Damping type amplitude-phase correction device for flexible direct-current power transmission and transformation and related system

Abstract

The invention discloses a damping type amplitude-phase correction device for flexible direct-current power transmission and transformation and a related system, and belongs to the technical field of flexible direct-current power transmission and transformation. The device can directly act on a negative damping-capacitive impedance pair formed by coupling MMC delay and capacitive impedance of an alternating current system through a series core topology of a first frequency doubling filter capacitor unit C1, a low-noise inductance-adjusting reactor unit L1 and a second frequency doubling filter capacitor unit C2 in cooperation with an R1 parallel damping structure; the C1 which is allocated and optimized for the even-order harmonics is used as an input end head end filtering unit, the C2 which is allocated and optimized for the even-order harmonics, the L1 and the R1 form a cooperative damping loop, the stable frequency doubling capacitive reactance characteristic ensures that the resonant frequency of a series branch of the L1 and the C2 accurately avoids the normal operation frequency band of the system, meanwhile, the resonant frequency and high-frequency inductive negative damping of the MMC form complementation, and the frequency doubling capacitive reactance characteristic is stable. Resonance excitation and harmonic divergence can be effectively suppressed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible direct current power transmission, in particular to a damping amplitude-phase correction device for flexible direct current power transmission and related system. BACKGROUND

[0002] With the rapid development of renewable energy generation technology, photovoltaic and wind power stations have become an important part of the power system. The output of such stations has significant volatility and intermittency, which poses a challenge to the stable operation of the power grid. To solve the problem of long-distance, large-capacity grid connection of new energy power and interconnection of alternating current systems, flexible direct current power transmission systems have been widely used. In this system, the modular multilevel converter (MMC) as the core converter unit, bears the key function of bidirectional conversion of AC and DC power.

[0003] In the actual control process of MMC, there is an unavoidable delay of hundreds of microseconds in the digital control link. This delay will cause the MMC output impedance to exhibit a significant "inductive negative damping" characteristic at a high frequency of 300Hz or above: the phase lag caused by the delay accumulates as the frequency increases, and when the phase deviation exceeds 90°, the real part of the impedance becomes negative. In the actual grid connection scenario of new energy stations, the alternating current system often has an inherent capacitive impedance component (such as converter transformer stray capacitance, submarine cable parameters, etc.), which is easy to form a "negative damping-capacitive" impedance pair with the negative damping characteristic of MMC at high frequencies, thereby exciting high-frequency resonance and causing harmonic amplitude divergence, which seriously threatens the power quality and operational stability of the grid-connected system. Traditional control methods mostly focus on the suppression of fundamental frequency (50Hz or 60Hz) and low-order harmonics (such as 3rd, 5th, 7th, etc. lower frequency harmonics), usually using active filters based on fixed frequency characteristics design, whose filtering frequency band, damping parameters and topology structure are matched for the characteristics of fundamental frequency and low-order harmonics.

[0004] However, the high-frequency resonance problem caused by the coupling of MMC delay and alternating current system capacitance mainly acts on the high frequency band of 300Hz or above, which has essential differences in frequency characteristics and impedance amplitude-phase characteristics from the low frequency band. The traditional harmonic control method does not match the suppression needs of the above-mentioned high frequency band, not only making it difficult to effectively suppress the resonance phenomenon caused by negative damping in this frequency band, but also unable to prevent the continuous amplification and divergence of high-frequency harmonics, resulting in a control blind area. SUMMARY

[0005] The purpose of the present application is to provide a damping amplitude-phase correction device for flexible direct current power transmission and related system to overcome the problem of effectively suppressing the high-frequency resonance problem caused by the interaction of MMC high-frequency negative damping characteristics and alternating current system capacitive impedance in the flexible direct current power transmission system.

