Method and system for acquiring broadband positive and negative sequence impedance parameters of grid-connected converter

Abstract

The invention relates to the technical field of impedance measurement, and provides a grid-connected converter broadband positive and negative sequence impedance parameter acquisition method and system, and the method comprises the steps: building a grid-connected converter simulation model; a positive and negative sequence harmonic disturbance small signal injection unit, an auxiliary phase-locked loop unit, a current signal auxiliary processing unit and an RLC circuit equivalent unit are added in a grid-connected converter simulation model; the positive and negative sequence harmonic disturbance small signal injection unit superposes harmonic disturbance with preset frequency and phase sequence at a power grid power frequency three-phase voltage source port; the auxiliary phase-locked loop unit obtains a phase angle of a power frequency three-phase voltage source of the power grid; the current signal auxiliary processing unit processes the grid-connected point current signal; and the RLC circuit equivalent unit obtains the impedance parameter of the grid-connected converter by measuring the loop current effective value and the phase angle. Positive and negative sequence impedance parameters with clear physical significance can be obtained, and the method has the advantages of being simple in algorithm, convenient to use, accurate in result, high in impedance data obtaining speed and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of impedance measurement, and particularly to a method and system for obtaining positive and negative sequence impedance parameters of a grid-connected converter with a wide frequency band. Background Art

[0002] The current new energy grid-connected system mainly uses grid-following voltage source converters (GF-VSCs). The VSC synchronizes with the grid voltage through a phase lock loop (PLL) and uses current vector control to achieve rapid power regulation, presenting as a controlled current source externally. The VSC is widely used in the grid connection control of wind power, photovoltaics, and energy storage due to its simple control structure, mature technology, and the characteristic of operating at the maximum power point. As the number of new energy power stations under construction increases, the installed capacity and power generation ratio expand continuously, a large number of new energy power stations are interconnected and connected to the public grid through long-distance transmission lines and multiple transformers, and the characteristics of weak grids will become stronger and stronger (a weak system refers to a grid with a short-circuit ratio lower than 3, and the short-circuit ratio refers to the ratio of the short-circuit capacity at the grid connection point to the installed capacity of the power station). The low short-circuit ratio causes the stability problems brought by the interaction between new energy power stations and the grid to become increasingly prominent, and the interaction between the VSC and the weak grid leads to frequent occurrence of wide-frequency oscillation accidents. The risk and influence range of wide-frequency oscillation problems are constantly expanding, posing a great challenge to system stability.

[0003] By establishing an impedance model of the grid-connected converter through small-signal analysis, the mechanism and interaction conditions of wide-frequency oscillation in new energy power stations can be better understood, so as to design more effective protection and control strategies to ensure that the system can quickly and stably resume operation in the face of transient disturbances, thereby providing technical support and guarantee for the reliable grid connection of new energy. However, the grid-connected converter has non-linear time-varying characteristics, complex internal control, and there is mutual coupling between different control links such as coordinate (inverse) transformation, phase lock loop, and proportional-integral regulation, and the impedance characteristics are closely related to the operating power point of the equipment. Therefore, it is very difficult to establish an accurate impedance model of the grid-connected converter.

[0004] Currently, the methods for impedance modeling of grid-connected converters are all relatively cumbersome and difficult to be directly applied to engineering. For example, for the invention patent with the application number 202110937215.6, it is necessary to establish a continuous analytical model of the main power circuit of a modular multilevel converter, and it is only applicable to the grid-connected system of a modular multilevel converter. The invention patent with the application number 202311820303.3 needs to construct the switching function of the converter; divide the switching function of the converter into a linear part and a nonlinear part through sinusoidal pulse width modulation to obtain the nonlinear characteristics of the converter in the modulation link; according to the real-time operation data of the new energy grid-connected system and the nonlinear characteristics of the converter in the modulation link, obtain the harmonic transfer function of the new energy grid-connected system through a preset multi-harmonic linearization method; wherein, the harmonic transfer function is used to describe the frequency coupling characteristics of the converter in the modulation link; according to the switching function of the converter, the harmonic transfer function and the actual control architecture of the new energy grid-connected system, construct a small-signal model of the new energy grid-connected system, and each link involves complex mathematical processing procedures. Summary of the Invention

[0005] The purpose of the present invention is to solve at least one technical problem in the background technology, and provide a method and system for obtaining the positive and negative sequence impedance parameters of a grid-connected converter with a wide frequency band.

[0006] To achieve the above purpose, the present invention provides a method for obtaining the positive and negative sequence impedance parameters of a grid-connected converter with a wide frequency band, including: Obtain the main circuit parameters and control circuit parameters of the grid-connected converter, and build a grid-connected converter simulation model in the electromagnetic simulation software according to the main circuit parameters and control circuit parameters; Add four simulation units to the grid-connected converter simulation model, namely a positive and negative sequence harmonic disturbance small-signal injection unit, an auxiliary phase-locked loop unit, a current signal auxiliary processing unit, and an RLC circuit equivalent unit; Use the positive and negative sequence harmonic disturbance small-signal injection unit to superimpose harmonic disturbances with a preset frequency and phase sequence at the grid power frequency three-phase voltage source port to obtain harmonic disturbance voltage signals; Obtain the phase angle of the grid power frequency three-phase voltage source through the auxiliary phase-locked loop unit; The current signal auxiliary processing unit processes the grid connection point current signal based on the phase angle and outputs three-phase voltage signals; Perform deviation calculation on the three-phase voltage signals, the output value of the original current signal processing unit in the grid-connected converter simulation model, and the harmonic disturbance voltage signals, and then input them into the RLC circuit equivalent unit. The RLC circuit equivalent unit obtains the impedance parameters of the grid-connected converter through the measurement of the effective value and phase angle of the loop current.

