CN112448398B - Stator side analog resistance-based doubly-fed wind power plant subsynchronous oscillation suppression method - Google Patents
Stator side analog resistance-based doubly-fed wind power plant subsynchronous oscillation suppression method Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
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- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
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- H02P21/28—Stator flux based control
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Abstract
The invention discloses a method for inhibiting doubly-fed wind power plant subsynchronous oscillation based on stator side analog resistance, 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, an equivalent impedance model of the doubly-fed wind turbine grid-connected system is deduced by combining a control strategy of a rotor side converter, and the damping characteristic of the system is analyzed; secondly, determining the value of a stator side analog resistor according to the analysis result of the damping characteristic of the doubly-fed fan grid-connected system so as to compensate the negative damping action of the system; and finally, applying a control strategy based on the stator side analog resistor to the control of the doubly-fed fan stator side converter to complete the suppression of the subsynchronous oscillation of the system. The method can effectively inhibit the subsynchronous oscillation phenomenon in the wind power plant grid-connected system, improves the stability of the system, does not need any additional device, saves the cost and is convenient for practical engineering application.
Description
Technical Field
The invention belongs to the technical field of stability control of wind driven generators, and particularly relates to a method for suppressing sub-synchronous oscillation of a doubly-fed wind power plant based on a stator side analog resistor.
Background
Among various renewable energy sources, the wind energy has the characteristics of rich resources and wide distribution, and has better economic and social benefits. The Chinese energy development strategy has developed and utilized wind power on a large scale as an important component. Because the wind power resource is not consistent with the load demand distribution, the wind power needs to be conveyed outwards in a large capacity and long distance. The series compensation capacitor technology has the advantages of reducing the loss of a power transmission line and improving the transmission capacity of the line, can be used as a technical support for realizing large-scale wind power delivery, but can be widely applied to possibly induce the problem of subsynchronous oscillation of a wind power plant. In recent years, many subsynchronous oscillation accidents of wind power plants occur at home and abroad, and the safe and stable operation of large-scale wind power bases and delivery systems is seriously influenced while huge economic loss is caused. Therefore, the problem of subsynchronous oscillation of the fan series compensation power transmission system is a common concern of scholars at home and abroad.
In the aspect of suppressing the subsynchronous oscillation of the doubly-fed wind power plant, research is mostly focused on the aid of an additional damping controller or an FACTS device, and although these methods have a certain effect on suppressing the oscillation, they usually require complicated parameter setting, and the suppression effect is influenced by the performance of a filter. In addition, the introduction of the additional device increases the cost of a single fan, which is not beneficial to the practical application of engineering.
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 a stator side analog resistor, which can improve the stability of a doubly-fed wind power plant grid-connected system through a series compensation capacitor.
The technical solution for realizing the purpose of the invention is as follows: a method for suppressing the sub-synchronous oscillation of a doubly-fed wind power plant based on a stator side analog resistor comprises the following steps:
step 3, determining a value of a stator side model resistor according to an analysis result of the damping characteristic of the doubly-fed fan grid-connected system so as to compensate the negative damping effect of the system;
and 4, applying a control strategy based on the stator side analog resistance to the control of the doubly-fed fan stator side converter 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, adopting a motor convention for a stator and a rotor in the doubly-fed induction generator, wherein the positive direction is a current inflow direction, the rotation direction is the same as the positive direction of electromagnetic torque, and transforming current, voltage and magnetic flux variables in the stator and the rotor from a three-phase static coordinate system to a dq coordinate system according to a coordinate transformation principle to obtain an electromagnetic relation in the stator and the rotor:
