Grid admittance adaptability method and device for enhancing grid-forming control of wind power grid-connected converters

Abstract

The present invention discloses a method and device for enhancing the grid admittance adaptability of the grid-forming control of a wind power grid-connected converter. The method includes: dividing the wind power grid-connected converter system into a rotor-side converter and a grid-side converter for admittance modeling to obtain an RSC admittance model and a GSC admittance model; the grid-connected converter system includes an RSC, a DC bus, and a GSC. The RSC is used to convert the AC electric energy generated by wind power into DC electric energy, the GSC is used to convert the DC electric energy into grid-connected AC electric energy, and the DC bus connects the RSC and the GSC; using a preset phase correction scheme to adjust the admittance phases of the RSC admittance model and the GSC admittance model; the preset phase correction scheme adjusts the admittance phases of the RSC admittance model and the GSC admittance model based on a lead-lag correction transfer function. The present invention can reduce the risks of AC power oscillation and DC voltage oscillation.

Description

Technical Field

[0001] The present invention relates to the technical field of power system stability analysis and control, and particularly to a method and device for enhancing the grid admittance adaptability of a grid-forming control of a wind power grid-connected converter. Background Art

[0002] This section aims to provide background or context for the embodiments of the present invention described in the claims. The description herein is not admitted to be prior art merely by including it in this section.

[0003] With the development of large-scale renewable energy, renewable energy mainly based on wind power and photovoltaic will become the main energy source of the future power system. As the interface between renewable energy and the power grid, the grid-connected converter is a key device for power transmission. In the existing grid-forming control, methods such as virtual synchronous generator control, droop control, and virtual oscillator control are adopted. However, due to the large-scale access of wind power and photovoltaic, the grid inertia will continue to decrease, resulting in the future power grid being in a weak grid state. At this time, there is a risk of interaction between the wind power generation system or photovoltaic power generation system with the grid-connected converter as the interface on the AC side, causing AC side power oscillation. For the more complex wind power grid-connected converter system, there will also be interaction between different power units inside, causing DC voltage oscillation. Summary of the Invention

[0004] An embodiment of the present invention provides a method for enhancing the grid admittance adaptability of a grid-forming control of a wind power grid-connected converter, which is used to effectively suppress the interaction between the grid-connected converter system and the grid on the AC side, as well as the interaction inside the grid-connected converter system on the DC side, and reduce the risks of AC power oscillation and DC voltage oscillation. The method includes:

[0005] The wind power grid-connected converter system is divided into a rotor side converter (RSC) and a grid side converter (GSC) for admittance modeling to obtain an RSC admittance model and a GSC admittance model; the grid-connected converter system is connected to renewable energy power generation systems such as wind power and photovoltaic and the public power grid. The grid-connected converter system includes an RSC, a DC bus, and a GSC. The RSC is used to convert the AC electric energy generated by the renewable energy power generation system into DC electric energy, the GSC is used to convert the DC electric energy into grid-connected AC electric energy, and the DC bus connects the RSC and the GSC;

[0006] Using a preset phase correction scheme, adjust the admittance phases of the RSC admittance model and the GSC admittance model; the preset phase correction scheme adjusts the admittance phases of the RSC admittance model and the GSC admittance model based on a lead-lag correction transfer function to eliminate the interaction on the AC side between the GSC and the public grid, as well as the interaction on the DC side between the RSC and the GSC.

[0007] An embodiment of the present invention provides a grid admittance adaptability device for enhancing the grid-connected control of a wind power grid-connected converter, which is used to effectively suppress the AC-side interaction between the grid-connected converter system and the grid, as well as the DC-side interaction inside the grid-connected converter system, and reduce the risks of AC power oscillation and DC voltage oscillation. The device includes:

[0008] An admittance modeling module, which is used to divide the wind power grid-connected converter system into an RSC and a GSC for admittance modeling to obtain an RSC admittance model and a GSC admittance model; the grid-connected converter system is connected to a renewable energy power generation system and the public grid, and the grid-connected converter system includes an RSC, a DC bus, and a GSC. The RSC is used to convert the electric energy generated by the renewable energy power generation system into DC electric energy, the GSC is used to convert the DC electric energy into AC electric energy, and the DC bus connects the RSC and the GSC;

[0009] A phase compensation control module, which is used to adjust the admittance phases of the RSC admittance model and the GSC admittance model by using a preset phase correction scheme; the preset phase correction scheme adjusts the admittance phases of the RSC admittance model and the GSC admittance model based on a lead-lag correction transfer function to eliminate the interaction on the AC side between the GSC and the public grid and the interaction on the DC side between the RSC and the GSC.

[0010] An embodiment of the present invention also provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the above-mentioned method for enhancing the grid admittance adaptability of grid-connected converter grid-forming control is implemented.

[0011] An embodiment of the present invention also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the above-mentioned method for enhancing the grid admittance adaptability of grid-connected converter grid-forming control is implemented.

[0012] An embodiment of the present invention also provides a computer program product, which includes a computer program. When the computer program is executed by a processor, the above-mentioned method for enhancing the grid admittance adaptability of grid-connected converter grid-forming control is implemented.

