Transient power angle instability suppression method for grid-forming type doubly-fed wind turbine generator

Abstract

The invention discloses a transient power angle instability suppression method for a network-constructed doubly-fed wind turbine generator, solves the problem of power angle instability possibly occurring when a virtual synchronous machine controls a doubly-fed wind turbine generator under the condition of a power grid fault, and belongs to the field of stability control of a power system. The method comprises the steps that the power angle instability risk is judged according to voltage information and angle information, collected in real time, of a machine side converter and a grid side converter, if power angle instability exists, on the basis of an original power given value Pref, a new active power given value Pref is formed, new = Pref-P'ref, P'ref = beta * Pref, PI + (1-beta) * Pref and adaptive, and the power angle instability risk is obtained; and inputting the angle difference value delta of the machine-side converter and the grid-side converter into a proportional-integral controller to obtain an active power basic compensation value Pref, PI and an adaptive compensation value Pref, adaptive = K (t) * e (t). According to the invention, on the basis of the basic compensation value obtained by the proportional-integral controller, the compensation value is corrected in real time by using the recorded previous data through an adaptive control strategy.

Description

Technical Field

[0001] The invention relates to a method for suppressing transient power angle instability of a grid-connected double-fed wind turbine generator set, and belongs to the field of power system stability control. Background Art

[0002] As the proportion of distributed power sources such as wind power in the power grid gradually increases, the degree of power electronics in the power system continues to improve. Traditional grid-following control doubly-fed wind turbines cannot provide flexible dynamic voltage and frequency regulation characteristics, while the grid-building control method can actively support voltage and frequency and improve the inertia of the system. Virtual synchronous machine control simulates the dynamic characteristics of synchronous generators, introduces active swing equations and reactive droop equations in the control system, and enables the equipment to have similar voltage and frequency regulation capabilities as synchronous machines. However, virtual synchronous machine control may have power angle stability problems in transient processes, especially when the power grid fails. Although the inertia link of the doubly-fed wind turbine under the control of the virtual synchronous machine enhances the steady-state anti-disturbance capability, it also leads to the problem of slow transient response speed, which is not conducive to the suppression of transient current. When the voltage of the doubly-fed wind turbine under the control of the virtual synchronous machine drops symmetrically in the power grid, it not only has a negative impact on the transient power angle characteristics of the power system, but it may also experience power angle instability, making it more difficult to achieve fault ride-through. Summary of the invention

[0003] In view of the problem of power angle instability that may occur when a virtual synchronous machine controls a doubly-fed wind turbine generator set in the event of a power grid failure, the present invention provides a method for suppressing transient power angle instability of a grid-connected doubly-fed wind turbine generator set.

[0004] A method for suppressing transient power angle instability of a grid-connected double-fed wind turbine generator system of the present invention comprises:

[0005] Real-time collection and acquisition of voltage information, angle information and power information of the machine-side converter and grid-side converter during the operation of the grid-connected double-fed wind turbine set;

[0006] The risk of power angle instability is determined based on the voltage and angle information of the machine-side converter and the grid-side converter collected in real time. If power angle instability exists, the original active power given value P is used to ref Based on the proportional integral controller and adaptive controller, a new active power given value P is formed. ref,new ;

[0007] The new power setting value P ref,new for:

[0008] P ref,new =P ref -P r ' ef

[0009] Among them, the comprehensive compensation value Pr ' ef =β·P ref,PI +(1-β)·P ref,adaptive , β is the weight coefficient;

[0010] The angle difference δ between the machine-side converter and the grid-side converter is used as the input of the proportional-integral controller, and the active power basic compensation value P output by the proportional-integral controller is ref,PI ;

[0011] The adaptive compensation value P is obtained by using the adaptive controller ref,adaptive , P ref,adaptive =K(t)·e(t), e(t) is the error signal;

[0012] The update formula of adaptive gain K(t) is: K(t+1)=K(t)+α·▽J(K(t))

[0013] α is the learning rate, is the gradient of the performance index J with respect to the gain K(t).

[0014] As a preferred option, the active power basic compensation value P ref,PI for:

[0015]

[0016] Among them, K p is the proportional gain, K i is the integral gain.

[0017] Preferably, the method for judging the power angle instability risk according to the angle information of the machine-side converter and the grid-side converter collected in real time includes:

[0018] After the grid voltage drop is detected, the power angle curve is calculated in real time according to the voltage information and angle information of the double-fed wind turbine generator set. The power angle value where the acceleration area and the deceleration area meet is used as the power given threshold P under the current grid voltage through the relationship between the acceleration area and the deceleration area in the power angle curve before and after the grid fault. refm ;

[0019] When δ is greater than the intersection angle between the acceleration area and the deceleration area and the original active power given value P ref Greater than P refm When the power angle is unstable, the risk of power angle instability is determined.

