WO2011092302A2 - Electric energy grid connecting system and electric energy transmission system and method - Google Patents

Electric energy grid connecting system and electric energy transmission system and method Download PDF

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Publication number
WO2011092302A2
WO2011092302A2 PCT/EP2011/051245 EP2011051245W WO2011092302A2 WO 2011092302 A2 WO2011092302 A2 WO 2011092302A2 EP 2011051245 W EP2011051245 W EP 2011051245W WO 2011092302 A2 WO2011092302 A2 WO 2011092302A2
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WO
WIPO (PCT)
Prior art keywords
controllable switch
switch device
voltage
electric energy
current
Prior art date
Application number
PCT/EP2011/051245
Other languages
French (fr)
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WO2011092302A3 (en
Inventor
Xue Zhi Wu
Jing KE
Ji Long Yao
Original Assignee
Siemens Aktiengesellschaft
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Publication of WO2011092302A2 publication Critical patent/WO2011092302A2/en
Publication of WO2011092302A3 publication Critical patent/WO2011092302A3/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/06—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider
    • H02M3/07—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider using capacitors charged and discharged alternately by semiconductor devices with control electrode, e.g. charge pumps
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Definitions

  • the present invention relates to an electric energy grid connecting system and an electric energy transmission system and method.
  • FIG 1 is a schematic diagram showing a conventional electric energy grid connecting system which generates electric power by using offshore wind power.
  • the electric energy grid connecting system 10 comprises the offshore electric energy transmission system 100 and the onshore electric energy receiving system 150.
  • the electric energy transmission system 100 comprises N wind power generation units 102, N AC/DC converters 104, N
  • N is a positive integer.
  • the N wind power generation units 102 separately generate electric power using wind power to generate N ACs .
  • the N AC/DC converters 104 convert the generated N ACs into N DCs.
  • the N capacitors 108 filter the received N DCs to further remove the AC part from the N DCs.
  • the N DC/AC converters 110 convert the filtered N DCs to N ACs and input them to the local power grid 112.
  • the AC transformer 114 transforms the ACs in the local power grid 112 into the ACs which are suited for rectification.
  • the silicon controlled rectifier 118 rectifies the ACs transformed by the AC transformer 114 to obtain HVDC and input it into the HVDC link in the electric energy receiving system 150 for transmission.
  • the electric energy receiving system 150 comprises the HVDC link 152 and the silicon controlled inverter 156.
  • the HVDC link 152 transmits the HVDC input from the electric energy transmission system 100.
  • the silicon controlled inverter 156 converts the HVDC from the HVDC link 152 into AC and inputs it to the power grid on shore.
  • FIG. 1 shows a schematic diagram of another conventional electric energy grid connecting system
  • another conventional electric energy grid connecting system 20 comprises the offshore electric energy transmission system 200 and the onshore electric energy receiving system 250.
  • the electric energy transmission system 200 comprises N wind power generation units 202, N rectifiers (AC/DC) 206 and N capacitors 210.
  • the N wind power generation units 202 are configured to generate N wind power.
  • the N rectifiers 206 convert the generated N ACs to N DCs.
  • the N capacitors 210 filter the converted N DCs to further remove the AC part from the N DCs, wherein HVDC from the cascaded connection of the filtered N DCs is input to the HVDC link in the electric energy
  • the electric energy receiving system 250 comprises the HVDC transmission link 252, the grid connecting inverter 256 and the inverter transformer 260.
  • the HVDC transmission link 252 transmits the HVDC input from the electric energy
  • the grid connecting inverter 256 converts the HVDC from the HVDC transmission link 252 to AC.
  • the inverter transformer 260 transforms the AC converted by the grid connecting inverter 256 into the AC meeting the requirements of the power grid on shore and inputs it to the power grid on shore.
  • the electric energy grid connecting system 20 also has its shortcomings. Particularly, in the electric energy grid connecting system 20, the transmission is realized by converting the N ACs generated by the N wind power generation units 202 into N DCs and connecting them in series to become the HVDC. As a result, each wind power generation unit in the N wind power generation units 202 requires different voltage withstand capacity and insulation magnitude to the ground, wherein the wind power generation unit at the highest end may require dozens to hundreds of kilovolts of insulation voltage to the ground, which results in the need for diversified designs of the wind power generation units and AC/DC
  • the object of this invention is to provide an electric energy grid connecting system, wherein the electric energy grid connecting system does not require diversified designs of generation units, and has a smaller size and higher
  • a further object of this invention is to provide an electric energy transmission system and method, which does not require diversifying the design of generation units.
  • An electric energy grid connecting system comprising: N generation units for generating N ACs where N is an integer larger than 1; N rectifiers for translating said N ACs into N DCs; a booster for boosting the DC with a first voltage from the parallel connection of said N DCs to the DC with a second voltage for HVDC transmission; an HVDC transmission link for transmitting the DC with said second voltage; the grid connecting inverter for translating the DC with said second voltage from said HVDC transmission link into a second AC; and an inverter transformer for translating said second AC into the AC meeting said power grid requirements and outputting it to said power grid.
  • the electric energy transmission system comprising: N generation units for generating N ACs where N is an integer larger than 1; N rectifiers for translating said N ACs into N DCs; and a booster for boosting the DC with a first voltage from the parallel connection of said N DCs to the DC with a second voltage for HVDC
  • An electric energy transmission method comprising: translating the N ACs generated from the N generation units into N DCs where N is an integer larger than 1; connecting said N DCs in parallel to obtain the DC with the first voltage; boosting said DC with said first voltage DC with the second voltage for HVDC
  • Figure 1 is a schematic diagram showing a conventional electric energy grid connecting system for generating
  • Figure 2 is a schematic diagram showing another conventional electric energy grid connecting system for generating
  • Figure 3 is a schematic diagram showing the electric energy grid connecting system according to one embodiment of this invention .
