A method and device for suppressing low-frequency oscillation of extra-high voltage direct current transmission

Abstract

This invention discloses a method and apparatus for suppressing low-frequency oscillations in ultra-high voltage direct current (UHVDC) transmission. The suppression method includes the following steps: acquiring the actual DC voltage value; calculating the difference between the actual DC voltage value and a preset DC voltage value to obtain the DC voltage difference; acquiring the low-frequency oscillation component of the DC voltage value; determining whether the amplitude of the oscillation component after amplitude limiting is greater than or equal to a preset value; if the amplitude of the oscillation component is greater than or equal to the preset value, then adding the oscillation component to the DC voltage difference and transmitting it to the DC voltage controller to limit the oscillation of the trigger angle output by the DC voltage controller. By acquiring the actual DC voltage value, extracting the low-frequency oscillation component, and processing it to cancel out the input deviation of the DC voltage controller, it is beneficial to reduce the oscillation of the controller's output trigger angle, thereby suppressing the low-frequency oscillations of DC voltage and DC current.

Description

Technical Field

[0001] This invention relates to the field of DC transmission control technology, and in particular to a method and apparatus for suppressing low-frequency oscillations in ultra-high voltage DC transmission. Background Technology

[0002] With the advancement of the "West-to-East Power Transmission" project and the national air pollution prevention and control plan, high-voltage direct current (HVDC) transmission technology has been widely applied, offering advantages such as large transmission capacity, asynchronous grid interconnection, fast regulation speed, reduced transmission line corridor space, and good economic efficiency. Currently, more than 30 HVDC projects have been completed and put into operation in my country, playing a vital role in addressing the imbalance between energy resources and economic development between the eastern and western regions.

[0003] Ultra-high voltage direct current (UHVDC) transmission, with voltage levels above ±800kV, offers greater economic advantages compared to conventional high-voltage direct current (HVDC) transmission, boasting higher voltage levels and larger power capacities. However, it places higher demands on the external insulation overvoltage requirements of power equipment. Because each pole consists of two converter valve groups connected in series, the structure and control functions of the secondary control and protection system for DC transmission are more complex. In a DC system, the DC filter on the DC side is connected in parallel with the DC line and then in series with a smoothing reactor. With the converter valves in operation, the converter transformers on the DC and AC sides are connected in series. Combined with inappropriate control methods in the control and protection system, multiple system resonant frequencies exist in the DC system, determined by equipment parameters, wiring methods, and control methods. At these resonant frequencies, the impedance of the DC system is relatively low. If an excitation source occurs at this frequency, it may cause resonance in the DC system, resulting in significant overvoltage, converter transformer saturation, and other problems, seriously threatening the safe and stable operation of the power grid and limiting the power transmitted by the grid.

[0004] Existing technical solutions primarily address low-frequency oscillations on the DC side by adding blocking filters to the neutral bus or adding tuning frequencies to the DC filters. This blocks DC-side harmonics or alters the system's inherent resonant frequency, reducing resonant overvoltages at certain frequencies. Existing solutions involve adding primary wave traps and filters to the DC side to block harmonics or change the system's inherent resonant frequency. However, this method requires the addition of surge arresters, significantly increasing investment in primary equipment and resulting in poor economic efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a method and device for suppressing low-frequency oscillations in ultra-high voltage direct current (UHVDC) transmission. By collecting the actual value of DC voltage, a certain low-frequency oscillation component is extracted. After processing, it is offset against the input deviation of the constant DC voltage controller, which helps to reduce the oscillation of the controller's output firing angle, thereby suppressing the low-frequency oscillations of DC voltage and DC current. The structure is simple, requires no additional primary equipment investment, and is economical.

[0006] To address the aforementioned technical problems, a first aspect of this invention provides a method for suppressing low-frequency oscillations in ultra-high voltage direct current (UHVDC) transmission. Each pole of the UHVDC transmission system includes two valve groups, with the rectifier controller operating in a constant DC current control mode and the inverter-side controller operating in a constant DC voltage control mode. The method includes the following steps:

[0007] Obtain the actual value of the DC voltage;

[0008] The difference between the actual DC voltage value and the preset DC voltage value is calculated to obtain the DC voltage difference.