[0006] The present invention solves the above-mentioned technical problems through the following technical solution: This invention provides a damped amplitude and phase correction device for flexible DC power transmission and transformation, comprising a first frequency-doubling filter capacitor unit C1, a low-noise adjustable inductance reactor unit L1, and a second frequency-doubling filter capacitor unit C2 connected in series; a resistor unit R1 is connected in parallel across the two ends of the series circuit of the low-noise adjustable inductance reactor unit L1 and the second frequency-doubling filter capacitor unit C2; the end of the second frequency-doubling filter capacitor unit C2 that is not connected in series with the low-noise adjustable inductance reactor unit L1 is grounded. Among them, the first frequency doubling filter capacitor unit C1 and the second frequency doubling filter capacitor unit C2 are both capacitors optimized with dual harmonic modulation; in use, the end of the first frequency doubling filter capacitor unit C1 that is not connected to the low noise inductance reactor unit L1 is used as the input terminal and connected to the output terminal of the AC system.

[0007] A further improvement of the present invention is that the low-noise adjustable inductance reactor unit L1 is a filter reactor after ±10% inductance adjustment by tapping the secondary coil.

[0008] A further improvement of the present invention is that the first frequency doubling filter capacitor unit C1 is composed of a first series circuit and a second series circuit connected in parallel, wherein the first series circuit consists of a first capacitor and a second capacitor connected in series in sequence; and the second series circuit consists of a third capacitor and a fourth capacitor connected in series in sequence.

[0009] A further improvement of the present invention is that the damped amplitude and phase correction device for flexible DC power transmission and transformation further includes a first current transformer CT1, which is disposed between the connection point of the first capacitor and the second capacitor and the connection point of the third capacitor and the fourth capacitor.

[0010] A further improvement of the present invention is that the damped amplitude and phase correction device for flexible DC power transmission and transformation also includes a second current transformer CT2, a resistor unit R1 connected in series with the second current transformer CT2, and a series circuit of resistor unit R1 and second current transformer CT2 connected in parallel across the two ends of the series circuit of low-noise adjustable inductance reactor unit L1 and second frequency doubling filter capacitor unit C2.

[0011] A further improvement of the present invention is that the damped amplitude and phase correction device for flexible DC power transmission and transformation also includes a third current transformer CT3, and the second frequency doubling filter capacitor unit C2 is grounded through the third current transformer CT3.

[0012] A further improvement of the present invention is that the damped amplitude and phase correction device for flexible DC power transmission and transformation also includes a surge arrester FV1, and one end of the first frequency doubling filter capacitor unit C1 connected in series with the low noise adjustable inductance reactor unit L1 serves as the output terminal and is grounded through the surge arrester FV1; the surge arrester FV1 is a zinc oxide surge arrester.

[0013] A further improvement of the present invention is that the resistor unit R1 is a filter resistor with a stainless steel shell and an internal metal wire.

[0014] A further improvement of the present invention is that, when the output voltage on the AC grid side is 500KV, the rated capacitance of the first frequency doubling filter capacitor unit C1 is 3.112μF; the rated capacitance of the second frequency doubling filter capacitor unit C2 is 200μF; the rated inductance of the low-noise adjustable inductance reactor unit L1 is 50.66mH; and the rated resistance of the resistor unit R1 is 826.9Ω.

[0015] The present invention also provides a flexible DC transmission and transformation system, including at least one damped amplitude and phase correction device for flexible DC transmission and transformation as described above.

[0016] Compared with the prior art, the positive and progressive effects of the present invention are as follows: The damped amplitude and phase correction device for flexible DC power transmission provided by this invention constructs a dedicated impedance adjustment system for high-frequency bands through a series core topology of a first frequency-harmonic filter capacitor unit C1, a low-noise adjustable inductance reactor unit L1, and a second frequency-harmonic filter capacitor unit C2, combined with a parallel damping structure of R1. Its frequency response characteristics accurately cover the high-frequency resonance range above 300Hz, and it can directly act on the "negative damping-capacitive" impedance pair formed by the MMC delay and the capacitive impedance coupling of the AC system, breaking the resonance condition from the impedance matching level; it also provides superior even-order harmonic modulation. The optimized C1 serves as the input-side filter unit. Its optimized frequency doubling characteristic allows for preliminary screening and phase pre-correction of high-frequency harmonics in the AC system output, reducing the adjustment load on subsequent units. The even-order harmonic-optimized C2, together with L1 and R1, forms a synergistic damping circuit. Its stable frequency doubling capacitive reactance ensures that the resonant frequency of the L1-C2 series branch precisely avoids the normal operating frequency band of the system. Simultaneously, it complements the high-frequency inductive negative damping of the MMC, making the real part of the overall system impedance positive through impedance real-part compensation, effectively suppressing resonance excitation and harmonic divergence. This synergistic design of dual optimized capacitors ensures the stability and reliability of high-frequency harmonic suppression. Attached Figure Description

