CN113238166B - Single-point grounding fault detection and positioning method for cascade H-bridge battery energy storage system - Google Patents

Single-point grounding fault detection and positioning method for cascade H-bridge battery energy storage system Download PDF

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CN113238166B
CN113238166B CN202110471145.XA CN202110471145A CN113238166B CN 113238166 B CN113238166 B CN 113238166B CN 202110471145 A CN202110471145 A CN 202110471145A CN 113238166 B CN113238166 B CN 113238166B
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point
storage system
ground fault
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CN113238166A (en
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陈满
凌志斌
彭鹏
李勇琦
胡振恺
李毓烜
雷旗开
朱焕杰
梁靓
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Shanghai Jiaotong University
Peak and Frequency Regulation Power Generation Co of China Southern Power Grid Co Ltd
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Peak and Frequency Regulation Power Generation Co of China Southern Power Grid Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/52—Testing for short-circuits, leakage current or ground faults
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
    • G01R19/16566—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533
    • G01R19/16576—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533 comparing DC or AC voltage with one threshold
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R25/00—Arrangements for measuring phase angle between a voltage and a current or between voltages or currents

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Abstract

The invention provides a single-point grounding fault detection and positioning method of a cascade H-bridge battery energy storage system, which aims at the cascade H-bridge battery energy storage system in a central ungrounded power grid and comprises the following steps: s1, acquiring alternating-current side voltage and phase of each energy storage unit of the cascade H-bridge battery energy storage system; s2, measuring the voltage of the center point of the cascade H-bridge battery energy storage system to the ground and the phase thereof; s3, judging whether the single-point grounding fault occurs or not, and if the single-point grounding fault occurs, entering S4; otherwise, the single-point ground fault does not exist, and the step goes to S1; s4, judging the phase of the single-point earth fault; and S5, judging the electrical position of the single-point ground fault in the fault phase. The invention can effectively detect the single-point grounding fault of the CHB-BESS in the neutral point ungrounded power grid, and position the electrical position where the grounding fault occurs, thereby greatly facilitating the fault overhaul and maintenance of the CHB-BESS.

Description

Single-point grounding fault detection and positioning method for cascade H-bridge battery energy storage system
Technical Field
The invention relates to the field of battery energy storage systems, in particular to a method for detecting and positioning single-point grounding faults of a cascade H-bridge battery energy storage system running in a neutral point ungrounded power grid.
Background
The battery energy storage system mainly realizes the storage and the release of energy, can well solve the problem of electric energy quality caused by the power generation of renewable energy sources such as wind energy, solar energy and the like, and maintains the power balance of a power grid. In a high-capacity battery energy storage system, the cascade H-bridge energy storage system has wide application prospect due to the advantages of strong expansibility, high capacity, high voltage, small harmonic content of output voltage and current and the like. The battery energy storage system has a wide occupied area, and the faced ground fault is increasingly prominent along with the popularization and the application of the battery energy storage system.
At present, the grounding fault of the cascade H-bridge battery energy storage system is not deeply researched at home and abroad, and only one problem is discussed. L.Zhi-Bin et al in "grouping faults of cascaded H bridge Battery energy storage System,"2014IEEE PES General Meeting & Exposion, National Harbor, MD, USA 2014, pp.1-5 "briefly classify the ground faults of the cascaded H bridge Battery energy storage System according to the number of the ground points, and propose an idea of detecting and locating the faults by monitoring the voltage change of the center point of the cascaded H bridge Battery energy storage System. However, the explanation is rough, the influence of the central point voltage deviation caused by the voltage unbalance of the power grid on fault detection and positioning is not considered, the influence of the voltage difference of the alternating current side of the energy storage unit and the zero sequence voltage on positioning caused by the balance control of the phase inside and the phase between phases is not considered, how to judge the phase with the ground fault is not explained, and a specific positioning method is not explained.
