[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work shall fall within the protection scope of the present invention.
[0045] figure 1 It is a schematic diagram of the connection of wind turbines connected to the grid via series compensation lines, such as figure 1 As shown, the converter controller controls the converter, and transmits the electric energy generated by the doubly-fed induction generator 1 to the power grid 6 through the transformer 4 and the series compensation line 5. The converter controller includes the machine-side controller 21 and The grid-side controller 22, the corresponding converter also includes the generator-side converter 31 and the grid-side converter 32, the grid-side controller 22 receives the stator current (provided by the current transformer CT), the generator-side converter and the grid The DC voltage between the side converters (provided by the voltage transformer PT3) and the grid voltage (provided by the voltage transformer PT1) are used as input signals. The signal received by the machine-side controller 21 is based on the signal received by the grid-side controller 22. Also includes stator voltage (provided by voltage transformer PT2). In view of the topological characteristics of the doubly-fed unit and the feature that the subsynchronous oscillation occurs between the doubly-fed induction generator 1 and the series compensation circuit 5, the invention uses the original detection and calculation performance of the grid-side controller 22 to control the grid-side converter The device 32 realizes the subsynchronous oscillation damping effect, optimizes the output performance of the whole machine, and realizes the subsynchronous oscillation suppression of the doubly-fed wind turbine connected to the grid via the series compensation line.
[0046] figure 2 It is a flowchart of steps of a method for suppressing subsynchronous oscillations of a wind turbine according to an embodiment of the present invention, such as figure 2 As shown, the subsynchronous oscillation suppression method of the wind turbine generator of this embodiment includes:
[0047] S100: Obtain the stator current signals of the d-axis and q-axis in the synchronous rotating coordinate system of the wind turbine, and calculate the subsynchronous oscillation frequency according to the stator current signals of the d-axis and q-axis; S200, according to the phase angle deviation table and the proportional coefficient Table and sub-synchronous oscillation frequency, query and obtain the phase angle deviation coefficient, phase angle deviation time constant, and proportional coefficient corresponding to the sub-synchronous oscillation frequency; S300, according to the phase angle deviation coefficient, phase angle deviation time constant, proportional coefficient, The stator current signals of the d-axis and the q-axis generate sub-synchronous oscillation control signals for the d-axis and q-axis; S400, input the signals of the sub-synchronous oscillation control d-axis and q-axis to the basic grid-side control inner loop of the wind turbine.
[0048] image 3 It is a control principle diagram of the subsynchronous oscillation suppression method of a wind turbine according to an embodiment of the present invention, combined with Figure 1 to Figure 3 As shown, in step S100 of this embodiment, the stator current signals of the d-axis and the q-axis in the synchronous rotating coordinate system of the wind turbine are acquired, and the subsynchronous oscillation frequency is calculated according to the stator current signals of the d-axis and the q-axis. The specific implementation can include:
[0049] First, obtain the stator current signals of the d-axis and q-axis in the synchronous rotating coordinate system of the wind turbine. Since the machine-side controller is connected to the output line of the doubly-fed induction generator through a voltage transformer, it can directly obtain the stator current of the wind turbine and convert it into the stator current of the d-axis and q-axis in the synchronous rotating coordinate system Signals (Isd, Isq), the stator current signals of the d-axis and the q-axis are used to extract the subsynchronous current components (Isd_ssr, Isq_ssr) in the subsequent steps.
[0050] Then, the subsynchronous component signals in the stator current signals of the d-axis and the q-axis are separated and extracted through the cascade of low-pass filtering and high-pass filtering. In the stator current signals (Isd, Isq) of the d-axis and q-axis, the sub-synchronous current components (Isd_ssr, Isq_ssr) are extracted by the sub-synchronous oscillation separator in the machine-side controller. The sub-synchronous oscillation separator uses a software filter The method is formed by cascading low-pass filtering and high-pass filtering, which can separate and extract the subsynchronous current components in the stator current signals of the d-axis and the q-axis.
[0051] Finally, according to the subsynchronous component signal, the fast Fourier transform is used to calculate the subsynchronous oscillation frequency. Fast Fourier analysis (DFFT analysis) is performed on the subsynchronous current components (Isd_ssr, Isq_ssr) to obtain the subsynchronous oscillation frequency (fssr_dq). Taking into account the existing oscillatory separators to avoid interference from other signals, the idea of maintaining the number of calculation points but reducing the sampling frequency of Fourier analysis is adopted, which not only improves the frequency resolution, but also ensures the feasibility of real-time calculation. In the specific implementation process, it is possible to first determine whether the oscillation amplitude of the sub-synchronous component signal is within a preset range according to the oscillation amplitude of the sub-synchronous component signal, and then proceed to subsequent steps.