[0009] Obtain the low-frequency oscillation component of the DC voltage value;

[0010] Determine whether the amplitude of the oscillation component after amplitude limiting is greater than or equal to a preset value;

[0011] If the amplitude of the oscillation component is greater than or equal to a preset value, the oscillation component is added to the DC voltage difference and then transmitted to the DC voltage controller to limit the trigger angle oscillation of the DC voltage controller output, thereby suppressing the oscillation of DC voltage and DC current.

[0012] Furthermore, the preset value is 0.1% of the DC voltage.

[0013] Further, the acquisition of the low-frequency oscillation component of the DC voltage value includes:

[0014] The actual value of the DC voltage is passed through a quasi-resonant circuit to extract the oscillation component in the low-frequency range;

[0015] Invert the oscillation component and multiply it by the oscillation coefficient;

[0016] The oscillation component is subjected to amplitude limiting processing.

[0017] Furthermore, the amplitude limiting processing of the oscillation component includes:

[0018] When the amplitude of the oscillation component is greater than or equal to the first preset amplitude, the amplitude of the oscillation component is adjusted to the first preset amplitude.

[0019] When the amplitude of the oscillation component is less than or equal to the second preset amplitude, the amplitude of the oscillation component is adjusted to the second preset amplitude.

[0020] When the amplitude of the oscillation component is less than the first preset amplitude but greater than the second preset amplitude, the amplitude of the oscillation component remains unchanged.

[0021] Furthermore, the numerical range of the low-frequency range is 0.5Hz-5Hz.

[0022] Accordingly, a second aspect of the present invention provides a low-frequency oscillation suppression device for ultra-high voltage direct current (UHVDC) transmission. Each pole of the UHVDC transmission system includes two valve groups, with its rectifier controller operating in a constant DC current control mode and its inverter-side controller operating in a constant DC voltage control mode, comprising:

[0023] The first acquisition module is used to acquire the actual value of the DC voltage.

[0024] The calculation module is used to calculate the difference between the actual value of the DC voltage and the preset value of the DC voltage to obtain the DC voltage difference.

[0025] The second acquisition module is used to acquire the low-frequency oscillation component of the DC voltage value;

[0026] The judgment module is used to determine whether the amplitude of the oscillation component after the amplitude limiting process is greater than or equal to a preset value;

[0027] The control module is used to add the oscillation component to the DC voltage difference and transmit it to the DC voltage controller when the amplitude of the oscillation component is greater than or equal to a preset value, so as to limit the trigger angle oscillation of the DC voltage controller output, thereby suppressing the oscillation of DC voltage and DC current.

[0028] Furthermore, the second acquisition module includes:

[0029] An extraction unit is used to pass the actual value of the DC voltage through a quasi-resonant circuit to extract the oscillation component in the low-frequency range;

[0030] A calculation unit is used to invert the oscillation component and multiply it by the oscillation coefficient;

[0031] A limiting unit is used to limit the amplitude of the oscillation component.

[0032] Furthermore, the limiting unit includes:

[0033] The first processing unit is used to adjust the amplitude of the oscillation component to the first preset amplitude when the amplitude of the oscillation component is greater than or equal to the first preset amplitude.

[0034] The second processing unit is used to adjust the amplitude of the oscillation component to the second preset amplitude when the amplitude of the oscillation component is less than or equal to the second preset amplitude.

[0035] The third processing unit is used to maintain the amplitude of the oscillation component unchanged when the amplitude of the oscillation component is less than the first preset amplitude and greater than the second preset amplitude.

[0036] Accordingly, a third aspect of the present invention provides an electronic device, comprising: at least one processor; and a memory connected to the at least one processor; wherein the memory stores instructions executable by the processor, the instructions being executed by the processor to cause the at least one processor to perform any of the above-described methods for suppressing low-frequency oscillations in ultra-high voltage direct current transmission.

