Harmonic suppression method and device for network-forming converter

Abstract

The invention provides a harmonic suppression method and device for a network-forming converter, and belongs to the field of power grids. The method comprises the following steps: acquiring a three-phase output voltage of a target converter, and determining a harmonic component according to the three-phase output voltage of the target converter; determining a first reference voltage correction value according to the harmonic component; correcting the target reference voltage according to the first reference voltage correction value to obtain a corrected target reference voltage; and inputting the corrected target reference voltage into a control loop, and controlling the target converter. According to the method, the target voltage reference value is adjusted according to the harmonic component, feedback is introduced, and the impedance of the grid-forming converter is equivalently reduced, so that the impedance of the power grid is equivalently increased, more harmonic current is absorbed by the grid-forming converter, and the quality of grid-side current is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power grids, and in particular to a harmonic suppression method and device for a grid-connected converter. Background Art

[0002] With global warming and environmental pollution, the power system dominated by fossil energy faces huge challenges. The gradual replacement of traditional energy with green and clean energy has become an inevitable trend in my country's energy development. At present, the grid-connected control of new energy sources such as wind power and photovoltaic power is mainly achieved through grid-following converters and grid-building converters. With the gradual increase in the installed capacity of new energy, the power system gradually presents the "three lows" characteristics of low inertia, weak damping, and low short-circuit ratio. The grid-building converter can provide damping and inertia for the system and has been widely used in grid-connected control.

[0003] When the inverter under grid control supplies power to the grid, it is often connected to a large number of nonlinear loads. These nonlinear loads can be regarded as harmonic sources that inject harmonics from the public connection point into the inverter and the grid, which will increase line losses, interfere with the normal operation of electronic instruments and communication systems, and may even cause circuit resonance and cause fires. Therefore, it is very important to suppress harmonics in grid-type inverters.

[0004] In the prior art, active power filters are usually used to eliminate harmonics, or the grid-connected converter is controlled to have a resistance characteristic at frequencies other than the fundamental wave, thereby bypassing the harmonic components. However, the effects of both methods when applied to grid-connected converter harmonic suppression are not very ideal. Summary of the invention

[0005] The embodiments of the present invention provide a harmonic suppression method and device for a grid-type converter, so as to solve the problem that the harmonic suppression method for a grid-type converter in the prior art has unsatisfactory effect.

[0006] In a first aspect, an embodiment of the present invention provides a harmonic suppression method for a grid-connected converter, comprising:

[0007] Obtaining a three-phase output voltage of a target converter, and determining harmonic components according to the three-phase output voltage of the target converter;

[0008] Determining a first reference voltage correction value according to the harmonic component;

[0009] Correcting the target reference voltage according to the first reference voltage correction value to obtain a corrected target reference voltage;

[0010] The corrected target reference voltage is input into the control loop to control the target converter.

[0011] In a second aspect, an embodiment of the present invention provides a harmonic suppression device for a grid-connected converter, comprising:

[0012] A harmonic component determination module, used to obtain the three-phase output voltage of the target converter and determine the harmonic component according to the three-phase output voltage of the target converter;

[0013] A first correction value determination module, used for determining a first reference voltage correction value according to a harmonic component;

[0014] A first correction module, used for correcting the target reference voltage according to the first reference voltage correction value to obtain a corrected target reference voltage;

[0015] The output control module is used to input the corrected target reference voltage into the control loop to control the target converter.

