CN112448399B - Doubly-fed wind power plant subsynchronous oscillation suppression method based on analog inductance - Google Patents
Doubly-fed wind power plant subsynchronous oscillation suppression method based on analog inductance Download PDFInfo
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Abstract
The invention discloses a method for inhibiting doubly-fed wind power plant subsynchronous oscillation based on analog inductance, which comprises the following steps: firstly, establishing a system model of a doubly-fed wind power plant which is connected with the grid through a series compensation capacitor; then applying an analog inductance control strategy to the inner loop control of a double-fed fan rotor side controller to control the output voltage of the rotor; then, carrying out self-adaptive on-line setting on the simulated inductance value by utilizing a PSO algorithm, and determining the optimal value of the simulated inductance under a specific working condition; and finally, applying an analog inductance control strategy and a rotor side converter control strategy to the control of the rotor side of the doubly-fed fan to complete the suppression of the subsynchronous oscillation of the system. The invention improves the electrical damping in the subsynchronous frequency band, improves the stability of the system and can meet the subsynchronous oscillation suppression requirement under multiple working conditions.
Description
Technical Field
The invention belongs to the technical field of stability control of wind driven generators, and particularly relates to a method for inhibiting doubly-fed wind power plant subsynchronous oscillation based on analog inductance.
Background
From the viewpoint of sustainable development, fossil energy, which is currently relied on by mankind, is eventually exhausted, and in order to solve the current energy and environmental problems, development and utilization of clean energy instead of conventional energy is an inevitable trend in human social development. The wind energy is an ideal clean energy which is inexhaustible, environment-friendly and pollution-free. The wind power generation technology is mature, can be developed in a large scale, has good commercial prospect, and is the main form of the current new energy power generation. When wind energy resources are developed and utilized, different types of wind driven generators are used, and in the wind power plant which is put into operation at present, the doubly-fed induction wind driven generator is the most widely applied type. Due to the fact that resources and load centers are distributed in a reverse mode, large-capacity and long-distance wind power delivery is imperative. The series compensation capacitor technology is widely applied, but the problem of subsynchronous oscillation of a wind power system can be induced, and the safe and stable operation of a large-scale wind power base and a delivery system is influenced.
Due to uniqueness of a wind power plant, many control methods for obtaining ideal effects in thermal power plant subsynchronous oscillation suppression may be difficult to obtain the ideal effects in the wind power plant. In actual operation, different operation conditions exist, so that the self-adaption problem of the designed controller must be considered. At present, researches on a subsynchronous oscillation mechanism of a doubly-fed wind power plant are not completely thorough, and measures for inhibiting subsynchronous oscillation are relatively single. Therefore, further research on the suppression measures of the doubly-fed wind power plant subsynchronous oscillation is needed, and the method has important significance for stable grid connection of the wind power plant.
Disclosure of Invention
The invention aims to provide a method for inhibiting the sub-synchronous oscillation of a doubly-fed wind power plant based on analog inductance, which can inhibit the sub-synchronous oscillation caused by series compensation capacitance and improve the stability of a doubly-fed wind power plant through a series compensation capacitance grid-connected system.
The technical solution for realizing the purpose of the invention is as follows: a doubly-fed wind power plant subsynchronous oscillation suppression method based on analog inductance comprises the following steps:
step 2, applying an analog inductance control strategy to inner loop control of a double-fed fan rotor side controller to control the output voltage of the rotor;
step 3, carrying out self-adaptive on-line setting on the simulated inductance value by utilizing a PSO algorithm, and determining the optimal value of the simulated inductance under a specific working condition;
and 4, applying an analog inductance control strategy and a rotor side converter control strategy to the control of the rotor side of the doubly-fed wind turbine to complete the suppression of the subsynchronous oscillation of the system.
