Control method of sea breeze DC system

Abstract

The present application relates to a control method for a sea breeze DC system. The method comprises: controlling the operation of an MMC converter valve based on a target DC voltage, and obtaining the DC current of a diode converter valve; determining a reference value of the effective value of the line voltage at a PCC point of the sea breeze DC system according to the DC current of the diode converter valve; and controlling the AC voltage at the PCC point according to the reference value. The present method can dynamically control the AC voltage at the PCC point according to the DC current of the diode converter valve, ensuring that the DC voltage of the diode converter valve remains constant under different DC currents, thereby ensuring that the DC voltage of the MMC converter valve remains constant under different wind power.

Description

Technical Field

[0001] The present application relates to the field of electric power engineering technology, and in particular to a control method and device for a sea breeze direct current system, a sea breeze direct current system, a computer-readable storage medium, and a computer program product. Background Art

[0002] Offshore wind power has become a hot topic in the field of renewable energy due to its advantages such as stable wind power, no land occupation, clean and green. Due to the limited and gradually saturated offshore wind power resources, offshore wind power generation is being promoted to develop in the open sea.

[0003] At present, the common way of transmitting offshore wind power is direct current transmission, that is, the offshore direct current transmission scheme based on MMC (Modular Multilevel Converter). However, the large number of MMC sub-modules, heavy weight, and large size make the construction of offshore converter platforms difficult and costly. The characteristics of diode converter valves, such as small size, light weight, simple control, and unidirectional current, are very consistent with the characteristics of unidirectional transmission of offshore wind power. Therefore, diode converter valves can be used in offshore wind power DC transmission converter valves to reduce the capacity of offshore MMC converter valves in offshore wind power DC systems, thereby reducing system costs.

[0004] However, during the operation of the diode converter valve, its DC voltage will fluctuate with the DC current. Since the overall DC voltage of the MMC converter valve in series with the diode converter valve remains constant, this fluctuation will cause the DC voltage of the MMC converter valve to change. When the DC voltage of the MMC converter valve is too high, the submodule will be subject to overvoltage risks; when the DC voltage is too low, it cannot support the output voltage on the AC side. Therefore, how to control the DC voltage of the MMC converter valve to remain stable is an urgent problem to be solved. Summary of the invention

[0005] Based on this, it is necessary to provide a control method, device, sea breeze DC system, computer equipment, computer readable storage medium and computer program product for a sea breeze DC system that can control the DC voltage of the MMC converter valve to maintain stability in response to the above technical problems.

[0006] In a first aspect, the present application provides a control method for a sea breeze DC system, wherein the sea breeze DC system is a diode converter valve in series with an MMC converter valve type sea breeze DC system, and the method comprises:

[0007] Controlling the operation of the MMC converter valve based on the target DC voltage, and obtaining the DC current of the diode converter valve;

[0008] Determine a reference value of the effective value of the PCC point line voltage of the sea breeze DC system according to the DC current of the diode converter valve;

[0009] The AC voltage at the PCC point is controlled according to the reference value.

[0010] In one embodiment, the method further comprises:

[0011] Determining system DC parameters of the sea breeze DC system;

[0012] Determine a first corresponding relationship, a capacity restriction condition and a voltage restriction condition of the MMC converter valve according to the system DC parameters; wherein the first corresponding relationship represents the relationship between the reactive capacity and the DC voltage of the MMC converter valve;

[0013] A target DC voltage is determined based on the first corresponding relationship, the capacity restriction condition, and the voltage restriction condition.

[0014] In one embodiment, the system DC parameters include a system DC voltage and a system DC current; and determining the first corresponding relationship according to the system DC parameters includes:

[0015] Determining the ergodic DC voltage range of the MMC converter valve according to the system DC voltage;

[0016] Determining a maximum reactive power range of the diode converter valve based on the ergodic DC voltage range, the system DC voltage, and the system DC current;

[0017] Based on the ergodic DC voltage range, the maximum reactive power range of the diode converter valve and the system DC current, a first corresponding relationship between the reactive capacity of the MMC converter valve and the DC voltage is determined.

[0018] In one embodiment, the system DC parameters include system DC voltage and system DC current; and determining the capacity limitation condition of the MMC converter valve according to the system DC parameters includes:

[0019] Determining the ergodic DC voltage range of the MMC converter valve according to the system DC voltage;

[0020] Determining a bridge arm current limit value of the MMC converter valve;

[0021] The capacity limitation condition of the MMC converter valve is determined based on the ergodic DC voltage range, the bridge arm current limit and the system DC current.

[0022] In one embodiment, determining the voltage limit condition of the MMC converter valve according to the system DC parameter includes:

[0023] Determining the fluctuation range of the PCC point line voltage;

[0024] The voltage limit condition of the MMC converter valve is determined based on the system DC parameters and the fluctuation range of the PCC point line voltage.

[0025] In one embodiment, the determining the target DC voltage based on the first corresponding relationship, the capacity limitation condition and the voltage limitation condition includes:

[0026] Determining a minimum capacity value of the MMC converter valve based on the first corresponding relationship, the capacity restriction condition and the voltage restriction condition;

[0027] The DC voltage corresponding to the minimum capacity is used as the target DC voltage.

[0028] In a second aspect, the present application further provides a control device for a sea breeze DC system, wherein the sea breeze DC system is a sea breeze DC system of a diode converter valve in series with an MMC converter valve, and the device comprises:

[0029] An initial control module, used to control the operation of the MMC converter valve based on a target DC voltage and obtain a DC current of the diode converter valve;

[0030] A reference value determination module, used to determine a reference value of the effective value of the PCC point line voltage of the sea breeze DC system according to the DC current of the diode converter valve;

[0031] A voltage control module is used to control the AC voltage of the PCC point according to the reference value.

