A disturbance injection and impedance measurement method and system suitable for impedance measurement of a new energy grid-connected system

Abstract

The application discloses a disturbance injection and impedance measurement method and system suitable for impedance measurement of a new energy grid-connected system. A disturbance injection controlled voltage source is connected in series at a new energy grid-connected side where impedance measurement is needed, a disturbance injection controller is used for controlling injection of a controlled voltage signal, pure d-axis and q-axis voltage signals at different frequencies are injected into the grid-connected system, current actually fed back to the disturbance signal is measured, and an impedance matrix of the system to be solved is calculated after transformation to the dq axis, so that the impedance of the grid-connected inverter system in the dq coordinate system can be obtained without detailed grid-connected inverter system parameters, and problems such as wideband resonance of the grid-connected inverter system in actual engineering application, theoretical model verification and the like can be conveniently analyzed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy grid-connected technology, and particularly to a disturbance injection and impedance measurement method and system suitable for new energy grid-connected system impedance measurement. BACKGROUND

[0002] With the increasing proportion of renewable energy and power electronics in power systems, the wideband resonance and harmonic stability problems caused by the dynamic interaction between grid-connected inverter systems and power grids have become increasingly prominent. Establishing a mathematical model of the grid-connected inverter system to the power grid will be beneficial for researchers to analyze the source of wideband resonance and harmonic stability problems in the grid-connected inverter system, and to develop appropriate countermeasures against the problem source.

[0003] In order to obtain the impedance of the grid-connected inverter system, the commonly used method is to establish an impedance model using detailed system parameters, which can accurately express the transfer function of the system. However, this method is difficult to establish an accurate mathematical model in actual grid-connected inverter systems due to the influence of complex parameter coupling, parasitic parameters and other factors in engineering applications. SUMMARY

[0004] The purpose of the present application is to provide a disturbance injection and impedance measurement method and system suitable for new energy grid-connected system impedance measurement, which can inject voltage disturbance signals into the grid-connected system when impedance measurement of the new energy grid-connected system is needed, and then impedance measurement can be realized according to the response of the grid-connected system to the disturbance signal without detailed grid-connected inverter system parameters. The technical scheme adopted by the present application is as follows.

[0005] In one aspect, the present application provides a disturbance injection method suitable for new energy grid-connected system impedance measurement, comprising:

[0006] obtaining real-time grid voltage , determining the initial phase and frequency of the real-time grid voltage;

[0007] determining disturbance control parameters, the disturbance control parameters including the amplitude and frequency of a pure d-axis disturbance voltage signal, and the amplitude and frequency of a pure q-axis disturbance voltage signal;

[0008] injecting the disturbance control parameters and the initial phase and frequency of the real-time grid voltage into the grid-connected system., as the input of the preset signal conversion model, two sets of three-phase disturbance voltage signals output by the signal conversion model are obtained, and components on the q-axis or the d-axis of the two sets of three-phase disturbance voltage signals can be offset after superposition;

[0009] The two sets of three-phase disturbance voltage signals are superposed by phase to obtain a target three-phase disturbance voltage signal ;

[0010] The pure d-axis disturbance voltage signal and the pure q-axis disturbance voltage signal are set as given values, and the controlled voltage source outputs the corresponding three-phase disturbance voltage signal to the grid side three-phase AC bus through the converter AC output end and the grid side three-phase AC bus.

[0011] Optionally, the disturbance control parameter is determined as follows: if the target three-phase disturbance voltage signal is a pure d-axis disturbance voltage signal, the amplitude of the pure d-axis disturbance voltage signal is determined not to be 0, and the amplitude of the pure q-axis disturbance voltage signal is determined to be 0; if the target three-phase disturbance voltage signal is a pure q-axis disturbance voltage signal, the amplitude of the pure d-axis disturbance voltage signal is set to 0, and the amplitude of the pure q-axis disturbance voltage signal is set not to be 0.

[0012] Optionally, the preset signal conversion model obtains two sets of three-phase disturbance voltage signals according to the input disturbance control parameters and the grid voltage initial phase and frequency , and includes the following steps:

[0013] According to the amplitude of the disturbance voltage signal in the disturbance control parameter that is not 0 or , the amplitudes of the two sets of three-phase disturbance voltage signals are determined; according to and , the frequency of the first three-phase disturbance voltage signal is determined .

[0014] The frequency is compared with the size of the real-time grid voltage , the frequency of the second three-phase disturbance voltage signal is determined according to the comparison result , and the relationship between the phase of the two sets of three-phase disturbance voltage signals and the grid voltage initial phase is determined, with the goal that the components of the three-phase positive sequence disturbance voltage and the three-phase negative sequence disturbance voltage on the q-axis or the d-axis can be offset.

[0015] According to and ​​and and , the first three-phase disturbance voltage signal and the second three-phase disturbance voltage signal .

[0016] Optionally, if the target three-phase disturbance voltage signal is a pure d-axis disturbance voltage signal, the amplitudes of the two sets of three-phase disturbance voltage signals satisfy ; if the target three-phase disturbance voltage signal is a pure q-axis disturbance voltage signal, the amplitudes of the two sets of three-phase disturbance voltage signals satisfy .

[0017] The frequency of the first three-phase disturbance voltage signal and is determined according to , and the formula is: .

[0018] If , then , , the second three-phase disturbance voltage signal is:

[0019]

[0020] If , then , , the second three-phase disturbance voltage signal is:

[0021]

[0022] The first three-phase disturbance voltage signal is:

[0023] .

[0024] The above, the first three-phase disturbance voltage signal and the second three-phase disturbance voltage signal are superimposed through an adder to obtain a target pure d-axis or pure q-axis three-phase disturbance injection voltage. Taking the target three-phase disturbance injection voltage as a given voltage to control the controlled voltage source can make the controlled voltage source output a corresponding disturbance voltage signal to the new energy grid-side three-phase line.

[0025] Optionally, the determination of the disturbance control parameter includes: looking up a pre-set disturbance control parameter table, selecting a disturbance voltage signal frequency point and its corresponding pure d-axis disturbance voltage amplitude or pure q-axis disturbance voltage amplitude , and determining all disturbance control parameters of the to-be-input signal conversion model.

[0026] The disturbance control parameter table records a plurality of disturbance voltage signal frequency points and corresponding pure d-axis disturbance voltage amplitude values or pure q-axis disturbance voltage amplitude values .

[0027] Generally, the disturbance voltage amplitude range has a fixed corresponding relationship with the voltage level and the power level. The exploration process of the corresponding relationship can be performed before disturbance control, to obtain a disturbance amplitude selection range table corresponding to the power level and the voltage level of the actual system impedance test scenario. The disturbance voltage amplitude written in the disturbance control parameter table is selected within the range.