[0007] According to one aspect of the present invention, the positive and negative sequence harmonic disturbance small-signal injection unit consists of a set of three-phase symmetrical voltage sources U pa 、Upb , U pc are composed and connected in series between the grid connection point and the equivalent three-phase voltage source U sa、 U sb、 U sc of the external power grid. Among them, U pa is in series with U sa , U pb is in series with U sb , and U pc is in series with U sc ; U pa , U pb , U pc have the same effective value of voltage U prms , U prms = kU srms , where k ≤ 0.1, and U srms is the effective value of the equivalent three-phase voltage source of the external power grid.

[0008] According to one aspect of the present invention, a harmonic disturbance small-signal injection unit for positive and negative sequences is used to superimpose harmonic disturbances with a preset frequency and phase sequence at the port of the power grid power frequency three-phase voltage source to obtain a harmonic disturbance voltage signal, including: The frequencies of the positive and negative sequence harmonic disturbance small-signals injected by the positive and negative sequence harmonic disturbance small-signal injection unit take a preset frequency within the range of 1 to 10 kHz; When inputting the positive sequence disturbance small-signal disturbance amount, the phase angles are set to 0°, -120°, 120°, and when inputting the negative sequence disturbance small-signal disturbance amount, the phase angles are set to 0°, 120°, -120°; When injecting the three-phase positive sequence disturbance small-signal disturbance, the three-phase disturbance voltage components are respectively: ; When injecting the three-phase negative sequence disturbance small-signal disturbance, the three-phase disturbance voltage components are respectively: ; In the formula: t is time.

[0009] According to one aspect of the present invention, the input voltage of the auxiliary phase-locked loop unit is U 2 , U 2 corresponds to the three-phase voltages U sa , U sb , U sc , with an effective value of U srms , and phase angles of 0°, -120°, 120°. The voltage U 2 signal is input into the auxiliary phase-locked loop unit to obtain the phase angle θ 2 .

[0010] According to one aspect of the present invention, the voltage U2 The signal input auxiliary phase-locked loop unit obtains the phase angle θ 2 , including: The voltage signal U 2 After entering the auxiliary phase-locked loop unit, it undergoes coordinate positive transformation processing and outputs the dq-axis components U d2 and U q2 ; U q2 The output value after proportional-integral processing is subjected to integral processing, and the output value after integral processing is the voltage signal U 2 The synchronous phase angle θ 2 ; Among them, the coordinate positive transformation is the synchronous rotation coordinate transformation, and the synchronous phase angle is θ 2 .

[0011] According to one aspect of the present invention, the current signal auxiliary processing unit processes the grid-connected point current signal based on the phase angle and outputs three-phase voltage signals, including: The grid-connected point current After entering the current signal auxiliary processing unit, it undergoes coordinate positive transformation to obtain axis components and , and this coordinate positive transformation is the synchronous rotation coordinate transformation, and the synchronous phase angle is ; The current , and the target values , are compared through deviation calculation to calculate the deviation value; The deviation value is subjected to proportional-integral processing, and the output value after proportional-integral processing is subjected to decoupling processing, and decoupling components are added. Among them, the d-axis decoupling component is U d2 and -KI q2 , and the q-axis decoupling component is U q2 and KI d2 , and the output value after proportional-integral processing is respectively summed with the d-axis and q-axis decoupling components. K is the coupling coefficient, and its value is ; The output value after decoupling processing undergoes coordinate inverse transformation, and the output result is U abc2 ; Among them, the coordinate inverse transformation is the synchronous rotation coordinate inverse transformation, and the synchronous phase angle is θ 2 .

[0012] According to one aspect of the present invention, the RLC circuit equivalent unit includes: an RLC equivalent circuit and an impedance phase angle measurement module; After calculating the deviation of the three-phase voltage signal, the output value of the original model current signal processing unit, and the harmonic disturbance voltage signal, the result is input into the RLC circuit equivalent unit. By measuring the effective value and phase angle of the loop current, the impedance parameters of the grid-connected converter can be obtained, including: The three-phase voltage signal U output by the original model current signal processing unit abc1 The phase A voltage U of a1 And the three-phase voltage signal U output by the current signal auxiliary processing unit abc2 The phase A voltage U of a2 Perform deviation calculation to obtain the difference signal U a1- U a2 ; The three-phase positive sequence small signal disturbance phase A voltage signal is U pa (f p ). The three-phase positive sequence disturbance small signal disturbance phase A voltage signal U pa (f p ) and the difference signal U a1- U a2 Perform deviation calculation, and the output signal is U pa (f p ) - (U a1- U a2 ); Input the output signal U pa (f p ) - (U a1- U a2 ) into the RLC equivalent circuit composed of a single-phase controlled voltage source U DZ , an inductor L DZ , a resistor R DZ , and a capacitor C DZ to obtain the current signal I; Input the three-phase positive sequence disturbance small signal disturbance phase A voltage signal U pa and the current signal I of the RLC equivalent circuit into the impedance phase angle measurement module, and output the impedance and the phase angle .

[0013] To achieve the above object, the present invention also provides a system for obtaining the broadband positive and negative sequence impedance parameters of a grid-connected converter, including: A grid-connected converter simulation model construction module, which obtains the main circuit parameters and control circuit parameters of the grid-connected converter, and builds a grid-connected converter simulation model in the electromagnetic simulation software according to the main circuit parameters and control circuit parameters; A simulation unit setting module, which adds four simulation units to the grid-connected converter simulation model, namely a positive and negative sequence harmonic disturbance small signal injection unit, an auxiliary phase-locked loop unit, a current signal auxiliary processing unit, and an RLC circuit equivalent unit; Harmonic disturbance voltage signal acquisition module: The harmonic disturbance voltage signal is obtained by superimposing harmonic disturbances with a preset frequency and phase sequence on the ports of the power grid's industrial-frequency three-phase voltage source using positive and negative sequence harmonic disturbance small-signal injection units. Phase angle acquisition module: The phase angles of the power grid's industrial-frequency three-phase voltage source are obtained through an auxiliary phase-locked loop unit. Three-phase voltage signal acquisition module: The current signal auxiliary processing unit processes the grid-connected point current signal based on the phase angles and outputs three-phase voltage signals. Impedance parameter acquisition module: The three-phase voltage signals, the output values of the original current signal processing unit in the grid-connected converter simulation model, and the harmonic disturbance voltage signals are subjected to deviation calculation and then input into the RLC circuit equivalent unit. The RLC circuit equivalent unit obtains the impedance parameters of the grid-connected converter through the measurement of the effective value and phase angle of the loop current.

