Converter primary and secondary harmonic source model construction method, device, equipment and medium

Abstract

The invention relates to the technical field of power grid harmonic treatment, in particular to a converter primary and secondary harmonic source model construction method, device and equipment and a medium. The method comprises the following steps: establishing a first secondary harmonic emission model according to a frequency coupling effect caused by asymmetry of dq-axis control of the converter; establishing a second secondary harmonic emission model according to the sampling and PWM frequency coupling effect generated in the sampling link and the PWM link of the converter; establishing a dead-zone native harmonic emission model according to the dead-zone effect of the converter; and establishing a converter primary and secondary harmonic source model according to the first secondary harmonic emission model, the second secondary harmonic emission model and the dead zone primary harmonic emission model. According to the method, primary and secondary harmonic source models of the converter are constructed by combining asymmetric control of dq axes of the grid-connected converter and a frequency coupling effect caused by PWM and a sampling sideband effect. When the model is used for harmonic power flow analysis, the analysis result is comprehensive and accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid harmonic control, and in particular to a method, device, equipment and medium for constructing a primary and secondary harmonic source model of a converter. Background Art

[0002] In power grids with a high proportion of new energy and power electronic devices connected, the importance of power quality issues such as harmonics has increased. For example, when a large number of new energy converters are connected to the grid, their own native harmonic emissions and the interaction with the background harmonics of the grid will cause harmonic pollution in the grid and increase the risk of resonance. Therefore, it is necessary to establish an accurate primary and secondary harmonic source model of multiple grid-connected converters for grid harmonic flow analysis, provide a basis for grid resonance analysis and harmonic governance, and improve the robustness of the grid under the condition of large-scale access to new energy power generation systems. Summary of the invention

[0003] In view of this, the present invention provides a method, device, equipment and medium for constructing a primary and secondary harmonic source model of a converter to solve the problem of lack of a primary and secondary harmonic source model of a converter for power grid harmonic flow analysis in the prior art.

[0004] In the first aspect, the present invention provides a method for constructing a primary and secondary harmonic source model of a converter, the method comprising: establishing a first harmonic emission model according to the frequency coupling effect caused by the asymmetric dq axis control of the converter; establishing a second harmonic emission model according to the sampling and PWM frequency coupling effects generated by the sampling link and PWM link of the converter; establishing a dead zone native harmonic emission model according to the dead zone effect of the converter; establishing a primary and secondary harmonic source model of the converter according to the first harmonic emission model, the second harmonic emission model and the dead zone native harmonic emission model.

[0005] The method for constructing the primary and secondary harmonic source model of the converter provided in the embodiment of the present invention combines the frequency coupling effect caused by the dq axis control asymmetry of the grid-connected converter and the PWM and sampling sideband effects, and comprehensively considers the interaction between the converter and the background harmonics of the power grid, as well as the converter dead zone and PWM native harmonic emission, to construct the primary and secondary harmonic source model of the converter. The model can be connected to the existing harmonic analysis tools to perform harmonic flow analysis of the power grid, and the analysis results are comprehensive and accurate.

[0006] In an optional embodiment, a primary and secondary harmonic source model of the converter is established according to the first generated harmonic emission model, the second generated harmonic emission model and the dead zone native harmonic emission model, including: establishing a PWM switching native high-frequency harmonic emission model according to the high-frequency harmonic component introduced when the converter adopts PWM modulation; establishing a primary and secondary harmonic source model of the converter according to the first generated harmonic emission model, the second generated harmonic emission model, the dead zone native harmonic emission model and the PWM switching native high-frequency harmonic emission model.

[0007] In this embodiment, when establishing the primary and secondary harmonic source model of the converter, the primary harmonic emission of the PWM switching frequency is additionally considered, so that the model finally established considers the problem more comprehensively and has a wider scope of application.

[0008] In an optional embodiment, a first harmonic emission model is established according to the frequency coupling effect caused by the asymmetric dq-axis control of the converter, including: when there is positive-sequence background harmonic current injection or negative-sequence background harmonic current injection at any converter node in the power grid, based on the frequency coupling effect caused by the asymmetric dq-axis control of the converter, determining the first coupling relationship matrix between the grid-connected point coupling voltage and the coupling current of the converter and the first relationship between the grid-connected point coupling voltage and the coupling current; determining the first calculation expression of the coupling current based on the first coupling relationship matrix and the first relationship between the grid-connected point coupling voltage and the coupling current, and constructing the first harmonic emission model in positive sequence or the first harmonic emission model in negative sequence.

[0009] In this embodiment, through the first coupling relationship matrix between the grid-connected point coupling voltage and the coupling current of the converter and the first relationship between the grid-connected point coupling voltage and the coupling current, a complete and accurate characterization of the coupling mechanism between background disturbance harmonics and harmonics caused by dq-axis control asymmetry is achieved. Therefore, the first harmonic emission model established through the first coupling relationship matrix and the first relationship can quantitatively analyze the harmonic emission characteristics caused by the asymmetric control of multiple grid-connected converters.

[0010] In an optional embodiment, a second harmonic emission model is established based on the sampling and PWM frequency coupling effects generated by the converter sampling link and the PWM link, including: when there is positive-sequence background harmonic current injection or negative-sequence background harmonic current injection at any converter node in the power grid, based on the harmonic frequency under the sampling and PWM sideband effects in the converter sampling delay link and the PWM link; based on the converter current inner loop control, PWM and filter transfer function, determining the second coupling relationship matrix between the grid-connected point coupling voltage and the coupling current of the converter and the second relationship between the grid-connected point coupling voltage and the coupling current, the coupling current being the coupling current caused by the harmonic frequency coupling effect; based on the second coupling relationship matrix and the second relationship between the grid-connected point coupling voltage and the coupling current, determining the second calculation expression of the coupling current, and constructing a second harmonic emission model in positive sequence or a second harmonic emission model in negative sequence.

[0011] In this embodiment, through the second coupling relationship matrix between the grid-connected point coupling voltage and the coupling current of the converter and the second relationship between the grid-connected point coupling voltage and the coupling current, a complete and accurate characterization of the frequency coupling mechanism between the background disturbance harmonics, sampling sideband harmonics and PWM sideband harmonics is achieved. Therefore, the secondary harmonic emission model established through the second coupling relationship matrix and the second relationship can quantitatively analyze the sampling and PWM sideband secondary harmonic emission characteristics of multiple grid-connected converters.

[0012] In an optional embodiment, a dead zone native harmonic emission model is established according to the dead zone effect of the converter, including: determining the positive sequence dead zone harmonic voltage and the negative sequence dead zone harmonic voltage according to the low frequency native harmonic introduced by the dead zone effect of the converter; determining a third calculation expression for the coupling current caused by the positive sequence dead zone harmonic voltage under the frequency coupling effect of asymmetric control; determining a fourth calculation expression for the coupling current caused by the negative sequence dead zone harmonic voltage under the frequency coupling effect of asymmetric control; and constructing the dead zone native harmonic emission model according to the third calculation expression and the fourth calculation expression.