[0020] As a preferred embodiment, the power given threshold P refm How to obtain:

[0021] According to the real-time grid voltage U g The stator side voltage value U of the double-fed wind turbine sCalculate the power angle curve of the doubly-fed wind turbine:

[0022]

[0023] Among them, X g is the inductive reactance of the power grid line; s represents the Laplace operator;

[0024] The power given threshold P is calculated in real time based on the relationship between the acceleration area and the deceleration area of ​​the power angle curve. refm :

[0025]

[0026] Among them, δ0 is the power angle value at the time of grid fault, P s1 is the power after the grid fault, δ k With δ h They are the power angle values ​​corresponding to the two intersection points of the power given threshold and the power angle curve after the power grid fault.

[0027] Preferably, the grid-type doubly-fed wind turbine generator set-side converter adopts virtual synchronous control, simulating the dynamic characteristics of the synchronous generator by introducing an inertia link; the grid-type wind turbine generator set-side converter adopts vector control.

[0028] Preferably, the grid-type doubly-fed wind turbine generator set side converter adopts virtual synchronous control, and the control expression is:

[0029]

[0030] Among them, D p is the active power-frequency droop coefficient; P s , Q s , P ref , Q ref are the active power, reactive power and reference values ​​of active power and reactive power output on the stator side respectively; J is the virtual moment of inertia; ω n is the rated synchronous angular frequency; ω is the VSG output angular frequency; ω ref is the angular frequency reference value; K is the inertia coefficient; E is the potential amplitude inside the VSG; D q is the reactive power-voltage droop coefficient; U n is the base value of output voltage; U is the output voltage amplitude; u rdref 、u rqref are the d-axis and q-axis components of the given voltage on the rotor side respectively; u sq 、u sd are the d-axis and q-axis components of the stator side output voltage respectively; i rd 、i rq are the d-axis and q-axis components of the rotor side output current, i sd 、i sqare the d-axis and q-axis components of the stator side output current respectively, ω2 is the slip angular frequency; k pu , k iu are the PI control parameters of the voltage loop, k pi , k ii are the PI control parameters of the current loop respectively; s represents the Laplace operator;

[0031] L r Indicates the rotor side inductance, L m Represents the mutual inductance between the stator and the rotor.

[0032] Preferably, the grid-side converter of the grid-type wind turbine adopts vector control, and the control expression is:

[0033]

[0034] Among them, L f is the grid-side filter inductance; k pdc , k idc are the PI control parameters of the grid-side DC voltage control loop, k pil , k iil are the PI control parameters of the grid-side current control loop, k ppll , k ipll are the PI control parameters of the phase-locked loop; ω n is the rated synchronous angular frequency; u ldref 、u lqref are the d-axis and q-axis components of the grid-side output voltage given value respectively; u dc 、u dcref are the DC bus voltage and the DC bus voltage given value respectively; i ld 、i lq d and q axis components of the grid-side output current; θ pll is the phase angle of the phase-locked loop output, and s represents the Laplace operator.

[0035] The beneficial effect of the present invention is that the present invention combines the control angles of the machine-side and grid-side converters, determines the risk of system instability by real-time calculation of the power angle curve and the active power given threshold, and timely invests in active power improvement control strategy; the improved control strategy uses the recorded past data to make real-time corrections to the compensation value through an adaptive control strategy based on the basic compensation value obtained by the proportional-integral controller. The present invention can calculate the active power given threshold in real time and quantitatively under the condition of a grid fault, greatly reducing the risk of power angle instability of the grid-connected double-fed wind turbine unit under the condition of a grid fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the machine-side control block diagram of the grid-type doubly-fed wind turbine unit;

[0037] Figure 2 This is the control block diagram of the grid-side of the grid-type doubly-fed wind turbine;

[0038] Figure 3 It is a schematic diagram of the power angle curve and the corresponding acceleration and deceleration areas under the condition of power grid fault;

[0039] Figure 4 This is a block diagram of the adaptive active power control of the present invention;

[0040] Figure 5 The voltage and current waveforms are when the transient power angle instability suppression method of the present invention is not adopted;

[0041] Figure 6 The voltage and current waveforms are shown when the transient power angle instability suppression method of the present invention is adopted. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0045] refer to Figures 1 to 6 This embodiment is described in detail. This embodiment is based on the combination of the machine-grid side converter and is used to improve the transient power angle stability of the doubly-fed wind turbine when a power grid fault occurs. A method for suppressing transient power angle instability of a grid-connected doubly-fed wind turbine is proposed, including:

[0046] Step 1, acquiring data: collecting and acquiring in real time the voltage information, angle information, active power and reactive power measurement values ​​of the machine-side converter and the grid-side converter during the operation of the grid-type double-fed wind turbine set;

[0047] The grid-type double-fed wind turbine generator set side converter in this embodiment adopts virtual synchronous control, and introduces an inertia link to simulate the dynamic characteristics of the synchronous generator, so that the double-fed wind turbine generator set has the operating characteristics of inertia and damping, such as Figure 1 As shown, the control expression is:

[0048]

[0049] Among them, D pis the active power-frequency droop coefficient; P s , Q s , P ref , Q ref are the active power, reactive power and reference values ​​of active power and reactive power output on the stator side respectively; J is the virtual moment of inertia; ω n is the rated synchronous angular frequency; ω is the VSG output angular frequency; ω ref is the angular frequency reference value; K is the inertia coefficient; E is the potential amplitude inside the VSG; D q is the reactive power-voltage droop coefficient; U n is the base value of output voltage; U is the output voltage amplitude; u rdref 、u rqref are the d-axis and q-axis components of the given voltage on the rotor side respectively; u sq 、u sd are the d-axis and q-axis components of the stator side output voltage respectively; i rd 、i rq are the d-axis and q-axis components of the rotor side output current, i sd 、i sq are the d-axis and q-axis components of the stator side output current respectively, ω2 is the slip angular frequency; k pu , k iu are the PI control parameters of the voltage loop, k pi , k ii are the PI control parameters of the current loop respectively; s represents the Laplace operator;

[0050] L r Indicates the rotor side inductance, L m Represents the mutual inductance between the stator and the rotor.

[0051] In this embodiment, the grid-type wind turbine grid-side converter adopts vector control, which can quickly handle sudden voltage and current changes. Figure 2 As shown, the control expression is:

[0052]

[0053] Among them, L f is the grid-side filter inductance; k pdc , k idc are the PI control parameters of the grid-side DC voltage control loop, k pil , k iil are the PI control parameters of the grid-side current control loop, k ppll , k ipll are the PI control parameters of the phase-locked loop; ω n is the rated synchronous angular frequency; u ldref 、u lqref are the d-axis and q-axis components of the grid-side output voltage given value respectively; udc 、u dcref are the DC bus voltage and the DC bus voltage given value respectively; i ld 、i lq d and q axis components of the grid-side output current; θ pll is the phase angle of the phase-locked loop output;

[0054] In this embodiment, the angles of the machine-side converter and the grid-side converter are obtained through the machine-side active power link and the grid-side phase-locked loop link respectively, wherein the machine-side angle is the integral of the virtual synchronous angular frequency output by the active link, and the grid-side angle is directly the grid-side phase-locked loop output angle.

[0055] Step 2: After the grid voltage drops, the power angle instability threshold is calculated. The power angle curve is calculated in real time based on the voltage and angle information of the double-fed wind turbine generator set. Figure 3 As shown in the figure, the power given threshold of the current grid voltage under the handover power angle value of the acceleration and deceleration area is calculated by the relationship between the acceleration area and the deceleration area; when δ is greater than the handover power angle value of the acceleration area and the deceleration area and the original active power given value P ref Greater than P refm When the power angle is unstable, the risk of power angle instability is determined.

[0056] In a preferred embodiment, the power angle δ of the grid-type double-fed wind turbine generator set is obtained by subtracting the angle of the machine-side converter from the angle of the grid-side converter. g The stator side voltage value U of the double-fed wind turbine s Calculate the power angle curve of the unit:

[0057]

[0058] Where X g is the inductive reactance of the power grid line.

[0059] When the grid voltage value obtained by the hardware device is lower than the pre-set threshold, the power setting threshold is calculated in real time based on the relationship between the acceleration area and the deceleration area of ​​the power angle curve:

[0060]

[0061] Among them, δ0 is the power angle value at the time of grid fault; P refm is the power given threshold; P s1 is the power after the grid failure; k With δ h They are the power angle values ​​corresponding to the two intersection points of the power given threshold and the power angle curve after the power grid fault, and the two are obtained by solving the following equations:

[0062]

[0063] Among them, the subscript 1 represents the corresponding value after the power grid failure.

[0064] The subscript 1 represents the corresponding value after the power grid failure.

[0065] The above method can detect the power given threshold after the power grid fault occurs and compare it with the power given value. If the power given value exceeds the power given threshold, an adaptive active power control strategy is implemented.

