CN111651947B - 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

Info

Publication number
CN111651947B
CN111651947B CN202010769715.9A CN202010769715A CN111651947B CN 111651947 B CN111651947 B CN 111651947B CN 202010769715 A CN202010769715 A CN 202010769715A CN 111651947 B CN111651947 B CN 111651947B
Authority
CN
China
Prior art keywords
impedance
bus
stability
impedance ratio
energy storage
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
CN202010769715.9A
Other languages
Chinese (zh)
Other versions
CN111651947A (en
Inventor
潘本仁
胡斯登
朱正斌
张妍
谢国强
桂小智
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Zhejiang University ZJU
State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Jiangxi Electric Power Co Ltd
Original Assignee
Zhejiang University ZJU
State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Jiangxi Electric Power Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Zhejiang University ZJU, State Grid Corp of China SGCC, Electric Power Research Institute of State Grid Jiangxi Electric Power Co Ltd filed Critical Zhejiang University ZJU
Priority to CN202010769715.9A priority Critical patent/CN111651947B/en
Publication of CN111651947A publication Critical patent/CN111651947A/en
Application granted granted Critical
Publication of CN111651947B publication Critical patent/CN111651947B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/30—Circuit design
    • G06F30/32—Circuit design at the digital level
    • G06F30/33—Design verification, e.g. functional simulation or model checking
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F7/00—Methods or arrangements for processing data by operating upon the order or content of the data handled
    • G06F7/38—Methods or arrangements for performing computations using exclusively denominational number representation, e.g. using binary, ternary, decimal representation
    • G06F7/48—Methods or arrangements for performing computations using exclusively denominational number representation, e.g. using binary, ternary, decimal representation using non-contact-making devices, e.g. tube, solid state device; using unspecified devices
    • G06F7/52—Multiplying; Dividing
    • G06F7/535—Dividing only
    • 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
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
    • G06F2119/02—Reliability analysis or reliability optimisation; Failure analysis, e.g. worst case scenario performance, failure mode and effects analysis [FMEA]
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]

