GFM Control Method, System, Medium and Device for Active Harmonic Suppression

Abstract

The present invention relates to the technical field of power systems, and provides a GFM control method, system, medium and device for active harmonic suppression. The GFM control method for active harmonic suppression includes: selecting the harmonic current frequencies to be suppressed, superimposing a GFM harmonic voltage source with a fixed amplitude gain and a fixed phase angle on the voltage outer loop control command, and determining the optimal compensation phase according to the PCC harmonic voltage amplitude curve in the voltage vector optimization process and iterative calculation; separating the harmonic voltage components at the harmonic current frequencies to be suppressed based on the acquired PCC voltage sampling data and GFM output current data of the GFM access node, so as to construct a virtual harmonic impedance at the harmonic current frequencies to be suppressed; determining the amplitude range of the virtual harmonic impedance under the multiple constraints of the GFM stability region and the modulation voltage limit; determining the optimal gain of the virtual harmonic impedance within the GFM stability region. It can effectively reduce the harmonic current content of the GFM connected to the power grid.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular, to a GFM control method, system, medium and device for active harmonic suppression. Background Technique

[0002] The statements in this part only provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] The typical control modes of renewable energy can be divided into two categories: Grid-following (GFL) and Grid-forming (GFM). GFL converters have been applied earlier and the technology is relatively mature. The prerequisite for their stable operation is to obtain the accurate grid phase through a phase-locked loop. Therefore, when a GFL converter is connected to a weak grid in a remote area or the end of a distribution network, it is difficult to track the grid phase and thus the waveform quality cannot be guaranteed. Compared with GFL, GFM has the characteristics of a voltage source rather than a current source. Therefore, GFM has stronger support ability and greater harmonic suppression potential in a distorted grid.

[0004] Currently, the research on GFM mainly focuses on its dynamic characteristics, inertia and damping, etc. In a few studies on using GFM to participate in grid harmonic improvement, the method of collaborative control of active and passive means is usually adopted. The impedance regulation technology realizes the suppression of harmonic current in a distorted grid by increasing the harmonic equivalent impedance; the shunt admittance can make GFM exhibit similar characteristics to an active power filter, so as to absorb more harmonics in the grid. The inventor found that the self-control of GFM must face the dilemma of choosing between the above two directions, and additional passive impedance needs to be added to improve the unconsidered harmonic components. At present, there is no method that only relies on the active control of GFM to achieve stable suppression of grid-connected point harmonics in a distorted grid. Summary of the Invention

[0005] In order to solve the technical problems existing in the above background technique, the present invention provides a GFM control method, system, medium and device for active harmonic suppression, realizing the transformation of the harmonic suppression in a distorted grid from the current situation of collaborative control of GFM control and passive impedance to the improvement of the grid-connected point harmonic problem completely supported by GFM independently.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The first aspect of the present invention provides a GFM control method for active harmonic suppression.

[0008] A GFM control method for active harmonic suppression includes:

[0009] Select the harmonic current frequencies to be suppressed, superimpose a GFM harmonic voltage source with a fixed amplitude gain and a fixed phase angle on the voltage outer-loop control command, and determine the optimal compensation phase based on the PCC harmonic voltage amplitude curve in the voltage vector optimization process and iterative calculation;

[0010] According to the PCC voltage sampling data and GFM output current data of the obtained GFM access node, separate the harmonic voltage components at the harmonic current frequencies to be suppressed to construct a virtual harmonic impedance at the harmonic current frequencies to be suppressed; under the multiple constraints of the GFM stability region and modulation voltage limit, determine the amplitude range of the virtual harmonic impedance; keep the optimal compensation phase unchanged, and determine the optimal gain of the virtual harmonic impedance within the GFM stability region within the amplitude range of the virtual harmonic impedance.

[0011] Further, the method for determining the optimal compensation phase based on the compensation voltage vector optimization process and the PCC harmonic voltage amplitude curve in the iterative calculation includes:

[0012] Keep the fixed amplitude gain unchanged, iterate the phase angle from 0 degrees to 360 degrees in a certain step, and record the PCC point harmonic voltage amplitude after each phase angle change, record the phase angle corresponding to the maximum PCC point harmonic voltage and the phase angle corresponding to the minimum value during the vector optimization process;

[0013] Take the phase angle corresponding to the maximum PCC point harmonic voltage as the input of the voltage command, increase the amplitude gain of the constructed GFM harmonic voltage source, and finally reduce the harmonic voltage at the corresponding frequency of the PCC point to zero, and record the amplitude gain corresponding to the reduction of the PCC point harmonic voltage to zero;

[0014] Aggregate all non-GFM devices connected to the PCC point into an equivalent harmonic Norton model, rely on Kirchhoff's voltage law and superposition theorem, and combine the proportional relationship between the fixed amplitude gain and the amplitude gain corresponding to the reduction of the PCC point harmonic voltage to zero, that is, the PCC point harmonic voltage amplitudes under the two gains, to obtain the optimal compensation phase of the GFM harmonic voltage source.