Further, the establishment of the system model of the doubly-fed wind farm through the series compensation capacitor grid connection in the step 1 specifically includes:
step 1.1, obtaining the corresponding relation among the rotating speed, the output power and the wind speed of the rotor of the doubly-fed wind turbine according to a wind energy capture model;
step 1.2, writing out an electromagnetic equation of the system in a dq coordinate system as follows:
step 1.2.1, the stator and the rotor in the doubly-fed induction generator adopt the motor convention, the positive direction is the current flowing direction, and the rotating direction is the same as the positive direction of the electromagnetic torque; according to the coordinate transformation principle, current, voltage and magnetic flux variables in the stator and the rotor are transformed from a three-phase static coordinate to a dq coordinate system, and the electromagnetic relation in the stator and the rotor is obtained as follows:
wherein ω is 1 For synchronizing the angular velocities of rotation, ω s ＝ω 1 -ω r Is the slip angular velocity, omega r Is the rotor rotational angular velocity; u. of ds 、u qs Is the stator dq-axis voltage, u dr 、u qr Is the rotor dq axis voltage; i.e. i ds 、i qs For stator dq axis current, i dr 、i qr Is the rotor dq axis current; psi ds 、ψ qs For stator dq axis flux, psi dr 、ψ qr A rotor dq axis flux linkage; r s Is stator resistance, R r Is the rotor resistance; l is a radical of an alcohol ls For stator leakage inductance, L lr For rotor leakage inductance, L m For coaxial mutual inductance of stator and rotor, L s 、L r Equivalent self-inductance of stator and rotor windings;
step 1.2.2, controlling a target of a double-fed fan rotor side converter by tracking the maximum wind energy, keeping the frequency of generated energy constant and controlling reactive output; fixing the stator flux linkage direction on a d axis to realize active and reactive decoupling; and (3) adopting PI control to regulate the rotor voltage, and writing a relation column expressed by a control block diagram into a differential equation:
wherein Te ref 、Q sref Reference value for electromagnetic torque and stator reactive power, K Te 、K Qs Proportional coefficient, K, for the external power loop PI control of the rotor-side converter iq 、K id Proportional coefficient for PI control of current loop in the rotor side converter; t is Te 、T Qs Integral coefficient, T, for rotor side converter outer power loop PI control iq 、T id Integral coefficient of current loop PI control in the rotor side converter; i.e. i qrref 、i drref Rotor dq axis current reference, x, output for rotor side converter outer loop PI control 1 ～x 4 Four intermediate variables were introduced.
Further, the step 2 of applying the analog inductance control strategy to the inner loop control of the double-fed fan rotor side converter to control the rotor output voltage specifically comprises the following steps:
step 2.1, detecting external wind speed to obtain a torque reference value corresponding to the wind speed, determining a reactive reference value of a stator according to a control target, establishing a relevant state equation of a simultaneous system, and calculating a steady-state expected value of a current dq axis component of a rotor of the doubly-fed fan by combining a corresponding control strategy
Step 2.2, after the actual value of the rotor current dq axis component is subjected to difference gain with the steady-state expected value, the difference gain is used as an additional signal to act on the input of the rotor voltage, and the formula is as follows:
and 2.3, enabling the rotor voltage output by the rotor side converter to meet the relation of an equation (13) under the action of the additional signal of the equation (12):
wherein G is P Namely the analog inductance.
