A general harmonic source modeling method based on load equivalent impedance

Abstract

The application provides a general harmonic source modeling method based on load equivalent impedance, which comprises the following steps: S1, collecting voltage and current sampling data of each feeder to construct a time-domain load equivalent impedance model; S2, constructing a virtual three-phase symmetrical system based on the vector relationship between three-phase symmetrical system voltage and current; S3, calculating the equivalent impedance R on the time-domain load equivalent model by using the measured voltage and current data; S4, estimating the harmonic source current by using voltage data and load equivalent impedance; and S5, establishing a harmonic source load model. t) And L(t) The application is aimed at the problem that the calculation of load equivalent impedance generates abnormal values and is not highly applicable when the harmonic distortion rate is too large; the data driving and mechanism modeling ideas are comprehensively used, the data requirement is low, the applicable scene is more extensive, and the practicability is stronger.

Description

Technical Field

[0001] This invention relates to the field of power operation and maintenance technology, and in particular to a general harmonic source modeling method based on load equivalent impedance. Background Technology

[0002] With the rapid development of power electronics technology, numerous nonlinear devices are widely used in power grids, industries, and homes. Consequently, harmonic pollution has become increasingly serious, bringing many adverse effects to power systems and user equipment. To effectively address harmonic pollution, targeted power quality management measures are needed. Modeling harmonic sources can help us understand and analyze harmonic phenomena, predict and assess their impact on power systems, thereby facilitating the development of reasonable harmonic pollution prevention and control measures and improving the power supply reliability and power quality of the power system.

[0003] The current technology has the following drawbacks:

[0004] 1. Since the equivalent impedance of a load is the link between voltage and current waveforms, determining the equivalent impedance of a nonlinear load can fundamentally extract the characteristics of the harmonic source load. Solving for the equivalent impedance of a load using identification methods based on instantaneous current and voltage measurements of the system is theoretically unaffected by background harmonic voltage and system-side harmonic impedance. However, current methods for calculating the equivalent impedance of a load can produce outliers when the harmonic distortion rate is too high due to the zero-crossing of the coefficient denominator. Furthermore, existing methods are not applicable to three-phase unbalanced loads or single-phase loads with large fluctuations.

[0005] 2. Current harmonic source modeling methods can be broadly categorized into two types based on their approach: harmonic source mechanistic modeling and harmonic source data-driven modeling. The former is a method based on detailed analysis of physical principles, capable of accurately describing and analyzing the behavior and characteristics of harmonic sources, but it is not suitable for analyzing complex harmonic sources. The latter predicts harmonic sources through data processing and modeling, without requiring knowledge of the circuit topology, but it lacks physical interpretability. Summary of the Invention

[0006] This invention proposes a general harmonic source modeling method based on load equivalent impedance, addressing the problems of outliers and limited applicability when calculating load equivalent impedance with excessive harmonic distortion rate. It comprehensively utilizes data-driven and mechanistic modeling approaches, resulting in lower data requirements, wider applicability, and greater practicality.

[0007] The present invention adopts the following technical solution.

[0008] A general harmonic source modeling method based on equivalent load impedance includes the following steps;

[0009] Step S1: Collect voltage and current sampling data of each feeder and construct a time-domain load equivalent impedance model;

[0010] Step S2: Construct a virtual three-phase symmetrical system based on the voltage-current vector relationship of the three-phase symmetrical system;

[0011] Step S3: Calculate the equivalent impedances R(t) and L(t) on the time-domain load equivalent model using measured voltage and current data;

[0012] Step S4: Estimate the harmonic source current using voltage data and load equivalent impedance.

[0013] Step S5: Establish a harmonic source load model.

[0014] In the aforementioned time-domain load equivalent impedance model, the identification method for the load equivalent impedance is based on Thevenin's law. The time-domain load equivalent model is represented by an RL series equivalent impedance circuit. In the model, Es and Zs are the equivalent voltage source and equivalent impedance on the system side, respectively; i(t) and u(t) are the instantaneous values ​​of current and voltage measured at the monitoring point at the user's incoming line, respectively; R(t) and L(t) are the equivalent impedances of the load, both of which are functions of time t.

