CN116087621B - Broadband impedance measurement device resistant to frequency coupling interference and control method thereof - Google Patents
Broadband impedance measurement device resistant to frequency coupling interference and control method thereof Download PDFInfo
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- CN116087621B CN116087621B CN202310356209.0A CN202310356209A CN116087621B CN 116087621 B CN116087621 B CN 116087621B CN 202310356209 A CN202310356209 A CN 202310356209A CN 116087621 B CN116087621 B CN 116087621B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/40—Arrangements for reducing harmonics
Abstract
The invention discloses a broadband impedance measurement device for resisting frequency coupling interference and a control method thereof, and relates to the technical field of new energy grid-connected converter control; the control part mainly comprises a power synchronizing ring, an alternating voltage control ring, a current ring, an anti-coupling broadband signal amplitude-frequency control ring and a PWM modulation ring; the data acquisition and impedance calculation part mainly comprises a voltage sensor, a current sensor, a data acquisition card and an upper computer, and is used for generating a broadband disturbance voltage reference signal without frequency coupling influence by selecting proper measurement starting frequency and interval frequency and superposing the broadband disturbance voltage reference signal into an alternating current voltage ring reference signal, so that a given broadband voltage disturbance signal resisting frequency coupling is injected into a tested system, and the broadband impedance characteristic of the tested current transformer can be obtained rapidly.
Description
Technical Field
The invention relates to the technical field of new energy grid-connected converter control, in particular to a broadband impedance measurement device for resisting frequency coupling interference and a control method thereof.
Background
At present, more and more new energy sources such as photovoltaic and wind power are connected into a large power grid through a converter, and a 'double-high' novel power system of high-proportion new energy sources and high-proportion power electronic equipment is gradually formed. In recent years, a series of broadband oscillation problems are caused by mismatching of port impedance of the converter and power grid impedance, and operation safety of a novel power system is seriously threatened, so that obtaining broadband impedance characteristics of the grid-connected converter has important significance for analyzing grid-connected stability of the grid-connected converter.
At present, the active measurement technology of the impedance measurement device of the grid-connected current transformer has been widely studied, and the method of the active measurement technology can be mainly divided into single-frequency disturbance point-by-point measurement and broadband disturbance disposable measurement. The single-frequency disturbance point-by-point measurement can realize impedance measurement in any frequency band, is not interfered by a converter frequency coupling system, has good measurement precision, and takes longer time; for the broadband impedance measurement technology, the broadband impedance measurement can be realized by one injection, but the measurement precision is very poor due to the fact that the frequency coupling characteristic exists in the current transformer and the coupling frequency components are overlapped. In addition, as for the measuring device, the current measuring device mostly adopts a phase-locked loop synchronous type network-following converter, and the device presents the characteristic of a controllable current source, injects broadband harmonic current into a system to be measured, and cannot run off the network. Therefore, in order to solve the above problems, the present invention firstly designs a method for selecting the initial frequency and the interval frequency of a wideband disturbance signal, which can effectively avoid the problem of poor measurement accuracy caused by overlapping of coupling frequency components of the wideband signal, and secondly, integrates the method for generating the wideband signal with anti-coupling frequency disturbance into a converter adopting power synchronization, and the device presents the voltage source characteristic to the outside, injects wideband harmonic voltage into a tested system, and can work in off-grid and grid mode. The broadband impedance measurement device for resisting the frequency coupling interference and the control method thereof have important significance for the impedance characteristic identification and the grid-connected stability analysis of the new energy grid-connected converter.
Disclosure of Invention
The invention aims to provide a broadband impedance measurement device for resisting frequency coupling interference and a control method thereof, which are used for solving the interference problem of coupling frequency harmonic components generated by an asymmetric control loop when a converter to be tested is in grid-connected operation in the prior art, so as to realize measurement of broadband impedance external characteristics of a new energy grid-connected converter in an off-line/on-line mode.