  • Figure 4 is a schematic diagram showing the booster according to one embodiment of this invention.
  • Figure 5 is a schematic diagram showing the boosting unit according to one embodiment of this invention.
  • Figure 6 shows an example of how the controllable switch device according to one embodiment of this invention works.
  • Figure 7 is a schematic diagram showing the booster according to another embodiment of this invention.
  • FIG 3 is a schematic diagram showing the electric energy grid connecting system according to one embodiment of this invention.
  • the electric energy grid connecting system 30 comprises the offshore electric energy transmission system 300 and the onshore electric energy receiving system 350.
  • the electric energy transmission system 300 comprises the offshore electric energy transmission system 300 and the onshore electric energy receiving system 350.
  • N is an integer larger than 1.
  • N wind power generation units 302 are used to generate N ACs with the wind power on the sea. Wherein, each wind power generation unit of the N wind power generation units 302 generates 1 AC which can be a single-phase AC or multi-phase AC.
  • N rectifiers 306 are used to convert the N ACs generated by the N wind power generation units 302 into N DCs. Wherein, each rectifier of the N rectifiers 306 converts the AC generated by one of the N wind power generation units 302 into a DC, so that the N rectifiers 306 obtain N DCs by conversion .
  • the N capacitors 310 are used to filter the N DCs converted by the N rectifiers 306 to further remove the AC part from the N DCs. Wherein, each of the N capacitors 310 filters one of the N DCs converted by the N rectifiers 306.
  • the filtered N DCs are connected in parallel to form a DC ZL1 with the first voltage.
  • the first voltage is a low voltage .
  • the booster 314 is used to boost the DC ZL1 with the first voltage formed by parallel connection of the filtered N DCs to the DC ZL2 with the second voltage (high voltage DC) for HVDC transmission, and to export the DC ZL2 with the second voltage to the HVDC output link of the electric energy receiving system 350 for transmission.
  • the second voltage is higher than the first voltage.
  • the electric energy receiving system 350 comprises the HVDC transmission link 352, the grid connecting inverter 356 and the inverter transformer 360.
  • the HVDC transmission link 352 transmits the DC ZL2 with the second voltage input from the electric energy transmission system 300.
  • the grid connecting inverter 356 converts the DC ZL2 with the second voltage from the HVDC transmission link 352 into the AC.
  • the grid connecting inverter 356, for example, can be a conventional HVDC voltage source inverter, such as the HVDC light inverter of ABB or the HVDC plus inverter of Siemens.
  • the inverter transformer 360 converts the AC converted by the grid connecting inverter 356 into the AC meeting the
  • the electric energy grid connecting system 30 first, the N ACs generated by the N wind power generation units 302 are converted into N DCs, and then the N DCs are connected in parallel to become a low voltage DC, and then the low voltage DC is boosted to the HVDC for transmitting. Therefore, both the voltage withstand capability and the insulation magnitude to the ground are the same for each of the N wind power generation units 302, and there is no need to diversify the design of the N wind power generation units 302. In addition, the electric energy grid connecting system 30 only requires 4 energy conversions.
  • the electric energy grid connecting system 30 has a smaller size and higher efficiency.
  • FIG 4 is a schematic diagram showing the booster according to one embodiment of this invention.
  • the booster 314 comprises the M boosting stages 410 in cascaded connection and the HVDC loop formed by series connection of M+l filter capacitors 440, wherein M is a positive integer.
  • Each of the M boosting stages 410 in cascaded connection is used to boost the received DC by a preset multiple, wherein the DC received by the first boosting stage of the M boosting stages 410 in cascaded connection is the DC ZL1 with the first voltage, and every boosting stage of the M boosting stages 410 in cascaded connection comprises a boosting unit 412.
  • the two sides of the first filter capacitor of the M+l filter capacitors 440 are separately connected to the positive pole (Vin+) and negative pole (Vin-) of the DC ZL1 with the first voltage, the two sides of each of the M+l filter capacitors 440 with a serial number from 2 to M+l are separately
  • FIG. 5 is a schematic diagram showing the boosting unit according to one embodiment of this invention.
  • the boosting unit 412 comprises the first capacitor CI, the second capacitor C2, the first to the fifth
  • controllable switch devices T1-T5 the inductor LI and the control module KZ .
  • the two sides of the first capacitor CI are separately connected to the positive pole and negative pole of the input of its boosting unit 412.
  • the positive pole and negative pole of the first controllable switch device Tl are separately connected to the positive pole of the input of the boosting unit 412 and the positive pole of the second controllable switch device T2.
  • controllable switch device T2 are separately connected to the negative pole of the first controllable switch device Tl and the negative pole of the input of the boosting unit 412.
  • the positive and negative poles of the third controllable switch device T3 are separately connected to the positive pole of the input of the boosting unit 412 and the positive pole of the fourth controllable switch device T4.
  • controllable switch device T4 are separately connected to the negative pole of the third controllable switch device T3 and the positive pole of the output of the boosting unit 412.
  • the positive and negative poles of the fifth controllable switch device T5 are separately connected to the negative pole of the first controllable switch device Tl and the negative pole of the output of the boosting unit 412.
  • the two sides of the second capacitor C2 are separately connected to the negative pole of the third controllable switch device T3 and to one end of inductor LI, and the other end of inductor LI is connected to the positive pole of the fifth controllable switch device T5, that is, the inductor LI is connected between the positive poles of the second
  • the control module KZ is connected to the control poles of the first to the fifth controllable switch devices T1-T5 to control the first to the fifth controllable switch devices T1-T5, so that the second and the third controllable switch devices T2 and T3 complete the current while the other controllable switch devices break the current in the first time interval si of every work cycle Ts, that the first and the fourth controllable switch devices Tl and T4 complete the current while the other controllable switch devices break the current in the second time interval s2 of every work cycle Ts, and that the fourth and the fifth controllable switch devices T4 and T5 complete the current while the other controllable switch devices break the current in the third time interval s3 of every work cycle Ts, wherein the first time interval si, the second time interval s2 and the third time interval s3 can be the same or different in length.