[0015] Further, the method for determining the amplitude range of the virtual harmonic impedance under the multiple constraints of the GFM stability region and modulation voltage limit includes: under the constraint of the GFM stability region, determine the upper limit of the amplitude of the virtual harmonic impedance, and the constraint of the GFM stability region is expressed by the following formula:

[0016]

[0017] Where Z vir ( s ) represents the virtual impedance transfer function to be injected, H i ( s) represents the transfer function of the current inner loop, C represents the filtering capacitor of the LCL filter, s represents the operation symbol in the discrete domain. M(s) represents an intermediate variable without physical meaning, R represents the resistance, L 1 and L 2 both represent the inductor parameters of the GFM converter filter, ω represents the grid angular frequency, h represents the harmonic order.

[0018] Further, under the multiple constraints of the GFM stability region and the modulation voltage limit, determining the amplitude range of the virtual harmonic impedance; the method further includes: under the constraint of the modulation voltage limit, determining the lower limit of the amplitude of the virtual harmonic impedance, and the constraint of the modulation voltage limit is represented by the following formula:

[0019]

[0020] where, Z vir ( s ) is the virtual impedance transfer function to be injected, I oh is the amplitude of the harmonic current output by the GFM, u m is the amplitude of the current modulation voltage, M is the modulation voltage limit, H i ( s ) represents the transfer function of the current inner loop, ω represents the grid angular frequency, h represents the harmonic order.

[0021] Further, keeping the optimal compensation phase unchanged, within the amplitude range of the virtual harmonic impedance, determining the optimal gain of the virtual harmonic impedance within the GFM stability region; the method includes: keeping the optimal compensation phase unchanged, within the amplitude range of the virtual harmonic impedance, making the amplitude gain of the virtual impedance at the frequency of the harmonic current to be suppressed increase iteratively from zero in a certain step, and at the same time recording the harmonic voltage amplitude at the PCC point after each iteration. When the harmonic voltage amplitude at the PCC point shows an inflection point, it is considered that the virtual impedance amplitude gain has obtained the optimal gain that should be obtained theoretically. If no inflection point appears after reaching the limit, stop the iteration and consider that the virtual impedance amplitude gain has obtained the optimal gain of the virtual harmonic impedance within the stability region.

[0022] Further, the optimal compensation phase is represented by the following formula:

[0023]

[0024] where,θ hc represents the optimal compensation phase, θ gh for the distorted power grid h phase angle of the h - th harmonic voltage, Δ θ h is the phase - angle error between the GFM voltage command and the actually constructed GFM harmonic voltage source, θ pcch is the PCC point h phase angle of the h - th harmonic voltage, θ h1 represents the input phase angle at which the h - th harmonic voltage of the PCC takes the maximum value, θ oh represents the h phase angle of the h - th harmonic output impedance of the GFM.

[0025] Furthermore, the method of selecting the harmonic - current frequency to be suppressed includes: determining the frequency and phase - angle information of the grid harmonic voltage according to the historical data of the low - voltage side of the transformer where the GFM is connected to the grid or the short - time recorded - wave analysis result, and selecting the harmonic - current frequency to be suppressed.

[0026] The second aspect of the present invention provides a GFM control system for active harmonic suppression.

[0027] A GFM control system for active harmonic suppression includes:

[0028] A phase - compensation module, which is configured to: select the harmonic - current frequency to be suppressed, superimpose a GFM harmonic voltage source with a fixed amplitude gain and a fixed phase angle on the voltage - outer - loop control command, and determine the optimal compensation phase according to the PCC harmonic - voltage amplitude curve in the voltage - vector optimization process and the iterative calculation;

[0029] A virtual - harmonic - impedance optimal - gain module, which is configured to: separate the harmonic - voltage component at the harmonic - current frequency to be suppressed according to the PCC voltage sampling data and the GFM output - current data obtained at the GFM - connected node, so as to construct the virtual harmonic impedance at the harmonic - current frequency to be suppressed; determine the amplitude range of the virtual harmonic impedance under the multiple constraints of the GFM stable region and the modulation - voltage limit; keep the optimal compensation phase unchanged, and determine the optimal gain of the virtual harmonic impedance within the GFM stable region within the amplitude range of the virtual harmonic impedance.