[0032] In a third aspect, the present application further provides a sea breeze DC system, which is a diode converter valve series MMC converter valve type sea breeze DC system, comprising: an offshore wind farm, a first transformer, a first AC circuit breaker, a second transformer, a second AC circuit breaker, a diode converter valve, an MMC converter valve, an MMC converter valve controller, an onshore converter valve, a third transformer, a third AC circuit breaker, and an onshore power grid; wherein the offshore wind farm is sequentially connected to the first AC circuit breaker, the first transformer, and the diode converter valve through an offshore AC bus, and sequentially connected to the second AC circuit breaker, the second transformer, and the MMC converter valve through an offshore AC bus, and the diode converter valve is connected to the MMC converter valve; the diode converter valve and the MMC converter valve are respectively connected to the onshore converter valve through a submarine DC submarine cable, and the onshore converter valve is connected to the onshore power grid through the third transformer and the third AC circuit breaker;

[0033] Among them, the MMC converter valve controller is connected to the MMC converter valve and the PCC point respectively, and the MMC converter valve controller is used to implement the control method of the sea breeze DC system as mentioned above; the PCC point is a common connection point connecting the offshore wind farm and the offshore AC busbar of the first AC circuit breaker and the second AC circuit breaker.

[0034] In a fourth aspect, the present application further provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the following steps are implemented:

[0035] Controlling the operation of the MMC converter valve based on the target DC voltage, and obtaining the DC current of the diode converter valve;

[0036] Determine a reference value of the effective value of the PCC point line voltage of the sea breeze DC system according to the DC current of the diode converter valve;

[0037] The AC voltage at the PCC point is controlled according to the reference value.

[0038] In a fifth aspect, the present application further provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the following steps are implemented:

[0039] Controlling the operation of the MMC converter valve based on the target DC voltage, and obtaining the DC current of the diode converter valve;

[0040] Determine a reference value of the effective value of the PCC point line voltage of the sea breeze DC system according to the DC current of the diode converter valve;

[0041] The AC voltage at the PCC point is controlled according to the reference value.

[0042] In a sixth aspect, the present application further provides a computer program product, including a computer program, which implements the following steps when executed by a processor:

[0043] Controlling the operation of the MMC converter valve based on the target DC voltage, and obtaining the DC current of the diode converter valve;

[0044] Determine a reference value of the effective value of the PCC point line voltage of the sea breeze DC system according to the DC current of the diode converter valve;

[0045] The AC voltage at the PCC point is controlled according to the reference value.

[0046] The control method, device, sea breeze DC system, computer equipment, computer readable storage medium and computer program product of the sea breeze DC system are as follows: the sea breeze DC system is a diode converter valve series MMC converter valve type sea breeze DC system, firstly, the operation of the MMC converter valve is controlled based on the target DC voltage, and the DC current of the diode converter valve is obtained; the reference value of the effective value of the line voltage at the PCC point of the sea breeze DC system is determined according to the DC current of the diode converter valve; the AC voltage at the PCC point is controlled according to the reference value. Therefore, during the operation of the system, the reference value of the effective value of the line voltage at the PCC point can be determined according to the DC current of the diode converter valve, so as to dynamically control the AC voltage at the PCC point according to the reference value. Since the DC voltage of the diode converter valve changes with the AC voltage and DC current, the DC voltage of the diode converter valve can be kept constant under different DC currents by dynamically controlling the AC voltage at the PCC point, thereby ensuring that the DC voltage of the MMC converter valve is constant under different wind power. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments of the present application or related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 This is an application environment diagram of a control method for a sea breeze DC system in one embodiment;

[0049] Figure 2 A schematic flow chart of a control method for a sea breeze DC system in one embodiment;

[0050] Figure 3 A partial flow chart of a control method for a sea breeze DC system in another embodiment;

[0051] Figure 4 It is a schematic diagram of a flow chart of determining a first corresponding relationship according to a system DC parameter in an embodiment;

[0052] Figure 5 A schematic diagram of a control, capacity limiting condition and voltage limiting condition of a first corresponding relationship in one embodiment;

[0053] Figure 6 It is a schematic diagram of a flow chart for determining a capacity limitation condition of an MMC converter valve according to a system DC parameter in an embodiment;

[0054] Figure 7 It is a schematic diagram of a flow chart of determining a voltage limiting condition of an MMC converter valve according to a system DC parameter in an embodiment;

[0055] Figure 8 is a structural block diagram of a control device for a sea breeze DC system in one embodiment;

[0056] Fig. 9 FIG. 4 is a diagram showing the internal structure of a computer device in one embodiment. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0058] The control method of the sea breeze DC system provided in the embodiment of the present application can be applied to Figure 1 In the application environment shown. Among them, the sea breeze DC system is a diode converter valve series MMC converter valve type sea breeze DC system. In actual implementation, the system may include: an offshore wind farm 101, a first transformer 103, a first AC circuit breaker 102, a second transformer 105, a second AC circuit breaker 104, a diode converter valve 106, an MMC converter valve 107, an MMC converter valve controller (not shown), an onshore converter valve 108, a third transformer 109, a third AC circuit breaker 110, and an onshore power grid 111. The offshore wind farm 101 is connected to the first AC circuit breaker 102, the first transformer 103, and the diode converter valve 106 in sequence through the offshore AC bus, and is connected to the second AC circuit breaker 104, the second transformer 105, and the MMC converter valve 107 in sequence through the offshore AC bus, and the diode converter valve 106 is connected to the MMC converter valve 107. The diode converter valve 106 and the MMC converter valve 107 are respectively connected to the onshore converter valve 108 through the submarine DC cable 112, and the onshore converter valve 108 is connected to the onshore power grid 111 through the third transformer 109 and the third AC circuit breaker 110. The diode converter valve 106, the MMC converter valve 107 and the onshore converter valve 108 can be set according to actual conditions. For example, the diode converter valve 106 can be a twelve-pulse diode converter valve; the MMC converter valve 107 and the onshore converter valve 108 are both half-bridge MMC.