[0028] Optionally, the determination method of the disturbance voltage signal frequency in the disturbance control parameter comprises:

[0029] S11, injecting a corresponding test frequency and equivalent positive and negative sequence harmonic voltage combination of pure d-axis or q-axis disturbance voltage, recording three-phase current at the inverter output side in steady state operation ;

[0030] S12, performing Fourier transform on the obtained three-phase current to extract the phase components corresponding to and positive and negative sequence harmonic frequencies ,

[0031] S13, separating the positive and negative zero sequence components in the harmonic current response , by using the symmetrical component method, wherein two linear quantities are: positive sequence component current of and negative sequence component current of four nonlinear quantities are: negative sequence component current of positive sequence component current of ;

[0032] S14, calculating the nonlinear rate , the formula is:

[0033]

[0034] wherein, are the current peak values of the currents ; ​

[0035] nonlinear rate is less than or equal to a set value, if satisfied, the current test frequency is increased, go to step S11 and execute steps S11 to S14 again until the nonlinear rate is greater than the set value, then the test frequency before the last time of increase is taken as the maximum disturbance voltage signal frequency;

[0036] S15, select the disturbance voltage signal frequency in the disturbance control parameters in the range less than or equal to the maximum disturbance voltage signal frequency .

[0037] In the above process of determining the maximum disturbance voltage signal range, the initial test frequency is selected from a smaller value, the nonlinear rate The set value of the nonlinear rate can be 3%.

[0038] Optionally, the predetermined method of the disturbance voltage amplitude in the disturbance control parameters comprises:

[0039] S21, inject a positive and negative sequence harmonic voltage combination corresponding to the test frequency fdq(m) and equivalent to a pure d-axis or q-axis disturbance voltage, and record the three-phase current at the inverter output side in steady state operation ;

[0040] S22, Fourier transform the obtained three-phase current , extract the phase components corresponding to and the positive and negative sequence harmonic frequencies , ;

[0041] S23, separate the positive and negative zero sequence components in the harmonic current response , using the symmetrical component method, wherein two linear quantities are: the positive sequence component current and the negative sequence component current ; four nonlinear quantities are: the negative sequence component current , the positive sequence component current and the zero sequence component current , ;

[0042] S24, calculate the nonlinear rate and the stable operating point deviation rate , the formula is:

[0043]

[0044]

[0045] wherein, is the peak value of the current is the peak value of the current; is the fundamental current amplitude of the stable operating point before injecting the disturbance quantity, is the fundamental current amplitude after injecting the disturbance;

[0046] If the nonlinearity rate and the stable operating point shift rate are both less than or equal to a set value, the amplitude of the current pure d-axis or q-axis disturbance voltage can be used as the disturbance injection amplitude in the disturbance control parameter; if the nonlinearity rate is greater than the set value, an amplitude amount is added to the current disturbance injection voltage amplitude, and steps S21-S24 are repeated until the nonlinearity rate is less than or equal to the set value; if the stable operating point shift rate is greater than the set value, an amplitude amount is subtracted from the current disturbance injection voltage amplitude, and steps S21-S24 are repeated until the stable operating point shift rate is less than or equal to the set value.

[0047] S25, the amplitude of the pure d-axis or q-axis disturbance voltage that makes the nonlinearity rate and the stable operating point shift rate both less than or equal to the set value is selected as the disturbance injection amplitude in the disturbance control parameter.

[0048] In a second aspect, the present application provides a new energy grid-connected system impedance measurement method, comprising:

[0049] The disturbance injection method of the first aspect is used to inject a disturbance voltage signal between the grid-connected three-phase line between the AC output end of the converter and the grid connected three-phase bus, wherein the disturbance voltage signal is a pure d-axis voltage signal or a pure q-axis voltage signal.

[0050] A response disturbance current signal generated by the grid under the excitation of the disturbance voltage signal is obtained.

[0051] The disturbance voltage signal and the response disturbance current signal are transformed to the dq axis, and the impedance matrix of the new energy grid-connected system is calculated according to the disturbance voltage signal and the response disturbance current signal after the dq axis transformation.

[0052] The disturbance current signal is the response of the injected disturbance voltage signal, and comes from the current of the line at the disturbance voltage injection position. After the disturbance voltage is injected, the current that can be detected actually contains the main circuit current and the current responding to the injection of the disturbance voltage signal. The required responding disturbance current signal can be separated by using FFT. The disturbance injection voltage is a signal in the abc coordinate axis, and the d-axis component and the q-axis component can be obtained by dq-axis transformation . .

[0053] Optionally, the impedance Bode diagram corresponding to the impedance matrix in the dq coordinate system includes the impedance Bode diagrams of the dd, dq, qd and qq channels. Therefore, in the present application, the injection of the disturbance voltage signal into the grid-connected three-phase line is that the disturbance voltage signals corresponding to multiple frequency points are injected multiple times, and a pure d-axis voltage signal and a pure q-axis voltage signal are injected once for each frequency point, respectively.

[0054] The impedance matrix in the dq coordinate system is calculated according to the following formula for the disturbance voltage injection corresponding to each frequency point.

[0055]

[0056] In the formula, Zdd, Zdq, Zqd and Zqq represent the impedances of the dd, dq, qd and qq channels, respectively. , , , , Vd and Vq represent the d-axis and q-axis voltage components of the pure d-axis disturbance injection voltage, respectively, , Vd and Vq represent the d-axis and q-axis voltage components of the pure q-axis disturbance injection voltage, respectively. , Id and Iq represent the d-axis and q-axis current components of the responding disturbance current signal of the pure d-axis disturbance injection voltage, respectively, , Id and Iq represent the d-axis and q-axis current components of the responding disturbance current signal of the pure q-axis disturbance injection voltage, respectively.

[0057] In a third aspect, the present application provides a disturbance injection system suitable for impedance measurement of a new energy grid-connected system, which comprises a measured new energy grid-connected system, a controlled AC voltage source for three-phase disturbance injection , and a disturbance injection controller; the measured new energy grid-connected system comprises a new energy power source, a power grid , and a converter;

[0058] The converter AC output end and the power grid are connected through a grid-connected three-phase line provided with a three-phase circuit breaker ; and a controlled DC voltage source​ The power output ends of the power supply are respectively connected in parallel to the two ends of the three-phase circuit breaker ;

[0059] The disturbance injection controller is configured to control the controlled DC voltage source to inject a disturbance voltage signal into the grid-connected three-phase line when the three-phase circuit breaker is open, the disturbance voltage signal being a pure d-axis voltage signal or a pure q-axis voltage signal. Optionally, the converter is an inverter DC / AC or an AC / DC / AC converter; and the new energy power generation source is a photovoltaic power generation unit or a wind power generation unit.

[0060] In a fourth aspect, the present application provides an impedance measurement system suitable for impedance measurement of a new energy grid-connected system, comprising the disturbance injection system of the third aspect and a signal collector for collecting a current signal in response to the disturbance injection voltage, the signal collector collecting a current on a line where the disturbance voltage signal injection point is located.

[0061] The impedance of the new energy grid-connected system is calculated according to the disturbance injection voltage signal and the response disturbance current signal collected in the current signal.

[0062] In a fifth aspect, the present application provides a computer readable storage medium having a computer program stored thereon, the computer program being executed by a processor to implement the disturbance injection method suitable for impedance measurement of a new energy grid-connected system according to the first aspect, or to implement the new energy grid-connected system impedance measurement method according to the second aspect.

