Frequency conversion flexible tuning device, half-wavelength AC power transmission system and control method thereof

Abstract

The present invention provides a variable frequency flexible tuning device, which includes a rotary transformer, a DC drive motor and a collector ring; the rotor winding of the rotary transformer is connected to the collector ring; the DC drive motor is used to drive the rotary transformer to change the rotor speed and rotor-side transmission power of the rotary transformer. Compared with the prior art, the variable frequency flexible tuning device provided by the present invention can adjust the rotor speed and rotor-side transmission power of the rotary transformer by adjusting the output torque of the DC drive motor, thereby flexibly adjusting the frequency, voltage amplitude, phase and other electrical parameters of the output signal of the variable frequency flexible tuning device.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a variable frequency flexible tuning device, a half-wavelength AC power transmission system and a control method thereof. Background Art

[0002] The development of technologies such as photovoltaics and wind power has promoted intensive and large-scale development in areas with less than optimal resource conditions, making the transmission of ultra-long-distance, high-power electricity and its implementation of broad significance and practical value.

[0003] Half Wavelength AC Transmission (HWACT) refers to the transmission of three-phase AC power over an electrical distance close to one half wavelength of the power frequency, i.e., ultra-long-distance transmission of 3000km (50Hz) or 2600km (60Hz). A lossless half-wavelength AC line is like an ideal transformer with a transformation ratio of -1.0, where the voltage at the head and the voltage at the end are the same in magnitude and opposite in phase. With the increasing demand for ultra-long-distance and high-power transmission, half-wavelength AC transmission technology, especially ultra-high voltage half-wavelength AC transmission, has once again attracted much attention and research. One of the advantages of half-wavelength AC transmission technology is that the power factor of the half-wavelength AC transmission line is relatively high, and when the transmission distance is equal to or slightly greater than half a wavelength, its structure is simpler than the existing ultra-long-distance AC and DC transmission systems; furthermore, for developing countries, the manufacture of AC transmission equipment is simpler and more economical than the introduction, operation and maintenance of converters.

[0004] The distance between China's western energy base (such as Xinjiang coal power) and the eastern load center (such as the Pearl River Delta) can reach 3,000 km in some cases, and the transmission capacity is huge. In the future, it is also possible to develop electric energy from Russia, Mongolia and other countries adjacent to China and transmit it to China, North Korea and other countries, and the transmission distance is also more than 3,000 km. This special need for ultra-long-distance power transmission makes ultra-high voltage half-wavelength AC transmission technology likely to become one of China's possible power transmission methods in the future. At present, countries with vast territories such as Brazil and Canada are also promoting the research of half-wavelength AC transmission technology to meet the increasingly urgent ultra-long-distance and large-capacity power transmission needs. Therefore, the application prospects of half-wavelength AC transmission are very broad.

[0005] Half-wavelength AC transmission is limited by objective conditions, and the natural length of the actual line is difficult to be exactly half a wavelength. When the line length is insufficient or too long, it is necessary to use a tuning circuit or compensation circuit to artificially compensate the electrical length of the transmission line to achieve the purpose of artificial half-wavelength AC transmission line. At present, the existing half-wavelength AC transmission compensation scheme is based on passive network transmission line tuning, as shown in the attached Figure 1 The π-type tuning circuit / device shown, attached Figure 2The T-type tuning circuit / device shown. These two tuning schemes have affected the development and application of half-wavelength AC transmission technology to a certain extent. This is because:

[0006] (1) Passive tuning circuits have relatively poor adaptability to changes in system structure, operating mode or parameters, and are prone to losing their half-wavelength characteristics;

[0007] (2) The passive tuning circuit has a relatively single function and only solves the tuning problem, which cannot meet the development requirements of flexible and intelligent power grids;

[0008] (3) When a short circuit occurs in a passive tuned circuit or a half-wavelength AC transmission line, it is easy to cause resonance and generate a very high amplitude overvoltage. This requires the lines and equipment to improve the corresponding insulation requirements, or to install corresponding overvoltage limiting measures to suppress the overvoltage of the line. Summary of the invention

[0009] In order to overcome the defects of the prior art, the present invention provides a variable frequency flexible tuning device, a half-wavelength AC power transmission system and a control method thereof.

