CN114336571A - Direct current power grid access method and system - Google Patents
Direct current power grid access method and system Download PDFInfo
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- CN114336571A CN114336571A CN202011062130.XA CN202011062130A CN114336571A CN 114336571 A CN114336571 A CN 114336571A CN 202011062130 A CN202011062130 A CN 202011062130A CN 114336571 A CN114336571 A CN 114336571A
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Abstract
The invention provides a direct current power grid access method and a direct current power grid access system, wherein the direct current power grid access method is applied to a first system, the first system at least comprises a DCDC module, the direct current power grid access method connects a first input end of a high-voltage side of the DCDC module with a positive end of a first bus, connects a first output end of a low-voltage side of the DCDC module and a second input end of the high-voltage side of the DCDC module with a positive end of a second bus, and connects a second output end of the low-voltage side of the DCDC module with the ground, and the voltage value of the positive end of the first bus is larger than the voltage value of the positive end of the second bus. The full power conversion is changed into partial power conversion, namely only partial power is connected into a low-voltage-level direct-current power grid through the converter, so that the system cost is reduced.
Description
Technical Field
The invention relates to the technical field of power grid control, in particular to a direct-current power grid access method and a direct-current power grid access system.
Background
With the development of the modular multilevel converter, the direct current power grid formed by the modular multilevel converter is rapidly developed in the power industry, and at present, part of the countries begin to plan a plurality of direct current transmission lines to form the direct current power grid. The direct-current power grid and the multi-terminal flexible direct-current technology have obvious technical advantages in the fields of large-scale renewable energy grid connection, offshore wind power access, urban power distribution network construction and the like.
The high-voltage large-capacity DC/DC converter is used as one of key equipment of a direct-current power grid, and the main functions of the high-voltage large-capacity DC/DC converter at least comprise: firstly, the connection of direct current networks with different voltage grades, different direct current technologies and different topological types is realized; and secondly, realizing power exchange among different subsystems. Therefore, the DC/DC converter for the DC power grid needs to overcome the technical difficulties of high voltage, high power, bidirectional energy flow, flexible transformation ratio, high transmission efficiency, strong expansibility, and the like.
The inventor finds that a key problem restricting the development of a direct current power grid at present is that an effective high-voltage large-capacity DC/DC conversion device is not available, and the direct current power transmission lines with different voltage grades cannot be interconnected. With the continuous development of the direct-current power grid and the multi-terminal flexible direct-current technology, how to realize interconnection, power interaction and power flow control of power grids with different direct-current voltage levels at low cost is a great technical problem to be solved urgently by technical personnel in the field.
Disclosure of Invention
The invention provides a direct current power grid access method and a direct current power grid access system, which can realize interconnection of output electric lines with different voltage grades and are low in cost.
In order to achieve the purpose, the technical scheme provided by the application is as follows:
a direct current power grid access method is applied to a first system, the first system at least comprises one DCDC module, and the direct current power grid access method comprises the following steps:
connecting a first input end of a high-voltage side of the DCDC module with a positive end of a first bus, connecting a first output end of a low-voltage side of the DCDC module and a second input end of the high-voltage side of the DCDC module with a positive end of a second bus, and connecting a second output end of the low-voltage side of the DCDC module with the ground, wherein the voltage value of the positive end of the first bus is greater than that of the positive end of the second bus.
Optionally, the DCDC module includes a first converter, a first converter transformer and a second converter, an output end of the first converter is connected to an input end of the second converter through the first converter transformer, and the dc power grid access method includes:
connecting the first input end of the first converter with the positive end of the first bus bar, connecting the second input end of the first converter and the first output end of the second converter with the positive end of the second bus bar, and connecting the second output end of the second converter with the ground.
Optionally, the first system includes two DCDC modules, one DCDC module is a first DCDC module, and the other DCDC module is a second DCDC module, where the direct current grid access method includes:
connecting the first input end of the first DCDC module with the positive end of a first bus, connecting the first output end of the first DCDC module and the second input end of the first DCDC module with the positive end of a second bus, connecting the first input end of the second DCDC module and the second output end of the second DCDC module with the negative end of the second bus, connecting the second output end of the first DCDC module with the first output end of the second DCDC module and grounding, and connecting the second input end of the second DCDC module with the negative end of the first bus.
