CN110045187B - Grid-connected inverter power grid impedance identification method based on high-frequency signal injection - Google Patents

Grid-connected inverter power grid impedance identification method based on high-frequency signal injection Download PDF

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CN110045187B
CN110045187B CN201910375598.5A CN201910375598A CN110045187B CN 110045187 B CN110045187 B CN 110045187B CN 201910375598 A CN201910375598 A CN 201910375598A CN 110045187 B CN110045187 B CN 110045187B
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grid
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CN110045187A (en
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郭磊磊
金楠
秦世耀
王瑞明
代林旺
曹玲芝
李琰琰
武洁
吴振军
窦智峰
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China Electric Power Research Institute Co Ltd CEPRI
Zhengzhou University of Light Industry
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Zhengzhou University of Light Industry
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Abstract

The invention provides a grid-connected inverter power grid impedance identification method based on high-frequency signal injection, which comprises the steps of firstly, respectively measuring the voltage and the bridge arm side current of a grid-connected inverter by using a voltage sensor and a current sensor, and transforming the voltage and the bridge arm side current by using a proportional-integral controller to obtain a modulation voltage signal; then, injecting a three-phase high-frequency voltage signal into the modulation voltage signal to update the voltage of the grid-connected inverter, measuring the current of the grid side of the grid-connected inverter by using a current sensor, and respectively substituting the updated voltage and the current of the grid side into a voltage extraction module and a current extraction module; and finally, extracting the high-frequency voltage signal and the high-frequency current signal of the power grid of the grid-connected inverter by using the improved complex filter, thereby solving the impedance value of the power grid in real time. According to the invention, the three-phase high-frequency voltage signal is directly superposed on the modulation voltage signal, so that effective injection of the high-frequency signal is ensured, the signal-to-noise ratio of the power grid can be improved, and the impedance identification precision of the power grid is further improved.

Description

Grid-connected inverter power grid impedance identification method based on high-frequency signal injection
Technical Field
The invention relates to the technical field of power electronics, in particular to a grid-connected inverter power grid impedance identification method based on high-frequency signal injection.
Background
In recent years, with the rapid expansion of the installation scale of a new energy grid-connected inverter, the power grid increasingly presents the characteristic of a weak power grid, the impedance of the power grid is also increasingly large, and the stable operation of the grid-connected inverter is greatly influenced. In order to improve the operation stability of the grid-connected inverter under the weak grid, the impedance of the grid must be identified in real time, and the operation mode of the grid-connected inverter must be adjusted in real time according to the impedance value of the grid. The commonly used power grid impedance identification methods mainly include a passive method and an active method. The passive method calculates the impedance of the power grid by detecting the inherent voltage and current harmonics of the power grid, and the method cannot increase harmonic disturbance to the power grid, but the impedance identification precision of the passive method is low due to low signal-to-noise ratio. The active method is used for injecting voltage harmonic waves of characteristic frequency into a power grid and extracting harmonic current of the power grid so as to realize power grid impedance identification, and the active method is used for improving the signal-to-noise ratio by injecting high-frequency signals so as to improve the power grid impedance identification precision, so that the active method is more widely applied.
At present, a plurality of power grid impedance identification methods are applied for patents, such as the power grid impedance identification verification method and the power grid impedance identification experimental device with the application number of 201710113861.4, and the invention name is that a power grid impedance identification method and an experimental device are provided, wherein a high-frequency current signal is injected into a current reference value, and the injected high-frequency signal is contained in the output current and voltage of a grid-connected inverter through current closed-loop control; although the method can realize the identification of the impedance of the power grid, the current loop proportional-integral controller can only realize the non-static tracking of the direct current signal but cannot realize the non-static tracking of the injected high-frequency signal, so that the effect of the actually injected high-frequency signal is poor. For example, the application number is 201710361584.9, the invention name is a power grid impedance online identification method and device based on PRBS disturbance injection, and provides a power grid impedance online identification method and device based on PRBS disturbance injection and a power grid impedance detection method [ J ] based on a multi-module complex filter under a Poplar, Zhang, Li Ming, unbalance and harmonic power grid, a power source academic report, 2018,16(2):69-75 ] to provide a power grid impedance identification method considering the influences of power grid unbalance and harmonic waves, wherein high-frequency disturbance signals need to be superposed in current, so that a current loop proportional integral controller needs to be reasonably designed to possibly ensure that current and voltage signals actually output by a grid-connected inverter contain corresponding high-frequency signals.
Application number is 201820339286.X, the utility model discloses a circuit and method are discerned to identification based on online impedance, provide an impedance identification circuit and method, this method is through annotating current pulse signal into to the current instruction to electric wire netting voltage and current signal after the sampling injection signal obtain electric wire netting impedance through the analysis and calculation, this method has the calculated amount great, realizes complicated scheduling problem.
Disclosure of Invention
The invention provides a grid-connected inverter power grid impedance identification method based on high-frequency signal injection, which aims at solving the technical problems that an effective high-frequency signal cannot be injected into the existing power grid impedance identification method and direct current bias is not considered to be introduced into a voltage and current sampling channel, so that the identification precision of the power grid impedance is lower. Secondly, a high-pass filter is added on the basis of the complex filter to extract high-frequency voltage signals and high-frequency current signals, so that the influence of direct current bias introduced into a voltage and current sampling channel on impedance identification can be eliminated, and the impedance identification precision of the power grid is further improved.