[0015] In step S2, based on the vector relationship between the three-phase voltage and current in the symmetrical system, the three-phase asymmetrical system is virtually decomposed into three independent virtual three-phase symmetrical systems.

[0016] The method for virtual decomposition of phase A in the three phases is as follows:

[0017] The voltage u of phase A in an actual three-phase system a (t) is considered as the A-phase voltage u of a virtual symmetric system. aa (t), i.e., u aa (t)=u a (t), taking advantage of the characteristic that the C-phase voltage leads the A-phase voltage by 120° and the B-phase voltage lags the A-phase voltage by 120° in a symmetrical system, a virtual three-phase symmetrical voltage is constructed as shown in Formula 1 below. The current is similarly constructed as shown in Formula 2 below.

[0018]

[0019]

[0020] In the formula: T is the period, which is 0.02s; u A (t), i A (t) represents the instantaneous voltage and current values ​​of phase A in the actual three-phase system, respectively; u aa (t), u ab (t), u ac (t) represent the instantaneous values ​​of the three-phase voltages A, B, and C in the virtual symmetrical system of phase A constructed from the phase A voltage of the actual system; i aa(t), i ab (t), i ac (t) represent the instantaneous values ​​of the three-phase currents A, B, and C in the virtual symmetrical system of phase A constructed from the phase A voltage of the actual system;

[0021] The method for constructing virtual symmetrical systems of phase B and phase C from the voltage and current of phase B and phase C of the actual system is similar to that of Formula 1 and Formula 2. The construction methods are shown in Formula 3, Formula 4, Formula 5, and Formula 6.

[0022]

[0023]

[0024] In the formula: u B (t), i B (t) represents the instantaneous voltage and current values ​​of phase B in the actual three-phase system, respectively; u ba (t), u bb (t), u bc (t) represent the instantaneous values ​​of the three-phase voltages A, B, and C in the virtual symmetrical system of phase B constructed from the phase B voltage of the actual system; i ba (t), i bb (t), i bc (t) represent the instantaneous values ​​of the three-phase currents A, B, and C in the virtual symmetrical system of phase B constructed from the phase B voltage of the actual system;

[0025]

[0026]

[0027] In the formula: u C (t), i C (t) represents the instantaneous voltage and current values ​​of phase C in the actual three-phase system, respectively; u ca (t), u cb (t), u cc (t) represent the instantaneous values ​​of the three-phase voltages A, B, and C in the virtual symmetrical system of phase C constructed from the phase C voltage of the actual system; i ca (t), i cb (t), i cc (t) represent the instantaneous values ​​of the three-phase currents A, B, and C in the virtual symmetrical system of phase C constructed from the phase C voltage of the actual system.

[0028] In step S3, the coordinate transformation of the three-phase voltage and current in the virtual symmetrical system is performed using the αβ transformation to obtain u. α (t), u β (t) and i α (t), iβ (t), which utilizes the information contained in the voltage and current monitoring data to improve the calculation accuracy of the load equivalent impedance, the specific formula is as follows;

[0029]

[0030]

[0031] In the formula: u aα (t), u aβ (t) represent the voltage components of the three-phase voltage in the A-phase virtual symmetrical system on the α-axis and β-axis, respectively, after αβ transformation; i aα (t), i aβ (t) represent the current components on the α-axis and β-axis of the three-phase current in the A-phase virtual symmetric system after αβ transformation;

[0032] The voltage and current vectors in the stationary αβ reference frame are represented as follows: and

[0033] Similarly, by performing coordinate transformation on the B-phase virtual symmetrical system and the C-phase virtual symmetrical system, we can obtain the voltage components of the three-phase voltage and current in the B-phase virtual symmetrical system on the α-axis and β-axis, i.e., u. bα (t), u bβ (t) and i bα (t), i bβ (t). And obtain the voltage components of the three-phase voltage and current in the C-phase virtual symmetrical system on the α and β axes, i.e., u cα (t), u cβ (t) and i cα (t), i cβ (t).