wherein ω is 1 For synchronizing angular velocities of rotation, omega 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 currents, i dr 、i qr Is the rotor dq axis current; psi ds 、ψ qs For stator dq axis flux linkage, psi dr 、ψ qr Is the rotor dq axis flux linkage; r s Is stator resistance, R r Is the rotor resistance; l is a radical of an alcohol ls Leakage inductance of stator, 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, the control target of the rotor side converter of the double-fed fan comprises maximum wind energy tracking, constant frequency of generated energy and reactive output control, and the stator flux linkage direction is fixed on a d axis to realize active and reactive decoupling; the control of the rotor side converter consists of a power loop and a current loop, the rotor voltage is adjusted by adopting PI control, and the control equation of the rotor side converter is obtained as follows:
wherein Te ref 、Q s ref Reference value, K, for electromagnetic torque and stator reactive power 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 qr ref 、i dr ref Rotor dq axis current reference, x, for rotor side converter outer loop PI control output 1 ～x 4 Four intermediate variables are introduced;
step 1.2.3, the doubly-fed wind turbine normally operates in a subsynchronous state, the grid-side converter is used for realizing the electric energy conversion from alternating current to direct current, the voltage of a direct-current bus is kept constant, the harmonic wave of the alternating current side is reduced, and the control equation of the grid-side converter is as follows:
i qg ref ＝K p1 (U dc ref -U dc )+T i1 x 5 (13)
u qg ＝K p2 [K p1 (U dc ref -U dc )+T i1 x 5 -i qg ]+T i2 x 6 (15)
i dg ref ＝K p1 (U s ref -U s )+T i1 x 7 (17)
u dg ＝K p2 [K p1 (U s ref -U s )+T i1 x 7 -i dg ]+T i2 x 8 (19)
wherein, U dc ref 、U dc Reference and actual operating values, U, of the converter DC voltage s ref 、U s Respectively a reference value and an actual value of the terminal voltage; k p1 Proportional coefficient, K, for the external power loop PI control of the network-side converter p2 Proportional coefficient for current loop PI control in the network side converter; t is i1 Integral coefficient, T, for the PI control of the external power loop of the network-side converter i2 The integral coefficient is controlled by a current loop PI in the network side converter; i.e. i dg ref 、i qg ref Reference values, i, for the components of the grid-side converter current dq axes, respectively dg 、i qg Is the actual value of the grid side converter current dq axis component; x is a radical of a fluorine atom 5 ～x 8 Is the 4 intermediate variables introduced.
Further, the step 2 is combined with a control strategy of the rotor side converter, an equivalent impedance model of the doubly-fed wind turbine grid-connected system is deduced, and a damping characteristic of the system is analyzed, specifically as follows:
step 2.1, a control equation of the double-fed fan rotor side converter can be obtained:
the formula (20) and the formula (2) are combined to form:
order to
Then there are:
wherein K is id And K iq Taking K as the same value iq ＝K id ＝K i ，K i The scale factor of the outer ring of the rotor side converter can take a typical value;
step 2.2, as can be seen from the formula (22), the value K is introduced into the rotor loop of the doubly-fed wind turbine rotor side converter i The resistance of (1); the frequency of the exciting current in the rotor winding is converted to the stator side, and the union of the DFIG wind power plant can be obtainedNet equivalent impedance model.
Further, in step 3, according to an analysis result of the damping characteristic of the doubly-fed wind turbine grid-connected system, a value of the stator side-mode analog resistor is determined so as to compensate the negative damping action of the system, specifically as follows:
step 3.1, impedance of the doubly-fed fan system is as follows:
Z DFIG ＝(R r +K i )/s n +R s +(X ls +X lr +X T )s (23)
wherein s is n For slip corresponding to subsynchronous component, X T Is a transformer reactance;
let the angular frequency of the subsynchronous oscillation components present in the system be ω er If ω is er ＜ω r Then the corresponding slip s n ＝(jω er -jω r )/jω er If the equivalent resistance is less than 0, the equivalent resistance of the rotor loop is a negative value; when the absolute value of the negative resistance is larger than the value of the positive resistance in the system, the negative damping in the system needs to be compensated, and the negative damping in the rotor loop is:
subsynchronous oscillation frequency f of the system n Comprises the following steps:
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;
the angular frequency corresponding to the subsynchronous oscillation component is:
ω er ＝2πf n (26)
determining the corresponding rotor speed under the specific wind speed, and calculating the slip corresponding to the subsynchronous component, wherein the formula is as follows:
s n ＝(jω er -jω r )/jω er (27)
and 3.2, taking 80-100% of the negative damping amplitude value as a value of the stator side-die analog resistor to compensate the negative damping effect of the system.