The technical scheme of the invention is realized as follows:
a grid-connected inverter power grid impedance identification method based on high-frequency signal injection comprises the following steps:
s1, sampling the grid of the grid-connected inverter by using the voltage sensor to obtain the line voltage u of the grid-connected invertergabSum line voltage ugbcAnd calculating to obtain the phase voltage u of the three-phase power gridgaPhase voltage ugbAnd phase voltage ugcAnd phase voltage ugaPhase voltage ugbAnd phase voltage ugcTransforming into two-phase static DQ coordinate system to obtain voltage ugDAnd voltage ugQAnd applying a voltage ugDAnd voltage ugQSubstituting the phase-locked loop to obtain the synchronous angular frequency omega of the power grid0And angle theta0；
S2, sampling bridge arm side current of the grid-connected inverter by using a current sensor to obtain three-phase current iaThree-phase current ibAnd three-phase current icAnd apply three-phase current iaThree-phase current ibAnd three-phase current icConverting into two-phase static DQ coordinate system to obtain two current components as current iDAnd current iQAngle of reuse theta0Will current iDAnd current iQMapping to a synchronous rotation dq coordinate system to obtain two current components which are respectively current idAnd current iq；
S3, setting the current reference value as the current idrefAnd current iqrefWill current idrefCurrent iqrefAnd the current i obtained in step S2dCurrent iqObtaining a modulation voltage signal u in a synchronously rotating dq coordinate system through a proportional-integral controllerdrefAnd a modulated voltage signal uqrefThen modulating the voltage signal udrefAnd a modulated voltage signal uqrefConverting the two-phase static DQ coordinate system to obtain a modulation voltage signal uDrefAnd a modulated voltage signal uQref；
S4, modulating voltage signal u obtained in step S3DrefAnd a modulated voltage signal uQrefConverting into a three-phase static abc coordinate system to obtain three modulation voltage signals which are respectively modulation voltage signals uarefModulating the voltage signal ubrefAnd a modulated voltage signal ucrefThen, the high frequency signal u is appliedahHigh frequency signal ubhAnd a high frequency signal uchSeparately injecting modulated voltage signals uarefModulating the voltage signal ubrefAnd a modulated voltage signal ucrefObtaining three-phase modulation voltage signals which are respectively modulation voltage signals uahrefModulating the voltage signal ubhrefAnd a modulated voltage signal uchref；
S5, modulating voltage signal u obtained in step S4ahrefModulating the voltage signal ubhrefAnd a modulated voltage signal uchrefInputting the voltage u to a PWM modulation unit, outputting 6 paths of PWM signals, inputting the PWM signals to a grid-connected inverter through a control system in the grid-connected inverter, and updating the voltage u in the step S1gDAnd voltage ugQ；
S6, converting the voltage u obtained in the step S5 into a voltage ugDAnd voltage ugQRespectively substituted into uDhExtraction Module and uQhAn extraction module for respectively aligning u with the improved complex filterDhExtraction Module and uQhThe extraction module performs extraction operation to obtain a high-frequency voltage signal uDhAnd a high frequency voltage signal uQh；
S7, sampling the current of the grid side of the grid-connected inverter by using the current sensor to obtain a three-phase current igaThree-phase current igbAnd three-phase current igcAnd apply three-phase current igaThree-phase current igbAnd three-phase current igcConverting into two-phase static DQ coordinate system to obtain two current components as current igDAnd current igQ；
S8, converting the current i obtained in the step S7gDAnd current igQRespectively substitute in iDhExtraction Module and iQhAn extraction module for respectively aligning i with the improved complex filterDhExtraction Module and iQhThe extraction module performs extraction operation to obtain a high-frequency current signal iDhAnd a high-frequency current signal iQh；
S9, obtaining the high-frequency voltage signal u according to the step S6DhHigh frequency voltage signal uQhAnd the high-frequency current signal i obtained in step S8DhHigh frequency current signal iQhCalculating the resistance value of the grid-connected inverter
Figure BDA0002051547160000031
And inductance value
Figure BDA0002051547160000032
And further obtaining the impedance value of the power grid.
Preferably, the voltage u in the step S1gDAnd voltage ugQComprises the following steps:
Figure BDA0002051547160000033
wherein the content of the first and second substances,
Figure BDA0002051547160000034
then use the voltage ugDAnd voltage ugQCalculating to obtain the angle theta of the power grid0Comprises the following steps:
Figure BDA0002051547160000035
synchronous angular frequency omega of a power grid0Comprises the following steps:
Figure BDA0002051547160000036
preferably, the current i in the step S2dAnd current iqComprises the following steps:
Figure BDA0002051547160000037
wherein the content of the first and second substances,
Figure BDA0002051547160000038
preferably, the modulation voltage signal u in the step S3DrefAnd a modulated voltage signal uQrefComprises the following steps:
Figure BDA0002051547160000039
wherein the content of the first and second substances,
Figure BDA00020515471600000310
k1is the proportionality coefficient, k, of a proportional-integral regulator2Is the integral coefficient of the proportional integral regulator, and s is the laplacian operator.
