Method and device for suppressing direct current magnetic bias current of flexible direct current transformer

Abstract

The invention discloses a flexible direct current transformer direct current magnetic bias current suppression method and device, direct current magnetic bias current suppression equipment is connected to a direct current side preset position of a flexible direct current power transmission system, the direct current magnetic bias current suppression equipment comprises an inductor and a capacitor which are connected in parallel, and after it is judged that the direct current magnetic bias current suppression equipment is connected, the direct current magnetic bias current suppression equipment is connected. Whether the impedance of the direct-current loop of the flexible direct-current power transmission system within the system operation frequency range is improved to a target value compared with the impedance at the 50Hz frequency when the direct-current magnetic bias current suppression equipment is not connected or not is judged, if yes, the direct-current magnetic bias current suppression configuration of the flexible direct-current transformer is completed, and if not, the direct-current magnetic bias current suppression configuration of the flexible direct-current transformer is completed. If yes, adding a resistor which is connected in parallel with the inductor and the capacitor and has a preset resistance value into the direct-current magnetic bias current suppression equipment to finish the direct-current magnetic bias current suppression configuration of the flexible direct-current transformer. The technical problem that safe and stable operation of a direct-current power transmission system and equipment is difficult to guarantee due to the lack of a reliable method for suppressing direct-current magnetic bias current flowing through a flexible direct-current transformer winding in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of DC transmission system technology, and in particular to a method and apparatus for suppressing DC bias current in a flexible DC transformer. Background Technology

[0002] When the DC-side circuit impedance of a DC transmission system is low at 50Hz, the positive-sequence second harmonic on the AC side will cause an excessive DC component in the AC-side transformer, leading to transformer saturation, equipment heating and vibration, and affecting equipment safety. Therefore, it is necessary to suppress the DC component current (i.e., DC bias current) flowing through the windings of the flexible DC transmission system transformer. Existing DC bias suppression methods rely on control mechanisms, which require high accuracy in current sampling and reasonable setting of control parameters, resulting in low overall reliability. Therefore, how to reliably suppress the DC bias current flowing through the windings of the flexible DC transmission system transformer (hereinafter referred to as the flexible DC transformer), reduce the DC bias current of the flexible DC transformer, and ensure the safe and stable operation of the DC transmission system and equipment is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0003] This invention provides a method and apparatus for suppressing DC bias current in flexible DC transformers, which addresses the technical problem that the lack of a reliable method for suppressing DC bias current flowing through the windings of flexible DC transformers makes it difficult to ensure the safe and stable operation of DC transmission systems and equipment.

[0004] In view of this, the first aspect of the present invention provides a method for suppressing DC bias current in a flexible DC transformer, comprising:

[0005] Calculate the impedance of the DC loop of the flexible DC transmission system at a frequency of 50 Hz;

[0006] A DC bias current suppression device is connected at a preset position on the DC side of the flexible DC transmission system. The DC bias current suppression device includes an inductor and a capacitor connected in parallel.

[0007] After connecting the DC bias current suppression device, determine whether the impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range has increased to the target value compared to the impedance at 50Hz when the DC bias current suppression device is not connected. If yes, the DC bias current suppression configuration of the flexible DC transformer is completed. If not, add a resistor with a preset resistance value in parallel with the inductor and capacitor to the DC bias current suppression device to complete the DC bias current suppression configuration of the flexible DC transformer.

[0008] Optionally, the system operating frequency range is: , The rated frequency for the flexible DC transmission system. This refers to the operating frequency deviation of the flexible DC transmission system.

[0009] Optionally, the target value is above 200Ω.

[0010] Optionally, a resistor with a preset resistance value is added in parallel with the inductor and capacitor in the DC bias current suppression device, including:

[0011] Within the range of 500Ω to 2000Ω, with a resistance value adjustment step of 500Ω, a resistor connected in parallel with the inductor and capacitor is added to the DC bias current suppression device. The impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range after adding resistors of different resistance values ​​is calculated. The resistance value at which the impedance of the DC circuit of the flexible DC transmission system is highest within the system operating frequency range is taken as the preset resistance value. A resistor of the preset resistance value connected in parallel with the inductor and capacitor is added to the DC bias current suppression device to complete the DC bias current suppression configuration of the flexible DC transformer.

[0012] Optionally, a DC bias current suppression device is connected at a predetermined location on the DC side of the flexible DC transmission system, including:

[0013] If the flexible DC transmission system is a symmetrical monopole system, then a DC bias current suppression device is connected in series at the DC pole line of the converter station of the flexible DC transmission system.

