Impedance measurement method and system

Abstract

The application relates to an impedance measurement method and system. The method comprises the following steps: acquiring grid-connected point voltage, measurement frequency, disturbance amplitude and n-th inverter grid-connected current of a multi-inverter grid-connected system; inputting the grid-connected point voltage into an improved phase-locked loop in a fundamental wave and disturbance control unit to generate grid frequency and grid phase; inputting the grid phase and the n-th inverter grid-connected current into a current control loop to generate fundamental wave current control instructions; inputting the measurement frequency, disturbance amplitude and the grid frequency into the disturbance control loop to generate disturbance instructions; inputting the disturbance instructions and the fundamental wave current control instructions into the modulation loop, and generating control driving signals according to the modulation strategy of the inverter to control the switches of each inverter; and acquiring the controlled grid-connected point voltage through an impedance calculation unit to generate the impedance of the to-be-measured inverter and the grid impedance. The method can efficiently and low-cost inject disturbance to measure impedance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, in particular to an impedance measurement method and system. BACKGROUND

[0002] With the large number of power electronic inverters such as distributed wind generators, distributed photovoltaic, energy storage converters, etc. being connected to the power grid, the problem of wideband resonance and harmonic overlimiting of the distribution network is prominent. The wideband impedance of the grid-connected inverter is an important parameter for resonance risk analysis and harmonic responsibility quantification, and accurate acquisition of the wideband impedance is a prerequisite for resonance risk analysis and harmonic responsibility quantification.

[0003] In order to obtain the wideband impedance of the inverter, the traditional method usually introduces a special disturbance injection device. Such impedance measurement method is low in efficiency and high in hardware cost. SUMMARY

[0004] Therefore, it is necessary to provide an impedance measurement method, device, computer equipment, computer readable storage medium and computer program product capable of measuring the impedance of the inverter and the impedance of the power grid at low cost in view of the above technical problems.

[0005] In a first aspect, the present application provides an impedance measurement method applied to a multi-inverter grid-connected system, the multi-inverter grid-connected system comprising n parallel-connected inverters and an impedance calculation unit, the n parallel-connected inverters being connected to a power grid, the nth inverter comprising a fundamental wave and disturbance control unit, the impedance calculation unit being connected to a to-be-measured inverter, and comprising:

[0006] obtaining a grid-connected point voltage, a measurement frequency, a disturbance amplitude and an nth inverter grid-connected current of the multi-inverter grid-connected system;

[0007] inputting the grid-connected point voltage into an improved phase-locked loop in the fundamental wave and disturbance control unit to generate a power grid frequency and a power grid phase; the fundamental wave and disturbance control unit further comprising a disturbance control loop, a current control loop and a modulation loop;

[0008] inputting the power grid phase and the nth inverter grid-connected current into the current control loop to generate a fundamental wave current control instruction; inputting the measurement frequency, the disturbance amplitude and the power grid frequency into the disturbance control loop to generate a disturbance instruction; inputting the disturbance instruction and the fundamental wave current control instruction into the modulation loop, and generating a control driving signal according to the modulation strategy of the inverter, and controlling the switches of each inverter according to the control driving signal;

[0009] obtaining the grid-connected point voltage, the to-be-measured inverter grid-connected current and the power grid current after the switches of each inverter are controlled according to the control driving signal; inputting the controlled grid-connected point voltage, the to-be-measured inverter grid-connected current, the power grid frequency, the measurement frequency and the power grid current into the impedance calculation unit to generate the impedance of the to-be-measured inverter and the impedance of the power grid.

[0010] In one of the embodiments, the grid-connected point voltage is input into an improved phase-locked loop in the fundamental wave and disturbance control unit to generate the grid frequency and the grid phase, including:

[0011] The grid-connected point voltage is input into a grid frequency detection module to generate the grid frequency; and the grid-connected point voltage is input into a grid phase detection module to generate the grid phase.

[0012] In one of the embodiments, the grid-connected point voltage is input into a grid frequency detection module to generate the grid frequency, including:

[0013] According to the grid-connected point voltage, the output frequency is generated; the output frequency is input into a notch filter to filter out the influence of the disturbance injected at the last moment on the output frequency to obtain the output frequency of the notch filter; and the output frequency of the notch filter is input into a moving average filter to filter out the integer harmonic in the output frequency of the notch filter and suppress the disturbance injected at the last moment to obtain the grid frequency.

[0014] In one of the embodiments, the disturbance instruction includes a positive sequence disturbance instruction and a negative sequence disturbance instruction.

