A wind turbine impedance reshaping method and device based on damping ratio sensitivity

Abstract

The application provides a wind turbine impedance remodeling method and device based on damping ratio sensitivity, comprising: selecting multiple groups of operating conditions and multiple groups of control parameters; based on each condition, the stability of each group of control parameters combined with the sensitivity of the parameters to the damping ratio under all oscillation modes is analyzed in sequence to determine the optimal parameter group under the condition; selecting the optimal parameter group meeting the stability requirements of all conditions to remodel the wind turbine generation impedance, the application considers the influence of different conditions on the parameter optimization effect and the influence of each optimizable parameter on the oscillation stability of different frequency bands, realizes the collaborative optimization of multi-loop control parameters and the overall improvement of the wideband dynamic characteristics of the wind turbine under a weak power grid. Meanwhile, the method is suitable for different types of wind turbine devices and has universality, which is beneficial to solving various types of new energy generation grid oscillation problems.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation technology, specifically to a method and apparatus for impedance reshaping of wind turbine units based on damping ratio sensitivity. Background Technology

[0002] Unlike traditional synchronous generator sets, wind and solar power generation units mostly achieve grid connection through power electronic converters. Therefore, the grid connection characteristics of renewable energy generation mainly depend on the control method and parameters of the converter. Converter control methods generally include PWM modulation, current inner loop, phase-locked loop, and DC voltage outer loop, with each control loop covering a wide bandwidth from several Hz to hundreds of Hz. The wide-bandwidth control characteristics of the converter interact with the grid characteristics, easily causing oscillations over a wide frequency range. The frequent oscillation problems in renewable energy grid-connected systems in recent years have become one of the important factors restricting the transmission and consumption of renewable energy power generation.

[0003] Since the grid-connected characteristics of renewable energy generation mainly depend on the control characteristics of the grid-connected converter, the suppression of grid-connected oscillations is primarily achieved by modifying the control parameters of the grid-connected converter. However, current methods for optimizing the control parameters of grid-connected converters for broadband oscillations in renewable energy have the following problems: First, they typically only consider the optimization of a single control loop, neglecting the superposition effect of multiple control loops with oscillation modes in different frequency bands; second, they lack a quantitative relationship between control parameters and oscillation stability, and parameter optimization lacks quantitative guidance. Therefore, current methods for suppressing broadband grid-connected oscillations in renewable energy have poor adaptability. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a wind turbine impedance reshaping method based on damping ratio sensitivity, comprising:

[0005] Impedance model determined based on the structure of wind turbine generator set;

[0006] Based on the impedance model, multiple sets of operating conditions and multiple sets of control parameters are selected.

[0007] Based on each operating condition, the stability analysis of each set of control parameters is performed in each oscillation mode to determine the optimal parameter set under the operating condition.

[0008] The generation impedance characteristics of the wind turbine are reshaped by selecting at least one set of optimized parameters that meet the stability requirements of all operating conditions.

[0009] The impedance model includes at least multiple control parameters and multiple operating conditions; the stability analysis under each oscillation mode includes determining the optimal parameter set under each operating condition based on the sensitivity of each parameter to the damping ratio under all oscillation modes.

[0010] Preferably, the impedance model includes: Y p (s,K,O),Y c (s,K,O),Y r (s′,K,O) and Y n (s′,K,O);

[0011] Among them, Y p (s,K,O) represents the positive-sequence admittance of the wind turbine at the disturbance frequency, Y c (s,K,O) represents the coupling admittance from the wind turbine disturbance frequency to the coupling frequency, Y r (s′,K,O) represents the coupling admittance from the wind turbine's coupling frequency to the disturbance frequency, Y n (s′,K,O) represents the negative sequence admittance of the wind turbine at the coupling frequency, O represents the set of operating parameters of the wind turbine, and O={P,Q,V,I}, where P is the active power output of the wind turbine, Q is the reactive power of the wind turbine, V is the port voltage of the wind turbine, I is the fundamental phasor of the output current of the wind turbine, and K is the alternative control parameter.

[0012] Preferably, the step of performing stability analysis on each set of control parameters under each oscillation mode based on each operating condition to determine the optimal parameter set under the operating condition includes:

[0013] Step 1: Select operating conditions sequentially from multiple sets of operating conditions;

[0014] Step 2: Based on the selected operating conditions, calculate the damping ratio for each oscillation mode for each control parameter group in sequence;

[0015] Step 3: When the damping ratio of each oscillation mode corresponding to the control parameter group meets the stability requirements, the parameter group is the optimized parameter group corresponding to the working condition. Continue to execute Step 1 until all working conditions are calculated and then exit; otherwise, execute Step 4.

[0016] Step 4: For each parameter in each parameter group, calculate the sensitivity of each parameter to the damping ratio under all oscillation modes by superimposing the disturbance; and calculate the sum of the sensitivities of the damping ratio of the parameter under all oscillation modes.

[0017] Step 5: Optimize and adjust each parameter based on the sum of the sensitivities using a weighted method, and then execute step 2.

[0018] Preferably, the step of calculating the damping ratio for each oscillation mode based on each operating condition and for each set of control parameters includes:

[0019] The operating conditions and control parameter set are substituted into the pre-constructed power grid impedance calculation formula and admittance calculation formula for calculation, and the non-zero roots are solved using the closed-loop function to obtain the various oscillation modes of the system.