[0014] If the flexible DC transmission system is a bipolar system, then a DC bias current suppression device is connected in series at the neutral bus of each pole of the converter station of the flexible DC transmission system.

[0015] Optionally, the inductance value of the inductor of the DC bias current suppression device is taken as the inductance value of the reactor connected in series with the DC transmission line.

[0016] A second aspect of the present invention provides a DC bias current suppression device for a flexible DC transformer, comprising:

[0017] The fundamental frequency impedance calculation module is used to calculate the impedance of the DC circuit of a flexible DC transmission system at a frequency of 50Hz.

[0018] The suppression device access module is used to connect a DC bias current suppression device at a preset position on the DC side of the flexible DC transmission system. The DC bias current suppression device includes an inductor and a capacitor connected in parallel.

[0019] The judgment module is used to determine whether the impedance of the DC circuit of the flexible DC transmission system in the system operating frequency range has increased to the target value after the DC bias current suppression device is connected. If yes, the DC bias current suppression configuration of the flexible DC transformer is completed. If no, a resistor with a preset resistance value connected in parallel with the inductor and capacitor is added to the DC bias current suppression device to complete the DC bias current suppression configuration of the flexible DC transformer.

[0020] Optionally, the system operating frequency range is: , The rated frequency for the flexible DC transmission system. This refers to the operating frequency deviation of the flexible DC transmission system.

[0021] Optionally, the target value is above 200Ω.

[0022] Optionally, the determination module is specifically used for:

[0023] After connecting the DC bias current suppression device, determine whether the impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range has increased to the target value compared to the impedance at 50Hz when the DC bias current suppression device is not connected. If yes, the DC bias current suppression configuration of the flexible DC transformer is completed. If not, within the range of 500Ω to 2000Ω, adjust the resistance value in 500Ω increments, add a resistor in parallel with the inductor and capacitor in the DC bias current suppression device, calculate the impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range after adding resistors of different resistance values, take the resistance value at which the impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range is the highest, and add a resistor of the preset resistance value in parallel with the inductor and capacitor in the DC bias current suppression device to complete the DC bias current suppression configuration of the flexible DC transformer.

[0024] As can be seen from the above technical solutions, the DC bias current suppression method for flexible DC transformers provided by the present invention has the following advantages:

[0025] The present invention provides a method for suppressing DC bias current in flexible DC transmission transformers. A DC bias current suppression device is connected at a predetermined position on the DC side of the flexible DC transmission system. The device includes an inductor and a capacitor connected in parallel. The method determines whether the impedance of the DC circuit of the flexible DC transmission system within the system's operating frequency range has increased to a target value after connecting the device compared to the impedance at 50Hz without the device. If so, the DC bias current suppression configuration of the flexible DC transmission transformer is complete. If not, a resistor of a predetermined resistance value connected in parallel with the inductor and capacitor is added to the DC bias current suppression device to complete the configuration. The present invention suppresses the DC current component flowing through the windings of the AC-side flexible DC transmission transformer by connecting a DC bias current suppression device on the DC side of the flexible DC transmission system. Compared to existing DC bias current suppression methods that rely on control measures, this method offers higher reliability. It solves the technical problem of the lack of a reliable method for suppressing the DC bias current flowing through the windings of flexible DC transmission transformers, which makes it difficult to ensure the safe and stable operation of DC transmission systems and equipment. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flowchart illustrating a method for suppressing DC bias current in a flexible DC transformer, as provided in an embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram of a DC circuit resonance analysis model for a single valve group provided in an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the DC circuit resonance analysis model of the flexible DC converter provided in an embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram of the DC circuit resonance analysis model of the flexible DC transmission system provided in this embodiment of the invention;

[0031] Figure 5 This is a schematic diagram of the DC bias current suppression device provided in an embodiment of the present invention;

[0032] Figure 6 This is a schematic diagram of a DC bias current suppression device for a flexible DC transformer provided in an embodiment of the present invention. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] For easier understanding, please refer to Figure 1 This invention provides an embodiment of a method for suppressing DC bias current in a flexible DC transformer, comprising:

[0035] Step 101: Calculate the impedance of the DC circuit of the flexible DC transmission system at a frequency of 50Hz.