[0015] The measured frequency, the disturbance amplitude and the grid frequency are input into a disturbance control loop to generate the disturbance instruction, including:

[0016] According to the impedance measurement requirement, the required disturbance instruction is determined; if the required disturbance instruction is the positive sequence disturbance instruction, the positive sequence disturbance instruction is generated based on the grid frequency, the measured frequency and the disturbance amplitude; and if the required disturbance instruction is the negative sequence disturbance instruction, the negative sequence disturbance instruction is generated based on the grid frequency, the measured frequency and the disturbance amplitude.

[0017] In one of the embodiments, the controlled grid-connected point voltage, the grid-connected current of the to-be-tested inverter, the grid frequency, the measured frequency and the grid current are input into an impedance calculation unit to generate the to-be-tested inverter impedance and the grid impedance, including:

[0018] The controlled grid-connected point voltage, the grid-connected current of the to-be-tested inverter and the grid current are subjected to noise reduction processing to obtain noise reduction data; the noise reduction data is subjected to truncation processing based on the grid frequency and the measured frequency to generate truncated data; the truncated data is subjected to disturbance extraction to generate disturbance extraction data; and the to-be-tested inverter impedance and the grid impedance are determined according to the disturbance extraction data.

[0019] In one of the embodiments, the noise reduction data is subjected to truncation processing based on the grid frequency and the measured frequency to generate the truncated data, including:

[0020] The truncation length is determined based on the grid frequency and the measured frequency; and the noise reduction data is subjected to truncation processing according to the truncation length to obtain the truncated data.

[0021] In a second aspect, the application further provides a multi-inverter grid-connected system, comprising n parallel inverters and an impedance calculation unit, the n parallel inverters are connected to a power grid, the nth inverter comprises a fundamental and disturbance control unit, the impedance calculation unit is connected to the to-be-tested inverter; the fundamental and disturbance control unit comprises an improved phase-locked loop, a disturbance control loop, a current control loop and a modulation loop;

[0022] The improved phase-locked loop is used for receiving a grid point voltage, and generating a grid frequency and a grid phase based on the grid point voltage;

[0023] The current control loop is used for receiving the grid phase and the nth inverter grid-connected current, and generating a fundamental current control instruction according to the grid phase and the nth inverter grid-connected current;

[0024] The disturbance control loop is used for receiving the grid frequency, a measurement frequency and a disturbance amplitude, and generating a disturbance instruction according to the grid frequency, the measurement frequency and the disturbance amplitude;

[0025] The modulation loop is used for generating a control driving signal according to a modulation strategy of the inverter, and controlling switches of each inverter according to the control driving signal;

[0026] The impedance calculation unit is used for obtaining the grid point voltage, the to-be-tested inverter grid-connected current and the grid current after the control of the switches of each inverter according to the control driving signal; and inputting the controlled grid point voltage, the to-be-tested inverter grid-connected current, the grid frequency, the measurement frequency and the grid-connected current into the impedance calculation unit to generate the to-be-tested inverter impedance and the grid impedance.

[0027] In one embodiment, the impedance calculation unit comprises a voltage and current data acquisition module, a disturbance extraction module and an impedance calculation and output module;

[0028] The voltage and current data acquisition module is used for obtaining the controlled grid point voltage, the to-be-tested inverter grid-connected current and the grid current, performing noise reduction processing on the controlled grid point voltage, the to-be-tested inverter grid-connected current and the grid current to obtain noise reduction data, and inputting the noise reduction data into the disturbance extraction module; the disturbance extraction module is used for performing disturbance extraction on the noise reduction data according to the grid frequency to generate disturbance extraction data, and inputting the disturbance extraction data into the impedance calculation and output module; and the impedance calculation and output module is used for determining the to-be-tested inverter impedance and the grid impedance according to the disturbance extraction data.

[0029] In one embodiment, the improved phase-locked loop comprises a grid frequency detection module and a grid phase detection module;

[0030] The grid frequency detection module is used for generating the grid frequency according to the grid point voltage; and the grid phase detection module is used for generating the grid phase according to the grid point voltage.

[0031] In one embodiment, the grid frequency detection module comprises: an output power unit and a harmonic and disturbance removal unit.

[0032] The output power unit is configured to generate output power according to the grid point voltage; and the harmonic and disturbance removal unit is configured to remove harmonics and the disturbance injected at the previous moment from the output power to generate the grid frequency.

[0033] The impedance measurement method, device, computer equipment, computer readable storage medium and computer program product, obtain the grid point voltage, measurement frequency, disturbance amplitude and the nth inverter grid current of the multi-inverter grid-connected system; input the grid point voltage into the improved phase-locked loop in the fundamental wave and disturbance control unit to generate the grid frequency and grid phase; the fundamental wave and disturbance control unit further comprises: a disturbance control loop, a current control loop and a modulation loop; input the grid phase and the nth inverter grid current into the current control loop to generate a fundamental wave current control instruction; input the measurement frequency, disturbance amplitude and grid frequency into the disturbance control loop to generate a disturbance instruction; input the disturbance instruction and the fundamental wave current control instruction into the modulation loop, and generate a control drive signal according to the modulation strategy of the inverter, and control the switches of each inverter according to the control drive signal; obtain the grid point voltage, the to-be-measured inverter grid current and the grid current after the switches of each inverter are controlled according to the control drive signal; input the controlled grid point voltage, the to-be-measured inverter grid current, the grid frequency, the measurement frequency and the grid current into the impedance calculation unit to generate the impedance of the to-be-measured inverter and the grid impedance. The disturbance instruction can be generated conveniently and at low cost, and the disturbance is injected into the circuit, so that the impedance of the inverter and the grid can be measured conveniently. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the drawings needed to be used in the description of the embodiments of the present application or the related art will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other related drawings can be obtained by those skilled in the art without creative labor.

[0035] Figure 1 The flowchart of the impedance measurement method in one embodiment;

[0036] Figure 2 The structure diagram of the improved phase-locked loop in one embodiment;

[0037] Figure 3 The detailed structure diagram of the improved phase-locked loop in one embodiment;

[0038] Figure 4 The structure diagram of the disturbance control loop in another embodiment;

[0039] Figure 5 Fig. 1 is a schematic diagram of the structure of the fundamental and disturbance control unit in one embodiment;

[0040] Figure 6 Fig. 2 is a block diagram of the structure of the multi-inverter grid-connected system in one embodiment. DETAILED DESCRIPTION

[0041] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application.

[0042] In one exemplary embodiment, as shown in Fig. 1, a broadband impedance measurement method is provided, which is applied to a multi-inverter grid-connected system, the multi-inverter grid-connected system includes n parallel inverters and an impedance calculation unit, the n parallel inverters are connected to a grid, the nth inverter includes a fundamental and disturbance control unit, the impedance calculation unit is connected to a to-be-measured inverter, and the method includes: Figure 1

[0043] Step 102, obtaining the grid-connected point voltage, measurement frequency, disturbance amplitude and nth inverter grid-connected current of the multi-inverter grid-connected system.

[0044] The multi-inverter grid-connected system refers to a system in which multiple inverters are connected in parallel and supply power to the grid together. The grid-connected point refers to the connection point of the distributed power supply to the grid. For the distributed power supply with a booster station, the grid-connected point is the high-voltage side bus or node of the distributed power supply booster station. For the distributed power supply without a booster station, the grid-connected point is the output summary point of the distributed power supply. The measurement frequency refers to the frequency corresponding to the impedance positive sequence component that needs to be measured. The disturbance amplitude refers to the amplitude of the voltage or current change in the alternating current signal. The nth inverter grid-connected current is the current input to the grid-connected system by the nth inverter.

[0045] For example, the grid-connected point voltage, measurement frequency, disturbance amplitude and nth inverter grid-connected current of the multi-inverter grid-connected system are obtained.

[0046] Step 104, inputting the grid-connected point voltage into an improved phase-locked loop in the fundamental and disturbance control unit to generate the grid frequency and grid phase; the fundamental and disturbance control unit further includes a disturbance control loop, a current control loop and a modulation loop.

[0047] For example, the grid-connected point voltage is input into the improved phase-locked loop in the fundamental and disturbance control unit to obtain the grid frequency and grid phase, and the fundamental and disturbance control unit further includes a disturbance control loop, a current control loop and a modulation loop.

[0048] ​Step 106, input the grid phase and the nth inverter grid-connected current into a current control loop to generate a fundamental current control instruction; input the measured frequency, the disturbance amplitude and the grid frequency into a disturbance control loop to generate a disturbance instruction; input the disturbance instruction and the fundamental current control instruction into a modulation loop, and generate a control drive signal according to the modulation strategy of the inverter, and control the switches of each inverter according to the control drive signal.

[0049] The disturbance instruction includes a required injected disturbance.

[0050] Optionally, the switches of each inverter are insulated gate bipolar transistors.

[0051] Optionally, input the grid phase and the nth inverter grid-connected current into a current control loop to generate a fundamental current control instruction; input the measured frequency, the disturbance amplitude and the grid frequency into a disturbance control loop to generate a disturbance instruction; input the disturbance instruction and the fundamental current control instruction into a modulation loop, and generate a control drive signal according to the modulation strategy of the inverter, and control the switches of each inverter according to the control drive signal.

[0052] Step 108, obtain the grid-connected point voltage, the grid-connected current of the to-be-tested inverter and the grid current after the switches of each inverter are controlled according to the control drive signal; input the controlled grid-connected point voltage, the grid-connected current of the to-be-tested inverter, the grid frequency, the measured frequency and the grid current into an impedance calculation unit to generate the impedance of the to-be-tested inverter and the impedance of the grid.

[0053] Optionally, obtain the grid-connected point voltage, the grid-connected current of the to-be-tested inverter and the grid current after the switches of each inverter are controlled according to the control drive signal; input the controlled grid-connected point voltage, the grid-connected current of the to-be-tested inverter, the grid frequency, the measured frequency and the grid current into an impedance calculation unit to calculate the impedance of the to-be-tested inverter and the impedance of the grid.

[0054] The impedance measurement method, device, computer equipment, computer readable storage medium and computer program product obtain grid-connected point voltage, measurement frequency, disturbance amplitude and the nth inverter grid-connected current of the multi-inverter grid-connected system; input the grid-connected point voltage into an improved phase-locked loop in a fundamental wave and disturbance control unit to generate a grid frequency and a grid phase; the fundamental wave and disturbance control unit further comprises a disturbance control loop, a current control loop and a modulation loop; input the grid phase and the nth inverter grid-connected current into the current control loop to generate a fundamental wave current control instruction; input the measurement frequency, the disturbance amplitude and the grid frequency into the disturbance control loop to generate a disturbance instruction; input the disturbance instruction and the fundamental wave current control instruction into the modulation loop, and generate a control drive signal according to the modulation strategy of the inverter, and control the switches of each inverter according to the control drive signal; obtain the grid-connected point voltage, the to-be-measured inverter grid-connected current and the grid current after the switches of each inverter are controlled according to the control drive signal; input the controlled grid-connected point voltage, the to-be-measured inverter grid-connected current, the grid frequency, the measurement frequency and the grid current into an impedance calculation unit to generate the impedance of the to-be-measured inverter and the grid impedance. The disturbance instruction can be conveniently and low-costly generated, and the disturbance is injected into the circuit, so that the impedance of the inverter and the grid can be conveniently measured.

[0055] In one exemplary embodiment, as shown in FIG. 1, the grid-connected point voltage is input into an improved phase-locked loop in a fundamental wave and disturbance control unit to generate a grid frequency and a grid phase, which comprises: Figure 2

[0056] The grid-connected point voltage is input into a grid frequency detection module to generate a grid frequency, and the grid-connected point voltage is input into a grid phase detection module to generate a grid phase.

[0057] The grid phase detection module adopts the original design of the inverter.

[0058] In one exemplary embodiment, the grid-connected point voltage is input into a grid frequency detection module to obtain a grid frequency , and the grid-connected point voltage is input into a grid phase detection module to obtain a grid phase .

[0059] In this embodiment, the grid frequency and the grid phase are generated according to the grid-connected point voltage, so as to subsequently inject the disturbance.

[0060] In one exemplary embodiment, the grid-connected point voltage is input into a grid frequency detection module to generate a grid frequency, which comprises:

[0061] ​​According to the grid-connected point voltage, an output frequency is generated; the output frequency is input into a notch filter to filter out the influence of the injected disturbance on the output frequency, to obtain the output frequency of the notch filter; the output frequency of the notch filter is input into a moving average filter to filter out the integer harmonic in the output frequency of the notch filter and suppress the influence of the injected disturbance on the output frequency, to obtain the grid frequency.

[0062] As shown in Figure 3 , the grid-connected point voltage is input into an abc stationary coordinate system to obtain the component of the grid-connected point voltage in the abc stationary coordinate system , and ; the grid-connected point three-phase voltage and the grid phase at the previous time are transformed from the abc stationary coordinate system to the dq rotating coordinate system to obtain the voltage components in the dq coordinate system and ; then the q-axis voltage is input into a proportional-integral control function , combined with the reference frequency and the difference between the actual grid frequency and the reference frequency , to obtain the output angular frequency, wherein is the proportional control parameter of the phase-locked loop, is the integral control parameter of the phase-locked loop, and S is the Laplace factor; the output angular frequency is input into a notch filter NF to preliminarily filter out the disturbance injected at the previous time based on the notch frequency , the notch frequency being: , wherein is the measured frequency, is the grid frequency output at the previous time; after the disturbance injected at the previous time is preliminarily filtered out by the notch filter, the output angular frequency of the notch filter is obtained; the output frequency of the notch filter is input into a moving average filter MAF, and the window time of the MAF is: ; the integer harmonic is filtered out by the moving average filter, and the influence of the disturbance injected at the previous time is filtered out and suppressed again, to obtain the output angular frequency of the MAF; then the output angular frequency of the MAF is converted into the frequency to obtain the grid frequency , and the formula is: .

[0063] In this embodiment, the influence of the harmonic and the disturbance injected at the previous time on the output power is filtered out by the notch filter and the moving average filter, and a more accurate grid frequency can be obtained.

[0064] In an exemplary embodiment, as shown in Figure 4The disturbance instruction includes positive sequence disturbance instruction and negative sequence disturbance instruction.

[0065] The measurement frequency, the disturbance amplitude and the grid frequency are input into the disturbance control loop to generate the disturbance instruction, including:

[0066] According to the required disturbance instruction, if the required disturbance instruction is the positive sequence disturbance instruction, the positive sequence disturbance instruction is generated based on the grid frequency, the measurement frequency and the disturbance amplitude; if the required disturbance instruction is the negative sequence disturbance instruction, the negative sequence disturbance instruction is generated based on the grid frequency, the measurement frequency and the disturbance amplitude.

[0067] For example, according to the requirement of impedance measurement, the required disturbance instruction is determined by the disturbance sequence component determination module; if the required disturbance instruction is the positive sequence disturbance instruction, the switch is connected to the positive sequence disturbance instruction generation module, and the positive sequence disturbance instruction is generated based on the disturbance amplitude , the measurement frequency , and the grid frequency , and the disturbance instruction is output to the modulation loop; the formula is as follows:

[0068] ,

[0069] If the required disturbance instruction is the negative sequence disturbance instruction, the switch is connected to the negative sequence disturbance instruction generation module, and the negative sequence disturbance instruction is generated based on the disturbance amplitude , the measurement frequency , and the grid frequency , and the disturbance instruction is output to the modulation loop; the formula is as follows:

[0070] ,

[0071] In this embodiment, the corresponding disturbance instruction is generated based on the requirement of impedance measurement, and the corresponding disturbance is generated to inject the disturbance into the system efficiently and at low cost, so as to measure the impedance.

[0072] In an exemplary embodiment, the controlled grid-connected point voltage, the to-be-measured inverter grid-connected current, the grid frequency, the measurement frequency and the grid current are input into the impedance calculation unit to generate the to-be-measured inverter impedance and the grid impedance, including:

[0073] The controlled grid-connected point voltage, the to-be-measured inverter grid-connected current and the grid current are subjected to noise reduction processing to obtain noise reduction data; the noise reduction data is subjected to truncation processing based on the grid frequency and the measurement frequency to generate truncated data; the truncated data is subjected to disturbance extraction to generate disturbance extraction data; and the to-be-measured inverter impedance and the grid impedance are determined according to the disturbance extraction data.

[0074] The grid point voltage after control, the to-be-measured inverter grid-connected current and the grid current are denoised to obtain denoised data. The denoised data is truncated based on the grid frequency and the measurement frequency to generate truncated data. Disturbances in the truncated data are extracted to generate disturbance extraction data. The to-be-measured inverter impedance and the grid impedance are calculated based on the disturbance extraction data.

[0075] In this embodiment, by extracting the disturbance and calculating the impedance based on the extracted disturbance, the resonance risk can be analyzed and the harmonic responsibility can be quantified.

[0076] In an example embodiment, the denoised data is truncated based on the grid frequency and the measurement frequency to generate the truncated data, including:

[0077] The truncation length is determined based on the grid frequency and the measurement frequency. The denoised data is truncated based on the truncation length to obtain the truncated data.

[0078] In an example embodiment, the truncation length is determined based on the grid frequency and the measurement frequency , and the formula is as follows:

[0079]

[0080] wherein, the grid frequency and the measurement frequency are the least common multiple; the denoised data is truncated based on the truncation length to obtain the truncated data.

[0081] In this embodiment, by truncating the data, it is ensured that the positive sequence disturbance component and the negative sequence disturbance component can be accurately identified, and the influence of the fundamental wave and harmonic component spectrum leakage on accurate extraction of the disturbance is avoided.

[0082] In an example embodiment, as shown in Figure 5 , the detailed structure diagram of the fundamental wave and disturbance control unit includes an improved phase-locked loop, a disturbance control loop, a current control loop and a modulation loop. The improved phase-locked loop includes a grid frequency detection module and a grid phase detection module. The grid frequency detection module and the grid phase detection module generate the grid frequency and the grid phase according to the grid point voltage . The current control loop obtains the q-axis component based on the nth inverter output current q-axis component , the nth inverter output current q-axis component reference value and the conventional dq-axis controller PI. The current control loop obtains the d-axis component based on the nth inverter output current d-axis component , the nth inverter output current d-axis component reference value​ Compared with traditional dq-axis controllers (PI), the d-axis component is obtained; the grid phase is... The q-axis and d-axis components are transformed into the abc / dq coordinate system to obtain the fundamental current control command. The disturbance control loop is based on the grid frequency. Measurement frequency and disturbance amplitude Generate disturbance command The modulation loop controls the fundamental current according to the command. and disturbance commands The system is controlled by sinusoidal pulse width modulation (SPWM).

[0083] In an exemplary embodiment, a multi-inverter grid-connected system includes n inverters connected in parallel and an impedance calculation unit. All n inverters are connected to the power grid. The nth inverter includes a fundamental frequency and disturbance control unit. The impedance calculation unit is connected to the inverter under test. The method includes:

[0084] Obtain the grid connection point voltage, measurement frequency, disturbance amplitude, and grid connection current of the nth inverter in a multi-inverter grid-connected system. Set the grid connection point voltage... The components in the abc coordinate system are: , and The three-phase voltage at the grid connection point and the grid phase at the previous moment are transformed from the abc stationary coordinate system to the dq rotating coordinate system to obtain the voltage components in the dq coordinate system. and Then the q-axis voltage After proportional-integral control function Combined with reference frequency The difference between the actual frequency of the power grid and the reference frequency The output angular frequency is obtained, where These are the proportional control parameters for the phase-locked loop. Here are the integral control parameters for the phase-locked loop, and S is the Laplace factor; the output angular frequency is... After passing through the notch filter NF, based on the notch filter frequency To initially filter out disturbances injected in the previous moment, the notch filter frequency... for: ,in, It measures frequency. The output frequency is the grid frequency from the previous moment; after the notch filter initially filters out the disturbance injected from the previous moment, the output angular frequency of the notch filter is obtained; the output frequency of the notch filter is then input into the moving average filter (MAF), where the window time of the MAF is... for: , the integer harmonic is filtered out by the moving average filter, and the influence of the disturbance injected at the previous moment is filtered out and suppressed again, to obtain the output angular frequency of the MAF , and then the output angular frequency of the MAF is converted into a frequency to obtain the grid frequency , the formula is as follows: The grid phase and the nth inverter grid-connected current input current control loop to generate the fundamental current control instruction; based on the demand for impedance measurement, the required disturbance instruction is determined by the disturbance sequence component judgment module; if the required disturbance instruction is a positive sequence disturbance instruction, the switch is connected to the positive sequence disturbance instruction generation module, based on the disturbance amplitude , the measurement frequency , the positive sequence disturbance instruction is generated and output to the modulation loop; the formula is as follows:

[0085] ,

[0086] If the required disturbance instruction is a negative sequence disturbance instruction, the switch is connected to the negative sequence disturbance instruction generation module, based on the disturbance amplitude , the measurement frequency , the grid frequency , the negative sequence disturbance instruction is generated and output to the modulation loop; the formula is as follows:

[0087] ,

[0088] The disturbance instruction and the fundamental current control instruction are input into the modulation loop, and the control drive signal is generated according to the modulation strategy of the inverter; the switches of each inverter are controlled according to the control drive signal. The controlled grid-connected point voltage, the grid-connected current of the to-be-tested inverter and the grid current are subjected to noise reduction processing to obtain noise reduction data; the interception length is determined based on the grid frequency and the measurement frequency , and the formula is as follows:

[0089]

[0090] , wherein represents the least common multiple of the grid frequency and the measurement frequency ; based on the interception length, the noise reduction data is truncated to obtain truncated data; the disturbance in the truncated data is extracted to generate disturbance extraction data; based on the disturbance extraction data, the impedance of the to-be-tested inverter and the grid impedance are calculated.

[0091] ​It should be understood that although the steps in the flowcharts involved in the above embodiments are shown in sequence according to the arrows, the steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, the execution of the steps is not strictly limited in sequence, and the steps can be executed in other orders. Moreover, at least some of the steps in the flowcharts involved in the above embodiments can include multiple steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution order of the steps or stages is not necessarily sequential, but can be alternately executed with at least some of the other steps or the steps or stages in the other steps.

[0092] In an exemplary embodiment, as shown in Figure 6 a multi-inverter grid-connected system is provided, the multi-inverter grid-connected system comprises n parallel inverters and an impedance calculation unit, the n parallel inverters are connected to a grid, the nth inverter comprises a fundamental and disturbance control unit, the impedance calculation unit is connected to a to-be-tested inverter; the fundamental and disturbance control unit comprises an improved phase-locked loop, a disturbance control loop, a current control loop and a modulation loop;

[0093] The improved phase-locked loop is configured to receive a grid point voltage, and generate a grid frequency and a grid phase based on the grid point voltage;

[0094] The current control loop is configured to receive the grid phase and an nth inverter grid-connected current, and generate a fundamental current control instruction according to the grid phase and the nth inverter grid-connected current;

[0095] The disturbance control loop is configured to receive the grid frequency, a measurement frequency and a disturbance amplitude, and generate a disturbance instruction according to the grid frequency, the measurement frequency and the disturbance amplitude;

[0096] The modulation loop is configured to generate a control driving signal according to a modulation strategy of the inverter, and control switches of each inverter according to the control driving signal;

[0097] The impedance calculation unit is configured to obtain a grid point voltage after the control, a to-be-tested inverter grid-connected current and a grid current after the control of the switches of each inverter according to the control driving signal; input the grid point voltage after the control, the to-be-tested inverter grid-connected current, a grid frequency, a measurement frequency and a grid-connected current into the impedance calculation unit, and generate a to-be-tested inverter impedance and a grid impedance.

