No-load pressurization test method, control device and control equipment

Abstract

The invention discloses a no-load pressurization test method, a control device and control equipment, and is used for a flexible low-frequency power transmission system, the flexible low-frequency power transmission system comprises a frequency conversion station, the frequency conversion station comprises an industrial frequency transformer, an AC-frequency converter and a low-frequency transformer which are sequentially connected in series, and the low-frequency transformer is connected with a low-frequency power transmission network. The no-load pressurization test method comprises the following steps: acquiring an electrical analog quantity and a switch state of a frequency conversion station; in response to the condition that the line voltage from the frequency conversion station to the low-frequency power transmission network is zero and the switch is switched off, starting an AC-frequency converter; controlling the voltage of the output end of the AC-AC converter to rise to a rated voltage value; controlling the voltage of the output end of the AC-frequency converter to maintain a rated voltage value, and detecting a circuit of the output end of the AC-frequency converter; in response to stable operation of the AC-frequency converter, controlling the voltage of the output end of the AC-frequency converter to drop to zero; and stopping the alternating current-alternating current frequency converter to complete the no-load pressurization test. Detection of a low-frequency side circuit is completed through voltage slow rising and slow falling, and engineering application conditions are met.

Description

Technical Field

[0001] The present application belongs to the field of flexible power transmission technology, and specifically relates to a no-load pressurization test method, a control device and a control equipment. Background Art

[0002] Flexible low-frequency transmission technology is a new type of transmission technology that combines the advantages of AC and DC transmission. It has broad application prospects in large-scale transmission scenarios of new energy such as medium and long-distance offshore wind power.

[0003] In the construction of flexible low-frequency transmission frequency conversion stations, the insulation safety of low-frequency side equipment such as low-frequency connecting transformers, low-frequency busbars, and low-frequency lines needs to be verified in a certain way. In addition, the low-frequency connecting transformer needs to eliminate residual magnetism in a certain way before the frequency conversion station is put into operation to avoid large excitation surge currents during normal operation, which will affect the safe operation of the equipment. At the same time, the phase verification work of the low-frequency side voltage sampling also needs to be completed by the frequency converter outputting a certain low-frequency side voltage. No-load pressurization can achieve slow and stable control of the low-frequency side voltage of the flexible low-frequency transmission frequency conversion station from zero voltage to rated voltage in the entire range, thereby providing conditions for the insulation safety verification of low-frequency side equipment, demagnetization of low-frequency connecting transformers, and phase verification of low-frequency side voltage sampling. Therefore, it is necessary to provide a no-load pressurization test method and control system to achieve the above goals.

[0004] The no-load voltage test methods that have been proposed so far are mainly aimed at DC transmission application scenarios. The converter output voltage is DC rather than three-phase AC voltage. No literature has yet proposed a no-load voltage test method for flexible low-frequency transmission application scenarios. Summary of the invention

[0005] The present application provides a no-load pressurization test method, a control device and a control equipment, which are intended to achieve slow and stable control of the voltage on the low-frequency side of a flexible low-frequency transmission frequency conversion station over the entire range from zero voltage to rated voltage.

[0006] The embodiment of the present application provides a no-load pressurization test method for a flexible low-frequency power transmission system, wherein the flexible low-frequency power transmission system includes a frequency conversion station, wherein the frequency conversion station includes an industrial frequency transformer, an AC-AC converter, and a low-frequency transformer connected in series in sequence, wherein the low-frequency transformer is connected to a low-frequency power transmission network, and wherein the no-load pressurization test method includes:

[0007] Obtaining electrical analog quantities and switch states of the frequency conversion station;

[0008] In response to the line voltage from the frequency conversion station to the low-frequency power transmission network being zero and the switch being disconnected, starting the AC-AC converter and beginning to detect the output end circuit of the AC-AC converter;

[0009] Controlling the voltage at the output end of the AC-DC converter to rise to a rated voltage value;

[0010] Controlling the voltage at the output end of the AC-DC converter to maintain a rated voltage value;

[0011] In response to the AC-converter running stably, controlling the voltage at the output end of the AC-converter to drop to zero;

[0012] The AC-inverter is shut down, the detection of the output circuit of the AC-inverter is ended, and the no-load pressurization test is completed.