[0014] To achieve the above object, the present invention also provides an electronic device, including a processor, a memory, and a computer program stored on the memory and executable on the processor. When the computer program is executed by the processor, it implements the above-mentioned method for obtaining the broadband positive and negative sequence impedance parameters of the grid-connected converter.

[0015] To achieve the above object, the present invention also provides a computer-readable storage medium with a computer program stored thereon. When the computer program is executed by a processor, it implements the above-mentioned method for obtaining the broadband positive and negative sequence impedance parameters of the grid-connected converter.

[0016] According to the solution of the present invention, the present invention can obtain the positive and negative sequence impedance parameters of a general grid-connected converter at any frequency point, which have clear and definite physical meanings, and the positive and negative sequence impedance parameters are independent and have no cross-coupling influence, simplifying subsequent stability analysis.

[0017] The present invention does not need to establish a complex mathematical equation for the grid-connected converter. Only by building a simulation model and adding four supplementary units can the impedance characteristics of the grid-connected converter be obtained. Therefore, it can be applied to impedance modeling of grid-connected converters with any structure and parameters.

[0018] The present invention has good versatility. When the parameters of the main circuit and control circuit of the grid-connected converter change, the parameter setting principle of the four auxiliary units remains unchanged, and new impedance parameters can be directly output. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the principle of the method for obtaining the broadband positive and negative sequence impedance parameters of the grid-connected converter in Embodiment 1; Figure 2 Schematic diagram of the simulation interface of the grid-connected converter simulation model in Embodiment 1; Figure 3Simulation waveform diagram of three-phase voltage and three-phase current of the grid-connected converter in Embodiment 1; Figure 4 Simulation waveform diagram of d-axis and q-axis currents of the grid-connected converter in Embodiment 1; Figure 5 Diagram of the positive and negative sequence harmonic disturbance small signal injection unit added to the simulation model in Embodiment 1; Figure 6 Diagram of the auxiliary phase-locked loop unit added to the simulation model in Embodiment 1; Figure 7 Diagram of the current signal auxiliary processing unit added to the simulation model in Embodiment 1; Figure 8 Diagram of the RLC circuit equivalent unit added to the simulation model in Embodiment 1; Figure 9 Simulation result diagram in Embodiment 1; Figure 10 MATLAB code diagram for impedance parameter verification in Embodiment 1; Figure 11 Comparison diagram of impedance / phase angle values obtained by simulation and theoretical calculation values in Embodiment 1; Figure 12 Positive and negative sequence impedance curve diagram of the grid-connected converter obtained by cyclic scanning in Embodiment 1. Detailed implementation

[0020] The content of the present invention will now be described with reference to exemplary embodiments. It should be understood that the described embodiments are only for enabling those of ordinary skill in the art to better understand and thus implement the content of the present invention, rather than implying any limitation on the scope of the present invention.

[0021] As used herein, the term "comprising" and its variants are to be construed as open-ended terms meaning "including but not limited to". The term "based on" is to be construed as "at least partially based on". The terms "one embodiment" and "an embodiment" are to be construed as "at least one embodiment".

[0022] According to an embodiment of the present invention, a method for obtaining the positive and negative sequence impedance parameters of a grid-connected converter includes: Obtain the main circuit parameters and control circuit parameters of the grid-connected converter, and build a grid-connected converter simulation model in an electromagnetic simulation software according to the main circuit parameters and control circuit parameters; Add four simulation units to the grid-connected converter simulation model, namely a positive and negative sequence harmonic disturbance small signal injection unit, an auxiliary phase-locked loop unit, a current signal auxiliary processing unit, and an RLC circuit equivalent unit; A positive and negative sequence harmonic disturbance small-signal injection unit is used to superimpose harmonic disturbances with a preset frequency and phase sequence on the grid power frequency three-phase voltage source port to obtain a harmonic disturbance voltage signal (a three-phase voltage signal with specific harmonic disturbance components). An auxiliary phase-locked loop unit is used to obtain the phase angle of the grid power frequency three-phase voltage source. The current signal auxiliary processing unit processes the grid-connected point current signal based on the phase angle and outputs a three-phase voltage signal. The three-phase voltage signal, the output value of the original current signal processing unit in the grid-connected converter simulation model, and the harmonic disturbance voltage signal are subjected to deviation calculation and then input into the RLC circuit equivalent unit. The RLC circuit equivalent unit obtains the impedance parameters of the grid-connected converter through the measurement of the loop current effective value and phase angle.

[0023] Furthermore, it is worth noting that a typical grid-connected converter consists of a main circuit and a control circuit. The main circuit includes a DC-side support capacitor C V , a three-phase bridge voltage source converter VSC, and a connecting reactor L. The control circuit includes a phase-locked loop (PLL), a current signal processing unit, and a PWM signal generation unit. The phase-locked loop (PLL) internally includes three links: coordinate positive transformation, proportional integral, and integral. The current signal processing unit internally includes five links: coordinate positive transformation, deviation calculation, decoupling, proportional integral, and coordinate inverse transformation. The DC-side voltage of the three-phase bridge voltage source converter VSC is U dc , and the grid-connected point (the connection point between the reactor and the grid) voltage is U 1 .

