CN116073398A - Additional damping control system for improving synchronous stability of doubly-fed wind turbine generator - Google Patents

Abstract

The invention discloses an additional damping control system for improving the synchronous stability of doubly-fed wind turbines. Its grid-side control structure includes a phase-locked loop, a damping control module, and a grid-side converter current control loop, wherein the PI in the phase-locked loop The controller is used to calculate the phase-locked loop frequency error signal ω _err between the phase-locked loop coordinate system and the reference coordinate system according to the q-axis DC voltage u _sq ; the damping control module is used to output the compensation voltage according to the phase-locked loop frequency error signal ω _err U _damp is added to the output of the q-axis current controller in the current control loop of the grid-side converter to achieve disturbance suppression, where the transfer function of the damping control module is

Among them, ω ₀ is the reference value of angular velocity, K _w is the additional damping gain coefficient, and s is the Laplacian operator.

Description

An additional damping control system to improve the synchronous stability of doubly-fed wind turbines

technical field

The invention belongs to the technical field of wind power generation, and more specifically relates to an additional damping control system for improving the synchronous stability of a doubly-fed wind turbine.

Background technique

With the continuous increase of wind power grid-connected capacity and the continuous improvement of wind power penetration rate, the sustainable, safe and stable operation of the power system is facing many challenges. In particular, large-scale wind farms are usually located in remote areas and connected to the AC grid through high-impedance long transmission lines, which will significantly reduce the grid strength, making wind turbines more susceptible to grid dynamic disturbances and reducing the synchronization stability of the system.

In order to alleviate the small-disturbance broadband oscillation problem of double-fed wind turbines under weak power grids, the most common method is to adjust and optimize the parameters of the phase-locked loop, and reduce the bandwidth of the phase-locked loop to improve stability. However, changing the structure of the phase-locked loop will increase the The complexity of the phase loop reduces the dynamic performance of the phase-locked loop. In addition to changing the phase-locked loop, active damping control can also be achieved by adding a feed-forward channel in the rotor-side current controller. However, the rotor-side current loop control of DFIG usually includes various EMF and feed-forward items. Improving the rotor-side control structure will increase the complexity of the rotor-side converter control structure, resulting in insufficient capacity of the rotor-side converter.

Contents of the invention

In view of the above defects or improvement needs of the prior art, the present invention provides an additional damping control system to improve the synchronous stability of doubly-fed wind turbines, the purpose of which is to make full use of the capacity of the grid-side converter, Adjust to achieve oscillation suppression.

In order to achieve the above object, according to one aspect of the present invention, an additional damping control system for improving the synchronous stability of doubly-fed wind turbines is provided, including a grid-side converter and a grid-side converter that provides three-phase voltage for the grid-side converter Control structure, the grid-side control structure includes a phase-locked loop, a damping control module and a grid-side converter current control loop, wherein,

The phase-locked loop includes a Park transformation module, a phase-locked PI controller and an integrator, and the Park transformation module is used to perform Park transformation on the grid-connected point three-phase voltage u _sabc to obtain d-axis and q-axis DC voltages u _sd and u _sq ; the phase-locked PI controller is used to calculate the phase-locked loop frequency error signal ω _err between the phase-locked loop coordinate system and the reference coordinate system according to the q-axis DC voltage u _sq , and the integrator is used for the lock The phase loop frequency error signal ω _err is integrated to obtain the output angle θ _pll and fed back to the Park transformation module;

其中，ω₀是角速度基准值，K_w是附加阻尼增益系数，s为拉普拉斯算子；The damping control module is used to output the compensation voltage U _damp according to the phase-locked loop frequency error signal ω _err , and the transfer function of the damping control module is:

Wherein, _ω0 is the angular velocity reference value, _Kw is the additional damping gain coefficient, and s is the Laplacian operator;

The grid-side converter current control loop includes a voltage calculation module and a Park inverse conversion module, and the voltage calculation module is used to calculate the grid-side d-axis voltage _Ugd and the initial grid-side q-axis voltage and superimpose the compensation voltage U _damp on the initial grid-side q-axis voltage to obtain the grid-side q-axis voltage U _gq ; the Park inverse transformation module is used to convert the grid-side d-axis voltage U _gd and grid-side The shaft voltage _Ugq is subjected to Park inverse transformation to obtain the three-phase voltage input to the grid-side converter.

In one of the embodiments, the expression of the phase-locked loop frequency error signal ω _err output by the phase-locked PI controller is:

ω _err =k _p u _sq +k _i ∫u _sq dt

Among them, k _p is the proportional coefficient of the PI controller, and _ki is the integral coefficient of the PI controller.

