CN-121983993-A - High-frequency oscillation suppression method and device for MMC-HVDC system

Abstract

The invention discloses a high-frequency oscillation suppression method and device for an MMC-HVDC system, which belong to the technical field of stable control of a flexible direct current transmission system, and are used for constructing a system high-frequency impedance model containing delay aiming at the problem that the control link delay causes MMC non-minimum phase characteristics and further causes 1000-2500Hz high-frequency oscillation, defining an oscillation mechanism leading by the non-minimum phase characteristics, connecting a three-order high-pass filter in parallel with PCC points of an MMC and alternating current power grid, optimizing filter parameters to realize-90 DEG phase compensation in a negative damping interval, reducing fundamental wave active power loss, researching impedance characteristics by an impedance detection method, judging high-frequency oscillation risk and verifying remodelling effect to suppress oscillation.

Inventors

• SUN YINFENG
• HAO JIAQI
• LU MINGZHI
• JIANG TAO
• ZHANG CHUNSHENG
• ZHAO ZHI
• XIN YECHUN
• LI PEIYUAN
• Qi Yanran

Assignees

• 东北电力大学

Dates

Publication Date

20260505

Application Date

20260407

Claims (10)

1. 1. A high-frequency oscillation suppression method of an MMC-HVDC system, characterized by comprising: (1) Constructing a high-frequency impedance model of the MMC-HVDC system with control link delay, researching MMC equivalent impedance and AC power grid equivalent impedance through an impedance detection method, determining a high-frequency oscillation mechanism which is not dominant by the minimum phase characteristic, and analyzing whether the MMC-HVDC system generates high-frequency oscillation or not; (2) A third-order high-pass filter is connected in parallel at a common connection point PCC of the MMC and the alternating current power grid; (3) The parameters of the third-order high-pass filter are optimally designed, so that the third-order high-pass filter provides-90 DEG phase compensation, and active power loss under fundamental wave frequency is reduced; (4) And the MMC equivalent impedance and the AC power grid equivalent impedance are researched through an impedance detection method, the remolding effect of the third-order high-pass filter on the MMC-HVDC system equivalent impedance is verified, and the inhibition of the MMC-HVDC system high-frequency oscillation is realized.
2. 2. The method for suppressing high frequency oscillation of MMC-HVDC system as claimed in claim 1, wherein said constructing a MMC-HVDC system high frequency impedance model with control link delay comprises: Neglecting the influence of phase-locked loop, power outer loop, loop inhibition and current inner loop decoupling on high-frequency impedance, simplifying the control process of MMC, and deducing the open-loop equivalent impedance expression of MMC And closed loop equivalent impedance expression : (1) (2) (3) (4) Wherein, the Is a complex variable representing the frequency in the Laplace transform domain; Is MMC equivalent reactance; A transfer function of the current inner loop PI controller; The gain is the current inner loop proportion gain; Integrating gain for the inner loop of the current; And Voltage feedforward delay and current measurement delay of the MMC-HVDC system respectively; And (3) with The time of voltage feedforward delay and current measurement delay of the MMC-HVDC system are respectively; Is the base of natural logarithms.
3. 3. The method for suppressing high-frequency oscillation of MMC-HVDC system according to claim 2, wherein said researching MMC equivalent impedance and ac grid equivalent impedance by impedance detection method, determining a high-frequency oscillation mechanism not dominant by minimum phase characteristics, analyzing whether high-frequency oscillation occurs in MMC-HVDC system specifically comprises: Phase margin For evaluating the stability of an MMC-HVDC system: (5) Wherein, the Equivalent impedance of an alternating current power grid; Requiring taking out And (3) with Amplitude curve intersection point frequency; equivalent impedance phase of the alternating current power grid; The phase is MMC equivalent impedance phase; according to the Nyquist stability criterion, when When >0, the MMC-HVDC system can stably operate according to Will (C) be The expression is rewritten as a stability criterion for MMC-HVDC system oscillation: (6) as the frequency is increased, Is much larger in amplitude than The amplitude of (2) and therefore the MMC phase is mainly dependent on The voltage feedforward delay is approximately represented by a first-order pad expansion approximation: (7) obtaining an equivalent impedance ratio expression containing the right half plane zero point : (8) (9) (10) Wherein, the Is the equivalent impedance in the MMC; a non-minimum phase zero influence factor introduced for the voltage feed-forward delay; The phase of (2) is determined by the difference between the numerator and denominator, thus Is of the phase of (a) Expressed as: (11) Wherein, the Is an imaginary unit; is angular frequency; The MMC has the advantages that the MMC has the high-frequency equivalent impedance phase, the MMC has the additional phase offset due to the non-minimum phase characteristic of the MMC, the MMC has the non-minimum phase characteristic due to the definite control link delay, the zero point of the right half plane expands the high-frequency oscillation frequency range, the MMC has the negative damping characteristic due to the impedance phase larger than 90 degrees, and the high-frequency oscillation is induced when the capacitive impedance phase difference of the MMC and the alternating current network exceeds 180 degrees.