Further, in step 4, combining the analysis result in step 3, applying a control strategy based on the stator-side analog resistance to the control of the doubly-fed fan stator-side converter to complete the suppression of the subsynchronous oscillation of the system, which is specifically as follows:
step 4.1, detecting external wind speed, determining 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 stator current dq axis component of the doubly-fed fan by combining a corresponding control strategy
Step 4.2, subtracting the actual value of the stator current dq axis component from the steady-state expected value, taking the gain and then using the gain as an additional signal to act on the input of the grid-side converter GSC, wherein the formula is as follows:
wherein G P Taking values according to the result in the step 3;
and 4.3, under the action of the additional signal of the formula (28), outputting the rotor voltage by the rotor side converter to satisfy the relation of the formula (29):
for the steady-state component in the system, the electromagnetic relation is unchanged, and the relation shown in the formula (1) is still satisfied;
step 4.4, using u for stator dq axis voltage corresponding to subsynchronous oscillation component in the system qs sub And u ds sub Denotes the stator dq axis current by i qs sub And i ds sub Indicating stator dq axis flux linkage by psi qs sub And psi ds sub It is shown that the relationship satisfied by the subsynchronous oscillation components is:
and 4.5, replacing a grid-side converter control strategy with a control strategy based on the stator side analog resistor to realize the suppression of the subsynchronous oscillation of the doubly-fed fan.
Compared with the prior art, the invention has the remarkable advantages that: (1) the method can effectively inhibit the subsynchronous oscillation phenomenon in the wind power plant grid-connected system, and improves the stability of the system; (2) the invention has few parameters needing to be set, and avoids complex parameter setting; (3) the invention only improves the PI control of the double-fed fan rotor side converter, does not change the basic control structure of the RSC converter, and meets the requirements of current fan manufacturers; (4) the doubly-fed fan is controlled to inhibit subsynchronous oscillation without any additional device, so that the cost is saved, and the practical engineering application is facilitated.
Drawings
FIG. 1 is a flow chart of a method for suppressing the sub-synchronous oscillation of the doubly-fed wind power plant based on a stator side analog resistor.
FIG. 2 is a schematic structural diagram of a doubly-fed wind power plant grid-connected model through series compensation capacitors.
FIG. 3 is a control block diagram of a double-fed wind turbine rotor side converter in the invention.
Fig. 4 is a control block diagram of the doubly-fed wind turbine grid-side converter in the invention.
Fig. 5 is an equivalent impedance diagram of the doubly-fed wind turbine grid-connected system in the invention.
FIG. 6 is a schematic flow chart of a stator-based analog resistance control strategy in accordance with the present invention.
FIG. 7 is a simulation result graph of a conventional PI control strategy adopted in an embodiment of the present invention, wherein (a) is a simulation result graph corresponding to a wind speed of 7m/s and a series compensation degree of 40%; (b) a simulation result curve chart corresponding to the wind speed of 7m/s and the series compensation degree of 62.5 percent is obtained; (c) is a simulation result curve chart corresponding to the wind speed of 7m/s and the 67 percent series compensation degree.
FIG. 8 is a simulation diagram of a fan electromagnetic torque curve after a stator-side analog resistance control strategy is adopted in the embodiment of the present invention, wherein (a) is a simulation result curve corresponding to a wind speed of 7m/s and a series compensation degree of 62.5%; (b) a simulation result curve chart corresponding to the wind speed of 7m/s and the series compensation degree of 67 percent is obtained; (c) is a simulation result curve chart corresponding to the wind speed of 7m/s and the 80% series compensation degree.
Detailed Description
With reference to fig. 1, the invention provides a method for suppressing the sub-synchronous oscillation of a doubly-fed wind power plant based on a stator side analog resistor, 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 among the rotating speed of the rotor of the doubly-fed wind turbine, the output power and the wind speed 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 And outputting the 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 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, the 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 currents, 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 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 The stator and rotor windings are equivalent to self inductance.