Similar research is mainly directed to open or short circuit faults of switching devices and power distribution network faults. Mukherjee et al, in "Fast fault detection of open power switch in clamped H-bridge multilevel inverters",2016IEEE transfer electric selection reference and Expo (ITEC), Dearborn, MI,2016, pp.1-5, propose to use the output voltage of each module of CHB as a detection variable to detect whether an open circuit fault occurs in a transistor. Chowdhury et al, in "Wavelet decomposition based fault detection in clamped H-bridge multilevel inverting using an annular network", 20172 nd IEEE International Conference on recovery trees in Electronics, Information & Communication Technology (RTEICT), Bangalore,2017, pp.1931-1935, propose to use artificial neural networks and Wavelet transforms as signal preprocessors to detect open circuit faults of CHBs. Zhao Youyao et al studied transient characteristics of DC bus unipolar ground fault in MMC-HVDC DC unipolar ground fault analysis and converter station fault recovery strategy [ J ] Chinese Motor engineering report 2014,34(21):3518 and 3526. The fault detection research on the cascaded H-bridge battery energy storage system mainly aims at the open-circuit or short-circuit fault of a switching device and the fault of a power distribution network, and has no direct relation with the internal ground fault of the cascaded H-bridge battery energy storage system.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method for detecting and positioning the single-point grounding fault of a cascade H-bridge battery energy storage system running in a neutral ungrounded power grid. The method avoids the influence of three-phase unbalanced voltage of the power grid, and detects and positions the ground fault according to the voltage deviation value of the central point of the cascade H-bridge battery energy storage system (CHB-BESS) in the ground fault state and the size of the alternating-current side voltage of each energy storage unit of the CHB-BESS.
The invention provides a method for detecting and positioning single-point grounding faults of a cascaded H-bridge battery energy storage system, aiming at the cascaded H-bridge battery energy storage system in a central ungrounded power grid, which comprises the following steps:
s1, acquiring alternating-current side voltage and phase of each energy storage unit of the cascade H-bridge battery energy storage system;
s2, measuring the voltage of the center point of the cascade H-bridge battery energy storage system to the ground and the phase thereof;
and S3, judging whether the single-point grounding fault occurs: comparing the central point-to-ground voltage value of S2 with the alternating-current side voltage of each energy storage unit of S1, judging whether a single-point ground fault occurs, and if the single-point ground fault occurs, entering S4; otherwise, the single-point ground fault does not exist, and the step goes to S1;
s4, comparing the alternating-current side voltage phase and the S2 center point ground voltage phase of each energy storage unit obtained in the S1, and judging the phase of the single-point ground fault;
and S5, judging the electrical position of the single-point earth fault in the fault phase according to the alternating-current side voltage of each energy storage unit and the set threshold.
Optionally, the obtaining the alternating-current side voltage and the phase of each energy storage unit of the cascaded H-bridge battery energy storage system includes: and measuring the alternating-current side voltage of each energy storage unit, or calculating through a modulation ratio and the direct-current side voltage, or directly obtaining a modulation target value from a control system of the cascade H-bridge battery energy storage system to obtain the alternating-current side voltage and the phase of each energy storage unit of the cascade H-bridge battery energy storage system.
Optionally, the obtained 3 × N alternating-current voltage values of the energy storage units form a three-phase energy storage unit voltage vector [ U ] according to the sequence from the center point to the grid-connected point of the energy storage unitsa1,Ua2,…,Uan]、[Ub1,Ub2,…,Ubn]And [ U ]c1,Uc2,…,Ucn](ii) a The subscripts a, b and c respectively represent the phases where the energy storage units are located, and N is the number of the energy storage units in each phase; 1,2, … …, N represents the number from the central point to the grid-connected point of the energy storage unit of each phase, the number directly connected with the central point is 1, and the number directly connected with the grid-connected reactor is N; because the phases of the alternating current sides of the energy storage units of each phase are the same, the phases of the energy storage units of the three phases a, b and c are respectively obtained
Figure BDA0003045422650000031
Figure BDA0003045422650000032
And
Figure BDA0003045422650000033
optionally, the measuring the center point-to-ground voltage and the phase thereof of the cascaded H-bridge battery energy storage system includes: measuring the center-to-ground voltage U of the cascaded H-bridge battery energy storage system through a voltage transformer connected between the center point of the cascaded H-bridge battery energy storage system and the groundoAnd phase
Figure BDA0003045422650000034
Optionally, the determining whether the single-point ground fault occurs includes: measuring the measured voltage value U of the central point of the energy storage system of the cascaded H-bridge batteryoAnd three-phase energy storage unit voltage vector Ua1、Ub1、Uc1For comparison, let k1 be Uo/Ua1、k2＝Uo/Ub1And k3 ═ Uo/Uc1And if any one of k1, k2 and k3 is equal to or larger than the set threshold, determining that the single-point ground fault occurs.
