Method, device, related equipment and storage medium for measuring power grid impedance

Abstract

The present application discloses a method, device, related equipment and storage medium for measuring the impedance of a power grid; the method includes: synchronously injecting a harmonic signal into the modulation signal of an inverter based on a common clock signal; when the sampled current on the AC power grid side is greater than or equal to a set threshold, determining the harmonic current corresponding to the harmonic signal based on a plurality of sampled currents; wherein, the sampled current is obtained by performing Clarke transformation on three-phase alternating current; determining the impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current and the total number of parallel-operating inverters.

Description

Technical Field

[0001] The present application relates to the field of electronic power technology, and particularly to a method, device, related equipment and storage medium for measuring the impedance of a power grid. Background Art

[0002] In related technologies, various types of power generation systems such as wind turbines, photovoltaic panels, and fuel cells all need to be connected to the AC power grid through an inverter for grid connection and power transmission to the AC power grid. Due to the impedance existing on the transmission line of the power grid and various power transmission equipment possibly existing on the transmission line, the power grid connected by the inverter through the grid connection point (the connection point between the inverter and the AC power grid) is not an ideal power grid. It is generally considered that the inverter is connected to the AC power grid through an equivalent impedance.

[0003] In view of the fact that the equivalent impedance is located in the equivalent control loop of the inverter, in order to enable the entire system to operate safely and stably, it is necessary to measure the value of the equivalent impedance and adjust the operating parameters of the inverter in real time according to the value of the equivalent impedance. In related technologies, the value of the equivalent impedance is measured by injecting a disturbance current into the power grid, but for the scenario where at least two parallel inverters are connected to the AC power grid, the measured equivalent impedance is inaccurate. Summary of the Invention

[0004] In view of this, embodiments of the present application provide a method, device, related equipment and storage medium for measuring the impedance of a power grid.

[0005] To achieve the above object, the technical solution of the present application is implemented as follows:

[0006] Embodiments of the present application provide a method for measuring the impedance of a power grid, including:

[0007] Synchronously injecting a harmonic signal into the modulation signal of the inverter based on a common clock signal;

[0008] When the sampled current on the AC power grid side is greater than or equal to a set threshold, determining the harmonic current corresponding to the harmonic signal based on a plurality of sampled currents; wherein, the sampled current is obtained by performing Clarke transformation on three-phase alternating current;

[0009] Determining the impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and the total number of inverters operating in parallel.

[0010] In the above solution, the method further includes:

[0011] When the sampled current is less than the set threshold, increasing the voltage amplitude of the harmonic signal by a set step length, and synchronously injecting the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal.

[0012] In the above solution, the frequency of the harmonic signal does not coincide with the frequency of the set Nth harmonic.

[0013] In the above solution, the harmonic signal includes at least one group of harmonics with the same voltage amplitude. Each group of harmonics includes a first harmonic and a second harmonic, and the frequency of the first harmonic is symmetric with respect to the frequency of the second harmonic about the frequency of the set Nth harmonic.

[0014] In the above solution, determining the harmonic current corresponding to the harmonic signal based on multiple sampled currents includes: performing a Fourier transform on the multiple sampled currents based on the expression of the harmonic signal to obtain the harmonic current corresponding to each group of harmonics in the harmonic signal.

[0015] In the above solution, the harmonic current corresponding to each group of harmonics includes a first harmonic current corresponding to the first harmonic and a second harmonic current corresponding to the second harmonic; determining the impedance of the AC power grid includes:

[0016] Determining a first impedance value based on the voltage amplitude of the first harmonic, and based on the first harmonic current corresponding to the first harmonic and the total number of parallel-operating inverters;

[0017] Determining a second impedance value based on the voltage amplitude of the second harmonic, and based on the second harmonic current corresponding to the second harmonic and the total number of parallel-operating inverters;

[0018] Determining the mean value between the determined first impedance value and the determined second impedance value as the impedance of the AC power grid.

[0019] In the above solution, determining the impedance of the AC power grid includes:

[0020] Determining the impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, the total number of parallel-operating inverters, and based on the impedance of the filter; wherein, the filter is located between the inverter and the AC power grid.

[0021] An embodiment of the present application further provides a device for measuring the impedance of a power grid, characterized by including:

[0022] A signal injection module, configured to synchronously inject a harmonic signal into the modulation signal of the inverter based on a common clock signal;

[0023] A first determination module, configured to determine the harmonic current of the harmonic signal based on multiple sampled currents when the sampled current on the AC power grid side is greater than or equal to a set threshold; wherein, the sampled current is obtained by performing a Clarke transform on the three-phase alternating current.