Step 1.2.2, the control target of the doubly-fed wind turbine rotor side converter comprises the following steps: maximum wind energy tracking, keeping the generated energy frequency 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; rotor voltage regulation using PI controlThe control block diagram of the sub-side converter is shown in FIG. 3, where Te ref 、Q s ref Reference value, K, for electromagnetic torque and stator reactive power Te 、K Qs Proportional coefficient, K, for rotor side converter outer power loop PI control iq 、K id Proportional coefficient for PI control of current loop in 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 qr ref 、i dr ref And controlling the output rotor dq axis current reference value for the rotor side converter outer ring PI.
Writing a relation column expressed by a control block diagram into a differential equation, wherein the control equation of the doubly-fed fan rotor side converter is shown in equations (4) to (11):
wherein x is 1 ～x 4 Four intermediate variables are introduced;
step 1.2.3, when the doubly-fed wind turbine normally operates in a sub-synchronous state, the grid-side converter mainly has the functions of realizing electric energy conversion from alternating current to direct current, keeping the voltage of a direct-current bus constant and reducing harmonic waves on the alternating current side, and a control block diagram of the grid-side converter is shown in fig. 4. Wherein, U dc ref 、U dc Reference and actual operating values, U, of the converter DC voltage s ref 、U s Respectively a reference value and an actual value of the terminal voltage; k p1 Proportional coefficient, K, for the external power loop PI control of the network-side converter p2 Proportional coefficient for controlling current loop PI in the network side converter; t is i1 Integral coefficient, T, for PI control of the external power loop of the network-side converter i2 And the integral coefficient is controlled by a current loop PI in the network side converter.
The relation column expressed by the control block diagram is written into a differential equation as shown in equations (12) to (19):
i qg ref ＝K p1 (U dc ref -U dc )+T i1 x 5 (13)
u qg ＝K p2 [K p1 (U dc ref -U dc )+T i1 x 5 -i qg ]+T i2 x 6 (15)
i dg ref ＝K p1 (U s ref -U s )+T i1 x 7 (17)
u dg ＝K p2 [K p1 (U s ref -U s )+T i1 x 7 -i dg ]+T i2 x 8 (19)
wherein i dg ref 、i qg ref Reference values, i, for the components of the grid-side converter current dq axes, respectively dg 、i qg Is the actual value of the grid side converter current dq axis component; x is the number of 5 ～x 8 Is the 4 intermediate variables introduced.
step 2.1, a control equation of the double-fed fan rotor side converter can be obtained:
the formula (20) and the formula (2) are combined to form:
order to
Then there are:
step 2.2, K in actual engineering id And K iq Are equal in value, i.e. K iq ＝K id ＝K i From the equation (22), it can be seen that the doubly-fed wind turbine rotor-side converter introduces a value K in the rotor circuit i The resistance of (1); compared with other branches, the impedances of the excitation branch and the network side converter branch are very large, so that the impedances are ignored in the impedance model; the grid-connected equivalent impedance model of the DFIG wind farm can be obtained by converting the frequency of the exciting current in the rotor winding to the stator side, and as shown in fig. 5, in the graph, slip is (s-j ω) r ) And/s is the slip rate of the fan during operation.