[0016] The embodiment of the present invention provides a harmonic suppression method and device for a grid-type converter. The harmonic suppression method for the above-mentioned grid-type converter includes: obtaining the three-phase output voltage of the target converter, and determining the harmonic component according to the three-phase output voltage of the target converter; determining a first reference voltage correction value according to the harmonic component; correcting the target reference voltage according to the first reference voltage correction value to obtain a corrected target reference voltage; inputting the corrected target reference voltage into a control loop to control the target converter. The embodiment of the present invention adjusts the target voltage reference value according to the harmonic component, introduces feedback, and equivalently reduces the impedance of the grid-type converter, thereby equivalently increasing the grid impedance, so that more harmonic currents will be absorbed by the grid-type converter, effectively improving the quality of the grid-side current. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, 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 some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 This is an application scenario diagram of a harmonic suppression method for a grid-connected converter provided by an embodiment of the present invention;

[0019] Figure 2 is a flow chart of a method for suppressing harmonics in a grid-connected converter provided by an embodiment of the present invention;

[0020] Figure 3 It is a schematic diagram of the principle of connecting a virtual negative impedance in series between a converter and a power grid provided by an embodiment of the present invention;

[0021] Figure 41 is a schematic diagram of a control loop of a grid-connected converter provided by an embodiment of the present invention;

[0022] Figure 5 This is a comparison diagram of the output impedance after and without impedance reshaping using the harmonic suppression method of the grid-type converter;

[0023] Figure 6 This is the grid-side current waveform before impedance reshaping;

[0024] Figure 7 It is a grid-side current waveform diagram after impedance reshaping by using the harmonic suppression method of the grid-type converter provided by the embodiment of the present invention;

[0025] Figure 8 It is a structural schematic diagram of a harmonic suppression device for a grid-connected converter provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0028] The grid-connected control of new energy sources such as wind power and photovoltaic power is mainly achieved through grid-following converters and grid-building converters. The grid-following converter is synchronized with the grid voltage through a phase-locked loop, and is connected to the grid using current control. It shows the characteristics of a "current source" to the outside, and is widely used because of its simple control structure and mature technology. The grid-building converter simulates the external characteristics of a traditional synchronous generator and shows the characteristics of a "voltage source" to the outside. The grid-building converter adjusts the grid-connected power by controlling the amplitude and phase of the output voltage on the AC side, and adopts a power synchronization strategy similar to that of a synchronous generator instead of relying on a phase-locked loop to achieve synchronization with the grid.

[0029] refer to Figure 1 When the inverter under grid-type control supplies power to the grid, it is often connected to a large number of nonlinear loads. These nonlinear loads can be regarded as harmonic sources that inject harmonics from the public connection point into the inverter and the grid, causing a significant impact on the power quality. When the grid contains a large number of harmonics, it will cause increased line losses and interfere with the normal operation of electronic instruments and communication systems. In severe cases, it may even cause circuit resonance and cause a fire.

[0030] However, in the prior art, source power filters can be used to eliminate harmonics. Based on the instantaneous reactive power theory, the harmonic components of the system can be detected, and the grid-connected converter can be controlled to emit a current with the opposite phase and equal amplitude. The grid-connected converter can also be controlled to have a resistance characteristic at frequencies other than the fundamental wave, thereby bypassing the harmonic components. However, the above methods are not ideal for suppressing harmonics.

[0031] See also Figure 1 and Figure 2 , Figure 1 An application scenario diagram of a harmonic suppression method for a grid-connected converter is shown; Figure 2 The following is a flowchart of a method for suppressing harmonics in a grid-connected converter according to an embodiment of the present invention, which is described in detail as follows:

[0032] The harmonic suppression method of the above-mentioned grid-connected converter comprises:

[0033] S101: Acquire a three-phase output voltage of a target converter, and determine a harmonic component according to the three-phase output voltage of the target converter;

[0034] S102: Determine a first reference voltage correction value according to the harmonic component;

[0035] S103: Correcting the target reference voltage according to the first reference voltage correction value to obtain a corrected target reference voltage;

[0036] S104: Input the corrected target reference voltage into the control loop to control the target converter.

