A LPF droop control method for a doubly-fed wind turbine generator based on transient component compensation

Abstract

The present invention discloses an LPF droop control method based on transient component compensation for a doubly fed wind generator, comprising the following steps: calculating the voltage drop depth on the stator side of the doubly fed wind generator; calculating the time constant during the transient period; obtaining the transient component of the stator side flux of the doubly fed wind generator based on the voltage drop depth and the time constant; determining the transient component compensation coefficient of the rotor side voltage of the doubly fed wind generator; obtaining the transient compensation component of the rotor side voltage of the doubly fed wind generator based on the transient component compensation coefficient of the rotor side voltage of the doubly fed wind generator and the transient component of the stator side flux of the doubly fed wind generator; superimposing the transient compensation component of the rotor side voltage of the doubly fed wind generator to the rotor voltage expected value output end of the reactive voltage control branch in the LPF droop control system. The present invention can not only improve the active support capability, fault ride-through capability and network control capability.

Description

Technical Field

[0001] The present invention relates to the technical field of doubly-fed wind generators, and more particularly to an LPF droop control method of a doubly-fed wind generator based on transient component compensation. Background Art

[0002] At present, the LPF droop control methods used in the existing doubly fed wind turbine system do not take into account the transient component of the rotor side voltage, that is, the corresponding control process cannot effectively adjust the transient component of the rotor side voltage, which will bring two serious problems: 1) The transient component of the rotor side voltage cannot be adjusted, which will make the doubly fed wind turbine rotor side voltage unable to offset the transient component of the rotor back electromotive force of the doubly fed wind turbine rα The influence of the rotor side voltage will generate a large voltage difference on the rotor side, resulting in overcurrent on the rotor side, which directly affects the active support capability and fault ride-through capability of the doubly fed wind turbine generator during the transient period (i.e., during the stator side voltage drop fault period). 2) The inability to adjust the transient component of the rotor side voltage will inevitably cause the stator internal electromotive force e of the doubly fed wind turbine generator to in Equal to the stator electromotive force e of the simulated synchronous generator vir This cannot be established. As a result, when the voltage on the stator side drops, the doubly-fed wind turbine generator with LPF droop control will not be able to equivalently simulate the characteristics of the synchronous generator, which directly affects the network control capability of the LPF droop control in the doubly-fed wind turbine generator system.

[0003] Therefore, how to provide an LPF droop control method that takes into account the transient component of the rotor side voltage, which can not only improve the active support capability and fault ride-through capability of the doubly fed wind turbine during transient periods, but also improve the grid control capability of the LPF droop control in the doubly fed wind turbine system, is a problem that technical personnel in this field urgently need to solve. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a LPF droop control method for a doubly-fed wind generator based on transient component compensation.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A LPF droop control method for a doubly-fed wind turbine generator based on transient component compensation comprises the following steps:

[0007] S1: Calculate the voltage drop depth on the stator side of the doubly-fed wind turbine generator;

[0008] Calculate the time constant during transients;

[0009] S2: based on the voltage drop depth and the time constant, obtaining the transient component of the stator-side flux of the doubly-fed wind generator;

[0010] S3: Minimize the difference between the rotor-side current of the doubly-fed wind generator and its rated current under the premise of ensuring that the DC bus voltage is less than or equal to the DC bus voltage threshold, thereby determining the transient component compensation coefficient of the rotor-side voltage of the doubly-fed wind generator; wherein the DC bus voltage is obtained after the rotor-side voltage of the doubly-fed wind generator is rectified by a converter;

[0011] S4: obtaining a transient compensation component of the rotor side voltage of the doubly fed wind generator based on the transient component compensation coefficient of the rotor side voltage of the doubly fed wind generator and the transient component of the stator side flux of the doubly fed wind generator;

[0012] S5: superimposing the transient compensation component of the rotor side voltage of the doubly-fed wind turbine generator to the rotor voltage expected value output end of the reactive voltage control branch in the LPF droop control system.

[0013] Preferably, the voltage drop depth is calculated based on the following formula:

[0014]

[0015] Wherein, h represents the voltage drop depth; u s|0| Indicates the stator side voltage of the doubly-fed wind turbine generator before voltage drop occurs; u s Indicates the stator side voltage of the doubly-fed wind generator after a voltage drop occurs.

[0016] Preferably, the time constant is calculated based on the following formula:

[0017]

[0018] Among them, T s represents the time constant, L s represents the stator side inductance of the doubly-fed wind turbine generator; R s Represents the stator side resistance of the doubly-fed wind turbine generator.

[0019] Preferably, the transient component of the stator-side flux of the doubly-fed wind generator is calculated based on the following formula:

[0020]

[0021] Among them, ψ sa represents the transient component of the stator-side flux of the doubly-fed wind turbine generator; h represents the voltage drop depth; U s|0| Indicates u s|0| The amplitude of s represents the stator side angular frequency of the doubly-fed wind turbine generator; Ts represents the time constant.

[0022] Preferably, the transient component compensation coefficient of the rotor side voltage of the doubly-fed wind turbine generator is calculated based on the following formula:

[0023]

[0024] Among them, K cmp represents the transient component compensation coefficient of the rotor side voltage of the doubly-fed wind turbine generator; K vir Represents the equivalent simulation coefficient; L r represents the rotor side inductance of the doubly-fed wind turbine generator; L m Represents the mutual inductance on the rotor and stator sides of the doubly-fed wind turbine generator.

[0025] Preferably, the equivalent simulation coefficient K is calculated based on the following formula: vir :

[0026]

[0027] Among them, K vir Represents the equivalent simulation coefficient; M vt represents the mutual inductance between the stator and the simulated excitation winding of the doubly-fed wind turbine generator; L vt Represents the inductance of the simulated excitation winding; L vir Represents the equivalent simulated inductance of the equivalent simulated synchronous generator.

[0028] Preferably, the transient compensation component of the rotor side voltage of the doubly-fed wind turbine generator is calculated based on the following formula:

[0029]

[0030] Among them, u ra represents the transient compensation component of the rotor side voltage of the doubly-fed wind turbine generator; ψ sa represents the transient component of the stator-side flux of the doubly-fed wind turbine generator; K cmp represents the transient component compensation coefficient of the rotor side voltage of the doubly-fed wind turbine generator; K vir Represents the equivalent simulation coefficient; M vt represents the mutual inductance between the stator and the simulated excitation winding of the doubly-fed wind turbine generator; L vt Represents the inductance of the simulated excitation winding; L vir represents the equivalent simulated inductance of the equivalent simulated synchronous generator; L r represents the rotor side inductance of the doubly-fed wind turbine generator; L m Represents the mutual inductance on the rotor and stator sides of the doubly-fed wind turbine generator.

[0031] Preferably, the DC bus voltage threshold is 1.15 times the rated value of the DC bus voltage.

[0032] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a LPF droop control method for a doubly-fed wind turbine generator based on transient component compensation, which can achieve the following beneficial technical effects:

[0033] (1) The present invention can effectively suppress the overcurrent on the rotor side of the doubly-fed wind turbine during the fault ride-through period, so that the rotor-side converter is always kept in a controlled state during the fault ride-through period, which helps to improve the fault ride-through capability of the doubly-fed wind turbine;

[0034] (2) The present invention performs transient component compensation for the reactive voltage control branch, thereby satisfying the conditions for the doubly-fed wind turbine to equivalently simulate the characteristics of a synchronous generator, so that the doubly-fed wind turbine after transient component compensation can still equivalently simulate the characteristics of a synchronous generator during fault ride-through, thereby achieving the goal of power synchronization control of the doubly-fed wind turbine in the full state stage.

[0035] (3) The compensation of the transient component of the present invention does not require an additional switching circuit or switching switch. After the doubly-fed wind turbine system operates normally or a fault ends, the transient component compensation is naturally 0, which will not affect the normal application of LPF droop control in the steady-state condition of the doubly-fed wind turbine system, thereby fundamentally avoiding a large switching shock to the doubly-fed wind turbine system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0037] Figure 1 A flow chart of an LPF droop control method based on transient component compensation for a doubly-fed wind turbine provided by the present invention;

[0038] Figure 2 The waveform diagram of rotor side current under three droop control methods when the voltage drop depth is 20%;

[0039] Figure 3 The stator side current waveforms under three droop control methods when the voltage drop depth is 20%;

[0040] Figure 4 This is a comparison diagram of electromagnetic torque under three droop control methods when the voltage drop depth is 20%;

[0041] Figure 5 The DC bus voltage comparison diagram under three droop control methods when the voltage drop depth is 20%;

[0042] Figure 6 The waveform diagram of rotor side current under three droop control methods when the voltage drop depth is 70%;

[0043] Figure 7 The stator side current waveforms under three droop control methods when the voltage drop depth is 70%;

[0044] Figure 8 This is a comparison diagram of electromagnetic torque under three droop control methods when the voltage drop depth is 70%;

[0045] Fig. 9 The figure is a comparison diagram of DC bus voltage under three droop control methods when the voltage drop depth is 70%. DETAILED DESCRIPTION

[0046] 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.

[0047] like Figure 1 As shown, an embodiment of the present invention discloses a LPF droop control method of a doubly-fed wind turbine generator based on transient component compensation, comprising the following steps:

[0048] S1: Calculate the voltage drop depth on the stator side of the doubly-fed wind turbine generator;

[0049] Calculate the time constant during transients;

[0050] S2: based on the voltage drop depth and the time constant, obtaining the transient component of the stator-side flux of the doubly-fed wind generator;

[0051] S3: Minimize the difference between the rotor-side current of the doubly-fed wind generator and its rated current under the premise of ensuring that the DC bus voltage is less than or equal to the DC bus voltage threshold, thereby determining the transient component compensation coefficient of the rotor-side voltage of the doubly-fed wind generator; wherein the DC bus voltage is obtained after the rotor-side voltage of the doubly-fed wind generator is rectified by a converter;

[0052] It can be understood that: after a voltage drop fault occurs on the stator side of the doubly fed wind turbine generator, the output power on the stator side of the doubly fed wind turbine generator is blocked, causing excess power to flow from the rotor side, which in turn causes overcurrent on the rotor side of the doubly fed wind turbine generator. In order to limit the overcurrent, the voltage on the rotor side of the doubly fed wind turbine generator is compensated for the transient component to offset the influence of the back electromotive force induced on the rotor side during the transient period (the transient period refers to the duration of the voltage drop). However, a larger transient component compensation will cause the voltage on the rotor side of the doubly fed wind turbine generator applied to the converter to increase, which may cause the occurrence of DC bus overvoltage. Therefore, we cannot blindly pursue rotor side overcurrent limitation while ignoring the impact on the DC bus voltage. Therefore, we should ensure that the overcurrent on the rotor side of the doubly fed wind turbine generator is limited as much as possible under the premise that the DC bus voltage does not exceed the limit.

[0053] S4: obtaining a transient compensation component of the rotor side voltage of the doubly fed wind generator based on the transient component compensation coefficient of the rotor side voltage of the doubly fed wind generator and the transient component of the stator side flux of the doubly fed wind generator;

[0054] S5: superimposing the transient compensation component of the rotor side voltage of the doubly-fed wind turbine generator to the rotor voltage expected value output end of the reactive voltage control branch in the LPF droop control system.

[0055] In one embodiment, the voltage drop depth is calculated based on the following formula:

[0056]

[0057] Wherein, h represents the voltage drop depth; u s|0| Indicates the stator side voltage of the doubly-fed wind turbine generator before voltage drop occurs; u s Indicates the stator side voltage of the doubly-fed wind generator after a voltage drop occurs.

[0058] In one embodiment, the time constant is calculated based on the following formula:

[0059]

[0060] Among them, T s represents the time constant, L s represents the stator side inductance of the doubly-fed wind turbine generator; R s Represents the stator side resistance of the doubly-fed wind turbine generator.

[0061] In one embodiment, the transient component of the stator-side flux of the doubly-fed wind turbine generator is calculated based on the following formula:

[0062]

[0063] Among them, ψ sarepresents the transient component of the stator-side flux of the doubly-fed wind turbine generator; h represents the voltage drop depth; U s|0| Indicates u s|0| The amplitude of s represents the stator side angular frequency of the doubly-fed wind turbine generator; T s represents the time constant.

[0064] In one embodiment, the transient component compensation coefficient of the rotor side voltage of the doubly-fed wind turbine generator is calculated based on the following formula:

[0065]

[0066] Among them, K cmp represents the transient component compensation coefficient of the rotor side voltage of the doubly-fed wind turbine generator; K vir Represents the equivalent simulation coefficient; L r represents the rotor side inductance of the doubly-fed wind turbine generator; L m Represents the mutual inductance on the rotor and stator sides of the doubly-fed wind turbine generator.

[0067] In one embodiment, the equivalent simulation coefficient K is calculated based on the following formula: vir :

[0068]

[0069] Among them, K vir Represents the equivalent simulation coefficient; M vt represents the mutual inductance between the stator and the simulated excitation winding of the doubly-fed wind turbine generator; L vt Represents the inductance of the simulated excitation winding; L vir Represents the equivalent simulated inductance of the equivalent simulated synchronous generator.

[0070] It should be noted that:

[0071] The reactive voltage control link in LPF droop control simulates the stator internal electromotive force of the synchronous generator vir It can be expressed as:

[0072]

[0073] According to the characteristics of synchronous generators:

[0074]

[0075] Among them, e vira Indicates e vir The transient component of vir represents the equivalent simulated angular frequency of the equivalent simulated synchronous generator, M vt represents the mutual inductance between the stator and the simulated excitation winding of the doubly-fed wind turbine generator; ita Indicates i t The transient component of t It represents the expected value of rotor voltage u of reactive voltage control branch in LPF droop control system t The corresponding current value.

[0076] Stator internal electromotive force e of a doubly-fed wind turbine generator in (That is, the internal electromotive force induced by the magnetic flux on the stator side of the doubly fed wind turbine rotor side) is:

[0077]

[0078] Among them, L r represents the rotor side inductance of the doubly-fed wind turbine generator; L m represents the mutual inductance between the rotor side and the stator side of the doubly-fed wind turbine generator; ψ r Represents the rotor-side flux linkage of the doubly-fed wind turbine generator.

[0079] For the rotor side of the doubly-fed wind turbine generator, considering its small resistance, it is generally ignored. Then the voltage u r It can be expressed as:

[0080]

[0081] Among them, ψ r represents the rotor-side flux linkage of the doubly-fed wind turbine generator;

[0082] According to the formula

[0083] and

[0084] It can be seen that the stator internal potential e of the doubly fed wind turbine generator is in and the rotor side voltage u of the doubly-fed wind turbine generator r The following relationship exists:

[0085]

[0086] By formula

[0087] and

[0088] It can be seen that: using the rotor voltage expected value u of the reactive voltage control branch in the LPF droop control system t (where i t It represents the expected value of rotor voltage u of reactive voltage control branch in LPF droop control system t The corresponding current value) can control the rotor side voltage u of the doubly fed wind turbine generator r, which makes the stator potential e of the doubly fed wind turbine during the transient period in The stator potential e of the simulated synchronous generator vir If the voltages of the doubly-fed wind turbine generator and the loads of the wind turbine generator are equal, it can be ensured that the doubly-fed wind turbine generator can simulate the characteristics of a synchronous generator during the transient period, that is, synchronization can be achieved during the transient period.

[0089] It can be understood that: the present invention performs transient component compensation on the rotor voltage expected value output end of the reactive voltage control branch in the LPF droop control system, thereby offsetting the flux linkage ψ of the space air gap magnetic field generated by the transient component of the stator side flux linkage of the doubly fed wind turbine when the doubly fed wind turbine is equivalent to the simulated synchronous generator characteristics. vtα :

[0090]

[0091] Among them, M vt represents the mutual inductance between the stator and the simulated excitation winding of the doubly-fed wind turbine generator; L vir represents the equivalent simulated inductance of the equivalent simulated synchronous generator; ψ sa represents the stator side flux linkage ψ of the doubly-fed wind turbine generator s transient component of .

[0092] The magnetic flux ψ vtα It can also be expressed as:

[0093] L vt i tα =ψ vtα ;

[0094] Among them, L vt represents the inductance of the simulated excitation winding; i ta Indicates i t The transient component of t Indicates the current value corresponding to the expected value of the rotor voltage of the reactive voltage control branch in the LPF droop control system;

[0095] According to the formula and L vt i tα =ψ vtα The internal electromotive force e of the stator of the simulated synchronous generator can be obtained vir The transient component

[0096] The present invention will Represented as K vir ,Right now Also called K vir is the equivalent simulation coefficient.

[0097] In order to make in =evir If established, The transient component With e vir The transient component should also be equal, so we can get:

[0098]

[0099] So we can get:

[0100]

[0101] The present invention will Denoted as K cmp ,Right now Also called K cmp is the transient component compensation coefficient of the rotor side voltage of the doubly-fed wind generator.

[0102] It is understandable that if K cmp and When the transient component of the voltage on the rotor side of the doubly fed wind turbine generator is equal to The rotor back electromotive force of the doubly-fed wind turbine generator The transient component If the two are exactly the same, they can cancel each other out. At this time, the transient component of the rotor side overcurrent is 0, achieving complete compensation. cmp and When they are not equal, the transient component of the rotor side overcurrent will be reduced, but the effect of complete compensation cannot be achieved.

[0103] Although the transient compensation component of the rotor-side voltage of the doubly-fed wind turbine generator can effectively limit the rotor-side current, it will also cause the rotor-side voltage to increase. Therefore, when selecting K cmp When the voltage and current on the rotor side of the doubly fed wind turbine generator are within the allowable range, that is, K cmp It is necessary to ensure that the rotor side voltage of the doubly fed wind turbine generator cannot exceed the DC bus voltage. In addition, the maximum peak value of the DC bus voltage cannot exceed the hardware protection trigger value. In general projects, the maximum peak value of the DC bus voltage (i.e., the DC bus voltage threshold) is 1.15 times the rated value of the DC bus voltage. On the basis of meeting the above voltage limit conditions, the rotor side current of the doubly fed wind turbine generator is limited as much as possible, and ultimately ensure that the rotor side converter of the doubly fed wind turbine generator is always controlled during fault ride-through, thereby effectively improving the active support capability and fault ride-through capability of the doubly fed wind turbine generator during transient periods.

[0104] In one embodiment, the transient compensation component of the rotor side voltage of the doubly-fed wind turbine generator is calculated based on the following formula:

[0105]

[0106] Among them, u ra represents the transient compensation component of the rotor side voltage of the doubly-fed wind turbine generator; ψ sa represents the transient component of the stator-side flux of the doubly-fed wind turbine generator; K cmp represents the transient component compensation coefficient of the rotor side voltage of the doubly-fed wind turbine generator; K vir Represents the equivalent simulation coefficient; M vt represents the mutual inductance between the stator and the simulated excitation winding of the doubly-fed wind turbine generator; L vt Represents the inductance of the simulated excitation winding; L vir represents the equivalent simulated inductance of the equivalent simulated synchronous generator; L r represents the rotor side inductance of the doubly-fed wind turbine generator; L m Represents the mutual inductance on the rotor and stator sides of the doubly-fed wind turbine generator.

[0107] In this embodiment, the present invention conducts simulation experiments on two cases where the voltage drop depth is 20% and 70%. In the simulation experiments, the main parameters of the doubly-fed wind turbine generator are shown in Table 1:

[0108] Table 1 Main parameters of doubly-fed wind turbine generator

[0109]

[0110] The present invention uses the MATLAB / Simulink simulation platform to build a doubly-fed wind turbine simulation system as shown in the parameters of Table 1, and sets the simulation system to have a stator side voltage drop fault at 3s and last for 0.5s, that is, the simulation system returns to normal at 3.5s.

[0111] In order to verify the effectiveness and correctness of the control method proposed in the present invention (i.e., the LPF droop control method based on transient component compensation), the control method proposed in the present invention is compared with the traditional droop control method and the LPF droop control method:

[0112] When the voltage drop depth of the doubly-fed wind turbine system is 20% (mild voltage drop), the rotor-side current waveforms and stator-side current waveforms of the three droop control methods during the fault ride-through period are shown as follows: Figure 2 and Figure 3 It is not difficult to find that the control method proposed in the present invention can effectively limit the overcurrent on the stator side and the rotor side of the doubly-fed wind turbine generator;

[0113] exist Figure 2Middle: The rotor side overcurrent peak value under the traditional droop control method can be as high as 2.5 times the rated current; the rotor side overcurrent peak value under the LPF droop control method is still as high as 2.1 times the rated current, which shows that: the control method proposed in the present invention can basically achieve complete compensation of the rotor side overcurrent under the condition of mild voltage drop. This is because under the condition of mild voltage drop, the overvoltage problem of the DC bus voltage is not very serious and does not exceed the limit. The control method proposed in the present invention can fully obtain the transient compensation component of the rotor side voltage of the doubly fed wind generator according to the goal of limiting the rotor side overcurrent as much as possible.

[0114] exist Figure 3 Middle: The stator side overcurrent peak value under the traditional droop control method can be as high as 2 times the rated current; the stator side overcurrent peak value under the LPF droop control method is still as high as 1.6 times the rated current, while the stator side overcurrent peak value under the control method proposed in the present invention is less than 1.2 times the rated current. The present invention effectively improves the ability of the doubly fed wind generator to operate safely and reliably.

[0115] Figure 4 A comparison diagram of electromagnetic torque under three droop control methods is shown. The fluctuation amplitude of electromagnetic torque under the control method proposed in the present invention is 0.25, which is significantly smaller than 0.9 under the traditional droop control method and 0.5 under the LPF droop control method. This proves that the control method proposed in the present invention has the ability to achieve full-state stage synchronization of the doubly fed wind turbine.

[0116] Figure 5 A comparison diagram of DC bus voltage under three droop control methods is shown. Since the control method proposed in the present invention compensates for the transient component of the rotor side voltage, it will aggravate the deterioration of the DC bus overvoltage. Specifically: the peak value of the DC bus voltage under the control method proposed in the present invention is 1.08, which is higher than 1.06 under the traditional droop control method and 1.05 under the LPF droop control method, but is still within the safety limit, that is, it does not exceed 1.15 times the rated value of the DC bus voltage.