In one of the embodiments, in the current control loop of the grid-side converter, the expression of the grid-side q-axis voltage _Ugq is:

U _gq ＝G _gpi (I _{gq_ref} -I _gq )+ω _s L ₁ I _gd +U _damp

Among them, G _gpi represents the PI controller in the grid side current control loop, I _{gq_ref} represents the reference value of the q-axis current of the network point, I _gq represents the actual value of the q-axis current of the network point, ω _s L ₁ I _gd represents the cross decoupling item, Among them, ω _s , L ₁ , and I _gd respectively represent the rated angular frequency, grid-side filter inductance and grid-side d-axis current;

The expression of grid side d-axis voltage U _gd is:

U _gd ＝ G _gpi (I _{gd_ref} -I _gd )+ω _s L ₁ I _gq

Among them, I _{gd_ref} represents the reference value of the d-axis current of the network point, I _gd represents the actual value of the d-axis current of the network point, and ω _s L ₁ I _gq represents the cross decoupling item

In one embodiment, the value of I _{gq_ref} is 0.

In one of the embodiments, the grid-side control structure further includes:

An isolation module, arranged between the damping control module and the phase-locked loop, before the phase-locked loop frequency error signal ω _err is input to the damping control module, the frequency of the phase-locked loop is adjusted by the isolation module The error signal ω _err is filtered and then input to the damping control module. When the double-fed wind turbine is in a steady state, the isolation module isolates the phase-locked loop frequency error signal ω _err . When the double-fed wind turbine is disturbed, The isolation module passes the PLL frequency error signal ω _err .

其中，T_w是隔离环节时间常数，s为拉普拉斯算子。In one of the embodiments, the transfer function of the isolation module is

Among them, T _w is the time constant of the isolation link, and s is the Laplacian operator.

In one of the embodiments, T _w ranges from 1s to 20s.

In one embodiment, in the damping control module, the angular velocity reference value ω ₀ is 314, and the value range of the additional damping gain coefficient K _w is 50-200.

In one of the embodiments, the grid-connected point three-phase current is used as the input current of the grid-side converter.

In one of the embodiments, the control system further includes a rotor-side converter and a rotor-side control structure providing three-phase voltages for the rotor-side converter.

Generally speaking, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

输出特定的补偿电压U_damp，并反馈至网侧变换器电流控制环中，可以补偿双馈风电风电机组的系统阻尼，确保系统阻尼系数为正，从而抑制系统小干扰振荡。1. The present invention leads the phase-locked loop frequency error signal and inputs the damping control module with specific design, and the transfer function of the damping control module is

Outputting a specific compensation voltage U _damp and feeding it back to the current control loop of the grid-side converter can compensate the system damping of the doubly-fed wind turbine and ensure that the system damping coefficient is positive, thereby suppressing small disturbance oscillations of the system.

2. The present invention changes the grid-side control structure, which can make full use of the capacity of the double-fed fan grid-side converter and avoid increasing the complexity of the rotor-side converter control structure.

3. The parameter change of the grid-side converter controller has a greater impact on the system stability, so the control effect of the grid-side additional damping controller of the present invention is stronger than that of the generator-side.

Description of drawings

Figure 1 is a schematic structural diagram of the control system of a traditional doubly-fed wind turbine;

Fig. 2 is a circuit diagram of an additional damping control system for improving the synchronous stability of doubly-fed wind turbines in an embodiment;

Fig. 3 is a simulation waveform diagram of a small disturbance instability phenomenon occurring when the DFIG in an embodiment does not add a damping control module, wherein, (a) is the frequency fpll detected by _{the PLL} of the DFIG, (b ) inputting the q-axis voltage signal U _gq of the IGBT to the grid-side converter;

Fig. 4 is a simulated waveform diagram of small disturbance suppression after adding a damping control module to the double-fed fan unit in an embodiment, (a) is the frequency f _pll detected by the phase-locked loop of the double-fed fan, and (b) is the grid-side transformation The device inputs the q-axis voltage signal U _gq of the IGBT.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not constitute a conflict with each other.

