Multi-branch power system stabilizer suitable for wind-fire bundling system

Abstract

The invention discloses a multi-branch power system stabilizer suitable for a wind-thermal bundling system, which adopts a cooperative control structure in which a low-frequency branch and a subsynchronous branch are connected in parallel, and suppresses low-frequency oscillation in a frequency band of 0.1-4Hz through a second-order filtering module, a blocking compensation module and a lead-lag module of the low-frequency branch. And the subsynchronous branch extracts a subsynchronous risk mode based on an inverse transformation matrix of a generator shafting torsional vibration mode quantity, and directionally injects a damping signal in combination with a phase compensation module to suppress subsynchronous oscillation in a frequency band of 10-50 Hz. And the parallel output module performs superposition amplitude limiting on the multi-branch signals and then accesses an excitation regulator to dynamically regulate the electromagnetic torque so as to realize wide-frequency-domain oscillation suppression. Through modal quantity directional control, parameter adaptive setting and multi-branch dynamic decoupling, the problems of insufficient multi-band suppression capability, parameter mismatch, controller conflict and the like of a traditional power system stabilizer in a wind-fire coupling system are solved, and the stability and robustness of a new energy high-permeability power grid are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of automatic control of power systems, and particularly relates to a multi-branch power system stabilizer applicable to a thermal-wind bundling system. Background Art

[0002] With the rapid development of new energy power generation technologies, renewable energy sources such as wind power have been massively connected to the power grid, and the "thermal-wind bundling" system operating in parallel with thermal power units has gradually become an important mode in the power field. However, due to the significant differences in the dynamic characteristics between wind turbines and thermal power units in such systems, the problem of low-frequency oscillation in the power system has become increasingly prominent. The strong randomness and weak inertia characteristics of wind power, combined with the synchronous machine dynamic response characteristics of thermal power units, make the system prone to exciting multi-band oscillation modes under disturbances, seriously threatening the safe and stable operation of the power grid.

[0003] Traditional Power System Stabilizers (PSS) are mainly designed for thermal power synchronous units and suppress local or regional oscillation modes by introducing additional damping control. However, in a thermal-wind bundling system, the dynamic coupling characteristics of wind power connected to the grid through converters and thermal power connected to the grid through synchronous machines are complex, and it is difficult for traditional single-branch PSS to meet the requirements of suppressing broadband oscillations under multi-energy interactions. In addition, the existing PSS parameters are usually set based on a single operating point and cannot adapt to the system condition changes caused by the random fluctuations of thermal and wind power outputs, which may lead to parameter mismatch problems and even exacerbate the oscillation risk.

[0004] In recent years, for the stable control of multi-energy power systems, some studies have attempted to improve system stability by coordinating multiple PSSs or combining additional damping control of wind turbines. However, such methods still have limitations: firstly, the coupling mechanisms of multiple branches (such as the shafting modes of thermal power units, the resonance of the wind farm collector network, and the oscillations of AC / DC tie lines) in the thermal-wind bundling system have not been fully analyzed, resulting in insufficient pertinence of control strategies; secondly, there is a lack of a dynamic coordination mechanism between multiple controllers, which is prone to causing control conflicts or response lags; thirdly, existing technologies mostly rely on accurate models and are difficult to adapt to the strong uncertainties and time-varying characteristics caused by the high proportion of new energy access. Summary of the Invention