[0024] A second determination module, configured to determine the impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and the total number of inverters operating in parallel.

[0025] An embodiment of the present application further provides a controller, including: a processor and a memory for storing a computer program that can run on the processor,

[0026] wherein, when the processor is used to run the computer program, it executes the steps of the above-mentioned method for measuring the impedance of the power grid.

[0027] An embodiment of the present application further provides a storage medium, on which a computer program is stored, characterized in that when the computer program is executed by a processor, it implements the steps of the method for measuring the impedance of the power grid.

[0028] In the embodiment of the present application, a harmonic signal is synchronously injected into the modulation signal of the inverter based on a common clock signal. When the sampled current on the AC power grid side is greater than or equal to a set threshold, the harmonic current corresponding to the harmonic signal is determined based on a plurality of sampled currents; based on the voltage amplitude of the harmonic signal, the determined harmonic current, and the total number of inverters operating in parallel, the value of the impedance of the AC power grid is determined. Thus, the controller of each inverter operating in parallel in the grid-connected system synchronously injects a harmonic signal into the modulation signal of the corresponding inverter based on the common clock signal, which can ensure that the timing of injecting the harmonic signal into each inverter operating in parallel is synchronized, and there will be no situation where the harmonic signal injected into a certain inverter affects the control signal of the inverter that has not been injected with the harmonic signal, nor will there be a situation where the harmonic signals injected into different inverters cancel each other out on the power grid impedance, making the calculated power grid impedance more accurate. Description of the Drawings

[0029] Figure 1 Schematic diagram for measuring the impedance of the power grid in the related art;

[0030] Figure 2 Schematic diagram of the implementation process of the method for measuring the impedance of the power grid provided by the embodiment of the present application;

[0031] Figure 3 Schematic diagram of the grid-connected system provided by the embodiment of the present application;

[0032] Figure 4 Schematic diagram of the grid-connected system provided by another embodiment of the present application;

[0033] Figure 5 Schematic diagram of the implementation process of the method for measuring the impedance of the power grid provided by the application embodiment of the present application;

[0034] Figure 6 Schematic diagram of the structure of the device for measuring the impedance of the power grid provided by the embodiment of the present application;

[0035] Figure 7 This is a schematic diagram of the hardware composition structure of the controller provided by the embodiment of the present application. Specific embodiments

[0036] In the related art, in the scenario where at least two parallel-connected inverters are connected to the AC power grid, a disturbance current is injected into the modulation signal of one of the inverters. For example, Figure 1 As shown, a disturbance current is injected into the modulation signal of inverter 1. The injected disturbance current generates a response voltage on the equivalent impedance Zg of the AC power grid. Based on the response voltage and the injected disturbance current, the value of the equivalent impedance of the AC power grid is calculated. Among them, the connection point between the inverter and the AC power grid is the point of common coupling (PCC), also known as the grid connection point.

[0037] However, after injecting the disturbance current into the control signal of inverter 1, part of the disturbance current will flow into other inverters, resulting in inaccurate obtained response voltage, and further resulting in inaccurate value of the equivalent impedance calculated by the response voltage and the injected disturbance current.

[0038] Based on this, the embodiment of the present application provides a method for measuring the grid impedance. A harmonic signal is synchronously injected into the modulation signal of the inverter based on a common clock signal. When the sampled current on the AC power grid side is greater than or equal to the set threshold, the harmonic current corresponding to the harmonic signal is determined based on multiple sampled currents; based on the voltage amplitude of the harmonic signal, the determined harmonic current, and the total number of parallel-operating inverters, the value of the impedance of the AC power grid is determined. Thus, the controller of each inverter in the grid-connected system synchronously injects a harmonic signal into the modulation signal of the inverter based on a common clock signal, and there will be no situation where the harmonic signal injected into a certain inverter affects the control signal of the inverter that has not been injected with the harmonic signal, nor will there be a situation where the harmonic signals injected into different inverters cancel each other out on the grid impedance, improving the accuracy of the calculated grid impedance.

[0039] In order to make the purpose, technical solution and advantages of the present application clearer, the present application will be further described in detail below with reference to 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.

[0040] Figure 2 This is a schematic diagram of the implementation process of the method for measuring the grid impedance provided by the embodiment of the present application. Among them, the method for measuring the grid impedance is applied to a grid-connected system in which M inverters are connected in parallel, and M is an integer greater than or equal to 2; the execution subject of the process is the controller, and the controller is used to control the inverter, and each inverter corresponds to a controller. For example, Figure 3As shown, the controller can be disposed in the inverter. As Figure 2 shown, the method for measuring the grid impedance includes:

[0041] Step 201: Synchronously inject a harmonic signal into the modulation signal of the inverter based on a common clock signal.