[0030] The third aspect of the present invention provides a computer - readable storage medium.

[0031] A computer - readable storage medium, on which a computer program is stored, and when the program is executed by a processor, it implements the steps in the GFM control method for active harmonic suppression as described in the first aspect above.

[0032] The fourth aspect of the present invention provides a computer device.

[0033] A computer device includes a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, it implements the steps in the GFM control method for harmonic active suppression described in the first aspect above.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] The present invention provides a GFM control method, system, medium, and device for harmonic active suppression, which breaks through the practical problem in traditional methods that a passive impedance must be added on the basis of GFM control improvement, realizes the core function of GFM independently improving grid-connected harmonic current, can actively support harmonic current for any distorted grid scenario, and has strong adaptability and versatility in high-proportion power electronic distribution system scenarios.

[0036] The present invention does not require adding any passive components on the low-voltage side of the transformer, nor does it require adding an additional new sampling module. On the premise of aggregating other disturbance sources connected to the PCC into a harmonic Norton model, the optimal compensation voltage phase can be determined through the superposition theorem and vector optimization, and then the optimal compensation voltage amplitude can be determined by observing the harmonic voltage inflection point of the PCC, thereby minimizing the impact of the distorted grid on the GFM.

[0037] By analyzing the stability domain and modulation ability limit of the GFM control system, the present invention can clarify the GFM frequency-domain variation range under multiple constraints. Reducing the harmonic frequency impedance to be suppressed to the lowest within this range can make more harmonics flow from the PCC to the GFM, so the harmonics flowing from the PCC to the grid will be effectively reduced. In the current scenario of voltage distortion in the distribution system, it fills the technical gap that the GFM can fully independently and actively participate in harmonic suppression at the grid connection point. The method has stronger robustness and stability than traditional methods and is suitable for different types of new energy grid connection scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0039] Figure 1 is a flowchart of the GFM control method for harmonic active suppression in Embodiment 1 shown in the present invention;

[0040] Figure 2 is a flowchart of a grid harmonic voltage compensation control method based on GFM under the condition of no grid-side sampling in Embodiment 1 shown in the present invention;

[0041] Figure 3 It is the equivalent circuit diagram of the harmonic impedance equivalent model of the GFM converter in Embodiment 1 shown by the present invention under PCC;

[0042] Figure 4 It is the equivalent circuit diagram of the GFM grid-connected system considering the disturbance source in Embodiment 1 shown by the present invention;

[0043] Figure 5 It is the equivalent circuit diagram of the GFM grid-connected system considering compensation in Embodiment 1 shown by the present invention;

[0044] Figure 6 It is the equivalent circuit diagram of the GFM grid-connected system considering virtual impedance in Embodiment 1 shown by the present invention;

[0045] Figure 7 It is the structural diagram of the GFM control system for active harmonic suppression in Embodiment 2 shown by the present invention. Detailed implementation manners

[0046] The present invention will be further described below in conjunction with the drawings and embodiments.

[0047] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further descriptions of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0048] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0049] It should be noted that the flowcharts and block diagrams in the accompanying drawings illustrate the possible architectures, functions, and operations of the methods and systems according to various embodiments of the present disclosure. It should be noted that each block in the flowchart or block diagram may represent a module, a program segment, or a part of code, and the module, the program segment, or the part of code may include one or more executable instructions for implementing the logical functions specified in the respective embodiments. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order from that marked in the accompanying drawings. For example, two consecutively represented blocks may actually be executed substantially in parallel, or they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the flowchart and / or block diagram, as well as the combinations of blocks in the flowchart and / or block diagram, may be implemented using a dedicated hardware-based system for performing the specified functions or operations, or may be implemented using a combination of dedicated hardware and computer instructions.

[0050] Embodiment 1

[0051] As Figure 1 shown, this embodiment provides a GFM control method for active harmonic suppression. This embodiment takes the application of this method to a server as an example for illustration. It can be understood that this method can also be applied to a terminal, and can also be applied to a system including a terminal and a server, and is implemented through the interaction between the terminal and the server. The server can be an independent physical server, or a server cluster or distributed system composed of multiple physical servers, or a cloud server providing basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, web servers, cloud communications, middleware services, domain name services, security services CDN, and big data and artificial intelligence platforms. The terminal can be a smart phone, a tablet computer, a laptop computer, a desktop computer, etc., but is not limited thereto. The terminal and the server can be directly or indirectly connected through wired or wireless communication methods, and this application does not limit this. In this embodiment, the method includes the following steps:

[0052] Step 1: Select the harmonic current frequencies to be suppressed, superimpose a GFM harmonic voltage source with a fixed amplitude gain and a fixed phase angle on the voltage outer loop control command, and determine the optimal compensation phase based on the PCC harmonic voltage amplitude curve in the voltage vector optimization process and the iterative calculation.