[0005] The present invention is to solve the above-mentioned deficiencies existing in the prior art, and proposes a multi-branch power system stabilizer applicable to a thermal-wind bundling system, aiming to significantly improve the stability of a system with a high proportion of wind power and thermal power operating in parallel through multi-branch cooperative control, broadband domain adaptive regulation, and dynamic characteristic decoupling technologies, thereby overcoming the problems of insufficient multi-band oscillation suppression ability, poor parameter robustness, and difficult coordination of multiple controllers existing in traditional Power System Stabilizers (PSS) in the thermal-wind bundling system.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A multi-branch power system stabilizer applicable to a wind-fire bundling system, the wind-fire bundling system includes: an equivalent wind turbine multiplied by n wind turbines, an equivalent generator multiplied by n generators, a series-compensated transmission line, and an AC power grid. Among them, the equivalent generator includes an excitation system and a six-mass equivalent model; the equivalent wind turbine and the equivalent synchronous machine are respectively connected in parallel through transformers and then connected to the AC power grid through the series-compensated transmission line. The feature is that a multi-branch power system stabilizer is also provided in the equivalent generator, which includes: a low-frequency branch, a sub-synchronous branch, and a parallel output module. After the low-frequency branch and the sub-synchronous branch are connected in parallel, they are connected in series with the parallel output module and connected to an additional control port of the excitation regulator in the excitation system;

[0008] The low-frequency branch includes: a first input channel and a second input channel;

[0009] Among them, the first input channel sequentially includes: a second-order band-pass filter module, a first DC-blocking module, a second DC-blocking module, a lead-lag compensation module, and a first gain module, and processes the electromagnetic power deviation of the input equivalent generator to output a low-frequency damping signal;

[0010] The second input channel sequentially includes: a first-order high-pass filter, a second-order band-pass filter, a time constant compensation module, and a second gain module, and processes the speed deviation of the input equivalent generator to output a sub-low-frequency damping signal;

[0011] The sub-synchronous branch sequentially includes: a DC-blocking module, a phase compensation module, and a third gain module, and processes the shaft torsional oscillation modal quantity pq in the i-th sub-synchronous oscillation risk mode of the equivalent generator i to generate the i-th additional damping control signal;

[0012] The parallel output module superimposes and limits the output signals of the low-frequency branch and the sub-synchronous branch to obtain a stabilizer output signal U PSS and connects it to the additional control port of the excitation regulator, so that the excitation regulator adjusts the excitation voltage of the equivalent generator according to the stabilizer output signal U PSS to change its electromagnetic torque, thereby suppressing the broadband oscillation of the equivalent generator.

[0013] The feature of the multi-branch power system stabilizer of the present invention is also that the shaft torsional oscillation modal quantity pq in the i-th sub-synchronous oscillation risk mode of the equivalent generator i is obtained by using Equation (1):

[0014] (1)

[0015] In formula (1), are six constants obtained through the modal inverse transformation matrix P; is the electrical angular velocity of each mass block in the six-mass-block equivalent model with respect to the synchronous rotating reference axis.

[0016] Furthermore, the lead-lag compensation module of the first input channel is formed by connecting a first lead link and a first lag link in series, and is used to compensate for the phase lag of the excitation system in the frequency band of 0.1 Hz to 4 Hz; the time constant compensation module of the second input channel is formed by connecting a second lead link and a second lag link in series, and is used to suppress the high-frequency interference of its own input signal.

[0017] Furthermore, it is characterized in that the phase compensation link of the subsynchronous branch is formed by connecting a third lead link and a third lag link in series, and is used to compensate for the phase lag of the subsynchronous frequency band of the excitation system.

[0018] Furthermore, the upper output amplitude limit of the parallel output module is V max and the lower output amplitude limit V min , which is used to restrict the amplitude range of the superimposed control signal and prevent overshoot of the excitation system.

[0019] Furthermore, the parameters of the low-frequency branch are set according to the following steps:

[0020] Step 1: Use the test signal method to obtain the phase lag characteristic of the excitation system, which is used to design the parameters of the lead-lag compensation link to match the phase requirements of the target low-frequency band;

[0021] Step 2: Use the critical gain method to determine the total gain of the low-frequency branch:

[0022] Gradually increase the gain coefficient of the multi-branch power system stabilizer in the single-machine infinite system until the output of the excitation regulator in the excitation system or the rotor voltage of the equivalent generator oscillates, so as to obtain the critical gain, and use 1 / 3 to 1 / 5 times of the critical gain as the total gain of the power system stabilizer.