Further, the step 3 of utilizing the PSO algorithm to perform adaptive online tuning on the analog inductance value, and determining the optimal value of the analog inductance under the specific working condition, specifically as follows:
step 3.1, writing a system state equation in a row, linearizing the system state equation at a balance point to obtain a small signal equation:
dΔX/dt＝AΔX (14)
in the formula, X is the state variable of the system, and the number of X is 20; a is a Jacobian matrix determined by system parameters and balance point states;
step 3.2, calculating the subsynchronous oscillation frequency f of the system n The formula is as follows:
in the formula, f 1 For mains frequency, X C For series compensation of capacitive reactance of capacitor, X ∑ Is the sum of effective inductive reactance in the system;
corresponding to a power oscillation frequency of f SSR ＝f 1 -f n Based on the characteristic value, determining a corresponding subsynchronous oscillation mode in the characteristic value of the Jacobian matrix A;
step 3.3 at G P When the value is changed, two groups of characteristic value real parts are changed, one group corresponds to a subsynchronous mode, and the corresponding characteristic value is sigma 1 ±jω 1 (ii) a The other group corresponds to low-frequency mode, and the corresponding characteristic value is sigma 2 ±jω 2 The PSO algorithm is adopted to carry out self-adaptive setting on the analog inductance value, the primary objective of the algorithm is to inhibit subsynchronous oscillation, and therefore the damping ratio corresponding to the subsynchronous modal characteristic value is taken as a fitness function, as shown in the formula (16):
step 3.4, limiting the real part of the characteristic value corresponding to the low-frequency mode in a certain range to obtain a constraint of the algorithm:
σ 2 ≤σ 2max (17)
in the formula sigma 2max A constant less than zero;
and 3.5, updating the position and the search speed of the ith particle according to the formula (18):
in the formula, k is the current iteration number; w is the inertial weight; c. C 1 And c 2 Is a learning factor; r is 1 And r 2 A random number in the range of 0 to 1;
is the current best position of the ith particle,
is the current global optimum position;
3.6, establishing a dynamic adjustment model of the inertial weight, and searching by using the fixed weight at the initial stage of the algorithm; after a set number of iterations, w is varied according to equation (19):
in the formula, w max And w min Is a fixed value, f i For the current particle adaptation value, f av Average of the adapted values for all particles, f best Adapting the value for the globally optimal particle;
step 3.7, simulating the inductor G P The optimum range of values and particle velocity are constrained:
wherein G is Pmin And G Pmax To a fixed value selected as required, v max And v min The upper and lower limits of the particle search speed can be selected according to typical values.
Further, the step 4 of applying the analog inductance control strategy and the rotor side converter control strategy to the control of the rotor side of the doubly-fed wind turbine to complete the suppression of the subsynchronous oscillation of the system is as follows:
the simulation inductor G obtained by PSO algorithm setting P The value is applied to the control of the converter, the control of the analog inductance of the double-fed fan is realized, and the suppression of the subsynchronous oscillation of the system is completed.
Compared with the prior art, the invention has the remarkable advantages that: (1) the method inhibits subsynchronous oscillation caused by series compensation capacitance, and improves the stability of a doubly-fed wind power plant through a series compensation capacitance grid-connected system; (2) the invention has few parameters needing to be set, and avoids complex parameter setting; (3) the PI control of the double-fed fan rotor side converter is improved, the basic control structure of the RSC converter is not changed, and the requirements of current fan manufacturers are met; (4) the method can suppress subsynchronous oscillation under multiple working conditions.
Drawings
Fig. 1 is a flow chart of a method for suppressing the subsynchronous oscillation of a doubly-fed wind power plant based on an analog inductor according to the present invention.
FIG. 2 is a schematic structural diagram of a doubly-fed wind farm grid-connected model through series compensation capacitors.
Fig. 3 is a control block diagram of the double-fed wind turbine rotor side converter in the invention.
Fig. 4 is a control block diagram of the doubly-fed wind turbine rotor side converter based on the analog inductance in the invention.
Fig. 5 is a schematic diagram of the principle of analog inductance adaptive parameter tuning using the PSO algorithm in the present invention.
Fig. 6 is an oscillation curve diagram of the electromagnetic torque of the doubly-fed wind turbine when the wind speed is kept fixed and the series compensation degree is changed under the conventional PI control scheme in the embodiment of the invention.
Fig. 7 is an oscillation curve of the electromagnetic torque of the doubly-fed wind turbine under three different working conditions when the control strategy based on the simulated inductance is adopted in the embodiment of the present invention, wherein (a) is a wind speed of 7m/s and a series compensation degree of 70%; (b) the wind speed is 7m/s, and the series compensation degree is 80 percent; (c) the wind speed is 8m/s, and the degree of serial compensation is 80%.
