Power generation and transmission system, control device, control method, facility method for power transmission cable, and computer program

Abstract

A power generation and transmission system according to an embodiment of the present invention comprises: a power conditioner capable of outputting single-phase or three-phase AC power having a prescribed frequency and voltage; a conversion device that supplies the AC power output of the power conditioner to a power grid; power transmission cables for at least three phases and for transmitting the output power of the power conditioner to the conversion device; a detection unit that detects a ground-fault accident that occurred in the power transmission cables; and a control device that, if a ground fault accident was detected, generates an instruction signal for a single-phase operation mode in which single-phase power transmission is carried out using, among the power transmission cables, cables other than the cables in which the ground-fault accident has occurred. The power conditioner is characterized by outputting, in accordance with the instruction signal, single-phase AC power via the cables other than the cables in which the ground-fault accident has occurred.

Description

Power generation and transmission system, control device, control method, power transmission cable installation method, and computer program

[0001] An embodiment of the present invention relates to a power generation and transmission system, a control device, a control method, a method for installing a power transmission cable, and a computer program.

[0002] In preparation for the large-scale introduction of offshore wind power generation, development of systems that transmit electricity from offshore wind turbines to the onshore power grid is progressing. Some proposed power generation and transmission systems include those with matrix converters or modular multilevel converters. Other power generation and transmission systems include those with long-distance cables, such as those tens of kilometers or hundreds of kilometers. Furthermore, some power generation and transmission systems transmit electricity using three-phase AC. These systems include those that use triplex cables, which are made up of three cables, and those that use three single-phase cables. Power generation and transmission systems that operate multiple circuits in parallel improve transmission capacity.

[0003] However, if a fault occurs in one of the three-phase cables, power transmission cannot be continued, resulting in the loss of opportunities to transmit and generate power.

[0004] CN114142463ACN114156878A

[0005] The problem that the present invention aims to solve is to provide a power generation and transmission system, a control device, a control method, a method for installing power transmission cables, and a computer program that enable continuous power transmission using single-phase operation using two of the three-phase cables in a power generation and transmission system that has converters only on land.

[0006] According to an embodiment, the power generation and transmission system includes a power conditioner capable of outputting single-phase or three-phase AC power of a predetermined frequency and voltage, a converter that supplies the AC power output of the power conditioner to a power grid, at least three-phase power transmission cables that transmit the output power of the power conditioner to the converter, a detector that detects a ground fault that occurs in the power transmission cables, and a controller that, when a ground fault is detected, generates an instruction signal for switching to a single-phase operation mode in which single-phase power is transmitted through the remaining cables of the power transmission cables except for the cable in which the ground fault occurred. The power conditioner outputs single-phase AC power through the remaining cables except for the cable in which the ground fault occurred in response to the instruction signal.

[0007] FIG. 1 is a block diagram showing the configuration of a power generation and transmission system according to a first embodiment. FIG. 2 is a block diagram showing the detailed configuration of the power generation and transmission system according to the first embodiment. FIG. 3 is a flowchart showing the operation of the power generation and transmission system according to the first embodiment. FIG. 4 is a block diagram explaining the operation of the power generation and transmission system according to the first embodiment. FIG. 5 is a block diagram explaining the operation of the power generation and transmission system according to the first embodiment. FIG. 6 is a block diagram showing the configuration of a power generation and transmission system according to a second embodiment. FIG. 7 is a block diagram showing the configuration of a power generation and transmission system according to a third embodiment. FIG. 8 is a flowchart showing a method of installing a power transmission cable according to a fourth embodiment.

[0008] (Configuration of First Embodiment) Hereinafter, a power generation and transmission system according to an embodiment will be described with reference to the drawings. In the following description, components having the same or similar functions will be denoted by the same reference numerals, and duplicated descriptions may be omitted.

[0009] 1 shows a power generation and transmission system 100 according to a first embodiment. The power generation and transmission system 100 includes, for example, a wind turbine 1, a power collection cable 2, a step-up substation 3, an export cable 4, and a grid-connection converter station 5. The power generation and transmission system 100 may be operated based on commands from a control device 6.