[0020] The damping ratio for each oscillation mode is determined based on the relationship between the oscillation mode and the damping ratio.

[0021] Preferably, when the power grid is an inductive weak power grid, the formulas for calculating the power grid impedance and admittance are as follows:

[0022]

[0023] When the power grid is a series-compensated grid, the formulas for calculating the grid impedance and admittance are as follows:

[0024]

[0025] In the formula, R g L is the equivalent resistance of the power grid impedance. g C is the equivalent inductance of the mains impedance. g Z is the equivalent capacitance of the grid impedance. gp (s) is the positive-sequence impedance of the power grid at the disturbance frequency, Y gp (s) is the grid admittance at the disturbance frequency, Z gn (s′) is the negative sequence impedance of the power grid at the coupling frequency, Y gn (s′) is the grid admittance at the coupling frequency, s is the complex frequency at the disturbance frequency, and s′ is the complex frequency at the coupling frequency.

[0026] Preferably, the relationship between the oscillation mode and the damping ratio is as follows:

[0027]

[0028] Where, ξ i Let be the damping ratio under the i-th oscillation.

[0029] Preferably, the sensitivity of the control parameters to the damping ratio of the oscillation mode is calculated using the following formula:

[0030]

[0031] In the formula, ρ ij Let i be the sensitivity of the i-th oscillation of the j-th parameter, i = 1, 2, ..., N. s j = 1, 2, ..., N k , Δξ i Δk represents the change in damping ratio of the oscillation mode. j The disturbances are superimposed, and Δk j It is a per-unit value based on the initial value.

[0032] Preferably, the Δk j The range of values ​​for is as follows:

[0033] 0.01≤Δk j≤0.05.

[0034] Preferably, the optimization parameters are adjusted using a weighted method based on the following expression:

[0035]

[0036] In the formula, k j For optimizable parameters, ρ Tj k is the sum of the sensitivities of the damping ratio of all oscillation modes for the j-th parameter. j0 These are the initial values ​​for the parameters.

[0037] Based on the same inventive concept, this invention also provides a wind turbine impedance reshaping device based on damping ratio sensitivity, comprising:

[0038] The model determination module is used to determine the impedance model based on the structure of the wind turbine generator set.

[0039] An initialization module is used to select multiple sets of operating conditions and multiple sets of control parameters based on the impedance model.

[0040] The optimization parameter determination module is used to perform stability analysis on each set of control parameters under each oscillation mode based on each working condition, and determine the optimization parameter set under the working condition.

[0041] The impedance reshaping module is used to select at least one optimized parameter set that meets the stability requirements of all operating conditions to reshape the generation impedance characteristics of the wind turbine.

[0042] The impedance model includes at least multiple control parameters and multiple operating conditions; the stability analysis under each oscillation mode includes determining the optimal parameter set under each operating condition based on the sensitivity of each parameter to the damping ratio under all oscillation modes.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] This invention proposes a method and apparatus for impedance reshaping of wind turbine generators based on damping ratio sensitivity, comprising: determining an impedance model based on the structure of the wind turbine generator; selecting multiple operating conditions and multiple control parameters based on the impedance model; performing stability analysis on each set of control parameters under each oscillation mode based on each operating condition to determine the optimal parameter set under the operating condition; and selecting at least one optimal parameter set that meets the stability requirements of all operating conditions to reshape the power generation impedance characteristics of the wind turbine generator. The impedance model includes at least multiple control parameters and multiple operating conditions. The stability analysis under each oscillation mode includes determining the optimal parameter set under each operating condition based on the sensitivity of each parameter to the damping ratio under all oscillation modes. Therefore, this invention considers the impact of different operating conditions on the parameter optimization effect, as well as the impact of each optimizable parameter on the oscillation stability of different frequency bands, achieving coordinated optimization of multi-loop control parameters and overall improvement of the broadband dynamic characteristics of the wind turbine generator under weak power grid conditions.

[0045] This invention proposes a method and apparatus for impedance reshaping of wind turbines based on damping ratio sensitivity. It selects multiple sets of operating conditions and multiple sets of control parameters based on the impedance model determined by the structure of various wind turbine generators, and optimizes based on the selected control parameters. Therefore, this invention is applicable to different types of wind turbines, has universality, and is helpful in solving the grid-connected oscillation problem of various types of wind turbines. Attached Figure Description

[0046] Figure 1 A simplified flowchart of the wind turbine impedance reshaping method based on damping ratio sensitivity provided by the present invention;

[0047] Figure 2 This is a block diagram of the wind turbine impedance reshaping method based on damping ratio sensitivity in Example 1;

[0048] Figure 3 The effect of inverter impedance characteristic reshaping under a short-circuit ratio of 1.3 (full power operation);

[0049] Figure 4 Nyquist analysis of an inverter grid-connected system (full power operation) under a short-circuit ratio of 1.3;

[0050] Figure 5 Nyquist analysis of inverter grid-connected systems under different short-circuit ratios (full power operation);

[0051] Figure 6 This is a typical circuit and control block diagram of a grid-connected inverter;

[0052] Figure 7 The circuit and control structure of a doubly fed wind turbine;

[0053] Figure 8 This is a schematic diagram of a wind turbine grid connection system.