[0013] In an optional embodiment, a third calculation expression for the coupling current caused by the positive-sequence dead-zone harmonic voltage under the frequency coupling effect of asymmetric control is determined, including: based on the positive-sequence dead-zone harmonic voltage, according to the grid-connected point coupling current, a third coupling relationship matrix between the coupling voltage and the positive-sequence dead-zone harmonic voltage, and a third relationship between the grid-connected point coupling voltage and the coupling current under the frequency coupling effect of asymmetric control of any converter node in the power grid; determining the third calculation expression for the coupling current based on the third coupling relationship matrix and the third relationship between the grid-connected point coupling voltage and the coupling current; determining the fourth calculation expression for the coupling current caused by the negative-sequence dead-zone harmonic voltage under the frequency coupling effect of asymmetric control, including: based on the negative-sequence dead-zone harmonic voltage, according to the grid-connected point coupling current, a fourth coupling relationship matrix between the coupling voltage and the negative-sequence dead-zone harmonic voltage, and a fourth relationship between the grid-connected point coupling voltage and the coupling current under the frequency coupling effect of asymmetric control of any converter node in the power grid; determining the fourth calculation expression for the coupling current based on the fourth coupling relationship matrix and the fourth relationship between the grid-connected point coupling voltage and the coupling current.

[0014] In this embodiment, the dead zone native harmonic emission caused by the dead zone effect is analyzed, and the transmission process of the dead zone native harmonic after sampling at the grid connection point and entering the converter control loop is considered; the traditional method of treating the dead zone harmonic as a constant source is abandoned, and the dead zone harmonic is divided into an inherent component and a coupled component. By combining the control of the asymmetric frequency coupling effect, the inherent and coupled components of the adjacent frequency dead zone harmonics can be calculated respectively, and the components with the same frequency are superimposed by phase, and the emission characteristics of the dead zone native coupled harmonics are quantitatively analyzed.

[0015] In an optional embodiment, a PWM switching native high-frequency harmonic emission model is established based on the high-frequency harmonic components introduced when the converter adopts PWM modulation, including: performing Fourier series calculation on the converter output voltage to determine the high-frequency harmonic components introduced when PWM modulation is adopted; calculating the harmonic current of the high-frequency harmonic components after being processed by a filter and grid equivalent impedance, and constructing a PWM switching native high-frequency harmonic emission model.

[0016] In a second aspect, the present invention provides a device for constructing a primary and secondary harmonic source model of a converter, the device comprising: a first model construction module, used to establish a first harmonic emission model according to the frequency coupling effect caused by the asymmetric dq axis control of the converter; a second model construction module, used to establish a second harmonic emission model according to the sampling and PWM frequency coupling effects generated by the sampling link and PWM link of the converter; a third model construction module, used to establish a dead zone native harmonic emission model according to the dead zone effect of the converter; a fourth model construction module, used to establish a primary and secondary harmonic source model of the converter according to the first harmonic emission model, the second harmonic emission model and the dead zone native harmonic emission model.

[0017] In a third aspect, the present invention provides a computer device, comprising: a memory and a processor, the memory and the processor being communicatively connected to each other, the memory storing computer instructions, and the processor executing the method for constructing a primary and secondary harmonic source model of a converter according to the first aspect or any corresponding embodiment thereof by executing the computer instructions.

[0018] In a fourth aspect, the present invention provides a computer-readable storage medium having computer instructions stored thereon, the computer instructions being used to enable a computer to execute the method for constructing a primary and secondary harmonic source model of a converter according to the first aspect or any corresponding embodiment thereof.

[0019] In a fifth aspect, the present invention provides a computer program product, comprising computer instructions for causing a computer to execute the method for constructing a primary and secondary harmonic source model of a converter according to the first aspect or any corresponding embodiment thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 is a flow chart of a method for constructing a primary and secondary harmonic source model of a converter according to an embodiment of the present invention;

[0022] Figure 2 is a schematic diagram of a main circuit and a control link of a single grid-connected converter according to an embodiment of the present invention;

[0023] Figure 3 is a schematic diagram of a network structure formed by multiple grid-connected voltage source converters according to an embodiment of the present invention;

[0024] Figure 4 is a structural block diagram of a device for constructing a primary and secondary harmonic source model of a converter according to an embodiment of the present invention;

[0025] Figure 5 It is a schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0027] According to an embodiment of the present invention, an embodiment of a method for constructing a primary and secondary harmonic source model of a converter is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0028] In this embodiment, a method for constructing a primary and secondary harmonic source model of a converter is provided, which can be used in electronic devices such as computers, mobile phones, tablet computers, etc. Figure 1 is a flow chart of a method for constructing a primary and secondary harmonic source model of a converter according to an embodiment of the present invention. Figure 1 As shown, the process includes the following steps:

[0029] Step S101, establishing a first harmonic emission model according to the frequency coupling effect caused by the asymmetric control of the dq axes of the converter.

[0030] Step S102, establishing a second harmonic emission model according to the sampling and PWM frequency coupling effects generated by the converter sampling link and the PWM link.

[0031] Step S103, establishing a dead zone native harmonic emission model according to the dead zone effect of the converter.

[0032] Step S104, establishing a converter primary and secondary harmonic source model according to the first harmonic emission model, the second harmonic emission model and the dead zone primary harmonic emission model.

[0033] Among them, for a single grid-connected converter, its main circuit and control links are as follows Figure 2 As shown, Figure 2 The converter shown in is an LCL type grid-connected inverter. Figure 2 Middle,U DC is the DC side voltage of the converter, L1, L2 and C1 form a third-order LCL filter, Z g It represents the equivalent impedance of the power grid obtained from the perspective of a certain converter, which is related to the network structure and the converters of other nodes. ac 、i bc and i cc Respectively represent the three-phase filter capacitor current; u ap 、u bp and u cp Respectively represent the three-phase output voltage of the inverter port; i a 、i b and i c Represents the three-phase grid-connected current; u a 、u b and u c They represent the three-phase grid-connected point voltages respectively; at the same time, it should be noted that the above variables are all values ​​of a certain phase.

[0034] In the sampling phase of the control link, the i a 、i b and i c and u a 、u b and u c Perform low-pass filtering, and then transform the processed signal into a coordinate system, that is, transform the signal from the abc coordinate system to the dq coordinate system to obtain the transformed signal i d 、i q 、u d 、u q Among them, the converted signal u d 、u q Input to the phase locked loop (PLL), the phase angle θ of the phase locked loop output PLL Used for coordinate transformation. At the same time, i ac 、i bc and i cc Combined with the phase angle θ of the phase-locked loop output PLL Perform coordinate system transformation to obtain the transformed signal i dc 、i qc .

[0035] In the power outer loop of the control link, the collected active power P and reactive power Q are respectively compared with the active power reference value P ref and reactive power reference value Q ref After the difference calculation is performed, the current reference value i is obtained through PI control (Proportional-Integral) processing. dref and i qref In the current outer loop of the control link, the coordinate converted signal i d 、i q and the current reference value i dref 、i qref After the difference calculation is performed, the two first voltage values ​​of the calculated voltage reference value are obtained through PI processing, and then the coordinate-converted signal i d 、i q and the dq axis current decoupling coefficient K i Multiply them to get the second voltage value of the calculated voltage reference value, and then convert the coordinate converted signal u d 、u q and the voltage feedforward compensation coefficient K n Finally, the two first voltage values ​​are added and subtracted from the second voltage value and the third voltage value to obtain two voltage reference values ​​u dref and u qref At the same time, for the converted signal i dc 、i qc and the capacitance current compensation coefficient K c Multiply them to get the voltage value, and add the calculated voltage value to the voltage reference value u dref 、u qref Perform difference calculation. Combine the result of the calculation with the phase angle θ output by the phase-locked loop. PLL A coordinate system conversion is performed from the dq coordinate system to the abc coordinate system to obtain a signal for PWM (Pulse Width Modulation) control, that is, PWM realizes modulation of the conduction time of the switch tube in the converter according to the signal obtained by the coordinate system conversion.