[0023] Furthermore, the parameters of the subsynchronous branch are set according to the following steps:

[0024] Step a: Identify the subsynchronous oscillation risk mode in the wind-fire bundling system through the eigenvalue analysis method;

[0025] Step b: Construct the modal inverse transformation matrix P = K -1 T jm, where K is the stiffness coefficient K between two adjacent masses of the six-mass block of the equivalent generator in the wind-fire bundling system 12 , K 23 ,…, K 56 that form a matrix, and T jm is the diagonal matrix formed by the inertia time constants T jm1 , T jm2 ,…, T jm6 of each mass block of the equivalent generator, and there is:

[0026] (2)

[0027] (3)

[0028] Step c, calculate the shaft torsional vibration modal quantity in the i-th subsynchronous oscillation risk mode of the equivalent generator , where represents the i-th row vector of the modal inverse transformation matrix, and , represents the column vector composed of the electrical angular velocities of each mass block in the six-mass block equivalent model relative to the synchronous rotating reference axis, and , T represents the transpose;

[0029] Step d, according to the transfer function of the excitation system and the modal damping requirement, use Equation (4) to calculate the gain coefficient K G of the subsynchronous branch:

[0030]

[0031] In Equation (4), is the damping coefficient in the i-th subsynchronous oscillation risk mode; Q 5i represents the element in the fifth row and the i-th column of the modal transformation matrix Q, and Q = P -1 , V mi is the modal frequency in the i-th subsynchronous oscillation risk mode, M mi and D mi are the modal inertia and modal damping in the i-th subsynchronous oscillation risk mode respectively, is the transfer function of the excitation system before phase compensation, represents the transfer function of the excitation system after phase compensation, is the additional damping torque coefficient of the subsynchronous branch electromagnetic torque of the multi-branch power system stabilizer in the i-th subsynchronous oscillation risk mode; is the additional damping torque coefficient of the subsynchronous branch of the multi-branch power system stabilizer in the i-th subsynchronous oscillation risk mode; j represents the imaginary unit.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. The present invention realizes multi-band coordinated damping control: through the parallel structure of the low-frequency branch and the subsynchronous branch, directional damping compensation is provided for different frequency band oscillation modes respectively, effectively suppressing the oscillation risk in the wide frequency domain, especially solving the defect that the traditional PSS cannot take into account both low-frequency and subsynchronous oscillations.

[0034] 2. The present invention adopts modal quantity directional control: the subsynchronous branch is based on the accurate calculation of the torsional oscillation modal quantity of the generator shafting, extracts specific subsynchronous oscillation risk modes through the modal inverse transformation matrix, realizes the precise injection of damping signals, and avoids the control conflicts caused by multi-modal coupling.

[0035] 3. The application of the present invention will significantly improve the stable operation ability of the wind-fire bundled system in the scenario of high new energy penetration rate, provide technical guarantee for the grid safety, and at the same time provide a new solution for the stable control of the multi-energy power system. Description of the Drawings

[0036] Figure 1 is the structure diagram of the wind-fire bundled system;

[0037] Figure 2 is the structure diagram of the multi-branch PSS;

[0038] Figure 3 is the phase lag curve diagram of the excitation system;

[0039] Figure 4 is the simulation waveform diagram of the critical gain and tuning gain of the multi-branch PSS;

[0040] Figure 5 is the output power response diagram of the synchronous machine with a 10% sudden change in mechanical power;

[0041] Figure 6 is the output power response diagram of the synchronous machine with a 5% sudden change in the excitation reference voltage;

[0042] Figure 7 is the synchronous machine speed response diagram under the power fluctuation of the wind farm;

[0043] Figure 8 is the synchronous machine speed frequency spectrum diagram under the power fluctuation of the wind farm;

[0044] Figure 9 is the output power and speed response diagram of the synchronous machine under the three-phase short-circuit fault;