A system comprising at least one DCDC module,
the first input end of the high-voltage side of the DCDC module is connected with the positive end of a first bus, the first output end of the low-voltage side of the DCDC module and the second input end of the high-voltage side of the DCDC module are connected with the positive end of a second bus, the second output end of the low-voltage side of the DCDC module is grounded, and the voltage value of the positive end of the first bus is larger than that of the positive end of the second bus.
Optionally, the DCDC module includes a first converter, a first converter transformer and a second converter,
the output end of the first converter is connected with the input end of the second converter through the first converter transformer, the first input end of the first converter is connected with the positive end of the first bus, the second input end of the first converter and the first output end of the second converter are connected with the positive end of the second bus, and the second output end of the second converter is grounded.
Optionally, two DCDC modules are included, one DCDC module is a first DCDC module, and the other DCDC module is a second DCDC module;
the first input end of the first DCDC module is connected with the positive end of a first bus, the first output end of the first DCDC module and the second input end of the first DCDC module are connected with the positive end of a second bus, the first input end of the second DCDC module and the second output end of the second DCDC module are connected with the negative end of the second bus, the second output end of the first DCDC module is connected with the first output end of the second DCDC module and is grounded, and the second input end of the second DCDC module is connected with the negative end of the first bus.
Optionally, the first converter transformer is a double-winding transformer.
Optionally, the first converter transformer is a three-winding transformer, and one phase of the three-winding transformer is connected to an ac power grid.
Optionally, the DCDC module is a full-bridge submodule MMC converter or a thyristor-based LCC converter.
The invention provides a direct current power grid access method and a direct current power grid access system, wherein the direct current power grid access method is applied to a first system, the first system at least comprises a DCDC module, the direct current power grid access method connects a first input end of a high-voltage side of the DCDC module with a positive end of a first bus, connects a first output end of a low-voltage side of the DCDC module and a second input end of the high-voltage side of the DCDC module with a positive end of a second bus, and connects a second output end of the low-voltage side of the DCDC module with the ground, and the voltage value of the positive end of the first bus is larger than the voltage value of the positive end of the second bus. The full power conversion is changed into partial power conversion, namely only partial power is connected into a low-voltage-level direct-current power grid through the converter, so that the system cost is reduced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic circuit diagram of a DC DCDC transformer interconnection;
FIG. 2 is a schematic circuit diagram of another DC DCDC transformer interconnection;
FIG. 3 is a schematic circuit diagram of another DC DCDC transformer interconnection;
FIG. 4 is a schematic circuit diagram of another DC DCDC transformer interconnection;
fig. 5 is a schematic flowchart of a dc power grid access method according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of a system according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a system provided by an embodiment of the present invention;
FIG. 8 is a schematic diagram of another embodiment of a system according to the present invention;
fig. 9 is a schematic structural diagram of a system according to an embodiment of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
The inventor finds that at present, for the interconnection of direct current systems with different voltage levels, the interconnection of direct current DCDC transformers shown in FIG. 1 is mainly adopted. Specifically, there are various schemes for the DCDC dc transformer, one of which is an iso p scheme, in which input stages are connected in series and output stages are connected in parallel, voltages are superimposed, and a high-frequency isolation transformer is used in the middle, as shown in fig. 2.
In addition to this, there are also dc autotransformers as shown in fig. 3, and dc converters using a face-to-face topology as shown in fig. 4. No matter which scheme is adopted, the existing DCDC direct current transformer is full power conversion, for example, a high-voltage direct current line transmits 8000MW power, so that a 8000MW power converter is required, and the requirement on the capacity of the power converter is high. The capacity of the power electronic equipment cannot realize the conversion of the large capacity, so that the development of the current multi-voltage-level direct-current power grid is restricted.
Based on this, referring to fig. 5, fig. 5 is a schematic flow chart of a dc power grid connection method according to an embodiment of the present invention, where the dc power grid connection method is applied to a first system, as shown in fig. 6, the first system at least includes a DCDC module 60, and the dc power grid connection method includes:
s51, connecting the first input terminal a of the DCDC module 60 at the high voltage side to the positive terminal of the first bus 61.
S52, connecting the first output terminal B of the DCDC module 60 on the low voltage side and the second input terminal C of the DCDC module 60 on the high voltage side to the positive terminal of the second bus bar 62.