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 And (3) 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 does not surround the (-1,0j) point, 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 is provided withThe characteristic of bidirectional power flow brings obstacles to the application of the traditional impedance ratio criterion. In addition, the conventional impedance ratio criterion requires the power subsystem to be stable, i.e., the subsystem output impedance transfer function Zo(s) there is no right pole. In a multi-source system, although each source converter is stable, when a plurality of source converters are combined with each other, the transfer function Z of the total output impedance iso(s) there may be a right pole where a false positive may occur using conventional impedance ratio criteria. 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 GDA0002701296190000022
Simultaneous measurement of voltage disturbance signals
Figure GDA0002701296190000023
According to the formula
Figure GDA0002701296190000024
Obtaining parallel impedance Z of all converters of the distributed energy storage systembus；
Step 2, the system bus capacitance parameter and the parallel impedance Z are usedbusCalculating the impedance ratio Zc/Znc；
Step 3, calculating the obtained impedance ratio Zc/ZncA 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 Zc/ZncTo remove the parallel impedance Z of all converters after the bus capacitor is removedncAs impedance ratio Zc/ZncThe denominator of (a).
Further, in the step 2, the impedance ratio Zc/ZncBy the impedance Z of the bus capacitorcAs impedance ratio Zc/ZncThe molecule of (1).
Further, in the step 2, the impedance Z is connected in parallelbusThe capacitance parameter and impedance ratio Z of the system busc/ZncThe relationship of (A) is as follows:
Figure GDA0002701296190000021
where j is an imaginary unit, θ is the phase angle of the parallel impedance, | ZbusI is the mode of the parallel impedance, omega is the angular frequency, C is the bus capacitance.
Further, in said step 4, the stability of the system is determined by the parallel impedance transfer function Zbus(s) whether the system has a right half-plane pole is judged, s is a complex variable and is equivalent to a resistance ratio Z when each converter in the system is stablec/ZncWhether 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 on the division of the amplitude-phase curve when ω approaches 0When 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 additional 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 link, the system is an I-type system, and the clockwise omega-0 needs to be supplemented at the moment-To ω ═ 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 type II system, and the clockwise omega 0 needs to be drawn in a supplementing way-To ω ═ 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 inventionbusAnd (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 GDA0002701296190000042
Simultaneous measurement of voltage disturbance signals
Figure GDA0002701296190000043
According to the formula
Figure GDA0002701296190000044
Obtaining parallel impedance Z of all converters of the distributed energy storage systembus；
Step 2, the system bus capacitance parameter and the parallel impedance Z are usedbusCalculating the impedance ratio Zc/Znc；
Step 3, calculating the obtained impedance ratio Zc/ZncA 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 Zc/ZncTo remove the parallel impedance Z of all converters after the bus capacitor is removedncAs impedance ratio Zc/ZncThe denominator of (a).
Further, in the step 2, the impedance ratio Zc/ZncBy the impedance Z of the bus capacitorcAs impedance ratio Zc/ZncThe molecule of (1).
Further, in the step 2, the impedance Z is connected in parallelbusThe capacitance parameter and impedance ratio Z of the system busc/ZncThe relationship of (A) is as follows:
Figure GDA0002701296190000041
wherein j is an imaginary unitTheta is the phase angle of the parallel impedance, | ZbusI is the mode of the parallel impedance, omega is the angular frequency, C is the bus capacitance.
Further, in said step 4, the stability of the system is determined by the parallel impedance transfer function Zbus(s) whether the system has a right half-plane pole is judged, s is a complex variable and is equivalent to a resistance ratio Z when each converter in the system is stablec/ZncWhether 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.
The system type in step 3 is determined according to the distribution of the amplitude-phase curve when ω approaches 0, when the amplitude-phase curve converges on a fixed point, the impedance ratio transfer function does not include an integral element, the system is a zero-type system, and at this time, a supplementary 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 link, the system is an I-type system, and the clockwise omega-0 needs to be supplemented at the moment-To ω ═ 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 type II system, and the clockwise omega 0 needs to be drawn in a supplementing way-To ω ═ 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 GDA0002701296190000061
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 GDA0002701296190000062
the Neisser criterion can simplify the judgment of the system stability, and the core formula is as follows:
h＝w+q (3)
in the formula, h is the number of right poles of the equivalent closed-loop system transfer function, w is the number of turns of a point (1, 0j) surrounded clockwise by a curve of the equivalent open-loop transfer function T of the system, and q is the number of right poles of the transfer function T. According to the Neisser criterion, under the condition that the order of T is less than or equal to 0 and q is known, the stability of the system can be judged by means of the amplitude-phase curve of T.
With this property of the Neisseria criterion, the conventional impedance ratio criterion transforms equation 2 by Zbus(s) constructing an impedance ratio T as an equivalent closed loop transfer functionc＝Zo(s)/Zi(s) as an equivalent open loop transfer function.
The order of the input impedance of the load converter is generally greater than or equal to the order of the output impedance of the source converter, TcCan meet the order requirement of the Neisser criterion. Furthermore, in a single source system, the source converter is self-stabilizing and the equivalent open-loop transfer function T iscWithout the right pole, i.e. q is 0, the criterion of nefart can be simplified to h w, i.e. when T iscWhen the curve of (a) does not enclose the (-1,0j) point, the parallel impedance transfer function Zbus(s) without right pole, 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 multiple source variants exist in the systemWhen the converters are connected in parallel, the total output impedance transfer function Z is stable even if each power converter is self-stabilizedo(s) may still contain the right pole. Taking two parallel power converters as an example, the total output impedance transfer function is:
Figure GDA0002701296190000064
in the formula N1(s)、N2(s)、D1(s)、D2(s) are known polynomials for s. Even if D1(s)、D2(s) there is no zero point whose real part is positive, the denominator term N of equation 51D2+N2D1There may still be zeros with positive real parts, i.e. ZoThe right pole of(s). 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 obtain Zo(s) that violates the impedance ratio criterion' advantage of judging stability by impedance. Furthermore, the conventional impedance ratio criterion is of the form Zo/ZiI.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 GDA0002701296190000071
in the formula YoFor the output admittance, Y, of the power subsystemiFor the load subsystem input admittance, YxAdmittance 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 there is no longer a need to distinguish the power flow direction of the converter.
In passive devices, the impedance of the capacitorThe order of the transfer function is lowest and therefore the capacitive 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 to combine into a bus capacitor C to construct a new equivalent open-loop transfer function Tn＝Zc/ZncAs shown in formula 7:
Figure GDA0002701296190000072
in the formula
Figure GDA0002701296190000073
For all converters with the admittance sum, Z, after removal of the bus capacitancenc(s)＝1/Ync(s)。
The transfer function of the capacitance impedance only has one pole on an imaginary axis and does not influence the stability of the system, so ZbusThe stability of(s) is determined by the latter term of equation 7. Through impedance ratio TnThe 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 an equivalent open-loop transfer function TnIs 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 does not have a right half-plane pole, such that the admittance and Y of the systemnc(s) there is also no right half-plane pole, so the equivalent open-loop transfer function TnThere is no right pole. The core formula that can simplify the Neisseria criterion is h ═ w, i.e. when TnZ does not enclose the (-1,0j) pointbus(s) there is no right pole, the system is stable, otherwise the system is unstable.
Figure GDA0002701296190000074
Figure GDA0002701296190000081
TABLE 1
Figure GDA0002701296190000082
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 two operating phases of the systemAnd the energy storage units in the discharge mode exist, and output currents, so that an operating scene comprising a plurality of power converters is formed. Through small signal modeling, the transfer function Z of the output impedance of the power subsystem in two stages can be obtainedo(s): at stage one, the system includes three power converters, in this case ZoThe absence of the right pole(s) stabilizes the power subsystem with a pole-zero distribution as shown in fig. 5. Stage two, the system includes two power converters, in which case Zo(s) there are two right poles, the power subsystem is unstable, and its pole-zero distribution is shown in FIG. 6.
Parallel impedance ZbusThe 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 GDA0002701296190000091
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 an equivalent open-loop transfer function TcAs 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 Z of the total output impedance of the system power subsystemo(s) there are two right poles. The premise of the application of the traditional impedance ratio criterion is that the equivalent open-loop transfer function T iscNo right pole is not established, so that the traditional impedance ratio criterion generates wrong judgment results.
Meanwhile, by means of the measured parallel impedance, a novel impedance ratio can be obtained according to the following formula:
Figure GDA0002701296190000092
according to the above calculation result, an equivalent open-loop transfer function T can be madenBy ω 0+Amplitude-phase curve to ω ═ infinity. Firstly, supplement drawing TnFrom ω ═ infinity to ω ═ 0-Then, the system type is determined according to the distribution of the amplitude-phase curve when ω approaches 0, and the amplitude-phase curves in fig. 10 and 11 are both divergent and approximately parallel to the real axis, at which time the equivalent open-loop transfer function T isnThe transfer function of (2) comprises two integral links, and the system is a II type system. Therefore, the supplementary drawing is clockwise and is made of omega 0-To ω ═ 0+And a circular curve with a radius of ∞. 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 T under the premise that each converter is stablenWhether 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 (2)

