Resonance identification and suppression method and system for power distribution system under distributed photovoltaic access

Abstract

The method and system for identifying and suppressing resonance of a power distribution system under distributed photovoltaic access, the frequency corresponding to the maximum value of modal impedance is the resonance frequency point, the element corresponding to the maximum value of total response index is the resonance key element, and the modal impedance of the resonance key element at the resonance frequency point is the resonance impedance; the current harmonic component and the voltage harmonic component of the grid-connected point of the inverter and the filter inductance of the inverter are obtained; the equivalent admittance of the inverter is calculated based on the control coefficient of the current controller by using the resonance impedance and the filter inductance of the inverter; the harmonic component of the current control instruction value is calculated by using the equivalent admittance of the inverter and the voltage harmonic component of the grid-connected point; the difference between the harmonic component of the current control instruction value and the current harmonic component of the grid-connected point of the inverter is used by the current controller to output the sum of the voltage instruction value of the grid-connected point and the voltage harmonic component of the grid-connected point as the harmonic component of the inverter bridge arm voltage and input to the driving circuit to obtain the trigger pulse signal, thereby suppressing the resonance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and is applied to an active distribution network, in particular, relates to a resonance identification and harmonic resonance suppression method and system for a distribution system under distributed photovoltaic access. BACKGROUND

[0002] With large-scale access of distributed photovoltaic to the distribution system, the distribution system with a large number of nodes, complex types of components, and large power fluctuations of sources and loads has the possibility of multiple resonances, which may cause the modal impedance at the resonance frequency to present a maximum value, and only a small harmonic current excitation can cause a large harmonic voltage, resulting in harmonic voltage out-of-limit, affecting the normal operation of the power grid and even damaging equipment. When the output impedance of the photovoltaic inverter matches the inductive and capacitive impedance of the power grid under certain conditions, resonance will be caused. The harmonic resonance of the distribution system with photovoltaic access needs to be identified and managed.

[0003] In the prior art, on the basis of the study on the harmonic resonance mechanism of the distribution system with photovoltaic access, some management measures and harmonic elimination devices are proposed. These measures and devices can be divided into two categories: one is to change the network structure parameters to make the system far away from the resonance frequency and far away from the harmonic source excitation; the other is to install harmonic filtering devices such as active power filters. However, the two methods have the problems of single application scene, inability to achieve targeted suppression of resonance, poor flexibility, and increased cost of harmonic management, and cannot be completely applied to the photovoltaic access distribution network scene. SUMMARY

[0004] To solve the problems in the prior art, the application provides a resonance identification and suppression method and system for a distribution system under distributed photovoltaic access, which identifies the harmonic resonance of the system and evaluates the risk, is convenient to operate, has clear process, and does not affect the output of the power frequency power of photovoltaic.

[0005] The application adopts the following technical solutions.

[0006] The application provides a resonance identification and suppression method for a distribution system under distributed photovoltaic access. The components of the distribution system include an inverter, an inductive component, a capacitive component, and an active load. The inverter includes a current controller, a driving circuit, and a filter inductor, and comprises:

[0007] The resonance admittance matrix of the distribution system at the resonance frequency is obtained, the eigenvalues of the resonance admittance matrix are solved, the reciprocals of the eigenvalues are taken as the modal impedances of the components, and the frequency corresponding to the maximum value of the modal impedance is taken as the resonance frequency point;

[0008] The total response index of the modal impedance of each element at the resonance frequency point is calculated by using the Scobol sensitivity analysis method, the element corresponding to the maximum total response index is taken as the resonance key element, and the modal impedance of the resonance key element at the resonance frequency point is taken as the resonance impedance;

[0009] The current harmonic component and the voltage harmonic component of the grid-connected point of the inverter and the filter inductance of the inverter are obtained; the equivalent admittance of the inverter is calculated based on the control coefficient of the current controller by using the resonance impedance and the filter inductance of the inverter; the harmonic component of the current control instruction value is calculated by using the equivalent admittance of the inverter and the voltage harmonic component of the grid-connected point of the inverter; the difference between the harmonic component of the current control instruction value and the current harmonic component of the grid-connected point of the inverter is taken as the input data of the current controller, and the sum of the voltage instruction value of the grid-connected point of the inverter output by the current controller and the voltage harmonic component of the grid-connected point of the inverter is taken as the harmonic component of the bridge arm voltage of the inverter and input to the driving circuit to obtain the trigger pulse signal of the switching device of the inverter, thereby controlling the inverter to suppress the resonance of the power distribution system.

[0010] Preferably, the resonance admittance matrix of the power distribution system at the resonance frequency satisfies the following relationship:

[0011] U f =Y f -1 I f

[0012] In the formula, U f is the node voltage vector at the resonance frequency f, I f is the node injection current vector at the resonance frequency f, and Y f is the resonance admittance matrix at the resonance frequency f.