[0063] Advantages

[0064] The disturbance injection method and the new energy grid-connected system impedance measurement method of the present application can be used to inject pure d-axis and q-axis voltage signals with different frequency components into the grid-connected system without knowing the specific parameters of the actual inverter grid-connected system, to obtain the actual feedback disturbance current signal on the grid-connected line, and then to quickly and accurately calculate the impedance matrix of the grid-connected inverter system in the dq coordinate system according to the disturbance injection voltage and the response current. The present application can be more conveniently and efficiently applied to the analysis of wideband resonance of the grid-connected system in actual engineering applications, theoretical model verification and other problem researches. BRIEF DESCRIPTION OF DRAWINGS

[0065] FIG. 1 is a schematic diagram of a main circuit structure of a disturbance injection system of the present application;

[0066] Figure 1 FIG. 2 is a schematic diagram of a disturbance injection method of the present application;

[0067] Figure 2 FIG. 3 is a schematic diagram of a conversion process of a pure d-axis disturbance injection signal in the disturbance injection method of the present application;

[0068] ​Figure 3 This is a schematic diagram of the conversion process of the pure q-axis perturbation injection signal in the perturbation injection method of the present invention;

[0069] Figure 4 This is a schematic diagram of the dq disturbance injection amplitude adjustment process in the disturbance injection method of the present invention;

[0070] Figure 5 This is a schematic diagram of the dq perturbation injection frequency adjustment process in the perturbation injection method of the present invention;

[0071] Figure 6 For the three-phase first disturbance voltage signal source under pure d-axis disturbance at 20Hz Three-phase second disturbance voltage signal source The combined voltage signal of the first and second three-phase disturbance voltage injection sources A waveform diagram;

[0072] Figure 7 To synthesize a voltage signal under pure d-axis perturbation at 20Hz A schematic diagram of the signal waveform after transformation to the d-axis and q-axis;

[0073] Figure 8 The three-phase first disturbance voltage signal source under pure q-axis disturbance at 20Hz. Three-phase second disturbance voltage signal source The combined voltage signal of the first and second three-phase disturbance voltage injection sources A waveform diagram;

[0074] Figure 9 It is the synthesized voltage signal of the first and second disturbance voltage injection sources of the three phases under pure q-axis disturbance at 20Hz. A schematic diagram of the signal waveform after transformation to the d-axis and q-axis;

[0075] Figure 10 For the three-phase first disturbance voltage signal source under pure d-axis disturbance at 120Hz Three-phase second disturbance voltage signal source The combined voltage signal of the first and second three-phase disturbance voltage injection sources A waveform diagram;

[0076] Figure 11 It is the synthesized voltage signal of the first and second disturbance voltage injection sources of the three phases under pure d-axis disturbance at 120Hz. A schematic diagram of the signal waveform after transformation to the d-axis and q-axis;

[0077] Figure 12 The three-phase first disturbance voltage signal source under pure q-axis disturbance at 120Hz. Three-phase second disturbance voltage signal source and the resultant voltage signal of the three-phase first-second disturbance voltage injection source waveform diagram;

[0078] Figure 13 is the resultant voltage signal of the three-phase first-second disturbance voltage injection source under a pure q-axis disturbance at 120Hz waveform diagram of the signal after transformation to the d-axis and q-axis. DETAILED DESCRIPTION

[0079] Further described below in combination with the drawings and specific embodiments.

[0080] The technical concept of the present application is that a disturbance injection controlled voltage source is connected in series at the grid-connected side of a new energy source where impedance measurement is required, a disturbance injection controller controls the injection of a controlled voltage signal by the disturbance injection controlled voltage source, pure d-axis and q-axis voltage signals at different frequencies are injected into the grid-connected system, the current actually fed back by the disturbance signal is measured, and the impedance matrix of the system to be solved is calculated after transformation to the dq-axis, so that the impedance measurement result of the grid-connected inverter system can be obtained without detailed grid-connected inverter system parameters and related complex modeling processes.

[0081] Reference Figure 1 As shown in the figure, the new energy grid-connected system to which the present application is applied includes a new energy power generation source, a grid and a converter; the AC output end of the converter is connected to the grid through a grid-connected three-phase line and a three-phase AC bus at the grid-connected side. The new energy power generation source includes a photovoltaic power generation unit or a wind power generation unit, and the corresponding converter is an inverter DC / AC or an AC / DC / AC converter.

[0082] Embodiment 1

[0083] This embodiment introduces a disturbance injection method suitable for impedance measurement of a new energy grid-connected system, which includes the following steps:

[0084] acquiring a real-time grid voltage , determining the initial phase and frequency of the grid voltage through phase locking;

[0085] setting disturbance control parameters, the disturbance control parameters including the amplitude and frequency of a pure d-axis disturbance sinusoidal voltage signal, and the amplitude and frequency of a pure q-axis disturbance sinusoidal voltage signal;

[0086] inputting the disturbance control parameters and the initial phase and frequency of the grid voltage., as the input of the preset signal conversion model, two sets of three-phase disturbance voltage signals are obtained, and after superposition, the components on the q-axis can cancel each other out or the components on the d-axis can cancel each other out;

[0087] The two sets of three-phase disturbance voltage signals are superposed by phase to obtain a target three-phase disturbance voltage signal ;

[0088] The is given as a value, and the controlled voltage source outputs the corresponding three-phase disturbance voltage signal to the grid between the grid side three-phase AC bus and the grid

[0089] The above signal conversion model performs amplitude conversion, frequency conversion and phase conversion based on input data, and the conversion idea is that positive sequence disturbance voltage and negative sequence disturbance voltage are injected at the same time in the time domain, and the disturbance voltage signal synthesized by them can be equivalent to pure d-axis disturbance or q-axis disturbance after transformation to the dq coordinate system. Specifically, the time-domain disturbance three-phase positive sequence voltage with amplitude, frequency and a-phase initial phase of is subjected to Park transformation based on the phase reference obtained by grid phase locking to obtain the amplitude, frequency and phase of the positive sequence disturbance in the dq coordinate system; the time-domain disturbance three-phase negative sequence with amplitude, frequency and a-phase initial phase of is subjected to Park transformation based on the phase reference obtained by grid phase locking to obtain the amplitude, frequency and phase of the negative sequence disturbance in the dq coordinate system. Then, in the dq coordinate system, the d-axis components of the positive sequence disturbance and the negative sequence disturbance are canceled to obtain a pure q-axis disturbance injection signal; and the q-axis components of the positive sequence disturbance and the negative sequence disturbance are canceled to obtain a pure d-axis disturbance injection signal; according to the mathematical relationship of the amplitude, frequency and phase obtained by canceling, the amplitude model, frequency model and phase model of the positive sequence disturbance and the negative sequence disturbance in the time domain when the pure d-axis signal is injected are obtained.

[0090] Setting of disturbance control parameters

[0091] In the disturbance control parameters of the embodiment, if the target three-phase disturbance voltage signal is a pure d-axis disturbance injection signal, the amplitude of the pure d-axis disturbance sinusoidal voltage signal is set to be not 0, and the amplitude of the pure q-axis disturbance sinusoidal voltage signal is set to be 0; if the target three-phase disturbance voltage signal is a pure q-axis disturbance injection signal, the amplitude of the pure d-axis disturbance sinusoidal voltage signal is set to be 0, and the amplitude of the pure q-axis disturbance sinusoidal voltage signal is set to be not 0.