[0045] Figure 10 is the synchronous machine shafting torque response diagram under the three-phase short-circuit fault;

[0046] Figure 11It is the speed spectrum diagram of the synchronous machine under the three-phase short-circuit fault. Specific implementation manner

[0047] In this embodiment, a power system stabilizer that can adapt to the multi-branch dynamic characteristics of the wind-fire bundling system, has strong robustness and adaptive ability, is used to solve key technical problems such as multi-band oscillation suppression, multi-controller coordination optimization, and complex working condition adaptability, and ensure the safe and stable operation of the new power system. Specifically, the multi-branch power system stabilizer applicable to the wind-fire bundling system includes: an equivalent wind turbine multiplied by n wind turbines, an equivalent generator multiplied by n generators, a series-compensated transmission line, and an AC power grid. Among them, the equivalent generator includes an excitation system and a six-mass equivalent model; the equivalent wind turbine and the equivalent synchronous machine are respectively connected in parallel through transformers and then connected to the AC power grid through the series-compensated transmission line. The specific structure diagram of the wind-fire bundling system can be seen in Figure 1 .

[0048] A multi-branch power system stabilizer is also set in the equivalent generator, and includes: a low-frequency branch, a sub-synchronous branch, and a parallel output module. After the low-frequency branch and the sub-synchronous branch are connected in parallel, they are connected in series with the parallel output module and connected to the additional control port of the excitation regulator in the excitation system. The power system stability structure diagram can be seen in Figure 2 .

[0049] The low-frequency branch includes: a first input channel and a second input channel;

[0050] Among them, the first input channel sequentially includes: a second-order band-pass filter module , a first DC-blocking module , a second DC-blocking module , a lead-lag compensation module and and a first gain module , and processes the electromagnetic power deviation of the input equivalent generator to output a low-frequency damping signal.

[0051] In this embodiment, the lead-lag compensation module of the first input channel is composed of a first lead link and a first lag link in series, and is used to compensate for the phase lag of the excitation system in the frequency band of 0.1 Hz to 4 Hz; the time constant compensation module of the second input channel is composed of a second lead link and a second lag link in series, and is used to suppress the high-frequency interference of its own input signal.

[0052] The second input channel sequentially includes: a first-order high-pass filter , a second-order band-pass filter , a third DC-blocking module , a time constant compensation module and a second gain module , and process the speed deviation of the input equivalent generator to output a sub - low - frequency damping signal.

[0053] In specific implementation, the parameters of the low - frequency branch are set according to the following steps:

[0054] Step 1: Use the test signal method to obtain the phase - lag characteristic of the excitation system, which is used to design the parameters of the lead - lag compensation link to match the phase requirements of the target low - frequency band;

[0055] Step 1.1: First, apply a series of very small sine disturbances to the reference voltage U ref of the excitation regulator of the generator. Apply the disturbance once every 0.1 Hz in the range of 0.1 - 3 Hz and once every 1 Hz in the range of 3 - 50 Hz;

[0056] Step 1.2: Take the output response of the generator terminal voltage at steady state , and perform Fourier decomposition on and within the common period to obtain the phasors of and at different frequencies. Finally, calculate the frequency characteristic of ;

[0057] Step 1.3: Plot the frequency - lag phase curve of the excitation system, find the phase jump point, and determine the targeted compensation frequency point;

[0058] Step 2: Use the critical gain method to determine the total gain of the low - frequency branch:

[0059] In the single - machine infinite - bus system, gradually increase the gain coefficient of the multi - branch power system stabilizer until the output of the excitation regulator in the excitation system or the rotor voltage of the equivalent generator oscillates. Thus, obtain the critical gain, and use 1 / 3 to 1 / 5 times of the critical gain as the total gain of the power system stabilizer.

[0060] The sub - synchronous branch successively includes: a DC - blocking module , a phase - compensation module and a third - gain module , and process the shaft - torsional oscillation modal quantity pq i of the equivalent generator under the i - th sub - synchronous oscillation risk mode to generate the i - th additional damping control signal.