[0117] When the voltage drop depth of the doubly-fed wind turbine system is 70% (severe voltage drop), the rotor-side current waveforms and stator-side current waveforms of the three droop control methods during the fault ride-through period are shown as follows: Figure 6 and Figure 7As shown. Similar to the case where the voltage drop depth is 20%, the control method proposed in the present invention has a significantly better ability to limit overcurrent on the rotor side and the stator side than the other two control methods. That is, the present invention can limit the maximum peak overcurrent on the rotor side and the stator side to within 1.5 and 1.6 times the rated current. However, unlike the case where the voltage drop depth is 20%, the control method proposed in the present invention cannot achieve complete compensation for rotor side overcurrent in the case of severe voltage drop. This is because in the case of severe voltage drop, the DC bus overvoltage is serious and has exceeded the limit, and the transient compensation component of the rotor side voltage of the doubly fed wind power generation is obtained under the premise of ensuring that the DC bus voltage does not exceed the limit. In this way, part of the ability to limit rotor side overcurrent is lost, and thus complete compensation cannot be achieved.

[0118] The electromagnetic torque comparison of the three droop control methods when the voltage drop depth is 70% (severe voltage drop) is shown in the figure below: Figure 8 As shown, it is the same as when the voltage drop depth is 20% (mild voltage drop): that is, in the case of severe voltage drop, the electromagnetic torque fluctuation amplitude under the control method proposed in the present invention is 0.4, which is significantly smaller than 1.2 under the traditional droop control method and 0.8 under the LPF droop control method, verifying that the control method proposed in the present invention still has the ability to achieve full-state stage synchronization of the doubly fed wind turbine under severe voltage drop conditions.

[0119] Fig. 9 It is a comparison diagram of the DC bus voltage under the three droop control methods when the voltage drop depth is 70% (severe voltage drop). As mentioned above, in the case of severe voltage drop, the overvoltage problem of the DC bus of the doubly fed wind turbine is relatively serious, and it must be ensured that it does not exceed 1.15 times the rated value of the DC bus voltage. It is obvious that the maximum peak value of the DC bus voltage under the control method proposed in the present invention does not exceed the maximum limit of the DC bus voltage, that is, 1.15 times the rated value of the DC bus voltage. Although this will affect the limiting ability of the rotor side overcurrent, it is consistent with the previous analysis of the rotor side overcurrent limitation, but it can still limit the current on the rotor side to within the range where the doubly fed wind turbine can operate reliably.

[0120] In summary, compared with the traditional droop control method and the LPF droop control method, the control method proposed in the present invention can enable the doubly fed wind generator to still be able to equivalently simulate the characteristics of the synchronous generator during the transient period, thereby synchronizing the doubly fed wind generator system. The control method proposed in the present invention can also effectively limit the overcurrent on the rotor side of the doubly fed wind generator, so that the rotor side converter can continue to be controllable during the fault period, so that the doubly fed wind generator still has a good grid-building capability during the transient period. At the same time, the determination of the compensation coefficient of the present invention takes into account the constraint that the DC bus voltage does not exceed the limit, so that the doubly fed wind generator can operate safely and reliably during the transient period.

[0121] In addition, the compensation term of the control method proposed in the present invention (i.e., the transient compensation component of the voltage on the rotor side of the doubly fed wind generator) is related to the transient component of the stator side flux. After the doubly fed wind generator system operates normally or the fault ends, the transient component of the stator side flux no longer exists. The transient component compensation in the LPF droop control based on transient component compensation of the present invention (i.e., the transient compensation component of the voltage on the rotor side of the doubly fed wind generator) naturally becomes 0, that is, the control method proposed in the present invention will not have an adverse effect on the control of the doubly fed wind generator system during normal operation. This fundamentally avoids the control method proposed in the present invention from causing a large switching shock to the system like most improved control methods, and it can be easily implemented in actual engineering applications.