[0034] In step S4, based on Ohm's law and the RL series equivalent impedance circuit of the time-domain load equivalent model, the complex form equations of the voltage and current at the port of the load equivalent circuit of the A-phase virtual symmetrical system are as follows:

[0035]

[0036] In the formula: Represent the voltage and current vectors at the circuit ports of the load in the A-phase virtual symmetrical system, respectively; R a (t), X a (t), L a (t) represents the resistance, reactance, and inductance of the load in phase A at time t, respectively; f is the system frequency, which is 50Hz;

[0037] Will and Substituting into formula nine, we get:

[0038]

[0039] The least squares solution to the formula is shown below:

[0040]

[0041]

[0042] Similarly, the equivalent impedance R of the load in the B-phase virtual symmetrical system can be obtained. b (t), X b (t) and the load R of the C-phase virtual symmetrical system c (t), X c (t);

[0043] In Formulas 11 and 12, the denominators are all greater than zero under normal three-phase operation to avoid abnormal value problems caused by the denominator crossing the zero point.

[0044] Step S4 involves estimating the harmonic source current by estimating the load current. Specifically, this is done using the three-phase voltage u′. a 、u′ b 、u′ c Based on the equivalent load impedance obtained in this step, the output current i′ of the harmonic source is estimated through inverse matrix transformation. a 、i′ b 、i′ c ;

[0045] When estimating phase A, first use the phase A voltage u′ a A virtual three-phase symmetrical system is constructed, and the virtual three-phase voltage is transformed using the αβ transformation. The current after coordinate transformation is solved by combining the equivalent impedance of the load in the harmonic source load equivalent impedance model with an inverse matrix transformation, as shown in Equation Thirteen below:

[0046]

[0047] In the formula: i′ aα (t) and i′ aβ (t) represents the estimates of the current on the α-axis and β-axis of the virtual symmetric system of phase A at time t, respectively;

[0048] Since the constructed virtual system is a three-phase symmetrical system, the virtual three-phase currents also have the following relationship:

[0049] i aa (t)+i ab (t)+i ac Formula Fourteen: (t) = 0

[0050] The three-phase current i′ of the virtual symmetrical system of phase A is obtained by combining the inverse αβ transformation.aa (t), i′ ab (t), i′ ac (t), as shown in Formulas 15 and 16 below:

[0051]

[0052]

[0053] In the formula: Similarly, the three-phase current i′ of the B-phase virtual symmetrical system is obtained. ba (t), i′ bb (t), i′ bc (t) and the three-phase current i′ of the C-phase virtual symmetrical system ca (t), i′ cb (t), i′ cc (t);

[0054] The estimation results of the three-phase current of the harmonic source based on the general harmonic source modeling method of equivalent load impedance are shown in Equation 17 below:

[0055]

[0056] In the formula: i′ a (t), i′ b (t), i′ c (t) represents the current values ​​of the three phases A, B, and C of the harmonic source load estimated by this modeling method.

[0057] The harmonic source load model established in step S5 includes three modules: a voltage processing module, an impedance module, and a current estimation module. The voltage processing module is used to construct a virtual three-phase symmetrical system from the measured voltage and perform coordinate transformation using the αβ transformation. The impedance module stores the equivalent impedance of the harmonic source load for 10 cycles and calculates the current i′ in the stationary coordinate system using Formula 9. α (t) and i′ β (t); The current estimation module converts the output of the impedance module into the estimated current of the harmonic source load through matrix inverse transformation;

[0058] The specific steps of step S5 are as follows:

[0059] Step S51: Obtain the specific type of harmonic source load based on the ledger information;

[0060] Step S52: Use a waveform recording device to collect voltage and current data for 10 cycles at the load port of the harmonic source, and record the sampling frequency;

[0061] Step S53: Calculate the equivalent impedance of the harmonic source load over 10 cycles, store it in the impedance module, and form a harmonic source load model together with the voltage processing module and the current estimation module.

