Starting and coordination control method and device for offshore low-frequency power transmission system

Abstract

The invention provides a starting and coordination control method and device for an offshore low-frequency power transmission system. The method comprises the following steps: a control step: controlling the uncontrolled rectification power transmission converter to perform single-end unlocking in a constant direct current voltage and power frequency alternating current side reactive mode and determining a direct current voltage set value; a starting step: starting the auxiliary current converter in a mode of constant AC voltage and constant AC frequency to carry out soft charging on the low-frequency bus and related low-frequency equipment and establish low-frequency network voltage; and an adjusting step: unlocking the single fan in a network following control mode, sending power to the land side, and smoothly transferring active power transmitted between the auxiliary current converter and the uncontrolled rectification power transmission converter by adjusting the low-frequency voltage amplitude of the low-frequency network voltage according to the direct-current voltage set value. All active power of the auxiliary converter is transferred to the uncontrolled rectification power transmission converter. The problems that low-frequency side voltage cannot be established and an offshore wind turbine generator converter is difficult to start in the prior art are solved.

Description

Technical Field

[0001] The present application relates to the technical field of starting and coordinated control of an offshore low-frequency power transmission system, and in particular to a method, device, computer-readable storage medium and electronic device for starting and coordinated control of an offshore low-frequency power transmission system. Background Art

[0002] In the field of offshore wind power long-distance transmission, the traditional industrial frequency transmission method is often affected by the equivalent capacitance of the submarine cable, which greatly limits its power transmission distance and is not suitable for long-distance wind power transmission. The low-frequency transmission solution based on the diode twelve-pulse uncontrolled rectifier (DRU) can overcome the shortcomings of limited industrial frequency AC transmission distance and high cost of DC transmission, and can support transmission distances of more than 200km, completely solving the problem of offshore wind power long-distance transmission. It is a low-cost low-frequency AC transmission solution suitable for the open sea.

[0003] However, since the DRU cannot transmit power in the reverse direction and cannot establish low-frequency side voltage, there is a problem of difficulty in starting the offshore wind turbine converter. Summary of the invention

[0004] The main purpose of the present application is to provide a method, device, computer-readable storage medium and electronic device for starting and coordinating control of an offshore low-frequency power transmission system, so as to at least solve the problem that the prior art cannot establish low-frequency side voltage and has difficulty in starting the offshore wind turbine converter.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a method for starting and coordinating control of an offshore low-frequency power transmission system is provided. The offshore low-frequency power transmission system includes an auxiliary converter VSC and an uncontrolled rectifier transmission converter DRU-MMC. The method includes: a control step, controlling the uncontrolled rectifier transmission converter to be single-ended unlocked in a fixed DC voltage and industrial frequency AC side reactive mode and determining a DC voltage setting value; a starting step, starting the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage; an adjustment step, unlocking a single wind turbine in a grid-following control mode and sending power to the onshore side, and smoothly transferring the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter according to the DC voltage setting value by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter.

[0006] Optionally, after transferring all active power of the auxiliary converter to the uncontrolled rectifier transmission converter, the method further includes: controlling the single wind turbine to switch from the grid-following control mode to the grid-forming control mode, and starting other wind turbines in the grid-following control mode, and after starting, controlling the other wind turbines to switch from the grid-following control mode to the grid-forming control mode, so as to control the other wind turbines to deliver power through the uncontrolled rectifier transmission converter.

[0007] Optionally, the control step, controlling the uncontrolled rectifier transmission converter to be single-ended unlocked in a fixed DC voltage and industrial frequency AC side reactive mode and determining a DC voltage setting value, includes: controlling the industrial frequency AC incoming line switch of the uncontrolled rectifier transmission converter to be closed, and performing uncontrolled charging on the uncontrolled rectifier transmission converter and the auxiliary converter; when the uncontrolled charging reaches a preset voltage, controlling the uncontrolled rectifier transmission converter to be single-ended unlocked in the industrial frequency AC side reactive mode, performing controllable charging on the capacitor voltage of the uncontrolled rectifier transmission converter and determining the DC voltage setting value of the uncontrolled rectifier transmission converter.

[0008] Optionally, the starting step, starting the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage, includes: determining a low-frequency AC voltage amplitude target value and a voltage ramp rate; starting the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment according to the low-frequency AC voltage amplitude target value and the voltage ramp rate; and completing the establishment of the low-frequency grid voltage when the voltage of the low-frequency bus reaches the low-frequency AC voltage amplitude target value.

[0009] Optionally, the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter is smoothly transferred by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, including: determining a first power target value of the uncontrolled rectifier transmission converter and a second power target value of the auxiliary converter; determining the AC voltage amplitude of the auxiliary converter at least according to the first power target value and the second power target value, and adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the AC voltage amplitude; when it is determined that the low-frequency voltage amplitude reaches the DC voltage setting value, completing the smooth transfer of the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter.

[0010] Optionally, the AC voltage amplitude of the auxiliary converter is determined at least based on the first power target value and the second power target value, including: determining the first transmission active power of the uncontrolled rectifier transmission converter and the second transmission active power of the auxiliary converter; determining the voltage upper limit value of the AC voltage amplitude based on the first transmission active power and the first power target value, and determining the AC voltage amplitude based on the voltage upper limit value, the second transmission active power and the second power target value.

[0011] Optionally, determining a voltage upper limit value of the AC voltage amplitude according to the first transmission active power and the first power target value, and determining the AC voltage amplitude according to the voltage upper limit value, the second transmission active power and the second power target value comprises: according to a first formula: Determine the voltage upper limit value, where V VSCMAX is the voltage upper limit, P DMREF is the first power target value, P DM is the first transmission active power, k1 and τ1 are respectively the active power closed-loop proportional coefficient and the integral time constant of the uncontrolled rectifier transmission converter, and s is the differential operator symbol; according to the second formula: 0≤V VSCLIM -V0≤V VSCMAX , determine the AC voltage amplitude, where V VSCLIM is the AC voltage amplitude, P VSCREF is the second power target value, P VSC is the second transmitted active power, k2 and τ2 are respectively the active power closed-loop proportional coefficient and the integral time constant of the auxiliary converter.