[0092] ​​​​In general, the disturbance voltage amplitude range has a fixed corresponding relationship with the voltage level and power level, so the exploration process of the corresponding relationship can be performed before the disturbance control, to obtain a power level and voltage level corresponding disturbance amplitude frequency selection range table of the actual system impedance test scene, and the disturbance voltage amplitude and frequency written in the disturbance control parameter table are selected in the range.

[0093] Specifically, in the embodiment, the disturbance control parameters are set, that is, the pre-set disturbance control parameter table is searched, the disturbance voltage signal frequency point and the corresponding pure d-axis disturbance voltage amplitude or the pure q-axis disturbance voltage amplitude are selected, and all the disturbance control parameters of the to-be-input signal conversion model are determined.

[0094] The disturbance control parameter table records a plurality of disturbance voltage signal frequency points and the corresponding pure d-axis disturbance voltage amplitude or the pure q-axis disturbance voltage amplitude .

[0095] In the disturbance injection process of the actual impedance test, disturbance voltage injection needs to be performed for a plurality of frequency points, and for each frequency point, at least one pure d-axis disturbance voltage signal and one pure q-axis disturbance voltage signal are injected respectively, and subsequently, a set of impedance matrices of the grid-connected inverter system can be obtained for each frequency point.

[0096] Regarding the signal conversion model

[0097] Referring to FIGS. 1 and 2, Figure 2 and Figure 3 In the embodiment, the pre-set signal conversion model obtains two sets of three-phase disturbance voltage signals according to the input disturbance control parameters and the grid voltage initial phase and the frequency , including:

[0098] According to the non-zero disturbance voltage signal amplitude in the disturbance control parameter or , the amplitudes of the two sets of three-phase disturbance voltage signals are determined; according to and , the frequency of the first three-phase disturbance voltage signal is determined ; here, as described above, if the target three-phase disturbance voltage signal is a pure d-axis disturbance injection signal, such as Figure 2 , the amplitudes of the two sets of three-phase disturbance voltage signals satisfy ; if the target three-phase disturbance voltage signal is a pure q-axis disturbance injection signal, such as Figure 3 , the amplitudes of the two sets of three-phase disturbance voltage signals satisfy ; the frequency of the first three-phase disturbance voltage signal is: ;

[0099] the comparison frequency with the size of the real-time voltage of the power grid , according to the comparison result, the frequency of the second three-phase disturbance voltage signal is determined, and the relationship between the phase of the two groups of three-phase disturbance voltage signals and the initial phase of the grid voltage is determined, so that the components of the three-phase positive sequence disturbance voltage and the three-phase negative sequence disturbance voltage on the q-axis or the d-axis can be offset each other;

[0100] According to the relationship between and , and and , the first three-phase disturbance voltage signal and the second three-phase disturbance voltage signal are determined.

[0101] If , then , , the second three-phase disturbance voltage signal is:

[0102]

[0103] If , then , , the second three-phase disturbance voltage signal is:

[0104]

[0105] The first three-phase disturbance voltage signal is:

[0106] .

[0107] The above, the first three-phase disturbance voltage signal and the second three-phase disturbance voltage signal are superimposed through an adder to obtain the target pure d-axis or pure q-axis three-phase disturbance injection voltage. Taking the target three-phase disturbance injection voltage as a given voltage to control the controlled voltage source can make the controlled voltage source output the corresponding disturbance voltage signal to the new energy grid-side three-phase line.

[0108] The derivation process of the above signal conversion principle is given below.

[0109] The pure d-axis voltage excitation signal is injected into the system, that is, the q-axis component of the three-phase disturbance signal ua, ub, uc after Park transformation of abc / dq is 0, and only the d-axis signal exists. Certain conditions need to be met in the converter so that the three-phase first disturbance voltage signal source The component on the q-axis and the three-phase second disturbance voltage signal source The components on the q-axis cancel each other out, that is, the q-axis voltage signal injected at this time is equal to 0. Similarly, the pure q-axis voltage excitation signal is injected, that is, the three-phase disturbance signal The d-axis component after Park transformation of abc / dq is 0, and only the q-axis signal exists. Certain conditions need to be met in the converter so that the three-phase first disturbance voltage signal source The component on the d-axis and the three-phase second disturbance voltage signal source The components on the d-axis cancel each other out, that is, the d-axis voltage signal injected at this time is equal to 0.

[0110] Further, in order to realize the injection of pure d-axis or q-axis disturbance voltage in the system, the three-phase first disturbance signal And the three-phase second disturbance signal The mathematical expression after Park transformation of abc / dq to dq axis is determined, thereby determining the design conditions of the amplitude, frequency and phase of the signal conversion model input into the disturbance injection controller.

[0111] In order to select the reference of coordinate transformation, let be the real-time phase of the voltage fundamental wave, then the coordinate abc / dq transformation matrix is:

[0112] (1)

[0113] Let be the initial phase angle of the grid voltage, be the angular frequency of the grid voltage, The expression of is:

[0114] (2)

[0115] Assuming that there is a positive sequence harmonic component with an angular frequency of be the frequency of the three-phase positive sequence harmonic voltage, be the peak value of the three-phase positive sequence harmonic voltage, be the initial phase of the a-phase of the three-phase positive sequence harmonic voltage, then the three-phase positive sequence harmonic voltage can be expressed as:

[0116] (3)

[0117] ​After multiplying the coordinate transformation matrix shown in equation (1) with equation (3), the d-axis component expression and the simplified result of the harmonic are:

[0118] (4)

[0119] (5)

[0120] Similarly, the q-axis component simplified result is:

[0121] (6)

[0122] Suppose there is a negative sequence harmonic voltage component with an angular frequency of , the frequency of the three-phase negative sequence harmonic voltage is , the peak value of the three-phase negative sequence harmonic voltage is , and the initial phase of the a-phase of the three-phase negative sequence harmonic voltage is , then the three-phase negative sequence harmonic voltage can be expressed as:

[0123] (7)

[0124] Similarly, the d-axis component and q-axis component expressions after coordinate transformation are shown in equations (8) and (9);

[0125] (8)

[0126] (9)

[0127] After arranging the above equations, the expressions of the positive sequence harmonic disturbance voltage and the negative sequence harmonic disturbance voltage converted to the dq coordinate system are:

[0128] (10)

[0129] (11)

[0130] In order to realize the mutual cancellation of and in equations (10) and (11) so as to inject a pure q-axis disturbance signal, or to realize the mutual cancellation of and so as to inject a pure d-axis disturbance signal, it is necessary to meet the following conditions from the aspects of amplitude, frequency and phase in the converter of the disturbance injection controller:

[0131] 1) The amplitude condition must satisfy , that is, Figure 1 ;

[0132] ​2) The frequency conversion relationship satisfies: From equations (10) and (11), when the frequencies fdq of the d-axis and q-axis disturbance voltages in the dq coordinate system are determined, the frequencies fp and fn of the three-phase positive-sequence disturbance voltages are also determined. When At that time, the frequency of the three-phase positive sequence disturbance voltage is Three-phase negative sequence disturbance voltage frequency At this time, the first disturbance voltage signal of the three phases frequency Three-phase second disturbance voltage signal frequency ;when At that time, the frequency of the three-phase positive sequence disturbance voltage is or At this time, the negative sequence has no corresponding frequency, and the first disturbance voltage signal of the three phases is... frequency Three-phase second disturbance voltage signal frequency .