[0062] This invention constructs a virtual three-phase symmetrical system based on the load equivalent time-domain circuit model, derives the relationship between load impedance and port electrical quantities, and constructs a general load impedance estimation equation by combining αβ transformation, thereby reducing the complexity of system analysis and calculation and improving computational efficiency.

[0063] This invention is based on the intersection of data-driven and mechanism-based modeling. It utilizes measured voltage and current data from the system and combines the principle that the equivalent impedance of the load reflects the nonlinear characteristics of the harmonic source. It proposes a general harmonic source modeling method based on the equivalent impedance of the load, which requires less data, has a wider range of applications, and is more practical.

[0064] The advantages of this invention also include:

[0065] The method described in this invention proposes a new method for calculating load impedance. By performing αβ coordinate transformation on the measured three-phase voltage and current, the problem of abnormal values ​​generated during the calculation of the equivalent impedance of the load is avoided. Furthermore, by constructing a virtual three-phase symmetrical system, this calculation method is applicable not only to three-phase symmetrical loads but also to the calculation of the equivalent impedance of three-phase unbalanced loads or single-phase loads.

[0066] This invention addresses the fundamental cause of harmonic generation in nonlinear loads: the nonlinear fluctuation of the load's equivalent impedance. In contrast, the equivalent impedance of linear loads is typically time-invariant. The method described in this invention utilizes current and voltage data from the user's incoming line to calculate the load's equivalent impedance and then establish a harmonic source load model. The resulting model reflects the inherent characteristics of the load and can be used to analyze and estimate harmonic generation.

[0067] In deriving the relationship between load impedance and port electrical quantities, this invention combines αβ transformation to construct a general load impedance estimation equation, which can reduce the complexity of system analysis and calculation and improve computational efficiency. Attached Figure Description

[0068] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0069] Appendix Figure 1 This is a flowchart illustrating the present invention;

[0070] Appendix Figure 2 This is a schematic diagram of the time-domain load equivalent model;

[0071] Appendix Figure 3 This is a schematic diagram of a constructed virtual three-phase symmetrical system;

[0072] Appendix Figure 4This is a schematic diagram of the load model of a harmonic source. Detailed Implementation

[0073] As shown in the figure, a general harmonic source modeling method based on load equivalent impedance includes the following steps;

[0074] Step S1: Collect voltage and current sampling data of each feeder and construct a time-domain load equivalent impedance model;

[0075] Step S2: Construct a virtual three-phase symmetrical system based on the voltage-current vector relationship of the three-phase symmetrical system;

[0076] Step S3: Calculate the equivalent impedances R(t) and L(t) on the time-domain load equivalent model using measured voltage and current data;

[0077] Step S4: Estimate the harmonic source current using voltage data and load equivalent impedance.

[0078] Step S5: Establish a harmonic source load model.

[0079] In the time-domain load equivalent impedance model, such as Figure 2 As shown, the identification method of load equivalent impedance is based on Thevenin's law, and the time-domain load equivalent model is represented by an RL series equivalent impedance circuit. In the model, Es and Zs are the equivalent voltage source and equivalent impedance on the system side, respectively; i(t) and u(t) are the instantaneous values ​​of current and voltage measured at the monitoring point at the user's incoming line, respectively; R(t) and L(t) are the equivalent impedance of the load, both of which are functions of time t.

[0080] In step S2, based on the vector relationship between the three-phase voltage and current in the symmetrical system, the three-phase asymmetrical system is virtually decomposed into three independent virtual three-phase symmetrical systems.