[0036] Therefore, based on the control link of the above-mentioned converter, considering the influence of control links such as power outer loop, current inner loop, phase-locked loop, sampling delay link and low-pass filter, when the converter is connected to the grid, the converter dq axis control asymmetry and PWM modulation and sampling sideband effect will produce frequency coupling effect, resulting in secondary harmonic emission, further aggravating the harmonic / resonance problem. Therefore, when establishing the primary and secondary harmonic source model of the converter, the influence of these factors needs to be considered. Based on this, when establishing the primary and secondary harmonic source model of the converter, this embodiment analyzes these links, establishes corresponding harmonic emission models respectively, and obtains the primary and secondary harmonic source model of the converter by combining these models.

[0037] Among them, the asymmetric control of the dq axis of the converter can be understood as the inconsistent control strategy or parameter setting of the d axis (direct axis) and the q axis (quadrature axis). For example, the current phase-locked loop control link uses a closed-loop control scheme to control the q axis voltage to 0, thereby obtaining the frequency and phase of the grid voltage. That is, the phase-locked loop only controls the q axis voltage, resulting in the problem of asymmetric control. When the dq axis control is asymmetric, the sensitivity to the grid frequency increases, that is, small fluctuations in the grid frequency may be amplified, and the control error is further aggravated through the interaction of the control loop. This causes a frequency coupling effect, which may cause additional harmonics and oscillations. Therefore, when establishing the first harmonic emission model based on the frequency coupling effect caused by the asymmetric control of the dq axis of the converter, the first harmonic emission model can be established based on the frequency of the injected background harmonics and the change in the response current corresponding to the coupling frequency generated by the control asymmetric frequency coupling effect.

[0038] For the sampling link and PWM link, there is a sideband effect in the signal processing process. When there is a background harmonic disturbance at the grid connection point, the grid-connected converter will not only affect the size of the disturbance frequency component, but also generate a series of sideband harmonic components centered on the sampling and switching frequency, namely, secondary harmonics. When analyzing the harmonic, a secondary harmonic emission model is established based on the change in the response current corresponding to the harmonic.

[0039] In addition, during the operation of the converter, in order to avoid the instantaneous large current impact caused by the direct conduction of the switching device under the high voltage difference and the short circuit caused by the simultaneous conduction of the two switching devices, a non-conducting time interval is set when the switch state changes, that is, the dead time. During this time interval, no matter how the control signal changes, the switch maintains its current state unchanged and does not switch. However, during the dead time, the current that should have been continuous will be temporarily interrupted, thereby introducing additional harmonics. This harmonic will also produce a coupled current response, so the dead zone native harmonic emission model can be established by analyzing the coupled current.

[0040] The primary and secondary frequency domain harmonic source model of the multi-voltage source type grid-connected converter taking into account frequency coupling is constructed through the first harmonic emission model, the second harmonic emission model and the dead zone native harmonic emission model established above. When constructing the primary and secondary harmonic source model of the converter, the coupling current analyzed in the secondary harmonic generation model and the native harmonic emission model established above can be added. Therefore, through the primary and secondary harmonic source model of the converter, the specific distribution of the primary and secondary harmonic current output by the converter can be analyzed, providing a theoretical model for harmonic control and resonance analysis of the power grid.

[0041] The method for constructing the primary and secondary harmonic source model of the converter provided in the embodiment of the present invention combines the frequency coupling effect caused by the dq axis control asymmetry of the grid-connected converter and the PWM and sampling sideband effects, and comprehensively considers the interaction between the converter and the background harmonics of the power grid, as well as the converter dead zone and PWM native harmonic emission, to construct the primary and secondary harmonic source model of the converter. The model can be connected to the existing harmonic analysis tools to perform harmonic flow analysis of the power grid, and the analysis results are comprehensive and accurate.

[0042] In this embodiment, a method for constructing a primary and secondary harmonic source model of a converter is provided, and the process includes the following steps:

[0043] Step S201, establishing a first harmonic emission model according to the frequency coupling effect caused by the asymmetric control of the dq axes of the converter.

[0044] Specifically, the above step S201 includes:

[0045] Step S2011, when there is positive-sequence background harmonic current injection or negative-sequence background harmonic current injection at any converter node in the power grid, based on the frequency coupling effect caused by the asymmetric dq-axis control of the converter, determine the first coupling relationship matrix between the grid-connected point coupling voltage and the coupling current of the converter and the first relationship between the grid-connected point coupling voltage and the coupling current.

[0046] Step S2012: determining a first calculation expression for coupling current based on the first coupling relationship matrix and a first relationship between the grid connection point coupling voltage and coupling current, and constructing a first harmonic emission model in a positive sequence or a first harmonic emission model in a negative sequence.

[0047] Specifically, when analyzing the harmonics generated by the asymmetric dq axis control of the converter, the harmonic emission under the action of background harmonics is considered, that is, the secondary harmonic voltage and current generated by the converter grid connection point when the background harmonic disturbance occurs in the power grid are analyzed. Among them, the background harmonics can be divided into positive sequence background harmonics and negative sequence background harmonics, that is, the corresponding first-order harmonic emission models can be established for the situations when the positive sequence background harmonic current is injected and the negative sequence background harmonic current is injected.

[0048] In an optional implementation, when a node in a power grid has a frequency of f x1 (f x1 >2f0) positive sequence background harmonic current injection, based on Figure 2 The main circuit and control link of the single grid-connected converter shown in FIG. 1 can be used to obtain a network structure diagram of a network (multiple grid-connected voltage source converters (Voltage-Source-Converter, VSC) as shown in FIG. Figure 3 As shown, Figure 3 There is a coupling relationship matrix between the grid-connected point coupling voltage and coupling current under the frequency coupling effect of asymmetric control (including converters VSC1-VSCn) at any node converter (frequencies are f x1 、f x2 , f x2 Indicates frequency f x1 (f x1 >2f0) positive sequence background harmonic current injection, the coupling frequency generated by the asymmetric frequency coupling effect is controlled, and the coupling relationship matrix (i.e., the first coupling relationship matrix) is expressed by the following formula:

[0049]

[0050]

[0051]

[0052] In the formula, I nx1 , U nx1 Respectively represent the frequency point f x1 The corresponding coupling current and coupling voltage, I nx2 , U nx2 Respectively represent the frequency point f x2 The corresponding coupling current and coupling voltage, Z L1x1 , Z L2x1 , Z Cx1 Respectively represent the frequency point f x1 The corresponding LCL filter parameters, Z L1x2 , Z L2x2 , Z Cx2 Respectively represent the frequency point f x1 The corresponding LCL filter parameters, ω0, ω x1 and ω x2 Respectively represent the frequency point f 0、 f x1 and f x2 The corresponding angular frequency, frequency point f0 represents the fundamental frequency, Gf1 represents the low-pass filter at the harmonic frequency f x1 The expression below, U mn0 Indicates the fundamental frequency component u of the grid connection point voltagen0 The amplitude, T S represents the coefficient of the zero-order holder, H PLL represents the phase-locked loop transfer function, H IN represents the current inner loop transfer function, H OUT represents the power outer loop transfer function, L2 represents the grid-side inductance of the LCL filter, C represents the filter capacitor, K PWM represents the gain of PWM, Gf0 represents the expression of the low-pass filter at the harmonic frequency f0, I mn0 Represents the fundamental frequency component i of the grid-connected current n0 The amplitude of Represents the fundamental frequency component i of the grid-connected current n0 The initial phase angle, u dref0 、u qref0 They respectively represent the voltage reference values ​​corresponding to the fundamental frequency.

