Modeling method for multi-time-scale small-signal frequency domain impedance model of offshore wind and light storage channel flexible direct transmission system

Abstract

The invention belongs to the technical field of offshore new energy grid-connected power generation systems, and particularly discloses a method for modeling a multi-time-scale small-signal frequency domain impedance model of an offshore wind and light storage flexible direct transmission system, which considers the influence of offshore environmental factors, realizes multi-time-scale coupling control of offshore wind and light storage and multi-port system coupling, and realizes multi-time-scale small-signal frequency domain impedance modeling of the offshore wind and light storage flexible direct transmission system. A method based on harmonic linearization is adopted to establish a model of an offshore wind and light storage channel flexible direct transmission system so as to analyze impedance characteristics of the system and provide a theoretical basis for research of a broadband oscillation mechanism of the system; the harmonic linearization-based impedance modeling method for the offshore wind and light storage flexible direct transmission system has the advantages of clear physical concept, high engineering applicability, capability of reflecting impedance characteristics of the system and the like, so that the method has extremely high practicability in engineering practice and can be applied to impedance modeling of the offshore wind and light storage flexible direct transmission system.

Description

Technical Field

[0001] This invention relates to the field of offshore new energy grid-connected power generation system technology, and in particular to a multi-time-scale small-signal frequency domain impedance modeling method for offshore wind-solar-storage-flexible direct transmission systems. Background Technology

[0002] With the rapid development of clean energy sources such as wind power and photovoltaics, offshore wind power, offshore photovoltaics, and offshore energy storage have been vigorously developed and practiced in my country due to their advantages such as high power generation efficiency and low land occupation. my country's development status of "resources and loads being inversely distributed" has also promoted the increasingly widespread application scenarios of multiple complementary new energy sources via flexible direct current transmission. However, in the complex grid structure where multiple types of power sources such as offshore wind power, offshore photovoltaics, and offshore energy storage are transmitted through flexible direct current systems and connected to onshore power grids with a large number of asynchronous power sources, the dynamic characteristics of the system are more complex, and the diverse coupling effects between the receiving and receiving grids of flexible direct current transmission can easily lead to broadband oscillation risks.

[0003] Unlike onshore renewable energy transmission via flexible DC systems, offshore renewable energy units and flexible DC transmission systems have more complex control structures and are affected by more factors. Furthermore, the offshore operating environment is more complex and variable, leading to more severe power output fluctuations in offshore renewable energy units. Additionally, the ground capacitance effect of submarine cables exacerbates the risk of broadband oscillations. Therefore, offshore wind, solar, and energy storage systems differ significantly from onshore renewable energy units in terms of grid configuration and system stability. Establishing a system model is fundamental and crucial for analyzing the broadband oscillation mechanism and studying system stability. Therefore, research on frequency domain impedance modeling methods for offshore wind, solar, and energy storage transmission systems via flexible DC systems is particularly important.

[0004] Current research on the scenario of multiple complementary offshore renewable energy sources transmitted via flexible direct current (FDDC) mainly focuses on the transmission of a single renewable energy source via FDDC, with an emphasis on the transmission system side. Modeling and researching complex scenarios involving complementary transmission of multiple offshore power sources connected to onshore power grids with asynchronous power sources is a pressing issue. Therefore, establishing a multi-timescale small-signal frequency domain impedance model for offshore wind, solar, and energy storage FDDC transmission systems is the challenge this invention aims to address. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a modeling method for a multi-timescale small-signal frequency domain impedance model of a marine wind-solar-storage-flexible direct transmission system. This method combines the characteristics of the marine environment, considers multi-timescale coupled control and multi-port system coupling, and establishes a small-signal frequency domain impedance model for a marine multi-type complementary power source-flexible direct transmission system. This enables the analysis of the system's impedance characteristics and provides a theoretical basis for analyzing the system's broadband oscillation mechanism and constructing the system's stable operating range.

