CN109039180B - Fractional order control method for grid connection process of doubly-fed induction generator - Google Patents

Fractional order control method for grid connection process of doubly-fed induction generator Download PDF

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CN109039180B
CN109039180B CN201810874974.0A CN201810874974A CN109039180B CN 109039180 B CN109039180 B CN 109039180B CN 201810874974 A CN201810874974 A CN 201810874974A CN 109039180 B CN109039180 B CN 109039180B
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fractional order
stator
doubly
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induction generator
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CN109039180A (en
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仲慧
王英杰
彭博纬
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Shandong University
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    • 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
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/007—Control circuits for doubly fed generators
    • 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
    • H02P21/22—Current control, e.g. using a current control loop
    • 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
    • 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
    • H02P2205/00—Indexing scheme relating to controlling arrangements characterised by the control loops
    • H02P2205/01—Current loop, i.e. comparison of the motor current with a current reference

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Abstract

The invention discloses a fractional order control method for a grid connection process of a doubly-fed induction generator, which comprises the following steps: constructing a motor control model and constructing a fractional operator; aiming at a double-fed wind power generation system, a continuous transfer function method is adopted to realize the physicochemical realization of a fractional order operator, namely, the fractional order operator can be effectively simulated on amplitude-frequency characteristics and phase-frequency characteristics through a rational transfer function; establishing fractional order PIλA controller: and controlling the motor control model to control the no-load grid-connection process of the doubly-fed induction generator. Fractional order PIλThe controller can effectively reduce active power and reactive power in a starting stage, so that the system stably enters a steady state stage, and an electric network is prevented from being subjected to overlarge impact; in the short-circuit fault state, fractional order PI is adoptedλThe control method can also reduce the system oscillation.

Description

Fractional order control method for grid connection process of doubly-fed induction generator
Technical Field
The invention relates to the technical field of control, in particular to a fractional order control method for a grid connection process of a doubly-fed induction generator.
Background
The double-fed induction generator (DFIG) is widely applied to variable-speed constant-frequency wind power generation systems and ship power systems due to the advantages of flexible frequency conversion control, good regulation performance, good dynamic and steady-state characteristics, capability of realizing active and reactive decoupling control and the like. The control of the doubly-fed induction generator is realized by controlling the rotor AC excitation converter. A stator system and a rotor system of a double-fed induction motor are strong coupling systems, in order to realize decoupling control, a vector control method of stator flux linkage orientation is often adopted, alternating current quantity is decomposed into active power and reactive power, and a double-closed-loop PI regulator is adopted to respectively control the active power and the reactive power.
The PI control is still the most common control method in the double-fed power generation control system, and has the advantages of simple structure, convenient implementation, wide adaptability and the like, but the control method is based on an accurate model, and the control performance of a controlled object is reduced after the working condition of the controlled object is changed. Considering that the double-fed power generation system actually becomes a multivariable nonlinear system due to the fact that the double-fed power generation system contains a relatively complex dynamic part, and at the moment, the defects of poor dynamic performance, large overshoot, weak anti-interference capability and the like of the traditional PI control system are more prominent.
Aiming at the defects of the traditional PI control, the improvement schemes related to domestic and foreign documents mainly comprise:
1. the PID controller parameters are adjusted on line by using the RBF neural network, the influence of system parameter uncertainty and external interference on the control performance is processed, more historical data is needed, and the training process is longer.
2. An integral sliding mode control strategy based on a neural network is provided, and the method is verified to have strong robustness to disturbance and good grid-connected performance, but the buffeting phenomenon of the sliding mode control strategy cannot be solved.
3. The novel excitation control strategy for the variable parameter PI and neural network coordinated control is provided, the control effect of the novel excitation control strategy does not depend on the parameters of a system, and the novel excitation control strategy has good dynamic adjustment and online decoupling capabilities, but the online parameter adjustment has the defects of large calculation amount, lag in adjustment and the like.
4. A model reference self-adaptive control technology of the doubly-fed induction generator without the speed sensor is researched, and the control idea is lack of a system design method and low in control accuracy.