[0024] The working mode and process of a typical grid-connected converter are as follows: Step 1: A capacitor C is connected to the DC side of the three-phase bridge voltage source converter VSC V to maintain the DC voltage stable. The AC side is connected to the grid through a reactor L. The grid-connected point voltage is U 1 , and the grid-connected point current is I g . Step 2: The grid-connected point voltage U 1 passes through the phase-locked loop to obtain the phase angle θ 1 . The phase-locked loop consists of three links: coordinate positive transformation, proportional integral, and integral. The grid-connected point voltage U 1 first passes through the coordinate positive transformation to output the dq-axis components U d1 and U q1 . U q1 enters the proportional integral (the proportional and integral coefficients are K pllp and K plli ). The output value of the proportional integral link enters the integral link, and the output value of the integral link is the synchronous phase angle θ of the grid-connected point voltage U 1 1 ​. The positive coordinate transformation is the synchronous rotation coordinate transformation, and the synchronous phase angle is θ 1 , and the positive coordinate transformation formula is as follows: ; Step 3: The grid-connected point current I g enters the current signal processing unit, and the current signal processing unit internally includes 5 links: positive coordinate transformation, deviation calculation, proportional integral, decoupling, and inverse coordinate transformation.

[0025] First, the grid-connected point current enters the positive coordinate transformation to obtain the d-axis component and , the positive coordinate transformation is the synchronous rotation coordinate transformation (same as formula 1), and the synchronous phase angle is ; Then, the deviation calculation link compares the current , and the target values , to calculate the deviation value; Next, the deviation value is sent to the proportional integral, and its proportional and integral coefficients are respectively and ; Then, the output value of the proportional integral adds the decoupling component in the decoupling link, where the d-axis decoupling component is U d1 and -KI q1 , the q-axis decoupling component is U q1 and KI d1 , the output value of the proportional integral link is respectively summed with the d-axis and q-axis decoupling components, K is the coupling coefficient, and the general value is .

[0026] Finally, the output value of the decoupling link performs inverse coordinate transformation, and the output result is U abc1 . The inverse coordinate transformation is the synchronous rotation inverse coordinate transformation, and the synchronous phase angle is θ 1 , and the inverse coordinate transformation formula is as follows: ; Step 4: The output result U abc1 of the current signal processing unit is subjected to PWM modulation through the PWM signal generation unit, and the output signal S abc is connected to the three-phase bridge voltage source converter VSC.

[0027] Adopting the above control strategy, the steady-state current output by the grid-connected converter to the grid-connected point of the d-axis component , and the target values , will remain consistent.

[0028] As can be seen from the above, the main circuit parameters and control circuit parameters of the grid-connected converter can be obtained through the above typical grid-connected converter and its working process.

[0029] After obtaining the main circuit and control circuit parameters of the grid-connected converter, a complete model of the grid-connected converter can be built in an electromagnetic simulation software (such as MATLAB or PSCAD).

[0030] Furthermore, according to an embodiment of the present invention, the positive and negative sequence harmonic disturbance small signal injection unit consists of a set of three-phase symmetrical voltage sources U pa , U pb , U pc which are connected in series and inserted between the grid connection point and the equivalent three-phase voltage source U sa、 U sb、 U sc of the external power grid, where U pa is in series with U sa , U pb is in series with U sb , U pc is in series with U sc ; U pa , U pb , U pc have the same effective value of U prms , U prms = kU srms , k ≤ 0.1, and U srms is the effective value of the equivalent three-phase voltage source of the external power grid.

[0031] Furthermore, according to an embodiment of the present invention, using the positive and negative sequence harmonic disturbance small signal injection unit to superimpose harmonic disturbances with a preset frequency and phase sequence at the port of the power grid power frequency three-phase voltage source to obtain harmonic disturbance voltage signals includes: The frequency f p of the positive and negative sequence harmonic disturbance small signals injected by the positive and negative sequence harmonic disturbance small signal injection unit takes a specific frequency within the range of 1 to 10 kHz; The phase angles of the input positive sequence disturbance small signal disturbance amount are set to 0°, -120°, 120°, and the phase angles of the input negative sequence disturbance small signal disturbance amount are set to 0°, 120°, -120°; When injecting three-phase positive sequence disturbance small signal disturbances, the three-phase disturbance voltage components are respectively: ; When injecting three-phase negative sequence disturbance small signal disturbances, the three-phase disturbance voltage components are respectively: ; Where: t is time, with the unit of s.

[0032] Further, according to an embodiment of the present invention, the auxiliary phase-locked loop unit has exactly the same structure and parameters as the phase-locked loop in the above typical grid-connected inverter, except for the input signal. The input voltage of the phase-locked loop is the grid connection point voltage U 1 , and the input voltage of the auxiliary phase-locked loop unit is U 2 , U 2 corresponds to the three-phase voltages U sa , U sb , U sc , with the effective value being U srms , and the phase angles being 0°, -120°, 120°. The voltage U 2 signal is input into the auxiliary phase-locked loop unit to obtain the phase angle θ 2 .

[0033] Further, according to an embodiment of the present invention, the auxiliary phase-locked loop consists of three links: coordinate positive transformation, proportional integral, and integral. The voltage U 2 signal is input into the auxiliary phase-locked loop unit to obtain the phase angle θ 2 , including: The voltage signal U 2 after being input into the auxiliary phase-locked loop unit is processed by coordinate positive transformation and outputs the dq-axis components U d2 and U q2 ; After being processed by proportional integral (the proportional and integral parameters are respectively and , which are strictly consistent with the phase-locked loop parameters), the output value is subjected to integral processing, and the output value after integral processing is the voltage signal synchronous phase angle ; Among them, the coordinate positive transformation is a synchronous rotating coordinate transformation, and the synchronous phase angle is θ 2 . The coordinate transformation formula is as follows: .

[0034] Further, according to an embodiment of the present invention, the current signal auxiliary processing unit internally includes five links: coordinate positive transformation, deviation calculation, decoupling, proportional integral, and coordinate inverse transformation.