[0006] To achieve the above objectives, the present invention is implemented according to the following technical solution:

[0007] This invention employs a "from local to global" modeling strategy, performing small-signal frequency domain impedance modeling on each functional module of the wind power, photovoltaic, energy storage, and flexible DC systems, and then using structural superposition to form the equivalent impedance expression of the overall system. The modeling steps and impedance expressions for each module are as follows:

[0008] A multi-timescale small-signal frequency domain impedance modeling method for offshore wind-solar-storage-flexible direct transmission systems, comprising the process of establishing four sub-models and the process of combining the four established sub-models;

[0009] Among them, the four sub-models are the impedance model of offshore wind power system, the impedance model of photovoltaic system, the impedance model of energy storage system, and the impedance model of flexible direct transmission system;

[0010] (1) Impedance model of offshore wind power system;

[0011] This invention uses the Permanent Magnet Synchronous Generator (PMSG) as an example, primarily considering the impedance characteristics of its grid-side converter (GSC) and its controller in the frequency domain. Ignoring the influence of the generator-side converter, the impedance model of the wind power system is constructed from the GSC stage and combined with the DC-side output impedance.

[0012] The small-signal frequency domain impedance expression for a wind power system is:

[0013] Y PMSG (s)=C PMSG +[I-(P1E1′+P3)]·[L PMSG -(P1E1′L PMSG +P1E2′+P2)] -1

[0014] Where: Y PMSG (s) represents the output impedance of the wind power system in the frequency domain; C PMSG The initial bias term for wind resistance impedance reflects the steady-state DC component; I is the identity matrix; the coefficient matrix P1 represents the modulation effect of the wind power system voltage loop and current loop on the DC voltage harmonics, P2 represents the modulation effect of the wind power system current loop on the current harmonics, and P3 represents the influence of the wind power system current loop on the modulation signal harmonics; E′1 is the relationship between the wind power system GSC output voltage harmonics and the DC voltage harmonics, and E′2 is the relationship between the wind power system GSC output current harmonics and the DC voltage harmonics; L PMSG This is the inductance matrix for wind power filtering.

[0015] (2) Impedance model of photovoltaic system;

[0016] Offshore photovoltaic systems typically employ a structure of "photovoltaic array + boost converter + three-phase inverter". Since the dynamic characteristics of the boost converter have a relatively small impact on the AC side, it can be modeled as a constant voltage source, and only the grid-connected inverter is modeled, with its structure consistent with the GSC model of wind power systems.

[0017] Therefore, the impedance expression for a photovoltaic system is:

[0018] Y PV (s)=C PV +[I-(P4E3′+P6)]·[L PV -(P4E3′L PV +P4E4′+P5)] -1

[0019] Where: Y PV (s) represents the output impedance of the photovoltaic system in the frequency domain; C PV The initial bias term for photovoltaic impedance reflects the steady-state DC component; I is the identity matrix; coefficient matrix P4 represents the modulation effect of the photovoltaic system voltage loop and current loop on the DC voltage harmonics, P5 represents the modulation effect of the photovoltaic system current loop on the current harmonics, and P6 represents the influence of the photovoltaic system current loop on the modulation signal harmonics; E′3 is the relationship between the photovoltaic system GSC output voltage harmonics and the DC voltage harmonics, and E′4 is the relationship between the photovoltaic system GSC output current harmonics and the DC voltage harmonics; L PV This is a photovoltaic filter inductor matrix.

[0020] (3) Impedance model of energy storage system;

[0021] The energy storage system adopts a control structure with power control as the outer loop and current control as the inner loop, while also considering the effects of active damping and phase-locked loop on frequency domain characteristics. The frequency domain impedance model of the energy storage converter is as follows:

[0022] Y ES (s)=[G si (s)·(1+H zv (s))·Z f (s)] -1

[0023] in: For the inner loop PI controller of energy storage current, K si,p K si,i These are the proportional and integral coefficients of the controller, respectively. For energy storage active damping controller, G N (s) is an energy storage notch filter, R v Z represents the virtual damping coefficient for energy storage. f (s)=R f +sLf The impedance of the energy storage output filter is E. f For the filter resistor, L f For the filter inductance, s represents the complex variable in the complex plane. (4) Impedance modeling of the flexible direct current transmission system (MMC-HVDC)