[0013] The following relationship is obtained:

[0014]

[0015] In the formula, U f1 , U f2 , …, U fn are respectively the voltages of nodes 1, 2, …, n at the resonance frequency f, λ f1 , λ f2 , …, λ fn are respectively the first, second, …, n characteristic values of the resonance admittance matrix, and J f1 , J f2 , …, J fn are respectively the modal currents of nodes 1, 2, …, n at the resonance frequency f.

[0016] Each characteristic value λ f1 , λ f2 , …, λfn The reciprocal of is the modal impedance of each component, and the smallest eigenvalue corresponds to the maximum modal impedance.

[0017] Preferably, the modal impedance of each component is used as sample data, the modal impedance at a certain resonant frequency point of the power distribution system is used as the output variable, and the Scobol sensitivity analysis method is used to calculate the total response index of each sample data, satisfying the following relationship:

[0018]

[0019] Where E() is the mathematical expectation function, Var() is the mathematical variance function, y is the output variable, and x i is the input variable, x~ i To remove the input variable x i The vector formed by all the remaining variables, ST i is the total response index of the i-th sample data.

[0020] Preferably, the current harmonic component and voltage harmonic component of the inverter grid connection point and the filter inductance of the inverter are obtained through the harmonic detection link;

[0021] The harmonic detection link includes a trap filter;

[0022] The transfer function of the notch filter satisfies the following relationship:

[0023]

[0024] Where G F is the transfer function of the notch filter, ω n is the center angular frequency of the notch filter, is the fundamental angular frequency, Q is the quality factor of the notch filter, and s is the integration operator.

[0025] Preferably, the equivalent admittance of the inverter is calculated based on the control coefficient of the current controller using the resonant impedance and the filter inductance of the inverter, satisfying the following relationship:

[0026]

[0027] Where Y is the equivalent admittance of the inverter, Z P is the resonant impedance, K p is the proportional coefficient of the current controller, s is the integral operator, and L is the filter inductance of the inverter.

[0028] Preferably, the harmonic component of the current control command value is calculated using the equivalent admittance of the inverter and the voltage harmonic component of the inverter grid connection point; and the following relationship is satisfied:

[0029] i ref,H =VB,H Y

[0030] wherein i ref,H is the Hth harmonic component of the current controller command value i ref , V B,H is the voltage harmonic component of the inverter grid point.

[0031] Preferably, the difference between the harmonic component of the current control command value and the current harmonic component of the inverter grid point is taken as the input data of the current controller, the sum of the voltage command value of the inverter grid point output by the current controller and the voltage harmonic component of the inverter grid point is taken as the harmonic component of the inverter bridge arm voltage; the following relationship is satisfied:

[0032] (i ref,H -i H )G i +V B,H =V PWM,H

[0033] wherein G i is the transfer function of the current controller, (i ref,H -i H )G i is the voltage command value of the inverter grid point output by the current controller, V PWM,H is the Hth harmonic component of the inverter bridge arm voltage, i H is the current harmonic component of the inverter grid point.

[0034] The application further provides a resonance identification and suppression system of a distributed photovoltaic access lower power distribution system, elements of the power distribution system comprising: an inverter, an inductive element, a capacitive element, an active load, the inverter comprising: a current controller, a driving circuit, a filter inductor, comprising:

[0035] a resonance identification module, configured to acquire a resonance admittance matrix of the power distribution system at a resonance frequency, solve eigenvalues of the resonance admittance matrix, take reciprocals of the eigenvalues as modal impedances of the elements, take a frequency corresponding to a maximum value of the modal impedances as a resonance frequency point, calculate total response indexes of the modal impedances of the elements at the resonance frequency point by using a Scobol sensitivity analysis method, take an element corresponding to a maximum value of the total response indexes as a resonance key element, and take a modal impedance of the resonance key element at the resonance frequency point as a resonance impedance.

[0036] The resonance suppression module is used to obtain the current harmonic components and voltage harmonic components of the inverter grid-connected point, as well as the filter inductance of the inverter; using the resonant impedance and the filter inductance of the inverter, based on the control coefficient of the current controller, the equivalent admittance of the inverter is calculated; using the equivalent admittance of the inverter and the voltage harmonic components of the inverter grid-connected point to calculate the harmonic components of the current control command value; using the difference between the harmonic components of the current control command value and the current harmonic components of the inverter grid-connected point as the input data of the current controller, and the sum of the inverter grid-connected point voltage command value output by the current controller and the voltage harmonic components of the inverter grid-connected point is used as the harmonic component of the inverter bridge arm voltage and is input to the drive circuit to obtain a trigger pulse signal for the inverter switching device, thereby controlling the inverter to suppress the resonance of the distribution system.

[0037] A terminal includes a processor and a storage medium; the storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the method.

[0038] A computer-readable storage medium stores a computer program thereon, which implements the steps of the method when executed by a processor.

[0039] The beneficial effects of the present invention are that, compared with the prior art, the method proposed in the present invention can accurately locate the frequency and intensity of the resonance, reduce the risk of harmonic exceeding the limit caused by harmonic source interference, and effectively improve the quality of power.