[0133] 3) Based on the frequency condition, the phase relationship obviously falls into two categories:

[0134] When in As can be seen from equations (10) and (11) under these circumstances, at this time... and positive sequence initial phase The first disturbance voltage signal is assigned to the three phases. , and negative sequence initial phase The second disturbance voltage signal is assigned to the three phases. ,when The positive and negative d-axis components are canceled out. What remains is the pure q-axis component; when The positive and negative q-axis components are canceled out. What remains is the pure d-axis component.

[0135] When in In this case, by Figure 2 It is known that there are two positive-sequence angular frequencies at this time. and ,satisfy ,in , There are no negative sequence frequencies. At this time, [the frequency will be...]. and positive sequence initial phase The first disturbance voltage signal is assigned to the three phases. , and positive sequence initial phase The second disturbance voltage signal is assigned to the three phases. We obtain equations (12) and (13). At this point, when When the d-axis component is cancelled, i.e. , the pure q-axis component is left; when the q-axis component is cancelled, i.e. , the pure d-axis component is left.

[0136] Thus, the conversion principle of the signal conversion model shown in Figure 2 and Figure 3 can be obtained.

[0137] Range selection of disturbance control parameters

[0138] Considering that the impedance nature of the grid-connected inverter is a small-signal linearization model, the linear characteristics of the "response-excitation" must be maintained in the specific test process. Due to actual factors such as three-phase current asymmetry and stable working point offset, nonlinearity will be caused, so a constraint condition should also be imposed on the selection of the disturbance quantity amplitude in the actual impedance test process. According to the positive and negative sequence separation results of the current response quantity, the same sequence and frequency as the disturbance voltage in the abc coordinate system is the linear component, and the rest is the nonlinear quantity, and the nonlinear rate is defined to measure the three-phase asymmetry degree; based on the fundamental component of the current response FFT analysis, the stable working point offset rate is defined to measure the stable working point offset degree. The calculation formulas of the nonlinear rate and the stable working point offset rate are respectively:

[0139] (14)

[0140] (15)

[0141] In formula (14), the numerator is the sum of the amplitudes of the harmonic current nonlinear quantities, and the denominator is the sum of the amplitudes of the harmonic current linear quantities; in formula (15), I0is the fundamental current amplitude of the stable working point before the disturbance is injected, I1is the fundamental current amplitude after the disturbance is injected.

[0142] In order to make the injected disturbance voltage not affect the normal operation of the system and accurately reflect the impedance characteristics of the system, the amplitudes of the injected positive sequence disturbance and negative sequence disturbance voltage are restricted by the nonlinear rate and the stable working point offset rate. According to the positive and negative sequence separation results of the current response quantity, when the injected disturbance amplitude is too small, the nonlinearity increases, which affects the impedance measurement accuracy; when the injected disturbance amplitude is too large, the stable working point will be offset, and the system characteristics cannot be accurately reflected. Therefore, in this embodiment, the nonlinear rate constraint determines the lower limit of the disturbance quantity amplitude, and the stable working point offset rate constraint determines the upper limit of the disturbance quantity amplitude, when the nonlinear rate and the stable working point offset rate are both less than 3%, the influence of the slight three-phase asymmetry and the stable working point offset can be ignored, and the excitation and response relationship meets the linear requirements of the test.

[0143] ​The disturbance voltage in the disturbance control parameter table should be selected within a reasonable amplitude range, and in addition, a linear calibration link can also be added in the test step: if the nonlinearity rate is large, appropriately increase the disturbance amplitude to increase the linear amount in the response and reduce the nonlinearity rate to less than 3%; if the stable operating point offset rate is large, then appropriately reduce the disturbance amount to make the stable operating point offset rate less than 3%.

[0144] Specifically, referring to Figure 4 , the pre-determination or online adjustment method of the disturbance voltage amplitude includes:

[0145] S21, inject positive and negative sequence harmonic voltage combinations corresponding to the test frequency fdq(m) and equivalent to pure d-axis or q-axis disturbance voltage, record the three-phase current at the inverter output side in steady state operation ;

[0146] S22, Fourier transform the obtained three-phase current , extract the phase components corresponding to and positive and negative sequence harmonic frequencies , ;

[0147] S23, separate the positive and negative zero sequence components in the harmonic current response , using the symmetrical component method, wherein two linear quantities are: the positive sequence component current of and the negative sequence component current of ; four nonlinear quantities are: the negative sequence component current of , and the zero sequence component currents of two frequencies , ;

[0148] S24, calculate the nonlinearity rate and the stable operating point offset rate , the formula is:

[0149]

[0150]

[0151] In the formula, are the current peak values of the currents ; is the fundamental current amplitude of the stable operating point before the disturbance amount is injected, is the fundamental current amplitude after the disturbance is injected;

[0152] If the nonlinearity rate and the stable operating point shift rate are less than or equal to a set value, the amplitude of the current pure d-axis or q-axis disturbance voltage can be used as the disturbance injection amplitude in the disturbance control parameter; if the nonlinearity rate is greater than the set value, the amplitude is increased by a certain amount on the basis of the current disturbance injection voltage amplitude, steps S21-S24 are repeated until the nonlinearity rate is less than or equal to the set value; if the stable operating point shift rate is greater than the set value, the amplitude is decreased by a certain amount on the basis of the current disturbance injection voltage amplitude, steps S21-S24 are repeated until the stable operating point shift rate is less than or equal to the set value; the set values of the nonlinearity rate and the stable operating point shift rate can also be set to 3%;

[0153] Here, reference can be made to Figure 4 First, it is determined whether the nonlinearity rate is less than or equal to a set value, if not, the disturbance amount amplitude is increased and the disturbance voltage signal is re-injected for signal acquisition separation and nonlinearity rate calculation until the set value range is met, if the set value range is met, it is determined whether the stable operating point shift rate is less than or equal to a set value, if not, the disturbance amount amplitude is decreased and the disturbance voltage signal is re-injected for signal acquisition separation, nonlinearity rate calculation, etc., until the nonlinearity rate and the stable operating point shift rate are less than or equal to a set value;

[0154] S25, the amplitude of the pure d-axis or q-axis disturbance voltage that makes the nonlinearity rate and the stable operating point shift rate are less than or equal to a set value is selected as the disturbance injection amplitude in the disturbance control parameter.

[0155] The above amplitude selection method can also explore the amplitude selection range, and the amplitude can be selected within the range.

[0156] Similarly, considering that the impedance of the grid-connected inverter is essentially a small-signal linearization model, the linear characteristics of "response-excitation" must be maintained during the specific test process. As the disturbance frequency increases, the system impedance exhibits nonlinear characteristics, for example, in a grid-connected system containing a transformer, as the frequency increases, the transformer core gradually saturates, exhibiting nonlinear characteristics. The maximum disturbance frequency is limited by the nonlinearity rate shown in equation (14). Therefore, the disturbance voltage frequency is limited by the nonlinearity of the actual grid-connected system, and a too high disturbance frequency will cause magnetic saturation problems of the transformer and filter, thereby causing the nonlinearity rate to be too high, affecting the accuracy of the system impedance measurement, and making the nonlinearity rate constraint determine the upper limit of the disturbance voltage frequency.