[0013] In some embodiments, the step of controlling the voltage at the output end of the AC-DC converter to rise to a rated voltage value further comprises:

[0014] Putting the frequency conversion station into an automatic no-load pressurization test control word, wherein the automatic no-load pressurization test control word includes a preset pressurization rate;

[0015] The voltage at the output end of the AC-AC converter is controlled to automatically rise to a rated voltage value according to a preset voltage increase rate.

[0016] In some embodiments, the step of controlling the voltage at the output end of the AC-DC converter to rise to a rated voltage value further comprises:

[0017] Put the frequency conversion station into manual no-load pressurization test control word;

[0018] Manually set the voltage target value and the pressure increase rate of each stage;

[0019] The voltage at the output end of the AC-AC converter is controlled to rise to the rated voltage value in stages according to the manually set stage voltage target value and the pressure increase rate of each stage.

[0020] In some embodiments, the step of controlling the voltage at the output end of the AC-converter to drop to zero further comprises:

[0021] The frequency conversion station is put into automatic no-load pressurization test control word, and the automatic no-load pressurization test control word includes a preset voltage reduction rate;

[0022] The voltage at the output end of the AC-DC converter is controlled to automatically drop to zero according to a preset voltage reduction rate.

[0023] In some embodiments, the step of controlling the voltage at the output end of the AC-converter to drop to zero further comprises:

[0024] Put the frequency conversion station into manual no-load pressurization test control word;

[0025] Manually set the voltage target value and voltage reduction rate of each stage;

[0026] The voltage at the output end of the AC-DC converter is controlled to decrease to zero in stages according to the manually set stage voltage target value and the voltage reduction rate of each stage.

[0027] In some embodiments, the step of detecting the output circuit of the AC-DC converter further includes:

[0028] Verifying the insulation safety of the equipment of the output circuit of the AC-AC converter; and / or,

[0029] Measuring the excitation inrush current of the low-frequency transformer and determining the residual magnetism; and / or,

[0030] The voltage of the output circuit of the AC-AC converter is sampled and phase checked.

[0031] In some embodiments, the electrical analog quantity includes a voltage of an output circuit of the AC-converter.

[0032] An embodiment of the present application also provides a flexible low-frequency power transmission system, comprising at least two frequency conversion stations, wherein the input ends of the frequency conversion stations are connected to respective industrial frequency power transmission networks, and the output ends of the frequency conversion stations are connected to the same low-frequency power transmission network, and the flexible low-frequency power transmission system completes a no-load pressurization test by the no-load pressurization test method described in any of the above embodiments.

[0033] The embodiment of the present application also provides a no-load pressurization test control device for a flexible low-frequency power transmission system, wherein the flexible low-frequency power transmission system includes a frequency conversion station, wherein the frequency conversion station includes an industrial frequency transformer, an AC-AC converter, and a low-frequency transformer connected in series in sequence, wherein the low-frequency transformer is connected to a low-frequency power transmission network, and includes:

[0034] A signal acquisition module, configured to obtain electrical analog quantities and switch states of the frequency conversion station;

[0035] A starting module, configured to start the AC-AC converter in response to the line voltage from the frequency conversion station to the low-frequency power transmission network being zero and the switch being disconnected;

[0036] A control module is configured to control the voltage at the output end of the AC-converter to rise to a rated voltage value; control the voltage at the output end of the AC-converter to maintain the rated voltage value; and control the voltage at the output end of the AC-converter to drop to zero in response to the AC-converter running stably;

[0037] A detection module, configured to detect the output terminal circuit of the AC-AC converter in response to the AC-AC converter being started;

[0038] The termination module is configured to stop the AC-AC converter, end the detection of the output circuit of the AC-AC converter, and complete the no-load pressurization test.