[0037] For a grid-type converter, the nonlinear impedance is relatively large, resulting in relatively large harmonics. Since the grid impedance is difficult to increase under control, the output impedance of the grid-type converter can be equivalently reduced. When the output impedance of the grid-type converter is much smaller than the grid impedance, more harmonic components will be absorbed by the grid-type converter. Based on this, in an embodiment of the present invention, the harmonic components are first extracted, the target reference voltage is corrected based on the harmonic components, the grid-type converter is controlled based on the corrected target reference voltage, and the output impedance is reshaped so that more harmonics are absorbed by the grid-type converter, the harmonic components are reduced, and the power quality on the grid side is improved.

[0038] In a possible implementation manner, the first reference voltage correction value may include: a first d-axis voltage correction value and a first q-axis voltage correction value; S101 may include:

[0039] S1011: performing Park transformation on the three-phase output voltage of the target converter to obtain a voltage d-axis component and a voltage q-axis component;

[0040] S1012: Obtaining a first d-axis voltage correction value according to the voltage d-axis component;

[0041] S1013: Obtain a first q-axis voltage correction value according to the q-axis voltage component.

[0042] In the embodiment of the present invention, the three-phase output voltage (v ca 、v cb 、v cc ) and perform Park transformation. The specific transformation formula is as follows:

[0043]

[0044] Among them, v cd is the voltage d-axis component, v cq is the q-axis component of the voltage; ω is the fundamental angular frequency.

[0045] After Park transformation, the fundamental component of the current is transformed into a DC quantity, and the harmonic component is still an AC quantity. The result after Park transformation is filtered by a second-order low-pass filter to obtain the DC component, that is, the fundamental frequency component in the three-phase coordinate system. The formula is G LPF (s)v cd and G LPF (s)v cq ;

[0046] Among them, G LPF (s) is the transfer function of the second-order low-pass filter, G LPF The calculation formula of (s) is:

[0047]

[0048] Among them, f c is the cut-off frequency, ξ is the damping ratio, and s is the Laplace operator.

[0049] For example, the cut-off frequency f c It can be 10Hz and the damping ratio ξ can be 0.707.

[0050] Reuse cd and v cq Subtracting the above DC component, we can get the AC component, that is, the AC component is: [1-G LPF (s)]v cd and [1-G LPF (s)]v cq .

[0051] Based on the above, in the embodiment of the present invention, the AC component can be multiplied by the correction coefficient M for feedback, so as to proportionally adjust the output impedance of the grid-type converter and reshape the output impedance. Specifically as follows:

[0052] In a possible implementation, S1012 may include:

[0053] According to the voltage d-axis component, a first d-axis voltage correction value is obtained in combination with the first formula;

[0054] The first formula can be:

[0055] Δv dref1 =M[1-G LPF (s)]v cd

[0056]

[0057] S1013 may include:

[0058] According to the q-axis component of the voltage, a first q-axis voltage correction value is obtained in combination with the second formula;

[0059] The second formula can be:

[0060] Δv qref1 =M[1-G LPF (s)]v cq

[0061] Where Δv dref1 is the first d-axis voltage correction value, Δv qref1 is the first q-axis voltage correction value, M is the correction coefficient, v cd is the voltage d-axis component, v cq is the voltage q-axis component; G LPF (s) is the transfer function of the second-order low-pass filter, f c is the cut-off frequency, ξ is the damping ratio, and s is the Laplace operator.

[0062] Specifically, the value of the correction coefficient M can be set according to actual application requirements and is not specifically limited here.

[0063] In a possible implementation, the target reference voltage includes: a d-axis reference voltage and a q-axis reference voltage; the corrected target reference voltage includes: a corrected d-axis reference voltage and a corrected q-axis reference voltage; S103 may include:

[0064] S1031: subtracting the first d-axis voltage correction value from the d-axis reference voltage to obtain a corrected d-axis reference voltage;

[0065] S1032: Subtract the first q-axis voltage correction value from the q-axis reference voltage to obtain a corrected q-axis reference voltage.