[0024] The flexible DC system employs a Modular Multilevel Converter (MMC). AC side impedance modeling needs to consider current control, circulating current control, and phase-locked loop (PLL). The frequency domain admittance expression for the MMC is:

[0025]

[0026] Where: E is the identity matrix; Y L Q represents the line impedance. c Q i For the MMC output current control and circulating current control related matrices; V u ,I u M u These represent the upper arm voltage, current, and modulation coefficient of the MMC; Z c is the capacitor impedance of the submodule; P is the current controller gain matrix; K is the control decoupling matrix.

[0027] (5) Overall system impedance integration

[0028] After modeling each module, the overall system impedance model is superimposed in the frequency domain using a series-parallel connection of different power supply modules. The final overall system impedance expression is as follows:

[0029] Y equ (s)=N wt ·Y PMSG (s)+N pv ·Y PV (s)+N es ·Y ES (s)

[0030] in:

[0031] Y equ (s) represents the equivalent frequency domain impedance of the wind-solar-storage transmission system; N wt N pv N es These represent the number of wind power, photovoltaic, and energy storage units connected to the system, respectively.

[0032] This expression clarifies the impedance contribution ratio of different types of new energy sources, providing fundamental support for impedance matching, stability assessment, and system structure optimization between flexible DC systems and new energy power generation systems.

[0033] This invention belongs to the technical field of offshore renewable energy grid-connected power generation systems. Specifically, it discloses a modeling method for a multi-timescale small-signal frequency domain impedance model of an offshore wind-solar-storage-flexible direct transmission system. Considering the influence of marine environmental factors, multi-timescale coupling control of offshore wind-solar-storage systems, and multi-port system coupling, a harmonic linearization-based method is used to establish a model of the offshore wind-solar-storage-flexible direct transmission system. This model is used to analyze the impedance characteristics of the system and provide a theoretical basis for the study of the system's broadband oscillation mechanism. The harmonic linearization-based impedance modeling method for offshore wind-solar-storage-flexible direct transmission systems has advantages such as clear physical concepts, high engineering applicability, and the ability to reflect the impedance characteristics of the system. Therefore, it has strong practicality in engineering practice and can be applied to impedance modeling of offshore wind-solar-storage-flexible direct transmission systems.

[0034] Compared with existing technologies, this invention considers the differences in structure and control methods brought about by the characteristics of the marine environment to offshore new energy power stations and flexible DC transmission systems. It also considers the impact of multi-timescale coupled control and multi-port system coupling on system modeling, and adopts the harmonic linearization method to establish a small-signal frequency domain impedance model for offshore multi-type complementary power transmission systems via flexible DC transmission. The impedance modeling method for offshore wind, solar and energy storage systems via flexible DC transmission based on harmonic linearization has advantages such as clear physical concepts, high engineering applicability, and the ability to reflect the impedance characteristics of the system. Therefore, it has strong practicality in engineering practice and can be applied to impedance modeling of offshore wind, solar and energy storage systems via flexible DC transmission. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the offshore wind and solar energy storage and direct transmission system of the present invention;

[0036] Figure 2 A block diagram of the multi-time-scale small-signal frequency domain impedance modeling method for the offshore wind-solar-storage-flexible direct transmission system of the present invention;

[0037] Figure 3 This is a frequency sweep diagram of the multi-timescale small-signal frequency domain impedance model for the offshore wind, solar, and energy storage system of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0039] like Figure 1The diagram shows a schematic of an offshore wind-solar-storage-flexible DC transmission system, consisting of offshore wind power, offshore photovoltaic power, offshore energy storage, and a flexible DC transmission system. With the large-scale grid connection of offshore renewable energy via flexible DC structures, the more complex control structures and networking methods of offshore units and flexible DC transmission, along with the offshore working environment, lead to severe fluctuations in renewable energy output. This increases the risk of broadband oscillations in the system, necessitating research into the oscillation mechanism to establish a stable operating range and optimize control. As the foundation for studying oscillation problems, the comprehensiveness and accuracy of system modeling are crucial. Therefore, research on the small-signal frequency domain impedance modeling method for offshore wind-solar-storage-flexible DC transmission systems is particularly critical.