[0059] The MMC converter valve controller is connected to the MMC converter valve 107 and the PCC point respectively. The PCC point is a common connection point of the offshore AC bus connecting the offshore wind farm 101 with the first AC circuit breaker 102 and the second AC circuit breaker 104, that is, a common bus. The MMC converter valve controller is used to control the operation of the MMC converter valve 107 based on the target DC voltage, and obtain the DC current of the diode converter valve 106; determine the reference value of the effective value of the line voltage at the PCC point of the sea breeze DC system according to the DC current of the diode converter valve 106; and control the AC voltage at the PCC point according to the reference value. During the operation of the sea breeze DC system, the reference value of the effective value of the line voltage at the PCC point can be determined according to the DC current of the diode converter valve 106, so as to dynamically control the AC voltage at the PCC point according to the reference value. Since the DC voltage of the diode converter valve 106 changes with the AC voltage and DC current, the DC voltage of the diode converter valve 106 can be kept constant under different DC currents by dynamically controlling the AC voltage at the PCC point, thereby ensuring that the DC voltage of the MMC converter valve 107 is constant under different wind power powers.

[0060] In an exemplary embodiment, Figure 2 As shown, a control method for a sea breeze DC system is provided. The sea breeze DC system is a sea breeze DC system of a diode converter valve in series with an MMC converter valve. The method is applied to Figure 1 The MMC converter valve controller in the embodiment is taken as an example to illustrate, and the method includes the following steps 202 to 206. Among them:

[0061] Step 202: Control the operation of the MMC converter valve based on the target DC voltage, and obtain the DC current of the diode converter valve.

[0062] The target DC voltage can be generated by the MMC converter valve controller according to the specific parameters of the system at the initial stage of system operation, or it can be set by professionals. Since the voltage level of the target DC voltage can match the specific situation of the system, when the MMC converter valve is controlled based on the target DC voltage, the system optimization control operation and the economy of the entire system can be guaranteed.

[0063] It can be understood that the sea breeze DC system also includes a detection device connected to the MMC converter valve controller, which can detect the DC current of the diode converter valve and output the detection result to the MMC converter valve controller, thereby realizing the monitoring of the DC current of the diode converter valve during the operation of the system.

[0064] Step 204, determining a reference value of the effective value of the PCC point line voltage of the sea breeze DC system according to the DC current of the diode converter valve.

[0065] The PCC point is a common connection point of the offshore AC busbar connecting the offshore wind farm and the first AC circuit breaker and the second AC circuit breaker, that is, a common busbar.

[0066] After obtaining the DC current of the diode converter valve, the effective value of the PCC point-to-line voltage can be determined first, and then the reference value can be determined according to the effective value of the PCC point-to-line voltage.

[0067] In one embodiment, the effective value of the line voltage at the PCC point can be determined based on the DC current of the diode converter valve in combination with the following formula (1):

[0068] (1)

[0069] Where U pcc Indicates the effective value of the PCC point line voltage, I d1 Indicates the DC current of the diode commutator valve, U d1 represents the DC side voltage of the diode converter valve, and Xc represents the leakage reactance of the transformer (i.e., the first transformer) to which the diode converter valve is connected. In some embodiments, the DC side voltage U d1 And the leakage reactance Xc of the first transformer is the initial setting value.

[0070] Specifically, the DC side voltage U of the diode converter valve can be guaranteed. d1 Under the condition of no change, according to the DC current I of the diode commutation valve d1 Determine the effective value of the PCC line voltage U pcc . Then, the effective value U can be directly pcc As a reference value, it can also be based on the effective value U pcc Perform calculations (such as multiplying by a certain coefficient) and use the result as a reference value.

[0071] Step 206, controlling the AC voltage at the PCC point according to the reference value.

[0072] The specific implementation method of controlling the AC voltage at the PCC point according to the reference value does not need to be limited. Since the reference value is to ensure that the DC side voltage U d1 Therefore, in the process of dynamically controlling the AC voltage at the PCC point, the DC voltage of the diode converter valve can be kept constant, thereby ensuring that the DC voltage of the diode converter valve remains constant under different DC currents.

[0073] It should be noted that the total DC voltage of the diode converter valve and the MMC converter valve is controlled by the onshore converter valve, for example, the total DC voltage is maintained at 640kV. When the operation strategy of the control method in this embodiment is not adopted, the effective value Upcc of the PCC point-to-line voltage remains constant. When the DC current is 0, the DC side output voltage of the diode converter valve is about 491.6kV, and the DC voltage of the MMC converter valve is about 148.4kV; when the DC current is 1.5625kA (such as the rated value), the DC side output voltage of the diode converter valve is about 440kV, and the DC voltage of the MMC converter valve is about 200kV. It can be seen that the DC voltage of the MMC converter valve fluctuates greatly.

[0074] When the operating strategy of the control method in this embodiment is adopted, it can be ensured that the DC voltage of the diode converter valve remains constant under different DC currents. Since the total DC voltage remains unchanged, the DC voltage of the MMC converter valve remains unchanged, thereby achieving the goal of making the DC voltage of the MMC converter valve constant.

[0075] The control method of the above-mentioned sea breeze DC system first controls the operation of the MMC converter valve based on the target DC voltage, and obtains the DC current of the diode converter valve; determines the reference value of the effective value of the line voltage at the PCC point of the sea breeze DC system according to the DC current of the diode converter valve; and controls the AC voltage at the PCC point according to the reference value. Therefore, during the operation of the system, the reference value of the effective value of the line voltage at the PCC point can be determined according to the DC current of the diode converter valve, so as to dynamically control the AC voltage at the PCC point according to the reference value. Since the DC voltage of the diode converter valve changes with the AC voltage and DC current, the DC voltage of the diode converter valve can be kept constant under different DC currents by dynamically controlling the AC voltage at the PCC point, thereby ensuring that the DC voltage of the MMC converter valve is constant under different wind power.