[0010] In the first aspect, a technical solution of a variable frequency flexible tuning device in the present invention is:

[0011] The variable frequency flexible tuning device comprises a rotary transformer, a DC drive motor and a slip ring; the rotor winding of the rotary transformer is connected to the slip ring;

[0012] The DC drive motor is used to drive the rotary transformer to change the rotor speed and rotor-side transmission power of the rotary transformer.

[0013] Furthermore, a preferred technical solution provided by the present invention is: the rotor side resistance of the rotary transformer is the same as the stator side resistance, or the rotor side resistance is different from the stator side resistance; and,

[0014] The rotor-side leakage inductance of the rotary transformer is the same as the stator-side leakage inductance, or the rotor-side leakage inductance is different from the stator-side leakage inductance.

[0015] In a second aspect, a technical solution of a half-wavelength AC power transmission system in the present invention is:

[0016] The half-wavelength AC power transmission system comprises a sending-end AC system, a half-wavelength AC transmission line and a receiving-end AC system connected in sequence, and the half-wavelength AC power transmission system comprises two variable frequency flexible tuning devices according to any one of claims 1 or 2;

[0017] One of the variable frequency flexible tuning devices is installed between the sending-end AC system and the half-wavelength AC transmission line, and the other variable frequency flexible tuning device is installed between the receiving-end AC system and the half-wavelength AC transmission line.

[0018] Furthermore, a preferred technical solution provided by the present invention is: the stator side of the rotary transformer in the variable frequency flexible tuning device is connected to the sending-end AC system, and the rotor side is connected to the half-wavelength AC transmission line;

[0019] The stator side of the rotary transformer in the other variable frequency flexible tuning device is connected to the receiving-end AC system, and the rotor side is connected to the half-wavelength AC transmission line.

[0020] In a third aspect, a technical solution of a control method for a half-wavelength AC power transmission system in the present invention is:

[0021] The control method includes adjusting the operation mode of the variable frequency flexible tuning device to perform flexible tuning and flexible grid connection on the half-wavelength AC power transmission system.

[0022] Furthermore, a preferred technical solution provided by the present invention is: the flexible tuning of the half-wavelength AC power transmission system comprises:

[0023] When the electrical distance of the half-wavelength AC transmission line is less than one and a half wavelength corresponding to the grid frequency, the rotor speed of the rotary transformer is changed by controlling the DC drive motor of the variable frequency flexible tuning device to increase the operating frequency of the half-wavelength AC transmission line until the electrical distance is equal to one and a half wavelength corresponding to the increased operating frequency;

[0024] When the electrical distance of the half-wavelength AC transmission line is greater than one and a half wavelength corresponding to the grid frequency, the rotor speed of the rotary transformer is changed by controlling the DC drive motor of the variable frequency flexible tuning device to reduce the operating frequency of the half-wavelength AC transmission line until the electrical distance is equal to one and a half wavelength corresponding to the reduced operating frequency;

[0025] When the line structure, line parameters or operating mode of the half-wavelength AC transmission line changes, the rotor speed of the rotary transformer is changed by controlling the DC drive motor of the variable frequency flexible tuning device to adjust the operating frequency of the half-wavelength AC transmission line until the electrical distance of the half-wavelength AC transmission line after the line structure, line parameters or operating mode changes is equal to a half wavelength corresponding to the changed operating frequency.

[0026] Furthermore, a preferred technical solution provided by the present invention is: when the grid-connected type is that the sending-end AC system is connected to the half-wavelength AC transmission line and then connected to the receiving-end AC system, the flexible grid-connection of the half-wavelength AC transmission system includes:

[0027] Adjusting the stator / rotor winding ratio of the rotary transformer in the variable frequency flexible tuning device on the receiving-end AC system side so that the voltage amplitude on the stator side of the rotary transformer is the same as the voltage amplitude of the receiving-end AC system;

[0028] The DC drive motor of the variable frequency flexible tuning device is controlled to change the rotor speed of the rotary transformer, so that the stator side voltage frequency and the stator side voltage phase of the rotary transformer are respectively the same as the voltage frequency and the voltage phase of the receiving end AC system; when the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the stator side of the rotary transformer are respectively the same as the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the receiving end AC system, the grid-connected mechanical switch between the variable frequency flexible tuning device and the receiving end AC system is closed to complete the grid connection.