In order to achieve the above object, the present invention provides a broadband impedance measurement apparatus for resisting frequency coupling interference,
comprises a main circuit part, a control part and a data acquisition and impedance calculation part,
the main circuit part comprises a direct current power supply, a three-phase inverter bridge, a filter inductor, a filter capacitor and an isolation transformer, wherein the direct current power supply provides an energy source for a measuring device, the three-phase inverter bridge converts direct current into alternating current, the filter inductor and the filter capacitor are used for inhibiting current and voltage harmonic waves, and the isolation transformer with a series-parallel connection mode is used for matching measured objects with different voltage grades;
the control part comprises a power synchronizing ring, an alternating current voltage ring, a current ring, an anti-coupling broadband signal amplitude-frequency control ring and a PWM modulation ring, wherein the power synchronizing ring is used for providing frequency and reference emission power required by control, and the alternating current voltage ring is used for realizing the control of constant amplitude of output voltage of the converter; the anti-coupling broadband signal amplitude-frequency control loop realizes the synthesis and amplitude control of broadband signals according to an anti-coupling measurement initial frequency and interval frequency selection method; the current loop is used for generating a PWM modulation reference voltage signal so as to ensure that a main circuit can generate an expected broadband measurement signal;
the data acquisition and impedance calculation part comprises a voltage sensor, a current sensor, a data acquisition card and an upper computer, wherein the voltage sensor and the current sensor are used for acquiring voltage and current signals at grid connection points for circuit control and impedance calculation; the data acquisition card uploads the measurement data in the voltage and current sensors to the upper computer by acquiring the measurement data, and impedance calculation is realized by FFT analysis.
The invention also discloses a control method of the broadband impedance measurement device for resisting the frequency coupling interference, which is used for controlling the broadband impedance measurement device for resisting the frequency coupling interference, and comprises the following steps:
s1: collecting three-phase voltage u of common connection point abc ，i abc Obtaining u through dq transformation d 、u q 、i d 、i q And calculates active power P and reactive power Q according to formula I, wherein the active power is subjected to low-pass filter with cut-off frequency of 1Hz and then is differed from rated reference power Pref, and the difference is amplified by power synchronous proportionality coefficient Kp to obtain frequency deviation delta omega, delta omega and reference angular frequency omega 0 The sum passes through an integrator to obtain a synchronous phase theta;
formula I is as follows:
s2: amplitude reference signal E of fundamental wave of given grid-connected point reference voltage under dq coordinate system d0 And E is q0 The method comprises the steps of carrying out a first treatment on the surface of the Disturbance reference signal u under dq coordinate system given disturbance voltage p As shown in formula II, the fundamental wave amplitude reference signal E d0 And E is q0 Respectively with disturbance reference signal u p Adding to obtain an AC voltage ring reference signal u dref 、u qref ；
Formula II is as follows:
wherein A is i Representing the reference amplitude of the ith disturbance signal, f i Represents the reference frequency, phi, of the ith disturbance signal i A reference phase representing an ith perturbation signal, n representing a reference phase having n perturbation signals;
s3: reference signal u of alternating current voltage ring dref 、u qref And u actually collected d 、u q Respectively subtracting the two values, and generating a current loop reference signal i after the difference value passes through a proportional-integral controller dref 、i qref ；
S4: reference signal i to the current loop dref 、i qref From i actually collected d 、i q Respectively subtracting the difference value from each otherThe proportional-integral controller obtains an output signal e dref 、e qref Then the SPWM modulation reference signal e is obtained through dq inverse transformation abc Generating a switching signal after PWM modulation to control a main circuit inverter bridge to generate a disturbance voltage signal, and injecting the disturbance voltage signal into a converter to be tested;
s5: collecting the port voltage and current signals u of the converter to be tested ta 、u tb 、u tc 、i ta 、i tb 、i tc And the three-phase voltage and current signals are firstly transformed into a two-phase static coordinate system by utilizing a formula III, and u is obtained by the transformation tα And i tα After FFT analysis, a broadband impedance curve of the converter to be tested under an alpha beta coordinate system can be obtained by using a formula IV;
wherein formula III is as follows:
formula IV is as follows:
wherein, the control method further comprises the following steps:
and designing the amplitude, frequency and phase of the disturbance signal for the anti-coupling broadband signal amplitude-frequency control loop.
