CN112448398A - 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 PDF

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CN112448398A
CN112448398A CN201910810767.3A CN201910810767A CN112448398A CN 112448398 A CN112448398 A CN 112448398A CN 201910810767 A CN201910810767 A CN 201910810767A CN 112448398 A CN112448398 A CN 112448398A
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rotor
stator
doubly
side converter
grid
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CN112448398B (en
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王宝华
单碧涵
蒋海峰
饶新亮
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Nanjing University of Science and Technology
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Nanjing University of Science and Technology
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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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • 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
    • H02P21/24—Vector control not involving the use of rotor position or rotor speed sensors
    • H02P21/28—Stator flux based control
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects

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

Stator side analog resistance-based doubly-fed wind power plant subsynchronous oscillation suppression method
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 stator side analog resistance.
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 transmitted 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 inhibiting 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 inhibiting the oscillation, they usually require complicated parameter setting, and the inhibition effect is affected 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 1, establishing a system model of a doubly-fed wind power plant which is connected with the 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;
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 establishing of the system model of the doubly-fed wind farm through the series compensation capacitor grid connection in the step 1 is as follows:
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:
Figure BDA0002184980700000021
Figure BDA0002184980700000022
Figure BDA0002184980700000023
wherein ω is1For synchronizing the angular velocities of rotation, ωs＝ω1-ωrIs the slip angular velocity, omegarIs the rotor rotational angular velocity; u. ofds、uqsIs the stator dq-axis voltage, udr、uqrIs the rotor dq axis voltage; i.e. ids、iqsFor stator dq axis current, idr、iqrIs the rotor dq axis current; psids、ψqsFor stator dq axis flux linkage, psidr、ψqrA rotor dq axis flux linkage; rsIs stator resistance, RrIs the rotor resistance; l islsFor stator leakage inductance, LlrFor rotor leakage inductance, LmFor coaxial mutual inductance of stator and rotor, Ls、LrEquivalent 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:
Figure BDA0002184980700000024
Figure BDA0002184980700000025
Figure BDA0002184980700000031
Figure BDA0002184980700000038
Figure BDA0002184980700000032
Figure BDA0002184980700000039
Figure BDA0002184980700000033
Figure BDA00021849807000000310
wherein Teref、Qs refReference value for electromagnetic torque and stator reactive power, KTe、KQsProportional coefficient, K, for the external power loop PI control of the rotor-side converteriq、KidProportional coefficient for PI control of current loop in the rotor side converter; t isTe、TQsIntegral coefficient, T, for rotor side converter outer power loop PI controliq、TidIntegral coefficient of current loop PI control in the rotor side converter; i.e. iqr ref、idr refRotor dq axis current reference, x, for rotor side converter outer loop PI control output1～x4Four 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:
Figure BDA0002184980700000034
iqg ref＝Kp1(Udc ref-Udc)+Ti1x5 (13)
Figure BDA0002184980700000035
uqg＝Kp2[Kp1(Udc ref-Udc)+Ti1x5-iqg]+Ti2x6 (15)
Figure BDA0002184980700000036
idg ref＝Kp1(Us ref-Us)+Ti1x7 (17)
Figure BDA0002184980700000037
udg＝Kp2[Kp1(Us ref-Us)+Ti1x7-idg]+Ti2x8 (19)
wherein, Udc ref、UdcReference and actual operating values, U, of the converter DC voltages ref、UsRespectively a reference value and an actual value of the terminal voltage; kp1Proportional coefficient, K, for the external power loop PI control of the network-side converterp2Proportional coefficient for controlling current loop PI in the network side converter; t isi1Integral coefficient, T, for the PI control of the external power loop of the network-side converteri2The integral coefficient is controlled by a current loop PI in the network side converter; i.e. idg ref、iqg refReference values, i, for the components of the grid-side converter current dq axes, respectivelydg、iqgIs the actual value of the grid side converter current dq axis component; x is the number of5～x8Is 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:
Figure BDA0002184980700000041
the formula (20) and the formula (2) are combined to form:
Figure BDA0002184980700000042
order to
Figure BDA0002184980700000043
Then there are:
Figure BDA0002184980700000044
wherein KidAnd KiqTaking K as the same valueiq＝Kid＝Ki，KiThe 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 converteriThe 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.