  • Figure 6 shows an example of how the controllable switch device according to one embodiment of this invention works.
  • the shaded areas indicate that the controllable switch devices make the circuits, and the first time interval si, the second time interval s2 and the third time interval s3 are the same in length.
  • the control module KZ Under the control of the control module KZ, when the second controllable switch device T2 and the third controllable switch device T3 complete the current and the other
  • controllable switch devices break the current, the electric energy will be exchanged between the first capacitor CI and the second capacitor C2; when the first controllable switch device Tl and the fourth controllable switch device T4 complete the current and the other controllable switch devices break the current, the electric energy will be exchanged between the second capacitor C2 and the filter capacitor 440 connected to the positive pole of the input and the output of the boosting stage which the boosting unit 412 belongs to, so that the voltage is boosted; and when the fourth controllable switch device T4 and the fifth
  • controllable switch device T5 complete the current and the other controllable switch devices break the current, the electric energy will be exchanged between the second
  • the boosting units adopt the standardized and modularized design.
  • control mode of in-line hot backup can be adopted to improve reliability of the system and to reduce the amount of maintenance work.
  • each boosting stage comprises only one boosting unit; however, this invention is not limited to that.
  • each boosting stage near the low voltage side can comprise several boosting units that are connected in parallel. Therefore, when the DC with the first voltage has a large current, each boosting stage near the low voltage side can provide
  • FIG. 7 is a schematic diagram showing the booster according to another embodiment of this invention. As shown in Figure 7, the boosting stages closer to the low voltage side have more boosting units, and the boosting stages further away from the low voltage side have less boosting units.
  • the 1 st to the 5 th switch devices T1-T5 are all bidirectional-current switch devices, so that the
  • the 2 nd and the 4 th switch devices T2 and T4 when electric energy is transmitted only from the low voltage side to the high voltage side, can be diodes which allow current to flow in one way only, and their connection method is the same as an anti-parallel diode.
  • control module KZ is connected to the control poles of the 1 st , 3 rd and 5 th controllable switch devices Tl, T3 and T5 to control the 1 st , 3 rd and 5 th
  • controllable switch devices Tl, T3 and T5 so that the 3 rd controllable switch device T3 will complete the current and the other controllable switch devices will break the current in the 1 st time interval si of every work cycle Ts, that the 1 st controllable switch device Tl will complete the current and the other controllable switch devices will break the current in the 2 nd time interval s2 of every work cycle Ts, and that the 5 th controllable switch device T5 will complete the current and the other controllable switch devices will break the current in the 3 rd time interval s3 of every work cycle Ts.
  • the I s and 4 controllable switch devices Tl and T4 will complete the current and the other controllable switch devices will break the current so the electric energy will be exchanged between the 2 nd capacitor C2 and the filter capacitor 440 connected to the positive poles of the input and output of the boosting stage which the boosting unit 412 belongs to, so that the voltage is boosted.
  • the 4 th and 5 th In the 3 rd time interval s3 of every work cycle Ts, the 4 th and 5 th
  • the electric energy transmission system 300 comprises N capacitors 310.
  • this invention is not limited to that. In some other embodiments of this invention, for example, when the N DCs obtained from
  • the boosting unit 412 comprises the inductor LI to limit the charging current of the 2 nd
  • the present invention is not limited to that.
  • the inductor LI can be omitted.
  • the inductor LI is located between the 2 nd capacitor C2 and the 5 th
  • the present invention is not limited to that.
  • the inductor LI can be located in a place other than between the 2 n capacitor C2 and the 5 controllable switch device T5.
  • the inductor LI will consist of the 1 st inductor and the 2 nd inductor, wherein the 1 st inductor is connected between the positive poles of the 1 st capacitor CI and the input of the boosting unit 412, and the 2 nd inductor is connected between the positive poles of the 1 st controllable switch device Tl and the input of the boosting unit 412; alternatively, the 1 st inductor is
  • embodiments can be a gate-turn-off thyristor (GTO) , a giant transistor (GTR) , a vertical metal-oxide-semiconductor field- effect transistor (VMOSFET) , an insulated gate bipolar transistor (IGBT), an integrated gate commutated thyristor (IGCT) , a symmetrical gate commutated thyristor (SGCT) , etc.
  • GTO gate-turn-off thyristor
  • GTR giant transistor
  • VMOSFET vertical metal-oxide-semiconductor field- effect transistor
  • IGBT insulated gate bipolar transistor
  • IGCT integrated gate commutated thyristor
  • SGCT symmetrical gate commutated thyristor
  • the electricity generation units can also be hydropower electric generation units, solar power electric generation units, etc.
  • control module KZ can be implemented by using software or hardware such as an electric circuit.

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  • Dc-Dc Converters (AREA)
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Abstract

The present invention pertains to an electric energy grid connecting system and an electric energy transmission system and method, wherein the electric energy transmission system comprises: N generation units for generating N alternating currents (ACs) where N is an integer larger than 1; N rectifiers for translating said N ACs into N direct currents (DCs); and a booster for boosting the DC with a first voltage from the parallel connection of said N DCs to the DC with a second voltage for high-voltage DC (HVDC) transmission and outputting the DC with said second voltage to the HVDC transmission link for transmitting. With the electric energy grid connecting system and the electric energy transmission system and method, there is no need for diversifying the design of generation units.

