CN111082434A - Method and system for judging small disturbance inter-harmonic amplification phenomenon of inverter - Google Patents

Method and system for judging small disturbance inter-harmonic amplification phenomenon of inverter Download PDF

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CN111082434A
CN111082434A CN201911294616.3A CN201911294616A CN111082434A CN 111082434 A CN111082434 A CN 111082434A CN 201911294616 A CN201911294616 A CN 201911294616A CN 111082434 A CN111082434 A CN 111082434A
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朱淼
侯川川
李铮钊
徐莉婷
蔡旭
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Shanghai Jiaotong University
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Abstract

The invention provides a method and a system for judging the small disturbance inter-harmonic amplification phenomenon of an inverter, wherein the method comprises the following steps: simplifying and establishing an inverter model: simplifying a main circuit and a control structure of the inverter into a phase-locked loop to obtain a simplified model of the phase-locked loop of the inverter; and (3) association establishment step: establishing a correlation analysis expression of the inverter output quantity and a phase-locked loop linearization transfer function under small disturbance by using a phase-locked loop simplified model; a judging step: and judging the inter-harmonic amplification range of the output quantity of the inverter under the small disturbance and the disturbance frequency with the most obvious amplification effect according to the correlation analytical expression. The invention can quickly and accurately determine the inter-harmonic amplification range of the inverter output quantity under small disturbance and the disturbance frequency with the most obvious amplification effect by only utilizing the traditional phase-locked loop linearization transfer function.

Description

Method and system for judging small disturbance inter-harmonic amplification phenomenon of inverter
Technical Field
The invention relates to the field of alternating current power generation and distribution, in particular to a method and a system for judging a small disturbance inter-harmonic amplification phenomenon of an inverter.
Background
The grid connection of the new energy is beneficial to the adjustment of a primary energy structure of a power system, the reduction of the carbon emission level of power generation and the promotion of clean grid connection of electric energy. With the maturity of new energy power generation technology, the power consumption cost is greatly reduced, and the new energy power generation technology has stronger competitive power with the traditional fossil energy in economy. The high proportion of new energy power generation in the power system becomes a big feature of the future power system, but is limited by natural condition factors, and the randomness, uncertainty and high proportion of the new energy power generation increase the difficulty of stable operation and regulation control of the system. At present, nearly hundreds times/super-synchronous oscillation occurs in the put-into-operation Hami-Zheng state direct current sending end wind power base, so that part of wind fields are forced to reduce power to operate or stop, and the maximum utilization of renewable energy sources is limited.
Aiming at the problems of disturbance and oscillation caused by renewable energy sources, the existing analysis means comprises a characteristic root method, an impedance method and a frequency domain relative gain matrix method. The impedance analysis method is widely used, and the current output quantity of the device under small disturbance voltage is analyzed by means of the impedance characteristics of the new energy grid-connected device, so that the stability of the system under small disturbance is judged. The existing impedance models mainly comprise two types, one is an impedance model decoupled in positive and negative sequence, and the other is a dq impedance model under a dq axis of a synchronous rotating coordinate. Although the two impedance models can accurately describe the self impedance characteristics of the grid-connected inverter and can analyze the current output quantity corresponding to disturbance, the modeling process is relatively complex and is not easy to popularize in the rapid simplification analysis process. In addition, due to the characteristics of the grid-connected inverter, under small disturbance, not only the current amount corresponding to the disturbance is output, but also a new current amount is generated, and the impedance model cannot analyze the current amount.
In summary, although the existing method for determining the small disturbance output quantity by using the impedance model has a certain effect, the modeling process is relatively complex, and meanwhile, the new current output quantity excited by the small disturbance cannot be analyzed, so that certain limitations exist.
The literature: zhong, Wangweisen, which national celebration, et al. direct-drive wind power plant subsynchronous oscillation analysis and phase-locked loop parameter optimization design based on sequence impedance. 6757 step 6767. an impedance model of the inverter is established by using a harmonic linearization method, and the influence of the control parameters of the phase-locked loop and the current loop on the impedance model is considered. However, the impedance model established in the document for determining the inverter output under small disturbance mainly has two disadvantages: firstly, an impedance model is established in the document, and when the output quantity of the inverter is determined, the disturbance voltage and the analysis model need to be subjected to numerical operation, so that the output quantity of the inverter is indirectly obtained; second, the impedance model established in this document considers only the impedance analysis value corresponding to the disturbance frequency, and does not take into account the new frequency component output by the own characteristics of the inverter phase-locked loop.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method and a system for judging the small disturbance inter-harmonic amplification phenomenon of an inverter.