[0040] The present invention proposes a harmonic suppression strategy based on modal impedance sensitivity analysis. According to the results of the sensitivity analysis, the component with the greatest influence on a certain harmonic resonance is obtained. Then, a control strategy is used to eliminate the influence of the non-fundamental components of the component, which equivalently changes the capacitive (inductive) characteristics of the component, thereby achieving targeted suppression of harmonic resonance and having a better suppression effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a flow chart of a method for resonance identification and suppression of a power distribution system under distributed photovoltaic access proposed by the present invention;

[0042] Figure 2 is the resonant modal impedance analysis result of the power distribution system in the embodiment of the present invention;

[0043] Figure 3 is a circuit diagram of a power distribution system in an embodiment of the present invention;

[0044] Figure 4 is an equivalent circuit diagram of a power distribution system in an embodiment of the present invention;

[0045] Figure 5 is the Scobol sensitivity analysis result at a resonant frequency of 10.5 pu in an embodiment of the present invention;

[0046] Figure 6 is the Scobol sensitivity analysis result at the resonant frequency 25 p.u. in the embodiment of the application;

[0047] Figure 7 is a schematic diagram of the control structure of the harmonic management of the inverter;

[0048] Figure 8 is a schematic diagram of the control structure of the inverter identification and suppression of resonance in the embodiment of the application;

[0049] Figure 9 is a comparison chart of the suppression effect of the suppression method of the application and the existing suppression method when a 10.5th harmonic source disturbance exists in the embodiment of the application;

[0050] Figure 10 is a comparison chart of the suppression effect of the suppression method of the application and the existing suppression method when a 25.0th harmonic source disturbance exists in the embodiment of the application. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical scheme and advantages of the application clearer, the technical scheme of the application will be described clearly and completely below in combination with the drawings in the embodiments of the application. The embodiments described in the application are only a part of the embodiments of the application, not all the embodiments. All other embodiments obtained by those skilled in the art without creative labor based on the spirit of the application are within the protection scope of the application.

[0052] The application proposes a resonance identification and suppression method for a power distribution system with distributed photovoltaic access, as shown in Figure 1 , which comprises:

[0053] Step 1, obtain the resonance admittance matrix of the power distribution system at the resonant frequency, solve the eigenvalues of the resonance admittance matrix, and take the reciprocal of each eigenvalue as the modal impedance of each element; take the frequency corresponding to the maximum value of the modal impedance as the resonant frequency point.

[0054] Specifically, step 1 comprises:

[0055] Step 1.1, obtain the resonance admittance matrix of the power distribution system at the parallel resonant frequency.

[0056] When the power distribution system resonates, the resonant frequency is f, and a small current injected at any node will still produce a large node voltage, and the resonance admittance matrix of the power distribution system at the resonant frequency satisfies the following relationship:

[0057] U f =Y f -1 I f

[0058] where U is the node voltage vector at the resonance frequency f, I is the node injection current vector at the resonance frequency f, Y is the resonance admittance matrix at the resonance frequency f. f f f

[0059] Step 1.2, solve the eigenvalues of the resonance admittance matrix, and take the reciprocal of each eigenvalue as the modal impedance of each element.

[0060] When the power distribution system resonates, there is an eigenvalue in the resonance admittance matrix that is approximately zero.

[0061] Y f is decomposed into the following relationship:

[0062] Y f = LΛT

[0063] where Λ is the eigenvalue diagonal matrix of Y f , L is the left eigenvector, and T is the right eigenvector.

[0064] Therefore, the node voltage vector satisfies the following relationship:

[0065] U f = LΛ -1 TI f

[0066] Define U f = TV f , J f = TI f , where V f is the node injection voltage vector at the resonance frequency f, and J f is the modal current vector at the resonance frequency f, to obtain the following relationship:

[0067]

[0068] where U f1 , U f2 , …, U fn are the voltages of nodes 1, 2, …, n at the resonance frequency f, λ f1 , λ f2 , …, λ fn are the first, second, …, n eigenvalues of the resonance admittance matrix, respectively, and J f1 , J f2 , …, J fn are the modal currents of nodes 1, 2, …, n at the resonance frequency f, respectively.

[0069] ​​​In step 1.3, the frequency corresponding to the maximum value of the modal impedance is taken as the resonant frequency point.

[0070] Define each eigenvalue λ f1 ,λ f2 ,……,λ fn The reciprocal of The modal impedance is characterized by its minimum eigenvalue, corresponding to the modal impedance maximum. At this maximum, a small modal current generates a large modal voltage. Therefore, the present invention proposes identifying the resonant frequency and resonance strength in a power distribution system by determining the characteristics of the broadband modal impedance.

[0071] The results of the modal impedance analysis of the power distribution system resonance by the method proposed in this invention are as follows: Figure 2 As shown, Figure 2 The waveform diagram is based on the results of the resonant modal impedance analysis of the distribution system. The maximum modal impedance is approximately 100Ω at the resonant frequencies of 3.6pu and 10.5pu, and exceeds 250Ω at the resonant frequency of 25.0pu.