[0066] Step 3: After detecting the risk of power angle instability, start the active power improvement control loop of the generator-side converter. The loop adopts a hybrid control strategy, such as Figure 4 As shown in the figure, based on the original active power given value, the proportional integral controller and the adaptive controller are used for compensation to form a new active power given value P ref,new , thereby increasing the deceleration area.

[0067] Proportional-integral controller: The angle difference between the machine-side converter and the grid-side converter is passed through the proportional-integral control link to output a basic compensation value P of the active power given value related to the angle difference. ref,PI The output formula of the proportional-integral controller is:

[0068]

[0069] Among them, K p is the proportional gain, K i is the integral gain.

[0070] Adaptive controller: According to the actual operation status and historical data of the power grid, dynamically adjust the parameters of the compensation signal to further optimize the response speed and stability of the system, and output the adaptive compensation value P of the active power given value. ref,adaptive The output formula of the adaptive controller is:

[0071] P ref,adaptive =K(t)·e(t)

[0072] Among them, K(t) is the adaptive gain, which is dynamically adjusted according to the real-time status and historical data of the system; e(t) is the error signal, that is, the difference between the set value and the actual measured value.

[0073] The update formula of adaptive gain K(t) is:

[0074]

[0075] Among them, α is the learning rate, which determines the speed of parameter update. It is the gradient of the performance index J to the gain K(t), which reflects the quality of the current control effect.

[0076] After the above two controllers are allocated according to certain weights, a comprehensive compensation value for the given active power value is obtained. The calculation formula is:

[0077] P r ' ef =β·P ref,PI +(1-β)·P ref,adaptive

[0078] Among them, β is the weight coefficient, which is used to balance the effects of proportional-integral control and adaptive control, and can be adjusted according to specific scenarios.

[0079] Based on all the above, the calculation formula of the new active power given value is:

[0080] P ref,new =P ref -P r ' ef

[0081] Among them, P ref,new is the new active power given value, P ref is the original active power given value, P r ' ef is the comprehensive compensation signal.

[0082] The method of this embodiment also includes real-time monitoring of the power angle change on the machine-grid side after starting the improved control loop. If the risk of grid failure is eliminated, the normal control mode is automatically restored after the power angle returns to a stable state.

[0083] After starting the improved control loop, the method records the operating data during the fault period in each switching cycle, draws the power angle curve and calculates the active power given threshold in real time according to the above method, so as to quickly adjust the parameter settings of the adaptive control part in a targeted manner.

[0084] Specifically, refer to Figure 3 , which is a schematic diagram of the power angle curve and the corresponding acceleration and deceleration areas under the condition of power grid fault. When the acceleration area is larger than the deceleration area, the system is at risk of instability;

[0085] refer to Figure 4 , is the block diagram of the proposed adaptive active power control;

[0086] refer to Figure 5 , which is the voltage and current waveform when the transient power angle instability suppression method is not adopted. The system has a grid voltage drop of 50% at 2s, and the grid voltage recovers at 6s. At this time, the grid-type double-fed wind turbine generator system has a power angle instability;

[0087] refer to Figure 6, which is the voltage and current waveform diagram when the transient power angle instability suppression method is adopted. At this time, the system can achieve fault ride-through.

[0088] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A method for suppressing transient power angle instability of a grid-connected doubly-fed wind turbine generator system, characterized in that: The method comprises: Real-time collection and acquisition of voltage information, angle information and power information of the machine-side converter and grid-side converter during the operation of the grid-connected double-fed wind turbine set; The risk of power angle instability is determined based on the voltage and angle information of the machine-side converter and the grid-side converter collected in real time. If power angle instability exists, the original active power given value P is used to ref Based on the proportional integral controller and adaptive controller, a new active power given value P is formed. ref,new ; The new power setting value P ref,new for: P ref,new =P ref -P′ ref Among them, the comprehensive compensation value P′ ref =β·P ref,PI +(1-β)·P ref,adaptive , β is the weight coefficient; The angle difference δ between the machine-side converter and the grid-side converter is used as the input of the proportional-integral controller, and the active power basic compensation value P output by the proportional-integral controller is ref,PI ; The adaptive compensation value P is obtained by using the adaptive controller ref,adaptive , P ref,adaptive =K(t)·e(t), e(t) is the error signal; The update formula of adaptive gain K(t) is: α is the learning rate, is the gradient of the performance index J with respect to the gain K(t).

2. The method for suppressing transient power angle instability of a grid-connected double-fed wind turbine generator set according to claim 1, characterized in that: Active power basic compensation value P ref,PI for: Among them, K p is the proportional gain, K i is the integral gain.