[0053] From equations (2) and (3), it can be seen that the elements in the first coupling relationship matrix are only related to the parameters of the converter itself and are not affected by the parameters of the connected network. Figure 2 and Figure 3 It can be seen that the grid-connected point coupling voltage and coupling current of a converter in the network also satisfy the following relationship (i.e., the first relationship):

[0054]

[0055] In the formula, Z gx1 , Z gx2 Represents the frequency f x1 and f x2 The system impedance obtained by performing Thevenin equivalent on a converter branch is as follows; U gx1 , U gx2 Represents the frequency f x1 and f x2 The open-circuit voltage component obtained by performing Thevenin equivalent on a converter branch is mainly related to the converter harmonic injection of other nodes and the background harmonic current of the power grid.

[0056] Any n-node converter can be listed as a group of equations similar to equation (4), and by combining equation (1), the coupling voltage and coupling current of each node converter under the control of the asymmetric frequency coupling effect can be obtained as follows:

[0057]

[0058]

[0059] In formulas (5)-(10), U nx ,I nxThey are the grid-connected coupling voltage and current vectors of each node converter under the control of asymmetric frequency coupling effect; Y sumx It is the collection matrix of the coupled voltage and current relationship matrix of each node converter, with a dimension of 2n*2n; Z netx Contains the self-impedance and corresponding mutual impedance of each converter node, with a dimension of 2n*2n; Z skx Contains the mutual impedance between each converter node and the background harmonic injection node, with a dimension of 2n*2; Z netx , Z skx It also contains two coupling frequencies under the effect of asymmetric frequency coupling; I sk represents the injected background harmonic current vector, the two elements of which represent the currents of two frequencies under the asymmetric frequency coupling effect; E is the unit matrix with a dimension of 2n*2n.

[0060] When negative-sequence background harmonics are injected, the overall relationship between the coupled voltage and coupled current remains unchanged under the frequency coupling effect of asymmetric control of the grid connection point, but equations (2) and (3) need to be modified as follows:

[0061]

[0062]

[0063] In the formula, C1 represents the size of the filter capacitor.

[0064] When f x1 <2f0, for negative sequence background harmonic injection, the relationship and f x1 >2f0; when the positive sequence background harmonic is injected, it is necessary to change ω in equations (1)-(10) x2 From ω x1 -2ω x0 Modified to 2ω x0 -ω x1 The first harmonic emission model established can be obtained by equation (6) and the corresponding coupling current I when the negative sequence background harmonic current is injected. nx The first calculation expression represents .

[0065] Step S202: establishing a second harmonic emission model according to the sampling and PWM frequency coupling effects generated by the converter sampling link and the PWM link.

[0066] Specifically, the above step S202 includes:

[0067] Step S2021, when there is positive sequence background harmonic current injection or negative sequence background harmonic current injection at any converter node of the power grid, based on the harmonic frequency under the effect of sampling and PWM sideband effect in the converter sampling delay link and PWM link.

[0068] Step S2022, based on the converter current inner loop control, PWM and filter transfer function, determine the second coupling relationship matrix between the grid-connected point coupling voltage and the coupling current of the converter and the second relationship between the grid-connected point coupling voltage and the coupling current, wherein the coupling current is the coupling current caused by the harmonic frequency coupling effect.

[0069] Step S2023, determining a second calculation expression for the coupling current based on the second coupling relationship matrix and the second relationship between the grid connection point coupling voltage and the coupling current, and constructing a second harmonic emission model in a positive sequence or a second harmonic emission model in a negative sequence.

[0070] Specifically, the sampling frequency of the grid-connected converter controller is recorded as f s , the switching frequency is recorded as f c , when the frequency of the grid connection point is f x1 When the background disturbance voltage is , the frequency of ±n is generated in the grid-connected converter port voltage under the action of sampling and PWM sideband effect. s f s ±n p f x1 (n s , n x1 =1,2,3…) and a series of sampling sideband subharmonics with frequencies of ±n c f c ±n0f0±n p f x1 (n c ,n x1 ,n0=1,2,3…) a series of PWM sideband secondary harmonics. When symmetrical sampling is adopted, that is, f s =f c , and consider the significant suppression effect of the grid-connected converter port filter, the anti-aliasing filter at the front end of the A / D sampling link, and the low-pass characteristics of the controller on the sampling and PWM sideband secondary harmonic components above the sampling frequency, and only consider the relatively large harmonics below the sampling frequency, with frequencies f x1 、f s -f x1 、f c -f x1 -f0,f x1 +f0 (indicates the secondary frequency generated), the last three frequencies are recorded as f x3 、f x4 、f x5 .

[0071] In an optional implementation, when a node in a power grid has a frequency of f x1 Positive sequence background harmonic current injection based on Figure 2The main circuit and control link of the single grid-connected converter shown in the figure can be obtained that there is a coupling relationship matrix (i.e., the second coupling relationship matrix) between the coupling voltage and coupling current of the grid-connected converter at any node in the network under the action of sampling and PWM sideband effect, as shown below:

[0072]

[0073]

[0074] In the formula, I nx3 , U nx3 Respectively represent the frequency point f x3 The corresponding coupling current and coupling voltage, I nx4 , U nx4 Respectively represent the frequency point f x4 The corresponding coupling current and coupling voltage, I nx5 , U nx5 Respectively represent the frequency point f x5 The corresponding coupling current and coupling voltage. The other parameters in the above formulas (14) to (16) can be determined by the following calculation and derivation process:

[0075] (1) Considering the current decoupling control and the frequency difference of the dq-axis PI controller, when the positive-sequence background harmonic current is injected and the negative-sequence background harmonic current is injected, the current inner loop control transfer function of the PI controller is expressed by the following formula:

[0076] Positive sequence:

[0077] Negative sequence:

[0078] In the formula, k p and k i are the proportional coefficient and integral coefficient of PI control respectively, ω is the background disturbance angular frequency; ω0 is the fundamental angular frequency; L1 and L2 are the filter inductors on the port side and grid side of the LCL filter respectively.

[0079] (2) SPWM modulation process is equivalent to:

[0080]

[0081]

[0082] In the formula, ω x3 ,ω x4 and ω x5 Respectively represent the frequency point f x3 、f x4 and f x5 The corresponding angular frequency, M0, θ0 are the amplitude and initial phase angle of the fundamental signal, ωc ,θ c Respectively represent the switching angular frequency and the PWM carrier initial phase angle, J0, J1 and J -1 represents the Bessel function.

[0083] (3) The LCL filter transfer function is expressed by the following formula:

[0084]

[0085] Z L1 (jω)=R L1 +jωL1 (A-8)

[0086] Z L2 (jω)=R L2 +jωL2 (A-9)

[0087]

[0088] In the formula, Z L1 , Z L2 , Z C Represents LCL filter parameters; R L1 , R L2 , R C G represents the additional resistance of the LCL filter converter side resistance, the LCL filter grid side resistance and the filter capacitor. F1 (jω), G F2 (jω) represents the transfer function of the LCL filter link.