[0010] The wind turbine 1 is, for example, a wind power generation device that can be located offshore. The current collection cable 2 is a cable that transmits the power generated by the wind turbine 1 to a step-up substation 3. The step-up substation 3 is, for example, a transforming device that can be located offshore, and boosts the voltage to a level suitable for power transmission. The export cable 4 is a cable that transmits the output power of the step-up substation 3 to a grid-connection converter station 5.

[0011] The power generation and transmission system 100 may include a plurality of wind turbines 1 and a plurality of power collection cables 2. Furthermore, a plurality of wind turbines 1 may be connected to each of the plurality of power collection cables 2. The power generation and transmission system 100 may also include a plurality of export cables 4 and a plurality of step-up substations 3. The plurality of step-up substations 3 may be electrically connected to one another.

[0012] The wind turbine 1 includes a wind turbine generator 11, a power conditioning subsystem (PCS) 12, and a wind turbine step-up transformer 13. The wind turbine generator 11 is, for example, a generator equipped with a wind turbine and powered by wind power. The wind turbine generator 11 may also be a generator that generates electricity using other energy sources such as solar power generation.

[0013] The PCS 12 is a conversion device capable of converting voltages generated by the wind turbine generator 11, solar power generation, or other energy sources, into grid power voltages. The PCS 12 has a conversion function for converting direct current to alternating current, and an adjustment function for adjusting the output frequency, output voltage, output current, etc. The PCS 12 of the embodiment has a three-phase operation mode and a single-phase operation mode. The three-phase operation mode is an operation mode in which the output power of the wind turbine generator 11 is output as a three-phase AC output, and the single-phase operation mode is an operation mode in which the output power of the wind turbine generator 11 is output as a single-phase AC output.

[0014] The step-up substation 3 is a transforming device equipped with a step-up transformer 31 that steps up the input voltage to a predetermined voltage. The step-up substation 3 may be equipped with either or both of a circuit breaker on the collector cable side (not shown) and a circuit breaker on the export cable side. The circuit breaker may constitute a three-phase isolation circuit breaker. The step-up substation 3 may also be equipped with an instrument transformer, an instrument current transformer, a bus monitoring device, an on-site power supply, and the like (not shown). The step-up transformer 31 may have, for example, a Y-Y-Δ connection or a Y-Δ connection. The step-up transformer 31 may be a three-phase transformer, or may be three single-phase transformers connected in a three-phase configuration.

[0015] The grid-connection converter station 5 is a conversion device that includes a converter 51 and connects the power generated by the wind turbine 1 to the grid power. The grid-connection converter station 5 includes, for example, a back-to-back (BTB) converter or a modular multilevel matrix converter (MMMC). The BTB converter includes, for example, two sets of modular multilevel converters (MMC). The BTB converter is, for example, a converter that provides an AC / DC / AC conversion function. The MMMC is, for example, a converter that provides an AC / AC conversion function. The grid-connection converter station 5 may include a converter transformer (not shown). The grid-connection converter station 5 may include a circuit breaker, which may serve to protect the converter transformer. It is preferable that the grid-connection converter station 5 be located on land.

[0016] The collecting cable 2 is a cable that transmits the power generated by the wind turbine 1 to the step-up substation 3. The export cable 4 is a cable that transmits the generated power that has been boosted by the step-up substation 3 to the grid-connection converter station 5. The collecting cable 2 and the export cable 4 may each be made of, for example, XLPE (Cross-linked polyethylene insulated vinyl sheath) cable. Multiple collecting cables 2 and multiple export cables 4 may be used in parallel. The collecting cable 2 and the export cable 4 include cables corresponding to each phase of the generated power. In other words, to transmit three-phase AC power, cables corresponding to the three phases are provided. The cable corresponding to the three phases may be composed of at least one cable, for example, three single-phase cables as one cable.

