Method for measuring broadband impedance of power grid

Abstract

The invention relates to the technical field of power system parameter measurement, and discloses a power grid broadband impedance measurement method, which comprises the following steps of: dividing a target broadband into three complementary or staggered frequency groups, and alternately injecting multi-frequency harmonic current disturbance signals into a three-phase power grid in a cyclic rotation mode, acquiring a node response voltage signal of the three-phase common coupling point and a network side branch disturbance current signal; and frequency spectrum components of voltage and current signals are extracted from the node response voltage signal of the three-phase common coupling point and the network side branch disturbance current signal by adopting a fast Fourier transform method, and node impedance information of the power grid is calculated based on the frequency spectrum components of the voltage and current signals. The power grid impedance is effectively measured, the influence of the frequency response overlapping effect in the impedance measurement process is eliminated, and the measurement speed and precision are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system parameter measurement, and in particular to a method for measuring broadband impedance of a power grid. Background Art

[0002] With the increasing penetration of grid-connected renewable energy sources such as wind and solar power in three-phase systems, the application of power electronic converters has seen explosive growth. However, the complex interaction between the grid and the converter often leads to significant small-signal instability or oscillation. Impedance-based analysis methods have been recognized as an effective means of studying small-signal stability. In this method, grid impedance is a key parameter. Therefore, accurately identifying grid impedance is crucial for stability analysis of grid-connected converter systems.

[0003] Grid impedance identification requires structural assumptions. Traditionally, grid impedance is typically modeled as a series resistor-inductor circuit, or, in complex scenarios, as a multi-conductor network. Due to the unknown topology and parameters of actual grids, deriving their impedance through mathematical models is challenging. Therefore, impedance measurement methods that do not require internal grid information are widely used. Depending on whether external perturbations are applied to the system, impedance measurement methods can be categorized as passive or active. Passive methods suffer from incomplete background signal frequency distribution, a small frequency band, and random frequency. Active measurement methods based on external harmonic perturbation injection inject harmonic perturbations into the system under test and calculate the impedance using the collected response data, offering the advantage of a high signal-to-noise ratio. The generation and injection strategies for harmonic perturbations are central to active measurement.

[0004] Numerous studies have explored various measurement methods based on external disturbance injection. Early impedance measurements used a sinusoidal signal frequency sweep, but this required repeated injections to cover a wide frequency band, resulting in a lengthy measurement time. To overcome this limitation, multi-frequency disturbance injection methods have been widely investigated. For example, impedance measurements are performed by injecting a broadband signal into the control loop of a grid-connected inverter. While this approach, which superimposes broadband signals on the control system of a grid-connected inverter, can reduce measurement costs and enable real-time measurement, it requires access to the grid-connected inverter controller, which poses challenges due to the confidentiality and inaccessibility of converter controller designs. Broadband disturbance injection methods based on external devices, while costly, offer higher accuracy. Power electronic converter injection methods, while complex in topology and control, offer more precise control over disturbance generation and injection. Despite significant advances in grid impedance measurement technology, the issue of response frequency aliasing is often overlooked when simultaneously injecting the same disturbance into three phases in a multi-conductor grid model. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for measuring the broadband impedance of a power grid, which can effectively measure the impedance of the power grid, eliminate the influence of the frequency response overlap effect during the impedance measurement process, and improve the measurement speed and accuracy.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: A method for measuring broadband impedance of a power grid comprises the following steps: The target wide frequency band is divided into three complementary or interleaved frequency groups. Multi-frequency harmonic disturbance signals are injected into the three-phase power grid in a cyclic rotation manner. The node response voltage signal at the three-phase common coupling point and the grid-side branch disturbance current signal are collected. The fast Fourier transform method is used to extract the spectral components of the voltage and current signals from the node response voltage signal of the three-phase common coupling point and the grid-side branch disturbance current signal, and the node impedance information of the power grid is calculated based on the spectral components of the voltage and current signals.