Wherein, the disturbance amplitude A in the amplitude design i The voltage amplitude of the grid-connected point is set to be 1% -10%.
In the frequency design, the initial frequency of the broadband disturbance is f start At an interval of Δf, the ith disturbance frequency f i As shown in formula V, wherein the initial frequency f in formula V start And the separation frequency Deltaf, if within a given wide frequency disturbance range (f 1 ～f n ) In the method, for the ith disturbance frequency, condition judgment is carried out, if a positive integer k is not present and the formula VI is satisfied, superposition synthesis is outputIf a positive integer k is present to establish the formula VI, resetting the frequency interval Deltaf and repeating the condition judgment step;
formula V is as follows:
f i ＝f start +iΔf；
in the formula V, i is a positive integer;
formula VI is as follows:
f start +iΔf≠|f start +kΔf-2f 0 |；
in the formula VI, i and k are positive integers, f 0 Is the fundamental frequency.
Wherein, the liquid crystal display device comprises a liquid crystal display device,
in the phase design, the phase phi i of the ith disturbance signal satisfies formula VII.
Formula VII is as follows:
for the anti-coupling broadband signal amplitude-frequency control loop:
setting amplitude A of broadband disturbance i Secondly, setting the number n of required disturbance frequencies, and setting the initial frequency f of the broadband disturbance signal start Then, the phase of each disturbance frequency corresponding signal is set
Finally, setting a frequency interval delta f, and expelling and judging whether the frequencies of i=1 to n meet f start +iΔf≠|f start +kΔf-2f 0 |(i，k∈Z + ) If yes, outputting the superimposed and synthesized broadband multitone signal, and if not, resetting the frequency interval delta f and repeating the condition judgment step. The broadband disturbance reference signal u meeting the requirement of resisting the frequency coupling interference is finally obtained through the loop p ；
For the power synchronization loop:
collecting three-phase voltage u of common connection point abc ，i abc Obtaining u through dq transformation d 、u q 、i d 、i q And calculates the active power P and the reactive power Q according to formula I. Wherein the active power passes through a low-pass filter with a cut-off frequency of 1Hz and then is matched with rated reference power P ref Making difference, the difference passing through power synchronous proportional coefficient K p After amplification, the frequency deviation delta omega, delta omega and the reference angular frequency omega are obtained 0 The sum is passed through an integrator to obtain the synchronization phase θ.
For an ac voltage ring:
will fundamental amplitude reference signal E d0 And E is q0 Respectively with disturbance reference signal u p Adding to obtain an AC voltage ring reference signal u dref 、u qref . Reference signal u of alternating current voltage ring dref 、u qref And u actually collected d 、u q Respectively subtracting the two values, and generating a current loop reference signal i after the difference value passes through a proportional-integral controller dref 、i qref ；
For the current loop:
reference signal i to the current loop dref 、i qref From i actually collected d 、i q Respectively subtracting, and obtaining an output signal e after the difference value passes through a proportional-integral controller dref 、e qref Then the SPWM modulation reference signal e is obtained through dq inverse transformation abc The signal is subjected to PWM modulation to generate a switching signal to control the main circuit inverter bridge to generate a disturbance voltage signal, and the disturbance voltage signal is injected into the converter to be tested.