[0054] Figure 9 The positive sequence diagram of the disturbance frequency in the equivalent circuit model of the wind turbine grid-connected system;

[0055] Figure 10 The negative sequence diagram of the disturbance frequency in the equivalent circuit model of the wind turbine grid-connected system;

[0056] Figure 11 This is the transfer function model for a wind turbine grid-connected system. Detailed Implementation

[0057] To better understand this invention, the following description, in conjunction with the accompanying drawings and examples, will further illustrate the invention.

[0058] Example 1:

[0059] This invention provides a wind turbine impedance reshaping method based on damping ratio sensitivity. Based on the frequency domain impedance method, it establishes the intrinsic relationship between the multi-loop control parameters of the wind turbine and its broadband dynamic characteristics. It defines a damping ratio sensitivity index for the multi-loop control parameters to the oscillation mode of renewable energy grid connection. Based on this damping ratio sensitivity index, a renewable energy generation impedance reshaping method based on multi-loop parameter collaborative optimization is proposed to suppress broadband oscillations. The renewable energy generation device in this invention is a wind turbine.

[0060] The impedance characteristics of new energy power generation devices are affected by circuit parameters, control parameters, and operating conditions. Considering that the circuit parameters are determined during the device design, the impedance model can only be reshaped by optimizing the control parameters to make it applicable to a wider range of operating conditions.

[0061] This invention provides a wind turbine impedance reshaping method based on damping ratio sensitivity, such as... Figure 1 As shown, it includes:

[0062] S1. Determine the impedance model based on the structure of the wind turbine generator set;

[0063] S2. Based on the impedance model, select multiple sets of operating conditions and multiple sets of control parameters;

[0064] S3. Based on each working condition, perform stability analysis on each set of control parameters under each oscillation mode in sequence, and determine the optimal parameter set under the working condition.

[0065] S4. Select at least one set of optimized parameters that meets the stability requirements of all operating conditions to reshape the generation impedance characteristics of the wind turbine.

[0066] The impedance model includes at least multiple control parameters and multiple operating conditions; the stability analysis under each oscillation mode includes determining the optimal parameter set under each operating condition based on the sensitivity of each parameter to the damping ratio under all oscillation modes.

[0067] Before performing step S1 of the present invention, the relationship between the control parameters and the sensitivity of the damping ratio under each oscillation mode is first determined:

[0068] Let N be the number of control parameters that can be optimized for a new energy power generation device. k By assigning different values ​​to each parameter, a parameter set K is formed.

[0069] K={k j}, j = 1, 2, ..., N k (1-1)

[0070] Define the sensitivity of the control parameters to the damping ratio of the oscillation mode as ,

[0071]

[0072] If ρ ij If k > 0, it indicates that the control parameter k is increased. j The damping ratio ξ of oscillation mode i i As the control parameter k increases, the oscillation mode tends to stabilize, i.e., the oscillation mode stabilizes. j It is positively correlated with the stability of oscillation mode i; conversely, it indicates that the control parameter k is not positively correlated with the stability of oscillation mode i. j It is negatively correlated with the stability of oscillation mode i. Meanwhile, ρ ij The larger the absolute value, the stronger the control parameter k. j The greater the effect on the stability of oscillation mode i, the better. The optimization direction that maximizes the improvement of the system's broadband oscillation stability can be obtained by weighted summation of the damping ratio sensitivity of multiple oscillation modes using the control parameters.

[0073] The following is a detailed description of the wind turbine impedance reshaping method based on damping ratio sensitivity proposed in this invention, such as... Figure 2 As shown.

[0074] Step S1: Determine the impedance model based on the structure of the wind turbine generator set, specifically including:

[0075] 1. Determine the grid impedance (or admittance). For an inductive weak grid, given the short-circuit ratio and the resistance-to-inductance ratio of the equivalent grid impedance, and for a series compensated grid, given the resistance, reactance, and series capacitance of the equivalent grid impedance, write the grid impedance in the following form.

[0076]

[0077]

[0078] Among them, R g L is the equivalent resistance of the power grid impedance. g C is the equivalent inductance of the mains impedance. g Z is the equivalent capacitance of the grid impedance. gp (s) and Y gp (s) represents the positive-sequence impedance and admittance of the power grid at the disturbance frequency, Z gn (s′) and Y gn (s′) represents the negative sequence impedance and admittance of the power grid at the coupling frequency.

[0079] It should be noted that for series-compensated power grids, the equivalent impedance expression may vary depending on the location of the series compensation capacitor. Only the standard form is given here to illustrate the method.

[0080] 2. Determine the circuit and control structure of the wind turbine and derive its impedance model. To describe the influence of control parameters and operating conditions on the impedance characteristics, the impedance model is rewritten as follows:

[0081] Y p (s,K,O),Y c (s,K,O),Y r (s′,K,O) and Y n (s′,K,O) (1-5) where,

[0082] O = {P, Q, V, I} is the operating parameter set of the wind turbine, indicating the fundamental phasor of the unit's output active and reactive power, port voltage, and output current; Y p (s,K,O) represents the positive-sequence admittance of the wind turbine at the disturbance frequency, Y c (s,K,O) represents the coupling admittance from the wind turbine disturbance frequency to the coupling frequency, Y r (s′,K,O) represents the coupling admittance from the wind turbine's coupling frequency to the disturbance frequency, Y n (s′,K,O) represents the negative sequence admittance of the wind turbine at the coupling frequency.

