CN111651947A - Impedance ratio stability judgment method suitable for distributed energy storage system - Google Patents

Impedance ratio stability judgment method suitable for distributed energy storage system Download PDF

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CN111651947A
CN111651947A CN202010769715.9A CN202010769715A CN111651947A CN 111651947 A CN111651947 A CN 111651947A CN 202010769715 A CN202010769715 A CN 202010769715A CN 111651947 A CN111651947 A CN 111651947A
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bus
stability
impedance ratio
energy storage
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CN111651947B (en
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潘本仁
胡斯登
朱正斌
张妍
谢国强
桂小智
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Zhejiang University ZJU
State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Jiangxi Electric Power Co Ltd
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State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Jiangxi Electric Power Co Ltd
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Abstract

The invention discloses an impedance ratio stability judgment method suitable for a distributed energy storage system, which comprises the following steps of: measuring parallel impedance of all transducers of a distributed energy storage systemZ bus According toZ bus And bus capacitorCCalculating a novel impedance ratioZ c /Z nc The denominator is the parallel impedance Z of all converters after the bus capacitance is removed nc The molecule being the capacitive impedance Z c In terms of impedance ratioZ c /Z nc Making a Neisseria diagram as an equivalent open-loop transfer function, judging the stability of the system according to the Neisseria diagram, and if the amplitude-phase curve is not wrappedAnd (4) surrounding the point (-1,0j), the system is stable, otherwise, the system is unstable. The impedance ratio stability criterion provided by the invention is suitable for a distributed energy storage system, and the stability of the system is judged by virtue of the impedance, so that the limitation that the traditional impedance ratio criterion can only judge the stability of a single-source system is overcome, the power flow direction of a converter does not need to be distinguished, and the application range of the impedance ratio stability criterion is wider compared with the traditional impedance ratio criterion.

Description

Impedance ratio stability judgment method suitable for distributed energy storage system
Technical Field
The invention relates to the technical field of distributed power supply, in particular to an impedance ratio stability judgment method suitable for a distributed energy storage system.
Background
The distributed energy storage system comprises a plurality of energy storage units, can access wind, light and other renewable energy sources and various types of direct current electric loads, has the advantages of good reliability, flexible interface, high power density and the like, and is widely applied to the field of new energy sources. The distributed energy storage system is composed of a plurality of converters, although each converter is stable when working independently, the combination of the converters can change the total impedance of the system, influence the dynamic performance of the system, even cause the instability of the system and damage electric devices, and the stability problem is a key problem of the distributed energy storage system.
The traditional method for analyzing the stability of the system is based on a small signal model of the system, obtains a transfer function of the system by using the small signal model, and judges the stability of the system according to the distribution of the extreme points of the transfer function of the system, namely a characteristic value analysis method. Eigenvalue analysis requires modeling of each transformer and must obtain the internal parameters of the transformer.
For the problem, researchers at home and abroad, such as professor Middlebrook, provide various impedance ratio criteria, and stability can be judged and analyzed according to external impedance information of the converter without internal parameters of the converter. These impedance ratio criteria include: the traditional impedance ratio criterion is to divide the system into a power subsystem and a load subsystem, and judge the stability of the system by the ratio of the impedances of the two parts.
When the traditional impedance ratio criterion is used for judging and analyzing the stability of the system, the converters in the system need to be classified according to the power flow direction, and the energy storage unit has the characteristic of bidirectional power flow, so that the application of the traditional impedance ratio criterion is hindered. In addition, the conventional impedance ratio criterion requires the power subsystem to be stable, i.e., the subsystem output impedance transfer functionZ o (s)There is no right pole. In a multi-source system, the transfer function of the total output impedance of a plurality of source converters when combined with each other is such that each source converter is stable on its ownZ o (s)There may be a right pole where a conventional impedance ratio criterion may be used to generate a false positive. The traditional impedance ratio criterion is only established in a single-source system and a multi-source system with a stable power subsystem, and the traditional impedance ratio criterion is generally only applied to the single-source system because whether the power subsystem is stable or not can not be judged according to the impedance.
