SVG control algorithm for improving offshore wind power quality

Abstract

The invention relates to the technical field of wind power generation, in particular to an SVG control algorithm for improving the quality of offshore wind power electric energy. The controller comprises a novel repetitive controller and a novel PR controller. A high-precision feedback control system is formed by implanting a controller into a kinetic model of an external signal, and an input signal can be tracked without static error, so that a repetitive controller and a resonance controller are constructed, the electric energy quality and the power generation efficiency can be improved, the equipment loss can be reduced, and the reliability of the system can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of wind power generation, and in particular to an SVG control algorithm for improving the quality of offshore wind power. Background Art

[0002] Facing the unknown energy structure in the future, multiple power generation methods can effectively alleviate the energy supply problem. Among them, wind power generation is the cleanest and most environmentally friendly power generation method, and it is also the most valued new energy power generation method in most countries.

[0003] Wind power generation has its own particularity. Since the original power of wind turbines comes from the wind energy flowing through the wind turbines and the wind speed and wind direction have the natural characteristics of random changes, the power output of wind turbines also changes randomly. In other words, wind turbines are power supply devices that cannot adjust the output, so the short-term changes in wind power generation are more significant. In addition, due to the obvious differences in wind speed and wind direction at different installation locations, even wind turbines in the same wind farm have asynchronous output changes. This random power injection into the power grid that changes with wind speed will damage the stability of the power grid. The fluctuations in the switching and stable operation of wind turbines will cause large fluctuations in the entire system. In addition, harmonics will also affect the power quality of the system. The sources of harmonics include the generator itself, the electronic components of the unit, etc. The magnitude of the harmonic current is basically linearly related to the output power, that is, it is related to the wind speed. Therefore, in order to make full use of the exploitable wind energy resources, on the basis of existing wind power generation, it is urgent to improve the operating performance of the system by installing dynamic reactive power compensation devices.

[0004] There are abundant wind energy resources at sea. Compared with onshore wind, offshore wind has smaller shear and turbulence intensity and has extremely high economic value. Offshore wind farms are also under large-scale construction. Wind farms will be equipped with a certain capacity of geostationary reactive power generators (SVG) as needed to improve system stability. Unlike onshore wind, the SVG in the offshore wind power grid-connected system is usually configured in the onshore centralized control station. There are also differences in system structure. It is also necessary to compensate for the excess capacitive reactive power of the offshore AC cable. Figure [1] is an example of an offshore wind power system connected to the AC grid. Summary of the invention

[0005] The purpose of the present invention is to provide an SVG control algorithm for improving the power quality of offshore wind power. By implanting the dynamic model of the external signal into the controller, a high-precision feedback control system is formed, which can track the input signal without static error, thereby constructing a repetitive controller and a resonant controller, which can improve the power quality and power generation efficiency, reduce equipment losses, and improve the reliability of the system.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solution: The present invention provides an SVG control algorithm for improving the quality of offshore wind power, including a repetitive controller and a resonant controller (PR controller). A high-precision feedback control system is formed by implanting a dynamic model of an external signal into the repetitive controller to achieve tracking of the input signal without static error, thereby constructing the repetitive controller and the PR controller.

[0007] Preferably, in the PR controller, a transfer function is introduced With K R As the gain at the fundamental frequency increases, it shows that it plays a role in eliminating errors. If other factors remain unchanged, only ω c Change, with ω c The gain at the fundamental frequency becomes larger, the frequency band becomes narrower, and it has good selectivity for the signal. c Determines the bandwidth of the controller.

[0008] Preferably, in the structure of the repetitive controller, r is the target signal, P(z) is the control object, C(z) is set to compensate for the phase and amplitude, Q(z) is 0.95, and the transfer function of the repetitive controller is: It is to make the closed-loop pole of the system within the unit circle, and e is the difference between the target value and the control value in each cycle;

[0009] When the repetitive controller starts working, the difference between the controlled signal and the target signal will generate feedback. The feedback signal will circulate continuously within a certain sampling period and continuously correct the control signal.

[0010] Preferably, for a step signal, the Laplace transform is The transfer function of proportional integral is Use PI controller to track step signal without static error;

[0011] For a sinusoidal signal, its Laplace transform is The transfer function of proportional resonance is PR controller can track without static error;

[0012] For the periodic repetitive signal that appears when the RCD load is applied, its Laplace transform form is: Therefore a similar transfer function tracking is required.