[0017] The power generation and transmission system 100 may include a compensating reactor in the step-up substation 3 or the link converter station 5 to compensate for leading reactive power generated in the collector cable 2 or the export cable 4 .

[0018] Next, the configuration of the power generation and transmission system 100 of the first embodiment will be described in more detail with reference to FIG.

[0019] The PCS 12 of this embodiment is configured to be able to output three-phase power or single-phase power by receiving the power output from the generator 11. In the example shown in FIG. 2, the PCS 12 converts the power output into a voltage E １ａ , E １ｂ , E １ｃ Output as

[0020] In the example shown in Fig. 2, the wind turbine step-up transformer 13 of this embodiment has a Y-Δ connection. １ａ , E １ｂ , E １ｃ Voltage E ２ａ , E ２ｂ , E ２ｃ The wind turbine step-up transformer 13 converts the current I １ａ , I １ｂ , I １ｃ current I ２ａ , I ２ｂ , I ２ｃConvert to.

[0021] The current collecting cable 2 has cables 2a to 2c corresponding to three phases. The cables 2a to 2c are connected to the wind turbine step-up transformer 13. ２ａ ~E ２ｃ and current I ２ａ ~I ２ｃ At this time, the voltage and current on the step-up substation 3 side of the cables 2a to 2c are respectively E ３ａ ~E ３ｃ and I ３ａ ~I ３ｃ is.

[0022] The step-up substation 3 includes a Y-Y connected step-up transformer 31, primary-side circuit breakers 32a to 32c, and secondary-side circuit breakers 33a to 33c. The primary-side circuit breakers 32a to 32c are circuit breakers that can disconnect the cables 2a to 2c that make up the current collecting cable 2 from the primary side of the step-up transformer 31. The secondary-side circuit breakers 33a to 33c are circuit breakers that can disconnect the cables 4a to 4c that make up the export cable 4 from the secondary side of the step-up transformer 31. The Y-Y connected step-up transformer 31 may further include a delta-connected tertiary winding (not shown).

[0023] 2, the step-up substation 3 is equipped with primary-side circuit breakers 32a to 32c and secondary-side circuit breakers 33a to 33c, but is not limited to this. Circuit breakers may be provided at the connection ends of the wind turbine 1 with the cables 2a to 2c, and at the connection ends of the grid-connection converter station 5 with the cables 4a to 4c that make up the export cable 4.

[0024] The export cable 4 includes cables 4a to 4c corresponding to three phases. The cables 4a to 4c are connected to the secondary side voltage E ４ａ ~E ４ｃ and current I ４ａ ~I ４ｃ is transmitted to the interconnection converter station 5.

[0025] The grid-connection converter station 5 includes a converter 51 and a converter transformer 52. The converter transformer 52 is a transformer that converts the voltage of the power received from the export cable 4 into a voltage suitable for the converter 51. In the example shown in FIG. 2, the converter transformer 52 of this embodiment has a Y-Y connection. The converter transformer 52 converts the voltage E ５ａ ~E ５ｃ and current I ５ａ ~I ５ｃ Voltage E ６ａ ~E ６ｃ and current I ６ａ ~I ６ｃ The converter 51 is a group of devices that connects the power generated by the wind turbine 1 to the power grid. In addition to the example shown in Fig. 2, an additional converter transformer 52 may be connected between the converter 51 and the power grid. Furthermore, the grid-connected converter station 5 may include a circuit breaker.

[0026] The control device 6 is a computer device capable of controlling the opening and closing of the primary-side circuit breakers 32a-32c and the secondary-side circuit breakers 33a-33c. The control device 6 may have a function to determine the location of a fault in the current collection cable 2 or the export cable 4 by receiving signals from relays and the like provided in the wind turbine 1, the step-up substation 3, and the grid-connection converter station 5. The control device 6 may also have a function to control the operating state of the wind turbine 1, and a function to control the wind turbine 1, the step-up substation 3, and the grid-connection converter station 5 according to their states. Examples of the functions of the control device 6 include limiting the output of the wind turbine 1 when there is excess power on the receiving side of the grid-connection converter station 5, stopping the wind turbine 1 or changing the load tap at the step-up substation 3 when a typhoon is approaching, and switching the operating mode of the grid-connection converter station 5 according to the power generation capacity of the wind turbine 1.