[0036] It should be noted that in this embodiment of the invention, the impedance of the DC circuit of the flexible DC transmission system at a frequency of 50Hz, i.e., the fundamental frequency impedance, is calculated first. Specifically, a unit impulse voltage source can be connected in series in the DC circuit of the flexible DC transmission system to obtain the current response of the DC circuit. Fourier analysis is performed on the voltage and current of the voltage source to obtain the frequency response characteristics of the DC voltage and DC current at 50Hz. The impedance of the DC circuit at a frequency of 50Hz is then calculated using the following formula:

[0037]

[0038] in, The impedance of the DC circuit in a flexible DC transmission system at a frequency of 50Hz. This represents the frequency response of the DC voltage at 50Hz. This represents the frequency response of the DC current at 50Hz.

[0039] Step 102: Connect a DC bias current suppression device at a preset position on the DC side of the flexible DC transmission system. The DC bias current suppression device includes an inductor and a capacitor connected in parallel.

[0040] It should be noted that, in this embodiment of the invention, a DC bias current suppression device is connected at a predetermined position on the DC side of the flexible DC transmission system to improve impedance characteristics. For example... Figure 2 As shown, the resonant analysis model of the DC circuit of a flexible DC transmission system converter with a single valve group consists of the bridge arm reactor Ls, the flexible DC module capacitor C, and the equivalent impedance Zeq (Zeq = Req + jLeq, where Req is the equivalent resistance of the flexible DC transformer and Leq is the equivalent inductance of the flexible DC transformer) connected in series. Generally, a flexible DC transmission system has multiple valve groups connected in series. If there are n valve groups connected in series, it represents n... Figure 3 The structure shown is connected in series. If the flexible DC transmission system is equipped with a DC reactor Lp, then the reactor Lp is connected in series to the corresponding position to form... Figure 3 The diagram shows a resonant analysis model of the DC loop of a flexible DC converter considering a flexible DC transformer. The DC transmission line can be an overhead line or a cable, and the resonant analysis process is the same as for traditional DC converters and flexible DC converters without considering the influence of the flexible DC transformer, using a frequency-dependent (Phase) parameter model. Combined with... Figure 3 The flexible DC converter model shown can be used to establish Figure 4The diagram shows a DC loop resonance analysis model for a flexible DC transmission system. For multi-terminal flexible DC transmission systems, a corresponding model can be established based on the series and parallel connections of the converter stations. If the flexible DC transmission system is a symmetrical monopolar system, a DC bias current suppression device is connected in series at the DC pole of the converter station. If the flexible DC transmission system is a bipolar system, a DC bias current suppression device is connected in series at the neutral bus of each pole of the converter station. For example... Figure 5 As shown, the DC bias current suppression device includes an inductor and a capacitor connected in parallel, and the resonant frequency formed by the capacitor and inductor is the fundamental frequency. The inductance value of the DC bias current suppression device is taken as the inductance value of the reactor Lp connected in series with the DC transmission line, which can save the number of spare reactors.

[0041] Step 103: Determine whether the impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range has increased to the target value after the DC bias current suppression device is connected. If yes, the DC bias current suppression configuration of the flexible DC transformer is completed. If no, a resistor with a preset resistance value connected in parallel with the inductor and capacitor is added to the DC bias current suppression device to complete the DC bias current suppression configuration of the flexible DC transformer.

[0042] It should be noted that the impedance of the DC circuit of the flexible DC transmission system after the DC bias current suppression device is connected is calculated within the system operating frequency range. It is observed whether the impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range at 50Hz can be increased to the target value compared with that without the DC bias current suppression device. If so, the DC bias current suppression of the flexible DC transformer is completed. If not, it indicates that there are still points with low impedance within the system operating range. A resistor with a preset resistance value needs to be added in parallel with the inductor and capacitor in the DC bias current suppression device to further improve the impedance characteristics of the DC circuit of the flexible DC transmission system and suppress the DC component of the AC side flexible DC transformer.

[0043] In one embodiment, considering the operating frequency deviation of the flexible DC transmission system The system operating frequency range is , This is the rated frequency for the flexible DC transmission system.

[0044] In one embodiment, after connecting the DC bias current suppression device, if the impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range fails to increase to the target value compared to the impedance at 50Hz when the DC bias current suppression device is not connected, then within the range of 500Ω to 2000Ω, in 500Ω increments, a resistor connected in parallel with the inductor and capacitor is added to the DC bias current suppression device. The impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range after adding resistors of different resistance values ​​is calculated. The resistance value at which the impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range is the highest is taken as the preset resistance value, and a resistor of the preset resistance value connected in parallel with the inductor and capacitor is added to the DC bias current suppression device.