[0040] Based on this, such as Figure 2 As shown in the figure, this embodiment provides a multi-time-scale small-signal frequency domain impedance modeling method for offshore wind-solar-storage-flexible direct transmission systems. The specific method is as follows:

[0041] This invention employs a "from local to global" modeling strategy, performing small-signal frequency domain impedance modeling on each functional module of the wind power, photovoltaic, energy storage, and flexible DC systems, and then using structural superposition to form the equivalent impedance expression of the overall system. The modeling steps and impedance expressions for each module are as follows:

[0042] (1) Impedance model of offshore wind power system;

[0043] This invention uses the Permanent Magnet Synchronous Generator (PMSG) as an example, primarily considering the impedance characteristics of its grid-side converter (GSC) and its controller in the frequency domain. Ignoring the influence of the generator-side converter, the impedance model of the wind power system is constructed from the GSC stage and combined with the DC-side output impedance.

[0044] The small-signal frequency domain impedance expression for a wind power system is:

[0045] Y PMSG (s)=C PMSG +[I-(P1E1′+P3)]·[L PMSG -(P1E1′L PMSG +P1E2′+P2)] -1

[0046] Where: Y PMSG (s) represents the output impedance of the wind power system in the frequency domain; C PMSGThe initial bias term for wind resistance impedance reflects the steady-state DC component; I is the identity matrix; the coefficient matrix P1 represents the modulation effect of the wind power system voltage loop and current loop on the DC voltage harmonics, P2 represents the modulation effect of the wind power system current loop on the current harmonics, and P3 represents the influence of the wind power system current loop on the modulation signal harmonics; E′1 is the relationship between the wind power system GSC output voltage harmonics and the DC voltage harmonics, and E′2 is the relationship between the wind power system GSC output current harmonics and the DC voltage harmonics; L PMSG This is the inductance matrix for wind power filtering.

[0047] (2) Impedance model of photovoltaic system;

[0048] Offshore photovoltaic systems typically employ a structure of "photovoltaic array + boost converter + three-phase inverter". Since the dynamic characteristics of the boost converter have a relatively small impact on the AC side, it can be modeled as a constant voltage source, and only the grid-connected inverter is modeled, with its structure consistent with the GSC model of wind power systems.

[0049] Therefore, the impedance expression for a photovoltaic system is:

[0050] Y PV (s)=C PV +[I-(P4E3′+P6)]·[L PV -(P4E3′L PV +P4E4′+P5)] -1

[0051] Where: Y PV (s) represents the output impedance of the photovoltaic system in the frequency domain; C PV The initial bias term for photovoltaic impedance reflects the steady-state DC component; I is the identity matrix; coefficient matrix P4 represents the modulation effect of the photovoltaic system voltage loop and current loop on the DC voltage harmonics, P5 represents the modulation effect of the photovoltaic system current loop on the current harmonics, and P6 represents the influence of the photovoltaic system current loop on the modulation signal harmonics; E′3 is the relationship between the photovoltaic system GSC output voltage harmonics and the DC voltage harmonics, and E′4 is the relationship between the photovoltaic system GSC output current harmonics and the DC voltage harmonics; L PV This is a photovoltaic filter inductor matrix.

