CN114527326A - Method and device for measuring power grid impedance, related equipment and storage medium - Google Patents
Method and device for measuring power grid impedance, related equipment and storage medium Download PDFInfo
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- CN114527326A CN114527326A CN202111672903.0A CN202111672903A CN114527326A CN 114527326 A CN114527326 A CN 114527326A CN 202111672903 A CN202111672903 A CN 202111672903A CN 114527326 A CN114527326 A CN 114527326A
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Abstract
The application discloses a method and a device for measuring the impedance of a power grid, related equipment and a storage medium; the method comprises the following steps: synchronously injecting a harmonic signal to a modulation signal of the inverter based on the common clock signal; under the condition that the sampling current on the alternating current network side is larger than or equal to a set threshold value, determining harmonic current corresponding to the harmonic signal based on a plurality of sampling currents; the sampling current is obtained by performing Clarke transformation on three-phase alternating current; determining an impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel.
Description
Technical Field
The present disclosure relates to the field of electronic power technologies, and in particular, to a method and an apparatus for measuring a grid impedance, a related device, and a storage medium.
Background
In the related art, various types of power generation systems such as a wind power generator, a photovoltaic cell panel, and a fuel cell are connected to an ac power grid through an inverter, and perform power transmission to the ac power grid. Due to the impedance present on the transmission line of the grid and the possible presence of various transmission devices on the transmission line, a grid in which the inverters are connected via a point of connection (the point of connection of the inverter to the ac grid) is not an ideal grid, and it is generally considered that the inverter is connected to the ac grid via an equivalent impedance.
Considering that the equivalent impedance is located in an equivalent control loop of the inverter, in order to enable the whole system to operate safely and stably, the value of the equivalent impedance needs to be measured, and the operation parameters of the inverter need to be adjusted in real time according to the value of the equivalent impedance. In the related art, a value of equivalent impedance is measured by injecting a disturbance current into a power grid, but the measured equivalent impedance is inaccurate in a scene that at least two inverters connected in parallel are connected with an alternating current power grid.
Disclosure of Invention
In view of this, embodiments of the present application provide a method and an apparatus for measuring a grid impedance, a related device, and a storage medium.
In order to achieve the purpose, the technical scheme of the application is realized as follows:
the embodiment of the application provides a method for measuring power grid impedance, which comprises the following steps:
synchronously injecting a harmonic signal to a modulation signal of the inverter based on the common clock signal;
under the condition that the sampling current on the AC power grid side is greater than or equal to a set threshold, determining harmonic current corresponding to the harmonic signal based on a plurality of sampling currents; the sampling current is obtained by performing Clarke transformation on three-phase alternating current;
determining an impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel.
In the above scheme, the method further comprises:
and under the condition that the sampling current is smaller than the set threshold, increasing the voltage amplitude of the harmonic signal according to a set step length, and synchronously injecting the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal.
In the above-mentioned scheme, the frequency of the harmonic signal does not coincide with the frequency of the set N-th harmonic.
In the above scheme, 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 and the frequency of the second harmonic are symmetrical with respect to the frequency of the set N-th harmonic.
In the foregoing solution, the determining a harmonic current corresponding to the harmonic signal based on a plurality of sampling currents includes: and carrying out Fourier transform on the plurality of sampling currents based on the expression of the harmonic signals to obtain the harmonic current corresponding to each group of harmonics in the harmonic signals.
In the above scheme, the harmonic current corresponding to each group of harmonics includes a first harmonic current corresponding to a first harmonic and a second harmonic current corresponding to a second harmonic; the determining the impedance of the ac power grid includes:
determining a first impedance value based on the voltage amplitude of the first harmonic wave, and based on the first harmonic wave current corresponding to the first harmonic wave and the total number of inverters running in parallel;
determining a second impedance value based on the voltage amplitude of the second harmonic, and based on a second harmonic current corresponding to the second harmonic and the total number of inverters operating in parallel;
and determining the mean value between the determined first impedance value and the determined second impedance value as the impedance of the alternating current power grid.
In the foregoing solution, the determining the impedance of the ac power grid includes:
determining an impedance of the AC power grid based on a voltage amplitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel, and based on an impedance of a filter; wherein the filter is located between the inverter and the AC power grid.