Description

Specification
Electric Energy Grid Connecting System and Electric Energy
Transmission System and Method
Technical Field
The present invention relates to an electric energy grid connecting system and an electric energy transmission system and method.
Background Technology
With the energy shortage, people begin turning to renewable energy power generation for more energy. In this context, the wind power gengeration has been gained increasing attention because it has the advantages of low installation cost and less maintenance work needed, and being clean and
environmentally friendly. There is increasing offshore use of wind to generate electric power as the offshore wind farms have huge wind power resources.
Figure 1 is a schematic diagram showing a conventional electric energy grid connecting system which generates electric power by using offshore wind power. As shown in Figure 1, the electric energy grid connecting system 10 comprises the offshore electric energy transmission system 100 and the onshore electric energy receiving system 150.
The electric energy transmission system 100 comprises N wind power generation units 102, N AC/DC converters 104, N
capacitors 108, N DC/AC converters 110, a local power grid 112, an AC transformer 114 and a silicon controlled rectifier 118, wherein N is a positive integer. The N wind power generation units 102 separately generate electric power using wind power to generate N ACs . The N AC/DC converters 104 convert the generated N ACs into N DCs. The N capacitors 108 filter the received N DCs to further remove the AC part from the N DCs. The N DC/AC converters 110 convert the filtered N DCs to N ACs and input them to the local power grid 112. The AC transformer 114 transforms the ACs in the local power grid 112 into the ACs which are suited for rectification. The silicon controlled rectifier 118 rectifies the ACs transformed by the AC transformer 114 to obtain HVDC and input it into the HVDC link in the electric energy receiving system 150 for transmission.
The electric energy receiving system 150 comprises the HVDC link 152 and the silicon controlled inverter 156. Wherein, the HVDC link 152 transmits the HVDC input from the electric energy transmission system 100. The silicon controlled inverter 156 converts the HVDC from the HVDC link 152 into AC and inputs it to the power grid on shore.
From Figure 1, we can see that, in the electric energy grid connecting system 10, the ACs generated from the wind power generation units 102 are connected to the power grid on shore, requiring up to 5 energy conversions during this process, and use of a large number of energy conversion devices, which results in a huge bulk of the electric energy grid connecting system 10; moreover, there will be much energy loss during the 5 energy conversions, leading to a low efficiency of the electric energy grid connecting system 10. In order to overcome the shortcomings of the electric energy grid connecting system as shown in Figure 1, another
conventional electric energy grid connecting system for generating electric power by using wind power on the sea is provided. Figure 2 shows a schematic diagram of another conventional electric energy grid connecting system
generating electric power by using wind power on the sea. As shown in Figure 2, another conventional electric energy grid connecting system 20 comprises the offshore electric energy transmission system 200 and the onshore electric energy receiving system 250.
The electric energy transmission system 200 comprises N wind power generation units 202, N rectifiers (AC/DC) 206 and N capacitors 210. The N wind power generation units 202
respectively generate electric power by using the offshore wind power to generate N ACs. The N rectifiers 206 convert the generated N ACs to N DCs. The N capacitors 210 filter the converted N DCs to further remove the AC part from the N DCs, wherein HVDC from the cascaded connection of the filtered N DCs is input to the HVDC link in the electric energy
receiving system 250 for transmission.
The electric energy receiving system 250 comprises the HVDC transmission link 252, the grid connecting inverter 256 and the inverter transformer 260. The HVDC transmission link 252 transmits the HVDC input from the electric energy
transmission system 200. The grid connecting inverter 256 converts the HVDC from the HVDC transmission link 252 to AC. The inverter transformer 260 transforms the AC converted by the grid connecting inverter 256 into the AC meeting the requirements of the power grid on shore and inputs it to the power grid on shore.
From Figure 2 we can see that, in the electric energy grid connecting system 20, the AC generated by each wind power generation unit 202 is connected to the power grid on shore, requiring only 3 energy conversions during this process;
therefore, with respect to the electric energy grid
connecting system 10 in Figure 1, the electric energy grid connecting system 20 is more compact and has higher
efficiency.
However, the electric energy grid connecting system 20 also has its shortcomings. Particularly, in the electric energy grid connecting system 20, the transmission is realized by converting the N ACs generated by the N wind power generation units 202 into N DCs and connecting them in series to become the HVDC. As a result, each wind power generation unit in the N wind power generation units 202 requires different voltage withstand capacity and insulation magnitude to the ground, wherein the wind power generation unit at the highest end may require dozens to hundreds of kilovolts of insulation voltage to the ground, which results in the need for diversified designs of the wind power generation units and AC/DC
converters. In addition, this method also requires an
additional AC transmission line for supplying power from shore to sea to provide power to other devices of the wind power generation units when the wind power generation units are being repaired or cannot generate power normally. Considering these shortcomings of the existing prior art, the object of this invention is to provide an electric energy grid connecting system, wherein the electric energy grid connecting system does not require diversified designs of generation units, and has a smaller size and higher
efficiency .
A further object of this invention is to provide an electric energy transmission system and method, which does not require diversifying the design of generation units.
Summery of the invention
An electric energy grid connecting system according to this invention, comprising: N generation units for generating N ACs where N is an integer larger than 1; N rectifiers for translating said N ACs into N DCs; a booster for boosting the DC with a first voltage from the parallel connection of said N DCs to the DC with a second voltage for HVDC transmission; an HVDC transmission link for transmitting the DC with said second voltage; the grid connecting inverter for translating the DC with said second voltage from said HVDC transmission link into a second AC; and an inverter transformer for translating said second AC into the AC meeting said power grid requirements and outputting it to said power grid.
