 1 and a static synchronous series compensator 2; the static synchronous compensator 1 includes A converter 7 and a parallel transformer 8; the static synchronous series compensator 2 includes a converter 9 and a series transformer 10;

The converter 7 is composed of three-phase six bridge arms, and the six bridge arms have the same structure, and each bridge arm includes a reactor and N (N is a natural number) sub-modules with the same structure; after the sub-modules are cascaded, they pass The reactor is connected to the starting circuit 5; specifically, the midpoint of the half-bridge structure of the sub-module and the emitter of the lower tube IGBT are respectively used as the lead-out ends of the sub-module, which are cascaded with the front and rear modules in sequence, and then connected in series with a reactor to form a 1 The upper and lower bridge arms are connected in series to form a 1-phase commutation device, and the 3-phase commutation device is connected in parallel as a whole, and the positive and negative busbars of the converter 7 are led out. The midpoint of the upper and lower bridge arms is used as the output end of the static synchronous compensator, that is, after the submodule is connected in parallel with the starting circuit 5 after the reactor is connected in series, it is connected to the transmission line I. The starting circuit 5 includes a resistor and a switch connected in parallel.

Converter 9 has the same structure as converter 7, consisting of three-phase six bridge arms, and each bridge arm includes a reactor and M (M is a natural number, M may or may not be equal to N) with the same structure The sub-modules; after the sub-modules are cascaded, they are connected to the load through a reactor and a series transformer 10. The positive and negative bus bars of the converter 7 and the positive and negative bus bars of the converter 9 are correspondingly connected. The sub-modules of this embodiment are connected to the system through a reactor, which can suppress the damage to the equipment caused by lightning and operating waves from the power grid on the one hand, and can suppress the output harmonics of the converter device on the other hand.

The series transformer 10 is connected to the load in series and connected to the transmission line II.

Preferably, in this embodiment, a support capacitor 3 is provided between the static synchronous compensator 1 and the static synchronous series compensator 2; the positive and negative bus bars of the converter 7 and the positive and negative bus bars of the converter 9 are connected in parallel Support capacitor 3. The two converter devices are connected through the intermediate DC link formed by the supporting capacitor 3, so that the active power can be bidirectionally transmitted between the two converter devices; the reactive power can be independently connected to the system by each converter device on its AC side. Make an exchange.

Preferably, the secondary side of the parallel transformer 8 of the static synchronous compensator 1 of this embodiment is connected to the starting circuit 5, and the primary side of the parallel transformer 8 is connected to the transmission line I in parallel. The shunt transformer 8 is used to match the grid voltage with the output voltage of the static synchronous compensator.

Preferably, the static synchronous series compensator 2 of this embodiment may further include a start-up circuit 6, and the start-up circuit 6 is composed of resistors and switches connected in parallel. One end of the starting circuit 6 is connected to the converter 9, and the other end is connected to one end of the series transformer 10, and the other end of the series transformer 10 is connected in series to the transmission line II. The starting circuit 6 can realize the smooth starting of the converter 9 . The series transformer 10 is used to match the grid voltage with the output voltage of the static synchronous series compensator.

Preferably, the unified power flow controller of this embodiment is also provided with a bypass switch 4 for safe setting, and the bypass switch 4 is connected in parallel with the series transformer 10 to realize the withdrawal of the static synchronous series compensator.

The sub-module of this embodiment is used to output the required voltage. The structure of the inter-line power flow controller sub-module based on the modular multilevel converter structure provided by the present invention is shown in Figure 4. It consists of a half-bridge structure and a direct current The half-bridge structure includes two upper and lower IGBT modules connected in series, a DC capacitor is connected in parallel between the collector of the upper IGBT and the emitter of the lower IGBT, and a sub-module is connected in parallel between the midpoint of the half-bridge structure and the emitter of the lower IGBT In the bypass circuit, the energy-taking power supply takes power from the DC capacitor to provide control power for the control circuit of the sub-module. The DC capacitor of the sub-module is used to provide voltage support for the sub-module. When the sub-module fails internally, its bypass circuit is used to stop the sub-module from running, so as to realize the redundant operation of the static synchronous compensator. The energy-taking power supply is used to provide control power to the sub-module control circuit. The control circuit is used to realize the control, monitoring and protection of the sub-modules. The bypass circuit in this embodiment can be implemented by a switch, and the control circuit can be implemented by a digital or analog circuit. The energy harvesting power supply can be realized by referring to patent 201010624225.6 or ZL201020700480.X.

Example 2

This embodiment is basically the same as Embodiment 1, but the difference is:

The positions of the reactors in the inverter 7 and the inverter 9 are different. The reactor in this embodiment is connected in series on the positive and negative busbar sides of the converter 7 and the converter 9, as shown in FIG. 3 . It is used to suppress the output harmonics of the converter device.