[0013] In the embodiments of the present invention, first, the wind power grid-connected converter system is divided into two parts, the RSC and the GSC, for admittance modeling to obtain the corresponding admittance models. Secondly, through the admittance models, it is analyzed that the admittance on the AC side of the GSC will also affect the coupled admittance on the DC side of the GSC, and the phase-lead-lag correction is used to adjust the phases of the admittance on the AC side of the GSC and the coupled admittance on the DC side of the RSC respectively, so as to eliminate the AC-side interaction between the GSC and the public grid and ensure that there is no DC-side interaction between the RSC and the GSC inside the grid-connected converter system. The embodiments of the present invention can effectively suppress the AC-side interaction between the grid-connected converter system and the grid, reduce the AC power oscillation condition, and at the same time effectively suppress the DC-side interaction between the RSC and the GSC inside the grid-connected converter system, reducing the risk of DC voltage oscillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts. In the drawings:

[0015] Figure 1 It is a schematic flow chart of a method for enhancing the grid admittance adaptability of the grid-forming control of a wind power grid-connected converter in the embodiments of the present invention;

[0016] Figure 2 It is a schematic diagram of the main circuit of a wind power generation system in the embodiments of the present invention;

[0017] Figure 3 It is a schematic control diagram of the rotor-side converter RSC in the grid-connected converter system in the embodiments of the present invention;

[0018] Figure 4 It is a schematic control diagram of the grid-side converter GSC in the grid-connected converter system in the embodiments of the present invention;

[0019] Figure 5 It is a schematic diagram of the amplitude-phase curve of the lead-lag link in the embodiments of the present invention;

[0020] Figure 6 It is a schematic diagram of the lead-lag compensation correction in the embodiments of the present invention;

[0021] Figure 7 It is a Bode diagram comparing the interaction between the GSC AC admittance and the grid admittance before and after adding the lead-lag correction only to the AC side of the GSC in the embodiments of the present invention;

[0022] Figure 8Bode diagrams of the interaction between the AC and DC coupling admittances of the RSC and the AC and DC coupling admittances of the GSC before and after adding lead-lag correction only to the GSC and before and after adding lead-lag correction to both the GSC and the RSC in the embodiments of the present invention;

[0023] Figure 9 Bode diagrams of the interaction between the DC admittances of the GSC and the DC admittance of the RSC before and after adding lead-lag correction only to the GSC and before and after adding lead-lag correction to both the GSC and the RSC in the embodiments of the present invention;

[0024] Figure 10 Waveforms of the output voltage, current, power, and DC voltage of the GSC before and after adding lead-lag correction to the AC side of the GSC only in the embodiments of the present invention;

[0025] Figure 11 Waveforms of the output voltage, current, power, and DC voltage on the AC side of the GSC before and after adding lead-lag correction to both the GSC and the RSC in the embodiments of the present invention;

[0026] Figure 12 Schematic diagram of the grid admittance adaptability device for enhancing the grid-forming control of the wind power grid-connected converter in the embodiments of the present invention. Detailed implementation manners

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer and more understandable, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Herein, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but not to limit the present invention.

[0028] Aiming at the problems existing in the prior art, the embodiments of the present invention take the grid-connected converter system as the research object, and propose to use lead-lag phase correction to adjust the phase of the AC-side admittance of the GSC and the phase of the DC-side coupling admittance of the RSC in the grid-connected converter system, so as to eliminate the AC-side interaction between the GSC and the grid and the DC-side interaction between the RSC and the GSC, suppress the AC power and DC voltage oscillations, and this method is also convenient to extend to the multiple interaction occasions with multiple oscillation frequencies.

[0029] Figure 1 Schematic flowchart of the grid admittance adaptability method for enhancing the grid-forming control of the wind power grid-connected converter in the embodiments of the present invention, as Figure 1 shown, the method includes:

[0030] Step 101: Divide the wind power grid-connected converter system into the RSC and the GSC for admittance modeling to obtain the RSC admittance model and the GSC admittance model. The grid-connected converter system is connected to the renewable energy power generation system and the public power grid. The grid-connected converter system includes the RSC, the DC bus, and the GSC. The RSC is used to convert the electric energy generated by the renewable energy power generation system into DC electric energy, and the GSC is used to convert the DC electric energy into AC electric energy. The DC bus is connected to the RSC and the GSC.

[0031] Step 102: Use a preset phase correction scheme to adjust the admittance phases of the RSC admittance model and the GSC admittance model. The preset phase correction scheme adjusts the admittance phases of the RSC admittance model and the GSC admittance model based on the lead-lag correction transfer function to eliminate the interaction on the AC side between the GSC and the public power grid and the interaction on the DC side between the RSC and the GSC.

[0032] The grid admittance adaptability method in the embodiments of the present invention will be explained in detail below.

[0033] In the embodiments of the present invention, the renewable energy power generation system can be photovoltaic power generation, wind power generation, etc. Taking wind power generation as an example, refer to Figure 2 , Figure 2 which is the schematic diagram of the main circuit of the wind power generation system in the embodiments of the present invention. As Figure 2 shown, in the main circuit of the wind power generation system, the wind turbine is on the leftmost side, PMSG represents the permanent magnet synchronous generator, θr represents the PMSG rotor angle, the middle part includes the RSC, the DC bus, and the GSC, and the rightmost side represents connecting to the public power grid. u dc is the DC bus voltage, C dc is the DC bus capacitor, i dc is the DC bus current, L c and R c are the inductor and resistor of the output filter, L g and R g are the line inductor and line resistor of the power grid. represents the output voltage of the GSC module, represents the grid connection point voltage, represents the grid-connected current, that is, the GSC output current. In the embodiments of the present invention is the d-q component of the modulation coefficient, d abc is the duty cycle of the modulation waves of the three phases A, B, and C, and Sabc is the IGBT switch signal.