[0037] Accordingly, a fourth aspect of the present invention provides a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implement any of the above-described methods for suppressing low-frequency oscillations in ultra-high voltage direct current transmission.

[0038] The above-described technical solutions of the embodiments of the present invention have the following beneficial technical effects:

[0039] By collecting the actual value of DC voltage, the low-frequency oscillation component is extracted and processed to cancel out the input deviation of the constant DC voltage controller. This helps to reduce the oscillation of the controller output firing angle, thereby suppressing the low-frequency oscillation of DC voltage and DC current. The structure is simple, requires no additional primary equipment investment, and is economical. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of an ultra-high voltage direct current transmission system provided in an embodiment of the present invention;

[0041] Figure 2 This is a flowchart of the method for suppressing low-frequency oscillations in ultra-high voltage direct current transmission provided in this embodiment of the invention;

[0042] Figure 3 This is a schematic diagram illustrating the principle of low-frequency oscillation suppression in ultra-high voltage direct current transmission provided in this embodiment of the invention.

[0043] Figure 4 This is a logic diagram of the low-frequency oscillation suppression method for ultra-high voltage direct current transmission provided in this embodiment of the invention;

[0044] Figure 5 This is a module diagram of the ultra-high voltage direct current transmission low-frequency oscillation suppression device provided in an embodiment of the present invention;

[0045] Figure 6 This is a schematic diagram of the second acquisition unit provided in an embodiment of the present invention;

[0046] Figure 7 This is a schematic diagram of the limiting unit provided in an embodiment of the present invention.

[0047] Figure label:

[0048] 1. First acquisition module, 2. Calculation module, 3. Second acquisition module, 31. Extraction unit, 32. Calculation unit, 33. Limiting unit, 331. First processing subunit, 332. Second processing subunit, 333. Third processing subunit, 4. Judgment module, 5. Control module. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0050] Figure 1 This is a schematic diagram of an ultra-high voltage direct current transmission system provided in an embodiment of the present invention.

[0051] Figure 2 This is a flowchart of the method for suppressing low-frequency oscillations in ultra-high voltage direct current transmission provided in this embodiment of the invention.

[0052] Figure 3 This is a schematic diagram of the principle of low-frequency oscillation suppression in ultra-high voltage direct current transmission provided in an embodiment of the present invention.

[0053] Figure 4 This is a logic diagram of the low-frequency oscillation suppression method for ultra-high voltage direct current transmission provided in this embodiment of the invention.

[0054] Please refer to Figure 1 , Figure 2 , Figure 3 and Figure 4 This invention provides a method for suppressing low-frequency oscillations in ultra-high voltage direct current (UHVDC) transmission. Each pole of the UHVDC transmission system includes two valve groups. The rectifier controller is in constant DC current control mode, and the inverter controller is in constant DC voltage control mode. The method includes the following steps:

[0055] S100, obtain the actual DC voltage value Ud_act.

[0056] S200, calculate the difference between the actual DC voltage value Ud_act and the preset DC voltage value Ud_REF to obtain the DC voltage difference.

[0057] S300, obtains the low-frequency oscillation component Ud(t) of the DC voltage value.

[0058] S400 determines whether the amplitude of the oscillation component Ud(t) after amplitude limiting is greater than or equal to the preset value M.

[0059] S500 If the amplitude of the oscillation component Ud(t) is greater than or equal to the preset value M, the oscillation component Ud(t) is added to the DC voltage difference and then transmitted to the DC voltage controller to limit the trigger angle oscillation of the DC voltage controller output, thereby suppressing the oscillation of DC voltage and DC current.

[0060] When the value of the low-frequency oscillation component is less than the preset value, the amplitude of the low-frequency oscillation component is approximately zero. When the low-frequency oscillation component is greater than or equal to the preset value, it is added to the DC voltage difference and transmitted to the DC voltage controller.