[0081] The method for virtual decomposition of phase A in the three phases is as follows:

[0082] like Figure 3 As shown, the voltage u of phase A in the actual three-phase system is... a (t) is considered as the A-phase voltage u of a virtual symmetric system. aa (t), i.e., u aa (t)=u a (t), taking advantage of the characteristic that the C-phase voltage leads the A-phase voltage by 120° and the B-phase voltage lags the A-phase voltage by 120° in a symmetrical system, a virtual three-phase symmetrical voltage is constructed as shown in Formula 1 below. The current is similarly constructed as shown in Formula 2 below.

[0083]

[0084]

[0085] In the formula: T is the period, which is 0.02s; u A (t), i A (t) represents the instantaneous voltage and current values ​​of phase A in the actual three-phase system, respectively; u aa (t), u ab (t), u ac (t) represent the instantaneous values ​​of the three-phase voltages A, B, and C in the virtual symmetrical system of phase A constructed from the phase A voltage of the actual system; i aa (t), i ab (t), u ac (t) represent the instantaneous values ​​of the three-phase currents A, B, and C in the virtual symmetrical system of phase A constructed from the phase A voltage of the actual system;

[0086] The method for constructing virtual symmetrical systems of phase B and phase C from the voltage and current of phase B and phase C of the actual system is similar to that of Formula 1 and Formula 2. The construction methods are shown in Formula 3, Formula 4, Formula 5, and Formula 6.

[0087]

[0088]

[0089] In the formula: u B (t), i B (t) represents the instantaneous voltage and current values ​​of phase B in the actual three-phase system, respectively; u ba (t), u bb (t), u bc (t) represent the instantaneous values ​​of the three-phase voltages A, B, and C in the virtual symmetrical system of phase B constructed from the phase B voltage of the actual system; i ba (t), i bb (t), i bc (t) represent the instantaneous values ​​of the three-phase currents A, B, and C in the virtual symmetrical system of phase B constructed from the phase B voltage of the actual system;

[0090]

[0091]

[0092] In the formula: u C (t), i C (t) represent the instantaneous voltage and current values ​​of phase C in the actual three-phase system, respectively; i ca (t), u cb (t), u cc (t) represent the instantaneous values ​​of the three-phase voltages A, B, and C in the virtual symmetrical system of phase C constructed from the phase C voltage of the actual system; i ca (t), icb (t), i cc (t) represent the instantaneous values ​​of the three-phase currents A, B, and C in the virtual symmetrical system of phase C constructed from the phase C voltage of the actual system.

[0093] In step S3, the coordinate transformation of the three-phase voltage and current in the virtual symmetrical system is performed using the αβ transformation to obtain u. α (t), u β (t) and i α (t), i β (t), which utilizes the information contained in the voltage and current monitoring data to improve the calculation accuracy of the load equivalent impedance, the specific formula is as follows;

[0094]

[0095]

[0096] In the formula: u aα (t), u aβ (t) represent the voltage components of the three-phase voltage in the A-phase virtual symmetrical system on the α-axis and β-axis, respectively, after αβ transformation; i aα (t), i αβ (t) represent the current components on the α-axis and β-axis of the three-phase current in the A-phase virtual symmetric system after αβ transformation;

[0097] The voltage and current vectors in the stationary αβ reference frame are represented as follows: and

[0098] Similarly, by performing coordinate transformation on the B-phase virtual symmetrical system and the C-phase virtual symmetrical system, we can obtain the voltage components of the three-phase voltage and current in the B-phase virtual symmetrical system on the α-axis and β-axis, i.e., u. bα (t), u bβ (t) and i bα (t), i bβ (t). And obtain the voltage components of the three-phase voltage and current in the C-phase virtual symmetrical system on the α and β axes, i.e., u cα (t), u cβ (t) and i cα (t), i cβ (t).