[0039] In some embodiments, the control module includes:

[0040] A no-load pressurization test enabling module is configured to put the frequency conversion station into an automatic no-load pressurization test control word, and / or to put the frequency conversion station into a manual no-load pressurization test control word;

[0041] An automatic adjustment module is configured to automatically generate a rated voltage value, a voltage increase rate and a voltage reduction rate of the output end circuit of the AC-AC converter in response to the control word of putting the frequency conversion station into an automatic no-load pressure test, and output a real-time instruction value of a low-frequency voltage;

[0042] A manual adjustment module is configured to manually set a low-frequency voltage target value, a rise and fall rate, etc., in response to the control word of putting the frequency conversion station into a manual no-load pressurization test, and output a real-time low-frequency voltage command value;

[0043] The output module is configured to control the frequency converter to output a voltage corresponding to the low-frequency voltage real-time instruction value according to the low-frequency voltage real-time instruction value.

[0044] In some embodiments, the detection module is configured to:

[0045] Verifying the insulation safety of the equipment of the output circuit of the AC-AC converter; and / or,

[0046] The excitation inrush current of the low-frequency transformer and the residual magnetism size are determined; and / or,

[0047] The voltage of the output circuit of the AC-AC converter is sampled and phase checked.

[0048] The present application also provides a no-load pressurization test control device, including:

[0049] Processor; and

[0050] The memory stores computer instructions, and when the computer instructions are executed by the processor, the processor executes the method described in any one of the above embodiments.

[0051] The no-load pressurization test method, control device and control equipment provided in this application can realize the slow and stable control of the low-frequency side voltage of the flexible low-frequency transmission frequency conversion station from zero voltage to rated voltage in the entire range. By adopting the no-load pressurization test method and control device provided in this application, the insulation safety of the low-frequency side equipment of the flexible low-frequency transmission frequency conversion station can be verified by slowly rising and falling the low-frequency side voltage, the residual magnetism of the low-frequency connection transformer can be eliminated, and the low-frequency side voltage sampling and phase verification can be completed. It has the conditions for engineering application and has great application prospects in aspects such as safety verification of frequency conversion station equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A circuit structure diagram of a flexible low-frequency power transmission system provided in an embodiment of the present application;

[0053] Figure 2 A flow chart of a no-load pressurization test method provided in an embodiment of the present application;

[0054] Figure 3 A structural diagram of a no-load pressurization test method control device provided in an embodiment of the present application;

[0055] Figure 4 This is a structural diagram of a control module in a no-load pressurization test method control device provided in an embodiment of the present application.

[0056] Reference numerals:

[0057] 1-power frequency transformer, 2-AC-converter, 3-low frequency transformer, 4-first switch, 5-second switch. DETAILED DESCRIPTION

[0058] The technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0059] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be directly connected, or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more features.

[0060] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application.

[0061] First, an embodiment of the present application provides a no-load pressurization test method for a flexible low-frequency power transmission system.

[0062] like Figure 1 As shown, the flexible low-frequency power transmission system includes at least one frequency conversion station, which includes an industrial frequency transformer 1, an AC-converter 2 and a low-frequency transformer 3 connected in series in sequence; wherein the industrial frequency transformer 1 is connected to the industrial frequency power transmission network through a first switch 4, and the low-frequency transformer 3 is connected to the low-frequency power transmission network through a second switch 5. The voltage in the low-frequency power transmission network is a three-phase AC voltage with a frequency lower than the industrial frequency; each frequency conversion station is isolated from other frequency conversion stations in the flexible low-frequency power transmission system.

[0063] The no-load pressurization test method applicable to flexible low-frequency power transmission system is as follows: Figure 2 As shown, the following steps are included:

[0064] S100: Acquire the electrical analog quantity and switch status of the frequency conversion station;

[0065] S200: in response to the line voltage from the frequency conversion station to the low-frequency power transmission network being zero and the switch being disconnected, starting the AC-AC converter 2 and beginning to detect the output end circuit of the AC-AC converter 2;

[0066] S300: Control the voltage at the output end of the AC-AC converter 2 to rise to a rated voltage value;

[0067] S400: Control the voltage at the output end of the AC-AC converter 2 to maintain a rated voltage value, and detect the circuit at the output end of the AC-AC converter 2;

[0068] S500: In response to the AC-AC converter 2 operating stably, controlling the voltage at the output end of the AC-AC converter 2 to drop to zero;

[0069] S600: shut down the AC-inverter 2, end the detection of the output circuit of the AC-inverter 2, and complete the no-load pressurization test.