[0066] When the harmonics are large, it is desired to reduce the output impedance of the grid-type converter so that the grid-type converter absorbs more harmonics. Therefore, in the embodiment of the present invention, the first reference voltage correction value is introduced into negative feedback to proportionally reduce the output impedance of the grid-type converter, reshape the output impedance, thereby absorbing harmonics and improving the power quality.

[0067] Based on the above, the d-axis and q-axis are symmetrical in the control. Taking the d-axis as an example, the output voltage of the grid-type converter can be expressed as follows according to the Thevenin theorem:

[0068] v cd =G close v dref -i gd Z o

[0069] Among them, G close (s) is the closed-loop transfer function of the control loop; v dref is the d-axis reference voltage, i gd is the d-axis component of the current, Z o (s) is the output impedance.

[0070] The power loop of the grid-type converter mainly affects the impedance characteristics at the fundamental frequency. Since the embodiments of the present invention mainly involve the impedance characteristics of the harmonic frequency band, the power loop can be ignored to calculate the equivalent output impedance of the grid-type converter. According to the topology and control strategy of the grid-type converter, its equivalent output impedance can be obtained as:

[0071]

[0072] Among them, s is the Laplace operator, L f is the filter inductor, r c is the parasitic resistance of the filter capacitor, C f is the filter capacitor, G v (s) is the voltage controller transfer function, G c (s) is the current controller transfer function, G d (s) is the sampling delay transfer function. G v (s), G c (s) and G d (s) can be expressed as

[0073]

[0074] Among them, k vp and k vi are the proportional coefficient and integral coefficient of the voltage controller, k cp and k ci are the proportional coefficient and integral coefficient of the current controller respectively; T sis the sampling time.

[0075] After introducing negative feedback using the above method, the output voltage of the grid-connected converter can be described as:

[0076] v cd =G close {v dref -M[1-G LPF (s)]v cd}-i gd Z o

[0077] Rearranging the above formula gives the reshaped output impedance:

[0078]

[0079] That is, at the harmonic frequency point, the output impedance of the grid-type converter is reshaped to the original 1 / (1+M), and the output impedance of the grid-type converter is proportionally reduced, so that the grid-type converter can bypass most of the harmonic components, and the harmonic suppression effect is good.

[0080] Furthermore, the embodiment of the present invention can also construct a virtual negative impedance on the output side of the grid-forming converter to equivalently increase the grid impedance. In order to connect a virtual negative impedance in series between the grid-forming converter and the grid, it can be reflected from the voltage drop on the virtual impedance. For details, refer to Figure 3 By subtracting the voltage drop on the virtual impedance from the target reference voltage of the grid-type converter, a new target reference voltage can be obtained, and the new target reference voltage contains information about the virtual impedance.

[0081] Specifically, the virtual impedance voltage is defined as the second reference voltage correction value. In a possible implementation manner, before S104, the method may further include:

[0082] S105: Acquire the three-phase output current of the target converter, and determine the second reference voltage correction value according to the three-phase output current of the target converter;

[0083] S106: updating the corrected target reference voltage according to the second reference voltage correction value.

[0084] In a possible implementation manner, the second reference voltage correction value includes: a second d-axis voltage correction value and a second q-axis voltage correction value; S105 may include:

[0085] S1051: Perform Park transformation on the three-phase output current of the target converter to obtain a current d-axis component and a current q-axis component;

[0086] S1052: Obtaining a second d-axis voltage correction value according to the d-axis component of the current;

[0087] S1053: Obtain a second q-axis voltage correction value according to the q-axis component of the current.

[0088] In the embodiment of the present invention, the three-phase output current (i ga 、i gb 、i gc ) and perform Park transformation. The specific transformation formula is as follows:

[0089]

[0090] Among them, i gd is the d-axis component of the current, i gq is the q-axis component of the current.

