CN113671257A - Impedance measurement method for perturbation mode switching - Google Patents

Abstract

The invention provides an impedance measurement method for switching disturbance modes, and belongs to the field of power quality and control. The impedance measuring device related by the method comprises a disturbance unit and an impedance measuring and disturbance selecting unit, wherein the impedance measuring method selects a disturbance injection mode according to predicted impedance and judges whether to measure again according to the amplitude relation of measured values. The method can lead the side of the grid-connected equipment to be divided into more disturbances, and improve the impedance measurement precision; compared with the existing switching method, the method saves the measurement time.

Description

Impedance measurement method for switching disturbance mode

Technical Field

The invention belongs to the field of power quality and control, relates to an impedance measurement method for switching disturbance modes, and particularly relates to an impedance measurement method for switching current disturbance injection and voltage disturbance injection under a grid-connected condition.

Background

In the problem of stability analysis of a grid-connected system, a stability judgment method based on an impedance ratio is widely used, and accurate measurement of output impedance of grid-connected equipment also becomes an actual requirement. The disturbance injection method has the advantages of real-time, accuracy and rapidness when the impedance of the inverter is measured. The perturbation injection method injects a voltage perturbation or a current perturbation at the PCC. When the impedance of the grid-connected equipment is greater than the impedance of the power grid, the voltage disturbance can cause the grid-connected equipment to be subjected to more disturbance; on the contrary, the current disturbance can cause the grid-connected equipment side to have more disturbances, and the measurement precision is improved. The two disturbance modes are matched for use, and an accurate impedance measurement result can be obtained in a wide frequency band. However, an efficient perturbation mode selection scheme is lacking. For example:

1) in patent document "impedance measurement method for adaptive control of disturbance frequency and disturbance amplitude" (CN110456161A) of li fei et al in 11 months in 2019, impedance information obtained in an online measurement process is used to predict grid-connected equipment impedance, adjust amplitude of injection voltage disturbance, and improve measurement accuracy. However, the voltage disturbance has the following disadvantages: when the impedance of the power grid is far larger than the impedance of the grid-connected equipment, the disturbance obtained by the side of the grid-connected equipment only accounts for a small part of the total injected disturbance due to the voltage division effect, so that the response signal-to-noise ratio is too low; if the disturbance amplitude is increased, the voltage on the network side is seriously distorted, and the normal operation of the system is disturbed. The method does not predict the power grid impedance, but simultaneously predicts the power grid impedance and the grid-connected equipment impedance, and can provide a basis for selecting a disturbance mode.

2) Xue shie et al published in "on-line accurate measurement method of wide frequency band sequence impedance of new energy power generation equipment under dual-mode disturbance" in volume 44, 9 of the Chinese electro-mechanical engineering journal of 2020, and the article carries out on-line measurement on output impedance of a grid-connected inverter. And firstly, performing voltage disturbance injection, measuring the impedance of the inverter and the impedance of the power grid, comparing the amplitudes of the inverter and the power grid, switching to current disturbance injection if the impedance of the power grid is larger, and taking the current disturbance injection as a final measurement result, otherwise, taking the voltage disturbance injection as a final measurement result. The method can improve the measurement precision. However, in the measurement frequency band where the grid impedance is greater than the grid-connected device impedance, the method needs to perform two measurements, which is time-consuming.

In summary, the existing impedance online measurement technology has the following problems:

1) the impedance of the grid-connected equipment is measured only by using voltage disturbance or current disturbance, and when the amplitude difference between the impedance of the power grid and the impedance of the grid-connected equipment is large, the measurement precision is reduced or the system deviates from a static working point.

2) The scheme of voltage and current dual-mode disturbance cannot judge a proper disturbance mode before measurement, and measurement time is wasted. The power grid impedance and the grid-connected equipment impedance are not predicted at the same time, and the disturbance mode is selected by using the prediction result.

Disclosure of Invention

The invention provides an impedance measuring method for switching disturbance modes. The method is used for solving the disturbance mode selection problem of online measurement of the impedance of the grid-connected equipment in the grid-connected system, improving the measurement precision and saving the measurement time.