The distributed energy storage system comprises a plurality of energy storage units. When the energy storage unit works in a discharging mode, the energy storage unit is essentially a power converter, so that the system has the characteristic of multiple sources, and the traditional impedance ratio criterion is difficult to apply to a distributed energy storage system. How to use the impedance information to judge and analyze the stability of the distributed energy storage system needs to be further researched.
Disclosure of Invention
The present invention is directed to solve at least one of the technical problems in the prior art, and provides a method for determining stability of impedance ratio for a distributed energy storage system.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows: an impedance ratio stability judgment method suitable for a distributed energy storage system comprises the following steps:
step 1, injecting a current disturbance signal into a direct current bus
Figure 434735DEST_PATH_IMAGE001
While measuring voltage disturbance signals
Figure 86296DEST_PATH_IMAGE002
According to the formula
Figure 288869DEST_PATH_IMAGE003
Obtaining parallel impedances of all converters of a distributed energy storage systemZ bus ；
Step 2, through the capacitance parameter and parallel impedance of the system busZ bus Calculating the impedance ratioZ c /Z nc ；
Step 3, the calculated impedance ratioZ c /Z nc A Neisseria diagram is made as an equivalent open-loop transfer function, the system type is judged according to the amplitude-phase curve of the Neisseria diagram, and the amplitude-phase curve is subjected to compensation drawing;
and 4, judging the stability of the system according to the amplitude-phase curve of the Neisseria cepstrum.
Further, in the step 2, the impedance ratio is setZ c /Z nc To remove the parallel impedance Z of all converters after the bus capacitor is removed nc As a ratio of impedancesZ c /Z nc The denominator of (a).
Further, in the step 2, the impedance ratio is setZ c /Z nc By impedance of bus capacitorZ c As a ratio of impedancesZ c /Z nc The molecule of (1).
Further, in the step 2, impedances are connected in parallelZ bus System bus capacitance parameter to impedance ratioZ c /Z nc The relationship of (A) is as follows:
Figure 621762DEST_PATH_IMAGE004
in the formulajIs the unit of an imaginary number,θis the phase angle of the parallel impedance,|Z bus |is a mode of the parallel impedance,ωin order to be the angular frequency of the frequency,Cis a bus capacitor.
Further, in step 4, the stability of the system is determined by the parallel impedance transfer functionZ bus (s)Whether the system contains a right half-plane pole or not is judged, and when each converter in the system is stable, the judgment is equivalent to an equivalent open-loop transfer functionZ c /Z nc Whether the amplitude-phase curve surrounds the point (-1,0j) or not is judged, if the amplitude-phase curve does not surround the point (-1,0j), the system is stable, otherwise, the system is unstable, wherein j in 0j is an imaginary unit.
Wherein the system type in step 3 is based onωThe distribution of the amplitude-phase curve is judged when the amplitude-phase curve approaches to 0, when the amplitude-phase curve converges to a fixed point, the impedance ratio transfer function does not contain an integral link, the system is a zero-type system, and at the moment, the complementary drawing is not needed. When the amplitude-phase curve is divergent and approximately parallel to the virtual axis, the impedance ratio transfer function comprises an integral element, the system is an I-type system, and the clockwise motion of the system is needed to be supplementedω=0-Toω=0+Semi-circle curve with radius of ∞. When the amplitude-phase curve is divergent and approximately parallel to the real axis, the impedance ratio transfer function comprises two integral links, the system is a II-type system, and the clockwise one needs to be supplemented at the momentω=0-Toω=0+And a circular curve with a radius of ∞. In actual engineering, more than II type systems generally cannot appear.
Compared with the prior art, the invention has at least one of the following technical effects:
1. the novel impedance ratio criterion can judge the stability of a multi-source system, overcomes the limitation that the traditional impedance ratio criterion can only judge the stability of a single-source system, can be applied to a distributed energy storage system, and has wider application range;
2. the stability of the system is judged according to the parallel impedance Zbus and the bus capacitor C by the novel impedance ratio criterion, the converter does not need to be classified, and the limitation that the traditional impedance ratio criterion needs to distinguish the power flow direction is overcome;
3. the provided impedance ratio stability criterion suitable for the distributed energy storage system judges the stability of the system according to the parallel impedance Zbus and the bus capacitor C, and the stability of the distributed energy storage system can be judged only by external impedance information without internal parameters of a converter;
4. the stability judgment is a key step of system stability analysis and is also a precondition and basis for designing a stability controller, and the impedance ratio criterion establishes a foundation for analyzing and designing a stable system.