[0070] Through the above-mentioned no-load pressure test method, the low-frequency side voltage of the flexible low-frequency transmission frequency conversion station can be slowly and steadily controlled from zero voltage to the rated voltage in the entire range: start the AC-converter 2, keep the rated operation of the power frequency side voltage, and the zero amplitude operation of the low-frequency side voltage; gradually increase the low-frequency side voltage to the rated value, and keep it for a period of time, and detect the low-frequency side circuit; gradually reduce the low-frequency side voltage to zero voltage, and keep it for a period of time; shut down the AC-converter 2. By controlling the slow rise and fall of the low-frequency side voltage, the residual magnetism of the low-frequency transformer 3 can be eliminated, which is suitable for the flexible low-frequency transmission frequency conversion station where the converter outputs three-phase AC voltage.

[0071] The low-frequency side includes the circuit from the AC-AC converter 2 to the low-frequency power transmission network.

[0072] In some implementations, the step of controlling the voltage at the output end of the AC-AC converter 2 to rise to a rated voltage value further includes:

[0073] The frequency conversion station is put into automatic no-load pressurization test control word, and the automatic no-load pressurization test control word includes a preset pressurization rate;

[0074] The voltage at the output end of the control AC-AC converter 2 automatically rises to the rated voltage value according to a preset voltage increase rate.

[0075] In some embodiments, the step of controlling the voltage at the output end of the AC-AC converter 2 to drop to zero further comprises:

[0076] The frequency conversion station is put into automatic no-load pressurization test control word, and the automatic no-load pressurization test control word includes a preset voltage reduction rate;

[0077] The voltage at the output end of the AC-AC converter 2 is controlled to automatically drop to zero according to a preset voltage reduction rate.

[0078] According to the pre-collected electrical analog quantities and the specific environment in which the system is located, automatic control can be used for the no-load pressurization test method of the flexible low-frequency transmission system. The system can automatically set the appropriate rated voltage value, pressurization rate and voltage reduction rate according to environmental requirements, making the no-load pressurization test method more efficient.

[0079] In some implementations, the step of controlling the voltage at the output end of the AC-AC converter 2 to rise to a rated voltage value further includes:

[0080] Put the frequency conversion station into manual no-load pressurization test control word;

[0081] Manually set the voltage target value and the pressure increase rate of each stage;

[0082] The voltage at the output end of the AC-AC converter 2 is controlled to rise to the rated voltage value in stages according to the manually set stage voltage target value and the voltage increase rate of each stage.

[0083] In some scenarios, the flexible low-frequency transmission system is more complex, or it is necessary to perform staged detection on the circuits at different voltage values. At this time, you can switch to the manual setting mode, manually enter the low-frequency side voltage target value, and gradually increase the low-frequency side voltage in stages at a settable rate until the rated value is reached.

[0084] In some embodiments, the step of controlling the voltage at the output end of the AC-AC converter 2 to drop to zero further comprises:

[0085] Put the frequency conversion station into manual no-load pressurization test control word;

[0086] Manually set the voltage target value and voltage reduction rate of each stage;

[0087] The voltage at the output end of the AC-AC converter 2 is controlled to decrease to zero in stages according to the manually set stage voltage target value and the voltage reduction rate of each stage.

[0088] Based on the same principle, the flexible low-frequency transmission system is used in more complex scenarios, or it is necessary to perform staged detection of circuits at different voltage values. At this time, you can switch to the manual setting mode, manually enter the low-frequency side voltage target value for each stage, and gradually reduce the low-frequency side voltage in stages at a settable rate until the low-frequency side voltage drops to zero.