[0017] The accompanying drawings are provided to further understand the invention and constitute a part of this invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 This is a schematic diagram of the main wiring of a damped amplitude-phase correction device for flexible DC power transmission and transformation according to the present invention; Figure 2 This is a schematic diagram of the wiring arrangement of a damped amplitude-phase correction device for flexible DC power transmission and transformation according to the present invention; Figure 3 The amplitude-frequency characteristic curve of a damped amplitude-phase correction device for flexible DC power transmission and transformation according to the present invention; Figure 4 The phase angle characteristic curve of a damped amplitude-phase correction device for flexible DC power transmission and transformation according to the present invention; Figure 5 This is an assembly diagram of the damped amplitude and phase correction device for flexible DC power transmission and transformation provided by the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] Furthermore, it should be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. This is an explanation of the present invention and not a limitation thereof.

[0025] In flexible DC transmission systems, due to control delays, the MMC (Multi-Mode Damping Compensator) may exhibit inductive negative damping characteristics at high frequencies (e.g., hundreds to thousands of Hz), particularly at even multiples of the fundamental frequency (e.g., 100 Hz, 200 Hz, 400 Hz). This negative damping characteristic weakens the system's positive damping margin, causing resonance between the AC system and the converter station at specific frequencies. This leads to problems such as high-frequency harmonic current divergence and power oscillations, seriously threatening the safe and stable operation of grid-side equipment. Traditional active damping compensation devices rely on complex control systems, which suffer from response delays and low reliability, making it difficult to meet the rapid dynamic requirements of high-voltage, high-capacity scenarios.

[0026] The core benchmark for the design and manufacturing of traditional power capacitors (including those used in UHVDC transmission and transformation) is the fundamental frequency of the power grid, namely the globally common 50Hz or 60Hz power frequency. Their structural design (electrode type, dielectric selection and thickness), performance parameter optimization (dielectric loss tangent, equivalent series resistance, insulation strength), and thermal stability matching are all based on the core objectives of electric field energy storage and reactive power compensation at the fundamental frequency. They are adapted to the operating conditions of conventional converter topologies and can effectively cope with the fundamental frequency and a small number of low-order odd harmonic environments. Their long-term reliable operation performance boundaries and lifespan guarantees are all based on the operating scenario dominated by the 50Hz / 60Hz fundamental frequency.

[0027] Under this operating condition, traditional baseband capacitors may experience problems such as a sharp increase in dielectric loss, an increase in equivalent series resistance, and local overheating due to their design not being adapted to the high-frequency polarization characteristics of the frequency harmonic field. This can lead to a shortened equipment lifespan, increased partial discharge, and other safety hazards. Furthermore, because the capacitance at the main operating frequency, such as 100 Hz, is actually calculated for 50 Hz during the design process, the actual volume of the manufactured capacitor is often several times larger than the actual required capacitor. In practical applications, this means increased manufacturing costs, larger footprint, and increased losses.

[0028] To address the aforementioned problems, this invention provides a damped amplitude and phase correction device for flexible DC power transmission and transformation, comprising a first frequency-doubling filter capacitor unit C1, a low-noise adjustable inductance reactor unit L1, and a second frequency-doubling filter capacitor unit C2 connected in series. A resistor unit R1 is connected in parallel across the two ends of the series circuit of the low-noise adjustable inductance reactor unit L1 and the second frequency-doubling filter capacitor unit C2, and the end of the second frequency-doubling filter capacitor unit C2 that is not connected in series with the low-noise adjustable inductance reactor unit L1 is grounded. Among them, the first frequency doubling filter capacitor unit C1 and the second frequency doubling filter capacitor unit C2 are both capacitors optimized with dual harmonic modulation; in use, the end of the first frequency doubling filter capacitor unit C1 that is not connected to the low noise inductance reactor unit L1 is used as the input terminal and connected to the output terminal of the AC system.