The broadband impedance measuring device for resisting frequency coupling interference and the control method thereof utilize the broadband signal generating device for resisting frequency coupling interference, the device externally presents voltage source characteristics, injects broadband harmonic voltage into a tested system, can work in off-grid and on-grid modes, correspondingly designs a method for selecting the initial frequency and the interval frequency of broadband disturbance signals, provides stable test voltage source signals, can realize off-grid/on-grid test, adds a broadband measurement multitone signal generating algorithm for resisting frequency coupling interference in network construction control, and avoids interference of coupling frequency harmonic components generated by an asymmetric control loop when the to-be-tested current transformer is in on-grid operation, thereby realizing measurement of broadband impedance external characteristics of the new energy grid-connected current transformer in off-line/on-line modes.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a main circuit of a broadband impedance measurement apparatus for resisting frequency coupling interference according to the present invention;
FIG. 2 is a flow chart of the anti-coupling broadband disturbance reference signal generation according to the present invention;
FIG. 3 is a control block diagram of a broadband impedance measurement apparatus for resisting frequency coupling interference according to the present invention;
FIG. 4 is an off-grid/on-grid mode wiring diagram of the broadband impedance measurement device for resisting frequency coupling interference of the present invention;
FIG. 5 is a waveform of three-phase voltage and current of an inverter port to be measured during off-grid measurement of the broadband impedance measurement device for resisting frequency coupling interference according to the present invention; wherein, (a) is a voltage diagram of a port of the converter to be tested, and (b) is a current diagram of the port of the converter to be tested;
FIG. 6 is a comparison of the measured result and the theoretical result of the port impedance of the inverter when the anti-coupling broadband disturbance signal generation method is adopted;
fig. 7 is a comparison of the measured result and the theoretical result of the port impedance of the inverter without the anti-coupling broadband disturbance signal generation method according to the present invention.
Detailed Description
Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative and intended to explain the present invention and should not be construed as limiting the invention.
Referring to fig. 1 to 4, the present invention provides a broadband impedance measurement apparatus for resisting frequency coupling interference,
comprises a main circuit part, a control part and a data acquisition and impedance calculation part,
the main circuit part comprises a direct current power supply, a three-phase inverter bridge, a filter inductor, a filter capacitor and an isolation transformer, wherein the direct current power supply provides an energy source for a measuring device, the three-phase inverter bridge converts direct current into alternating current, the filter inductor and the filter capacitor are used for inhibiting current and voltage harmonic waves, and the isolation transformer with a series-parallel connection mode is used for matching measured objects with different voltage grades;
the control part comprises a power synchronizing ring, an alternating current voltage ring, a current ring, an anti-coupling broadband signal amplitude-frequency control ring and a PWM modulation ring, wherein the power synchronizing ring is used for providing frequency and reference emission power required by control, and the alternating current voltage ring is used for realizing the control of constant amplitude of output voltage of the converter; the anti-coupling broadband signal amplitude-frequency control loop realizes the synthesis and amplitude control of broadband signals according to an anti-coupling measurement initial frequency and interval frequency selection method; the current loop is used for generating a PWM modulation reference voltage signal so as to ensure that a main circuit can generate an expected broadband measurement signal;
the data acquisition and impedance calculation part comprises a voltage sensor, a current sensor, a data acquisition card and an upper computer, wherein the voltage sensor and the current sensor are used for acquiring voltage and current signals at grid connection points for circuit control and impedance calculation; the data acquisition card uploads the measurement data in the voltage and current sensors to the upper computer by acquiring the measurement data, and impedance calculation is realized by FFT analysis.
FIG. 1 is a schematic diagram of a main circuit of a broadband impedance measurement apparatus with anti-interference of frequency coupling in the present invention: the DC-DC converter consists of a DC voltage source (VDC), an inverter bridge (H), a filter (LC) and an isolation transformer (T).