[0061] The preset value M is 0.1% of the DC voltage.

[0062] The above technical solution extracts the low-frequency oscillation component Ud(t) from the actual DC voltage value Ud_act, and after processing, it cancels out the input deviation of the constant DC voltage controller. This helps to reduce the oscillation of the controller output firing angle, thereby suppressing the low-frequency oscillation of DC voltage and DC current. The structure is simple, requires no additional primary equipment investment, and is economical.

[0063] Specifically, in step S300, obtaining the low-frequency oscillation component Ud(t) of the DC voltage value includes:

[0064] S310 allows the actual DC voltage value Ud_act to pass through a quasi-resonant circuit, extracting the oscillation component Ud(t) in the low-frequency range.

[0065] The low-frequency band ranges from 0.5Hz to 5Hz.

[0066] The transfer function for quasi-resonant mitigation is G(s).

[0067]

[0068] Specifically, k p It is the proportional gain, k r It is the resonant gain, w c Cutoff frequency, w0 resonant frequency.

[0069] S320, invert the oscillation component Ud(t) and multiply it by the oscillation coefficient.

[0070] The oscillation coefficient is -K. Optionally, the value of K can be 0.001. Specifically, the value of K varies within a certain range depending on the specific application scenario.

[0071] S330 performs amplitude limiting on the oscillation component Ud(t).

[0072] Further, in step S330, the oscillation component Ud(t) is subjected to amplitude limiting processing, including:

[0073] S331, when the amplitude of the oscillation component Ud(t) is greater than or equal to the first preset amplitude + limA, the amplitude of the oscillation component Ud(t) is adjusted to the first preset amplitude + limA.

[0074] S332, when the amplitude of the oscillation component Ud(t) is less than or equal to the second preset amplitude -limA, the amplitude of the oscillation component Ud(t) is adjusted to the second preset amplitude -limA.

[0075] S333, when the amplitude of the oscillation component Ud(t) is less than the first preset amplitude + limA and greater than the second preset amplitude, the amplitude of the oscillation component Ud(t) remains unchanged.

[0076] Optionally, the preset amplitude value limA is 0.01, which can be varied within a certain range depending on the specific application scenario.

[0077] Figure 5 This is a module diagram of the low-frequency oscillation suppression device for ultra-high voltage direct current transmission provided in an embodiment of the present invention.

[0078] Accordingly, please refer to Figure 5 The second aspect of the present invention provides a low-frequency oscillation suppression device for ultra-high voltage direct current transmission, characterized in that each pole of the ultra-high voltage direct current transmission system includes two valve groups, the rectifier controller is in constant DC current control mode, and the inverter side controller is in constant DC voltage control mode, including: a first acquisition module 1, a calculation module 2, a second acquisition module 3, a judgment module 4, and a control module 5. The first acquisition module 1 is used to acquire the actual DC voltage value Ud_act; the calculation module 2 is used to calculate the difference between the actual DC voltage value Ud_act and the preset DC voltage value Ud_REF to obtain the DC voltage difference; the second acquisition module 3 is used to acquire the low-frequency oscillation component Ud(t) of the DC voltage value; the judgment module 4 is used to judge whether the amplitude of the oscillation component Ud(t) after amplitude limiting is greater than or equal to the preset value M; the control module 5 is used to add the oscillation component Ud(t) to the DC voltage difference and transmit it to the DC voltage controller when the amplitude of the oscillation component Ud(t) is greater than or equal to the preset value M, so as to limit the trigger angle oscillation of the DC voltage controller output, thereby suppressing the oscillation of DC voltage and DC current; the control module 5 is also used to maintain the existing control mode of the DC voltage controller when the amplitude of the oscillation component Ud(t) is less than the preset value M.

[0079] Figure 6 This is a schematic diagram of the second acquisition unit provided in an embodiment of the present invention.