[0013] Preferably, the transfer function of the repetitive controller is expressed in the form of a differential function: y(m)-0.95y(mn)=K r e(m+kn), where C(z) is K r Z k .

[0014] Preferably, the PR controller, i.e., the proportional resonant controller, can achieve zero static error control for sinusoidal quantities. The ideal PR controller transfer function is: Where ω0 is the resonant frequency;

[0015] After the PR transfer function, the sinusoidal signal Msin(ωt+φ) becomes Integral part of PR controller There will be very large gain at the resonant frequency and almost no change outside the resonance point, so it can selectively compensate for harmonics.

[0016] Preferably, since the ideal PR controller has a very small gain at non-resonance, it cannot suppress grid harmonics when the grid voltage frequency deviates; therefore, an approximate PR transfer function is selected: It is called a quasi-PR controller, and its differential function is

[0017] y(n)=(C+D)y(n-1)-CDy(n-2)+(A+B)x(n)-(AD-BC)x(n-1),

[0018] in

[0019]

[0020] Beneficial effects of the present invention:

[0021] The SVG control algorithm for improving the power quality of offshore wind power of the present invention forms a high-precision feedback control system by implanting the dynamic model of the external signal into the controller, and can track the input signal without static error. A repetitive controller and a resonant controller are constructed in this way, which can improve the power quality and power generation efficiency, reduce equipment loss, and improve the reliability of the system, thereby bringing many benefits to the operation and development of offshore wind power plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of an example system for calculating an AC grid connection of offshore wind power according to the present invention;

[0023] Figure 2 It is a schematic diagram of the structure of the repetitive controller of the present invention;

[0024] Figure 3 It is a digital simulation circuit diagram of the present invention;

[0025] Figure 4 It is a schematic diagram of SVG parameter setting of the present invention;

[0026] Figure 5 This is a comparison diagram of the Hall current before and after the PR controller is turned on when the third harmonic is added under the output power 10% capacity of the present invention;

[0027] Figure 6 This is a comparison diagram of the Hall current before and after the PR controller is turned on when the fifth harmonic is added under the output power 10% capacity of the present invention;

[0028] Figure 7 This is a comparison diagram of the Hall current before and after the PR controller is turned on when the 7th harmonic is added under the output power 10% capacity of the present invention;

[0029] Figure 8 This is a comparison diagram of the Hall current before and after the PR controller is turned on when the output power of the present invention is 50% of the capacity and the third harmonic is added;

[0030] Fig. 9 This is a comparison diagram of the Hall current before and after the PR controller is turned on when the fifth harmonic is added under the output power of the present invention at 50% capacity;

[0031] Fig.10 This is a comparison diagram of the Hall current before and after the PR controller is turned on when the output power of the present invention is 50% of the capacity and the 7th harmonic is added;

[0032] Fig.11 This is a comparison diagram of the Hall current before and after the repetitive controller is turned on when the output power of the present invention is 10% capacity;

[0033] Fig.12 This is a comparison diagram of the Hall current before and after the repetitive controller is turned on when the output power of the present invention is 20% capacity;

[0034] Fig.13 This is a comparison diagram of the Hall current before and after the repetitive controller is turned on when the output power of the present invention is 50% capacity;

[0035] Fig.14 This is a comparison diagram of the Hall current before and after the repetitive controller is turned on when the output power of the present invention is 100% capacity. DETAILED DESCRIPTION

[0036] In order to make the technical means, creative features and effects achieved by the present invention easy to understand, the technical solutions in the embodiments of the present invention will be further clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0037] Example 1

[0038] like Figure 1-Figure 2As shown, the present invention provides an SVG control algorithm for improving the power quality of offshore wind power, including a new repetitive controller and a new PR controller; a high-precision feedback control system is formed by implanting a dynamic model of an external signal into the controller, which can track the input signal without static error, thereby constructing a repetitive controller and a resonant controller.

[0039] The SVG control algorithm for improving the power quality of offshore wind power provided by the present invention includes a repetitive controller and a resonant controller (PR controller). A high-precision feedback control system is formed by implanting a dynamic model of an external signal into the repetitive controller to achieve tracking of the input signal without static error, thereby constructing the repetitive controller and the PR controller.