Detailed Description
As shown in fig. 1, the invention provides a method for suppressing the sub-synchronous oscillation of a doubly-fed wind power plant based on analog inductance, which comprises the following steps:
step 1.1, obtaining the corresponding relation among the rotating speed, the output power and the wind speed of the rotor of the doubly-fed wind turbine according to the wind energy capture model. As shown in FIG. 2, a 100MW wind farm is formed by 50 fans of 2MW capacity per unit, where X is tg 、X T Is a net side smoothing reactor and a transformer reactor, R L 、X L And X C The resistance, reactance and series compensation capacitance reactance of the power transmission line are obtained; in order to fully utilize the wind speed, the unit operates under the maximum wind energy tracking strategy, and the corresponding relation of the rotor speed, the output power and the wind speed of the doubly-fed wind turbine is shown in table 1, wherein V is w Is the wind speed, ω r As the rotor speed, P w For wind turbine output power, T w Outputting torque for the wind turbine;
TABLE 1 reference table for rotor speed and wind turbine output power
| V w (m/s) | 7 | 8 | 9 | 10 | 11 | 12 |
| ω r (p.u) | 0.75 | 0.85 | 0.95 | 1.05 | 1.15 | 1.25 |
| P w (p.u) | 0.32 | 0.49 | 0.69 | 0.95 | 1.25 | 1.6 |
| T w ＝P w /ω r | 0.43 | 0.58 | 0.73 | 0.90 | 1.09 | 1.28 |
Step 1.2, writing out an electromagnetic equation of the system in a dq coordinate system as follows:
step 1.2.1, the stator and the rotor in the doubly-fed induction generator all adopt the motor convention, the positive direction is the current flowing direction, and the rotating direction is the same as the positive direction of the electromagnetic torque. According to the coordinate transformation principle, variables such as current, voltage, magnetic flux and the like in the stator and the rotor are transformed from a three-phase static coordinate to a dq coordinate system, and the electromagnetic relation in the stator and the rotor is obtained as follows:
wherein omega 1 For synchronizing the angular velocities of rotation, ω s ＝ω 1 -ω r Is slip angular velocity，ω r Is the rotor rotational angular velocity; u. of ds 、u qs Is the stator dq-axis voltage, u dr 、u qr Is the rotor dq axis voltage; i all right angle ds 、i qs For stator dq axis current, i dr 、i qr Is the rotor dq axis current; psi ds 、ψ qs For stator dq axis flux linkage, psi dr 、ψ qr A rotor dq axis flux linkage; r s Is stator resistance, R r Is the rotor resistance; l is ls For stator leakage inductance, L lr For rotor leakage inductance, L m For coaxial mutual inductance of stator and rotor, L s 、L r The stator and rotor windings are equivalent to self inductance.
Step 1.2.2, controlling a target of a double-fed fan rotor side converter by tracking the maximum wind energy, keeping the frequency of generated energy constant and controlling reactive output; the stator flux linkage direction is fixed on the d axis, so that active and reactive decoupling can be realized; the rotor voltage is regulated using PI control, and the control block diagram of the rotor-side converter is shown in fig. 3. Wherein Te ref 、Q sref Reference value for electromagnetic torque and stator reactive power, K Te 、K Qs Proportional coefficient, K, for the external power loop PI control of the rotor-side converter iq 、K id Proportional coefficient for PI control of current loop in the rotor side converter; t is Te 、T Qs Integral coefficient, T, for rotor side converter outer power loop PI control iq 、T id Integral coefficient of current loop PI control in the rotor side converter; i.e. i qrref 、i drref And a rotor dq axis current reference value output by the rotor side converter outer ring PI control.
The relation column expressed by the control block diagram is written into a differential equation as shown in formulas (4) to (11):
wherein x is 1 ～x 4 Four intermediate variables were introduced.
