A control method of rotor side converter of double-fed wind turbine based on q-axis voltage orientation

Abstract

The application discloses a kind of based on q-axis voltage orientation's doubly-fed fan rotor side converter control method, the method is as follows: controller will the mechanical power of wind turbine output as active reference signal, obtain generator stator voltage and stator rotor current by voltage and current sensor, after coordinate transformation, stator voltage is aligned to q-axis, the active power and reactive power of stator side output are calculated, then by feedforward compensation and decoupling control, generate rotor voltage modulation signal under dq axis, by coordinate inverse change is sent to SVPWM link input end, exports the switch tube control signal of doubly-fed generator machine side converter, to realize the independent control of active power and reactive power by rotor current.It can effectively solve the problems such as large flux linkage measurement error, active and reactive power coupling, limited reactive power compensation in traditional stator flux linkage orientation control, without observing stator flux linkage, can improve the power supply quality of doubly-fed wind power system.

Description

Technical Field

[0001] This invention relates to a grid-connected control method for wind turbine generator sets, specifically to a control method for a doubly fed wind turbine rotor-side converter based on q-axis voltage orientation. Background Technology

[0002] Advances in wind power technology have driven the continuous growth of single-unit capacity for wind turbines. Against this backdrop, the advantages of doubly-fed induction generators (DFIGs) have become increasingly apparent, as they can achieve constant-frequency power output during variable-speed operation by controlling rotor-side slip power, thereby reducing the cost of corresponding power electronics equipment. Due to these technological and economic advantages, DFIGs are widely used in high-power wind turbine units for variable-speed, constant-frequency power generation.

[0003] High-power doubly-fed wind turbines typically employ dual PWM converters for control. This design enables bidirectional power flow from the generator rotor. Of the mechanical power output by the wind turbine, a portion is directly supplied to the grid, while the other portion is regulated by converters; therefore, these converters are classified as partial-power converters. Functionally, the grid-side PWM converter primarily maintains the stability of the DC bus voltage, typically using grid-side voltage-oriented control. The rotor-side PWM converter, on the other hand, regulates the active and reactive power output from the doubly-fed generator to the grid and provides the excitation current required to maintain the rotor's rotating magnetic field.

[0004] The traditional generator-side converter control strategy is stator flux orientation, which faces three main problems: (1) Large flux measurement error. The current model method is easily affected by motor parameters, while the voltage model method, although it can reduce the influence of parameters, may still have integral drift problems due to the nature of integral operations. (2) Coupling exists 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 large 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 connection performance of the wind power system. Summary of the Invention

[0005] This invention addresses the problems of traditional control strategies by providing a q-axis voltage-oriented control method for the rotor-side converter of a doubly-fed induction generator (DFIG). This method eliminates the need to observe the quantum flux linkage and enables independent decoupled control of the generator's active and reactive power, thereby improving the grid-connected power quality of the DFIG wind power system.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A control method for a doubly-fed induction generator rotor-side converter based on q-axis voltage orientation includes the following steps:

[0008] Step S1, due to the reactive power reference quantity Q * Adjustments are made according to the grid's demand. To meet the requirements for unity power factor grid connection, Q is... * Set to 0;

[0009] Step S2: Detect the rotor angle θ of the doubly-fed wind turbine using a position encoder. r The rotor's mechanical angular velocity ω is obtained through differential calculation. r The blade rotational angular velocity ω of the wind turbine is calculated using the given gearbox gear ratio σ, and the tip speed ratio λ is calculated using the given blade radius R and real-time wind speed V.

[0010] Step S3, due to the wind energy utilization coefficient C p The peak value decreases as the blade pitch angle β of the wind turbine increases. β is set to 0 to capture maximum wind energy, and 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, use the wind energy utilization coefficient C p The mechanical output power P of the wind turbine is calculated from the real-time wind speed V and the blade radius R. m It is set as the active power reference quantity, and the mechanical torque T of the wind turbine is calculated based on the blade rotation angular velocity ω. m It 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 Subtract the number of pole pairs p and rotor angle θ of the doubly-fed motor. r The product of these two factors yields the position difference angle θ. Δ For the stator three-phase voltage U abc_s and current I abc_s and rotor three-phase current I abc_r Perform Clarke and Park transforms to obtain the stator voltage U along the dq axis. sd U sq and stator current I sd I sq and rotor current I rd I rq After aligning the stator voltage to the q-axis, the actual values ​​of the active and reactive power outputs P and Q of the doubly-fed wind turbine are calculated.

