CN-122019927-A - Flexible direct-current leveling modeling method considering negative sequence control and amplitude limiting links

CN122019927ACN 122019927 ACN122019927 ACN 122019927ACN-122019927-A

Abstract

The invention relates to the technical field of electric power systems and automation thereof, in particular to a flexible direct-current leveling modeling method considering negative sequence control and amplitude limiting links, which comprises the following steps of S1, establishing a stabilized double-loop state space equation by decomposing MMC period time-varying state quantity into a differential mode component and a common mode component through multi-frequency coordinate transformation, S2, realizing positive and negative sequence separation of voltage/current through a dynamic equation aiming at a negative sequence control system containing DDSRF-PLL, and S3, continuously converting step switch characteristics of the amplitude limiting links through a continuous approximation tool. By constructing an average state space model containing negative sequence control and amplitude limiting links, the problems of complex calculation and insufficient dynamic accuracy of MMC-HVDC modeling are solved.

Inventors

LIU HANG
ZHAO PEILIN
CHEN QIAN
Liao Fangqun
HUANG YILONG
ZHANG PEIRAN
ZOU YANSHENG
ZHANG NAN
Hong Quanwei
HUANG YUNFENG

Assignees

中国南方电网有限责任公司超高压输电公司电力科研院

Dates

Publication Date: 20260512
Application Date: 20251205

Claims (15)