In order to facilitate the understanding of the present invention, the traditional doubly-fed wind turbine control system is introduced first. As shown in Figure 1, the entire doubly-fed wind turbine control system is divided into a grid-side structure and a rotor-side structure, wherein the grid side has a grid-side converter GSC and grid-side control structure. The rotor side has a rotor-side converter RSC and a rotor-side control structure. Both the rotor side and the grid side realize the control of the converter through the current loop. This case is to improve the network-side control structure, so the traditional network-side control structure will be described. Specifically, the phase-locked loop collects the stator three-phase voltage u _sabc at the point of common connection (PCC), and then through the phase-locked loop, the phase-locked loop output angle θ _pll can be obtained. In steady state, the three-phase voltage u _sabc of the stator coincides with the d-axis dpll of the phase-locked loop coordinate system and the coordinate reference ds, and the coordinate reference ds rotates at a constant frequency. In the dynamic process, the stator three-phase voltage u _sabc first has a disturbance, and the d-axis dpll of the phase-locked loop coordinate system tracks this disturbance. The output angle of the phase-locked loop is the angle between the phase-locked loop coordinate system and the reference coordinate system . Specifically, in the phase-locked loop, the three-phase voltage u _sabcc is firstly park-transformed by the Park transformation module to obtain d-axis and q-axis dc voltages u _sd and u _sq , and then the q-axis dc voltage u _sq is input The phase-locked PI controller outputs the phase-locked loop frequency error signal ω _err through the phase-locked PI controller, and the phase-locked loop frequency error signal ω _err represents the frequency error of the phase-locked loop coordinate system relative to the reference coordinate system (ds), and then The phase-locked loop frequency error signal ω _err is superimposed on the reference coordinate system rotation frequency ω ₁ and then integrated to obtain the phase-locked loop output angle θ _pll and fed back to the Park transformation module as the transformation parameter of the Park transformation module. In the grid-side current loop, the output current of the grid-side converter is collected and Park transformed to obtain the actual value of the q-axis current I _gq and the actual value of the d-axis current I _gd , and the set q-axis current reference value I _{gq_ref} and the q-axis The current actual value I _gq is input to one of the PI controllers G _gpi in the grid-side current control loop, and the set d-axis current reference value I _{gd_ref} and the d-axis current actual value I _gd are input to one of the grid-side current control loops In another PI controller G _gpi , the output results of the two PI controllers G _gpi are cross-decoupled to obtain the grid-side q-axis voltage U _gq and the grid-side d-axis voltage U _gd , and then perform Park inverse transformation to obtain the input The three-phase voltage of the grid-side converter is used to realize the control of the grid-side converter.

On the basis of the traditional structure, the present invention improves the network side control structure.

Figure 2 is a circuit diagram of an additional damping control system for improving the synchronous stability of doubly-fed wind turbines in an embodiment of the present invention, and its grid-side control structure includes a phase-locked loop, a damping control module, and a grid-side converter current control loop .

Wherein, the phase-locked loop includes a Park transformation module, a phase-locked PI controller and an integrator, and the Park transformation module is used to perform Park transformation on the grid-connected point three-phase voltage u _sabc to obtain d-axis and q-axis DC voltage u _sd and u _sq ; the phase-locked PI controller is used to calculate the phase-locked loop frequency error signal ω _err between the phase-locked loop coordinate system and the reference coordinate system according to the q-axis DC voltage u _sq , and the integrator is used for the The phase-locked loop frequency error signal ω _err is integrated to obtain the output angle θ _pll and fed back to the Park transformation module.

其中，ω₀是角速度基准值，K_w是附加阻尼增益系数，s为拉普拉斯算子。具体的，ω₀是角速度基准值，取值314；K_w是附加阻尼的增益系数，增益系数增大能够提升阻尼效果，但同时受网侧变换器容量的限制。在本例中K_w取100。The damping control module is used to output the compensation voltage U _damp according to the phase-locked loop frequency error signal ω _err , and the transfer function of the damping control module is:

Among them, ω ₀ is the reference value of angular velocity, K _w is the additional damping gain coefficient, and s is the Laplacian operator. Specifically, ω ₀ is the angular velocity reference value, which takes a value of 314; _Kw is the gain coefficient of additional damping. Increasing the gain coefficient can improve the damping effect, but at the same time it is limited by the capacity of the grid-side converter. Kw _takes 100 in this example.

The current control loop of the grid-side converter includes a voltage calculation module and a Park inverse conversion module, and the voltage calculation module is used to calculate the grid-side d-axis voltage _Ugd and the initial grid-side q-axis according to the grid-connected point current reference value and current actual value voltage and superimpose the compensation voltage U _damp on the initial grid-side q-axis voltage to obtain the grid-side q-axis voltage U _gq ; the Park inverse transformation module is used for the grid-side d-axis voltage U _gd and the grid-side q-axis voltage U _gq performs Park inverse transformation to obtain the three-phase voltage input to the grid-side converter.