[0091] In a possible implementation, S1052 may include:

[0092] According to the d-axis component of the current, a second d-axis voltage correction value is obtained in combination with the third formula;

[0093] The third formula can be:

[0094] Δv dref2 =i gd Z v

[0095] S1053 may include:

[0096] According to the q-axis component of the current, the second q-axis voltage correction value is obtained by combining the fourth formula;

[0097] The fourth formula can be:

[0098] Δv qref2 =i gq Z v

[0099] Where Δv dref2 is the second d-axis voltage correction value, Δv qref2 is the second q-axis voltage correction value; i gd is the d-axis component of the current, i gq is the q-axis component of the current; Z v is the virtual impedance value.

[0100] In a possible implementation manner, the corrected target reference voltage includes: a corrected d-axis reference voltage and a corrected q-axis reference voltage; S106 may include:

[0101] S1061: subtract the second d-axis voltage correction value from the corrected d-axis reference voltage to obtain a new corrected d-axis reference voltage;

[0102] S1062: Subtract the second q-axis voltage correction value from the corrected q-axis reference voltage to obtain a new corrected q-axis reference voltage.

[0103] In the embodiment of the present invention, the voltage on the virtual impedance is used as feedback to further correct the target reference voltage.

[0104] After the introduction of virtual impedance feedback, the output voltage of the grid-connected converter can be further described as:

[0105] v cd =G close {v dref -i gd Z v -M[1-G LPF (s)]v cd}-i gd Z o

[0106] Rearranging the above formula gives the reshaped output impedance:

[0107]

[0108] Based on the above embodiments, the output impedance of the grid-type converter is further reduced, thereby better absorbing harmonics.

[0109] It can be seen from the above formula that the larger the parameter of the virtual impedance of the grid-type converter is, the smaller the impedance after being reshaped is, which is more conducive to the grid-type converter to absorb more harmonics; but when the virtual impedance parameter is larger, it will affect the stability of the system. Therefore, a larger virtual impedance value should be selected as much as possible under the premise of system stability.

[0110] In a possible implementation, the expression of the control loop may be:

[0111] v cd =G close (s){v dref -Δv dref2 -Δv dref1}-i gd Z o (s)

[0112] v cq =G close (s){v qref -Δv qref2 -Δv qref1}-i gq Z o (s)

[0113] Among them, v cd is the voltage d-axis component, v cq is the voltage q-axis component; Gclose (s) is the closed-loop transfer function of the control loop; v dref is the d-axis reference voltage, v qref is the q-axis reference voltage, Δv dref2 is the second d-axis voltage correction value, Δv qref2 is the second q-axis voltage correction value; Δv dref1 is the first d-axis voltage correction value, Δv qref1 is the first q-axis voltage correction value; i gd is the d-axis component of the current, i gq is the q-axis component of the current; Z o (s) is the output impedance.

[0114] The above method is described below in conjunction with specific embodiments.

[0115] Figure 4 The control loop diagram using both harmonic negative feedback and virtual impedance negative feedback is shown. Figure 4 After the control loop shown, Figure 5 It can be seen that, over a wider frequency band, the impedance of the grid-type converter is greatly reduced, which means that a large amount of harmonic current will flow into the grid-type converter with a smaller impedance.

[0116] Figure 6 Reshape the grid-side current waveform diagram before impedance; Figure 6 It can be seen that before impedance reshaping, when the system is polluted by harmonics, there are more harmonic currents on the grid side, the current distortion is larger, and the power quality is poor;

[0117] Figure 7 The grid-side current waveform after impedance reshaping. Figure 7 It can be seen that after the impedance is reshaped, more harmonic currents are absorbed by the grid-connected converter, and the current and power quality on the grid side is greatly improved.

[0118] Based on the above, it can be seen that the method provided by the embodiment of the present invention can effectively absorb harmonics and improve the power quality on the grid side.

[0119] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0120] The following is an embodiment of the device of the present invention. For details not described in detail therein, reference may be made to the corresponding method embodiment described above.