[0007] Furthermore, the target wide frequency band is divided into three complementary frequency groups, including: Set the frequency range to [ f min , f max ] is divided into three groups of continuous and equally spaced harmonic disturbance signals: F 1=[ f i1 , f e1 ]、 F 2=[ f i2 , f e2 ]and F 3=[ f i3 , f e3 ], set the frequency resolution to Δ f ,in f i1 equal f min , f i2 equal f e1 +Δ f , f i3 equal f e2 +Δ f , f e3 equal f max .

[0008] Furthermore, three groups of continuously equally spaced harmonic disturbance signals are:

[0009] in, i p,F1 is the first group of broadband harmonic current disturbances, i p,F2 is the second group of broadband harmonic current disturbances, i p,F3 is the third group of broadband harmonic current disturbances, I m is the disturbance amplitude at each frequency point, N 1 is the frequency point number of the first group of broadband harmonic disturbances, N 2 is the frequency point number of the second group of broadband harmonic disturbances, N 3 is the frequency point number of the third group of broadband harmonic disturbance, f i1 is the starting frequency, i is the frequency point number, Δ f is the frequency resolution, t For time.

[0010] Furthermore, the target wide frequency band is divided into three interleaved frequency groups, including: Set the frequency range to [ f min , f max The harmonic signals of ] are divided into three groups of harmonic disturbance signals with equal frequency resolution and interlaced: F 1=[ f 1, f 4. f 7,…, f 3n-2 ]、 F 2=[ f 2, f 5. f 8,…, f 3n-1 ]and F 3=[ f 3. f 6. f 9,…, f 3n ],in f n = f min + n Δ f , n is the frequency point number.

[0011] Furthermore, the three sets of harmonic disturbance signals with equal frequency resolution and interleaving are:

[0012] in, i p,F1 is the first group of broadband harmonic current disturbances, i p,F2 is the second group of broadband harmonic current disturbances, i p,F3 is the third group of broadband harmonic current disturbances, I m is the disturbance amplitude at each frequency point, N 1 is the frequency point number of the first group of broadband harmonic disturbances, N 2 is the frequency point number of the second group of broadband harmonic disturbances, N 3 is the frequency point number of the third group of broadband harmonic disturbance, f 0 is the starting frequency, i is the frequency point number, Δ f is the frequency resolution, t For time.

[0013] Furthermore, a multi-frequency harmonic current disturbance signal is alternately injected into the three-phase power grid in a cyclic rotation manner, including: First injection F 1. F 2 and F 3. Broadband harmonic current disturbance signals of three frequency bands are sent to the three-phase A, B, and C of the three-phase power grid; The second injection F 2. F 3 and F 1. Broadband harmonic current disturbance signals of three frequency bands are sent to the three-phase A, B, and C of the three-phase power grid; The third injection F 3. F 1 and F 2 Three frequency bands of broadband harmonic current disturbance signals are transmitted to the three-phase A, B, and C of the three-phase power grid.

[0014] Furthermore, a fast Fourier transform method is used to extract the spectral components of the voltage and current signals from the node response voltage signal of the three-phase common coupling point and the grid-side branch disturbance current signal, and the node impedance information of the power grid is calculated based on the spectral components of the voltage and current signals, including: The fast Fourier transform method is used to extract the spectral components of the voltage and current signals from the node response voltage signal of the three-phase common coupling point and the grid-side branch disturbance current signal collected for the first time, and the impedance information is calculated; The fast Fourier transform method is used to extract the spectral components of the voltage and current signals from the node response voltage signal of the three-phase common coupling point and the grid-side branch disturbance current signal collected for the second time, and the impedance information is calculated; The fast Fourier transform method is used to extract the spectral components of the voltage and current signals from the node response voltage signal of the three-phase common coupling point and the grid-side branch disturbance current signal collected for the third time, and the impedance information is calculated.