The electric energy transmission system according to this invention, comprising: N generation units for generating N ACs where N is an integer larger than 1; N rectifiers for translating said N ACs into N DCs; and a booster for boosting the DC with a first voltage from the parallel connection of said N DCs to the DC with a second voltage for HVDC
transmission and outputting the DC with said second voltage to the HVDC transmission link for transmission. An electric energy transmission method according to this invention, comprising: translating the N ACs generated from the N generation units into N DCs where N is an integer larger than 1; connecting said N DCs in parallel to obtain the DC with the first voltage; boosting said DC with said first voltage DC with the second voltage for HVDC
transmission; and outputting said DC with said second voltage to the HVDC transmission link for transmitting.
Brief Description of the Drawings
Other purposes, features and advantages of this invention are made more evident by the following detailed description in combination with the figures. In these figures,
Figure 1 is a schematic diagram showing a conventional electric energy grid connecting system for generating
electric power by using the wind power on the sea;
Figure 2 is a schematic diagram showing another conventional electric energy grid connecting system for generating
electric power by using the wind power on the sea;
Figure 3 is a schematic diagram showing the electric energy grid connecting system according to one embodiment of this invention ;
Figure 4 is a schematic diagram showing the booster according to one embodiment of this invention;
Figure 5 is a schematic diagram showing the boosting unit according to one embodiment of this invention;
Figure 6 shows an example of how the controllable switch device according to one embodiment of this invention works; and
Figure 7 is a schematic diagram showing the booster according to another embodiment of this invention.
Exemplary Embodiments
Embodiments of this invention will be described in detail as follows in conjunction with the attached figures.
Figure 3 is a schematic diagram showing the electric energy grid connecting system according to one embodiment of this invention. As shown in Figure 3, the electric energy grid connecting system 30 comprises the offshore electric energy transmission system 300 and the onshore electric energy receiving system 350. Wherein, the electric energy transmission system 300
comprises N wind power generation units 302, N rectifiers (AC/DC) 306, N capacitors 310 and boosters 314, wherein N is an integer larger than 1.
N wind power generation units 302 are used to generate N ACs with the wind power on the sea. Wherein, each wind power generation unit of the N wind power generation units 302 generates 1 AC which can be a single-phase AC or multi-phase AC.
N rectifiers 306 are used to convert the N ACs generated by the N wind power generation units 302 into N DCs. Wherein, each rectifier of the N rectifiers 306 converts the AC generated by one of the N wind power generation units 302 into a DC, so that the N rectifiers 306 obtain N DCs by conversion .
The N capacitors 310 are used to filter the N DCs converted by the N rectifiers 306 to further remove the AC part from the N DCs. Wherein, each of the N capacitors 310 filters one of the N DCs converted by the N rectifiers 306.
The filtered N DCs are connected in parallel to form a DC ZL1 with the first voltage. Wherein, the first voltage is a low voltage .
The booster 314 is used to boost the DC ZL1 with the first voltage formed by parallel connection of the filtered N DCs to the DC ZL2 with the second voltage (high voltage DC) for HVDC transmission, and to export the DC ZL2 with the second voltage to the HVDC output link of the electric energy receiving system 350 for transmission. Wherein, the second voltage is higher than the first voltage.
The electric energy receiving system 350 comprises the HVDC transmission link 352, the grid connecting inverter 356 and the inverter transformer 360.
Wherein, the HVDC transmission link 352 transmits the DC ZL2 with the second voltage input from the electric energy transmission system 300. The grid connecting inverter 356 converts the DC ZL2 with the second voltage from the HVDC transmission link 352 into the AC. The grid connecting inverter 356, for example, can be a conventional HVDC voltage source inverter, such as the HVDC light inverter of ABB or the HVDC plus inverter of Siemens. The inverter transformer 360 converts the AC converted by the grid connecting inverter 356 into the AC meeting the
requirements of the onshore power grid 390, and inputs it to the onshore power grid 390.
From the above description, we can see that, in the electric energy grid connecting system 30, first, the N ACs generated by the N wind power generation units 302 are converted into N DCs, and then the N DCs are connected in parallel to become a low voltage DC, and then the low voltage DC is boosted to the HVDC for transmitting. Therefore, both the voltage withstand capability and the insulation magnitude to the ground are the same for each of the N wind power generation units 302, and there is no need to diversify the design of the N wind power generation units 302. In addition, the electric energy grid connecting system 30 only requires 4 energy conversions.
Therefore, with respect to the conventional electric energy grid connecting system 10 as shown in Figure 1, the electric energy grid connecting system 30 has a smaller size and higher efficiency.
Figure 4 is a schematic diagram showing the booster according to one embodiment of this invention. As shown in Figure 4, the booster 314 comprises the M boosting stages 410 in cascaded connection and the HVDC loop formed by series connection of M+l filter capacitors 440, wherein M is a positive integer.
Each of the M boosting stages 410 in cascaded connection is used to boost the received DC by a preset multiple, wherein the DC received by the first boosting stage of the M boosting stages 410 in cascaded connection is the DC ZL1 with the first voltage, and every boosting stage of the M boosting stages 410 in cascaded connection comprises a boosting unit 412.
The two sides of the first filter capacitor of the M+l filter capacitors 440 are separately connected to the positive pole (Vin+) and negative pole (Vin-) of the DC ZL1 with the first voltage, the two sides of each of the M+l filter capacitors 440 with a serial number from 2 to M+l are separately
connected to the positive poles of the input and the output of one of the M boosting stages 440 in cascaded connection, and the DC output from the HVDC loop is the DC ZL2 with the second voltage.
Figure 5 is a schematic diagram showing the boosting unit according to one embodiment of this invention. As shown in Figure 5, the boosting unit 412 comprises the first capacitor CI, the second capacitor C2, the first to the fifth
controllable switch devices T1-T5, the inductor LI and the control module KZ .
