An adaptive virtual rotor inductance control method for a doubly-fed wind power generator

Abstract

The application discloses a kind of adaptive virtual rotor inductance control methods of doubly-fed wind generator.The method is aimed at the small disturbance instability problem caused by the interaction of doubly-fed wind generator and weak grid, and proposes a kind of virtual rotor inductance adaptive adjustment control method based on stator terminal voltage q-axis disturbance component suppression, which can realize the adaptive adjustment of virtual rotor inductance value according to the change of stator terminal voltage q-axis disturbance component, and then realize the real-time suppression of stator terminal voltage disturbance component, improve the stability of doubly-fed wind turbine grid-connected system, and improve grid-connected power quality.The control method disclosed by the application does not need to increase additional grid monitoring equipment, and is easy to implement in engineering.

Description

Technical Field

[0001] This invention relates to a grid-connected control method for a doubly fed wind turbine (doubly fed wind turbine), particularly a stability control method under weak grid conditions. Background Technology

[0002] Doubly-fed induction generators (DFIGs) play an indispensable role in wind power generation systems due to their advantages such as controllable power factor, small rated power converter, and low cost. However, in weak grid conditions, the interaction between DFIGs and the grid is significant, easily leading to instability caused by small disturbances. Therefore, the stability of DFIGs under faulty and weak grid conditions has become a challenging problem of common concern to both academia and industry.

[0003] Under weak grid conditions, the q-axis disturbance component of the stator voltage of a doubly-fed induction generator (DFIG) wind turbine extends to the entire control system through phase-locked loops, coordinate transformations, and current loops, exacerbating the grid-connected current disturbance component. Furthermore, this current disturbance, through a faulty grid, further intensifies the stator voltage disturbance component, ultimately creating a vicious cycle. In severe cases, this interaction between the DFIG wind turbine and the weak grid can lead to system instability, with the risk increasing as the grid strength decreases. In other words, the q-axis disturbance component of the stator voltage is the root cause of small-disturbance instability in DFIG wind power generation systems. Therefore, from the perspective of suppressing the q-axis disturbance component of the stator voltage, in-depth research into control methods for adaptive adjustment of the virtual rotor inductance is crucial for improving the stability of DFIG wind power generation systems under weak grid conditions. This is precisely the key technical problem that this invention aims to solve. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing an adaptive virtual rotor inductance control method for doubly-fed wind turbines, thereby improving the system's ability to operate in weak grid conditions and enhancing the stability of the doubly-fed wind turbine grid-connected system.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] An adaptive virtual rotor inductance control method for a doubly-fed wind turbine as described above, characterized in that the method includes the following steps:

[0007] (1) Measure the stator line voltage U of the doubly fed wind turbine using a voltage sensor. sab U sbc The stator phase current I of a doubly-fed wind turbine is measured using a current sensor. sa I sb With rotor phase current I ra I rb The rotor angular velocity ω of a doubly-fed wind turbine was measured using a photoelectric encoder disk. r .

[0008] (2) The stator line voltage U obtained in step 1 sab U sbc Stator phase current I sa I sb With rotor phase current I ra I rb Perform a stationary coordinate transformation (Clarke transform) to obtain U in the two-phase stationary coordinate system. sαβ I sαβ with I rαβ .

[0009] Among them, U sαβ I sαβ with I rαβ This represents the composite vector, specifically denoted as: U sαβ =U sα +jU sβ I sαβ =I sα +jI sβ ,I rαβ =I rα +jI rβ ;U sα jU sβ It represents U sαβ The α and β axis components; similarly, I sα I sβ I rα I rβ The physical meanings are similar.

[0010] (3) Obtain the grid voltage position angle θ using a phase-locked loop. pll The rotor angular velocity ω obtained in step (1) r By performing integration, the rotor position angle θ can be obtained. r The grid voltage position angle θ pll With rotor position angle θ r By subtracting the values, we can obtain the rotation position angle θ. slip .