[0015] Furthermore, the node impedance information of the power grid is calculated as follows:

[0016] in, v pa 、 v pb 、 v pc The node response voltage signal of the three-phase common coupling point is i gpa 、 i gpb 、 i gpc is the disturbance current signal of the grid-side branch at the three-phase common coupling point, Z AA 、 Z BB 、 Z CC , Z AB 、 Z BC 、 Z CA is the phase-to-phase mutual impedance of phases A, B, and C of the three-phase grid, oh p is the disturbance frequency.

[0017] Furthermore, a three-phase multi-frequency harmonic disturbance generating device based on a cascaded H-bridge is used to generate a multi-frequency harmonic disturbance signal; the three-phase multi-frequency harmonic disturbance generating device based on the cascaded H-bridge includes three independent harmonic disturbance generating units and a step-down transformer, the harmonic disturbance generating unit includes a cascaded H-bridge of N modules, and the output end of the cascaded H-bridge in each harmonic disturbance generating unit is connected in parallel to the power grid through a step-down transformer.

[0018] Furthermore, the three-phase multi-frequency harmonic disturbance generating device based on the cascaded H-bridge is controlled by a power control layer, a voltage balance control layer and a multi-frequency harmonic control layer; The power control layer adopts a dual closed-loop control strategy, including a DC voltage outer loop, a single-phase phase-locked loop, and an AC current inner loop. The single-phase phase-locked loop provides a phase reference for the entire control system, while the DC voltage outer loop and AC current inner loop regulate the power absorption of the grid and control the DC side voltage. The voltage balance control layer is used to balance the DC side voltage of each sub-module of the cascaded H-bridge; The multi-frequency harmonic control layer includes a quasi-resonant controller and a fundamental frequency notch filter; the quasi-resonant controller is used to track multi-sinusoidal signals without static error, and the fundamental frequency notch filter is used to suppress the interference of the fundamental component on the broadband disturbance output; The fundamental modulation signal output by the power control, the voltage balance control signal and the multi-frequency harmonic control signal are superimposed, and the switch control signal of the cascaded H-bridge sub-module is generated through carrier phase-shift pulse width modulation.

[0019] The present invention has the following beneficial effects: (1) Based on the inter-phase coupling and frequency response overlap phenomena that occur in the three-phase power grid impedance measurement, the present invention designs three groups of disturbances with different frequencies to be injected alternately, avoiding the response overlap caused by the simultaneous injection of disturbances with the same frequency, and making the measurement results more accurate.

[0020] (2) The present invention uses three sets of complementary / interleaved multi-frequency harmonic disturbances to achieve alternating harmonic disturbance injection, which makes the measurement speed faster.

[0021] (3) The method proposed in the present invention can realize the grid impedance measurement of the resistance-inductance series model and the grid impedance measurement of the distributed transmission line model, and the measurement scenario is more comprehensive.

[0022] (4) The multi-frequency harmonic disturbance device based on the cascade H-bridge topology designed by the present invention generates a broadband harmonic current disturbance with flexible and controllable concentrated frequency band and uniform amplitude distribution through the superposition control loop of multiple sinusoidal signals. At the same time, the cascade H-bridge topology has high output voltage resolution, low switching stress and high equivalent switching frequency. It is connected to the three-phase power grid through a broadband transformer, which reduces the withstand voltage requirement of the cascade H-bridge and realizes safe coupling. It adopts a parallel access method, which has little impact on the stability of the system under test and is easy to implement in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a structural diagram of a three-phase power grid broadband impedance measurement system based on harmonic disturbance injection; Figure 2 This is a flow chart of a three-phase power grid broadband impedance measurement method based on harmonic disturbance injection; Figure 3 The topological structure diagram and grid connection diagram of the multi-frequency harmonic disturbance device suitable for three-phase system impedance measurement; Figure 4 This is a control block diagram of a cascaded H-bridge in a multi-frequency harmonic disturbance device. DETAILED DESCRIPTION

[0024] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0025] like Figure 1 The figure shows the structure of a three-phase power grid broadband impedance measurement system based on harmonic disturbance injection provided by the present invention. The system consists of a measured power grid, a parallel harmonic current disturbance source, and a three-phase load. The measured power grid includes a three-phase power supply and its equivalent impedance, and the power grid impedance is equivalent to a multi-conductor model. The self-impedance of each phase is defined as Z aa 、 Z bb 、 Z cc , Z ab 、 Z bc 、 Z ca is the phase-to-phase mutual impedance. i pa 、 i pb 、 i pc is the harmonic current disturbance injected into the system.