[0121] Figure 8The structure diagram of the harmonic suppression device of the grid-type converter provided by the embodiment of the present invention is shown. For the convenience of description, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0122] As shown in the figure, the harmonic suppression device of the grid-type converter includes:

[0123] A harmonic component determination module 21, used to obtain the three-phase output voltage of the target converter and determine the harmonic component according to the three-phase output voltage of the target converter;

[0124] A first correction value determination module 22, used to determine a first reference voltage correction value according to the harmonic component;

[0125] A first correction module 23, used to correct the target reference voltage according to the first reference voltage correction value to obtain a corrected target reference voltage;

[0126] The output control module 24 is used to input the corrected target reference voltage into the control loop to control the target converter.

[0127] In a possible implementation manner, the first reference voltage correction value includes: a first d-axis voltage correction value and a first q-axis voltage correction value; the harmonic component determination module 21 may:

[0128] A first conversion unit is used to perform Park transformation on the three-phase output voltage of the target converter to obtain a voltage d-axis component and a voltage q-axis component;

[0129] A first d-axis correction value calculation unit, used for obtaining a first d-axis voltage correction value according to a voltage d-axis component;

[0130] The first q-axis correction value calculation unit is used to obtain a first q-axis voltage correction value according to a q-axis voltage component.

[0131] In a possible implementation manner, the first d-axis correction value calculation unit may be specifically configured to: obtain the first d-axis voltage correction value according to the voltage d-axis component in combination with the first formula;

[0132] The first formula can be:

[0133] Δv dref1 =M[1-G LPF (s)]v cd

[0134]

[0135] The second q-axis correction value calculation unit may be specifically used to: obtain the first q-axis voltage correction value according to the voltage q-axis component in combination with the second formula;

[0136] The second formula can be:

[0137] Δv qref1 =M[1-G LPF (s)]v cq

[0138] Where Δv dref1 is the first d-axis voltage correction value, Δv qref1 is the first q-axis voltage correction value, M is the correction coefficient, v cd is the voltage d-axis component, v cq is the voltage q-axis component; G LPF (s) is the transfer function of the second-order low-pass filter, f c is the cut-off frequency, ξ is the damping ratio, and s is the Laplace operator.

[0139] In a possible implementation, the target reference voltage includes: a d-axis reference voltage and a q-axis reference voltage; the corrected target reference voltage includes: a corrected d-axis reference voltage and a corrected q-axis reference voltage; the first correction module 23 may include:

[0140] A first d-axis correction unit, used for subtracting the first d-axis voltage correction value from the d-axis reference voltage to obtain a corrected d-axis reference voltage;

[0141] The first q-axis correction unit is used for subtracting the first q-axis voltage correction value from the q-axis reference voltage to obtain a corrected q-axis reference voltage.

[0142] In a possible implementation manner, the above device may further include:

[0143] A second correction value determination module, used for obtaining a three-phase output current of a target converter and determining a second reference voltage correction value according to the three-phase output current of the target converter;

[0144] The second correction module is used to update the corrected target reference voltage according to the second reference voltage correction value.

[0145] In a possible implementation manner, the second reference voltage correction value includes: a second d-axis voltage correction value and a second q-axis voltage correction value; the second correction value determination module may include:

[0146] A second transformation unit is used to perform Park transformation on the three-phase output current of the target converter to obtain a current d-axis component and a current q-axis component;

[0147] A second d-axis correction value calculation unit, used for obtaining a second d-axis voltage correction value according to the current d-axis component;

[0148] The second q-axis correction value calculation unit is used to obtain a second q-axis voltage correction value according to the current q-axis component.