The embodiment of the present application further provides a measuring device of power grid impedance, which is characterized in that, includes:
the signal injection module is used for synchronously injecting harmonic signals to modulation signals of the inverter based on the common clock signals;
the harmonic signal processing device comprises a first determining module, a second determining module and a harmonic signal generating module, wherein the first determining module is used for determining the harmonic current of the harmonic signal based on a plurality of sampling currents under the condition that the sampling current on the alternating current power grid side is larger than or equal to a set threshold; the sampling current is obtained by performing Clarke transformation on three-phase alternating current;
a second determination module to determine an impedance of the AC power grid based on a voltage magnitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel.
An embodiment of the present application further provides a controller, including: a processor and a memory for storing a computer program capable of running on the processor,
wherein the processor is configured to execute the steps of the method for measuring the grid impedance when running the computer program.
The embodiment of the present application further provides a storage medium, on which a computer program is stored, where the computer program is executed by a processor to implement the steps of the method for measuring the impedance of the power grid.
In the embodiment of the application, harmonic signals are synchronously injected into modulation signals of an inverter based on a common clock signal, and under the condition that the sampling current on the alternating current network side is greater than or equal to a set threshold, the harmonic current corresponding to the harmonic signals is determined based on a plurality of sampling currents; determining a value of the impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel. Therefore, the controller of each inverter in parallel operation in the grid-connected system synchronously injects the harmonic signals into the modulation signals of the corresponding inverters based on the common clock signals, so that the time for injecting the harmonic signals into each inverter in parallel operation can be ensured to be synchronous, the harmonic signals injected into a certain inverter cannot influence the control signals of the inverters which are not injected with the harmonic signals, and the harmonic signals injected into different inverters cannot be mutually offset on the impedance of the power grid, so that the calculated impedance of the power grid is more accurate.
Drawings
FIG. 1 is a schematic diagram of measuring grid impedance in the related art;
fig. 2 is a schematic implementation flow diagram of a method for measuring a grid impedance provided in an embodiment of the present application;
fig. 3 is a schematic diagram of a grid-connected system provided in an embodiment of the present application;
fig. 4 is a schematic diagram of a grid-connected system according to another embodiment of the present application;
fig. 5 is a schematic implementation flow diagram of a method for measuring a grid impedance provided in an application embodiment of the present application;
fig. 6 is a schematic structural diagram of a device for measuring grid impedance according to an embodiment of the present disclosure;
fig. 7 is a schematic diagram of a hardware component structure of a controller according to an embodiment of the present application.
Detailed Description
In the related art, under a scenario that at least two inverters connected in parallel are connected to an ac power grid, a disturbance current is injected into a modulation signal of one of the inverters, as shown in fig. 1, a disturbance current is injected into a modulation signal of the inverter 1, the injected disturbance current generates a response voltage at an equivalent impedance Zg of the ac power grid, and a value of the equivalent impedance of the ac power grid is calculated through the response voltage and the injected disturbance current. The connection point between the inverter and the ac power grid is a Point of Common Coupling (PCC), also called a grid-connected point.
However, after the disturbance current is injected to the control signal of the inverter 1, part of the disturbance current flows into other inverters, thereby causing inaccuracy in the obtained response voltage and further causing inaccuracy in the value of the equivalent impedance calculated from the response voltage and the injected disturbance current.
Based on this, the embodiment of the application provides a power grid impedance measuring method, which includes synchronously injecting a harmonic signal into a modulation signal of an inverter based on a common clock signal, and determining a harmonic current corresponding to the harmonic signal based on a plurality of sampling currents under the condition that a sampling current on the alternating current grid side is greater than or equal to a set threshold value; determining a value of the impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel. Therefore, the controller of each inverter in the grid-connected system synchronously injects harmonic signals into the modulation signals of the inverters based on the common clock signals, the harmonic signals injected into a certain inverter cannot influence the control signals of the inverters which are not injected with the harmonic signals, the harmonic signals injected into different inverters cannot be mutually offset on the impedance of the power grid, and the accuracy of the calculated impedance of the power grid is improved.
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
Fig. 2 is a schematic view of an implementation flow of a method for measuring a grid impedance provided in an embodiment of the present application, where the method for measuring a grid impedance is applied to a grid-connected system in which M inverters operate in parallel, and M is an integer greater than or equal to 2; the main execution body of the process is a controller, the controller is used for controlling inverters, each inverter corresponds to one controller, and as shown in fig. 3, the controllers may be arranged in the inverters. As shown in fig. 2, the method for measuring the grid impedance includes:
step 201: harmonic signals are synchronously injected into modulation signals of the inverter based on a common clock signal.