[0040] In the PR controller, the transfer function is introduced With K R As the gain at the fundamental frequency increases, it shows that it plays a role in eliminating errors. If other factors remain unchanged, only ω c Change, with ω c The gain at the fundamental frequency becomes larger, the frequency band becomes narrower, and it has good selectivity for the signal. c Determines the bandwidth of the controller.

[0041] Preferably, in the structure of the repetitive controller, r is the target signal, P(z) is the control object, C(z) is set to compensate for the phase and amplitude, Q(z) is 0.95, and the transfer function of the repetitive controller is: It is to make the closed-loop pole of the system within the unit circle, and e is the difference between the target value and the control value in each cycle;

[0042] When the repetitive controller starts working, the difference between the controlled signal and the target signal will generate feedback. The feedback signal will circulate continuously within a certain sampling period and continuously correct the control signal.

[0043] For a step signal, its Laplace transform is The transfer function of proportional integral is Use PI controller to track step signal without static error;

[0044] For a sinusoidal signal, its Laplace transform is The transfer function of proportional resonance is PR controller can track without static error;

[0045] For the periodic repetitive signal that appears when the RCD load is applied, its Laplace transform form is: Therefore a similar transfer function tracking is required.

[0046] Preferably, the transfer function of the repetitive controller is expressed in the form of a differential function: y(m)-0.95y(mn)=K r e(m+kn), where C(z) is K r Z k .

[0047] PR controller, also known as proportional resonant controller, can achieve zero static error control for sinusoidal quantities. The ideal PR controller transfer function is: Where ω0 is the resonant frequency;

[0048] After the PR transfer function, the sinusoidal signal Msin(ωt+φ) becomes Integral part of PR controller There will be very large gain at the resonant frequency and almost no change outside the resonance point, so it can selectively compensate for harmonics.

[0049] Since the ideal PR controller has a small gain at non-resonance, it cannot suppress grid harmonics when the grid voltage frequency deviates; therefore, an approximate PR transfer function is selected: It is called a quasi-PR controller, and its differential function is

[0050] y(n)=(C+D)y(n-1)-CDy(n-2)+(A+B)x(n)-(AD-BC)x(n-1),

[0051] in

[0052]

[0053] Example 2

[0054] Through Figure 3-Figure 4 The digital simulation circuit is set up to test the resonant controller and repetitive controller functions of the program. The capacity of the test system is 30Mva r , the voltage is 35KV.

[0055] Under normal operation at rated voltage, in each capacity segment (only capacitive capacity segments are listed), test the improvement of the resonant controller on the power quality of the SVG itself, and pay attention to the impact of equipment investment on the system. The system short-circuit ratio is set to 20, and harmonic sources of different orders are added. The device is in constant reactive power control mode, and the output power is set to 10% and 50% of the rated capacity in turn. The THD harmonic content is analyzed through a virtual oscilloscope / FFT spectrum.

[0056] like Figure 5-Figure 7 As shown, for 10% capacity, Figure 5The upper part shows the change of A-phase Hall current before and after the resonant controller is turned on. The third harmonic accounts for the largest proportion. At this time, the total harmonic content changes from 40% before turning on to 20% after turning on. The harmonic content is greatly reduced, and the harmonic control rate reaches 50%. Figure 6 The first five harmonics accounted for the highest proportion in the control. After turning on the resonant controller, the total harmonic content dropped from 25% to 10%, and the harmonic control rate reached 60%. Figure 7 The first seven harmonics accounted for the highest proportion in the treatment. After turning on the resonant controller, the total harmonic content dropped from 18% to 11%, and the harmonic treatment rate reached 38%.

[0057] like Figure 8-Figure 10 As shown, for 50% capacity, Figure 8 The first three harmonics accounted for the highest proportion in the treatment. After turning on the resonant controller, the total harmonic content dropped from 8.5% to 3.9%, and the harmonic treatment rate reached 54%. Fig. 9 The first five harmonics accounted for the highest proportion in the treatment. After turning on the resonant controller, the total harmonic content dropped from 5.5% to 3.2%, and the harmonic treatment rate reached 41%. Fig.10 The first seven harmonics accounted for the highest proportion in the treatment. After turning on the resonant controller, the total harmonic content dropped from 4.8% to 2.5%, and the harmonic treatment rate reached 47%.