[0083] Step S2: Based on the impedance model, select multiple sets of operating conditions and multiple sets of control parameters, specifically including:

[0084] 1. Select N o Group operating conditions, O m m = 1, 2, ..., N o N o Generally, a value of 10 to 20 is used; the following section focuses on N. o The parameters of multiple loops were optimized for each operating condition of the group.

[0085] Step S3: Based on each operating condition, perform stability analysis on each set of control parameters under each oscillation mode to determine the optimal parameter set under the operating condition, specifically including:

[0086] Step 1: Select operating conditions sequentially from multiple sets of operating conditions;

[0087] Step 2: Based on the selected operating conditions, calculate the damping ratio for each oscillation mode for each control parameter group in sequence;

[0088] Step 3: When the damping ratio of each oscillation mode corresponding to the control parameter group meets the stability requirements, the parameter group is the optimized parameter group corresponding to the working condition. Continue to execute Step 1 until all working conditions are calculated and then exit; otherwise, execute Step 4.

[0089] Step 4: For each parameter in each parameter group, calculate the sensitivity of each parameter to the damping ratio under all oscillation modes by superimposing the disturbance; and calculate the sum of the sensitivities of the damping ratio of the parameter under all oscillation modes.

[0090] Step 5: Optimize and adjust each parameter based on the sum of the sensitivities using a weighted method, and then execute step 2.

[0091] The process is as follows:

[0092] Substitute the parameter set K (into the initial parameter K from the first round of optimization) o ) and operating condition O m Substituting the values, according to the formula below,

[0093]

[0094] The closed-loop transfer function Y of the system is obtained according to equation (1-4). 1wt (s,K,O m Find the non-zero roots to obtain the N of the system. s One oscillation pattern, s i =-σ i +jω i and damping ratio ξ i i = 1, 2, ..., N s ,

[0095] Y 1wt (s,K,O m )=0 (1-7)

[0096] For any oscillation mode s i All have a damping ratio ξ i ≥ξ ε ξ ε If the value is greater than 0, parameter set K can guarantee stability under this operating condition, and is defined as obtaining operating condition O. m The optimization parameter group Km Returning to step three, continue parameter optimization for the next set of operating conditions; conversely, obtain all damping ratios ξ. i <ξ ε The risk oscillation pattern, assuming there exists N... sr A risk oscillation pattern, s i =-σ i +jω i i = 1, 2, ..., N sr .

[0097] For all optimizable parameters k in turn j Superimposed disturbance Δk j j = 1, 2, ..., N k Δk j It is a per-unit value based on the initial value.

[0098] 0.01≤Δk j ≤0.05 (1-8) Calculate each parameter k using equation (1-4) j Sensitivity to damping ratio for each oscillation mode, ρ ij i = 1, 2, ..., N sr j = 1, 2, ..., N k Next, calculate each parameter k. j The sum of the sensitivities to the damping ratio of all oscillation modes.

[0099]

[0100] It is worth noting that the control parameter k j The damping ratio change may have opposite effects on different oscillation modes, meaning the sensitivity may be positive or negative. By summing the damping ratio sensitivity, the overall effect of this parameter on all oscillation modes can be obtained, thus determining the optimization direction for improving the overall broadband characteristics. Furthermore, for prominent unstable oscillation modes in practical oscillation problems, a weighted approach can be used to accelerate the improvement of stability and parameter optimization efficiency for those modes.

[0101] For the optimizable parameter k j j = 1, 2, ..., N k Optimize and adjust.

[0102]

[0103] Return to step four for the next round of iteration and optimization.

[0104] Finally obtain N o Optimization parameter group K under group operating conditions m m = 1, 2, ..., N o.

[0105] The above method comprehensively considers the impact and quantitative indicators of different control loop parameters on the oscillation stability of wind turbine grid-connected systems at different frequency bands. In practical applications, control parameters can be dynamically adjusted according to operating conditions to meet stability requirements under different conditions; alternatively, an optimized parameter set under the worst operating conditions can be selected, and the stability under different operating conditions can be verified to select one or more sets of parameters that can meet the stability requirements under all operating conditions.

[0106] Example 2:

[0107] To realize the wind turbine impedance reshaping method based on damping ratio sensitivity of the present invention, the present invention also provides a wind turbine impedance reshaping device based on damping ratio sensitivity, comprising:

[0108] The model determination module is used to determine the impedance model based on the structure of the wind turbine generator set.

[0109] An initialization module is used to select multiple sets of operating conditions and multiple sets of control parameters based on the impedance model.

[0110] The optimization parameter determination module is used to perform stability analysis on each set of control parameters under each oscillation mode based on each working condition, and determine the optimization parameter set under the working condition.

[0111] Impedance reshaping module is used to select at least one optimized parameter set that meets the stability requirements of all operating conditions to reshape the generating impedance of the wind turbine.

[0112] The impedance model includes at least multiple control parameters and multiple operating conditions; the stability analysis under each oscillation mode includes determining the optimal parameter set under each operating condition based on the sensitivity of each parameter to the damping ratio under all oscillation modes.