Here, the controller synchronously injects a harmonic signal to the modulation signal of the inverter based on the common clock signal in the stationary coordinate system to control the inverter to operate by the modulation signal injected with the harmonic signal. Wherein, the static coordinate system comprises a two-phase static alpha beta coordinate system, which is called alpha beta coordinate system for short; the α β coordinate system includes an α axis and a β axis. In some embodiments, an o-axis, i.e., a zero-axis, may also be included in the stationary coordinate system. In the embodiment of the application, the impedance of the ac power grid to be calculated at least comprises the grid impedance Z of the α axisαAnd the grid impedance Z of the beta axisβ(ii) a In a stationary coordinate systemIn the case of an o-axis, the impedance of the AC mains also includes the grid impedance Z of the o-axiso。
It should be noted that harmonic signals injected synchronously by all inverters in parallel operation in the grid-connected system on the same axis are the same. The harmonic signal injected in the α axis and the harmonic signal injected in the β axis in the same inverter may be the same or different.
Considering each axis under a static coordinate system, harmonic signals are synchronously injected into modulation signals of the inverter based on a common clock signal, and the method for calculating the power grid impedance of the corresponding axis is similar. Then, under an alpha-beta coordinate system, harmonic signals are injected into an alpha axis to calculate the grid impedance Z of the alpha axisαThe description is given for the sake of example.
The controller sets the time in the common clock signal, and synchronously injects harmonic signals to modulation signals of the corresponding inverters in the alpha axis direction.
The set time can be the arrival time of the rising edge or the falling edge of the Kth pulse in the common clock signal; k is a positive integer. The injection of the harmonic signal into the modulation signal of the inverter means that the harmonic signal is superimposed 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.
In this embodiment, the controller of each inverter that operates in parallel in the grid-connected system synchronously injects the harmonic signal to the modulation signal of the corresponding inverter based on the common clock signal, and thus, the timing for injecting the harmonic signal into each inverter that operates in parallel can be ensured to be synchronous, thereby avoiding the situation that the harmonic signals injected into different inverters cancel each other out on the grid impedance, and making the calculated grid impedance more accurate.
To reduce the effect of background harmonics on the injected harmonic signal, which in some embodiments does not coincide with the frequency of the set nth harmonic, the accuracy of the calculated grid impedance is further improved, taking into account the presence of background harmonics in the ac grid.
To reduce measurement errors and further improve the accuracy of the calculated grid impedance, 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 frequencies of the first harmonic and the second harmonic are symmetric about the set frequency of the nth harmonic.
Here, in the case where the harmonic signal injected by the α axis includes at least two sets of harmonics, the frequencies of each set of harmonics are different from each other. The harmonics of different groups can be used to eliminate the interference of harmonics of different orders in the background harmonics, and can also be used to eliminate the interference of harmonics of the same order in the background harmonics. Therefore, errors can be reduced, and the power grid impedance can be determined more accurately.
Each set of harmonics comprises a first harmonic and a second harmonic, that is, the injected harmonic signal comprises an even number of harmonics. Wherein, the value of N can be set according to background harmonic. In practical application, the value of N may be 3, 5, 7 or 11, so as to eliminate the interference or influence of the 3 rd harmonic, 5 th harmonic, 7 th harmonic or 11 th harmonic in the background harmonic on the injected harmonic signal.
The first ratio and the second ratio corresponding to each group of harmonics are symmetrical with respect to the order of the set N harmonics, that is, the frequency of the first harmonic and the frequency of the second harmonic are symmetrical with respect to the frequency of the set N harmonics. The first ratio characterizes a ratio of a frequency of the first harmonic to a frequency of a fundamental of the ac power grid; the second ratio characterizes a ratio of a frequency of the second harmonic to a fundamental frequency of the ac power grid.
For example, in the case where the injected harmonic signal includes a first harmonic and a second harmonic, the expression of the harmonic signal injected in the α axis may be:
Vα-H＝UA(cos2πfHt+cos2πfLt); wherein f isH＝(N+d)×fg，fL＝(N-d)×fg。
Wherein, N represents the order of harmonic wave, and in practical application, 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 application, d is greater than zero and less than or equal to 0.1; f. ofgCharacterizing the fundamental frequency, f, of an AC networkg50 Hz. (N + d) tableA first ratio is obtained; (N-d) characterizing the second ratio.