[0052] In step S200 of this embodiment, according to the phase angle offset table, the proportional coefficient table, and the subsynchronous oscillation frequency, the phase angle offset coefficient, the phase angle offset time constant, and the proportional coefficient corresponding to the subsynchronous oscillation frequency are inquired. The phase angle deviation table and proportional coefficient table are preset in the grid-side controller for technicians, and used to query the preset phase angle deviation coefficient and phase angle deviation time constant using the subsynchronous oscillation frequency (fssr_dq) , Scale factor.
[0053] In step S300 of this embodiment, according to the phase angle offset coefficient, the phase angle offset time constant, the proportional coefficient, the stator current signals of the d-axis and the q-axis, the signals (Issrd , Issrq). According to the phase angle offset coefficient, the phase angle offset time constant, and the proportional coefficient, the stator current signals of the d-axis and q-axis input to the grid-side controller are adjusted to generate subsynchronous oscillation control d-axis and q-axis signals. The adjustment process can be realized by setting up a subsynchronous oscillation separator and a phase shift corrector. The subsynchronous oscillation phase shift corrector is composed of a lead-lag link and a proportional link. The continuous domain transfer function of the lead-lag link is taken as a> Phase is advanced at 1, a <1, the phase lags behind. The maximum phase angle offset value of the lead-lag link and its corresponding frequency can be changed. The proportional coefficient Ka corrects the amplitude-frequency change caused by the lead-lag link. It is supplemented that the phase shift corrector is digitally implemented in the grid-side converter controller, and discretization is required. It is recommended to use the bilinear transformation method ( s is the Laplace transform operator; T c Is the control period; z is the z-transformation operator) to ensure that the phase-frequency characteristics before and after discretization are consistent.
[0054] In the specific implementation process, in step S300, the online adjustment of the phase angle offset coefficient, the phase angle offset time constant, and the proportional coefficient is controlled. Specifically, it includes two parts: parameter lookup table and execution logic. The execution logic is based on whether the oscillation amplitude of the sub-synchronous component signal (Isd_ssr, Isq_ssr) is within a predetermined range, decides the reliability of the calculation result of the sub-synchronization frequency, and whether to adopt the sub-synchronization suppression. Online adjustment of control parameters (phase angle offset coefficient, phase angle offset time constant, proportional coefficient) refers to querying the phase angle offset table and coefficient table according to the detected subsynchronous oscillation frequency (fssr_dq), the phase angle offset The table and coefficient table can be pre-made, the input is fssr_dq, the points are taken every 2Hz within the range of 2~50Hz, and the output is the phase angle θ1, which characterizes the lag of sampling hardware filtering, software filtering and other inherent links of the system to the subsynchronous oscillation frequency fssr_dq; output coefficient The value K1 represents the amplitude loss of the subsynchronous oscillation component of the frequency fssr_dq by the inherent link of the system. The phase angle θ1 and the coefficient value K1 determine the amplitude-frequency and phase-frequency characteristics of the lead-lag link, and then a, T 1 And the Ka value.
[0055] In step S400 of this embodiment, the signals of the sub-synchronous oscillation control d-axis and q-axis are input to the basic grid-side control inner loop of the wind turbine. The signals (Issrd, Issrq) for controlling the d-axis and q-axis of the subsynchronous oscillation generated in step S300 are input to the grid-side converter to control the conversion operation of the grid-side converter, and realize the subsynchronous oscillation damping effect.
[0056] After introducing the method for suppressing the sub-synchronous oscillation of the wind turbine in the embodiment of the present invention, next, the device for suppressing the sub-synchronous oscillation of the wind turbine in the embodiment of the present invention is introduced. The implementation of the device can refer to the implementation of the above method, and the repetition will not be repeated. The terms "module" and "unit" used below may be software and/or hardware that implements predetermined functions.
[0057] Figure 4 It is a schematic structural diagram of a subsynchronous oscillation suppression device of a wind turbine generator according to an embodiment of the present invention, such as Figure 4 As shown, a subsynchronous oscillation suppression device of a wind turbine generator in this embodiment includes:
[0058] The subsynchronous oscillation frequency calculation module 100 is used to obtain the stator current signals of the d-axis and the q-axis in the synchronous rotating coordinate system of the wind turbine, and calculate the sub-synchronous oscillation frequency according to the stator current signals of the d-axis and the q-axis;
[0059] The oscillation control parameter query module 200 is used to query and obtain the phase angle deviation coefficient, the phase angle deviation time constant, and the proportional coefficient according to the phase angle deviation table, the proportional coefficient table, and the subsynchronous oscillation frequency;
[0060] The subsynchronous oscillation control signal generation module 300 is used to generate subsynchronous oscillation control d-axis and q-axis signals according to the phase angle offset coefficient, the phase angle offset time constant, the proportional coefficient, and the stator current signals of the d-axis and q-axis ;
[0061] The sub-synchronous oscillation control signal output module 400 is used to input the signals of the sub-synchronous oscillation control d-axis and q-axis to the inner loop of the basic grid-side control of the grid-side converter.