[0035] The current signal auxiliary processing unit processes the grid connection point current signal based on the phase angle and outputs three-phase voltage signals, including: The grid connection point current after entering the current signal auxiliary processing unit, undergoes coordinate positive transformation to obtain axis component and , this coordinate forward transformation is a synchronous rotation coordinate transformation (same as Formula 5), and the synchronous phase angle is ; Calculate the deviation of the current , and the target value , Compare to calculate the deviation value; Perform proportional-integral on the deviation value (the proportional and integral coefficients are and , which are strictly consistent with the parameters of the proportional-integral link in the above-mentioned phase-locked loop). After the proportional-integral processing, the output value is decoupled, and the decoupling component is added. Among them, The decoupling component of the axis is , The decoupling component of the axis is . The output value after proportional-integral processing is summed with the axis and axis decoupling components respectively. is the coupling coefficient, and its value is ; Perform coordinate inverse transformation on the output value after decoupling processing, and the output result is U abc2 ; among them, the coordinate inverse transformation is a synchronous rotation coordinate inverse transformation, and the synchronous phase angle is θ 2 . The coordinate inverse transformation formula 2 is as follows: .

[0036] Furthermore, according to an embodiment of the present invention, the RLC circuit equivalent unit includes: an RLC equivalent circuit and an impedance phase angle measurement module; Perform deviation calculation on the three-phase voltage signal, the output value of the original model current signal processing unit, and the harmonic disturbance voltage signal, and then input them into the RLC circuit equivalent unit. The impedance parameters of the grid-connected converter can be obtained by measuring the effective value and phase angle of the loop current, including: Compare the A-phase voltage U abc1 of the three-phase voltage signal U a1 output by the original model current signal processing unit with the A-phase voltage U abc2 of the three-phase voltage signal U a2 output by the current signal auxiliary processing unit to calculate the deviation and obtain the difference signal U a1- U a2 ; The three-phase positive-sequence small-signal disturbance A-phase voltage signal is U pa (f p ). The three-phase positive-sequence disturbance small-signal disturbance A-phase voltage signal U pa (f p) Calculate the deviation with the difference signal U a1- U a2 and output the signal U pa (f p ) - (U a1- U a2 ); Input the output signal U pa (f p ) - (U a1- U a2 ) into the RLC equivalent circuit composed of a single-phase controlled voltage source U DZ , an inductor L DZ , a resistor R DZ , and a capacitor C DZ to obtain the current signal I; Among them, the control signal of the single-phase controlled voltage source U DZ is the output signal U pa (f p ) - (U a1- U a2 ), that is: ; The value of the resistor R DZ is consistent with the proportional parameter K p of the proportional-integral link in the current signal processing unit of the above typical grid-connected converter, that is: ; For the positive-sequence harmonic small-signal perturbation, the value of the inductor L DZ is taken according to the following formula: ; In the formula, L is the value of the main circuit connecting reactor, f 1 is the reference frequency of the external power grid equivalent power supply, and f p is the perturbation frequency; For the negative-sequence harmonic small-signal perturbation, the value of the inductor L DZ is taken according to the following formula: ; In the formula, L is the value of the main circuit connecting reactor, f 1 is the reference frequency of the external power grid equivalent power supply, and f p is the perturbation frequency; For the positive-sequence harmonic small-signal perturbation, the value of the capacitor C is taken according to the following formula: ; In the formula, K i is the integral parameter of the proportional-integral link in the current signal processing unit of the above typical grid-connected converter, and f 1 is the reference frequency of the external power grid equivalent power supply, fp is the disturbance frequency; For negative-sequence harmonic small-signal disturbances, the value of the capacitor C is taken according to the following formula: ; In the formula, K i is the integral parameter of the proportional-integral link in the current signal processing unit of a typical grid-connected converter, f 1 is the reference frequency of the equivalent power supply of the external power grid, f p is the disturbance frequency.

[0037] Input the three-phase positive-sequence disturbance small-signal A-phase voltage signal U pa and the current signal I input impedance phase angle measurement module of the RLC equivalent circuit, and output the impedance and the phase angle .

[0038] Furthermore, according to an embodiment of the present invention, when changing the frequencies of the A-phase, B-phase, and C-phase voltage signals of the three-phase positive-sequence small-signal disturbance, the impedance and the phase angle values at other frequency points can be obtained; by changing the phase sequence of the A-phase, B-phase, and C-phase voltage signals of the three-phase positive-sequence small-signal disturbance, the corresponding sequence impedance values can be obtained. For example, if the disturbance signal is a positive-sequence component, the impedance value is the positive-sequence impedance, and if the disturbance signal is set as a negative-sequence component, the impedance value is the negative-sequence impedance.

[0039] According to the above solution of the present invention, the present invention provides a method for obtaining the broadband positive and negative sequence impedance parameters of a grid-connected converter based on double synchronous coordinate transformation and RLC equivalent circuit. The present invention can obtain the positive and negative sequence impedance parameters of a general grid-connected converter at any frequency point, has clear and distinct physical meanings, and the positive and negative sequence impedance parameters are independent and have no cross-coupling influence, simplifying the subsequent stability analysis.

[0040] The present invention does not need to establish a complex mathematical equation of the grid-connected converter. Only by building a simulation model and adding four supplementary units can the impedance characteristics of the grid-connected converter be obtained. Therefore, it can be applied to impedance modeling of grid-connected converters with any structure and parameters.

[0041] The present invention has good versatility. When the parameters of the main circuit and control circuit of the grid-connected converter change, the parameter setting principle of the four auxiliary units remains unchanged, and new impedance parameters can be directly output.