After the harmonic signal is injected into the alpha axis, the controller samples the three-phase alternating current on the alternating current network side to obtain the three-phase alternating current Ia、IbAnd Ic. In practical application, as shown in fig. 3, the three-phase alternating current is sampled at a position between a grid-connected point and an equivalent impedance Zg of an alternating current grid to obtain a three-phase alternating current Ia、IbAnd Ic. For three-phase alternating current Ia、IbAnd IcIabcPerforming Clarke transformation to obtain sampling current I under alpha-beta coordinate systemα-H(ii) a Judgment of Iα-HAnd judging whether the threshold value is larger than or equal to the set threshold value or not to obtain a judgment result. Characterization of I at the judgmentα-HIf the value is greater than or equal to the set threshold value, step 202 is executed.
Wherein, the formula of the Clarke transformation can be:
in some embodiments, the method further comprises:
and under the condition that the sampling current is smaller than the set threshold, increasing the voltage amplitude of the harmonic signal according to a set step length, and synchronously injecting the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal.
Here, I is characterized in the judgment resultα-HUnder the condition of being smaller than a set threshold, increasing the voltage amplitude of the harmonic signal injected in the alpha axis according to a set step length; synchronously injecting the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal on the alpha axis, and re-determining the sampling current Iα-H(ii) a At the redetermined Iα-HIf the value is greater than or equal to the set threshold value, executing step 202; at the redetermined Iα-HAnd when the voltage amplitude is smaller than the set threshold, increasing the voltage amplitude of the harmonic signal according to the set step length again, and synchronously injecting the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal.
Step 202: under the condition that the sampling current on the alternating current network side is larger than or equal to a set threshold value, determining harmonic current corresponding to the harmonic signal based on a plurality of sampling currents; wherein the sampling current is obtained by performing Clarke transformation on the three-phase alternating current.
Here, in Iα-HUnder the condition that the sampling time is larger than or equal to a set threshold value, a plurality of I are collected in a set sampling periodα-HAnd based on a plurality of collected Iα-HAnd determining the harmonic current corresponding to the harmonic signal injected in the alpha axis. The set sampling period is set according to the period of the harmonic signal, and the set sampling period may 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.
In practical application, the controller in the inverter can perform conversion on a plurality of I based on the expression of the injected harmonic signalsα-HAnd performing Fourier transform to obtain harmonic current corresponding to the harmonic signal injected in the alpha axis.
On the basis that the harmonic signal includes at least one group of harmonics having the same voltage amplitude, each group of harmonics including a first harmonic and a second harmonic, in some embodiments, the determining a harmonic current corresponding to the harmonic signal based on a plurality of sampling currents includes:
and carrying out Fourier transform on the plurality of sampling currents based on the expression of the harmonic signals to obtain the harmonic current corresponding to each group of harmonics in the harmonic signals.
And the harmonic current corresponding to each group of harmonics comprises a first harmonic current corresponding to the first harmonic and a second harmonic current corresponding to the second harmonic.
Illustratively, the harmonic signal injected in the α axis is expressed as Vα-H＝UA(cos2πfHt+cos2πfLt), the harmonic signal is expressed as Iα-H＝[IAH×cos(2πfHt+θH)+IAL×cos(2πfLt+θL)]and/M. To Iα-HThe expression of (c) is simplified to yield: i isα-H＝(IAH/M)∠θH|fH+(IAL/M)∠θL|fL. Wherein, IAHAmplitude of harmonic current, theta, characterizing the first harmonicHCharacterizing a phase difference of the first harmonic; i isALAmplitude of harmonic current, theta, characterizing the second harmonicLCharacterizing a phase difference of the second harmonic; m represents the total number of inverters in parallel operation in the grid-connected system.
The controller samples a plurality of currents I based on the expression of the harmonic signalα-HFourier transform is carried out to determine a first harmonic current I corresponding to the harmonic signalAHAnd a second harmonic current IALAlso, θ can be determinedHAnd thetaL。
Step 203: determining an impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel.
Here, since the determined harmonic current is a total harmonic current of the plurality of inverters connected in parallel, the controller in the inverter determines a quotient of the determined harmonic current and a total number of the inverters operated in parallel as a final harmonic current; and calculating the quotient of the voltage amplitude of the harmonic signal and the final harmonic current to obtain the impedance of the alternating current power grid. The voltage amplitude of the harmonic signal and the determined harmonic current are data in the same coordinate system (alpha beta coordinate system).
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. The controller can determine the impedance corresponding to each harmonic according to the voltage amplitude of each harmonic, the harmonic current and the total number of the inverters running in parallel; and under the condition that the impedance corresponding to all the harmonic waves included in the harmonic wave signal is determined, determining an average value based on the impedance corresponding to all the harmonic waves to obtain the impedance of the alternating current power grid.
On the basis that the harmonic current corresponding to each group of harmonics includes a first harmonic current corresponding to a first harmonic and a second harmonic current corresponding to a second harmonic, in some embodiments, the determining the value of the impedance of the ac power grid includes:
determining a first impedance value based on the voltage amplitude of the first harmonic, and based on a first harmonic current corresponding to the first harmonic and the total number of inverters operating in parallel;
determining a second impedance value based on the voltage amplitude of the second harmonic, and based on a second harmonic current corresponding to the second harmonic and the total number of inverters operating in parallel;
and determining the mean value between the determined first impedance value and the determined second impedance value as the impedance of the alternating current power grid.
Here, the first harmonic current corresponding to the first harmonic is a total harmonic current of the first harmonic injected into the inverters operated in parallel, and the second harmonic current corresponding to the second harmonic is a total harmonic current of the second harmonic injected into the inverters operated in parallel.
Under the condition that the first harmonic current and the second harmonic current corresponding to each group of harmonics in the harmonic signal are determined, the controller determines the quotient of the first harmonic current corresponding to the first harmonic and the total number of inverters running in parallel as the harmonic current of the corresponding inverter; and determining the voltage amplitude of the first harmonic wave and the quotient of the harmonic wave current as a first impedance value corresponding to the alpha axis. The controller determines the quotient of a second harmonic current corresponding to the second harmonic and the total number of the inverters running in parallel as the harmonic current of the corresponding inverter; and determining the voltage amplitude of the second harmonic wave and the quotient of the harmonic wave current as a second impedance value corresponding to the alpha axis.
Under the condition of determining a first impedance value and a second impedance value corresponding to the alpha axis, calculating the mean value of the first impedance value and the second impedance value to obtain the power grid impedance Z of the alpha axisα。
Illustratively, the harmonic signal injected in the α axis is expressed as Vα-H＝UA(cos2πfHt+cos2πfLt), according to the formula Zα-H＝(UA×M/IAH)∠θHCalculating a first impedance value Z corresponding to the alpha axisα-H(ii) a According to formula Zα-L＝(UA×M/IAL)∠θLCalculating a second impedance value Z corresponding to the alpha axisα-L(ii) a According to formula Zα＝(Zα-H+Zα-L) Calculating the corresponding power grid impedance Z of the alpha axisα. Thus, the corresponding grid impedance Z at the alpha-axis Nth harmonic can be obtainedα。
It should be noted that, when the harmonic signal injected in the α axis includes at least two groups of harmonics, the first impedance value and the second impedance value respectively corresponding to the first harmonic and the second harmonic in each group of harmonics may be calculated in the above manner, and based on all the determined first impedance values and all the determined second impedance values, the average value is calculated to obtain the grid impedance Z of the α axisα。
It should be noted that the controller in the inverter can inject the harmonic signal into the β axis synchronously according to the above method, so as to determine the grid impedance Z of the β axisβ(ii) a Harmonic signals are synchronously injected in the o axis, so that the grid impedance Z of the o axis is determinedo。
As shown in fig. 3, the grid impedance calculated in the above manner actually includes the impedance of the filter, considering that the harmonic current generated by the injected harmonic signal passes through the filter in the grid-connected system, which is located between the inverter and the ac grid. In the case of very small impedance of the filter, the impedance of the filter is negligible; under the condition that the impedance of the filter is large, the real power grid impedance can be obtained only by subtracting the impedance of the filter after the power grid impedance calculated by the method is calculated. To improve the accuracy of the determined grid impedance, in some embodiments, said determining the impedance of the ac grid comprises:
a value of an impedance of the AC power grid based on a voltage magnitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel, and based on a value of an impedance of a filter; wherein the filter is located between the inverter and the AC power grid.