[0089] (4) Other intermediate variables are expressed using the following formula:

[0090]

[0091]

[0092]

[0093]

[0094] In the formula, G d (jω) represents the delay link transfer function, K M , K M1 , K M2 , K M3 , K AP1 , K AP2 , K AP3 , K BP1 , K BP2 , K BP3 , K CP1 , K CP2 , KCP3 , K DP1 , K DP2 , K DP3 It is an intermediate variable used to simplify the formula expression and has no specific meaning.

[0095] Any n-node grid-connected converter can be listed as a group of equations similar to equation (5) in the previous section, and the simultaneous equation (13) can be solved to obtain the coupled voltage and current of each node converter under the control of the asymmetric frequency coupling effect, giving a series of equations similar to equations (5) to (10) in the previous section, as shown in the following equation, where the matrix dimension of each equation is expanded to match the voltage and current response under the PWM and sampling sideband frequency coupling effect.

[0096]

[0097]

[0098] In formulas (17)-(22), U nx ,I nx They are the grid-connected voltage and current vectors of each node converter under sampling and PWM effects, with dimensions of 4n*1, where U vsci and I vsci are the background harmonic voltage vector of node i and the sum of the current vectors injected into the grid by all VSCs connected to the grid at node i, both with dimensions of 4*1; sumx It is the collection matrix of the coupled voltage and current relationship matrix of each node converter, with a dimension of 4n*4n; Z netx Contains the self-impedance and corresponding mutual impedance of each converter node, with a dimension of 4n*4n, where Z ii and Z ij are the self-impedance matrix of node i and the mutual impedance matrix between nodes i and j, both with dimensions of 4*4; Z im Contains the mutual impedance between each converter node and the background harmonic injection node, with a dimension of 4n*4, where Z im is the mutual impedance between node i and the injection node, with a dimension of 4*4; Z netx , Z skx It also contains four coupling frequencies under sampling and PWM effects; I sk represents the injected background harmonic current vector, in which the four elements represent the currents of four frequencies under the sampling and PWM effects; E is the unit matrix with a dimension of 4n*4n.

[0099] The specific expressions of each sub-vector and sub-matrix in equations (17)-(22) are as follows:

[0100]

[0101]

[0102] In the formula, I vsci,nx1 ,I * vsci,nx3 ,I * vsci,nx4 ,I vsci,nx5 are the harmonic currents of the four coupling frequencies flowing from the VSC to the connected grid at the node i connected to the VSC; U vsci,nx1 , U * vsci,nx3 , U * vsci,nx4 , U vsci,nx5 are the harmonic voltages of different frequencies of background harmonics on node i connected to the VSC; Z gx1_ii , Z gx3_ii , Z gx4_ii , Z gx5_ii are the grid self-impedance of node i connected to VSC at different frequencies; Z gx1_ij , Z gx3_ij , Z gx4_ij , Z gx5_ij are the grid mutual impedances of nodes i and j connected to VSC at different frequencies; Z gx1_im , Z gx3_im , Z gx4_im , Z gx5_im are the grid mutual impedances between node i connected to the VSC and the background disturbance injection node at different frequencies.

[0103] When the injection frequency is f x1 When the negative sequence background harmonic current is used, only the frequencies f x1 、f s -f x1 、f c -f x1 +f0、f x1 -f0 harmonic components, the last three frequencies are recorded as f x3 、f x4 、f x5 The overall relationship between the coupling voltage and coupling current under grid-connected point sampling and PWM effect remains unchanged, but some intermediate variables in equations (14) to (16) need to be modified. Among them, some intermediate variables are modified according to the following formula:

[0104]

[0105]

[0106] Based on the above calculation process, the second harmonic emission model established can be obtained by equation (18) and the corresponding coupling current I when the negative sequence background harmonic current is injected. nxThe second calculation expression is expressed as .

[0107] Step S203: establishing a dead zone native harmonic emission model according to the dead zone effect of the converter.

[0108] Specifically, the above step S203 includes:

[0109] Step S2031, determining the positive sequence dead zone harmonic voltage and the negative sequence dead zone harmonic voltage according to the low frequency native harmonics introduced by the converter dead zone effect.

[0110] Step S2032, determine a third calculation expression for the coupling current caused by the positive-sequence dead-zone harmonic voltage under the frequency coupling effect of asymmetric control; wherein the third calculation expression can be determined in the following manner: based on the positive-sequence dead-zone harmonic voltage, according to the grid-connected point coupling current, the third coupling relationship matrix between the coupling voltage and the positive-sequence dead-zone harmonic voltage, and the third relationship between the grid-connected point coupling voltage and the coupling current under the frequency coupling effect of asymmetric control of any converter node in the power grid; determine the third calculation expression for the coupling current based on the third coupling relationship matrix and the third relationship between the grid-connected point coupling voltage and the coupling current.

[0111] Step S2033, determine the fourth calculation expression of the coupling current caused by the negative-sequence dead-zone harmonic voltage under the frequency coupling effect of asymmetric control; wherein the fourth calculation expression can be determined as follows: based on the negative-sequence dead-zone harmonic voltage, according to the fourth coupling relationship matrix between the grid-connected point coupling current, the coupling voltage and the negative-sequence dead-zone harmonic voltage under the frequency coupling effect of asymmetric control of any converter node in the power grid, and the fourth relationship between the grid-connected point coupling voltage and the coupling current; determine the fourth calculation expression of the coupling current based on the fourth coupling relationship matrix and the fourth relationship between the grid-connected point coupling voltage and the coupling current.

[0112] Step S2034: construct a dead zone native harmonic emission model according to the third calculation expression and the fourth calculation expression.

[0113] Specifically, at a certain switching frequency f c And the dead time t d Under the working condition, the dead zone effect mainly introduces a series of 6k±1 low-frequency native harmonics at the three-phase converter port, and its expression is:

[0114]

[0115] Where U dc Indicates the DC side voltage of the grid-connected converter, Indicates the power factor angle of the inverter.

[0116] The dead zone native harmonics enter the control link after sampling at the grid connection point. When transmitted in the control link, they will be affected by the asymmetric control frequency coupling effect. The positive sequence dead zone native harmonic voltage with a frequency of 6k+1 will additionally generate a 6k-1 coupling current response. Similarly, the negative sequence dead zone native harmonic voltage with a frequency of 6k-1 will additionally generate a 6k+1 coupling current response. The current responses of the dead zone harmonic voltages of two adjacent frequencies will superimpose on each other.

[0117] The dead zone harmonics of two adjacent frequencies will be coupled and superimposed, so we first consider that only the frequency f Dx1 (f Dx1 =(6k+1)f0) of the positive sequence dead zone harmonic voltage U Dx1 The dead zone harmonic model is then used to perform phasor superposition on the final results of the two frequencies.