[0027] Additionally, the control device 6 can control the operation mode of the PCS 12. The control device 6 can also have a function to issue instructions to disconnect the location where the accident occurred from the grid. After disconnection control due to an accident, the control device 6 can switch the operation mode of the PCS 12 and converter 51 of the wind turbine 1 constituting the power generation and transmission system 100 from three-phase to single-phase, and resume operation. That is, the PCS 12 is controlled to output single-phase AC power when the power collection cable 2 and the export cable 4 consist of two single-phase cables, and is controlled to output three-phase AC power when the power collection cable 2 and the export cable 4 consist of three single-phase cables. When it is necessary to disconnect a neutral grounding resistor installed in the power generation and transmission system, the control unit 101 or the control center 102 may be responsible for controlling the disconnection of the neutral grounding resistor.

[0028] A plurality of control devices 6 may be provided. In this case, the plurality of control devices 6 may switch the operation state of the power generation and transmission system independently or in cooperation with each other. The control device 6 performs opening and closing control of the primary-side circuit breakers 32a to 32c and the secondary-side circuit breakers 33a to 33c by, for example, a hardware processor such as a CPU (Central Processing Unit) (computer) executing a computer program (software).

[0029] The control device 6 may execute control using hardware (including circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit), or may execute control using a combination of software and hardware. The program may be stored in advance in a storage device (a storage device having a non-transitory storage medium) such as an HDD or flash memory of the controller, or may be stored in a removable storage medium such as a DVD or CD-ROM, and installed in the storage device by inserting the storage medium (non-transitory storage medium) into a drive device. The program may be stored in the storage device.

[0030] 2 and 3, the operation of the power generation and transmission system 100 will be described. In the following, when a single-phase accident occurs while the power generation and transmission system 100 is operating in a three-phase operation mode, control for switching to single-phase operation and continuing operation will be described.

[0031] In the power generation and transmission system 100, the PCS 12 and the converter 51 are operated in a three-phase operation mode during normal operation. １ａ ~E １ｃ , current I １ａ ~I １ｃ The control device 6 connects the primary-side circuit breakers 32a to 32c and the secondary-side circuit breakers 33a to 33c. The current collecting cable 2 transmits three-phase AC power via cables 2a to 2c, and the export cable 4 transmits three-phase AC power via cables 4a to 4c. The grid-connection converter station 5 outputs three-phase AC power (S200).

[0032] If a ground fault occurs in cable 4c of the export cable 4, a current will flow from the power generation and transmission system 100 toward the ground fault point. The step-up substation 3 and converter station 5, which are connected to both ends of the export cable 4, detect an increase in the current flowing into the ground fault point and disconnect (open) the secondary-side circuit breakers 33a to 33c, which are the circuit breakers closest to the ground fault location (S210). If a circuit breaker is provided on the export cable side of the interconnection converter station 5, the circuit breaker on the export cable side of the interconnection converter station 5 may be shut off. Opening the circuit breaker stops the current flowing into the ground fault point and resolves the fault. Additionally, a gate block may be provided to protect the converter 51.

[0033] 4 shows the state where the circuit breakers are opened and the fault is resolved. In FIG. 4, as a result of the fault occurring in the cable 4c, the secondary circuit breakers 33a to 33c are shut off (disconnected).

[0034] Next, the control device 6 of the power generation and transmission system 100 identifies the phase in which the fault has occurred (S220). When the step-up substation 3 and the grid-connection converter station 5 detect an increase in the current flowing into the ground fault point, i.e., the occurrence of a fault, they notify the control device 6 of the occurrence of the fault and the phase in which the fault has occurred. The notification of the occurrence of the fault to the control device 6 may be made by the wind turbine 1 or the grid-connection converter station 5, or may be made by a higher-level control system (not shown).