Drawings
FIG. 1 is a diagram illustrating a distributed energy storage system with a common DC bus according to an embodiment of the present invention;
FIG. 2 is an equivalent circuit of a distributed energy storage system according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of bus capacitor extraction according to an embodiment of the present invention;
FIG. 4 illustrates an exemplary topology of a distributed energy storage system in accordance with embodiments of the present invention;
FIG. 5 is a distribution diagram of the output impedance transfer function Zo(s) of the power subsystem at the first stage of the system according to the embodiment of the present invention;
FIG. 6 is a diagram of the distribution of pole-zero distribution of the output impedance transfer function Zo(s) of the power subsystem at the second stage of the system according to the embodiment of the present invention;
FIG. 7 is a schematic diagram of measuring the parallel impedance Zbus according to an embodiment of the present invention;
FIG. 8 is a Neisseria diagram of a conventional impedance ratio at a first stage of the system in accordance with an embodiment of the present invention;
FIG. 9 is a Neisseria diagram of a conventional impedance ratio at a second stage of the system in accordance with the present invention;
FIG. 10 is a Neisseria diagram of the novel impedance ratio at the first stage of the system in accordance with the present invention;
FIG. 11 is a Neisseria diagram of the novel impedance ratio at the second stage of the system in accordance with the exemplary embodiment of the present invention;
FIG. 12 shows the bus voltage V of the system in an embodiment of the invention bus And (5) simulating a waveform.
Detailed Description
The technical solutions in the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments.
In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "connected" and "connected" are to be interpreted broadly, e.g., as being fixed or detachable or integrally connected; can be mechanically or electrically connected; may be directly connected or indirectly connected through an intermediate. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Referring to fig. 1 to 12, in a preferred embodiment of the present invention, a method for determining stability of impedance ratio of a distributed energy storage system includes the following steps:
step 1, injecting a current disturbance signal into a direct current bus
Figure 445547DEST_PATH_IMAGE006
While measuring voltage disturbance signals
Figure 181422DEST_PATH_IMAGE007
According to the formula
Figure 849164DEST_PATH_IMAGE008
Obtaining parallel impedances of all converters of a distributed energy storage systemZ bus ；
Step 2, through the capacitance parameter and parallel impedance of the system busZ bus Calculating the impedance ratioZ c /Z nc ；
Step 3, the calculated impedance ratioZ c /Z nc A Neisseria diagram is made as an equivalent open-loop transfer function, the system type is judged according to the amplitude-phase curve of the Neisseria diagram, and the amplitude-phase curve is subjected to compensation drawing;
and 4, judging the stability of the system according to the amplitude-phase curve of the Neisseria cepstrum.
Further, in the step 2, the impedance ratio is setZ c /Z nc To remove the parallel impedance Z of all converters after the bus capacitor is removed nc As a ratio of impedancesZ c /Z nc The denominator of (a).
Further, in the step 2, the impedance ratio is setZ c /Z nc By impedance of bus capacitorZ c As a ratio of impedancesZ c /Z nc The molecule of (1).
Further, in the step 2, impedances are connected in parallelZ bus System bus capacitance parameter to impedance ratioZ c /Z nc The relationship of (A) is as follows:
Figure 783621DEST_PATH_IMAGE009
in the formulajIs the unit of an imaginary number,θis the phase angle of the parallel impedance,|Z bus |is a mode of the parallel impedance,ωin order to be the angular frequency of the frequency,Cis a bus capacitor.
Further, in step 4, the stability of the system is determined by the parallel impedance transfer functionZ bus (s)Whether the system contains a right half-plane pole or not is judged, and when each converter in the system is stable, the judgment is equivalent to an equivalent open-loop transfer functionZ c /Z nc Whether the amplitude-phase curve of (1) surrounds the point (1, 0j) or notJudging that the system is stable if the amplitude-phase curve does not surround the (-1,0j) point, otherwise, the system is unstable, wherein j in 0j is an imaginary unit.
