A method for suppressing current harmonics and DC current of wind turbines under excitation inrush current

Abstract

The present invention belongs to the technical field of power quality management, and discloses a method for suppressing current harmonics and DC of a wind turbine set under excitation inrush, comprising: suppressing current harmonics and DC of a grid-side converter and suppressing current harmonics and DC of a machine-side converter; the present invention suppresses current harmonics and DC of a doubly-fed wind turbine under excitation inrush by adopting a repetitive controller in combination with a resonant regulator, reduces the DC content and the content of each harmonic by using the high gain of the repetitive controller and the resonant regulator at each harmonic and DC frequency point, suppresses current harmonics and DC of a grid-side converter and a machine-side converter, keeps current harmonics and DC at a relatively low level during the entire process of excitation inrush injection, avoids affecting the power quality output by the doubly-fed wind turbine, and can well ensure the power quality output by the wind turbine.

Description

Technical Field

[0001] The invention relates to the technical field of power quality management, and in particular to a method for suppressing current harmonics and direct current of a wind turbine set under an excitation surge current. Background Art

[0002] In the field of cross-regional power transmission in the power industry, long-distance, large-capacity, ultra-high voltage transmission lines play an important role. Long-distance power transmission is inseparable from the widespread use of large-capacity power transformers. In addition to playing an important role in the power transmission and distribution links of the power system, the excitation inrush current generated when the transformer is closed at no load will also bring many negative effects to the power system.

[0003] Excitation inrush current refers to the overcurrent phenomenon that occurs when the transformer is connected to the power grid without load, and the excitation current increases sharply to dozens or even hundreds of times the normal excitation current due to core saturation. Excitation inrush current can cause voltage and current waveform distortion, leading to malfunction of relay protection devices, seriously affecting the safe and stable operation of the power system. In addition, the excitation inrush current also contains a high DC component and various harmonics, with the second harmonic being the main one. Its injection into the power grid will cause the voltage and current waveforms to contain a large number of harmonics and DC components.

[0004] Taking a doubly-fed wind turbine as an example, when the transformer is closed at no-load at a certain point on the line, an excitation surge current is generated, which enters the grid-side converter and the machine-side converter through the PCC point. This will cause the grid-side converter current and the machine-side stator current to contain higher DC quantities and harmonic components, causing serious pollution to the power quality of the wind turbine.

[0005] According to the above analysis, the excitation inrush current will cause the output current of the doubly fed wind turbine to contain a high amount of DC and harmonic components. However, most of the existing research focuses on the identification of the excitation inrush current. Many scholars have developed various methods for identifying the excitation inrush current and used them in the transformer differential protection to achieve the braking function to prevent the excitation inrush current from causing the transformer protection to malfunction. There are also some studies on the suppression of the excitation inrush current, which use traditional methods such as phase selection and closing, increasing the closing resistance, and various new methods to suppress the excitation inrush current. For the DC amount and harmonic components contained in the excitation inrush current, the existing research only stays at simple analysis and calculation, and there are few studies on the suppression of the output current harmonics and DC components of new energy units under the influence of the excitation inrush current. Summary of the invention

[0006] The technical problem to be solved by the present invention is that the excitation surge current will cause voltage and current waveform distortion and cause serious pollution to the power quality of the wind turbine. The purpose is to provide a method for suppressing current harmonics and DC quantities of a wind turbine set under excitation surge current, by suppressing current harmonics and DC quantities in the grid-side converter and the machine-side converter, so as to ensure the power quality of the wind turbine output.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for suppressing current harmonics and DC quantity of a wind turbine set under excitation inrush current, comprising: suppressing current harmonics and DC quantity of a grid-side converter and suppressing current harmonics and DC quantity of a machine-side converter;

[0009] Methods for suppressing current harmonics and DC of the grid-side converter include:

[0010] Obtain the current THD of the grid-side converter;

[0011] Obtaining a first input feedback value of a resonant regulator and a repetitive controller;

[0012] Lock the grid voltage fundamental frequency phase, and transform the voltage and current of the grid-side converter from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system;

[0013] Obtaining a d-axis command value of a grid-side converter voltage and a positive-sequence fundamental frequency component of a grid-side converter voltage;

[0014] Outputting a first compensation voltage component for suppressing each harmonic in the grid-side converter current;

[0015] Outputting a second compensation voltage component for suppressing a DC component in a current of a grid-side converter;

[0016] The grid-side converter is suppressed by using the grid-side converter voltage positive sequence fundamental frequency component, the first compensation voltage component, and the second compensation voltage component;

[0017] Methods for suppressing current harmonics and DC of the machine-side converter include:

[0018] Obtain the machine-side stator current THD;

[0019] obtaining a second input feedback value of the resonant regulator and the repetitive controller;

[0020] Lock the fundamental frequency phase of the stator voltage on the machine side, and transform the voltage and current of the stator and rotor from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system;

[0021] Obtain the positive sequence fundamental frequency component of the generator side rotor voltage;

[0022] Outputting the third compensation voltage component for suppressing each harmonic in the stator current on the machine side;

[0023] Outputting a fourth compensation voltage component for suppressing a DC component in a stator current on the machine side;

[0024] The machine-side converter is suppressed by the machine-side rotor voltage positive-sequence fundamental frequency component, the third compensation voltage component, and the fourth compensation voltage component.

[0025] Specifically, the method for obtaining the first output feedback value includes:

[0026] Obtain the grid-side converter current THD, and set the grid-side converter THD reference value and compensation coefficient;

[0027] The first output feedback value C gdq The calculation formula is: Among them, k1 is the compensation coefficient, I + gdq is the grid-side converter current in the dq coordinate system, U + gdq is the grid-side converter voltage in the dq coordinate system, THD g is the total harmonic distortion of the grid-side converter current, THD g * is the reference value of total harmonic distortion of the grid-side converter.

[0028] Specifically, the method for obtaining the first compensation voltage component includes:

[0029] The first output feedback value is filtered by a high-pass filter, and the transfer function is:

[0030] Among them, T s is the sampling period, z is the first output feedback value;

[0031] The filtered first output feedback value is input into the repetitive controller, and the first compensation voltage component is output through the repetitive controller. The transfer function is: Wherein, Q(z') is the set constant, N is the number of samples per unit time of the system, and z' is the first output feedback value after filtering;

[0032] The method for obtaining the second compensation voltage component includes:

[0033] The first output feedback value is input into the resonant regulator, and the second compensation voltage component is output through the resonant regulator. The transfer function is: ω r = -ω1, where K r is the gain coefficient, ω c is the bandwidth factor, ω r is the resonant frequency point, and ω1 is the synchronous rotation angular frequency.

[0034] Optionally, a d-axis command value of the grid-side converter voltage is obtained through a first PI regulator, and a positive-sequence fundamental frequency component of the grid-side converter voltage is obtained through a second PI regulator; and a grid voltage fundamental frequency phase is locked through a grid voltage phase-locked loop.

[0035] Specifically, the method for obtaining the second output feedback value includes:

[0036] Obtain the machine-side stator current THD, and set the machine-side stator THD reference value and compensation coefficient;

[0037] The second output feedback value C sdq The calculation formula is: in,

[0038] k2 is the compensation coefficient, I + sdq is the stator current in the dq coordinate system, U + sdq is the stator voltage in the dq coordinate system, THD s is the total harmonic distortion of the stator current, THD s * is the reference value of total harmonic distortion of stator current.

[0039] Specifically, the method for obtaining the third compensation voltage component includes:

[0040] The second output feedback value is filtered by a high-pass filter, and the transfer function is:

[0041] Among them, T s is the sampling period, f is the second output feedback value;

[0042] The filtered second output feedback value is input into the repetitive controller, and the third compensation voltage component is output through the repetitive controller. The transfer function is: Wherein, Q(f') is the set constant, N is the number of samples per unit time of the system, and f' is the second output feedback value after filtering;

[0043] The method for obtaining the fourth compensation voltage component includes:

[0044] The second output feedback value is input into the resonant regulator, and the second compensation voltage component is output through the resonant regulator. The transfer function is: ω r = -ω1, where K r is the gain coefficient, ω c is the bandwidth factor, ω r is the resonant frequency point, and ω1 is the synchronous rotation angular frequency.

[0045] Optionally, a positive-sequence fundamental frequency component of the machine-side rotor voltage is obtained through a third PI regulator; and a fundamental frequency phase of the machine-side stator voltage is locked through a stator voltage phase-locked loop.

[0046] A device for suppressing current harmonics and DC under excitation inrush, used to implement the above-mentioned method for suppressing current harmonics and DC under excitation inrush of a wind turbine generator set, the device comprising:

[0047] A first calculation module, which is used to calculate and obtain the current THD of the grid-side converter, the first input feedback value, the machine-side stator current THD and the second input feedback value;

[0048] The coordinate transformation module is used to transform the voltage and current of the grid-side converter from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system; and to transform the voltage and current of the stator and rotor from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system.

[0049] A terminal for suppressing current harmonics and DC amount under excitation inrush current comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of a method for suppressing current harmonics and DC amount of a wind turbine set under excitation inrush current are implemented as described above.

[0050] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the method for suppressing current harmonics and DC amount of a wind turbine set under an excitation inrush current are implemented as described above.

[0051] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0052] The present invention suppresses the current harmonics and DC amount of the doubly-fed wind turbine under the excitation surge current by adopting a method of cooperating with a repetitive controller and a resonant regulator, reduces the DC amount and the content of each harmonic by utilizing the high gain of the repetitive controller and the resonant regulator at each harmonic and DC frequency point, suppresses the current harmonics and DC amount of the grid-side converter and the machine-side converter, so that the current harmonics and DC amount are kept at a low level during the whole process of the excitation surge current injection, avoids affecting the power quality output by the doubly-fed wind turbine, and can well ensure the power quality output by the wind turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The accompanying drawings illustrate exemplary embodiments of the present invention and, together with the description thereof, are used to explain the principles of the present invention. These drawings are included to provide a further understanding of the present invention, and the accompanying drawings are included in and constitute a part of this specification and do not constitute a limitation of the embodiments of the present invention.

[0054] Figure 1 The invention discloses a control block diagram of a method for suppressing current harmonics and DC current of a wind turbine set under an excitation inrush current.

[0055] Figure 2 This is a structural diagram of a doubly-fed wind turbine selected according to the present invention.

[0056] Figure 3These are the voltage, current and DC bus voltage waveforms of the grid-side converter when no suppression measures are taken during the injection of the excitation surge current in the second embodiment.

[0057] Figure 4 It is the voltage, current and DC bus voltage waveform of the grid-side converter after adding the repetitive controller and the resonant regulator during the excitation inrush current injection in the second embodiment.

[0058] Figure 5 These are the waveforms of the stator voltage, current and electromagnetic torque on the machine side when the excitation surge current is injected without any suppression measures in the second embodiment.

[0059] Figure 6 It is the waveform of the stator voltage, current and electromagnetic torque on the machine side after adding the repetitive controller and the resonant regulator during the excitation surge current injection in the second embodiment. DETAILED DESCRIPTION

[0060] To make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and implementation methods. It is understood that the specific implementation methods described herein are only used to explain the relevant content, rather than to limit the present invention.

[0061] It should also be noted that, for the convenience of description, only the parts related to the present invention are shown in the drawings.

[0062] In the absence of conflict, the embodiments and features of the embodiments of the present invention may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0063] Figure 2 This is a structural diagram of a doubly-fed wind turbine applicable to the present invention, comprising a wind turbine, a gearbox, a grid-side converter, a machine-side converter, a DC bus, a power grid, a transformer, a line inductor, etc.

[0064] And provide a specific implementable parameters, specifically: grid voltage: 35kV; stator voltage: 1140V; wind turbine rated power: 3.45MW; line inductance: 0.35mH; DC bus capacitance: 8.1mF.

[0065] Embodiment 1

[0066] like Figure 1 As shown, this embodiment provides a method for suppressing current harmonics and DC of a wind turbine under excitation inrush current. The suppression strategies in this embodiment are based on a repetitive controller and a resonant regulator. The specific method includes:

[0067] (1) Methods for suppressing current harmonics and DC quantities of the grid-side converter.

[0068] The current harmonic and DC suppression strategy of the grid-side converter mainly includes the grid-side converter current THD calculation link, feedback quantity calculation link, grid voltage phase-locked loop, coordinate transformation link, fundamental frequency component calculation link, and compensation voltage component calculation link.

[0069] The compensation voltage component and fundamental frequency component output by the repetitive controller and the resonant regulator are added together, and the decoupling compensation term is added to finally obtain the voltage command value for PWM modulation. The grid-side converter is controlled by the voltage command value to achieve the purpose of suppressing current harmonics and DC.

[0070] (2) Methods for suppressing current harmonics and DC quantities of the machine-side converter.

[0071] The current harmonic and DC suppression strategy of the machine-side converter mainly includes the stator current THD calculation link, the feedback calculation link, the stator voltage phase-locked loop, the coordinate transformation link, the fundamental frequency component calculation link, and the compensation voltage component calculation link.

[0072] The compensation voltage component and fundamental frequency component output by the repetitive controller and the resonant regulator are added together, and the decoupling compensation term is added to finally obtain the rotor voltage command value to be modulated. The machine-side converter is controlled by the voltage command value to achieve the purpose of suppressing current harmonics and DC.

[0073] The specific methods for suppressing the current harmonics and DC of the grid-side converter include:

[0074] The first step is to obtain the current THD of the grid-side converter. In this embodiment, for convenience, the DC quantity of the grid-side converter is unified into THD. THD is the ratio of the root mean square value of the harmonic content in the periodic alternating current to the root mean square value of its fundamental component, which is obtained by calculation.

[0075] The second step is to obtain the first input feedback value of the resonant regulator and the repetitive controller. The specific method includes: the first output feedback value C gdq The calculation formula is: Wherein, k1 is the compensation coefficient (which is set in advance, in this embodiment, k1=0.5), I + gdq is the grid-side converter current in the dq coordinate system, U + gdq is the grid-side converter voltage in the dq coordinate system, THD g is the total harmonic distortion of the grid-side converter current, THD g * is the reference value of total harmonic distortion of the grid-side converter (set it in advance, taking into account the limitation of the suppression ability of the repetitive controller and the resonant regulator, THD g *Take about 10%).

[0076] Since the grid-side converter current THD is large when the excitation surge current is just injected, if the first input feedback value is selected as current at this time, the suppression effect of current harmonics and DC is not good. Therefore, we only partially suppress the current harmonics and DC at this time.

[0077] By introducing the compensation coefficient k1, the first input feedback value is set to a combination of current and voltage, which can suppress current harmonics and DC values ​​to a certain extent while taking into account the voltage of the grid-side converter.

[0078] After a period of time, under the dual effects of the repetitive controller and the resonant regulator as well as the attenuation of the excitation inrush current itself, the grid-side converter current THD is reduced to THD g * At this time, we select the first input feedback value as the grid-side converter current to completely suppress the current harmonics and DC values.

[0079] The third step is to lock the grid voltage fundamental frequency phase through the grid voltage phase-locked loop, and transform the voltage and current of the grid-side converter from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system;

[0080] In the fourth step, the d-axis command value of the grid-side converter voltage is obtained through the first PI regulator, and the positive-sequence fundamental frequency component of the grid-side converter voltage is obtained through the second PI regulator.

[0081] The fifth step is to output a first compensation voltage component for suppressing each harmonic in the grid-side converter current; the method for obtaining the first compensation voltage component includes:

[0082] The first output feedback value is filtered by a high-pass filter to reduce the gain of the repetitive controller at DC to reduce the impact on the fundamental frequency component. The transfer function is:

[0083] Among them, T s is the sampling period, z is the first output feedback value, and in this embodiment, T s =0.1ms, the cutoff frequency of the high-pass filter is 10Hz.

[0084] The filtered first output feedback value is input into the repetitive controller, and the first compensation voltage component is output through the repetitive controller. The transfer function is: Among them, Q(z') is a set constant, N is the number of samples per unit time of the system, and z' is the first output feedback value after filtering; Q(z') is to enhance the stability of the system so that the closed-loop pole of the system is within the unit circle, and is generally taken as a constant less than 1. In this embodiment, Q(z') = 0.95, N = 200.

[0085] Step 6: outputting a second compensation voltage component for suppressing the DC component in the grid-side converter current; the method for obtaining the second compensation voltage component includes:

[0086] The first output feedback value is input into the resonant regulator, and the second compensation voltage component is output through the resonant regulator. The transfer function is: ω r = -ω1, where K r is the gain coefficient, which can change the gain peak height of the resonant regulator; ω c is the bandwidth factor, which can change the gain peak width of the resonant regulator; ω r is the resonant frequency point. Since the DC component appears as a -50Hz component in the two-phase dq synchronous rotating coordinate system, the resonant frequency point ω r =-ω1, ω1 is the synchronous rotation angular frequency.

[0087] Step 7: Suppressing the grid-side converter by using the grid-side converter voltage positive sequence fundamental frequency component, the first compensation voltage component, and the second compensation voltage component;

[0088] The specific methods for suppressing the current harmonics and DC value of the machine-side converter include:

[0089] The first step is to obtain the machine-side stator current THD and unify the DC quantity of the machine-side converter into the THD.

[0090] The second step is to obtain the second input feedback value of the resonant regulator and the repetitive controller; the second output feedback value C sdq The calculation formula is: Among them, k2 is the compensation coefficient, I + sdq is the stator current in the dq coordinate system, U + sdq is the stator voltage in the dq coordinate system, THD s is the total harmonic distortion of the stator current, THD s * is the reference value of stator current total harmonic distortion.

[0091] Since the stator current THD is large when the excitation surge current is just injected, if the second input feedback value is selected as current, the suppression effect of current harmonics and DC is not good at this time. Therefore, we only partially suppress the current harmonics and DC at this time. By introducing the compensation coefficient k2, the second input feedback value is set to a combination of current and voltage. This can not only suppress the current harmonics and DC to a certain extent, but also take into account the voltage on the stator side.

[0092] The selection of the feedback value k2 of the machine-side converter is determined by referring to the grid-side converter, so that the stator current THD decays to the stator current total harmonic distortion reference value THD after the same time. s * .THD s * =THD g * =10%. After a period of time, under the dual effects of the repetitive controller, the resonant regulator and the excitation surge current attenuation, the stator current THD is reduced to THD s * At this time, we select the second input feedback value as the stator current to completely suppress the current harmonics and DC.

[0093] The third step is to lock the fundamental frequency phase of the stator voltage on the machine side through the stator voltage phase-locked loop, and transform the voltage and current of the stator and rotor from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system.

[0094] The fourth step is to obtain the positive sequence fundamental frequency component of the machine-side rotor voltage through the third PI regulator.

[0095] The fifth step is to output a third compensation voltage component for suppressing each harmonic in the stator current on the machine side; the method for obtaining the third compensation voltage component includes:

[0096] The second output feedback value is filtered by a high-pass filter to reduce the gain of the repetitive controller at DC to reduce the impact on the fundamental frequency component. The transfer function is:

[0097] Among them, T s is the sampling period, f is the second output feedback value; T s =0.1ms, the cutoff frequency of the high-pass filter is 10Hz.

[0098] The filtered second output feedback value is input into the repetitive controller, and the third compensation voltage component is output through the repetitive controller. The transfer function is: Among them, Q(f') is a set constant, N is the number of samples per unit time of the system, and f' is the second output feedback value after filtering; Q(f') is to enhance the stability of the system so that the closed-loop pole of the system is within the unit circle, and is generally taken as a constant less than 1. In this embodiment, Q(f') = 0.95, N = 200.

[0099] The sixth step is to output a fourth compensation voltage component for suppressing the DC component in the stator current on the machine side; the method for obtaining the fourth compensation voltage component includes:

[0100] The second output feedback value is input into the resonant regulator, and the second compensation voltage component is output through the resonant regulator. The transfer function is: ω r = -ω1, where K r is the gain coefficient, which can change the gain peak height of the resonant regulator; ω c is the bandwidth factor, which can change the gain peak width of the resonant regulator; ω r is the resonant frequency point. Since the DC component appears as a -50Hz component in the two-phase dq synchronous rotating coordinate system, the resonant frequency point ω r =-ω1, ω1 is the synchronous rotation angular frequency.

[0101] In the seventh step, the machine-side converter is suppressed by the machine-side rotor voltage positive sequence fundamental frequency component, the third compensation voltage component, and the fourth compensation voltage component.

[0102] Embodiment 2

[0103] In order to verify the effectiveness of the method for suppressing current harmonics and DC current proposed in Example 1, a simulation model based on the Matlab / Simulink platform is provided.

[0104] Figure 3 The voltage, current and DC bus voltage waveforms of the grid-side converter without any suppression measures when the excitation surge current is injected. At t=1s, the transformer is closed at no-load at a certain point on the line, and the excitation surge current enters the grid-side converter through the PCC point, causing the voltage and current of the grid-side converter to have various harmonics and DC components, and the DC bus voltage to have various harmonics.

[0105] The THD of the grid-side converter voltage is 3.97% at t=1.04s, decays to 3.08% at t=1.22s, and decays to 2.47% at t=1.38s; the THD of the grid-side converter current is 33.98% at t=1.04s, decays to 20.69% at t=1.22s, and decays to 14.46% at t=1.38s; the harmonic content of the DC bus voltage is 0.32% at t=1.04s, decays to 0.22% at t=1.22s, and decays to 0.18% at t=1.38s.

[0106] Figure 4 The voltage, current and DC bus voltage waveforms of the grid-side converter after adding the repetitive controller and resonant regulator during the injection of the excitation inrush current. At t=1s, since the excitation inrush current has just been injected, the THD of the grid-side converter current is large. At this time, if the feedback amount is set to current, the suppression effect of the current harmonics and DC amount is not good. Therefore, only partial suppression of the current harmonics is performed at this time, while taking into account the grid-side converter voltage, the input feedback value of the resonant regulator and the repetitive controller is set to a combination of current and voltage by introducing the compensation coefficient k1.

[0107] The k1 value of the grid-side converter is 0.5, so that after about 0.2s, after the action of the repetitive controller and the resonant regulator, plus the attenuation of the excitation surge current itself, the grid-side converter current is reduced to THD g * After adding the repetitive controller and the resonant regulator, at t = 1.04s, the grid-side converter voltage THD was reduced from 3.97% to 3.33%, the grid-side converter current THD was reduced from 33.98% to 26.76%, and the DC bus voltage harmonic content was reduced from 0.32% to 0.18%; at t = 1.22s, under the dual effects of the repetitive controller and the resonant regulator, plus the attenuation of the excitation surge current itself, the grid-side converter current THD dropped to 10.06%, close to THD g * At the same time, the grid-side converter voltage THD dropped to 2.55%, and the DC bus voltage harmonic content dropped to 0.13%.

[0108] At this time, the input feedback quantity of the repetitive controller and the resonant regulator is set to current to achieve complete suppression of current harmonics and DC quantities; at t=1.38s, the grid-side converter current THD is 1.94%, which is significantly lower than 14.46% without suppression measures, and the current waveform is greatly improved. At the same time, the DC bus voltage harmonic content is also reduced from the original 0.18% to 0.01%, the bus voltage is close to stable, and the grid-side converter voltage THD is almost unchanged at 2.47%.

[0109] Figure 5 The waveforms of the stator voltage, current and electromagnetic torque on the machine side when the excitation surge current is injected without any suppression measures. At t=1s, the transformer is closed at no-load at a certain point on the line, and the excitation surge current enters the machine side converter through the PCC point, causing the stator voltage and current of the machine side converter to have various harmonics and DC components, and the electromagnetic torque to have various harmonics. The THD of the stator voltage is 5.04% at t=1.04s, decays to 3.74% at t=1.22s, and decays to 2.97% at t=1.38s; the THD of the stator current is 39.07% at t=1.04s, decays to 28.97% at t=1.22s, and decays to 15.10% at t=1.38s; the harmonic content of the electromagnetic torque is 47.85% at t=1.04s, decays to 36.39% at t=1.22s, and decays to 22.94% at t=1.38s.

[0110] Figure 6The waveforms of the stator voltage, current and electromagnetic torque of the machine-side converter after adding the repetitive controller and resonant regulator when the excitation surge current is injected. At t=1s, since the excitation surge current has just been injected, the THD of the stator current of the machine-side converter is relatively large. At this time, setting the feedback amount to current is not very effective in suppressing current harmonics and DC quantities. Therefore, we only partially suppress the current harmonics at this time, while taking into account the stator voltage. By introducing the compensation coefficient k2, the input feedback value of the repetitive controller and the resonant regulator is set to a combination of current and voltage. The selection of the k2 value of the machine-side converter refers to the grid-side converter. The selection is based on the fact that after the same period of time, the THD of the stator current decays to the reference value THD of the stator current total harmonic distortion. s * After comparing different k2 values, we finally chose k2 = 0.7, which can reduce the stator current THD to THD after about 0.2s, after the repeated action of the controller and the resonant regulator, plus the attenuation of the excitation inrush current itself. s * about.

[0111] After adding the repetitive controller and the resonant regulator, at t=1.04s, the stator voltage THD was reduced from 5.04% to 3.95%, and the stator current THD was reduced from 39.07% to 20.89%. At the same time, the electromagnetic torque harmonic content was also reduced to a certain extent, from 47.85% to 31.56%. At t=1.22s, under the dual effects of the repetitive controller and the resonant regulator, coupled with the attenuation of the excitation surge current itself, the stator current THD dropped to 10.19%, close to the THD s * At the same time, the stator voltage THD dropped to 2.84%, and the electromagnetic torque harmonic content dropped to 15.48%. At this time, the input feedback of the repetitive controller and the resonant regulator is set to current to achieve complete suppression of current harmonics and DC quantities; at t = 1.38s, the stator current THD is 1.15%, which is significantly reduced compared to 15.10% without suppression measures. The current waveform is greatly improved, and the electromagnetic torque pulsation amplitude is also greatly reduced from the original 22.94% to 1.86%. The electromagnetic torque is close to stable, while the stator voltage THD is almost unchanged at 2.97%.

[0112] Embodiment 3

[0113] A device for suppressing current harmonics and DC amount under excitation inrush is used to implement a method for suppressing current harmonics and DC amount of a wind turbine set under excitation inrush as described above. The device comprises a first calculation module and a coordinate transformation module.

[0114] The first calculation module is used to calculate and obtain the current THD of the grid-side converter, the first input feedback value, the machine-side stator current THD and the second input feedback value;

[0115] The coordinate transformation module is used to transform the voltage and current of the grid-side converter from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system; and to transform the voltage and current of the stator and rotor from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system.

[0116] That is, the components of the grid-side converter and the machine-side converter can be controlled by the same set of modules. The modules in this embodiment can be multiple independent modules or multiple processing programs in one module.

[0117] Embodiment 4

[0118] A terminal for suppressing current harmonics and DC amount under excitation inrush current comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of a method for suppressing current harmonics and DC amount of a wind turbine set under excitation inrush current as described above are implemented.

[0119] The memory can be used to store software programs and modules. The processor executes various functional applications and data processing of the terminal by running the software programs and modules stored in the memory. The memory can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, an execution program required for at least one function, etc.

[0120] The data storage area can store data created according to the use of the terminal, etc. In addition, the memory may include a high-speed random access memory, and may also include a non-volatile memory, such as at least one disk storage device, a flash memory device, or other volatile solid-state storage devices.

[0121] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of a method for suppressing current harmonics and DC current of a wind turbine set under an excitation inrush current as described above.

[0122] Without loss of generality, computer readable media may include computer storage media and communication media. Computer storage media include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information such as computer readable instruction data structures, program modules or other data. Computer storage media include RAM, ROM, EPROM, EEPROM, flash memory or other solid-state storage technology, CD-ROM, DVD or other optical storage, cassettes, magnetic tapes, disk storage or other magnetic storage devices. Of course, those skilled in the art will appreciate that computer storage media are not limited to the above. The above-mentioned system memory and mass storage devices can be collectively referred to as memory.

[0123] In the description of this specification, the description with reference to the terms "one embodiment / method", "some embodiments / methods", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment / method or example are included in at least one embodiment / method or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment / method or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments / methods or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments / methods or examples described in this specification and the features of the different embodiments / methods or examples, unless they are contradictory.

[0124] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0125] It should be understood by those skilled in the art that the above embodiments are only for the purpose of clearly illustrating the present invention, and are not intended to limit the scope of the present invention. For those skilled in the art, other changes or modifications may be made based on the above invention, and these changes or modifications are still within the scope of the present invention.

Claims

1. A method for suppressing current harmonics and DC of a wind turbine under excitation inrush current, characterized in that: include: Suppression of current harmonics and DC quantity of the grid-side converter and suppression of current harmonics and DC quantity of the machine-side converter; Methods for suppressing current harmonics and DC of the grid-side converter include: Obtain the current THD of the grid-side converter; Obtaining a first input feedback value of a resonant regulator and a repetitive controller; Lock the grid voltage fundamental frequency phase, and transform the voltage and current of the grid-side converter from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system; Obtaining a d-axis command value of a grid-side converter voltage and a positive-sequence fundamental frequency component of a grid-side converter voltage; Outputting a first compensation voltage component for suppressing each harmonic in the grid-side converter current; Outputting a second compensation voltage component for suppressing a DC component in a current of a grid-side converter; The grid-side converter is suppressed by using the grid-side converter voltage positive sequence fundamental frequency component, the first compensation voltage component, and the second compensation voltage component; Methods for suppressing current harmonics and DC of the machine-side converter include: Obtain the machine-side stator current THD; obtaining a second input feedback value of the resonant regulator and the repetitive controller; Lock the fundamental frequency phase of the stator voltage on the machine side, and transform the voltage and current of the stator and rotor from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system; Obtain the positive sequence fundamental frequency component of the generator side rotor voltage; Outputting the third compensation voltage component for suppressing each harmonic in the stator current on the machine side; Outputting a fourth compensation voltage component for suppressing a DC component in a stator current on the machine side; The machine-side converter is suppressed by the machine-side rotor voltage positive-sequence fundamental frequency component, the third compensation voltage component, and the fourth compensation voltage component.

2. The method for suppressing current harmonics and DC of a wind turbine generator set under excitation inrush current according to claim 1, characterized in that: The method for obtaining the first output feedback value includes: Obtain the grid-side converter current THD, and set the grid-side converter THD reference value and compensation coefficient; The first output feedback value C gdq The calculation formula is: Among them, k1 is the compensation coefficient, I + gdq is the grid-side converter current in the dq coordinate system, U + gdq is the grid-side converter voltage in the dq coordinate system, THD g is the total harmonic distortion of the grid-side converter current, THD g * is the reference value of total harmonic distortion of the grid-side converter.

3. The method for suppressing current harmonics and DC of a wind turbine generator set under excitation inrush current according to claim 2, characterized in that: The method for obtaining the first compensation voltage component includes: The first output feedback value is filtered by a high-pass filter, and the transfer function is: Among them, T s is the sampling period, z is the first output feedback value; The filtered first output feedback value is input into the repetitive controller, and the first compensation voltage component is output through the repetitive controller. The transfer function is: Wherein, Q(z') is the set constant, N is the number of samples per unit time of the system, and z' is the first output feedback value after filtering; The method for obtaining the second compensation voltage component includes: The first output feedback value is input into the resonant regulator, and the second compensation voltage component is output through the resonant regulator. The transfer function is: ω r = -ω1, where K r is the gain coefficient, ω c is the bandwidth factor, ω r is the resonant frequency point, and ω1 is the synchronous rotation angular frequency.

4. The method for suppressing current harmonics and DC of a wind turbine generator set under excitation inrush current according to claim 2, characterized in that: The grid-side converter voltage d-axis command value is obtained through the first PI regulator, and the grid-side converter voltage positive sequence fundamental frequency component is obtained through the second PI regulator; the grid voltage fundamental frequency phase is locked through the grid voltage phase-locked loop.

5. The method for suppressing current harmonics and DC of a wind turbine generator set under excitation inrush current according to claim 1, characterized in that: The method for obtaining the second output feedback value includes: Obtain the machine-side stator current THD, and set the machine-side stator THD reference value and compensation coefficient; The second output feedback value C sdq The calculation formula is: in, k2 is the compensation coefficient, I + sdq is the stator current in the dq coordinate system, U + sdq is the stator voltage in the dq coordinate system, THD s is the total harmonic distortion of the stator current, THD s * is the reference value of total harmonic distortion of stator current.

6. The method for suppressing current harmonics and DC of a wind turbine generator set under excitation inrush current according to claim 5, characterized in that: The method for obtaining the third compensation voltage component includes: The second output feedback value is filtered by a high-pass filter, and the transfer function is: Among them, T s is the sampling period, f is the second output feedback value; The filtered second output feedback value is input into the repetitive controller, and the third compensation voltage component is output through the repetitive controller. The transfer function is: Wherein, Q(f') is the set constant, N is the number of samples per unit time of the system, and f' is the second output feedback value after filtering; The method for obtaining the fourth compensation voltage component includes: The second output feedback value is input into the resonant regulator, and the second compensation voltage component is output through the resonant regulator. The transfer function is: ω r = -ω1, where K r is the gain coefficient, ω c is the bandwidth factor, ω r is the resonant frequency point, and ω1 is the synchronous rotation angular frequency.

7. The method for suppressing current harmonics and DC of a wind turbine generator set under excitation inrush current according to claim 2, characterized in that: The positive sequence fundamental frequency component of the machine-side rotor voltage is obtained through the third PI regulator; the fundamental frequency phase of the machine-side stator voltage is locked through the stator voltage phase-locked loop.

8. A device for suppressing current harmonics and DC current under excitation inrush, characterized in that: A method for suppressing current harmonics and DC current of a wind turbine set under an excitation inrush current according to any one of claims 1 to 7, the device comprising: A first calculation module, which is used to calculate and obtain the current THD of the grid-side converter, the first input feedback value, the machine-side stator current THD and the second input feedback value; The coordinate transformation module is used to transform the voltage and current of the grid-side converter from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system; and to transform the voltage and current of the stator and rotor from the three-phase abc stationary coordinate system to the two-phase dq synchronous rotating coordinate system.

9. A terminal for suppressing current harmonics and DC current under excitation inrush, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of a method for suppressing current harmonics and DC current of a wind turbine set under an excitation inrush current are implemented as described in any one of claims 1-7.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of a method for suppressing current harmonics and DC current of a wind turbine set under an excitation inrush current are implemented as described in any one of claims 1 to 7.

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