[0029] The frequency doubling filter capacitor unit is specifically designed for power capacitors that may appear in UHV flexible DC transmission and transformation systems, with the fundamental frequency being 100Hz or 120Hz and its harmonics being integer multiples thereof. Its core operating frequency band is the even harmonics and integer multiples of the grid fundamental frequency (50Hz or 60Hz), that is, the harmonic frequency band dominated by 100Hz / 120Hz (including 100Hz, 200Hz... or 120Hz, 240Hz... etc.). This type of capacitor focuses on electric field energy storage, reactive power compensation, and harmonic suppression in the frequency doubling frequency band. Through design methods such as optimizing electrode structure and optimizing equivalent series parameters, it achieves the performance goals of low dielectric loss, low heat generation, and high insulation stability under frequency doubling conditions. Its key parameters such as dielectric loss tangent, heat capacity, resonant frequency, and insulation strength have all been specially matched for the frequency doubling frequency band. It can operate reliably for a long time under the main operating conditions of 100Hz / 120Hz and its integer multiples, providing core support for the improvement of power quality and stable operation of UHV flexible DC transmission and transformation systems.

[0030] The damped amplitude-phase correction device provided by this invention, although it does not generate energy itself, can construct a channel with negative resistance characteristics within a specific frequency range (e.g., 400Hz) through its network structure. In this channel, the voltage and current phase relationships are opposite, thus simulating the effect of negative resistance from a system perspective. This means it can cancel oscillation energy at specific frequencies (e.g., 400Hz), thereby providing positive damping to compensate for the inductive negative damping caused by control delay at high frequencies, preventing the impedance of the flexible DC transmission system from satisfying the oscillation condition with the AC system impedance in the critical frequency band. As a passive device, the amplitude-phase corrector does not rely on a complex control system, avoiding the adverse effects of control link delay, and has a fast response speed and high reliability.

[0031] This invention provides a damped amplitude and phase correction device for flexible DC power transmission. Through a series core topology of a first frequency-harmonic filter capacitor unit C1, a low-noise adjustable inductance reactor unit L1, and a second frequency-harmonic filter capacitor unit C2, combined with a parallel damping structure R1, a dedicated impedance adjustment system for the high-frequency band is constructed. Its frequency response characteristics accurately cover the high-frequency resonance range above 300Hz. It can directly act on the "negative damping-capacitive" impedance pair formed by the MMC delay and the capacitive impedance coupling of the AC system, breaking the resonance condition from the impedance matching level; and modulating even-order harmonics. The optimized C1 serves as the input-side filter unit. Its optimized frequency doubling characteristic allows for preliminary screening and phase pre-correction of high-frequency harmonics in the AC system output, reducing the adjustment load on subsequent units. The even-order harmonic-matched optimized C2, together with L1 and R1, forms a synergistic damping circuit. Its stable frequency doubling capacitive reactance ensures that the resonant frequency of the L1-C2 series branch precisely avoids the normal operating frequency band of the system. Simultaneously, it complements the high-frequency inductive negative damping of the MMC, making the overall system impedance positive through impedance real-part compensation, effectively suppressing resonance excitation and harmonic divergence. This synergistic design of dual optimized capacitors ensures the stability and reliability of high-frequency harmonic suppression.

[0032] Preferably, the low-noise adjustable inductance reactor unit L1 is a filter reactor with ±10% inductance adjustment by tapping the secondary coil.

[0033] By tapping the secondary coil, the low-noise adjustable inductance reactor unit L1 is designed to be ±10%, enabling the resonant frequency of the entire device to flexibly match the resonant point of the actual system, thus enhancing adaptability. This also improves the device's tolerance to field parameter deviations, ensuring that it can effectively exert its damping effect under different operating conditions.