[0089] In some implementations, the step of detecting the output circuit of the AC-DC converter 2 further includes:

[0090] Verify the insulation safety of the equipment in the output circuit of the AC-AC converter 2; and / or,

[0091] Measuring the excitation inrush current of the low-frequency transformer 3 and determining the residual magnetism; and / or,

[0092] The voltage of the output circuit of the AC-AC converter 2 is sampled and phase checked.

[0093] In some embodiments, the electrical analog quantity includes the voltage of the input circuit and the voltage of the output circuit of the AC-converter 2. When the voltage of the input circuit of the AC-converter 2, i.e., the power frequency side, is stable and the voltage amplitude of the output circuit of the AC-converter 2, i.e., the low frequency side, is zero, the AC-converter 2 is started and a no-load pressurization test is performed.

[0094] It should be understood that, although the various steps in the above flowchart 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 description in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a part of the steps in the above flowchart may 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.

[0095] Based on the same inventive concept, the embodiment of the present application also provides a no-load pressurization test control device, such as Figure 3 As shown, it is used for a flexible low-frequency power transmission system, the flexible low-frequency power transmission system includes a frequency conversion station, the frequency conversion station includes an industrial frequency transformer 1, an AC-converter 2 and a low-frequency transformer 3 connected in series in sequence, and the low-frequency transformer 3 is connected to a low-frequency power transmission network, including:

[0096] A signal acquisition module is configured to obtain electrical analog quantities and switch states of the frequency conversion station;

[0097] A starting module, configured to start the AC-AC converter 2 in response to the line voltage from the frequency conversion station to the low-frequency power transmission network being zero and the switch being disconnected;

[0098] The control module is configured to control the voltage at the output end of the AC-converter 2 to rise to a rated voltage value; control the voltage at the output end of the AC-converter 2 to maintain the rated voltage value; and control the voltage at the output end of the AC-converter 2 to drop to zero in response to the AC-converter 2 running stably;

[0099] A detection module is configured to detect the output end circuit of the AC-AC converter 2 in response to the AC-AC converter 2 starting;

[0100] The termination module is configured to stop the AC-AC converter 2, end the detection of the output circuit of the AC-AC converter 2, and complete the no-load pressurization test.

[0101] like Figure 4 As shown, in some embodiments, the control module includes:

[0102] The no-load pressurization test enabling module is configured to put the frequency conversion station into an automatic no-load pressurization test control word, and / or to put the frequency conversion station into a manual no-load pressurization test control word;

[0103] The automatic adjustment module is configured to automatically generate the rated voltage value, the voltage increase rate and the voltage reduction rate of the output end circuit of the AC-AC converter 2 in response to the control word of putting the frequency conversion station into the automatic no-load pressure test, and output the real-time instruction value of the low-frequency voltage;

[0104] A manual adjustment module is configured to manually set a low-frequency voltage target value, a rise and fall rate, etc., in response to a control word for putting the frequency conversion station into a manual no-load pressurization test, and output a real-time low-frequency voltage command value;

[0105] The output module is configured to control the frequency converter to output a voltage corresponding to the low-frequency voltage real-time instruction value according to the low-frequency voltage real-time instruction value.

[0106] In some embodiments, the detection module is configured to verify the equipment insulation safety of the circuit at the output end of the AC-DC converter 2 .

[0107] In some implementations, the detection module is configured to measure the excitation inrush current of the low-frequency transformer 3 and determine the magnitude of the residual magnetism.

[0108] In some implementations, the detection module is configured to perform voltage sampling and phase checking on the output circuit of the AC-DC converter 2 .

[0109] It should be noted that the above-mentioned functional modules can be fully or partially integrated into one physical entity during actual implementation, or they can be physically separated. And these modules can all be implemented in the form of software called by processing elements; they can also be all implemented in the form of hardware; some modules can also be implemented in the form of software called by processing elements, and some modules can be implemented in the form of hardware. In addition, these modules can be fully or partially integrated together, or they can be implemented independently. The processing element here can be an integrated circuit with signal processing capabilities. In the implementation process, some or all of the steps of the above method, or the above functional modules can be completed by hardware integrated logic circuits in the processor element or instructions in software form.