S53, grounding the second output D of the DCDC module 60 on the low voltage side.
Wherein, in the present scheme, the voltage value U of the positive terminal of the first bus 61H+ greater than the voltage value U of the positive terminal of the second busbar 62L+。
Specifically, referring to fig. 7, in the present embodiment, the voltage level of the dc power grid or the dc line with a higher voltage level is defined as UH. The voltage class of the dc network or dc line of the lower voltage class is defined as UL. The power of interaction or transmission is defined as P. Considering UH and UL as two dc sources, respectively, a schematic diagram of the interconnection of the two dc sources is shown in fig. 6.
Assuming that UH and UL are constant voltages, the magnitude of the dc current can be controlled by controlling the magnitude of source E1, and the expression for the dc current is:
Id＝(UH-E1-UL)/R；
the power sent by the sending end is P1-UH Id; the power P2 ═ UL × Id that the low voltage class grid can receive directly; there is therefore another portion of power P3 — E1 Id, which, if injected into the low voltage class grid, can be fully injected into the low voltage class grid.
Based on the principle, the invention provides a direct current access method and system based on partial power conversion, as shown in fig. 6, the loss of a DC/DC converter is ignored, and the following relation is satisfied in fig. 6:
(UH-UL)*Id1＝UL*Id2
UH*Id1＝UL*(Id1+Id2)
the converter has a capacity of (UH-UL) Id1, and when the converter is in full power conversion, the converter has a capacity of UH Id1, so that the access scheme provided by the embodiment can greatly reduce the capacity of the converter.
On the basis of the above embodiments, the DCDC module provided in the embodiments of the present invention may include a first converter, a first converter transformer, and a second converter. And the output end of the first converter is connected with the input end of the second converter through the first converter transformer. The first input end of the first converter is connected with the positive end of the first bus, the second input end of the first converter and the first output end of the second converter are connected with the positive end of the second bus, and the second output end of the second converter is grounded.
In addition, as shown in fig. 8, the first system may further include two DCDC modules, one DCDC module is a first DCDC module, and the other DCDC module is a second DCDC module. The first input end of the first DCDC module is connected with the positive end of the first bus, the first output end of the first DCDC module and the second input end of the first DCDC module are connected with the positive end of the second bus, the first input end of the second DCDC module and the second output end of the second DCDC module are connected with the negative end of the second bus, the second output end of the first DCDC module is connected with the first output end of the second DCDC module and is grounded, and the second input end of the second DCDC module is connected with the negative end of the first bus.
On the basis of the foregoing embodiment, the first DCDC module provided in the embodiment of the present invention may include a first converter, a first converter transformer, and a second converter, an output end of the first converter is connected to an input end of the second converter through the first converter transformer, the second DCDC module includes a third converter, a second converter transformer, and a fourth converter, an output end of the third converter is connected to an input end of the fourth converter through the second converter transformer, and the dc power grid access method includes:
connecting the first input of the first converter to the positive terminal of the first bus bar and the first output of the second converter to the positive terminal of the second bus bar;
connecting a second input end of the second converter with the negative end of the first bus, and connecting a second output end of the second converter with the negative end of a second bus;
connecting the second input end of the first converter with the positive end of the first bus bar, and connecting the first input end of the second converter with the negative end of the second bus bar;
and connecting the second output end of the first converter with the first input end of the second converter, and grounding the second output end of the first converter.
Optionally, the first converter transformer and the first converter transformer are both double-winding transformers.
The first converter transformer and the first converter transformer are both three-winding transformers, and one phase of each three-winding transformer is connected with an alternating current power grid.
Schematically, the face-to-face converter shown in fig. 4, the MMC converter is relatively mature at present and is suitable for high voltage and extra-high voltage applications, so the DCDC is used to explain the access method of the present invention in detail. Taking an example that a +/-800 kV extra-high voltage direct current transmission line is connected into a +/-500 kV direct current power grid, symmetrical bipolar connection wires are adopted, and the connection method is shown in fig. 8.
