Offshore wind power transmission scheme comparison method considering life cycle cost

Abstract

The application discloses a kind of offshore wind power transmission scheme comparison and selection methods considering life cycle cost, in view of the problem that offshore wind power transmission engineering lacks the economic comparison and selection method of transmission scheme comprehensively considering construction and operation maintenance cost, a kind of offshore wind power transmission scheme comparison and selection method of life cycle cost is proposed, which comprehensively considers one-off investment cost, operation loss cost, periodic maintenance cost and fault loss cost and other factors, and the economy of different transmission schemes is comprehensively evaluated, to select the most suitable transmission scheme for offshore wind power.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation technology, specifically relating to a method for comparing and selecting offshore wind power transmission schemes that considers the entire life cycle cost. Background Technology

[0002] Currently, offshore wind power is developing towards deep-sea areas, and power transmission solutions such as power frequency AC transmission, flexible DC transmission, and low frequency AC transmission have been applied in the offshore wind power field.

[0003] When offshore wind farms are located far from shore, the power frequency AC transmission scheme suffers from excessive reactive power consumption due to the equivalent capacitance of the submarine cable. The active power transmission capacity of the power frequency AC submarine cable is limited, and the cost of the cable increases rapidly with transmission capacity and distance. Offshore wind power flexible DC transmission systems are not limited by transmission distance, and single-circuit submarine cables have strong transmission capacity. However, offshore converter stations using the MMC topology are large in size and weight, resulting in high construction and transportation costs. Offshore wind power low-frequency transmission schemes do not require converter valves on the offshore electrical platform, significantly reducing platform construction costs. However, onshore stations require converter valves with an M3C topology, which also presents a high equipment cost problem. The active power transmission capacity of low-frequency submarine cables falls between that of power frequency AC and DC.

[0004] The above analysis shows that, for different offshore wind power project application scenarios, power frequency AC transmission, flexible DC transmission, and low-frequency AC transmission each have their own advantages and disadvantages in terms of construction costs. Furthermore, it is necessary to comprehensively consider factors such as operating loss costs, regular maintenance costs, and failure loss costs to fully evaluate the economics of different transmission schemes and select the most suitable one for offshore wind power. Currently, there is no research on a method for comparing offshore wind power transmission schemes considering the entire life cycle cost; therefore, there is an urgent need to propose an economic comparison method for offshore wind power transmission schemes. Summary of the Invention

[0005] The purpose of this invention is to provide a method for comparing and selecting offshore wind power transmission schemes that considers the total life cycle cost. This method comprehensively considers the total life cycle cost, including one-time investment cost, operating loss cost, regular maintenance cost, and failure loss cost, to fully evaluate the economics of different transmission schemes and select the most suitable transmission scheme for offshore wind power.

[0006] To achieve the above-mentioned objectives, this method adopts the following technical solution:

[0007] A method for comparing and selecting offshore wind power transmission schemes that considers the total life cycle cost is proposed. Based on the capacity of offshore wind power transmission projects and the layout of wind farms, the method calculates the total life cycle cost of offshore wind power power frequency AC transmission scheme, offshore wind power low frequency AC transmission scheme, and offshore wind power flexible DC transmission scheme, and selects the transmission scheme with the lowest total life cycle cost as the preferred scheme.

[0008] The total life cycle cost includes one-time investment cost, operating loss cost, periodic maintenance cost, and failure loss cost, etc.

[0009] The one-time investment cost of the offshore wind power power frequency AC transmission scheme includes the cost of power frequency collection submarine cable and laying, the cost of construction, transportation and installation of power frequency offshore booster station, the cost of power frequency AC transmission submarine cable and laying, the construction cost of onshore control center, and the construction cost of offshore reactive power compensation station.

[0010] The one-time investment cost of the offshore wind power low-frequency AC transmission scheme includes the cost of low-frequency collection submarine cable and laying, the construction and transportation installation cost of low-frequency offshore booster station, the cost of low-frequency AC transmission submarine cable and laying, the construction cost of onshore frequency converter station, and the increased cost of low-frequency wind turbines compared to power frequency wind turbines.