Preferably, the modulation voltage signal u in the step S4ahrefModulating the voltage signalubhrefAnd a modulated voltage signal uchrefRespectively as follows:
Figure BDA0002051547160000041
wherein the content of the first and second substances,
Figure BDA0002051547160000042
Uht represents time, which is the amplitude of the injected high frequency signal.
Preferably, the high-frequency voltage signal u in the step S6DhAnd a high frequency voltage signal uQhThe extraction method comprises the following steps:
s61, utilizing the voltage u obtained in the step S5gDAnd voltage ugQCalculating error voltage signals u respectivelygDerr1And error voltage signal ugQerr1：
Figure BDA0002051547160000043
Wherein u isgDAnd ugQRespectively the voltage, u, on a stationary DQ coordinate system of two phasesDhAnd uQhAre all high-frequency voltage signals to be extracted,
Figure BDA0002051547160000044
and
Figure BDA0002051547160000045
are all positive sequence components of the grid voltage;
s62, using high-pass filter
Figure BDA0002051547160000046
For the error voltage signal u obtained in step S61gDerr1And error voltage signal ugQerr1Filtering to obtain error voltage signal ugDerrAnd error voltage signal ugQerr：
Figure BDA0002051547160000047
S63 error obtained from step S62Differential voltage signal ugDerrAnd error voltage signal ugQerrCalculating a high frequency voltage signal uDhHigh frequency voltage signal uQhPositive sequence component of the grid voltage
Figure BDA0002051547160000048
Positive sequence component of network voltage
Figure BDA0002051547160000049
Figure BDA00020515471600000410
Wherein, ω ishc,uFor a high-frequency voltage signal uDhExtraction unit and high-frequency voltage signal uQhCut-off frequency, omega, of the extraction unitc,uFor positive sequence voltage of network voltage
Figure BDA00020515471600000411
Extraction unit and grid voltage positive sequence voltage
Figure BDA00020515471600000412
Cut-off frequency, omega, of the extraction unit0For the synchronous angular frequency of the power grid,
Figure BDA00020515471600000413
θ0in the context of the power grid,
Figure BDA00020515471600000414
j represents an imaginary number;
s64, converting the high-frequency voltage signal u obtained in the step S63DhHigh frequency voltage signal uQhPositive sequence component of the grid voltage
Figure BDA0002051547160000051
And the positive sequence component of the network voltage
Figure BDA0002051547160000052
Substituting into step S61, updating the error voltage signalNumber ugDerr1And error voltage signal ugQerr1；
S65, repeating the steps S61 to S64 until reaching the set command signal, stopping the operation, and outputting the extracted high-frequency voltage signal uDhAnd a high frequency voltage signal uQh。
Preferably, the current i in the step S7gDAnd current igQComprises the following steps:
Figure BDA0002051547160000053
preferably, the high-frequency current signal i in the step S8DhAnd a high-frequency current signal iQhThe extraction method comprises the following steps:
s81, utilizing the current i obtained in the step S7gDAnd current igQSeparately calculating error current signals igDerr1And an error current signal igQerr1：
Figure BDA0002051547160000054
Wherein igDAnd igQCurrent i in the two-phase stationary DQ coordinate system, respectivelyDhAnd iQhAre all high-frequency current signals to be extracted,
Figure BDA0002051547160000055
and
Figure BDA0002051547160000056
are all the positive sequence components of the power grid current;
s82, using high-pass filter to process the error current signal i obtained in the step S81gDerr1And an error current signal igQerr1Filtering to obtain an error current signal igDerrAnd an error current signal igQerr：
Figure BDA0002051547160000057
S83 error obtained from step S82Differential current signal igDerrAnd an error current signal igQerrCalculating a high frequency current signal iDhHigh frequency current signal iQhPositive sequence component of grid current
Figure BDA0002051547160000058
Positive sequence component of grid current
Figure BDA0002051547160000059
Figure BDA00020515471600000510
Wherein, ω ishc,iFor high-frequency current signals iDhAnd a high-frequency current signal iQhCut-off frequency of the extraction unit, andhc,i＝ωhc,u，ωc,ifor positive sequence component of network current
Figure BDA0002051547160000061
And the positive sequence component of the network current
Figure BDA0002051547160000062
Cut-off frequency, omega, of the extraction unitc,i＝ωc,u；
S84, converting the high-frequency current signal i obtained in the step S83DhHigh frequency current signal iQhPositive sequence component of grid current
Figure BDA0002051547160000067
And the positive sequence component of the network current
Figure BDA0002051547160000063
Substituting step S81 to update error current signal igDerr1And an error current signal igQerr1；
S85, repeating the steps S81 to S84 until reaching the set command signal, stopping the operation, and outputting the extracted high-frequency current signal iDhAnd a high-frequency current signal iQh。
Preferably, the resistance value of the grid
Figure BDA0002051547160000064
And inductance value
Figure BDA0002051547160000065
Comprises the following steps:
Figure BDA0002051547160000066
the beneficial effect that this technical scheme can produce: compared with the prior art, the method has the advantages that the high-frequency signal is not selected to be superposed on the current instruction, but the three-phase high-frequency voltage signal is directly superposed on the modulation voltage signal, so that the effective injection of the high-frequency signal is ensured, and the proportional-integral controller of the modulation current loop is not required to be modified again.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic view of the overall structure of the grid impedance identification module according to the present invention.