[0098] In an exemplary embodiment, the impedance calculation unit further comprises a voltage and current data acquisition module, a disturbance extraction module and an impedance calculation and output module;

[0099] The voltage current data acquisition module is used for acquiring the controlled grid-connected point voltage, the to-be-tested inverter grid-connected current and the grid current, performing noise reduction processing on the controlled grid-connected point voltage, the to-be-tested inverter grid-connected current and the grid current, obtaining noise reduction data, and inputting the noise reduction data into the disturbance extraction module;

[0100] The disturbance extraction module is used for performing disturbance extraction on the noise reduction data according to the grid frequency, generating disturbance extraction data, and inputting the disturbance extraction data into the impedance calculation and output module.

[0101] The impedance calculation and output module is used for determining the to-be-tested inverter impedance and the grid impedance according to the disturbance extraction data.

[0102] In an exemplary embodiment, the improved phase-locked loop further comprises a grid frequency detection module and a grid phase detection module.

[0103] The grid frequency detection module is used for generating the grid frequency according to the grid-connected point voltage.

[0104] The grid phase detection module is used for generating the grid phase according to the grid-connected point voltage.

[0105] In an exemplary embodiment, the grid frequency detection module further comprises an output power unit and a harmonic and disturbance removal unit.

[0106] The output power unit is used for generating the output power according to the grid-connected point voltage.

[0107] The harmonic and disturbance removal unit is used for removing the harmonic and the disturbance injected at the last moment in the output power, and generating the grid frequency.

[0108] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer readable storage medium, and when executed, can include the processes of the above-mentioned embodiment methods. Any reference to memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile memory and volatile memory. The non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical storage, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. The volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration but not limitation, the RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc. The database involved in the embodiments provided in the present application can include at least one of a relational database and a non-relational database. The non-relational database can include a distributed database based on a block chain, etc., without being limited thereto. The processor involved in the embodiments provided in the present application can be a general-purpose processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, an artificial intelligence (AI) processor, etc., without being limited thereto.

[0109] The technical features of the above embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present application.

[0110] The above-described embodiments are merely illustrative of several embodiments of the present application, which are described in more detail and in a specific manner, but should not be construed as limiting the scope of the patent of the present application. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. An impedance measurement method, characterized in that, An application is made to a multi-inverter grid-connected system, wherein the multi-inverter grid-connected system includes n inverters connected in parallel and an impedance calculation unit, all n inverters are connected to the power grid, the nth inverter includes a fundamental frequency and a disturbance control unit, and the impedance calculation unit is connected to the inverter under test, the method comprising: Obtain the grid connection point voltage, measurement frequency, disturbance amplitude, and grid connection current of the nth inverter in a multi-inverter grid-connected system; The grid connection point voltage is input into the improved phase-locked loop in the fundamental frequency and disturbance control unit to generate the grid frequency and grid phase; the fundamental frequency and disturbance control unit further includes: a disturbance control loop, a current control loop, and a modulation loop; The grid phase and the grid-connected current of the nth inverter are input into the current control loop to generate a fundamental current control command; the measured frequency, disturbance amplitude, and grid frequency are input into the disturbance control loop to generate a disturbance command; the disturbance command and the fundamental current control command are input into the modulation loop, and a control drive signal is generated according to the inverter's modulation strategy, and the switches of each inverter are controlled according to the control drive signal; The grid connection point voltage, the grid connection current of the inverter under test, and the grid current are obtained after controlling the switches of each inverter according to the control drive signal. The grid connection point voltage after control, the grid connection current of the inverter under test, the grid frequency, the measurement frequency, and the grid current are input to the impedance calculation unit to generate the impedance of the inverter under test and the grid impedance.

2. The method according to claim 1, characterized in that, The step of using the improved phase-locked loop in the grid connection point voltage input fundamental frequency and disturbance control unit to generate grid frequency and grid phase includes: The grid connection point voltage is input into the power grid frequency detection module to generate the power grid frequency; The grid connection point voltage is input into the grid phase detection module to generate the grid phase.