[0026] like Figure 2 The figure shows a flow chart of a method for measuring broadband impedance of a three-phase power grid based on harmonic disturbance injection provided by the present invention. A method for measuring broadband impedance of a power grid comprises the following steps: The target wide frequency band is divided into three complementary or interleaved frequency groups. Multi-frequency harmonic current disturbance signals are injected into the three-phase power grid in a cyclic rotation manner. The node response voltage signal at the three-phase common coupling point and the grid-side branch disturbance current signal are collected. The fast Fourier transform method is used to extract the spectral components of the voltage and current signals from the node response voltage signal of the three-phase common coupling point and the grid-side branch disturbance current signal, and the node impedance information of the power grid is calculated based on the spectral components of the voltage and current signals.

[0027] When the same frequency harmonic disturbance signal is injected into the three-phase power grid impedance measurement, frequency response overlap and phase coupling effects will occur. For example, when the frequency of the A phase is injected into the f pWhen harmonic current is disturbed, due to the interphase coupling, corresponding frequency components will appear in phases B and C. If the harmonic disturbance of the same frequency is injected into the three phases at the same time, the voltage response will overlap in spectrum, resulting in the inability to extract the effective response component, which will cause measurement ambiguity and reduce the accuracy of impedance estimation. The traditional method can be achieved by injecting the same frequency into phases A, B, and C respectively. f p , respectively collect the voltage and current data after the disturbance injection, extract the relevant spectrum components through FFT, and calculate the impedance according to the following three formulas to obtain the 3×3 impedance matrix of the three-phase power grid.

[0028] The calculation formula when injecting phase A is:

[0029] in, v pa 、 v pb 、 v pc The node response voltage signal of the three-phase common coupling point is i gpa is the grid-side branch disturbance current signal of the common coupling point of phase A, Z AA 、 Z BB 、 Z CC , Z AB 、 Z BC 、 Z CA is the phase-to-phase mutual impedance of phases A, B, and C of the three-phase grid, oh p is the disturbance frequency.

[0030] The calculation formula when injecting phase B is:

[0031] in, i gpb It is the grid-side branch disturbance current signal of the common coupling point of phase B.

[0032] The calculation formula when injecting phase C is:

[0033] in, i gpc It is the grid-side branch disturbance current signal of the C-phase common coupling point.

[0034] However, this method requires three independent harmonic injections, which is a complex and time-consuming process. In order to improve the measurement speed while avoiding the influence of frequency response overlap, different frequencies are injected into phases A, B, and C respectively ( f 1. f 2. f 3) harmonic disturbances, and two rounds of alternating frequency injection effectively avoid frequency overlap. By alternating the phases of the injected frequencies, frequency response overlap is avoided and multi-frequency grid impedance measurement is achieved. Expanding a single frequency signal to a broadband signal enables fast and accurate grid impedance measurement.

[0035] The design method of the broadband harmonic disturbance signal in the present invention is: set the frequency range to [ f min , f max ] is divided into three groups of continuous and equally spaced harmonic disturbance signals: F 1=[ f i1 , f e1 ]、 F 2=[ f i2 , f e2 ]and F 3=[ f i3 , f e3 ], set the frequency resolution to Δ f ,in f i1 equal f min , f i2 equal f e1 +Δ f , f i3 equal f e2 +Δ f , f e3 equal f max ; or divide the disturbance frequency band into three groups of harmonic disturbance signals with equal frequency resolution and interlaced: F 1=[ f 1, f 4. f 7,…, f 3n-2 ]、 F 2=[ f 2, f 5. f 8,…,f 3n-1 ]and F 3=[ f 3. f 6. f 9,…, f 3n ],in f n = f min + n Δ f .