[0011] (4) Using the grid voltage position angle θ obtained in step (3) pll The U obtained in step (2) sαβ with I sαβ Perform a rotational coordinate transformation (Park transformation) to obtain the d-axis and q-axis components of the stator voltage in the rotating coordinate system, i.e., U. sd U sq And the d-axis and q-axis components of the stator current, i.e., I sd I sq Using the slip position angle θ obtained in step (3) slip For the I obtained in step (2) rαβPerform a rotating coordinate transformation (Park transformation) to obtain the d-axis and q-axis components of the rotor current in the two-phase rotating coordinate system, i.e., I. rd with I rq .

[0012] (5) Adaptive virtual rotor inductance control and its adaptive coefficient K v The design is as follows:

[0013] (5.1) For different adaptive coefficients K v Continuously adjust the active current until the generalized Nyquist curve is tangent to the safety margin circle. At this point, the system is in a critical stable state, and the adaptive coefficient K can be obtained. v The maximum active current that a doubly-fed induction generator (DFIG) can output is denoted by the stable operating limit Sol. The stable operating limit Sol is related to the adaptive coefficient K. v The relationship is Sol=g (K v );

[0014] (5.2) Considering dynamic performance, for different adaptive coefficients K v Calculate the phase margin γ of the system separately, and obtain the relationship between the two as γ = f (K v );

[0015] (5.3) Taking into account both system stability and dynamic performance, i.e. the constraints of steps (5.1) and (5.2), the adaptive coefficient K is given. v The design principle, namely the adaptive coefficient K v The optimal range of values ​​S v The design is as follows: (1)

[0016] Among them, Sol max Represents taking different adaptive coefficients K v The maximum stable operating limit at that time. Adaptive coefficient K v Within the optimal range S v You can select from the options.

[0017] (6) The q-axis component U of the stator voltage obtained in step (4) sq The q-axis disturbance component ΔU of the stator voltage is obtained by using a second-order bandpass filter. sq , will ΔU sq The adaptive coefficient K obtained in step (5) v Multiply by, and then by, the rotor inductance L of the doubly-fed wind turbine. r Multiplying these values ​​yields the adaptively adjusted virtual rotor inductance value L. v The specific calculation is as follows:

[0018] (2)

[0019] The transfer function of the bandpass filter is:

[0020] (3)

[0021] In the formula, ω c1 To filter out the cutoff frequency corresponding to the DC component, ω c2 The cutoff frequency is used to filter out high-frequency noise.

[0022] (7) Using the adaptive virtual rotor inductance L obtained in step (6) v The rotor current loop is designed such that the voltage drop of the virtual rotor winding inductance can be expressed as the differential of the rotor current. The designed rotor current loop controller is shown in the following equation:

[0023] (3)

[0024] In the formula, K prcc With K ircc These are the proportional and integral coefficients of the PI controller, I rdref I rqref These are the reference values ​​for the d-axis component and q-axis component of the rotor current, respectively, where s is the differential operator, and L... m This represents the mutual inductance between the stator and rotor windings.

[0025] (8) The rotor voltage control vector U obtained in step (7) rdq Perform an inverse rotating coordinate transformation (inverse Park transformation) to obtain the two-phase rotor voltage control vector U. rαβ .

[0026] (9) The rotor voltage control vector U obtained in step (8) rαβ By performing space vector modulation, the switching control signal of the doubly fed wind turbine converter can be obtained, thereby realizing the adaptive virtual rotor inductance control described in this invention.

[0027] The above steps (1) to (9) together constitute the adaptive virtual rotor inductance control method for doubly fed wind turbines of the present invention.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1) Taking into full account the stator q-axis voltage disturbance component as the root cause of system instability, a control method is proposed that adaptively adjusts the virtual rotor inductance value according to the stator voltage disturbance component, which can realize the real-time suppression of the stator q-axis voltage disturbance component.

[0030] 2) It effectively suppressed the oscillation components of grid-connected voltage and grid-connected current, and improved the stability of the doubly fed wind turbine grid-connected system under weak grid conditions.

[0031] 3) Traditional virtual rotor inductance control methods introduce additional low-order harmonics, which is detrimental to the safe and stable operation of doubly-fed wind turbines. This invention effectively suppresses the oscillation distortion of grid-connected voltage and current without introducing additional low-order harmonics, thus improving grid-connected power quality. Attached Figure Description

[0032] Figure 1 This is a diagram showing the topology of the doubly fed wind turbine grid-connected system and its adaptive virtual rotor inductor control structure as described in this invention.