Alternatively, the set threshold is 0.5, and deviations of k1, k2, and k3 from 0.5 are considered equal in the range of (80% -120%) in consideration of the measurement error.
Optionally, the determining a phase where the single-point ground fault is located includes: measuring the measured central point voltage phase of the cascaded H-bridge battery energy storage system
Figure BDA0003045422650000035
Phase with three-phase energy storage unit
Figure BDA0003045422650000036
And comparing, namely:
if it is
Figure BDA0003045422650000037
Is equal to
Figure BDA0003045422650000038
Judging that the single-point grounding fault occurs in the phase A;
if it is
Figure BDA0003045422650000039
Is equal to
Figure BDA00030454226500000310
Judging that the single-point grounding fault occurs in the phase B;
if it is
Figure BDA00030454226500000311
Is equal to
Figure BDA00030454226500000312
Judging that the single-point ground fault occurs in the phase C;
considering the error in the actual measurement loop, the deviation of the two phases is within 3 °, and the two phases are considered to be equal.
Optionally, the determining the electrical position of the single-point ground fault in the fault phase includes:
from three-phase energy storage cell voltage vector Ua1,Ua2,…,Uan]、[Ub1,Ub2,…,Ubn]And [ U ]c1,Uc2,…,Ucn]And taking out the voltage vector of the energy storage unit of the fault phase and recording the voltage vector as Ugz1,Ugz2,…,Ugzn]；
Mark k as Uo/Ugz1If k is equal to 0.5, judging that the ground fault occurs on the direct current side of the 1 st energy storage unit of the phase; if k is equal to 1, judging that the ground fault occurs between the 1 st energy storage unit and the 2nd energy storage unit of the phase; deviations of k from 0.5 and 1 in the range of (80% -120%) are considered equal;
if k is greater than 1, re-noting that k is equal to (U)o-Ugz1)/Ugz2If k is equal to 0.5, judging that the ground fault occurs on the direct current side of the 2nd energy storage unit of the phase; if k is equal to 1, judging that the ground fault occurs between the 2nd energy storage unit and the 3 rd energy storage unit of the phase;
if k is still greater than 1, re-noting that k is (U)o-Ugz1-Ugz2)/Ugz3If k is equal to 0.5, judging that the ground fault occurs on the direct current side of the 3 rd energy storage unit of the phase; if k is etcAt 1, judging that the ground fault occurs between the 3 rd energy storage unit and the 4 th energy storage unit of the phase;
and sequentially recursion, namely realizing the electrical positioning of the ground fault point.
In a second aspect of the present invention, a single-point ground fault detecting and positioning device for a cascade H-bridge battery energy storage system is provided, including:
a memory for storing non-transitory computer readable instructions; and
and the processor is used for executing the computer readable instructions, and when the computer readable instructions are executed by the processor, the single-point ground fault detection and positioning method for the cascaded H-bridge battery energy storage system is executed.
In a third aspect of the present invention, a computer-readable storage medium is provided for storing non-transitory computer-readable instructions, which when executed by a computer perform the method for detecting and locating single-point ground fault of a cascaded H-bridge battery energy storage system.
Compared with the prior art, the embodiment of the invention has the following beneficial effects:
the invention provides a method for detecting and positioning single-point ground faults of a cascade H-bridge battery energy storage system in a neutral point ungrounded power grid. The invention greatly facilitates the troubleshooting and maintenance of the CHB-BESS.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
fig. 1 is a flowchart of a method for detecting and locating a single-point ground fault of a cascade H-bridge battery energy storage system according to an embodiment of the present invention;
fig. 2 is a schematic diagram of measuring the voltage of the CHB-BESS center point to ground and a single point ground fault by using a voltage transformer according to an embodiment of the present invention.