[0035] If the power generation and transmission system 100 cannot perform single-phase operation (No in S230), the control device 6 maintains the primary-side circuit breakers 32a to 32c and the secondary-side circuit breakers 33a to 33c in the open state (S210). An example of a case in which the power generation and transmission system 100 cannot perform single-phase operation is when the accident is large enough that two or more of the cables 4a to 4c are faulted.

[0036] If the power generation and transmission system 100 is capable of single-phase operation (Yes in S230), the control device 6 switches the PCS 12 and the converter 51 to the single-phase operation mode (S240). Specifically, the control device 6 generates an instruction signal instructing the single-phase operation mode and transmits it to the PCS 12 and the converter 51. In the single-phase operation mode, the power generation and transmission system 100 transmits power from the wind turbine 1 to the grid-connection converter station 5 as single-phase power.

[0037] Next, when the step-up substation 3 and the converter station 5 receive the instruction signal for the single-phase operation mode, they reconnect the secondary-side circuit breakers 33a to 33c, which are the open circuit breakers closest to the ground fault location, except for the faulty phase (S250). In other words, the circuit breaker corresponding to the faulty phase remains disconnected. When circuit breakers are provided on the export cable side of the interconnection converter station 5, the circuit breakers corresponding to the faulty phase are also reconnected.

[0038] Furthermore, when the PCS 12 and converter 51 receive a signal indicating the single-phase operation mode, they control the current and voltage output to each phase to prevent excessive current from flowing into the neutral grounding resistor NGR of each transformer. Of course, there are cases where a transformer does not have a neutral grounding resistor NGR. In addition, the PCS 12 and converter 51 control the current and voltage output to each phase to prevent excessive current from flowing into the neutral grounding resistor NGR and to prevent excessive potentials at the neutral and at each part of each phase.

[0039] For example, the PCS 12 and the converter 51 are connected to the neutral ground resistor NGR in FIG. １ｎ ~E ６ｎ and current I １ｎ ~I ６ｎ The output voltage and output current are controlled so that they do not exceed a predetermined value and do not become excessive.

[0040] 5 shows the current and voltage of each part in single-phase operation mode when cable 4c has failed. In the grid converter station 5, no current flows through the phase corresponding to the failed cable 4c on the wind turbine side, so the voltage to ground E ５ｄ and current I ５ｄ The converter transformer 52 operates in a single phase. ５ｄ and current I ５ｄ voltage to ground E ６ｄ and current I ６ｄ and outputs it to the converter 51.

[0041] In the export cable 4 connecting the interconnection converter station 5 and the step-up substation 3, the voltage to ground E ５ｄ and E ４ｄ and current I ５ｄ and I ４ｄ The capacitance and leakage current of the export cable cause the ５ｄ and E ４ｄ , I ５ｄ and I ４ｄ There may be differences in.

[0042] In the step-up substation 3, no current flows through the faulty phase on either the primary or secondary side. In addition, to prevent a voltage from being induced in the phase of the transformer 31, a voltage to ground E ４ｄand current I ４ｄ and voltage to ground E ３ｄ and current I ３ｄ Single-phase operation is performed.

[0043] In the wind turbine step-up transformer 13 of the wind turbine 1 connected via the cables 2a and 2c of the current collecting cable 2, the delta-connected transformer on the secondary side is ２ｄ and current I ２ｄ Due to the capacitance and leakage current of the collector cable 2, ３ｄ and E ２ｄ , I ３ｄ and I ２ｄ There may be differences in.

[0044] On the other hand, the Y-connection transformer on the primary side of the wind turbine step-up transformer 13 of the wind turbine 1 has one phase with a ground voltage E １ｄ and current I １ｄ , and the other two phases are the voltages to ground E １ｄ / 2 and current I １ｄ One phase of the delta-connected transformer on the primary side of the wind turbine step-up transformer 13 of the wind turbine 1 is operated at a voltage to ground E １ｄ and current I １ｄ , and the other two phases are the voltages to ground E １ｄ / 2 and current I １ｄ By operating in single-phase / 2 mode, even if cable 4c fails, excessive current will not flow through the neutral grounding resistors of the transformers that make up power generation and transmission system 100, and excessive voltage will not be induced in the windings or cables, causing them to fail. In other words, power transmission to the grid can be continued in single-phase operation mode.