[0034] Preferably, the first frequency doubling filter capacitor unit C1 is composed of a first series circuit and a second series circuit connected in parallel, wherein the first series circuit consists of a first capacitor and a second capacitor connected in series in sequence; and the second series circuit consists of a third capacitor and a fourth capacitor connected in series in sequence.

[0035] The dual-series parallel structure improves redundancy. When any capacitor in a series circuit fails and becomes open-circuited, the other series circuit can still continue to work and maintain the basic functions of the device. This enhances the operational reliability and fault tolerance of the device and reduces the risk of overall failure due to a single point of failure.

[0036] Preferably, the damped amplitude-phase correction device for flexible DC transmission and transformation further includes a first current transformer CT1, which is disposed between the connection point of the first capacitor and the second capacitor and the connection point of the third capacitor and the fourth capacitor.

[0037] Unbalanced current can accelerate capacitor aging, cause internal breakdown, and in severe cases lead to short circuits or even explosions, threatening the stability of the power system. CT1 can monitor and report abnormal unbalanced current in real time, triggering alarms or tripping mechanisms in a timely manner, preventing the expansion of capacitor faults from the source, and solving the risk of equipment damage caused by untimely protection in existing technologies. The first current transformer CT1, together with the device's frequency doubling filter and damping regulation functions, forms a synergistic protection, suppressing high-frequency resonance and harmonics while specifically ensuring the operational safety of core capacitor components, avoiding secondary power grid accidents caused by capacitor faults, and overcoming the problem of the separation between filtering, damping and component protection in traditional technologies.

[0038] Preferably, the damped amplitude and phase correction device for flexible DC power transmission and transformation further includes a second current transformer CT2, a resistor unit R1 connected in series with the second current transformer CT2, and a series circuit of resistor unit R1 and second current transformer CT2 connected in parallel across the two ends of the series circuit of low-noise adjustable inductance reactor unit L1 and second frequency doubling filter capacitor unit C2.

[0039] The damping branch current is measured by the second current transformer CT2 to assess the energy dissipation of the device under resonant conditions; a means of monitoring the health status of the damping branch is provided to support preventive maintenance and fault early warning.

[0040] Preferably, the damped amplitude and phase correction device for flexible DC transmission and transformation also includes a third current transformer CT3, and the second frequency doubling filter capacitor unit C2 is grounded through the third current transformer CT3.

[0041] The total current flowing through the second frequency-doubling filter capacitor unit C2 is measured by the third current transformer CT3. This can be used for harmonic analysis under normal operating conditions, and can also provide protection criteria when a ground fault occurs. This enables comprehensive monitoring of the grounding branch and improves the overall safety of the device.

[0042] Preferably, the damped amplitude and phase correction device for flexible DC transmission and transformation also includes a surge arrester FV1. One end of the first frequency doubling filter capacitor unit C1 connected in series with the low-noise adjustable inductance reactor unit L1 serves as the output terminal and is grounded through the surge arrester FV1. The surge arrester FV1 is a zinc oxide surge arrester.

[0043] The surge arrester FV1 quickly conducts and discharges energy when transient overvoltage occurs, clamps the node voltage, and protects the upstream capacitor from damage; it significantly improves the device's tolerance to harsh electromagnetic environments and extends the life of key components.

[0044] Preferably, the resistor unit R1 is a filter resistor with a stainless steel housing and built-in metal wire.

[0045] The stainless steel casing provides both physical and chemical protection, while the internal structure ensures stable electrical performance, guaranteeing long-term stable operation of the resistor in complex environments and preventing resistance drift or short-circuit failures due to aging.

[0046] Based on the same inventive concept, the present invention also provides a flexible DC transmission and transformation system, including at least one damped amplitude and phase correction device for flexible DC transmission and transformation as described above.

[0047] In a specific embodiment of the present invention, when the output voltage on the AC grid side is 500KV, the rated capacitance of the first frequency doubling filter capacitor unit C1 is 3.112μF; the rated capacitance of the second frequency doubling filter capacitor unit C2 is 200μF; the rated inductance of the low-noise adjustable inductance reactor unit L1 is 50.66mH; and the rated resistance of the resistor unit R1 is 826.9Ω.