[0072] Step 2: Use the Scobol sensitivity analysis method to calculate the total response index of the modal impedance of each component at the resonant frequency point, take the component corresponding to the maximum value of the total response index as the resonant key component, and take the modal impedance of the resonant key component at the resonant frequency point as the resonant impedance.

[0073] Specifically, step 2 includes:

[0074] In step 2.1, the Scobol sensitivity analysis method is used to calculate the total response index of the parameters in the modal impedance of each component at the resonant frequency point.

[0075] The Scobol sensitivity analysis method, including variance-based sensitivity analysis, decomposes the variance of the modal impedance to derive a combination of single and multi-parameter sub-functions. The variance of a single input parameter or a collection of parameters is then used to quantify the influence of the parameters and the interactions between them. The Scobol sensitivity analysis method is suitable for solving parameter sensitivities in nonlinear models and models with uncertain parameters. It can quantitatively analyze the sensitivity of multiple parameter types and the influence of multivariate parameter interactions. As a global sensitivity analysis method, its results are relatively reliable and it is widely used in sensitivity analysis work in various fields, including power, civil engineering, and machinery.

[0076]

[0077] Where E() is the mathematical expectation function, Var() is the mathematical variance function, y is the output variable, and x i is the input variable, x~ i To remove the input variable xi The vector formed by all the remaining input variables, S i is the first-order response index corresponding to the i-th sample data, ST i is the total response index corresponding to the i-th sample data.

[0078] In a non-limiting preferred embodiment, the modal impedance of each element is taken as the sample data, the modal impedance at a resonance frequency point of the power distribution system is taken as the output variable, the Scobol sensitivity analysis method is used to calculate the first-order response index and the total response index corresponding to each sample data, which is used as the influence degree of each element on the resonance of the power distribution system, the first-order response index S i The greater the value of S i , the more significant the influence of the input variable x i on the modal impedance, and the total response index ST i The greater the value of ST g , the greater the influence of the interaction between the input variable x g and other input variables on the modal impedance. Therefore, when the modal impedance at a resonance frequency point of the power distribution system is taken as the output variable, the Scobol sensitivity analysis is mainly used to determine which input variable has a greater influence on the output variable.

[0079] Step 2.2. Take the element corresponding to the maximum total response index as the resonance key element, and take the modal impedance of the resonance key element at the resonance frequency point as the resonance impedance.

[0080] The present application determines the influence degree of each element on the resonance of the power distribution system in the set frequency band by obtaining the modal impedance of each element and using the characteristic that a very small modal current will produce a very large modal voltage at the modal impedance maximum value, effectively avoiding the influence of the volatility and uncertainty of the current and voltage parameters of each node in the power distribution system under the distributed photovoltaic access on the resonance identification, and therefore, the present application is more suitable for resonance identification in the power distribution system under new energy access and is suitable for the scene of the variable parameters of the power distribution system.

[0081] Figure 3 The present application is a power distribution system in which the resonance identification method and harmonic resonance suppression strategy of the power distribution system under the distributed photovoltaic access are implemented, and the elements of the power distribution system include: an inverter, an inductive element, a capacitive element, and an active load; wherein the inverter includes but is not limited to: a current controller, a PWM driving circuit, and a filter device.

[0082] The equivalent circuit of the power distribution system shown in FIG. 1 is shown in FIG. 2. Figure 3 The equivalent circuit of the power distribution system shown in FIG. 1 is shown in FIG. 2. Figure 4 The equivalent circuit of the power distribution system shown in FIG. 1 is shown in FIG. 2. Figure 4 The power distribution system shown in FIG. 1 includes seven nodes, wherein the system equivalent impedance connected to node 1 is R g +jX g, the equivalent resistance between node 1 and node 2 is R=0.01Ω, the equivalent inductance is L=0.1273mH; the equivalent resistance between node 1 and node 3 is R=0.003Ω, the equivalent inductance is L=0.1273mH, the equivalent resistance of two 2MVA transformers connected in parallel between node 1 and node 2 is R=0.01Ω, the equivalent inductance is L=0.1273mH, the equivalent resistance of one 1MVA and one 3MVA transformer connected in parallel between node 1 and node 3 is R=0.003Ω, the equivalent inductance is L=0.1273mH, the equivalent resistance of a 2MVA transformer between node 2 and node 4 is R=0.0246Ω, the equivalent inductance is L=2.006mH, the equivalent resistance of a 2MVA transformer between node 2 and node 5 is R=0.0209Ω, the equivalent inductance is L=1.667mH, the equivalent resistance of a 1MVA transformer between node 3 and node 6 is R=0.023Ω, the equivalent inductance is L=1.83mH, the equivalent resistance of a 3MVA transformer between node 3 and node 7 is R=0.0823Ω, the equivalent inductance is L=5.27mH; the output impedance of the inverter connected to node 4 is R0+jX0, the equivalent capacitance of the 150kvar capacitive reactive power compensation device connected to node 4 is C p1 , the equivalent resistance of a 100HP motor connected to node 4 is R=13Ω, the equivalent inductance is L=9mH, the equivalent resistance between node 4 and node 5 is R=0.023Ω, the equivalent inductance is L=0.842mH, the equivalent capacitance of the 300kvar capacitive reactive power compensation device connected to node 5 is C p2 , the equivalent resistance of a 150HP motor connected to node 5 is R=8.67Ω, the equivalent inductance is L=9mH; the equivalent resistance of a 100HP motor connected to node 6 is R=38Ω, the equivalent inductance is L=6mH; the equivalent capacitance of the 200kvar capacitive reactive power compensation device connected to node 7 is C p3 , the equivalent inductance is L=28.5mH, the equivalent capacitance of the 100kvar capacitive reactive power compensation device connected to node 7 is C p4 , the equivalent inductance is L=23mH. The parameters in the modal impedance of each node include: equivalent resistance, equivalent reactance, equivalent capacitance and equivalent inductance.