[0034] Figure 3 is the control schematic diagram of the rotor side converter RSC in the grid-connected converter system in the embodiments of the present invention. As Figure 3 shown, the RSC control mainly includes: the current loop and the DC voltage control. Figure 3In represents the d-axis current reference value of the RSC, represents the sampled value of the d-axis current of the RSC, represents the sampled value of the q-axis current of the RSC, represents the q-axis current reference value of the RSC, H cc represents the current control transfer function, represents the steady-state value of the grid angular frequency, L p represents the stator inductance of the PMSG, represents the d-axis component of the input voltage of the RSC, represents the q-axis component of the input voltage of the RSC, , represents the d-axis and q-axis components of the modulation coefficient of the RSC, u dc.ref represents the reference value of the DC bus voltage, represents the sampled value of the DC bus voltage, G dc represents the DC bus control transfer function.

[0035] According to Figure 3 the AC voltage and DC current expressions of the RSC can be deduced as:

[0036] (1)

[0037] (2)

[0038] In the formula, represents the small-signal variation of the d-q components of the input voltage of the RSC, represents the small-signal variation of the d-q components of the output voltage of the PMSG, Δi dc represents the small-signal variation of the DC bus current, represents the small-signal variation of the d-q components of the modulation coefficient of the RSC, Δu dc represents the small-signal variation of the DC bus voltage, respectively represent the steady-state value of the DC bus voltage, the steady-state value of the d-q components of the modulation coefficient of the RSC, the steady-state value of the d-q components of the output voltage of the PMSG, the steady-state value of the d-q components of the input current of the RSC, and the steady-state value of the DC bus current, represents the small-signal variation of the d-q components of the input current of the RSC, represents the small-signal variation of the d-q components of the output voltage of the PMSG.

[0039] According to Figure 3 the small-signal model of the modulation coefficient of the RSC can also be deduced as:

[0040] (3)

[0041] Substituting Equation (3) into Equation (1) gives:

[0042] (4)

[0043] By deriving Equation (4), the expressions of and for RSC can be obtained as:

[0044] (5)

[0045] Wherein, , and and can be expressed as:

[0046] (6)

[0047] Wherein, , substituting Equation (5) into Equation (2), the expressions of and for RSC can be obtained as:

[0048] (7)

[0049] Wherein, and can be expressed as:

[0050] (8)

[0051] Therefore, by modeling the main circuit and control process of the RSC in the grid-connected converter system, conducting theoretical derivation, and combining Ohm's law, the admittance model of the RSC can be obtained. The specific steps are as follows: First, model and analyze the main circuit of the RSC to obtain Equation (1) and Equation (2), then model the control strategy to obtain Equation (3), substitute Equation (3) into Equation (1) to get Equation (4), derive Equation (4) to obtain Equation (5) and Equation (6), and then substitute Equation (5) into Equation (2) to obtain Equation (7) and Equation (8), where Equation (6) and Equation (8) are the admittance models of the RSC. The admittance model of the RSC can be represented by respectively, and is composed of DC admittance, AC admittance, DC coupling admittance, and AC coupling admittance. That is, the admittance model of the RSC is expressed as in Equations (6) and (8).

[0052] Figure 4 is the control schematic diagram of the grid-side converter GSC in the grid-connected converter system according to the embodiment of the present invention. As shown in Figure 4 , the GSC control mainly includes: governor, active power loop, reactive power loop, voltage loop, and current loop. Figure 4 、 Figure 3The same characters represent the same physical parameters, and the repeated parts will not be described again. Figure 4 Among them, ω g , ω 0 , ω respectively represent the instantaneous value of the grid angular frequency, the steady-state value of the grid angular frequency, and the instantaneous value of the grid-connected converter angular frequency. k pv represents the primary frequency modulation coefficient, P e , P ref respectively represent the sampled value of the electromagnetic power of the grid-connected converter and the reference value of the electromagnetic power. D p represents the virtual damping coefficient, J s represents the virtual inertia coefficient, s represents the differential operator, θ represents the GSC power angle, Q e , Q ref respectively represent the sampled value of the reactive power of the grid-connected converter and the reference value of the reactive power. k q represents the reactive power droop coefficient. , , , respectively represent the d-axis component and q-axis component of the GSC output voltage, the d-axis component and q-axis component of the GSC output voltage reference value, G vc , G cc , G f respectively represent the voltage control transfer function matrix, the current control transfer function matrix, and the feed-forward link transfer function matrix. , respectively represent the q-axis component and d-axis component of the modulation coefficient in the GSC control coordinate system. L c represents the output filter inductor. , , , respectively represent the d-axis component of the GSC current reference value, the q-axis component of the GSC current reference value, the d-axis component of the GSC current sample, and the q-axis component of the GSC current sample.

[0053] The GSC adopts the virtual synchronous generator control method. According to Figure 4 the AC voltage and DC current expressions of the GSC can be derived as:

[0054] (9)

[0055] (10)

[0056] (11)

[0057] Among them, Z f is the filter impedance of the GSC. represents the steady-state value of the relevant variables. Represents the d-q axis components of the output voltage in the GSC control coordinate system, R c Represents the output filter resistance, Respectively represent the small-signal variations of the d-axis and q-axis components of the GSC output current, 、 Respectively represent the small-signal variations of the d-q axis components of the output voltage in the GSC control coordinate system, u dc0 Represents the steady-state value of the DC bus voltage, Represents the steady-state values of the d-q axis components of the GSC modulation coefficient, Δu dc Represents the small-signal variation of the DC bus voltage, Δi dc Represents the small-signal variation of the DC bus current.

[0058] According to Figure 4 The small-signal model of the GSC modulation coefficient can be deduced as:

[0059] (12)

[0060] Among them, Represents the d-q components of the modulation coefficient in the GSC control coordinate system, Represents the d-q components of the reference value of the GSC output current in the GSC control coordinate system, Z del Represents the coupling impedance, Represents the d-q components of the sampled value of the GSC output current in the GSC control coordinate system, Represents the d-q components of the sampled value of the GSC output voltage in the GSC control coordinate system.