Step 2, applying the analog inductance control strategy to the inner loop control of the rotor side converter of the doubly-fed wind turbine to control the output voltage of the rotor, and combining with the graph 4, the method specifically comprises the following steps:
step 2.1, detecting external wind speed, finding a torque reference value corresponding to the wind speed by referring to the table 1, determining a reactive reference value of a stator according to a specific control target, establishing a relevant state equation of a simultaneous system, and calculating a steady-state expected value of a current dq axis component of a rotor of the doubly-fed fan by combining with a corresponding control strategy
Step 2.2, taking the difference between the actual value of the rotor current dq axis component and the steady-state expected value to obtain a gain, and then using the gain as an additional signal to act on the input of the rotor voltage, wherein the formula is as follows:
and 2.3, enabling the rotor voltage output by the rotor side converter to meet the relation of an equation (13) under the action of the additional signal of the equation (12):
wherein G is P I.e. the analog inductor, the value-taking principle of which is introduced in step 3.
Step 3, carrying out self-adaptive online setting on the simulated inductance value by utilizing a PSO algorithm, and determining the optimal value of the simulated inductance, wherein the method specifically comprises the following steps:
step 3.1, writing a system state equation in a row, linearizing the system state equation at a balance point to obtain a small signal equation:
dΔX/dt＝AΔX (14)
in the formula, X is the state variable of the system, and the number of X is 20; a is a Jacobian matrix determined by system parameters and balance point states;
step 3.2, determining the subsynchronous oscillation frequency f of the system according to the formula (15) n The power oscillation frequency corresponding thereto is f SSR ＝f 1 -f n Based on the above, determining the corresponding subsynchronous oscillation mode in the eigenvalue of the jacobian matrix a, the formula is:
in the formula (f) 1 For mains frequency, X C For series compensation of capacitive reactance of capacitor, X ∑ Is the sum of effective inductive reactance in the system;
step 3.3 at G P When the value is changed, two groups of characteristic value real parts are changed, one group corresponds to a subsynchronous mode, the other group corresponds to a low-frequency mode, and the characteristic value corresponding to the subsynchronous mode is used as sigma 1 ±jω 1 Indicating features corresponding to low-frequency modesEigenvalues are σ 2 ±jω 2 The method is characterized in that a Particle Swarm Optimization (PSO) algorithm is adopted to perform self-adaptive setting on an analog inductance value, the primary goal of the algorithm is to inhibit subsynchronous oscillation, and therefore a damping ratio corresponding to a subsynchronous modal characteristic value is taken as a fitness function, as shown in a formula (16):
step 3.4, G P The improper value selection can introduce low-frequency oscillation, so that the real part of the characteristic value corresponding to the low-frequency mode needs to be limited in a certain range, and one constraint of the algorithm is obtained:
σ 2 ≤σ 2max (17)
in the formula sigma 2max A constant less than zero;
and 3.5, updating the position and the search speed of the ith particle according to the formula (18):
in the formula, k is the current iteration number; w is the inertial weight; c. C 1 And c 2 Is a learning factor; r is a radical of hydrogen 1 And r 2 A random number in the range of 0 to 1;
is the current (iterated to kth) best position for the ith particle,
is the current global optimum position;
and 3.6, in the standard PSO algorithm, the inertia weight w is constant, and the algorithm is easy to fall into a local optimal solution under the condition. Therefore, a dynamic adjustment model of the inertial weight is established, and in the initial stage of the algorithm, the global search capability is enhanced by searching with fixed weight; and after the set number of iterations, varying w according to equation (19):
in the formula, w max And w min Is a fixed value, f i For the current particle adaptation value, f av Average of the fitness values for all particles, f best Adapting the value for the global optimum particle;
under the model, the larger the fitness of the particles is, the smaller the corresponding inertial weight is, and the stronger the local searching capability is, so that a new optimal position can be found;
step 3.7, in order to reduce the operation amount, the analog inductor G needs to be simulated P The optimizing range of the value is restricted; in order to avoid too large a particle search speed, the particle speed needs to be constrained, as shown in equation (20):
wherein G is Pmin And G Pmax To a fixed value selected as required, v max And v min The upper and lower limits of the particle search speed can be selected according to typical values. A simplified block diagram of the rotor side converter control strategy with the addition of the PSO optimization algorithm is shown in fig. 5.