FIG. 2 shows the high-frequency voltage u in FIG. 1DhAnd (5) a schematic structure diagram of the extraction module.
FIG. 3 shows the high-frequency voltage u in FIG. 1QhAnd (5) a schematic structure diagram of the extraction module.
FIG. 4 shows the high-frequency current i in FIG. 1DhAnd (5) a schematic structure diagram of the extraction module.
FIG. 5 shows the high-frequency current i in FIG. 1QhAnd (5) a schematic structure diagram of the extraction module.
Fig. 6 is a schematic view of the overall structure of the present invention.
Fig. 7 is an impedance identification simulation result diagram of a power grid impedance detection method [ J ] of a power source report, 2018,16(2):69-75 ] based on a multi-module complex filter under a document [ Yangying, Zhanging, Liming, unbalanced and harmonic power grid ].
Fig. 8 is a partial result graph of the region a in fig. 7.
FIG. 9 is a diagram of simulation results of impedance identification according to the present invention.
Fig. 10 is a partial result diagram of the region B in fig. 9.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
As shown in fig. 1 and fig. 6, the invention provides a grid-connected inverter power grid impedance identification method based on high-frequency signal injection, which includes firstly, obtaining voltage of a grid-connected inverter and current of a bridge arm side by using a voltage sensor and a current sensor, and transforming the voltage and the current of the bridge arm side by using a proportional integrator to obtain a modulation voltage signal; then, injecting a three-phase high-frequency voltage signal into the modulation voltage signal to update the voltage of the grid-connected inverter, obtaining the current of the grid side of the grid-connected inverter by using a current sensor, and respectively substituting the updated voltage and the current of the grid side into a voltage extraction module and a current extraction module; and finally, extracting a high-frequency voltage signal and a high-frequency current signal of a power grid of the grid-connected inverter by using the improved complex filter, thereby solving the impedance value of the power grid in real time, wherein the method comprises the following specific steps:
s1, sampling the grid of the grid-connected inverter by using the voltage sensor to obtain the line voltage u of the grid-connected invertergabSum line voltage ugbcAnd the line voltage u is measured by the formula (1)gabSum line voltage ugbcCalculating to obtain phase voltage u of three-phase power gridgaPhase voltage ofugbAnd phase voltage ugc：
Figure BDA0002051547160000071
Then according to the formula (2) phase voltage ugaPhase voltage ugbAnd phase voltage ugcTransforming into two-phase static DQ coordinate system to obtain voltage ugDAnd voltage ugQ：
Figure BDA0002051547160000072
Then the voltage u is appliedgDAnd voltage ugQSubstituting the phase-locked loop to obtain the synchronous angular frequency omega of the power grid0And angle theta0，
Figure BDA0002051547160000073
S2, sampling bridge arm side current of the grid-connected inverter by using a current sensor to obtain three-phase current iaThree-phase current ibAnd three-phase current icAnd the three-phase current i is converted according to the formula (3)aThree-phase current ibAnd three-phase current icConverting into two-phase static DQ coordinate system to obtain two current components as current iDAnd current iQ：
Figure BDA0002051547160000081
Then, the current i is adjusted according to the formula (4)DAnd current iQMapping to a synchronous rotation dq coordinate system to obtain two current components which are respectively current idAnd current iq：
Figure BDA0002051547160000082
Wherein, theta0In the context of a power grid.
S3, setting the current reference value as the current idrefAnd current iqrefThe current i is set according to equation (5)drefCurrent iqrefAnd the current i in step S2dCurrent iqObtaining a modulation voltage signal u in a synchronously rotating dq coordinate system through a proportional-integral controllerdrefAnd a modulated voltage signal uqref：
Figure BDA0002051547160000083
Modulating voltage signal u according to formula (6)drefAnd a modulated voltage signal uqrefConverting the two modulation voltage signals into a two-phase static DQ coordinate system to obtain two modulation voltage signals which are respectively modulation voltage signals uDrefAnd a modulated voltage signal uQref：
Figure BDA0002051547160000084
Wherein k is1Is the proportionality coefficient, k, of a proportional-integral regulator2Is the integral coefficient of the proportional integral regulator, and s is the laplacian operator.
S4, according to the formula (7), the modulation voltage signal u obtained in the step S3DrefAnd a modulated voltage signal uQrefConverting into a three-phase static abc coordinate system to obtain three modulation voltage signals which are respectively modulation voltage signals uarefModulating the voltage signal ubrefAnd a modulated voltage signal ucrefRespectively as follows:
Figure BDA0002051547160000085
then, the high frequency signal u is processed according to the formula (8)ahHigh frequency signal ubhAnd a high frequency signal uchInjecting a modulated voltage signal uarefModulating the voltage signal ubrefAnd a modulated voltage signal ucrefObtaining three-phase modulation voltage signals which are respectively modulation voltage signalsuahrefModulating the voltage signal ubhrefAnd a modulated voltage signal uchref：
Figure BDA0002051547160000091
Wherein the content of the first and second substances,
Figure BDA0002051547160000092
Uht represents time, which is the amplitude of the injected high frequency signal.