[0013] Step S6: The actual values ​​of active and reactive power P and Q output by the doubly-fed wind turbine are respectively compared with the mechanical output power P of the wind turbine.m Reactive power reference quantity Q * The power outer loop error is obtained by subtraction, and the reference value of the rotor current dq-axis component is obtained by PI regulation. and And subtract the rotor current dq axis component I respectively rd I rq This generates the inner loop error of the rotor current in the dq coordinate system, and the reference value of the dq axis component of the rotor voltage is obtained through PI regulation. and

[0014] Step S7: Using a feedforward compensation and decoupling control strategy, the rotor control voltage U in the synchronous rotating coordinate system dq is obtained based on the stator and rotor voltage equations and flux linkage equations of the doubly-fed wind turbine. rdc U rqc ;

[0015] Step S8: Based on the reference value of the rotor voltage dq axis component and and rotor control voltage U rdc U rqc The rotor voltage modulation signal U of the doubly fed motor is calculated. rdt and U rqt The inverse Park transform converts the signal into the reference voltage signal U required by the SVPWM stage. α U β Finally, the output switching signal controls the rotor-side converter of the doubly fed wind turbine.

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

[0017] This invention can effectively solve the problems of large flux measurement error, active and reactive power coupling, and limited reactive power compensation in traditional stator flux orientation control. It eliminates the need to observe the stator flux and can realize independent decoupled control of generator active and reactive power and grid connection with unity power factor, thereby improving the power supply quality of doubly-fed wind power systems. Attached Figure Description

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

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

[0020] Figure 3 Simulation results of the instantaneous active and reactive power output from the stator side of the doubly-fed generator;

[0021] Figure 4 Simulation results of instantaneous grid-connected voltage and current values ​​for a doubly-fed induction generator (DFIG) wind power generation system;

[0022] Figure 5 The results are Fourier analysis of the grid-connected current of the doubly-fed wind power generation system. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0024] Figure 1 To illustrate the structural diagram of the doubly-fed induction generator (DFIG) wind turbine grid-connected power generation system applicable to this invention, the q-axis voltage-oriented DFIG rotor-side converter control method proposed in this invention can be applied to the DFIG rotor-side converter, enabling independent decoupling control of the generator's active and reactive power without requiring stator flux measurement. Furthermore, due to the adoption of a voltage feedforward compensation strategy, unity power factor grid connection can be achieved when the grid's reactive power demand is adjusted to zero. Figure 2 As shown, the controller uses the mechanical power output by the wind turbine as the active power reference signal. It acquires the generator stator voltage and stator / rotor current through voltage and current sensors, performs coordinate transformation to align the stator voltage to the q-axis, calculates the active and reactive power output from the stator side, and then generates a rotor voltage modulation signal along the dq-axis through feedforward compensation and decoupling control. This signal is then sent to the input of the SVPWM stage via inverse coordinate transformation, outputting the switching control signal for the doubly-fed generator's generator-side converter. This achieves independent control of active and reactive power by the rotor current. The specific steps include:

[0025] Step S1, due to the reactive power reference quantity Q * Adjustments are typically made based on grid demand. To meet the requirements for unity power factor grid connection, Q is... * Set to 0.

[0026] Step S2: Detect the rotor angle θ of the doubly-fed wind turbine using a position encoder. r The rotor's mechanical angular velocity ω is obtained through differential calculation. r The blade rotational angular velocity ω of the wind turbine is calculated using the given gearbox gear 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 formulas for calculating the blade rotational angular velocity ω and the tip speed ratio λ are as follows:

[0028]

[0029] Step S3, due to the wind energy utilization coefficient C pThe peak value decreases as the blade pitch angle β of the wind turbine increases. β is set to 0 to capture maximum wind energy, and 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, As an intermediate coefficient, when the blade pitch angle β is 0, the wind energy utilization coefficient C p The peak value is approximately 0.48, at which point the doubly fed wind turbine maintains the optimal tip speed ratio λ = 8.1 to continuously capture maximum wind energy.