4. 4. The method for suppressing high-frequency oscillation of MMC-HVDC system according to claim 1, wherein said third-order high-pass filter is connected in parallel at the common connection point PCC of MMC and ac grid, specifically comprising: the third-order high-pass filter is composed of two parts connected in series and comprises a capacitor Inductance Resistance of resistor And a capacitor Connected in parallel at the common connection point PCC, wherein the first part is a capacitor A second part is a resistor And a capacitor Series branch and inductor The third-order high-pass filter is connected to a PCC corresponding phase high-voltage bus in one-to-one parallel at A, B, C three-phase input ends, and the third-order high-pass filter is in parallel connection with an MMC grid-connected main loop and an alternating current grid side loop; The third-order high-pass filter provides-90 deg. phase cancellation The phase gain is brought about by The phase difference between MMC and the equivalent impedance of the alternating current power grid is reduced to be within 180 degrees.
5. 5. The method for suppressing high-frequency oscillation of MMC-HVDC system as claimed in claim 4, wherein said optimizing parameters of third-order high-pass filter comprises: Determining capacitance according to reactive power demand of MMC-HVDC system The value of (2) satisfies Wherein The power frequency is MMC-HVDC system power frequency; rated voltage for MMC-HVDC system; Reactive power for MMC-HVDC system; Design inductance To take the value of (1) to make the capacitance And inductor Tuning angular frequency at target Resonance at the position meeting ; Setting resistance And capacitor The impedance of the series branch at the fundamental frequency is higher than the inductance Is satisfied by the impedance of , The fundamental wave active power loss is reduced; Through Routh criteria, it is verified that the impedance transfer function of the third-order high-pass filter has no right half plane zero point, the third-order high-pass filter is ensured to be a minimum phase system, and the requirements are met , , 。
6. 6. The method for suppressing high frequency oscillation of MMC-HVDC system in accordance with claim 5, wherein said capacitor The value of (2) is 3.6 mu F, and the inductance The value of (2) is 2814mH, resistance The value of (2) is 1250 omega or more, and the capacitance The value of (2) is less than or equal to 3.6 mu F.
7. 7. The method for suppressing high frequency oscillations of an MMC-HVDC system according to claim 1, characterized in that said control link delay ranges from 400 to 600 μs, corresponding to a negative damping interval of 1000 to 2500Hz of the MMC system.
8. 8. The method for suppressing the high-frequency oscillation of the MMC-HVDC system according to claim 1, wherein the method for detecting the impedance is used for researching the MMC equivalent impedance and the AC power grid impedance, and verifying the remodeling effect of the third-order high-pass filter on the MMC-HVDC system equivalent impedance is that the phase difference between the MMC equivalent impedance and the AC power grid impedance is smaller than 180 degrees, so that the negative damping characteristic of the system is eliminated, and the occurrence of the high-frequency oscillation is avoided.
9. 9. An apparatus for implementing the method for suppressing high frequency oscillations of the MMC-HVDC system according to any one of claims 1-8, characterized by comprising: The modeling analysis module is used for constructing a high-frequency impedance model of the MMC-HVDC system with control link delay and determining a high-frequency oscillation mechanism which is not dominant by the minimum phase characteristic; The parameter optimization module is used for optimally designing parameters of the third-order high-pass filter, so that the parallel third-order high-pass filter can effectively inhibit high-frequency oscillation, the fundamental frequency active power loss is the lowest, and the fact that the impedance transfer function of the third-order high-pass filter has no right half plane zero point is verified; And the impedance analysis and verification module is used for researching MMC equivalent impedance and AC power grid equivalent impedance, analyzing whether the MMC-HVDC system generates high-frequency oscillation or not, and verifying the remolding effect of the third-order high-pass filter on the MMC-HVDC system equivalent impedance.
10. 10. The apparatus according to claim 9, wherein: The modeling analysis module comprises a high-frequency impedance model building unit and a high-frequency oscillation analysis unit; the high-frequency impedance model building unit is used for building a high-frequency impedance model of an MMC-HVDC system with control link delay; The analysis high-frequency oscillation unit is used for researching MMC equivalent impedance and AC power grid equivalent impedance through an impedance detection method, determining a high-frequency oscillation mechanism which is not dominant by the minimum phase characteristic and analyzing whether the MMC-HVDC system generates high-frequency oscillation or not; The parameter optimization module comprises a third-order high-pass filter parameter optimization unit and a third-order high-pass filter impedance verification unit; The parameter optimization unit of the third-order high-pass filter is used for optimally designing parameters of the third-order high-pass filter, so that the third-order high-pass filter provides-90 DEG phase compensation in a 1000-2500Hz negative damping interval, and meanwhile active power loss under fundamental wave frequency is reduced; the verification third-order high-pass filter impedance unit is used for verifying that the third-order high-pass filter impedance transfer function has no right half plane zero point through Routh criteria, and ensuring that the third-order high-pass filter is a minimum phase system; The impedance analysis and verification module comprises an impedance analysis unit and a verification module unit; The impedance analysis unit is used for researching MMC equivalent impedance and AC power grid equivalent impedance through an impedance detection method after the three-order high-pass filter is connected in parallel at the common connection point PCC of the MMC and the AC power grid; the verification module unit is used for verifying the remodeling effect of the third-order high-pass filter on the equivalent impedance of the MMC-HVDC system and realizing the inhibition of the high-frequency oscillation of the MMC-HVDC system.