[0076] In one embodiment, Figure 3 As shown, the control method of the sea breeze DC system also includes steps 302 to 306. Among them:

[0077] Step 302, determining the system DC parameters of the sea breeze DC system.

[0078] The system DC parameters may be generated by the MMC converter valve controller (e.g., generated by the MMC converter valve controller according to the design requirements input by professionals), or may be directly input into the MMC converter valve controller after being designed by professionals. The system DC parameters may specifically include the system DC voltage and the system DC current. Still taking the above embodiment as an example, the system DC voltage may be 640 kV, and the system DC current may be 1.5625 kA.

[0079] Step 304: Determine the first corresponding relationship, the capacity limitation condition and the voltage limitation condition of the MMC converter valve according to the system DC parameters.

[0080] The first corresponding relationship is used to characterize the relationship between the reactive capacity and the DC voltage of the MMC converter valve. The capacity limitation condition of the MMC converter valve is used to limit the reactive capacity of the MMC converter valve; the voltage limitation condition of the MMC converter valve is used to limit the DC voltage of the MMC converter valve.

[0081] Step 306: determine the target DC voltage based on the first corresponding relationship, the capacity restriction condition, and the voltage restriction condition.

[0082] Specifically, based on the relationship between the reactive capacity of the MMC converter valve and the DC voltage, combined with the capacity restriction condition of the reactive capacity of the MMC converter valve and the voltage restriction condition of the DC voltage, the optimal DC voltage of the MMC converter valve can be screened and obtained according to the principle of minimum MMC converter valve power as the target DC voltage. When the MMC converter valve is controlled to operate based on the voltage level of the target DC voltage, the reactive capacity of the MMC converter valve can be made smaller than that of other voltage levels.

[0083] In this embodiment, after the DC voltage and DC current of the system are determined, the target DC voltage can be obtained according to the determined system DC voltage and system DC current. When the operation of the MMC converter valve is controlled based on the target DC voltage, the reactive capacity of the MMC converter valve can be optimized, thereby improving the overall efficiency of the system.

[0084] It should be noted that the current related research has not paid attention to the configuration method of the DC voltage level of the MMC converter valve in the system where the diode converter valve is connected in series with the MMC converter valve. During the system construction process, it is impossible to accurately design the DC voltage level of the MMC converter valve, and when the DC voltage level of the MMC converter valve is relatively large, it will significantly increase the construction cost of the entire system. Therefore, it is very necessary to study the configuration method of the DC voltage level of the MMC converter valve in the system where the diode converter valve is connected in series with the MMC converter valve.

[0085] Based on this, at the beginning of system design, after the system DC voltage and system DC current have been determined, the target DC voltage can be determined by the method in this embodiment to reduce the construction cost of the entire system. Alternatively, at the beginning of system operation, the target DC voltage can be determined by the method in this embodiment to facilitate timely optimization and adjustment of the system.

[0086] In one embodiment, the system DC parameters include the system DC voltage and the system DC current. Figure 4 As shown, the step of determining the first corresponding relationship according to the system DC parameters includes: step 402 to step 406. Among them:

[0087] Step 402: Determine the ergodic DC voltage range of the MMC converter valve according to the system DC voltage.

[0088] The target DC voltage is within the range of the ergodic DC voltage.

[0089] After the system DC voltage is determined, the range of the ergodic DC voltage can be determined according to the system DC voltage, thereby obtaining a possible interval of the target DC voltage. In some embodiments, the range of the ergodic DC voltage can be 0 to the system DC voltage, and correspondingly, the target DC voltage is within the range of 0 to the system DC voltage.

[0090] Step 404: determine the maximum reactive power range of the diode converter valve based on the traversed DC voltage range, the system DC voltage, and the system DC current.

[0091] In actual implementation, the maximum reactive power range of the diode converter valve can be determined based on the commutation overlap angle and the ergodic DC voltage range, the system DC voltage, and the system DC current.

[0092] The commutation overlap angle can be determined based on the electrical parameters of the system and the system DC current. Specifically, the electrical parameters of the system may include: the leakage reactance of the transformer (i.e., the first transformer) connected to the diode commutation valve, the transformation ratio of the transformer connected to the diode commutation valve, and the effective value of the PCC line voltage. The commutation overlap angle can then be obtained by combining the following formula (2):

[0093] (2)

[0094] Where, μ represents the commutation overlap angle; T represents the transformation ratio of the transformer connected to the diode commutation valve; I d Indicates the system DC current.

[0095] Further, the maximum reactive power range of the diode converter valve is determined based on the commutation overlap angle and the ergodic DC voltage range, the system DC voltage, the system DC current, and the correspondence between the maximum reactive power of the diode converter valve and the DC voltage of the MMC converter valve. Exemplarily, the correspondence between the maximum reactive power of the diode converter valve and the DC voltage of the MMC converter valve can be the following formula (3):

[0096] (3)

[0097] Among them, Q dio Indicates the maximum reactive power of the diode commutator valve; P dio Indicates the active power transmitted by the diode commutator valve; U dall Indicates the system DC voltage; U dm Indicates the DC voltage within the ergodic DC voltage range of the MMC circulating valve.

[0098] In this embodiment, the DC voltages within the traversed DC voltage range are all traversed once, so the maximum reactive power Q of the diode converter valve corresponding to each DC voltage within the traversed DC voltage range can be obtained. dio , and then the maximum reactive power Q dio The set is used as the maximum reactive power range of the diode commutator valve.

[0099] Step 406, determining a first corresponding relationship between the reactive capacity of the MMC converter valve and the DC voltage based on the traversed DC voltage range, the maximum reactive power range of the diode converter valve and the system DC current.

[0100] In actual implementation, the first corresponding relationship between the reactive capacity of the MMC valve and the DC voltage can be determined based on the traversed DC voltage range, the maximum reactive power range of the diode valve and the system DC current, and further combined with the ratio of the reactive capacity of the MMC valve to the maximum reactive capacity transmitted by the diode valve.