[0113] Since this device is designed to implement the wind turbine impedance reshaping method based on damping ratio sensitivity of the present invention, the specific functions implemented by all functional modules of this device can be referred to in Embodiment 1, and will not be repeated here.

[0114] Example 3:

[0115] Taking a direct-drive wind turbine grid-connected inverter as an example, this paper analyzes the parameter optimization effect under different grid short-circuit ratios. Let the damping ratio index ξ be the one required to achieve stability. ε =0.05, which means that all oscillation modes are required to be increased to a damping level of more than 5%.

[0116] (1) Parameter optimization results under the condition of short-circuit ratio 1.3

[0117] Table 1 presents the parameter optimization results for achieving stability at different power levels ranging from 0.1 pu to 1.0 pu under a short-circuit ratio of 1.3. It can be seen that the initial parameters meet the system stability requirements at active power levels of 0.6 pu and below. However, when the active power reaches 0.7 pu and above, the optimization algorithm improves the multi-loop control parameters significantly, particularly the PLL and DC voltage loop parameters which have a greater impact on the secondary and supersynchronous oscillation modes, while the current loop control parameters, which have a smaller impact on the secondary and supersynchronous oscillation modes, show less improvement. The system exhibits a mid-frequency oscillation mode around 160 Hz; however, the damping ratio of this mode consistently meets the performance requirements during parameter optimization, therefore, it has no impact on the optimization results.

[0118] Table 1. Optimization results of inverter multi-loop control parameters under a short-circuit ratio of 1.3.

[0119]

[0120] Figure 3 A comparison of inverter impedance characteristics under full-power operation with initial and optimized parameters is presented. It can be seen that through multi-loop control parameter optimization, the intersection point of the inverter's sub / supersynchronous frequency band impedance amplitude and the grid impedance amplitude shifts, reducing the corresponding phase angle difference from approximately 180° to approximately 160°, and increasing the system stability margin to 20°.

[0121] Figure 4 The Nyquist curve of the ratio of inverter impedance to grid impedance under the above conditions is given. It can be seen that under the initial parameters, the Nyquist curve bypasses the point (-1, 0j), and the system is unstable. Through parameter optimization, the Nyquist curve no longer bypasses the point (-1, 0j), and the system is stable.

[0122] (2) Parameter optimization results under different short-circuit ratios

[0123] Table 2 presents the parameter optimization results for ensuring system stability at full power level (1.0 pu) under different short-circuit ratios. It can be seen that at short-circuit ratios of 2.5 and above, the initial parameters can meet the system stability requirements, meaning that the damping ratio for all oscillation modes reaches ξ. ε =Above 0.05. When the short-circuit ratio is below 2.5, the optimization algorithm optimizes the multi-loop control parameters, significantly improving the parameters of the phase-locked loop and DC voltage loop, which have a greater impact on the secondary and supersynchronous oscillation modes, while the improvement of the current loop control parameters, which have a smaller impact on the secondary and supersynchronous oscillation modes, is smaller. Although the system has a mid-frequency oscillation mode around 160Hz, the damping ratio of this mode always meets the requirements during the parameter optimization process; therefore, it has no impact on the parameter optimization results.

[0124] Table 2 Optimization results of inverter multi-loop control parameters under different short-circuit ratios.

[0125]

[0126]

[0127] Figure 5 Table 2 presents the Nyquist curves of the system under short-circuit ratios of 1.3 and 1.5, respectively, with the optimized parameters for a short-circuit ratio of 1.3. It can be seen that the control parameters meeting the short-circuit ratio requirement of 1.3 provide a greater stability margin under a short-circuit ratio of 1.5. Therefore, it is generally recommended to optimize the control parameters based on more severe conditions and operating scenarios to adapt to the complex and variable power grid and operating conditions of actual systems.

[0128] Frequency domain impedance method is an effective approach for modeling and analyzing the aforementioned oscillation problems.

[0129] The theoretical basis of this invention includes the construction of an impedance model for grid-connected inverters for new energy power generation and broadband dynamic modeling and stability analysis of grid-connected new energy systems, which will be described in detail below:

[0130] (1) Impedance Model of Grid-Connected Inverter for New Energy Power Generation

[0131] The circuit and control structure of a typical grid-connected inverter for new energy sources are as follows: Figure 6 As shown, it mainly includes circuit components such as DC bus capacitor, three-phase H-bridge switching circuit, AC filter inductor, as well as control components such as phase-locked loop, current loop, DC bus voltage loop, and PWM modulation.

[0132] The new energy power generation side is equivalent to a constant current source I. d The function of DC bus voltage control is to maintain the DC bus voltage at the rated value V. dc And provide the reference value i for d-axis current control. dref The function of phase-locked loop (PLL) control is to track the grid voltage and obtain the phase angle θ. PLL It is used for the transformation between the three-phase stationary coordinate system and the dq rotating coordinate system. The function of current control is to control the current tracking command value i output by the grid-connected inverter. dref and i qref .