[0053] Step 2: According to the obtained PCC voltage sampling data and GFM output current data of the GFM access node, separate the harmonic voltage components at the harmonic current frequencies to be suppressed, so as to construct the virtual harmonic impedance at the harmonic current frequencies to be suppressed; under the multiple constraints of the GFM stability domain and the modulation voltage limit, determine the amplitude range of the virtual harmonic impedance; keep the optimal compensation phase unchanged, and within the amplitude range of the virtual harmonic impedance, determine the best gain of the virtual harmonic impedance within the GFM stability domain.

[0054] The present invention provides a GFM control method, system, medium and device for active harmonic suppression. By using a GFM-based grid harmonic voltage compensation control method under the condition of no grid-side sampling, other devices at the grid connection point are equivalent to a Norton harmonic model. The model parameters are determined by harmonic voltage vector optimization and the optimal compensation phase is designed. Furthermore, a harmonic virtual impedance for weakening the GFM harmonic internal impedance is constructed. By using a harmonic virtual impedance tuning method considering the control stability domain, the optimal compensation voltage amplitude is determined. The two cooperate with each other to effectively reduce the harmonic current content at the grid connection point where the GFM is connected to the grid.

[0055] In some embodiments, as Figure 2 shown, the implementation steps of the said Step 1 (using a GFM-based grid harmonic voltage compensation control method under the condition of no grid-side sampling) include:

[0056] (1) Determine the harmonic current frequencies to be suppressed h , obtain the inductor parameters L 1 and L 2, and resistance parameter R (usually set to 0) of the GFM converter filter, so as to establish an equivalent harmonic impedance model of the GFM converter at the PCC (as Figure 3 shown) as shown in Equation (1):

[0057] (1)

[0058] where, θ oh is the phase angle of the h th harmonic output impedance of the GFM, Z oh is the absolute value of the h th harmonic output impedance amplitude of the GFM, ω is the grid angular frequency.

[0059] Among them, the equivalent harmonic impedance model is as Figure 3 shown. In the figure, Z gh refers to the equivalent impedance of the grid, U gh refers to the equivalent voltage of the grid. The equivalent harmonic impedance model can adopt a Thevenin harmonic model, etc.

[0060] (2) Superimpose a fixed-amplitude gain on the voltage outer-loop control command K h , a fixed phase angle θ h of the voltage command signal , as shown in Equation (2), keep the fixed-amplitude gain unchanged, and make the phase angle θ h iterate from 0 degrees to 360 degrees in a certain step.

[0061] (2)

[0062] Wherein, T s is the GFM control period, z is the operation symbol in the discrete domain.

[0063] (3) By comparing the h th harmonic voltage amplitudes at different phase angles of the PCC, find the input phase angle θ h1 that makes the hth harmonic voltage of the PCC reach the maximum value.

[0064] (4) Equivalent the remaining disturbance sources at the PCC to a harmonic Norton model. The GFM grid-connected system considering the disturbance sources is equivalent to Figure 4 shown (in the figure, Z Lh is the equivalent impedance of the load at the PCC point, and I Lh is the equivalent current of the load at the PCC point), and use θ h1 as the input phase angle of the vector, and adjust the amplitude gain K h until the h th harmonic voltage of the PCC is reduced to zero. At this time, the amplitude gain is K h1 .

[0065] (5) Calculate the optimal harmonic voltage compensation phase through the superposition theorem and Kirchhoff's voltage theorem, as shown in Equation (3):

[0066] (3)

[0067] Wherein, θ gh is the phase angle of the h th harmonic voltage of the distorted power grid, Δ θ h is the phase angle error between the GFM voltage command and the actually constructed voltage source, θ pcch is the at the PCC pointh Sub - harmonic voltage phase angle

[0068] (6) Take the optimal harmonic voltage compensation phase angle θ hc as the input phase angle of the vector, and adjust the amplitude gain K h until the inflection point of the sub - harmonic voltage amplitude at the PCC appears. At this time, the amplitude gain is considered as the optimal compensation voltage amplitude for matching the distorted grid voltage. h

[0069] The equivalent circuit diagram of the GFM grid - connected system considering compensation is shown in Figure 5 as follows. In the figure, U gh is the harmonic voltage of the constructed GFM harmonic voltage source that is consistent with the harmonic voltage in the grid voltage.