[0011] The one-time investment cost of the offshore wind power flexible DC transmission scheme includes the cost of power frequency collection submarine cable and laying, the construction and transportation installation cost of offshore converter station, the cost of DC transmission submarine cable and laying, and the construction cost of onshore converter station.

[0012] The operating loss cost of the offshore wind power power frequency AC transmission scheme includes the power frequency collection submarine cable loss cost, the power frequency AC transmission submarine cable loss cost, the power frequency offshore booster station and onshore control center equipment loss cost, the power frequency collection submarine cable sea area usage cost, and the power frequency AC transmission submarine cable sea area usage cost.

[0013] The operating loss cost of the offshore wind power low-frequency AC transmission scheme includes the loss cost of the low-frequency collection submarine cable, the loss cost of the low-frequency AC transmission submarine cable, the equipment loss cost of the low-frequency offshore booster station and onshore frequency converter station, the marine usage cost of the low-frequency collection submarine cable, and the marine usage cost of the low-frequency AC transmission submarine cable.

[0014] The operational loss cost of the offshore wind power flexible DC transmission scheme includes the loss cost of the power frequency collection submarine cable, the loss cost of the DC transmission submarine cable, the equipment loss cost of the offshore converter station and the onshore converter station, the marine usage cost of the power frequency collection submarine cable, and the marine usage cost of the DC transmission submarine cable.

[0015] The periodic maintenance costs of the offshore wind power power frequency AC transmission scheme, offshore wind power low frequency AC transmission scheme, and offshore wind power flexible DC transmission scheme are calculated based on different transmission schemes, following the maintenance principle of minimizing power generation loss during equipment maintenance, to determine the cost of power generation loss from periodic maintenance devices.

[0016] The failure loss costs of the offshore wind power power frequency AC transmission scheme, offshore wind power low frequency AC transmission scheme, and offshore wind power flexible DC transmission scheme are all calculated based on the principle that during the maintenance period, the system connected to the faulty submarine cable or electrical equipment stops operating, while the other systems operate normally.

[0017] Furthermore, the on-state losses of the converter valve switching devices in the flexible DC transmission system are calculated using the following method:

[0018]

[0019] Among them, P Tcon , P Dcon These represent the conduction losses of the IGBT and diode in the converter valve, respectively; V CE0 V f0 The on-state voltage biases for the IGBT and diode are respectively; r CE , r f These are the on-state resistances of the IGBT and the diode, respectively; i CE i f These represent the current flowing through the devices during IGBT and diode conduction, respectively.

[0020] Furthermore, the no-load loss of the transformer is calculated using the following method:

[0021]

[0022] Among them, P T0 K represents the no-load loss of the transformer. p0 G is an additional factor for no-load loss. Fe P represents the total mass of the silicon steel sheets. t This refers to the unit mass loss of silicon steel sheets in the iron core column.

[0023] Furthermore, the load loss of the transformer is calculated using the following method:

[0024]

[0025] Among them, P TD For transformer load losses, I 1N I 2N R1 and R2 are the operating currents of the primary and secondary windings, respectively; R1 and R2 are the resistances of the primary and secondary windings, respectively.

[0026] Furthermore, the reactor losses are calculated using the following method:

[0027]

[0028] Among them, P L For reactor losses, I dc For direct current, R dc I is the DC resistance. n R is the nth harmonic current. n Let n be the resistance of the nth harmonic, where n is a natural number between 1 and 50.

[0029] Furthermore, the periodic maintenance cost of the offshore wind power AC transmission scheme is calculated according to the following method: the periodic maintenance cost of the offshore wind power AC transmission scheme is calculated based on the principle that each step-up transformer is maintained separately during the periodic maintenance period, and the transmission capacity of other step-up transformers is not affected, thus calculating the cost of lost power generation.