[0045] In the power generation and transmission system 100, even if the cable 4c breaks down, the power transmission can be continued in the single-phase operation mode, and therefore the power generation and transmission system 100 can reduce the loss of power transmission opportunities.

[0046] When comparing the operating state before the fault with the operating state during the fault, the power transmission capacity is reduced. The converter 51 of the grid-connection converter station 5 will be described below with AC input.

[0047] Before the fault, the phase voltage of each phase was E ６ The current flowing through each phase is I ６Then the capacity is 3E ６ I ６ The phase voltage of each phase after the fault was E ６ｄ If the allowable maximum value of the line voltage does not change before and after the fault, the line voltage before the fault is three-phase operation, so √3E ６ Since the line voltage after the fault is single-phase operation, ６ｄ Therefore, E ６ｄ =√3E ６ It is necessary to suppress it to / 2.

[0048] If the maximum allowable current flowing through each phase remains the same before and after the fault, then I ６ｄ =I ６ Therefore, after the fault, the transmittable capacity is 2E ６ｄ I ６ｄ =√3E ６ I ６ This reduces the power consumption to 1 / √3 of the value before the failure.

[0049] In this way, although the transmission capacity decreases in single-phase operation mode, power transmission can continue until the cable is replaced, thereby reducing the loss of power transmission opportunities. To avoid problems such as heat, electric fields, magnetic fields, and vibrations that arise when switching from three-phase operation mode to single-phase operation mode, the operating voltage and transmission current may be further reduced from before the fault. In this case, the transmission capacity will be less than 1 / √3 times that before the fault.

[0050] Second Embodiment Next, a power generation and transmission system according to a second embodiment will be described with reference to Fig. 6. A power generation and transmission system 101 according to this embodiment is configured by connecting two power generation and transmission systems according to the first embodiment in parallel. In the following description, common elements will be denoted by common reference numerals, and duplicated descriptions will be omitted.

[0051] In a power generation and transmission system 101 of this embodiment, the grid-connection converter station 5 of the power generation and transmission system 100 of the first embodiment includes a plurality of AC / DC converters 53, such as modular multilevel converters. A plurality of AC / DC converters 53 may be connected in parallel. A power generation and transmission system 100a having a common configuration with the power generation and transmission system 100 is connected in parallel. When the converter 51 is configured by connecting a plurality of AC / DC converters 53, a DC bus 54 is provided between the AC / DC converters 53, and the converters 51 may be connected to other AC / DC converters 53a via the DC bus 54. That is, the AC / DC converter may be connected back-to-back (BTB) to a plurality of modular multilevel converters via the DC bus.

[0052] According to the power generation and transmission system 101 of this embodiment, power generation and transmission systems each having a plurality of wind turbines can be interconnected.

[0053] Third Embodiment Next, a power generation and transmission system according to a third embodiment will be described with reference to Fig. 7. The power generation and transmission system 102 of this embodiment is configured by further connecting a DC power generation and transmission system in parallel to the power generation and transmission system according to the first or second embodiment. In the following description, common elements will be denoted by common reference numerals, and duplicated descriptions will be omitted.

[0054] In the power generation and transmission system 102 of the embodiment shown in Figure 7, the grid-connection converter station 5 of the power generation and transmission system 101 of the second embodiment has a plurality of AC / DC converters 53, such as modular multilevel converters. A plurality of AC / DC converters 53 may be connected in parallel. A DC power generation and transmission system 101b having a step-up transformer 31 and an AC / DC converter 53 is connected in parallel. When the converter 51 is configured by connecting a plurality of AC / DC converters 53, a DC bus 54 is provided between the AC / DC converters 53, and the converters 53 can be connected to other AC / DC converters 53 via the DC bus 54.