[0012] According to another aspect of the present application, a starting and coordination control device for an offshore low-frequency power transmission system is provided. The offshore low-frequency power transmission system includes an auxiliary converter VSC and an uncontrolled rectifier transmission converter DRU-MMC. The device includes: a control unit, used to execute a control step, control the uncontrolled rectifier transmission converter to be single-ended unlocked in a fixed DC voltage and industrial frequency AC side reactive mode and determine a DC voltage setting value; a starting unit, used to execute a starting step, start the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage; an adjustment unit, used to execute an adjustment step, unlock a single wind turbine in a grid-following control mode and send power to the onshore side, and smoothly transfer the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter.

[0013] According to another aspect of the present application, a computer-readable storage medium is provided, wherein the computer-readable storage medium includes a stored program, wherein when the program is running, the device where the computer-readable storage medium is located is controlled to execute any one of the methods for starting and coordinating control of an offshore low-frequency power transmission system.

[0014] According to another aspect of the present application, an electronic device is provided, comprising: one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and are configured to be executed by the one or more processors, and the one or more programs include methods for executing any one of the startup and coordination control methods for the offshore low-frequency power transmission system.

[0015] The technical solution of the present application is applied, the control step is to control the uncontrolled rectifier transmission converter to single-end unlock in a fixed DC voltage and industrial frequency AC side reactive mode and determine the DC voltage setting value; the starting step is to start the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency network voltage; the adjustment step is to unlock a single wind turbine in a grid-following control mode and send power to the onshore side, and smoothly transfer the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter by adjusting the low-frequency voltage amplitude of the low-frequency network voltage according to the DC voltage setting value, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter. The auxiliary converter VSC is used to smoothly boost the voltage to solve the problem of difficulty in charging low-frequency equipment and difficulty in energy extraction of wind turbine secondary equipment, and reactive impact starting can be achieved during the startup of the offshore low-frequency transmission system, solving the problem that the existing technology cannot establish the low-frequency side voltage and there is difficulty in starting the offshore wind turbine converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0017] Figure 1 A hardware structure block diagram of a mobile terminal for executing a method for starting and coordinating control of an offshore low-frequency power transmission system provided in an embodiment of the present application is shown;

[0018] Figure 2 A schematic flow chart of a method for starting and coordinating control of an offshore low-frequency power transmission system provided according to an embodiment of the present application is shown;

[0019] Figure 3 A schematic diagram of a main circuit for start-up and power coordination control of an offshore low-frequency power transmission system based on a DRU-MMC according to an embodiment of the present application is shown;

[0020] Figure 4 A schematic diagram of the control principle of the start-up and power coordination control of the offshore low-frequency power transmission system based on DRU-MMC provided according to an embodiment of the present application is shown;

[0021] Figure 5 A schematic diagram showing the effect of start-up and power coordination control of an offshore low-frequency power transmission system based on a DRU-MMC according to an embodiment of the present application is shown;

[0022] Figure 6 A structural block diagram of a startup and coordination control device for an offshore low-frequency power transmission system provided according to an embodiment of the present application is shown.

[0023] The above drawings include the following reference numerals:

[0024] 102, processor; 104, memory; 106, transmission device; 108, input and output devices. DETAILED DESCRIPTION

[0025] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0026] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0027] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0028] As introduced in the background technology, the existing technology is unable to establish a low-frequency side voltage, and there is difficulty in starting the offshore wind turbine converter. In order to solve the problem that the existing technology is unable to establish a low-frequency side voltage, and there is difficulty in starting the offshore wind turbine converter, the embodiments of the present application provide a starting and coordination control method, device, computer-readable storage medium and electronic device for an offshore low-frequency power transmission system.

[0029] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0030] The method embodiments provided in the embodiments of the present application can be executed in a mobile terminal, a computer terminal or a similar computing device. Taking running on a mobile terminal as an example, Figure 1 1 is a hardware structure block diagram of a mobile terminal for a method for starting and coordinating control of an offshore low-frequency power transmission system according to an embodiment of the present invention. Figure 1 As shown, the mobile terminal may include one or more ( Figure 1 Only one is shown in the figure) a processor 102 (the processor 102 may include but is not limited to a processing device such as a microprocessor MCU or a programmable logic device FPGA) and a memory 104 for storing data, wherein the mobile terminal may also include a transmission device 106 and an input / output device 108 for communication functions. It can be understood by those skilled in the art that Figure 1 The structure shown is only for illustration and does not limit the structure of the mobile terminal. Figure 1 More or fewer components as shown, or with Figure 1 Different configurations are shown.

[0031] The memory 104 can be used to store computer programs, for example, software programs and modules of application software, such as the computer program corresponding to the startup and coordinated control method of the offshore low-frequency power transmission system in the embodiment of the present invention. The processor 102 executes various functional applications and data processing by running the computer program stored in the memory 104, that is, to implement the above method. The memory 104 may include a high-speed random access memory, and may also include a non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some examples, the memory 104 may further include a memory remotely arranged relative to the processor 102, and these remote memories can be connected to the mobile terminal via a network. Examples of the above network include but are not limited to the Internet, an intranet, a local area network, a mobile communication network, and a combination thereof. The transmission device 106 is used to receive or send data via a network. The specific example of the above network may include a wireless network provided by a communication provider of the mobile terminal. In one example, the transmission device 106 includes a network adapter (Network Interface Controller, referred to as NIC), which can be connected to other network devices through a base station so as to communicate with the Internet. In one example, the transmission device 106 may be a radio frequency (RF) module, which is used to communicate with the Internet wirelessly.

[0032] In this embodiment, a method for starting and coordinating control of an offshore low-frequency power transmission system running on a mobile terminal, a computer terminal or a similar computing device is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in an order different from that shown here.