[0118] At a certain switching frequency f c And the dead time t d Under the working condition, based on Figure 2 The main circuit and control link of a single grid-connected converter shown in the figure can obtain the grid-connected point current, voltage and positive sequence dead zone harmonic voltage U of any node converter in the network under the frequency coupling effect of asymmetric control. Dx1 There is a coupling relationship matrix (ie, the third coupling relationship matrix), as shown below:

[0119]

[0120] In the formula, I Dnx1 , U Dnx1 Respectively represent the frequency point f Dx1 The corresponding coupling current and coupling voltage, I Dnx2 , U Dnx2 Respectively represent the frequency point f Dx2 (f Dx2 =(6k-1)f0) corresponding to the coupling current and coupling voltage. Since the same transfer process is followed, the coefficient Y in equation (26) i The expression of y1 is the same as that of formula (2).

[0121] Depend on Figure 2 and Figure 3 It can be seen that the grid-connected point coupling voltage and coupling current of a converter in the network also satisfy the following relationship (i.e., the third relationship):

[0122]

[0123] In the formula, Z Dgx1 , Z Dgx2 Represents the frequency f Dx1 and f Dx2The system impedance obtained by performing Thevenin equivalent on a converter branch is as follows; U Dgx1 , U Dgx2 Represents the frequency f Dx1 and f Dx2 The open-circuit voltage component obtained from the Thevenin equivalent of a converter branch is mainly related to the converter harmonic injection of other nodes.

[0124] Any converter with n nodes can be written into a system of equations similar to equation (27), and by combining equation (26), the control asymmetric frequency coupling effect and the positive sequence dead zone harmonic voltage U can be obtained: Dx1 The grid-connected dead zone coupling voltage and current of each node converter under the joint action are as follows:

[0125]

[0126]

[0127] In the formula, Z Dgx1 , Z Dgx2 The subscript ij represents the mutual (self) impedance between different nodes; U Dx The subscript i in / y1 represents different nodes; the subscript i in the other equations also represents different converter nodes.

[0128] Furthermore, the frequency is f x2 (f x2 =(6k-1)f0) of negative sequence dead zone harmonic voltage U Dx2 Take it into consideration. The fourth coupling relationship matrix between the grid-connected point coupling current, coupling voltage and negative sequence dead zone harmonic voltage under the frequency coupling effect of asymmetric control of any converter node in the power grid and the fourth relationship between the grid-connected point coupling voltage and coupling current can be determined by referring to the third coupling relationship matrix and the third relationship. Thus, similar relationship equations to equations (28) and (29) can also be obtained:

[0129]

[0130] Because U Dx2 It is a negative sequence, so it is necessary to use equations (11) and (12) to calculate A, b, U Dx2 / y1 and Y sumx Modify the corresponding elements in to get A', b', U Dx2 / y'1 and Y' sumx .

[0131] Finally, I Dx1 and I Dx2The currents of the same node and the same frequency are superimposed in phase (the third calculation expression corresponding to equation 29 and the fourth calculation expression corresponding to equation (34)), and the coupled harmonic current expression caused by the dead zone native harmonic and the control asymmetric frequency coupling effect at each node converter grid connection point is obtained (i.e., the dead zone native harmonic emission model):

[0132]

[0133] Step S204: establish a converter primary and secondary harmonic source model based on the first harmonic emission model, the second harmonic emission model and the dead zone original harmonic emission model. Specifically, the converter primary and secondary harmonic source model established by this step includes the multi-frequency coupling current I of the grid-connected converter under the background harmonic effect. nx1 -I nx5 And the dead zone coupled harmonic current I Dnx1 with I Dnx2 Among them, the frequency relationship between voltage input and current response under the frequency coupling effect is shown in Table 1:

[0134] Table 1

[0135]

[0136] The method for constructing the primary and secondary harmonic source model of the converter provided in the embodiment of the present invention takes into account the frequency coupling effect caused by control asymmetry and PWM and sampling sideband effects, and can calculate the harmonic emission of multiple converters when background harmonics of arbitrary phase sequence and frequency are injected.

[0137] The method for constructing the primary and secondary harmonic source model of the converter provided in the embodiment of the present invention completely and accurately describes the frequency coupling mechanism between background disturbance harmonics, sampling sideband harmonics and PWM sideband harmonics, and can quantitatively analyze the sampling and PWM sideband secondary harmonic emission characteristics of multiple grid-connected converters.

[0138] The method for constructing the primary and secondary harmonic source model of the converter provided in the embodiment of the present invention takes into account the transmission process of the background harmonic injection after entering the converter control loop through the sampling link, and fully considers the effects of control links such as the sampling delay link, low-pass filter, power outer loop, current inner loop, phase-locked loop, and voltage feedforward, and can quantitatively analyze the asymmetric frequency-coupled harmonic emission characteristics of multi-grid-connected converter control.

[0139] The method for constructing the primary and secondary harmonic source model of the converter provided in the embodiment of the present invention analyzes the emission of the dead zone native harmonics caused by the dead zone effect, and considers the transmission process of the dead zone native harmonics after entering the converter control loop after being sampled at the grid connection point; abandons the traditional method of regarding the dead zone harmonics as a constant source, and divides the dead zone harmonics into inherent components and coupled components.

[0140] The method for constructing the primary and secondary harmonic source model of the converter provided in an embodiment of the present invention can calculate the inherent and coupled components of the adjacent frequency dead zone harmonics respectively by combining the control of the asymmetric frequency coupling effect, and perform phasor superposition of the components with the same frequency, thereby quantitatively analyzing the emission characteristics of the native coupled harmonics in the dead zone.

[0141] The method for constructing a primary and secondary harmonic source model of a converter provided in an embodiment of the present invention has very good scalability. By expanding the dimensions of the coupling relationship summary matrix and the network node impedance matrix, the phase angle and amplitude of the primary and secondary coupled harmonics of each converter can be calculated when different nodes in a larger and more complex network are connected to different numbers of converters.

[0142] The method for constructing the primary and secondary harmonic source model of the converter provided in the embodiment of the present invention assumes that the network is in a steady state and all the necessary harmonic components already exist at the grid-connected points of each converter, and this assumption is brought into the derivation process. This avoids the iterative coupling between the converter's own harmonics and the iterative coupling between different converters after they are connected to the network flow, greatly simplifies the model, and ensures accuracy.

[0143] The method for constructing the primary and secondary harmonic source model of the converter provided in the embodiment of the present invention fully and comprehensively considers the frequency coupling effect caused by dq-axis control asymmetry and PWM and sampling sideband effects, as well as the combined effect of control asymmetric frequency coupling effect and dead zone effect, and additionally considers the PWM modulation native harmonic emission, forming a complete wide-band converter harmonic emission model, which can calculate the amplitude and phase angle of the primary and secondary currents of multi-node grid-connected converters.

[0144] In this embodiment, a method for constructing a primary and secondary harmonic source model of a converter is provided, and the method comprises the following steps:

[0145] Step S301: Establish a first harmonic emission model based on the frequency coupling effect caused by the asymmetric control of the dq axis of the converter; see Figure 1 Step S101 of the illustrated embodiment will not be described in detail here.

[0146] Step S302: establish a second harmonic emission model based on the sampling and PWM frequency coupling effects generated by the converter sampling link and the PWM link; see Figure 1 Step S102 of the illustrated embodiment will not be described in detail here.

[0147] Step S303: establish a dead zone native harmonic emission model based on the dead zone effect of the converter; see Figure 1 Step S103 of the illustrated embodiment will not be described in detail here.

[0148] Step S304, establishing a converter primary and secondary harmonic source model according to the first harmonic emission model, the second harmonic emission model and the dead zone primary harmonic emission model.