[0083] Figure 5 is the Scobol sensitivity analysis result at the resonance frequency 10.5p.u., Figure 5 , S represents the first-order response index, ST represents the total response index, and the maximum value of the total response index at the resonance frequency 10.5p.u. Figure 5 is about 0.8, and the parameters corresponding to the maximum value of the total response index are the equivalent reactance X gand the inverter output reactance X0, and these two parameters are taken as the key parameters of resonance at the resonant frequency of 10.5pu.

[0084] Figure 6 This is the Scobol sensitivity analysis result at the resonant frequency of 25 p.u., Figure 6 Where S represents the first-order response index, ST represents the total response index, according to Figure 6 It is determined that the maximum value of the total response index at the resonant frequency of 25p.u. is approximately 1.0. The parameter corresponding to the maximum value of the total response index is the equivalent capacitance C of the 150kvar capacitive reactive power supplement device connected to node 4. p1 , and use this parameter as the key parameter of resonance at the resonant frequency of 25p.u.

[0085] Step 3, obtain the harmonic current of the grid-connected line and the filter inductance of the inverter; use the resonant impedance and the harmonic current of the grid-connected line to calculate the harmonic component of the inverter grid-connected point voltage; use the resonant impedance and the filter inductance of the inverter, based on the control coefficient of the current controller, to calculate the equivalent admittance of the inverter; use the equivalent admittance of the inverter and the harmonic component of the inverter grid-connected point voltage to calculate the harmonic component of the current control command value; use the difference between the harmonic component of the current control command value and the harmonic current of the grid-connected line as the input data of the current controller, and use the sum of the inverter grid-connected point voltage command value output by the current controller and the voltage harmonic component of the inverter grid-connected point as the harmonic component of the inverter bridge arm voltage and input it into the drive circuit to obtain a trigger pulse signal of the inverter switching device, so as to control the inverter to suppress the resonance of the distribution system.

[0086] Specifically, step 3 includes:

[0087] When using the harmonic control capability of the inverter, its control structure diagram is as follows: Figure 7 As shown, the inverter grid-connected voltage V t Perform harmonic detection to obtain the grid voltage harmonic component V t,h , grid voltage harmonic component V t,h Through the virtual harmonic resistor R h Then the harmonic component of the current controller command value is obtained Fundamental component of current controller command value Harmonic components of the current controller command value The difference is used as the current controller command value I * In the harmonic control process of the inverter, the inverter is controlled as a virtual harmonic resistor at the harmonic frequency to compensate for the harmonic components emitted by the harmonic source, which is equivalent to providing a part of the damping for the harmonic resonance and plays a certain positive role in the resonance suppression. However, considering the stability of the inverter control structure, its virtual harmonic resistor R h It cannot completely offset the influence of harmonic sources.Figure 7 In, V dc is the DC voltage of the inverter, L is the filter inductance of the inverter, i tabc is the line current, Z g is the equivalent impedance of the power grid system, V g is the grid system voltage, PCC is the grid connection point, S 1～6 is the trigger pulse signal of the inverter switching device, Current Controller is the current controller, and SPWM is the drive circuit.

[0088] Specifically, step 3 includes:

[0089] Step 3.1: Obtain the current harmonic component i at the inverter grid connection point through the harmonic detection link H And voltage harmonic components V B,H , and the filter inductor L of the inverter;

[0090] Specifically, Figure 8 In the process, the harmonic detection link is used to extract the harmonic components. The harmonic detection link includes but is not limited to a notch filter. The central angular frequency of the notch filter is the fundamental angular frequency. The transfer function of the notch filter satisfies the following relationship:

[0091]

[0092] Where G F is the transfer function of the notch filter, ω n is the center angular frequency of the notch filter, and Q is the quality factor of the notch filter.