[0070] This embodiment is not limited by the GFM converter model, topology structure, control strategy and parameters. Without the need to add any new sampling modules, only through the harmonic voltage source constructed by the GFM converter itself, the influence of the distorted grid voltage on the GFM can be offset. The method is simple and practical, and has strong adaptability and versatility in actual engineering.

[0071] In some embodiments, the implementation steps of step 2 (harmonic virtual impedance tuning method considering the control stability region) include:

[0072] According to the PCC voltage sampling signal, use a quasi - resonant controller to decompose the component corresponding to the harmonic frequency to be suppressed, multiply it by a certain gain and then superimpose it on the modulation voltage signal to construct the virtual harmonic impedance at this frequency. The effect is to reduce the GFM output harmonic impedance, and the reduction in amplitude is positively correlated with the multiplied gain. The equivalent circuit diagram of the GFM grid - connected system considering the virtual impedance is shown in Figure 6 as follows.

[0073] As a further technical limitation, during the design of the GFM harmonic virtual impedance, judge the GFM control system closed - loop transfer function and the modulation voltage limit to identify the range of the harmonic virtual impedance amplitude that can be constructed within the GFM control system stability region:

[0074] The gain representing the amplitude of the constructed virtual harmonic impedance should have upper and lower limits. The upper limit is determined according to the poles of the GFM closed - loop transfer function. A reasonable gain should ensure that there are no poles in the right - half plane in the entire closed - loop system. The lower limit is restricted by the modulation voltage limit of the GFM control system, and its upper limit should be the maximum modulation ratio that can operate.

[0075] On this basis, keep the optimal compensation phase obtained in the first scheme unchanged, and make the virtual impedance amplitude gain corresponding to the frequency Z ​h Iteratively grow from zero with a certain step size, while recording the harmonic voltage amplitude of the PCC point after each iteration. When an inflection point appears, it is considered that Z h the best gain that should be obtained theoretically is achieved. If no inflection point appears after reaching the limit, the iteration is stopped and it is considered that Z h the best gain within the stable region is achieved.

[0076] Specifically, the constraint for determining the upper limit of the modulation voltage limit is:

[0077] Determine the stable range of the closed-loop poles according to the Nyquist law, and the upper limit of the designed harmonic virtual impedance amplitude is constrained by this stable region and should satisfy the range as shown in Equation (4):

[0078] (4)

[0079] where Z vir ( s ) is the virtual impedance transfer function to be injected, H i ( s ) is the current inner-loop transfer function, C is the filter capacitor of the LCL filter, s is the operation symbol in the discrete domain, and M(s) is an intermediate variable without physical meaning.

[0080] Specifically, the constraint for determining the lower limit of the modulation voltage limit is:

[0081] ( 5 )

[0082] where I oh is the harmonic current amplitude of the GFM output, u m is the current modulation voltage amplitude, M is the modulation voltage limit.

[0083] By analyzing the stable region and modulation capacity limit of the GFM control system, the present invention can clarify the GFM frequency-domain change range under multiple constraints. Within this range, the harmonic frequency impedance to be suppressed can be reduced to the lowest, enabling more harmonics at the PCC to flow towards the GFM. Therefore, the harmonics flowing from the PCC to the power grid can be effectively reduced. In the current scenario of voltage distortion in the distribution system, it fills the technical gap of the GFM fully independently and actively participating in the harmonic suppression at the grid connection point. The method has stronger robustness and stability than traditional methods and is suitable for different types of new energy grid connection scenarios.

[0084] Embodiment 2

[0085] As Figure 7 shown, this embodiment provides a GFM control system for active harmonic suppression, including:

[0086] A phase compensation module, which is configured to: select the harmonic current frequency to be suppressed, superimpose a GFM harmonic voltage source with a fixed amplitude gain and a fixed phase angle on the voltage outer loop control command, and determine the optimal compensation phase according to the PCC harmonic voltage amplitude curve in the voltage vector optimization process and iterative calculation;

[0087] A virtual harmonic impedance optimal gain module, which is configured to: separate the harmonic voltage component at the harmonic current frequency to be suppressed according to the acquired PCC voltage sampling data and GFM output current data of the GFM access node, so as to construct a virtual harmonic impedance at the harmonic current frequency to be suppressed; determine the amplitude range of the virtual harmonic impedance under the multiple constraints of the GFM stability region and the modulation voltage limit; keep the optimal compensation phase unchanged, and determine the optimal gain of the virtual harmonic impedance within the GFM stability region within the amplitude range of the virtual harmonic impedance.