[0061] In specific implementation, the shaft - torsional oscillation modal quantity pq i of the equivalent generator under the i - th sub - synchronous oscillation risk mode is obtained by using Equation (1):

[0062] (1)

[0063] In formula (1), are the six constants obtained through the modal inverse transformation matrix P; is the electrical angular velocity of each mass block in the six-mass equivalent model relative to the synchronously rotating reference axis.

[0064] The phase compensation link of the sub-synchronous branch is composed of a third leading link and a third lagging link connected in series, and is used to compensate for the phase lag of the sub-synchronous frequency band of the excitation system.

[0065] In this embodiment, the parameters of the secondary synchronization branch are adjusted according to the following steps:

[0066] Step a, identifying the subsynchronous oscillation risk mode in the wind-fire bundling system by using the characteristic root analysis method;

[0067] (1) Establish a dynamic model of the system: The wind-fire bundling system includes an equivalent wind turbine, an equivalent synchronous generator (six-mass block shaft system model), a series compensation transmission line and an AC power grid. Linearize the mathematical model of each module in the system to obtain the state space model of each submodule:

[0068]

[0069] In the formula, subscript k represents each submodule; X k , U k , Y k are the state variable matrix, input variable matrix, and output variable matrix of submodule k respectively; A k , B k , C k , D k They are the coefficient matrix, input matrix, output matrix and transfer matrix of the kth submodule respectively, and the elements in each matrix are obtained from the steady state of the system.

[0070] The linearized equations of each module are combined to obtain the small signal model of the whole system:

[0071]

[0072] In the formula, It is the state variable of the submodule; It is the input matrix composed of given quantities for system control, and becomes a zero matrix after the system is closed.

[0073] (2) The above system is linearized at a certain equilibrium point using Taylor expansion to obtain

[0074]

[0075] Where A represents the state matrix, through Study the key factors of the small-signal stability of the power system, solve all the eigenvalues of the A matrix to analyze the stability of the power system, and assume the eigenvalues . The eigenvalues of A reflect the oscillation modes that the power system may generate, that is , so reflects the damping performance, reflects the oscillation frequency; is an increasing oscillation, and the system is unstable; is a decreasing oscillation, and the system is stable; is an equal-amplitude oscillation, a critical state.

[0076] (3) Sub-synchronous oscillation mode screening: According to the definition of sub-synchronous oscillation, screen the eigenvalues that meet the following conditions: the frequency range is between 10 Hz and 50 Hz, and the damping ratio (close to zero or negative), indicating poor modal stability.

[0077] Step b, construct the modal inverse transformation matrix P = K -1 T jm , where K is the matrix composed of the stiffness coefficients K 12 , K 23 , …, K 56 of adjacent two mass blocks of the six-mass block of the equivalent generator in the integrated wind and thermal power system, and T jm is the diagonal matrix composed of the inertia time constants T jm1 , T jm2 , …, T jm6 of each mass block of the equivalent generator, and there are:

[0078] (2)

[0079] (3)

[0080] Step c, calculate the shaft torsional oscillation modal quantity of the equivalent generator under the i-th sub-synchronous oscillation risk mode, where represents the i-th row vector of the modal inverse transformation matrix, and , represents the column vector composed of the electrical angular velocities of each mass block in the six-mass block equivalent model relative to the synchronous rotating reference axis, and , T represents the transpose;

[0081] Step d, according to the transfer function of the excitation system and the modal damping requirement, calculate the gain coefficient K G of the sub-synchronous branch using Equation (4):

[0082]