Wherein the type of system in step 3 is based onωThe distribution of the amplitude-phase curve is judged when the amplitude-phase curve approaches to 0, when the amplitude-phase curve converges to a fixed point, the impedance ratio transfer function does not contain an integral link, the system is a zero-type system, and at the moment, the complementary drawing is not needed. When the amplitude-phase curve is divergent and approximately parallel to the virtual axis, the impedance ratio transfer function comprises an integral element, the system is an I-type system, and the clockwise motion of the system is needed to be supplementedω=0-Toω=0+Semi-circle curve with radius of ∞. When the amplitude-phase curve is divergent and approximately parallel to the real axis, the impedance ratio transfer function comprises two integral links, the system is a II-type system, and the clockwise one needs to be supplemented at the momentω=0-Toω=0+And a circular curve with a radius of ∞. In actual engineering, more than II type systems generally cannot appear.
The novel impedance ratio criterion provided by the invention can judge the stability of a multi-source system, overcomes the limitation that the traditional impedance ratio criterion can only judge the stability of a single-source system, can be applied to a distributed energy storage system, and has wider application range. The novel impedance ratio criterion provided by the invention judges the stability of the system according to the parallel impedance Zbus and the bus capacitor C, does not need to classify the converters, and overcomes the limitation that the traditional impedance ratio criterion needs to distinguish the power flow direction. The impedance ratio stability criterion suitable for the distributed energy storage system provided by the invention judges the stability of the system according to the parallel impedance Zbus and the bus capacitor C, and the stability of the distributed energy storage system can be judged only by external impedance information without internal parameters of a converter. The stability judgment provided by the invention is a key step of system stability analysis and is also a precondition and basis for designing a stability controller, and the impedance ratio criterion establishes a foundation for analyzing and designing a stable system.
For the purpose of facilitating an understanding of the present invention, the following provides a more detailed explanation of the principles of the present invention:
in a distributed energy storage system, a power generation device, an energy storage device and a power load are connected to a direct current bus through power electronic converters, and the converters are mainly connected in a cascade connection mode, a parallel connection mode and the like. The distributed energy storage system sharing the dc bus is formed by cascading a power subsystem and a load subsystem, as shown in fig. 1, where each subsystem includes n power converters and m load converters, respectively.
For a distributed energy storage system, the stability of the bus voltage is a main standard for judging whether the system is stable, and the stability of the bus voltage can be analyzed by means of small-signal modeling.
Firstly, a linear equivalent circuit of each converter is solved through small signal modeling, then a power converter circuit is simplified by virtue of the Thevenin theorem, a load converter circuit is simplified by virtue of the Nuton theorem, an equivalent circuit of each converter is obtained, equivalent circuits in a subsystem are combined, and finally a small signal equivalent circuit of the distributed energy storage system is obtained, as shown in figure 2. The transfer function expression of the bus voltage can be solved according to the equivalent circuit:
Figure 245827DEST_PATH_IMAGE011
(1)
in the formula, Ux is a disturbance amount of an output voltage of the xth power converter, Zx is an output impedance of the xth power converter, Ix is a disturbance amount of a load-side current of the xth load converter, Zo is a total output impedance of all the power converters, and Zi is a total input impedance of all the load converters.
According to the control principle, the system stability is determined by the pole distribution of the system transfer function, and when the transfer function does not have the right half-plane pole, the system is stable. In the distributed energy storage system, since each converter is stable, no zero pole of the right half plane exists in ux(s), ix(s) and zx(s), and the stability of ubus(s) is determined by the parallel impedance of the 1 st part of equation 1, i.e. all converters:
Figure 399555DEST_PATH_IMAGE012
(2)
the Neisser criterion can simplify the judgment of the system stability, and the core formula is as follows:
Figure 605408DEST_PATH_IMAGE013
(3)
in the formula (I), the compound is shown in the specification,hthe number of right poles of the equivalent closed loop system transfer function,wopen loop transfer function for system equivalenceTThe curve of (a) encloses clockwise the number of turns of the (-1,0j) point,qis composed ofTNumber of right poles of the transfer function. According to the Neisser criterion, inTIs not more than 0 andqunder known conditions, byTThe stability of the system can be judged by the amplitude-phase curve.