S5, modulating voltage signal u obtained in step S4ahrefModulating the voltage signal ubhrefAnd a modulated voltage signal uchrefInputting the voltage u to a PWM modulation unit, outputting 6 paths of PWM signals, inputting the PWM signals to a grid-connected inverter through a control system in the grid-connected inverter, and updating the voltage u in the step S1gDAnd voltage ugQ。
S6, as shown in FIG. 2 and FIG. 3, the voltage u obtained in the step S5gDAnd voltage ugQRespectively substituted into uDhExtraction Module and uQhAn extraction module for respectively aligning u with the improved complex filterDhExtraction Module and uQhThe extraction module performs extraction operation to obtain a high-frequency voltage signal uDhAnd a high frequency voltage signal uQhThe method comprises the following specific steps:
s61, utilizing the voltage u obtained in the step S5gDAnd voltage ugQCalculating error voltage signals u respectivelygDerr1And error voltage signal ugQerr1：
Figure BDA0002051547160000098
Wherein u isgDAnd ugQRespectively the voltage, u, on a stationary DQ coordinate system of two phasesDhAnd uQhAre all high-frequency voltage signals to be extracted,
Figure BDA0002051547160000093
and
Figure BDA0002051547160000094
are all positive sequence components of the grid voltage; initially, a high-frequency voltage signal uDhHigh frequency voltage signal uQhPositive sequence component of the grid voltage
Figure BDA0002051547160000095
And the positive sequence component of the network voltage
Figure BDA0002051547160000096
Are all set to zero.
S62, using high-pass filter
Figure BDA0002051547160000097
For the error voltage signal u obtained in step S61gDerr1And error voltage signal ugQerr1Filtering to obtain error voltage signal ugDerrAnd error voltage signal ugQerr：
Figure BDA0002051547160000101
Wherein, ω is0For the synchronous angular frequency of the power grid,
Figure BDA0002051547160000102
θ0in the context of the power grid,
Figure BDA0002051547160000103
s is the laplace operator.
S63, obtaining the error voltage signal u according to the step S62gDerrAnd error voltage signal ugQerrCalculating a high frequency voltage signal uDhHigh frequency voltage signal uQhPositive sequence component of the grid voltage
Figure BDA0002051547160000104
Positive sequence component of network voltage
Figure BDA0002051547160000105
Figure BDA0002051547160000106
Wherein, ω ishc,uFor a high-frequency voltage signal uDhExtraction unit and high-frequency voltage signal uQhCut-off frequency, omega, of the extraction unitc,uFor positive sequence voltage of network voltage
Figure BDA0002051547160000107
Extraction unit and grid voltage positive sequence voltage
Figure BDA0002051547160000108
Cut-off frequency, omega, of the extraction unit0For the synchronous angular frequency of the power grid,
Figure BDA0002051547160000109
θ0in the context of the power grid,
Figure BDA00020515471600001010
j represents an imaginary number and s is the laplacian operator.
S64, converting the high-frequency voltage signal u obtained in the step S63DhHigh frequency voltage signal uQhPositive sequence component of the grid voltage
Figure BDA00020515471600001011
And the positive sequence component of the network voltage
Figure BDA00020515471600001012
Substituting into step S61, the error voltage signal u is updatedgDerr1And error voltage signal ugQerr1。
S65, repeating the steps S61 to S64 until reaching the set command signal, stopping the operation, and outputting the extracted high-frequency voltage signal uDhAnd a high frequency voltage signal uQh。
S7, utilizing current sensor to carry out grid-connected inversionSampling the current at the power grid side of the device to obtain three-phase current igaThree-phase current igbAnd three-phase current igcAnd the three-phase current i is converted according to the formula (13)gaThree-phase current igbAnd three-phase current igcConverting into two-phase static DQ coordinate system to obtain two current components as current igDAnd current igQ：
Figure BDA00020515471600001013
S8, as shown in FIGS. 4 and 5, the current i obtained in step S7 is measuredgDAnd current igQRespectively substitute in iDhExtraction Module and iQhAn extraction module for respectively aligning i with the improved complex filterDhExtraction Module and iQhThe extraction module performs extraction operation to obtain a high-frequency current signal iDhAnd a high-frequency current signal iQhThe method comprises the following specific steps:
s81, utilizing the current i obtained in the step S7gDAnd current igQSeparately calculating error current signals igDerr1And an error current signal igQerr1：
Figure BDA0002051547160000111
Wherein igDAnd igQCurrent i in the two-phase stationary DQ coordinate system, respectivelyDhAnd iQhAre all high-frequency current signals to be extracted,
Figure BDA0002051547160000112
and
Figure BDA0002051547160000113
are all the positive sequence components of the power grid current; initially, a high frequency current signal iDhHigh frequency current signal iQhPositive sequence component of grid current
Figure BDA0002051547160000114
And the positive sequence component of the network current
Figure BDA0002051547160000115
Are all set to zero.
