Double-fed fan rotor side converter control method based on q-axis voltage orientation

Abstract

The invention discloses a doubly-fed fan rotor side converter control method based on q-axis voltage orientation, and the method comprises the following steps: enabling a controller to take mechanical power output by a wind turbine as an active reference signal, and obtaining the stator voltage and the stator and rotor current of a generator through a voltage sensor and a current sensor; after coordinate transformation, stator voltage is aligned to the q axis, active power and reactive power output by the stator side are obtained through calculation, then rotor voltage modulation signals under the dq axis are generated through feedforward compensation and decoupling control, the rotor voltage modulation signals are sent to the input end of the SVPWM link through coordinate inverse transformation, and switching tube control signals of the doubly-fed generator side converter are output. Therefore, independent control of active power and reactive power by the rotor current is realized. The problems of large flux linkage measurement error, active and reactive power coupling, reactive compensation limitation and the like in traditional stator flux linkage directional control can be effectively solved, the stator flux linkage does not need to be observed, and the power supply quality of a doubly-fed wind power system can be improved.

Description

Technical Field

[0001] The invention relates to a wind turbine grid-connected control method, and in particular to a q-axis voltage-oriented doubly-fed wind turbine rotor-side converter control method. Background Art

[0002] The progress of wind power technology has promoted the continuous growth of the capacity of wind turbines. In this context, the advantages of doubly-fed induction generators have gradually become prominent, because they can achieve constant frequency power output during variable speed by controlling the rotor side slip power, thereby reducing the cost of corresponding power electronic equipment. Due to this technical and economic superiority, doubly-fed induction generators are widely used in large-power wind turbines for variable speed constant frequency power generation.

[0003] High-power doubly-fed wind turbines are usually controlled by dual PWM converters, which enable bidirectional flow of power in the generator rotor. Part of the mechanical power output by the wind turbine is directly supplied to the grid, while the other part is regulated by the converter, so these converters are classified as partial power converters. In terms of specific functions, the grid-side PWM converter is mainly responsible for maintaining the stability of the DC bus voltage, usually using the grid-side voltage-oriented control method. The rotor-side PWM converter is used to regulate the active and reactive power output of the doubly-fed generator to the grid, and provide the excitation current required to maintain the rotating magnetic field of the rotor.

[0004] The traditional control strategy for the machine-side converter is stator flux orientation, which faces three main problems: (1) The flux measurement error is large. The current model method is easily disturbed by the motor parameters. Although the voltage model method can reduce the influence of the parameters, due to the nature of the integral operation, the problem of integral drift may still occur. (2) There is coupling between the active and reactive power of the doubly fed generator stator. In the stator field oriented control mode, due to the existence of stator resistance, the flux and stator voltage vectors are not strictly orthogonal. (3) The larger d-axis component of the rotor current will affect the stability of the control system and limit the compensation of reactive power. Therefore, it is urgent to develop a converter control strategy that can realize independent decoupling control of the active and reactive power of the doubly fed generator and improve the grid-connected performance of the wind power system. Summary of the invention

[0005] In view of the problems existing in the traditional control strategy, the present invention provides a control method for the rotor-side converter of a doubly-fed wind turbine based on q-axis voltage orientation. The method does not require observation of the stator flux, can realize independent decoupling control of the active and reactive power of the generator, and improve the grid-connected power quality of the doubly-fed wind power system.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A q-axis voltage-oriented doubly-fed wind turbine rotor-side converter control method comprises the following steps:

[0008] Step S1: Since the reactive power reference Q * Adjust according to the needs of the power grid. To meet the requirements of unity power factor grid connection, Q * Set to 0;

[0009] Step S2: Detect the rotor angle θ of the doubly-fed fan by using a position encoder r , the rotor mechanical angular velocity ω is obtained by differential operation r , the blade rotation angular velocity ω of the wind turbine is calculated using the given gearbox speed ratio σ, and the tip speed ratio λ is calculated using the given blade radius R and the real-time wind speed V;

[0010] Step S3: Wind energy utilization coefficient C p The peak value decreases with the increase of the pitch angle β of the wind turbine blade. β is set to 0 to capture the maximum wind energy. The wind energy utilization coefficient C is calculated using the tip speed ratio λ and the blade pitch angle β. p ;