[0029] Furthermore, a preferred technical solution provided by the present invention is: when the grid-connected type is that the receiving-end AC system is connected to the half-wavelength AC transmission line and then connected to the sending-end AC system, the flexible grid-connection of the half-wavelength AC transmission system includes:

[0030] Adjusting the stator / rotor winding ratio of the rotary transformer in the variable frequency flexible tuning device on the sending-end AC system side so that the voltage amplitude on the stator side of the rotary transformer is the same as the voltage amplitude of the sending-end AC system;

[0031] The DC drive motor of the variable frequency flexible tuning device is controlled to change the rotor speed of the rotary transformer, so that the stator side voltage frequency and the stator side voltage phase of the rotary transformer are respectively the same as the voltage frequency and the voltage phase of the sending-end AC system; when the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the stator side of the rotary transformer are respectively the same as the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the sending-end AC system, the grid-connected mechanical switch between the variable frequency flexible tuning device and the sending-end AC system is closed to complete the grid connection.

[0032] Furthermore, a preferred technical solution provided by the present invention is: the control method also includes adjusting the transmission power of the half-wavelength AC transmission line by controlling the variable frequency flexible tuning device to suppress the inter-regional low-frequency oscillation between the sending-end AC system and the receiving-end AC system, specifically:

[0033] When inter-regional low-frequency oscillation occurs in the half-wavelength AC power transmission system, the DC drive motor of the variable frequency flexible tuning device is controlled to output a preset damping torque, thereby changing the rotor-side transmission power of the rotary transformer in the variable frequency flexible tuning device, thereby changing the transmission power of the half-wavelength AC transmission line and suppressing the inter-regional low-frequency oscillation.

[0034] Furthermore, a preferred technical solution provided by the present invention is: the control method further includes starting the half-wavelength AC power transmission system that is shut down due to a fault by controlling the variable frequency flexible tuning device, specifically:

[0035] Controlling the variable frequency flexible tuning device on the sending-end AC system side to output a preset rotor-side transmission power to start the sending-end AC system and the half-wavelength AC transmission line; controlling the variable frequency flexible tuning device on the receiving-end AC system side to flexibly connect the receiving-end AC system to the grid;

[0036] or,

[0037] The variable frequency flexible tuning device on the receiving-end AC system side is controlled to output a preset rotor-side transmission power to start the receiving-end AC system and the half-wavelength AC transmission line; the variable frequency flexible tuning device on the sending-end AC system side is controlled to flexibly connect the sending-end AC system to the grid.

[0038] Furthermore, a preferred technical solution provided by the present invention is: the control method further includes isolating the half-wavelength AC power transmission system from faults by controlling the variable frequency flexible tuning device, specifically:

[0039] Controlling the DC drive motor of the variable frequency flexible tuning device on the sending-end AC system side to output a preset drive torque, changing the rotor speed and rotor-side transmission power of the rotary transformer in the variable frequency flexible tuning device, and realizing fault isolation between the sending-end AC system and the half-wavelength AC transmission line;

[0040] or,

[0041] The DC drive motor of the variable frequency flexible tuning device on the receiving-end AC system side is controlled to output a preset drive torque, the rotor speed and rotor-side transmission power of the rotary transformer in the variable frequency flexible tuning device are changed, and fault isolation between the receiving-end AC system and the half-wavelength AC transmission line is achieved.

[0042] Compared with the closest prior art, the beneficial effects of the present invention are:

[0043] 1. A variable frequency flexible tuning device provided by the present invention adjusts the output torque of a DC drive motor to adjust the rotor speed of a rotary transformer and the transmission power on the rotor side, thereby flexibly adjusting the frequency, voltage amplitude, phase and other electrical parameters of the output signal of the variable frequency flexible tuning device;

[0044] 2. A half-wavelength AC power transmission system provided by the present invention, wherein the variable frequency flexible tuning device is installed at both ends of the half-wavelength AC power transmission line, and the half-wavelength AC power transmission line can be tuned after the line structure, line parameters or operation mode of the half-wavelength AC power transmission line changes, so that the half-wavelength AC power transmission line does not lose its half-wavelength characteristics;

[0045] 3. The present invention provides a control method for a half-wavelength AC power transmission system, which performs flexible tuning and flexible grid connection on the half-wavelength AC power transmission system by changing the operating mode of the variable frequency flexible tuning device, and the operation is flexible and simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 :Schematic diagram of π-type tuning circuit / device structure;