The two sides of the first capacitor CI are separately connected to the positive pole and negative pole of the input of its boosting unit 412.
The positive pole and negative pole of the first controllable switch device Tl are separately connected to the positive pole of the input of the boosting unit 412 and the positive pole of the second controllable switch device T2.
The positive pole and the negative pole of the second
controllable switch device T2 are separately connected to the negative pole of the first controllable switch device Tl and the negative pole of the input of the boosting unit 412.
The positive and negative poles of the third controllable switch device T3 are separately connected to the positive pole of the input of the boosting unit 412 and the positive pole of the fourth controllable switch device T4.
The positive pole and the negative pole of the fourth
controllable switch device T4 are separately connected to the negative pole of the third controllable switch device T3 and the positive pole of the output of the boosting unit 412. The positive and negative poles of the fifth controllable switch device T5 are separately connected to the negative pole of the first controllable switch device Tl and the negative pole of the output of the boosting unit 412.
The two sides of the second capacitor C2 are separately connected to the negative pole of the third controllable switch device T3 and to one end of inductor LI, and the other end of inductor LI is connected to the positive pole of the fifth controllable switch device T5, that is, the inductor LI is connected between the positive poles of the second
capacitor C2 and the fifth controllable switch device T5. The control module KZ is connected to the control poles of the first to the fifth controllable switch devices T1-T5 to control the first to the fifth controllable switch devices T1-T5, so that the second and the third controllable switch devices T2 and T3 complete the current while the other controllable switch devices break the current in the first time interval si of every work cycle Ts, that the first and the fourth controllable switch devices Tl and T4 complete the current while the other controllable switch devices break the current in the second time interval s2 of every work cycle Ts, and that the fourth and the fifth controllable switch devices T4 and T5 complete the current while the other controllable switch devices break the current in the third time interval s3 of every work cycle Ts, wherein the first time interval si, the second time interval s2 and the third time interval s3 can be the same or different in length.
Figure 6 shows an example of how the controllable switch device according to one embodiment of this invention works. In the example shown in Figure 6, the shaded areas indicate that the controllable switch devices make the circuits, and the first time interval si, the second time interval s2 and the third time interval s3 are the same in length. Under the control of the control module KZ, when the second controllable switch device T2 and the third controllable switch device T3 complete the current and the other
controllable switch devices break the current, the electric energy will be exchanged between the first capacitor CI and the second capacitor C2; when the first controllable switch device Tl and the fourth controllable switch device T4 complete the current and the other controllable switch devices break the current, the electric energy will be exchanged between the second capacitor C2 and the filter capacitor 440 connected to the positive pole of the input and the output of the boosting stage which the boosting unit 412 belongs to, so that the voltage is boosted; and when the fourth controllable switch device T4 and the fifth
controllable switch device T5 complete the current and the other controllable switch devices break the current, the electric energy will be exchanged between the second
capacitor C2 and the boosting unit of the next boosting stage.
From the above description, we can see that, the boosting units adopt the standardized and modularized design.
Therefore, when constructing the electric energy grid
connecting system, the control mode of in-line hot backup can be adopted to improve reliability of the system and to reduce the amount of maintenance work.
Other variations
Those skilled in this field should appreciate that in the above embodiment, each boosting stage comprises only one boosting unit; however, this invention is not limited to that. In some other embodiments of this invention, each boosting stage near the low voltage side can comprise several boosting units that are connected in parallel. Therefore, when the DC with the first voltage has a large current, each boosting stage near the low voltage side can provide
sufficient current capacity, wherein the phase shift control method can be adopted for each boosting unit of the same boosting stage to reduce DC ripple of this boosting stage. Figure 7 is a schematic diagram showing the booster according to another embodiment of this invention. As shown in Figure 7, the boosting stages closer to the low voltage side have more boosting units, and the boosting stages further away from the low voltage side have less boosting units. Those skilled in this field should appreciate that in the above embodiments, the 1st to the 5th switch devices T1-T5 are all bidirectional-current switch devices, so that the
electric energy can be transmitted not only from the low voltage side to the high voltage side, but also from the high voltage side to the low voltage side. However, this invention is not limited to that. In some embodiments of this
invention, when electric energy is transmitted only from the low voltage side to the high voltage side, the 2nd and the 4th switch devices T2 and T4 can be diodes which allow current to flow in one way only, and their connection method is the same as an anti-parallel diode.
In the event that both the 2nd and the 4th switch devices T2 and T4 are diodes, the control module KZ is connected to the control poles of the 1st, 3rd and 5th controllable switch devices Tl, T3 and T5 to control the 1st, 3rd and 5th
controllable switch devices Tl, T3 and T5, so that the 3rd controllable switch device T3 will complete the current and the other controllable switch devices will break the current in the 1st time interval si of every work cycle Ts, that the 1st controllable switch device Tl will complete the current and the other controllable switch devices will break the current in the 2nd time interval s2 of every work cycle Ts, and that the 5th controllable switch device T5 will complete the current and the other controllable switch devices will break the current in the 3rd time interval s3 of every work cycle Ts.