In order to solve the technical problem, the invention provides an impedance measurement method for switching disturbance modes, wherein a topological structure related to the impedance measurement method for switching disturbance modes comprises a power grid, grid-connected equipment and an impedance measurement device connected to the power grid and connected with the grid-connected equipment at a Point of Common Coupling (PCC); the impedance measuring device comprises a disturbance unit and an impedance measuring and disturbance selecting unit; the disturbance unit comprises a voltage disturbance device and a current disturbance device, and the impedance measurement and disturbance selection unit comprises a network side sampling device, an equipment side sampling device, an impedance calculation unit and a disturbance selection unit; the voltage disturbance device is connected in series with a PCC (point of common coupling) connected with a power grid and grid-connected equipment, the current disturbance device is connected in parallel with the PCC connected with the power grid and the grid-connected equipment, the grid-side sampling device is connected between the power grid and the PCC, the equipment-side sampling device is connected between the PCC and the grid-connected equipment, the input end of the impedance calculation unit is respectively connected with the output ends of the grid-side sampling device and the equipment-side sampling device, and the disturbance selection unit is in communication connection with the disturbance unit;

the impedance measurement method is characterized in that M preset disturbance frequencies are firstly appointed, and then the impedance measurement method is carried out at the M preset disturbance frequencies from small to large according to the magnitude of the M preset disturbance frequency valuesMeasuring impedance; recording any one of M preset disturbance frequencies as a preset disturbance frequency f_kK is 1, 2 … M at a predetermined disturbance frequency f_kThe specific steps of performing impedance measurement are as follows:

step 1, setting parameters, including the following parameters:

preset disturbance frequency f_kPredicted value Z of grid-connected impedance_cPredicted value Z of grid impedance_g；

The grid-connected impedance predicted value Z_cFor obtaining the preset disturbance frequency f of the grid-connected equipment by using an impedance prediction method_kThe output impedance predicted value, the grid impedance predicted value Z_gFor the power network obtained by the impedance prediction method at the preset disturbance frequency f_kThe predicted value of the impedance of the output;

step 2, comparing the grid-connected impedance predicted value Z_cAnd the predicted value Z of the network impedance_gThe magnitude of (2):

if Z_g|＜|Z_cI, entering the step 3;

if Z_g|≥|Z_cI, entering a step 5;

step 3, the disturbance selection unit controls the injection frequency of the voltage disturbance device to the PCC to be a preset disturbance frequency f_kControlling the output current of the current disturbance device to be 0;

collecting voltage response and current response of the power grid under the sinusoidal voltage disturbance through a grid side sampling device, and presetting disturbance frequency f under the voltage response_kThe voltage component is recorded as the voltage harmonic component u on the voltage disturbance network side_g1Preset disturbance frequency f under current response_kThe current component is marked as the harmonic component i of the voltage disturbance network side current_g1(ii) a Collecting voltage response and current response of the grid-connected equipment under the sinusoidal voltage disturbance through an equipment side sampling device, and presetting disturbance frequency f under the voltage response_kThe voltage component is recorded as the voltage harmonic component u on the voltage disturbance device side_c1Preset disturbance frequency f under current response_kThe current component is marked as the harmonic component i of the current on the voltage disturbance equipment side_c1；

Recording the measured impedance of the power grid under the sinusoidal voltage disturbance as the measured impedance Z of the primary power grid_g1Recording the measured impedance of the grid-connected equipment under the sinusoidal voltage disturbance as primary grid-connected measured impedance Z_c1Calculating the primary power grid measurement impedance Z by an impedance calculation unit_g1And primary grid-connected impedance Z_c1：

Z_g1＝u_g1÷i_g1

Z_c1＝u_c1÷i_c1

Step 4, comparing the primary grid-connected measured impedance Z_c1And primary grid measured impedance Z_g1The magnitude of (2):

if Z_g1|≤|Z_c1|，Z_g1And Z_c1The measurement is finished for the final measurement result;

if Z_g1|＞|Z_C1I, entering a step 5;

step 5, the disturbance selection unit controls the current disturbance device to inject a preset disturbance frequency f to the PCC of the common coupling point_kControlling the output voltage of the voltage disturbance device to be 0;

collecting voltage response and current response of the power grid under the sinusoidal current disturbance through a grid side sampling device, and presetting disturbance frequency f under the voltage response_kThe voltage component is marked as the harmonic component u of the current disturbance network side voltage_g2Preset disturbance frequency f under current response_kThe current component is marked as the current disturbance network side current harmonic component i_g2(ii) a Collecting voltage response and current response of the grid-connected equipment under the sinusoidal current disturbance through an equipment side sampling device, and presetting disturbance frequency f under the voltage response_kThe voltage component is recorded as the harmonic component u of the current disturbance device side voltage_c2Preset disturbance frequency f under current response_kThe current component is marked as the current harmonic component i on the current disturbance equipment side_c2；

Recording the measured impedance of the power grid under the sinusoidal current disturbance as the measured impedance Z of the secondary power grid_g2The grid-connected equipment is arranged atThe measured impedance under the sine current disturbance is recorded as secondary grid-connected measured impedance Z_c2Calculating the measured impedance Z of the secondary power grid through an impedance calculation unit_g2And secondary grid-connected measurement impedance Z_c2：

Z_g2＝u_g2÷i_g2

Z_c2＝u_c2÷i_c2

Step 6, comparing the secondary grid-connected measured impedance Z_c2And secondary grid measured impedance Z_g2The magnitude of (2):

if Z_g2|≥|Z_c2|，Z_g2And Z_c2The measurement is finished for the final measurement result;

if Z_g2|＜|Z_c2And | returning to the step 3.

Compared with the prior art, the invention has the following beneficial effects:

1) and selecting a disturbance mode which enables the grid-connected equipment side to obtain more disturbances according to the relation of the predicted values of the impedance, so that the response signal-to-noise ratio is increased, and the impedance measurement precision is improved.

2) Before impedance measurement, a disturbance mode is selected by using the predicted value, and whether the second measurement is needed or not is judged according to the measured value, so that the measurement time is saved.

Drawings

FIG. 1 is a topological diagram relating to the impedance measurement method of the present invention;

FIG. 2 is a flow chart of the impedance measurement method of the present invention;

FIG. 3 is a model topology graph established in an embodiment of the present invention;

FIG. 4 is a Bode plot of voltage disturbance impedance measurement results in an embodiment of the present invention;

FIG. 5 is a Bode plot of the current disturbance impedance measurement results in an embodiment of the present invention;

FIG. 6 is a Bode plot of the impedance measurements for the proposed scheme in the example of the present invention.

Detailed Description

The invention is described below with reference to the accompanying drawings and specific embodiments.

Fig. 1 is a topological diagram according to the impedance measurement method for switching the disturbance mode of the present invention. As shown in fig. 1, the topology structure related to the impedance measurement method for switching the disturbance mode includes apower grid 10, grid-connectedequipment 40, and an impedance measurement device at a PCC of a public coupling point connected to thepower grid 10 and the grid-connectedequipment 40; the impedance measuring device comprises aperturbation unit 20 and an impedance measuring andperturbation selecting unit 30; thedisturbance unit 20 comprises avoltage disturbance device 201 and acurrent disturbance device 202, and the impedance measurement anddisturbance selection unit 30 comprises a networkside sampling device 301, an equipmentside sampling device 302, animpedance calculation unit 303 and adisturbance selection unit 304; thevoltage disturbance device 201 is connected in series to a PCC connected between thepower grid 10 and the grid-connecteddevice 40, thecurrent disturbance device 202 is connected in parallel to a PCC connected between thepower grid 10 and the grid-connecteddevice 40, the grid-side sampling device 301 is connected between thepower grid 10 and the PCC, the device-side sampling device 302 is connected between the PCC and the grid-connecteddevice 40, the input end of theimpedance calculation unit 303 is connected to the output ends of the grid-side sampling device 301 and the device-side sampling device 302, and thedisturbance selection unit 304 is connected to thedisturbance unit 20 in a communication manner;

the method obtains a grid-connected impedance predicted value Z according to an impedance prediction method_cAnd the predicted value Z of the network impedance_gAnd selecting a disturbance mode to measure the impedance, and judging whether to switch the disturbance mode to measure again according to the measured value so as to improve the measurement precision. The impedance measurement method comprises the steps of firstly appointing M preset disturbance frequencies, and then carrying out impedance measurement at the M preset disturbance frequencies from small to large according to the magnitude of the M preset disturbance frequency values. FIG. 2 is a flow chart of the impedance measuring method of the present invention, in which any one of M preset disturbance frequencies is recorded as a preset disturbance frequency f_kK is 1, 2 … M, as can be seen from FIG. 2, at the predetermined disturbance frequency f_kThe specific steps of performing impedance measurement are as follows:

step 1, setting parameters, including the following parameters:

preset disturbance frequency f_kPredicted value Z of grid-connected impedance_cPredicted value Z of grid impedance_g；

The grid-connected impedance predicted value Z_cFor the grid-connectedequipment 40 obtained by the impedance prediction method at the preset disturbance frequency f_kThe output impedance predicted value, the grid impedance predicted value Z_gFor thepower network 10 obtained by the impedance prediction method at a predetermined disturbance frequency f_kThe impedance prediction value of the output.

Step 2, comparing the grid-connected impedance predicted value Z_cAnd the predicted value Z of the network impedance_gThe magnitude of (2):

if Z_g|＜|Z_cI, entering the step 3;

if Z_g|≥|Z_cGo to step 5.

Step 3, thedisturbance selection unit 304 controls the injection frequency of thevoltage disturbance device 201 to the PCC of the PCC to be a preset disturbance frequency f_kThe sinusoidal voltage of (1) is disturbed, and the output current of the currentdisturbing device 202 is controlled to be 0;

the voltage response and the current response of thepower grid 10 under the sinusoidal voltage disturbance are collected through the gridside sampling device 301, and the preset disturbance frequency f under the voltage response is set_kThe voltage component is recorded as the voltage harmonic component u on the voltage disturbance network side_g1Preset disturbance frequency f under current response_kThe current component is marked as the harmonic component i of the voltage disturbance network side current_g1(ii) a Acquiring voltage response and current response of the grid-connectedequipment 40 under the sinusoidal voltage disturbance through the equipmentside sampling device 302, and presetting disturbance frequency f under the voltage response_kThe voltage component is recorded as the voltage harmonic component u on the voltage disturbance device side_c1Current response at a predetermined disturbance frequency f_kThe current component is marked as the harmonic component i of the current on the voltage disturbance equipment side_c1；

Recording the measured impedance of thepower grid 10 under the sinusoidal voltage disturbance as the measured impedance Z of the primary power grid_g1Recording the measured impedance of the grid-connectedequipment 40 under the sinusoidal voltage disturbance as the measured impedance Z of the primary grid-connected equipment_c1Theimpedance calculation unit 303 calculates the primary grid measurement impedance Z_g1And primary grid-connected impedance Z_c1：

Z_g1＝u_g1÷i_g1

Z_c1＝u_c1÷i_c1

Step 4, comparing the primary grid-connected measured impedance Z_c1And primary grid measured impedance Z_g1The magnitude of (2):

if Z_g1|≤|Z_c1|，Z_g1And Z_c1The measurement is finished for the final measurement result;

if Z_g1|＞|Z_c1Go to step 5.

Step 5, thedisturbance selection unit 304 controls thecurrent disturbance device 202 to inject a preset disturbance frequency f to the PCC of the PCC_kThe output voltage of the voltagedisturbing device 201 is controlled to be 0;

the voltage response and the current response of thepower grid 10 under the sinusoidal current disturbance are collected through the gridside sampling device 301, and the preset disturbance frequency f under the voltage response is set_kThe voltage component is marked as the harmonic component u of the current disturbance network side voltage_g2Preset disturbance frequency f under current response_kThe current component is marked as the current disturbance network side current harmonic component i_g2(ii) a Acquiring voltage response and current response of the grid-connectedequipment 40 under the sinusoidal current disturbance through the equipmentside sampling device 302, and presetting disturbance frequency f under the voltage response_kThe voltage component is recorded as the harmonic component u of the current disturbance device side voltage_c2Preset disturbance frequency f under current response_kThe current component is marked as the current harmonic component i on the current disturbance equipment side_c2；

Recording the measured impedance of thepower grid 10 under the sinusoidal current disturbance as the measured impedance Z of the secondary power grid_g2Recording the measured impedance of the grid-connectedequipment 40 under the sinusoidal current disturbance as secondary grid-connected measured impedance Z_c2Theimpedance calculation unit 303 calculates the measured impedance Z of the secondary grid_g2And secondary grid-connected measurement impedance Z_c2：

Z_g2＝u_g2÷i_g2

Z_c2＝u_c2÷i_c2

Step 6, comparing the secondary grid-connected impedance Z_c2And secondary grid impedance Z_g2The magnitude of (2):

if Z_g2|≥|Z_c2|，Z_g2And Z_c2The measurement is finished for the final measurement result;

if Z_g2|＜|Z_c2And | returning to the step 3.

In this embodiment, step 1 is to obtain a grid-connected impedance predicted value Z by an impedance prediction method_cPredicted value Z of power grid impedance_gThe specific process is as follows:

recording the k-1 th preset disturbance frequency f_k-1For the first adjacent disturbance frequency f_AThe k-2 th preset disturbance frequency f is recorded_k-2For a second adjacent disturbance frequency f_B. The first adjacent disturbance frequency f_AThe measured result is recorded as the impedance Z of the first adjacent grid-connected equipment_cAAnd a first adjacent grid impedance Z_gASecond adjacent disturbance frequency f_BThe measured result is recorded as the impedance Z of the second adjacent grid-connected equipment_cBAnd a second adjacent grid impedance Z_gB。

Preset disturbance frequency f_kImpedance predicted value Z of grid-connected equipment_cExpression:

preset disturbance frequency f_kTo the predicted value Z of the grid impedance_gExpression:

wherein theta () means a complex phase angle, e, expressed as an angle^jtheta0Is a complex phase angle expressed in terms of a rotation factor. With Z_cFor example, theta (Z)_c) The meaning of (A) is Z in degrees_cThe phase angle is set to be,

z in a rotation factor_cPhase angle.

In particular, when k is 1, 2, information for predicting the impedance is missing, and the grid-connected impedance predicted value Z may be defaulted_cGreater or less than the predicted value Z of the grid impedance_g。

Fig. 3 is a model topology diagram established in the embodiment of the present invention. A model of the grid-connected inverter system is built in simulation software Matlab/Simulink according to the graph 3. Using a three-phase voltage source U_ga、U_gb、U_gcAnd three network inductances L_gForm an electric network, U_ga、U_gb、U_gcAmplitude of 563.4V, output frequency of 50Hz, and grid inductance L_gThe value was 0.4 mH. And N is a neutral point of the power grid. An L-type three-phase grid-connected inverter is used as grid-connected equipment, the rated current 1183A of the inverter and a filter inductor L_pThe value was 0.2 mH. Using a three-phase voltage source U_a、U_b、U_cConstituting a voltage perturbation means, U_a、U_b、U_cThe output voltage amplitude is 16.9V. Using a three-phase current source I_a、I_b、I_cAnd three parallel resistors R forming a current perturbation device, I_a、I_b、I_cThe amplitude is 35.5A, and the value of the parallel resistor R is 100M omega. At the output end of the equipment side sampling unit, a white noise signal module with a power parameter of 0.1 is addedAnd simulating the noise of the actual sampling signal.

In this example, a set of disturbance frequencies ordered from small to large is taken, and an impedance measurement experiment is performed by using voltage disturbance injection, current disturbance injection and the method of the present invention, respectively. At the minimum of two disturbance frequencies, 1Hz and 3Hz, the method of the invention first selects the voltage disturbance to measure because of the lack of information for impedance prediction. FIG. 4 is a Bode plot of the voltage disturbance impedance measurement results, divided into an amplitude-frequency plot and a phase-frequency plot, with the abscissa representing the frequency of the impedance in Hertz; the ordinate of the amplitude-frequency diagram represents the impedance amplitude in decibels; the ordinate of the phase frequency diagram represents the impedance phase in degrees. In FIG. 4, the symbol Z_c(s) is a grid-connected impedance theoretical curve, and is marked with Z_gThe curve of(s) is the theoretical curve of the network impedance. The o-shaped point in fig. 4 is the voltage disturbance impedance measurement result, and it can be seen that a significant error occurs in a high frequency band. FIG. 5 is a bode plot of the current disturbance impedance measurement, the coordinate definition, Z in FIG. 5_c(s) and Z_g(s) has the same meaning as in FIG. 4. The shape points in fig. 5 are the current disturbance impedance measurement results, and it can be seen that a significant error occurs in the low frequency band. FIG. 6 is a Bode plot of the impedance measurements of the proposed scheme, the coordinate definition, Z in FIG. 6_c(s) and Z_g(s) has the same meaning as in FIG. 4. In fig. 6, the o-shaped points are voltage disturbance impedance measurement results, and the x-shaped points are current disturbance impedance measurement results. As can be seen from fig. 6, in the frequency range from 1Hz to 102Hz, the inverter impedance is greater than the grid impedance, and the scheme finally selects the voltage disturbance injection mode; in the frequency range of 103Hz to 10kHz, the impedance of the inverter is smaller than the impedance of the power grid, the scheme finally selects a current disturbance injection mode, and the measurement results of the low frequency range and the high frequency range have no obvious error. In the embodiment, at the disturbance frequencies of 84Hz and 102Hz, two measurements are performed because the predicted amplitude relationship is the same as the actual amplitude relationship, and only one measurement is needed at other disturbance frequencies, so that the measurement time is saved.

In conclusion, the disturbance injection mode is selected according to the predicted amplitude relation between the grid-connected impedance and the grid impedance. And after the measurement, judging whether to switch the disturbance injection mode for re-measurement according to the amplitude relation of the actual measurement value. Compared with single voltage or current disturbance injection, the method has the advantage of improving the measurement accuracy; compared with the scheme of firstly injecting voltage disturbance and then judging whether to switch current disturbance, the method makes full use of the predicted impedance information, selects a disturbance injection mode according to the predicted value, and saves the measurement time.

Claims (1)

1. A disturbance mode switching impedance measurement method is provided, wherein a topological structure related to the disturbance mode switching impedance measurement method comprises a power grid (10), grid-connected equipment (40) and an impedance measurement device connected to the power grid (10) and the grid-connected equipment (40) at a PCC (point of common coupling); the impedance measuring device comprises a disturbance unit (20) and an impedance measuring and disturbance selecting unit (30); the disturbance unit (20) comprises a voltage disturbance device (201) and a current disturbance device (202), and the impedance measurement and disturbance selection unit (30) comprises a network side sampling device (301), an equipment side sampling device (302), an impedance calculation unit (303) and a disturbance selection unit (304); the voltage disturbance device (201) is connected in series to a public coupling point PCC (PCC) connected with a power grid (10) and grid-connected equipment (40), the current disturbance device (202) is connected in parallel to the PCC connected with the power grid (10) and the grid-connected equipment (40), the grid-side sampling device (301) is connected between the power grid (10) and the PCC, the equipment-side sampling device (302) is connected between the PCC and the grid-connected equipment (40), the input end of the impedance calculation unit (303) is connected with the output ends of the grid-side sampling device (301) and the equipment-side sampling device (302) respectively, and the disturbance selection unit (304) is connected with the disturbance unit (20) in a communication mode;

the method is characterized in that the method firstly designates M preset disturbance frequencies, and then carries out impedance measurement at the M preset disturbance frequencies from small to large according to the magnitude of the M preset disturbance frequency values; recording any one of M preset disturbance frequencies as a preset disturbance frequency f_kK is 1, 2 … M at a predetermined disturbance frequency f_kThe specific steps of performing impedance measurement are as follows:

step 1, setting parameters, including the following parameters:

preset disturbance frequency f_kPredicted value Z of grid-connected impedance_cPredicted value Z of grid impedance_g；