The method for judging the small disturbance inter-harmonic amplification phenomenon of the inverter provided by the invention comprises the following steps:
simplifying and establishing an inverter model: simplifying a main circuit and a control structure of the inverter into a phase-locked loop to obtain a simplified model of the phase-locked loop of the inverter;
and (3) association establishment step: establishing a correlation analysis expression of the inverter output quantity and a phase-locked loop linearization transfer function under small disturbance by using a phase-locked loop simplified model;
a judging step: and judging the inter-harmonic amplification range of the output quantity of the inverter under the small disturbance and the disturbance frequency with the most obvious amplification effect according to the correlation analytical expression.
Preferably, in the association establishing step:
the A phase output of the inverter under small disturbance is as follows:
Id·cos(θPLL)≈Id·[cos(θ1)-sin(θ1)·Δθ]；
delta theta is the phase error, theta1For phase of fundamental frequency of power network, IdIs the amplitude of the inverter output current, thetaPLLOutputting the phase for the phase locked loop;
cos (theta)PLL) In the frequency domain:
Figure BDA0002320164320000021
L[]for Laplace transformed symbols, V1Is a frequency domain expression of voltage amplitude of fundamental wave phase of a power grid, VeFor the frequency domain expression of the small disturbance phase voltage amplitude, G () is the phase-locked loop transfer function, s is the frequency domain symbol, j is the imaginary number symbol, omega1Is the angular frequency of the fundamental wave of the power grid, f is the frequency sign, f1At fundamental frequency of the grid, fpIs the disturbance voltage frequency.
Preferably, the voltage distortion THD under small disturbance is obtained according to harmonic fundamental variableVComprises the following steps:
Figure BDA0002320164320000031
Vethe phase voltage amplitude is a small perturbation.
Preferably, the voltage distortion THD under the simplified model and the small disturbance is obtained according to the phase-locked loopVObtaining the current output distortion THD of the inverter under small disturbanceIComprises the following steps:
THDI＝THDV·|G(s)|
g(s) is a phase-locked loop linearization transfer function.
Preferably, THD is satisfied when | G(s) | ≧ 1I≥THDVAll the frequencies in the frequency interval of (2) can generate inter-harmonic amplification under small disturbance, and when | G(s) | takes the maximum value, the corresponding frequency is the disturbance frequency with the most obvious amplification effect.
The invention provides a system for judging the small disturbance inter-harmonic amplification phenomenon of an inverter, which comprises:
an inverter model simplification and association establishment module: simplifying a main circuit and a control structure of the inverter into a phase-locked loop to obtain a simplified model of the phase-locked loop of the inverter;
an association establishing module: establishing a correlation analysis expression of the inverter output quantity and a phase-locked loop linearization transfer function under small disturbance by using a phase-locked loop simplified model;
a determination module: and judging the inter-harmonic amplification range of the output quantity of the inverter under the small disturbance and the disturbance frequency with the most obvious amplification effect according to the correlation analytical expression.
Preferably, the association establishing module is configured to:
the A phase output of the inverter under small disturbance is as follows:
Id·cos(θPLL)≈Id·[cos(θ1)-sin(θ1)·Δθ]；
delta theta is the phase error, theta1For phase of fundamental frequency of power network, IdIs the amplitude of the inverter output current, thetaPLLOutputting the phase for the phase locked loop;
cos (theta)PLL) In the frequency domain:
Figure BDA0002320164320000032
L[]for Laplace transformed symbols, V1Is a frequency domain expression of voltage amplitude of fundamental wave phase of a power grid, VeFor the frequency domain expression of the small disturbance phase voltage amplitude, G () is the phase-locked loop transfer function, s is the frequency domain symbol, j is the imaginary number symbol, omega1Is the angular frequency of the fundamental wave of the power grid, f is the frequency sign, f1At fundamental frequency of the grid, fpIs the disturbance voltage frequency.
Preferably, the voltage distortion THD under small disturbance is obtained according to harmonic fundamental variableVComprises the following steps:
Figure BDA0002320164320000041
Vethe phase voltage amplitude is a small perturbation.
Preferably, the voltage distortion THD under the simplified model and the small disturbance is obtained according to the phase-locked loopVObtaining the current output distortion THD of the inverter under small disturbanceIComprises the following steps:
THDI＝THDV·|G(s)|
g(s) is a phase-locked loop linearization transfer function.