S82, using high-pass filter
Figure BDA0002051547160000116
For the error current signal i obtained in step S81gDerr1And an error current signal igQerr1Filtering to obtain an error current signal igDerrAnd an error current signal igQerr：
Figure BDA0002051547160000117
S83, obtaining the error current signal i according to the step S82gDerrAnd an error current signal igQerrCalculating a high frequency current signal iDhHigh frequency current signal iQhPositive sequence component of grid current
Figure BDA0002051547160000118
Positive sequence component of grid current
Figure BDA0002051547160000119
Figure BDA00020515471600001110
Wherein, ω ishc,iFor high-frequency current signals iDhExtraction unit and high-frequency current signal iQhCut-off frequency of the extraction unit, andhc,i＝ωhc,u，ωc,ifor positive sequence component of network current
Figure BDA00020515471600001111
Extraction unit and grid current positive sequence component
Figure BDA00020515471600001112
Cut-off frequency, omega, of the extraction unitc,i＝ωc,u。
S84, converting the high-frequency current signal i obtained in the step S83DhHigh frequency current signal iQhPositive sequence component of grid current
Figure BDA0002051547160000121
And the positive sequence component of the network current
Figure BDA0002051547160000122
Substituting step S81 to update error current signal igDerr1And an error current signal igQerr1。
S85, repeating the steps S81 to S84 until reaching the set command signal, stopping the operation, and outputting the extracted high-frequency current signal iDhAnd a high-frequency current signal iQh。
S9, obtaining the high-frequency voltage signal u according to the step S6DhHigh frequency voltage signal uQhAnd the high-frequency current signal i obtained in step S8DhHigh frequency current signal iQhCalculating the resistance value of the grid-connected inverter
Figure BDA0002051547160000123
And inductance value
Figure BDA0002051547160000124
And further obtaining the impedance value of the power grid. Wherein the resistance value of the power grid
Figure BDA0002051547160000125
And inductance value
Figure BDA0002051547160000126
The calculation method of (2) is shown in formula (17):
Figure BDA0002051547160000127
in order to verify the effectiveness of the present invention, simulation verification was performed. Simulation adoptsDirect-current side voltage u of grid-connected inverterdc700V, grid-connected inverter side output inductor Li5mH, filter capacitor C of 15.6 muF, and damping resistor R d2 omega, grid angular frequency omega0314rad/s, 311V grid phase voltage amplitude, and the amplitude U of the injected high-frequency signalh121V, the frequency of the injected high-frequency signal is 3424rad/s, and the cut-off frequency omegahc,uAnd a cut-off frequency omegahc,iIs 400rad/s, cut-off frequency omegac,uAnd a cut-off frequency omegac,iFor 221rad/s, set the current idrefAnd current iqrefAre 40A and 0A, respectively. In order to verify the effectiveness of the invention, the invention is compared with a power grid impedance detection method based on a multi-module complex filter under a document [ Yangying, Zhanging, Liming, unbalanced and harmonic power grid [ J ]]The power source academic newspaper, 2018,16(2):69-75.]The proposed protocol was subjected to comparative studies. In simulation, the resistance R of the power gridgSet to 1 Ω, grid inductance LgThe sudden increase from 1.2mH to 2.4mH at 0.4s and the sudden decrease from 2.4mH to 1.2mH at 0.8 s. During simulation, the measured grid voltage u is subjected to direct current bias in order to simulate the direct current bias introduced into a voltage sampling channel and a current sampling channelgaA dc bias of 25V is superimposed. FIG. 7 and FIG. 8 show a power grid impedance detection method [ J ] based on a multi-module complex filter under the condition of a Yangying, Zhanging, Liming, unbalanced and harmonic power grid]The power source academic newspaper, 2018,16(2):69-75.]The power grid impedance identification simulation result of the proposed scheme is shown in fig. 9 and 10. It can be seen from comparison that the power grid impedance detection method based on the multi-module complex filter is adopted under the document [ Yangying, Zhangxing, Liming, unbalanced and harmonic power grid [ J]The power source academic newspaper, 2018,16(2):69-75.]According to the scheme, the influence of direct current bias in the sampling channel is not considered, so that the identified power grid impedance contains large fundamental frequency fluctuation, and the identification accuracy is poor. The invention considers the influence of the direct current bias in the sampling channel and inhibits the direct current bias by the high-pass filter, thereby eliminating the influence of the direct current bias on the identification of the impedance of the power grid and improving the identification precision of the impedance of the power grid.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (9)

1. A grid-connected inverter power grid impedance identification method based on high-frequency signal injection is characterized by comprising the following steps:
s1, sampling the grid of the grid-connected inverter by using the voltage sensor to obtain the line voltage u of the grid-connected invertergabSum line voltage ugbcAnd calculating to obtain the phase voltage u of the three-phase power gridgaPhase voltage ugbAnd phase voltage ugcAnd phase voltage ugaPhase voltage ugbAnd phase voltage ugcTransforming into two-phase static DQ coordinate system to obtain voltage ugDAnd voltage ugQAnd applying a voltage ugDAnd voltage ugQSubstituting the phase-locked loop to obtain the synchronous angular frequency omega of the power grid0And angle theta0；