With this property of the Neisseria criterion, the conventional impedance ratio criterion morphs equation 2 toZ bus (s)Constructing impedance ratio as equivalent closed loop transfer functionT c =Z o (s)/Z i (s)As an equivalent open loop transfer function.
Figure 597635DEST_PATH_IMAGE014
(4)
The order of the load converter input impedance is generally equal to or greater than the order of the source converter output impedance,T c can meet the order requirement of the Neisser criterion. Furthermore, in a single source system, the source converter is self-stabilizing, equivalent open loop transfer functionT cWithout the right pole, i.e.q=0, so the Neisser criterion can be simplified toh=wI.e. whenT cWhen the curve of (a) does not enclose the (-1,0j) point, the parallel impedance transfer functionZ bus (s)And if the right pole does not exist, the system is stable, otherwise, the system is unstable.
The traditional impedance ratio criterion can only be applied to a single-source distributed power supply system, and the stability of the multi-source system cannot be judged. When there are multiple source converters in parallel in the system, the total output impedance transfer function of each power converter is stable even though the power converter is stableZ o (s)The right pole may still be present. To be provided withFor example, two parallel power converters have a total output impedance transfer function of:
Figure 745589DEST_PATH_IMAGE016
(5)
in the formulaN 1 (s)、N 2 (s)、D 1 (s)、D 2 (s)Are all made ofsKnown polynomials of (a). Even ifD 1 (s)、D 2 (s)The denominator term of equation 5 without zero points whose real parts are positiveN 1 D 2 +N 2 D 1 There may still be zeros whose real part is positive, i.e. zeroZ o (s)The right pole of (a). The parallel connection of more than two power converters also has the above-mentioned problem.
At the moment, the stability of the multi-source system needs to be judged, the internal parameters of the power converter need to be obtained, and small signal modeling is carried out on the power subsystem to obtainZ o (s)Against the impedance ratio criterion, which determines stability by means of impedance. In addition, the conventional impedance ratio criterion is in the form ofZ o /Z i I.e. the output impedance of the source converter is higher than the input impedance of the up-load converter, and thus the power flow direction of the converter in the system must be determined, so that the converter is divided into two types, i.e. a power source and a load.
To address this problem, equation 4 can be further modified, and new forms can be obtained:
Figure 456056DEST_PATH_IMAGE018
(6)
in the formulaY o For the output admittance of the power subsystem,Y i for the load subsystem input admittance,Y x admittance for each transformer. The system admittance is equal to the sum of all the converter admittances, the output admittance of the source and the input admittance of the load have equal status, and the region is no longer neededThe power flow direction of the sub-converter.
In passive devices, the order of the impedance transfer function of the capacitance is the lowest, so the capacitance impedance can be used as a molecular term for the impedance ratio. In the distributed energy storage system, the converters share the same direct current bus and all have voltage stabilizing capacitors, as shown in fig. 3, so that the capacitors of the converters can be separated and combined into a bus capacitorCConstructing a new equivalent open-loop transfer functionT n =Z c /Z nc As shown in formula 7:
Figure 200021DEST_PATH_IMAGE020
(7)
in the formula
Figure 312333DEST_PATH_IMAGE021
To remove the admittance sums of all the inverters after the bus capacitance,Z nc (s)=1/Y nc (s)。
the transfer function of the capacitance impedance only has one pole on the virtual axis, and the stability of the system is not influenced, so that the stability of the system is not influencedZ bus (s)The stability of (d) is determined by the latter term of equation 7. Through impedance ratioT n The system stability can be judged by the amplitude-phase curve.
To distinguish from the conventional impedance ratio criterion, the impedance ratio criterion is referred to as a novel impedance ratio criterion.
In a distributed energy storage system, closed-loop impedance transfer functions of common converters are all larger than or equal to-1 order, so that equivalent open-loop transfer functionsT n Is also less than or equal to 0, and the novel impedance ratio criterion meets the use condition of the Neisseria criterion.
In a distributed energy storage system, each converter is self-stabilized, and its admittance has no right half-plane pole, so that the admittance and the sum of the systemY nc (s)There is also no right half-plane pole, so the equivalent open-loop transfer functionT n There is no right pole. Core formula capable of simplifying Neisser criterionIs composed ofh=w，Namely whenT n When the curve of (c) does not enclose the point (-1,0j),Z bus (s)and if the right pole does not exist, the system is stable, otherwise, the system is unstable.
Figure 913079DEST_PATH_IMAGE023
TABLE 1
Figure 861574DEST_PATH_IMAGE025
TABLE 2
The application of the novel impedance ratio criterion is illustrated in detail by taking the typical distributed energy storage system in fig. 4 as an example, and compared with the conventional impedance ratio criterion. The system comprises four converters, namely a No. 1 photovoltaic converter and a Boost topology, and adopts voltage control; no. 2 and No. 3 energy storage converters, bidirectional Buck-Boost topology, adopt constant power control (voltage control is adopted during charging, and average current control is adopted during discharging); and a No. 4 load converter and a Buck topology adopt voltage control. The four converters work in a continuous conduction mode and share one direct current bus. The main circuit parameters are shown in table 1, and the controller parameters are shown in table 2.
The system has two operation stages, and in the first stage, the No. 2 and No. 3 energy storage converters all work in a discharge mode, and the system is stable at the moment. In the second stage, the No. 3 energy storage converter is switched to a charging mode, the power flow direction is changed, meanwhile, due to the fact that the illumination intensity is weakened, the input voltage of the No. 1 photovoltaic converter is reduced to 200V, at the moment, the bus voltage generates obvious low-frequency oscillation, and the system stability is damaged. The simulation result is shown in fig. 12, and at 0.7-0.9s, the system works in the first stage, and the bus voltage is stable. And starting from 0.9s, switching the working state of the system, and when the system works in the second stage in 1.1s, the bus voltage generates obvious low-frequency oscillation, the bus voltage fluctuation is generally required to be not more than +/-5% of a rated value by the distributed power supply system, the bus oscillation amplitude in the stage is about 23.8V and exceeds the 20V fluctuation range required by the system, and the system stability is damaged.
In both operation phases of the system, there is an energy storage unit in discharge mode, which outputs current, forming a working scenario involving multiple power converters. By small signal modeling, the transfer function of the output impedance of the power subsystem in two stages can be obtainedZ o (s): at stage one, the system includes three power converters, in which caseZ o (s)The power subsystem is stable with its pole-zero distribution as shown in figure 5. Stage two, the system includes two power converters, in which caseZ o (s)There are two right poles and the power subsystem is unstable with a pole-zero distribution as shown in figure 6.
Parallel impedanceZ bus The measuring circuit is shown in fig. 7, when the system is at a steady-state working point, the disturbance current source injects disturbance with different frequencies into the bus, and the disturbance current source injects the disturbance with different frequencies into the bus according to a formula
Figure 612493DEST_PATH_IMAGE026
The impedance information of the first stage can be obtained. In the second stage of system operation, because the system stability is damaged, the parallel impedance cannot be directly measured, and the impedance of each converter at a steady-state working point is measured respectively, so that the total parallel impedance is obtained through calculation. This example uses the AC tool of the PSIM to measure the impedance of the system in various states.
And judging the stability of the system by means of the conventional impedance ratio criterion according to the measured impedance information. Dividing the converter into two types according to the power flow direction to obtain the equivalent open-loop transfer functionT c As shown in fig. 7, in both operation stages, the amplitude-phase curve does not surround the (-1,0j) point, and the judgment system is stable in both stages, which is obviously inconsistent with the simulation result of fig. 12, and the judgment is wrong.
In the second phase of the example, the transfer function of the total output impedance of the system power subsystemZ o (s)There are two right poles. The premise of the application of the traditional impedance ratio criterion, namely the equivalent open-loop transfer functionT c No right pole is not established,resulting in erroneous determinations by conventional impedance ratio criteria.