[0093] Step 3.2, using the resonant impedance and the filter inductance of the inverter, based on the control coefficient of the current controller, calculate the equivalent admittance of the inverter;

[0094] In the embodiment, the current control method adopted by the current controller includes but is not limited to proportional control, and the control coefficient of the current controller is the proportional coefficient K p , the equivalent admittance of the inverter satisfies the following relationship:

[0095]

[0096] Where Y is the equivalent admittance of the inverter, Z P is the resonant impedance, K p is the proportional coefficient of the current controller, s is the integral operator, and L is the filter inductance of the inverter;

[0097] In the embodiment, Figure 4 Middle capacitor C p1 is the key component of resonance, Z in the above formula P is the capacitance C p1The modal impedance at the resonant frequency of 25 p.u. is the equivalent capacitance of the 150 kvar capacitive reactive power compensation device connected at node 4.

[0098] Step 3.3, calculating the harmonic component of the current control instruction value by using the equivalent admittance of the inverter and the voltage harmonic component of the grid-connected point of the inverter; satisfying the following relationship:

[0099] i ref,H =V B,H Y

[0100] In the formula, i ref,H is the Hth harmonic component of the current control instruction value i ref , and V B,H is the voltage harmonic component of the grid-connected point of the inverter;

[0101] Step 3.4, taking the difference between the harmonic component of the current control instruction value and the current harmonic component of the grid-connected point of the inverter as the input data of the current controller, and taking the sum of the voltage instruction value of the grid-connected point of the inverter output by the current controller and the voltage harmonic component of the grid-connected point of the inverter as the harmonic component of the inverter bridge arm voltage; satisfying the following relationship:

[0102] (i ref,H -i H )G i +V B,H =V PWM,H

[0103] In the formula, G i is the transfer function of the current controller, (i ref,H -i H )G i is the voltage instruction value of the grid-connected point of the inverter output by the current controller, V PWM,H is the Hth harmonic component of the inverter bridge arm voltage, and i H is the current harmonic component of the grid-connected point of the inverter;

[0104] Step 3.5, driving the circuit to send a trigger pulse signal to the inverter switching device according to the harmonic component of the inverter bridge arm voltage.

[0105] Figure 8 In the formula, V tabc is the line voltage, in the coordinate transformation module, the line voltage V tabc passes through a phase-locked loop PLL to obtain a phase angle θ, the current control instruction value i ref and the phase angle θ pass through abc / dq coordinate transformation to obtain the dq-axis components i dref , i qref of the current control instruction value, and the line current i tabc and the phase angle θ pass through abc / dq coordinate transformation to obtain the dq-axis components itd tq tabc and phase angle θ through abc / dq coordinate transformation to obtain dq axis components V td tq The coordinate transformation module sends data to the current controller. The voltage value obtained through transfer function G i and ωL in the current controller is subtracted from the dq axis components V td tq to obtain the dq axis components V md mq .

[0106] The application further proposes a resonance control strategy of the inverter on the control architecture of the inverter for harmonic governance, and the suppression of harmonic resonance is realized by means of offsetting the resonance amount of the resonance key element. In the inverter control system, a harmonic detection link is connected in series to extract the current harmonic component and the voltage harmonic component of the inverter grid point; the equivalent admittance of the inverter is calculated based on the control coefficient of the current controller by using the resonance impedance and the filter inductance of the inverter, the harmonic component of the current control instruction value is calculated by using the equivalent admittance of the inverter and the voltage harmonic component of the inverter grid point, which is actually to obtain the influence component of the resonance key element on the harmonic resonance, and the difference between the harmonic component of the current control instruction value and the current harmonic component of the inverter grid point is taken as the input data of the current controller, and the sum of the voltage instruction value of the inverter grid point output by the current controller and the harmonic component of the voltage of the inverter grid point is taken as the harmonic component of the inverter bridge arm voltage and input to the driving circuit, so as to eliminate the influence component of the resonance key element on the harmonic resonance, and under the control of the trigger pulse signal, the output impedance characteristics of the inverter and the characteristics of the resonance key element are offset to each other, so that more effective suppression of the harmonic resonance is realized, and better suppression effect is achieved,

[0107] In the photovoltaic access power distribution system, the method proposed in the application is simulated and analyzed by using Matlab / Simulink software, and from the simulation results, it can be seen that the resonance risk identification method and the harmonic resonance suppression strategy proposed in the application can accurately locate the frequency and strength of resonance, reduce the harmonic out-of-limit risk possibly caused by harmonic source interference, and effectively improve the power quality.

[0108] Figure 9 ​​​​​For the existence of 10.5 harmonic source disturbance, the suppression effect of the suppression method of the present application and the existing suppression method is compared, when the suppression method of the present application is put into, the harmonic voltage distortion rate is reduced from 4.39% to 1.90%, the suppression effect is 56.72%, and when the existing suppression method is put into, the harmonic voltage distortion rate is reduced from 4.39% to 2.85%, the suppression effect is weaker than the suppression method of the present application, which proves the effectiveness of the suppression strategy.