[0033] Figure 2 1 is a flow chart of a method for starting and coordinating control of an offshore low-frequency power transmission system according to an embodiment of the present application, wherein the offshore low-frequency power transmission system includes an auxiliary converter VSC and an uncontrolled rectifier transmission converter DRU-MMC. Figure 2 As shown, the method comprises the following steps:

[0034] Step S201, a control step, controlling the above-mentioned uncontrolled rectifier transmission converter to be single-ended unlocked in a fixed DC voltage and industrial frequency AC side reactive mode and determining a DC voltage setting value;

[0035] Specifically, the incoming line switches are closed successively, and the MMC power frequency transformer and auxiliary converter are charged uncontrollably by means of series resistance until the capacitor voltage of the converter unit is stable. Subsequently, the MMC is single-ended unlocked in a mode of fixed DC voltage and power frequency AC side reactive power, and the MMC converter valve capacitor voltage is controllably charged and the DRU-MMC DC voltage is established to the set value Udcn, completing the single-ended unlocking of the DRU-MMC.

[0036] Step S202, a start step, starts the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage;

[0037] Specifically, the DRU-MMC low-frequency side switch, the auxiliary converter VSC low-frequency side switch and the wind turbine converter high-voltage side switch are closed in sequence, and all low-frequency side devices are connected to the low-frequency bus; the low-frequency AC voltage amplitude target value U is set. ACVSC And the voltage ramp rate U SPD , where U ACVSC Need to be less than U dcn , so that the DRU-MMC uncontrolled rectifier valve is in the cut-off state, to prevent the DRU valve from accidentally turning on and causing power return during the subsequent VSC establishment of the low-frequency bus voltage.

[0038] Step S203, an adjustment step, unlocks a single wind turbine in a grid-following control mode and sends power to the onshore side, and smoothly transfers the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter.

[0039] Specifically, the power transfer ramp rate is set by the coordinated control device, and the DRU-MMC power target value P is set. DMREF is the rated value, and the VSC power target value is set to P VSCREF (less than or equal to the rated value). After the target value is set, the coordinated control device generates the VSC output AC voltage amplitude command value according to the power command closed loop and sends it to the VSC. The VSC gradually increases the low-frequency AC bus voltage amplitude. When the low-frequency AC bus voltage amplitude exceeds the DRU-MMC DC voltage, the DRU-MMC uncontrolled rectifier valve is naturally turned on, and the VSC transmission power is smoothly transferred to the DRU-MMC.

[0040] Through this embodiment, the control step controls the above-mentioned uncontrolled rectifier transmission converter to be unlocked in a single-end mode with a fixed DC voltage and a reactive mode on the industrial frequency AC side and determines the DC voltage setting value; the start step starts the above-mentioned auxiliary converter in a mode with a fixed AC voltage and a fixed AC frequency to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency network voltage; the adjustment step unlocks a single wind turbine in a grid-following control mode and sends power to the onshore side, and smoothly transfers the active power transmitted between the above-mentioned auxiliary converter and the above-mentioned uncontrolled rectifier transmission converter according to the above-mentioned DC voltage setting value by adjusting the low-frequency voltage amplitude of the above-mentioned low-frequency network voltage, so as to transfer all the active power of the above-mentioned auxiliary converter to the above-mentioned uncontrolled rectifier transmission converter. The auxiliary converter VSC is used to smoothly boost the voltage to solve the problem of difficulty in charging low-frequency equipment and difficulty in energy extraction of wind turbine secondary equipment, and reactive impact starting can be achieved during the startup of the offshore low-frequency transmission system, solving the problem that the existing technology cannot establish the low-frequency side voltage and there is difficulty in starting the offshore wind turbine converter.

[0041] In the specific implementation process, after all the active power of the above-mentioned auxiliary converter is transferred to the above-mentioned uncontrolled rectifier transmission converter, the above-mentioned method also includes: controlling the above-mentioned single wind turbine to switch from the above-mentioned grid-following control mode to the above-mentioned grid-forming control mode, and starting other wind turbines in the above-mentioned grid-following control mode, and after starting, controlling the above-mentioned other wind turbines to switch from the above-mentioned grid-following control mode to the above-mentioned grid-forming control mode, so as to control the above-mentioned other wind turbines to deliver power through the above-mentioned uncontrolled rectifier transmission converter.

[0042] The method sets the active power set value of the VSC to 0, transfers all active power to the DRU-MMC side, and sets the wind turbine to switch from the grid-following control mode to the grid-forming control mode. The VSC exits, and the coordinated control loop fails. The wind turbine converter in the grid-forming operation mode adaptively adjusts the low-frequency bus voltage amplitude, so that all active power is sent out through the DRU-MMC. Subsequently, the remaining wind turbines are started in the grid-following mode one by one. After the start-up is completed, the grid-following mode is switched to the grid-forming mode, and all wind turbines send out stable power through the DRU-MMC.

[0043] Specifically, the control step controls the above-mentioned uncontrolled rectifier transmission converter to be single-ended unlocked in a fixed DC voltage and industrial frequency AC side reactive mode and determines the DC voltage setting value, including: controlling the industrial frequency AC incoming line switch of the above-mentioned uncontrolled rectifier transmission converter to be closed, and performing uncontrolled charging on the above-mentioned uncontrolled rectifier transmission converter and the above-mentioned auxiliary converter; when the uncontrolled charging reaches a preset voltage, controlling the above-mentioned uncontrolled rectifier transmission converter to be single-ended unlocked in the industrial frequency AC side reactive mode, performing controllable charging on the capacitor voltage of the above-mentioned uncontrolled rectifier transmission converter and determining the above-mentioned DC voltage setting value of the above-mentioned uncontrolled rectifier transmission converter.

[0044] More specifically, the starting step, starting the above-mentioned auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency network voltage, includes: determining the low-frequency AC voltage amplitude target value and the voltage ramp rate; according to the above-mentioned low-frequency AC voltage amplitude target value and the above-mentioned voltage ramp rate, starting the above-mentioned auxiliary converter in the fixed AC voltage and the above-mentioned fixed AC frequency mode to soft-charge the above-mentioned low-frequency bus and the above-mentioned related low-frequency equipment; when the voltage of the above-mentioned low-frequency bus reaches the above-mentioned low-frequency AC voltage amplitude target value, completing the establishment of the above-mentioned low-frequency network voltage.

