Impedance measurement method and system

Abstract

The invention relates to an impedance measurement method and system. The method comprises the following steps: acquiring grid-connected point voltage, measurement frequency, disturbance amplitude and nth inverter grid-connected current of the 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 a power grid frequency and a power grid phase; inputting the power grid phase and the nth inverter grid-connected current into the current control loop to generate a fundamental current control instruction; inputting the measurement frequency, the disturbance amplitude and the power grid frequency into the disturbance control ring to generate a disturbance instruction; inputting the disturbance instruction and the fundamental current control instruction into the modulation ring, generating a control driving signal according to a modulation strategy of an inverter, and controlling each inverter switch; and obtaining the controlled grid-connected point voltage through an impedance calculation unit, and generating the impedance of the inverter to be tested and the impedance of the power grid. By adopting the method, disturbance can be injected efficiently at low cost so as to measure impedance.

Description

Technical Field

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

[0002] With the massive access of distributed wind turbines, distributed photovoltaics, energy storage converters and other power electronic inverters, the problems of broadband resonance and excessive harmonics in distribution networks have become prominent. The broadband impedance of grid-connected inverters is an important parameter for resonance risk analysis and harmonic liability quantification. Accurately obtaining broadband impedance is a prerequisite for resonance risk analysis and harmonic liability quantification.

[0003] In order to obtain the broadband impedance of the inverter, the traditional method usually introduces a special disturbance injection device. This type of impedance measurement method has low efficiency and high hardware cost. Summary of the invention

[0004] Based on this, it is necessary to provide an impedance measurement method, device, computer equipment, computer-readable storage medium and computer program product that can measure inverter impedance and grid impedance at low cost in response to the above technical problems.

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

[0006] Obtaining the grid connection point voltage, measurement frequency, disturbance amplitude and grid connection current of the nth inverter of the multi-inverter grid connection system;

[0007] Inputting the grid connection 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 also includes: a disturbance control loop, a current control loop and a modulation loop;

[0008] Input the grid phase and the grid-connected current of the nth inverter into the current control loop to generate a fundamental current control instruction; input the measured 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 current control instruction into the modulation loop, and generate a control drive signal according to the modulation strategy of the inverter, and control each inverter switch according to the control drive signal;

[0009] The grid-connected point voltage, the grid-connected current of the inverter to be tested and the grid current are obtained after each inverter switch is controlled according to the control drive signal; the controlled grid-connected point voltage, the grid-connected current of the inverter to be tested, the grid frequency, the measurement frequency and the grid current are input into the impedance calculation unit to generate the impedance of the inverter to be tested and the grid impedance.

[0010] In one embodiment, the grid connection 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, including:

[0011] The grid connection point voltage is input into the grid frequency detection module to generate the grid frequency; the grid connection point voltage is input into the grid phase detection module to generate the grid phase.

[0012] In one embodiment, the grid connection point voltage is input into a grid frequency detection module to generate a grid frequency, including:

[0013] The output frequency is generated according to the grid connection point voltage; the output frequency is input into the notch filter to filter out the influence of the disturbance injected last 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 the sliding average filter to filter out the integer harmonics in the output frequency of the notch filter and suppress the disturbance injected last moment to obtain the grid frequency.

[0014] In one embodiment, the disturbance instruction includes a positive sequence disturbance instruction and a negative sequence disturbance instruction;

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

[0016] The required disturbance instruction is determined according to the impedance measurement requirements. If the required disturbance instruction is a positive-sequence disturbance instruction, a positive-sequence disturbance instruction is generated based on the grid frequency, the measurement frequency and the disturbance amplitude; if the required disturbance instruction is a negative-sequence disturbance instruction, a negative-sequence disturbance instruction is generated based on the grid frequency, the measurement frequency and the disturbance amplitude.

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

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

[0019] In one embodiment, based on the grid frequency and the measurement frequency, the noise reduction data is truncated to generate the truncated data, including:

[0020] The interception length is determined based on the grid frequency and the measurement frequency; the noise reduction data is shortened according to the interception length to obtain the intercepted data.

[0021] In a second aspect, the present application further provides a multi-inverter grid-connected system, the multi-inverter grid-connected system comprising n parallel inverters and an impedance calculation unit, the n parallel inverters are all connected to a power grid, the nth inverter comprises a fundamental wave and disturbance control unit, and the impedance calculation unit is connected to the inverter to be tested; the fundamental wave 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 the grid connection point voltage and generating the grid frequency and grid phase based on the grid connection point voltage;

[0023] 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 instruction according to the grid phase and the grid-connected current of the nth inverter;

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

[0025] The modulation ring is used to generate a control drive signal according to the modulation strategy of the inverter, and control each inverter switch according to the control drive signal;

[0026] The impedance calculation unit is used to obtain the grid-connected point voltage, the grid-connected current of the inverter to be tested and the grid current after controlling each inverter switch according to the control drive signal; the controlled grid-connected point voltage, the grid-connected current of the inverter to be tested, the grid frequency, the measurement frequency and the grid current are input into the impedance calculation unit to generate the impedance of the inverter to be tested and the grid impedance.

[0027] In one of the embodiments, the impedance calculation unit includes: 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 to obtain the grid-connected point voltage after control, the grid-connected current of the inverter to be tested and the grid current, perform noise reduction processing on the grid-connected point voltage after control, the grid-connected current of the inverter to be tested and the grid current, obtain the noise reduction data, and input the noise reduction data into the disturbance extraction module; the disturbance extraction module is used to perform disturbance extraction on the noise reduction data according to the 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 to be tested and the grid impedance according to the disturbance extraction data.

[0029] In one of the embodiments, the improved phase-locked loop includes: a power grid frequency detection module and a power grid phase detection module;

[0030] The grid frequency detection module is used to generate the grid frequency according to the grid connection point voltage; the grid phase detection module is used to generate the grid phase according to the grid connection point voltage.

[0031] In one of the embodiments, the power grid frequency detection module includes: an output power unit and a harmonic and disturbance removal unit;

[0032] The output power unit is used to generate output power according to the grid connection point voltage; the harmonic and disturbance removal unit is used to remove the harmonics in the output power and the disturbance injected at the last moment to generate the grid frequency.

[0033] The impedance measurement method, device, computer equipment, computer-readable storage medium and computer program product described above obtain the grid-connected point voltage, measurement frequency, disturbance amplitude and grid-connected current of the nth inverter of the multi-inverter grid-connected system; input the grid-connected 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 also includes: a disturbance control loop, a current control loop and a modulation loop; input the grid phase and the grid-connected current of the nth inverter into the current control loop to generate the fundamental wave current control instruction; input the measurement frequency, disturbance amplitude and the grid-connected current of the nth inverter ... The value and grid frequency are input into the disturbance control loop to generate a disturbance command; the disturbance command and fundamental current control command are input into the modulation loop, and a control drive signal is generated according to the modulation strategy of the inverter, and each inverter switch is controlled according to the control drive signal; the grid connection point voltage, the grid connection current of the inverter to be tested and the grid current are obtained after each inverter switch is controlled according to the control drive signal; the controlled grid connection point voltage, the grid connection current of the inverter to be tested, the grid frequency, the measurement frequency and the grid current are input into the impedance calculation unit to generate the impedance of the inverter to be tested and the grid impedance. The disturbance command can be generated conveniently and at low cost to inject disturbance into the circuit to facilitate the measurement of the impedance of the inverter and the grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 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 of the present application or related technical descriptions 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 related drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 is a schematic flow chart of an impedance measurement method in one embodiment;

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

[0037] Figure 3 is a detailed structural diagram of an improved phase-locked loop in one embodiment;

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

[0039] Figure 5 is a schematic structural diagram of a fundamental wave and disturbance control unit in one embodiment;

[0040] Figure 6 FIG. 4 is a structural block diagram of a multi-inverter grid-connected system in one embodiment. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0042] In an exemplary embodiment, Figure 1 As shown, a wide-band 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 all connected to the power grid. The nth inverter includes a fundamental wave and a disturbance control unit. The impedance calculation unit is connected to the inverter to be measured. The method includes:

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

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

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

[0046] Step 104, input the grid connection 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 also includes: a disturbance control loop, a current control loop and a modulation loop.

[0047] Exemplarily, the grid connection point voltage is input into the improved phase-locked loop in the fundamental wave and disturbance control unit to obtain the grid frequency and grid phase. The fundamental wave and disturbance control unit also includes: a disturbance control loop, a current control loop and a modulation loop.

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

[0049] The disturbance instruction includes the disturbance to be injected.

[0050] Optionally, each inverter switch is a switch of an insulated gate bipolar transistor in n inverters.

[0051] Exemplarily, 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 instruction; the measured frequency, the disturbance amplitude and the grid frequency are input into the disturbance control loop to generate a disturbance instruction; the disturbance instruction and the fundamental current control instruction are input into the modulation loop, and a control drive signal is generated according to the modulation strategy of the inverter, and each inverter switch is controlled according to the control drive signal.

[0052] Step 108, obtaining the grid-connected point voltage, the grid-connected current of the inverter to be tested and the grid current after controlling each inverter switch according to the control drive signal; inputting the controlled grid-connected point voltage, the grid-connected current of the inverter to be tested, the grid frequency, the measurement frequency and the grid current into the impedance calculation unit to generate the impedance of the inverter to be tested and the grid impedance.

[0053] Exemplarily, after each inverter switch is controlled according to the control drive signal, the controlled grid-connected point voltage, the grid-connected current of the inverter to be tested and the grid current are obtained; the controlled grid-connected point voltage, the grid-connected current of the inverter to be tested, the grid frequency, the measurement frequency and the grid current are input into the impedance calculation unit to calculate the impedance of the inverter to be tested and the grid impedance.

[0054] The impedance measurement method, device, computer equipment, computer-readable storage medium and computer program product described above obtain the grid-connected point voltage, measurement frequency, disturbance amplitude and grid-connected current of the nth inverter of the multi-inverter grid-connected system; input the grid-connected 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 also includes: a disturbance control loop, a current control loop and a modulation loop; input the grid phase and the grid-connected current of the nth inverter into the current control loop to generate the fundamental wave current control instruction; input the measurement frequency, disturbance amplitude and the grid-connected current of the nth inverter ... The value and grid frequency are input into the disturbance control loop to generate a disturbance command; the disturbance command and fundamental current control command are input into the modulation loop, and a control drive signal is generated according to the modulation strategy of the inverter, and each inverter switch is controlled according to the control drive signal; the grid connection point voltage, the grid connection current of the inverter to be tested and the grid current are obtained after each inverter switch is controlled according to the control drive signal; the controlled grid connection point voltage, the grid connection current of the inverter to be tested, the grid frequency, the measurement frequency and the grid current are input into the impedance calculation unit to generate the impedance of the inverter to be tested and the grid impedance. The disturbance command can be generated conveniently and at low cost to inject disturbance into the circuit to facilitate the measurement of the impedance of the inverter and the grid.

[0055] In an exemplary embodiment, Figure 2 As shown, the grid connection point voltage is input into the improved phase-locked loop in the fundamental wave and disturbance control unit to generate the grid frequency and grid phase, including:

[0056] The grid connection point voltage is input into the grid frequency detection module to generate the grid frequency; the grid connection point voltage is input into the grid phase detection module to generate the grid phase.

[0057] Among them, the grid phase detection module adopts the original design of the inverter.

[0058] For example, the grid voltage Input the grid frequency detection module to obtain the grid frequency ; Input the grid connection point voltage into the grid phase detection module to obtain the grid phase .

[0059] In this embodiment, the grid frequency and grid phase are generated according to the grid connection point voltage, so as to facilitate subsequent disturbance injection.

[0060] In an exemplary embodiment, the grid connection point voltage is input into a grid frequency detection module to generate a grid frequency, including:

[0061] The output frequency is generated according to the grid connection point voltage; the output frequency is input into the notch filter to filter out the influence of the injected disturbance on the output frequency, and the output frequency of the notch filter is obtained; the output frequency of the notch filter is input into the sliding average filter to filter out the integer harmonics in the output frequency of the notch filter, and suppress the influence of the injected disturbance on the output frequency, and obtain the grid frequency.

[0062] For example, Figure 3 As shown, the grid voltage The components in the abc coordinate system are , and , the three-phase voltage of 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 component in the dq coordinate system and , then the q-axis voltage Through the proportional integral control function , combined with the reference frequency The difference between the actual frequency of the power grid and the reference frequency , the output angular frequency is obtained, where is the proportional control parameter of the phase-locked loop, is the integral control parameter of the phase-locked loop, S is the Laplace factor; the output angular frequency After the notch filter NF, based on the notch frequency To preliminarily filter out the disturbance injected at the previous moment, the notch frequency for: ,in, is the measurement frequency, is the grid frequency output at the previous moment; after the notch filter initially filters out the disturbance injected at the previous moment, the output angular frequency of the notch filter is obtained; the output frequency of the notch filter is input into the moving average filter MAF, and the window time of MAF is for: , the output angular frequency of MAF is obtained by filtering out the integer harmonics through a sliding average filter and filtering out and suppressing the influence of the disturbance injected at the previous moment. , then the output angular frequency of MAF Convert to frequency to get grid frequency , the formula is: .

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

[0064] In an exemplary embodiment, Figure 4As shown, the disturbance command includes a positive sequence disturbance command and a negative sequence disturbance command;

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

[0066] The required disturbance instruction is determined according to the impedance measurement requirements. If the required disturbance instruction is a positive-sequence disturbance instruction, a positive-sequence disturbance instruction is generated based on the grid frequency, the measurement frequency and the disturbance amplitude; if the required disturbance instruction is a negative-sequence disturbance instruction, a negative-sequence disturbance instruction is generated based on the grid frequency, the measurement frequency and the disturbance amplitude.

[0067] Exemplarily, based on the requirement of impedance measurement, the required disturbance instruction is determined by the disturbance sequence component determination module; if the required disturbance instruction is a positive sequence disturbance instruction, the switch is connected to the positive sequence disturbance instruction generation module, and based on the disturbance amplitude , measuring frequency , generate a positive sequence disturbance command and output the disturbance command to the modulation loop; the formula is as follows:

[0068] ,

[0069] If the required disturbance command is a negative-sequence disturbance command, the switch is connected to the negative-sequence disturbance command generation module, based on the disturbance amplitude , measuring frequency , grid frequency , generate a negative sequence disturbance command and output the disturbance command to the modulation loop; the formula is as follows:

[0070] ,

[0071] In this embodiment, a corresponding disturbance instruction is generated based on the requirement of impedance measurement to generate a corresponding disturbance, so that the disturbance can be injected into the system efficiently and at a low cost to measure the impedance.

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

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

[0074] Exemplarily, the controlled grid-connected point voltage, the grid-connected current of the inverter to be tested and the grid current are subjected to noise reduction processing to obtain noise reduction data; based on the grid frequency and the measurement frequency, the noise reduction data is truncated to generate intercepted data; the disturbance in the intercepted data is extracted to generate disturbance extraction data; based on the disturbance extraction data, the impedance of the inverter to be tested and the grid impedance are calculated.

[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 exemplary embodiment, based on the grid frequency and the measurement frequency, the noise reduction data is truncated to generate the truncated data, including:

[0077] The interception length is determined based on the grid frequency and the measurement frequency; the noise reduction data is shortened according to the interception length to obtain the intercepted data.

[0078] For example, based on the grid frequency and measurement frequency Determine the cut length , the formula is as follows:

[0079]

[0080] in, Indicates the grid frequency and measurement frequency The least common multiple of ; based on the interception length, the noise reduction data is truncated to obtain the intercepted data.

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

[0082] In an exemplary embodiment, Figure 5 The figure shows the detailed structure of the fundamental wave and disturbance control unit. It 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 power grid frequency detection module and a power grid phase detection module; the power grid frequency detection module and the power grid phase detection module detect the power grid frequency according to the grid connection point voltage. Generate grid frequency and grid phase The current control loop is based on the q-axis component of the nth inverter output current , Reference value of the q-axis component of the output current of the nth inverter and the traditional dq-axis controller PI to obtain the q-axis component; the current control loop is based on the d-axis component of the output current of the nth inverter , nth inverter output current d-axis component reference value and the traditional dq axis controller PI to obtain the d axis component; The q-axis component and the d-axis component are transformed through the abc / dq coordinate system to obtain the fundamental current control instruction The disturbance control loop is based on the grid frequency , measurement frequency and the disturbance amplitude Generate perturbation instructions The modulation loop controls the command according to the fundamental current and disturbance instructions , Sinusoidal Pulse Width Modulation (SPWM) is used to control the system.

[0083] In an exemplary embodiment, a multi-inverter grid-connected system includes n parallel inverters and an impedance calculation unit, the n parallel inverters are all connected to a power grid, the nth inverter includes a fundamental wave and disturbance control unit, the impedance calculation unit is connected to the inverter to be tested, and the method includes:

[0084] Obtain the grid-connected point voltage, measured frequency, disturbance amplitude, and grid-connected current of the nth inverter of the multi-inverter grid-connected system. The components in the abc coordinate system are , and , the three-phase voltage of 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 component in the dq coordinate system and , then the q-axis voltage Through the proportional integral control function , combined with the reference frequency The difference between the actual frequency of the power grid and the reference frequency , the output angular frequency is obtained, where is the proportional control parameter of the phase-locked loop, is the integral control parameter of the phase-locked loop, S is the Laplace factor; the output angular frequency After the notch filter NF, based on the notch frequency To preliminarily filter out the disturbance injected at the previous moment, the notch frequency for: ,in, is the measurement frequency, is the grid frequency output at the previous moment; after the notch filter initially filters out the disturbance injected at the previous moment, the output angular frequency of the notch filter is obtained; the output frequency of the notch filter is input into the moving average filter MAF, and the window time of MAF is for: , the output angular frequency of MAF is obtained by filtering out the integer harmonics through a sliding average filter and filtering out and suppressing the influence of the disturbance injected at the previous moment. , then the output angular frequency of MAF Convert to frequency to get grid frequency , the formula is: The grid phase and the grid-connected current of the nth inverter are input into the current control loop to generate the fundamental current control command; based on the impedance measurement requirements, the required disturbance command is judged by the disturbance sequence component judgment module; if the required disturbance command is a positive sequence disturbance command, the switch is connected to the positive sequence disturbance command generation module, and based on the disturbance amplitude , measuring frequency , generate a positive sequence disturbance command and output the disturbance command to the modulation loop; the formula is as follows:

[0085] ,

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

[0087] ,

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

[0089]

[0090] in, Indicates the grid frequency and measurement frequency The least common multiple of ; based on the interception length, the noise reduction data is shortened to obtain the intercepted data; the disturbance in the intercepted data is extracted to generate the disturbance extraction data; based on the disturbance extraction data, the impedance of the inverter to be measured and the grid impedance are calculated.

[0091] It should be understood that, although the steps in the flowcharts involved in the above embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above embodiments may include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0092] In an exemplary embodiment, Figure 6 As shown, a multi-inverter grid-connected system is provided, the multi-inverter grid-connected system includes n parallel inverters and an impedance calculation unit, the n parallel inverters are all connected to the power grid, the nth inverter includes a fundamental wave and disturbance control unit, and the impedance calculation unit is connected to the inverter to be tested; 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;

[0093] The improved phase-locked loop is used for receiving the grid connection point voltage and generating the grid frequency and grid phase based on the grid connection point voltage;

[0094] 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 instruction according to the grid phase and the grid-connected current of the nth inverter;

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

[0096] The modulation ring is used to generate a control drive signal according to the modulation strategy of the inverter, and control each inverter switch according to the control drive signal;

[0097] The impedance calculation unit is used to obtain the grid-connected point voltage, the grid-connected current of the inverter to be tested and the grid current after controlling each inverter switch according to the control drive signal; the controlled grid-connected point voltage, the grid-connected current of the inverter to be tested, the grid frequency, the measurement frequency and the grid current are input into the impedance calculation unit to generate the impedance of the inverter to be tested and the grid impedance.

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

[0099] The voltage and current data acquisition module is used to obtain the grid-connected point voltage after control, the grid-connected current of the inverter to be tested and the grid current, perform noise reduction processing on the grid-connected point voltage after control, the grid-connected current of the inverter to be tested and the grid current, obtain noise reduction data, and input the noise reduction data into the disturbance extraction module;

[0100] A disturbance extraction module is used to extract disturbances from 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;

[0101] The impedance calculation and output module is used to extract data according to the disturbance and determine the impedance of the inverter to be tested and the impedance of the power grid.

[0102] In an exemplary embodiment, the improved phase-locked loop further includes: a power grid frequency detection module and a power grid phase detection module;

[0103] A power grid frequency detection module is used to generate the power grid frequency according to the voltage at the grid connection point;

[0104] The grid phase detection module is used to generate the grid phase according to the grid connection point voltage.

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

[0106] An output power unit, used to generate output power according to the grid connection point voltage;

[0107] The harmonic and disturbance removal unit is used to remove the harmonics in the output power and the disturbance injected at the last moment to generate the grid frequency.

[0108] A person of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment method can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the 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. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, an artificial intelligence (AI) processor, etc., but are not limited to this.

[0109] 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 application.

[0110] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations 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 shall be subject to the attached claims.

Claims

1. An impedance measurement method, characterized in that: 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 all connected to a power grid, the nth inverter includes a fundamental wave and a disturbance control unit, the impedance calculation unit is connected to the inverter to be tested, and the method includes: Obtaining the grid connection point voltage, measurement frequency, disturbance amplitude and grid connection current of the nth inverter of the multi-inverter grid connection system; Input the grid connection 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 also includes: a disturbance control loop, a current control loop and a modulation loop; Input the grid phase and the grid-connected current of the nth inverter into the current control loop to generate a fundamental 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 current control instruction into the modulation loop, and generate a control drive signal according to the modulation strategy of the inverter, and control each inverter switch according to the control drive signal; The grid-connected point voltage, the grid-connected current of the inverter to be tested and the grid current are obtained after each inverter switch is controlled according to the control drive signal; the controlled grid-connected point voltage, the grid-connected current of the inverter to be tested, the grid frequency, the measurement frequency and the grid current are input into an impedance calculation unit to generate the impedance of the inverter to be tested and the grid impedance.

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

3. The method according to claim 2, characterized in that The step of inputting the grid connection point voltage into a grid frequency detection module to generate a grid frequency comprises: generating an output frequency according to the grid connection point voltage; Input the output frequency into a notch filter, filter out the influence of the disturbance injected at the last moment on the output frequency, and obtain the output frequency of the notch filter; The output frequency of the notch filter is input into a sliding average filter, integer harmonics in the output frequency of the notch filter are filtered out, and the disturbance injected at the last moment is suppressed to obtain the grid frequency.

4. The method according to claim 1, characterized in that: The disturbance instruction includes a positive sequence disturbance instruction and a negative sequence disturbance instruction; The step of inputting the measured frequency, the disturbance amplitude and the grid frequency into the disturbance control loop to generate a disturbance instruction comprises: The required disturbance instruction is determined according to the impedance measurement requirement. If the required disturbance instruction is a positive-sequence disturbance instruction, a positive-sequence disturbance instruction is generated based on the grid frequency, the measurement frequency and the disturbance amplitude; if the required disturbance instruction is a negative-sequence disturbance instruction, a negative-sequence disturbance instruction is generated based on the grid frequency, the measurement frequency and the disturbance amplitude.

5. The method according to claim 1, characterized in that The step of inputting the controlled grid-connected point voltage, the grid-connected current of the inverter to be tested, the grid frequency, the measurement frequency and the grid current into an impedance calculation unit to generate the impedance of the inverter to be tested and the grid impedance includes: Performing noise reduction processing on the controlled grid-connected point voltage, the grid-connected current of the inverter to be tested, and the grid current 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; Performing disturbance extraction on the intercepted data to generate disturbance extraction data; The impedance of the inverter to be measured and the impedance of the power grid are determined according to the disturbance extraction data.

6. The method according to claim 5, characterized in that The truncating the noise reduction data based on the grid frequency and the measurement frequency to generate intercepted data includes: Determining a cut length based on the grid frequency and the measurement frequency; The noise reduction data is truncated according to the truncation length to obtain truncation data.

7. A multi-inverter grid-connected system, characterized in that: The multi-inverter grid-connected system comprises n parallel inverters and an impedance calculation unit, wherein the n parallel inverters are all connected to a power grid, the nth inverter comprises a fundamental wave and disturbance control unit, and the impedance calculation unit is connected to the inverter to be tested; the fundamental wave and disturbance control unit comprises: 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 instruction according to the grid phase and the grid-connected current of the nth inverter; The disturbance control loop is used to receive the grid frequency, the measurement frequency and the disturbance amplitude, and generate a disturbance instruction according to the grid frequency, the measurement frequency and the disturbance amplitude; The modulation ring is used to generate a control drive signal according to the modulation strategy of the inverter, and control each inverter switch according to the control drive signal; The impedance calculation unit is used to obtain the grid-connected point voltage, the grid-connected current of the inverter to be tested and the grid current after each inverter switch is controlled according to the control drive signal; the controlled grid-connected point voltage, the grid-connected current of the inverter to be tested, the grid frequency, the measurement frequency and the grid current are input into the impedance calculation unit to generate the inverter impedance to be tested 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 obtain the grid-connected point voltage after control, the grid-connected current of the inverter to be tested and the grid current, perform noise reduction processing on the grid-connected point voltage after control, the grid-connected current of the inverter to be tested 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 perform disturbance extraction on 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 extract data according to the disturbance and determine the impedance of the inverter to be tested and the impedance of the power grid.

9. The multi-inverter grid-connected system according to claim 7, characterized in that: The improved phase-locked loop comprises: a power grid frequency detection module and a power grid phase detection module; The grid frequency detection module is used to generate the grid frequency according to the grid connection point voltage; The grid phase detection module is used to generate a grid phase according to 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 according to the grid connection point voltage; The harmonic and disturbance removal unit is used to remove the harmonics in the output power and the disturbance injected at the last moment to generate the grid frequency.

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