Furthermore, the invention also discloses a control method of the broadband impedance measurement device for resisting the frequency coupling interference, which is used for controlling the broadband impedance measurement device for resisting the frequency coupling interference, and the control method comprises the following steps:
s1: collecting three-phase voltage u of common connection point abc ，i abc Obtaining u through dq transformation d 、u q 、i d 、i q And calculates active power P and reactive power Q according to formula I, wherein the active power is subjected to low-pass filter with cut-off frequency of 1Hz and then is differed from rated reference power Pref, and the difference is amplified by power synchronous proportionality coefficient Kp to obtain frequency deviation delta omega, delta omega and reference angular frequency omega 0 The sum passes through an integrator to obtain a synchronous phase theta;
formula I is as follows:
s2: amplitude E of fundamental wave of given grid-connected point reference voltage under dq coordinate system d0 And E is q0 The method comprises the steps of carrying out a first treatment on the surface of the Disturbance reference signal u under dq coordinate system given disturbance voltage p As shown in formula II, the fundamental wave amplitude reference signal E d0 And E is q0 Respectively with disturbance reference signal u p Adding to obtain an AC voltage ring reference signal u dref 、u qref ；
Formula II is as follows:
wherein A is i Representing the reference amplitude of the ith disturbance signal, f i Represents the reference frequency, phi, of the ith disturbance signal i A reference phase representing an ith perturbation signal, n representing a reference phase having n perturbation signals;
s3: reference signal u of alternating current voltage ring dref 、u qref And u actually collected d 、u q Respectively subtracting the two values, and generating a current loop reference signal i after the difference value passes through a proportional-integral controller dref 、i qref ；
S4: reference signal i to the current loop dref 、i qref From i actually collected d 、i q Respectively subtracting, and obtaining an output signal e after the difference value passes through a proportional-integral controller dref 、e qref Then the SPWM modulation reference signal e is obtained through dq inverse transformation abc Generating a switching signal after PWM modulation to control a main circuit inverter bridge to generate a disturbance voltage signal, and injecting the disturbance voltage signal into a converter to be tested;
s5: collecting the voltage and current signals uta, utb, utc, ita, itb, itc of the port of the converter to be tested, uploading the signals to an upper computer through a data collecting card, firstly converting the three-phase voltage and current signals into a two-phase static coordinate system by utilizing III, and obtaining u through the conversion tα And i tα After FFT analysis, a broadband impedance curve of the converter to be tested under an alpha beta coordinate system can be obtained by using a formula IV;
wherein formula III is as follows:
formula IV is as follows:
further, the control method further comprises the following steps:
and designing the amplitude, frequency and phase of the disturbance signal for the anti-coupling broadband signal amplitude-frequency control loop.
Further, the disturbance amplitude A in the amplitude design i The voltage amplitude of the grid-connected point is set to be 1% -10%.
Further, in the frequency design, the initial frequency of the broadband disturbance is f start At an interval of Δf, the ith disturbance frequency f i As shown in formula V, wherein the initial frequency f in formula V start And the separation frequency Deltaf, if within a given wide frequency disturbance range (f 1 ～f n ) In the method, for the ith disturbance frequency, the condition judgment is carried out, if no disturbance frequency existsOutputting a broadband multi-tone signal synthesized by superposition if the positive integer k enables the formula VI to be met, resetting the frequency interval delta f if the positive integer k enables the formula VI to be met, and repeating the step of judging conditions;
formula V is as follows:
f i ＝f start +iΔf；
in the formula V, i is a positive integer;
formula VI is as follows:
f start +iΔf≠|f start +kΔf-2f 0 |；
in the formula VI, i and k are positive integers, f 0 Is the fundamental frequency.
Wherein, the liquid crystal display device comprises a liquid crystal display device,
in the phase design, the phase phi i of the ith disturbance signal satisfies formula VII.