[0157] Therefore, in the embodiment, the disturbance voltage signal frequency is predetermined or adjusted in a test process, as shown in the following steps: Figure 5

[0158] S11, a positive and negative sequence harmonic voltage combination corresponding to the test frequency and equivalent to a pure d-axis or q-axis disturbance voltage is injected, and the three-phase current at the inverter output side in steady state operation is recorded ;

[0159] S12, the obtained three-phase current is subjected to Fourier transform to extract the phase components corresponding to and the positive and negative sequence harmonic frequencies ,

[0160] S13, the positive and negative zero sequence components in the harmonic current response , are separated by using the symmetrical component method, wherein two linear quantities are: the positive sequence component current and the negative sequence component current ; four nonlinear quantities are: the negative sequence component current , the positive sequence component current and the zero sequence component currents of the two frequencies , ;

[0161] S14, the nonlinear rate is calculated, and the formula is:

[0162]

[0163] wherein are the current peak values of the currents ;

[0164] If the nonlinear rate is less than or equal to a set value, if it is satisfied, the disturbance frequency is increased on the basis of the current test frequency , step S11 is turned to and steps S11 to S14 are executed again until the nonlinear rate is greater than the set value, and the test frequency before the last increase is taken as the maximum disturbance voltage signal frequency;

[0165] S15, the disturbance voltage signal frequency in the disturbance control parameters is selected in the range less than or equal to the maximum disturbance voltage signal frequency.

[0166] ​​In the process of determining the maximum disturbance voltage signal range, the initial test frequency was... Start by selecting a smaller value; non-linear rate. The set value can be 3%.

[0167] Figures 6 to 9 This is a simulation waveform diagram of dq voltage perturbation injection at 20Hz in an application example of the present invention, wherein... Figure 6 The source of the three-phase first disturbance voltage signal under pure d-axis disturbance at 20 Hz is shown. Three-phase second disturbance voltage signal source The combined voltage signal from the first and second three-phase disturbance voltage injection sources According to the above-mentioned disturbance injection controller, the converter must satisfy three conditions: amplitude, frequency, and initial phase.

[0168] 1) At this time, the first disturbance voltage signal of the three phases Three-phase second disturbance voltage signal The peak voltage is 5V;

[0169] 2) The fundamental frequency is ,because At this time, the frequency of the first disturbance voltage signal in the three phases The frequency of the three-phase second disturbance voltage signal ;

[0170] 3) The initial phases of the three-phase first disturbance voltage signal and the three-phase second disturbance voltage signal are equal. And satisfy ,get Figure 7 As shown The pure d-axis disturbance is canceled out by the q-axis signal.

[0171] The initial phases of the three-phase first disturbance voltage signal and the three-phase second disturbance voltage signal are equal. And satisfy ,get Figure 8 As shown in Three-phase first disturbance voltage signal under pure q-axis disturbance Three-phase second disturbance voltage signal and three-phase disturbance injection controlled voltage signal At this point, we obtain the following on the dq axis: Figure 9 As shown The pure q-axis disturbance is canceled out by the d-axis signal.

[0172] Figures 10-13 The figure shows a simulated waveform of dq voltage perturbation injection at 120Hz in one application example of the present invention, wherein... Figure 10The combined voltage signals ua, ub, and uc are generated from the three-phase first disturbance voltage signal sources ua1, ub1, and uc1, the three-phase second disturbance voltage signal sources ua2, ub2, and uc2, and the three-phase first and second disturbance voltage injection sources under a pure d-axis disturbance at 120Hz. The converter of the aforementioned disturbance injection controller is required to satisfy three conditions regarding amplitude, frequency, and initial phase:

[0173] 1) At this time, the peak voltages of the three-phase first disturbance voltage signals ua1, ub1, uc1 and the three-phase second disturbance voltage signals ua2, ub2, uc2 are all 5V;

[0174] 2) The fundamental frequency is ,because >50Hz, at which point the frequency of the first disturbance voltage signal in the three phases is... The frequency of the three-phase second disturbance voltage signal ;

[0175] 3) The initial phases of the three-phase first disturbance voltage signal and the three-phase second disturbance voltage signal are respectively... and φ0n, and satisfy ,get Figure 11 As shown The pure d-axis disturbance is canceled out by the q-axis signal.

[0176] The initial phases of the three-phase first disturbance voltage signal and the three-phase second disturbance voltage signal are respectively... and φ0n, and satisfy ,get Figure 12 As shown in Three-phase first disturbance voltage signal under pure q-axis disturbance Three-phase second disturbance voltage signal and three-phase disturbance injection controlled voltage signal At this point, we obtain the following on the dq axis: Figure 13 As shown The pure q-axis disturbance is canceled out by the d-axis signal.

[0177] Example 2

[0178] This embodiment introduces a method for measuring the impedance of a new energy grid-connected system, including:

[0179] Using the disturbance injection method described in Example 1, disturbances are injected into the AC output terminal of the converter and the power grid. A pure d-axis voltage signal or a pure q-axis voltage signal is injected into the grid-connected three-phase lines between the three-phase AC buses on the grid-connected side.

[0180] Obtain the response disturbance current signal generated by the line where the disturbance voltage injection point is located under the excitation of the disturbance voltage signal;

[0181] The disturbance voltage signal and the response disturbance current signal are transformed to dq axes, and the impedance matrix of the new energy grid-connected system is calculated according to the disturbance voltage signal and the response disturbance current signal after the transformation.

[0182] The Bode plot of the system impedance is obtained by sweeping the frequency, and a series of impedance amplitudes and phases corresponding to the frequency points are required. Therefore, in the embodiment, the disturbance voltage signal corresponding to multiple frequency points needs to be injected multiple times, and the pure d-axis voltage signal and the pure q-axis voltage signal are injected once for each frequency point, respectively. The impedance matrix in the dq coordinate system corresponds to the impedance Bode plot of the dd, dq, qd and qq channels, and the impedance calculation methods are as follows: the dd channel impedance is equal to the pure d-axis voltage disturbance signal divided by the d-axis component of the response current signal of the pure d-axis voltage disturbance signal; the dq channel impedance is equal to the pure d-axis voltage disturbance signal divided by the d-axis component of the response current signal of the pure q-axis voltage disturbance signal; the qq channel impedance is equal to the pure q-axis voltage disturbance signal divided by the q-axis component of the response current signal of the pure q-axis voltage disturbance signal; and the qd channel impedance is equal to the pure q-axis voltage disturbance signal divided by the q-axis component of the response current signal of the pure d-axis voltage disturbance signal. Specifically:

[0183] The voltage, current and impedance relationship expression corresponding to one disturbance injection is:

[0184]

[0185] After injecting the pure d-axis disturbance voltage, obtaining the first group of current response data and coordinate transformation, and substituting into the above formula, we get:

[0186]

[0187] After injecting the q-axis disturbance voltage, obtaining the second group of current response data and coordinate transformation, and substituting into the above formula, we get:

[0188]

[0189] By combining the above two formulas, the equivalent matrix equation can be obtained:

[0190]

[0191] At this point, the disturbance voltage injection corresponding to each frequency point, the impedance matrix in the dq coordinate system is:

[0192]

[0193] In the formula, , , , respectively represent the impedance of the dd, dq, qd and qq channels. , Let represent the d-axis and q-axis voltage components of the pure d-axis perturbation injection voltage, respectively. , These are the d-axis and q-axis voltage components of the pure q-axis perturbation injection voltage, respectively; , These represent the d-axis and q-axis current components of the response disturbance current signal to a pure d-axis disturbance injection voltage, respectively. , These represent the d-axis and q-axis current components of the response disturbance current signal to the pure q-axis disturbance injection voltage, respectively.