[0048] By rationally configuring the parameters of the first frequency-harmonic filtering capacitor unit C1, the low-noise adjustable inductance reactor unit L1, the second frequency-harmonic filtering capacitor unit C2, and the resistor unit R1, a path with negative resistance characteristics is formed near the target frequency. When the system experiences harmonic disturbances in this frequency band, this device exhibits capacitive behavior with current leading voltage, manifesting as a negative resistance effect externally. This injects positive damping energy into the system, offsetting the inductive negative damping caused by the control delay of the MMC and suppressing resonance development. It effectively suppresses specific high-frequency resonant modes, improving the stability of the flexible DC system. As a passive device, it requires no external power supply or complex control, has a fast response speed, and is reliable in operation, making it suitable for high-voltage, high-capacity applications.

[0049] In a specific embodiment of the present invention, a damped amplitude-phase correction device for flexible DC power transmission is provided, comprising a first frequency-doubling filter capacitor unit C1, a second frequency-doubling filter capacitor unit C2, a low-noise adjustable inductance reactor L1, a resistor unit R1, a zinc oxide surge arrester FV1, a first current transformer CT1, a second current transformer CT2, and a third current transformer CT3, a steel frame, a mesh barrier, insulators, connecting conductors, etc. Taking the HP8 type amplitude-phase corrector as an example, according to... Figure 1 Connect the main wiring as shown, in order to... Figure 2 The arrangement is shown in Table 1, and the typical parameters selected for each main device are shown in Table 2. The resulting impedance amplitude-frequency characteristics are shown in Table 3. Figure 3 Phase frequency characteristics are shown in Figure 4 .

[0050] Table 1 Typical parameters of HP8 type amplitude and phase correction device

[0051] The first frequency-doubled filter capacitor unit C1, the low-noise adjustable inductance reactor unit L1, and the second frequency-doubled filter capacitor unit C2 are connected in series. A resistor unit R1 is connected in parallel across the two ends of the series circuit of the low-noise adjustable inductance reactor unit L1 and the second frequency-doubled filter capacitor unit C2. The second frequency-doubled filter capacitor unit C2 is grounded. Both the first frequency-doubled filter capacitor unit C1 and the second frequency-doubled filter capacitor unit C2 are capacitors optimized with dual-order harmonic modulation. The first frequency doubling filter capacitor unit C1 is composed of a first series circuit and a second series circuit connected in parallel. The first series circuit consists of a first capacitor and a second capacitor connected in series; the second series circuit consists of a third capacitor and a fourth capacitor connected in series. The damped amplitude-phase correction device for flexible DC transmission also includes a first current transformer CT1, which is located between the connection point of the first capacitor and the second capacitor and the connection point of the third capacitor and the fourth capacitor. The damped amplitude-phase correction device for flexible DC transmission also includes a second current transformer CT2, with a resistor unit R1 connected in series with the second current transformer CT2, and a low-noise adjustable inductance reactor unit L1 and... The two ends of the series circuit of the second frequency doubling filter capacitor unit C2 are connected in parallel with the series circuit of the resistor unit R1 and the second current transformer CT2; the damping amplitude and phase correction device for flexible DC transmission and transformation also includes a third current transformer CT3, and the second frequency doubling filter capacitor unit C2 is grounded through the third current transformer CT3; the damping amplitude and phase correction device for flexible DC transmission and transformation also includes a surge arrester FV1, and one end of the first frequency doubling filter capacitor unit C1 connected in series with the low-noise adjustable inductance reactor unit L1 is used as the output terminal and grounded through the surge arrester FV1. In use, the end of the first frequency doubling filter capacitor unit C1 that is not connected to the low-noise adjustable inductance reactor unit L1 is used as the input terminal and connected to the output terminal of the AC system.

[0052] The first harmonic filtering capacitor unit C1 and the second harmonic filtering capacitor unit C2 are unit capacitors optimized for even-order harmonic modulation. They are capacitors with a fundamental frequency of 100Hz and have dedicated harmonic silencing cavities placed at the top and bottom of the capacitor, which can better eliminate resonance caused by even-order harmonics.