[0061] In Equation (13), L, P, and Q can be expressed as:

[0062] (13)

[0063] (14)

[0064] (15)

[0065] Substituting Equation (12) into Equation (9), we can obtain:

[0066] (16)

[0067] Therefore, the and of the GSC can be expressed as:

[0068] (17)

[0069] Among them and can be expressed as:

[0070] (18)

[0071] Among them, , and the and of GSC can be expressed as:

[0072] (19)

[0073] Wherein and can be expressed as:

[0074] (20)

[0075] Therefore, by modeling the main circuit and control process of the grid-connected converter system GSC, conducting theoretical derivation and combining with Ohm's law, the admittance model of GSC can be obtained. The specific steps are as follows: First, model and analyze the main circuit of GSC to obtain formulas (9), (10), and (11), then model the control strategy to obtain formula (12), substitute formula (12) into formula (9) to obtain formula (16), derive formula (16) to obtain formulas (17) and (18), and then substitute formulas (16) and (17) into formula (11) to obtain formulas (19) and (20), where formulas (18) and (20) are the RSC admittance models. The admittance model of GSC consists of . That is, the admittance model of GSC is expressed as in equations (18) and (20).

[0076] Among them, ;

[0077] ;

[0078] ;

[0079] Among them, θ 0 represents the steady-state value of the GSC power angle, H cc represents the current control transfer function, G vc represents the voltage control transfer function, k q represents the reactive power droop coefficient, s represents the differential operator, , represent the d-axis component and q-axis component of the GSC output voltage, Z del represents the coupling impedance, represents the steady-state value of the GSC modulation coefficient d-q, represents the steady-state value of the d-q components of the output current in the control coordinate system, Represents the d-q steady-state values of the GSC output voltage in the control coordinate system, G v1 、G i1 、G m1 Represents the matrix expressions of the output voltage, output current, and modulation coefficient in the system coordinate system, Represents the parameter matrix composed of the GSC output voltage and output current, k pv Represents the primary frequency modulation coefficient, 、 Represents the parameter matrix, C dc Represents the DC bus capacitor, Represents the d-q component steady-state values of the GSC output voltage, Represents the q-axis component steady-state value of the GSC output current, H f Represents the feed-forward control transfer function, D p Represents the virtual damping coefficient, ω 0 Represents the steady-state value of the grid angular frequency, Represents the d-q component steady-state values of the GSC output current, Represents the proportional coefficient of the DC voltage control, Represents the integral coefficient of the DC voltage control, Represents the vector form of the d-q steady-state values of the GSC modulation coefficient.

[0080] After dividing the wind power grid-connected converter system into the rotor-side converter RSC and the grid-side converter GSC for admittance modeling to obtain the RSC admittance model and the GSC admittance model, a preset phase correction scheme is used to adjust the admittance phases of the RSC admittance model and the GSC admittance model; the preset phase correction scheme adjusts the admittance phases of the RSC admittance model and the GSC admittance model based on the lead-lag correction transfer function to eliminate the AC-side interaction between the GSC and the common grid, as well as the DC-side interaction between the RSC and the GSC. The grid-connected converter system is used to convert the electric energy generated by renewable energy into alternating current that meets the grid standards.

[0081] In the embodiments of the present invention, the GSC uses virtual synchronous generator (VSG) control for grid-forming control. According to the admittance modeling analysis of the GSC, the interaction between the weak grid and the GSC will cause AC-side power oscillation in the grid-connected converter system. Generally, the mainstream control methods eliminate the interaction between the AC side and the grid and reduce the AC power oscillation by changing the GSC output impedance, but this will affect the power generation efficiency, and too large output impedance will cause system instability. Similarly, it can be seen from the GSC admittance modeling process that the change of the GSC AC-side admittance will affect its DC-side coupling admittance, and there is also a risk of causing the DC-side voltage to oscillate due to the DC-side interaction. And when there are multiple interaction points in the system, the entire system may oscillate at multiple frequencies.

[0082] The present invention embodiment presets a phase correction scheme, which uses the lead-lag phase correction strategy including a lead-lag correction transfer function to adjust the phase of the AC admittance of the GSC and the phase of the DC-side coupling admittance of the RSC in the grid-connected converter system, eliminating the AC power oscillation caused by the interaction on the AC side between the GSC and the power grid in the grid-connected converter system, and also eliminating the DC voltage oscillation problem caused by the interaction between the RSC and the GSC on the DC side.

[0083] Figure 5 It is a schematic diagram of the amplitude-phase curve of the lead-lag link in the embodiment of the present invention. Figure 5 In it, the upper red curve is the amplitude-frequency characteristic curve of the lead-lag correction, and the lower red curve is the phase-frequency characteristic curve of the lead-lag link. The vertical coordinates L(s), respectively represent amplitude and phase, and the horizontal coordinate ω com represents frequency. By Figure 5 the curve in it, it can be reflected that the lead-lag correction can perform lead correction and lag correction on the system phase in different angular frequency bands. If it is applied to the admittance phase correction, the purpose of eliminating the interaction can be achieved by correcting the admittance phases of the GSC and the RSC. The specific lead-lag correction transfer function can be expressed as:

[0084] (21)

[0085] In the formula, G c (s) represents the lead-lag correction transfer function, α and β are parameters, s represents the differential operator, and T 1 , T 2 respectively represent the corresponding time constants.