[0101] The ratio of the reactive capacity of the MMC converter valve to the maximum reactive capacity transmitted by the diode converter valve may be input by a professional, or may be generated by the MMC converter valve controller. For example, a professional inputs the voltage level of the system DC voltage, and the MMC converter valve controller generates the ratio according to the DC voltage level. In some embodiments, the ratio may be 0.5.

[0102] Furthermore, the first corresponding relationship between the reactive capacity of the MMC converter valve and the DC voltage can be obtained by combining the following formula (4).

[0103] (4)

[0104] Where, k represents the ratio of the reactive capacity of the MMC converter valve to the maximum reactive capacity transmitted by the diode converter valve; S mmc Indicates the reactive capacity of the MMC converter valve.

[0105] Thus, the reactive capacity S of the MMC converter valve corresponding to each DC voltage in the traversal DC voltage range can be obtained. mmc , and can be based on the corresponding data of each group (each DC voltage and its corresponding MMC converter valve reactive capacity S mmc As a set of data), a first corresponding relationship between the reactive capacity of the MMC converter valve and the DC voltage is obtained. Exemplarily, the first corresponding relationship can be in the form of a function curve. In some embodiments, the function curve is Figure 5 Function Curve in . Figure 5 The horizontal axis represents the DC voltage of the MMC converter valve, and the vertical axis represents the reactive capacity of the MMC converter valve.

[0106] In this embodiment, after the system DC voltage is determined, the range of the ergodic DC voltage including the target DC voltage is determined according to the system DC voltage, and then a function curve that can characterize the relationship between each DC voltage within the ergodic DC voltage range and the corresponding reactive capacity of the MMC converter valve is obtained. The curve is obtained by accurate calculation based on various parameters, so it can accurately reflect the relationship between the reactive capacity of the MMC converter valve and each DC voltage within the ergodic DC voltage range, so that the target DC voltage finally determined is more accurate.

[0107] In an exemplary embodiment, Figure 6 As shown, the step of determining the capacity limitation condition of the MMC converter valve according to the system DC parameters includes: step 602 to step 606.

[0108] Step 602: Determine the ergodic DC voltage range of the MMC converter valve according to the system DC voltage.

[0109] The ergodic DC voltage range is determined according to the system DC voltage. In some embodiments, the ergodic DC voltage range can be 0 to the system DC voltage.

[0110] Step 604, determining the arm current limit of the MMC converter valve.

[0111] The "bridge arm" is a key component of the MMC converter valve. In the topological structure of the MMC converter valve, the converter valve is composed of multiple submodules, which form the "bridge arm" of the converter valve. The bridge arm current specifically refers to the current passing through the bridge arm during the commutation process of the MMC converter valve. The bridge arm current limit is the maximum value of the bridge arm current.

[0112] In actual implementation, the arm current limit is usually set according to the flow capacity of the IGBT (Insulated Gate Bipolar Transistor) device inside the MMC converter valve. The arm current limit can be set and input by professionals according to the flow capacity of the IGBT device; or the flow capacity of the IGBT device can be input by professionals, so that the MMC converter valve controller determines the arm current limit according to the flow capacity. In some embodiments, the arm current limit is 1500A.

[0113] Step 606, determining the capacity limitation condition of the MMC converter valve based on the traversed DC voltage range, the bridge arm current limit and the system DC current.

[0114] Specifically, the capacity limit of the MMC converter valve can be determined based on the ergodic DC voltage range, the bridge arm current limit and the system DC current in combination with the following formula (5).

[0115] (5)

[0116] Where S1 represents the capacity limit of the MMC converter valve; m ac Indicates the AC modulation ratio of the MMC converter valve (needs to be determined according to the actual situation of the project, usually 0.89); i m It can be determined by the following formula (6):

[0117] (6)

[0118] Among them, i1 represents the bridge arm current limit.

[0119] It can be understood that the capacity limit S1 of the MMC converter valve obtained in this embodiment is obtained by traversing each DC voltage within the DC voltage range, that is, the capacity limit S1 of the MMC converter valve corresponds to each DC voltage within the DC voltage range. In some embodiments, the corresponding relationship between the capacity limit S1 of the MMC converter valve and each DC voltage can be expressed in the form of a capacity limit function curve. For example, the capacity limit function curve is Figure 5 The dashed curve "Limit 1" in .

[0120] Furthermore, the capacity limit condition may be determined according to the capacity limit value S1. In some implementations, the capacity limit condition may be that the reactive capacity of the MMC converter valve is less than the capacity limit value. Figure 5 In the illustrated embodiment, the reactive capacity of the MMC converter valve is less than the MMC capacity value corresponding to the "Limit 1" dashed curve.

[0121] In this embodiment, the bridge arm current limit is determined according to the flow capacity of the IGBT device inside the MMC converter valve, and then the reactive capacity limit of the MMC is calculated according to the bridge arm current limit, and then the capacity limit condition that the reactive capacity of the MMC is less than the capacity limit is determined. This capacity limit condition can optimize the capacity of the MMC converter valve as much as possible on the basis of considering the safe and stable operation of the MMC.

[0122] In one embodiment, Figure 7 As shown, the step of determining the voltage limiting condition of the MMC converter valve according to the system DC parameters includes: step 702 and step 704.

[0123] Step 702, determining the fluctuation range of the PCC point line voltage.

[0124] The fluctuation range of the PCC point-to-line voltage may be input by professionals or generated by the MMC converter valve controller according to specific project conditions. In one embodiment, the fluctuation range of the PCC point-to-line voltage may be 0.9 pu to 1 pu.

[0125] Step 704: Determine the voltage limit condition of the MMC converter valve based on the system DC parameters and the fluctuation range of the PCC point line voltage.

[0126] In actual implementation, the DC voltage limit of the MMC converter valve can be calculated based on the system DC parameters and the fluctuation range of the PCC point line voltage in combination with the following formula (7):

[0127] (7)

[0128] Where U dm1 Indicates the DC voltage limit of the MMC converter valve.