[0110] Finally, an embodiment of the present application further provides a no-load pressurization test control device, comprising:

[0111] Processor; and

[0112] The memory stores computer instructions, and when the computer instructions are executed by the processor, the processor executes the method in any of the above embodiments.

[0113] If the integrated unit / module is implemented in the form of hardware, the hardware may be a digital circuit, an analog circuit, etc. The physical implementation of the hardware structure includes but is not limited to transistors, memristors, etc. Unless otherwise specified, the processor or chip may be any appropriate hardware processor, such as CPU, GPU, FPGA, DSP, and ASIC, etc. Unless otherwise specified, the on-chip cache, off-chip memory, and storage may be any appropriate magnetic storage medium or magneto-optical storage medium, such as Resistive Random Access Memory (RRAM), Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM), Enhanced Dynamic Random Access Memory (EDRAM), High-Bandwidth Memory (HBM), Hybrid Memory Cube (HMC), etc.

[0114] If the integrated unit / module is implemented in the form of a software program module and sold or used as an independent product, it can be stored in a computer-readable memory. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a memory and includes several instructions for a computer device (which can be a personal computer, a server or a network device, etc.) to perform all or part of the steps of the various embodiments of the present disclosure. The aforementioned memory includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk and other media that can store program codes.

[0115] The above is a detailed introduction to a no-load pressurization test method, a control device and a control equipment provided in the embodiments of the present application. Specific examples are used in the present application to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solution and its core idea of ​​the present application. Ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A no-load pressurization test method for a flexible low-frequency power transmission system, wherein the flexible low-frequency power transmission system comprises a frequency conversion station, wherein the frequency conversion station comprises an industrial frequency transformer (1), an AC-converter (2) and a low-frequency transformer (3) connected in series in sequence, wherein the low-frequency transformer (3) is connected to a low-frequency power transmission network, wherein: The no-load pressurization test method comprises: Obtaining electrical analog quantities and switch states of the frequency conversion station; In response to the line voltage from the frequency conversion station to the low-frequency power transmission network being zero and the switch being disconnected, starting the AC-AC converter (2) and beginning to detect the output end circuit of the AC-AC converter (2); Controlling the voltage at the output end of the AC-converter (2) to rise to a rated voltage value; Controlling the voltage at the output end of the AC-AC converter (2) to maintain a rated voltage value; In response to the AC-converter (2) operating stably, controlling the voltage at the output end of the AC-converter (2) to drop to zero; The AC-converter (2) is shut down, the detection of the output end circuit of the AC-converter (2) is ended, and the no-load pressurization test is completed.

2. A no-load pressurization test method according to claim 1, characterized in that: The step of controlling the voltage at the output end of the AC-AC converter (2) to rise to a rated voltage value further comprises: Putting the frequency conversion station into an automatic no-load pressurization test control word, wherein the automatic no-load pressurization test control word includes a preset pressurization rate; The voltage at the output end of the AC-converter (2) is controlled to automatically rise to a rated voltage value according to a preset voltage increase rate.

3. A no-load pressurization test method according to claim 1, characterized in that: The step of controlling the voltage at the output end of the AC-AC converter (2) to rise to a rated voltage value further comprises: Put the frequency conversion station into manual no-load pressurization test control word; Manually set the voltage target value and the pressure increase rate of each stage; The voltage at the output end of the AC-AC converter (2) is controlled to rise in stages to a rated voltage value according to the manually set stage voltage target value and the voltage increase rate of each stage.

4. A no-load pressurization test method according to claim 1, characterized in that: The step of controlling the voltage at the output end of the AC-AC converter (2) to drop to zero further comprises: The frequency conversion station is put into automatic no-load pressurization test control word, and the automatic no-load pressurization test control word includes a preset voltage reduction rate; The voltage at the output end of the AC-converter (2) is controlled to automatically drop to zero according to a preset voltage reduction rate.