The principle of analog inductance parameter tuning can be summarized as follows: detecting the current running state of the fan system at a fixed time point, and reading in system data; the PSO algorithm program optimizes parameters according to the current system state and adjusts the corresponding G P A value; and detecting the system working condition again after a fixed time period, and repeating the process.
And 4, applying the control strategies determined in the steps II and III of the analog inductance control strategy and the rotor side converter control strategy to the control of the rotor side of the double-fed fan to complete the suppression of the subsynchronous oscillation of the system.
The simulated inductor G obtained by PSO algorithm setting in the third step P The values are applied to the block diagram shown in fig. 4 to replace the control mode of the rotor converter shown in fig. 3, so that the double-fed wind turbine is realizedAnalog inductance control of (1).
The present invention will be described in detail with reference to examples.
Examples
Under a Matlab platform, a system shown in fig. 2 is built, a wind power plant in the system is boosted by a transformer and then is connected to an infinite system through a series compensation line, wherein the 100MW wind power plant is formed by combining 50 double-fed wind power generators of 2MW, and specific system parameters are shown in tables 2 to 4:
TABLE 2 Induction Generator parameters
TABLE 3 Transmission line and shafting parameters
| Name (R) | Parameter(s) | Name(s) | Parameter(s) |
| Transformation ratio of |
690V/161kV | Inertia of fan | 4.29s |
| Reference capacity | 100MVA | Inertia of generator | 0.90s |
| Line resistor | 0.02pu | Generator damping | 0.00pu |
| Line reactance | 0.50pu | Shafting damping system | 0.00pu |
| Reactance of transformer | 0.14pu | Wind turbine damping | 1.50pu |
| System impedance X S | 0.06pu | Shafting stiffness system | 0.15pu/rad |
TABLE 4 RSC controller parameters
| Name (R) | Parameter(s) | Name (R) | Parameter(s) |
| T Te | 0.05 | K iq | 0.0001 |
| T Qs | 0.025 | K id | 0.0001 |
| T iq | 0.005 | K Te | 0.0001 |
| T id | 0.0025 | K Qs | 0.0001 |
Fig. 6 is a simulation result of the conventional PI control strategy, and the operation conditions are as follows: the wind speed is 7m/s, the initial series compensation degree of the line is 20%, and the line is in steady-state operation. When the series compensation degrees are changed to 40%, 62.5% and 65% respectively at the time t being 0.5s, an oscillation curve of the fan electromagnetic torque Te is obtained. According to the simulation result, when the series compensation degree is 40%, the oscillation caused by disturbance can be automatically subsided; when the series compensation degree is 62.5%, the electromagnetic torque becomes constant-amplitude oscillation, the stability of the system is poor, and the system is in a critical stable state; when the series compensation degree is further increased to 65%, the stability of the system continues to be deteriorated, the subsynchronous oscillation component is rapidly dispersed, and the system is unstable. The above results indicate that the larger the degree of crosstalk, the worse the stability of the system, and the more likely subsynchronous oscillation occurs.
The method for restraining the subsynchronous oscillation of the doubly-fed wind power plant based on the simulated inductance is adopted for time domain simulation, and the algorithm parameters are set as follows: the particle swarm size is 200; the number of iterations is 3000; inertial weight w max ＝1.2，w min 0.4; learning factor c 1 ＝c 2 2; particle search Range [0,50 ]](ii) a The particle search speed range is [ -5,5 [)]. Selecting three typical working conditions, and obtaining the optimal G of the three typical working conditions by using a PSO algorithm respectively P The values and time domain simulation results are shown in fig. 7, wherein (a) is an oscillation curve of the electromagnetic torque when the series compensation degree is 70% at a wind speed of 7 m/s; (b) the system is still stable due to the oscillation curve of the electromagnetic torque at the wind speed of 7m/s and the series compensation degree of 80 percent; (c) the wind speed is 8m/s, and the electromagnetic torque oscillation curve when the series compensation degree is 80 percent, and the figure shows that the method for inhibiting the sub-synchronous oscillation of the doubly-fed wind power plant based on the simulated inductance can effectively inhibit the sub-synchronous oscillation under different working conditions, and can not bring other adverse effects to the stability of the system.