[0011] Step S4: Given the air density ρ, the wind energy utilization coefficient C p , real-time wind speed V and blade radius R to calculate the mechanical output power P of the wind turbine m , and set it as the active power reference, and calculate the mechanical torque T of the wind turbine according to the blade rotation angular velocity ω m , which is converted into electromagnetic torque T by the gearbox e Input doubly-fed induction motor;

[0012] Step S5: Obtain the stator voltage angle θ using a phase-locked loop s And subtract the number of double-fed machine pole pairs p and the rotor angle θ r The product of the position difference angle θ is obtained Δ , for the stator three-phase voltage U abc_s and current I abc_s And the rotor three-phase current I abc_r Perform Clarke transformation and Park transformation to obtain the stator voltage U under the dq axis sd , U sq and stator current I sd ,I sq and the rotor current I rd ,I rq , after aligning the stator voltage to the q axis, the actual values ​​of active and reactive power output of the doubly-fed wind turbine, P and Q, are calculated;

[0013] Step S6: Output the active power and reactive power actual values ​​P and Q of the double-fed wind turbine and the mechanical output power P of the wind turbine respectively.m , reactive power reference Q * The error of the outer power loop is obtained by difference, and the reference value of the dq axis component of the rotor current is obtained by PI adjustment. and And subtract the rotor current dq axis component I rd ,I rq , generating the rotor current inner loop error in the dq coordinate system, and obtaining the reference value of the rotor voltage dq axis component through PI adjustment and

[0014] Step S7: adopt feedforward compensation and decoupling control strategy, and obtain the rotor control voltage U in the synchronous rotating coordinate system dq according to the stator and rotor voltage equation and flux equation of the doubly fed wind turbine. rdc , U rqc ;

[0015] Step S8: Based on the reference value of the dq axis component of the rotor voltage and And the rotor control voltage U rdc , U rqc Calculate and obtain the double-fed machine rotor voltage modulation signal U rdt and U rqt , which is converted into the reference voltage signal U required by the SVPWM link through inverse Park transformation. α , U β , and finally outputs a switching signal to control the rotor-side converter of the doubly-fed wind turbine.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The present invention can effectively solve the problems of large flux measurement error, active and reactive power coupling, and limited reactive compensation in traditional stator flux directional control. Without observing the stator flux, independent decoupling control of the active and reactive power of the generator and unity power factor grid connection can be achieved, thereby improving the power supply quality of the doubly-fed wind power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A structural diagram of a double-fed wind power grid-connected power generation system applicable to the present invention;

[0019] Figure 2 It is a schematic diagram of a control method for a rotor-side converter of a doubly-fed wind turbine;

[0020] Figure 3 The simulation results of the instantaneous values ​​of active and reactive power output on the stator side of the doubly-fed generator;

[0021] Figure 4 The simulation results of the instantaneous values ​​of grid-connected voltage and current of the doubly-fed wind power generation system;

[0022] Figure 5 This is the Fourier analysis result of the grid-connected current of the doubly-fed wind power generation system. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described below in conjunction with the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0024] Figure 1 The structure diagram of the doubly-fed wind power grid-connected power generation system applicable to the present invention is as follows. By applying the doubly-fed wind turbine rotor-side converter control method based on q-axis voltage orientation proposed by the present invention to the doubly-fed wind turbine rotor-side converter, the independent decoupling control of the active and reactive power of the generator can be achieved without measuring the stator flux. At the same time, due to the use of the voltage feedforward compensation strategy, when the reactive power demand of the power grid is adjusted to 0, the system can be connected to the grid with a unity power factor. Figure 2 As shown in FIG. 1 , the controller uses the mechanical power output by the wind turbine as the active reference signal, obtains the generator stator voltage and stator-rotor current through voltage and current sensors, aligns the stator voltage to the q-axis after coordinate transformation, calculates the active and reactive power output on the stator side, and then generates the rotor voltage modulation signal under the dq-axis through feedforward compensation and decoupling control. The signal is sent to the input end of the SVPWM link through coordinate inverse transformation, and the switch tube control signal of the double-fed generator machine-side converter is output, thereby realizing the independent control of the rotor current on the active and reactive power. Specifically, the following steps are included:

[0025] Step S1: Since the reactive power reference Q * Usually it is adjusted according to the needs of the power grid. In order to meet the requirements of unity power factor grid connection, Q * Set to 0.