[0109] Figure 10 For the existence of 25.0 harmonic source disturbance, the suppression effect of the suppression method of the present application and the existing suppression method is compared, when the suppression method of the present application is put into, the harmonic voltage distortion rate is reduced from 13.48% to 5.34%, the suppression effect is 57.05%, and when the existing suppression method is put into, the harmonic voltage distortion rate is reduced from 4.39% to 7.87%, the suppression effect is weaker than the suppression method of the present application, which proves the effectiveness of the suppression strategy.

[0110] The present application also provides a resonant identification and suppression system for a power distribution system with distributed photovoltaic access, the elements of the power distribution system comprising: an inverter, an inductive element, a capacitive element, an active load, the inverter comprising: a current controller, a drive circuit, a filter inductor, comprising:

[0111] A resonant identification module is used to obtain the resonant admittance matrix of the power distribution system at the resonant frequency, solve the eigenvalues of the resonant admittance matrix, and take the reciprocal of each eigenvalue as the modal impedance of each element; take the frequency corresponding to the maximum value of the modal impedance as the resonant frequency point; use the Scobol sensitivity analysis method to calculate the total response index of the modal impedance of each element at the resonant frequency point, and take the element corresponding to the maximum value of the total response index as the resonant key element, and take the modal impedance of the resonant key element at the resonant frequency point as the resonant impedance.

[0112] A resonant suppression module is used to obtain the current harmonic component and the voltage harmonic component of the inverter grid connection point, and the filter inductor of the inverter; use the resonant impedance and the filter inductor of the inverter to calculate the equivalent admittance of the inverter based on the control coefficient of the current controller; use the equivalent admittance of the inverter and the voltage harmonic component of the inverter grid connection point to calculate the harmonic component of the current control instruction value; take the difference between the harmonic component of the current control instruction value and the current harmonic component of the inverter grid connection point as the input data of the current controller, and take the sum of the voltage harmonic component of the inverter grid connection point and the voltage instruction value of the inverter grid connection point output by the current controller as the harmonic component of the inverter bridge arm voltage and input to the drive circuit to obtain the trigger pulse signal of the inverter switching device, and control the inverter to suppress the resonance of the power distribution system.

[0113] The present disclosure can be a system, a method, and / or a computer program product. The computer program product can include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present disclosure.

[0114] The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium can be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium include the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or punched tape, a

[0115] The computer readable program instructions described herein can be downloaded to respective computing / processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and / or a wireless network. The network can comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and / or edge servers. A network adapter card or network interface in each computing / processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing / processing device.

[0116] Computer readable program instructions for carrying out operations of the present disclosure can be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like, and conventional procedural programming languages such as the "C" programming language or similar programming languages. The computer readable program instructions can execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer can be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection can be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) can execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present disclosure.

[0117] Finally, it should be noted that the above-mentioned embodiments are merely used to illustrate the technical solutions of the present application, but not to limit it. Although the present application has been described in detail with reference to the above-mentioned embodiments, those skilled in the art should understand that the specific embodiments of the present application can be modified or replaced, and any modification or replacement without departing from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.

Claims

1. A method for identifying and suppressing resonance in a distributed photovoltaic power distribution system, wherein the components of the power distribution system include: Inverter, inductive element, capacitive element, active load, the inverter includes: current controller, drive circuit, filter inductor, characterized in that it includes: Obtain the resonant admittance matrix of the power distribution system at the resonant frequency, solve the eigenvalues ​​of the resonant admittance matrix, and use the reciprocal of each eigenvalue as the modal impedance of each component; and use the frequency corresponding to the maximum value of the modal impedance as the resonant frequency point; The Sobol sensitivity analysis method is used to calculate the total response index of the modal impedance of each component at the resonant frequency. The component corresponding to the maximum total response index is used as the key resonant component, and the modal impedance of the key resonant component at the resonant frequency is used as the resonant impedance. Obtain the current harmonic components and voltage harmonic components at the inverter grid connection point, as well as the inverter's filter inductance. Calculate the inverter's equivalent admittance based on the resonant impedance and the inverter's filter inductance and the control coefficient of the current controller, satisfying the following relationship: Where Y is the equivalent admittance of the inverter, Z P is the resonant impedance, K p is the proportional coefficient of the current controller, s is the integral operator, and L is the filter inductance of the inverter; The harmonic component of the current control command value is calculated using the equivalent admittance of the inverter and the voltage harmonic component of the inverter grid-connected point; the difference between the harmonic component of the current control command value and the current harmonic component of the inverter grid-connected point is used as the input data of the current controller, and the sum of the inverter grid-connected point voltage command value output by the current controller and the voltage harmonic component of the inverter grid-connected point is used as the harmonic component of the inverter bridge arm voltage and input into the drive circuit to obtain a trigger pulse signal for the inverter switching device, thereby controlling the inverter to suppress the resonance of the distribution system.