[0042] Furthermore, to achieve the above object, the present invention also provides a system for obtaining the broadband positive and negative sequence impedance parameters of a grid-connected converter, including: Grid-connected converter simulation model construction module, which obtains the main circuit parameters and control circuit parameters of the grid-connected converter, and builds a grid-connected converter simulation model in electromagnetic simulation software according to the main circuit parameters and control circuit parameters; Simulation unit setting module, which adds four simulation units to the grid-connected converter simulation model, namely positive and negative sequence harmonic disturbance small signal injection unit, auxiliary phase-locked loop unit, current signal auxiliary processing unit and RLC circuit equivalent unit; Harmonic disturbance voltage signal acquisition module, which uses the positive and negative sequence harmonic disturbance small signal injection unit to superimpose harmonic disturbances with preset frequencies and phase sequences at the grid power frequency three-phase voltage source port to obtain harmonic disturbance voltage signals; Phase angle acquisition module, which obtains the phase angle of the grid power frequency three-phase voltage source through the auxiliary phase-locked loop unit; Three-phase voltage signal acquisition module, the current signal auxiliary processing unit processes the grid connection point current signal based on the phase angle and outputs three-phase voltage signals; Impedance parameter acquisition module, which calculates the deviation of the three-phase voltage signals, the output value of the original current signal processing unit in the grid-connected converter simulation model and the harmonic disturbance voltage signal, and then inputs them into the RLC circuit equivalent unit. The RLC circuit equivalent unit obtains the impedance parameters of the grid-connected converter through the measurement of the effective value and phase angle of the loop current.

[0043] The above-mentioned grid-connected converter broadband positive and negative sequence impedance parameter acquisition system according to the present invention can implement the above-mentioned grid-connected converter broadband positive and negative sequence impedance parameter acquisition method. The specific process steps are as described above and will not be elaborated here.

[0044] Furthermore, to achieve the above object, the present invention also provides an electronic device, including a processor, a memory, and a computer program stored on the memory and executable on the processor. When the computer program is executed by the processor, it implements the above-mentioned grid-connected converter broadband positive and negative sequence impedance parameter acquisition method.

[0045] Furthermore, to achieve the above object, the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by the processor, it implements the above-mentioned grid-connected converter broadband positive and negative sequence impedance parameter acquisition method.

[0046] To make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described here are only the best embodiments of the present invention, which are only used to explain the present invention and do not limit the protection scope of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0047] Embodiment 1

[0048] Figure 1 It is the principle block diagram of the method for obtaining the broadband positive and negative sequence impedance parameters of the grid-connected converter in Embodiment 1.

[0049] The specific parameters of the grid-connected converter in this embodiment are as follows: Rated AC voltage: 800V; Rated frequency: 50Hz; Target value of d-axis (active) current: 500A; Target value of q-axis (reactive) current: 0A; Connecting reactor L: 20mH; Proportional coefficient of PI inside the phase-locked loop PLL : 100; Integral coefficient of PI inside the phase-locked loop PLL : 1000; Proportional coefficient of the PI link of the current signal processing unit : 100; Integral coefficient of the PI link of the current signal processing unit : 1000; Coupling coefficient K: 6.28; Figure 1 in represents impedance calculation, where , which outputs the corresponding amplitude and phase according to the input voltage and current.

[0050] Build a grid-connected converter simulation model on the MATLAB / simulink software platform according to the above parameters, which can run normally. The simulation interface of the grid-connected converter simulation model is as shown in Figure 2 , and the simulation waveforms of three-phase voltage and three-phase current are as shown in Figure 3 , and the simulation waveforms of d-axis current and q-axis current are as shown in Figure 4 . It can be seen from Figure 3 and Figure 4 that the d-axis current is stable at 500A, which is consistent with the target value; the q-axis current is stable at 0A, which is consistent with the target value.

[0051] Adopt the method of the present invention. As shown in Figure 1 , on the basis of the original current signal processing unit, phase-locked loop and PWM signal generation unit in the grid-connected converter simulation model, add 4 unit modules, which are respectively: ① Positive and negative sequence harmonic disturbance small signal injection unit; ② Auxiliary phase-locked loop unit; ③ Current signal auxiliary processing unit; ④ RLC circuit equivalent unit.

[0052] In this embodiment, the injection voltage amplitude of the positive and negative sequence harmonic disturbance small signal injection unit is set to (taking 5% of the power grid), and the small signal frequency is , and the phases are 0°, -120°, and 120° (positive sequence disturbance), as Figure 5 shown. Figure 5 Among them, is the three-phase voltage signal at the grid connection point, is the three-phase current signal at the grid connection point, is the inductance value of the connecting reactor, is the of the three-phase voltage source converter three-phase sine wave modulation signal, is the of the three-phase voltage source converter in the three-phase sine wave modulation signal phase signal, is phase disturbance small signal, is the three-phase voltage signal of the grid equivalent three-phase voltage source.

[0053] The input signal of the auxiliary phase-locked loop unit is the three-phase grid equivalent voltage , the internal proportional parameter is 100, the integral parameter is 1000, which is exactly the same as the phase-locked loop circuit parameters, and the output synchronous phase angle is , as Figure 6 shown. Figure 6 Among them, is the three-phase voltage signal of the grid equivalent three-phase voltage source, and of the phase-locked loop module represents the three-phase AC electrical quantity signal input to this module for coordinate transformation, represents the rotating coordinate phase synchronization signal input to this phase-locked loop module, represents the output from this phase-locked loop axis, axis and axis components, where the axis component is , axis component is , The output of the axis component is blocked, indicating that this signal does not need to be output. represents the proportional integral link, represents the integral link, is the​​ The three-phase voltage signal corresponds to the synchronous phase signal.

[0054] The current signal auxiliary processing unit is as Figure 7 shown, and the synchronous phase angles of the coordinate transformation and the inverse transformation are both (the output signal of the auxiliary phase-locked loop unit), the proportional parameter of the proportional-integral link is 100, and the integral parameter is 1000, which is exactly the same as the proportional-integral parameters inside the current signal processing unit. Figure 7 in is the three-phase current signal at the grid connection point, and the of the phase-locked loop module represents the three-phase AC electrical quantity signal input into this module for coordinate transformation, represents the rotational coordinate phase synchronization signal input into this phase-locked loop module, axis, axis and axis components. represents the axis current target value, represents the axis current target value, is the axis quantity generated by performing a rotational coordinate transformation on the three-phase voltage signal of the grid equivalent three-phase voltage source, axis quantity, is the axis quantity generated by performing a rotational coordinate transformation on the three-phase voltage signal of the grid equivalent three-phase voltage source, axis quantity, is a coefficient used for axis decoupling, represents the proportional-integral link, is the synchronous phase signal corresponding to the three-phase voltage signal of the grid equivalent three-phase voltage source, is the phase signal output by the coordinate inverse transformation link.