[0033] Figure 2 The adaptive coefficient K described in this invention v Design schematic diagram;

[0034] Figure 3 The simulation results of a 3MW doubly-fed wind turbine using the control method of this invention are shown in the figure.

[0035] Figure 4 The figure shows the experimental results of a 5.5kW doubly-fed wind turbine generator using the control method of the present invention. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] Figure 1 The diagram shows the topology of the doubly-fed induction generator (DFIG) wind turbine grid-connected system and its adaptive virtual rotor inductor control structure as described in this invention. The current flowing into the grid from the DFIG wind turbine is mainly divided into two parts: stator current (controlled by the generator-side converter RSC) and grid-side current (controlled by the grid-side converter GSC). The generator-side converter RSC is controlled using the adaptive virtual rotor inductor control method described in this invention; the grid-side converter GSC is controlled using a traditional vector control method, the control process of which is well known in the art and will not be described further.

[0038] like Figure 1 As shown, the adaptive virtual rotor inductance control method for a doubly-fed wind turbine of the present invention mainly includes the following steps:

[0039] 1. Measure the stator line voltage U of a doubly-fed wind turbine using a voltage sensor. sab U sbc The stator phase current I of a doubly-fed wind turbine is measured using a current sensor. sd I sb With rotor phase current I ra I rb The rotor angular velocity ω of a doubly-fed wind turbine was measured using a photoelectric encoder disk. r .

[0040] 2. The stator line voltage U obtained in step 1sab U sbc Stator phase current I sa I sb With rotor phase current I ra I rb Perform a stationary coordinate transformation (Clarke transform) to obtain U in the two-phase stationary coordinate system. sαβ I sαβ with I rαβ Taking stator voltage and stator current as an example, the specific solution process is shown in the following formula:

[0041] (1)

[0042] (2)

[0043] Among them, U sαβ I sαβ with I rαβ This represents the composite vector, specifically denoted as: U sαβ =U sα +jU sβ I sαβ =I sα +jI sβ ,I rαβ =I rα +jI rβ ;U sα jU sβ It represents U sαβ The α and β axis components; similarly, I sα I sβ I rα I rβ The physical meanings are similar.

[0044] 3. Obtain the grid voltage position angle θ using a phase-locked loop. pll The rotor angular velocity ω obtained in step 1 r By performing integration, the rotor position angle θ can be obtained. r The grid voltage position angle θ pll With rotor position angle θ r By subtracting the values, we can obtain the rotation position angle θ. slip As shown in the following formula:

[0045] (3)

[0046] 4. Using the grid voltage position angle θ obtained in step 3 pll For the U obtained in step 2 sαβ with I sαβ Perform a rotational coordinate transformation (Park transformation) to obtain the d-axis and q-axis components of the stator voltage in the rotating coordinate system, i.e., U.sd U sq And the d-axis and q-axis components of the stator current, i.e., I sd I sq Using the slip position angle θ obtained in step 3 slip For the I obtained in step 2 rαβ Perform a rotating coordinate transformation (Park transformation) to obtain the d-axis and q-axis components of the rotor current in the two-phase rotating coordinate system, i.e., I. rd with I rq The specific transformation process is shown in the following formula:

[0047] (4)

[0048] (5)

[0049] (6)

[0050] 5. The rotor current reference value I of the doubly-fed wind turbine generator. rdqref The rotor current I obtained in step 4 rdq The difference is then processed through a PI controller, and decoupling terms for both rotor and stator currents are added to obtain the fundamental rotor voltage vector U. rdq0 Its equation is:

[0051] (7)

[0052] In the formula K prcc With K ircc These are the proportional and integral coefficients of the PI controller, I rdref I rqref These are the reference values ​​for the d-axis component and the q-axis component of the rotor current, respectively. r L is the rotor winding inductance value. m Let be the mutual inductance between the stator and rotor windings, and s be the differential operator.