[0052] (3) Impedance model of energy storage system;

[0053] The energy storage system adopts a control structure with power control as the outer loop and current control as the inner loop, while also considering the effects of active damping and phase-locked loop on frequency domain characteristics. The frequency domain impedance model of the energy storage converter is as follows:

[0054] Y ES (s)=[G si (s)·(1+H zv (s))·Zf (s)] -1

[0055] in: For the inner loop PI controller of energy storage current, K si,p K si,i These are the proportional and integral coefficients of the controller, respectively. For energy storage active damping controller, G N (s) is an energy storage notch filter, R v Z represents the virtual damping coefficient for energy storage. f (s)=R f +sL f R is the impedance of the energy storage output filter, where R f For the filter resistor, L f For the filter inductance, s represents the complex variable in the complex plane. (4) Impedance modeling of the flexible direct current transmission system (MMC-HVDC)

[0056] The flexible DC system employs a Modular Multilevel Converter (MMC). AC side impedance modeling needs to consider current control, circulating current control, and phase-locked loop (PLL). The frequency domain admittance expression for the MMC is:

[0057]

[0058] Where: E is the identity matrix; Y L Q represents the line impedance. c Q i For the MMC output current control and circulating current control related matrices; V u ,I u M u These represent the upper arm voltage, current, and modulation coefficient of the MMC; Z c is the capacitor impedance of the submodule; P is the current controller gain matrix; K is the control decoupling matrix.

[0059] (5) Overall system impedance integration

[0060] After modeling each module, the overall system impedance model is superimposed in the frequency domain using a series-parallel connection of different power supply modules. The final overall system impedance expression is as follows:

[0061] Y equ (s)=N wt ·Y PMSG (s)+N pv ·Y PV (s)+N es ·Y ES (s)

[0062] in:

[0063] Y equ (s) represents the equivalent frequency domain impedance of the wind-solar-storage transmission system; N wt N pv N es These represent the number of wind power, photovoltaic, and energy storage units connected to the system, respectively.

[0064] This expression clarifies the impedance contribution ratio of different types of new energy sources, providing fundamental support for impedance matching, stability assessment, and system structure optimization between flexible DC systems and new energy power generation systems.

[0065] This embodiment constructs a multi-timescale small-signal frequency domain impedance model for an offshore wind-solar-storage-flexible direct transmission system. By characterizing the system impedance model, it reflects the impedance characteristics of multiple types of complementary power supply systems under the influence of offshore environmental factors, considering the effects of multi-timescale coupled control and multi-port system coupling, providing a basis for the oscillation analysis of the system in the wide frequency domain.

[0066] Figure 3 This is a frequency sweep diagram of a multi-timescale small-signal frequency domain impedance model for a marine wind-solar-storage-flexible direct transmission system according to an embodiment of the present invention. From... Figure 3 As can be seen, within the frequency sweep range of 1Hz-3000Hz, the sweep results of the amplitude and phase of the positive and negative sequence impedance (admittance) and coupling impedance (admittance) of the simulated system correspond to their theoretical analytical curves. This indicates that the system impedance modeling method of this embodiment can reflect the impedance characteristics of the offshore wind-solar-storage-flexible direct transmission system, and the modeling method is correct.

[0067] In summary, this invention, based on harmonic linearization, considers the impact of the marine environment on the system structure and control methods. Combining the effects of multi-timescale coupled control and multi-port system coupling, it establishes impedance models for offshore wind power, offshore photovoltaic, offshore energy storage, and flexible DC transmission systems. Considering various combinations of complementary power sources at sea, it constructs a multi-timescale small-signal frequency domain impedance model for an offshore wind-solar-storage-flexible DC transmission system in a wide frequency domain. This model reflects the system's impedance characteristics. As a foundation for analyzing the system's wide-frequency oscillation mechanism, it provides a theoretical basis for research on the grid connection and grid security of offshore new energy sources. It achieves multi-timescale small-signal frequency domain impedance modeling for an offshore wind-solar-storage-flexible DC transmission system, solving the problems of incomplete consideration of factors and insufficient refinement in impedance modeling of such systems.

[0068] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

[0069] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for modeling a multi-timescale small-signal frequency domain impedance model of a marine wind-solar-storage-flexible direct transmission system, characterized in that: The method includes the process of establishing four sub-models and the process of combining the four established sub-models; The four sub-models are the impedance model of offshore wind power system, photovoltaic system, energy storage system, and flexible direct transmission system.