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:
ZDFIG＝(Rr+Ki)/sn+Rs+(Xls+Xlr+XT)s (23)
wherein s isnFor slip corresponding to subsynchronous component, XTIs a transformer reactance;
let the angular frequency of the subsynchronous oscillation components present in the system be ωerIf ω iser＜ωrThen the corresponding slip sn＝(jωer-jωr)/jωerIf 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:
Figure BDA0002184980700000051
subsynchronous oscillation frequency f of the systemnComprises the following steps:
Figure BDA0002184980700000052
in the formula (f)1For mains frequency, XCFor 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:
ωer＝2πfn (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:
sn＝(jωer-jωr)/jωer (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
Figure BDA0002184980700000053
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:
Figure BDA0002184980700000054
wherein G isPTaking 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):
Figure BDA0002184980700000061
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 systemqs subAnd uds subIndicating stator dq-axis current by iqs subAnd ids subIndicating that stator dq axis flux linkage is byqs subAnd psids subIt is shown that the relationship satisfied by the subsynchronous oscillation components is:
Figure BDA0002184980700000062
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 the 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 series compensation degree of 67 percent.
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, establishing a system model of a doubly-fed wind power plant connected through a series compensation capacitor, which comprises the following specific 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 wind farm with a capacity of 100MW is formed by equivalent of 50 fans with a single capacity of 2MW,wherein, Xtg、XTIs a net side smoothing reactor and a transformer reactor, RL、XLAnd XCThe 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 iswIs the wind speed, ωrAs the rotor speed, PwFor wind turbine output power, TwAnd outputting the torque for the wind turbine.
TABLE 1 reference table for rotor speed and wind turbine output power
Vw(m/s) 7 8 9 10 11 12
ωr(p.u) 0.75 0.85 0.95 1.05 1.15 1.25
Pw(p.u) 0.32 0.49 0.69 0.95 1.25 1.6
Tw＝Pw/ωr 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:
Figure BDA0002184980700000071
Figure BDA0002184980700000081
Figure BDA0002184980700000082
wherein ω is1To rotate synchronouslyAngular velocity, omegas＝ω1-ωrIs the slip angular velocity, omegarIs the rotor rotational angular velocity; u. ofds、uqsIs the stator dq-axis voltage, udr、uqrIs the rotor dq axis voltage; i.e. ids、iqsFor stator dq axis current, idr、iqrIs the rotor dq axis current; psids、ψqsFor stator dq axis flux linkage, psidr、ψqrA rotor dq axis flux linkage; rsIs stator resistance, RrIs the rotor resistance; l islsFor stator leakage inductance, LlrFor rotor leakage inductance, LmFor coaxial mutual inductance of stator and rotor, Ls、LrThe 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; the control block diagram of the rotor side converter using PI control for regulating the rotor voltage is shown in FIG. 3, where Teref、Qs refReference value for electromagnetic torque and stator reactive power, KTe、KQsProportional coefficient, K, for the external power loop PI control of the rotor-side converteriq、KidProportional coefficient for PI control of current loop in the rotor side converter; t isTe、TQsIntegral coefficient, T, for rotor side converter outer power loop PI controliq、TidIntegral coefficient of current loop PI control in the rotor side converter; i.e. iqr ref、idr refAnd a rotor dq axis current reference value output by the rotor side converter outer ring PI control.
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):
Figure BDA0002184980700000083
Figure BDA0002184980700000084
Figure BDA0002184980700000085
Figure BDA0002184980700000086
Figure BDA0002184980700000087
Figure BDA0002184980700000088
Figure BDA0002184980700000091
Figure BDA0002184980700000092
wherein x is1～x4Four 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, Udc ref、UdcReference and actual operating values, U, of the converter DC voltages ref、UsRespectively a reference value and an actual value of the terminal voltage; kp1Proportional coefficient, K, for the external power loop PI control of the network-side converterp2Proportional coefficient for controlling current loop PI in the network side converter; t isi1Integral coefficient, T, for the PI control of the external power loop of the network-side converteri2And 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):
Figure BDA0002184980700000093
iqg ref＝Kp1(Udc ref-Udc)+Ti1x5 (13)
Figure BDA0002184980700000094
uqg＝Kp2[Kp1(Udc ref-Udc)+Ti1x5-iqg]+Ti2x6 (15)
Figure BDA0002184980700000095
idg ref＝Kp1(Us ref-Us)+Ti1x7 (17)
Figure BDA0002184980700000096
udg＝Kp2[Kp1(Us ref-Us)+Ti1x7-idg]+Ti2x8 (19)
wherein idg ref、iqg refReference values, i, for the components of the grid-side converter current dq axes, respectivelydg、iqgIs the actual value of the grid side converter current dq axis component; x is the number of5～x8Is the 4 intermediate variables introduced.
