Resistance-frequency characteristic test method and system for power distribution network based on reactive current reference value disturbance

Abstract

The invention discloses a power distribution network resistance-frequency characteristic testing method and system based on reactive current reference value disturbance, and relates to the technical field of power distribution network testing, and the method comprises the steps: periodically injecting a pulse disturbance signal into a reactive current reference signal of a current loop controller through a pulse disturbance channel, and stopping the injection of the pulse disturbance signal, enabling the grid-connected inverter to be in a disturbance state and a non-disturbance state periodically; in the last disturbance period and the non-disturbance period, three-phase voltage and three-phase current of the common grid-connected point are collected, and first three-phase voltage, first three-phase current, second three-phase voltage and second three-phase current are obtained; and based on the first three-phase voltage, the first three-phase current, the second three-phase voltage and the second three-phase current, determining a power grid input impedance sequence of the to-be-tested power distribution network system. When the resistance-frequency characteristic of the power distribution network is tested, the influence of inherent harmonic waves of the power grid on a measurement result is eliminated, and meanwhile, the influence of instability of the power grid is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of distribution network testing, and in particular to a method and system for testing the frequency blocking characteristics of a distribution network based on reactive current reference value disturbance. Background Art

[0002] As an important measure to achieve energy transformation, renewable distributed power sources such as wind power generation, photovoltaic power generation and electric vehicles are connected to the distribution network on a large scale. The increase in power electronic conversion interfaces makes the distribution network present the characteristics of a weak grid. The grid impedance cannot be ignored, which is one of the characteristics of a weak grid. When a large number of new energy grid-connected inverters are connected to a weak grid, the real-time change of the grid impedance will cause the resonance point of the grid-connected inverter to shift, which will cause stability problems in the distribution network system. The stability of the distribution network system depends on the ratio of the grid impedance to the inverter output impedance. The use of grid impedance online identification technology can obtain accurate grid frequency blocking characteristics.

[0003] At present, the online identification methods of grid impedance mainly include passive methods and active methods. Among them, the passive method uses the inherent harmonics of the grid distortion or the grid-connected inverter to obtain the grid impedance after certain harmonic extraction and calculation. The passive method will not affect the normal operation of the grid during the identification process, but the amplitude and repetition rate of the grid distortion are difficult to measure correctly, so the grid impedance cannot be accurately measured. The active method injects a certain voltage or current disturbance into the grid through the grid-connected inverter or the additional power electronic equipment, and performs frequency analysis on the disturbance and response signals to obtain their respective frequency components. After calculation, the frequency blocking characteristics of the grid impedance can be obtained. At present, the traditional active method is to superimpose sinusoidal disturbance signals of multiple frequencies on the active current reference value of the current loop controller of the grid-connected inverter to measure the frequency blocking characteristics of the distribution network. This method is complicated to operate, time-consuming, and the active current reference value disturbance has a great impact on the active stability of the system. Summary of the invention

[0004] The purpose of the present application is to provide a distribution network blocking frequency characteristic testing method and system based on reactive current reference value disturbance, so as to solve the problem that the active current reference value disturbance has a great influence on the active stability of the system when testing the distribution network blocking frequency characteristic.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides a distribution network blocking frequency characteristic test method based on reactive current reference value disturbance, wherein the distribution network blocking frequency characteristic test method based on reactive current reference value disturbance is implemented based on a distribution network blocking frequency characteristic test device connected to a distribution network system to be tested; the distribution network system to be tested comprises: a distributed DC power supply, a grid-connected inverter, a public grid-connected point and a distribution network; the distribution network blocking frequency characteristic test device comprises: a sampling device, a current loop controller and an impedance identification unit;

[0007] The distributed DC power supply, the current loop controller and the sampling device are all connected to the grid-connected inverter, the sampling device and the distribution network are respectively connected to the public grid-connected point, and the impedance identification unit is connected to the sampling device;

[0008] The distribution network frequency blocking characteristic testing method based on reactive current reference value disturbance includes:

[0009] Setting a pulse disturbance channel in the current loop controller;

[0010] In multiple disturbance cycles, the pulse disturbance signal is periodically injected into the reactive current reference signal of the current loop controller through the pulse disturbance channel, and in multiple non-disturbance cycles, the pulse disturbance signal is periodically stopped from being injected into the reactive current reference signal of the current loop controller through the pulse disturbance channel, so that the grid-connected inverter is periodically in a disturbance state and a non-disturbance state;

[0011] In the last disturbance cycle in the disturbance state, the sampling device collects the three-phase voltage and the three-phase current of the common grid connection point to obtain the first three-phase voltage and the first three-phase current;

[0012] In the last disturbance-free period in the disturbance-free state, the sampling device collects the three-phase voltage and the three-phase current of the common grid connection point to obtain a second three-phase voltage and a second three-phase current;

[0013] The impedance identification unit determines a grid input impedance sequence of the power distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage and the second three-phase current.

[0014] Optionally, the amplitude of the pulse disturbance signal is less than 10% of the amplitude of the output current of the grid-connected inverter.

[0015] Optionally, determining a grid input impedance sequence of the distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage, and the second three-phase current includes:

[0016] Performing a discrete Fourier transform on the first three-phase voltage to obtain a plurality of corresponding first voltage harmonic components, calculating the average values ​​of the amplitudes and phases of all the first voltage harmonic components respectively to obtain a first voltage amplitude mean value and a first voltage phase mean value, and determining a first voltage index signal based on the first voltage amplitude mean value and the first voltage phase mean value; the first voltage index signal is a complex number signal of the first three-phase voltage;

[0017] Performing a discrete Fourier transform on the first three-phase current to obtain a plurality of corresponding first current harmonic components, calculating the average values ​​of the amplitude and phase of all the first current harmonic components respectively to obtain a first current amplitude mean value and a first current phase mean value, and determining a first current index signal based on the first current amplitude mean value and the first current phase mean value; the first current index signal is a complex number signal of the first three-phase current;

[0018] Performing a discrete Fourier transform on the second three-phase voltage to obtain a plurality of corresponding second voltage harmonic components, calculating the average values ​​of the amplitudes and phases of all the second voltage harmonic components respectively to obtain a second voltage amplitude mean value and a second voltage phase mean value, and determining a second voltage index signal based on the second voltage amplitude mean value and the second voltage phase mean value; the second voltage index signal is a complex number signal of the second three-phase voltage;

[0019] Performing a discrete Fourier transform on the second three-phase current to obtain a plurality of corresponding second current harmonic components, calculating the average values ​​of the amplitudes and phases of all the second current harmonic components respectively to obtain a second current amplitude mean value and a second current phase mean value, and determining a second current index signal based on the second current amplitude mean value and the second current phase mean value; the second current index signal is a complex number signal of the second three-phase current;

[0020] determining a voltage increment based on the first voltage index signal and the second voltage index signal;

[0021] determining a current increment based on the first current index signal and the second current index signal;

[0022] Based on the voltage increment and the current increment, a grid input impedance sequence of the power distribution network system to be tested is determined.

[0023] Optionally, determining a voltage increment based on the first voltage index signal and the second voltage index signal comprises:

[0024] The voltage increment is obtained by subtracting the first voltage index signal from the second voltage index signal.

[0025] Optionally, determining the current increment based on the first current index signal and the second current index signal includes:

[0026] The first current index signal and the second current index signal are subtracted to obtain a current increment.

[0027] Optionally, determining a grid input impedance sequence of the distribution network system to be tested based on the voltage increment and the current increment includes:

[0028] A division operation is performed on the voltage increment and the current increment to obtain a grid input impedance sequence of the distribution network system to be tested.

[0029] In a second aspect, the present application provides a distribution network frequency blocking characteristic test system based on reactive current reference value disturbance, wherein the distribution network frequency blocking characteristic test system based on reactive current reference value disturbance is implemented based on a distribution network frequency blocking characteristic test device connected to a distribution network system to be tested; the distribution network system to be tested includes: a distributed DC power supply, a grid-connected inverter, a public grid connection point and a distribution network; the distribution network frequency blocking characteristic test device includes: a sampling device, a current loop controller and an impedance identification unit;

[0030] The distributed DC power supply, the current loop controller and the sampling device are all connected to the grid-connected inverter, the sampling device and the distribution network are respectively connected to the public grid-connected point, and the impedance identification unit is connected to the sampling device;

[0031] The distribution network frequency blocking characteristic testing system based on reactive current reference value disturbance comprises:

[0032] A channel setting module, used for setting a pulse disturbance channel in the current loop controller;

[0033] A disturbance injection module, used for periodically injecting a pulse disturbance signal into the reactive current reference signal of the current loop controller through the pulse disturbance channel in multiple disturbance cycles, and periodically stopping injecting the pulse disturbance signal into the reactive current reference signal of the current loop controller through the pulse disturbance channel in multiple non-disturbance cycles, so that the grid-connected inverter is periodically in a disturbance state and a non-disturbance state;

[0034] A first sampling module, configured to collect the three-phase voltage and the three-phase current of the common grid connection point in the last disturbance cycle in the disturbance state, so as to obtain a first three-phase voltage and a first three-phase current;

[0035] A second sampling module, configured to collect the three-phase voltage and the three-phase current of the common grid connection point in the last disturbance-free period in the disturbance-free state, so as to obtain a second three-phase voltage and a second three-phase current;

[0036] An impedance analysis module is used for the impedance identification unit to determine the grid input impedance sequence of the distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage and the second three-phase current.

[0037] Optionally, the amplitude of the pulse disturbance signal is less than 10% of the amplitude of the output current of the grid-connected inverter.

[0038] Optionally, determining a grid input impedance sequence of the distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage, and the second three-phase current includes:

[0039] Performing a discrete Fourier transform on the first three-phase voltage to obtain a plurality of corresponding first voltage harmonic components, calculating the average values ​​of the amplitudes and phases of all the first voltage harmonic components respectively to obtain a first voltage amplitude mean value and a first voltage phase mean value, and determining a first voltage index signal based on the first voltage amplitude mean value and the first voltage phase mean value; the first voltage index signal is a complex number signal of the first three-phase voltage;

[0040] Performing a discrete Fourier transform on the first three-phase current to obtain a plurality of corresponding first current harmonic components, calculating the average values ​​of the amplitude and phase of all the first current harmonic components respectively to obtain a first current amplitude mean value and a first current phase mean value, and determining a first current index signal based on the first current amplitude mean value and the first current phase mean value; the first current index signal is a complex number signal of the first three-phase current;

[0041] Performing a discrete Fourier transform on the second three-phase voltage to obtain a plurality of corresponding second voltage harmonic components, calculating the average values ​​of the amplitudes and phases of all the second voltage harmonic components respectively to obtain a second voltage amplitude mean value and a second voltage phase mean value, and determining a second voltage index signal based on the second voltage amplitude mean value and the second voltage phase mean value; the second voltage index signal is a complex number signal of the second three-phase voltage;

[0042] Performing a discrete Fourier transform on the second three-phase current to obtain a plurality of corresponding second current harmonic components, calculating the average values ​​of the amplitudes and phases of all the second current harmonic components respectively to obtain a second current amplitude mean value and a second current phase mean value, and determining a second current index signal based on the second current amplitude mean value and the second current phase mean value; the second current index signal is a complex number signal of the second three-phase current;

[0043] determining a voltage increment based on the first voltage index signal and the second voltage index signal;

[0044] determining a current increment based on the first current index signal and the second current index signal;

[0045] Based on the voltage increment and the current increment, a grid input impedance sequence of the power distribution network system to be tested is determined.

[0046] Optionally, determining a voltage increment based on the first voltage index signal and the second voltage index signal comprises:

[0047] The voltage increment is obtained by subtracting the first voltage index signal from the second voltage index signal.

[0048] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0049] The present application discloses a method and system for testing the frequency-blocking characteristics of a distribution network based on the disturbance of a reactive current reference value. First, a pulse disturbance channel is set in a current loop controller; then, in multiple disturbance cycles, a pulse disturbance signal is periodically injected into the reactive current reference signal of the current loop controller through the pulse disturbance channel, and in multiple non-disturbance cycles, the pulse disturbance signal is periodically stopped from being injected into the reactive current reference signal of the current loop controller through the pulse disturbance channel, so that the grid-connected inverter is periodically in a disturbance state and a non-disturbance state; secondly, in the last disturbance cycle in the disturbance state, a sampling device collects the three-phase voltage and the three-phase current of a common grid-connected point to obtain a first three-phase voltage and a first three-phase current; thirdly, in the last non-disturbance cycle in the non-disturbance state, a sampling device collects the three-phase voltage and the three-phase current of the common grid-connected point to obtain a second three-phase voltage and a second three-phase current; finally, an impedance identification unit determines the grid input impedance sequence of the distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage and the second three-phase current. The present application applies a pulse signal to the reactive current reference value, and adopts a cycle-to-cycle sampling method, and adopts a method of subtracting the three-phase voltage and three-phase current of the common grid-connected point when not disturbed from the three-phase voltage and three-phase current of the common grid-connected point in the disturbance period. When testing the frequency-blocking characteristics of the distribution network, the influence of the inherent harmonics of the power grid on the measurement results is eliminated, and the influence of the instability of the power grid is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0051] Figure 1A schematic flow chart of a method for testing the frequency blocking characteristics of a distribution network based on reactive current reference value disturbance provided in an embodiment of the present application;

[0052] Figure 2 The schematic diagram of the test process of the frequency blocking characteristics of the distribution network when the disturbance period and the non-disturbance period are both 4 periods;

[0053] Figure 3 This is a topological diagram of a distribution network blocking frequency characteristic test device;

[0054] Figure 4 This is a schematic diagram of the principle of the distribution network blocking frequency characteristic test device;

[0055] Figure 5 It is the waveform diagram of pulse disturbance signal;

[0056] Figure 6 It is the spectrum diagram of pulse disturbance signal. DETAILED DESCRIPTION

[0057] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0058] The purpose of this application is to provide a distribution network blocking frequency characteristic testing method and system based on reactive current reference value disturbance, aiming to eliminate the influence of the inherent harmonics of the power grid on the measurement results and reduce the influence of the instability of the power grid when testing the blocking frequency characteristics of the distribution network.

[0059] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0060] In an exemplary embodiment, Figure 1 and Figure 2 As shown, a distribution network blocking frequency characteristic test method based on reactive current reference value disturbance is provided, including: the distribution network blocking frequency characteristic test method based on reactive current reference value disturbance is implemented based on a distribution network blocking frequency characteristic test device connected to a distribution network system to be tested; the distribution network system to be tested includes: a distributed DC power supply, a grid-connected inverter, a public grid-connected point and a distribution network (grid); as shown Figure 3 and Figure 4 As shown, the distribution network frequency blocking characteristic test device includes: a sampling device, a current loop controller and an impedance identification unit.

[0061] The distributed DC power supply, the current loop controller and the sampling device are all connected to the grid-connected inverter, the sampling device and the distribution network are respectively connected to the public grid-connected point, and the impedance identification unit is connected to the sampling device.

[0062] The test method of the frequency blocking characteristics of the distribution network based on the disturbance of the reactive current reference value includes:

[0063] Step 1: Set up the pulse disturbance channel in the current loop controller.

[0064] Step 2: In multiple disturbance cycles, a pulse disturbance signal is periodically injected into the reactive current reference signal of the current loop controller through a pulse disturbance channel; in multiple non-disturbance cycles, the pulse disturbance signal is periodically stopped from being injected into the reactive current reference signal of the current loop controller through a pulse disturbance channel, so that the grid-connected inverter is periodically in a disturbance state and a non-disturbance state.

[0065] Specifically, Figure 3 As shown in the figure, the distribution network system consists of distributed DC power source U dc , grid-connected inverter VSC, public grid connection point (Point of Common Coupling, PCC) and distribution network. Among them, the sampling module will monitor the three-phase voltage u of PCC pa 、u pb 、u pc and three-phase current i pa 、i pb 、i pc Sampling and recording are performed, and then the active current i is obtained after the phase-locked loop (PLL) and Park transformation (abc / dq) d and reactive current i q The grid-connected inverter is connected to the current loop controller. When the grid is stable, the reactive current reference signal i in the current loop controller of the grid-connected inverter can be qref The pulse disturbance signal is superimposed on the current loop controller to generate a pulse width modulation (PWM) modulation signal c a 、c b 、c c , thus causing u pa 、u pb 、u pc and i pa 、i pb 、i pc The amplitude and phase changes of the harmonic components are generated to inject pulse disturbance pulses into the distribution network, and the impedance Z of the power grid is identified through the impedance identification module. gDuring the pulse disturbance signal injection process, the harmonic distortion limit of the current loop controller and other control parameters need to be adjusted to reduce the voltage harmonic distortion limit to less than 5%. pa 、u pb 、u pc and three-phase current i pa 、i pb 、i pc Sampling and recording are performed; the collected data is subjected to Discrete Fourier Transform (DFT) analysis, and the amplitude and phase of each harmonic component of the voltage and current under the sampling period can be averaged, and the grid impedance sequence is calculated using the obtained pulse disturbance excitation and the amplitude and phase average of the harmonic components of the power grid, thereby obtaining the resistance-frequency characteristic curve of the distribution network system.

[0066] The pulse disturbance injection period affects the accuracy of the test results of the distribution network's frequency blocking characteristics. The pulse signal period of the present invention is selected to be 10 periods of the grid's sine wave. The pulse disturbance signal is injected in the first 5 consecutive sine cycles, and the injection of the pulse disturbance signal is stopped in the next 5 consecutive sine cycles. It can be seen here that the waveform of the first 5 cycles contains the pulse disturbance signal, and there is no pulse disturbance signal in the next 5 cycles. A pulse disturbance signal with a suitable amplitude and pulse width is selected and injected at the input of the reactive current reference value. Among them, the pulse disturbance signal is as follows: Figure 5 and Figure 6 shown.

[0067] As an optional implementation manner, the amplitude of the pulse disturbance signal is less than 10% of the amplitude of the output current of the grid-connected inverter.

[0068] Step 3: In the last disturbance cycle in the disturbance state, the sampling device collects the three-phase voltage and the three-phase current of the public grid connection point to obtain the first three-phase voltage and the first three-phase current.

[0069] Step 4: In the last disturbance-free period in the disturbance-free state, the sampling device collects the three-phase voltage and the three-phase current of the common grid-connected point to obtain the second three-phase voltage and the second three-phase current.

[0070] Step 5: The impedance identification unit determines the grid input impedance sequence of the distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage and the second three-phase current.

[0071] As an optional implementation, determining a grid input impedance sequence of the distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage, and the second three-phase current includes:

[0072] Step 51: Perform discrete Fourier transform on the first three-phase voltage to obtain a plurality of corresponding first voltage harmonic components, calculate the average values ​​of amplitude and phase for all first voltage harmonic components, and obtain the first voltage amplitude mean value and the first voltage phase mean A first voltage index signal is determined based on the first voltage amplitude mean value and the first voltage phase mean value. The first voltage index signal is a complex signal of the first three-phase voltage. The expression of the first voltage index signal is: Among them, e is a natural constant; Is an imaginary unit.

[0073] Step 52: Perform discrete Fourier transform on the first three-phase current to obtain a plurality of corresponding first current harmonic components, calculate the average values ​​of amplitude and phase for all first current harmonic components, and obtain the first current amplitude mean value. and the first current phase mean A first current index signal is determined based on the first current amplitude mean value and the first current phase mean value; the first current index signal is a complex number signal of the first three-phase current. The expression of the first current index signal is:

[0074] Step 53: Perform discrete Fourier transform on the second three-phase voltage to obtain a plurality of corresponding second voltage harmonic components, calculate the average values ​​of the amplitude and phase of all the second voltage harmonic components, and obtain the second voltage amplitude mean value and the second voltage phase mean The second voltage index signal is determined based on the second voltage amplitude mean and the second voltage phase mean; the second voltage index signal is a complex form signal of the second three-phase voltage. The expression of the second voltage index signal is:

[0075] Step 54: Perform discrete Fourier transform on the second three-phase current to obtain a plurality of corresponding second current harmonic components, calculate the average values ​​of the amplitude and phase of all the second current harmonic components, and obtain the second current amplitude mean value. and the second current phase mean A second current index signal is determined based on the second current amplitude mean and the second current phase mean; the second current index signal is a complex signal of the second three-phase current. The expression of the second current index signal is:

[0076] Step 55: Determine a voltage increment based on the first voltage index signal and the second voltage index signal.

[0077] As an optional implementation, step 55 includes:

[0078] The first voltage index signal and the second voltage index signal are subtracted to obtain a voltage increment.

[0079] Specifically, the voltage increment The calculation formula is:

[0080] Step 56: Determine a current increment based on the first current index signal and the second current index signal.

[0081] As an optional implementation, step 56 includes:

[0082] The first current index signal and the second current index signal are subtracted to obtain a current increment.

[0083] Specifically, the current increment The calculation formula is:

[0084] Step 57: Based on the voltage increment and the current increment, determine the grid input impedance sequence of the distribution network system to be tested.

[0085] As an optional implementation, step 57 includes:

[0086] The voltage increment and the current increment are divided to obtain the grid input impedance sequence of the distribution network system to be tested.

[0087] Specifically, the grid input impedance series The calculation formula is:

[0088] Among them, the calculation formula for the amplitude of the impedance in the grid input impedance series is: The calculation formula of the phase angle of impedance is: The exponential form of is:

[0089] In an exemplary embodiment, a distribution network frequency blocking characteristic test system based on reactive current reference value disturbance is provided. The distribution network frequency blocking characteristic test system based on reactive current reference value disturbance is implemented based on a distribution network frequency blocking characteristic test device connected to the distribution network system to be tested; the distribution network system to be tested includes: a distributed DC power supply, a grid-connected inverter, a public grid connection point and a distribution network; the distribution network frequency blocking characteristic test device includes: a sampling device, a current loop controller and an impedance identification unit.

[0090] The distributed DC power supply, the current loop controller and the sampling device are all connected to the grid-connected inverter, the sampling device and the distribution network are respectively connected to the public grid-connected point, and the impedance identification unit is connected to the sampling device.

[0091] The distribution network frequency blocking characteristic test system based on reactive current reference value disturbance includes:

[0092] The channel setting module is used to set the pulse disturbance channel in the current loop controller.

[0093] The disturbance injection module is used to periodically inject pulse disturbance signals into the reactive current reference signal of the current loop controller through the pulse disturbance channel during multiple disturbance cycles, and to periodically stop injecting pulse disturbance signals into the reactive current reference signal of the current loop controller through the pulse disturbance channel during multiple non-disturbance cycles, so that the grid-connected inverter is periodically in a disturbance state and a non-disturbance state.

[0094] The first sampling module is used for, in the last disturbance cycle in the disturbance state, the sampling device collects the three-phase voltage and the three-phase current of the common grid connection point to obtain the first three-phase voltage and the first three-phase current.

[0095] The second sampling module is used for, in the last disturbance-free period in the disturbance-free state, the sampling device collects the three-phase voltage and the three-phase current of the common grid-connected point to obtain the second three-phase voltage and the second three-phase current.

[0096] The impedance analysis module is used for the impedance identification unit to determine the grid input impedance sequence of the distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage and the second three-phase current.

[0097] As an optional implementation manner, the amplitude of the pulse disturbance signal is less than 10% of the amplitude of the output current of the grid-connected inverter.

[0098] As an optional implementation, determining a grid input impedance sequence of the distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage, and the second three-phase current includes:

[0099] A discrete Fourier transform is performed on the first three-phase voltage to obtain a corresponding plurality of first voltage harmonic components, and average values ​​of amplitude and phase are calculated for all first voltage harmonic components to obtain a first voltage amplitude mean value and a first voltage phase mean value, and a first voltage index signal is determined based on the first voltage amplitude mean value and the first voltage phase mean value; the first voltage index signal is a complex form signal of the first three-phase voltage.

[0100] A discrete Fourier transform is performed on the first three-phase current to obtain a corresponding plurality of first current harmonic components, the average values ​​of the amplitude and the phase of all the first current harmonic components are respectively calculated to obtain a first current amplitude mean value and a first current phase mean value, and a first current index signal is determined based on the first current amplitude mean value and the first current phase mean value; the first current index signal is a complex number signal of the first three-phase current.

[0101] A discrete Fourier transform is performed on the second three-phase voltage to obtain a corresponding plurality of second voltage harmonic components, and average values ​​of amplitude and phase are calculated for all second voltage harmonic components to obtain a second voltage amplitude mean value and a second voltage phase mean value, and a second voltage index signal is determined based on the second voltage amplitude mean value and the second voltage phase mean value; the second voltage index signal is a complex form signal of the second three-phase voltage.

[0102] A discrete Fourier transform is performed on the second three-phase current to obtain a corresponding plurality of second current harmonic components, and the average values ​​of the amplitudes and phases are calculated for all the second current harmonic components to obtain a second current amplitude mean value and a second current phase mean value, and a second current index signal is determined based on the second current amplitude mean value and the second current phase mean value; the second current index signal is a complex form signal of the second three-phase current.

[0103] Based on the first voltage index signal and the second voltage index signal, a voltage increment is determined.

[0104] Based on the first current index signal and the second current index signal, a current increment is determined.

[0105] Based on the voltage increment and the current increment, a grid input impedance sequence of the distribution network system to be tested is determined.

[0106] As an optional implementation, determining the voltage increment based on the first voltage index signal and the second voltage index signal includes:

[0107] The first voltage index signal and the second voltage index signal are subtracted to obtain a voltage increment.

[0108] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0109] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for testing the frequency blocking characteristics of a distribution network based on reactive current reference value disturbance, characterized in that: The distribution network frequency blocking characteristic test method based on reactive current reference value disturbance is implemented based on a distribution network frequency blocking characteristic test device connected to the distribution network system to be tested; The distribution network system to be tested includes: a distributed DC power supply, a grid-connected inverter, a public grid-connected point and a distribution network; the distribution network blocking frequency characteristic test device includes: a sampling device, a current loop controller and an impedance identification unit; The distributed DC power supply, the current loop controller and the sampling device are all connected to the grid-connected inverter, the sampling device and the distribution network are respectively connected to the public grid-connected point, and the impedance identification unit is connected to the sampling device; The distribution network frequency blocking characteristic testing method based on reactive current reference value disturbance includes: Setting a pulse disturbance channel in the current loop controller; In multiple disturbance cycles, the pulse disturbance signal is periodically injected into the reactive current reference signal of the current loop controller through the pulse disturbance channel, and in multiple non-disturbance cycles, the pulse disturbance signal is periodically stopped from being injected into the reactive current reference signal of the current loop controller through the pulse disturbance channel, so that the grid-connected inverter is periodically in a disturbance state and a non-disturbance state; In the last disturbance cycle in the disturbance state, the sampling device collects the three-phase voltage and the three-phase current of the common grid connection point to obtain the first three-phase voltage and the first three-phase current; In the last disturbance-free period in the disturbance-free state, the sampling device collects the three-phase voltage and the three-phase current of the common grid connection point to obtain a second three-phase voltage and a second three-phase current; The impedance identification unit determines a grid input impedance sequence of the power distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage and the second three-phase current.

2. The method for testing the frequency blocking characteristics of a distribution network based on reactive current reference value disturbance according to claim 1, characterized in that: The amplitude of the pulse disturbance signal is less than 10% of the amplitude of the output current of the grid-connected inverter.

3. The method for testing the frequency blocking characteristics of a distribution network based on reactive current reference value disturbance according to claim 1, characterized in that: Determining a grid input impedance sequence of the distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage, and the second three-phase current includes: Performing a discrete Fourier transform on the first three-phase voltage to obtain a plurality of corresponding first voltage harmonic components, calculating the average values ​​of the amplitudes and phases of all the first voltage harmonic components respectively to obtain a first voltage amplitude mean value and a first voltage phase mean value, and determining a first voltage index signal based on the first voltage amplitude mean value and the first voltage phase mean value; the first voltage index signal is a complex number signal of the first three-phase voltage; Performing a discrete Fourier transform on the first three-phase current to obtain a plurality of corresponding first current harmonic components, calculating the average values ​​of the amplitude and phase of all the first current harmonic components respectively to obtain a first current amplitude mean value and a first current phase mean value, and determining a first current index signal based on the first current amplitude mean value and the first current phase mean value; the first current index signal is a complex number signal of the first three-phase current; Performing a discrete Fourier transform on the second three-phase voltage to obtain a plurality of corresponding second voltage harmonic components, calculating the average values ​​of the amplitudes and phases of all the second voltage harmonic components respectively to obtain a second voltage amplitude mean value and a second voltage phase mean value, and determining a second voltage index signal based on the second voltage amplitude mean value and the second voltage phase mean value; the second voltage index signal is a complex number signal of the second three-phase voltage; Performing a discrete Fourier transform on the second three-phase current to obtain a plurality of corresponding second current harmonic components, calculating the average values ​​of the amplitudes and phases of all the second current harmonic components respectively to obtain a second current amplitude mean value and a second current phase mean value, and determining a second current index signal based on the second current amplitude mean value and the second current phase mean value; the second current index signal is a complex number signal of the second three-phase current; determining a voltage increment based on the first voltage index signal and the second voltage index signal; determining a current increment based on the first current index signal and the second current index signal; Based on the voltage increment and the current increment, a grid input impedance sequence of the power distribution network system to be tested is determined.

4. The method for testing the frequency blocking characteristics of a distribution network based on reactive current reference value disturbance according to claim 3 is characterized in that: Determining a voltage increment based on the first voltage index signal and the second voltage index signal includes: The voltage increment is obtained by subtracting the first voltage index signal from the second voltage index signal.

5. The method for testing the frequency blocking characteristics of a distribution network based on reactive current reference value disturbance according to claim 3, characterized in that: Determining a current increment based on the first current index signal and the second current index signal includes: The first current index signal and the second current index signal are subtracted to obtain a current increment.

6. The method for testing the frequency blocking characteristics of a distribution network based on reactive current reference value disturbance according to claim 3, characterized in that: Determining a grid input impedance sequence of the distribution network system to be tested based on the voltage increment and the current increment includes: A division operation is performed on the voltage increment and the current increment to obtain a grid input impedance sequence of the distribution network system to be tested.

7. A distribution network frequency blocking characteristic test system based on reactive current reference value disturbance, characterized in that: The distribution network frequency blocking characteristic test system based on reactive current reference value disturbance is implemented based on a distribution network frequency blocking characteristic test device connected to the distribution network system to be tested; The distribution network system to be tested includes: a distributed DC power supply, a grid-connected inverter, a public grid-connected point and a distribution network; the distribution network blocking frequency characteristic test device includes: a sampling device, a current loop controller and an impedance identification unit; The distributed DC power supply, the current loop controller and the sampling device are all connected to the grid-connected inverter, the sampling device and the distribution network are respectively connected to the public grid-connected point, and the impedance identification unit is connected to the sampling device; The distribution network frequency blocking characteristic testing system based on reactive current reference value disturbance comprises: A channel setting module, used for setting a pulse disturbance channel in the current loop controller; A disturbance injection module, used for periodically injecting a pulse disturbance signal into the reactive current reference signal of the current loop controller through the pulse disturbance channel in multiple disturbance cycles, and periodically stopping injecting the pulse disturbance signal into the reactive current reference signal of the current loop controller through the pulse disturbance channel in multiple non-disturbance cycles, so that the grid-connected inverter is periodically in a disturbance state and a non-disturbance state; A first sampling module, configured to collect the three-phase voltage and the three-phase current of the common grid connection point in the last disturbance cycle in the disturbance state, so as to obtain a first three-phase voltage and a first three-phase current; A second sampling module, configured to collect the three-phase voltage and the three-phase current of the common grid connection point in the last disturbance-free period in the disturbance-free state, so as to obtain a second three-phase voltage and a second three-phase current; An impedance analysis module is used for the impedance identification unit to determine the grid input impedance sequence of the distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage and the second three-phase current.

8. The distribution network frequency blocking characteristic test system based on reactive current reference value disturbance according to claim 7, characterized in that: The amplitude of the pulse disturbance signal is less than 10% of the amplitude of the output current of the grid-connected inverter.

9. The distribution network frequency blocking characteristic test system based on reactive current reference value disturbance according to claim 7, characterized in that: Determining a grid input impedance sequence of the distribution network system to be tested based on the first three-phase voltage, the first three-phase current, the second three-phase voltage, and the second three-phase current includes: Performing a discrete Fourier transform on the first three-phase voltage to obtain a plurality of corresponding first voltage harmonic components, calculating the average values ​​of the amplitudes and phases of all the first voltage harmonic components respectively to obtain a first voltage amplitude mean value and a first voltage phase mean value, and determining a first voltage index signal based on the first voltage amplitude mean value and the first voltage phase mean value; the first voltage index signal is a complex number signal of the first three-phase voltage; Performing a discrete Fourier transform on the first three-phase current to obtain a plurality of corresponding first current harmonic components, calculating the average values ​​of the amplitude and phase of all the first current harmonic components respectively to obtain a first current amplitude mean value and a first current phase mean value, and determining a first current index signal based on the first current amplitude mean value and the first current phase mean value; the first current index signal is a complex number signal of the first three-phase current; Performing a discrete Fourier transform on the second three-phase voltage to obtain a plurality of corresponding second voltage harmonic components, calculating the average values ​​of the amplitudes and phases of all the second voltage harmonic components respectively to obtain a second voltage amplitude mean value and a second voltage phase mean value, and determining a second voltage index signal based on the second voltage amplitude mean value and the second voltage phase mean value; the second voltage index signal is a complex number signal of the second three-phase voltage; Performing a discrete Fourier transform on the second three-phase current to obtain a plurality of corresponding second current harmonic components, calculating the average values ​​of the amplitudes and phases of all the second current harmonic components respectively to obtain a second current amplitude mean value and a second current phase mean value, and determining a second current index signal based on the second current amplitude mean value and the second current phase mean value; the second current index signal is a complex number signal of the second three-phase current; determining a voltage increment based on the first voltage index signal and the second voltage index signal; determining a current increment based on the first current index signal and the second current index signal; Based on the voltage increment and the current increment, a grid input impedance sequence of the power distribution network system to be tested is determined.

10. The distribution network frequency blocking characteristic test system based on reactive current reference value disturbance according to claim 9, characterized in that: Determining a voltage increment based on the first voltage index signal and the second voltage index signal includes: The voltage increment is obtained by subtracting the first voltage index signal from the second voltage index signal.

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