S2, sampling bridge arm side current of the grid-connected inverter by using a current sensor to obtain three-phase current iaThree-phase current ibAnd three-phase current icAnd apply three-phase current iaThree-phase current ibAnd three-phase current icConverting into two-phase static DQ coordinate system to obtain two current components as current iDAnd current iQAngle of reuse theta0Will current iDAnd current iQMapping to a synchronous rotation dq coordinate system to obtain two current components which are respectively current idAnd current iq；
S3, setting the current reference value as the current idrefAnd current iqrefWill current idrefCurrent iqrefAnd the current i obtained in step S2dCurrent iqObtaining a modulation voltage signal u in a synchronously rotating dq coordinate system through a proportional-integral controllerdrefAnd a modulated voltage signal uqrefThen modulating the voltage signal udrefAnd a modulated voltage signal uqrefConverting the two-phase static DQ coordinate system to obtain a modulation voltage signal uDrefAnd modulating electricityPressure signal uQref；
S4, modulating voltage signal u obtained in step S3DrefAnd a modulated voltage signal uQrefConverting into a three-phase static abc coordinate system to obtain three modulation voltage signals which are respectively modulation voltage signals uarefModulating the voltage signal ubrefAnd a modulated voltage signal ucrefThen, the high frequency signal u is appliedahHigh frequency signal ubhAnd a high frequency signal uchSeparately injecting modulated voltage signals uarefModulating the voltage signal ubrefAnd a modulated voltage signal ucrefObtaining three-phase modulation voltage signals which are respectively modulation voltage signals uahrefModulating the voltage signal ubhrefAnd a modulated voltage signal uchref；
S5, modulating voltage signal u obtained in step S4ahrefModulating the voltage signal ubhrefAnd a modulated voltage signal uchrefInputting the voltage u to a PWM modulation unit, outputting 6 paths of PWM signals, inputting the PWM signals to a grid-connected inverter through a control system in the grid-connected inverter, and updating the voltage u in the step S1gDAnd voltage ugQ；
S6, converting the voltage u obtained in the step S5 into a voltage ugDAnd voltage ugQRespectively substituted into uDhExtraction Module and uQhAn extraction module for respectively aligning u with the improved complex filterDhExtraction Module and uQhThe extraction module performs extraction operation to obtain a high-frequency voltage signal uDhAnd a high frequency voltage signal uQh；
S7, sampling the current of the grid side of the grid-connected inverter by using the current sensor to obtain a three-phase current igaThree-phase current igbAnd three-phase current igcAnd apply three-phase current igaThree-phase current igbAnd three-phase current igcConverting into two-phase static DQ coordinate system to obtain two current components as current igDAnd current igQ；
S8, converting the current i obtained in the step S7gDAnd current igQRespectively substitute in iDhExtraction Module and iQhExtraction module by improved complex filteringDevices are respectively paired with iDhExtraction Module and iQhThe extraction module performs extraction operation to obtain a high-frequency current signal iDhAnd a high-frequency current signal iQh；
S9, obtaining the high-frequency voltage signal u according to the step S6DhHigh frequency voltage signal uQhAnd the high-frequency current signal i obtained in step S8DhHigh frequency current signal iQhCalculating the resistance value of the grid-connected inverter
Figure FDA0002750878650000021
And inductance value
Figure FDA0002750878650000022
And further obtaining the impedance value of the power grid.
2. The grid-connected inverter grid impedance identification method based on high-frequency signal injection as claimed in claim 1, wherein the voltage u in the step S1gDAnd voltage ugQComprises the following steps:
Figure FDA0002750878650000023
wherein the content of the first and second substances,
Figure FDA0002750878650000024
then use the voltage ugDAnd voltage ugQCalculating to obtain the angle theta of the power grid0Comprises the following steps:
Figure FDA0002750878650000025
synchronous angular frequency omega of a power grid0Comprises the following steps:
Figure FDA0002750878650000026
3. the grid-connected inverter grid impedance identification method based on high-frequency signal injection as claimed in claim 1 or 2, wherein the current i in the step S2dAnd current iqComprises the following steps:
Figure FDA0002750878650000027
wherein the content of the first and second substances,
Figure FDA0002750878650000028
4. the grid-connected inverter grid impedance identification method based on high-frequency signal injection as claimed in claim 3, wherein the modulation voltage signal u in the step S3DrefAnd a modulated voltage signal uQrefComprises the following steps:
Figure FDA0002750878650000029
wherein the content of the first and second substances,
Figure FDA00027508786500000210
k1is the proportionality coefficient, k, of a proportional-integral regulator2Is the integral coefficient of the proportional integral regulator, and s is the laplacian operator.
5. The grid-connected inverter grid impedance identification method based on high-frequency signal injection as claimed in claim 4, wherein the modulation voltage signal u in the step S4ahrefModulating the voltage signal ubhrefAnd a modulated voltage signal uchrefRespectively as follows:
Figure FDA0002750878650000031
wherein the content of the first and second substances,
Figure FDA0002750878650000032
Uht represents time, which is the amplitude of the injected high frequency signal.