[0149] Specifically, the above step S304 includes:

[0150] Step S3041, establishing a PWM switching native high-frequency harmonic emission model based on the high-frequency harmonic components introduced when the converter adopts PWM modulation; specifically, when the converter adopts PWM modulation, high-frequency harmonic components of the switching frequency and its multiples will be introduced. Therefore, the native harmonic current corresponding to the high-frequency harmonic components can be calculated to construct a PWM switching native high-frequency harmonic emission model.

[0151] In an optional implementation, the above step S3041 includes:

[0152] Step a1, perform Fourier series calculation on the converter output voltage to determine the high-frequency harmonic components introduced when PWM modulation is adopted; specifically, the expression of PWM high-frequency harmonics can be obtained by performing double Fourier series analysis on the converter output voltage. As shown below:

[0153]

[0154] In the formula, J n is the first kind of Bessel function, k is the order; m and n are not odd or even numbers at the same time, m represents the switching frequency and its multiples. M represents the modulation degree of PWM modulation, N represents the ratio of the switching frequency to the fundamental frequency, ω s Represents the sampling angular frequency.

[0155] Step a2, calculate the harmonic current of the high-frequency harmonic component after being processed by the filter and the grid equivalent impedance, and construct a PWM switching native high-frequency harmonic emission model. Specifically, the PWM native harmonic output by the converter is injected into the network after passing through the LCL filter and the grid equivalent impedance, and the grid-connected point PWM native harmonic current expression (PWM switching native high-frequency harmonic emission model) is as follows:

[0156]

[0157] In the formula, I PWM is the PWM native harmonic current at the grid-connected point, with a frequency near the switching frequency and its multiples; the subscript PWM represents the frequency corresponding to the PWM harmonic current; Z L1 , Z L2 , Z C is the LCL filter parameter; Z g The equivalent impedance of the power grid obtained from the perspective of a certain converter is related to the network structure and the converters at other nodes.

[0158] Step S3042: establish a converter primary and secondary harmonic source model based on the first harmonic emission model, the second harmonic emission model, the dead zone native harmonic emission model, and the PWM switching native high-frequency harmonic emission model. Specifically, the converter primary and secondary harmonic source model can be expressed by the following formula:

[0159] I h =I nx +I Dnx +I PWM =F h (U nx )+F 6k±1 (U Dnx )+F H (U PWM ) (38)

[0160] In the formula, I h is the primary and secondary coupled harmonic current phasor of the multi-converter grid connection point, I nx F represents the coupling current caused by the frequency coupling effect caused by control asymmetry and the sampling and PWM frequency coupling effect; h and F 6k±1 are functions of converter and network parameters, F H is a function of the network parameters.

[0161] The method for constructing the primary and secondary harmonic source model of the converter provided by the embodiment of the present invention takes into account the frequency coupling effect and dead zone effect caused by the asymmetric control of the dq axis and the PWM and sampling sideband effects, and completely analyzes the transmission process of harmonics in the outer loop, inner loop, phase-locked loop, sampling delay and low-pass filter of the converter, and can accurately obtain the phase angle and amplitude of the dead zone harmonic current of the multi-node grid-connected converter under the background harmonic injection and the control asymmetric frequency coupling effect and dead zone effect, and additionally considers the primary harmonic emission of the PWM switching frequency, providing a theoretical model for harmonic control and resonance analysis of the power grid. It considers the problem more comprehensively and has a wider scope of application.

[0162] The method for constructing the primary and secondary harmonic source model of the converter provided by the embodiment of the present invention can accurately obtain the response current of the multi-node grid-connected converter under the background harmonic injection, as well as the phase angle and amplitude of the dead zone harmonic current under the joint action of the asymmetric frequency coupling effect and the dead zone effect, and considers the PWM modulation of the original harmonic emission, forming a complete wide-band converter harmonic emission model, and providing a theoretical model for the harmonic control and resonance analysis of the power grid. In the specific modeling process, it is assumed that the system is already in a steady state, and the grid-connected current harmonic phasor contains all the primary and secondary harmonic components, which enter the control system after sampling delay; the mutual coupling iterative process between harmonics is already included in the final result. Therefore, the model obtained is a linear model in the frequency domain, and the primary and secondary coupling harmonics of each node converter can be obtained without iteration, which greatly reduces the amount of calculation while ensuring the calculation accuracy. By implementing the method provided by the present invention, the harmonic voltage and current responses of the complete spectrum of the converter of each node when any phase sequence and frequency background harmonics are injected into any node can be calculated; and by combining the control of asymmetric frequency coupling effect and dead zone effect, the native coupled harmonic current in the dead zone can also be accurately calculated, and combined with PWM modulated harmonic emission, a native harmonic emission model of the converter considering the frequency coupling effect is constructed; it can be connected to the existing harmonic analysis tool to carry out harmonic flow analysis of the power grid, and the analysis results are comprehensive and accurate.

[0163] In this embodiment, a device for constructing a primary and secondary harmonic source model of a converter is also provided, and the device is used to implement the above-mentioned embodiments and preferred implementation modes, and the descriptions that have been made are not repeated here. As used below, the term "module" can implement a combination of software and / or hardware of a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable.

[0164] This embodiment provides a device for constructing a primary and secondary harmonic source model of a converter, such as Figure 4 As shown, including:

[0165] A first model building module 41 is used to establish a first harmonic emission model according to the frequency coupling effect caused by the asymmetric control of the dq axis of the converter;

[0166] The second model building module 42 is used to establish a second harmonic emission model according to the sampling and PWM frequency coupling effects generated by the converter sampling link and the PWM link;

[0167] The third model building module 43 is used to establish a dead zone native harmonic emission model according to the dead zone effect of the converter;

[0168] The fourth model building module 44 is used to establish the converter primary and secondary harmonic source model according to the first harmonic emission model, the second harmonic emission model and the dead zone primary harmonic emission model.

[0169] The further functional description of each of the above modules and units is the same as that of the above corresponding embodiments and will not be repeated here.

[0170] The embodiment of the present invention also provides a computer device having the above Figure 4 The device for building the primary and secondary harmonic source model of the converter is shown.

[0171] See also Figure 5 , Figure 5 is a schematic diagram of the structure of a computer device provided by an optional embodiment of the present invention, such as Figure 5 As shown, the computer device includes: one or more processors 10, a memory 20, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. Various components are connected to each other using different buses for communication, and can be installed on a common mainboard or installed in other ways as needed. The processor can process the instructions executed in the computer device, including instructions stored in or on the memory to display the graphical information of the GUI on an external input / output device (such as, a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Similarly, multiple computer devices can be connected, and each device provides some necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system). Figure 5 A processor 10 is taken as an example.

[0172] The processor 10 may be a central processing unit, a network processor or a combination thereof. The processor 10 may further include a hardware chip. The hardware chip may be a dedicated integrated circuit, a programmable logic device or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic or any combination thereof.

[0173] The memory 20 stores instructions executable by at least one processor 10, so that at least one processor 10 executes the method shown in the above embodiment.

[0174] The memory 20 may include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application required for at least one function; the data storage area may store data created by the use of a computer device based on the presentation of a small program landing page, etc. In addition, the memory 20 may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some optional embodiments, the memory 20 may optionally include a memory remotely arranged relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0175] The memory 20 may include a volatile memory, such as a random access memory; the memory may also include a non-volatile memory, such as a flash memory, a hard disk or a solid state drive; the memory 20 may also include a combination of the above types of memory.