[0055] According to the power generation and transmission system 102 of this embodiment, power generation and transmission systems each having a plurality of wind turbines can be interconnected.

[0056] According to at least one of the embodiments described above, there is provided a power generation and transmission system comprising: a converter station connected to an electric power grid; an export cable connected to the converter station; a step-up substation connected to the export cable; a collector cable connected to the step-up substation; and a wind turbine connected to the collector cable, wherein the converter station comprises a converter; the wind turbine comprises a power conditioning system; and the converter and the power conditioning system have a three-phase operation mode and a single-phase operation mode, thereby making it possible to reduce loss of power transmission opportunities in the power generation and transmission system when a failure occurs.

[0057] (Fourth Embodiment) Next, a control method for a power generation and transmission system according to a fourth embodiment will be described. In the first to third embodiments, a three-phase operation mode and a single-phase operation mode are combined to shorten the interruption period of the power transmission line. However, in the fourth embodiment, the three-phase operation mode and the single-phase operation mode are switched in stages to effectively utilize the power transmission line. Here, an example in which the export cable 4 is laid in stages is described, but the fourth embodiment can also be applied to a case in which the power collection cable 2 is laid in stages. In other words, the fourth embodiment can be applied to a case in which the cable that transmits the output power of the PCS 12 to the grid-connection converter station 5 is laid in stages from two-phase to three-phase.

[0058] First, the power generation and transmission system 100 having the configuration shown in Fig. 2 is constructed. At this time, only cables 4a and 4b of the export cable 4 that should include a three-phase cable are laid (S300).

[0059] The control device 6 operates the PCS 12 and converter 51 in single-phase operation mode (S310). At this time, the PCS 12 and converter 51 control the current and voltage output to each phase to prevent excessive current from flowing into the neutral grounding resistor NGR of each transformer and excessive voltage from being generated in each transformer. That is, power transmission begins with the configuration shown in Figure 5. Single-phase power transmission is possible with only two export cables 4.

[0060] Next, the third phase cable 4c of the export cable 4 is laid (S320).

[0061] Then, the control device 6 switches the PCS 12 and the converter 51 to the three-phase operation mode (S330).

[0062] Through these steps, power transmission is first started using two cables for export cable 4 in single-phase operation, and then by adding another cable, it is possible to finally switch to three-phase operation using three cables. In other words, by first transmitting power in single-phase operation using two cables, the power generation and transmission system can begin operation without waiting for the installation of the remaining cable. This allows for effective use of power generation facilities and transmission facilities, reducing loss of power transmission opportunities. Of course, circuit breakers and disconnecting switches not shown in Figure 8 may be opened or closed when cables are installed or operation begins.

[0063] The section of the power generation and transmission system between the converter and the wind turbine may be operated at commercial frequency or at a frequency lower than commercial frequency. When operated at a frequency lower than commercial frequency, the leading reactive power generated in the export cable can be reduced, making it possible to build a power generation and transmission system that can cover longer distances than when commercial frequency is used.

[0064] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

[0065] DESCRIPTION OF SYMBOLS 1... Wind turbine 11... Wind turbine generator 12... Power conditioner (PCS) 13... Wind turbine step-up transformer 2 (2a to 2c)... Current collection cable 3... Step-up substation 31... Step-up transformer 4 (4a to 4c)... Export cable 5... Grid-connected converter station 51... Converter 52... Converter transformer 53... AC / DC converter 54... DC bus 6... Control device 100... Power generation and transmission system

Claims

1. A power generation and transmission system comprising: a power conditioner capable of outputting single-phase or three-phase AC power of a predetermined frequency and voltage; a conversion device that supplies the AC power output of the power conditioner to a power grid; at least three-phase power transmission cables that transmit the output power of the power conditioner to the conversion device; a detection unit that detects a ground fault that has occurred in the power transmission cables; and a control device that, when the ground fault is detected, generates an instruction signal for a single-phase operation mode in which single-phase power is transmitted through other cables among the power transmission cables excluding the cable in which the ground fault has occurred, wherein the power conditioner outputs single-phase AC power through the other cables excluding the cable in which the ground fault has occurred in response to the instruction signal.