[0036] Using multi-sinusoidal signals as the reference signal of harmonic disturbance, its mathematical expression is:

[0037] in, m is the harmonic reference signal modulation ratio, f 0 is the starting frequency, Δ f is the frequency resolution, N h is the number of perturbation frequency points, π ( i -1) 2 / N h is the phase at each frequency point.

[0038] According to the multi-sinusoidal signal expression, the expressions of the three designed harmonic disturbance signals with equal intervals can be obtained as follows:

[0039] in, i p,F1 is the first group of broadband harmonic current disturbances, i p,F2 is the second group of broadband harmonic current disturbances, i p,F3 is the third group of broadband harmonic current disturbances, I m is the disturbance amplitude at each frequency point, N 1 is the frequency point number of the first group of broadband harmonic disturbances, N 2 is the frequency point number of the second group of broadband harmonic disturbances, N 3 is the frequency point number of the third group of broadband harmonic disturbance, f i1 is the starting frequency, i is the frequency point number, Δ f is the frequency resolution, t For time.

[0040] The expressions of three groups of harmonic disturbance signals with equal frequency resolution and interleaving are:

[0041] in, i p,F1 is the first group of broadband harmonic current disturbances, i p,F2 is the second group of broadband harmonic current disturbances, i p,F3 is the third group of broadband harmonic current disturbances, I m is the disturbance amplitude at each frequency point, N 1 is the frequency point number of the first group of broadband harmonic disturbances, N 2 is the frequency point number of the second group of broadband harmonic disturbances, N 3 is the frequency point number of the third group of broadband harmonic disturbance, f 0 is the starting frequency, i is the frequency point number, Δ f is the frequency resolution, t For time.

[0042] The disturbance injection method adopted by the present invention is: First injection F 1. F 2 and F 3. Send three-band broadband harmonic current disturbance signals to phases A, B, and C to collect disturbance currents. i gpa 、 i gpb 、 i gpc , and the corresponding response voltage v pa 、 v pb 、 v pc , use FFT to extract the spectral components of the voltage and current responses i gpa ( oh 1) i gpb ( oh 2) i gpc ( oh 3) v pa ( oh 1) v pb ( oh 1) v pc ( oh 1) v pa ( oh 2) vpb ( oh 2) v pc ( oh 2) v pa ( oh 3) v pb ( oh 3) and v pc ( oh 3) Calculate the impedance information according to the following formula:

[0043] The impedance is calculated [ Z AA ( oh 1) Z BA ( oh 1) Z CA ( oh 1)] T 、[ Z AB ( oh 2) Z BB ( oh 2) Z CB ( oh 2)] T and[ Z AC ( oh 3) Z BC ( oh 3) Z CC ( oh 3)] T .

[0044] The second injection F 2. F 3 and F 1 to collect disturbance current in phases A, B, and C i gpa 、 i gpb 、 i gpc , and the corresponding response voltage v pa 、 v pb 、 v pc , use FFT to extract the spectral components of the voltage and current responses igpa ( oh 2) i gpb ( oh 3) i gpc ( oh 1) v pa ( oh 2) v pb ( oh 2) v pc ( oh 2) v pa ( oh 3) v pb ( oh 3) v pc ( oh 3) v pa ( oh 1) v pb ( oh 1) and v pc ( oh 1) Calculate the impedance information according to the following formula:

[0045] The impedance is calculated [ Z AA ( oh 2) Z BA ( oh 2) Z CA ( oh 2)] T 、[ Z AB ( oh 3) Z BB ( oh 3) Z CB ( oh 3)] T and[ Z AC ( oh 1) Z BC ( oh 1) Z CC ( oh 1)] T .

[0046] The third injection F 3. F 1 and F 2. Collect disturbance current in phases A, B, and C i gpa 、 i gpb 、 i gpc , and the corresponding response voltage v pa 、 v pb 、 v pc , use FFT to extract the spectral components of the voltage and current responses i gpa ( oh 3) i gpb ( oh 1) i gpc ( oh 2) v pa ( oh 3) v pb ( oh 3) v pc ( oh 3) v pa ( oh 1) v pb ( oh 1) v pc ( oh 1) v pa ( oh 2) v pb ( oh 2) and v pc ( oh 2) Calculate the impedance information according to the following formula:

[0047] The impedance is calculated [ Z AA ( oh 3) Z BA ( oh 3) Z CA ( oh 3)]T 、[ Z AB ( oh 1) Z BB ( oh 1) Z CB ( oh 1)] T and[ Z AC ( oh 2) Z BC ( oh 2) Z CC ( oh 2)] T .

[0048] The present invention avoids frequency response overlap effect and completes multi-frequency point power grid impedance measurement by alternately injecting the phases of the frequencies.

[0049] In order to realize the generation of the desired harmonic current disturbance signal, a three-phase multi-frequency harmonic disturbance generating device based on cascaded H-bridge is designed. Figure 3 As shown in Figure 1, the measurement system includes the measured power grid, a multi-frequency harmonic disturbance generator, and voltage and current sensors. The device mainly consists of three independent units and a step-down transformer. Each unit is composed of a cascaded H-bridge consisting of N modules. The output end of the cascaded H-bridge is connected to the power grid in parallel through three single-phase step-down transformers. L A 、 L B ,and L C Located on the output side of each cascaded H-bridge unit, C aN 、 C bN ,and C cN The three corresponding cascade H-bridge DC side capacitors are A, B, and C respectively. One port on the high-voltage side of the three transformers is connected in parallel to the common coupling point of the A, B, and C phase power grids, and the other ports are connected to each other and grounded. The low-voltage sides of the step-down transformers are all connected to the output side of the harmonic generation unit based on the cascade H-bridge. The structural characteristics of the device include: (1) the cascade H-bridge topology has high output voltage resolution, low switching stress and high equivalent switching frequency; (2) it is connected to the three-phase power grid through a wide-band transformer, which reduces the withstand voltage requirement of the cascade H-bridge and achieves safe coupling; (3) the parallel connection method has minimal impact on the stability of the system under test and is easy to implement in engineering.

[0050] The control of broadband harmonic disturbance device mainly consists of three parts, such as Figure 4 Figure 1 shows power control, voltage balance control, and multi-frequency harmonic control. The power control layer employs a dual closed-loop control strategy, consisting of a DC voltage outer loop, a single-phase phase-locked loop (PLL), and an AC current inner loop. The PLL provides a phase reference for the entire control system. The dual closed-loop control strategy regulates the grid's power absorption and controls the DC side voltage. Voltage balance control balances the DC side voltages of the cascaded H-bridge submodules. Multi-frequency harmonic control includes a quasi-resonant (QR) controller and a fundamental frequency notch filter. The QR controller tracks multi-sinusoidal signals without static error, while the fundamental frequency notch filter suppresses interference from the fundamental component on the broadband disturbance output. Finally, the fundamental modulation signal output by the power control, the voltage balance control signal, and the multi-frequency harmonic control signal are superimposed to generate the switching control signals for the cascaded H-bridge submodules through carrier phase-shift pulse width modulation (CPS-PWM).

[0051] In summary, based on the inter-phase coupling and frequency response aliasing phenomena that occur in three-phase power grid impedance measurement, the present invention proposes a power grid impedance measurement method that effectively avoids frequency response aliasing. In order to achieve faster impedance measurement, a three-phase power grid impedance matrix fast broadband measurement method based on multi-sinusoidal signal disturbance injection is proposed. In order to achieve the generation of harmonic disturbances with flexible and controllable frequency bands and uniform amplitude distribution, a multi-frequency harmonic disturbance device based on cascaded H-bridge topology is designed. Through the proposed power grid fast impedance measurement method and device, the power grid impedance under wide frequency can be obtained quickly and accurately. It provides technical guidance and equipment support for impedance measurement in the field of power systems.