[0045] The method sequentially closes the DRU-MMC low-frequency side switch, the auxiliary converter VSC low-frequency side switch and the wind turbine converter high-voltage side switch, and connects all low-frequency side devices to the low-frequency bus; sets the low-frequency AC voltage amplitude target value UACVSC and the voltage ramp rate USPD, where UACVSC needs to be less than Udcn, so that the DRU-MMC uncontrolled rectifier valve is in the cut-off state to prevent the accidental conduction of the DRU valve during the subsequent VSC establishment of the low-frequency bus voltage, resulting in power return. Then, the VSC auxiliary converter is controlled in a fixed AC voltage amplitude and frequency (VF) control mode. The auxiliary converter gradually raises the low-frequency bus voltage at a certain ramp rate and soft-charges the transformer in the line to avoid damage to the converter caused by large excitation inrush current; after the VSC raises the low-frequency AC bus voltage to the set amplitude, the wind turbine secondary equipment can also be powered through the primary side of the wind turbine converter and ready, and send a ready signal to the coordination controller.

[0046] Furthermore, the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter is smoothly transferred by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, including: determining the first power target value of the uncontrolled rectifier transmission converter and the second power target value of the auxiliary converter; determining the AC voltage amplitude of the auxiliary converter at least according to the first power target value and the second power target value, and adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the AC voltage amplitude; and completing the smooth transfer of the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter when it is determined that the low-frequency voltage amplitude reaches the DC voltage setting value.

[0047] Furthermore, the AC voltage amplitude of the auxiliary converter is determined at least based on the above-mentioned first power target value and the above-mentioned second power target value, including: determining the first transmission active power of the above-mentioned uncontrolled rectifier transmission converter and the second transmission active power of the above-mentioned auxiliary converter; determining the voltage upper limit value of the above-mentioned AC voltage amplitude based on the above-mentioned first transmission active power and the above-mentioned first power target value, and determining the above-mentioned AC voltage amplitude based on the above-mentioned voltage upper limit value, the above-mentioned second transmission active power and the above-mentioned second power target value.

[0048] This method controls the start-up of a single wind turbine on the offshore side and sends out power. The coordinated controller smoothly transfers the active power transmitted between the VSC and the DRU-MMC by adjusting the low-frequency voltage amplitude. The specific steps are: First, unlock a single wind turbine in the grid-following control mode and send power to the onshore side. At this time, since the low-frequency AC bus voltage amplitude is lower than the DC voltage of the DRU-MMC, the wind turbine power in this stage is transmitted to the onshore side through the auxiliary converter VSC. Subsequently, the power transfer ramp rate is set through the coordinated control device, and the DRU-MMC power target value P is set. DMREF is the rated value, and the VSC power target value is set to P VSCREF After the target value is set, the coordinated control device generates the VSC output AC voltage amplitude command value V according to the VSC power command closed loop. VSCLIM And it is sent down to VSC, VSC gradually raises the low-frequency AC bus voltage amplitude. When the low-frequency AC bus voltage amplitude exceeds the DRU-MMC DC voltage, the DRU-MMC uncontrolled rectifier valve is naturally turned on, and the VSC transmission power is smoothly transferred to DRU-MMC. The DRU-MMC power size is proportional to the difference between the low-frequency voltage amplitude and the DC voltage.

[0049] Specifically, determining the voltage upper limit value of the AC voltage amplitude according to the first transmission active power and the first power target value, and determining the AC voltage amplitude according to the voltage upper limit value, the second transmission active power and the second power target value, includes: according to the first formula: Determine the voltage upper limit above, where V VSCMAX is the upper limit of the voltage mentioned above, P DMREF is the first power target value, P DM is the first transmission active power, k1 and τ1 are respectively the active power closed-loop proportional coefficient and the integral time constant of the uncontrolled rectifier transmission converter, and s is the differential operator symbol; according to the second formula: 0≤V VSCLIM -V0≤V VSCMAX , determine the above AC voltage amplitude, where V VSCLIM is the above AC voltage amplitude, P VSCREFis the second power target value, P VSC is the second transmitted active power, k2 and τ2 are respectively the active power closed-loop proportional coefficient and the integral time constant of the auxiliary converter.

[0050] This method converts the auxiliary converter power command P VSCREF With P VSC Perform PI closed loop to generate low-frequency AC voltage amplitude command V for auxiliary converter VSC VSC , through P DM Closed loop generates V VSC The upper limit value of the voltage command V VSCUP , and finally after limiting, V VSC Voltage command V VSCLIM The output is sent to the auxiliary converter for execution output, achieving smooth power transfer between the two.

[0051] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the implementation process of the startup and coordinated control method of the offshore low-frequency power transmission system of the present application will be described in detail below in combination with specific embodiments.

[0052] This embodiment relates to a specific method for starting and coordinating control of an offshore low-frequency power transmission system, which can realize reactive impact starting during the startup process of the offshore low-frequency power transmission system; it should be noted that the offshore wind power low-frequency power transmission system includes DRU-MMC, auxiliary converter VSC, N wind turbines supporting network control and network following control, low-frequency filters, low-frequency energy consumption devices, transformers and other equipment such as Figure 3 The specific start-up and coordination control method of the offshore low-frequency power transmission system includes the following steps:

[0053] Step S1: DRU-MMC is single-ended unlocked in constant DC voltage and reactive power (STATCOM) mode on the industrial frequency AC side and establishes the DC voltage to the set value Udnom. The specific operation is as follows: First, close the DRU-MMC industrial frequency AC incoming line switch, and uncontrollably charge the MMC industrial frequency transformer and converter by connecting a bypass resistor in series until the capacitor voltage of the converter unit is less than the set value within the range of ±50V. Subsequently, close the bypass switch on the industrial frequency side, and further uncontrollably charge to the voltage setting value within the range of ±20V. When the conditions are met, the MMC is single-ended unlocked in STATCOM mode, and the MMC converter valve capacitor voltage is controllably charged and the DRU-MMC DC voltage is established to the set value Udcn, completing the single-ended unlocking of the DRU-MMC.