In the event that both the 2nd and the 4th switch devices T2 and T4 are diodes, in the 1st time interval si of every work cycle Ts, the 2nd and 3rd controllable switch devices T2 and T3 will complete the current and the other controllable switch devices will break the current, and the electric energy will be exchanged between the 1st capacitor CI and the 2nd capacitor C2. In the 2nd time interval s2 of every work cycle Ts, the Is and 4 controllable switch devices Tl and T4 will complete the current and the other controllable switch devices will break the current so the electric energy will be exchanged between the 2nd capacitor C2 and the filter capacitor 440 connected to the positive poles of the input and output of the boosting stage which the boosting unit 412 belongs to, so that the voltage is boosted. In the 3rd time interval s3 of every work cycle Ts, the 4th and 5th
controllable switch devices T4 and T5 will complete the current and the other controllable switch devices will break the current so that the electric energy will be exchanged between the 2nd capacitor C2 and the boosting unit of the next boosting stage. Those skilled in this field should appreciate that in the above embodiments, the electric energy transmission system 300 comprises N capacitors 310. However, this invention is not limited to that. In some other embodiments of this invention, for example, when the N DCs obtained from
conversion by the N rectifiers 306 in the electric energy transmission system 300 contain only a little or no AC part, the N capacitors 310 are not necessary for the electric energy transmission system 300. Those skilled in this field should appreciate that in the above embodiments, the boosting unit 412 comprises the inductor LI to limit the charging current of the 2nd
capacitor C2. However, the present invention is not limited to that. In some other embodiments of this invention, for example, when the charging current of the 2nd capacitor C2 is not high, the inductor LI can be omitted.
Those skilled in this field should appreciate that in the above embodiments, in the boosting unit 412, the inductor LI is located between the 2nd capacitor C2 and the 5th
controllable switch device T5. However, the present invention is not limited to that. In some other embodiments of this invention, the inductor LI can be located in a place other than between the 2n capacitor C2 and the 5 controllable switch device T5.
If the inductor LI is not located between the 2nd capacitor C2 and the 5th controllable switch device T5, the inductor LI will consist of the 1st inductor and the 2nd inductor, wherein the 1st inductor is connected between the positive poles of the 1st capacitor CI and the input of the boosting unit 412, and the 2nd inductor is connected between the positive poles of the 1st controllable switch device Tl and the input of the boosting unit 412; alternatively, the 1st inductor is
connected between the negative poles of the 1st capacitor CI and the input of the boosting unit 412, and the 2nd inductor is connected between the negative poles of the 2nd switch device T2 and the input of the boosting unit 412.
Those skilled in this field should appreciate that the controllable switch devices as disclosed in the above
embodiments can be a gate-turn-off thyristor (GTO) , a giant transistor (GTR) , a vertical metal-oxide-semiconductor field- effect transistor (VMOSFET) , an insulated gate bipolar transistor (IGBT), an integrated gate commutated thyristor (IGCT) , a symmetrical gate commutated thyristor (SGCT) , etc.
Those skilled in this field should appreciate that the above embodiments are described by taking the example of using wind power generation units as the generation units. However, the present invention is not limited to that. In some other embodiments of this invention, the electricity generation units can also be hydropower electric generation units, solar power electric generation units, etc.
Those skilled in this field should appreciate that the control module KZ can be implemented by using software or hardware such as an electric circuit.
Those skilled in this field should appreciate that the embodiments of the present invention disclosed above, can be changed, altered or modified in various ways without departing from the spirit of the present invention, and thes changes, alterations and modifications should be within the protection scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

Claims
1. An electric energy transmission system, comprising:
N generation units for generating N alternating currents (ACs) where N is an integer larger than 1 ;
N rectifiers for translating said N ACs into N direct
currents (DCs) ; and
a booster for boosting the DC with a first voltage from the parallel connection of said N DCs to the DC with a second voltage for high-voltage DC (HVDC) transmission and
outputting the DC with said second voltage to the HVDC transmission link for transmitting.
2. The electric energy transmission system as claimed in claim 1, wherein
said booster further comprises M boosting stages in cascaded connection and an HVDC loop formed by cascaded connection of M+l filter capacitors, where M is a positive integer, wherein every one of said M boosting stages in cascaded connection is designed to increase the voltage of the received direct current by a preset multiple, wherein the DC received by the first boosting stage of said M boosting stages in cascaded connection is the DC with said first voltage,
and the two sides of the first filter capacitor of said M+l filter capacitors are separately connected to the positive and negative poles of the DC with said first voltage and the two sides of each of said M+l filter capacitors with a serial number from 2 to M+l are separately connected to the positive poles of the input and output of one of said M boosting stages in cascaded connection and the DC output from said high-voltage DC loop is the DC with said second voltage.
3. The electric energy transmission system as claimed in claim 2, wherein
each of said M boosting stages in cascaded connection
includes at least one boosting unit, wherein said at least one boosting unit is in parallel connection with one another.
4. The electric energy transmission system as claimed in claim 3, wherein every boosting unit of said at least one boosting unit comprises a first capacitor, a second
capacitor, a first controllable switch device, a second switch device, a third controllable switch device, a fourth switch device, a fifth controllable switch device and a control module,
wherein the two sides of said first capacitor are separately connected to the positive and negative poles of the input of the boosting unit which it belongs to,
and the positive and negative poles of said first
controllable switch device are separately connected to the positive pole of the input of its boosting unit and the positive pole of said second switch device, and the negative pole of said second switch device is connected to the
negative pole of the input of its boosting unit,
and the positive and negative poles of said third
controllable switch device are separately connected to the positive pole of the input of its boosting unit and the positive pole of said fourth switch device, and the negative pole of said fourth switch device is connected to the
positive pole of the output of its boosting unit,
and the positive and negative poles of said fifth
controllable switch device are separately connected to the negative pole of said first controllable switch device and the negative pole of the output of its boosting unit, the two sides of said second capacitor are separately
connected to the negative pole of said third controllable switch device and the positive pole of said fifth
controllable switch device, and
said control module is connected to the control poles of said first, third and fifth controllable switch devices to control said first, third and fifth controllable switch devices such that said third controllable switch device completes the current while said first and fifth controllable switch devices break the current in the first time interval of every work cycle, that said first controllable switch device completes the current while said third and fifth controllable switch devices break the current in the second time interval of every work cycle, and that said fifth controllable switch device completes the current while said first and third controllable switch devices break the current in the third time interval of every work cycle.