3. The method for suppressing transient power angle instability of a grid-connected double-fed wind turbine generator set according to claim 1, characterized in that: The method for judging the power angle instability risk based on the real-time collected angle information of the machine-side converter and the grid-side converter includes: After the grid voltage drop is detected, the power angle curve is calculated in real time according to the voltage information and angle information of the double-fed wind turbine generator set. The power angle value where the acceleration area and the deceleration area meet is used as the power given threshold P under the current grid voltage through the relationship between the acceleration area and the deceleration area in the power angle curve before and after the grid fault. refm ; When δ is greater than the intersection angle between the acceleration area and the deceleration area and the original active power given value P ref Greater than P refm When the power angle is unstable, the risk of power angle instability is determined.

4. The method for suppressing transient power angle instability of a grid-connected double-fed wind turbine generator set according to claim 3 is characterized in that: Power given threshold P refm How to obtain: According to the real-time grid voltage U g The stator side voltage value U of the double-fed wind turbine s Calculate the power angle curve of the doubly-fed wind turbine: Among them, X g is the inductive reactance of the power grid line; s represents the Laplace operator; The power given threshold P is calculated in real time based on the relationship between the acceleration area and the deceleration area of ​​the power angle curve. refm : Among them, δ0 is the power angle value at the time of grid fault, P s1 is the power after the grid fault, δ k With δ h They are the power angle values ​​corresponding to the two intersection points of the power given threshold and the power angle curve after the power grid fault.

5. The method for suppressing transient power angle instability of a grid-connected double-fed wind turbine generator set according to claim 1, characterized in that: The grid-type doubly-fed wind turbine generator set machine-side converter adopts virtual synchronous control, and simulates the dynamic characteristics of the synchronous generator by introducing an inertia link; the grid-type wind turbine generator set network-side converter adopts vector control.

6. The method for suppressing transient power angle instability of a grid-connected double-fed wind turbine generator set according to claim 5, characterized in that: The grid-type doubly-fed wind turbine generator set side converter adopts virtual synchronous control, and the control expression is: Among them, D p is the active power-frequency droop coefficient; P s , Q s , P ref , Q ref are the active power, reactive power and reference values ​​of active power and reactive power output on the stator side respectively; J is the virtual moment of inertia; ω n is the rated synchronous angular frequency; ω is the VSG output angular frequency; ω ref is the angular frequency reference value; K is the inertia coefficient; E is the potential amplitude inside the VSG; D q is the reactive power-voltage droop coefficient; U n is the base value of output voltage; U is the output voltage amplitude; u rdref 、u rqref are the d-axis and q-axis components of the given voltage on the rotor side respectively; u sq 、u sd are the d-axis and q-axis components of the stator side output voltage respectively; i rd 、i rq are the d-axis and q-axis components of the rotor side output current, i sd 、i sq are the d-axis and q-axis components of the stator side output current respectively, ω2 is the slip angular frequency; k pu , k iu are the PI control parameters of the voltage loop, k pi , k ii are the PI control parameters of the current loop respectively; s represents the Laplace operator; L r Indicates the rotor side inductance, L m Represents the mutual inductance between the stator and the rotor.

7. The method for suppressing transient power angle instability of a grid-connected double-fed wind turbine generator set according to claim 5, characterized in that: The grid-side converter of the grid-type wind turbine adopts vector control, and the control expression is: Among them, L f is the grid-side filter inductance; k pdc , k idc are the PI control parameters of the grid-side DC voltage control loop, k pil , k iil are the PI control parameters of the grid-side current control loop, k ppll , k ipll are the PI control parameters of the phase-locked loop; ω n is the rated synchronous angular frequency; u ldref 、u lqref are the d-axis and q-axis components of the grid-side output voltage given value respectively; u dc 、u dcref are the DC bus voltage and the DC bus voltage given value respectively; i ld 、i lq d and q axis components of the grid-side output current; θ pll is the phase angle of the phase-locked loop output, and s represents the Laplace operator.

8. A computer-readable storage device storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method for suppressing transient power angle instability of a grid-connected double-fed wind turbine generator set as claimed in any one of claims 1 to 7 are implemented.

9. A device for suppressing transient power angle instability of a grid-connected doubly-fed wind turbine generator system, comprising a storage device, a processor, and a computer program stored in the storage device and executable on the processor, characterized in that: The processor executes the computer program to implement the steps of the method for suppressing transient power angle instability of a grid-connected doubly-fed wind turbine generator set as claimed in any one of claims 1 to 7.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method for suppressing transient power angle instability of a grid-type doubly-fed wind turbine generator set as claimed in any one of claims 1 to 7 are implemented.

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