[0054] Step S2: Start VSC to soft-charge the low-frequency bus and related equipment and establish low-frequency grid voltage. The specific operation is: close the DRU-MMC low-frequency side switch, the auxiliary converter VSC low-frequency side switch and the wind turbine converter high-voltage side switch in sequence, connect all low-frequency side devices to the low-frequency bus; set the low-frequency AC voltage amplitude target value U ACVSC And the voltage ramp rate U SPD , where U ACVSC Need to be less than U dcn , so that the DRU-MMC uncontrolled rectifier valve is in the cut-off state, to prevent the accidental opening of the DRU valve and power return during the subsequent VSC to establish the low-frequency bus voltage. Then, the VSC auxiliary converter is controlled in a fixed AC voltage amplitude and frequency (VF) mode. The auxiliary converter gradually raises the low-frequency bus voltage at a certain ramp rate and soft-charges the transformer in the line to avoid damage to the converter caused by large excitation inrush current; after the VSC raises the low-frequency AC bus voltage to the set amplitude, the wind turbine secondary equipment can also be powered through the primary side of the wind turbine converter and ready, and send a ready signal to the coordination controller.

[0055] Step S3: A single wind turbine on the offshore side is started and power is delivered. The coordination controller smoothly transfers the active power transmitted between the VSC and the DRU-MMC by adjusting the low-frequency voltage amplitude. The specific operation steps are: First, unlock the single wind turbine in the grid-following control mode and deliver power to the onshore side. At this time, since the low-frequency AC bus voltage amplitude is lower than the DC voltage of the DRU-MMC, the wind turbine power in this stage is transmitted to the onshore side through the auxiliary converter VSC. Subsequently, the power transfer ramp rate is set through the coordination control device, and the DRU-MMC power target value P is set. DMREF is the rated value, and the VSC power target value is set to P VSCREF After the target value is set, the coordinated control device generates the VSC output AC voltage amplitude command value V according to the VSC power command closed loop. VSCLIM And it is sent down to VSC, VSC gradually raises the low-frequency AC bus voltage amplitude. When the low-frequency AC bus voltage amplitude exceeds the DRU-MMC DC voltage, the DRU-MMC uncontrolled rectifier valve is naturally turned on, and the VSC transmission power is smoothly transferred to DRU-MMC. The DRU-MMC power size is proportional to the difference between the low-frequency voltage amplitude and the DC voltage.

[0056] The power smoothing transfer between DRU-MMC and VSC is realized by the following methods: Figure 4 As shown:

[0057] 1) The coordination controller collects the low-frequency bus voltage Ua, Ub, Uc, the VSC low-frequency side AC current Ia, Ib, Ic, the DRU-MMC DC bus voltage Ud and current Idp, and calculates the active power PVSC and PDM transmitted by the VSC and DRU-MMC. The specific calculation formula is as follows:

[0058] P DM =U d ×I d ,

[0059]

[0060] Among them, s is the symbol of the differential operator, ω c It is the cut-off frequency of the low-frequency filter, usually twice the rated frequency.

[0061] 2) Set the auxiliary converter power command P VSCREF With P VSC Perform PI closed loop to generate low-frequency AC voltage amplitude command V for auxiliary converter VSC VSC , through P DM Closed loop generates V VSC The upper limit value of the voltage command V VSCUP , and finally after limiting, V VSC Voltage command V VSCLIM The output is sent to the auxiliary converter for execution output, achieving smooth power transfer between the two.

[0062]

[0063] 0≤V VSCLIM -V0≤V VSCMAX ,

[0064] Among them, k1 and τ1 are the closed-loop proportional coefficient and integral time constant of the active power of DRU-MMC, k2 and τ2 are the closed-loop proportional coefficient and integral time constant of the active power of VSC, and V0 is the initial value of the low-frequency current and voltage amplitude.

[0065] Step S4: The remaining two wind turbines are connected, and all power is sent out through the DRU-MMC. The specific operation steps are as follows:

[0066] First, the active power setpoint of the VSC is set to 0, and all active power is transferred to the DRU-MMC side. The coordinated controller sets the wind turbine to switch from the grid-following control mode to the grid-forming control mode, and the VSC exits. At this time, the coordinated control loop fails, and the wind turbine converter in the grid-forming operation mode adaptively adjusts the low-frequency bus voltage amplitude so that all active power is sent out through the DRU-MMC; then, the remaining two wind turbines are started in turn in the grid-following mode, and after the startup is completed, they are switched from the grid-following mode to the grid-forming mode. The three wind turbines send out stable power through the DRU-MMC.

[0067] The power transmission modes in this step are diverse and support flexible switching. The operation modes mainly include VSC+DRU-MMC+grid-following mode wind turbine operation (mode 1), DRU-MMC+grid-building mode wind turbine operation (mode 2) and VSC+DRU-MMC+grid-building mode wind turbine operation (mode 3). The switching method is as follows:

[0068] Switch from operation mode 1 to operation mode 2: Set the active power set value of the VSC to 0, transfer all active power to the DRU-MMC side, and set the wind turbine to switch from the grid-following control mode to the grid-forming control mode. The VSC exits, and the coordinated control loop fails. The wind turbine converter in the grid-forming operation mode adaptively adjusts the low-frequency bus voltage amplitude so that all active power is sent out through the DRU-MMC.

[0069] Operation mode 2 switches to operation mode 3: When the wind turbine is running in DRU-MMC+grid-building mode, the auxiliary converter VSC is started in the grid-following mode, and the VSC operates in the mode of controlling active power and reactive power. At this time, the power transfer can be achieved by directly sending active power instructions to the auxiliary converter through the coordination controller.

[0070] This embodiment uses the auxiliary converter VSC to smoothly boost the voltage to solve the problem of difficulty in charging low-frequency equipment and difficulty in extracting energy from wind turbine secondary equipment, and realizes the smooth start of the low-frequency DC transmission system. Figure 5 As shown; and after startup, through coordinated control logic, flexible and controllable combinations of various DC transmission lines and transmission power distribution can be achieved, greatly increasing the reliability of the low-frequency transmission system.