To enhance the interactivity of the power flow direction, the converter transformer in fig. 8 may adopt a three-winding transformer, and the third winding may be connected to the ac power grid, as shown in fig. 9. With a 3-winding transformer, the inverter 1 and the inverter 2 can be power-interfaced with an ac system. By adopting double winding, the direct power of the current converter 1 and the current converter 2 meets the condition that P1+ P2 is 0 (the positive power direction is directed to the direct current side by neglecting the loss of the current converter and the loss of a transformer); if a third winding is provided, the power of the third winding is assumed to be P3, and the power square points to the alternating current power grid, the power constraint relation is P1+ P2+ P3 is 0, namely the constraint relation is changed into three quantity constraints, and the degree of freedom of control is increased.
Of course, the two-side converter can adopt a double-winding transformer and is connected to an alternating current power grid at the same time. For other forms of DCDC, the access scheme described in the present invention may also be employed. Adopt in the above-mentioned scheme demonstration is half-bridge type MMC transverter, also can adopt the transverter of other submodule piece topological schemes, for example full-bridge submodule piece MMC transverter, also can adopt the LCC transverter based on thyristor, reduce engineering cost.
Therefore, in the system of the scheme, one part is directly connected to the low-voltage-level direct-current power grid, the other part is connected to the direct-current power grid through the converter, and the conversion power of the converter is greatly reduced through the connection scheme. For example, a +/-800 kV direct-current transmission line is connected to a +/-500 kV direct-current power grid, the transmission power is 8000MW, a full-power converter is used, 8000MW conversion capacity is needed, and by adopting the method provided by the scheme, only 3000MW conversion capacity is needed, and the capacity of the converter is greatly reduced. The capacity ratio of capacity to full power conversion required by the scheme is calculated according to the following formula: (UH-UL)/UH.
On the basis of the above embodiments, the embodiment of the present invention further provides a system, which at least includes one DCDC module.
The first input end of the high-voltage side of the DCDC module is connected with the positive end of a first bus, the first output end of the low-voltage side of the DCDC module and the second input end of the high-voltage side of the DCDC module are connected with the positive end of a second bus, the second output end of the low-voltage side of the DCDC module is grounded, and the voltage value of the positive end of the first bus is larger than that of the positive end of the second bus.
Specifically, the DCDC module may include a first converter, a first converter transformer, and a second converter,
the output end of the first converter is connected with the input end of the second converter through the first converter transformer, the first input end of the first converter is connected with the positive end of the first bus, the second input end of the first converter and the first output end of the second converter are connected with the positive end of the second bus, and the second output end of the second converter is grounded.
In addition, the system provided in the embodiment of the present invention may further include two DCDC modules, where one DCDC module is a first DCDC module, and the other DCDC module is a second DCDC module.
The first input end of the first DCDC module is connected with the positive end of a first bus, the first output end of the first DCDC module and the second input end of the first DCDC module are connected with the positive end of a second bus, the first input end of the second DCDC module and the second output end of the second DCDC module are connected with the negative end of the second bus, the second output end of the first DCDC module is connected with the first output end of the second DCDC module and is grounded, and the second input end of the second DCDC module is connected with the negative end of the first bus.
Specifically, the first DCDC module includes a first converter, a first converter transformer and a second converter, an output end of the first converter is connected to an input end of the second converter through the first converter transformer, the second DCDC module includes a third converter, a second converter transformer and a fourth converter, and an output end of the third converter is connected to an input end of the fourth converter through the second converter transformer;
the first input end of the first converter is connected with the positive end of the first bus bar, and the first output end of the second converter is connected with the positive end of the second bus bar; the second input end of the second converter is connected with the negative end of the first bus, and the second output end of the second converter is connected with the negative end of the second bus; the second input end of the first converter is connected with the positive end of the first bus bar, and the first input end of the second converter is connected with the negative end of the second bus bar; and the second output end of the first converter is connected with the first input end of the second converter and is grounded.
In addition, the first converter transformer and the first converter transformer are both double-winding transformers.
On the basis of the above embodiment, the first converter transformer and the first converter transformer are both three-winding transformers, and one phase of the three-winding transformer is connected to an ac power grid.
Specifically, the first DCDC module and the second DCDC module are full-bridge submodule MMC current converters or thyristor-based LCC current converters.
The working principle of the system is described in the above method embodiment, and the limitation is not repeated here.