[0047] Figure 2 : Schematic diagram of T-type tuning circuit / device structure;

[0048] Figure 3 : A schematic structural diagram of a variable frequency flexible tuning device in an embodiment of the present invention;

[0049] Figure 4 : A schematic diagram of the structure of a half-wavelength AC power transmission system in an embodiment of the present invention;

[0050] Among them, 11: rotary transformer; 12: DC drive motor; 13: collector ring; 21: variable frequency flexible tuning device on the sending end AC system side; 22: variable frequency flexible tuning device on the receiving end AC system side. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] A variable frequency flexible tuning device provided by an embodiment of the present invention is described below in conjunction with the accompanying drawings.

[0053] Figure 3This is a schematic diagram of the structure of a variable frequency flexible tuning device in an embodiment of the present invention. As shown in the figure, the variable frequency flexible tuning device in this embodiment includes a rotary transformer 11, a DC drive motor 12 and a slip ring 13. The rotor winding of the rotary transformer 11 is connected to the slip ring 13. The DC drive motor 12 is used to drive the rotary transformer 11 to change the rotor speed and rotor side transmission power of the rotary transformer 11. In this embodiment, the rotor side and the stator side of the rotary transformer 11 are respectively connected to two AC systems, and the two AC systems are used to realize power exchange through the rotary transformer 11, specifically: the output torque of the DC drive motor 12 is adjusted to drive the rotary transformer 11, the rotor speed and rotor side transmission power of the rotary transformer 11 are changed, and the slip ring 13 transmits the rotor side current of the rotary transformer 11 to the AC system connected to the variable frequency flexible tuning device.

[0054] In this embodiment, the resistance and / or leakage inductance on the rotor side of the rotary transformer 11 and the resistance and / or leakage inductance on the stator side of the rotary transformer 11 may be the same or different, specifically: the rotor side resistance of the rotary transformer 11 is the same as the stator side resistance, or the rotor side resistance is different from the stator side resistance. Also, the rotor side leakage inductance of the rotary transformer 11 is the same as the stator side leakage inductance, or the rotor side leakage inductance is different from the stator side leakage inductance.

[0055] In this embodiment, the output torque of the DC drive motor 12 is adjusted to adjust the rotor speed and the rotor-side transmission power of the rotary transformer 11, thereby flexibly adjusting the frequency, voltage amplitude, phase and other electrical parameters of the output signal of the variable frequency flexible tuning device.

[0056] Furthermore, the present invention also provides a half-wavelength AC power transmission system and gives a specific embodiment. The half-wavelength AC power transmission system provided by this embodiment is described below in conjunction with the accompanying drawings.

[0057] Figure 4 This is a schematic diagram of the structure of a half-wavelength AC power transmission system in an embodiment of the present invention. As shown in the figure, the half-wavelength AC power transmission system in this embodiment includes a sending-end AC system fs1, a half-wavelength AC transmission line, a receiving-end AC system fs2, a variable frequency flexible tuning device 21 and a variable frequency flexible tuning device 22.

[0058] Among them, the sending-end AC system fs1, the half-wavelength AC transmission line, and the receiving-end AC system fs2 are connected in sequence, the stator side of the variable frequency flexible tuning device 21 is connected to the sending-end AC system fs1, the rotor side of the variable frequency flexible tuning device 21 is connected to the half-wavelength AC transmission line, the stator side of the variable frequency flexible tuning device 22 is connected to the receiving-end AC system fs2, and the rotor side of the variable frequency flexible tuning device 22 is connected to the half-wavelength AC transmission line. In this embodiment, both the variable frequency flexible tuning device 21 and the variable frequency flexible tuning device 22 adopt Figure 3The variable frequency flexible tuning device shown.

[0059] In this embodiment, the variable frequency flexible tuning device is installed at both ends of the half-wavelength AC transmission line. After the line structure, line parameters or operation mode of the half-wavelength AC transmission line changes, the half-wavelength AC transmission line can be tuned so that it does not lose its half-wavelength characteristics.

[0060] Furthermore, the present invention also provides a control method for a half-wavelength AC power transmission system and gives a specific embodiment. The following describes a half-wavelength AC power transmission system provided by this embodiment.