[0086] When there are multiple interaction points between the grid-connected converter system and the power grid, the lead-lag link can be expressed as:

[0087] (22)

[0088] Among them, α j , β i , T i , T j respectively represent different parameters and time parameters, and j represents the number of specific correction links.

[0089] The essence of the lead-lag phase correction in the preset phase correction scheme of the present invention embodiment is to use the phase boosting characteristic of the lead link and the phase attenuation characteristic of the lag link to improve the system characteristics, which is mainly reflected in the steady-state error e ss , the cut-off frequency ω c0 , the phase margin γ 0 and other indicators.

[0090] In one embodiment, a preset phase correction scheme is used to adjust the admittance phases of the RSC admittance model and the GSC admittance model, including the following steps (1) to (3).

[0091] (1) Determine the system open-loop gain k according to the steady-state error e ss where the steady-state error e ss can be obtained by subtracting the output current sampling value from the output current reference value, and the open-loop gain k can be obtained by k = 1 / e ss .

[0092] (2) Calculate the open-loop transfer function L 0 (s) before phase correction, the cut-off frequency ω c0 , and the phase margin γ 0 . Use a lead link to correct the frequency band that needs phase correction, and use a lag link to adjust the system phase margin at the attenuation cut-off frequency.

[0093] (3) Lead-lag compensation correction. Specifically as follows:

[0094] 3-1) The GSC and RSC in the grid-connected converter are used as the system to be corrected. By determining the cut-off frequency ω cut of the system to be corrected, and calculating the maximum lead angle cut required at ω . The specific correction function is completed by connecting the lead-lag link in series with the RSC or GSC control structure.

[0095] 3-2) Refer to Figure 6 , Figure 6 which is the schematic diagram of the lead-lag compensation correction in the embodiment of the present invention. Among them, L 0 (s) is the open-loop transfer function before system correction, G c (s) is the lead-lag transfer function, and L * (s) is the open-loop transfer function after correction. Draw a vertical line at the cut-off frequency ω cut , which intersects the open-loop transfer function L 0 (s) of the GSC or RSC before compensation at point a, and draw the mirror image point b of a with respect to 0 dB. Then draw a 20 dB / dec line centered at point b, which intersects and at points c and d respectively.

[0096] 3-3) Determine point e on the horizontal line passing through point d, and then draw a -20 dB / dec line through point e that intersects 0 dB at point f. Then the lead-lag correction transfer function can be obtained as:

[0097] (23)

[0098] Among them, G c (s) represents the lead-lag correction transfer function, s represents the differential operator, ω d represents the angular frequency at point d, ω c represents the angular frequency at point c, ω f represents the angular frequency at point f, ω e represents the angular frequency at point e. Equation (21) and Equation (38) are two expressions of the lead-lag correction. Equation (38) is the lead-lag correction transfer function derived from the perspective of control theory, and Equation (21) is the lead-lag correction transfer function derived from the perspective of specific engineering design. The two are equivalent.

[0099] Figure 7 To compare the Bode diagrams of the interaction between the AC admittance of the GSC and the grid admittance before and after adding the lead-lag correction only to the AC side of the GSC, from Figure 7 it can be seen that after adding the lead-lag correction to the AC side of the GSC, the phase of the frequency interaction point corresponding to the interaction between the AC admittance of the GSC and the grid admittance drops from 223° to 164° and 106°. Although an additional interaction point is added, the phase margin remains within the stable range of [-90° - +90°], indicating that the method proposed in the embodiment of the present invention can eliminate the interaction on the AC side.

[0100] Figure 8 To compare the Bode diagrams of the interaction between the AC and DC coupling admittances of the GSC and the AC and DC admittances of the RSC before and after adding the lead-lag correction only to the GSC and adding the lead-lag correction to both the GSC and the RSC, as Figure 8 shown, since adding the phase correction to the AC side of the GSC will affect the phase of its DC side admittance, causing a DC side interaction between the RSC and the DC side of the GSC near 260 Hz and resulting in DC voltage oscillation. After adding the lead-lag correction to the DC side of the RSC, it can be seen that the DC side interaction is eliminated and the DC voltage oscillation is suppressed.

[0101] Figure 9 To compare the Bode diagrams of the interaction between the DC admittance of the GSC and the DC admittance of the RSC before and after adding the lead-lag correction only to the GSC and adding the lead-lag correction to both the GSC and the RSC, as Figure 9 shown, the change in the AC side admittance of the GSC has little effect on the and of the DC admittance of the GSC, but it will affect the DC coupling admittance of the GSC. The DC voltage oscillation is mainly caused by the DC side interaction between the and of the coupled admittances of the GSC and the RSC. Therefore, the DC voltage oscillation has little relation with the DC admittance and is more affected by the DC coupling admittance.

[0102] Figure 10 For comparison, the waveforms of the GSC output voltage, current, power, and DC voltage after adding lead-lag correction only to the AC side of the GSC are shown. Figure 10 The specific operating conditions in [reference] are when the grid is weak (SCR = 1.1), and the AC output and DC voltage waveforms of the GSC with only lead-lag correction added to the AC side of the GSC are shown. (a) is the GSC output voltage, (b) is the GSC output current, (c) is the GSC output active power, (d) is the amplified waveform of the GSC output active power, (e) is the DC voltage, and (f) is the amplified waveform of the DC voltage. It can be seen from Figure 9 that after adding lead-lag phase correction to the AC side of the GSC, the waveform of the GSC AC side output voltage is significantly improved, the oscillation of the output power is significantly reduced, and the output current is significantly improved. However, due to the influence on the DC side coupling admittance, the DC voltage oscillates.