[0071] The embodiment of the present application also provides a start-up and coordination control device for an offshore low-frequency power transmission system. It should be noted that the start-up and coordination control device for an offshore low-frequency power transmission system of the embodiment of the present application can be used to execute the start-up and coordination control method for an offshore low-frequency power transmission system provided by the embodiment of the present application. The device is used to implement the above-mentioned embodiments and preferred implementation modes, and those that have been described will not be repeated. As used below, the term "module" can implement a combination of software and / or hardware for a predetermined function. Although the device described in the following embodiments is preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceived.

[0072] The following is an introduction to the starting and coordination control device for the offshore low-frequency power transmission system provided in an embodiment of the present application.

[0073] Figure 6 It is a schematic diagram of a starting and coordination control device for an offshore low-frequency power transmission system according to an embodiment of the present application.

[0074] like Figure 6 As shown, the device comprises:

[0075] A first control unit is used to execute a control step to control the above-mentioned uncontrolled rectifier transmission converter to be single-ended unlocked in a constant DC voltage and power frequency AC side reactive mode and determine a DC voltage setting value;

[0076] A starting unit, used to execute a starting step, start the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage;

[0077] The regulating unit is used to execute the regulating step, unlock a single wind turbine in the grid-following control mode and send power to the onshore side, and smoothly transfer the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter.

[0078] In this embodiment, the control unit is used to execute the control step, control the above-mentioned uncontrolled rectifier transmission converter to single-end unlock in a fixed DC voltage and industrial frequency AC side reactive mode and determine the DC voltage setting value; the starting unit is used to execute the starting step, start the above-mentioned auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency network voltage; the adjustment unit is used to execute the adjustment step, unlock a single wind turbine in a grid-following control mode and send power to the onshore side, and smoothly transfer the active power transmitted between the above-mentioned auxiliary converter and the above-mentioned uncontrolled rectifier transmission converter according to the above-mentioned DC voltage setting value by adjusting the low-frequency voltage amplitude of the above-mentioned low-frequency network voltage, so as to transfer all the active power of the above-mentioned auxiliary converter to the above-mentioned uncontrolled rectifier transmission converter. The auxiliary converter VSC is used to smoothly boost the voltage to solve the problem of difficulty in charging low-frequency equipment and difficulty in energy extraction of wind turbine secondary equipment, and reactive impact starting can be achieved during the startup of the offshore low-frequency transmission system, solving the problem that the existing technology cannot establish the low-frequency side voltage and there is difficulty in starting the offshore wind turbine converter.

[0079] As an optional solution, the device also includes a second control unit, which is used to control the above-mentioned single wind turbine to switch from the above-mentioned grid-following control mode to the above-mentioned grid-forming control mode after transferring all the active power of the above-mentioned auxiliary converter to the above-mentioned uncontrolled rectifier transmission converter, and to start other wind turbines in the above-mentioned grid-following control mode, and after starting, control the above-mentioned other wind turbines to switch from the above-mentioned grid-following control mode to the above-mentioned grid-forming control mode, so as to control the above-mentioned other wind turbines to deliver power through the above-mentioned uncontrolled rectifier transmission converter.

[0080] An optional solution, the first control unit includes a first control module and a second control module; the first control module is used to control the closing of the industrial frequency AC incoming line switch of the above-mentioned uncontrolled rectifier transmission converter, and perform uncontrolled charging on the above-mentioned uncontrolled rectifier transmission converter and the above-mentioned auxiliary converter; the second control module is used to control the above-mentioned uncontrolled rectifier transmission converter to be single-ended unlocked in the above-mentioned industrial frequency AC side reactive mode when the uncontrolled charging reaches a preset voltage, and controllably charge the capacitor voltage of the above-mentioned uncontrolled rectifier transmission converter and determine the above-mentioned DC voltage setting value of the above-mentioned uncontrolled rectifier transmission converter.

[0081] An optional solution, the starting unit includes a first determination module, a starting module and an establishment module; the first determination module is used to determine the low-frequency AC voltage amplitude target value and the voltage ramp rate; the starting module is used to start the auxiliary converter to soft-charge the low-frequency bus and the above-mentioned related low-frequency equipment in the above-mentioned fixed AC voltage and the above-mentioned fixed AC frequency mode according to the above-mentioned low-frequency AC voltage amplitude target value and the above-mentioned voltage ramp rate; the establishment module is used to complete the establishment of the above-mentioned low-frequency grid voltage when the voltage of the above-mentioned low-frequency bus reaches the above-mentioned low-frequency AC voltage amplitude target value.

[0082] An optional scheme, the adjustment unit includes a second determination module, a third determination module and a smooth transfer module; the second determination module is used to determine the first power target value of the above-mentioned uncontrolled rectifier transmission converter and the second power target value of the above-mentioned auxiliary converter; the third determination module is used to determine the AC voltage amplitude of the above-mentioned auxiliary converter at least based on the above-mentioned first power target value and the above-mentioned second power target value, and adjust the above-mentioned low-frequency voltage amplitude of the above-mentioned low-frequency grid voltage according to the above-mentioned AC voltage amplitude; the smooth transfer module is used to complete the above-mentioned smooth transfer of the active power transmitted between the above-mentioned auxiliary converter and the above-mentioned uncontrolled rectifier transmission converter when it is determined that the above-mentioned low-frequency voltage amplitude reaches the above-mentioned DC voltage setting value.

[0083] An optional scheme, the third determination module includes a first determination submodule and a second determination submodule; the first determination submodule is used to determine the first transmission active power of the above-mentioned uncontrolled rectifier transmission converter and the second transmission active power of the above-mentioned auxiliary converter; the second determination submodule is used to determine the voltage upper limit value of the above-mentioned AC voltage amplitude according to the above-mentioned first transmission active power and the above-mentioned first power target value, and determine the above-mentioned AC voltage amplitude according to the above-mentioned voltage upper limit value, the above-mentioned second transmission active power and the above-mentioned second power target value.