[0099] In step S4, by Figure 1 According to Ohm's law and the RL series equivalent impedance circuit of the time-domain load equivalent model, the complex form equations of the voltage and current at the port of the load equivalent circuit of the A-phase virtual symmetrical system are as follows:

[0100] In the formula: Represent the voltage and current vectors at the circuit ports of the load in the A-phase virtual symmetrical system, respectively; R a (t), X a (t), L a (t) represents the resistance, reactance, and inductance of the load in phase A at time t, respectively; f is the system frequency, which is 50Hz;

[0101] Will and Substituting into formula nine, we get:

[0102]

[0103] The least squares solution to the formula is shown below:

[0104]

[0105]

[0106] Similarly, the equivalent impedance R of the load in the B-phase virtual symmetrical system can be obtained. b (t), X b (t) and the load R of the C-phase virtual symmetrical system c (t), X c (t);

[0107] In Formulas 11 and 12, the denominators are all greater than zero under normal three-phase operation to avoid abnormal value problems caused by the denominator crossing the zero point.

[0108] Step S4 involves estimating the harmonic source current by estimating the load current. Specifically, this is done using the three-phase voltage u′. a ,u′ b 、u′ c Based on the equivalent load impedance obtained in this step, the output current i′ of the harmonic source is estimated through inverse matrix transformation. a 、i′ b 、i′ c ;

[0109] When estimating phase A, first use the phase A voltage u′ a A virtual three-phase symmetrical system is constructed, and the virtual three-phase voltage is transformed using the αβ transformation. The current after coordinate transformation is solved by combining the equivalent impedance of the load in the harmonic source load equivalent impedance model with an inverse matrix transformation, as shown in Equation Thirteen below:

[0110]

[0111] In the formula: i′ aα (t) and i′ aβ (t) represents the estimates of the current on the α-axis and β-axis of the virtual symmetric system of phase A at time t, respectively;

[0112] Since the constructed virtual system is a three-phase symmetrical system, the virtual three-phase currents also have the following relationship:

[0113] i aa (t)+i ab (t)+i ac Formula Fourteen: (t) = 0

[0114] The three-phase current i′ of the virtual symmetrical system of phase A is obtained by combining the inverse αβ transformation. aa (t), i′ ab (t), i′ ac (t), as shown in Formulas 15 and 16 below:

[0115]

[0116]

[0117] In the formula: Similarly, the three-phase current i′ of the B-phase virtual symmetrical system is obtained. ba (t), i′ bb (t), i′ bc (t) and the three-phase current i′ of the C-phase virtual symmetrical system ca (t), i′ cb (t), i′ cc (t);

[0118] The estimation results of the three-phase current of the harmonic source based on the general harmonic source modeling method of equivalent load impedance are shown in Equation 17 below:

[0119]

[0120] In the formula: i′ a (t), i′ b (t), i′ c (t) represents the current values ​​of the three phases A, B, and C of the harmonic source load estimated by this modeling method.

[0121] The harmonic source load model established in step S5 is as follows: Figure 4 As shown, it contains three modules: a voltage processing module, an impedance module, and a current estimation module. The voltage processing module is used to construct a virtual three-phase symmetrical system from the measured voltage and perform coordinate transformation using the αβ transformation. The impedance module stores the equivalent impedance of the harmonic source load for 10 cycles and calculates the current i′ in the stationary coordinate system using Formula 9. α (t) and i′ β (t); The current estimation module converts the output of the impedance module into the estimated current of the harmonic source load through matrix inverse transformation;

[0122] The specific steps of step S5 are as follows:

[0123] Step S51: Obtain the specific type of harmonic source load based on the ledger information;

[0124] Step S52: Use a waveform recording device to collect voltage and current data for 10 cycles at the load port of the harmonic source, and record the sampling frequency;

[0125] Step S53: Calculate the equivalent impedance of the harmonic source load over 10 cycles, store it in the impedance module, and form a harmonic source load model together with the voltage processing module and the current estimation module.