[0062] In the specific implementation process, the subsynchronous oscillation frequency calculation module 100 includes:
[0063] The dq signal acquisition module is used to acquire the stator current signals of the d-axis and the q-axis in the synchronous rotating coordinate system of the wind turbine;
[0064] The sub-synchronous component signal separation module is used to separate and extract the sub-synchronous component signals from the stator current signals of the d-axis and the q-axis through the cascade of low-pass filtering and high-pass filtering;
[0065] The sub-synchronous oscillation frequency determination module uses fast Fourier transform to calculate the sub-synchronous oscillation frequency according to the sub-synchronous component signal.
[0066] In the specific implementation process, the subsynchronous oscillation suppression device of the wind turbine unit further includes: an oscillation amplitude judgment module for judging whether the oscillation amplitude of the subsynchronous component signal is within a preset range according to the oscillation amplitude of the subsynchronous component signal.
[0067] In the specific implementation process, in the subsynchronous oscillation control signal generation module 300, the continuous domain transfer function is:
[0068]
[0069] Among them, a is the phase angle deviation coefficient;
[0070] T 1 Is the phase angle offset time constant;
[0071] s is the Laplace transform operator.
[0072] In the specific implementation process, the subsynchronous oscillation control signal generation module 300 includes: a discretization module, which is used to discretize the continuous domain function using a bilinear transformation method. The bilinear transformation equation is:
[0073]
[0074] Among them, s is the Laplace transform operator; T c Is the control period; z is the z transformation operator.
[0075] The following describes the subsynchronous oscillation suppression method of the wind turbine generator of the present invention with specific examples. Considering that a large-scale wind turbine in a certain area of China is connected to the grid via a series compensation line, the measured AC side subsynchronous oscillation frequency is about 3-8Hz. The following embodiments are developed using this application scenario as an example.
[0076] The above-mentioned subsynchronous oscillation suppression method for wind turbines is implemented based on the simulation in Matlab\Simulink electromagnetic transient model, and it is verified that this method can effectively suppress the subsynchronous oscillations of doubly-fed wind turbines via series compensation lines. Figure 5 This is the simulation comparison waveform of the subsynchronous oscillation of the doubly-fed wind turbine through the series-compensated line grid-connected system in the embodiment of the present invention and the oscillation is suppressed after applying the method of the present invention, refer to Figure 5 , Which selects the simulation waveforms of the side-line voltage AB phase, the stator current A phase and the grid-side converter current A phase of the doubly-fed wind turbine. The dashed line shows the simulation waveform without suppression method. From the stator current A phase and grid-side converter current A phase waveforms, you can see an obvious 7.6Hz oscillation component, and the stator current oscillation amplitude is higher than 3000A, which will cause actual wind power The unit overcurrent protection trips. The solid line waveform is the subsynchronous oscillation suppression method of the wind turbine generator of the present invention, and the voltage and current waveforms are improved significantly. The system appears as a normal grid-connected waveform, and the oscillation is suppressed.
[0077] Image 6 (A) represents the Fourier analysis output when the oscillation occurs, and (b) represents the real-time Fourier analysis output of the subsynchronous oscillation frequency after applying the subsynchronous oscillation suppression method of the wind turbine according to the embodiment of the present invention. The Fourier analysis frequency resolution is 2Hz. It can be seen that the harmonic content of the 21st order, that is, fssr_dq=42Hz, is large. The real-time display of the harmonic content in the figure is 1098A, which corresponds to the three-phase frequency fssr1=8Hz. Figure 5 The medium oscillation components are similar, indicating that the real-time calculation results are more reliable. by Image 6 In (b) it can be seen that after applying the subsynchronous oscillation suppression method of the wind turbine of the present invention, the Fourier analysis output of the subsynchronous oscillation frequency real-time calculator shows that there is no obvious oscillation phenomenon in the 0-80Hz frequency band, indicating that the oscillation is suppressed .
[0078] The technical effect of the present invention is that through the synchronous oscillation suppression method of the wind turbine generator of the present invention, the subsynchronous oscillation between the wind turbine generator and the series compensation line can be suppressed, and in terms of performance, it can adapt to a certain degree of operating mode changes. In terms of specific implementation, only the original detection and calculation performance of the grid-side converter of the doubly-fed unit needs to be used, and the subsynchronous oscillation can be suppressed through the upgrade of the software control strategy. There is no hardware loop modification cost and easy engineering modification.
[0079] The above specific embodiments further describe the purpose, technical solutions and beneficial effects of the present invention in further detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the protection scope of the present invention. Within the spirit and principle of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.