[0129] It should be noted that formula (7) is a calculation formula obtained based on the PCC point line voltage fluctuation range of 0.9pu~1pu. Based on this formula, the DC voltage limit of the MMC converter valve can be obtained. For example, the DC voltage can be Figure 5 The dash-dot straight line of "Limit 2" in the figure.

[0130] Furthermore, a voltage limiting condition is determined according to the voltage limit value. In one embodiment, the voltage limiting condition may be: the DC voltage of the MMC converter valve is not lower than the limit value. Figure 5 In the illustrated embodiment, the DC voltage of the MMC converter valve is greater than the DC voltage value corresponding to the dotted straight line of "Limit 2".

[0131] In this embodiment, the DC voltage limit of the MMC converter valve is calculated based on the fluctuation range of the PCC point-to-line voltage and the system DC parameters, and then the voltage limit condition is obtained. This voltage limit condition takes into account the fluctuation of the PCC point-to-line voltage and can ensure the safe and stable operation of the system. At the same time, ensuring that the DC voltage of the MMC converter valve is greater than the voltage limit value can prevent the converter valve from being abnormal due to low voltage, and further ensure the stable operation of the system.

[0132] In one embodiment, the step of determining the target DC voltage based on the first corresponding relationship, the capacity limitation condition and the voltage limitation condition includes:

[0133] Determining a minimum capacity value of the MMC converter valve based on the first corresponding relationship, the capacity restriction condition and the voltage restriction condition;

[0134] The DC voltage corresponding to the minimum capacity is used as the target DC voltage.

[0135] In this embodiment, the optimal DC voltage of the MMC converter valve is determined according to the principle of minimum MMC converter valve power.

[0136] Specifically, firstly, based on the first corresponding relationship, capacity limitation condition and voltage limitation condition, according to the principle of minimum MMC valve power, the minimum capacity of the MMC valve is determined, and then the DC voltage corresponding to the minimum capacity is used as the target DC voltage.

[0137] For example, see Figure 5 , the solid line curve represents the first correspondence between the reactive capacity of the MMC converter valve and the DC voltage within the traversal DC voltage range. The capacity limitation condition is that the reactive capacity of the MMC is less than the capacity limit (the dashed line curve represented by "Limit 1" in the figure). The voltage limitation condition is that the DC voltage of the MMC converter valve is not less than the DC voltage limit (the dotted line straight line represented by "Limit 2" in the figure), that is, Figure 5 In the figure, the area to the right of the dotted line and below the dashed line is the area of ​​the capacity and voltage level of the MMC converter valve that can be set. In this area, the minimum MMC capacity point is found according to the functional relationship between the DC voltage of the MMC converter valve and the capacity of the MMC converter valve ( Figure 5 In the embodiment, the minimum capacity value is 317e8VA), and the corresponding DC voltage is the DC voltage of the optimal MMC converter valve, that is, the target DC voltage ( Figure 5 1.74e5 V in the embodiment).

[0138] In this embodiment, the capacity of the MMC converter valve can be minimized while the target DC voltage can be minimized, thereby lowering the overall cost of the system and making the system more reliable during operation.

[0139] In order to better understand the above embodiment, a detailed explanation is given below in conjunction with a specific embodiment. In one embodiment, the sea breeze DC system is a sea breeze DC system in which a diode converter valve is connected in series with an MMC converter valve, the diode converter valve is a twelve-pulse diode converter valve, and the MMC converter valve is a half-bridge MMC. Specifically, the control method of the sea breeze DC system includes:

[0140] 1) Determine the system DC voltage and system DC current according to the design requirements input by professionals. For example, the system DC voltage can be 640kV and the system DC current can be 1.5625kA.

[0141] 2) Determine the range of the ergodic DC voltage according to the system DC voltage. For example, the range of the ergodic DC voltage is 0-640kV.

[0142] 3) Calculate the commutation overlap angle using formula (2):

[0143] (2)

[0144] Based on the commutation overlap angle and the ergodic DC voltage range, the system DC voltage, the system DC current, and formula (3), the maximum reactive power range of the diode commutator valve is obtained.

[0145] (3)

[0146] 4) Generate a ratio of the reactive capacity of the MMC converter valve to the maximum reactive capacity transmitted by the diode converter valve according to the level of the DC voltage. For example, the ratio may be 0.5.

[0147] Combining formula (4) to obtain the first corresponding relationship between the reactive capacity of the MMC converter valve and the DC voltage, the first corresponding relationship can be in the form of a function curve. For example, the function curve can refer to Figure 5 Function Curve in .

[0148] (4)

[0149] 5) Set the arm current limit value according to the current carrying capacity of the IGBT device inside the MMC converter valve, and determine the capacity limit value of the MMC converter valve based on the ergodic DC voltage range, the arm current limit value and the system DC current in combination with formula (5).

[0150] (5)

[0151] Then, the condition that the reactive capacity of the MMC converter valve is less than the capacity limit is used as the capacity restriction condition.

[0152] 6) Determine the fluctuation range of the PCC point-to-line voltage. For example, the fluctuation range of the PCC point-to-line voltage is set to 0.9pu to 1pu.

[0153] Next, based on the system DC parameters and the fluctuation range of 0.9pu to 1pu, the DC voltage limit of the MMC converter valve is calculated in combination with formula (7):

[0154] (7)

[0155] Then, the condition that the DC voltage of the MMC converter valve is not lower than the limit value is used as the voltage limit condition.

[0156] 7) By combining the function curve, capacity constraint conditions and voltage constraint conditions, based on the principle of minimum MMC power, the minimum value that the capacity of the MMC converter valve can reach and the corresponding minimum voltage at this time are determined, so that the voltage is used as the target DC voltage.

[0157] 8) Based on the target DC voltage, the MMC converter valve is controlled to operate, and the DC current of the diode converter valve is obtained, so as to determine the effective value of the PCC point line voltage when the DC side voltage of the diode converter valve remains unchanged by combining formula (1):

[0158] (1)

[0159] The effective value is used as a reference value, and the AC voltage at the PCC point is controlled according to the reference value.