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 variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
Referring to fig. 1, a flowchart of a method for detecting and locating a single-point ground fault of a cascaded H-bridge battery energy storage system according to an embodiment of the present invention is shown. In the method in the embodiment, the size and the phase of the voltage to ground at the center point of a cascade H-Bridge Battery Energy Storage System (Cascade H Bridge Battery Energy Storage System-CHB-BESS) are combined with the alternating-current side voltage of each Energy Storage unit of the CHB-BESS, the ground fault of the System is monitored in real time, and the fault location is carried out, and the method specifically comprises the following steps:
s100, acquiring alternating-current side voltage and phase of each energy storage unit of the CHB-BESS;
in this step, the ac-side voltage and the phase of each energy storage unit of the CHB-BESS are obtained by measuring the ac-side voltage of each energy storage unit, or by calculating the modulation ratio and the dc-side voltage, or by directly obtaining a modulation target value from a control system of the CHB-BESS.
Specifically, the obtained 3 × N energy storage unit alternating-current voltage values form a three-phase energy storage unit voltage vector [ U ] according to the sequence from the center point to the grid-connected point of the energy storage unitsa1,Ua2,…,Uan]、[Ub1,Ub2,…,Ubn]And [ U ]c1,Uc2,…,Ucn]. The subscripts a, b and c respectively represent the phases where the energy storage units are located, and N is the number of the energy storage units in each phase. 1,2, … …, N represents the number from the central point to the grid-connected point of the energy storage unit of each phase, the number directly connected with the central point is 1, and the number directly connected with the grid-connected reactor is N. Because the phases of the alternating current sides of the energy storage units of each phase are the same, the phases of the energy storage units of the three phases a, b and c are respectively obtained
Figure BDA0003045422650000051
Figure BDA0003045422650000052
And
Figure BDA0003045422650000053
s200, measuring the voltage and the phase of the CHB-BESS central point to the ground;
in the step, the voltage U of the central point to the ground of the CHB-BESS is measured by a voltage transformer connected between the central point of the CHB-BESS and the groundoAnd phase
Figure BDA0003045422650000054
S300, judging whether the single-point grounding fault occurs or not; if the single-point grounding fault is judged to have occurred, the step (4) is carried out; if the single-point ground fault does not exist, jumping to S100;
in the step, the measured voltage value U of the central point of the CHB-BESS is measuredoAnd Ua1、Ub1And Uc1For comparison, let k1 be Uo/Ua1、k2＝Uo/Ub1And k3 ═ Uo/Uc1. Such as any one of k1, k2, and k3, equal to or greater than 0.5. Judging that a single point ground fault occurs; in general, deviations of k1, k2, and k3 from 0.5 in the range of (80% -120%) can be considered equal in consideration of measurement errors in terms of measurements S100, S200.
S400, judging the phase of the single-point ground fault;
in this step, the measured CHB-BESS center point voltage phase is compared with
Figure BDA0003045422650000061
And
Figure BDA0003045422650000062
a comparison is made.
Such as
Figure BDA0003045422650000063
Is approximately equal to
Figure BDA0003045422650000064
Judging that the single-point grounding fault occurs in the phase A;
such as
Figure BDA0003045422650000065
Is approximately equal to
Figure BDA0003045422650000066
Judging that the single-point grounding fault occurs in the phase B;
such as
Figure BDA0003045422650000067
Is approximately equal to
Figure BDA0003045422650000068
Judging that the single-point ground fault occurs in the phase C;
considering the angle difference of the voltage transformer in the actual measurement loop, the phase shift caused by the signal conditioning circuit and the calculation error, the deviation of the two phases is within 3 degrees, and the two phases can be considered to be equal.
And S500, judging the electrical position of the single-point ground fault in the fault phase.