[0030] Furthermore, the periodic maintenance cost of the offshore wind power low-frequency AC transmission scheme is calculated according to the following method: the periodic maintenance cost of the offshore wind power low-frequency AC transmission scheme is calculated based on the principle that the entire station is maintained during the periodic maintenance period, resulting in the loss of all power generation.

[0031] Furthermore, the periodic maintenance cost of the offshore wind power flexible DC transmission scheme is calculated according to the following method: If a symmetrical monopolar topology is adopted, the cost of lost power generation is calculated based on the principle that the entire station is maintained during the periodic maintenance period, resulting in the loss of all power generation; if a symmetrical bipolar topology is adopted, the cost of lost power generation is calculated based on the principle that the equipment of each pole is maintained separately during the periodic maintenance period, and the transmission capacity of the other pole is not affected.

[0032] The beneficial effects of this invention are:

[0033] By adopting the technical solution of this invention, and comprehensively considering factors such as the one-time investment cost, operating loss cost, regular maintenance cost, and failure loss cost of different offshore wind power transmission schemes, the economics of different offshore wind power transmission schemes can be comprehensively evaluated, and the most suitable transmission scheme can be selected for offshore wind power. Attached Figure Description

[0034] Figure 1 This is a typical topology diagram of the offshore wind power power frequency AC transmission scheme of the present invention.

[0035] Figure 2 This is a typical topology diagram of the offshore wind power low-frequency AC transmission scheme of the present invention.

[0036] Figure 3 This is a typical topology diagram of the symmetrical single-pole flexible DC transmission scheme for offshore wind power according to the present invention.

[0037] Figure 4 This is a typical topology diagram of the symmetrical bipolar flexible DC transmission scheme for offshore wind power according to the present invention. Detailed Implementation

[0038] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0039] In this embodiment of the invention, a 2000MW offshore wind farm with a transmission distance of 100km is used to illustrate the specific implementation of this solution.

[0040] The one-time investment cost of offshore wind power power frequency AC transmission scheme includes the cost of power frequency collection submarine cable and laying, the cost of construction, transportation and installation of power frequency offshore booster station, the cost of power frequency AC transmission submarine cable and laying, the construction cost of onshore control center, and the construction cost of offshore reactive power compensation station.

[0041] A typical topology diagram of an offshore wind power AC transmission scheme is shown below. Figure 1 As shown, offshore wind turbines are connected to an offshore booster station via a power frequency collection submarine cable. After boosting, the voltage is connected to an onshore control center via a power frequency AC transmission submarine cable. The onshore control center then connects to the onshore AC power grid. An offshore reactive power compensation station is located midway along the power frequency AC transmission submarine cable. In this embodiment, the wind farm uses a 66kV power frequency collection submarine cable, constructs two 500kV offshore booster stations, installs four 500kV transformers, transmits power through four 500kV power frequency AC submarine cables, constructs one 500kV onshore control center, and constructs one offshore reactive power compensation station. The total cost of the power frequency collection submarine cable and its laying is 1.608 billion yuan, the construction and transportation installation cost of the offshore booster station is 1.3 billion yuan, the cost of the power frequency AC transmission submarine cable and its laying is 5.751 billion yuan, the construction cost of the onshore control center is 360 million yuan, and the construction cost of the offshore reactive power compensation station is 520 million yuan. The total one-time investment cost of the offshore wind power power frequency AC transmission scheme is 9.539 billion yuan.

[0042] The one-time investment cost of the offshore wind power low-frequency AC transmission scheme includes the cost of low-frequency collection submarine cable and laying, the construction and transportation installation cost of low-frequency offshore booster station, the cost of low-frequency AC transmission submarine cable and laying, the construction cost of onshore frequency converter station, and the increased cost of low-frequency wind turbines compared to power frequency wind turbines.