[0045] The present invention provides a method for suppressing DC bias current in flexible DC transmission transformers. A DC bias current suppression device is connected at a predetermined position on the DC side of the flexible DC transmission system. The device includes an inductor and a capacitor connected in parallel. The method determines whether the impedance of the DC circuit of the flexible DC transmission system within the system's operating frequency range has increased to a target value after connecting the device compared to the impedance at 50Hz without the device. If so, the DC bias current suppression configuration of the flexible DC transmission transformer is complete. If not, a resistor of a predetermined resistance value connected in parallel with the inductor and capacitor is added to the DC bias current suppression device to complete the configuration. The present invention suppresses the DC current component flowing through the windings of the AC-side flexible DC transmission transformer by connecting a DC bias current suppression device on the DC side of the flexible DC transmission system. Compared to existing DC bias current suppression methods that rely on control measures, this method offers higher reliability. It solves the technical problem of the lack of a reliable method for suppressing the DC bias current flowing through the windings of flexible DC transmission transformers, which makes it difficult to ensure the safe and stable operation of DC transmission systems and equipment.

[0046] For easier understanding, please refer to Figure 6 This invention provides an embodiment of a DC bias current suppression device for a flexible DC transformer, comprising:

[0047] The fundamental frequency impedance calculation module is used to calculate the impedance of the DC circuit of a flexible DC transmission system at a frequency of 50Hz.

[0048] The suppression device access module is used to connect a DC bias current suppression device at a preset position on the DC side of the flexible DC transmission system. The DC bias current suppression device includes an inductor and a capacitor connected in parallel.

[0049] The judgment module is used to determine whether the impedance of the DC circuit of the flexible DC transmission system in the system operating frequency range has increased to the target value after the DC bias current suppression device is connected. If yes, the DC bias current suppression configuration of the flexible DC transformer is completed. If no, a resistor with a preset resistance value connected in parallel with the inductor and capacitor is added to the DC bias current suppression device to complete the DC bias current suppression configuration of the flexible DC transformer.

[0050] In one embodiment, the system operating frequency range is: , The rated frequency for the flexible DC transmission system. This refers to the operating frequency deviation of the flexible DC transmission system.

[0051] In one embodiment, the target value is above 200Ω.

[0052] In one embodiment, the determination module is specifically used for:

[0053] After connecting the DC bias current suppression device, determine whether the impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range has increased to the target value compared to the impedance at 50Hz when the DC bias current suppression device is not connected. If yes, the DC bias current suppression configuration of the flexible DC transformer is completed. If not, within the range of 500Ω to 2000Ω, adjust the resistance value in 500Ω increments, add a resistor in parallel with the inductor and capacitor in the DC bias current suppression device, calculate the impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range after adding resistors of different resistance values, take the resistance value at which the impedance of the DC circuit of the flexible DC transmission system within the system operating frequency range is the highest, and add a resistor of the preset resistance value in parallel with the inductor and capacitor in the DC bias current suppression device to complete the DC bias current suppression configuration of the flexible DC transformer.

[0054] In one embodiment, the device access suppression module is specifically used for:

[0055] If the flexible DC transmission system is a symmetrical monopole system, then a DC bias current suppression device is connected in series at the DC pole line of the converter station of the flexible DC transmission system.

[0056] If the flexible DC transmission system is a bipolar system, then a DC bias current suppression device is connected in series at the neutral bus of each pole of the converter station of the flexible DC transmission system.

[0057] In one embodiment, the inductance value of the DC bias current suppression device is taken as the inductance value of the reactor connected in series with the DC transmission line.

[0058] The DC bias current suppression device for flexible DC transformers provided in this invention is used to execute the DC bias current suppression method for flexible DC transformers provided in this invention. Its principle and the technical effect achieved are the same as those of the DC bias current suppression method for flexible DC transformers provided in this invention, and will not be repeated here.

[0059] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0060] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for suppressing direct current bias current of a CIGRTR, characterized in that, The method comprises the steps of: calculating the impedance of the DC circuit of the flexible HVDC power transmission system at a frequency of 50 Hz; inserting a DC bias current suppression device at a preset position on the DC side of the flexible HVDC power transmission system, the DC bias current suppression device comprising an inductor and a capacitor connected in parallel; determining whether the impedance of the DC circuit of the flexible HVDC power transmission system in a system operating frequency range is increased to a target value compared with the impedance at a frequency of 50 Hz when the DC bias current suppression device is not inserted, if yes, completing the DC bias current suppression configuration of the flexible HVDC transformer, and if no, adding a resistor with a preset resistance value connected in parallel with the inductor and the capacitor in the DC bias current suppression device, and completing the DC bias current suppression configuration of the flexible HVDC transformer.