Step 2, combining a control strategy of a rotor side converter, deducing an equivalent impedance model of the doubly-fed wind turbine grid-connected system, and analyzing the damping characteristic of the system, wherein the method specifically comprises the following steps:
step 2.1, a control equation of the double-fed fan rotor side converter can be obtained:
Figure BDA0002184980700000101
the formula (20) and the formula (2) are combined to form:
Figure BDA0002184980700000102
order to
Figure BDA0002184980700000103
Then there are:
Figure BDA0002184980700000104
step 2.2, K in actual engineeringidAnd KiqAre equal in value, i.e. Kiq＝Kid＝KiFrom the equation (22), it can be seen that the doubly-fed wind turbine rotor-side converter introduces a value K in the rotor circuitiThe 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, as shown in fig. 5, where slip is (s-j ω ═ c)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:
ZDFIG＝(Rr+Ki)/slip+Rs+(Xls+Xlr+XT)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 ωerIf ω iserωrThen the corresponding slip sn＝(jωer-jωr)/jωerIf 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:
Figure BDA0002184980700000111
to determine negative damping ZnegIs required to determine s under a specific working conditionnThe method comprises the following steps:
subsynchronous oscillation frequency f of the systemnComprises the following steps:
Figure BDA0002184980700000114
in the formula (f)1For mains frequency, XCFor 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:
ωer＝2πfn (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:
sn＝(jωer-jωr)/jωer (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, and calculating a steady-state expected value of the stator current dq axis component of the doubly-fed fan by combining a relevant state equation of a simultaneous system and a corresponding control strategy
Figure BDA0002184980700000112
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:
Figure BDA0002184980700000113
wherein G isPTaking 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):
Figure BDA0002184980700000121
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 systemqs subAnd uds subIndicating stator current by iqs subAnd ids subIndicating stator flux linkage byqs subAnd psids subIt is shown that the relationship satisfied by the subsynchronous oscillation components is:
Figure BDA0002184980700000122
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 (R) Single machine parameters Total parameter
Reference capacity 2MW 100MW
Reference line voltage 690V 690V
Stator leakage reactance Xls 0.09231pu 0.09231pu
Rotor leakage reactance Xlr 0.09955pu 0.09955pu
Stator-rotor mutual inductance XM 3.95279pu 3.95279pu
Stator resistance Rs 0.00488pu 0.00488pu
Rotor resistance Rr 0.00549pu 0.00549pu
Net side flat wave reactance Xtg 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 (R) Parameter(s)
Transformation ratio of transformer 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 XS 0.06pu Shafting stiffness system 0.15pu/rad
TABLE 4RSC controller parameters
Name (R) Parameter(s) Name (R) Parameter(s)
TTe 0.05 Kiq 0.0001
TQs 0.025 Kid 0.0001
Tiq 0.005 KTe 0.0001
Tid 0.0025 KQs 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 were changed to 40%, 62.5%, and 65% at the time t equal to 0.5s, oscillation curves of the fan electromagnetic torque Te were 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 is a simulation diagram of a DFIG electromagnetic torque curve after a stator-side simulated resistance control strategy is adopted, and the value of the simulated resistance is Gp0.8. As can be seen from (a) and (b) of fig. 8, 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 again. 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 (5)

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 the 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;
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:
Figure FDA0002184980690000011
Figure FDA0002184980690000012
Figure FDA0002184980690000013
wherein ω is1For synchronizing the angular velocities of rotation, ωs＝ω1-ωrIs the slip angular velocity, omegarIs the rotor rotational angular velocity; u. ofds、uqsIs the stator dq-axis voltage, udr、uqrIs the rotor dq axis voltage; i.e. ids、iqsFor stator dq axis current, idr、iqrIs the rotor dq axis current; psids、ψqsFor stator dq axis flux linkage, psidr、ψqrA rotor dq axis flux linkage; rsIs stator resistance, RrIs the rotor resistance; l islsFor stator leakage inductance, LlrFor rotor leakage inductance, LmFor coaxial mutual inductance of stator and rotor, Ls、LrEquivalent 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:
Figure FDA0002184980690000021
Figure FDA0002184980690000022
Figure FDA0002184980690000023
Figure FDA0002184980690000024
Figure FDA0002184980690000025
Figure FDA0002184980690000026