[0083] In Equation (4), is the damping coefficient in the \(i\)-th sub-synchronous oscillation risk mode; \(Q\) 5i represents the element in the \(i\)-th column of the fifth row of the modal transformation matrix \(Q\), and \(Q = P\) -1 , \(V\) mi is the modal frequency in the \(i\)-th sub-synchronous oscillation risk mode, \(M\) mi and \(D\) mi are the modal inertia and modal damping in the \(i\)-th sub-synchronous oscillation risk mode respectively, is the transfer function of the excitation system before phase compensation, represents the transfer function of the excitation system after phase compensation, is the additional damping torque coefficient of the sub-synchronous branch electromagnetic torque of the multi-branch power system stabilizer in the \(i\)-th sub-synchronous oscillation risk mode; is the additional damping torque coefficient of the sub-synchronous branch of the multi-branch power system stabilizer in the \(i\)-th sub-synchronous oscillation risk mode; \(j\) represents the imaginary unit.

[0084] The parallel output module superimposes and limits the output signals of the low-frequency branch and the sub-synchronous branch, and then obtains the stabilizer output signal \(U\) PSS and connects it to the additional control port of the excitation regulator, so that the excitation regulator adjusts the excitation voltage of the equivalent generator according to the stabilizer output signal \(U\) PSS , to change its electromagnetic torque, thereby suppressing the wide-frequency oscillation of the equivalent generator.

[0085] In specific implementation, the upper limit amplitude of the output of the parallel output module is \(V\) max and the lower limit amplitude \(V\) min , which are used to constrain the amplitude range of the superimposed control signal and prevent overshoot of the excitation system.

[0086] Embodiment:

[0087] 1. Establish the Figure 1 wind-fire bundled system in PSCAD / EMTDC (specific parameters are shown in Tables 1 - 5).

[0088] Table 1 shows the generator parameters

[0089]

[0090] Table 2 shows the inertia time constants of each mass segment of the generator;

[0091]

[0092] Table 3 shows the elastic coefficients of each shaft segment of the generator;

[0093]

[0094] Table 4 shows the parameters of the excitation system;

[0095]

[0096] Table 5 shows the main topology parameters;

[0097]

[0098] 2. Use the test signal method to calculate the phase lag characteristic curve of the excitation system. As Figure 3 shown, find the frequencies corresponding to the phase jump points: 1 Hz and 32 Hz.

[0099] 3. Build a single-machine infinite-bus model, and build an excitation model and PSS for simulation calculation and analysis. Gradually increase the gains of the low-frequency branches and respectively until the excitation voltage of the generator shows divergent oscillation. At this time, the and are the critical gains. It can be seen from Figure 4 that the critical gains obtained by simulation are K P = 98, K ω = 0.5. When the setting gains are taken as K P = 21, K ω = 0.1, the excitation voltage of the generator can be stabilized at about 1 pu, meeting the setting requirements. Then, according to the phase lag curve of the excitation system, the low-frequency branch parameters are set as shown in Table 6.

[0100] Table 6 shows the parameter setting results

[0101]

[0102] 4. Use the relevant parameters of the synchronous machine to calculate the corresponding modal inverse transformation matrix as shown in Table 7.

[0103] Table 7 shows the modal inverse transformation matrix

[0104]

[0105] 5. Conduct a characteristic root analysis on the integrated thermal power and wind power system in Figure 1 . The results are shown in Table 8. The results show that there is an oscillation risk at the modal 4 frequency (32.27 Hz). Therefore, select the modal quantity as the input signal of the subsynchronous branch.

[0106] Table 8 shows the characteristic root analysis results

[0107]

[0108] 6. For modal 4, set the damping coefficient = 0.01, the following subsynchronous branches are obtained according to the modal inverse transformation matrix and Equation (4):

[0109]

[0110] = -0.4106 + 0.2276 - 0.5891 + 0.1319 - 0.0484 + 0.0045

[0111] 7. Test the effect of the multi-branch PSS under the condition that the mechanical power of the equivalent synchronous machine suddenly changes by 10% at 15 s. The generator output power is as Figure 5 shown. After installing the multi-branch PSS, both the stable time and the oscillation peak value of the synchronous machine output power are smaller than those in the cases of installing PSS1A and without PSS. The damping effect of the multi-branch PSS on low-frequency oscillation is better than that of the traditional PSS.