[0042] Here, in the stationary coordinate system, the controller synchronously injects a harmonic signal into the modulation signal of the inverter based on the common clock signal to control the operation of the inverter by means of the modulation signal injected with the harmonic signal. Among them, the stationary coordinate system includes a two-phase stationary αβ coordinate system, simply referred to as the αβ coordinate system; the αβ coordinate system includes an α axis and a β axis. In some embodiments, the stationary coordinate system may further include an o axis, that is, a zero axis. In the embodiments of the present application, the impedance of the AC grid to be calculated includes at least the grid impedance Z α of the α axis and the grid impedance Z β of the β axis; in the case where the o axis is further included in the stationary coordinate system, the impedance of the AC grid further includes the grid impedance Z o of the o axis.

[0043] It should be noted that all the inverters operating in parallel in the grid-connected system inject the same harmonic signal in the same axis. The harmonic signal injected by the same inverter in the α axis and the harmonic signal injected in the β axis may be the same or different.

[0044] Considering each axis in the stationary coordinate system, the method for synchronously injecting a harmonic signal into the modulation signal of the inverter based on the common clock signal and calculating the grid impedance of the corresponding axis is similar. The following takes the case of injecting a harmonic signal in the α axis in the αβ coordinate system and calculating the grid impedance Z α of the α axis as an example for illustration.

[0045] The controller sets a moment in the common clock signal and synchronously injects a harmonic signal into the modulation signal of the corresponding inverter in the α axis.

[0046] Among them, the set moment may be the arrival moment of the rising edge or the falling edge of the Kth pulse in the common clock signal; K is a positive integer. Injecting a harmonic signal into the modulation signal of the inverter means superimposing a harmonic signal on the modulation signal of the inverter. The injected harmonic signal is a harmonic voltage signal, and the harmonic signal may be a cosine wave signal.

[0047] In this embodiment, the controller of each inverter operating in parallel in the grid-connected system synchronously injects a harmonic signal into the modulation signal of the corresponding inverter based on the common clock signal, which can ensure the synchronization of the timing of injecting the harmonic signal for each inverter operating in parallel, thereby avoiding the situation where the harmonic signals injected into different inverters cancel each other out on the grid impedance, making the calculated grid impedance more accurate.

[0048] Considering the background harmonics in the AC power grid, in order to reduce the influence of the background harmonics on the injected harmonic signals and further improve the accuracy of the calculated power grid impedance, in some embodiments, the frequency of the harmonic signals does not coincide with the frequency of the set Nth harmonic.

[0049] In order to reduce the measurement error and further improve the accuracy of the calculated power grid impedance, in some embodiments, the harmonic signals include at least one set of harmonics with the same voltage amplitude. Each set of harmonics includes a first harmonic and a second harmonic, and the frequency of the first harmonic is symmetric with respect to the frequency of the second harmonic about the frequency of the set Nth harmonic.

[0050] Here, when the harmonic signals injected on the α-axis include at least two sets of harmonics, the frequencies of each set of harmonics are different. Among them, different sets of harmonics can be used to eliminate the interference of harmonics of different orders in the background harmonics, or can also be used to eliminate the interference of harmonics of the same order in the background harmonics. Thus, the error can be reduced and the power grid impedance can be determined more accurately.

[0051] Each set of harmonics includes a first harmonic and a second harmonic, that is to say, the injected harmonic signals include an even number of harmonics. Among them, the value of N can be set according to the background harmonics. In practical applications, the value of N can be 3, 5, 7 or 11, so as to eliminate the interference or influence of the 3rd harmonic, 5th harmonic, 7th harmonic or 11th harmonic in the background harmonics on the injected harmonic signals.

[0052] The first ratio and the second ratio corresponding to each set of harmonics are symmetric about the order of the set Nth harmonic, which can make the frequency of the first harmonic symmetric with respect to the frequency of the second harmonic about the frequency of the set Nth harmonic. The first ratio represents the ratio of the frequency of the first harmonic to the fundamental frequency of the AC power grid; the second ratio represents the ratio of the frequency of the second harmonic to the fundamental frequency of the AC power grid.

[0053] Exemplarily, when the injected harmonic signals include a first harmonic and a second harmonic, the expression of the harmonic signals injected on the α-axis can be:

[0054] V α-H =U A (cos2πf H t+cos2πf L t); where, f H =(N + d)×f g , f L =(N - d)×f g .

[0055] Among them, N represents the order of the harmonics. In practical applications, the value of N can be 3, 5, 7 or 11. d represents a set value; d is greater than zero and less than 1; in practical applications, d is greater than zero and less than or equal to 0.1; fg Characterize the fundamental frequency of the AC power grid, f g = 50 Hz. (N + d) characterizes the first ratio; (N - d) characterizes the second ratio.

[0056] After the controller injects the harmonic signal on the α-axis, it samples the three-phase AC current on the AC grid side to obtain the three-phase AC current I a 、I b and I c . In actual application, such as Figure 3 , at the position between the grid connection point and the equivalent impedance Zg of the AC power grid, the three-phase AC current is sampled to obtain the three-phase AC current I a 、I b and I c . For the three-phase AC current I a 、I b and I c I abc Perform Clarke transformation to obtain the sampled current I α-H in the αβ coordinate system; determine whether I α-H is greater than or equal to the set threshold to obtain the judgment result. When the judgment result indicates that I α-H is greater than or equal to the set threshold, step 202 is executed.

[0057] Among them, the formula for Clarke transformation can be:

[0058]

[0059] In some embodiments, the method further includes:

[0060] When the sampled current is less than the set threshold, increase the voltage amplitude of the harmonic signal by a set step size, and synchronously inject the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal.

[0061] Here, when the judgment result indicates that I α-H is less than the set threshold, increase the voltage amplitude of the harmonic signal injected on the α-axis by a set step size; on the α-axis, synchronously inject the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal, and re-determine the sampled current I α-H ; when the re-determined I α-H is greater than or equal to the set threshold, execute step 202; when the re-determined I α-H is less than the set threshold, increase the voltage amplitude of the harmonic signal again according to the set step size, and synchronously inject the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal.

[0062] Step 202: When the sampled current on the AC grid side is greater than or equal to the set threshold, determine the harmonic current corresponding to the harmonic signal based on multiple sampled currents; wherein, the sampled current is obtained by performing Clarke transformation on the three-phase AC current.

[0063] Here, when I α-H is greater than or equal to the set threshold, collect multiple I α-H within the set sampling period, and determine the harmonic current corresponding to the harmonic signal injected on the α-axis based on the collected multiple I α-H . The set sampling period is set according to the period of the harmonic signal, and the set sampling period can be greater than or equal to half of the period of the harmonic signal and less than or equal to the period of the harmonic signal.

[0064] In practical applications, the controller in the inverter can perform Fourier transform on multiple I α-H based on the expression of the injected harmonic signal to obtain the harmonic current corresponding to the harmonic signal injected on the α-axis.

[0065] On the basis that the harmonic signal includes at least one group of harmonics with the same voltage amplitude, and each group of harmonics includes a first harmonic and a second harmonic, in some embodiments, the determining the harmonic current corresponding to the harmonic signal based on multiple sampled currents includes:

[0066] Performing Fourier transform on multiple sampled currents based on the expression of the harmonic signal to obtain the harmonic current corresponding to each group of harmonics in the harmonic signal.

[0067] Wherein, the harmonic current corresponding to each group of harmonics includes a first harmonic current corresponding to the first harmonic and a second harmonic current corresponding to the second harmonic.

[0068] Exemplarily, when the expression of the harmonic signal injected on the α-axis is V α-H =U A (cos2πf H t + cos2πf L t), the expression of the harmonic signal is I α-H =[I AH ×cos(2πf H t + θ H ) + I AL ×cos(2πf L t + θ L )] / M. Simplify the expression of I α-H to obtain: I α-H =(I AH / M)∠θ H |f H +(I AL / M)∠θL |f L Among them, I AH represents the harmonic current amplitude of the first harmonic, and θ H represents the phase difference of the first harmonic; I AL represents the harmonic current amplitude of the second harmonic, and θ L represents the phase difference of the second harmonic; M represents the total number of inverters operating in parallel in the grid-connected system.

[0069] Based on the expression of the harmonic signal, the controller performs Fourier transform on multiple sampled currents I α-H to determine the first harmonic current I AH corresponding to the harmonic signal and the second harmonic current I AL , and can also determine θ H and θ L .

[0070] Step 203: Based on the voltage amplitude of the harmonic signal, the determined harmonic current, and the total number of inverters operating in parallel, determine the impedance of the AC power grid.

[0071] Here, since the determined harmonic current is the total harmonic current of multiple parallel inverters, the controller determines the quotient of the determined harmonic current and the total number of inverters operating in parallel as the final harmonic current; calculates the quotient of the voltage amplitude of the harmonic signal and the final harmonic current to obtain the impedance of the AC power grid. The voltage amplitude of the harmonic signal and the determined harmonic current are data in the same coordinate system (αβ coordinate system).

[0072] It should be noted that on the basis that the injected harmonic signal includes at least one group of harmonics, the controller determines the impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the harmonic current corresponding to the group of harmonics, and the total number of inverters operating in parallel. Among them, the controller can determine the impedance corresponding to each harmonic according to the voltage amplitude, harmonic current, and total number of inverters operating in parallel of each harmonic; in the case of determining the impedances corresponding to all harmonics included in the harmonic signal, based on the impedances corresponding to all harmonics, determine the mean value to obtain the impedance of the AC power grid.

[0073] On the basis that the harmonic current corresponding to each group of harmonics includes the first harmonic current corresponding to the first harmonic and the second harmonic current corresponding to the second harmonic, in some embodiments, determining the value of the impedance of the AC power grid includes:

[0074] Based on the voltage amplitude of the first harmonic, and based on the first harmonic current corresponding to the first harmonic and the total number of inverters operating in parallel, determine the first impedance value;

[0075] Determine a second impedance value based on the voltage amplitude of the second harmonic and based on the second harmonic current corresponding to the second harmonic and the total number of parallel - operating inverters;

[0076] Determine the mean value between the determined first impedance value and the determined second impedance value as the impedance of the AC power grid.

[0077] Here, the first - harmonic current corresponding to the first harmonic is the total harmonic current of the first harmonic injected into the parallel - operating inverters, and the second - harmonic current corresponding to the second harmonic is the total harmonic current of the second harmonic injected into the parallel - operating inverters.

[0078] When the controller determines the first - harmonic current and the second - harmonic current corresponding to each group of harmonics in the harmonic signal, the controller determines the quotient of the first - harmonic current corresponding to the first harmonic and the total number of parallel - operating inverters as the harmonic current of the corresponding inverter; and determines the quotient of the voltage amplitude of the first harmonic and this harmonic current as the first impedance value corresponding to the α - axis. The controller determines the quotient of the second - harmonic current corresponding to the second harmonic and the total number of parallel - operating inverters as the harmonic current of the corresponding inverter; and determines the quotient of the voltage amplitude of the second harmonic and this harmonic current as the second impedance value corresponding to the α - axis.

[0079] When the first impedance value and the second impedance value corresponding to the α - axis are determined, calculate the mean value of the first impedance value and the second impedance value to obtain the grid impedance Z of the α - axis α 。

[0080] Exemplarily, the expression of the harmonic signal injected on the α - axis is V α-H =U A (cos2πf H t + cos2πf L t). In this case, calculate the first impedance value Z α-H =(U A ×M / I AH )∠θ H corresponding to the α - axis according to the formula; calculate the second impedance value Z α-H =(U α-L ×M / I A )∠θ AL corresponding to the α - axis according to the formula; calculate the grid impedance Z L corresponding to the α - axis according to the formula Z α-L =(Z α +Z α-H ) / 2. Thus, the grid impedance Z α-L corresponding to the N - th harmonic on the α - axis can be obtained. α 。 α 。

[0081] It should be noted that when the harmonic signals injected on the α-axis include at least two groups of harmonics, the first impedance value and the second impedance value corresponding to the first harmonic and the second harmonic in each group of harmonics can be calculated in the above manner, and based on all the determined first impedance values and all the second impedance values, the mean value can be calculated to obtain the grid impedance Z of the α-axis. α 。

[0082] It should be noted that the controller in the inverter can synchronously inject harmonic signals on the β-axis according to the above method, so as to determine the grid impedance Z of the β-axis β ; synchronously inject harmonic signals on the o-axis, so as to determine the grid impedance Z of the o-axis o 。

[0083] As Figure 3 shown, considering that the harmonic current generated by the injected harmonic signal passes through the filter in the grid-connected system, and this filter is located between the inverter and the AC grid, the grid impedance calculated by the above method actually includes the impedance of the filter. When the impedance of the filter is very small, the impedance of the filter can be ignored; when the impedance of the filter is large, after calculating the grid impedance by the above method, the impedance of the filter needs to be subtracted to obtain the true grid impedance. In order to improve the accuracy of the determined grid impedance, in some embodiments, the determining the impedance of the AC grid includes:

[0084] Based on the voltage amplitude of the harmonic signal, the determined harmonic current and the total number of parallel-operating inverters, and based on the value of the impedance of the filter, the value of the impedance of the AC grid; wherein, the filter is located between the inverter and the AC grid.

[0085] Here, when the controller in the inverter calculates the grid impedance Z of the α-axis α , subtract the impedance of the filter from the grid impedance Z of the α-axis α to obtain the grid impedance Z of the α-axis gα 。

[0086] It should be noted that the controller in the inverter can subtract the impedance of the filter from the grid impedance Z of the β-axis β to obtain the grid impedance Z of the β-axis gβ ; subtract the impedance of the filter from the grid impedance Z of the o-axis o to obtain the grid impedance Z of the o-axis go 。

[0087] Exemplarily, in the grid-connected system as Figure 4 shown, calculate Z gα , Z gβ and Z go respectively according to the following formulas:

[0088] Z gα =Z α -j2πNf g (L pwm -L line );

[0089] Z gβ =Z β -j2πNf g (L pwm -L line );

[0090]

[0091] Figure 5 is a schematic diagram of the implementation process of the method for measuring the grid impedance provided by the application implementation example of this application. As Figure 5 shown, the method for measuring the grid impedance includes:

[0092] Step 501: Synchronously inject a harmonic signal into the modulation signal of the inverter based on a common clock signal.

[0093] Among them, for the implementation process of step 501, please refer to the relevant description of step 201 above, and it will not be elaborated here.

[0094] Step 502: Determine whether the sampled current on the AC grid side is greater than or equal to a set threshold; among them, the sampled current is obtained by performing Clarke transformation on the three-phase AC current.

[0095] Here, when the sampled current on the AC grid side is less than the set threshold, step 503 is executed; when the sampled current on the AC grid side is greater than or equal to the set threshold, step 504 is executed.

[0096] Step 503: Increase the voltage amplitude of the harmonic signal by a set step size.

[0097] Here, after the controller executes step 503, it executes step 501 to synchronously inject the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal.

[0098] Step 504: Determine the harmonic current corresponding to the harmonic signal based on multiple sampled currents.

[0099] Among them, for the implementation processes of steps 504 to 505, please refer to the relevant descriptions of steps 202 to 203 above, and it will not be elaborated here.

[0100] Step 505: Determine the impedance of the AC grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and the total number of parallel-operating inverters.

[0101] To implement the method for measuring the grid impedance in the embodiments of the present application, the embodiments of the present application further provide a device for measuring the grid impedance, as Figure 6 shown. The device for measuring the grid impedance includes:

[0102] A signal injection module 61, configured to synchronously inject a harmonic signal into the modulation signal of the inverter based on a common clock signal;

[0103] A first determination module 62, configured to determine the harmonic current of the harmonic signal based on a plurality of sampled currents when the sampled current on the AC grid side is greater than or equal to a set threshold; wherein, the sampled current is obtained by performing Clarke transformation on the three-phase alternating current;

[0104] A second determination module 63, configured to determine the impedance of the AC grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and the total number of parallel-operating inverters.

[0105] In some embodiments, the device for measuring the grid impedance further includes:

[0106] An adjustment module, configured to increase the voltage amplitude of the harmonic signal by a set step when the sampled current is less than the set threshold;

[0107] The signal injection module 61 is further configured to: synchronously inject the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal.

[0108] In some embodiments, the frequency of the harmonic signal does not coincide with the frequency of the set Nth harmonic.

[0109] In some embodiments, the harmonic signal includes at least one set of harmonics with the same voltage amplitude, each set of harmonics includes a first harmonic and a second harmonic, and the frequency of the first harmonic is symmetric with respect to the frequency of the second harmonic about the frequency of the set Nth harmonic.

[0110] In some embodiments, the first determination module 62 is specifically configured to:

[0111] Perform Fourier transform on a plurality of sampled currents based on the expression of the harmonic signal to obtain the harmonic current corresponding to each set of harmonics in the harmonic signal.

[0112] In some embodiments, the harmonic current corresponding to each set of harmonics includes a first harmonic current corresponding to the first harmonic and a second harmonic current corresponding to the second harmonic; the second determination module 63 is specifically configured to:

[0113] Determine a first impedance value based on the voltage amplitude of the first harmonic, and based on the first harmonic current corresponding to the first harmonic and the total number of parallel-operating inverters;

[0114] Determine a second impedance value based on the voltage amplitude of the second harmonic, as well as the second harmonic current corresponding to the second harmonic and the total number of inverters operating in parallel.

[0115] Determine the mean value between the determined first impedance value and the determined second impedance value as the impedance of the AC power grid.

[0116] In some embodiments, the second determination module 63 is specifically configured to:

[0117] Determine the impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, the total number of inverters operating in parallel, and the impedance of the filter; wherein, the filter is located between the inverter and the AC power grid.

[0118] In practical applications, each module included in the measuring device for grid impedance can be implemented by a processor in a terminal, such as a central processing unit (CPU, Central Processing Unit), a digital signal processor (DSP, Digital Signal Processor), a microcontroller unit (MCU, Microcontroller Unit), or a field-programmable gate array (FPGA, Field-Programmable Gate Array), etc.