In the field of motors, researchers also apply a fractional order proportional-integral controller to maximum power tracking in a permanent magnet synchronous power generation system, and verify that the fractional order PI controller has a high response speed and a high power output performance. Or a fractional order PID controller is designed for an excitation system of the permanent magnet synchronous generator, and parameter optimization is carried out by using a particle swarm algorithm. And PI control improvement aiming at the doubly-fed induction generator is rarely reported.
Disclosure of Invention
In order to solve the defects of the prior art, the invention provides a fractional order control method for the grid connection process of a doubly-fed induction generator. The motor power oscillation under the grid-connected transient process and the fault disturbance is effectively weakened, and certain development potential and application value are achieved.
The fractional order control method for the grid connection process of the doubly-fed induction generator comprises the following steps:
constructing a motor control model, wherein the model is established based on a synchronous rotation coordinate system and consists of a voltage equation, a flux linkage equation and an electromagnetic torque equation;
constructing a fractional operator: determining a fractional order differential calculation algorithm by taking the Grunwald-Letnikov fractional order calculus definition as a theoretical basis, solving an approximate value of function numerical differentiation aiming at the fractional order differential calculation algorithm, proving the calculation precision of the approximate value, and calculating a fractional order derivative according to the Grunwald-Letnikov fractional order calculus definition;
aiming at a double-fed wind power generation system, a continuous transfer function method is adopted to realize the physicochemical realization of a fractional order operator, namely, the fractional order operator can be effectively simulated on amplitude-frequency characteristics and phase-frequency characteristics through a rational transfer function;
establishing fractional order PIλA controller: and controlling the motor control model to control the no-load grid-connection process of the doubly-fed induction generator.
Further preferred technical solution, fractional order PIλFractional order integral term I in controllerλObtained by improving the Oustaloup filtering algorithm.
In a further preferred technical scheme, a fractional order operator is constructed by adopting an improved Oustaloup filtering algorithm.
Further preferred technical solution, the doubly-fed induction generator is based on a mathematical model of a synchronous rotating coordinate system:
voltage equation:
Figure BDA0001752062860000021
wherein, ω issIs the slip angular velocity; omegas＝ω1-ωr，uds: stator voltage d-axis component, uqs: stator voltage q-axis component, udr: d-axis component, u, of rotor voltageqr: component of rotor voltage q-axis, ids: stator current d-axis component, iqs: stator current q-axis component, idr: d-axis component of rotor current, iqr: q-axis component of rotor current, Rs: stator side resistance, Rr: rotor side resistance psiqs: stator flux q-axis component, Ψds: component of stator flux linkage d-axis, Ψqr: component of rotor flux q-axis, Ψdr: rotor flux linkage d-axis component, p: the sign of the differential.
The flux linkage equation:
Figure BDA0001752062860000031
electromagnetic torque equation:
Te＝npLm(idsiqr-iqsidr) (3)。
according to a further preferable technical scheme, no-load grid connection control is required in the starting stage of the double-fed wind generating set, so that the motor is stably switched into a power grid, and the amplitude of each electrical component is required to be as small as possible. The stator current components are all 0 when the generator is in no-load, ids＝iqsThe no-load mathematical model of the doubly-fed induction generator is 0 as follows:
Figure BDA0001752062860000032
Figure BDA0001752062860000033
Te＝0 (6)
Figure BDA0001752062860000034
in the formula, T0-generator no-load torque.
In a further preferred technical scheme, a simplified equation of a motor model neglecting the resistance of a motor stator is as follows:
Figure BDA0001752062860000035
Figure BDA0001752062860000041
in a further preferred technical scheme, Grunwald-Letnikov fractional calculus is defined as follows:
in a further preferred technical scheme, the fractional order differential calculation algorithm is as follows:
Figure BDA0001752062860000044
in the formula (I), the compound is shown in the specification,
Figure BDA0001752062860000045
for the polynomial coefficient of the function, assuming that the step length h is small enough, the approximation of the numerical differentiation of the function can be directly found according to (12), and the calculation accuracy can be proved to be o (h), and when the functional expression of f (t) is determined, the fractional order derivative can be directly calculated by the formula (11).