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 FDA0002701296180000011
Simultaneous measurement of voltage disturbance signals
Figure FDA0002701296180000012
According to the formula
Figure FDA0002701296180000013
Obtaining parallel impedance Z of all converters of the distributed energy storage systembus；
Step 2, the system bus capacitance parameter and the parallel impedance Z are usedbusCalculating the impedance ratio Zc/ZncWherein Z isncFor parallel impedance of all converters after removal of bus capacitance, ZcImpedance of bus capacitor, parallel impedance ZbusThe capacitance parameter and impedance ratio Z of the system busc/ZncThe relationship of (A) is as follows:
Figure FDA0002701296180000014
where j is an imaginary unit, θ is the phase angle of the parallel impedance, | ZbusI is the mode of the parallel impedance, omega is the angular frequency, C is the bus capacitance;
step 3, calculating the obtained impedance ratio Zc/ZncMaking a Neisseria diagram as an equivalent open-loop transfer function, and determining a system according to the amplitude-phase curve of the Neisseria diagramUnifying types and supplementing a frame-phase curve;
and 4, judging the stability of the system according to the amplitude-phase curve of the Neisseria cepstrum.
2. 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 function Zbus(s) whether the system has a right half-plane pole is judged, s is a complex variable and is equivalent to a resistance ratio Z when each converter in the system is stablec/ZncWhether 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.
CN202010769715.9A 2020-08-04 2020-08-04 Impedance ratio stability judgment method suitable for distributed energy storage system Active CN111651947B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202010769715.9A CN111651947B (en) 2020-08-04 2020-08-04 Impedance ratio stability judgment method suitable for distributed energy storage system