Claims

1. A general harmonic source modeling method based on equivalent load impedance, characterized in that: Includes the following steps; Step S1: Collect voltage and current sampling data of each feeder and construct a time-domain load equivalent impedance model; Step S2: Construct a virtual three-phase symmetrical system based on the voltage-current vector relationship of the three-phase symmetrical system; Step S3: Calculate the equivalent impedance on the time-domain load equivalent impedance model using measured voltage and current data. L(t) and L(t); Step S4: Estimate the harmonic source current using voltage data and the equivalent impedance of the load; Step S5: Establish a harmonic source load model; In the time-domain load equivalent impedance model, the identification method of the load equivalent impedance is based on Thevenin's law, and the time-domain load equivalent impedance model is represented by an RL series equivalent impedance circuit. In the model, Es and Zs are the equivalent voltage source and equivalent impedance on the system side, respectively. and These are the instantaneous values ​​of current and voltage measured at the monitoring point at the user's incoming line, respectively; R(t) and L(t) are the equivalent impedance of the load, both of which are functions of time t. In step S2, based on the vector relationship between the three-phase voltage and current in the symmetrical system, the three-phase asymmetrical system is virtually decomposed into three independent virtual three-phase symmetrical systems. The method for virtual decomposition of phase A in the three phases is as follows: The voltage of phase A in an actual three-phase system Phase A voltage viewed as a virtual symmetrical system (t), that is = By utilizing the characteristic that the C-phase voltage leads the A-phase voltage by 120º and the B-phase voltage lags the A-phase voltage by 120º in a symmetrical system, a virtual three-phase symmetrical voltage is constructed as shown in Formula 1 below. The current is similarly constructed as shown in Formula 2 below. Formula 1; Formula 2; In the formula: T is the period, which is 0.02s; , These represent the instantaneous values ​​of voltage and current in phase A of a real three-phase system, respectively. , , These represent the instantaneous values ​​of the three-phase voltages A, B, and C in the virtual symmetrical system of phase A constructed from the phase A voltage of the actual system. , , These represent the instantaneous values ​​of the three-phase currents A, B, and C in the virtual symmetrical system of phase A constructed from the phase A voltage of the actual system. The method for constructing virtual symmetrical systems of phase B and phase C from the voltage and current of phase B and phase C of the actual system is similar to that of Formula 1 and Formula 2. The construction methods are shown in Formula 3, Formula 4, Formula 5, and Formula 6. Formula 3; Formula 4; In the formula: , These represent the instantaneous values ​​of voltage and current in phase B of the actual three-phase system, respectively. , , These represent the instantaneous values ​​of the three-phase voltages A, B, and C in the virtual symmetrical system of phase B constructed from the phase B voltage of the actual system. , , These represent the instantaneous values ​​of the three-phase currents A, B, and C in the virtual symmetrical system of phase B constructed from the phase B voltage of the actual system. Formula 5; Formula Six; In the formula: , These represent the instantaneous values ​​of voltage and current in phase C of a real three-phase system, respectively. , , These represent the instantaneous values ​​of the three-phase voltages A, B, and C in the virtual symmetrical system of phase C constructed from the phase C voltage of the actual system. , , These represent the instantaneous values ​​of the three-phase currents A, B, and C in the virtual symmetrical system of phase C constructed from the phase C voltage of the actual system. In step S3, the following is adopted: The transformation is performed on the coordinates of the three-phase voltage and current in the virtual symmetrical system to obtain... To improve the accuracy of load equivalent impedance calculation by utilizing the information contained in voltage and current monitoring data, the specific formula is as follows; Formula 7; Formula 8; In the formula: (t), (t) represent the three-phase voltages in the virtual symmetrical system of phase A, respectively. After transformation shaft and Voltage components on the axis; (t), (t) represent the three-phase currents in the virtual symmetrical system of phase A, respectively. After transformation shaft and Current components on the shaft; still Represented as and ; Similarly, by performing coordinate transformation on the B-phase virtual symmetrical system and the C-phase virtual symmetrical system, the three-phase voltage and current in the B-phase virtual symmetrical system can be obtained. shaft and The voltage component on the axis, i.e. (t), (t) and (t), (t); And obtain the three-phase voltage and current in the C-phase virtual symmetrical system. shaft and Voltage components on the axis, i.e. (t), (t) and (t), (t).