[0084] In an optional solution, the second determining submodule includes a third determining submodule and a fourth determining submodule; the third determining submodule is used to determine the value of the first formula: Determine the voltage upper limit above, where V VSCMAX is the upper limit of the voltage mentioned above, P DMREF is the first power target value, P DM is the first transmission active power, k1 and τ1 are respectively the active power closed-loop proportional coefficient and the integral time constant of the uncontrolled rectifier transmission converter, and s is the differential operator symbol; the fourth determination submodule is used to determine the active power according to the second formula: 0≤V VSCLIM -V0≤V VSCMAX , determine the above AC voltage amplitude, where V VSCLIM is the above AC voltage amplitude, P VSCREF is the second power target value, P VSC is the second transmitted active power, k2 and τ2 are respectively the active power closed-loop proportional coefficient and the integral time constant of the auxiliary converter.

[0085] The above-mentioned startup and coordination control device for the offshore low-frequency power transmission system includes a processor and a memory. The above-mentioned first control unit, startup unit, adjustment unit, etc. are all stored in the memory as program units, and the processor executes the above-mentioned program units stored in the memory to realize corresponding functions. The above-mentioned modules are all located in the same processor; or, the above-mentioned modules are located in different processors in any combination.

[0086] The processor includes a kernel, which retrieves the corresponding program unit from the memory. One or more kernels can be set, and the kernel parameters can be adjusted to solve the problem that the existing technology cannot establish the low-frequency side voltage and the offshore wind turbine converter is difficult to start.

[0087] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM, and the memory includes at least one memory chip.

[0088] An embodiment of the present invention provides a computer-readable storage medium, which includes a stored program, wherein when the program is running, the device where the computer-readable storage medium is located is controlled to execute the startup and coordination control method of the offshore low-frequency power transmission system.

[0089] Specifically, the startup and coordination control method of the offshore low-frequency power transmission system includes:

[0090] Step S201, a control step, controlling the above-mentioned uncontrolled rectifier transmission converter to be single-ended unlocked in a fixed DC voltage and industrial frequency AC side reactive mode and determining a DC voltage setting value;

[0091] Step S202, a start step, starts the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage;

[0092] Step S203, an adjustment step, unlocks a single wind turbine in a grid-following control mode and sends power to the onshore side, and smoothly transfers the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter.

[0093] An embodiment of the present invention provides a processor, which is used to run a program, wherein the program executes the startup and coordination control method of the offshore low-frequency power transmission system when running.

[0094] Specifically, the startup and coordination control method of the offshore low-frequency power transmission system includes:

[0095] Step S201, a control step, controlling the above-mentioned uncontrolled rectifier transmission converter to be single-ended unlocked in a fixed DC voltage and industrial frequency AC side reactive mode and determining a DC voltage setting value;

[0096] Step S202, a start step, starts the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage;

[0097] Step S203, an adjustment step, unlocks a single wind turbine in a grid-following control mode and sends power to the onshore side, and smoothly transfers the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter.

[0098] An embodiment of the present invention provides an electronic device, the device comprising a processor, a memory, and a program stored in the memory and executable on the processor, and when the processor executes the program, at least the following steps are implemented:

[0099] Step S201, a control step, controlling the above-mentioned uncontrolled rectifier transmission converter to be single-ended unlocked in a fixed DC voltage and industrial frequency AC side reactive mode and determining a DC voltage setting value;

[0100] Step S202, a start step, starts the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage;

[0101] Step S203, an adjustment step, unlocks a single wind turbine in a grid-following control mode and sends power to the onshore side, and smoothly transfers the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter.

[0102] The devices in this article can be servers, PCs, PADs, mobile phones, etc.

[0103] The present application also provides a computer program product, which, when executed on a data processing device, is suitable for executing a program for initializing at least the following method steps:

[0104] Step S201, a control step, controlling the above-mentioned uncontrolled rectifier transmission converter to be single-ended unlocked in a fixed DC voltage and industrial frequency AC side reactive mode and determining a DC voltage setting value;

[0105] Step S202, a start step, starts the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage;

[0106] Step S203, an adjustment step, unlocks a single wind turbine in a grid-following control mode and sends power to the onshore side, and smoothly transfers the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter.

[0107] Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, and in some cases, the steps shown or described can be executed in a different order than here, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.

[0108] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0109] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0110] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0111] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0112] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0113] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0114] Computer readable media include permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. Information can be computer readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic tape disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer readable media does not include temporary computer readable media (transitory media), such as modulated data signals and carrier waves.

[0115] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0116] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0117] 1) A method for starting and coordinating control of an offshore low-frequency power transmission system of the present application, the offshore low-frequency power transmission system includes an auxiliary converter VSC and an uncontrolled rectifier transmission converter DRU-MMC, the method includes: a control step, controlling the uncontrolled rectifier transmission converter to single-end unlock in a fixed DC voltage and industrial frequency AC side reactive mode and determine a DC voltage setting value; a starting step, starting the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage; an adjustment step, unlocking a single wind turbine in a grid-following control mode and sending power to the onshore side, and smoothly transferring the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter according to the DC voltage setting value by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter. The auxiliary converter VSC is used to smoothly boost the voltage to solve the problem of difficulty in charging low-frequency equipment and difficulty in obtaining energy from wind turbine secondary equipment. Reactive impact starting can be achieved during the startup of the offshore low-frequency power transmission system, solving the problem that the existing technology cannot establish low-frequency side voltage and there is difficulty in starting the offshore wind turbine converter.