[0149] In a possible implementation manner, the second d-axis correction value calculation unit may be specifically used to: obtain the second d-axis voltage correction value according to the current d-axis component in combination with the third formula;

[0150] The third formula can be:

[0151] Δv dref2 =i gd Z v

[0152] The second q-axis correction value calculation unit may be specifically used to: obtain the second q-axis voltage correction value according to the current q-axis component in combination with the fourth formula;

[0153] The fourth formula can be:

[0154] Δv qref2 =i gq Z v

[0155] Where Δv dref2 is the second d-axis voltage correction value, Δv qref2 is the second q-axis voltage correction value; i gd is the d-axis component of the current, i gq is the q-axis component of the current; Z v is the virtual impedance value.

[0156] In a possible implementation manner, the corrected target reference voltage includes: a corrected d-axis reference voltage and a corrected q-axis reference voltage; the second correction module may include:

[0157] a second d-axis correction unit, configured to subtract a second d-axis voltage correction value from the corrected d-axis reference voltage to obtain a new corrected d-axis reference voltage;

[0158] The second q-axis correction unit is used to subtract the second q-axis voltage correction value from the corrected q-axis reference voltage to obtain a new corrected q-axis reference voltage.

[0159] In a possible implementation, the expression of the control loop may be:

[0160] v cd =G close (s){v dref -Δv dref2 -Δv dref1}-i gd Z o (s)

[0161] v cq =G close (s){v qref -Δvqref2 -Δv qref1}-i gq Z o (s)

[0162] Among them, v cd is the voltage d-axis component, v cq is the voltage q-axis component; G close (s) is the closed-loop transfer function of the control loop; Δv dref2 is the second d-axis voltage correction value, Δv qref2 is the second q-axis voltage correction value; Δv dref1 is the first d-axis voltage correction value, Δv qref1 is the first q-axis voltage correction value; i gd is the d-axis component of the current, i gq is the q-axis component of the current; Z o (s) is the output impedance.

[0163] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0164] Those of ordinary skill in the art will appreciate that the templates, units, and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0165] If the module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, it can implement the steps of the above-mentioned harmonic suppression method embodiments of each grid-type converter. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. Computer-readable media may include: any entity or device that can carry computer program code, recording media, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium.

[0166] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A method for suppressing harmonics in a grid-connected converter, characterized in that: include: Acquire a three-phase output voltage of a target converter, and determine a harmonic component according to the three-phase output voltage of the target converter; Determining a first reference voltage correction value according to the harmonic component; Correcting the target reference voltage according to the first reference voltage correction value to obtain a corrected target reference voltage; The corrected target reference voltage is input into a control loop to control the target converter.

2. The harmonic suppression method of a grid-connected converter according to claim 1, characterized in that: The first reference voltage correction value includes: a first d-axis voltage correction value and a first q-axis voltage correction value; the determining of the harmonic component according to the three-phase output voltage of the target converter includes: Performing Park transformation on the three-phase output voltage of the target converter to obtain a voltage d-axis component and a voltage q-axis component; Obtaining the first d-axis voltage correction value according to the voltage d-axis component; The first q-axis voltage correction value is obtained according to the voltage q-axis component.

3. The harmonic suppression method of a grid-connected converter according to claim 2, characterized in that: The obtaining the first d-axis voltage correction value according to the voltage d-axis component includes: According to the voltage d-axis component, combining with the first formula, obtain the first d-axis voltage correction value; The first formula is: Δv dref1 =M[1-G LPF (s)]v cd The step of obtaining the first q-axis voltage correction value according to the voltage q-axis component includes: According to the voltage q-axis component, combining with a second formula, obtain the first q-axis voltage correction value; The second formula is: Δv qref1 =M[1-G LPF (s)]v cq Where Δv dref1 is the first d-axis voltage correction value, Δv qref1 is the first q-axis voltage correction value, M is the correction coefficient, v cd is the voltage d-axis component, v cq is the voltage q-axis component; G LPF (s) is the transfer function of the second-order low-pass filter, f c is the cut-off frequency, ξ is the damping ratio, and s is the Laplace operator.