[0053] The low-noise adjustable inductance reactor unit L1 is a filter reactor with a noise reduction structure and ±10% inductance adjustment through the secondary coil tap. It uses the viscoelastic energy dissipation characteristics of the damping material to convert the axial and radial vibration energy generated during reactor operation into heat energy for dissipation, reducing the risk of mechanical resonance and thus significantly reducing the overall noise level.

[0054] The resistor unit R1 is a filter resistor with a stainless steel shell, built-in metal wire, and is dustproof and condensation-proof.

[0055] The surge arrester FV1, the first current transformer CT1, the second current transformer CT2, and the third current transformer CT3 together constitute the protection of the device. Among them, the surge arrester FV1 is the capacitor bank relative to ground protection, CT1 is the unbalanced current protection for the H-bridge capacitor bank C1, CT3 is the phase current protection, and CT2 is the protection for the filter resistor branch measurement.

[0056] In flexible DC transmission systems, the digital control link delay (reaching hundreds of microseconds) of modular multilevel converters (MMCs) causes them to exhibit "inductive negative damping" characteristics in high-frequency bands above 300Hz. The phase lag caused by this delay accumulates with frequency; when the phase shift exceeds 90°, the real part of the impedance turns negative, forming a "negative damping-capacitive" resonant pair with the capacitive impedance of the AC system (such as stray capacitance of the converter transformer and submarine cable parameters). For example, in one project, the phase difference reached 181°~182° in the 2000~2500Hz frequency band, exceeding the stability critical value. Traditional active control (such as voltage feedforward) only compresses the phase difference to 172°~176°, failing to completely eliminate the negative damping range and remaining susceptible to changes in grid operating conditions.

[0057] In a specific embodiment provided by the State Grid Economic Research Institute, see [link / reference]. Figure 5 The passive compensation scheme of the damped amplitude-phase correction device for flexible DC transmission directly addresses the root cause of impedance characteristics: by connecting an LC-R network in parallel to the MMC AC bus, the frequency selectivity of the LC branch is utilized—high impedance at the fundamental frequency (C1-L1 parallel resonance isolates fundamental frequency loss), and short-circuiting of capacitors and open-circuiting of inductors in the high-frequency range (400Hz), which is equivalent to a pure resistance R1 (20~30Ω). The damped amplitude-phase correction device for flexible DC transmission injects a 20~30° phase lead in the 2000~3000Hz frequency band, correcting the phase of the original MMC impedance from -15°~-25° to +5°~+10°. Combined with the positive real part introduced by the resistor (Re(Z)>0), the phase difference at the system impedance intersection point is stabilized below 150°, fundamentally blocking the "negative damping-capacitive" resonance condition. This solution breaks through the parameter dependence of active control and achieves precise positive damping compensation in the high-frequency band through physical impedance reshaping, with a fundamental frequency loss of <0.1%. It is particularly suitable for harsh scenarios such as offshore wind power and provides a source control solution for broadband oscillation.

[0058] Finally, it should be noted that the embodiments listed above are merely one or more specific manifestations of the technical solution of this invention. Their purpose is to clearly illustrate the concept, principle, and application of this invention through specific examples, and is by no means intended to limit the scope of protection of this invention to these specific embodiments. In fact, the true value of this invention lies in its proposed technical ideas and innovations, rather than its manifestations or implementation methods.

[0059] For those skilled in the art, after thoroughly reading and understanding the technical solution of this invention, they are fully capable of making various changes, modifications, or equivalent substitutions to the specific implementation of the invention based on their own professional knowledge and skills. These changes may include, but are not limited to: adjusting the range of technical parameters, optimizing the algorithm flow to improve efficiency, and replacing some technical components to achieve better compatibility or reduce costs. As long as these modified technical solutions substantially retain the technical features claimed by the original invention, that is, they can still achieve the core functions and effects of this invention, then these changes should be considered to fall within the scope of protection of the pending claims of this invention.