6. High frequency based message according to claim 1The grid-connected inverter grid impedance identification method based on signal injection is characterized in that the high-frequency voltage signal u in the step S6DhAnd a high frequency voltage signal uQhThe extraction method comprises the following steps:
s61, utilizing the voltage u obtained in the step S5gDAnd voltage ugQCalculating error voltage signals u respectivelygDerr1And error voltage signal ugQerr1：
Figure FDA0002750878650000033
Wherein u isgDAnd ugQRespectively the voltage, u, on a stationary DQ coordinate system of two phasesDhAnd uQhAre all high-frequency voltage signals to be extracted,
Figure FDA0002750878650000034
and
Figure FDA0002750878650000035
are all positive sequence components of the grid voltage;
s62, using high-pass filter
Figure FDA0002750878650000036
For the error voltage signal u obtained in step S61gDerr1And error voltage signal ugQerr1Filtering to obtain error voltage signal ugDerrAnd error voltage signal ugQerr：
Figure FDA0002750878650000037
Wherein s is a Laplace operator;
s63, obtaining the error voltage signal u according to the step S62gDerrAnd error voltage signal ugQerrCalculating a high frequency voltage signal uDhHigh frequency voltage signal uQhPositive sequence component of the grid voltage
Figure FDA0002750878650000038
Positive sequence component of network voltage
Figure FDA0002750878650000039
Figure FDA00027508786500000310
Wherein, ω ishc,uFor a high-frequency voltage signal uDhExtraction unit and high-frequency voltage signal uQhCut-off frequency, omega, of the extraction unitc,uFor positive sequence voltage of network voltage
Figure FDA00027508786500000311
Extraction unit and grid voltage positive sequence voltage
Figure FDA00027508786500000312
Cut-off frequency, omega, of the extraction unit0For the synchronous angular frequency of the power grid,
Figure FDA0002750878650000041
θ0in the context of the power grid,
Figure FDA0002750878650000042
j represents an imaginary number;
s64, converting the high-frequency voltage signal u obtained in the step S63DhHigh frequency voltage signal uQhPositive sequence component of the grid voltage
Figure FDA0002750878650000043
And the positive sequence component of the network voltage
Figure FDA0002750878650000044
Substituting into step S61, the error voltage signal u is updatedgDerr1And error voltage signal ugQerr1；
S65, repeating the steps S61 to S64 until reaching the set command signal, stopping the operation, and outputting the extracted high-frequency voltage signal uDhAnd a high frequency voltage signal uQh。
7. The grid-connected inverter grid impedance identification method based on high-frequency signal injection as claimed in claim 1, wherein the current i in the step S7gDAnd current igQComprises the following steps:
Figure FDA0002750878650000045
8. the grid-connected inverter grid impedance identification method based on high-frequency signal injection as claimed in claim 1, wherein the high-frequency current signal i in the step S8DhAnd a high-frequency current signal iQhThe extraction method comprises the following steps:
s81, utilizing the current i obtained in the step S7gDAnd current igQSeparately calculating error current signals igDerr1And an error current signal igQerr1：
Figure FDA0002750878650000046
Wherein igDAnd igQCurrent i in the two-phase stationary DQ coordinate system, respectivelyDhAnd iQhAre all high-frequency current signals to be extracted,
Figure FDA0002750878650000047
and
Figure FDA0002750878650000048
are all the positive sequence components of the power grid current;
s82, using high-pass filter
Figure FDA0002750878650000049
For the error current signal i obtained in step S81gDerr1And an error current signal igQerr1Filtering to obtain an error current signal igDerrAnd an error current signal igQerr：
Figure FDA00027508786500000410
Wherein s is a Laplace operator;
s83, obtaining the error current signal i according to the step S82gDerrAnd an error current signal igQerrCalculating a high frequency current signal iDhHigh frequency current signal iQhPositive sequence component of grid current
Figure FDA00027508786500000411
Positive sequence component of grid current
Figure FDA00027508786500000412
Figure FDA0002750878650000051
Wherein, ω ishc,iFor high-frequency current signals iDhAnd a high-frequency current signal iQhCut-off frequency of the extraction unit, andhc,i＝ωhc,u，ωc,ifor positive sequence component of network current
Figure FDA0002750878650000052
And the positive sequence component of the network current
Figure FDA0002750878650000053
Cut-off frequency, omega, of the extraction unitc,i＝ωc,u；
S84, converting the high-frequency current signal i obtained in the step S83DhHigh frequency current signal iQhPositive sequence component of grid current
Figure FDA0002750878650000054
And the positive sequence component of the network current
Figure FDA0002750878650000055
Substituting step S81 to update error current signal igDerr1And an error current signal igQerr1；
S85, repeating the steps S81 to S84 until reaching the set command signal, stopping the operation, and outputting the extracted high-frequency current signal iDhAnd a high-frequency current signal iQh。
9. The grid-connected inverter grid impedance identification method based on high-frequency signal injection as claimed in claim 6 or 8, wherein the resistance value of the grid
Figure FDA0002750878650000056
And inductance value
Figure FDA0002750878650000057
Comprises the following steps:
Figure FDA0002750878650000058
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