[0160] The control method of the above-mentioned sea breeze DC system determines the reference value of the effective value of the PCC point-line voltage according to the DC current (active power) transmitted by the system, which can ensure that the DC voltage of the MMC converter valve remains constant under different DC currents (powers) transmitted.

[0161] This method obtains the relationship between the DC voltage and reactive power of the MMC converter valve, and combines the flow capacity with the constant DC voltage limit of the MMC converter valve to obtain the optimal DC voltage configuration value of the MMC converter valve, which can ensure the economy of the MMC converter valve with a series diode converter valve.

[0162] The method combines the dynamic characteristics of the diode valve in the system where the diode valve is connected in series with the MMC valve, combines the actual project, considers the flow capacity, and comprehensively compares and determines the voltage level of the optimal MMC valve.

[0163] This method realizes the optimized control of the sea breeze DC system. In the process of controlling the sea breeze DC system based on this method, it can ensure that when the active power transmitted by the entire system changes, the DC voltage of the MMC converter valve remains stable, so as to improve the AC voltage modulation ratio. The modulation ratio under steady-state operating conditions does not exceed 0.75, thereby optimizing the control operation.

[0164] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0165] Based on the same inventive concept, the embodiment of the present application also provides a control device for a sea breeze DC system for implementing the control method for the sea breeze DC system involved above. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in the embodiments of the control device for one or more sea breeze DC systems provided below can refer to the limitations of the control method for the sea breeze DC system above, and will not be repeated here.

[0166] In an exemplary embodiment, Figure 8 As shown, a control device for a sea breeze DC system is provided. The sea breeze DC system is a sea breeze DC system of a diode converter valve in series with an MMC converter valve. The device includes: an initial control module 802, a reference value determination module 804 and a voltage control module 806, wherein:

[0167] The initial control module 802 is used to control the operation of the MMC converter valve based on the target DC voltage and obtain the DC current of the diode converter valve.

[0168] The reference value determination module 804 is used to determine the reference value of the effective value of the PCC point line voltage of the sea breeze DC system according to the DC current of the diode converter valve.

[0169] The voltage control module 806 is used to control the AC voltage at the PCC point according to the reference value.

[0170] In one embodiment, the control device of the sea breeze DC system also includes a voltage determination module, which is used to determine the system DC parameters of the sea breeze DC system; according to the system DC parameters, determine the first corresponding relationship, the capacity limitation condition and the voltage limitation condition of the MMC converter valve; wherein the first corresponding relationship represents the relationship between the reactive capacity and the DC voltage of the MMC converter valve; and determine the target DC voltage based on the first corresponding relationship, the capacity limitation condition and the voltage limitation condition.

[0171] In one embodiment, the voltage determination module is also used to determine the ergodic DC voltage range of the MMC converter valve according to the system DC voltage; determine the maximum reactive power range of the diode converter valve based on the ergodic DC voltage range, the system DC voltage, and the system DC current; and determine the first corresponding relationship between the reactive capacity of the MMC converter valve and the DC voltage based on the ergodic DC voltage range, the maximum reactive power range of the diode converter valve, and the system DC current.

[0172] In one embodiment, the voltage determination module is also used to determine the traversable DC voltage range of the MMC converter valve according to the system DC voltage; determine the bridge arm current limit of the MMC converter valve; and determine the capacity limitation condition of the MMC converter valve based on the traversable DC voltage range, the bridge arm current limit and the system DC current.

[0173] In one embodiment, the voltage determination module is further used to determine the fluctuation range of the PCC point-to-line voltage; and determine the voltage limit condition of the MMC converter valve based on the system DC parameters and the fluctuation range of the PCC point-to-line voltage.

[0174] In one embodiment, the voltage determination module is further used to determine the minimum capacity of the MMC converter valve based on the first corresponding relationship, the capacity limitation condition and the voltage limitation condition; and use the DC voltage corresponding to the minimum capacity as the target DC voltage.

[0175] Each module in the control device of the above-mentioned sea breeze DC system can be implemented in whole or in part by software, hardware and their combination. Each of the above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the corresponding operations of each of the above modules.

[0176] In an exemplary embodiment, a sea breeze direct current system is provided. Figure 1 The sea breeze DC system is a diode converter valve series MMC converter valve type sea breeze DC system, including: an offshore wind farm 101, a first transformer 103, a first AC circuit breaker 102, a second transformer 105, a second AC circuit breaker 104, a diode converter valve 106, an MMC converter valve 107, an MMC converter valve controller (not shown), an onshore converter valve 108, a third transformer 109, a third AC circuit breaker 110, and an onshore power grid 111. The offshore wind farm 101 is sequentially connected to the first AC circuit breaker 102, the first transformer 103, and the diode converter valve 106 through an offshore AC busbar, and is sequentially connected to the second AC circuit breaker 104, the second transformer 105, and the MMC converter valve 107 through an offshore AC busbar, and the diode converter valve 106 is connected to the MMC converter valve 107. The diode converter valve 106 and the MMC converter valve 107 are respectively connected to the onshore converter valve 108 through the submarine DC cable 112, and the onshore converter valve 108 is connected to the onshore power grid 111 through the third transformer 109 and the third AC circuit breaker 110. The diode converter valve 106, the MMC converter valve 107 and the onshore converter valve 108 can be set according to actual conditions. For example, the diode converter valve 106 can be a twelve-pulse diode converter valve; the MMC converter valve 107 and the onshore converter valve 108 are both half-bridge MMC.

[0177] The MMC converter valve controller is connected to the MMC converter valve 107 and the PCC point respectively. The PCC point is a common connection point, i.e., a common bus, connecting the offshore wind farm 101 and the first AC circuit breaker 102 and the second AC circuit breaker 104. The MMC converter valve controller is used to implement the steps in the above-mentioned method embodiments.