Here, the controller in the inverter calculates the grid impedance Z of the alpha axisαIn the case of (2), the grid impedance Z of the alpha axis is adjustedαSubtracting filtersTo obtain the grid impedance Z of the alpha axisgα。
It should be noted that the controller in the inverter can adjust the grid impedance Z of the β axisβSubtracting the impedance of the filter to obtain the power grid impedance Z of the beta axisgβ(ii) a Impedance Z of O-axis power gridoSubtracting the impedance of the filter to obtain the grid impedance Z of the o axisgo。
Illustratively, in the grid-connected system as shown in fig. 4, Z is calculated according to the following formula, respectivelygα、ZgβAnd Zgo：
Zgα＝Zα-j2πNfg(Lpwm-Lline)；
Zgβ＝Zβ-j2πNfg(Lpwm-Lline)；
Fig. 5 is a schematic view of an implementation flow of a method for measuring a grid impedance provided in an application embodiment of the present application, and as shown in fig. 5, the method for measuring a grid impedance includes:
step 501: harmonic signals are synchronously injected into modulation signals of the inverter based on a common clock signal.
For the implementation process of step 501, please refer to the related description of step 201 above, which is not described herein again.
Step 502: judging whether the sampling current on the AC power grid side is greater than or equal to a set threshold value or not; wherein the sampling current is obtained by performing Clarke transformation on the three-phase alternating current.
Here, in the case where the sampling current on the ac power grid side is smaller than the set threshold, step 503 is executed; in case the sampled current on the ac mains side is larger than or equal to the set threshold, step 504 is performed.
Step 503: and increasing the voltage amplitude of the harmonic signal according to a set step length.
Here, the controller performs step 501 to synchronously inject the adjusted harmonic signal to the modulation signal of the inverter based on the common clock signal after performing step 503.
Step 504: and determining a harmonic current corresponding to the harmonic signal based on the plurality of sampling currents.
For the implementation process of step 504 to step 505, please refer to the related description of step 202 to step 203, which is not repeated herein.
Step 505: determining an impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel.
In order to implement the method for measuring the grid impedance of the embodiment of the present application, an embodiment of the present application further provides a device for measuring the grid impedance, as shown in fig. 6, the device for measuring the grid impedance includes:
a signal injection module 61, configured to synchronously inject a harmonic signal into a modulation signal of the inverter based on the common clock signal;
a first determination module 62, configured to determine a harmonic current of the harmonic signal based on a plurality of sampling currents if a sampling current on the ac power grid side is greater than or equal to a set threshold; the sampling current is obtained by performing Clarke transformation on three-phase alternating current;
a second determination module 63 for determining an 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.
In some embodiments, the apparatus for measuring the grid impedance further comprises:
the adjusting module is used for increasing the voltage amplitude of the harmonic signal according to a set step length under the condition that the sampling current is smaller than the set threshold;
the signal injection module 61 is further configured to: and synchronously injecting the adjusted harmonic signals into the modulation signals of the inverter based on the common clock signals.
In some embodiments, the frequency of the harmonic signal does not coincide with the frequency of the set nth harmonic.
In some embodiments, the harmonic signal includes at least one set of harmonics having the same voltage amplitude, each set of harmonics includes a first harmonic and a second harmonic, and the frequency of the first harmonic is symmetrical to the frequency of the second harmonic about the set N-th harmonic.
In some embodiments, the first determining module 62 is specifically configured to:
and carrying out Fourier transform on the plurality of sampling currents based on the expression of the harmonic signals to obtain the harmonic current corresponding to each group of harmonics in the harmonic signals.
In some embodiments, the harmonic currents for each set of harmonics include a first harmonic current for a first harmonic and a second harmonic current for a second harmonic; the second determining module 63 is specifically configured to:
determining a first impedance value based on the voltage amplitude of the first harmonic, and based on a first harmonic current corresponding to the first harmonic and the total number of inverters operating in parallel;
determining a second impedance value based on the voltage amplitude of the second harmonic, and based on a second harmonic current corresponding to the second harmonic and the total number of inverters operating in parallel;
and determining the mean value between the determined first impedance value and the determined second impedance value as the impedance of the alternating current power grid.
In some embodiments, the second determining module 63 is specifically configured to:
determining an impedance of the AC power grid based on a voltage amplitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel, and based on an impedance of a filter; wherein the filter is located between the inverter and the AC power grid.
In practical applications, each module included in the measuring apparatus for the grid impedance may be implemented by a Processor in the terminal, such as a Central Processing Unit (CPU), a Digital Signal Processor (DSP), a Micro Control Unit (MCU), or a Programmable Gate Array (FPGA).