2. The power generation and transmission system according to claim 1, wherein the conversion device is connected back-to-back to a plurality of modular multilevel converters via a DC bus.

3. The power generation and transmission system according to claim 1, characterized in that the conversion device comprises a matrix converter.

4. The power generation and transmission system according to claim 1, further comprising a step-up transformer device including: a transformer; and a circuit breaker capable of interrupting a connection between the transformer and the power transmission cable.

5. The power generation and transmission system according to claim 4, wherein the circuit breaker constitutes a three-phase isolation circuit breaker, which disconnects cables of all phases constituting the power transmission cable when the ground fault occurs in the power transmission cable, and connects only the other cables of the power transmission cable excluding the phase of the cable in which the ground fault occurred when the power conditioner outputs the single-phase AC voltage in response to the instruction signal.

6. The power generation and transmission system according to claim 1, characterized in that the power transmission cable is composed of at least one cable, each of which is made up of three single-phase cables.

7. The power generation and transmission system according to claim 1, characterized in that the power conditioner and the conversion device are capable of operating on alternating current having a frequency lower than the commercial frequency.

8. A power generation and transmission system as described in claim 4, characterized in that it comprises a plurality of step-up transformers.

9. The power generation and transmission system according to claim 1, characterized in that the power conditioner is configured to be capable of outputting single-phase AC power when the power transmission cable comprises two single-phase cables, and is configured to be capable of outputting three-phase AC power when the power transmission cable comprises three single-phase cables.

10. A control device for controlling a power transmission and reception system including a power conditioner capable of outputting single-phase or three-phase AC power of a predetermined frequency and voltage, a conversion device that supplies the AC power output of the power conditioner to a power grid, and at least three-phase power transmission cables that transmit the output power of the power conditioner to the conversion device, the control device comprising: a detection unit that detects a ground fault that has occurred in the power transmission cable; and a control device that, when the ground fault is detected, generates an instruction signal for a single-phase operation mode in which single-phase power is transmitted through the other cables among the power transmission cables excluding the cable in which the ground fault has occurred.

11. A method for controlling a power generation and transmission system including a power conditioner capable of outputting single-phase or three-phase AC power of a predetermined frequency and voltage, a conversion device that supplies the AC power output of the power conditioner to a power grid, and at least three-phase transmission cables that transmit the output power of the power conditioner to the conversion device, the method comprising: receiving a detection result of a ground fault occurring in the transmission cable; and, when the ground fault is detected, generating an instruction signal for a single-phase operation mode in which single-phase power is transmitted through other cables among the transmission cables excluding the cable in which the ground fault has occurred, thereby controlling the power conditioner.

12. A method for installing a transmission cable that transmits the output power of the power conditioner to a conversion device in a power generation and transmission system including a power conditioner capable of outputting single-phase or three-phase AC power of a predetermined frequency and voltage, and a conversion device that supplies the AC power output of the power conditioner to a power grid, comprising: installing a two-phase transmission cable that transmits the output power of the power conditioner to the conversion device; controlling the power conditioner to transmit single-phase AC power to the conversion device via the transmission cable; further installing a one-phase transmission cable that transmits the output power of the power conditioner to the conversion device; and controlling the power conditioner to transmit three-phase AC power to the conversion device via the transmission cable.

13. A computer program for controlling a power generation and transmission system including a power conditioner capable of outputting single-phase or three-phase AC power of a predetermined frequency and voltage, a conversion device that supplies the AC power output of the power conditioner to a power grid, and at least three-phase transmission cables that transmit the output power of the power conditioner to the conversion device, the computer program detecting a ground fault that has occurred in the transmission cables, and when the ground fault has been detected, generating an instruction signal for a single-phase operation mode in which single-phase power is transmitted through the other cables among the transmission cables excluding the cable in which the ground fault has occurred, to control the power conditioner.

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