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202010769715.9A CN111651947B (en) 2020-08-04 2020-08-04 Impedance ratio stability judgment method suitable for distributed energy storage system

Publications (2)

Publication Number Publication Date
CN111651947A CN111651947A (en) 2020-09-11
CN111651947B true CN111651947B (en) 2021-01-05

Family

ID=72346327

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202010769715.9A Active CN111651947B (en) 2020-08-04 2020-08-04 Impedance ratio stability judgment method suitable for distributed energy storage system

Country Status (1)

Country Link
CN (1) CN111651947B (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114336747B (en) * 2021-12-29 2023-07-21 湖南工业大学 Cluster resonance active damping frequency division control method for photovoltaic inverter
CN114204815A (en) * 2022-02-16 2022-03-18 广州疆海科技有限公司 Multi-terminal source cooperative energy conversion circuit and energy conversion method

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105406477A (en) * 2015-08-18 2016-03-16 华中科技大学 Method for parameter design of LCL filter of three-phase grid-connected system

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8190299B2 (en) * 2006-07-19 2012-05-29 Rovnyak Steven M Integrated and optimized distributed generation and interconnect system controller
CN106655166B (en) * 2016-11-28 2019-05-17 中国民航大学 Aircraft electrical power system method for analyzing stability based on Impedance Criterion
CN107994606B (en) * 2017-11-27 2020-03-31 浙江大学 Grid-connected inverter stability analysis method under condition of multi-frequency coupling factor coexistence
CN110011295B (en) * 2019-03-06 2023-11-03 中国电力科学研究院有限公司 Stability analysis method and system for distributed direct current power grid

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105406477A (en) * 2015-08-18 2016-03-16 华中科技大学 Method for parameter design of LCL filter of three-phase grid-connected system

Also Published As

Publication number Publication date
CN111651947A (en) 2020-09-11

Similar Documents

Publication Publication Date Title
Suntio et al. Issues on solar-generator interfacing with current-fed MPP-tracking converters
Leppäaho et al. Dynamic characteristics of current-fed superbuck converter
CN111651947B (en) Impedance ratio stability judgment method suitable for distributed energy storage system
Ahmed et al. Stability study of variable step size incremental conductance/impedance MPPT for PV systems
Guo et al. Reduced-order modeling and dynamic stability analysis of MTDC systems in DC voltage control timescale
Rong et al. Output feedback control of single-phase UPQC based on a novel model
Chen et al. Stability analysis of LCL-type grid-connected inverter in weak grid systems
CN112670975B (en) Taylor expansion-based direct current power distribution and utilization system state feedback control method
CN113054640B (en) Direct current converter parallel system stability criterion method based on impedance decomposition
CN105790252A (en) Composite energy storage system and energy optimization control system thereof
CN107994562B (en) Stability design method of diesel storage type vehicle-mounted power supply system considering load characteristics
CN113285486A (en) Droop control-based control method for loop current between parallel inverters
CN106972509A (en) A kind of net side control strategy for suppressing direct drive wind power sub-synchronous oscillation
CN108565896B (en) Photovoltaic power generation system stability analysis method considering power control influence
CN104319814A (en) Method and system for determining control parameters of photovoltaic grid-connected inverter
Wang et al. Impedance-based stability modeling and analysis of networked converter systems
Bi et al. Decoupling power balancing strategy with reduced current sensors for two-phase interleaved neutral point clamped DC/DC converter applied in energy storage system
Miao et al. Revisit Nyquist-Bode Stability Criteria for Power Electronic System with Non-minimum Phase System
CN116505534A (en) Modeling method of direct type AC/AC type hybrid distribution transformer
Ahmadi et al. Supervisory control of bipolar DC microgrids equipped with three-port multidirectional DC–DC converter for efficiency and system damping optimization
Jaksic et al. Multi-level single-phase shunt current injection converter used in small-signal dq impedance identification
Mohebalizadeh et al. An improved sliding mode controller for DC/DC boost converters used in EV battery chargers with robustness against the input voltage variations
Feng et al. Comparison of SPS, DPS and CTPS modulations with full consideration of stability of DAB converters with input LC filter
Azizi et al. Stability analysis of a DC microgrid with constant power loads using small-signal equivalent circuit
CN115663780A (en) Improved self-adaptive subsection droop control method for photovoltaic direct-current micro-grid

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant