CN112564219A - Off-line balancing method for cascade battery energy storage system with short circuit at outlet and direct current control - Google Patents

Off-line balancing method for cascade battery energy storage system with short circuit at outlet and direct current control Download PDF

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CN112564219A
CN112564219A CN202011393136.5A CN202011393136A CN112564219A CN 112564219 A CN112564219 A CN 112564219A CN 202011393136 A CN202011393136 A CN 202011393136A CN 112564219 A CN112564219 A CN 112564219A
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energy
dischargeable
sode
submodule
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CN112564219B (en
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陈满
凌志斌
李勇琦
彭鹏
李毓烜
胡振恺
雷旗开
朱焕杰
田凯
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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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    • 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
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0013—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries acting upon several batteries simultaneously or sequentially
    • H02J7/0014—Circuits for equalisation of charge between batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • H01M10/441—Methods for charging or discharging for several batteries or cells simultaneously or sequentially
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention provides an off-line equalization method of a cascade battery energy storage system with short circuit at an outlet and direct current control, which comprises the following steps: each phase power outlet of the short-circuit cascade battery energy storage system; obtaining battery voltage, SOC, SOH, SOF and rated capacity information of each submodule of the cascade battery energy storage system; calculating chargeable energy and dischargeable energy of each submodule; calculating chargeable energy, dischargeable energy and three-phase average dischargeable energy of each phase; calculating the error between the dischargeable energy of each phase and the average dischargeable energy of the three phases; phase direct current distribution realizes three-phase balance; the direct current voltage distribution of the submodules realizes the balance among the submodules in the phase; the phase current control generates balanced current; and judging the end condition of the off-line equalization. The method can more conveniently, safely realize the off-line balance of the battery energy before the operation of the cascade battery energy storage system, and greatly reduce the workload of balance maintenance before the operation of the battery energy storage system.