[0061] The control method of the half-wavelength AC transmission system in this embodiment mainly includes flexible tuning and flexible grid connection of the half-wavelength AC transmission system, suppressing the low-frequency oscillation of the half-wavelength AC transmission system, starting the half-wavelength AC transmission system that is shut down due to a fault as a black start power source, and isolating the fault of the half-wavelength AC transmission system. Specifically:

[0062] 1. Flexible tuning

[0063] In this embodiment, the flexible tuning of the half-wavelength AC power transmission system can be performed according to the following steps, specifically:

[0064] (1) When the electrical distance of the half-wavelength AC transmission line is less than one and a half wavelength corresponding to the grid frequency, the rotor speed of the rotary transformer is changed by controlling the DC drive motor of the variable frequency flexible tuning device to increase the operating frequency of the half-wavelength AC transmission line until the electrical distance is equal to one and a half wavelength corresponding to the increased operating frequency.

[0065] In this embodiment, when the system frequencies of the sending-end AC system and the receiving-end AC system of the half-wavelength AC transmission system are both preset fixed values, the rotor speed of the rotary transformer is changed, and the electrical frequency component corresponding to the rotor speed is superimposed on the system frequency, so that the rotor side frequency of the rotary transformer after superposition is increased, that is, the operating frequency of the half-wavelength AC transmission line is increased, so that the electrical distance of the half-wavelength AC transmission line is equal to one and a half wavelengths corresponding to the increased operating frequency.

[0066] (2) When the electrical distance of the half-wavelength AC transmission line is greater than one and a half wavelength corresponding to the grid frequency, the rotor speed of the rotary transformer is changed by controlling the DC drive motor of the variable frequency flexible tuning device to reduce the operating frequency of the half-wavelength AC transmission line until the electrical distance is equal to one and a half wavelength corresponding to the reduced operating frequency.

[0067] In this embodiment, when the system frequencies of the sending-end AC system and the receiving-end AC system of the half-wavelength AC transmission system are both preset fixed values, the rotor speed of the rotary transformer is changed, and the electrical frequency component corresponding to the rotor speed is superimposed on the system frequency, so that the rotor side frequency of the rotary transformer after superposition is reduced, that is, the operating frequency of the half-wavelength AC transmission line is reduced, so that the electrical distance of the half-wavelength AC transmission line is equal to one and a half wavelengths corresponding to the reduced operating frequency.

[0068] (3) When the line structure, line parameters or operating mode of the half-wavelength AC transmission line changes, the rotor speed of the rotary transformer is changed by controlling the DC drive motor of the variable frequency flexible tuning device to adjust the operating frequency of the half-wavelength AC transmission line until the electrical distance of the half-wavelength AC transmission line after the line structure, line parameters or operating mode changes is equal to one and a half wavelength corresponding to the changed operating frequency.

[0069] In this embodiment, when the system frequencies of the sending-end AC system and the receiving-end AC system of the half-wavelength AC transmission system are both preset fixed values, the rotor speed of the rotary transformer is changed, and the electrical frequency component corresponding to the rotor speed is superimposed on the system frequency, so that the rotor-side frequency of the rotary transformer after superposition is increased or decreased, that is, the operating frequency of the half-wavelength AC transmission line is increased or decreased, so that the electrical distance of the half-wavelength AC transmission line is equal to one and a half wavelengths corresponding to the changed operating frequency.

[0070] 2. Flexible grid connection

[0071] This embodiment includes two types of grid connection: one is that the sending-end AC system is connected to the half-wavelength AC transmission line and then connected to the receiving-end AC system, and the other is that the receiving-end AC system is connected to the half-wavelength AC transmission line and then connected to the sending-end AC system. The flexible grid connection methods of these two types of grid connection are specifically described below.

[0072] (1) When the grid-connected type is that the sending-end AC system is connected to the half-wavelength AC transmission line and then connected to the receiving-end AC system, the following steps can be followed:

[0073] ①: Adjust the stator / rotor winding ratio of the rotary transformer in the variable frequency flexible tuning device 22 so that the voltage amplitude on the stator side of the rotary transformer is the same as the voltage amplitude of the receiving AC system. The maximum error of the voltage amplitude on the stator side of the rotary transformer being the same as the voltage amplitude of the receiving AC system is no more than ±5% of the voltage amplitude of the receiving AC system.