2. The method of claim 1, wherein the DC bias current is suppressed by, The system operating frequency range is , is the rated frequency of the flexible DC power transmission system, is the operating frequency deviation of the flexible DC power transmission system.

3. The method of claim 1, wherein the DC bias current is suppressed by, The target value is 200 Ω or more.

4. The HVDC transformer DC bias current suppression method of any one of claims 1-3, wherein, The method of adding the resistor with the preset resistance value connected in parallel with the inductor and the capacitor in the DC bias current suppression device comprises: adding a resistor with a resistance value in a range of 500 Ω to 2000 Ω in steps of 500 Ω in parallel with the inductor and the capacitor in the DC bias current suppression device, calculating the impedance of the DC circuit of the flexible HVDC power transmission system in the system operating frequency range after adding the resistors with different resistance values, and taking the resistance value of the resistor with the highest impedance of the DC circuit of the flexible HVDC power transmission system in the system operating frequency range as the preset resistance value, and adding the resistor with the preset resistance value connected in parallel with the inductor and the capacitor in the DC bias current suppression device, and completing the DC bias current suppression configuration of the flexible HVDC transformer.

5. The method of claim 1, wherein the DC bias current is suppressed by, The method of inserting the DC bias current suppression device at a preset position on the DC side of the flexible HVDC power transmission system comprises: if the flexible HVDC power transmission system is a symmetric monopole system, inserting the DC bias current suppression device in series at the DC pole line of the converter station of the flexible HVDC power transmission system; if the flexible HVDC power transmission system is a bipolar system, inserting the DC bias current suppression device in series at the neutral bus of each pole of the converter station of the flexible HVDC power transmission system.

6. The method of claim 5, wherein the DC bias current is suppressed by, The inductance value of the inductor of the DC bias current suppression device is the inductance value of the reactor connected in series with the DC power transmission line.

7. A DC bias current suppression device for a CIGRTR, characterized by, The method comprises: a fundamental frequency impedance calculation module configured to calculate the impedance of the DC circuit of the flexible HVDC power transmission system at a frequency of 50 Hz; a suppression device insertion module configured to insert a DC bias current suppression device at a preset position on the DC side of the flexible HVDC power transmission system, the DC bias current suppression device comprising an inductor and a capacitor connected in parallel; a determination module configured to determine whether the impedance of the DC circuit of the flexible HVDC power transmission system in a system operating frequency range is increased to a target value compared with the impedance at a frequency of 50 Hz when the DC bias current suppression device is not inserted, if yes, completing the DC bias current suppression configuration of the flexible HVDC transformer, and if no, adding a resistor with a preset resistance value connected in parallel with the inductor and the capacitor in the DC bias current suppression device, and completing the DC bias current suppression configuration of the flexible HVDC transformer.

8. The transformer DC bias current suppression device of claim 7, wherein, The system operates in a frequency range of , is the rated frequency of the flexible HVDC system, is the frequency deviation of the flexible HVDC system.

9. The transformer DC bias current suppression device of claim 7, wherein, The target value is 200 Ω or more.

10. The HVDC transformer DC bias current suppression device of any one of claims 7-9, wherein, The determination module is specifically configured to: If the impedance of the DC circuit of the flexible HVDC power transmission system in the system operating frequency range is higher than the impedance of the DC circuit of the flexible HVDC power transmission system at 50 Hz when the DC bias current suppression device is not connected, and the impedance of the DC circuit of the flexible HVDC power transmission system in the system operating frequency range is increased to a target value, then the DC bias current suppression configuration of the flexible HVDC power transmission system is completed. If the impedance of the DC circuit of the flexible HVDC power transmission system in the system operating frequency range is not higher than the impedance of the DC circuit of the flexible HVDC power transmission system at 50 Hz when the DC bias current suppression device is not connected, and the impedance of the DC circuit of the flexible HVDC power transmission system in the system operating frequency range is not increased to the target value, then a resistance with a resistance value of 500 Ω is added to the DC bias current suppression device in the range of 500 Ω to 2000 Ω in steps of 500 Ω, the impedance of the DC circuit of the flexible HVDC power transmission system in the system operating frequency range after the resistance with different resistance values is added is calculated, the resistance value of the resistance with the highest impedance of the DC circuit of the flexible HVDC power transmission system in the system operating frequency range is taken as a preset resistance value, and the resistance with the preset resistance value is added to the DC bias current suppression device in parallel with the inductance and the capacitance, so that the DC bias current suppression configuration of the flexible HVDC power transmission system is completed.

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