It should be noted that: in the above-described embodiment, when measuring the grid impedance, the device for measuring the grid impedance is exemplified by only dividing the program modules, and in practical applications, the processing distribution may be completed by 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 processing described above. In addition, the measurement device of the power grid impedance provided by the above embodiment and the measurement method embodiment of the power grid impedance belong to the same concept, and the specific implementation process thereof is described in detail in the method embodiment and is not described herein again.
Based on the hardware implementation of the program module, and in order to implement the method of the embodiment of the present application, an embodiment of the present application further provides a controller. Fig. 7 is a schematic diagram of a hardware component structure of a controller according to an embodiment of the present application, and as shown in fig. 7, the controller 7 includes:
a communication interface 71 capable of information interaction with other devices such as network devices and the like;
and the processor 72 is connected with the communication interface 71 to realize information interaction with other equipment, and is used for executing the method for measuring the power grid impedance provided by one or more technical schemes when running a computer program. And the computer program is stored on the memory 73.
Of course, in practice, the various components in the controller 7 are coupled together by a bus system 74. It will be appreciated that the bus system 74 is used to enable communications among the components of the connection. The bus system 74 includes a power bus, a control bus, and a status signal bus in addition to a data bus. For clarity of illustration, however, the various buses are labeled as bus system 74 in fig. 7.
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 such data include: any computer program for operating on the controller 7.
It will be appreciated that the memory 73 can be either volatile memory or nonvolatile memory, and can include both volatile and nonvolatile memory. Among them, the nonvolatile Memory may be a Read Only Memory (ROM), a Programmable Read Only Memory (PROM), an Erasable Programmable Read-Only Memory (EPROM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a magnetic random access Memory (FRAM), a Flash Memory (Flash Memory), a magnetic surface Memory, an optical disk, or a Compact Disc Read-Only Memory (CD-ROM); the magnetic surface storage may be disk storage or tape storage. Volatile Memory can be Random Access Memory (RAM), which acts as external cache Memory. By way of illustration and not limitation, many forms of RAM are available, such as Static Random Access Memory (SRAM), Synchronous Static Random Access Memory (SSRAM), Dynamic Random Access Memory (DRAM), Synchronous Dynamic Random Access Memory (SDRAM), Double Data Rate Synchronous Dynamic Random Access Memory (DDRSDRAM), Enhanced Synchronous Dynamic Random Access Memory (ESDRAM), Enhanced Synchronous Dynamic Random Access Memory (Enhanced Synchronous Dynamic Random Access Memory), Synchronous linked Dynamic Random Access Memory (DRAM, Synchronous Link Dynamic Random Access Memory), Direct Memory (DRmb Random Access Memory). The memory 73 described in the embodiments of the present application is intended to comprise, without being limited to, these and any other suitable types of memory.
The method disclosed in the above embodiments of the present application may be applied to the processor 72, or implemented by the processor 72. The processor 72 may be an integrated circuit chip having signal processing capabilities. In implementation, the steps of the above method may be performed by instructions in the form of hardware, integrated logic circuits, or software in the processor 72. The processor 72 described above may be a general purpose processor, a DSP, or other programmable logic device, discrete gate or transistor logic device, discrete hardware components, or the like. Processor 72 may implement or perform the methods, steps, and logic blocks disclosed in the embodiments of the present application. A general purpose processor may be a microprocessor or any conventional processor or the like. The steps of the method disclosed in the embodiments of the present application may be directly implemented by a hardware decoding processor, or implemented by a combination of hardware and software modules in the decoding processor. The software modules may be located in a storage medium located in the memory 73, and the processor 72 reads the program in the memory 73 and performs the steps of the aforementioned method in conjunction with its hardware.
Optionally, when the processor 72 executes the program, the corresponding process implemented by the terminal in each method of the embodiment of the present application is implemented, and for brevity, no further description is given here.
In an exemplary embodiment, the present application further provides a storage medium, i.e. a computer storage medium, in particular a computer readable storage medium, for example comprising a first memory 73 storing a computer program, which is executable by a processor 72 of the terminal to perform the steps of the aforementioned method. The computer readable storage medium may be Memory such as FRAM, ROM, PROM, EPROM, EEPROM, Flash Memory, magnetic surface Memory, optical disk, or CD-ROM.