[0074] ②: Control the DC drive motor of the variable frequency flexible tuning device 22 to change the rotor speed of the rotary transformer, so that the stator side voltage frequency and the stator side voltage phase of the rotary transformer are respectively the same as the voltage frequency and the voltage phase of the receiving end AC system. When the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the stator side of the rotary transformer are respectively the same as the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the receiving end AC system, the grid-connected mechanical switch between the variable frequency flexible tuning device and the receiving end AC system is closed to complete the grid connection.

[0075] (2) When the receiving-end AC system is connected to the half-wavelength AC transmission line and then connected to the sending-end AC system, the following steps can be followed:

[0076] ①: Adjust the stator / rotor winding ratio of the rotary transformer in the variable frequency flexible tuning device 21 so that the stator side voltage amplitude of the rotary transformer is the same as the voltage amplitude of the sending-end AC system. The maximum error of the stator side voltage amplitude of the rotary transformer being the same as the voltage amplitude of the sending-end AC system is no more than ±5% of the voltage amplitude of the sending-end AC system.

[0077] ②: Control the DC drive motor of the variable frequency flexible tuning device 21 to change the rotor speed of the rotary transformer, so that the stator side voltage frequency and the stator side voltage phase of the rotary transformer are respectively the same as the voltage frequency and the voltage phase of the sending-end AC system. When the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the stator side of the rotary transformer are respectively the same as the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the sending-end AC system, the grid-connected mechanical switch between the variable frequency flexible tuning device and the sending-end AC system is closed to complete the grid connection.

[0078] 3. Suppress low-frequency oscillation

[0079] In this embodiment, the transmission power of the half-wavelength AC transmission line can be adjusted by controlling the variable frequency flexible tuning device to suppress the inter-regional low-frequency oscillation between the sending-end AC system and the receiving-end AC system. Specifically, when the inter-regional low-frequency oscillation occurs in the half-wavelength AC transmission system, the DC drive motor of the variable frequency flexible tuning device is controlled to output a preset damping torque, thereby changing the rotor-side transmission power of the rotary transformer in the variable frequency flexible tuning device, thereby changing the transmission power of the half-wavelength AC transmission line and suppressing the inter-regional low-frequency oscillation.

[0080] The damping torque can be determined as follows:

[0081] (1) A power step adjustment command is applied to the variable frequency flexible tuning device. After the variable frequency flexible tuning device executes the power step adjustment command, a response curve of the cross-sectional power flow change of the half-wavelength AC transmission system is measured. The equally spaced sampling data of the half-wavelength AC transmission system is obtained by a conventional curve fitting method. The response function of the half-wavelength AC transmission system is calculated based on the equally spaced sampling data, and then the transfer function between the input signal and the output signal of the half-wavelength AC transmission system is obtained.

[0082] (2) The root locus pole configuration and phase compensation method are used to determine the parameters of the low-frequency oscillation control link of the damping system of the half-wavelength AC transmission system, and the damping torque that the DC drive motor needs to output is determined based on the parameters.

[0083] 4. Start the half-wavelength AC transmission system

[0084] In this embodiment, the half-wavelength AC power transmission system that is out of service due to a fault can be started up according to the following two implementation methods, specifically:

[0085] Implementation 1:

[0086] The variable frequency flexible tuning device on the sending-end AC system side is controlled to output a preset rotor-side transmission power to start the sending-end AC system and the half-wavelength AC transmission line; the variable frequency flexible tuning device on the receiving-end AC system side is controlled to flexibly connect the receiving-end AC system to the grid, thereby realizing the startup of the entire half-wavelength AC transmission system.

[0087] Implementation 2:

[0088] The variable frequency flexible tuning device on the receiving-end AC system side is controlled to output a preset rotor-side transmission power to start the receiving-end AC system and the half-wavelength AC transmission line; the variable frequency flexible tuning device on the sending-end AC system side is controlled to flexibly connect the sending-end AC system to the grid, thereby realizing the startup of the entire half-wavelength AC transmission system.