Specifically, in the phase-locked loop, the ω _err output by the PI controller of the phase-locked loop is calculated according to the following formula:

ω _err =k _p u _sq +k _i ∫u _sq dt

Among them, k _p is the proportional coefficient of the PI controller, and _ki is the integral coefficient of the PI controller.

In an embodiment, the above-mentioned grid-side control system further includes an isolation module, which is essentially a filter, and is arranged between the damping control module and the phase-locked loop. Before the phase-locked loop frequency error signal ω _err is input to the damping control module, the phase-locked loop frequency error signal ω _err is filtered by the isolation module and then input to the damping control module. When the double-fed wind turbine is in a steady state, the isolation module cuts off the phase-locked loop frequency error signal ω _err , that is, the signal input to the damping control module is 0. At this time, control is performed according to the traditional mode; when the double-fed wind turbine When disturbed, the isolation module allows the phase-locked loop frequency error signal ω _err to pass through, that is, the non-zero phase-locked loop frequency error signal ω _err is input to the damping control module for voltage compensation regulation.

Specifically, the transfer function of the damping module can be expressed as:

Among them, ω ₀ is the angular velocity reference value, which takes a value of 314; _Kw is the gain coefficient of additional damping. Increasing the gain coefficient can improve the damping effect, but at the same time it is limited by the capacity of the grid-side converter. Kw _takes 100 in this example.

In an embodiment, in the grid-side converter current control loop, the obtained compensation voltage U _damp is superimposed on the output terminal of the grid-side q-axis current converter, so that:

U _gq ＝G _gpi (I _{gq_ref} -I _gq )+ω _s L ₁ I _gd +U _damp

Among them, G _gpi represents the PI link of the grid-side current controller, the expression is k _p +k _i /s, k _p represents the proportional coefficient of the PI controller, k _i represents the integral coefficient of the PI controller, and s is the Laplace operator. I _{gq_ref represents} the reference value of the q-axis current, which is generally 0; _{I gq} represents the output current of the grid-side converter; ω _s L _{1 I gd represents} the cross-decoupling Angular frequency, grid-side filter inductance and grid-side d-axis current.

The output terminal of the grid-side q-axis current converter maintains the traditional calculation formula, that is, the expression of the grid-side d-axis voltage U _gd is:

U _gd ＝ G _gpi (I _{gd_ref} -I _gd )+ω _s L ₁ I _gq

In the following, a 1.5MW double-fed wind turbine under typical parameters is taken as an example to carry out simulation research. In 2s, the bandwidth of the phase-locked loop PI controller increases from 20Hz to 70Hz, using the additional damping control system proposed by the present invention to improve the synchronous stability of the doubly-fed wind turbine, and automatically adjust the modulation voltage command of the grid-side q-axis current controller, It can suppress the instability of the system due to small disturbances. As for this, Fig. 3 is a simulation waveform diagram of a small disturbance instability phenomenon when the DFIG does not add a damping control module, where (a) is the frequency f _pll detected by the DFIG PLL, (b) Inputting the q-axis voltage signal U _gq of the IGBT to the grid-side converter, it can be seen that the system gradually oscillates and diverges after 2 seconds, that is, the small disturbance is not suppressed. Figure 4 is the simulated waveform diagram of small disturbance suppression after adding the damping control module to the double-fed fan unit, (a) is the frequency f _pll detected by the phase-locked loop of the double-fed fan, (b) is the q of the input IGBT of the grid-side converter Shaft voltage signal U _gq , it can be seen that the system can be quickly stabilized, that is, small disturbances are effectively suppressed. To sum up, the present invention can compensate the system damping of the DFIG by extracting the phase-locked loop frequency error signal and inputting it into a damping control module with a specific design, ensuring that the system damping coefficient is positive, thereby suppressing small disturbance oscillations of the system.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (10)

1. An additional damping control system for improving the synchronous stability of a doubly-fed wind turbine generator is characterized by comprising a grid-side converter and a grid-side control structure for providing three-phase voltage for the grid-side converter, wherein the grid-side control structure comprises a phase-locked loop, a damping control module and a grid-side converter current control loop,

the phase-locked loop comprises a Park conversion module, a phase-locked PI controller and an integrator, wherein the Park conversion module is used for converting grid-connected point three-phase voltage u _sabc Performing Park conversion to obtain d-axis and q-axis direct current voltages u _sd And u _sq The method comprises the steps of carrying out a first treatment on the surface of the The phase-locked PI controller is used for controlling the phase-locked PI controller according to the q-axis direct current voltage u _sq Calculating a phase-locked loop frequency error signal omega between a phase-locked loop coordinate system and a reference coordinate system _err The integrator is used for generating a phase-locked loop frequency error signal omega _err Integrating to obtain an output angle theta _pll And feeds back to the Park conversion module;

the damping control module is used for controlling the phase-locked loop frequency error signal omega _err Output compensation voltage U _damp The transfer function of the damping control module is that