[0055] An RLC circuit composed of a single-phase controlled voltage source U DZ , an inductor L DZ , a resistor R DZ , and a capacitor C DZ is established. The control signal of the single-phase controlled voltage source U DZ is U pa (f p ) - (U a1- U a2 ). The values of the inductor L DZ , the resistor R DZ , and the capacitor C DZ are as follows: ; The equivalent circuit is as shown in the appendix Figure 8 , and the impedance simulation result is as Figure 9 shown. Figure 8 Among them, is the three-phase voltage source converter 's cosine signal in the three-phase sine wave modulation signal, is the cosine signal output by the coordinate inverse transformation link, is the cosine signal, is the phase perturbation small signal, is the proportional coefficient of the inner loop of the converter , is the integral coefficient of the inner loop of the converter , is the frequency of the perturbation small signal, is the power frequency.

[0056] Furthermore, in order to verify whether the impedance and phase angle values obtained in Embodiment 1 are correct, the theoretical formula for the positive-sequence impedance of the grid-connected converter in Embodiment 1 was compiled in MATLAB, as Figure 10 shown.

[0057] The comparison between the impedance / phase angle values obtained by simulation in Embodiment 1 and the theoretical calculation values is as Figure 11 shown. The impedance value obtained by simulation in Embodiment 1 is 3.4 Ω, and the theoretical calculation value is 3.3998 Ω. The phase angle obtained by simulation in Embodiment 1 is -2.882°, and the theoretical calculation value is -2.8822°. It is proved that the impedance and phase angle values obtained in Embodiment 1 at this frequency point are both correct.

[0058] By adjusting the frequency point parameters and using the same method, the impedance values at other frequency points can be obtained; by adjusting the phase sequence of the harmonic small signal perturbation, the negative-sequence impedance value can be obtained. To improve efficiency, it can be set to a loop mode. Each time the frequency point is adjusted, the corresponding simulation model of Embodiment 1 is automatically executed, and the results are recorded and plotted, and the positive- and negative-sequence impedance curves of the grid-connected converter can be obtained, as Figure 12 shown.

[0059] Those of ordinary skill in the art can realize that the modules and algorithm steps described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods for each specific application to implement the described functions, but such implementation should not be considered to exceed the scope of the present invention.

[0060] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described devices and equipment can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0061] In the embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the modules is only a logical function division. In actual implementation, there may be other division methods. For example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces. The indirect couplings or communication connections of the devices or modules can be in electrical, mechanical or other forms.

[0062] The modules described as separate components may or may not be physically separated. The components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed to multiple network modules. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of the embodiments of the present invention.

[0063] In addition, each functional module in the embodiments of the present invention can be integrated into one processing module, or each module can exist physically alone, or two or more modules can be integrated into one module.

[0064] If the function is implemented in the form of a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method for sending / receiving energy-saving signals in various embodiments of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, ROM, RAM, magnetic disks, or optical discs that can store program codes.

[0065] The above description is only a preferred embodiment of the present application and an explanation of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the technical solution formed by mutually replacing the above features with the technical features (but not limited to) having similar functions disclosed in the present application.

[0066] It should be understood that the magnitude of the sequence numbers of the steps in the content and implementation manner of the present invention does not absolutely mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiment of the present invention.

Claims

1. A method for obtaining broadband positive and negative sequence impedance parameters of a grid-connected converter, characterized in that: include: Obtain the main circuit parameters and control circuit parameters of the grid-connected converter, and build a grid-connected converter simulation model in the electromagnetic simulation software according to the main circuit parameters and control circuit parameters; Four simulation units are added to the grid-connected converter simulation model, namely, a positive and negative sequence harmonic disturbance small signal injection unit, an auxiliary phase-locked loop unit, a current signal auxiliary processing unit, and an RLC circuit equivalent unit; A harmonic disturbance of preset frequency and phase sequence is superimposed on the power frequency three-phase voltage source port of the power grid by using a positive and negative sequence harmonic disturbance small signal injection unit to obtain a harmonic disturbance voltage signal; The phase angle of the three-phase voltage source of the power grid is obtained through the auxiliary phase-locked loop unit; The current signal auxiliary processing unit processes the grid-connected point current signal based on the phase angle and outputs a three-phase voltage signal; The three-phase voltage signal, the output value of the original current signal processing unit in the grid-connected converter simulation model and the harmonic disturbance voltage signal are input into the RLC circuit equivalent unit after deviation calculation. The RLC circuit equivalent unit obtains the impedance parameters of the grid-connected converter by measuring the effective value and phase angle of the loop current.

2. The method for obtaining broadband positive and negative sequence impedance parameters of a grid-connected converter according to claim 1, characterized in that: The positive and negative sequence harmonic disturbance small signal injection unit is composed of a set of three-phase symmetrical voltage sources U pa , U pb , U pc The three-phase voltage source U connected in series with the grid point and the external grid sa、 U sb、 U sc Between, among which U pa with U sa Series, U pb with U sb Series, U pc with U sc Series connection; U pa , U pb , U pc The effective value of voltage is also U prms , U prms =kU srms , k≤0.1, U srms is the effective value of the equivalent three-phase voltage source of the external power grid.

3. The method for obtaining broadband positive and negative sequence impedance parameters of a grid-connected converter according to claim 2, characterized in that: The harmonic disturbance of preset frequency and phase sequence is superimposed on the power frequency three-phase voltage source port of the power grid by using the positive and negative sequence harmonic disturbance small signal injection unit to obtain the harmonic disturbance voltage signal, including: The frequency of the positive and negative sequence harmonic disturbance small signal injected by the positive and negative sequence harmonic disturbance small signal injection unit is Take a preset frequency in the frequency range of 1~10kHz; When the positive sequence disturbance small signal disturbance amount is input, the phase angle is set to 0°, -120°, 120°, and when the negative sequence disturbance small signal disturbance amount is input, the phase angle is set to 0°, 120°, -120°; When a three-phase positive sequence disturbance small signal is injected, the three-phase disturbance voltage components are: ； When a three-phase negative sequence disturbance small signal is injected, the three-phase disturbance voltage components are: ； Where: t is time.