[0089] 5. Fault isolation

[0090] This embodiment can perform fault isolation on the half-wavelength AC power transmission system according to the following two implementation methods, specifically:

[0091] Implementation 1:

[0092] The DC drive motor of the variable frequency flexible tuning device on the sending-end AC system side is controlled to output a preset drive torque, the rotor speed and rotor-side transmission power of the rotary transformer in the variable frequency flexible tuning device are changed, and fault isolation between the sending-end AC system and the half-wavelength AC transmission line is achieved.

[0093] Implementation 2:

[0094] The DC drive motor of the variable frequency flexible tuning device on the receiving-end AC system side is controlled to output a preset drive torque, the rotor speed and rotor-side transmission power of the rotary transformer in the variable frequency flexible tuning device are changed, and fault isolation between the receiving-end AC system and the half-wavelength AC transmission line is achieved.

[0095] In this embodiment, by changing the operation mode of the variable frequency flexible tuning device, the half-wavelength AC transmission system is flexibly tuned and flexibly connected to the grid, the low-frequency oscillation of the half-wavelength AC transmission system is suppressed, the half-wavelength AC transmission system that has been shut down due to a fault is started as a black start power supply, and the fault isolation of the half-wavelength AC transmission system is performed. The operation is flexible and simple.

[0096] It should be noted that the above embodiments illustrate the present invention rather than limit it, and that those skilled in the art may devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference symbol between brackets shall not be construed as a limitation on the claims. The word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "one" or "an" preceding an element does not exclude the presence of a plurality of such elements. The present invention may be implemented with the aid of hardware comprising a number of different elements and with the aid of a suitably programmed PC. In a unit claim enumerating a number of devices, several of these devices may be embodied by the same hardware item. The use of the words first, second, and third, etc., does not indicate any order. These words may be interpreted as names.

[0097] 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.

[0098] 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 1A device that provides the functions specified in a block or multiple blocks.

[0099] 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 comprising 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.

[0100] 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. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0101] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A control method for a half-wavelength AC power transmission system, characterized in that: The half-wavelength AC power transmission system comprises a sending-end AC system, a half-wavelength AC transmission line and a receiving-end AC system connected in sequence, the half-wavelength AC power transmission system comprises two variable frequency flexible tuning devices, the variable frequency flexible tuning devices comprise a rotary transformer, a DC drive motor and a collector ring; the rotor winding of the rotary transformer is connected to the collector ring; the control method comprises performing flexible tuning and flexible grid connection on the half-wavelength AC power transmission system by adjusting the operation mode of the variable frequency flexible tuning device; The control method further includes adjusting the transmission power of the half-wavelength AC transmission line by controlling the variable frequency flexible tuning device to suppress the inter-regional low-frequency oscillation between the sending-end AC system and the receiving-end AC system, specifically: When inter-regional low-frequency oscillation occurs in the half-wavelength AC power transmission system, the DC drive motor of the variable frequency flexible tuning device is controlled to output a preset damping torque, so as to change the rotor-side transmission power of the rotary transformer in the variable frequency flexible tuning device, thereby changing the transmission power of the half-wavelength AC transmission line and suppressing the inter-regional low-frequency oscillation; The damping torque is determined as follows: Applying a power step adjustment command to the variable frequency flexible tuning device, measuring a response curve of a section power flow change of a half-wavelength AC transmission system after the variable frequency flexible tuning device executes the power step adjustment command, obtaining equally spaced sampling data of the half-wavelength AC transmission system by a conventional curve fitting method, calculating a response function of the half-wavelength AC transmission system based on the equally spaced sampling data, and further obtaining a transfer function between an input signal and an output signal of the half-wavelength AC transmission system; The root locus pole configuration and phase compensation method are used to determine the parameters of the low-frequency oscillation control link of the damping system of the half-wavelength AC transmission system, and the damping torque required to be output by the DC drive motor is determined based on the parameters. The flexible tuning of the half-wavelength AC power transmission system comprises: When the electrical distance of the half-wavelength AC transmission line is less than one and a half wavelength corresponding to the grid frequency, the rotor speed of the rotary transformer is changed by controlling the DC drive motor of the variable frequency flexible tuning device to increase the operating frequency of the half-wavelength AC transmission line until the electrical distance is equal to one and a half wavelength corresponding to the increased operating frequency; When the electrical distance of the half-wavelength AC transmission line is greater than one and a half wavelength corresponding to the grid frequency, the rotor speed of the rotary transformer is changed by controlling the DC drive motor of the variable frequency flexible tuning device to reduce the operating frequency of the half-wavelength AC transmission line until the electrical distance is equal to one and a half wavelength corresponding to the reduced operating frequency; When the line structure, line parameters or operating mode of the half-wavelength AC transmission line changes, the rotor speed of the rotary transformer is changed by controlling the DC drive motor of the variable frequency flexible tuning device to adjust the operating frequency of the half-wavelength AC transmission line until the electrical distance of the half-wavelength AC transmission line after the line structure, line parameters or operating mode changes is equal to one half wavelength corresponding to the changed operating frequency.