Further preferred technical solution, PIλThe controller function is:
Figure BDA0001752062860000046
where λ is the order of integration.
Further preferred technical solution, PIλThe control steps of the controller are as follows: firstly, detecting the voltage and current of the stator and the rotor of the motor, then carrying out coordinate transformation on the voltage and current, and calculating the stator flux linkage psi1Active power P and reactive power Q of the stator; setting an active power instruction P and a reactive power instruction Q of the stator according to actual needs, comparing, and enabling the obtained difference value to pass through a fractional order PIλThe regulator obtains an active component instruction i of the stator currentqsSum of reactive component instruction idsThen into the current inner loop control.
Compared with the prior art, the invention has the beneficial effects that:
(1) using fractional order PIλThe controller can enable a control system of the double-fed wind power generation system to flexibly deal with a nonlinear control object, and robustness in a dynamic process can be enhanced.
(2) Fractional order PIλThe controller can effectively reduce active power and reactive power in a starting stage, so that the system stably enters a steady state stage, and an electric network is prevented from being subjected to overlarge impact; in the short-circuit fault state, fractional order PI is adoptedλThe control method can also reduce the system oscillation.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
FIG. 1 is a dual PWM type converter;
FIG. 2 is a block diagram of power outer loop PI λ control;
FIG. 3 is a model of a double-fed induction machine RSC control structure;
FIG. 4 active power in integer and fractional order;
FIG. 5 reactive power at integer and fractional order;
fig. 6 shows the active power oscillation in the three-phase short-circuit fault state.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
In a typical embodiment of the present application, the steps of the present invention are:
(1) construction motor control model
The doubly-fed induction generator uses a double-PWM converter for ac excitation, which is called a grid-side PWM converter (GSC) and a rotor-side PWM converter (RSC), respectively. As shown in fig. 1, in the circuit structure, GSC and RSC are decoupled by dc bus and independent from each other, so that the mathematical model and control strategy on the grid side and rotor side can be studied separately.
GSC has the following effects: the waveform of the input current can be ensured to be close to sine, the GSC can be adopted to ensure lower harmonic content and power factor meeting the requirement, and a system power factor control method is provided; the input current is controlled to ensure the stability of the dc bus voltage.
The RSC aims to provide exciting current for a motor rotor so as to adjust reactive power output by a stator side and control the rotating speed of the motor or active power output by the motor by controlling DFIG rotor current and torque current, so that variable-speed constant-frequency operation of maximum wind energy tracking is realized.
Fractional order PI of the schemeλThe controller is applied to a rotor side power control outer ring in a double-fed asynchronous induction motor control strategy, so that a grid-connected dynamic process has better robustness, and the modeling focuses on RSC and no-load grid-connected control.
Since the active power and the reactive power output by the motor are closely related to the d-axis and q-axis current components of the rotor, the d-axis and q-axis components of the rotor current are the main control targets.
The doubly-fed induction generator mathematical model based on the synchronous rotating coordinate system is as follows:
voltage equation:
Figure BDA0001752062860000061
wherein, ω issIs the slip angular velocity; omegas＝ω1-ωr，uds: stator voltage d-axis component, uqs: stator voltage q-axis component, udr: d-axis component, u, of rotor voltageqr: component of rotor voltage q-axis, ids: stator current d-axis component, iqs: stator current q-axis component, idr: d-axis component of rotor current, iqr: q-axis component of rotor current, Rs: stator side resistance, Rr: rotor side resistance psiqs: stator flux q-axis component, Ψds: component of stator flux linkage d-axis, Ψqr: component of rotor flux q-axis, Ψdr: rotor flux linkage d-axis component, p: the sign of the differential.
The flux linkage equation:
Figure BDA0001752062860000062
Ls: stator self-inductance, Lr: self-inductance of the rotor, Lm: and (5) mutual inductance.
Electromagnetic torque equation:
Te＝npLm(idsiqr-iqsidr) (3)
Te: electromagnetic torque, np: the number of pole pairs.