[0088] In some embodiments, the phase compensation module is specifically configured to:

[0089] Keep the fixed amplitude gain unchanged, iterate the phase angle from 0 degree to 360 degrees in a certain step, and record the PCC point harmonic voltage amplitude after each phase angle change, record the phase angle corresponding to the maximum value of the PCC point harmonic voltage and the phase angle corresponding to the minimum value during the vector optimization process;

[0090] Take the phase angle corresponding to the maximum value of the PCC point harmonic voltage as the input of the voltage command, increase the amplitude gain of the constructed GFM harmonic voltage source, and finally reduce the harmonic voltage at the corresponding frequency of the PCC point to zero, and record the amplitude gain corresponding to the reduction of the PCC point harmonic voltage to zero;

[0091] Aggregate all non-GFM devices connected to the PCC point into an equivalent harmonic Norton model, rely on Kirchhoff's voltage law and superposition theorem, and combine the proportional relationship between the fixed amplitude gain and the amplitude gain corresponding to the reduction of the PCC point harmonic voltage to zero, that is, the PCC point harmonic voltage amplitudes under the two gains, to obtain the optimal compensation phase of the GFM harmonic voltage source.

[0092] In some embodiments, the virtual harmonic impedance optimal gain module is specifically configured to: determine the upper limit of the amplitude of the virtual harmonic impedance under the constraint of the GFM stability region, and the constraint of the GFM stability region is expressed by the following formula:

[0093]

[0094] Wherein, Zvir ( s ) represents the virtual impedance transfer function to be injected. H i ( s ) represents the current inner loop transfer function. C represents the filtering capacitor of the LCL filter. s represents the operation symbol in the discrete domain. M(s) represents an intermediate variable without physical meaning. R represents the resistance. L 1 and L 2 both represent the inductor parameters of the GFM converter filter. ω represents the grid angular frequency. h represents the harmonic order.

[0095] In some embodiments, the virtual harmonic impedance optimal gain module is further configured to: under the constraint of the modulation voltage limit, determine the lower limit of the amplitude of the virtual harmonic impedance. The modulation voltage limit constraint is expressed by the following formula:

[0096]

[0097] Wherein, Z vir ( s ) is the virtual impedance transfer function to be injected. I oh is the amplitude of the harmonic current output by the GFM. u m is the amplitude of the current modulation voltage. M is the modulation voltage limit. H i ( s ) represents the current inner loop transfer function. ω represents the grid angular frequency. h represents the harmonic order.

[0098] In some embodiments, the virtual harmonic impedance optimal gain module is further configured to: keep the optimal compensation phase unchanged. Within the amplitude range of the virtual harmonic impedance, make the virtual impedance amplitude gain of the harmonic current frequency to be suppressed increase iteratively from zero in a certain step length, and record the harmonic voltage amplitude at the PCC point after each iteration. When the harmonic voltage amplitude at the PCC point shows an inflection point, it is considered that the virtual impedance amplitude gain has obtained the optimal gain that should be obtained theoretically. If no inflection point appears after reaching the limit, stop the iteration and consider that the virtual impedance amplitude gain has obtained the optimal gain of the virtual harmonic impedance within the stable domain.

[0099] Further, the optimal compensation phase is expressed by the following formula:

[0100]

[0101] Among them, θ hc represents the optimal compensation phase, θ gh is the distorted power grid h phase angle of the h - th harmonic voltage, Δ θ h is the phase - angle error between the GFM voltage command and the actually constructed GFM harmonic voltage source, θ pcch is the h phase angle of the h - th harmonic voltage at the PCC point, θ h1 represents the input phase angle at which the h - th harmonic voltage of the PCC takes the maximum value, θ oh represents the h phase angle of the output impedance of the h - th harmonic of the GFM.

[0102] In some embodiments, the phase compensation module is specifically further configured as: selecting the harmonic current frequency to be suppressed, and the method includes: determining the frequency and phase information of the grid harmonic voltage according to the historical data of the low - voltage side of the transformer where the GFM is connected to the grid or the short - time recording and wave analysis results, and selecting the harmonic current frequency to be suppressed.

[0103] The present invention can effectively reduce the harmonic current content of the GFM connected to the grid, and without adding new sampling or passive impedance, it has good economic efficiency and engineering popularization value.