[0103] Figure 11 For comparison, the waveforms of the GSC AC side output voltage, current, power, and DC voltage before and after adding lead-lag correction to both the GSC and the RSC are shown. Figure 11 The specific operating conditions in [reference] are when the grid is weak (SCR = 1.1), and the AC output and DC voltage waveforms of the GSC with lead-lag correction added to both the AC side of the GSC and the DC side of the RSC are shown. (a) is the GSC output voltage, (b) is the GSC output current, (c) is the GSC output active power, (d) is the amplified waveform of the GSC output active power, (e) is the DC voltage, and (f) is the amplified waveform of the DC voltage. It can be seen from Figure 10 that after adding lead-lag phase correction to both the AC side of the GSC and the DC side of the RSC. First, the voltage quality of the GSC AC side is significantly improved, and at the same time, the oscillation of the output power is significantly reduced, and the output current is significantly improved. Moreover, the DC voltage quickly returns to stability after a short overshoot. This shows that the lead-lag phase correction proposed in the present invention can not only eliminate the interaction on the AC side but also effectively suppress the interaction on the DC side.

[0104] In the embodiments of the present invention, a device for enhancing the grid admittance adaptability of the grid-connected converter's grid-forming control is also provided, as described in the following embodiments. Since the principle of this device for solving problems is similar to the method for enhancing the grid admittance adaptability of the grid-connected converter's grid-forming control, the implementation of this device can refer to the implementation of the method for enhancing the grid admittance adaptability of the grid-connected converter's grid-forming control, and the repeated parts will not be elaborated.

[0105] Figure 12 The schematic diagram of the device for enhancing the grid admittance adaptability of the grid-connected converter's grid-forming control in the embodiments of the present invention is shown as Figure 12 shown, and this device 1200 includes:

[0106] The admittance modeling module 1201 is used to model the admittance of the wind power grid-connected converter system by dividing it into the RSC and the GSC, so as to obtain the RSC admittance model and the GSC admittance model; the grid-connected converter system is connected to the renewable energy power generation system and the public power grid, and the grid-connected converter system includes the RSC, the DC bus, and the GSC. The RSC is used to convert the electric energy generated by the renewable energy power generation system into DC electric energy, the GSC is used to convert the DC electric energy into AC electric energy, and the DC bus is connected to the RSC and the GSC;

[0107] The phase compensation control module 1202 is used to adjust the admittance phase of the RSC admittance model and the GSC admittance model by using a preset phase correction scheme; the preset phase correction scheme adjusts the admittance phase of the RSC admittance model and the GSC admittance model based on the lead-lag correction transfer function to eliminate the interaction on the AC side between the GSC and the public power grid and the interaction on the DC side between the RSC and the GSC.

[0108] In one embodiment, the RSC admittance model is expressed as follows:

[0109] ;

[0110] ;

[0111] In the formula, respectively represent the RSC AC admittance, the RSC DC admittance, the RSC DC coupling admittance, and the RSC AC coupling admittance, represents the parameter matrix, u dc0 represents the DC bus voltage steady-state value, G dc represents the DC voltage control transfer function, m dq0 represents the RSC modulation coefficient d-q steady-state value, represents the RSC input voltage d-q steady-state value, represents the RSC input current d-q steady-state value, i dc0 represents the DC bus current steady-state value.

[0112] In one embodiment, the GSC admittance model is expressed as follows:

[0113] ;

[0114] ;

[0115] In the formula, respectively represent the GSC AC admittance, the GSC DC admittance, the GSC DC coupling admittance, and the GSC AC coupling admittance, u dc0 represents the DC bus voltage steady-state value, Z f represents the RSC output filter impedance, Represents the d-q steady-state value of the GSC modulation coefficient, Represents the d-q steady-state value of the GSC output voltage, Represents the d-q steady-state value of the GSC output current, i dc0 Represents the steady-state value of the DC bus current; L, P, Q represent parameter matrices, specifically:

[0116] ;

[0117] ;

[0118] ;

[0119] ;

[0120] where, θ 0 Represents the steady-state value of the GSC power angle, H cc Represents the current control transfer function, G vc Represents the voltage control transfer function, k q Represents the reactive power droop coefficient, s represents the differential operator, 、 Represent the d-axis component and q-axis component of the GSC output voltage, Z del Represents the coupling impedance, Represents the d-q steady-state value of the GSC modulation coefficient, Represents the steady-state value of the d-q components of the output current in the control coordinate system, Represents the d-q steady-state value of the GSC output voltage in the control coordinate system, G v1 、G i1 、G m1 Represent the matrix expressions of the output voltage, output current, and modulation coefficient in the system coordinate system, Represents the parameter matrix composed of the GSC output voltage and output current, k pv Represents the primary frequency modulation coefficient, 、 Represent parameter matrices, C dc Represents the DC bus capacitor, Represents the steady-state value of the d-q components of the GSC output voltage, Represents the steady-state value of the q-axis component of the GSC output current, H f Represents the feedforward control transfer function, D p Represents the virtual damping coefficient, ω 0 Represents the steady-state value of the grid angular frequency, Represents the steady-state value of the d-q components of the GSC output current, Represents the proportional coefficient of the DC voltage control, Represents the integral coefficient of the DC voltage control, It represents the vector form of the d-q steady-state value of the GSC modulation coefficient.