In this step, a three-phase energy storage unit voltage vector [ U ] is useda1,Ua2,…,Uan]、[Ub1,Ub2,…,Ubn]And [ U ]c1,Uc2,…,Ucn]And taking out the voltage vector of the energy storage unit of the fault phase and recording the voltage vector as Ugz1,Ugz2,…,Ugzn]。
Mark k as Uo/Ugz1If k is equal to 0.5, judging that the ground fault occurs on the direct current side of the 1 st energy storage unit of the phase; if k is equal to 1, determining that the ground fault occurs between the 1 st energy storage unit and the 2nd energy storage unit of the phase;
if k is greater than 1, re-noting that k is equal to (U)o-Ugz1)/Ugz2If k is equal to 0.5, the 2nd energy storage unit DC of the phase is judged to have the ground faultA side; if k is equal to 1, judging that the ground fault occurs between the 2nd energy storage unit and the 3 rd energy storage unit of the phase;
if k is still greater than 1, recall that k is equal to (U)o-Ugz1-Ugz2)/Ugz3If k is equal to 0.5, judging that the ground fault occurs on the direct current side of the 3 rd energy storage unit of the phase; if k is equal to 1, judging that the ground fault occurs between the 3 rd energy storage unit and the 4 th energy storage unit of the phase;
and sequentially recursion is carried out, so that the electrical positioning of the ground fault point can be realized.
In another embodiment of the present invention, a single-point ground fault detecting and positioning apparatus for a cascaded H-bridge battery energy storage system is further provided, including: a memory for storing non-transitory computer readable instructions; and a processor for executing the computer readable instructions, wherein when the computer readable instructions are executed by the processor, the cascaded H-bridge battery energy storage system single point ground fault detection and location method is executed.
In another embodiment of the present invention, the present invention further provides a computer readable storage medium for storing non-transitory computer readable instructions, which when executed by a computer, perform the method for detecting and locating single point ground fault of cascaded H-bridge battery energy storage system.
In order to better illustrate the above technical solution, a specific simulation example is provided below for illustration:
in the embodiment, the research object is a 10kV/5MW cascaded H-bridge battery energy storage system, the actual power grid frequency is 50Hz, and the actual power grid voltage is 10 kV. And each phase of the CHB-BESS comprises 20 energy storage units. During the operation of the CHB-BESS, a single point ground fault occurs somewhere on the 20 energy storage cells of the phase a of the CHB-BESS and their connection lines for some reason.
The process of this example is as follows:
step (1): and acquiring the alternating-current side voltage value and the phase of the CHB-BESS energy storage unit in real time from a converter control system of the CHB-BESS. The data are obtained by arranging from the central point of the CHB-BESS to the point of grid connection in sequence: the a-phase energy storage cell voltage vector is 295,300,292,298,291,295,292,300,296,294,297,290,292,292,290,294,299,292,294,294]unit V, phase
Figure BDA0003045422650000071
(based on the A-phase grid voltage); the voltage vector of the B-phase energy storage unit is [300,294,297,292,297,289,299,289,289,292,298,294,289,300,296,290,291,296,294,304 ]]Unit V, phase
Figure BDA0003045422650000072
The C-phase energy storage unit has a voltage vector of [290,294,297,295,299,298,298,290,297,298,295,293,294,299,292,290,296,294,294,286 ]]Unit V, phase
Figure BDA0003045422650000073
And the number N of the energy storage units in each phase is 20.
Step (2): measuring the ground voltage of the central point of the CHB-BESS through a power frequency voltage transformer to obtain the voltage U of the CHB-BESSo600V, phase
Figure BDA0003045422650000074
And (3): measuring the measured voltage value U of the center point of the CHB-BESS o1 st element U of energy storage unit voltage vector in three phases with CHB-BESSa1、Ub1And Uc1For comparison, k1 ═ 600/295, k2 ═ 600/300, and k3 ═ 600/290 were obtained. k1, k2 and k3 are all greater than 0.5. Therefore, the single-point ground fault of the CHB-BESS is judged;
and (4): the measured CHB-BESS center point voltage phase is compared with
Figure BDA0003045422650000075
And
Figure BDA0003045422650000076
a comparison is made.
Figure BDA0003045422650000081
And
Figure BDA0003045422650000082
considering errors introduced by the voltage transformer and the measuring circuit, the voltage transformer and the measuring circuit are considered to be equal, so that the single-point ground fault is judged to occur in the phase A;
and (5): the A phase is a fault phase, so the energy storage unit voltage vector [ U ] of the fault phasegz1,Ugz2,…,Ugz20]＝[295,300,292,298,291,295,292,300,296,294,297,290,292,292,290,294,299,292,294,294]。
Calculating k as Uo/Ugz1600/295 2.03 for 1. Recalculate k (600-. And if the result is equal to 1, judging that the ground fault occurs between the 2nd energy storage unit and the 3 rd energy storage unit of the phase.
According to the method of the embodiment of the invention, the voltage transformer is arranged at the central point of the CHB-BESS, the detection and the positioning of the ground fault are carried out according to the voltage deviation of the central point of the CHB-BESS in the state of the ground fault, the single-point ground fault of the CHB-BESS in the neutral-point ungrounded power grid can be effectively detected, the electric position of the ground fault is positioned, and the fault overhaul and maintenance of the CHB-BESS are greatly facilitated.
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 and 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.

Claims (10)

1. A method for detecting and positioning single-point grounding faults of a cascaded H-bridge battery energy storage system is characterized in that the method aims at the cascaded H-bridge battery energy storage system in a central point ungrounded power grid, and comprises the following steps:
s1, acquiring alternating-current side voltage and phase of each energy storage unit of the cascade H-bridge battery energy storage system;
s2, measuring the voltage of the center point of the cascade H-bridge battery energy storage system to the ground and the phase thereof;
and S3, judging whether the single-point grounding fault occurs: comparing the central point-to-ground voltage value of S2 with the alternating-current side voltage of each energy storage unit of S1, judging whether a single-point ground fault occurs, and if the single-point ground fault occurs, entering S4; otherwise, the single-point ground fault does not exist, and the step goes to S1;
s4, comparing the alternating-current side voltage phase and the S2 center point ground voltage phase of each energy storage unit obtained in the S1, and judging the phase of the single-point ground fault;
and S5, judging the electrical position of the single-point earth fault in the fault phase according to the alternating-current side voltage of each energy storage unit and the set threshold.
2. The method for detecting and locating the single-point ground fault of the cascaded H-bridge battery energy storage system according to claim 1, wherein the obtaining the alternating-current side voltage and the phase of each energy storage unit of the cascaded H-bridge battery energy storage system comprises:
and measuring the alternating-current side voltage of each energy storage unit, or calculating through a modulation ratio and the direct-current side voltage, or directly obtaining a modulation target value from a control system of the cascade H-bridge battery energy storage system to obtain the alternating-current side voltage and the phase of each energy storage unit of the cascade H-bridge battery energy storage system.
3. The method for detecting and locating single-point ground fault of energy storage system of cascaded H-bridge battery according to claim 2, wherein the obtained 3 x N ac voltage values of the energy storage units are combined into a three-phase energy storage unit voltage vector [ U ] according to the sequence from the center point to the grid point of the energy storage unitsa1,Ua2,…,Uan]、[ Ub1,Ub2,…,Ubn]And [ U ]c1,Uc2,…,Ucn]；
The subscripts a, b and c respectively represent the phases where the energy storage units are located, and N is the number of the energy storage units in each phase; 1,2, … …, N represents the number from the central point to the grid-connected point of the energy storage unit of each phase, the number directly connected with the central point is 1, and the number directly connected with the grid-connected reactor is N; because the phases of the alternating current sides of the energy storage units of each phase are the same, the obtained energy storage units of the three phases a, b and cThe phases of the elements are respectively
Figure 578818DEST_PATH_IMAGE001
、
Figure 122932DEST_PATH_IMAGE002
And
Figure 739858DEST_PATH_IMAGE003
。
4. the cascaded H-bridge battery energy storage system single-point ground fault detection and location method of claim 3, wherein the step of measuring the voltage of the cascaded H-bridge battery energy storage system center point to the ground and the phase thereof comprises:
measuring the center-to-ground voltage U of the cascaded H-bridge battery energy storage system through a voltage transformer connected between the center point of the cascaded H-bridge battery energy storage system and the groundoAnd phase
Figure 561184DEST_PATH_IMAGE004
。
5. The method for detecting and locating the single-point ground fault of the cascaded H-bridge battery energy storage system according to claim 4, wherein the determining whether the single-point ground fault occurs comprises:
measuring the measured voltage value U of the central point of the energy storage system of the cascaded H-bridge batteryoAnd three-phase energy storage unit voltage vector Ua1、Ub1、Uc1For comparison, note k1= Uo/Ua1、k2=Uo/Ub1And k3= Uo/Uc1And if any one of k1, k2 and k3 is equal to or larger than the set threshold, determining that the single-point ground fault occurs.