[0104] Embodiment III

[0105] This embodiment provides a computer - readable storage medium, on which a computer program is stored, and when the program is executed by a processor, it implements the steps in the GFM control method for harmonic active suppression as described in Embodiment I above.

[0106] Embodiment IV

[0107] This embodiment provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, it implements the steps in the GFM control method for harmonic active suppression as described in Embodiment I above.

[0108] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer - usable storage media (including but not limited to disk memories and optical memories, etc.) containing computer - usable program code.

[0109] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, as well as the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0110] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing devices to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0111] These computer program instructions can also be loaded onto a computer or other programmable data processing devices, such that a series of operation steps are executed on the computer or other programmable devices to generate a computer-implemented process, so that the instructions executed on the computer or other programmable devices provide steps for implementing the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0112] Those of ordinary skill in the art can understand that to implement all or part of the processes in the above-described method embodiments, it can be completed by instructing relevant hardware through a computer program. The program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the above-described method embodiments. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM), etc.

[0113] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A GFM control method for active harmonic suppression, characterized in that: include: The harmonic current frequency to be suppressed is selected, a GFM harmonic voltage source with a fixed amplitude gain and a fixed phase angle is superimposed in the voltage outer loop control instruction, and the optimal compensation phase is determined according to the PCC harmonic voltage amplitude curve in the voltage vector optimization process and iterative calculation; the method includes: Keep the fixed amplitude gain unchanged, so that the phase angle is iterated from 0 degrees to 360 degrees at a certain step size, and record the harmonic voltage amplitude of the PCC point after each phase angle change, and record the phase angle corresponding to the maximum value and the phase angle corresponding to the minimum value of the harmonic voltage at the PCC point during the vector optimization process; The phase angle corresponding to the maximum value of the harmonic voltage at the PCC point is used as the input of the voltage command, and the amplitude gain of the constructed GFM harmonic voltage source is increased, so that the harmonic voltage at the corresponding frequency at the PCC point is finally reduced to zero, and the amplitude gain corresponding to the harmonic voltage at the PCC point being reduced to zero is recorded; The non-GFM devices connected to the PCC point are aggregated and equivalent to a harmonic Norton model. Based on Kirchhoff's voltage law and superposition theorem, the fixed amplitude gain and the amplitude gain proportional relationship corresponding to the harmonic voltage at the PCC point being reduced to zero are combined, that is, the harmonic voltage amplitude at the PCC point under two gains, to obtain the optimal compensation phase of the GFM harmonic voltage source. According to the acquired PCC voltage sampling data and GFM output current data of the GFM access node, the harmonic voltage component under the harmonic current frequency that needs to be suppressed is separated to construct the virtual harmonic impedance under the harmonic current frequency that needs to be suppressed; under the multiple constraints of the GFM stable domain and the modulation voltage limit, the amplitude range of the virtual harmonic impedance is determined; the optimal compensation phase is kept unchanged, and the optimal gain of the virtual harmonic impedance in the GFM stable domain is determined within the amplitude range of the virtual harmonic impedance; the method includes: keeping the optimal compensation phase unchanged, within the amplitude range of the virtual harmonic impedance, the virtual impedance amplitude gain of the harmonic current frequency that needs to be suppressed is iteratively increased from zero at a certain step size, and the harmonic voltage amplitude of the PCC point after each iteration is recorded. When the harmonic voltage amplitude of the PCC point has an inflection point, it is considered that the virtual impedance amplitude gain has achieved the optimal gain that should be obtained in theory. If no inflection point appears after reaching the limit, the iteration is stopped, and it is considered that the virtual impedance amplitude gain has achieved the optimal gain of the virtual harmonic impedance in the stable domain.

2. The GFM control method for active harmonic suppression according to claim 1, characterized in that: The method includes determining the amplitude range of the virtual harmonic impedance under the multiple constraints of the GFM stable domain and the modulation voltage limit. The method includes: determining the upper limit of the amplitude of the virtual harmonic impedance under the constraints of the GFM stable domain, and the constraints of the GFM stable domain are expressed by the following formula: in, Z vir ( s ) represents the virtual impedance transfer function to be injected, H i ( s ) represents the current inner loop transfer function, C Represents the filter capacitor of the LCL filter, s Indicates the operation symbol of the discrete domain, M(s) indicates that the intermediate variable has no physical meaning, R Represents resistance, L 1 and L 2 represents the inductance parameters of the GFM converter filter. ω represents the grid angular frequency, h Indicates the harmonic order.