According to the analysis, the method for inhibiting the sub-synchronous oscillation of the doubly-fed wind power plant based on the simulated inductance has good self-adaptability when the wind speed and the series compensation degree change in a large range, and can effectively inhibit the sub-synchronous oscillation phenomenon caused by the series compensation grid connection of the doubly-fed wind power plant.
Claims (4)
1. A doubly-fed wind power plant subsynchronous oscillation suppression method based on analog inductance is characterized by comprising the following steps:
step 1, establishing a system model of a doubly-fed wind power plant which is connected with a grid through a series compensation capacitor;
step 2, applying the analog inductance control strategy to the inner ring control of the rotor side converter of the double-fed fan to control the output voltage of the rotor, specifically as follows:
step 2.1, detecting external wind speed to obtain a torque reference value corresponding to the wind speed, determining a reactive reference value of a stator according to a control target, establishing a relevant state equation of a simultaneous system, and calculating a steady-state expected value of a current dq axis component of a rotor of the doubly-fed fan by combining a corresponding control strategy
Step 2.2, after the actual value of the rotor current dq axis component is subjected to difference gain with the steady-state expected value, the difference gain is used as an additional signal to act on the input of the rotor voltage, and the formula is as follows:
wherein ω is 1 For synchronizing the angular velocities of rotation, ω r As the rotational angular velocity of the rotor, i dr 、i qr For rotor dq axis currents, G P To simulate an inductance;
and 2.3, enabling the rotor voltage output by the rotor side converter to meet the relation of an equation (13) under the action of the additional signal of the equation (12):
wherein, K iq 、K id Proportional coefficient for PI control of current loop in the rotor side converter; t is iq 、T id Integral coefficient, i, of current loop PI control in a rotor-side converter qrref 、i drref A rotor dq axis current reference value which is output by rotor side converter outer ring PI control;
step 3, carrying out self-adaptive on-line setting on the simulated inductance value by utilizing a PSO algorithm, and determining the optimal value of the simulated inductance under the working condition;
and 4, applying an analog inductance control strategy and a rotor side converter control strategy to the control of the rotor side of the doubly-fed wind turbine to complete the suppression of the subsynchronous oscillation of the system.
2. The method for suppressing the subsynchronous oscillation of the doubly-fed wind farm based on the analog inductance according to claim 1, wherein the step 1 of establishing the system model of the doubly-fed wind farm through the series compensation capacitance grid connection specifically comprises the following steps:
step 1.1, obtaining the corresponding relation among the rotating speed, the output power and the wind speed of the rotor of the doubly-fed wind turbine according to a wind energy capture model;
step 1.2, writing out an electromagnetic equation of the system in a dq coordinate system as follows:
step 1.2.1, the stator and the rotor in the doubly-fed induction generator adopt the motor convention, the positive direction is the current flowing direction, and the rotating direction is the same as the positive direction of the electromagnetic torque; according to the coordinate transformation principle, current, voltage and magnetic flux variables in the stator and the rotor are transformed from a three-phase static coordinate to a dq coordinate system, and the electromagnetic relation in the stator and the rotor is obtained as follows:
wherein ω is s ＝ω 1 -ω r Is the slip angular velocity; u. of ds 、u qs Is the stator dq-axis voltage, u dr 、u qr Is the rotor dq axis voltage; i.e. i ds 、i qs Is the stator dq axis current; psi ds 、ψ qs For stator dq axis flux, psi dr 、ψ qr A rotor dq axis flux linkage; r is s Is stator resistance, R r Is a rotor resistance; l is ls For stator leakage inductance, L lr For rotor leakage inductance, L m For coaxial mutual inductance of stator and rotor, L s 、L r Equivalent self-inductance of stator and rotor windings;
step 1.2.2, controlling a target of a double-fed fan rotor side converter by tracking the maximum wind energy, keeping the frequency of generated energy constant and controlling reactive output; fixing the stator flux linkage direction on a d axis to realize active and reactive decoupling; and (3) regulating the rotor voltage by adopting PI control to obtain a differential equation:
wherein Te ref 、Q sref Reference value for electromagnetic torque and stator reactive power, K Te 、K Qs Proportional coefficient for rotor side converter outer power loop PI control; t is Te 、T Qs For rotor side converter outer power loop PI controlAn integral coefficient; x is the number of 1 ～x 4 Four intermediate variables were introduced.
