Joint algorithm for optimizing double-fed wind turbine generator subsynchronous oscillation impedance controller

Abstract

The invention discloses a joint algorithm for optimizing a double-fed wind turbine generator subsynchronous oscillation impedance controller. The joint algorithm comprises the following steps: collecting meteorological data and historical power data of a target photovoltaic power station region to form a data set; comprising frequency domain impedance calculation and additional damping controller design; the frequency domain impedance calculation method specifically comprises the step of constructing a total impedance model Ztotal of the doubly-fed wind power system based on a rotor side converter RSC of a control system, a grid side converter GSC of the control system, stator side impedance Zs, rotor side impedance Zr and line impedance Zl. The design of the additional damping controllers is that the additional damping controllers are respectively added into the rotor side converter and the grid side converter, the parameters of the additional damping controllers are jointly optimized, and the subsynchronous oscillation is inhibited; specifically, the additional damping controller is formed by connecting a filtering link, a gain link and a phase shift link in series. According to the algorithm designed by the method, on the premise that the power transmission capacity is guaranteed, the purpose of broadband domain stability of the wind power grid-connected system is achieved.

Description

Technical field:

[0001] The present invention belongs to the technical field of power system stabilization and control, and in particular relates to a joint algorithm for optimizing a subsynchronous oscillation impedance controller of a doubly-fed wind turbine generator set. Background technology:

[0002] As the global energy mix shifts toward a low-carbon economy, wind power continues to grow in power systems. Doubly-fed wind turbines (DFIGs) dominate the market due to their low cost and wide speed range. To improve line transmission capacity and enhance transient stability, AC transmission systems often employ series capacitor compensation technology. By offsetting line inductive impedance, this technology can increase transmission capacity by 30%-50%, while reducing line losses and investment costs, and mitigating natural and electromagnetic pollution. This technology has broad application potential in large-scale wind power transmission. However, the capacitive impedance introduced by this technology interacts with the power electronic converters of DFIGs, easily inducing sub-synchronous oscillations (SSOs). These are characterized by persistent voltage / current fluctuations in the 20-50 Hz frequency range. In severe cases, these fluctuations can cause wind turbines to disconnect from the grid and damage the equipment. Currently, there are three main strategies for suppressing subsynchronous oscillations: First, the risk of SSO can be eliminated by reducing the compensation degree or completely removing the capacitors, but this will lead to a reduction in wind power transmission capacity; second, the installation of dynamic reactive power compensation devices (such as SVG, STATCOM) to suppress oscillations by enhancing additional damping control, but this method is limited by the capacity of the SVG or STATCOME. Third, the control system of the wind turbine is adjusted, such as modifying the current loop parameters of the rotor-side converter (RSC) or increasing the virtual impedance of the grid-side converter (GSC). However, this method has problems such as poor adaptability to operating conditions and unsuppressed impedance coupling effects. The impedances of the RSC and GSC exhibit strong coupling characteristics in the subsynchronous frequency band, and unilateral control is difficult to coordinate the impedance phases of the two, resulting in limited damping effects. In summary, there is an urgent need to design a subsynchronous oscillation suppression method that is adaptive to all operating conditions and has bilateral collaborative optimization. Summary of the invention:

[0003] To address the above problems, the present invention provides a joint algorithm for optimizing the subsynchronous oscillation impedance controller of a doubly-fed wind turbine generator system to achieve wide-band stability of the wind power grid-connected system while ensuring power transmission capacity.

[0004] A joint algorithm for optimizing the subsynchronous oscillation impedance controller of a doubly-fed wind turbine generator system includes frequency-domain impedance calculation and added damping controller (SDC) design. The frequency-domain impedance calculation is used to calculate the system impedance in real time based on the oscillation situation, determine the system stability, and provide a basis for setting the parameters of the added damping controller, especially the gain stage. The added damping controller is designed to optimize the output signal and improve the suppression effect when the subsynchronous component in the voltage signal is high during an unstable negative damping state.

[0005] The specific method of the frequency domain impedance calculation method is:

[0006] Based on the control system rotor side converter RSC, control system grid side converter GSC, stator side impedance Z s , rotor side impedance Z r And line impedance Z l , construct the total impedance model Z of the doubly fed wind power system total :

[0007]

[0008] Among them, Z GSC and Z RSC are the impedances of the grid-side converter and the rotor-side converter respectively;

[0009]

[0010] Among them, K pg and K ig are the proportional and integral coefficients in GSC respectively; K pr and K ir are the proportional and integral coefficients in the RSC respectively; the proportional coefficients in the rotor-side converter and the grid-side converter will directly affect the size of the system impedance and are the key parameters for joint optimization. They work together with the gain link in the additional damping controller to achieve the purpose of suppressing subsynchronous oscillations.

[0011] The design of the additional damping controller is to add additional damping controllers to the rotor-side converter and the grid-side converter respectively, and jointly optimize the parameters of the additional damping controllers to suppress subsynchronous oscillations. Specifically, the design of the additional damping controller is composed of a filter link, a gain link, and a phase shift link connected in series:

[0012] Filtering: The core of the filtering process is to utilize the filter's frequency selection function to extract subsynchronous signals. The filter uses the oscillatory components in the feedback signal to select signals with specific subsynchronous frequencies while attenuating other frequencies. This allows the control system to accurately process subsynchronous oscillations, providing the correct signal for subsequent gain and phase adjustments, helping the DFIG better coordinate with the power grid and improving system stability and operational performance.

[0013]

[0014] Among them, H F (s) is the filter transfer function, ω S is the system frequency, ζ S is the damping coefficient of the band-stop filter, ζ P is the damping coefficient of the bandpass filter, H represents the number of wind turbines in the wind farm, ω0 is the subsynchronous oscillation frequency, s is used for counting, and k is the complex frequency in the Laplace transform;

[0015] Gain link: Adjusting the gain coefficient can ensure that the control system can quickly identify subsynchronous oscillations and accurately output corresponding voltage signals, preventing the oscillation from intensifying and enhancing the stability and reliability of the power system.

[0016]

[0017] Where K(s) is the gain transfer function, U out It represents the output voltage of the control system without adding the additional damping controller, U A (s), U B (s), U C (s) respectively represent the voltage signals of the wind farm lines;

[0018] Phase-shifting link: The PID phase compensation controller is highly robust. The phase-shifting link uses a lead-lag structure to generate a voltage loop reference signal, facilitating adjustment of gain and phase compensation parameters.

[0019]

[0020]

[0021] Where f(s) is the phase compensation transfer function, and T is the time constant of the phase compensation link;

[0022] The additional damping controller consists of three links in series: filtering, gain, and phase shift. The transfer function of the additional damping controller is:

[0023]

[0024] Where m is the number of phase compensation controllers in a set of additional damping controllers.

[0025] Preferably, the line impedance Z l , stator side impedance Z s and rotor side impedance Z r They are:

[0026]

[0027] Among them, n is the number of resistance, inductance and reactance components in each module, R, R s 、R l are the line resistance, stator side resistance and rotor side resistance of the doubly fed wind turbine respectively; L, L ls , L lr , M are the line inductance, stator side inductance, rotor side inductance and mutual inductance between stator and rotor of the doubly fed wind turbine respectively; η GR is the comprehensive optimization coefficient of the rotor side and grid side control system, δ Z is the line impedance optimization coefficient, ω is the nominal angular velocity, ω m is the rotor angular velocity, C is the series compensation capacitor, j is an imaginary unit, and all the electrical quantities on the rotor side have been converted to the stator side.

[0028] Preferably, S and ζ P The value is 0.1.

[0029] Preferably, n GR The value is 0.2, δ Z The value is 0.5, and the value of ω is 314rad / s.

[0030] Preferably, K(s) of the gain link is dynamically adjusted by real-time monitoring of the impedance and oscillation amplitude of the doubly-fed wind power system, and the gain value is limited to a preset amplitude upper limit.

[0031] The present invention designs a joint algorithm for optimizing the subsynchronous oscillation impedance controller of a doubly-fed wind turbine. Through the collaborative design and dynamic parameter optimization of the two-side (rotor-side and grid-side) controllers, the suppression capability of subsynchronous oscillations (SSO) is significantly improved. Compared with the traditional unilateral control strategy, this method can achieve full operating condition adaptation. It combines the frequency domain impedance model to calculate the total system impedance in real time, and dynamically adjusts the gain, filtering and phase shift parameters of the additional damping controller to ensure that oscillations can be effectively suppressed under different wind speeds, series compensation degrees and number of units. This solves the problem of poor operating condition adaptability caused by fixed parameters in existing methods. At the same time, additional damping controllers are introduced into the rotor-side converter (RSC) and the grid-side converter (GSC). The system damping characteristics are enhanced through impedance joint optimization, which makes up for the defect of unilateral control's insufficient response to complex impedance interactions and achieves bilateral collaborative optimization. In this method, the gain coefficient is adaptively adjusted based on the real-time monitored impedance and oscillation amplitude, and an amplitude upper limit is set to avoid harmonic distortion or equipment overload caused by overmodulation, taking into account both suppression effect and system safety. Description of the drawings:

[0032] Attachment Figure 1 3 is a comparison diagram of the a-phase current waveform in an embodiment of the present invention. Specific implementation method:

[0033] In order to make the technical solution of the present invention easier to understand, a joint algorithm for optimizing the subsynchronous oscillation impedance controller of a doubly-fed wind turbine generator system disclosed in the present invention is now clearly and completely described in combination with embodiments and drawings.

[0034] Assume a wind farm is equipped with 150 doubly-fed wind turbines (DFIGs), each rated at 2.5 MW, for a total installed capacity of 375 MW. The turbines are connected to the grid via a 220 kV collector line, which uses series capacitor compensation at a 35% compensation level. Specific parameters are as follows:

[0035] Doubly fed wind turbine parameters:

[0036] Stator side resistance R s =0.012Ω, inductance L ls =0.16mH;

[0037] Rotor side resistance R r =0.018Ω, inductance L lr =0.20mH;

[0038] Stator and rotor mutual inductance M = 2.8mH;

[0039] Rated speedω m =1.18pu.

[0040] Line parameters:

[0041] Line resistance R l =0.10Ω / km, inductance L l =1.4mH / km;

[0042] The series compensation capacitor C=120μF, and the compensation section length is 18km.

[0043] System frequency: f S =50Hz, subsynchronous oscillation frequency f P =28Hz, corresponding to angular frequency ω0=2π×28=175.93rad / s.

[0044] Calculate the line impedance Z l

[0045] According to the formula:

[0046]

[0047] Substitute the parameter R l =0.10Ω,L l =1.4mH, C=120μF, the calculated single-section line impedance is =: 0.1+j0.246-j47.62Ω.

[0048] The total line impedance is the single-segment value multiplied by the number of compensation segments (10 segments):

[0049] Z l =18×(0.1+j0.246-j47.62Ω=1.8+j4.43-j857.16Ω.

[0050] Calculate the stator side impedance:

[0051]

[0052] Calculate the rotor side impedance (converted to the stator side) and substitute ω m =1.18×314=371.32rad / s, calculate:

[0053]

[0054] Calculate GSC impedance Z GSC :

[0055]

[0056] Assume that the proportionality coefficient K pg＝ 0.4, integration coefficient K ig =8, substitute into the calculation to get: Z GSC ≈178.5∠98.2°Ω;

[0057] Calculate the RSC impedance ZRSC :

[0058]

[0059] Assume K pr =0.5,K ir =10, we get: Z RSC ≈150×0.93∠100.5°≈139.5∠100.5°Ω

[0060] Calculate the total system impedance Z total :Substitute the optimal parameter η GR =0.2,δ Z =0.5,n=2,H=150

[0061]

[0062] Substituting the above data into Z total =-1633.34+j15.4Ω.

[0063] Design an added damping controller:

[0064] Filtering step: Design a bandpass filter (ω0=175.93rad / s) and a bandstop filter (ω S =314rad / s) damping coefficient ζ S =ζ P =0.1:

[0065]

[0066] Taking k = 2, the second-order filter transfer function is generated:

[0067]

[0068] Gain link:

[0069] The dynamic gain function K(s) is based on the real-time impedance Z total Adjusted and limited by K max =10:

[0070]

[0071] In actual calculations, the gain amplitude is limited by normalization.

[0072] Phase shift link: time constant T = 0.018s, compensation frequency ω0 = 175.93rad / s:

[0073]

[0074] The first three harmonics (n=1, 2, 3) are intercepted, and the coefficients an and bn are calculated to generate the compensation signal.

[0075] like Figure 1 The a-phase current waveform after the GSC and RSC control systems are jointly connected to the SDC is shown by the purple line in the figure below, the a-phase current waveform after the RSC control system is only connected to the SDC is shown by the green line in the figure below, and the a-phase current waveform without SDC suppression is shown by the orange line in the figure below. This comparison clearly shows that SSO is suppressed after the addition of SDC, and the effect of combined optimization of the GSC and RSC control systems is better than that of optimizing a single control system, demonstrating that the present invention can more effectively solve the subsynchronous oscillation problem in doubly fed wind power grid-connected systems through series compensation.

[0076] It should be pointed out that for ordinary technicians in this technical field, they can make several improvements, replacements, modifications and embellishments without departing from the principles and purpose of the present invention. These improvements, replacements, modifications and embellishments should also be regarded as the scope of protection of the present invention.

Claims

1. A joint algorithm for optimizing the subsynchronous oscillation impedance controller of a doubly-fed wind turbine generator system, characterized in that: The algorithm includes frequency domain impedance calculation and added damping controller design; The specific method of the frequency domain impedance calculation method is: Based on the control system rotor side converter RSC, control system grid side converter GSC, stator side impedance Z s , rotor side impedance Z r And line impedance Z l , construct the total impedance model Z of the doubly fed wind power system total : Among them, Z GSC and Z RSC are the impedances of the grid-side converter and the rotor-side converter respectively; Among them, K pg and K ig are the proportional and integral coefficients in GSC respectively; K pr and K ir are the proportional and integral coefficients in RSC respectively; The design of the additional damping controller is to add additional damping controllers to the rotor-side converter and the grid-side converter respectively, and jointly optimize the parameters of the additional damping controllers to suppress subsynchronous oscillations. Specifically, the design of the additional damping controller is composed of a filter link, a gain link, and a phase shift link connected in series: Filtering stage: Among them, H F (s) is the filter transfer function, ω S is the system frequency, ζ S is the damping coefficient of the band-stop filter, ζ P is the damping coefficient of the bandpass filter, H represents the number of wind turbines in the wind farm, ω0 is the subsynchronous oscillation frequency, s is used for counting, and k is the complex frequency in the Laplace transform; Gain link: Where K(s) is the gain transfer function, U out It represents the output voltage of the control system without adding the additional damping controller, U A (s), U B (s), U C (s) respectively represent the voltage signals of the wind farm lines; Phase shift link: Where f(s) is the phase compensation transfer function, and T is the time constant of the phase compensation link; Then the transfer function of the additional damping controller is: Where m is the number of phase compensation controllers in a set of additional damping controllers.

2. The joint algorithm for optimizing the subsynchronous oscillation impedance controller of a doubly-fed wind turbine generator system according to claim 1, characterized in that: The line impedance Z l , stator side impedance Z s and rotor side impedance Z r They are: Among them, n is the number of resistance, inductance and reactance components in each module, R, R s 、R l are the line resistance, stator side resistance and rotor side resistance of the doubly fed wind turbine respectively; L, L ls 、L lr , M are the line inductance, stator side inductance, rotor side inductance and mutual inductance between stator and rotor of the doubly fed wind turbine respectively; η GR is the comprehensive optimization coefficient of the rotor side and grid side control system, δ Z is the line impedance optimization coefficient, ω is the nominal angular velocity, ω m is the rotor angular velocity, C is the series compensation capacitor, and j is the imaginary unit.

3. The joint algorithm for optimizing the subsynchronous oscillation impedance controller of a doubly-fed wind turbine generator system according to claim 1, characterized in that: ζ S and ζ P The value is 0.

1.

4. The joint algorithm for optimizing the subsynchronous oscillation impedance controller of a doubly-fed wind turbine generator system according to claim 2, characterized in that: η GR The value is 0.2, δ Z The value is 0.5, and the value of ω is 314rad / s.

5. The joint algorithm for optimizing the subsynchronous oscillation impedance controller of a doubly-fed wind turbine generator system according to claim 1, characterized in that: The K(s) of the gain link is dynamically adjusted by real-time monitoring of the impedance and oscillation amplitude of the doubly-fed wind power system, and the gain value is limited to a preset amplitude upper limit.

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