[0026] Step S2: Detect the rotor angle θ of the doubly-fed fan by using a position encoder r , the rotor mechanical angular velocity ω is obtained by differential operation r , the blade rotation angular velocity ω of the wind turbine is calculated using the given gearbox speed ratio σ, and the tip speed ratio λ is calculated using the given blade radius R and real-time wind speed V.

[0027] In this step, the calculation formulas for the blade rotation angular velocity ω and the blade tip speed ratio λ are as follows:

[0028]

[0029] Step S3: Wind energy utilization coefficient C pThe peak value decreases with the increase of the pitch angle β of the wind turbine blade. β is set to 0 to capture the maximum wind energy. The wind energy utilization coefficient C is calculated using the tip speed ratio λ and the blade pitch angle β. p .

[0030] In this step, the wind energy utilization coefficient C p The calculation formula is as follows:

[0031]

[0032] in, is the intermediate coefficient. When the blade pitch angle β is 0, the wind energy utilization coefficient C p The peak value is about 0.48, at which point the doubly fed wind turbine maintains at the optimal tip speed ratio λ=8.1 to continuously capture the maximum wind energy.

[0033] Step S4: Given the air density ρ, the wind energy utilization coefficient C p , real-time wind speed V and blade radius R to calculate the mechanical output power P of the wind turbine m , and set it as the active power reference, and calculate the mechanical torque T of the wind turbine according to the blade rotation angular velocity ω m , which is converted into electromagnetic torque T by the gearbox e Enter the doubly-fed induction motor.

[0034] In this step, the mechanical output power P m , Mechanical torque T m , electromagnetic torque T e The calculation formula is as follows:

[0035]

[0036] Where A is the swept area of ​​the wind turbine blade, and A = πR 2 .

[0037] Step S5: Obtain the stator voltage angle θ using a phase-locked loop s And subtract the number of double-fed machine pole pairs p and the rotor angle θ r The product of the position difference angle θ is obtained Δ , for the stator three-phase voltage U abc_s and current I abc_s And the rotor three-phase current I abc_r Perform Clarke transformation and Park transformation to obtain the stator voltage U under the dq axis sd , U sq and stator current I sd ,I sq and the rotor current I rd ,I rq, after aligning the stator voltage to the q-axis, the actual values ​​of active and reactive power output of the doubly-fed wind turbine, P and Q, are calculated.

[0038] In this step, the stator voltage U sd , U sq and stator current I sd ,I sq and the rotor current I rd ,I rq The specific expression is as follows:

[0039]

[0040] Among them, U sa , U sb , U sc are the A-phase, B-phase, and C-phase voltages of the doubly-fed induction motor stator side, I sa ,I sb ,I sc are the currents of phase A, phase B, and phase C on the stator side, I ra ,I rb ,I rc They are the A-phase, B-phase and C-phase currents on the rotor side respectively.

[0041] In this step, the stator voltage U sd , U sq The calculation formulas for the actual values ​​of active and reactive power P and Q output by the doubly fed wind turbine are as follows:

[0042]

[0043] Among them, U s is the stator voltage vector amplitude. After the stator of the doubly-fed generator is connected to the grid, the stator voltage is equal to the grid voltage, and the amplitude and frequency are approximately unchanged. That is, the voltage vector amplitude U of the stator three-phase voltage in the synchronous rotating coordinate system is s is constant.

[0044] Step S6: Output the active power and reactive power actual values ​​P and Q of the double-fed wind turbine and the mechanical output power P of the wind turbine respectively. m , reactive power reference Q * The error of the outer power loop is obtained by difference, and the reference value of the dq axis component of the rotor current is obtained by PI adjustment. and And subtract the rotor current dq axis component I rd ,I rq , generating the rotor current inner loop error in the dq coordinate system, and obtaining the reference value of the rotor voltage dq axis component through PI adjustment and

[0045] In this step, the reference value of the rotor current dq axis component and And the reference value of the dq axis component of the rotor voltage and The calculation formula is as follows:

[0046]

[0047] Among them, s is the Laplace operator, K pd is the proportional coefficient of the power outer loop d-axis PI controller, K id is the integral coefficient of the power outer loop d-axis PI controller, K pq K is the proportional coefficient of the q-axis PI controller of the power outer loop, iq is the integral coefficient of the q-axis PI controller of the power outer loop, is the proportional coefficient of the rotor current inner loop d-axis PI controller, is the integral coefficient of the rotor current inner loop d-axis PI controller, is the proportional coefficient of the rotor current inner loop q-axis PI controller, is the integral coefficient of the rotor current inner loop q-axis PI controller.