Step 3, determining the value of the stator side analog resistor according to the analysis result of the damping characteristic of the doubly-fed fan grid-connected system so as to compensate the negative damping action of the system, wherein the value is as follows:
step 3.1, in fig. 5, the impedance of the doubly-fed wind turbine system is:
Z DFIG ＝(R r +K i )/slip+R s +(X ls +X lr +X T )s (23)
according to the formula (23), the electric damping of the grid-connected system is influenced by the running slip ratio of the fan; setting the angular frequency of subsynchronous oscillation components occurring in the system to ω er If ω is er ω r Then the corresponding slip s n ＝(jω er -jω r )/jω er If the equivalent resistance is less than 0, the equivalent resistance of the rotor loop is a negative value; when the absolute value of the negative resistance is larger than the value of the positive resistance in the system, the system will present a negative damping characteristic to the oscillation component, so that the oscillation amplitude is continuously increased, therefore, in order to suppress the divergence of the oscillation, the negative damping in the system needs to be compensated, and the negative damping in the rotor circuit is:
to determine negative damping Z neg Size of (2), needDetermining s under a particular operating condition n The method comprises the following steps:
subsynchronous oscillation frequency f of the system n Comprises the following steps:
in the formula (f) 1 For mains frequency, X C For series compensation of capacitive reactance of a capacitor, X ∑ Is the sum of effective inductive reactance in the system;
the angular frequency corresponding to the subsynchronous oscillation component is:
ω er ＝2πf n (26)
determining the rotor speed corresponding to the wind speed according to the table 1, and then calculating the slip corresponding to the subsynchronous component, wherein the formula is as follows:
s n ＝(jω er -jω r )/jω er (27)
and 3.2, taking 80-100% of the negative damping amplitude value as a value of the stator side-die analog resistor to compensate the negative damping effect of the system.
And 4, combining the analysis result of the step 3, applying a control strategy based on the stator side analog resistance to the control of the doubly-fed fan stator side converter to complete the suppression of the subsynchronous oscillation of the system, and combining the figure 6, specifically as follows:
step 4.1, 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 control target, establishing a relevant state equation of a simultaneous system, and calculating a steady-state expected value of a stator current dq axis component of the doubly-fed fan by combining with a corresponding control strategy
Step 4.2, making a difference between the actual value of the stator current dq axis component and the steady-state expected value, and according to the result shown in fig. 6, taking the gain as an input of an additional signal applied to the grid-side converter GSC, wherein the formula is as follows:
wherein G P Taking values according to the result in the step 3;
and 4.3, under the action of the additional signal of the formula (28), outputting the rotor voltage by the rotor side converter to satisfy the relation of the formula (29):
for the steady-state component in the system, the electromagnetic relation is unchanged, and the relation shown in the formula (1) is still satisfied;
step 4.4, using u for stator voltage corresponding to subsynchronous oscillation component in the system qs sub And u ds sub Indicating stator current by i qs sub And i ds sub Indicating stator flux linkage by qs sub And psi ds sub It is shown that the relationship satisfied by the subsynchronous oscillation components is:
and 4.5, replacing the grid-side converter control scheme shown in the figure 4 with a control scheme based on the stator-side analog resistor, and realizing the suppression of the subsynchronous oscillation of the doubly-fed fan.
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 driven generators of 2MW, and specific system parameters are shown in tables 2-4:
TABLE 2 Induction Generator parameters
| Name(s) | Single machine parameters | Total parameter | |
| Reference capacity | 2MW | 100MW | |
| | 690V | 690V | |
| Stator leakage reactance X ls | 0.09231pu | 0.09231pu | |
| Rotor leakage reactance X lr | 0.09955pu | 0.09955pu | |
| Stator-rotor mutual inductance X M | 3.95279pu | 3.95279pu | |
| Stator resistance R s | 0.00488pu | 0.00488pu | |
| Rotor resistance R r | 0.00549pu | 0.00549pu | |
| Net side flat wave reactance X tg | 0.3pu | 0.3pu | |
| DC capacitor reference voltage | 1200V | 1200V | |
| DC capacitor C | 14000μF | 50×14000μF |
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 4RSC 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. 7 shows the 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% at the time t is 0.5s, oscillation curves of the fan electromagnetic torque Te are obtained as shown in fig. 7 (a), (b) and (c), respectively. 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.
FIG. 8 shows the stator sideSimulating a DFIG electromagnetic torque curve after a resistance control strategy, wherein the value of the simulated resistance is G p 0.8. It can be seen from (a) and (b) of fig. 8 that after the control strategy proposed by the present invention is adopted, the subsynchronous component of the original constant-amplitude or amplified oscillation is rapidly attenuated, and the system is restored to be stable. To further verify the suppression effect, the series compensation degree of the line is continuously increased to 80%, as shown in fig. 8(c), and the simulation result shows that the system can still smooth the subsynchronous oscillation component. In conclusion, the method for inhibiting the sub-synchronous oscillation of the doubly-fed wind power plant based on the stator side analog resistor can effectively inhibit the sub-synchronous oscillation phenomenon in a grid-connected system of the DFIG wind power plant, and improves the stability of the system.