3. The method for suppressing the subsynchronous oscillation of the doubly-fed wind power plant based on the simulated inductance according to claim 1, wherein the step 3 is to perform adaptive online tuning on the simulated inductance value by using a PSO algorithm to determine the optimal value of the simulated inductance under the working condition, and specifically comprises the following steps:
step 3.1, writing a system state equation in a row, linearizing the system state equation at a balance point to obtain a small signal equation:
dΔX/dt＝AΔX (14)
in the formula, X is the state variable of the system, and the number of X is 20; a is a Jacobian matrix determined by system parameters and balance point states;
step 3.2, calculating the subsynchronous oscillation frequency f of the system n The formula is as follows:
in the formula (f) 1 For mains frequency, X C For series compensation of capacitive reactance of capacitor, X ∑ Is the sum of effective inductive reactance in the system;
corresponding to a power oscillation frequency of f SSR ＝f 1 -f n Based on the characteristic value, determining a corresponding subsynchronous oscillation mode in the characteristic value of the Jacobian matrix A;
step 3.3 at G P When the value is changed, two groups of characteristic value real parts are changed, wherein one group corresponds to a subsynchronous mode, and the corresponding characteristic value is sigma 1 ±jω 1 (ii) a The other group corresponds to low-frequency mode, and the corresponding characteristic value is sigma 2 ±jω 2 The PSO algorithm is adopted to carry out self-adaptive setting on the analog inductance value, the primary objective of the algorithm is to inhibit subsynchronous oscillation, and therefore the damping ratio corresponding to the subsynchronous modal characteristic value is taken as a fitness function, as shown in the formula (16):
step 3.4, limiting the real part of the characteristic value corresponding to the low-frequency mode in a certain range to obtain a constraint of the algorithm:
σ 2 ≤σ 2max (17)
in the formula sigma 2max A constant less than zero;
and 3.5, updating the position and the search speed of the ith particle according to the formula (18):
in the formula, k is the current iteration number; w is the inertial weight; c. C 1 And c 2 Is a learning factor; r is 1 And r 2 A random number in the range of 0 to 1;
is the current best position of the ith particle,
is the current global optimum position;
3.6, establishing a dynamic adjustment model of the inertial weight, and searching by using the fixed weight at the initial stage of the algorithm; and after the set number of iterations, varying w according to equation (19):
in the formula, w max And w min Is a fixed value, f i For the current particle adaptation value, f av Average of the adapted values for all particles, f best Adapting the value for the global optimum particle;
step 3.7, simulating the inductor G P The optimum range of values and particle velocity are constrained:
wherein G is Pmin And G Pmax To a fixed value selected as required, v max And v min The upper and lower limits of the particle search speed can be selected according to typical values.
4. The method for suppressing the subsynchronous oscillation of the doubly-fed wind power plant based on the analog inductance of claim 1, wherein the analog inductance control strategy and the rotor-side converter control strategy are applied to the control of the rotor side of the doubly-fed wind turbine in the step 4, so as to suppress the subsynchronous oscillation of the system, specifically as follows:
the simulated inductance G obtained by PSO algorithm setting P The value is applied to the control of the converter, the control of the analog inductance of the double-fed fan is realized, and the suppression of the subsynchronous oscillation of the system is completed.
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