Preferably, THD is satisfied when | G(s) | ≧ 1I≥THDVAll the frequencies in the frequency interval of (2) can generate inter-harmonic amplification under small disturbance, and when | G(s) | takes the maximum value, the corresponding frequency is the disturbance frequency with the most obvious amplification effect.
Compared with the prior art, the invention has the following beneficial effects:
1. aiming at the output characteristic of the phase-locked loop under small disturbance, an output analysis model of the phase-locked loop under small disturbance is established by utilizing the traditional phase-locked loop linearization transfer function.
2. By establishing a phase-locked loop simplified model of the inverter, a correlation analytical expression of the output quantity of the inverter under small disturbance and a traditional phase-locked loop linearization transfer function is established, and the obtained analytical expression is simple and accurate, and can quickly and effectively judge the inter-harmonic amplification range of the output quantity of the inverter under small disturbance and the disturbance frequency with the most obvious amplification effect.
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Other features, objects and advantages of the present invention will become more apparent upon reading of the following detailed description of non-limiting embodiments thereof, with reference to the accompanying drawings.
FIG. 1 is a schematic diagram of an inverter PLL under small disturbances.
Fig. 2 is a topology diagram of an inverter grid-connected circuit.
Fig. 3 is a simplified inverter grid-connected system diagram.
Fig. 4 is a graph of inverter frequency impedance characteristics.
Fig. 5 is a comparison diagram of a small disturbance harmonic amplification determination method.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
Firstly, extracting disturbance factors from the angle of a phase-locked loop in an inverter; secondly, obtaining the output quantity of the phase-locked loop containing disturbance factors through theoretical derivation; thirdly, constructing an equivalent relation between the output quantity of the phase-locked loop under the disturbance and the traditional phase-locked loop linearization transfer function; and finally, obtaining the inter-harmonic amplification range of the output quantity of the inverter under small disturbance and the disturbance frequency with the most obvious amplification effect by utilizing a simplified phase-locked loop inverter model and a traditional phase-locked loop linearization transfer function. According to the invention, an output analytical model of the phase-locked loop under small disturbance is established by utilizing the traditional phase-locked loop linearization transfer function, and a correlation analytical expression of the output quantity of the inverter under small disturbance and the traditional phase-locked loop linearization transfer function is established by utilizing the phase-locked loop simplified model of the inverter, so that the inter-harmonic amplification range of the output quantity of the inverter under small disturbance and the most obvious disturbance frequency of the amplification effect can be quickly and accurately determined by only utilizing the traditional phase-locked loop linearization transfer function. The concrete implementation means is as follows: A. phase-locked loop output analysis model under small disturbance
The principle of the inverter phase-locked loop under small disturbance is shown in FIG. 1, wherein v is1a、v1b、v1cIs a three-phase grid voltage; v. ofpa、vpb、vpcThree-phase small disturbance voltage; v. ofqIs q-axis voltage under a rotating coordinate; hPIIs a proportional-derivative controller transfer function; 1/s represents an integral link; omegaPLLAnd thetaPLLThe phase-locked loop outputs angular frequency and phase, respectively. When the inverter is in a stable working state under small disturbance, the phase-locked loop output contains a small disturbance component, and therefore, an output analytical model of the phase-locked loop is firstly deduced.
Assuming that a voltage glitch can be written as:
Figure BDA0002320164320000051
wherein Vp、fpRespectively representing the amplitude and the frequency of the disturbance voltage, wherein pi is the circumferential rate and t is time. The voltage disturbance amount in the frequency domain can be written as:
Vp＝Vp/2,f＝±fp
lock with sliding boltTheta of phase loop outputPLLThe phase error Δ θ included in (a) can be written as:
Δθ＝θPLL-θ1
wherein theta is1The phase of the fundamental frequency of the power grid. At the original steady-state operation point of the system, after Park transformation, the voltage of the dq axis can be written as:
Figure BDA0002320164320000052
Figure BDA0002320164320000053
wherein Vd0And Vq0D-and q-axis voltages, respectively, f1For grid fundamental frequency, [ f]Is a frequency domain notation, U1For the fundamental phase voltage amplitude, dc is the dc component sign, and after considering the voltage disturbance at the original steady-state operating point, the q-axis voltage can be written as:
vq＝-sin(Δθ)·vd1+cos(Δθ)·vq1
is simple and easy to obtain
vq≈Δθ·vd0+vq0
Assuming a transfer function T between the phase error and the disturbance voltageB(s) then
Δθ[f]＝TB(s)·Vp,f＝±(fp-f1)
s is a frequency domain symbol.