5. The electric energy transmission system as claimed in claim 4, wherein
said second switch device and said fourth switch device are controllable switch devices;
said control module is also connected to the control poles of said second and fourth switch devices to control said first to fifth controllable switch devices such that said third and second controllable switch devices complete the current while said first, fourth and fifth controllable switch devices break the current in said first time interval of every work cycle, that said first and fourth controllable switch devices complete the current while said second, third and fifth controllable switch devices break the current in said second time interval of every work cycle, and that said fourth and fifth controllable switch devices complete the current while said first, second and third controllable switch devices break the current in said third time interval of every work cycle .
6. The electric energy transmission system as claimed in claim 4, wherein
each of said at least one boosting unit further comprises an inductor, wherein said inductor is located between the positive poles of said second capacitor and said fifth controllable switch device.
7. The electric energy transmission system as claimed in claim 4, wherein
each of said at least one boosting unit further comprises a first inductor and a second inductor,
wherein, said first inductor is located between the positive poles of the input of said first capacitor and its boosting unit, and said second inductor is located between the
positive poles of said first controllable switch device and the input of its boosting unit, or, said first inductor is located between the negative poles of the input of said first capacitor and its boosting unit, and said second inductor is located between negative poles of said second switch device and the input of its boosting unit.
8. The electric energy transmission system as claimed in claim 1, wherein said N generation units are wind power generation units.
9. An electric energy transmission method, comprising:
translating the N ACs generated by the N generation units into N DCs where N is an integer bigger than 1 ;
connecting said N DCs in parallel to form a DC with a first voltage ;
boosting said DC with said first voltage to a DC with a second voltage for HVDC transmission; and
outputting said DC with said second voltage to the HVDC transmission link for transmission.
10. The electric energy transmission method as claimed in claim 9, wherein the voltage boosting step further comprises: boosting the DC with said first voltage to the DC with said second voltage through several boostings, wherein each of said several boostings increases the voltage by a preset multiple .
11. An electric energy grid connecting system, comprising:
N generation units for generating N ACs where N is an integer larger than 1 ;
N rectifiers for translating said N ACs into N DCs;
a booster for boosting the DC with a first voltage from the parallel connection of said N DCs to the DC with a second voltage for HVDC transmission;
an HVDC transmission link for transmitting the DC with said second voltage; a grid connecting inverter for translating the DC with said second voltage from said HVDC transmission link into a second AC; and
an inverter transformer for translating said second AC into the AC meeting said power grid requirements and outputting it to said power grid.
12. The electric energy grid connecting system as claimed in claim 11, wherein
said booster further comprises M boosting stages in cascaded connection and a high-voltage DC loop formed by cascaded connection of M+l filter capacitors where M is a positive integer, wherein
each of said M boosting stages in cascaded connection is designed to increase the voltage of the received direct current by a preset multiple, wherein the DC received by the first boosting stage of said M boosting stages in cascaded connection is the DC with said first voltage,
and the two sides of the first filter capacitor of said M+l filter capacitors are separately connected to the positive and negative poles of the DC with said first voltage and the two sides of each of said M+l filter capacitors with a serial number from 2 to M+l are separately connected to the positive poles of the input and the output of one of said M boosting stages in cascaded connection, and the DC output from said high-voltage DC loop is the DC with said second voltage.
13. The electric energy grid connecting system as claimed in claim 12, wherein
each of said M boosting stages in cascaded connection
includes at least one boosting unit, wherein said at least one boosting unit is in parallel connection with one another.
14. The electric energy grid connecting system as claimed in claim 13, wherein each of said at least one boosting unit comprises a first capacitor, a second capacitor, a first controllable switch device, a second switch device, a third controllable switch device, a fourth switch device, a fifth controllable switch device and a control module,
wherein the two sides of said first capacitor are separately connected to the positive and negative poles of the input of the boosting unit which said first capacitor belongs to, and the positive and negative poles of said first
controllable switch device are separately connected to the positive pole of said input and the positive pole of said second switch device, and the negative pole of said second switch device is connected to the negative pole of said input,
and the positive and negative poles of said third
controllable switch device are separately connected to the positive pole of said input and the positive pole of said fourth switch device, and the negative pole of said fourth switch device is connected to the positive pole of the output which said fourth switch device belongs to,
and the positive and negative poles of said fifth
controllable switch device are separately connected to the negative pole of said first controllable switch device and the negative pole of said output,
the two sides of said second capacitor are separately
connected to the negative pole of said third controllable switch device and the positive pole of said fifth
controllable switch device, and
said control module is connected to the control poles of said first, third and fifth controllable switch devices to control said first, third and fifth controllable switch devices such that said third controllable switch device completes the current while said first and fifth controllable switch devices break the current in the first time interval of every work cycle, that said first controllable switch device completes the current while said third and fifth controllable switch devices break the current in the second time interval of every work cycle, and that said fifth controllable switch device completes the current while said first and third controllable switch devices break the current in the third time interval of every work cycle.
15. The electric energy grid connecting system as claimed in claim 14, wherein
said second switch device and said fourth switch device are controllable switch devices;
said control module is also connected to the control poles of said second and fourth switch devices to control said first to fifth controllable switch devices such that said third and second controllable switch devices complete the current while said first, fourth and fifth controllable switch devices break the current in said first time interval of every work cycle, that said first and fourth controllable switch devices complete the current while said second, third and fifth controllable switch devices break the current in said second time interval of every work cycle, and that said fourth and fifth controllable switch devices complete the current while said first, second and third controllable switch devices break the current in said third time interval of every work cycle .
PCT/EP2011/051245 2010-01-29 2011-01-28 Electric energy grid connecting system and electric energy transmission system and method WO2011092302A2 (en)

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