[0053] Figure 2 For the adaptive coefficient K v Design the schematic diagram; the specific design method is as follows:

[0054] 6. For different adaptive coefficients K v Continuously adjust the active current until the generalized Nyquist curve is tangent to the safety margin circle. At this point, the system is in a critical stable state, and the adaptive coefficient K can be obtained. v The maximum active current that a doubly-fed induction generator (DFIG) can output is denoted by the stable operating limit Sol. The stable operating limit Sol is related to the adaptive coefficient K. v The relationship is Sol=g (K v ),like Figure 2As shown by the solid line;

[0055] 7. Considering dynamic performance, for different adaptive coefficients K v Calculate the phase margin γ of the system separately, and obtain the relationship between the two as γ = f (K v ),like Figure 2 As shown by the dashed line at the midpoint;

[0056] 8. Taking into account both system stability and dynamic performance, i.e., the constraints in steps 6 and 7, give the adaptive coefficient K. v The design principle, namely the adaptive coefficient K v The optimal range of values ​​S v The design is as follows:

[0057] (8)

[0058] Among them, Sol max Represents taking different adaptive coefficients K v The maximum value of the stable operation limit at that time.

[0059] Within the optimal range S v Selecting the adaptive coefficient K v Thus, steps 6-8 above together constitute the adaptive coefficient K in this invention. v Design methodology.

[0060] 9. The q-axis component U of the stator voltage obtained in step 4 sq The q-axis disturbance component ΔU of the stator voltage is obtained by using a second-order bandpass filter (BPF). sq , will ΔU sq The adaptive coefficient K obtained in step 8 v Multiply by, and then by, the rotor inductance L of the doubly-fed wind turbine. r Multiplying these values ​​yields the adaptively adjusted virtual rotor inductance value L. v The specific calculation is as follows:

[0061] (9)

[0062] To prevent the amplification of high-frequency noise by the subsequent differentiating stage, a bandpass filter is selected to obtain the disturbance component of the stator q-axis voltage. The transfer function of the bandpass filter is:

[0063] (10)

[0064] In the formula, ω c1 To filter out the cutoff frequency corresponding to the DC component, ω c2 The cutoff frequency is used to filter out high-frequency noise.

[0065] The stator q-axis voltage disturbance component extends to the entire control system through the phase-locked loop and coordinate transformation, and can then create a vicious cycle through a weak power grid. The purpose of this step is to adjust the virtual rotor inductance value according to the change of the stator voltage q-axis voltage disturbance component, so as to achieve real-time suppression of the q-axis voltage disturbance component, thereby improving the stability of the doubly-fed induction generator (DFIG) grid-connected system.

[0066] 10. Based on the adaptive virtual rotor inductance L obtained in step 9... v The rotor current loop was redesigned, and the basic rotor voltage vector U obtained in step 5 was adjusted. rdq0 The revised and redesigned rotor current controller is shown in the following equation:

[0067] (11)

[0068] In the formula U rd U rq These are the d-axis and q-axis components of the rotor voltage control vector, respectively.

[0069] 11. The rotor voltage control vector U obtained in step 10 is... rd U rq Perform an inverse rotating coordinate transformation (inverse Park transformation) to obtain the two-phase rotor voltage control vector U. rαβ .

[0070] (12)

[0071] In the formula U rα U rβ These are the α-axis and β-axis components of the two-phase rotor voltage control vector, respectively.

[0072] 12. The rotor voltage control vector U obtained in step 11 is... rαβ By performing space vector modulation (SVM), the switching control signal S of the doubly-fed wind turbine converter can be obtained. abc This enables the adaptive virtual rotor inductance control described in this invention.

[0073] Steps 1 to 12 above together constitute the adaptive virtual rotor inductance control method for doubly-fed wind turbines of the present invention.

[0074] Figure 3 The simulation results of a 3MW doubly-fed wind turbine using the control method of this invention are shown in Table 1. The parameters of the 3MW doubly-fed wind turbine are also shown. To demonstrate the stability enhancement effect of the control method described in this invention, Figure 3The simulation is divided into three time periods: from 0.4 s to 0.6 s, the traditional vector control method is applied and the grid-connected active current command is set to 0.4 pu; from 0.6 s to 0.9 s, the traditional vector control method is applied and the grid-connected active current command is set to 0.59 pu; from 0.9 s to 1.2 s, the active current command remains unchanged at 0.59 pu, and the adaptive virtual rotor inductance control method is applied.