[0052] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure one a process or multiple processes and / or boxes Figure one A device that provides the functions specified in a block or multiple blocks.

[0053] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure one a process or multiple processes and / or boxes Figure one The function specified in one or more boxes.

[0054] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure one a process or multiple processes and / or boxes Figure one The steps for the function specified in one or more boxes.

[0055] Specific embodiments are used in the present invention to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas. At the same time, for those skilled in the art, according to the ideas of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

[0056] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific descriptions and embodiments. Those skilled in the art can make various other specific variations and combinations based on the technical teachings disclosed in the present invention without departing from the essence of the present invention, and such variations and combinations are still within the scope of protection of the present invention.

Claims

1. A method for measuring broadband impedance of a power grid, characterized in that: The following steps are involved: The target wide frequency band is divided into three complementary or interleaved frequency groups. Multi-frequency harmonic current disturbance signals are injected into the three-phase power grid in a cyclic rotation manner. The node response voltage signal at the three-phase common coupling point and the grid-side branch disturbance current signal are collected. The fast Fourier transform method is used to extract the spectral components of the voltage and current signals from the node response voltage signal of the three-phase common coupling point and the grid-side branch disturbance current signal, and the node impedance information of the power grid is calculated based on the spectral components of the voltage and current signals.

2. A method for measuring broadband impedance of a power grid according to claim 1, characterized in that: The target wide frequency band is divided into three complementary frequency groups, including: Set the frequency range to [ f min , f max ] is divided into three groups of continuous and equally spaced harmonic disturbance signals: F 1=[ f i1 , f e1 ]、 F 2=[ f i2 , f e2 ]and F 3=[ f i3 , f e3 ], set the frequency resolution to Δ f ,in f i1 equal f min , f i2 equal f e1 +Δ f , f i3 equal f e2 +Δ f , f e3 equal f max .

3. A method for measuring broadband impedance of a power grid according to claim 2, characterized in that: Three groups of continuously equally spaced harmonic disturbance signals are: in, i p,F1 is the first group of broadband harmonic current disturbances, i p,F2 is the second group of broadband harmonic current disturbances, i p,F3 is the third group of broadband harmonic current disturbances, I m is the disturbance amplitude at each frequency point, N 1 is the frequency point number of the first group of broadband harmonic disturbances, N 2 is the frequency point number of the second group of broadband harmonic disturbances, N 3 is the frequency point number of the third group of broadband harmonic disturbance, f i1 is the starting frequency, i is the frequency point number, Δ f is the frequency resolution, t For time.

4. A method for measuring broadband impedance of a power grid according to claim 1, characterized in that: Divide the target wide frequency band into three interleaved frequency groups, including: Set the frequency range to [ f min , f max The harmonic signals of ] are divided into three groups of harmonic disturbance signals with equal frequency resolution and interlaced: F 1=[ f 1, f 4. f 7,…, f 3n-2 ]、 F 2=[ f 2, f 5. f 8,…, f 3n-1 ]and F 3=[ f 3. f 6. f 9,…, f 3n ],in f n = f min + n Δ f , n is the frequency point number.

5. A method for measuring broadband impedance of a power grid according to claim 4, characterized in that: The three sets of harmonic disturbance signals with equal frequency resolution and interleaving are: in, i p,F1 is the first group of broadband harmonic current disturbances, i p,F2 is the second group of broadband harmonic current disturbances, i p,F3 is the third group of broadband harmonic current disturbances, I m is the disturbance amplitude at each frequency point, N 1 is the frequency point number of the first group of broadband harmonic disturbances, N 2 is the frequency point number of the second group of broadband harmonic disturbances, N 3 is the frequency point number of the third group of broadband harmonic disturbance, f 0 is the starting frequency, i is the frequency point number, Δ f is the frequency resolution, t For time.