3. The method according to claim 2, characterized in that, The step of inputting the grid connection point voltage into the grid frequency detection module to generate the grid frequency includes: The output frequency is generated based on the grid connection point voltage; The output frequency is input into the notch filter to filter out the influence of the disturbance injected in the previous moment on the output frequency, and the output frequency of the notch filter is obtained. The output frequency of the notch filter is input into a moving average filter to filter out integer harmonics in the output frequency of the notch filter and suppress disturbances injected in the previous moment, thereby obtaining the power grid frequency.

4. The method according to claim 1, characterized in that, The perturbation commands include positive-order perturbation commands and negative-order perturbation commands; The step of inputting the measured frequency, disturbance amplitude, and grid frequency into the disturbance control loop to generate a disturbance command includes: The required disturbance command is determined based on the impedance measurement requirements. If the required disturbance command is a positive-sequence disturbance command, a positive-sequence disturbance command is generated based on the power grid frequency, the measurement frequency, and the disturbance amplitude. If the required disturbance command is a negative-sequence disturbance command, a negative-sequence disturbance command is generated based on the power grid frequency, the measurement frequency, and the disturbance amplitude.

5. The method according to claim 1, characterized in that, The step of generating the inverter impedance and grid impedance by using the controlled grid connection point voltage, the grid connection current of the inverter under test, the grid frequency, the measurement frequency, and the grid current input impedance calculation unit includes: The controlled grid connection point voltage, the grid connection current of the inverter under test, and the grid current are subjected to noise reduction processing to obtain noise reduction data; Based on the power grid frequency and the measurement frequency, the noise reduction data is truncated to generate truncated data; The intercepted data is perturbed to generate perturbed extracted data; Based on the disturbance data, the impedance of the inverter under test and the grid impedance are determined.

6. The method according to claim 5, characterized in that, The step of truncating the noise reduction data based on the power grid frequency and the measurement frequency to generate truncated data includes: The cut-off length is determined based on the power grid frequency and the measurement frequency; The noise reduction data is truncated according to the specified truncation length to obtain the truncated data.

7. A multi-inverter grid-connected system, characterized in that, The multi-inverter grid-connected system includes n inverters connected in parallel and an impedance calculation unit. All n inverters are connected to the power grid. The nth inverter includes a fundamental frequency and a disturbance control unit. The impedance calculation unit is connected to the inverter under test. The fundamental frequency and disturbance control unit includes an improved phase-locked loop, a disturbance control loop, a current control loop, and a modulation loop. The improved phase-locked loop is used to receive the grid connection point voltage and generate the grid frequency and grid phase based on the grid connection point voltage; The current control loop is used to receive the grid phase and the grid-connected current of the nth inverter, and generate a fundamental current control command based on the grid phase and the grid-connected current of the nth inverter. The disturbance control loop is used to receive the power grid frequency, measurement frequency and disturbance amplitude, and generate a disturbance command based on the power grid frequency, measurement frequency and disturbance amplitude; The modulation loop is used to generate control drive signals according to the inverter's modulation strategy, and to control the switches of each inverter according to the control drive signals; The impedance calculation unit is used to obtain the grid connection point voltage, the grid connection current of the inverter under test, and the grid current after controlling the switches of each inverter according to the control drive signal; and inputs the controlled grid connection point voltage, the grid connection current of the inverter under test, the grid frequency, the measurement frequency, and the grid connection current into the impedance calculation unit to generate the impedance of the inverter under test and the grid impedance.

8. A multi-inverter grid-connected system according to claim 7, characterized in that, The impedance calculation unit includes: a voltage and current data acquisition module, a disturbance extraction module, and an impedance calculation and output module; The voltage and current data acquisition module is used to acquire the controlled grid connection point voltage, the grid connection current of the inverter under test, and the grid current, and to perform noise reduction processing on the controlled grid connection point voltage, the grid connection current of the inverter under test, and the grid current to obtain noise reduction data, and input the noise reduction data into the disturbance extraction module. The disturbance extraction module is used to extract disturbances from the noise reduction data according to the power grid frequency, generate disturbance extraction data, and input the disturbance extraction data into the impedance calculation and output module. The impedance calculation and output module is used to determine the impedance of the inverter under test and the grid impedance based on the data extracted from the disturbance.

9. A multi-inverter grid-connected system according to claim 7, characterized in that, The improved phase-locked loop includes: a power grid frequency detection module and a power grid phase detection module; The power grid frequency detection module is used to generate the power grid frequency based on the grid connection point voltage; The power grid phase detection module is used to generate the power grid phase based on the grid connection point voltage.

10. A multi-inverter grid-connected system according to claim 9, characterized in that, The power grid frequency detection channel includes: an output power unit and a harmonic and disturbance removal unit; The output power unit is used to generate output power based on the grid connection point voltage; The harmonic and disturbance removal unit is used to remove harmonics and disturbances injected in the previous moment from the output power and generate the grid frequency.

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