2. A control method for a half-wavelength AC power transmission system as claimed in claim 1, characterized in that: The type of flexible grid connection is that when the sending-end AC system is connected to the half-wavelength AC transmission line and then connected to the receiving-end AC system, the flexible grid connection of the half-wavelength AC transmission system includes: Adjusting the stator / rotor winding ratio of the rotary transformer in the variable frequency flexible tuning device on the receiving-end AC system side so that the voltage amplitude on the stator side of the rotary transformer is the same as the voltage amplitude of the receiving-end AC system; The DC drive motor of the variable frequency flexible tuning device is controlled to change the rotor speed of the rotary transformer, so that the stator side voltage frequency and the stator side voltage phase of the rotary transformer are respectively the same as the voltage frequency and the voltage phase of the receiving end AC system; when the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the stator side of the rotary transformer are respectively the same as the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the receiving end AC system, the grid-connected mechanical switch between the variable frequency flexible tuning device and the receiving end AC system is closed to complete the grid connection.

3. A control method for a half-wavelength AC power transmission system as claimed in claim 1, characterized in that: The type of flexible grid connection is that when the receiving-end AC system is connected to the half-wavelength AC transmission line and then connected to the sending-end AC system, the flexible grid connection of the half-wavelength AC transmission system includes: Adjusting the stator / rotor winding ratio of the rotary transformer in the variable frequency flexible tuning device on the sending-end AC system side so that the voltage amplitude on the stator side of the rotary transformer is the same as the voltage amplitude of the sending-end AC system; The DC drive motor of the variable frequency flexible tuning device is controlled to change the rotor speed of the rotary transformer, so that the stator side voltage frequency and the stator side voltage phase of the rotary transformer are respectively the same as the voltage frequency and the voltage phase of the sending-end AC system; when the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the stator side of the rotary transformer are respectively the same as the voltage frequency, voltage amplitude, voltage phase sequence and voltage phase of the sending-end AC system, the grid-connected mechanical switch between the variable frequency flexible tuning device and the sending-end AC system is closed to complete the grid connection.

4. A control method for a half-wavelength AC power transmission system as claimed in claim 1, characterized in that: The control method further includes starting the half-wavelength AC power transmission system that is shut down due to a fault by controlling the variable frequency flexible tuning device, specifically: Controlling the variable frequency flexible tuning device on the sending-end AC system side to output a preset rotor-side transmission power to start the sending-end AC system and the half-wavelength AC transmission line; controlling the variable frequency flexible tuning device on the receiving-end AC system side to flexibly connect the receiving-end AC system to the grid; or, The variable frequency flexible tuning device on the receiving-end AC system side is controlled to output a preset rotor-side transmission power to start the receiving-end AC system and the half-wavelength AC transmission line; the variable frequency flexible tuning device on the sending-end AC system side is controlled to flexibly connect the sending-end AC system to the grid.

5. The control method of a half-wavelength AC power transmission system according to claim 1, characterized in that: The control method further includes isolating the half-wavelength AC power transmission system from faults by controlling the variable frequency flexible tuning device, specifically: Controlling the DC drive motor of the variable frequency flexible tuning device on the sending-end AC system side to output a preset drive torque, changing the rotor speed and rotor-side transmission power of the rotary transformer in the variable frequency flexible tuning device, and realizing fault isolation between the sending-end AC system and the half-wavelength AC transmission line; or, The DC drive motor of the variable frequency flexible tuning device on the receiving-end AC system side is controlled to output a preset drive torque, the rotor speed and rotor-side transmission power of the rotary transformer in the variable frequency flexible tuning device are changed, and fault isolation between the receiving-end AC system and the half-wavelength AC transmission line is achieved.

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