[0194] Example 3

[0195] This embodiment introduces a disturbance injection system suitable for impedance measurement of renewable energy grid-connected systems. It includes the renewable energy grid-connected system under test and a controlled AC voltage source for three-phase disturbance injection. And disturbance injection controller; in the tested renewable energy grid-connected system, the AC output terminal of the converter is connected to the power grid. Three-phase circuit breakers are installed on the three-phase lines between the three-phase AC busbars on the grid-connected side. Controlled DC voltage source The power output terminals are connected in parallel to the three-phase circuit breaker. The two ends;

[0196] The disturbance injection controller is used in a three-phase circuit breaker. When disconnected, control the controlled DC voltage source. A disturbance voltage signal is injected into the grid-connected three-phase line. The disturbance voltage signal is either a pure d-axis voltage signal or a pure q-axis voltage signal.

[0197] The converter is an inverter (DC / AC) or an AC-DC-AC converter (AC / DC / AC); the new energy power source is a photovoltaic power generation unit or a wind power generation unit.

[0198] The process of the disturbance injection controller controlling the controlled voltage source to output a specified pure q-axis or pure d-axis voltage disturbance signal is described in the relevant content of Example 1 and will not be repeated here.

[0199] Example 4

[0200] This embodiment introduces an impedance measurement system suitable for impedance measurement in new energy grid-connected systems. It includes the disturbance injection system described in Embodiment 1 and a signal acquisition device for acquiring current signals in response to disturbance injection voltage. The signal acquisition device acquires the current on the line where the disturbance voltage signal injection point is located.

[0201] The impedance of the new energy grid-connected system is calculated based on the disturbance injection voltage signal and the response disturbance current signal in the collected current signal.

[0202] The specific calculation process and principle refer to the related content of Embodiments 1 and 2, which will not be repeated here.

[0203] Embodiment 5

[0204] This embodiment introduces a computer readable storage medium, which stores a computer program. When the computer program is executed by a processor, the disturbance injection method suitable for impedance measurement of a new energy grid-connected system as described in Embodiment 1 is implemented, or the new energy grid-connected system impedance measurement method as described in Embodiment 2 is implemented.

[0205] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage, etc.) containing computer-usable program code.

[0206] The present application is described with reference to flowcharts and / or block diagrams according to the methods, devices (systems), and computer program products of the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing apparatus to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing apparatus produce a device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in one or more flows and / or blocks. Figure 1 The functions specified in one or more flows and / or blocks.

[0207] These computer program instructions can also be stored in a computer readable memory that can direct the computer or other programmable data processing apparatus to work in a specific manner, so that the instructions stored in the computer readable memory produce a manufactured product including instruction devices that implement the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in one or more flows and / or blocks. Figure 1 The functions specified in one or more flows and / or blocks.

[0208] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so that a series of operation steps are performed on the computer or other programmable data processing apparatus to produce a computer-implemented process, so that the instructions executed on the computer or other programmable data processing apparatus provide a process for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1steps of the functions specified in the flowchart or flowcharts and / or block Figure 1

[0209] The embodiments of the present application are described above with reference to the accompanying drawings, but the present application is not limited to the above-described specific embodiments, and the above-described specific embodiments are merely illustrative, but not restrictive, and a person of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, and these all belong to the protection of the present application.​

Claims

1. A disturbance injection method suitable for impedance measurement of a new energy grid-connected system, characterized in that, The method comprises the following steps: acquiring real-time voltage of power grid , determining initial phase of real-time voltage of power grid and frequency ; determining disturbance control parameters, the disturbance control parameters comprising an amplitude and a frequency of a pure d-axis disturbance voltage signal and an amplitude and a frequency of a pure q-axis disturbance voltage signal and an amplitude and a frequency of a pure q-axis disturbance voltage signal ;​ The disturbance control parameters and the initial phase of the real-time grid voltage are used. and frequency As input to a pre-set signal conversion model, two sets of three-phase disturbance voltage signals are obtained from the output of the signal conversion model. After the two sets of three-phase disturbance voltage signals are superimposed, the components on the q-axis can cancel each other out or the components on the d-axis can cancel each other out. superimposing the two groups of three-phase disturbance voltage signals by phase to obtain a target three-phase disturbance voltage signal ; The As a given value, the controlled voltage source output is controlled to be equal to The corresponding three-phase disturbance voltage signal, to the converter AC output end and the grid The grid-side three-phase AC bus between the grid-side three-phase line; The pre-set signal conversion model is used to obtain two groups of three-phase disturbance voltage signals according to the input disturbance control parameters and the grid voltage initial phase and frequency . determining the amplitudes of the two sets of three-phase disturbance voltage signals from the disturbance control parameters whose disturbance voltage signal amplitudes are not zero or determining the amplitudes of the two sets of three-phase disturbance voltage signals from the disturbance control parameters whose disturbance voltage signal amplitudes are not zero and determining the frequency of the first three-phase disturbance voltage signal from the disturbance control parameters whose disturbance voltage signal amplitudes are not zero ​ Comparison frequency Real-time voltage of the power grid The magnitude of the disturbance voltage signal is used to determine the frequency of the second and third phase disturbance voltage signals based on the comparison results. The phases of the two sets of three-phase disturbance voltage signals are determined with the goal of ensuring that the components of the three-phase positive-sequence disturbance voltage and the three-phase negative-sequence disturbance voltage cancel each other out on the q-axis or d-axis. and the initial phase of the grid voltage The relationship between them; determining a first three-phase disturbance voltage signal and between and determining a second three-phase disturbance voltage signal and .

2. The method of claim 1, wherein, The determining the disturbance control parameter: if the target three-phase disturbance voltage signal is a pure d-axis disturbance voltage signal, determining the amplitude of the pure d-axis disturbance voltage signal is not 0, the amplitude of the pure q-axis disturbance voltage signal is 0; if the target three-phase disturbance voltage signal is a pure q-axis disturbance voltage signal, setting the amplitude of the pure d-axis disturbance voltage signal to 0, the amplitude of the pure q-axis disturbance voltage signal is not 0.