[0118] 2) A starting and coordination control device for an offshore low-frequency power transmission system of the present application, the offshore low-frequency power transmission system includes an auxiliary converter VSC and an uncontrolled rectifier transmission converter DRU-MMC, the device includes: a first control unit, used to execute a control step, control the uncontrolled rectifier transmission converter to single-end unlock in a fixed DC voltage and industrial frequency AC side reactive mode and determine a DC voltage setting value; a starting unit, used to execute a starting step, start the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage; an adjustment unit, used to execute an adjustment step, unlock a single wind turbine in a grid-following control mode and send power to the onshore side, and smoothly transfer the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter according to the DC voltage setting value by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter. The auxiliary converter VSC is used to smoothly boost the voltage to solve the problem of difficulty in charging low-frequency equipment and difficulty in obtaining energy from wind turbine secondary equipment. Reactive impact starting can be achieved during the startup of the offshore low-frequency power transmission system, solving the problem that the existing technology cannot establish low-frequency side voltage and there is difficulty in starting the offshore wind turbine converter.

[0119] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for starting and coordinating control of an offshore low-frequency power transmission system, characterized in that: The offshore low-frequency power transmission system includes an auxiliary converter VSC and an uncontrolled rectifier transmission converter DRU-MMC, and the method includes: A control step, controlling the uncontrolled rectifier transmission converter to single-end unlock in a fixed DC voltage and industrial frequency AC side reactive mode and determining a DC voltage setting value; A starting step, starting the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage; The adjustment step is to unlock a single wind turbine in a grid-following control mode and send power to the onshore side, and smoothly transfer the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter.

2. The method according to claim 1, characterized in that After all active power of the auxiliary converter is transferred to the uncontrolled rectifier transmission converter, the method further includes: Control the single wind turbine to switch from the grid-following control mode to the grid-building control mode, and start other wind turbines in the grid-following control mode, and after starting, control the other wind turbines to switch from the grid-following control mode to the grid-building control mode, so as to control the other wind turbines to deliver power through the uncontrolled rectifier transmission converter.

3. The method according to claim 1, characterized in that The control step controls the uncontrolled rectifier transmission converter to be unlocked at a fixed DC voltage and a power frequency AC side reactive mode and determines a DC voltage setting value, including: Controlling the power frequency AC incoming line switch of the uncontrolled rectifier transmission converter to close, and performing uncontrolled charging on the uncontrolled rectifier transmission converter and the auxiliary converter; In the case of uncontrolled charging to a preset voltage, the uncontrolled rectifier transmission converter is controlled to be single-ended unlocked in the reactive mode on the industrial frequency AC side, the capacitor voltage of the uncontrolled rectifier transmission converter is controllably charged and the DC voltage setting value of the uncontrolled rectifier transmission converter is determined.

4. The method according to claim 1, characterized in that: The starting step is to start the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage, including: Determine the low-frequency AC voltage amplitude target value and voltage ramp rate; According to the low-frequency AC voltage amplitude target value and the voltage ramp rate, starting the auxiliary converter in the fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and the related low-frequency equipment; When the voltage of the low-frequency bus reaches the target value of the low-frequency AC voltage amplitude, the establishment of the low-frequency grid voltage is completed.

5. The method according to claim 1, characterized in that The active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter is smoothly transferred by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, including: Determining a first power target value of the uncontrolled rectifier transmission converter and a second power target value of the auxiliary converter; determining an AC voltage amplitude of the auxiliary converter at least according to the first power target value and the second power target value, and adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the AC voltage amplitude; When it is determined that the low-frequency voltage amplitude reaches the DC voltage setting value, the smooth transfer of the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter is completed.

6. The method according to claim 5, characterized in that Determining the AC voltage amplitude of the auxiliary converter at least according to the first power target value and the second power target value includes: Determining a first transmission active power of the uncontrolled rectifier transmission converter and a second transmission active power of the auxiliary converter; The voltage upper limit value of the AC voltage amplitude is determined according to the first transmission active power and the first power target value, and the AC voltage amplitude is determined according to the voltage upper limit value, the second transmission active power and the second power target value.

7. The method according to claim 6, characterized in that Determining a voltage upper limit value of the AC voltage amplitude according to the first transmission active power and the first power target value, and determining the AC voltage amplitude according to the voltage upper limit value, the second transmission active power and the second power target value, comprising: According to the first formula: Determine the voltage upper limit value, where V VSCMAX is the voltage upper limit, P DMREF is the first power target value, P DM is the first transmission active power, k1 and τ1 are respectively the active power closed-loop proportional coefficient and the integral time constant of the uncontrolled rectifier transmission converter, and s is the differential operator symbol; According to the second formula: 0≤V VSCLIM -V0≤V VSCMAX , determine the AC voltage amplitude, where V VSCLIM is the AC voltage amplitude, P VSCREF is the second power target value, P VSC is the second transmitted active power, k2 and τ2 are respectively the active power closed-loop proportional coefficient and the integral time constant of the auxiliary converter.

8. A startup and coordination control device for an offshore low-frequency power transmission system, characterized in that: The offshore low-frequency power transmission system includes an auxiliary converter VSC and an uncontrolled rectifier transmission converter DRU-MMC, and the device includes: A first control unit is used to execute a control step to control the uncontrolled rectifier transmission converter to be single-ended unlocked in a constant DC voltage and power frequency AC side reactive mode and determine a DC voltage setting value; A starting unit, used for executing a starting step, starting the auxiliary converter in a fixed AC voltage and fixed AC frequency mode to soft-charge the low-frequency bus and related low-frequency equipment and establish a low-frequency grid voltage; The regulating unit is used to execute the regulating step, unlock the single wind turbine in the grid-following control mode and send power to the onshore side, and smoothly transfer the active power transmitted between the auxiliary converter and the uncontrolled rectifier transmission converter by adjusting the low-frequency voltage amplitude of the low-frequency grid voltage according to the DC voltage setting value, so as to transfer all the active power of the auxiliary converter to the uncontrolled rectifier transmission converter.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium includes a stored program, wherein when the program is executed, the device where the computer-readable storage medium is located is controlled to execute the startup and coordination control method of the offshore low-frequency power transmission system according to any one of claims 1 to 7.

10. An electronic device, characterized in that: include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and are configured to be executed by the one or more processors, and the one or more programs include a method for executing the startup and coordinated control method of the offshore low-frequency power transmission system as described in any one of claims 1 to 7.

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