1. A flexible direct-current leveling modeling method considering negative sequence control and amplitude limiting links is characterized by comprising the following steps: s1, transforming and constructing a differential mode-common mode double-loop averaging model of the MMC; Decomposing the MMC periodic time-varying state quantity into a differential mode component and a common mode component through multi-frequency coordinate transformation, establishing a stabilized double-loop state space equation, and providing a power circuit dynamic basis for modeling of a subsequent control link; step S2, establishing an average state space model of an MMC negative sequence control link; for a negative sequence control system comprising DDSRF-PLL, voltage/current positive and negative sequence separation is realized through a dynamic equation, a negative sequence current PI controller is designed and is converted into a standard dq coordinate system, and the dynamic characteristic of a negative sequence control link is completely represented; step S3, establishing an average state space model of the limiting link; The step switch characteristic of the amplitude limiting link is continuous through a continuous approximation tool, and then is integrated with the integrating link and the output link of the PI controller to reflect the amplitude limiting dynamic process under large disturbance.
2. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 1, wherein step S1 comprises: s1.1, analyzing a state equation of an MMC power circuit, and determining common mode and differential mode components; deducing an original state space equation based on MMC main loop topology, and separating common mode components and differential mode components through harmonic analysis; S1.2, realizing system stabilization by applying multi-frequency Park conversion; designing a multi-frequency Park transformation matrix based on state quantity harmonic characteristics, and converting time-varying state quantity into a rotating coordinate system to realize stabilization; Step S1.3, deducing an average state space equation; substituting the coordinate transformation result into an original state equation, and establishing a differential mode-common mode double-loop steady model after simplification to realize the average modeling of the MMC power circuit.
3. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 1, wherein step S2 comprises: s2.1, constructing DDSRF-PLL (phase locked loop) averaging model; Establishing DDSRF-PLL dynamic equation containing a PI controller, and realizing positive and negative sequence separation and synchronous phase tracking of the voltage; S2.2, establishing a positive and negative sequence current separation link model; adopting a coordinate transformation method similar to voltage separation to separate positive and negative sequences of alternating current, and providing a feedback signal for negative sequence current control; S2.3, deducing a negative sequence current control link model; and designing a PI controller based on the separated negative sequence current component, generating a negative sequence modulation signal, converting the negative sequence modulation signal into an abc coordinate system, and superposing the negative sequence modulation signal into a positive sequence modulation signal.
4. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 1, wherein step S3 comprises: step S3.1, defining a mathematical model of an amplitude limiting link; Defining a piecewise function description limiting characteristic, and designing a step switch function to represent a limiting state; s3.2, realizing continuous modeling of the limiting link; adopting a tanh activation function to perform continuous approximation on the switching function, and converting the step characteristic into a continuous derivative function; s3.3, integrating the amplitude limiting model into the PI controller; And establishing an integral link amplitude limiting dynamic equation, regulating an integral term through a continuous switching function, synthesizing PI output containing external amplitude limiting, and distinguishing integral amplitude limiting logic from output amplitude limiting logic.
5. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 2, wherein step S1.1 comprises: s1.1.1, establishing an MMC original state space equation; based on an MMC main loop topological structure, deriving differential equations of voltage and current according to kirchhoff's law, and forming a first-order differential equation set containing state quantities such as bridge arm current, capacitor voltage and the like; step S1.1.2, identifying state quantity harmonic characteristics; And carrying out harmonic analysis on the steady-state solution of the original state space equation, and identifying harmonic components of each state quantity.
6. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 5, wherein step S1.2 comprises: s1.2.1, deriving a general Park transformation matrix; Defining a rotational coordinate system transformation matrix The method comprises cosine/sine items and zero sequence components, and the concrete form is as follows: ; Wherein, the For the electrical angle of the rotating coordinate system, the first and second behavior dq-axis transformation components of the matrix and the third behavior zero sequence component (z-axis) are used for realizing the conversion from the three-intersection flow to the direct flow of the rotating coordinate system; step S1.2.2, forward sequence dq conversion of the differential mode component; based on the differential mode component harmonic characteristics identified in step S1.2.1, application The positive sequence Park transformation matrix of (2) performs coordinate transformation on the differential mode component, separates the differential mode component into dqz coordinate systems, converts the fundamental frequency positive sequence component into direct current quantity, and stores the frequency tripling zero sequence component temporarily in the z axis; Step S1.2.3, carrying out negative sequence double frequency conversion on common mode components; Direct current and double frequency negative sequence characteristic for common mode component and application The common mode component is converted into a negative sequence double frequency dq coordinate system to realize the stabilization of direct current and double frequency components; Step S1.2.4, triple frequency zero sequence component separation; Orthogonal coordinate transformation is carried out on the three-fold frequency zero sequence component of the z axis after the positive sequence transformation, by passing through Decomposing into d/q axis direct current quantity to finish the steady conversion of all differential mode components, wherein: And Is that D-axis component and q-axis component in a frequency tripled rotating coordinate system.
7. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 6, wherein step S1.3 comprises: step S1.3.1, substituting the coordinate transformation result into an original equation; Substituting the differential mode, common mode and zero sequence component conversion results obtained by multi-frequency Park conversion in the step S1.2 into an MMC original state space equation established in the step S1.1.1 to construct a composite dynamic equation containing coordinate conversion; step S1.3.2, simplifying the equation and ignoring higher harmonics; Developing a composite dynamic equation and applying the secondary side high-resistance grounding condition of the converter transformer ) Neglecting The higher harmonic component is eliminated to obtain a stabilized equation; Step S1.3.3, establishing a differential mode-common mode double-loop model; based on simplified stabilized equation, respectively deducing dynamic equations of differential mode loop and common mode loop to form double loop structure, wherein the double loop structure passes through modulation ratio component # ) And the coupling is used for jointly forming an average state space model of the MMC power circuit.
8. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 3, wherein step S2.1 comprises: step S2.1.1, establishing a phase-locked loop dynamic equation; based on the decoupling double synchronous reference frame phase-locked loop structure, a dynamic equation containing a Proportional Integral (PI) controller is designed: , ; Wherein, the For the PI controller proportional/integral coefficient, Is a positive sequence q-axis voltage component, In order for the phase to be offset, The output is the integral link, and the tracking of the frequency and the phase of the power grid is realized through the phase error adjustment; S2.1.2, realizing positive and negative sequence voltage separation; using phase information output by a phase-locked loop Respectively carrying out positive sequence on the three-phase voltages ) And negative sequence% ) Park conversion, eliminating high-frequency disturbance by combining a low-pass filter, and deducing a state space equation of a voltage separation link: , ; Wherein, the For the filter cut-off frequency to be the same, As a component of the positive sequence voltage dq, And the negative sequence voltage dq component is used for realizing the separation and extraction of the positive sequence voltage and the negative sequence voltage.
9. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 8, wherein step S2.2 comprises: step S2.2.1, current signal Park conversion; Synchronous phase output by step S2.1 Respectively carrying out positive sequence on three-phase current ) And negative sequence% ) Park transformation to obtain current component in dq coordinate system (Positive sequence) (Negative sequence); step S2.2.2, deducing a state equation of a separation link; the reference voltage separation link structure is used for designing a state space equation containing a low-pass filter, filtering and separating current signals after Park conversion, and eliminating cross coupling components: ; Wherein, the Ensuring separated negative sequence current components for filter cut-off frequency No positive sequence interference.
10. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 9, wherein step S2.3 comprises: step S2.3.1, designing a negative sequence PI controller; Negative sequence current component separated based on step S2.2 A proportional-integral (PI) controller is designed to regulate deviation of a current command and a feedback value, and a dq component of a negative sequence modulation signal is generated: , ; Wherein, the Is a negative sequence d-axis current command, For the output of the integration section, For a negative sequence d-axis modulation signal, the q-axis is similar; Step S2.3.2, controlling signal coordinate transformation; Synchronous phase output by step S2.1 The dq component of the negative sequence modulated signal is converted to the abc coordinate system by Park inverse transformation: ; Superimposed with positive sequence modulation signal and circulation suppression signal to form modulation ratio of upper bridge arm and lower bridge arm of MMC 、。
11. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 4, wherein step S3.1 comprises: step S3.1.1, defining a piecewise function; Definition of the upper limit value ) And lower limit value% ) Is a piecewise function of: ; Wherein u is the input of the amplitude limiting link, y is the output, when the input exceeds the limit, the threshold is output, otherwise, the input signal is directly output; Step S3.1.2, designing a switch function logic; Designing step switch function , ) Characterization of clipping states when u > Time of day =1, When u < Time of day =1, Within normal range The limited output can be expressed as 。
12. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 11, wherein step S3.2 comprises: step S3.2.1, setting tanh activation function parameters; selecting tanh activation function as serialization tool, and setting smoothing factor Controlling the transition characteristics, the switching function successive approximation is expressed as: , ; controlling the steepness of the transition region by a smoothing factor A, ensuring rapid transition near a threshold value, and keeping the function continuously conductive; Step S3.2.2, continuously approximating a switching function; Step switch function [ ] , ) Converting into a continuous conductive function, substituting into a limiting output expression to obtain: and eliminating discontinuous points and realizing smooth modeling of the amplitude limiting link.
13. The flexible direct current leveling modeling method considering negative sequence control and limiting links according to claim 12, wherein step S3.3 comprises: Step S3.3.1, integrating a link limiting model; based on continuous switch function , ) Establishing an integral link dynamic equation, and inhibiting integral growth through feedback regulation when an integral term exceeds a limit: ; Wherein, the For the output of the integration section, The deviation is input to the PI controller and, As an integral coefficient of the power supply, To limit the feedback coefficient , ) Limiting the amplitude limiting switch function for an integration link; Step S3.3.2, synthesizing external amplitude limiting and PI output; Overlapping the integral term after clipping with the proportional term, performing secondary clipping through an external clipping link, and synthesizing the output of the PI controller: ; Wherein, the Is a coefficient of proportionality and is used for the control of the power supply, And And (3) distinguishing integrating amplitude limiting logic from output amplitude limiting logic for an external amplitude limiting threshold value, and accurately reflecting the amplitude limiting dynamic process under large disturbance.
14. A data processing apparatus, comprising: A memory for storing a computer program; A processor for implementing the steps of a flexible direct current leveling modeling method taking into account negative sequence control and clipping links as defined in any one of claims 1 to 13 when executing said computer program.
15. A computer readable storage medium, characterized in that the computer readable storage medium has stored thereon a computer program which, when executed by a processor, implements the steps of a flexible direct-current leveling modeling method taking into account negative sequence control and clipping links as claimed in any one of claims 1 to 13.