[0075] Depend on Figure 3 It can be seen that: from 0.4 s to 0.6 s, the grid-connected voltage and grid-connected current are without distortion, and the system maintains stable operation; from 0.6 s to 0.9 s, the grid-connected current increases to 0.59 pu, and the waveforms of the grid-connected voltage and grid-connected current show obvious distortion, and the system becomes unstable; however, after the control method described in this invention is applied at 0.9 s, the oscillations of the grid-connected voltage and current immediately begin to decay and recover to a sine wave, and the system returns to stable operation. Figure 3 The implementation case of a 3MW doubly-fed wind turbine can fully verify the effectiveness of the control method described in this invention.

[0076] Figure 4 The experimental waveforms of a doubly-fed induction generator (DFIG) wind turbine using the control method proposed in this invention are shown. The grid-side converter of the DFIG wind turbine is mainly used to handle slip power and maintain the DC bus voltage; therefore, a DC power supply can be used instead to simplify the experimental procedure. The parameters of the DFIG wind turbine are shown in Table 2. Figure 4 (a) The three-phase current waveforms of the grid-connected system when using traditional vector control. Figure 4 (b) shows the rotor current waveform when using conventional vector control. Figure 4 (c) The FFT analysis results of the grid-connected current when applying traditional vector control; Figure 4 (d) shows the grid-connected three-phase current waveform when the adaptive virtual rotor inductance control method of the present invention is applied; 4(e) shows the rotor current waveform when the adaptive virtual rotor inductance control method of the present invention is applied. Figure 4 (f) is the FFT analysis result of the grid-connected current when the adaptive virtual rotor inductance control method of the present invention is applied.

[0077] Depend on Figure 4 It can be seen that when using the traditional vector control method, the grid-connected voltage and current waveforms are severely distorted, and the waveforms are no longer sinusoidal, oscillating at 250Hz and 350Hz, causing system instability. With other conditions unchanged, when using the control method described in this invention, the grid-connected voltage and current are restored to sinusoidal waveforms, the oscillation components are effectively suppressed, the grid-connected current quality is improved, and the system stability is significantly improved. Figure 4 The implementation examples can effectively verify the stability enhancement effect of the control method proposed in this invention.

[0078] In summary, the adaptive virtual rotor inductance control method for a doubly-fed induction generator (DFIG) wind turbine described in this invention has the following significant features: 1) It uses the stator terminal voltage q-axis disturbance component as the basis for adaptively adjusting the virtual rotor inductance value, which can effectively suppress the stator terminal voltage q-axis disturbance component and improve the stability of the DFIG grid-connected system from the root cause of small disturbance instability. 2) The virtual rotor inductance value is adaptively adjusted according to the stator voltage disturbance, enhancing the control flexibility of the system and enabling real-time suppression of disturbance components at the grid connection point. 3) It overcomes the problem of introducing additional low-order harmonics in traditional virtual rotor inductance control, effectively improving the grid-connected current quality. This invention is not only applicable to improving the stability of DFIG grid-connected systems, but can also provide guidance for enhancing the stability control of other grid-connected equipment.

[0079] Table 1 Parameters of 3MW Doubly Fed Wind Turbine

[0080] Rated power (kW) 3 <![CDATA[R s (pu)]]> 0.013 Rated voltage (V) 690 <![CDATA[R r (pu)]]> 0.024 Rated current (A) 8.33 <![CDATA[L s (pu)]]> 4.226 Turns ratio 2.857 <![CDATA[L r (pu)]]> 4.203 <![CDATA[V dc (V)]]> 1200 <![CDATA[L m (pu)]]> 3.99 Fault residual voltage (V) 414 <![CDATA[ω r (rpm)]]> 860

[0081] Table 2 Parameters of 5.5kW Doubly Fed Wind Turbine

[0082] Rated power (kW) 5.5 <![CDATA[R s (Oh)]]> 1.1 Rated voltage (V) 380 <![CDATA[R r (Oh)]]> 2.3 Rated current (A) 8.33 <![CDATA[L s (H)]]> 0.129 Turns ratio 1.63 <![CDATA[L r (H)]]> 0.129 <![CDATA[V dc (V)]]> 600 <![CDATA[L m (H)]]> 0.123