[0060] Furthermore, with the continuous progress and development of technology, new technical means and methods are constantly emerging, which provides ample space for further improvement and perfection of this invention. Therefore, the scope of protection of this invention should also include reasonable and foresightful improvements and extensions based on existing technology. As long as these improvements and extensions do not depart from the basic principles and core concepts of this invention, they should be considered equivalents of this invention and are equally protected by patent rights.

Claims

1. A damped amplitude-phase correction device for flexible DC transmission and transformation, characterized in that, It includes a first frequency-doubled filter capacitor unit C1, a low-noise adjustable inductance reactor unit L1, and a second frequency-doubled filter capacitor unit C2 connected in series. A resistor unit R1 is connected in parallel across the two ends of the series circuit of the low-noise adjustable inductance reactor unit L1 and the second frequency-doubled filter capacitor unit C2. The end of the second frequency-doubled filter capacitor unit C2 that is not connected in series with the low-noise adjustable inductance reactor unit L1 is grounded. Among them, the first frequency doubling filter capacitor unit C1 and the second frequency doubling filter capacitor unit C2 are both capacitors optimized with dual harmonic modulation; in use, the end of the first frequency doubling filter capacitor unit C1 that is not connected to the low noise inductance reactor unit L1 is used as the input terminal and connected to the output terminal of the AC system.

2. The damped amplitude-phase correction device for flexible DC transmission and transformation according to claim 1, characterized in that, The low-noise tuned inductance reactor unit L1 is a filtered reactor with ±10% inductance adjustment via taps on the secondary coil.

3. The damped amplitude-phase correction device for flexible DC transmission and transformation according to claim 1, characterized in that, The first frequency doubling filter capacitor unit C1 is composed of a first series circuit and a second series circuit connected in parallel. The first series circuit consists of a first capacitor and a second capacitor connected in series in sequence. The second series circuit consists of a third capacitor and a fourth capacitor connected in series in sequence in sequence.

4. A damped amplitude-phase correction device for flexible DC transmission and transformation according to claim 3, characterized in that, The damped amplitude and phase correction device for flexible DC power transmission and transformation also includes a first current transformer CT1, which is located between the connection point of the first capacitor and the second capacitor and the connection point of the third capacitor and the fourth capacitor.

5. A damped amplitude-phase correction device for flexible DC transmission and transformation according to claim 1, characterized in that, The damped amplitude and phase correction device for flexible DC power transmission also includes a second current transformer CT2, a resistor unit R1 connected in series with the second current transformer CT2, a low-noise adjustable inductance reactor unit L1 and a second frequency doubling filter capacitor unit C2 connected in parallel across the two ends of the series circuit of the resistor unit R1 and the second current transformer CT2.

6. A damped amplitude-phase correction device for flexible DC transmission and transformation according to claim 1, characterized in that, The damped amplitude and phase correction device for flexible DC power transmission also includes a third current transformer CT3, and the second frequency doubling filter capacitor unit C2 is grounded through the third current transformer CT3.

7. A damped amplitude-phase correction device for flexible DC transmission and transformation according to claim 1, characterized in that, The damped amplitude and phase correction device for flexible DC transmission and transformation also includes a surge arrester FV1. One end of the first frequency doubling filter capacitor unit C1 is connected in series with the low-noise adjustable inductance reactor unit L1 as the output terminal and grounded through the surge arrester FV1. The surge arrester FV1 is a zinc oxide surge arrester.

8. A damped amplitude-phase correction device for flexible DC transmission and transformation according to claim 1, characterized in that, The resistor unit R1 is a filter resistor with a stainless steel housing and built-in metal wire.

9. A damped amplitude-phase correction device for flexible DC transmission and transformation according to claim 1, characterized in that, When the output voltage on the AC grid side is 500KV, the rated capacitance of the first frequency doubling filter capacitor unit C1 is 3.112μF; the rated capacitance of the second frequency doubling filter capacitor unit C2 is 200μF; the rated inductance of the low-noise adjustable inductance reactor unit L1 is 50.66mH; and the rated resistance of the resistor unit R1 is 826.9Ω.

10. A flexible DC transmission and transformation system, characterized in that, It includes at least one damped amplitude and phase correction device for flexible DC transmission and transformation as described in any one of claims 1 to 9.

Images