2. The general harmonic source modeling method based on equivalent load impedance according to claim 1, characterized in that: In step S4, based on Ohm's law and the RL series equivalent impedance circuit of the time-domain load equivalent impedance model, the complex form equations of the voltage and current at the port of the load equivalent circuit of the A-phase virtual symmetrical system are as follows: Formula Nine; In the formula: (t), (t) represent the voltage and current vectors at the circuit ports such as the load in the virtual symmetrical system of phase A; (t), (t), (t) represents the resistance, reactance, and inductance of the load in phase A at time t, respectively; f is the system frequency, which is 50Hz; Will and Substituting into formula nine, we get: Formula 10; The least squares solution to the formula is shown below: Formula 11; Official Twelve; Similarly, the equivalent impedance of the load in the B-phase virtual symmetrical system can be obtained. (t), (t) and C-phase virtual symmetrical system load (t), (t); In Formulas 11 and 12, the denominators are all greater than zero under normal three-phase operation to avoid abnormal value problems caused by the denominator crossing the zero point.

3. The general harmonic source modeling method based on equivalent load impedance according to claim 2, characterized in that: Step S4 involves estimating the harmonic source current by estimating the load current. The specific method is as follows: Three-phase voltage , Based on the equivalent load impedance obtained in this step, the output current of the harmonic source is estimated through inverse matrix transformation. , ; When estimating phase A, first use the phase A voltage. Construct a virtual three-phase symmetrical system and adopt The virtual three-phase voltage is transformed by coordinate transformation; the current after coordinate transformation is solved by inverse matrix transformation using the equivalent impedance of the load in the harmonic source load model, as shown in Formula 13 below: Formula Thirteen; In the formula: (t) and (t) represent the current at time t in the virtual symmetrical system of phase A. shaft and Estimated values ​​on the axis; Since the constructed virtual system is a three-phase symmetrical system, the virtual three-phase currents also have the following relationship: Formula Fourteen; Inverse transformation yields the three-phase currents of the virtual symmetrical system in phase A. As shown in Formulas 15 and 16 below: Formula 15; Formula Sixteen; In the formula: ; Similarly, the three-phase currents of the B-phase virtual symmetrical system are obtained. Three-phase current of the C-phase virtual symmetrical system ; The estimation results of the three-phase current of the harmonic source based on the general harmonic source modeling method of equivalent load impedance are shown in Equation 17 below: Formula 17; In the formula: (t), (t), (t) represents the current values ​​of the three phases A, B, and C of the harmonic source load estimated by this modeling method.

4. The general harmonic source modeling method based on equivalent load impedance according to claim 3, characterized in that: The harmonic source load model established in step S5 includes three modules: a voltage processing module, an impedance module, and a current estimation module. The voltage processing module is used to construct a virtual three-phase symmetrical system from the measured voltage and utilize... The transformation performs a coordinate transformation. The impedance module stores the equivalent impedance of the harmonic source load for 10 cycles. Using Formula Nine, the current in the stationary coordinate system is calculated. (t) and (t); The current estimation module converts the output of the impedance module into the estimated current of the harmonic source load through matrix inverse transformation; The specific steps of step S5 are as follows: Step S51: Obtain the specific type of harmonic source load based on the ledger information; Step S52: Use a waveform recording device to collect voltage and current data for 10 cycles at the load port of the harmonic source, and record the sampling frequency; Step S53: Calculate the equivalent impedance of the harmonic source load over 10 cycles, store it in the impedance module, and form a harmonic source load model together with the voltage processing module and the current estimation module.

Images