In summary, the present invention provides a dc power grid connection method and a system, where the dc power grid connection method is applied to a first system, where the first system includes at least one DCDC module, the dc power grid connection method connects a first input terminal of a high-voltage side of the DCDC module to a positive terminal of a first bus, connects a first output terminal of a low-voltage side of the DCDC module and a second input terminal of the high-voltage side of the DCDC module to a positive terminal of a second bus, and connects a second output terminal of the low-voltage side of the DCDC module to ground, where a voltage value of the positive terminal of the first bus is greater than a voltage value of the positive terminal of the second bus. The full power conversion is changed into partial power conversion, namely only partial power is connected into a low-voltage-level direct-current power grid through the converter, so that the system cost is reduced.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make numerous possible variations and modifications to the present teachings, or modify equivalent embodiments to equivalent variations, without departing from the scope of the present teachings, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.
Claims (9)
1. A direct current power grid access method is applied to a first system, the first system at least comprises one DCDC module, and the direct current power grid access method comprises the following steps:
connecting a first input end of a high-voltage side of the DCDC module with a positive end of a first bus, connecting a first output end of a low-voltage side of the DCDC module and a second input end of the high-voltage side of the DCDC module with a positive end of a second bus, and connecting a second output end of the low-voltage side of the DCDC module with the ground, wherein the voltage value of the positive end of the first bus is greater than that of the positive end of the second bus.
2. The dc grid access method according to claim 1, wherein the DCDC module comprises a first converter, a first converter transformer, and a second converter, wherein an output terminal of the first converter is connected to an input terminal of the second converter through the first converter transformer, and the dc grid access method comprises:
connecting the first input end of the first converter with the positive end of the first bus bar, connecting the second input end of the first converter and the first output end of the second converter with the positive end of the second bus bar, and connecting the second output end of the second converter with the ground.
3. The direct current grid access method according to claim 1, wherein the first system includes two DCDC modules, one DCDC module is a first DCDC module, and the other DCDC module is a second DCDC module, and the direct current grid access method includes:
connecting the first input end of the first DCDC module with the positive end of a first bus, connecting the first output end of the first DCDC module and the second input end of the first DCDC module with the positive end of a second bus, connecting the first input end of the second DCDC module and the second output end of the second DCDC module with the negative end of the second bus, connecting the second output end of the first DCDC module with the first output end of the second DCDC module and grounding, and connecting the second input end of the second DCDC module with the negative end of the first bus.
4. A system comprising at least one DCDC module,
the first input end of the high-voltage side of the DCDC module is connected with the positive end of a first bus, the first output end of the low-voltage side of the DCDC module and the second input end of the high-voltage side of the DCDC module are connected with the positive end of a second bus, the second output end of the low-voltage side of the DCDC module is grounded, and the voltage value of the positive end of the first bus is larger than that of the positive end of the second bus.
5. The system of claim 4, wherein the DCDC module includes a first converter, a first converter transformer, and a second converter,
the output end of the first converter is connected with the input end of the second converter through the first converter transformer, the first input end of the first converter is connected with the positive end of the first bus, the second input end of the first converter and the first output end of the second converter are connected with the positive end of the second bus, and the second output end of the second converter is grounded.
6. The system of claim 4, comprising two of said DCDC modules, one of said DCDC modules being a first DCDC module and the other of said DCDC modules being a second DCDC module;
the first input end of the first DCDC module is connected with the positive end of a first bus, the first output end of the first DCDC module and the second input end of the first DCDC module are connected with the positive end of a second bus, the first input end of the second DCDC module and the second output end of the second DCDC module are connected with the negative end of the second bus, the second output end of the first DCDC module is connected with the first output end of the second DCDC module and is grounded, and the second input end of the second DCDC module is connected with the negative end of the first bus.
7. The system of claim 5, wherein the first converter transformer is a two-winding transformer.
8. The system of claim 5, wherein the first converter transformer is a three-winding transformer having one phase connected to an AC power grid.
9. The system of claim 4, wherein the DCDC module is a full bridge sub-module MMC converter or a thyristor-based LCC converter.
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| US20130197704A1 (en) * | 2012-02-01 | 2013-08-01 | Abb Research Ltd | Dc connection scheme for windfarm with internal mvdc collection grid |
| CN109713910A (en) * | 2019-01-16 | 2019-05-03 | 浙江省检验检疫科学技术研究院 | Only handle the alternating current steady voltage plug of Partial Power |
| CN110380631A (en) * | 2019-05-14 | 2019-10-25 | 浙江省检验检疫科学技术研究院 | High power density DC power supply |
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