[0133] Nonlinear factors in circuits and controls, such as the dynamic DC bus capacitor and phase-locked loop control, can cause frequency coupling effects in the inverter. Specifically, in a three-phase stationary coordinate system, this manifests as follows: at a frequency of f... p Under a positive-sequence small-signal voltage disturbance, in addition to generating a positive-sequence current response at the corresponding frequency, the inverter will also generate a current at a frequency of f. p The negative sequence current response is -2f1, and vice versa. For a three-phase AC system, when f pWhen <2f1, the negative frequency f p The negative sequence component at -2f1 is mathematically related to the positive frequency 2f1-f p The conjugate equivalence of the positive-sequence components. Inverters exhibit frequency coupling effects. To describe their disturbance and response characteristics, the sequence impedance model of a grid-connected inverter is generalized to a 2×2 matrix model with positive and negative sequence components coupled at different frequencies, as follows:

[0134]

[0135]

[0136] in, and The frequencies f in positive and negative sequences are respectively. p and frequency f p -2f1 small signal voltage disturbance and These are the corresponding current responses, Y p (s) represents the inverter at frequency f p The positive-sequence admittance of Y is given by Y. n (s-j2ω1) represents the inverter at frequency f. p Negative-order admittance at -2f1, Y c (s) and Y r (s-j2ω1) represents the inverter at frequency f. p Lower sequence and frequency f p Coupling admittance between negative sequences under -2f1.

[0137] Y p (s) represents the inverter at frequency f p The ratio of the positive-sequence current response to the positive-sequence voltage disturbance under the given positive-sequence voltage disturbance, Y c (s) represents the frequency generated by f p The ratio of the negative-sequence current response to the positive-sequence voltage disturbance of -2f1. Simultaneously, from the conjugate relationship between the negative-sequence component at negative frequency and the positive-sequence component at positive frequency, we can obtain...

[0138]

[0139]

[0140] Here, "*" represents the complex conjugate, therefore, it is possible to calculate only Y. p (s) and Y c Based on (s), Y is derived from the above relationship. n (s-j2ω1) and Y r (s-j2ω1).

[0141] Based on existing research, the impedance / admittance model of a grid-connected inverter considering DC bus capacitor dynamics and voltage control can be obtained as follows:

[0142]

[0143]

[0144] in,

[0145]

[0146]

[0147]

[0148]

[0149] Y 00 (s)=sC dc

[0150]

[0151]

[0152]

[0153] ω1 is the fundamental angular frequency. V1 is the inverter port voltage phasor. I1 is the inverter output current phasor. P S Q represents the active power output of the inverter. S The reactive power output of the inverter is V1, I1, P. S and Q S This indicates the steady-state operating point of the inverter. L is the inverter's filter inductance, and C... dc V is the DC bus capacitor of the inverter. dc K is the rated voltage of the DC bus, which is also the DC bus voltage at the steady-state operating point. d This is the decoupling coefficient for current control, typically equal to ω1L.

[0154] As can be seen from equations (2-5) and (2-6) above, the impedance / admittance model is closely related to the inverter's circuit parameters, control parameters, and operating conditions. Therefore, the method of impedance characteristic reshaping involves control parameter optimization and operating conditions. Impedance characteristic reshaping can be achieved by optimizing control parameters based on multiple sets of operating conditions, thereby improving and suppressing the oscillation problem of new energy grid-connected systems.

[0155] The circuit and control structure of a doubly fed wind turbine is as follows: Figure 7As shown, it includes: an induction asynchronous generator, back-to-back converters (grid-side converter and generator-side converter), and corresponding phase-locked loops, current loops, and other control circuits. In the figure, v a v b v c The voltage on the grid side (i.e., the stator side); i ca i cb i cc The grid-side converter outputs three-phase current; i sa i sb i sc i is the output current on the stator side of the induction generator; ra i rb i rc For the output current of the machine-side converter; θ m L is the rotor position angle; f For the AC filter inductor of the grid-side converter; θ PLL H is the phase angle of the grid voltage output by the phase-locked loop; PLL (s) is the transfer function of the phase-locked loop controller; I cd I cq For the dq-axis current command of the grid-side converter; I rd I rq For the dq-axis current command of the machine-side converter; H si (s), H ri (s) are the transfer functions of the grid-side and generator-side converter current controllers, respectively, and K... sd K rd These are the decoupling coefficients for current control of the grid-side and generator-side converters, respectively; m sa m sb m sc For the grid-side converter modulation signal; m ra m rb m rc This is the modulation signal for the machine-side converter.

[0156] As can be seen, both the stator side and grid-side converter of the doubly-fed induction generator (DFIG) wind turbine are connected to the grid. Therefore, its impedance is equivalent to the parallel combination of the generator-side impedance (including the stator, rotor, and generator-side converter) and the grid-side converter impedance. Since the circuitry and control of the grid-side converter are the same as those of the typical grid-connected inverter described above, its expression will not be detailed here. Referring to the frequency-coupled sequence impedance model of the grid-connected inverter, it is defined as follows:

[0157]

[0158] The generator-side impedance of a doubly-fed induction generator (DFIG) wind turbine is related to the circuit parameters, control loop, and operating point of the induction generator. The basic control loop is the same as that of the grid-side inverter, both considering phase-locked loops (PLLs) and current loops. The main difference between the generator-side impedance and the grid-side converter impedance lies in the basic circuit structure. The internal stator and rotor components of the induction generator consist of stator and rotor resistances, stator and rotor leakage inductances, and mutual inductance, and are affected by the motor speed. Therefore, the expression for the generator-side impedance is relatively complex; similarly, its form is defined as follows:

[0159]

[0160] in,

[0161]

[0162]

[0163] In the formula, s'=s-j2ω1; I r1 The fundamental phasor of the output current of the rotor-side converter at the stable operating point; M r1 The voltage modulation signal phasor for the rotor-side converter at the stable operating point; K e R is the stator-to-rotor turns ratio; r and R s For the stator and rotor resistances referred to the stator side; L r and L s For the stator and rotor inductances referred to the stator side; L m This is the equivalent mutual inductance between the stator and rotor referred to the stator side; σ p (s)=(s-j2πf m ) / s is the slip coefficient.

[0164] Based on the conjugate relationship of equations (2-3) and (2-4), Y can be obtained similarly. n,r (s′) and Y r,r The expression for (s′) can be derived. Finally, the impedance model of the doubly-fed wind turbine can be obtained as follows:

[0165] Y dfig (s)=Y dfig,gsc (s)+Y dfig,r (s) (2-11)

[0166] As can be seen from equations (2-7) to (2-11), the impedance model is closely related to the inverter's circuit parameters, control parameters, and operating conditions. Therefore, we can draw similar conclusions, namely, that the method of reshaping its impedance characteristics involves the optimization of control parameters and operating conditions.

[0167] (2) Broadband dynamic modeling and stability analysis of new energy grid-connected systems

[0168] Based on the established sequence impedance model of new energy power generation devices, it can be... Figure 8 The single-machine grid-connected system shown is modeled as follows: Figure 9 and 10 The equivalent circuit model is shown.

[0169] Assume a positive-sequence small disturbance signal is injected into the grid voltage. Wind turbine port voltage disturbance components The negative sequence current response generated at the coupling frequency is controlled by a current source. This indicates that the current, passing through the grid and the wind turbine's impedance, will generate a negative sequence voltage at the turbine's ports. This voltage will then generate a positive-sequence current response at the original disturbance frequency. and The expression is as follows:

[0170]

[0171]

[0172] The above equivalent circuit model can be described as being perturbed by positive and negative sequence voltages. As input, respond in positive and negative order. For a two-input two-output system with output as the output, its open-loop transfer function matrix is ​​shown in Equation (2-14). The stability of the system should be determined by the generalized Nyquist criterion. The stability of the system is determined by analyzing the trajectory of the two characteristic roots of Equation (2-7) around the point (-1, 0j).

[0173]

[0174] At the same time, after sorting out, Figure 8 The equivalent circuit model shown and the above two-input two-output system can be transformed into the following: Figure 11 The single-input single-output system shown is

[0175] Figure 11 The closed-loop transfer function of the single-input single-output system is:

[0176]

[0177] Among them, Y q (s) characterizes the frequency coupling effect between the inverter and the grid, and can be regarded as an additional admittance / impedance connected in parallel with the inverter.

[0178]

[0179] Therefore, the stability analysis of the system can still be based on the impedance ratio (Y). p (s)+Y q (s)) / Y g(s) The Nyquist stability criterion with single input and single output is used for analysis.

[0180] On the other hand, the stability of the system can be achieved by analyzing the pole distribution of the closed-loop transfer function. As shown in equation (2-15), solving for the closed-loop poles of the system...

[0181] Y 1wt (s)=Y p (s)+Y q (s)+Y gp (s) (2-17)

[0182] Suppose that there are N wind turbines connected to a given power grid system. s There are N oscillation modes, i.e., equation (2-17) has N. s The zeros are the closed-loop poles.

[0183] s i =-σ i +jω i i = 1, 2, ..., N s

[0184] When all closed-loop poles are in the left half of the complex plane, that is, for any s i All have σ i If σ > 0, the system is stable. In fact, in impedance-based system models, the closed-loop poles of the system are equivalent to its oscillation / resonance modes. i ω is the attenuation factor for the oscillation mode. i Let σ be the oscillation frequency. i If the attenuation factor is greater than 0, i.e., the attenuation factor is positive, then the oscillation mode i is stable; otherwise, it is unstable.

[0185] For each oscillation mode, the damping ratio can be calculated.

[0186]

[0187] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0188] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. 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. Furthermore, the present invention can take the form of a computer program product embodied 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.

[0189] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0190] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0191] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0192] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of the claims of the present invention pending approval.