Description

High-frequency oscillation suppression method and device for MMC-HVDC system Technical Field The invention belongs to the technical field of stable control of a flexible direct current transmission system, relates to a method and a device for suppressing high-frequency oscillation of an MMC-HVDC system, and particularly relates to a passive damping suppression method and a device for the high-frequency oscillation of the MMC-HVDC system caused by non-minimum phase characteristics caused by control link delay. Background The modular multilevel converter high-voltage direct current (MMC-HVDC) is a core scheme for realizing long-distance and large-scale grid connection of renewable energy sources in a modern flexible direct current transmission system. With the wide application of flexible direct current engineering, the potential high-frequency oscillation problem is gradually developed, and the safe and stable operation of the system is seriously threatened, so that the research on the high-frequency oscillation inhibition of the MMC-HVDC system becomes an important direction in the field of power systems. In the prior art, the inhibition strategy aiming at the high-frequency oscillation of the MMC-HVDC system is mainly divided into two types, namely active impedance remodeling and passive impedance remodeling, wherein the active impedance remodeling method is used for inhibiting through adding a filter or a control loop in the MMC system, but negative damping cannot be eliminated in a full frequency range, the system is easy to excite new oscillation when the working condition of a power grid changes, and the passive impedance remodeling method is used for inhibiting through blocking the oscillation of a specific frequency if a high-pass filter is added, so that the robustness is stronger, but the traditional passive filter can introduce obvious active power loss under the fundamental frequency, and the engineering practicability is limited. It has been found that MMC exhibits typical non-minimum phase characteristics (e.g., right half-plane zero, phase hysteresis) at the high frequency band, which are one of the sources of high frequency oscillation, and this characteristic is mainly caused by system control link delay. The MMC becomes a non-minimum phase system due to control link delay, the frequency range of high-frequency oscillation is enlarged due to the existence of a right half plane zero point, the MMC impedance presents negative damping characteristics, when the MMC presents the negative damping characteristics, inductive impedance coupling is carried out on the MMC and an alternating current system, the phase difference of the MMC and the alternating current system exceeds 180 degrees, and the high-frequency oscillation in the interval of 1000-2500Hz is easily excited. At present, research on MMC-HVDC high-frequency oscillation suppression with dominant non-minimum phase characteristics still has the defects, the influence of the non-minimum phase characteristics is not fully considered by the existing suppression strategy, effective phase compensation and negative damping elimination are difficult to realize, meanwhile, fundamental wave active power loss is reduced, and the adaptability to different power grid working conditions is poor. Therefore, it is needed to construct a high-frequency oscillation suppression scheme adapting to the non-minimum phase characteristics of the MMC, so that the fundamental wave power loss is reduced and the adaptability to different power grid working conditions is improved while the wide-frequency-band effective oscillation suppression is realized. Disclosure of Invention The invention aims to solve the problems of residual negative damping, overlarge fundamental active power loss and poor adaptability to power grid working conditions of the conventional MMC-HVDC system high-frequency oscillation suppression strategy, and provides a high-frequency oscillation suppression method and device for the MMC-HVDC system, which aim to define an oscillation mechanism which is not the minimum phase characteristic dominant from the impedance interaction angle, realize accurate phase compensation and impedance remodeling through a passive damping scheme, effectively suppress high-frequency oscillation, reduce fundamental active power loss at the same time, and do not degrade steady-state power control and transient fault response of the system. In order to achieve the above purpose, the present invention provides the following technical solutions: a high frequency oscillation suppression method of an MMC-HVDC system, comprising: (1) Constructing a high-frequency impedance model of the MMC-HVDC system with control link delay, researching MMC equivalent impedance and AC power grid equivalent impedance through an impedance detection method, determining a high-frequency oscillation mechanism which is not dominant by the minimum phase characteristic, and analyzing whether the MM