6. The cascade H-bridge battery energy storage system single-point ground fault detection and location method of claim 5, wherein the set threshold is 0.5, and the deviation of k1, k2 and k3 from 0.5 is considered equal in the range of (80% -120%) considering the measurement error.
7. The method for detecting and locating the single-point ground fault of the cascaded H-bridge battery energy storage system according to claim 4, wherein the step of judging the phase of the single-point ground fault comprises the following steps: measuring the measured central point voltage phase of the cascaded H-bridge battery energy storage system
Figure 113519DEST_PATH_IMAGE004
And
Figure 20295DEST_PATH_IMAGE005
、
Figure 175333DEST_PATH_IMAGE002
、
Figure 241378DEST_PATH_IMAGE003
and comparing, namely:
if it is
Figure 89248DEST_PATH_IMAGE004
Is equal to
Figure 358687DEST_PATH_IMAGE001
Judging that the single-point grounding fault occurs in the phase A;
if it is
Figure 317415DEST_PATH_IMAGE004
Is equal to
Figure 847754DEST_PATH_IMAGE002
Judging that the single-point grounding fault occurs in the phase B;
if it is
Figure 991159DEST_PATH_IMAGE004
Is equal to
Figure 872527DEST_PATH_IMAGE003
Judging that the single-point grounding fault occurs in the phase C;
taking into account the error in the actual measurement loop, the deviation of the two phases is
Figure 634947DEST_PATH_IMAGE006
Within, they are considered to be equal.
8. The method for detecting and locating the single-point ground fault of the cascaded H-bridge battery energy storage system according to claim 3, wherein the determining the electrical position of the single-point ground fault in the fault phase comprises:
from three-phase energy storage cell voltage vector Ua1,Ua2,…,Uan]、[ Ub1,Ub2,…,Ubn]And [ U ]c1,Uc2,…,Ucn]And taking out the voltage vector of the energy storage unit of the fault phase and recording the voltage vector as Ugz1,Ugz2,…,Ugzn]；
Note k = Uo/Ugz1，UoThe voltage value of the central point of the cascade H-bridge battery energy storage system is obtained; if k is equal to 0.5, judging that the ground fault occurs on the direct current side of the 1 st energy storage unit of the phase; if k is equal to 1, judging that the ground fault occurs between the 1 st energy storage unit and the 2nd energy storage unit of the phase; deviations of k from 0.5 and 1 in the range of (80% -120%) are considered equal;
if k is larger than 1, re-recording k = (U)o-Ugz1)/Ugz2If k is equal to 0.5, judging that the ground fault occurs on the direct current side of the 2nd energy storage unit of the phase; if k is equal to 1, judging that the ground fault occurs between the 2nd energy storage unit and the 3 rd energy storage unit of the phase;
if k is still larger than 1, re-recording k = (U)o-Ugz1-Ugz2)/Ugz3If k is equal to 0.5, judging that the ground fault occurs on the direct current side of the 3 rd energy storage unit of the phase; if k is equal to 1, judging that the ground fault occurs between the 3 rd energy storage unit and the 4 th energy storage unit of the phase;
and sequentially recursion, namely realizing the electrical positioning of the ground fault point.
9. A cascade H bridge battery energy storage system single point ground fault detection and locating device, includes:
a memory for storing non-transitory computer readable instructions; and
a processor for executing the computer readable instructions, wherein the computer readable instructions, when executed by the processor, perform the method for single point ground fault detection and location of a cascaded H-bridge battery energy storage system of any of claims 1-8.
10. A computer readable storage medium storing non-transitory computer readable instructions which, when executed by a computer, perform the cascaded H-bridge battery energy storage system single point ground fault detection and localization method of any of claims 1-8.
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