[0033] Step S4: Given the air density ρ, use the wind energy utilization coefficient C p The mechanical output power P of the wind turbine is calculated from the real-time wind speed V and the blade radius R. m It is set as the active power reference quantity, and the mechanical torque T of the wind turbine is calculated based on the blade rotation angular velocity ω. m It is converted into electromagnetic torque T by the gearbox. e Input a 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 Subtract the number of pole pairs p and rotor angle θ of the doubly-fed motor. r The product of these two factors yields the position difference angle θ. Δ For the stator three-phase voltage U abc_s and current I abc_s and rotor three-phase current I abc_r Perform Clarke and Park transforms to obtain the stator voltage U along the dq axis. sd U sq and stator current I sd I sq and rotor current I rd I rqAfter aligning the stator voltage to the q-axis, the actual values ​​of the active and reactive power outputs P and Q of the doubly fed wind turbine are calculated.

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

[0039]

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

[0041] In this step, the stator voltage U sd U sq The formulas for calculating the actual values ​​of active and reactive power P and Q of a doubly-fed induction generator (DFIG) are as follows:

[0042]

[0043] Among them, U s The value represents the stator voltage vector amplitude. Since the stator voltage of a doubly-fed generator is equal to the grid voltage after the stator is connected to the grid, the amplitude and frequency remain approximately unchanged. That is, the voltage vector amplitude U of the three-phase stator voltage in the synchronous rotating coordinate system is... s It is constant.

[0044] Step S6: The actual values ​​of active and reactive power P and Q output by the doubly-fed wind turbine are respectively compared with the mechanical output power P of the wind turbine. m Reactive power reference quantity Q * The power outer loop error is obtained by subtraction, and the reference value of the rotor current dq-axis component is obtained by PI regulation. and And subtract the rotor current dq axis component I respectively rd I rq This generates the inner loop error of the rotor current in the dq coordinate system, and the reference value of the dq axis component of the rotor voltage is obtained through PI regulation. and

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

[0046]

[0047] Where s is the Laplace operator, K pd K is the proportional coefficient of the d-axis PI controller in the power outer loop. id K represents the integral coefficient of the d-axis PI controller in the power outer loop. pq K is the proportional coefficient of the q-axis PI controller in the power outer loop. iq The integral coefficient of the q-axis PI controller in the power outer loop is... This is the proportional coefficient of the d-axis PI controller in the inner loop of the rotor current. The integral coefficient of the d-axis PI controller in the inner loop of the rotor current is given. This is the proportional coefficient of the q-axis PI controller in the inner loop of the rotor current. The integral coefficient of the q-axis PI controller in the inner loop of the rotor current is given.

[0048] Step S7: Using a feedforward compensation and decoupling control strategy, the rotor control voltage U in the synchronous rotating coordinate system dq is obtained based on the stator and rotor voltage equations and flux linkage equations 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 L is the excitation inductor for a doubly-fed induction motor. s For stator inductance, L r R is the rotor inductance. s For stator resistance, For the d-axis component of the stator flux linkage, Let ω be the q-axis component of the stator flux linkage, Δω be the slip angular velocity, and ω be the angular velocity. s ω is the stator voltage angular frequency, and f is the stator voltage frequency.

[0052] Step S8: Based on the reference value of the rotor voltage dq axis component and and rotor control voltage U rdc U rqc The rotor voltage modulation signal U of the doubly fed motor is calculated. rdt and Urqt The inverse Park transform converts the signal into the reference voltage signal U required by the SVPWM stage. α U β Finally, the output switching signal controls the rotor-side converter of the doubly fed wind turbine.

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

[0054]

[0055] The obtained signal is converted into a switching control signal for the rotor-side converter of the doubly fed wind turbine through inverse Park transform and SVPWM algorithm.