2. The modeling method for a multi-timescale small-signal frequency domain impedance model of a marine wind-solar-storage-flexible direct transmission system according to claim 1, characterized in that: In the impedance model of the offshore wind power system, the small-signal frequency domain impedance expression of the wind power system is: Y PMSG (s)=C PMSG +[I-(P1E1′+P3)]·[L PMSG -(P1E1′L PMSG +P1E2′+P2)] -1 Where: Y PMSG (s) represents the output impedance of the wind power system in the frequency domain; C PMSG The initial bias term for wind resistance impedance reflects the steady-state DC component; I is the identity matrix; the coefficient matrix P1 represents the modulation effect of the wind power system voltage loop and current loop on the DC voltage harmonics, P2 represents the modulation effect of the wind power system current loop on the current harmonics, and P3 represents the influence of the wind power system current loop on the modulation signal harmonics; E′1 is the relationship between the wind power system GSC output voltage harmonics and the DC voltage harmonics, and E′2 is the relationship between the wind power system GSC output current harmonics and the DC voltage harmonics; L PMSG This is the inductance matrix for wind power filtering.

3. The modeling method for a multi-timescale small-signal frequency domain impedance model of a marine wind-solar-storage-flexible direct transmission system according to claim 1, characterized in that: In the photovoltaic system impedance model, the photovoltaic system impedance expression is: Y PV (s)=C PV +[I-(P4E3′+P6)]·[L PV -(P4E3′L PV +P4E4′+P5)]-1 Where: Y PV (s) represents the output impedance of the photovoltaic system in the frequency domain; C PV The initial bias term for photovoltaic impedance reflects the steady-state DC component; I is the identity matrix; coefficient matrix P4 represents the modulation effect of the photovoltaic system voltage loop and current loop on the DC voltage harmonics, P5 represents the modulation effect of the photovoltaic system current loop on the current harmonics, and P6 represents the influence of the photovoltaic system current loop on the modulation signal harmonics; E′3 is the relationship between the photovoltaic system GSC output voltage harmonics and the DC voltage harmonics, and E′4 is the relationship between the photovoltaic system GSC output current harmonics and the DC voltage harmonics; L PV This is a photovoltaic filter inductor matrix.

4. The modeling method for a multi-timescale small-signal frequency domain impedance model of a marine wind-solar-storage-flexible direct transmission system according to claim 1, characterized in that: In the impedance model of the energy storage system, the frequency domain impedance model of the energy storage converter is: Y ES (s)=[G si (s)·(1+H zv (s))·Z f (s)] -1 in: For the inner loop PI controller of energy storage current, K si,p K si,i These are the proportional and integral coefficients of the controller, respectively. For energy storage active damping controller, G N (s) is an energy storage notch filter, R v Z represents the virtual damping coefficient for energy storage. f (s)=R f +sL f The impedance of the energy storage output filter is E. f For the filter resistor, L f Let be the filter inductance, and s represent the complex variable in the complex plane.

5. The modeling method for a multi-timescale small-signal frequency domain impedance model of a marine wind-solar-storage-flexible direct transmission system according to claim 1, characterized in that: In the impedance model of the flexible direct current transmission system, the frequency domain admittance expression of MMC is: Where: R is the identity matrix; Y L Q represents the line impedance. c Q i For the MMC output current control and circulating current control related matrices; V u ,I u M u These represent the upper arm voltage, current, and modulation coefficient of the MMC; Z c P represents the impedance of the submodule capacitor. Iu K is the current controller gain matrix; K is the control decoupling matrix.

6. The modeling method for a multi-timescale small-signal frequency domain impedance model of a marine wind-solar-storage-flexible direct transmission system according to claim 1, characterized in that: The overall impedance expression after combining the four sub-models is as follows: AND equ (s)=N wt ·AND PMSG (s)+N pv ·AND PV (s)+N es ·AND ES (s) Where: Y equ (s) represents the equivalent frequency domain impedance of the wind-solar-storage transmission system; N wt N pv N es These represent the number of wind power, photovoltaic, and energy storage units connected to the system, respectively.

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