3. The GFM control method for active harmonic suppression according to claim 1, characterized in that: The method further comprises: determining the amplitude range of the virtual harmonic impedance under the multiple constraints of the GFM stability domain and the modulation voltage limit; and determining the lower limit of the amplitude of the virtual harmonic impedance under the modulation voltage limit constraint, wherein the modulation voltage limit constraint is expressed by the following formula: in, Z vir ( s ) is the virtual impedance transfer function to be injected, I oh is the GFM output harmonic current amplitude, u m is the current modulation voltage amplitude, M is the modulation voltage limiter, H i ( s ) represents the current inner loop transfer function, ω represents the grid angular frequency, h Indicates the harmonic order.

4. The GFM control method for active harmonic suppression according to claim 1, characterized in that: The optimal compensation phase is expressed by the following formula: in, θ hc represents the optimal compensation phase, θ gh Distorted Grid h Subharmonic voltage phase angle, Δ θ h is the phase angle error between the GFM voltage command and the actual constructed GFM harmonic voltage source, θ pcch For PCC points h Subharmonic voltage phase angle, θ h1 Indicates the input phase angle at which the hth harmonic voltage of the PCC takes its maximum value, θ oh Indicates GFM h Subharmonic output impedance phase angle.

5. The GFM control method for active harmonic suppression according to claim 1, characterized in that: The method for selecting the harmonic current frequency to be suppressed includes: determining the frequency and phase information of the harmonic voltage of the power grid according to the historical data of the low-voltage side of the transformer connected to the GFM power grid or the short-time recording analysis result, and selecting the harmonic current frequency to be suppressed.

6. A GFM control system for active harmonic suppression, characterized in that: include: The phase compensation module is configured to: select the harmonic current frequency to be suppressed, superimpose a GFM harmonic voltage source with a fixed amplitude gain and a fixed phase angle in the voltage outer loop control instruction, and determine the optimal compensation phase according to the voltage vector optimization process and the PCC harmonic voltage amplitude curve in the iterative calculation; the method includes: Keep the fixed amplitude gain unchanged, so that the phase angle is iterated from 0 degrees to 360 degrees at a certain step size, and record the harmonic voltage amplitude of the PCC point after each phase angle change, and record the phase angle corresponding to the maximum value and the phase angle corresponding to the minimum value of the harmonic voltage at the PCC point during the vector optimization process; The phase angle corresponding to the maximum value of the harmonic voltage at the PCC point is used as the input of the voltage command, and the amplitude gain of the constructed GFM harmonic voltage source is increased, so that the harmonic voltage at the corresponding frequency at the PCC point is finally reduced to zero, and the amplitude gain corresponding to the harmonic voltage at the PCC point being reduced to zero is recorded; The non-GFM devices connected to the PCC point are aggregated and equivalent to a harmonic Norton model. Based on Kirchhoff's voltage law and superposition theorem, the fixed amplitude gain and the amplitude gain proportional relationship corresponding to the harmonic voltage at the PCC point being reduced to zero are combined, that is, the harmonic voltage amplitude at the PCC point under two gains, to obtain the optimal compensation phase of the GFM harmonic voltage source. The virtual harmonic impedance optimal gain module is configured as follows: according to the acquired PCC voltage sampling data and GFM output current data of the GFM access node, the harmonic voltage component under the harmonic current frequency that needs to be suppressed is separated to construct the virtual harmonic impedance under the harmonic current frequency that needs to be suppressed; under the multiple constraints of the GFM stable domain and the modulation voltage limit, the amplitude range of the virtual harmonic impedance is determined; the optimal compensation phase is kept unchanged, and within the amplitude range of the virtual harmonic impedance, the optimal gain of the virtual harmonic impedance in the GFM stable domain is determined; the method includes: keeping the optimal compensation phase unchanged, within the amplitude range of the virtual harmonic impedance, the virtual impedance amplitude gain of the harmonic current frequency that needs to be suppressed is iteratively increased from zero at a certain step size, and the harmonic voltage amplitude of the PCC point after each iteration is recorded at the same time. When the harmonic voltage amplitude of the PCC point has an inflection point, it is considered that the virtual impedance amplitude gain has achieved the optimal gain that should be obtained in theory. If the inflection point still does not appear after reaching the limit, the iteration is stopped, and it is considered that the virtual impedance amplitude gain has achieved the optimal gain of the virtual harmonic impedance in the stable domain.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the GFM control method for active harmonic suppression according to any one of claims 1 to 5 are implemented.

8. A computer device 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 program, the steps of the GFM control method for active harmonic suppression according to any one of claims 1 to 5 are implemented.

Images