Description

Flexible direct-current leveling modeling method considering negative sequence control and amplitude limiting links Technical Field The invention relates to the technical field of power systems and automation thereof, in particular to a flexible direct-current leveling modeling method considering negative sequence control and amplitude limiting links. Background The modular multilevel converter (Modular Multilevel Converter, MMC) is used as an advanced voltage source converter, and has become a core technology in the field of high-voltage direct current (High Voltage Direct Current, HVDC) power transmission due to the advantages of high output waveform quality, low loss, strong fault handling capability and the like. With the development of the power system towards high voltage, large capacity and high power electronics, MMC-HVDC is widely applied in the scenes of inter-regional power grid interconnection, new energy grid connection and the like, such as important projects of national power grid Yubei direct current engineering, world first flexible direct current power grid North-opening flexible direct current engineering, south power grid Luxi back-to-back flexible direct current engineering and the like. However, as MMC-HVDC voltage levels and capacities increase, system stability issues are increasingly prominent. Harmonic resonance phenomena are observed for many times in engineering practice, namely 700Hz and 1800Hz resonance occurs in the national power grid Yubei direct current engineering, about 1500Hz high-frequency resonance occurs in the Zhangbei flexible direct current engineering in the alternating current side charging process of the Kangbao station, and about 1200Hz resonance occurs when the Luxi back-to-back flexible direct current engineering is connected into a weak alternating current system. The resonance problems not only affect the electric energy quality, but also form a serious threat to the safe and stable operation of the power grid, and the importance of accurately modeling and analyzing MMC-HVDC dynamic characteristics is highlighted. The accurate modeling of MMC-HVDC systems is the basis for analyzing resonance mechanisms and proposing inhibition strategies. Because MMC has a period time-varying steady state solution characteristic, a harmonic state space method is mostly adopted for modeling in the prior art. According to the method, the time-varying system is converted into the linear steady system by carrying out frequency dimension-increasing processing on the full-order state equation of the system, so that harmonic characteristic analysis is realized. However, the modeling method has the obvious defects that on one hand, the dimension of the model is extremely high due to the frequency dimension increase, the calculation complexity is exponentially increased, the model is difficult to apply to simulation and analysis of a large-scale power system, and on the other hand, the model has poor expandability and cannot flexibly adapt to MMC-HVDC systems with different topological structures or control strategies. Meanwhile, the existing averaging state space model simplifies the modeling process to a certain extent, but fails to fully calculate key control links in engineering practice. The method is characterized in that firstly, a widely applied negative sequence control system is omitted, the system realizes positive and negative sequence separation of voltage/current through a decoupling double synchronous reference frame phase-locked loop (DDSRF-PLL), the stability of the system under unbalanced working conditions is critical, and secondly, an amplitude limiting link in a PI controller is not considered, and the link can trigger nonlinear switching characteristics under large disturbance to directly influence the dynamic response precision of the system. The defects cause that the existing model cannot accurately represent the dynamic behavior of MMC-HVDC under complex working conditions, and the requirements of engineering design and stability analysis are difficult to meet. In summary, the current MMC-HVDC modeling technology has double challenges that on one hand, the traditional harmonic state space method has high calculation cost and poor expandability due to frequency dimension increase, and on the other hand, the traditional averaging model has insufficient dynamic precision due to omitting negative sequence control and amplitude limiting links, and cannot cope with a large disturbance scene. Therefore, there is a need for an MMC-HVDC state space modeling method that combines modeling accuracy and computational efficiency to address the limitations of the prior art in engineering applications. Disclosure of Invention Aiming at the problems, the flexible direct current leveling modeling method considering the negative sequence control and limiting links is provided, and the problems of complex calculation and insufficient dynamic accuracy of MMC-HVDC modeling are s