[0043] A typical topology diagram of a low-frequency AC power transmission scheme for offshore wind power is shown below. Figure 2As shown, offshore wind turbines are connected to a low-frequency offshore booster station via a low-frequency collection submarine cable. After boosting, the voltage is connected to an onshore frequency converter station via a low-frequency AC transmission submarine cable. The onshore frequency converter station then converts the frequency to 50Hz before connecting to the onshore AC power grid. In this embodiment, the wind farm uses a 66kV low-frequency collection submarine cable, constructs one 500kV low-frequency offshore booster station, and installs three 500kV low-frequency transformers. The power is transmitted via three 500kV low-frequency AC submarine cables, and one 500kV onshore frequency converter station is also constructed. The cost of the low-frequency collection submarine cable and its installation is 1.45 billion yuan, the construction and transportation installation cost of the low-frequency offshore booster station is 1.25 billion yuan, the cost of the low-frequency AC transmission submarine cable and its installation is 4.05 billion yuan, the construction cost of the onshore frequency converter station is 1.9 billion yuan, and the cost of the low-frequency wind turbines compared to power frequency wind turbines is 200 million yuan. The total one-time investment cost of the offshore wind power low-frequency AC transmission scheme is 8.85 billion yuan.

[0044] The one-time investment cost of the offshore wind power flexible DC transmission scheme includes the cost of power frequency collection submarine cable and laying, the construction and transportation installation cost of offshore converter station, the cost of DC transmission submarine cable and laying, and the construction cost of onshore converter station.

[0045] A typical topology diagram of a symmetrical monopolar flexible DC transmission scheme for offshore wind power is shown below. Figure 3 As shown, offshore wind turbines are connected to an offshore converter station via a power frequency collection submarine cable. After being rectified into DC at the offshore converter station, the DC transmission submarine cable connects to an onshore converter station. The onshore converter station then inverts the DC power to AC and connects it to the onshore AC power grid. In this embodiment, the wind farm uses a 66kV power frequency collection submarine cable to collect power, constructing one ±500kV / 2000MW symmetrical monopolar offshore converter station. A ±500kV DC transmission submarine cable is used to transmit power, and one ±500kV / 2000MW symmetrical monopolar onshore converter station is also constructed. The cost of the power frequency collection submarine cable and its laying is 1.654 billion yuan, the construction and transportation installation cost of the offshore converter station is 2.63 billion yuan, the cost of the DC transmission submarine cable and its laying is 2.4 billion yuan, and the construction cost of the onshore converter station is 1.639 billion yuan. The total one-time investment cost for the symmetrical monopolar topology offshore wind power flexible DC transmission scheme is 8.323 billion yuan.

[0046] A typical topology diagram of a symmetrical bipolar flexible DC transmission scheme for offshore wind power is shown below. Figure 4As shown, offshore wind turbines are connected to an offshore converter station via a power frequency collection submarine cable. After being rectified into DC at the offshore converter station, the DC power is transmitted to an onshore converter station via a DC transmission submarine cable. The onshore converter station then inverts the DC power to AC and connects it to the onshore AC power grid. Compared to the symmetrical monopolar transmission scheme, the symmetrical bipolar scheme uses a symmetrical bipolar topology for both the offshore and onshore converter stations, and also requires an additional neutral submarine cable. In this embodiment of the invention, the wind farm uses a 66kV power frequency collection submarine cable to collect power, constructing one ±500kV / 2000MW symmetrical bipolar offshore converter station. Power is transmitted via one ±500kV DC submarine cable and one neutral submarine cable, constructing one ±500kV / 2000MW symmetrical bipolar onshore converter station. The total cost of the power frequency aggregation submarine cable and its laying is RMB 1.654 billion, the construction and transportation installation cost of the offshore converter station is RMB 3.015 billion, the cost of the DC transmission submarine cable and its laying is RMB 2.9 billion, the construction cost of the onshore converter station is RMB 1.842 billion, and the one-time investment cost of the offshore wind power flexible DC transmission scheme using a symmetrical bipolar topology is RMB 9.411 billion.