In the several embodiments provided in the present application, it should be understood that the disclosed apparatus and method may be implemented in other ways. The above-described device embodiments are merely illustrative, for example, the division of the unit is only a logical functional division, and there may be other division ways in actual implementation, such as: multiple units or components may be combined, or may be integrated into another system, or some features may be omitted, or not implemented. In addition, the coupling, direct coupling or communication connection between the components shown or discussed may be through some interfaces, and the indirect coupling or communication connection between the devices or units may be electrical, mechanical or in other forms.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed on a plurality of network units; some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, all functional units in the embodiments of the present application may be integrated into one processing module, or each unit may be separately regarded as one unit, or two or more units may be integrated into one unit; the integrated unit can be realized in a form of hardware, or in a form of hardware plus a software functional unit.
Those of ordinary skill in the art will understand that: all or part of the steps for implementing the method embodiments may be implemented by hardware related to program instructions, and the program may be stored in a computer readable storage medium, and when executed, the program performs the steps including the method embodiments; and the aforementioned storage medium includes: a mobile storage device, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The technical means described in the embodiments of the present application may be arbitrarily combined without conflict.
It should be noted that the term "and/or" in the embodiment of the present application is only an association relationship describing an associated object, and indicates that three relationships may exist, for example, a and/or B may indicate: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the term "at least one" herein means any combination of any one or more of a plurality, for example, including at least one of A, B, C, and may mean including any one or more elements selected from the group consisting of A, B and C.
The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (10)
1. A method of measuring grid impedance, comprising:
synchronously injecting a harmonic signal to a modulation signal of the inverter based on the common clock signal;
under the condition that the sampling current on the AC power grid side is greater than or equal to a set threshold, determining harmonic current corresponding to the harmonic signal based on a plurality of sampling currents; the sampling current is obtained by performing Clarke transformation on three-phase alternating current;
determining an impedance of the AC power grid based on the voltage amplitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel.
2. The method of claim 1, further comprising:
and under the condition that the sampling current is smaller than the set threshold, increasing the voltage amplitude of the harmonic signal according to a set step length, and synchronously injecting the adjusted harmonic signal into the modulation signal of the inverter based on the common clock signal.
3. 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 N-th harmonic.
4. The method of claim 3, wherein the harmonic signals comprise at least one set of harmonics having the same voltage amplitude, each set of harmonics comprises a first harmonic and a second harmonic, and the frequencies of the first harmonic and the second harmonic are symmetric about the frequency of the set Nth harmonic.
5. The method of claim 4, wherein determining the harmonic current corresponding to the harmonic signal based on the plurality of sampling currents comprises:
and carrying out Fourier transform on the plurality of sampling currents based on the expression of the harmonic signals to obtain the harmonic current corresponding to each group of harmonics in the harmonic signals.
6. The method of claim 5, wherein the harmonic current for each set of harmonics comprises a first harmonic current for a first harmonic and a second harmonic current for a second harmonic; the determining the impedance of the ac power grid includes:
determining a first impedance value based on the voltage amplitude of the first harmonic, and based on a first harmonic current corresponding to the first harmonic and the total number of inverters operating in parallel;
determining a second impedance value based on the voltage amplitude of the second harmonic, and based on a second harmonic current corresponding to the second harmonic and the total number of inverters operating in parallel;
and determining the mean value between the determined first impedance value and the determined second impedance value as the impedance of the alternating current power grid.
7. The method of claim 1, wherein the determining the impedance of the ac power grid comprises:
determining an impedance of the AC power grid based on a voltage amplitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel, and based on an impedance of a filter; wherein the filter is located between the inverter and the AC power grid.
8. A device for measuring the impedance of an electrical network, comprising:
the signal injection module is used for synchronously injecting harmonic signals to modulation signals of the inverter based on the common clock signals;
the device comprises a first determining module, a second determining module and a third determining module, wherein the first determining module is used for determining the harmonic current of the harmonic signal based on a plurality of sampling currents under the condition that the sampling current on the alternating current power grid side is larger than or equal to a set threshold; the sampling current is obtained by performing Clarke transformation on three-phase alternating current;
a second determination module to determine an impedance of the AC power grid based on a voltage magnitude of the harmonic signal, the determined harmonic current, and a total number of inverters operating in parallel.
9. A controller, comprising: a processor and a memory for storing a computer program capable of running on the processor,
wherein the processor is adapted to perform the steps of the method of any one of claims 1 to 7 when running the computer program.
10. A storage medium on which a computer program is stored which, when being executed by a processor, carries out the steps of the method according to any one of claims 1 to 7.
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| CN114720771A (en) * | 2022-06-08 | 2022-07-08 | 阳光电源股份有限公司 | Inverter and alternating current insulation impedance detection method thereof |
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