The grid-connected impedance predicted value Z_cFor the grid-connected equipment (40) obtained by an impedance prediction method at a preset disturbance frequency f_kThe output impedance predicted value, the grid impedance predicted value Z_gFor the power network (10) obtained by the impedance prediction method at a predetermined disturbance frequency f_kThe predicted value of the impedance of the output;

step 2, comparing the grid-connected impedance predicted value Z_cAnd the predicted value Z of the network impedance_gThe magnitude of (2):

if Z_g|＜|Z_cI, entering the step 3;

if Z_g|≥|Z_cI, entering a step 5;

step 3, the disturbance selection unit (304) controls the injection frequency of the voltage disturbance device (201) to the PCC to be a preset disturbance frequency f_kThe output current of the current disturbance device (202) is controlled to be 0;

collecting voltage response and current response of the power grid (10) under the sinusoidal voltage disturbance through a grid side sampling device (301), and presetting disturbance frequency f under the voltage response_kThe voltage component is recorded as the voltage harmonic component u on the voltage disturbance network side_g1Preset disturbance frequency f under current response_kThe current component is marked as the harmonic component i of the voltage disturbance network side current_g1(ii) a Acquiring voltage response and current response of the grid-connected equipment (40) under the sinusoidal voltage disturbance through an equipment side sampling device (302), and presetting disturbance frequency f under the voltage response_kThe voltage component is recorded as the voltage harmonic component u on the voltage disturbance device side_c1Preset disturbance frequency f under current response_kThe current component is marked as the harmonic component i of the current on the voltage disturbance equipment side_c1；

Recording the measured impedance of the power grid (10) under the sinusoidal voltage disturbance as a primary power grid measured impedance Z_g1Recording the measured impedance of the grid-connected equipment (40) under the sinusoidal voltage disturbance as primary grid-connected measured impedance Z_c1Calculating a primary grid measurement impedance Z by an impedance calculation unit (303)_g1And primary grid-connected impedance Z_c1：

Z_g1＝u_g1÷i_g1

Z_c1＝u_c1÷i_c1

Step 4, comparing the primary grid-connected measured impedance Z_c1And primary grid measured impedance Z_g1The magnitude of (2):

if Z_g1|≤|Z_c1|，Z_g1And Z_c1The measurement is finished for the final measurement result;

if Z_g1|＞|Z_c1I, entering a step 5;

step 5, the disturbance selection unit (304) controls the current disturbance device (202) to inject a preset disturbance frequency f to the PCC_kThe output voltage of the voltage disturbance device (201) is controlled to be 0;

collecting voltage response and current response of the power grid (10) under the sinusoidal current disturbance through a grid side sampling device (301), and presetting disturbance frequency f under the voltage response_kThe voltage component is marked as the harmonic component u of the current disturbance network side voltage_g2Preset disturbance frequency f under current response_kThe current component is marked as the current disturbance network side current harmonic component i_g2(ii) a Acquiring voltage response and current response of the grid-connected equipment (40) under the sinusoidal current disturbance through an equipment side sampling device (302), and presetting disturbance frequency f under the voltage response_kThe voltage component is recorded as the harmonic component u of the current disturbance device side voltage_c2Preset disturbance frequency f under current response_kThe current component is marked as the current harmonic component i on the current disturbance equipment side_c2；

Recording the measured impedance of the power grid (10) under the sinusoidal current disturbance as the measured impedance Z of the secondary power grid_g2Recording the measured impedance of the grid-connected equipment (40) under the sinusoidal current disturbance as secondary grid-connected measured impedance Z_c2Calculating the secondary grid measurement impedance Z by an impedance calculation unit (303)_g2And secondary grid-connected measurement impedance Z_c2：

Z_g2＝u_g2÷i_g2

Z_c2＝u_c2÷i_c2

Step 6, comparing the secondary grid-connected measured impedance Z_c2And secondary grid measured impedance Z_g2The magnitude of (2):

if Z_g2|≥|Z_C2|，Z_g2And Z_C2The measurement is finished for the final measurement result;

if Z_g2|＜|Z_c2And | returning to the step 3.

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