[0047] The operational loss cost of the offshore wind power power frequency AC transmission scheme includes the loss cost of the power frequency collection submarine cable, the loss cost of the power frequency AC transmission submarine cable, the equipment loss cost of the power frequency offshore booster station and onshore control center, the marine usage cost of the power frequency collection submarine cable, and the marine usage cost of the power frequency AC transmission submarine cable.

[0048] In this embodiment of the invention, the power generation loss of the power frequency collection submarine cable and the power frequency AC transmission submarine cable is calculated by multiplying the current squared by the resistance, and then multiplying by the annual equivalent loss hours; the power generation loss of the power frequency offshore booster station and onshore control center equipment is calculated by multiplying the equivalent loss coefficient of different equipment by the installed capacity, and then multiplying by the annual equivalent loss hours; the sea area usage fee for the power frequency collection submarine cable and the power frequency AC transmission submarine cable is calculated by multiplying the sea area used by the cable by the sea area usage fee per unit area. The calculated operating loss cost of the offshore wind power power frequency AC transmission scheme is 1.486 billion yuan.

[0049] The operating loss cost of the offshore wind power low-frequency AC transmission scheme includes the loss cost of the low-frequency collection submarine cable, the loss cost of the low-frequency AC transmission submarine cable, the equipment loss cost of the low-frequency offshore booster station and onshore frequency converter station, the marine usage cost of the low-frequency collection submarine cable, and the marine usage cost of the low-frequency AC transmission submarine cable.

[0050] In this embodiment of the invention, the power generation loss of the low-frequency collection submarine cable and the low-frequency AC transmission submarine cable is calculated by multiplying the square of the current by the resistance, and then multiplying by the annual equivalent loss hours; the power generation loss of the low-frequency offshore booster station and onshore frequency converter station equipment is calculated by multiplying the equivalent loss coefficient of different equipment by the installed capacity, and then multiplying by the annual equivalent loss hours; the sea area usage fee for the low-frequency collection submarine cable and the low-frequency AC transmission submarine cable is calculated by multiplying the sea area used by the cable by the sea area usage fee per unit area. The calculated operating loss cost of the offshore wind power low-frequency AC transmission scheme is 971 million yuan.

[0051] The operational loss cost of the offshore wind power flexible DC transmission scheme includes the loss cost of the power frequency collection submarine cable, the loss cost of the DC transmission submarine cable, the equipment loss cost of the offshore converter station and the onshore converter station, the marine usage cost of the power frequency collection submarine cable, and the marine usage cost of the DC transmission submarine cable.

[0052] In this embodiment of the invention, the power generation loss of the power frequency collection submarine cable and the DC transmission submarine cable is calculated by multiplying the current squared by the resistance, and then multiplying by the annual equivalent loss hours; the power generation loss of the offshore converter station and the onshore converter station equipment is calculated by multiplying the equivalent loss coefficient of different equipment by the installed capacity, and then multiplying by the annual equivalent loss hours; the sea area usage fee for the power frequency collection submarine cable and the DC transmission submarine cable is calculated by multiplying the sea area used by the cable by the sea area usage fee per unit area. The calculated operating loss cost of the symmetrical monopolar flexible DC transmission scheme for offshore wind power is 732 million yuan, and the operating loss cost of the symmetrical bipolar flexible DC transmission scheme for offshore wind power is 754 million yuan.

[0053] The periodic maintenance cost of the offshore wind power AC transmission scheme is calculated based on the principle that each step-up transformer is maintained separately during the periodic maintenance period, and the transmission capacity of other step-up transformers is not affected, which is the cost of lost power generation.

[0054] In this embodiment of the invention, a total of four 500kV transformers are installed, which are transmitted through four 500kV power frequency AC submarine cables. Each main transformer can be maintained separately. During the maintenance period, the other three 500kV transformers are not affected, and the entire power transmission system can still guarantee more than 75% of the power transmission capacity. Each maintenance is considered to take 3.5 days. According to the output characteristics of offshore wind farms, the time when the real-time power generation is greater than 75% is very rare. Therefore, the power generation loss is small. The maintenance is carried out in the month with the lowest average wind power output each year. According to the typical wind power output curve, the power generation loss due to regular maintenance in the 25-year system operation life cycle is calculated to be 0.21 billion yuan.