[0080] For details, please refer to Figure 6The second acquisition module 3 includes an extraction unit 31, a calculation unit 32, and a limiting unit 33. The extraction unit 31 is used to pass the actual DC voltage value Ud_act through a quasi-resonant circuit to extract the oscillation component Ud(t) in the low-frequency range; the calculation unit 32 is used to invert the oscillation component Ud(t) and multiply it by an oscillation coefficient; and the limiting unit 33 is used to limit the oscillation component Ud(t).

[0081] Figure 7 This is a schematic diagram of the limiting unit provided in an embodiment of the present invention.

[0082] Further, please refer to Figure 7 The limiting unit 33 includes a first processing subunit 331, a second processing subunit 332, and a third processing subunit 333. The first processing subunit 331 is used to adjust the amplitude of the oscillation component Ud(t) to the first preset amplitude + limA when the amplitude of the oscillation component Ud(t) is greater than or equal to the first preset amplitude + limA; the second processing subunit 332 is used to adjust the amplitude of the oscillation component Ud(t) to the second preset amplitude - limA when the amplitude of the oscillation component Ud(t) is less than or equal to the second preset amplitude - limA; and the third processing subunit 333 is used to maintain the amplitude of the oscillation component Ud(t) unchanged when the amplitude of the oscillation component Ud(t) is less than the first preset amplitude - limA and greater than the second preset amplitude - limA.

[0083] The above technical solution extracts the low-frequency oscillation component from the actual value of the collected DC voltage, and after processing, it cancels out the input deviation of the fixed DC voltage controller. This helps to reduce the oscillation of the controller's output firing angle, thereby suppressing the low-frequency oscillation of DC voltage and DC current. The structure is simple, requires no additional primary equipment investment, and is economical.

[0084] Accordingly, a third aspect of the present invention provides an electronic device, comprising: at least one processor; and a memory connected to the at least one processor; wherein the memory stores instructions executable by a processor, the instructions being executed by the processor to cause the at least one processor to perform the above-described method for suppressing low-frequency oscillations in ultra-high voltage direct current transmission.

[0085] Accordingly, a fourth aspect of the present invention provides a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implement the above-described method for suppressing low-frequency oscillations in ultra-high voltage direct current transmission.

[0086] This invention aims to protect a method for suppressing low-frequency oscillations in ultra-high voltage direct current (UHVDC) transmission. Each pole of the UHVDC transmission system includes two valve groups. The rectifier controller operates in a constant DC current control mode, and the inverter-side controller operates in a constant DC voltage control mode. The method includes the following steps: obtaining the actual DC voltage value; calculating the difference between the actual DC voltage value and a preset DC voltage value to obtain the DC voltage difference; obtaining the low-frequency oscillation component of the DC voltage value; determining whether the amplitude of the oscillation component after amplitude limiting is greater than or equal to a preset value; if the amplitude of the oscillation component is greater than or equal to the preset value, then adding the oscillation component to the DC voltage difference and transmitting it to the DC voltage controller to limit the trigger angle oscillation of the DC voltage controller output, thereby suppressing the oscillation of DC voltage and DC current. The above technical solution has the following effects:

[0087] By collecting the actual value of DC voltage, a low-frequency oscillation component is extracted. After processing, it is offset against the input deviation of the DC voltage controller, which helps to reduce the oscillation of the controller output firing angle, thereby suppressing the low-frequency oscillation of DC voltage and DC current. The structure is simple, requires no additional primary equipment investment, and is economical.