Claims

1. A damping ratio sensitivity based impedance reshaping method for wind turbines, characterized in that, The method comprises the following steps: determining an impedance model based on the structure of a wind turbine generator; selecting multiple sets of operating conditions and multiple sets of control parameters based on the impedance model; based on each operating condition, sequentially performing stability analysis on each set of control parameters under each oscillation mode to determine the optimal parameter set under the operating condition; selecting at least one optimal parameter set that meets the stability requirements of all operating conditions to reshape the impedance characteristics of the wind turbine generator; wherein the impedance model comprises at least multiple control parameters and multiple operating conditions; the stability analysis under each oscillation mode comprises determining the optimal parameter set under the operating condition based on the sensitivity of each parameter to the damping ratio under all oscillation modes; the stability analysis under each oscillation mode based on each operating condition comprises the following steps: Step 1: sequentially selecting an operating condition from multiple operating conditions; Step 2: based on the selected operating condition, sequentially calculating the damping ratio under each oscillation mode for each control parameter set; Step 3: when the damping ratio under each oscillation mode corresponding to the control parameter set meets the stability requirement, the parameter set is the optimal parameter set corresponding to the operating condition, and step 1 is continued until all operating conditions are calculated and the process is exited; otherwise, step 4 is executed; Step 4: sequentially adding perturbations to each parameter in each parameter set to continue calculating the sensitivity of each parameter to the damping ratio under all oscillation modes; and calculating the sum of the sensitivities of the parameters under all oscillation modes; Step 5: based on the sum of the sensitivities, optimizing and adjusting each parameter based on the weighting method, and executing step 2; the optimization and adjustment of the optimal parameters based on the weighting method are based on the following expression: wherein is an optimizable parameter, is the sum of the sensitivities of all oscillation mode damping ratios to the jth parameter, is the initial value of the parameter.

2. The method of claim 1, wherein, The impedance model comprises: , , and ; in, This represents the positive-sequence admittance of the wind turbine at the disturbance frequency. This is the coupling admittance from the wind turbine disturbance frequency to the coupling frequency. This is the coupling admittance from the wind turbine's coupling frequency to the disturbance frequency. This represents the negative-sequence admittance of the wind turbine at the coupling frequency. This is the operating condition parameter set for wind turbine units, and P represents the active power output of the wind turbine, Q represents the reactive power of the wind turbine, V represents the port voltage of the wind turbine, I represents the fundamental phasor of the output current of the wind turbine, and K represents the optional control parameters.

3. The method of claim 1, wherein, the calculation of the damping ratio under each oscillation mode for each control parameter set based on each operating condition comprises the following steps: the operating condition and the control parameter set are brought into the pre-constructed grid impedance calculation formula and the admittance calculation formula to calculate, and the non-zero root is solved by using the closed loop function to obtain each oscillation mode of the system; the damping ratio under each oscillation mode is determined based on the relationship between the oscillation mode and the damping ratio.

4. The method of claim 3, wherein: when the grid is an inductive weak grid, the grid impedance calculation formula and the admittance calculation formula are as follows: ， ； when the grid is a series compensation grid, the grid impedance calculation formula and the admittance calculation formula are as follows: ， wherein is the equivalent resistance of the grid impedance, is the equivalent inductance of the grid impedance, is the equivalent capacitance of the grid impedance, is the positive sequence impedance of the grid at the disturbance frequency, is the admittance of the grid at the disturbance frequency, is the negative sequence impedance of the grid at the coupling frequency, is the admittance of the grid at the coupling frequency, is the complex frequency at the disturbance frequency, is the complex frequency at the coupling frequency.

5. The method of claim 1, wherein, the relationship between the oscillation mode and the damping ratio is as follows: wherein, is the damping ratio under the i-th oscillation.

6. The method of claim 1, wherein, the calculation formula of the sensitivity of the control parameter to the oscillation mode damping ratio is as follows: wherein is the sensitivity of the i-th oscillation of the j-th parameter, , , is the change in the oscillation mode damping ratio, is the superimposed disturbance, and is the dimensionless value with respect to the initial value.

7. The method of claim 6, wherein, The The value range of the is as follows: 。 8. A damping ratio sensitivity based impedance reshaping device for a wind turbine generator characterized by, The method comprises the following steps: a model determination module for determining an impedance model based on the structure of a wind turbine generator; an initialization module for selecting multiple sets of operating conditions and multiple sets of control parameters based on the impedance model; an optimal parameter determination module for, based on each operating condition, sequentially performing stability analysis on each set of control parameters under each oscillation mode to determine the optimal parameter set under the operating condition; an impedance reshaping module for selecting at least one optimal parameter set that meets the stability requirements of all operating conditions to reshape the impedance characteristics of the wind turbine generator; The impedance model comprises at least a plurality of control parameters and a plurality of operating conditions; the stability analysis in each oscillation mode comprises determining the optimal parameter set in each operating condition based on the sensitivity of the damping ratio in all oscillation modes to each parameter in each condition; The stability analysis in each oscillation mode for each control parameter set in each operating condition comprises: Step 1: sequentially selecting an operating condition from a plurality of operating conditions; Step 2: calculating the damping ratio in each oscillation mode for each control parameter set based on the selected operating condition; Step 3: when the damping ratio in each oscillation mode corresponding to the control parameter set meets the stability requirement, the parameter set is the optimal parameter set corresponding to the operating condition, and step 1 is continued until all operating conditions are calculated and the program is exited; otherwise, step 4 is executed; Step 4: sequentially adding perturbations to each parameter in each parameter set to continue calculating the sensitivity of the damping ratio in all oscillation modes to each parameter; and calculating the sum of the sensitivities of the damping ratio in all oscillation modes to the parameters; Step 5: optimizing and adjusting each parameter based on the weighted method based on the sum of the sensitivities, and executing step 2; The optimal parameters are optimized and adjusted based on the weighted method based on the following expression: wherein is an optimizable parameter, is the sum of the sensitivities of all oscillation mode damping ratios to the jth parameter, is the initial value of the parameter.

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