[0055] The periodic maintenance cost of the offshore wind power low-frequency AC transmission scheme is calculated based on the principle that during the periodic maintenance period, the entire station is maintained, resulting in the loss of all power generation.

[0056] In this embodiment of the invention, during the maintenance of the onshore M3C converter valve, the entire system needs to be shut down. Each maintenance is considered to last 3.5 days. Maintenance is carried out in months with lower average wind power output each year. Based on the typical wind power output curve, the cost of lost power generation due to regular maintenance during the 25-year system operation life cycle is calculated to be 386 million yuan.

[0057] The periodic maintenance cost of the offshore wind power flexible DC transmission scheme is calculated as follows: if a symmetrical monopole topology is adopted, the cost of lost power generation is calculated based on the principle that the entire station is maintained during the periodic maintenance period, resulting in the loss of all power generation; if a symmetrical bipole topology is adopted, the cost of lost power generation is calculated based on the principle that the equipment of each pole is maintained separately during the periodic maintenance period, and the transmission capacity of the other pole is not affected.

[0058] In this embodiment of the invention, for a symmetrical unipolar topology, the entire system needs to be shut down during MMC converter valve maintenance. Each maintenance session is estimated at 3.5 days, and maintenance is performed in months with lower average annual wind power output. Based on typical wind power output curves, the calculated loss in power generation costs due to periodic maintenance over the 25-year system lifecycle is 386 million yuan. For a symmetrical bipolar topology, the positive and negative poles can be maintained separately, ensuring 50% power transmission capacity during maintenance. Each maintenance session is estimated at 3.5 days. Considering the output characteristics of offshore wind farms, maintenance is performed in months with lower average annual wind power output. The percentage of time with real-time power generation exceeding 50% is relatively small; therefore, the power generation loss is slightly greater than with the power frequency AC transmission scheme. Based on typical wind power output curves, the calculated loss in power generation costs due to periodic maintenance over the 25-year system lifecycle is 42 million yuan.

[0059] The failure loss costs of the offshore wind power power frequency AC transmission scheme, offshore wind power low frequency AC transmission scheme, and offshore wind power flexible DC transmission scheme are all calculated based on the principle that during the maintenance period, the system connected to the faulty submarine cable or electrical equipment stops operating, while the other systems operate normally.

[0060] In this embodiment of the invention, for the power frequency AC transmission scheme, a total of four 500kV transformers are installed, transmitting power through four 500kV power frequency AC submarine cables. During a fault, even if a single major device, such as a transformer or submarine cable, fails, the remaining devices can still guarantee 75% of the power transmission capacity. Since the timing of the fault is random, the power generation loss during the fault should be calculated based on the annual average power generation. Furthermore, since the location of the fault is also random, and the maintenance time for different devices varies significantly, the outage time caused by a single fault should also be calculated using the average of different fault outage times. Based on typical wind power output curves and combined with practical engineering experience, the calculated cost of power generation loss per fault is 0.064 billion.

[0061] For low-frequency AC transmission schemes, a failure in a single major device, such as the M3C converter valve or the bridge arm reactor, will cause the entire system to stop operating, resulting in the loss of all power generation. However, if a failure occurs in the low-frequency transmission submarine cable, the system will still retain more than 66% of its transmission capacity. The wind turbine output during a fault is calculated based on the annual average power generation, and the outage time caused by a single fault is calculated based on the average value. Based on typical wind power output curves and practical engineering experience, the cost of power generation loss due to a single fault is calculated to be 123.8 million yuan.