In the starting stage of the double-fed wind generating set, no-load grid connection control needs to be carried out, so that the motor is stably switched into a power grid, and the amplitude of each electrical component is required to be as small as possible. Stator current component of generator in no-load stateAre all 0, ids＝iqsThe unloaded mathematical model of DFIG is as follows, 0:
Figure BDA0001752062860000071
Figure BDA0001752062860000072
Te＝0 (6)
Figure BDA0001752062860000073
in the formula, T0-generator no-load torque.
Because the vector control is stator flux linkage orientation, and the resistance voltage drop of the stator under the power frequency is far lower than the reactance voltage drop and the counter electromotive force of the motor, the resistance of the stator of the motor can be ignored in the calculation.
From this, the simplified equation can be derived as follows:
Figure BDA0001752062860000074
Figure BDA0001752062860000075
Figure BDA0001752062860000076
the basic principle of the DFIG no-load grid-connected control can be determined from (8) to (10). After the doubly-fed generator is merged into a power grid, the motor mainly performs active and reactive adjustment.
(2) Fractional operator and physicochemical implementation
To be precise, fractional calculus should be referred to as "non-integer order" integration. The order of fractional calculus can be in fractional form, and theoretically can be expanded to complex number or even irrational order, but at present, the related research on the complex number order and irrational calculus is very little, no engineering application is carried out, and the application of fractional order is generally discussed only in the rational range.
This example uses the Grunwald-Letnikov fractional calculus definition as the theoretical basis:
Figure BDA0001752062860000081
based on the definition, fractional order rationalization is carried out, and according to the formula (11), a fractional order differential calculation algorithm is determined as follows:
Figure BDA0001752062860000082
in the formula (I), the compound is shown in the specification,
Figure BDA0001752062860000083
is a polynomial coefficient of a function. Assuming that the step length h is sufficiently small, the numerical derivative of the function can be directly approximated according to (12), and the calculation accuracy can be proved to be o (h). When the functional expression of f (t) is determined, its fractional order derivative can be calculated directly from equation (11).
Because the double-fed wind power generation system is a strong coupling and nonlinear system, an accurate function expression of the double-fed wind power generation system is difficult to obtain. Aiming at a double-fed wind power generation system, a continuous transfer function method is adopted to realize the physicochemical realization of the fractional order operator, namely, the fractional order operator can be effectively simulated on the amplitude-frequency characteristic and the phase-frequency characteristic through a rational transfer function.
In this embodiment, an improved osutaloup filtering algorithm is adopted to construct a fractional order operator:
Figure BDA0001752062860000084
the above fractional operator is the prior art, and the theoretical basis is taken from a series of papers of Oustaloup.
Conventionally, the weighting parameter values b-10 and d-9. The pole zero and gain of the above fractional differential operator can be calculated by the following formula:
to ensure the stability of the algorithm, the cutoff frequency and the parameter N are typically selected as [0.01,100] and N-4, respectively.
(3) Fractional order PIλController (the fractional order controller is used for controlling the fan grid-connected model)
The fractional order PID controller can be denoted as PIλDμ. After differential and integral orders mu and lambda are introduced into the fractional order controller, adjustable parameters are expanded, the setting range of the adjustable parameters is enlarged, and the controlled object can be controlled more flexibly. PI (proportional integral)λDμThe transfer function of (a) is:
Figure BDA0001752062860000086
due to PIλDμThe derivative term of the control mainly performs the correction of the lead and lag, and the correction of the term is not needed in the grid-connected control, thereby simplifying the adoption of PIλThe control block diagram of the controller is shown in fig. 2. Fractional order integral term IλThe method is realized by improving the Oustaloup filtering algorithm in the step (2).
PIλThe controller function is:
Figure BDA0001752062860000091
where λ is the order of integration.
The whole system adopts a double closed-loop control structure, namely a power outer loop and a current inner loop. Firstly, detecting the voltage and current of the stator and the rotor of the motor, then carrying out coordinate transformation on the voltage and current, and calculating the stator flux linkage psi1Active power P and reactive power Q of the stator; setting an active power instruction P and a reactive power instruction Q of the stator according to actual needs, comparing, and enabling the obtained difference value to pass through a fractional order PIλThe regulator obtains an active component instruction i of the stator currentqsSum of reactive component instruction idsThen into the current inner loop control.