Can be obtained by combining the above formulas
Figure BDA0002320164320000061
j is an imaginary symbol.
The phase error output after the voltage disturbance is subjected to PI adjustment is not difficult to obtain from a control block diagram of the phase-locked loop:
Δθ[f]＝(kp+ki/s)·(1/s)·Vq[f]
kpis a coefficient of proportionality，kiIs an integral coefficient.
The transfer function of the voltage small disturbance and the phase-locked loop error under the frequency domain obtained by combining the equations is as follows:
Figure BDA0002320164320000062
the traditional phase-locked loop linearization transfer function is:
Figure BDA0002320164320000063
comparison TBAfter(s) and g(s), the output of the pll under small perturbation can be expressed by the conventional pll linearization transfer function as:
Figure BDA0002320164320000064
then the phase-locked loop output under small perturbations can be written as:
Figure BDA0002320164320000065
in the above formula, disturbance factors are extracted from the phase-locked loop by theoretical derivation, and a correlation expression is constructed by the output quantity of the phase-locked loop under disturbance and the traditional phase-locked loop linearization transfer function, and the corresponding relationship is verified in embodiment 1.
B. Inverter simplified model and phase-locked loop correlation analysis formula
The topology of the inverter grid-connected circuit is shown in figure 2, wherein UdcThe inverter is used for converting the DC side voltage of the inverter, L is an inverter filter inductor, and the structure of sampling and control mainly comprises sampling, signal conditioning, a phase-locked loop and a current loop. In the process of outputting the small disturbance of the inverter, because the frequency of sampling and signal conditioning links is high, the influence on the small disturbance signal can be ignored. In addition, according to the actual engineering requirement, the control speed of the current loop of the inverter is far higher than that of the phase-locked loop, and the sensitivity of the phase-locked loop is higher under small disturbance, so that the phase-locked loop plays a leading role in outputting the small disturbance. The invention is toThe main circuit and the control structure of the inverter are simplified into a phase-locked loop simplified inverter model, and the simplified inverter grid-connected system is shown in figure 3, wherein IdThe current magnitude is output for the inverter.
According to the simplified inverter model, the output of the inverter (for example, phase A) under small disturbance can be written as Id·cosθPLL≈Id·[cos(θ1)-sin(θ1)·Δθ]
Cos (theta)PLL) In the frequency domain can be written as
Figure BDA0002320164320000071
From the above formula, cos (. theta.) can be seenPLL) Comprises three frequency components, namely a fundamental frequency, a disturbance frequency and a new frequency component 2f1-fpIn the existing impedance analysis method, the disturbance output quantity related to the frequency is usually ignored, and the invention includes the disturbance quantity in the inverter output quantity. According to the definition of harmonic distortion (THD), the voltage distortion THD of the system under small disturbance can be easily obtainedVIs composed of
Figure BDA0002320164320000072
According to the simplified model of the phase-locked loop of the inverter and the above formula, the current output distortion THD of the inverter under small disturbance can be obtainedIIs THDI＝THDV·|G(s)|
Satisfying THD in all frequency bandsI≥THDVThe frequency interval of (2) is called as inter-harmonic amplification frequency region, and it can be known from the above formula that the range of the interval and the disturbance frequency with the most obvious amplification effect depend on | g(s) |, i.e. the traditional phase-locked loop linearization transfer function can be used as a correlation analysis formula to determine the inter-harmonic amplification range of the inverter output quantity under small disturbance and the disturbance frequency with the most obvious amplification effect. When | G(s) | ≧ 1, inter-harmonic amplification under small disturbance occurs to all frequencies in the interval, and when | G(s) | takes the maximum value, the corresponding frequency is the disturbance frequency with the most obvious amplification effect. Existing resistorAn analysis method for analyzing the output quantity of the inverter and a judgment method for amplifying the inter-harmonic of the small disturbance of the inverter based on the phase-locked loop are shown in an implementation example 1.