[0062] For a symmetrical monopolar flexible DC transmission scheme, a failure in a single major device, such as a converter valve or submarine cable, will cause the entire system to stop operating, resulting in the loss of all power generation. The wind turbine output during the failure period is calculated based on the annual average power generation, and the outage time caused by a single failure is calculated based on the average value. Based on typical wind power output curves and combined with practical engineering experience, the cost of power generation loss due to a single failure is calculated to be 449.9 million yuan.

[0063] For a symmetrical bipolar flexible DC transmission scheme, even if a single major device, such as a single-pole converter valve, transformer, or submarine cable fails, the remaining equipment can still guarantee 50% of the power transmission capacity. The wind turbine output during the fault is calculated based on the annual average power generation, and the outage time caused by a single fault is calculated based on the average value. Based on typical wind power output curves and combined with practical engineering experience, the cost of power generation loss per fault is calculated to be 0.771 billion.

[0064] Based on the above calculations, in this embodiment of the invention, the life-cycle cost of different transmission schemes is calculated according to the assumption of one failure within the entire life-cycle. The life-cycle cost of the offshore wind power power frequency AC transmission scheme is 11.0524 billion yuan, the life-cycle cost of the offshore wind power low-frequency AC transmission scheme is 10.3308 billion yuan, the life-cycle cost of the offshore wind power symmetrical monopolar flexible DC transmission scheme is 9.8909 billion yuan, and the life-cycle cost of the offshore wind power symmetrical bipolar flexible DC transmission scheme is 10.2841 billion yuan. Therefore, for the 2000MW capacity offshore wind farm with a transmission distance of 100km in this embodiment of the invention, the symmetrical monopolar flexible DC transmission scheme is the most economically efficient transmission scheme throughout its life-cycle.

[0065] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be made to the above embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A method for comparing and selecting offshore wind power transmission schemes considering the entire life cycle cost, characterized in that, Based on the capacity of offshore wind power transmission projects and wind farm layout schemes, the life cycle costs of offshore wind power power frequency AC transmission scheme, offshore wind power low frequency AC transmission scheme, and offshore wind power flexible DC transmission scheme are calculated, and the transmission scheme with the lowest life cycle cost is selected as the preferred scheme. The total life cycle cost includes one-time investment cost, operating loss cost, periodic maintenance cost, and failure loss cost; The one-time investment cost of the offshore wind power power frequency AC transmission scheme includes the cost of power frequency collection submarine cable and laying, the cost of construction, transportation and installation of power frequency offshore booster station, the cost of power frequency AC transmission submarine cable and laying, the construction cost of onshore control center, and the construction cost of offshore reactive power compensation station. The one-time investment cost of the offshore wind power low-frequency AC transmission scheme includes the cost of low-frequency collection submarine cable and laying, the construction and transportation installation cost of low-frequency offshore booster station, the cost of low-frequency AC transmission submarine cable and laying, the construction cost of onshore frequency converter station, and the increased cost of low-frequency wind turbines compared to power frequency wind turbines. The one-time investment cost of the offshore wind power flexible DC transmission scheme includes the cost of power frequency collection submarine cable and laying, the construction and transportation installation cost of offshore converter station, the cost of DC transmission submarine cable and laying, and the construction cost of onshore converter station. The operating loss cost of the offshore wind power power frequency AC transmission scheme includes the power frequency collection submarine cable loss cost, the power frequency AC transmission submarine cable loss cost, the power frequency offshore booster station and onshore control center equipment loss cost, the power frequency collection submarine cable sea area usage cost, and the power frequency AC transmission submarine cable sea area usage cost. The operating loss cost of the offshore wind power low-frequency AC transmission scheme includes the loss cost of the low-frequency collection submarine cable, the loss cost of the low-frequency AC transmission submarine cable, the equipment loss cost of the low-frequency offshore booster station and onshore frequency converter station, the marine usage cost of the low-frequency collection submarine cable, and the marine usage cost of the low-frequency AC transmission submarine cable. The operational loss cost of the offshore wind power flexible DC transmission scheme includes the loss cost of the power frequency collection submarine cable, the loss cost of the DC transmission submarine cable, the equipment loss cost of the offshore converter station and the onshore converter station, the marine usage cost of the power frequency collection submarine cable, and the marine usage cost of the DC transmission submarine cable. The periodic maintenance costs of the offshore wind power power frequency AC transmission scheme, offshore wind power low frequency AC transmission scheme, and offshore wind power flexible DC transmission scheme are calculated based on different transmission schemes, following the maintenance principle of minimizing power generation loss during equipment maintenance, to determine the cost of power generation loss from periodic maintenance devices. The failure loss costs of the offshore wind power power frequency AC transmission scheme, offshore wind power low frequency AC transmission scheme, and offshore wind power flexible DC transmission scheme are all calculated based on the principle that during the maintenance period, the system connected to the faulty submarine cable or electrical equipment stops operating, while the other systems operate normally.