Formula VII is as follows:
for the anti-coupling broadband signal amplitude-frequency control loop:
setting amplitude A of broadband disturbance i Secondly, setting the number n of required disturbance frequencies, and setting the initial frequency f of the broadband disturbance signal start Then, the phase phi 1-phi n of each disturbance frequency corresponding signal is set, finally, the frequency interval delta f is set, and whether the frequency of i=1-n meets f is judged by eviction start +iΔf≠|f start +kΔf-2f 0 |(i，k∈Z + ) If yes, outputting the superimposed and synthesized broadband multitone signal, and if not, resetting the frequency interval delta f and repeating the condition judgment step. The broadband disturbance reference signal u meeting the requirement of resisting the frequency coupling interference is finally obtained through the loop p ；
For the power synchronization loop:
collecting three-phase voltage u of common connection point abc ，i abc Obtaining u through dq transformation d 、u q 、i d 、i q And calculates the active power P and the reactive power according to the formula IAnd (5) rate Q. Wherein the active power passes through a low-pass filter with a cut-off frequency of 1Hz and then is matched with rated reference power P ref Making difference, the difference passing through power synchronous proportional coefficient K p After amplification, the frequency deviation delta omega, delta omega and the reference angular frequency omega are obtained 0 The sum is passed through an integrator to obtain the synchronization phase θ.
For an ac voltage ring:
will fundamental amplitude reference signal E d0 And E is q0 Respectively with disturbance reference signal u p Adding to obtain an AC voltage ring reference signal u dref 、u qref . Reference signal u of alternating current voltage ring dref 、u qref And u actually collected d 、u q Respectively subtracting the two values, and generating a current loop reference signal i after the difference value passes through a proportional-integral controller dref 、i qref ；
For the current loop:
reference signal i to the current loop dref 、i qref From i actually collected d 、i q Respectively subtracting, and obtaining an output signal e after the difference value passes through a proportional-integral controller dref 、e qref Then the SPWM modulation reference signal e is obtained through dq inverse transformation abc The signal is subjected to PWM modulation to generate a switching signal to control the main circuit inverter bridge to generate a disturbance voltage signal, and the disturbance voltage signal is injected into the converter to be tested.
Referring to fig. 4, as an embodiment of the present invention,
the method comprises the steps of enabling a to-be-tested converter to run in a grid-connected mode, enabling a broadband impedance measuring device resistant to frequency coupling interference to be connected in parallel to a public coupling point of the to-be-tested converter and a power grid, controlling the port output voltage of the broadband impedance measuring device resistant to frequency coupling interference, namely controlling the public coupling point voltage to enable the public coupling point voltage to contain broadband disturbance voltage signals, exciting corresponding broadband harmonic response currents in the to-be-tested converter, and acquiring the voltage and current signals of the port of the to-be-tested converter to calculate broadband impedance characteristics of the to-be-tested converter. In addition, since the broadband impedance measurement device for resisting the frequency coupling interference adopts the power grid structure control technology, the broadband impedance measurement device for resisting the frequency coupling interference can still provide stable voltage support even when the switch S is disconnected, so that the converter to be tested normally works to realize impedance measurement in the off-grid mode, and main circuit parameters and control parameters of the broadband impedance measurement device for resisting the frequency coupling interference in fig. 4 are shown in table 1:
table 1 main circuit and control circuit parameters of broadband impedance measurement apparatus:
the parameters of the current transformer to be tested and the power grid are set as shown in table 2.
Table 2 parameters of the converter to be tested and the power grid:
referring to fig. 5 (a) and (b), when the system parameters are set according to tables 1 and 2, when the switch S is turned off, the three-phase voltage and current waveforms of the port of the to-be-tested converter can be seen, and even in the off-grid mode, the port voltage of the to-be-tested converter is still stable. It can also be seen that the port voltage and current are slightly distorted due to injection of the broadband disturbance voltage signal.
Referring to fig. 6, a broadband impedance characteristic curve of the to-be-measured converter port in the range of 1-100Hz is shown when the anti-coupling broadband disturbance signal set in table 1 is adopted for injection. It can be seen that when the measurement start frequency is set to 0, the disturbance frequency interval is set to 3Hz, and the number of disturbance frequencies is set to 33, the frequency range of measurement is 1-99Hz. For the broadband signal, any disturbance frequency satisfies f start +iΔf≠|f start +kΔf-2f 0 |(i，k∈Z + ) Therefore, the generated broadband disturbance reference signal has the capacity of resisting frequency coupling disturbance, and after the broadband disturbance reference signal is injected into a system to be tested, the measurement result is almost consistent with the theoretical impedance, so that the effectiveness of the method provided by the invention is verified.
Referring to fig. 7, a broadband impedance characteristic curve of the to-be-measured converter port in the range of 1-100Hz is shown when the anti-coupling broadband disturbance signal set in table 1 is not used. It can be seen that when the measurement start frequency is set to 0, the disturbance frequency interval is set to 2Hz, and the number of disturbance frequencies is set to 50, the frequency range of measurement is 1-100Hz. For the broadband signal, any disturbance frequency is not satisfied
f start +iΔf≠|f start +kΔf-2f 0 |(i，k∈Z + )。
For example, a 2Hz disturbance frequency generates a 98Hz coupling frequency due to frequency coupling, and the frequency just overlaps with the original 98Hz disturbance frequency in the broadband disturbance signal, so that the capability of resisting frequency coupling interference is not provided. After the broadband impedance measuring device is injected into a system to be measured, the measurement result is greatly disturbed, and the broadband impedance of the converter to be measured cannot be accurately measured.
Therefore, through the embodiment, the effectiveness and feasibility of the broadband impedance measurement device for resisting the frequency coupling interference are verified.
The broadband impedance measuring device for resisting frequency coupling interference and the control method thereof utilize the broadband signal generating device for resisting frequency coupling interference, the device externally presents voltage source characteristics, injects broadband harmonic voltage into a tested system, can work in off-grid and on-grid modes, correspondingly designs a method for selecting the initial frequency and the interval frequency of broadband disturbance signals, provides stable test voltage source signals, can realize off-grid/on-grid test, adds a broadband measurement multitone signal generating algorithm for resisting frequency coupling interference in network construction control, and avoids interference of coupling frequency harmonic components generated by an asymmetric control loop when the to-be-tested current transformer is in on-grid operation, thereby realizing measurement of broadband impedance external characteristics of the new energy grid-connected current transformer in off-line/on-line modes.
The above disclosure is only a preferred embodiment of the present invention, and it should be understood that the scope of the invention is not limited thereto, and those skilled in the art will appreciate that all or part of the procedures described above can be performed according to the equivalent changes of the claims, and still fall within the scope of the present invention.
Claims (6)
1. A broadband impedance measurement device for resisting frequency coupling interference is characterized in that,
comprises a main circuit part, a control part and a data acquisition and impedance calculation part,
the main circuit part comprises a direct current power supply, a three-phase inverter bridge, a filter inductor, a filter capacitor and an isolation transformer, wherein the direct current power supply provides an energy source for a measuring device, the three-phase inverter bridge converts direct current into alternating current, the filter inductor and the filter capacitor are used for inhibiting current and voltage harmonic waves, and the isolation transformer with a series-parallel connection mode is used for matching measured objects with different voltage grades;
the control part comprises a power synchronizing ring, an alternating current voltage ring, a current ring, an anti-coupling broadband signal amplitude-frequency control ring and a PWM modulation ring, wherein the power synchronizing ring is used for providing frequency and reference emission power required by control, and the alternating current voltage ring is used for realizing the control of constant amplitude of output voltage of the converter; the anti-coupling broadband signal amplitude-frequency control loop realizes the synthesis and amplitude control of broadband signals according to an anti-coupling measurement initial frequency and interval frequency selection method; the current loop is used for generating a PWM modulation reference voltage signal so as to ensure that a main circuit can generate an expected broadband measurement signal;
the data acquisition and impedance calculation part comprises a voltage sensor, a current sensor, a data acquisition card and an upper computer, wherein the voltage sensor and the current sensor are used for acquiring voltage and current signals at grid connection points for circuit control and impedance calculation; the data acquisition card uploads the measurement data in the voltage and current sensors to the upper computer by acquiring the measurement data, and impedance calculation is realized by FFT analysis.