5. A no-load pressurization test method according to claim 1, characterized in that: The step of controlling the voltage at the output end of the AC-AC converter (2) to drop to zero further comprises: Put the frequency conversion station into manual no-load pressurization test control word; Manually set the voltage target value and voltage reduction rate of each stage; The voltage at the output end of the AC-converter (2) is controlled to decrease to zero in stages according to the manually set stage voltage target value and the voltage reduction rate of each stage.

6. A no-load pressurization test method according to claim 1, characterized in that: The step of detecting the output circuit of the AC-converter (2) further comprises: Verifying the equipment insulation safety of the output end circuit of the AC-AC converter (2); and / or, measuring the excitation inrush current of the low-frequency transformer (3) and determining the magnitude of the residual magnetism; and / or, The voltage of the output end circuit of the AC-AC converter (2) is sampled and phase checked.

7. A no-load pressurization test method according to claim 1, characterized in that: The electrical analog quantity includes the voltage of the input end circuit of the AC-converter (2) and the voltage of the output end circuit of the AC-converter (2).

8. A flexible low-frequency power transmission system, comprising at least two frequency conversion stations, wherein the input ends of the frequency conversion stations are connected to respective power frequency power transmission networks, and the output ends of the frequency conversion stations are connected to the same low-frequency power transmission network, characterized in that: The flexible low-frequency power transmission system completes the no-load pressurization test by the no-load pressurization test method described in any one of claims 1 to 7.

9. A no-load pressurization test control device, used in a flexible low-frequency power transmission system, the flexible low-frequency power transmission system comprising a frequency conversion station, the frequency conversion station comprising an industrial frequency transformer (1), an AC-converter (2) and a low-frequency transformer (3) connected in series in sequence, the low-frequency transformer (3) being connected to a low-frequency power transmission network, characterized in that: include: A signal acquisition module, configured to obtain electrical analog quantities and switch states of the frequency conversion station; A starting module, configured to start the AC-AC converter (2) in response to the line voltage from the frequency conversion station to the low-frequency power transmission network being zero and the switch being disconnected; The control module is configured to control the voltage at the output end of the AC-converter (2) to rise to a rated voltage value; control the voltage at the output end of the AC-converter (2) to maintain the rated voltage value; and control the voltage at the output end of the AC-converter (2) to drop to zero in response to the AC-converter (2) running stably. A detection module, configured to detect the output end circuit of the AC-AC converter (2) in response to the AC-AC converter (2) being started; The termination module is configured to stop the AC-converter (2), end the detection of the output end circuit of the AC-converter (2), and complete the no-load pressurization test.

10. The no-load pressurization test control device according to claim 9, characterized in that: The control module comprises: A no-load pressurization test enabling module is configured to put the frequency conversion station into an automatic no-load pressurization test control word, and / or to put the frequency conversion station into a manual no-load pressurization test control word; The automatic adjustment module is configured to automatically generate a rated voltage value, a voltage increase rate and a voltage reduction rate of the output end circuit of the AC-AC converter (2) in response to the control word for putting the frequency conversion station into an automatic no-load voltage test, and output a real-time low-frequency voltage instruction value; A manual adjustment module is configured to manually set a low-frequency voltage target value, a rise and fall rate, etc., in response to the control word of putting the frequency conversion station into a manual no-load pressurization test, and output a real-time low-frequency voltage command value; The output module is configured to control the frequency converter to output a voltage corresponding to the low-frequency voltage real-time instruction value according to the low-frequency voltage real-time instruction value.

11. The no-load pressurization test control device according to claim 9, characterized in that: The detection module is configured as follows: Verifying the equipment insulation safety of the output end circuit of the AC-AC converter (2); and / or, measuring the excitation inrush current of the low-frequency transformer (3) and determining the magnitude of the residual magnetism; and / or, The voltage of the output end circuit of the AC-AC converter (2) is sampled and phase checked.

12. A no-load pressurization test control device, characterized in that: include: processor; as well as A memory storing computer instructions, which, when executed by the processor, causes the processor to execute the method according to any one of claims 1 to 7.

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