4. The harmonic suppression method of a grid-connected converter according to claim 3, characterized in that: The target reference voltage includes: a d-axis reference voltage and a q-axis reference voltage; the corrected target reference voltage includes: a corrected d-axis reference voltage and a corrected q-axis reference voltage; the correcting the target reference voltage according to the first reference voltage correction value to obtain the corrected target reference voltage includes: Subtracting the first d-axis voltage correction value from the d-axis reference voltage to obtain the corrected d-axis reference voltage; The first q-axis voltage correction value is subtracted from the q-axis reference voltage to obtain the corrected q-axis reference voltage.

5. The harmonic suppression method of a grid-connected converter according to any one of claims 2 to 4, characterized in that: Before inputting the modified target reference voltage into a control loop to control the target converter, the method further includes: Acquire the three-phase output current of the target converter, and determine the second reference voltage correction value according to the three-phase output current of the target converter; The corrected target reference voltage is updated according to the second reference voltage correction value.

6. The harmonic suppression method of a grid-connected converter according to claim 5, characterized in that: The second reference voltage correction value includes: a second d-axis voltage correction value and a second q-axis voltage correction value; and determining the second reference voltage correction value according to the three-phase output current of the target converter includes: Performing Park transformation on the three-phase output current of the target converter to obtain a current d-axis component and a current q-axis component; Obtaining the second d-axis voltage correction value according to the current d-axis component; The second q-axis voltage correction value is obtained according to the current q-axis component.

7. The harmonic suppression method of a grid-connected converter according to claim 6, characterized in that: The step of obtaining the second d-axis voltage correction value according to the current d-axis component includes: According to the current d-axis component, the second d-axis voltage correction value is obtained in combination with a third formula; The third formula is: Δv dref2 =i gd Z v The step of obtaining the second q-axis voltage correction value according to the current q-axis component includes: According to the current q-axis component, the second q-axis voltage correction value is obtained in combination with the fourth formula; The fourth formula is: Δv qref2 =i gq Z v Where Δv dref2 is the second d-axis voltage correction value, Δv qref2 is the second q-axis voltage correction value; i gd is the d-axis component of the current, i gq is the q-axis component of the current; Z v is the virtual impedance value.

8. The harmonic suppression method of a grid-connected converter according to claim 7, characterized in that: The corrected target reference voltage includes: a corrected d-axis reference voltage and a corrected q-axis reference voltage; and updating the corrected target reference voltage according to the second reference voltage correction value includes: Subtract the second d-axis voltage correction value from the corrected d-axis reference voltage to obtain a new corrected d-axis reference voltage; The second q-axis voltage correction value is subtracted from the corrected q-axis reference voltage to obtain a new corrected q-axis reference voltage.

9. The harmonic suppression method of a grid-connected converter according to claim 8, characterized in that: The expression of the control loop is: v cd =G close (s){v dref -Δv dref2 -Δv dref1 }-i gd Z o (s) v cq =G close (s){v qref -Δv qref2 -Δv qref1 }-i gq Z o (s) Among them, v cd is the voltage d-axis component, v cq is the voltage q-axis component; G close (s) is the closed-loop transfer function of the control loop; Δv dref2 is the second d-axis voltage correction value, Δv qref2 is the second q-axis voltage correction value; Δv dref1 is the first d-axis voltage correction value, Δv qref1 is the first q-axis voltage correction value; i gd is the d-axis component of the current, i gq is the q-axis component of the current; Z o (s) is the output impedance.

10. A harmonic suppression device for a grid-connected converter, characterized in that: include: A harmonic component determination module, used to obtain the three-phase output voltage of the target converter and determine the harmonic component according to the three-phase output voltage of the target converter; A first correction value determination module, used for determining a first reference voltage correction value according to the harmonic component; A first correction module, used for correcting the target reference voltage according to the first reference voltage correction value to obtain a corrected target reference voltage; The output control module is used to input the corrected target reference voltage into a control loop to control the target converter.

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