[0048] Step S7: adopt feedforward compensation and decoupling control strategy, and obtain the rotor control voltage U in the synchronous rotating coordinate system dq according to the stator and rotor voltage equation and flux equation of the doubly fed wind turbine. rdc , U rqc .

[0049] In this step, the rotor control voltage U rdc , U rqc The calculation formula is as follows:

[0050]

[0051] Among them, L m is the doubly-fed induction motor excitation inductance, L s is the stator inductance, L r is the rotor inductance, R s is the stator resistance, is the d-axis component of the stator flux, is the q-axis component of the stator flux, Δω is the slip angular velocity, ω s is the stator voltage angular frequency, and f is the stator voltage frequency.

[0052] Step S8: Based on the reference value of the dq axis component of the rotor voltage and And the rotor control voltage U rdc , U rqc Calculate and obtain the double-fed machine rotor voltage modulation signal U rdt and Urqt , which is converted into the reference voltage signal U required by the SVPWM link through inverse Park transformation. α , U β , and finally outputs a switching signal to control the rotor-side converter of the doubly-fed wind turbine.

[0053] In this step, the double-fed machine rotor voltage modulation signal U rdt and U rqt The calculation formula is as follows:

[0054]

[0055] The obtained signal is transformed by inverse Park and SVPWM algorithm to output the switch control signal of the doubly fed wind turbine rotor side converter.

[0056] The simulation effect after the implementation of the present invention is as follows Figure 3 to Figure 5 As shown, a 1.5MW doubly-fed wind power generation system is connected to a 690V grid for operation. It can be seen that the grid-connected active power is close to the rated value of the doubly-fed induction motor, the reactive power is stable at 0, and the grid-connected three-phase voltage and current are in the same frequency and opposite direction. The Fourier analysis results of the grid-connected current show that the harmonic distortion rate is 0.87%<5%, which meets the requirements of unity power factor grid connection. It can be explained that the control method of the present invention can realize the decoupling control of the active and reactive power of the doubly-fed wind turbine and improve the system grid-connected performance.

Claims

1. A control method for a doubly-fed wind turbine rotor-side converter based on q-axis voltage orientation, characterized in that The method comprises the following steps: Step S1: Since the reactive power reference Q * Adjust according to the needs of the power grid. To meet the requirements of unity power factor grid connection, Q * Set to 0; Step S2: Detect the rotor angle θ of the doubly-fed fan by using a position encoder r , the rotor mechanical angular velocity ω is obtained by differential operation r , the blade rotation angular velocity ω of the wind turbine is calculated using the given gearbox speed ratio σ, and the tip speed ratio λ is calculated using the given blade radius R and the real-time wind speed V; Step S3: Wind energy utilization coefficient C p The peak value decreases with the increase of the pitch angle β of the wind turbine blade. β is set to 0 to capture the maximum wind energy. The wind energy utilization coefficient C is calculated using the tip speed ratio λ and the blade pitch angle β. p ; Step S4: Given the air density ρ, the wind energy utilization coefficient C p , real-time wind speed V and blade radius R to calculate the mechanical output power P of the wind turbine m , and set it as the active power reference, and calculate the mechanical torque T of the wind turbine according to the blade rotation angular velocity ω m , which is converted into electromagnetic torque T by the gearbox e Input doubly-fed induction motor; Step S5: Obtain the stator voltage angle θ using a phase-locked loop s And subtract the number of double-fed machine pole pairs p and the rotor angle θ r The product of the position difference angle θ is obtained Δ , for the stator three-phase voltage U abc_s and current I abc_s And the rotor three-phase current I abc_r Perform Clarke transformation and Park transformation to obtain the stator voltage U under the dq axis sd , U sq and stator current I sd ,I sq and the rotor current I rd ,I rq , after aligning the stator voltage to the q axis, the actual values ​​of active and reactive power output of the doubly-fed wind turbine, P and Q, are calculated; Step S6: The actual values ​​of active power and reactive power P and Q output by the double-fed wind turbine are respectively calculated and compared with the mechanical output power P of the wind turbine. m , reactive power reference Q * The error of the outer power loop is obtained by difference, and the reference value of the dq axis component of the rotor current is obtained by PI adjustment. and And subtract the rotor current dq axis component I rd ,I rq , generating the rotor current inner loop error in the dq coordinate system, and obtaining the reference value of the rotor voltage dq axis component through PI adjustment and Step S7: adopt feedforward compensation and decoupling control strategy, and obtain the rotor control voltage U in the synchronous rotating coordinate system dq according to the stator and rotor voltage equation and flux equation of the doubly fed wind turbine. rdc , U rqc ; Step S8: Based on the reference value of the dq axis component of the rotor voltage and And the rotor control voltage U rdc , U rqc Calculate and obtain the double-fed machine rotor voltage modulation signal U rdt and U rqt , which is converted into the reference voltage signal U required by the SVPWM link through inverse Park transformation. α , U β , and finally outputs a switching signal to control the rotor-side converter of the doubly-fed wind turbine.