2. The method for resonance identification and suppression of a distributed photovoltaic access power distribution system according to claim 1, characterized in that: The resonant admittance matrix of the power distribution system at the resonant frequency satisfies the following relationship: Where U f is the node voltage vector at the resonant frequency f, I f The node current vector injected at the resonant frequency f is Y f is the resonant admittance matrix at the resonant frequency f; The following relationship is obtained: Where U f1 、U f2 、……、U fn are the voltages of nodes 1, 2, ..., n at the resonant frequency f, λ f1 ,λ f2 ,……,λ fn are the 1st, 2nd, ..., nth eigenvalues ​​of the resonant admittance matrix, J f1 、J f2 ,……,J fn are the modal currents of nodes 1, 2, ..., n at the resonant frequency f; Define each eigenvalue λ f1 ,λ f2 ,……,λ fn The reciprocal of is the modal impedance of each component, and the smallest eigenvalue corresponds to the maximum modal impedance.

3. The method for resonance identification and suppression of a distributed photovoltaic access power distribution system according to claim 1, characterized in that: The modal impedance of each component is used as sample data, and the modal impedance at a certain resonant frequency point of the distribution system is used as the output variable. The Sobol sensitivity analysis method is used to calculate the total response index of each sample data, which satisfies the following relationship: Where E() is the mathematical expectation function, Var() is the mathematical variance function, y is the output variable, and x i is the input variable, x~ i To remove the input variable x i The vector formed by all the remaining variables, ST i is the total response index of the i-th sample data.

4. The method for resonance identification and suppression of a distributed photovoltaic access power distribution system according to claim 1, characterized in that: The harmonic detection link is used to obtain the current harmonic components and voltage harmonic components of the inverter grid connection point, and the filter inductance of the inverter; The harmonic detection link includes a trap filter; The transfer function of the notch filter satisfies the following relationship: Where G F is the transfer function of the notch filter, ω n is the center angular frequency of the notch filter, is the fundamental angular frequency, Q is the quality factor of the notch filter, and s is the integration operator.

5. The method for resonance identification and suppression of a distributed photovoltaic access power distribution system according to claim 1, characterized in that: The harmonic components of the current control command value are calculated using the equivalent admittance of the inverter and the voltage harmonic components at the inverter grid connection point; the following relationship is satisfied: i ref,H =V B,H Y Where i ref,H is the current controller command value i ref The Hth harmonic component, V B,H is the voltage harmonic component at the inverter grid-connected point.

6. The method for resonance identification and suppression of a distributed photovoltaic access power distribution system according to claim 5, characterized in that: The difference between the harmonic component of the current control command value and the current harmonic component of the inverter grid connection point is used as the input data of the current controller. The sum of the voltage command value of the inverter grid connection point output by the current controller and the voltage harmonic component of the inverter grid connection point is used as the harmonic component of the inverter bridge arm voltage; the following relationship is satisfied: (i ref,H -i H )G i +V B,H =V PWM,H Where G i is the transfer function of the current controller, (i ref,H -i H )G i is the voltage command value of the inverter grid connection point output by the current controller, V PWM,H is the Hth harmonic component of the inverter bridge arm voltage, i H is the current harmonic component at the inverter grid-connected point.

7. A resonance identification and suppression system for a distributed photovoltaic access power distribution system, the components of the power distribution system comprising: Inverter, inductive element, capacitive element, active load, the inverter includes: current controller, drive circuit, filter inductor, characterized in that it includes: The resonance identification module is used to obtain the resonant admittance matrix of the distribution system at the resonant frequency, solve the eigenvalues ​​of the resonant admittance matrix, and use the reciprocal of each eigenvalue as the modal impedance of each component. The frequency corresponding to the maximum value of the modal impedance is used as the resonant frequency point. The Sobol sensitivity analysis method is used to calculate the total response index of the modal impedance of each component at the resonant frequency point. The component corresponding to the maximum value of the total response index is used as the resonant key component, and the modal impedance of the resonant key component at the resonant frequency point is used as the resonant impedance. The resonance suppression module is used to obtain the current harmonic components and voltage harmonic components of the inverter grid connection point, as well as the inverter's filter inductance. Using the resonant impedance and the inverter's filter inductance, based on the control coefficient of the current controller, the equivalent admittance of the inverter is calculated to satisfy the following relationship: Where Y is the equivalent admittance of the inverter, Z P is the resonant impedance, K p is the proportional coefficient of the current controller, s is the integral operator, and L is the filter inductance of the inverter; The harmonic component of the current control command value is calculated using the equivalent admittance of the inverter and the voltage harmonic component of the inverter grid-connected point; the difference between the harmonic component of the current control command value and the current harmonic component of the inverter grid-connected point is used as the input data of the current controller, and the sum of the inverter grid-connected point voltage command value output by the current controller and the voltage harmonic component of the inverter grid-connected point is used as the harmonic component of the inverter bridge arm voltage and input into the drive circuit to obtain a trigger pulse signal for the inverter switching device, thereby controlling the inverter to suppress the resonance of the distribution system.

8. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 6.

9. 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 method according to any one of claims 1 to 6 are implemented.

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