A detailed RSC control model, a Simulink block diagram and shown in an attached figure 3 are constructed, and a fractional order control theory is applied to the no-load grid-connection process of the doubly-fed induction generator, so that the robustness of the doubly-fed induction generator is enhanced.
In a PI controller of a rotor side power control outer ring in a double-fed asynchronous induction motor control strategy, an adjustable integral term order lambda is introduced, the control dimension of the lambda is increased, and the PI controller is designed as a fractional order controller. The control system can flexibly deal with the nonlinear control object, and effectively weaken the motor power oscillation in the grid-connected transient process and fault disturbance.
Simulation verification
According to the method, a doubly-fed induction motor grid-connected model is constructed under an MATLAB/simulink platform, and an RSC control structure model is shown in figure 3. Through simulation experiment tests, the results are shown in table 1:
TABLE 1 different order grid connection situation
Figure BDA0001752062860000092
Figure BDA0001752062860000101
And (4) comprehensively comparing, finally determining that the selected order of the fractional order control is 0.8, and simulating the grid connection process of the generator system, wherein the active power and the reactive power are shown in fig. 4 and fig. 5.
FIG. 4 is a graph of active power during grid connection, as can be seen, using fractional order PIλControl, although the time to complete steady state is slightly longer than the integer order PIλHowever, the fractional order control begins to approach the stable state at 0.17s, and the integer order PI control ends the large oscillation at 0.46s and begins to enter the stable state. Integer order PIλThe oscillation peak value interval under control is [ -4.47 × 106, 6.25 × 106]And fractional order PIλThe peak interval under control is far lower than this, and is only [ -3.11 × 106, 2.43 × 106]. Therefore, the system can enter a normal working state more stably, and the impact on a power grid during grid connection is reduced.
FIG. 5 is a grid connectionReactive power pattern in the process. Integer order and fractional order reactive power PIλThe reactive power state under control is consistent with the active power. Using fractional order PIλIn control, the time ratio of completely entering steady state is integral-order PIλThe control is slightly prolonged, but the oscillation peak value is remarkably reduced from [ -4.77X 106, 8.41X 106 [)]Is reduced to [ -1.018X 104, 7.55X 106]。
Fig. 6 shows the situation of active power oscillation under the action of two controllers when three-phase short circuit fault occurs in the steady-state operation of the system.
As shown in fig. 6, integer order PIλThe active oscillation interval under control is [ -1.349 × 106, 3.352 × 106]At fractional order PIλUnder the control, the oscillation interval becomes [ -1.349 × 106, 3.352 × 106]. Therefore, the oscillation can be effectively inhibited by using the fractional order control.
The application aims at the defects that a rotor side of a traditional double-fed induction generator generally adopts double-closed-loop PQ decoupling control, a PI controller used by a power outer ring has the defects of rough control, large overshoot and the like, and the dynamic performance of a double-fed motor is influenced. According to the method, a fractional order theory and a PI control technology are combined, the adjustable order of an integral term is introduced, the control dimension is increased, the control performance of the double-fed induction motor is improved, and grid connection and short circuit fault simulation research is carried out. Simulation results show that: the fractional order PI control can effectively reduce active and reactive oscillation in the starting stage, so that the system stably enters a steady state stage; under the short-circuit fault state, the fractional order PI control method can also be adopted to reduce the system oscillation.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (8)

1. The fractional order control method for the grid connection process of the doubly-fed induction generator is characterized by comprising the following steps of:
constructing a motor control model, wherein the model is established based on a synchronous rotation coordinate system and consists of a voltage equation, a flux linkage equation and an electromagnetic torque equation;
constructing a fractional operator: determining a fractional order differential calculation algorithm by taking the Grunwald-Letnikov fractional order calculus definition as a theoretical basis, solving an approximate value of function numerical differentiation aiming at the fractional order differential calculation algorithm, proving the calculation precision of the approximate value, and calculating a fractional order derivative according to the Grunwald-Letnikov fractional order calculus definition;