[0119] It should be noted that: when the measuring device for grid impedance provided in the above embodiments measures the grid impedance, only the division of the above program modules is used for illustration. In practical applications, the above processing can be allocated to different program modules according to needs, that is, the internal structure of the device is divided into different program modules to complete all or part of the above-described processing. In addition, the measuring device for grid impedance provided in the above embodiments and the embodiment of the method for measuring grid impedance belong to the same concept, and the specific implementation process is detailed in the method embodiment, which will not be elaborated here.

[0120] Based on the hardware implementation of the above program modules, and in order to implement the method of the embodiments of the present application, the embodiments of the present application further provide a controller. Figure 7 As shown in the schematic diagram of the hardware composition structure of the controller provided by the embodiments of the present application, as Figure 7 shown, the controller 7 includes:

[0121] A communication interface 71 capable of information interaction with other devices such as network devices, etc.;

[0122] A processor 72, connected to the communication interface 71 to achieve information interaction with other devices, and when running a computer program, execute the method for measuring grid impedance provided by one or more of the above technical solutions. And the computer program is stored on the memory 73.

[0123] Of course, in practical applications, the various components in the controller 7 are coupled together through the bus system 74. It can be understood that the bus system 74 is used to implement the connection and communication between these components. In addition to the data bus, the bus system 74 also includes a power bus, a control bus, and a status signal bus. However, for the sake of clear illustration, in Figure 7 all kinds of buses are labeled as the bus system 74.

[0124] The memory 73 in the embodiment of the present application is used to store various types of data to support the operation of the controller 7. Examples of these data include: any computer program for operating on the controller 7.

[0125] It can be understood that the memory 73 can be a volatile memory or a non-volatile memory, or can include both volatile and non-volatile memories. Among them, the non-volatile memory can be a read-only memory (ROM, Read Only Memory), a programmable read-only memory (PROM, Programmable Read-Only Memory), an erasable programmable read-only memory (EPROM, Erasable Programmable Read-Only Memory), an electrically erasable programmable read-only memory (EEPROM, Electrically Erasable Programmable Read-Only Memory), a ferromagnetic random access memory (FRAM, ferromagnetic random access memory), a flash memory (Flash Memory), a magnetic surface memory, an optical disc, or a compact disc read-only memory (CD-ROM, Compact Disc Read-Only Memory); the magnetic surface memory can be a disk memory or a tape memory. The volatile memory can be a random access memory (RAM, Random Access Memory), which is used as an external cache. By way of example but not limitation, many forms of RAM are available, such as a static random access memory (SRAM, Static Random Access Memory), a synchronous static random access memory (SSRAM, Synchronous Static Random Access Memory), a dynamic random access memory (DRAM, Dynamic Random Access Memory), a synchronous dynamic random access memory (SDRAM, Synchronous Dynamic Random Access Memory), a double data rate synchronous dynamic random access memory (DDR SDRAM, Double Data Rate Synchronous Dynamic Random Access Memory), an enhanced synchronous dynamic random access memory (ESDRAM, Enhanced Synchronous Dynamic Random Access Memory), a sync link dynamic random access memory (SLDRAM, Sync Link Dynamic Random Access Memory), a direct rambus random access memory (DRRAM, Direct Rambus Random Access Memory).The memory 73 described in the embodiments of the present application is intended to include, but not limited to, these and any other suitable types of memories.

[0126] The method disclosed in the embodiments of the present application above can be applied to or implemented by the processor 72. The processor 72 may be an integrated circuit chip with signal processing capabilities. In the implementation process, each step of the above method can be completed by the integrated logic circuit in the hardware of the processor 72 or the instructions in the form of software. The above-mentioned processor 72 may be a general-purpose processor, a DSP, or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The processor 72 can implement or execute each method, step, and logic block diagram disclosed in the embodiments of the present application. The general-purpose processor may be a microprocessor or any conventional processor, etc. Combining the steps of the method disclosed in the embodiments of the present application, it can be directly embodied as being executed and completed by the hardware decoding processor, or executed and completed by the combination of the hardware and software modules in the decoding processor. The software module may be located in the storage medium, which is located in the memory 73. The processor 72 reads the program in the memory 73 and combines its hardware to complete the steps of the foregoing method.

[0127] Optionally, when the processor 72 executes the program, it implements the corresponding processes implemented by the terminal in each method of the embodiments of the present application. For the sake of brevity, it will not be elaborated here.