Example 1:
the existing method for determining the output quantity of the inverter under small disturbance mainly utilizes numerical operation to indirectly obtain the output quantity of the inverter by establishing an inverter impedance model, and meanwhile, the output quantity of the inverter obtained has larger deviation with the actual working condition because the existing impedance model only considers disturbance frequency and ignores new response frequency. In order to verify the effect of the method, aiming at the judgment of the output quantity of the inverter under small disturbance, the output quantity of the inverter is judged according to the existing impedance model, and an output curve under a frequency domain is drawn based on the existing method; judging the output quantity of the inverter according to the judging method provided by the invention, and drawing an output curve in a frequency domain based on the method; and finally, scanning an inverter output curve in a frequency domain by an experimental method through injecting voltage small disturbances with different frequencies in sequence. The invention aims to provide a convenient and accurate judgment method for the output quantity of the inverter of the renewable energy grid connection under small disturbance. In the operated renewable energy grid-connected inverter, in order to suppress high-frequency disturbance, the bandwidth of each control loop of the inverter is low, so the existing method is mainly compared with the method in the embodiment with respect to small disturbance in a low-frequency range (1-99 Hz).
Fig. 4 shows a frequency impedance characteristic curve obtained from a conventional inverter impedance model, and the frequency characteristic curve of the inverter output quantity under small disturbances determined by the conventional method is shown in fig. 5 (the dotted line is the inverter output quantity curve obtained by the conventional method) by performing numerical calculation on the impedance model. The ordinate in fig. 5 is the amplification factor, i.e. the ratio of the inverter output response to the input disturbance, when the value is greater than 1, the inter-harmonic content generated by the inverter response is higher than that of the disturbance, and the disturbance frequency is in the inter-harmonic amplification range. According to the correlation analytic expression of the traditional phase-locked loop linearization transfer function and the inverter output quantity under small disturbance obtained by the invention, the frequency characteristic curve of the inverter output quantity under small disturbance is directly drawn, as shown in fig. 5 (the solid line is the inverter output quantity curve obtained by the invention). By using an experimental platform, voltage small disturbances with different frequencies are injected into an inverter grid-connected system in sequence in a frequency scanning mode, inverter output characteristics in a frequency domain are scanned point by an experimental method, and a result obtained by actual measurement is shown in fig. 5 (a point is an inverter output quantity actually measured). It can be seen from fig. 5 that the inverter output (shown by the dotted line) under small perturbation determined by the prior art method is greatly different from the frequency sweep result (shown by the dotted line) of the experiment; according to the invention, the frequency characteristic curve (shown by a solid line) of the inverter output under the condition of small disturbance is directly drawn to be in high coincidence with the frequency scanning result (shown by a point) of an experiment. The comparison result shows that: compared with the existing method, the method provided by the invention has higher accuracy; meanwhile, the association analytical expression constructed by the invention does not need to carry out indirect numerical operation, so that the method is more convenient and faster in the judgment process.
Based on the method for judging the small disturbance inter-harmonic amplification phenomenon of the inverter, the invention also provides a system for judging the small disturbance inter-harmonic amplification phenomenon of the inverter, which comprises the following steps:
simplifying and establishing an inverter model: simplifying the main circuit and the control structure of the inverter into a phase-locked loop to obtain a simplified model of the phase-locked loop of the inverter.
And (3) association establishment step: and establishing a correlation analysis expression of the inverter output quantity and the phase-locked loop linearization transfer function under small disturbance by using the phase-locked loop simplified model.
A judging step: and judging the inter-harmonic amplification range of the output quantity of the inverter under the small disturbance and the disturbance frequency with the most obvious amplification effect according to the correlation analytical expression.
Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, units provided by the present invention as pure computer readable program code, the system and its various devices, modules, units provided by the present invention can be fully implemented by logically programming method steps in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system and various devices, modules and units thereof provided by the invention can be regarded as a hardware component, and the devices, modules and units included in the system for realizing various functions can also be regarded as structures in the hardware component; means, modules, units for performing the various functions may also be regarded as structures within both software modules and hardware components for performing the method.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.

Claims (10)

1. A method for judging the small disturbance inter-harmonic amplification phenomenon of an inverter is characterized by comprising the following steps:
simplifying and establishing an inverter model: simplifying a main circuit and a control structure of the inverter into a phase-locked loop to obtain a simplified model of the phase-locked loop of the inverter;
and (3) association establishment step: establishing a correlation analysis expression of the inverter output quantity and a phase-locked loop linearization transfer function under small disturbance by using a phase-locked loop simplified model;
a judging step: and judging the inter-harmonic amplification range of the output quantity of the inverter under the small disturbance and the disturbance frequency with the most obvious amplification effect according to the correlation analytical expression.