[0178] In an exemplary embodiment, a computer device is provided. The computer device may be a server, and its internal structure diagram may be as shown in FIG. Fig. 9 As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. Among them, the processor, the memory and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store parameter data related to the sea breeze DC system. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a control method for a sea breeze DC system is implemented.

[0179] Those skilled in the art will understand that Fig. 9 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0180] In one embodiment, a computer device is further provided, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the steps in the above method embodiments when executing the computer program.

[0181] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps in the above-mentioned method embodiments are implemented.

[0182] In one embodiment, a computer program product is provided, including a computer program, which implements the steps in the above method embodiments when executed by a processor.

[0183] A person of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment method can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, an artificial intelligence (AI) processor, etc., but are not limited to this.

[0184] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0185] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A control method for a sea breeze DC system, characterized in that: The sea breeze DC system is a diode converter valve series MMC converter valve type sea breeze DC system, and the method comprises: Determining system DC parameters of the sea breeze DC system; Determine a first corresponding relationship, a capacity restriction condition and a voltage restriction condition of the MMC converter valve according to the system DC parameters; wherein the first corresponding relationship represents the relationship between the reactive capacity and the DC voltage of the MMC converter valve; determining a target DC voltage based on the first corresponding relationship, the capacity restriction condition, and the voltage restriction condition; Controlling the operation of the MMC converter valve based on the target DC voltage, and obtaining the DC current of the diode converter valve; Determine a reference value of the effective value of the PCC point line voltage of the sea breeze DC system according to the DC current of the diode converter valve; controlling the AC voltage at the PCC point according to the reference value; The system DC parameters include a system DC voltage and a system DC current; and determining the first corresponding relationship according to the system DC parameters includes: Determining the ergodic DC voltage range of the MMC converter valve according to the system DC voltage; Determining a maximum reactive power range of the diode converter valve based on the ergodic DC voltage range, the system DC voltage, and the system DC current; Based on the ergodic DC voltage range, the maximum reactive power range of the diode converter valve and the system DC current, a first corresponding relationship between the reactive capacity of the MMC converter valve and the DC voltage is determined.

2. The method according to claim 1, characterized in that The system DC parameters include a system DC voltage and a system DC current; and determining the capacity limitation condition of the MMC converter valve according to the system DC parameters includes: Determining the ergodic DC voltage range of the MMC converter valve according to the system DC voltage; Determining a bridge arm current limit value of the MMC converter valve; The capacity limitation condition of the MMC converter valve is determined based on the ergodic DC voltage range, the bridge arm current limit and the system DC current.

3. The method according to claim 1, characterized in that Determining the voltage limiting condition of the MMC converter valve according to the system DC parameter includes: Determining the fluctuation range of the PCC point line voltage; The voltage limit condition of the MMC converter valve is determined based on the system DC parameters and the fluctuation range of the PCC point line voltage.

4. The method according to claim 1, characterized in that The determining the target DC voltage based on the first corresponding relationship, the capacity restriction condition and the voltage restriction condition includes: Determining a minimum capacity value of the MMC converter valve based on the first corresponding relationship, the capacity restriction condition and the voltage restriction condition; The DC voltage corresponding to the minimum capacity is used as the target DC voltage.

5. A control device for a sea breeze DC system, characterized in that: The sea breeze DC system is a diode converter valve in series with an MMC converter valve type sea breeze DC system, and the device comprises: A voltage determination module, the voltage determination module is used to determine the system DC parameters of the sea breeze DC system; according to the system DC parameters, determine the first corresponding relationship, the capacity restriction condition and the voltage restriction condition of the MMC converter valve; wherein the first corresponding relationship represents the relationship between the reactive capacity and the DC voltage of the MMC converter valve; determine the target DC voltage based on the first corresponding relationship, the capacity restriction condition and the voltage restriction condition; An initial control module, used to control the operation of the MMC converter valve based on the target DC voltage and obtain the DC current of the diode converter valve; A reference value determination module, used to determine a reference value of the effective value of the PCC point line voltage of the sea breeze DC system according to the DC current of the diode converter valve; A voltage control module, used for controlling the AC voltage of the PCC point according to the reference value; Wherein, the system DC parameters include system DC voltage and system DC current; The voltage determination module is further used to determine the ergodic DC voltage range of the MMC converter valve according to the system DC voltage; determine the maximum reactive power range of the diode converter valve based on the ergodic DC voltage range, the system DC voltage, and the system DC current; and determine the first corresponding relationship between the reactive capacity of the MMC converter valve and the DC voltage based on the ergodic DC voltage range, the maximum reactive power range of the diode converter valve, and the system DC current.

6. A sea breeze direct current system, characterized in that: The sea breeze DC system is a diode converter valve series MMC converter valve type sea breeze DC system, including: an offshore wind farm, a first transformer, a first AC circuit breaker, a second transformer, a second AC circuit breaker, a diode converter valve, an MMC converter valve, an MMC converter valve controller, an onshore converter valve, a third transformer, a third AC circuit breaker, and an onshore power grid; wherein the offshore wind farm is sequentially connected to the first AC circuit breaker, the first transformer, and the diode converter valve through an offshore AC bus, and sequentially connected to the second AC circuit breaker, the second transformer, and the MMC converter valve through an offshore AC bus, and the diode converter valve is connected to the MMC converter valve; the diode converter valve and the MMC converter valve are respectively connected to the onshore converter valve through a submarine DC submarine cable, and the onshore converter valve is connected to the onshore power grid through the third transformer and the third AC circuit breaker; Among them, the MMC converter valve controller is connected to the MMC converter valve and the PCC point respectively, and the MMC converter valve controller is used to implement the control method of the sea breeze DC system according to any one of claims 1 to 4; the PCC point is a common connection point connecting the offshore wind farm and the offshore AC busbar of the first AC circuit breaker and the second AC circuit breaker.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

8. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

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