[0128] In an exemplary embodiment, the embodiments of the present application also provide a storage medium, namely a computer storage medium, specifically a computer-readable storage medium, such as the first memory 73 that stores a computer program. The above computer program can be executed by the processor 72 of the terminal to complete the steps of the foregoing method. The computer-readable storage medium may be a FRAM, ROM, PROM, EPROM, EEPROM, Flash Memory, magnetic surface memory, optical disc, or CD-ROM, etc.

[0129] In several embodiments provided by the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are only illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods, such as: multiple units or components can be combined, or integrated into another system, or some features can be ignored, or not executed. In addition, the coupling, direct coupling, or communication connection between the components shown or discussed with each other may be through some interfaces. The indirect coupling or communication connection of the devices or units may be electrical, mechanical, or other forms.

[0130] The units described above as separate components may or may not be physically separated. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed over multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0131] In addition, each functional unit in the embodiments of the present application may be all integrated in a processing module, or each unit may be separately used as a unit, or two or more units may be integrated in one unit. The above integrated units may be implemented in the form of hardware, or in the form of a combination of hardware and software functional units.

[0132] Those of ordinary skill in the art can understand that all or part of the steps of implementing the above method embodiments can be completed by hardware related to program instructions. The foregoing program can be stored in a computer-readable storage medium. When the program is executed, it performs the steps including the above method embodiments. The foregoing storage medium includes various media that can store program codes, such as removable storage devices, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical discs.

[0133] It should be noted that the technical solutions described in the embodiments of the present application can be arbitrarily combined without conflict.

[0134] It should be noted that the term "and / or" in the embodiments of the present application is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the term "at least one" in this article means any one of a plurality or any combination of at least two of a plurality. For example, including at least one of A, B, and C can represent any one or more elements selected from the set composed of A, B, and C.

[0135] As described above, the above are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, and all of them should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for measuring the impedance of a power grid, characterized in that, Including: Synchronously injecting a harmonic signal into the modulation signal of the inverter based on a common clock signal; When the sampled current on the AC grid side is greater than or equal to a set threshold, determining the harmonic current corresponding to the harmonic signal based on multiple sampled currents; wherein, the sampled current is obtained by performing Clarke transformation on three-phase AC currents; Determining the impedance of the AC grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and the total number of parallel-operated inverters.

2. The method according to claim 1, wherein The method further includes: When the sampled current is less than the set threshold, increasing the voltage amplitude of the harmonic signal by a set step size, and synchronously injecting the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal.

3. The method according to claim 1 or 2, characterized in that, The frequency of the harmonic signal does not coincide with the frequency of the set Nth harmonic.

4. The method according to claim 3, wherein The harmonic signal includes at least one group of harmonics with the same voltage amplitude, each group of harmonics includes a first harmonic and a second harmonic, and the frequency of the first harmonic is symmetric to the frequency of the second harmonic with respect to the frequency of the set Nth harmonic.

5. The method according to claim 4, characterized in that, The determining the harmonic current corresponding to the harmonic signal based on multiple sampled currents includes: Performing Fourier transform on multiple sampled currents based on the expression of the harmonic signal to obtain the harmonic current corresponding to each group of harmonics in the harmonic signal.

6. The method according to claim 5, characterized in that, The harmonic current corresponding to each group of harmonics includes the first harmonic current corresponding to the first harmonic and the second harmonic current corresponding to the second harmonic; the determining the impedance of the AC grid includes: Determining a first impedance value based on the voltage amplitude of the first harmonic, and based on the first harmonic current corresponding to the first harmonic and the total number of parallel-operated inverters; Determining a second impedance value based on the voltage amplitude of the second harmonic, and based on the second harmonic current corresponding to the second harmonic and the total number of parallel-operated inverters; Determining the mean value between the determined first impedance value and the determined second impedance value as the impedance of the AC grid.

7. The method according to claim 1, characterized in that, The determining the impedance of the AC grid includes: Determining the impedance of the AC grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, the total number of parallel-operated inverters, and based on the impedance of a filter; wherein, the filter is located between the inverter and the AC grid.

8. A measuring device for grid impedance, characterized in that, Including: A signal injection module for synchronously injecting a harmonic signal into the modulation signal of the inverter based on a common clock signal; A first determination module for determining the harmonic current of the harmonic signal based on multiple sampled currents when the sampled current on the AC grid side is greater than or equal to a set threshold; wherein, the sampled current is obtained by performing Clarke transformation on three-phase AC currents; A second determination module for determining the impedance of the AC grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and the total number of parallel-operated inverters.

9. A controller, characterized in that, Including: A processor and a memory for storing a computer program capable of running on the processor, wherein, when the processor is used to run the computer program, it executes the steps of the method according to any one of claims 1 to 7.

10. A storage medium, on which a computer program is stored, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

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