Claims

1. An adaptive virtual rotor inductance control method for a doubly-fed wind turbine, characterized in that, The method includes the following steps: (1) Measure the stator line voltage U of the doubly fed wind turbine using a voltage sensor. sab U sbc The stator phase current I of a doubly-fed wind turbine is measured using a current sensor. sa I sb With rotor phase current I ra I rb The rotor angular velocity ω of a doubly-fed wind turbine was measured using a photoelectric encoder disk. r; (2) The stator line voltage U obtained in step (1) sab U sbc Stator phase current I sa I sb With rotor phase current I ra I rb Perform a stationary coordinate transformation to obtain U in the two-phase stationary coordinate system. sαβ I sαβ with I rαβ; (3) Obtain the grid voltage position angle θ using a phase-locked loop. pll The rotor angular velocity ω obtained in step (1) r The rotor position angle θ is obtained by integration. r ; the grid voltage position angle θ pll With rotor position angle θ r By subtracting the values, we can obtain the rotation position angle θ. slip; (4) Using the grid voltage position angle θ obtained in step (3) pll The U obtained in step (2) sαβ with I sαβ Perform a coordinate transformation to obtain the d-axis and q-axis components of the stator voltage in the rotating coordinate system, i.e., U. sd U sq And the d-axis and q-axis components of the stator current, i.e., I sd I sq Using the slip position angle θ obtained in step (3) slip For the I obtained in step (2) rαβ By performing a rotating coordinate transformation, the d-axis and q-axis components of the rotor current in the two-phase rotating coordinate system are obtained, i.e., I. rd with I rq; (5) Adaptive virtual rotor inductance control and its adaptive coefficient K v The design is as follows: (5.1) For different adaptive coefficients K v Continuously adjust the active current until the generalized Nyquist curve is tangent to the safety margin circle. At this point, the system is in a critical stable state, and the adaptive coefficient K can be obtained. v The maximum active current that a doubly-fed induction generator (DFIG) can output is denoted by the stability operating limit Sol. The stability operating limit Sol is related to the adaptive coefficient K. v The relationship is Sol=g (K v ); (5.2) Considering dynamic performance, for different adaptive coefficients K v Calculate the phase margin γ of the system separately, and obtain the relationship between the two as γ = f (K v ); (5.3) Taking into account both system stability and dynamic performance, i.e. the constraints of steps (5.1) and (5.2), the adaptive coefficient K is given. v The design principle, namely the adaptive coefficient K v The optimal range of values ​​S v The design is as follows: (1) Among them, Sol max Represents taking different adaptive coefficients K v The maximum stable operating limit at that time, the adaptive coefficient K v Within the optimal value range S v Choose from the options; (6) The q-axis component U of the stator voltage obtained in step (4) sq The q-axis disturbance component ΔU of the stator voltage is obtained by using a second-order bandpass filter. sq , will ΔU sq The adaptive coefficient K obtained in step (5) v Multiply by, and then by, the rotor inductance L of the doubly-fed wind turbine. r Multiplying these values ​​yields the adaptively adjusted virtual rotor inductance value L. v The specific calculation is as follows: (2) (7) Using the adaptive virtual rotor inductance L obtained in step (6) v The rotor current loop is designed such that the voltage drop of the virtual rotor winding inductance can be expressed as the differential of the rotor current. The designed rotor current loop controller is shown in the following equation: (3) In the formula, K prcc With K ircc These are the proportional and integral coefficients of the PI controller, I rdref I rqref These are the reference values ​​for the d-axis component and q-axis component of the rotor current, respectively, where s is the differential operator, and L... m This refers to the mutual inductance between the stator and rotor windings. (8) The rotor voltage control vector U obtained in step (7) rdq Perform an inverse rotating coordinate transformation to obtain the two-phase rotor voltage control vector U. rαβ; (9) The rotor voltage control vector U obtained in step (8) rαβ By performing space vector modulation, the switching control signal of the doubly fed wind turbine converter can be obtained, thereby realizing the adaptive virtual rotor inductance control described in this invention.

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