2. The method for comparing offshore wind power transmission schemes considering life-cycle costs as described in claim 1, characterized in that, The on-state losses of the converter valve switching devices in a flexible DC transmission system are calculated using the following method: Among them, P Tcon , P Dcon These represent the conduction losses of the IGBT and diode in the converter valve, respectively; V CE0 V f0 The on-state voltage biases for the IGBT and diode are respectively; r CE , r f These are the on-state resistances of the IGBT and the diode, respectively; i CE i f These represent the current flowing through the devices during IGBT and diode conduction, respectively.

3. The method for comparing and selecting offshore wind power transmission schemes considering the entire life cycle cost as described in claim 1, characterized in that, The no-load loss of the transformer is calculated using the following method: Among them, P T0 K represents the no-load loss of the transformer. p0 G is an additional factor for no-load loss. Fe P represents the total mass of the silicon steel sheets. t This refers to the unit mass loss of silicon steel sheets in the iron core column.

4. The method for comparing and selecting offshore wind power transmission schemes considering total life-cycle costs as described in claim 1, characterized in that, The load loss of the transformer is calculated using the following method: Among them, P TD For transformer load losses, I 1N I 2N R1 and R2 are the operating currents of the primary and secondary windings, respectively; R1 and R2 are the resistances of the primary and secondary windings, respectively.

5. The method for comparing and selecting offshore wind power transmission schemes considering life-cycle costs as described in claim 1, characterized in that, The reactor loss is calculated using the following method: Among them, P L For reactor losses, I dc For direct current, R dc I is the DC resistance. n R is the nth harmonic current. n Let n be the resistance of the nth harmonic, where n is a natural number between 1 and 50.

6. The method for comparing offshore wind power transmission schemes considering life-cycle costs as described in claim 1, characterized in that, The periodic maintenance cost of the offshore wind power AC transmission scheme is calculated using the following method: The periodic maintenance cost of the offshore wind power AC transmission scheme is calculated based on the principle that each step-up transformer is maintained separately during the periodic maintenance period, and the transmission capacity of other step-up transformers is not affected, thus calculating the cost of lost power generation.

7. The method for comparing offshore wind power transmission schemes considering life-cycle costs as described in claim 1, characterized in that, The periodic maintenance cost of the offshore wind power low-frequency AC transmission scheme is calculated according to the following method: the periodic maintenance cost of the offshore wind power low-frequency AC transmission scheme is calculated based on the principle that the entire station is maintained during the periodic maintenance period, resulting in the loss of all power generation.

8. The method for comparing and selecting offshore wind power transmission schemes considering life-cycle costs as described in claim 1, characterized in that, The periodic maintenance cost of the offshore wind power flexible DC transmission scheme is calculated using the following method: If a symmetrical monopolar topology is adopted, the cost of lost power generation is calculated based on the principle that the entire station is maintained during the periodic maintenance period, resulting in the loss of all power generation; if a symmetrical bipolar topology is adopted, the cost of lost power generation is calculated based on the principle that the equipment of each pole is maintained separately during the periodic maintenance period, and the transmission capacity of the other pole is not affected.

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