2. A control method of a broadband impedance measurement apparatus for resisting frequency coupling interference as defined in claim 1, wherein,
the control method comprises the following steps:
S1：collecting three-phase voltage u of common connection point abc ，i abc Obtaining u through dq transformation d 、u q 、i d 、i q And calculates active power P and reactive power Q according to formula I, wherein the active power is subjected to low-pass filter with cut-off frequency of 1Hz and then is differed from rated reference power Pref, and the difference is amplified by power synchronous proportionality coefficient Kp to obtain frequency deviation delta omega, delta omega and reference angular frequency omega 0 The sum passes through an integrator to obtain a synchronous phase theta;
formula I is as follows:
s2: amplitude reference signal E of fundamental wave of given grid-connected point reference voltage under dq coordinate system d0 And E is q0 The method comprises the steps of carrying out a first treatment on the surface of the Disturbance reference signal u under dq coordinate system given disturbance voltage p As shown in formula II, the fundamental wave amplitude reference signal E d0 And E is q0 Respectively with disturbance reference signal u p Adding to obtain an AC voltage ring reference signal u dref 、u qref ；
Formula II is as follows:
wherein A is i Representing the reference amplitude of the ith disturbance signal, f i Representing the reference frequency of the ith disturbance signal,
a reference phase representing an ith perturbation signal, n representing a reference phase having n perturbation signals;
s3: reference signal u of alternating current voltage ring dref 、u qref And u actually collected d 、u q Respectively subtracting the two values, and generating a current loop reference signal i after the difference value passes through a proportional-integral controller dref 、i qref ；
S4: reference signal i to the current loop dref 、i qref From i actually collected d 、i q Respectively subtracting, and obtaining an output signal e after the difference value passes through a proportional-integral controller dref 、e qref Then the SPWM modulation reference signal e is obtained through dq inverse transformation abc Generating a switching signal after PWM modulation to control a main circuit inverter bridge to generate a disturbance voltage signal, and injecting the disturbance voltage signal into a converter to be tested;
s5: collecting the port voltage and current signals u of the converter to be tested ta 、u tb 、u tc 、i ta 、i tb 、i tc And the three-phase voltage and current signals are firstly transformed into a two-phase static coordinate system by utilizing a formula III, and u is obtained by the transformation tα And i tα After FFT analysis, a broadband impedance curve of the converter to be tested under an alpha beta coordinate system can be obtained by using a formula IV;
wherein formula III is as follows:
formula IV is as follows:
3. the method of claim 2, wherein,
the control method further comprises the following steps:
and designing the amplitude, frequency and phase of the disturbance signal for the anti-coupling broadband signal amplitude-frequency control loop.
4. A control method of a broadband impedance measurement apparatus resistant to frequency coupling interference as set forth in claim 3, wherein,
disturbance amplitude A in the amplitude design i Is arranged in parallel with1% -10% of the voltage amplitude of the net point.
5. The method of claim 4, wherein,
in the frequency design, the initial frequency of the broadband disturbance is f start At an interval of Δf, the ith disturbance frequency f i As shown in formula V, wherein the initial frequency f in formula V start And the separation frequency Deltaf, if within a given wide frequency disturbance range (f 1 ～f n ) In the method, for the ith disturbance frequency, condition judgment is carried out, if a positive integer k does not exist so that a formula VI is met, a broadband multi-tone signal synthesized by superposition is output, if the positive integer k exists so that the formula VI is met, a frequency interval delta f is reset, and the condition judgment is repeated;
formula V is as follows:
f i ＝f start +iΔf；
in the formula V, i is a positive integer;
formula VI is as follows:
f start +iΔf≠|f start +kΔf-2f 0 |；
in the formula VI, i and k are positive integers, f 0 Is the fundamental frequency.
6. The method of claim 5, wherein,
in the phase design, the phase phi of the ith disturbance signal i Satisfy formula VII;
formula VII is as follows:
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