[0112] 8. Test the effect of the multi-branch PSS under the condition that the excitation reference voltage of the equivalent synchronous machine suddenly changes by 10% at 10 s. The generator output power is as Figure 6 shown. After installing the multi-branch PSS, both the stable time and the oscillation peak value of the synchronous machine output power are smaller than those in the cases of installing PSS1A and without PSS. The damping effect of the multi-branch PSS on low-frequency oscillation is better than that of the traditional PSS.

[0113] 9. Set the power reference value of the wind farm to fluctuate periodically, and test the effect of the multi-branch PSS in suppressing forced oscillation. The generator speed and the spectrogram are as Figure 7 and Figure 8 shown. After installing the multi-branch PSS, the oscillation amplitude of the synchronous machine speed is reduced by nearly 25%, and the low-frequency component in the system is reduced from 0.03 pu to almost zero, and the effect of suppressing forced oscillation is remarkable.

[0114] 10. Set a three-phase short-circuit fault to excite the low-frequency oscillation of the generator. The generator output power is as Figure 9 shown. After installing the multi-branch PSS, the oscillation amplitude of the synchronous machine output power speed under the three-phase short-circuit fault is greatly reduced, and the speed of recovering to the steady state is also greatly accelerated.

[0115] 11. Adjust the series compensation line parameters, set a three-phase short-circuit fault to excite the subsynchronous oscillation of the generator. The shaft torque and the spectrogram of the generator are as Figure 10 and Figure 11As shown, after configuring the multi-branch PSS, the oscillation amplitude of the synchronous machine shaft torque is reduced by more than 90%, and the subsynchronous components existing in the system can be almost ignored, which greatly suppresses the torsional oscillation of the generator shafting.

Claims

1. A multi-branch power system stabilizer suitable for a wind-fire bundling system, the wind-fire bundling system comprising: An equivalent wind turbine multiplied by n wind turbines, an equivalent generator multiplied by n generators, a series compensation transmission line, and an AC power grid, wherein the equivalent generator includes an excitation system and a six-mass block equivalent model; the equivalent wind turbine and the equivalent synchronous machine are respectively connected in parallel through a transformer and connected to the AC power grid through the series compensation transmission line; it is characterized in that the multi-branch power system stabilizer is also provided in the equivalent generator, and includes: a low-frequency branch, a sub-synchronous branch and a parallel output module, and the low-frequency branch is connected in parallel with the sub-synchronous branch, and then connected in series with the parallel output module, and connected to the additional control port of the excitation regulator in the excitation system; The low-frequency branch includes: a first input channel and a second input channel; The first input channel includes: a second-order bandpass filter module, a first DC isolation module, a second DC isolation module, a lead-lag compensation module and a first gain module, and the electromagnetic power deviation of the input equivalent generator is Processing is performed to output a low-frequency damping signal; The second input channel includes: a first-order high-pass filter, a second-order band-pass filter, a time constant compensation module and a second gain module, and the input equivalent generator speed deviation Processing is performed to output a sub-low frequency damping signal; The sub-synchronous branch includes: a DC isolation module, a phase compensation module and a third gain module in sequence, and calculates the shaft torsional vibration modal quantity pq under the i-th sub-synchronous oscillation risk mode of the equivalent generator. i Processing is performed to generate an i-th additional damping control signal; The parallel output module superimposes and limits the output signals of the low-frequency branch and the sub-synchronous branch to obtain the stabilizer output signal U PSS And connected to the additional control port of the excitation regulator, so that the excitation regulator outputs the signal U according to the stabilizer PSS , adjusting the excitation voltage of the equivalent generator to change its electromagnetic torque, thereby suppressing the broadband oscillation of the equivalent generator.