2. The q-axis voltage oriented double-fed wind turbine rotor-side converter control method according to claim 1 is characterized in that In step S2, the calculation formulas for the blade rotation angular velocity ω and the blade tip speed ratio λ are as follows:

3. The q-axis voltage-oriented double-fed wind turbine rotor-side converter control method according to claim 1 is characterized in that In step S3, the wind energy utilization coefficient C p The calculation formula is as follows: in, is the intermediate coefficient. When the blade pitch angle β is 0, the wind energy utilization coefficient C p The peak value is about 0.48, at which point the doubly fed wind turbine maintains at the optimal tip speed ratio λ=8.1 to continuously capture the maximum wind energy.

4. The q-axis voltage-oriented doubly-fed wind turbine rotor-side converter control method according to claim 1 is characterized in that In step S4, the mechanical output power P m , Mechanical torque T m , electromagnetic torque T e The calculation formula is as follows: Where A is the swept area of ​​the wind turbine blade, and A = πR 2 .

5. The q-axis voltage-oriented doubly-fed wind turbine rotor-side converter control method according to claim 1 is characterized in that In step S5, the stator voltage U sd , U sq and stator current I sd ,I sq and the rotor current I rd ,I rq The specific expression is as follows: Among them, U sa , U sb , U sc are the A-phase, B-phase, and C-phase voltages of the doubly-fed induction motor stator side, I sa ,I sb ,I sc are the currents of phase A, phase B, and phase C on the stator side, I ra ,I rb ,I rc They are the A-phase, B-phase and C-phase currents on the rotor side respectively.

6. The q-axis voltage oriented double-fed wind turbine rotor-side converter control method according to claim 1 is characterized in that In step S5, the stator voltage U sd , U sq The calculation formulas for the actual values ​​of active and reactive power P and Q output by the doubly fed wind turbine are as follows: Among them, U s is the stator voltage vector magnitude.

7. The q-axis voltage-oriented doubly-fed wind turbine rotor-side converter control method according to claim 1 is characterized in that In step S6, the reference value of the dq-axis component of the rotor current and and the reference values ​​of the dq-axis components of the rotor voltage and The calculation formula is as follows: Among them, s is the Laplace operator, K pd is the proportional coefficient of the power outer loop d-axis PI controller, K id is the integral coefficient of the power outer loop d-axis PI controller, K pq K is the proportional coefficient of the q-axis PI controller of the power outer loop, iq is the integral coefficient of the q-axis PI controller of the power outer loop, is the proportional coefficient of the rotor current inner loop d-axis PI controller, is the integral coefficient of the rotor current inner loop d-axis PI controller, is the proportional coefficient of the rotor current inner loop q-axis PI controller, is the integral coefficient of the rotor current inner loop q-axis PI controller.

8. The q-axis voltage oriented double-fed wind turbine rotor-side converter control method according to claim 1 is characterized in that In step S7, the rotor control voltage U rdc , U rqc The calculation formula is as follows: Among them, L m is the doubly-fed induction motor excitation inductance, L s is the stator inductance, L r is the rotor inductance, R s is the stator resistance, is the d-axis component of the stator flux, is the q-axis component of the stator flux, Δω is the slip angular velocity, ω s is the stator voltage angular frequency, and f is the stator voltage frequency.

9. The q-axis voltage-oriented doubly-fed wind turbine rotor-side converter control method according to claim 1, characterized in that In step S8, the double-fed machine rotor voltage modulation signal U rdt and U rqt The calculation formula is as follows:

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