Figure FDA0002184980690000027
Figure FDA0002184980690000028
wherein Teref、QsrefReference value for electromagnetic torque and stator reactive power, KTe、KQsProportional coefficient, K, for the external power loop PI control of the rotor-side converteriq、KidProportional coefficient for PI control of current loop in the rotor side converter; t isTe、TQsIntegral coefficient, T, for rotor side converter outer power loop PI controliq、TidThe integral coefficient is controlled by a current loop PI in the rotor side converter; i.e. iqrref、idrrefRotor dq axis current reference, x, for rotor side converter outer loop PI control output1～x4Four 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:
Figure FDA0002184980690000029
iqgref＝Kp1(Udcref-Udc)+Ti1x5 (13)
Figure FDA0002184980690000031
uqg＝Kp2[Kp1(Udcref-Udc)+Ti1x5-iqg]+Ti2x6 (15)
Figure FDA0002184980690000032
idgref＝Kp1(Usref-Us)+Ti1x7 (17)
Figure FDA0002184980690000033
udg＝Kp2[Kp1(Usref-Us)+Ti1x7-idg]+Ti2x8 (19)
wherein, Udcref、UdcReference and actual operating values, U, of the converter DC voltagesref、UsRespectively a reference value and an actual value of the terminal voltage; kp1Proportional coefficient, K, for the external power loop PI control of the network-side converterp2Proportional coefficient for controlling current loop PI in the network side converter; t isi1Integral coefficient, T, for the PI control of the external power loop of the network-side converteri2The integral coefficient is controlled by a current loop PI in the network side converter; i.e. idgref、iqgrefReference values, i, for the components of the grid-side converter current dq axes, respectivelydg、iqgIs the actual value of the grid side converter current dq axis component; x is the number of5～x8Is 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 resistance of claim 1, wherein the step 2 is performed by combining a control strategy of a rotor-side converter, deducing an equivalent impedance model of a doubly-fed wind turbine grid-connected system, and analyzing a damping characteristic of the system, and specifically comprises the following steps:
step 2.1, a control equation of the double-fed fan rotor side converter can be obtained:
Figure FDA0002184980690000034
the formula (20) and the formula (2) are combined to form:
Figure FDA0002184980690000035
order to
Figure FDA0002184980690000036
Then there are:
Figure FDA0002184980690000041
wherein KidAnd KiqTaking K as the same valueiq＝Kid＝Ki，KiThe 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 converteriThe 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 1, wherein the value of the stator-side analog resistor is determined according to the analysis result of the damping characteristic of the doubly-fed wind turbine grid-connected system in the step 3 so as to compensate the negative damping action of the system, and the method specifically comprises the following steps:
step 3.1, impedance of the doubly-fed fan system is as follows:
ZDFIG＝(Rr+Ki)/sn+Rs+(Xls+Xlr+XT)s (23)
wherein s isnFor slip corresponding to subsynchronous component, XTIs a transformer reactance;
let the angular frequency of the subsynchronous oscillation components present in the system be ωerIf ω iser＜ωrThen the corresponding slip sn＝(jωer-jωr)/jωerIf 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:
Figure FDA0002184980690000042
subsynchronous oscillation frequency f of the systemnComprises the following steps:
Figure FDA0002184980690000043
in the formula (f)1For mains frequency, XCFor 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:
ωer＝2πfn (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:
sn＝(jωer-jωr)/jωer (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.
5. The method for suppressing the sub-synchronous oscillation of the doubly-fed wind power plant based on the stator-side analog resistance is characterized in that in the step 4, a control strategy based on the stator-side analog resistance is applied to the control of a stator-side converter of the doubly-fed wind power plant in combination with the analysis result in the step 3, so that the suppression of the sub-synchronous 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
Figure FDA0002184980690000051
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:
Figure FDA0002184980690000052
wherein G isPTaking 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):
Figure FDA0002184980690000053
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 systemqssubAnd udssubIndicating stator dq-axis current by iqssubAnd idssubIndicating that stator dq axis flux linkage is byqssubAnd psidssubIt is shown that the relationship satisfied by the subsynchronous oscillation components is:
Figure FDA0002184980690000054
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.
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