[0121] In one embodiment, the lead-lag correction transfer function is expressed as follows:

[0122] ;

[0123] In the formula, G c (s) represents the lead-lag correction transfer function, s represents the differential operator, ω d represents the angular frequency at point d, ω c represents the angular frequency at point c, ω f represents the angular frequency at point f, ω e represents the angular frequency at point e. Points d, c, f, and e are determined as follows:

[0124] On the graph where the open-loop transfer function before correction, the lead-lag transfer function, and the open-loop transfer function after correction coexist, draw a vertical line at the cut-off frequency, which intersects the open-loop transfer function before correction at point a. Draw the mirror image point b of point a with respect to 0 dB. Draw a line with a slope of 20 dB / dec centered on the mirror image point b, which intersects and at points c and d respectively. ω represents the angular frequency, and α is a parameter. Determine point e on the horizontal line passing through point d, and then draw a line with a slope of -20 dB / dec passing through point e, which intersects 0 dB at point f.

[0125] An embodiment of the present invention also provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the above-mentioned method for adapting the grid admittance of the enhanced grid-connected converter network-forming control is implemented.

[0126] An embodiment of the present invention also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the above-mentioned method for adapting the grid admittance of the enhanced grid-connected converter network-forming control is implemented.

[0127] An embodiment of the present invention also provides a computer program product, which includes a computer program. When the computer program is executed by a processor, the above-mentioned method for adapting the grid admittance of the enhanced grid-connected converter network-forming control is implemented.

[0128] In the embodiments of the present invention, first, the wind power grid-connected converter system is divided into two parts, i.e., the RSC and the GSC, for admittance modeling to obtain the corresponding admittance models. Secondly, through the admittance models, it is analyzed that the admittance of the AC side of the GSC will also affect the coupled admittance of its DC side. Phase lead-lag correction is used to adjust the phase of the admittance of the AC side of the GSC and the phase of the coupled admittance of the DC side of the RSC respectively, so as to eliminate the interaction on the AC side between the GSC and the public grid, and ensure that there is no interaction on the DC side between the RSC and the GSC inside the grid-connected converter system. The embodiments of the present invention can effectively suppress the interaction between the renewable energy power generation system and the grid, reduce the AC power oscillation situation, effectively suppress the interaction on the DC side inside the grid-connected converter system, and reduce the risk of DC voltage oscillation.

[0129] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0130] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, as well as the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for realizing the functions specified in Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0131] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device, and the instruction device realizes the functions specified in Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0132] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so that a series of operation steps are performed on the computer or other programmable apparatus to generate a computer-implemented process, thereby the instructions executed on the computer or other programmable apparatus provide steps for implementing the functions specified in one process or a plurality of processes and / or blocks Figure 1 one process or a plurality of processes and / or blocks Figure 1 steps for implementing the functions specified in one block or a plurality of blocks.

[0133] The specific embodiments described above further elaborate the objectives, technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for enhancing the grid admittance adaptability of wind power grid-connected converter network control, characterized in that: include: The wind power grid-connected converter system is divided into a rotor-side converter RSC and a grid-side converter GSC for admittance modeling, and an RSC admittance model and a GSC admittance model are obtained; the grid-connected converter system is connected to a renewable energy power generation system and a public power grid, and the grid-connected converter system includes an RSC, a DC bus and a GSC, the RSC is used to convert the electric energy generated by the renewable energy power generation system into DC electric energy, the GSC is used to convert the DC electric energy into AC electric energy, and the DC bus connects the RSC and the GSC; The preset phase correction scheme is used to adjust the admittance phase of the RSC admittance model and the GSC admittance model; the preset phase correction scheme adjusts the admittance phase of the RSC admittance model and the GSC admittance model based on the lead-lag correction transfer function to eliminate the interaction between the GSC and the public power grid on the AC side and the interaction between the RSC and the GSC on the DC side.

2. The method according to claim 1, characterized in that The RSC admittance model is expressed as follows: ； ； ； In the formula, They represent RSC AC admittance, RSC DC admittance, RSC DC coupling admittance, and RSC AC coupling admittance respectively; represents the parameter matrix, H cc represents the current control transfer function, Indicates the steady-state value of the grid angular frequency, L p represents the stator inductance of PMSG; u dc0 Represents the steady-state value of the DC bus voltage, G dc represents the DC voltage control transfer function, m dq0 represents the dq steady-state value of the RSC modulation coefficient, represents the dq steady-state value of the RSC input voltage, represents the dq steady-state value of the RSC input current, i dc0 Indicates the steady-state value of the DC bus current.

3. The method according to claim 1, characterized in that The GSC admittance model is expressed as follows: ； ； In the formula, They represent GSC AC admittance, GSC DC admittance, GSC DC coupling admittance, and GSC AC coupling admittance, respectively. dc0 Represents the steady-state value of the DC bus voltage, Z f represents the RSC output filter impedance, represents the steady-state value of the GSC modulation coefficient dq, represents the steady-state value of the GSC output voltage dq, represents the steady-state value of the GSC output current dq, i dc0 represents the steady-state value of the DC bus current; L, P, Q represent the parameter matrix, specifically: ； ； ； ； Where θ0 represents the steady-state value of the GSC power angle, H cc represents the current control transfer function, G vc represents the voltage control transfer function, k q represents the reactive droop coefficient, s represents the differential operator, Z del represents the coupling impedance, represents the steady-state value of the GSC modulation coefficient dq, represents the steady-state value of the output current dq component in the control coordinate system, represents the steady-state value of the GSC output voltage dq in the control coordinate system, G v1 , G i1 , G m1 Represents the matrix expression of output voltage, output current and modulation coefficient in the system coordinate system, represents the parameter matrix composed of the GSC output voltage and output current, k pv represents the primary frequency modulation coefficient, , represents the parameter matrix, C dc is the DC bus capacitance, represents the steady-state value of the dq component of the GSC output voltage, represents the steady-state value of the d-axis component of the GSC output current, represents the steady-state value of the q-axis component of the GSC output current, H f represents the feedforward control transfer function, D p represents the virtual damping coefficient, ω0 represents the steady-state value of the grid angular frequency, represents the steady-state value of the dq component of the GSC output current, represents the DC voltage control proportional coefficient, represents the DC voltage control integral coefficient, Represents the GSC modulation coefficient dq steady-state value vector form.