[0058] Under normal operation at rated voltage, in each capacity segment (only capacitive capacity segments are listed), test the improvement of the SVG's own power quality by the repetitive controller, and pay attention to the impact of equipment investment on the system. The device is in constant reactive power control mode, and the output power is set to 10%, 20%, 50%, and 100% of the rated capacity in turn, and the THD harmonic content is analyzed by virtual oscilloscope / FFT spectrum.

[0059] like Figure 11-Figure 14 As shown, Fig.11 The figure below is a comparison of the A-phase Hall current and the reference wave before and after the controller is turned on at 3M capacity. The sharp peak line 1 is the A-phase Hall current, and the gentle peak line 2 is the reference wave. After turning it on, the total harmonic content dropped from 43.7% to 19.7%, and the reference wave and the A-phase Hall current are more matched. Fig.12 The figure in the figure shows the situation with 6M capacity. After it is turned on, the total harmonic content drops from 21.3% to 10.7%. Fig.13 The figure shows the case of 15M capacity. After it is turned on, the total harmonic content drops from 10.1% to 5.1%. Fig.14 The figure shows the situation with 30M capacity. After it is turned on, the total harmonic content is reduced from 5.8% to 3.4%, and the overall harmonic control rate reaches about 50%.

[0060] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions claimed to be protected by the present invention.

Claims

1. An SVG control algorithm for improving offshore wind power quality, characterized in that: It includes a repetitive controller and a resonant controller (PR controller). The dynamic model of the external signal is implanted into the repetitive controller to form a high-precision feedback control system, so as to achieve zero-static error tracking of the input signal, thereby constructing the repetitive controller and the PR controller.

2. The SVG control algorithm for improving offshore wind power quality according to claim 1 is characterized in that: In the PR controller, the transfer function is introduced With K R As the gain at the fundamental frequency increases, it shows that it plays a role in eliminating errors. If other factors remain unchanged, only ω c Change, with ω c The gain at the fundamental frequency becomes larger, the frequency band becomes narrower, and it has good selectivity for the signal. c Determines the bandwidth of the controller.

3. The SVG control algorithm for improving offshore wind power quality according to claim 2 is characterized in that: In the structure of the repetitive controller, r is the target signal, P(z) is the control object, C(z) is set to compensate for the phase and amplitude, Q(z) is 0.95, and the transfer function of the repetitive controller is: It is to make the closed-loop pole of the system within the unit circle, and e is the difference between the target value and the control value in each cycle; When the repetitive controller starts working, the difference between the controlled signal and the target signal will generate feedback. The feedback signal will circulate continuously within a certain sampling period and continuously correct the control signal.

4. The SVG control algorithm for improving offshore wind power quality according to claim 3 is characterized in that: For a step signal, its Laplace transform is The transfer function of proportional integral is Use PI controller to track step signal without static error; For a sinusoidal signal, its Laplace transform is The transfer function of proportional resonance is PR controller can track without static error; For the periodic repetitive signal that appears when the RCD load is applied, its Laplace transform form is: Therefore a similar transfer function tracking is required.

5. The SVG control algorithm for improving offshore wind power quality according to claim 4 is characterized in that: The transfer function of the repetitive controller is expressed in the form of a differential function: y(m)-0.95y(mn)=K r e(m+kn), where C(z) is K r Z k .

6. The SVG control algorithm for improving offshore wind power quality according to claim 4, characterized in that: The PR controller, i.e., proportional resonant controller, can realize zero-static-error control for sinusoidal quantities. The ideal PR controller transfer function is: Where ω0 is the resonant frequency; After the PR transfer function, the sinusoidal signal Msin(ωt+φ) becomes Integral part of PR controller There will be very large gain at the resonant frequency and almost no change outside the resonance point, so it can selectively compensate for harmonics.

7. The SVG control algorithm for improving offshore wind power quality according to claim 6, characterized in that: Since the ideal PR controller has a small gain at non-resonance, it cannot suppress grid harmonics when the grid voltage frequency deviates; therefore, an approximate PR transfer function is selected: It is called a quasi-PR controller, and its differential function is y(n)=(C+D)y(n-1)-CDy(n-2)+(A+B)x(n)-(AD-BC)x(n-1), where

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