2. The method for determining the small disturbance inter-harmonic amplification phenomenon of the inverter according to claim 1, wherein the correlation establishing step comprises:
the A phase output of the inverter under small disturbance is as follows:
Id·cos(θPLL)≈Id·[cos(θ1)-sin(θ1)·Δθ]；
delta theta is the phase error, theta1For phase of fundamental frequency of power network, IdIs the amplitude of the inverter output current, thetaPLLOutputting the phase for the phase locked loop;
cos (theta)PLL) In the frequency domain:
Figure FDA0002320164310000011
L[]for Laplace transformed symbols, V1Is a frequency domain expression of voltage amplitude of fundamental wave phase of a power grid, VeFor the frequency domain expression of the small disturbance phase voltage amplitude, G () is the phase-locked loop transfer function, s is the frequency domain symbol, j is the imaginary number symbol, omega1Is the angular frequency of the fundamental wave of the power grid, f is the frequency sign, f1At fundamental frequency of the grid, fpIs the disturbance voltage frequency.
3. The method for determining the inter-harmonic amplification phenomenon of small disturbance of the inverter according to claim 2, wherein the voltage distortion THD under the small disturbance is obtained according to a harmonic fundamental variableVComprises the following steps:
Figure FDA0002320164310000012
Vethe phase voltage amplitude is a small perturbation.
4. The method for determining the inter-harmonic amplification phenomenon of small disturbances of the inverter according to claim 3, wherein the model is simplified according to a phase-locked loop and the voltage distortion THD under the small disturbancesVObtaining the current output distortion THD of the inverter under small disturbanceIComprises the following steps:
THDI＝THDV·|G(s)|
g(s) is a phase-locked loop linearization transfer function.
5. The method for determining the inter-harmonic amplification phenomenon of small disturbance of an inverter according to claim 4, wherein THD is satisfied when | G(s) | ≧ 1I≥THDVAll the frequencies in the frequency interval of (2) can be amplified by inter-harmonic waves under small disturbance, and when | G(s) | takes the maximum value, the corresponding frequency is the frequency with the most obvious amplification effectThe frequency of the disturbance.
6. A system for judging the small disturbance inter-harmonic amplification phenomenon of an inverter is characterized by comprising the following components:
an inverter model simplification and association establishment module: simplifying a main circuit and a control structure of the inverter into a phase-locked loop to obtain a simplified model of the phase-locked loop of the inverter;
an association establishing module: establishing a correlation analysis expression of the inverter output quantity and a phase-locked loop linearization transfer function under small disturbance by using a phase-locked loop simplified model;
a determination module: and judging the inter-harmonic amplification range of the output quantity of the inverter under the small disturbance and the disturbance frequency with the most obvious amplification effect according to the correlation analytical expression.
7. The system for determining the inter-harmonic amplification phenomenon of small disturbances of the inverter according to claim 6, wherein the correlation establishing module is configured to:
the A phase output of the inverter under small disturbance is as follows:
Id·cos(θPLL)≈Id·[cos(θ1)-sin(θ1)·Δθ]；
delta theta is the phase error, theta1For phase of fundamental frequency of power network, IdIs the amplitude of the inverter output current, thetaPLLOutputting the phase for the phase locked loop;
cos (theta)PLL) In the frequency domain:
Figure FDA0002320164310000021
L[]for Laplace transformed symbols, V1Is a frequency domain expression of voltage amplitude of fundamental wave phase of a power grid, VeFor the frequency domain expression of the small disturbance phase voltage amplitude, G () is the phase-locked loop transfer function, s is the frequency domain symbol, j is the imaginary number symbol, omega1Is the angular frequency of the fundamental wave of the power grid, f is the frequency sign, f1At fundamental frequency of the grid, fpIs the disturbance voltage frequency.
8. The system for determining the inter-harmonic amplification phenomenon of small disturbance of an inverter according to claim 7, wherein the voltage distortion THD under small disturbance is obtained according to a harmonic fundamental variableVComprises the following steps:
Figure FDA0002320164310000031
Vethe phase voltage amplitude is a small perturbation.
9. The system for determining the inter-harmonic amplification phenomenon of small disturbances of an inverter according to claim 8, wherein the model is simplified according to a phase-locked loop and the voltage distortion THD under small disturbancesVObtaining the current output distortion THD of the inverter under small disturbanceIComprises the following steps:
THDI＝THDV·|G(s)|
g(s) is a phase-locked loop linearization transfer function.
10. The system for determining the inter-harmonic amplification phenomenon of small disturbance of an inverter according to claim 9, wherein THD is satisfied when | G(s) | ≧ 1I≥THDVAll the frequencies in the frequency interval of (2) can generate inter-harmonic amplification under small disturbance, and when | G(s) | takes the maximum value, the corresponding frequency is the disturbance frequency with the most obvious amplification effect.
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