2. The multi-branch power system stabilizer according to claim 1, characterized in that: The shaft torsional vibration modal quantity pq of the equivalent generator under the i-th subsynchronous oscillation risk mode i Using formula (1), we can get: (1) In formula (1), are the six constants obtained through the modal inverse transformation matrix P; is the electrical angular velocity of each mass block in the six-mass equivalent model relative to the synchronously rotating reference axis.

3. The multi-branch power system stabilizer according to claim 1, characterized in that: The lead-lag compensation module of the first input channel is composed of a first lead link and a first lag link connected in series, and is used to compensate for the phase lag of the excitation system in the frequency range of 0.1Hz to 4Hz; the time constant compensation module of the second input channel is composed of a second lead link and a second lag link connected in series, and is used to suppress high-frequency interference of its own input signal.

4. The multi-branch power system stabilizer according to claim 1, characterized in that: The phase compensation link of the sub-synchronous branch is composed of a third leading link and a third lagging link connected in series, and is used to compensate for the phase lag of the sub-synchronous frequency band of the excitation system.

5. The multi-branch power system stabilizer according to claim 1, characterized in that: The output upper limit amplitude of the parallel output module is V max And the output lower limit value V min , which is used to constrain the amplitude range of the superimposed control signal to prevent over-modulation of the excitation system.

6. The multi-branch power system stabilizer according to claim 1, characterized in that: The parameters of the low-frequency branch are adjusted according to the following steps: Step 1: using a test signal method to obtain the phase lag characteristics of the excitation system, which is used to design the parameters of the lead-lag compensation link to match the phase requirements of the target low frequency band; Step 2: Use the critical gain method to determine the total gain of the low-frequency branch: In a single-machine infinite system, the gain coefficient of the multi-branch power system stabilizer is gradually increased until the output of the excitation regulator in the excitation system or the rotor voltage of the equivalent generator oscillates, thereby obtaining the critical gain, and 1 / 3 to 1 / 5 of the critical gain is used as the total gain of the power system stabilizer.

7. The multi-branch power system stabilizer according to claim 1, characterized in that: The parameters of the secondary synchronization branch are set according to the following steps: Step a, identifying the subsynchronous oscillation risk mode in the wind-fire bundling system by means of characteristic root analysis; Step b: construct the modal inverse transformation matrix P = K -1 T jm , where K is the stiffness coefficient K of two adjacent mass blocks of the six mass blocks of the equivalent generator in the wind-fire bundling system 12 , K 23 ,…, K 56 The matrix composed of jm is the inertial time constant T of each mass block of the equivalent generator jm1 , T jm2 ,…, T jm6 The diagonal matrix is ​​composed of: (2) (3) Step c, calculating the shaft torsional vibration modal quantity under the i-th subsynchronous oscillation risk mode of the equivalent generator ,in, represents the i-th row vector of the inverse modal transformation matrix, and , represents the column vector of electrical angular velocity of each mass block in the six-mass equivalent model relative to the synchronously rotating reference axis, and , T represents transpose; Step d: According to the transfer function and modal damping requirement of the excitation system, the gain coefficient K of the subsynchronous branch is calculated using equation (4): G : (4) In formula (4), is the damping coefficient under the i-th subsynchronous oscillation risk mode; Q 5i represents the element in the fifth row and the i-th column of the modal transformation matrix Q, and Q=P -1 , V mi is the modal frequency of the ith subsynchronous oscillation risk mode, M mi and D mi are the modal inertia and modal damping under the i-th subsynchronous oscillation risk mode, is the transfer function of the excitation system before phase compensation, represents the transfer function of the excitation system after phase compensation, is the additional damping torque coefficient of the electromagnetic torque of the subsynchronous branch of the multi-branch power system stabilizer under the i-th subsynchronous oscillation risk mode; is the additional damping torque coefficient of the subsynchronous branch of the multi-branch power system stabilizer under the i-th subsynchronous oscillation risk mode; j represents a complex unit.

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