Meanwhile, by means of the measured parallel impedance, a novel impedance ratio can be obtained according to the following formula:
Figure DEST_PATH_IMAGE027
(8)
based on the above calculation results, an equivalent open loop transfer function can be madeT n Byω=0 + Toω=+∞Amplitude-phase curve of (2). First, make up the pictureT n Byω=-∞Toω=0 - In accordance with the amplitude-phase curve ofωThe distribution of the amplitude-phase curve approaching 0 determines the system type, and the amplitude-phase curves in fig. 10 and 11 are both divergent and approximately parallel to the real axis, and the equivalent open-loop transfer function is determined when the amplitude-phase curve is approximately parallel to the real axisT n The transfer function of (2) comprises two integral links, and the system is a II type system. Therefore, the supplementary painting is clockwiseω=0-Toω=0+Of radius of∞The circular curve of (2). The final nefarian diagram is shown in fig. 8, and in the first stage of the system, the amplitude-phase curve does not enclose the point (-1,0j), and as shown in fig. 10, the system is judged to be stable. In the second stage of the system, the amplitude-phase curve encloses the point (-1,0j), as shown in FIG. 11, and the system is judged to be unstable. This judgment is consistent with the simulation result of fig. 12.
Therefore, the distributed energy storage system has the characteristic of multiple sources, and the impedance ratio stability criterion is as follows: the system stability can be controlled by a novel impedance ratio under the premise that each converter is stableT n Whether the amplitude-phase curve of (1) is enclosed by the point (-1,0j) is judged.
The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. The above additional technical features can be freely combined and used in superposition by those skilled in the art without conflict.
It is to be understood that the present invention has been described with reference to certain embodiments, and that various changes in the features and embodiments, or equivalent substitutions may be made therein by those skilled in the art without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims (5)

1. The method for judging the stability of the impedance ratio of the distributed energy storage system is characterized by comprising the following steps of:
step 1, injecting a current disturbance signal into a direct current bus
Figure 901425DEST_PATH_IMAGE002
While measuring voltage disturbance signals
Figure 536674DEST_PATH_IMAGE004
According to the formula
Figure 785253DEST_PATH_IMAGE006
Obtaining parallel impedances of all converters of a distributed energy storage systemZ bus ；
Step 2, through the capacitance parameter and parallel impedance of the system busZ bus Calculating the impedance ratioZ c /Z nc ；
Step 3, the calculated impedance ratioZ c /Z nc A Neisseria diagram is made as an equivalent open-loop transfer function, the system type is judged according to the amplitude-phase curve of the Neisseria diagram, and the amplitude-phase curve is subjected to compensation drawing;
and 4, judging the stability of the system according to the amplitude-phase curve of the Neisseria cepstrum.
2. A method as claimed in claim 1The method for judging the stability of the impedance ratio of the distributed energy storage system is characterized by comprising the following steps of: in the step 2, the impedance ratioZ c /Z nc ，Z nc To remove the parallel impedance of all transformers after the bus capacitance.
3. The method for judging the stability of the impedance ratio of the distributed energy storage system according to claim 1, wherein the method comprises the following steps: in the step 2, the impedance ratioZ c /Z nc ，Z c Is the impedance of the bus capacitance.
4. The method for judging the stability of the impedance ratio of the distributed energy storage system according to claim 1, wherein the method comprises the following steps: in the step 2, impedances are connected in parallelZ bus System bus capacitance parameter to impedance ratioZ c /Z nc The relationship of (A) is as follows:
Figure 914883DEST_PATH_IMAGE008
in the formulajIs the unit of an imaginary number,θis the phase angle of the parallel impedance,|Z bus |is a mode of the parallel impedance,ωin order to be the angular frequency of the frequency,Cis a bus capacitor.
5. The method for judging the stability of the impedance ratio of the distributed energy storage system according to claim 1, wherein the method comprises the following steps: in said step 4, the stability of the system is determined by the parallel impedance transfer functionZ bus (s)Whether the system contains a right half-plane pole or not is judged, and when each converter in the system is stable, the judgment is equivalent to an equivalent open-loop transfer functionZ c /Z nc Whether the amplitude-phase curve surrounds the point (-1,0j) or not is judged, if the amplitude-phase curve does not surround the point (-1,0j), the system is stable, otherwise, the system is unstable.
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