[0056] The simulation effect after the implementation of this invention is as follows: Figures 3-5 As shown, a 1.5MW doubly-fed induction generator (DFIG) wind power system is connected to a 690V grid. It can be seen that the active power connected to the grid is close to the rated value of the DFIG induction generator, while the reactive power is stable at 0. Furthermore, the three-phase voltage and current are in opposite directions at the same frequency. Fourier analysis of the grid-connected current shows a harmonic distortion rate of 0.87% (<5%), meeting the requirements for unity power factor grid connection. This demonstrates that the control method of this invention can achieve decoupled control of the active and reactive power of the DFIG wind turbine and improve the grid connection performance of the system.

Claims

1. A control method for a doubly-fed induction generator rotor-side converter based on q-axis voltage orientation, characterized in that... The method includes the following steps: Step S1, due to the reactive power reference quantity Q * Adjustments are made according to the grid's demand. To meet the requirements for unity power factor grid connection, Q is... * Set to 0; Step S2: Detect the rotor angle θ of the doubly-fed wind turbine using a position encoder. r The rotor's mechanical angular velocity ω is obtained through differential calculation. r The blade rotational angular velocity ω of the wind turbine is calculated using the given gearbox gear ratio σ, and the tip speed ratio λ is calculated using the given blade radius R and real-time wind speed V. Step S3, due to the wind energy utilization coefficient C p The peak value decreases as the blade pitch angle β of the wind turbine increases. β is set to 0 to capture maximum wind energy, and 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, use the wind energy utilization coefficient C p The mechanical output power P of the wind turbine is calculated from the real-time wind speed V and the blade radius R. m It is set as the active power reference quantity, and the mechanical torque T of the wind turbine is calculated based on the blade rotation angular velocity ω. m It 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 Subtract the number of pole pairs p and rotor angle θ of the doubly-fed motor. r The product of these two factors yields the position difference angle θ. Δ For the stator three-phase voltage U abc_s and current I abc_s and rotor three-phase current I abc_r Perform Clarke and Park transforms to obtain the stator voltage U along the dq axis. sd U sq and stator current I sd I sq and rotor current I rd I rq After aligning the stator voltage to the q-axis, the actual values ​​of the active and reactive power outputs P and Q of the doubly-fed wind turbine are calculated. Step S6: The actual values ​​of active and reactive power P and Q output by the doubly-fed wind turbine are respectively compared with the mechanical output power P of the wind turbine. m Reactive power reference quantity Q * The power outer loop error is obtained by subtraction, and the reference value of the rotor current dq-axis component is obtained by PI regulation. and And subtract the rotor current dq axis component I respectively rd I rq This generates the inner loop error of the rotor current in the dq coordinate system, and the reference value of the dq axis component of the rotor voltage is obtained through PI regulation. and Step S7: Using a feedforward compensation and decoupling control strategy, the rotor control voltage U in the synchronous rotating coordinate system dq is obtained based on the stator and rotor voltage equations and flux linkage equations of the doubly-fed wind turbine. rdc U rqc ; Step S8: Based on the reference value of the rotor voltage dq axis component and and rotor control voltage U rdc U rqc The rotor voltage modulation signal U of the doubly fed motor is calculated. rdt and U rqt The inverse Park transform converts the signal into the reference voltage signal U required by the SVPWM stage. α U β Finally, the output switching signal controls the rotor-side converter of the doubly fed wind turbine.

2. The doubly fed wind turbine rotor-side converter control method based on q-axis voltage orientation according to claim 1, characterized in that... In step S2, the formulas for calculating the blade rotational angular velocity ω and the tip speed ratio λ are as follows:

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

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

6. The doubly fed wind turbine rotor-side converter control method based on q-axis voltage orientation according to claim 1, characterized in that... In step S5, the stator voltage U sd U sq The formulas for calculating the actual values ​​of active and reactive power P and Q of a doubly-fed induction generator (DFIG) are as follows: Among them, U s This represents the magnitude of the stator voltage vector.

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

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

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

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