[0176] The computer device further comprises a communication interface 30 for the computer device to communicate with other devices or a communication network.

[0177] The embodiment of the present invention also provides a computer-readable storage medium. The method according to the embodiment of the present invention can be implemented in hardware, firmware, or can be implemented as a computer code that can be recorded in a storage medium, or can be implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and will be stored in a local storage medium through a network download, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state hard disk, etc.; further, the storage medium can also include a combination of the above types of memories. It can be understood that a computer, a processor, a microprocessor controller, or programmable hardware includes a storage component that can store or receive software or computer code. When the software or computer code is accessed and executed by a computer, a processor, or hardware, the method shown in the above embodiment is implemented.

[0178] A part of the present invention may be applied as a computer program product, such as a computer program instruction, which, when executed by a computer, can call or provide the method and / or technical solution according to the present invention through the operation of the computer. Those skilled in the art should understand that the existence of the computer program instruction in a computer-readable medium includes, but is not limited to, a source file, an executable file, an installation package file, etc., and accordingly, the way in which the computer program instruction is executed by the computer includes, but is not limited to: the computer directly executes the instruction, or the computer compiles the instruction and then executes the corresponding compiled program, or the computer reads and executes the instruction, or the computer reads and installs the instruction and then executes the corresponding installed program. Here, the computer-readable medium may be any available computer-readable storage medium or communication medium accessible to the computer.

[0179] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for constructing a primary and secondary harmonic source model of a converter, characterized in that: The method comprises: The first harmonic emission model is established based on the frequency coupling effect caused by the asymmetric control of the converter dq axis; The second harmonic emission model is established based on the sampling and PWM frequency coupling effects generated by the converter sampling link and PWM link; According to the dead zone effect of converter, the dead zone native harmonic emission model is established; The converter primary and secondary harmonic source model is established based on the first harmonic emission model, the second harmonic emission model and the dead zone native harmonic emission model.

2. The method according to claim 1, characterized in that The converter primary and secondary harmonic source model is established based on the first harmonic emission model, the second harmonic emission model and the dead zone primary harmonic emission model, including: According to the high-frequency harmonic components introduced when the converter adopts PWM modulation, a PWM switching native high-frequency harmonic emission model is established; The converter primary and secondary harmonic source model is established based on the first-generated harmonic emission model, the second-generated harmonic emission model, the dead zone native harmonic emission model and the PWM switching native high-frequency harmonic emission model.

3. The method according to claim 1, characterized in that: The first harmonic emission model is established based on the frequency coupling effect caused by the asymmetric control of the converter dq axis, including: When there is positive-sequence background harmonic current injection or negative-sequence background harmonic current injection at any converter node of the power grid, based on the frequency coupling effect caused by the asymmetric dq axis control of the converter, determine the first coupling relationship matrix between the grid-connected point coupling voltage and the coupling current of the converter and the first relationship between the grid-connected point coupling voltage and the coupling current; A first calculation expression for the coupling current is determined based on the first coupling relationship matrix and the first relationship between the grid-connected point coupling voltage and the coupling current, and a first harmonic emission model for the positive sequence or a first harmonic emission model for the negative sequence is constructed.

4. The method according to claim 1, characterized in that The second harmonic emission model is established based on the sampling and PWM frequency coupling effects generated by the converter sampling link and PWM link, including: When there is positive sequence background harmonic current injection or negative sequence background harmonic current injection at any converter node of the power grid, the harmonic frequency under the effect of sampling and PWM sideband effect in the converter sampling delay link and PWM link; Determine a second coupling relationship matrix between the grid-connected point coupling voltage and the coupling current of the converter and a second relationship between the grid-connected point coupling voltage and the coupling current based on the converter current inner loop control, PWM and filter transfer function, wherein the coupling current is the coupling current caused by the harmonic frequency coupling effect; A second calculation expression for the coupling current is determined based on the second coupling relationship matrix and the second relationship between the grid-connected point coupling voltage and the coupling current, and a second harmonic emission model for the positive sequence or a second harmonic emission model for the negative sequence is constructed.

5. The method according to claim 1, characterized in that The dead zone native harmonic emission model is established based on the dead zone effect of the converter, including: According to the low-frequency native harmonics introduced by the converter dead zone effect, the positive sequence dead zone harmonic voltage and the negative sequence dead zone harmonic voltage are determined; Determine the third calculation expression of the coupling current caused by the positive sequence dead zone harmonic voltage under the frequency coupling effect of asymmetric control; Determine a fourth calculation expression for coupling current caused by negative sequence dead zone harmonic voltage under frequency coupling effect of asymmetric control; A dead zone native harmonic emission model is constructed according to the third calculation expression and the fourth calculation expression.

6. The method according to claim 5, characterized in that The third calculation expression for the coupling current caused by the positive sequence dead zone harmonic voltage under the frequency coupling effect of asymmetric control is determined, including: Based on the positive-sequence dead-zone harmonic voltage, according to the third coupling relationship matrix between the grid-connected point coupling current, the coupling voltage and the positive-sequence dead-zone harmonic voltage under the frequency coupling effect of asymmetric control of any converter node in the power grid, and the third relationship between the grid-connected point coupling voltage and the coupling current; Determine a third calculation expression for the coupling current based on the third coupling relationship matrix and a third relationship between the grid-connected point coupling voltage and the coupling current; The fourth calculation expression for determining the coupling current caused by the negative sequence dead zone harmonic voltage under the frequency coupling effect of asymmetric control includes: Based on the negative-sequence dead-zone harmonic voltage, according to the fourth coupling relationship matrix between the grid-connected point coupling current, the coupling voltage and the negative-sequence dead-zone harmonic voltage under the frequency coupling effect of asymmetric control of any converter node in the power grid, and the fourth relationship between the grid-connected point coupling voltage and the coupling current; A fourth calculation expression for the coupling current is determined based on the fourth coupling relationship matrix and a fourth relationship between the grid-connected point coupling voltage and the coupling current.

7. The method according to claim 2, characterized in that According to the high-frequency harmonic components introduced when the converter adopts PWM modulation, a PWM switching native high-frequency harmonic emission model is established, including: Perform Fourier series calculation on the converter output voltage to determine the high-frequency harmonic components introduced when PWM modulation is used; The harmonic current of the high-frequency harmonic component after being processed by the filter and the grid equivalent impedance is calculated, and a PWM switching native high-frequency harmonic emission model is constructed.

8. A device for constructing a primary and secondary harmonic source model of a converter, characterized in that: The device comprises: A first model building module is used to establish a first harmonic emission model according to the frequency coupling effect caused by the asymmetric control of the dq axis of the converter; The second model building module is used to establish a second harmonic emission model according to the sampling and PWM frequency coupling effects generated by the converter sampling link and the PWM link; The third model building module is used to establish a dead zone native harmonic emission model according to the dead zone effect of the converter; The fourth model building module is used to establish the converter primary and secondary harmonic source model according to the first harmonic emission model, the second harmonic emission model and the dead zone native harmonic emission model.

9. A computer device, characterized in that: include: A memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the method for constructing a primary and secondary harmonic source model of a converter according to any one of claims 1 to 7 by executing the computer instructions.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a computer to execute the method for constructing a primary and secondary harmonic source model of a converter according to any one of claims 1 to 7.

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