Claims (4)
1. A method for suppressing the sub-synchronous oscillation of a doubly-fed wind power plant based on a stator side analog resistor 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, combining a control strategy of a rotor side converter, deducing an equivalent impedance model of the doubly-fed fan grid-connected system, and analyzing the damping characteristic of the system;
step 3, determining the value of the stator side analog resistor according to the analysis result of the damping characteristic of the doubly-fed fan grid-connected system so as to compensate the negative damping action of the system, wherein the value is as follows:
step 3.1, impedance of the doubly-fed fan system is as follows:
Z DFIG ＝(R r +K i )/s n +R s +(X ls +X lr +X T )s (23)
wherein R is r Is rotor resistance, R s Is stator resistance, K i Is the proportionality coefficient, s, of the outer ring of the rotor-side converter n For slip corresponding to subsynchronous component, X T Is a transformer reactance;
let the angular frequency of the subsynchronous oscillation components present in the system be ω er Angular velocity of rotation of rotor is ω r If ω is er ＜ω r Then the corresponding slip s n ＝(jω er -jω r )/jω er If the equivalent resistance is less than 0, the equivalent resistance of the rotor loop is a negative value; when the absolute value of the negative resistance is larger than the value of the positive resistance in the system, the negative damping in the system needs to be compensated, and the negative damping in the rotor loop is:
subsynchronous oscillation frequency f of the system n Comprises the following steps:
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;
the angular frequency corresponding to the subsynchronous oscillation component is:
ω er ＝2πf n (26)
determining the corresponding rotor rotating speed under the wind speed, and calculating the slip corresponding to the subsynchronous component, wherein the formula is as follows:
s n ＝(jω er -jω r )/jω er (27)
3.2, taking 80-100% of the negative damping amplitude as a value of a stator side form analog resistor to compensate the negative damping effect of the system;
and 4, applying a control strategy based on the stator side analog resistance to the control of the doubly-fed fan stator side converter to complete the suppression of the subsynchronous oscillation of the system.
2. The method for suppressing the sub-synchronous oscillation of the doubly-fed wind farm based on the stator-side analog resistance is characterized in that the establishment of the system model of the doubly-fed wind farm subjected to series compensation capacitor grid connection in the step 1 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, adopting a motor convention for a stator and a rotor in the doubly-fed induction generator, wherein the positive direction is a current inflow direction, the rotation direction is the same as the positive direction of electromagnetic torque, and transforming current, voltage and magnetic flux variables in the stator and the rotor from a three-phase static coordinate system to a dq coordinate system according to a coordinate transformation principle to obtain an electromagnetic relation in the stator and the rotor:
wherein ω is 1 For synchronizing the angular velocities of rotation, ω s ＝ω 1 -ω r Is the slip angular velocity; u. u 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; l is ls For stator leakage inductance, L lr For rotor leakage inductance, L m Is coaxial mutual inductance of stator and rotor, L s 、L r Equivalent self-inductance of stator and rotor windings;
step 1.2.2, the control target of the rotor side converter of the double-fed fan comprises maximum wind energy tracking, constant frequency of generated energy and reactive output control, and the stator flux linkage direction is fixed on a d axis to realize active and reactive decoupling; the control of the rotor side converter consists of a power loop and a current loop, the rotor voltage is adjusted by adopting PI control, and the control equation of the rotor side converter is obtained as follows:
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 a unit of Te 、T Qs Integral coefficient, T, for rotor side converter outer power loop PI control iq 、T id The integral coefficient is controlled by a current loop PI in the rotor side converter; i all right angle qrref 、i drref Rotor dq axis current reference, x, for rotor side converter outer loop PI control output 1 ～x 4 Four intermediate variables are introduced;