Specifically, the converter 7 is composed of three-phase six bridge arms, and each bridge arm includes a reactor and N submodules with the same structure; the submodules of each bridge arm are cascaded and one end is connected to the starting circuit 5 The reactor at the other end is connected in series with the reactors of the other two bridge arms to form the positive and negative busbars of the converter 7 .

The converter 9 is composed of three-phase six bridge arms, and each bridge arm includes a reactor and M submodules with the same structure; the submodules of each bridge arm are cascaded and connected to the series transformer 10 at one end; One end of the reactor is connected in series with the reactors of the other two bridge arms to form the positive and negative busbars of the converter 9, which are connected to the positive and negative busbars of the converter 7.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims (10)

1. one kind based on flow controller between the line of modular multilevel converter structure, it is characterized in that flow controller comprises STATCOM (1) and Static Series Synchronous Compensator (2) between described line;

Described STATCOM (1) comprises converter (7) and shunt transformer (8);

Described Static Series Synchronous Compensator (2) comprises converter (9) and series transformer (10);

Described converter (7) is by among shunt transformer (8) the access in parallel transmission line I; Described converter (9) is by among series transformer (10) the series connection access transmission line II;

Described THE UPFC comprises by-pass switch (4); Described by-pass switch (4) is in parallel with described series transformer (10).

2. flow controller between line as claimed in claim 1 is characterized in that, between described STATCOM (1) and described Static Series Synchronous Compensator (2) Support Capacitor (3) is set; Described Support Capacitor (3) is in parallel with described STATCOM (1) and described Static Series Synchronous Compensator (2) respectively.

3. flow controller between line as claimed in claim 1 is characterized in that, described STATCOM (1) comprises start-up circuit (5); Described start-up circuit (5) is connected with the secondary of described shunt transformer (8), and the former limit of described shunt transformer (8) is in parallel with transmission line I.

4. flow controller between line as claimed in claim 3 is characterized in that, described start-up circuit (5) comprises resistance and switch in parallel.

5. flow controller between line as claimed in claim 1 is characterized in that, described Static Series Synchronous Compensator (2) comprises start-up circuit (6); Described start-up circuit (6) one ends are connected with described converter (9); Described start-up circuit (6) other end is connected with described series transformer (10).

6. flow controller between line as claimed in claim 5 is characterized in that, described start-up circuit (6) comprises resistance and switch in parallel.

7. flow controller between line as claimed in claim 1 is characterized in that, described series transformer (10) connects among the load series connection access transmission line II.

8. flow controller between line as claimed in claim 1 is characterized in that, described converter (7) is made of six brachium pontis of three-phase, and each brachium pontis comprises a reactor and N the submodule that structure is identical; An end is connected with described start-up circuit (5) by reactor after the submodule cascade of each brachium pontis; Submodule one end of the cascade of two brachium pontis of the other end and other is connected, and forms the both positive and negative polarity bus of described converter (7); Or

Described converter (7) is made of six brachium pontis of three-phase, and each brachium pontis comprises a reactor and N the submodule that structure is identical; An end is connected with described start-up circuit (5) after the submodule cascade of each brachium pontis, is connected with other reactor of two brachium pontis behind the other end series reactor, forms described converter (7) both positive and negative polarity bus.

9. flow controller between line as claimed in claim 1 is characterized in that, described converter (9) is made of six brachium pontis of 3 phases, and each brachium pontis comprises 1 reactor and M the submodule that structure is identical; An end is connected with described series transformer (10) by reactor after the submodule cascade of each brachium pontis; Submodule one end of the cascade of two brachium pontis of the other end and other is connected, and forms described converter (9) both positive and negative polarity bus, is connected with the both positive and negative polarity bus of described converter (7); Or

Described converter (9) is made of six brachium pontis of 3 phases, and each brachium pontis comprises 1 reactor and M the submodule that structure is identical; An end is connected with described series transformer (10) after the submodule cascade of each brachium pontis; Be connected with other reactor of two brachium pontis behind the other end series reactor, form described converter (9) both positive and negative polarity bus, be connected with the both positive and negative polarity bus of described converter (7).

10. such as flow controller between each described line among the claim 8-9, it is characterized in that, described submodule consists of by half-bridge structure is in parallel with dc capacitor, and described half-bridge structure comprises the IGBT module of two series connection, and each IGBT module comprises antiparallel IGBT and diode;

Submodule bypass circuit in parallel between described half-bridge structure mid point and the IGBT emitter;

Described dc capacitor can power supply provides power supply for the control circuit of submodule by getting.

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