aiming at a double-fed wind power generation system, a continuous transfer function method is adopted to realize the physicochemical realization of a fractional order operator, namely, the fractional order operator can be effectively simulated on amplitude-frequency characteristics and phase-frequency characteristics through a rational transfer function;
establishing fractional order PIλA controller: controlling a motor control model to control the no-load grid-connection process of the doubly-fed induction generator;
the doubly-fed induction generator is based on a mathematical model of a synchronous rotating coordinate system:
voltage equation:
Figure FDA0002226377400000011
wherein, ω issIs the slip angular velocity; omegas＝ω1-ωr，uds: stator voltage d-axis component, uqs: stator voltage q-axis component, udr: d-axis component, u, of rotor voltageqr: component of rotor voltage q-axis, ids: stator current d-axis component, iqs: stator current q-axis component, idr: d-axis component of rotor current, iqr: q-axis component of rotor current, Rs: stator side resistance, Rr: rotor side resistance psiqs: stator flux q-axis component, Ψds: component of stator flux linkage d-axis, Ψqr: component of rotor flux q-axis, Ψdr: rotor flux linkage d-axis component, p: a differential sign;
in the starting stage of the double-fed wind generating set, no-load grid-connected control is required to be carried out, so that the motor is enabled to be in a state of being startedThe stable cut-in of the power grid requires that the amplitude of each electrical component is as small as possible, and the stator current components are all 0 when the generator is in no-load, ids＝iqsThe no-load mathematical model of the doubly-fed induction generator is 0 as follows:
Figure FDA0002226377400000021
Te＝0 (6)
Figure FDA0002226377400000022
in the formula, T0Generator no-load torque, Te: electromagnetic torque, np: number of pole pairs, Lr: self-inductance of the rotor, Lm: and (5) mutual inductance.
2. The fractional order control method of the doubly-fed induction generator grid-connection process of claim 1, characterized in that the fractional order PI is adoptedλFractional order integral term I in controllerλObtained by improving the Oustaloup filtering algorithm.
3. The fractional order control method of the doubly fed induction generator grid-connection process as claimed in claim 1, characterized in that a fractional order operator is constructed by adopting an improved Oustaloup filter algorithm.
4. The fractional order control method of the grid-connected process of the doubly-fed induction generator of claim 1, characterized in that a flux linkage equation:
Figure FDA0002226377400000023
in the formula, Ls: the stator is self-inductive.
5. The fractional order control method for the grid connection process of the doubly fed induction generator of claim 1, characterized in that an electromagnetic torque equation:
Te＝npLm(idsiqr-iqsidr) (3)。
6. the fractional order control method of the doubly-fed induction generator grid-connection process as claimed in claim 5, wherein the simplified equation of the motor model neglecting the resistance of the motor stator is as follows:
Figure FDA0002226377400000024
Figure FDA0002226377400000031
Figure FDA0002226377400000032
in the formula, Ψ1Is the stator flux linkage.
7. The fractional order control method of the doubly-fed induction generator grid-connection process as claimed in claim 1, characterized in that Grunwald-Letnikov fractional order calculus defines:
Figure FDA0002226377400000033
the fractional order differential calculation algorithm is as follows:
Figure FDA0002226377400000034
in the formula (I), the compound is shown in the specification,for the polynomial coefficient of the function, assuming that the step length h is small enough, the approximation of the numerical differentiation of the function can be directly found according to (12), and the calculation accuracy can be proved to be o (h), and when the functional expression of f (t) is determined, the fractional order derivative can be directly calculated by the formula (11).
8. The fractional order control method of the grid-connection process of the doubly-fed induction generator of claim 1, characterized in that PIλThe controller function is:
Figure FDA0002226377400000036
wherein λ is an integration order;
PIλthe control steps of the controller are as follows: firstly, detecting the voltage and current of the stator and the rotor of the motor, then carrying out coordinate transformation on the voltage and current, and calculating the stator flux linkage psi1Active power P and reactive power Q of the stator; setting an active power instruction P and a reactive power instruction Q of the stator according to actual needs, comparing, and enabling the obtained difference value to pass through a fractional order PIλThe regulator obtains an active component instruction i of the stator currentqsSum of reactive component instruction idsThen into the current inner loop control.
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