step 1.2.3, under the condition that the double-fed fan runs in a subsynchronous state, the grid-side converter is used for realizing the electric energy conversion from alternating current to direct current, keeping the voltage of a direct current bus constant and reducing the harmonic wave at the alternating current side, and the control equation of the grid-side converter is as follows:
i qgref ＝K p1 (U dcref -U dc )+T i1 x 5 (13)
u qg ＝K p2 [K p1 (U dcref -U dc )+T i1 x 5 -i qg ]+T i2 x 6 (15)
i dgref ＝K p1 (U sref -U s )+T i1 x 7 (17)
u dg ＝K p2 [K p1 (U sref -U s )+T i1 x 7 -i dg ]+T i2 x 8 (19)
wherein, U dcref 、U dc Reference and actual operating values, U, of the converter DC voltage sref 、U s Respectively a reference value and an actual value of the terminal voltage; k p1 Proportional coefficient, K, for the external power loop PI control of the network-side converter p2 Proportional coefficient for current loop PI control in the network side converter; t is a unit of i1 Integral coefficient, T, for the PI control of the external power loop of the network-side converter i2 The integral coefficient is controlled by a current loop PI in the network side converter; i.e. i dgref 、i qgref Reference values, i, for the components of the grid-side converter current dq axes, respectively dg 、i qg Is the actual value of the grid side converter current dq axis component; x is the number of 5 ～x 8 Are the 4 intermediate variables introduced.
3. The method for suppressing the subsynchronous oscillation of the doubly-fed wind power plant based on the stator side analog resistor is characterized in that the step 2 is combined with a control strategy of a rotor side converter to deduce an equivalent impedance model of a doubly-fed wind turbine grid-connected system and analyze the damping characteristic of the system, and the method specifically comprises the following steps:
step 2.1, the control equation of the double-fed fan rotor side converter can be obtained:
the formula (20) and the formula (2) are combined to form:
order to
Then there are:
wherein K is id And K iq Taking K as the same value iq ＝K id ＝K i ，K i The scale factor of the outer ring of the rotor side converter can take a typical value;
step 2.2, as can be seen from the formula (22), the value K is introduced into the rotor loop of the doubly-fed wind turbine rotor-side converter i The resistance of (1); and converting the frequency of the exciting current in the rotor winding to the stator side to obtain a grid-connected equivalent impedance model of the DFIG wind power plant.
4. The method for suppressing the subsynchronous oscillation of the doubly-fed wind power plant based on the stator-side analog resistor of claim 2, wherein in the step 4, a control strategy based on the stator-side analog resistor is applied to control of a converter at the stator side of the doubly-fed wind turbine in combination with an analysis result of the step 3, so that suppression of the subsynchronous oscillation of the system is completed, and the method is specifically as follows:
step 4.1, detecting external wind speed, determining 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 stator current dq axis component of the doubly-fed fan by combining a corresponding control strategy
Step 4.2, subtracting the actual value of the stator current dq axis component from the steady-state expected value, taking the gain and then using the gain as an additional signal to act on the input of the grid-side converter GSC, wherein the formula is as follows:
wherein i ds 、i qs For stator dq axis currents, G P Taking values according to the result in the step 3;
and 4.3, under the action of the additional signal of the formula (28), outputting the rotor voltage by the rotor side converter to satisfy the relation of the formula (29):
for the steady-state component in the system, the electromagnetic relation is unchanged, and the relation shown in the formula (1) is still satisfied;
step 4.4, using u for stator dq axis voltage corresponding to subsynchronous oscillation component in the system qs sub And u ds sub Denotes the stator dq axis current by i qs sub And i ds sub Indicating that stator dq axis flux linkage is by qs sub And psi ds sub It is shown that the relationship satisfied by the subsynchronous oscillation components is:
and 4.5, replacing a grid-side converter control strategy with a control strategy based on a stator side analog resistor to realize the suppression of the sub-synchronous oscillation of the doubly-fed fan.
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| CN114006383B (en) * | 2021-10-19 | 2023-07-25 | 昆明理工大学 | Modeling and subsynchronous oscillation analysis method for doubly-fed wind turbine grid-connected system containing VSG |
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