4. The method according to claim 1, characterized in that The lead-lag correction transfer function is expressed as follows: ； In the formula, G c (s) represents the lead-lag correction transfer function, s represents the differential operator, ω d represents the angular frequency at point d, ω c represents the angular frequency at point c, ω f represents the angular frequency at point f, ω e It represents the angular frequency of point e. Points d, c, f and e are determined as follows: On the graph where the open-loop transfer function before correction, the lead-lag transfer function, and the open-loop transfer function after correction coexist, draw a vertical line at the cutoff frequency, intersecting the open-loop transfer function before correction at point a, draw the mirror image point b of point a about 0dB, and draw a straight line of 20dB / dec with the mirror image point b as the center, respectively. and It intersects at points c and d, ω represents the angular frequency, α is the parameter, point e is determined on the horizontal line passing through point d, and then a straight line of -20dB / dec is made through point e and intersects with 0dB at point f.

5. A grid admittance adaptability device for enhancing the grid control of wind power grid-connected converter, characterized in that: include: An admittance modeling module is used to divide the wind power grid-connected converter system into RSC and GSC for admittance modeling, and obtain an RSC admittance model and a GSC admittance model; the grid-connected converter system is connected to the renewable energy power generation system and the public power grid, and the grid-connected converter system includes an RSC, a DC bus and a GSC, the RSC is used to convert the electric energy generated by the renewable energy power generation system into DC electric energy, the GSC is used to convert the DC electric energy into AC electric energy, and the DC bus connects the RSC and the GSC; The phase compensation control module is used to adjust the admittance phase of the RSC admittance model and the GSC admittance model by using a preset phase correction scheme; the preset phase correction scheme adjusts the admittance phase of the RSC admittance model and the GSC admittance model based on a lead-lag correction transfer function to eliminate the interaction between the GSC and the public power grid on the AC side and the interaction between the RSC and the GSC on the DC side.

6. The device according to claim 5, characterized in that The RSC admittance model is expressed as follows: ； ； In the formula, They represent RSC AC admittance, RSC DC admittance, RSC DC coupling admittance, and RSC AC coupling admittance respectively. represents the parameter matrix, u dc0 Represents the steady-state value of the DC bus voltage, G dc represents the DC voltage control transfer function, m dq0 represents the steady-state value of the RSC modulation coefficient dq, Represents the steady-state value of the RSC input voltage dq, Represents the steady-state value of the RSC input current dq, i dc0 Indicates the steady-state value of the DC bus current.

7. The device according to claim 5, characterized in that The GSC admittance model is expressed as follows: ； ； In the formula, They represent GSC AC admittance, GSC DC admittance, GSC DC coupling admittance, and GSC AC coupling admittance, respectively. dc0 Represents the steady-state value of the DC bus voltage, Z f represents the RSC output filter impedance, represents the steady-state value of the GSC modulation coefficient dq, represents the steady-state value of the GSC output voltage dq, represents the steady-state value of the GSC output current dq, i dc0 represents the steady-state value of the DC bus current; L, P, Q represent the parameter matrix, specifically: ； ； ； ； Where θ0 represents the steady-state value of the GSC power angle, H cc represents the current control transfer function, G vc represents the voltage control transfer function, k q represents the reactive droop coefficient, s represents the differential operator, Z del represents the coupling impedance, represents the steady-state value of the GSC modulation coefficient dq, represents the steady-state value of the output current dq component in the control coordinate system, represents the steady-state value of the GSC output voltage dq in the control coordinate system, G v1 , G i1 , G m1 Represents the matrix expression of output voltage, output current and modulation coefficient in the system coordinate system, represents the parameter matrix composed of the GSC output voltage and output current, k pv represents the primary frequency modulation coefficient, , represents the parameter matrix, C dc is the DC bus capacitance, represents the steady-state value of the dq component of the GSC output voltage, represents the steady-state value of the q-axis component of the GSC output current, H f represents the feedforward control transfer function, D p represents the virtual damping coefficient, ω0 represents the steady-state value of the grid angular frequency, represents the steady-state value of the d-axis component of the GSC output current, represents the steady-state value of the dq component of the GSC output current, represents the DC voltage control proportional coefficient, represents the DC voltage control integral coefficient, Represents the GSC modulation coefficient dq steady-state value vector form.

8. The device according to claim 5, characterized in that The lead-lag correction transfer function is expressed as follows: ； In the formula, G c (s) represents the lead-lag correction transfer function, s represents the differential operator, ω d represents the angular frequency at point d, ω c represents the angular frequency at point c, ω f represents the angular frequency at point f, ω e It represents the angular frequency of point e. Points d, c, f and e are determined as follows: On the graph where the open-loop transfer function before correction, the lead-lag transfer function, and the open-loop transfer function after correction coexist, draw a vertical line at the cutoff frequency, intersecting the open-loop transfer function before correction at point a, draw the mirror image point b of point a about 0dB, and draw a straight line of 20dB / dec with the mirror image point b as the center, respectively. and It intersects at points c and d, ω represents the angular frequency, α is the parameter, point e is determined on the horizontal line passing through point d, and then a straight line of -20dB / dec is made through point e and intersects with 0dB at point f.

9. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method according to any one of claims 1 to 4 is implemented.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 4 is implemented.

11. A computer program product, characterized in that The computer program product comprises a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 4 is implemented.

Images