4. The method for obtaining broadband positive and negative sequence impedance parameters of a grid-connected converter according to claim 3, characterized in that: The input voltage of the auxiliary phase-locked loop unit is U2, which corresponds to the three-phase voltage U sa , U sb , U sc , the effective value is U srms , the phase angles are 0°, -120°, and 120°, and the voltage U2 signal is input into the auxiliary phase-locked loop unit to obtain the phase angle θ2.

5. The method for obtaining broadband positive and negative sequence impedance parameters of a grid-connected converter according to claim 4, characterized in that: The voltage U2 signal is input into the auxiliary phase-locked loop unit to obtain the phase angle θ2, including: The voltage signal U2 is input into the auxiliary phase-locked loop unit and then processed by the coordinate forward transformation to output the dq axis component U d2 and U q2 ; U q2 The output value after proportional integration is integrated, and the output value after integration is the voltage signal U2 synchronous phase angle θ2; Among them, the coordinate positive transformation is a synchronous rotating coordinate transformation, and the synchronous phase angle is θ2.

6. The method for obtaining broadband positive and negative sequence impedance parameters of a grid-connected converter according to claim 5, characterized in that: The current signal auxiliary processing unit processes the grid-connected point current signal based on the phase angle and outputs a three-phase voltage signal, including: Grid connection point current After entering the current signal auxiliary processing unit, the coordinates are transformed to obtain Axis Component and , the coordinate transformation is a synchronous rotation coordinate transformation, and the synchronous phase angle is ; The current is calculated by the deviation , and target value , Compare and calculate the deviation value; The deviation value is processed by proportional integration, and the output value after proportional integration is decoupled and a decoupling component is added, where the d-axis decoupling component is U d2 and-KI q2 , the q-axis decoupling component is U q2 and KI d2 The output value after proportional integral processing is summed with the d-axis and q-axis decoupling components respectively. K is the coupling coefficient, which is ; The output value after decoupling is transformed into the coordinate inverse, and the output result is U abc2 ; Among them, the coordinate inverse transformation is the synchronous rotation coordinate inverse transformation, and the synchronous phase angle is θ2.

7. The method for obtaining broadband positive and negative sequence impedance parameters of a grid-connected converter according to claim 6, characterized in that: The RLC circuit equivalent unit comprises: an RLC equivalent circuit and an impedance phase angle measurement module; The three-phase voltage signal, the output value of the original model current signal processing unit and the harmonic disturbance voltage signal are input into the RLC circuit equivalent unit after the deviation calculation. The impedance parameters of the grid-connected converter can be obtained by measuring the effective value and phase angle of the loop current, including: The three-phase voltage signal U output by the original model current signal processing unit abc1 Phase A voltage U a1 The three-phase voltage signal U output by the current signal auxiliary processing unit abc2 Phase A voltage U a2 Calculate the deviation and get the difference signal U a1- U a2 ; The three-phase positive sequence small signal disturbance A phase voltage signal is U pa (f p ), the three-phase positive sequence disturbance small signal disturbs the A phase voltage signal U pa (f p ) and the difference signal U a1- U a2 Deviation calculation is performed and the output signal is U pa (f p )-(U a1- U a2 ); The output signal U pa (f p )-(U a1- U a2 ) Input is from a single-phase controlled voltage source U DZ 、Inductance L DZ , resistor R DZ , capacitor C DZ The RLC equivalent circuit is composed to obtain the current signal I; The three-phase positive sequence disturbance small signal disturbs the A phase voltage signal U pa The current signal I of the RLC equivalent circuit is input impedance phase angle measurement module, and the output impedance and phase angle .

8. A wide-band positive and negative sequence impedance parameter acquisition system for a grid-connected converter, characterized in that: include: A grid-connected converter simulation model building module is used to obtain the main circuit parameters and control circuit parameters of the grid-connected converter, and to build a grid-connected converter simulation model in the electromagnetic simulation software according to the main circuit parameters and control circuit parameters; The simulation unit setting module adds four simulation units to the grid-connected converter simulation model, namely, a positive and negative sequence harmonic disturbance small signal injection unit, an auxiliary phase-locked loop unit, a current signal auxiliary processing unit, and an RLC circuit equivalent unit; The harmonic disturbance voltage signal acquisition module uses the positive and negative sequence harmonic disturbance small signal injection unit to superimpose the harmonic disturbance of preset frequency and phase sequence on the power frequency three-phase voltage source port of the power grid to obtain the harmonic disturbance voltage signal; A phase angle acquisition module, which acquires the phase angle of the power frequency three-phase voltage source of the power grid through an auxiliary phase-locked loop unit; A three-phase voltage signal acquisition module, a current signal auxiliary processing unit processes the grid-connected point current signal based on the phase angle and outputs a three-phase voltage signal; The impedance parameter acquisition module calculates the deviation of the three-phase voltage signal, the output value of the original current signal processing unit in the grid-connected converter simulation model, and the harmonic disturbance voltage signal, and then inputs them into the RLC circuit equivalent unit. The RLC circuit equivalent unit obtains the impedance parameters of the grid-connected converter by measuring the effective value and phase angle of the loop current.

9. An electronic device, characterized in that The method comprises a processor, a memory and a computer program stored in the memory and executable on the processor, wherein the computer program, when executed by the processor, implements a method for acquiring wide-band positive and negative sequence impedance parameters of a grid-connected converter as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for obtaining wide-band positive and negative sequence impedance parameters of a grid-connected converter according to any one of claims 1 to 7 is implemented.

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