6. A method for measuring broadband impedance of a power grid according to claim 1, characterized in that: The multi-frequency harmonic current disturbance signal is injected alternately into the three-phase power grid in a cyclic rotation manner, including: First injection F 1. F 2 and F 3. Broadband harmonic current disturbance signals of three frequency bands are sent to the three-phase A, B, and C of the three-phase power grid; The second injection F 2. F 3 and F 1. Broadband harmonic current disturbance signals of three frequency bands are sent to the three-phase A, B, and C of the three-phase power grid; The third injection F 3. F 1 and F 2 Three frequency bands of broadband harmonic current disturbance signals are transmitted to the three-phase A, B, and C of the three-phase power grid.

7. A method for measuring broadband impedance of a power grid according to claim 1, characterized in that: The fast Fourier transform method is used to extract the spectral components of the voltage and current signals from the node response voltage signal of the three-phase common coupling point and the grid-side branch disturbance current signal. The node impedance information of the power grid is calculated based on the spectral components of the voltage and current signals, including: The fast Fourier transform method is used to extract the spectral components of the voltage and current signals from the node response voltage signal of the three-phase common coupling point and the grid-side branch disturbance current signal collected for the first time, and the impedance information is calculated; The fast Fourier transform method is used to extract the spectral components of the voltage and current signals from the node response voltage signal of the three-phase common coupling point and the grid-side branch disturbance current signal collected for the second time, and the impedance information is calculated; The fast Fourier transform method is used to extract the spectral components of the voltage and current signals from the node response voltage signal of the three-phase common coupling point and the grid-side branch disturbance current signal collected for the third time, and the impedance information is calculated.

8. A method for measuring broadband impedance of a power grid according to claim 1, characterized in that: The calculation method of the node impedance information of the power grid is: in, v pa 、 v pb 、 v pc The node response voltage signal of the three-phase common coupling point is i gpa 、 i gpb 、 i gpc is the disturbance current signal of the grid-side branch at the three-phase common coupling point, Z AA 、 Z BB 、 Z CC , Z AB 、 Z BC 、 Z CA is the phase-to-phase mutual impedance of phases A, B, and C of the three-phase grid, ω p is the disturbance frequency, Z g is the grid impedance.

9. The method for measuring broadband impedance of a power grid according to claim 1, wherein: A three-phase multi-frequency harmonic disturbance generating device based on a cascaded H-bridge is used to generate a multi-frequency harmonic disturbance signal. The three-phase multi-frequency harmonic disturbance generating device based on the cascaded H-bridge includes three independent harmonic disturbance generating units and a step-down transformer. The harmonic disturbance generating unit includes a cascaded H-bridge of N modules. The output end of the cascaded H-bridge in each harmonic disturbance generating unit is connected in parallel to the power grid through a step-down transformer.

10. A method for measuring broadband impedance of a power grid according to claim 9, characterized in that: The three-phase multi-frequency harmonic disturbance generator based on cascaded H-bridge is controlled by power control layer, voltage balance control layer and multi-frequency harmonic control layer; The power control layer adopts a dual closed-loop control strategy, including a DC voltage outer loop, a single-phase phase-locked loop, and an AC current inner loop. The single-phase phase-locked loop provides a phase reference for the entire control system, while the DC voltage outer loop and AC current inner loop regulate the power absorption of the grid and control the DC side voltage. The voltage balance control layer is used to balance the DC side voltage of each sub-module of the cascaded H-bridge; The multi-frequency harmonic control layer includes a quasi-resonant controller and a fundamental frequency notch filter; the quasi-resonant controller is used to track multi-sinusoidal signals without static error, and the fundamental frequency notch filter is used to suppress the interference of the fundamental component on the broadband disturbance output; The fundamental modulation signal output by the power control, the voltage balance control signal and the multi-frequency harmonic control signal are superimposed, and the switch control signal of the cascaded H-bridge sub-module is generated through carrier phase-shift pulse width modulation.

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