[0088] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for suppressing low-frequency oscillations in ultra-high voltage direct current transmission, characterized in that, Each pole of the ultra-high voltage direct current (UHVDC) transmission system includes two valve groups. Its rectifier-side controller operates in constant DC current control mode, and its inverter-side controller operates in constant DC voltage control mode. The process includes the following steps: Obtain the actual value of DC voltage; The difference between the actual DC voltage value and the preset DC voltage value is calculated to obtain the DC voltage difference. Obtain the low-frequency oscillation component of the actual DC voltage value; Determine whether the amplitude of the oscillation component after amplitude limiting is greater than or equal to a preset value; If the amplitude of the oscillation component is greater than or equal to a preset value, the oscillation component is added to the DC voltage difference and then transmitted to the DC voltage controller to limit the trigger angle oscillation of the DC voltage controller output, thereby suppressing the oscillation of DC voltage and DC current. The process of acquiring the low-frequency oscillation component of the DC voltage value includes: The actual value of the DC voltage is passed through a quasi-resonant circuit to extract the oscillation component in the low-frequency range; Invert the oscillation component and multiply it by the oscillation coefficient; The oscillation component is subjected to amplitude limiting processing.

2. The method for suppressing low-frequency oscillations in ultra-high voltage direct current transmission according to claim 1, characterized in that, The preset value is 0.1% of the DC voltage.

3. The method for suppressing low-frequency oscillations in ultra-high voltage direct current transmission according to claim 1, characterized in that, The amplitude limiting process for the oscillation component includes: When the amplitude of the oscillation component is greater than or equal to the first preset amplitude, the amplitude of the oscillation component is adjusted to the first preset amplitude. When the amplitude of the oscillation component is less than or equal to the second preset amplitude, the amplitude of the oscillation component is adjusted to the second preset amplitude. When the amplitude of the oscillation component is less than the first preset amplitude but greater than the second preset amplitude, the amplitude of the oscillation component remains unchanged.

4. The method for suppressing low-frequency oscillations in ultra-high voltage direct current transmission according to claim 1, characterized in that, The low-frequency range is defined as 0.5Hz-5Hz.

5. A low-frequency oscillation suppression device for ultra-high voltage direct current transmission, characterized in that, Each pole of the ultra-high voltage direct current (UHVDC) transmission system includes two valve groups. Its rectifier-side controller operates in constant DC current control mode, and its inverter-side controller operates in constant DC voltage control mode, including: The first acquisition module is used to acquire the actual value of the DC voltage. The calculation module is used to calculate the difference between the actual value of the DC voltage and the preset value of the DC voltage to obtain the DC voltage difference. The second acquisition module is used to acquire the low-frequency oscillation component of the actual value of the DC voltage. The judgment module is used to determine whether the amplitude of the oscillation component after the amplitude limiting process is greater than or equal to a preset value; The control module is used to add the oscillation component to the DC voltage difference and transmit it to the DC voltage controller when the amplitude of the oscillation component is greater than or equal to a preset value, so as to limit the trigger angle oscillation of the DC voltage controller output, thereby suppressing the oscillation of DC voltage and DC current. The second acquisition module includes: An extraction unit is used to pass the actual value of the DC voltage through a quasi-resonant circuit to extract the oscillation component in the low-frequency range; A calculation unit is used to invert the oscillation component and multiply it by the oscillation coefficient; A limiting unit is used to limit the amplitude of the oscillation component.

6. The ultra-high voltage direct current transmission low-frequency oscillation suppression device according to claim 5, characterized in that, The limiting unit includes: The first processing subunit is used to adjust the amplitude of the oscillation component to the first preset amplitude when the amplitude of the oscillation component is greater than or equal to the first preset amplitude. The second processing subunit is used to adjust the amplitude of the oscillation component to the second preset amplitude when the amplitude of the oscillation component is less than or equal to the second preset amplitude. The third processing subunit is used to maintain the amplitude of the oscillation component unchanged when the amplitude of the oscillation component is less than the first preset amplitude and greater than the second preset amplitude.

7. An electronic device, characterized in that, include: At least one processor; The at least one processor is connected to a memory; wherein the memory stores instructions that can be executed by the processor to cause the at least one processor to perform the low-frequency oscillation suppression method for ultra-high voltage direct current transmission according to any one of claims 1-4.

8. A computer-readable storage medium, characterized in that, It stores computer instructions, which, when executed by a processor, implement the method for suppressing low-frequency oscillations in ultra-high voltage direct current transmission as described in any one of claims 1-4.

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