Wherein omega ₀ Is the angular velocity reference value, K _w Is an additional damping gain coefficient, s is a Laplacian operator;

the network side converter current control loop comprises a voltage calculation module and a Park inverse transformation module, wherein the voltage calculation module is used for calculating network side d-axis voltage U according to a network side converter current reference value and a current actual value _gd And an initial net side q-axis voltage and at an initial net side qSuperimposing the compensation voltage U on the shaft voltage _damp Obtaining the q-axis voltage U at the net side _gq The method comprises the steps of carrying out a first treatment on the surface of the The Park inverse transformation module is used for transforming the net side d-axis voltage U _gd And net side q-axis voltage U _gq And performing Park inverse transformation to obtain three-phase voltages input to the grid-side converter.

2. An additional damping control system for improving synchronization stability of a doubly-fed wind turbine according to claim 1, wherein the phase-locked PI controller outputs a phase-locked loop frequency error signal ω _err The expression of (2) is:

ω _err ＝k _p u _sq +k _i ∫u _sq dt

wherein k is _p Is the proportionality coefficient, k of the PI controller _i Is the integral coefficient of the PI controller.

3. An additional damping control system for improving synchronization stability of a doubly-fed wind turbine according to claim 1, wherein in said grid-side converter current control loop, a grid-side q-axis voltage U _gq The expression of (2) is:

U _gq ＝G _gpi (I _{gq_ref} -I _gq )+ω _s L ₁ I _gd +U _damp

wherein G is _gpi Representing PI controllers in a network side current control loop, I _{gq_ref} Reference value representing net point q-axis current, I _gq Representing the actual value of the net point q-axis current, ω _s L ₁ I _gd Represents cross-decoupling terms, ω therein _s 、L ₁ 、I _gd Respectively representing rated angular frequency, a net side filter inductance and net side d-axis current;

net side d-axis voltage U _gd The expression of (2) is:

U _gd ＝G _gpi (I _{gd_ref} -I _gd )+ω _s L ₁ I _gq

wherein I is _{gd_ref} Reference value representing net point d axis current, I _gd Representing the actual value of the dot d-axis current, omega _s L ₁ I _gq Representing cross-decoupling terms.

4. An additional damping control system for improving synchronization stability of a doubly-fed wind turbine according to claim 3, wherein I _{gq_ref} The value is 0.

5. The additional damping control system for improving synchronization stability of a doubly-fed wind turbine according to claim 1, wherein said grid-side control structure further comprises:

an isolation module arranged between the damping control module and the phase-locked loop for generating a phase-locked loop frequency error signal omega _err Before the damping control module is input, the isolation module is used for controlling the phase-locked loop frequency error signal omega _err After filtering, inputting the filtered signals into the damping control module, and when the doubly-fed wind turbine generator is in a steady state, isolating the phase-locked loop frequency error signal omega by the isolating module _err When the doubly-fed wind turbine generator is disturbed, the isolation module enables the phase-locked loop frequency error signal omega to be _err Through the device.

6. An additional damping control system for improving synchronization stability of a doubly-fed wind turbine according to claim 5, wherein said isolation module has a transfer function of

Wherein T is _w Is the time constant of the isolation link, s is the Laplacian.

7. An additional damping control system for improving synchronization stability of a doubly-fed wind turbine according to claim 6, wherein T is _w The value range is 1 s-20 s.

8. An additional damping control system for improving synchronization stability of a doubly-fed wind turbine according to claim 1, wherein in the damping control module, the angular velocity reference value ω ₀ For 314, add damping gainCoefficient K _w The range of the value of (2) is 50-200.

9. The additional damping control system for improving synchronization stability of a doubly-fed wind turbine according to claim 1, wherein grid-tied three-phase current is used as an input current of the grid-side converter.

10. An additional damping control system for improving synchronization stability of a doubly-fed wind turbine according to claim 1, wherein said control system further comprises a rotor-side inverter and a rotor-side control structure for providing a three-phase voltage to said rotor-side inverter.

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