3. The method according to claim 1 or 2, characterized in that, If the target three-phase disturbance voltage signal is a pure d-axis disturbance voltage signal, the amplitudes of the two sets of three-phase disturbance voltage signals satisfy ; if the target three-phase disturbance voltage signal is a pure q-axis disturbance voltage signal, the amplitudes of the two sets of three-phase disturbance voltage signals satisfy ; The method according to And Determining the frequency of the first three-phase disturbance voltage signal , is given by: ; If then , , the second three-phase disturbance voltage signal is: ， If then , , the second three-phase disturbance voltage signal is: ， A first three-phase disturbance voltage signal is: 。 4. The method of claim 1 wherein, The determining the disturbance control parameter comprises: searching a pre-set disturbance control parameter table, selecting a disturbance voltage signal frequency point and its corresponding pure d-axis disturbance voltage amplitude or pure q-axis disturbance voltage amplitude , and determining all the disturbance control parameters to be input into the signal conversion model. The disturbance control parameter table records a plurality of disturbance voltage signal frequency points and corresponding pure d-axis disturbance voltage amplitudes or pure q-axis disturbance voltage amplitudes .

5. The method of claim 1 wherein, a disturbance voltage signal frequency in the disturbance control parameters The determination method comprises: S11, inject corresponding test frequency and equivalent to the positive and negative sequence harmonic voltage combination of pure d-axis or q-axis disturbance voltage, record the three-phase current at the output side of the inverter during steady-state operation ; S12, Fourier transforming the resulting three-phase current and extracting the respective phase components corresponding to and positive and negative sequence harmonic frequencies , ; S13, separating the positive and negative zero sequence components of the harmonic current response using the symmetrical component method , , where two linear quantities are: the positive sequence component current and the negative sequence component current ; four non-linear quantities are: the negative sequence component current , the positive sequence component current and two zero sequence component currents at the frequencies , ; S14, calculate the non-linear rate The formula is: ， wherein are the current current peaks, respectively; determining whether the non-linearity rate is less than or equal to a set value, if satisfied, increasing the disturbance frequency on the basis of the current test frequency and turning to step S11 and executing steps S11 to S14 again until the non-linearity rate is greater than the set value, then taking the test frequency before the last increase as the maximum disturbance voltage signal frequency; S15, selecting a disturbance voltage signal frequency in the disturbance control parameters in a range less than or equal to the maximum disturbance voltage signal frequency .

6. The method of claim 1 wherein, The determination method of the disturbance voltage amplitude in the disturbance control parameter comprises: S21, inject corresponding test frequency and equivalent to the positive and negative sequence harmonic voltage combination of pure d-axis or q-axis disturbance voltage, record the three-phase current at the output side of the inverter during steady-state operation ; S22, Fourier transforming the resulting three-phase current and extracting the respective phase components corresponding to and positive and negative sequence harmonic frequencies , ; S23, separating the positive and negative zero sequence components of the harmonic current response using the symmetrical component method , , where two linear quantities are: the positive sequence component current and the negative sequence component current ; four non-linear quantities are: the negative sequence component current , the positive sequence component current and two zero sequence component currents at the frequencies , ; S24, calculate the non-linear rate and the stable operating point offset rate , the formula is: ， ， wherein is the peak value of the current is the peak value of the current; is the fundamental current amplitude of the stable operating point before the injection of the perturbation, is the fundamental current amplitude after the injection of the perturbation; a nonlinear rate and a stable operating point shift rate are less than or equal to a set value, the amplitude of the current pure d-axis or q-axis disturbance voltage can be used as the disturbance injection amplitude in the disturbance control parameter; if the nonlinear rate is greater than the set value, an amplitude amount is added to the current disturbance injection voltage amplitude, and steps S21-S24 are repeated until the nonlinear rate is less than or equal to the set value; if the stable operating point shift rate is greater than the set value, an amplitude amount is subtracted from the current disturbance injection voltage amplitude, and steps S21-S24 are repeated until the stable operating point shift rate is less than or equal to the set value. S25, selecting an amplitude of a pure d-axis or q-axis disturbance voltage having a non-linear rate and a stable operating point shift rate less than or equal to a set value as a disturbance injection amplitude in the disturbance control parameter.

7. A method for measuring impedance of a new energy grid-connected system, characterized in that, The method comprises the following steps: Using the disturbance injection method described in any one of claims 1-6, a disturbance is injected into the AC output terminal of the converter and the power grid. A disturbance voltage signal is injected into the grid-connected three-phase lines between the three-phase AC buses on the grid-connected side. The disturbance voltage signal is a pure d-axis voltage signal or a pure q-axis voltage signal. Obtaining a response disturbance current signal generated by the power grid under the excitation of the disturbance voltage signal; The disturbance voltage signal and the response disturbance current signal are transformed to the dq axis, and the impedance matrix of the new energy grid-connected system is calculated according to the disturbance voltage signal and the response disturbance current signal after the transformation.

8. The method of claim 7, wherein, The disturbance voltage signal injected into the grid three-phase line is injected multiple times at multiple frequency points, and a pure d-axis voltage signal and a pure q-axis voltage signal are injected once at each frequency point. The impedance matrix under the dq coordinate system is calculated according to the following formula for the disturbance voltage injection at each frequency point: ， wherein , , , Zdd, Zdq, Zqd, and Zqq represent the impedances of the dd, dq, qd, and qq channels, respectively; , id and iq represent the d-axis and q-axis voltage components of the purely d-axis disturbance injection voltage, , id and iq represent the d-axis and q-axis voltage components of the purely q-axis disturbance injection voltage; , id and iq represent the d-axis and q-axis current components of the response disturbance current signal of the purely d-axis disturbance injection voltage, , id and iq represent the d-axis and q-axis current components of the response disturbance current signal of the purely q-axis disturbance injection voltage.

9. A perturbation injection system suitable for impedance measurement of a grid-connected new energy system, characterized in that, A measured new energy grid-connected system, a controlled alternating voltage source for three-phase disturbance injection , and a disturbance injection controller; the measured new energy grid-connected system includes a new energy power generation source, a power grid , and a converter; Converter AC output and grid A three-phase circuit breaker is arranged on the grid connection three-phase line between the grid connection side three-phase AC bus ; controlled DC voltage source The power output ends of the controlled DC voltage source are respectively connected in parallel across the two ends of the three-phase circuit breaker ; The disturbance injection controller is configured to inject a disturbance voltage signal into a three-phase line of a power grid, the disturbance voltage signal being a purely d-axis voltage signal or a purely q-axis voltage signal. The disturbance injection controller is configured to inject a disturbance voltage signal into a three-phase line of a power grid, the disturbance voltage signal being a purely d-axis voltage signal or a purely q-axis voltage signal. The disturbance injection controller is configured to inject a disturbance voltage signal into a three-phase line of a power grid, the disturbance voltage signal being a purely d-axis voltage signal or a purely q-axis voltage signal.

10. The perturbation injection system of claim 9, wherein, The converter is an inverter DC / AC or an AC / DC / AC converter, and the new energy power source is a photovoltaic power generation unit or a wind power generation unit.

11. An impedance measurement system suitable for impedance measurement of a grid-connected system of new energy, characterized in that, The disturbance injection system of claim 9 or 10 and a signal collector for collecting the current signal responding to the disturbance injection voltage, wherein the signal collector collects the current on the line at the disturbance voltage injection point; The impedance of the new energy grid-connected system is calculated according to the disturbance injection voltage signal and the response disturbance current signal collected in the current signal.

12. A computer readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the disturbance injection method for measuring the impedance of the new energy grid-connected system according to any one of claims 1-6, or to implement the impedance measurement method of the new energy grid-connected system according to any one of claims 7-8.

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