[0122] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0123] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A LPF droop control method for a doubly-fed wind turbine generator based on transient component compensation, characterized in that: The following steps are involved: S1: Calculate the voltage drop depth on the stator side of the doubly-fed wind turbine generator; Calculate the time constant during transients; S2: based on the voltage drop depth and the time constant, obtaining the transient component of the stator-side flux of the doubly-fed wind generator; The transient component of the stator-side flux of the doubly-fed wind turbine generator is calculated based on the following formula: Among them, ψ sa represents the transient component of the stator-side flux of the doubly-fed wind turbine generator; h represents the voltage drop depth; U s|0| Indicates u s|0| The amplitude of s represents the stator side angular frequency of the doubly-fed wind turbine generator; T s represents the time constant; S3: Minimize the difference between the rotor-side current of the doubly-fed wind generator and its rated current under the premise of ensuring that the DC bus voltage is less than or equal to the DC bus voltage threshold, thereby determining the transient component compensation coefficient of the rotor-side voltage of the doubly-fed wind generator; wherein the DC bus voltage is obtained after the rotor-side voltage of the doubly-fed wind generator is rectified by a converter; The transient component compensation coefficient of the rotor side voltage of the doubly-fed wind turbine generator is calculated based on the following formula: Among them, K cmp represents the transient component compensation coefficient of the rotor side voltage of the doubly-fed wind turbine generator; K vir Represents the equivalent simulation coefficient; L r represents the rotor side inductance of the doubly-fed wind turbine generator; L m represents the mutual inductance between the rotor side and the stator side of the doubly-fed wind turbine generator; The equivalent simulation coefficient K is calculated based on the following formula vir : Among them, K vir Represents the equivalent simulation coefficient; M vt represents the mutual inductance between the stator and the simulated excitation winding of the doubly-fed wind turbine generator; L vt Represents the inductance of the simulated excitation winding; L vir represents the equivalent simulated inductance of the equivalent simulated synchronous generator; S4: obtaining a transient compensation component of the rotor side voltage of the doubly fed wind generator based on the transient component compensation coefficient of the rotor side voltage of the doubly fed wind generator and the transient component of the stator side flux of the doubly fed wind generator; The transient compensation component of the rotor side voltage of the doubly-fed wind turbine generator is calculated based on the following formula: Among them, u ra represents the transient compensation component of the rotor side voltage of the doubly-fed wind turbine generator; ψ sa represents the transient component of the stator-side flux of the doubly-fed wind turbine generator; K cmp represents the transient component compensation coefficient of the rotor side voltage of the doubly-fed wind turbine generator; K vir Represents the equivalent simulation coefficient; M vt represents the mutual inductance between the stator and the simulated excitation winding of the doubly-fed wind turbine generator; L vt Represents the inductance of the simulated excitation winding; L vir represents the equivalent simulated inductance of the equivalent simulated synchronous generator; L r represents the rotor side inductance of the doubly-fed wind turbine generator; L m Represents the mutual inductance between the rotor side and the stator side of the doubly-fed wind turbine generator; S5: superimposing the transient compensation component of the rotor side voltage of the doubly-fed wind turbine generator to the rotor voltage expected value output end of the reactive voltage control branch in the LPF droop control system.

2. The LPF droop control method of a doubly-fed wind turbine generator based on transient component compensation according to claim 1 is characterized in that: The voltage drop depth is calculated based on the following formula: Wherein, h represents the voltage drop depth; u s|0| Indicates the stator side voltage of the doubly-fed wind turbine generator before voltage drop occurs; u s Indicates the stator side voltage of the doubly-fed wind generator after a voltage drop occurs.

3. The LPF droop control method of a doubly-fed wind turbine generator based on transient component compensation according to claim 1 or 2, characterized in that: The time constant is calculated based on the following formula: Among them, T s represents the time constant, L s represents the stator side inductance of the doubly-fed wind turbine generator; R s Represents the stator side resistance of the doubly-fed wind turbine generator.

4. The LPF droop control method of a doubly-fed wind turbine generator based on transient component compensation according to claim 1 is characterized in that: The DC bus voltage threshold is 1.15 times the rated value of the DC bus voltage.

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