Description

Off-line balancing method for cascade battery energy storage system with short circuit at outlet and direct current control
Technical Field
The invention relates to the field of battery energy storage systems, in particular to an off-line balancing method for a cascade battery energy storage system with short circuit at an outlet and direct current control.
Background
The cascade H-bridge type battery energy storage system is suitable for being applied to high-voltage and high-power energy storage occasions due to the characteristics of high equivalent switching frequency, good harmonic characteristics of output voltage, easiness in expansion of modular design, convenience in fault redundancy control and the like. Before the cascade H-bridge type battery energy storage system operates, the electric quantity of each sub-module battery needs to be balanced so as to enable the system to operate normally, and the condition that the operation boundary of the system is reduced and even the starting fails due to the fact that the charge states of the batteries are excessively uneven is avoided. At present, a single module is mostly used for battery equalization work before a battery energy storage system operates, and manual charging and discharging are carried out, so that the battery modules of the system are equalized.
Through retrieval, the prior art has a plurality of battery equalization technologies, such as application numbers: 201810264044.3, filing date: 2018-03-28, which discloses a battery pack balancing system and a control method considering battery life, the battery pack balancing system comprises a sampling module, a balancing module, a battery life prediction module and a control module, wherein the battery life prediction module receives battery information collected by the sampling module to predict the battery life; the control module is used for receiving battery pack battery information acquired by the sampling module and battery life information acquired by the battery life prediction module when the battery pack enters a charging and discharging state, calculating the voltage difference of adjacent single batteries, judging whether the voltage difference reaches a preset value, determining the adjacent single batteries to be balanced and the time required by balancing, and controlling the balancing module to execute. The voltage difference of the adjacent single batteries is corrected by utilizing the battery life information provided by the battery life prediction module, the condition that the open-circuit voltages of the batteries are inconsistent due to different service life attenuation degrees of different single batteries is effectively considered, the energy waste caused by over-balance can be avoided, the balance efficiency is improved, the balance time is reduced, and the battery life is effectively prolonged.
However, until now, no research on the automatic off-line equalization technology of the cascaded H-bridge battery energy storage system has been reported.
Disclosure of Invention
Aiming at the blank existing in the prior art, the invention provides a method for realizing the offline balance of a cascade H-bridge battery energy storage system through direct current control in outlet short circuit.
The invention provides an off-line equalization method of a cascade battery energy storage system with short circuit at an outlet and direct current control, which comprises the following steps:
s1: each phase power outlet of the short-circuit cascade H-bridge type battery energy storage system;
s2: obtaining battery voltage, SOC, SOH, SOF and rated capacity information of each submodule of the cascade H-bridge type battery energy storage system;
s3: according to the SOC and SOH of each submodule battery and the rated capacity information of the battery obtained in the S2, the chargeable energy and the dischargeable energy of each submodule battery are calculated, and then the maximum error absolute value of the dischargeable energy of all submodules and the average value of the dischargeable energy is calculated;
s4: summing the chargeable energy and the dischargeable energy of the sub-modules obtained in the step S3 to obtain chargeable energy, dischargeable energy and three-phase average dischargeable energy of each phase:
s5: the dischargeable energy and the average dischargeable energy of each phase obtained in the step S4 are subjected to subtraction to obtain a dischargeable energy error of each phase, and the maximum absolute value of the error is obtained;
s6: on the result of S5, the direct current of each phase is distributed according to the principle that the direct current is in direct proportion to the error of the dischargeable electric quantity of the phase, the direct current of the phase does not exceed the rated value of the phase current, and the direct current distribution of the phase realizes the balance among three phases;
s7: on the basis of S6 phase direct current distribution, distributing sub-module balancing voltage to each sub-module in the phase according to the principle that the sub-module is in direct proportion to the dischargeable energy error, and distributing each phase voltage to the sub-modules according to the average distribution principle to realize the intra-phase sub-module balancing:
s8: on the basis of S7, controlling the phase current to generate balanced current, and enabling each phase current to reach the distributed direct current value through current closed-loop control;
s9: and judging whether the off-line equalization is finished or not according to the ratio of the maximum absolute value of the sub-module dischargeable energy error to the sub-module average dischargeable energy, and when the ratio is smaller than a set range, considering that the off-line equalization is finished.
In a second aspect of the present invention, a terminal is provided, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, where the processor is configured to execute the method for offline balancing of a cascaded battery energy storage system with outlet short-circuiting and dc control when executing the program.
The invention aims to realize the off-line equalization of the battery in the cascade H-bridge type battery energy storage system, realizes the equalization of the battery modules with different initial electric quantities by using the direct current control, and realizes the purpose of off-line equalization of the battery in a convenient mode while considering the safe operation boundary of the system. According to the method, only the outlet of the cascade H-bridge battery energy storage system needs to be in short circuit, and the offline balance can be conveniently realized by utilizing the initial electric quantity of the battery energy storage system through controlling the output voltage and the phase current of each module, so that the workload of the traditional single pre-charging and discharging process of the battery module is saved.
Compared with the prior art, the embodiment of the invention has the following beneficial effects:
the invention provides a quick offline equalization method for a cascaded H-bridge type battery energy storage system, which realizes offline equalization of the battery energy storage system by realizing the cascaded H-bridge type battery energy storage system through direct current control by adopting outlet short circuit and provides a quick method for offline equalization maintenance of the battery energy storage system. Meanwhile, the method considers the safe operation boundary of the system, so that the balanced voltage and current of the system are all below the rated value. Finally, the purpose of quickly and safely realizing off-line balance in the cascade H-bridge type battery energy storage system is achieved.
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 an offline balancing method for a cascade battery energy storage system with outlet short circuit and dc control according to a preferred embodiment of the present invention;
fig. 2 is a schematic diagram of off-line equalization of a cascade battery energy storage system with outlet short circuit and dc control according to a preferred embodiment of the present invention.
Detailed Description
The following examples illustrate the invention in detail: the embodiment is implemented on the premise of the technical scheme of the invention, and a detailed implementation mode and a specific operation process are given. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.
Fig. 1 is a flowchart of an offline balancing method for a cascade battery energy storage system with outlet short circuit and dc control according to a preferred embodiment of the present invention. Referring to fig. 1, the method for implementing offline equalization of a cascaded H-bridge battery energy storage system by using outlet short circuit in this embodiment includes the following steps:
s1: each phase power outlet of the short-circuit cascade H-bridge type battery energy storage system;
s2: acquiring battery voltage, SOC (state of charge), SOH (state of health), SOF (state of function, functional state of battery) and rated capacity information of each submodule of the cascade H-bridge type battery energy storage system; in the cascade H-bridge type Battery energy storage System, each submodule comprises a Battery unit and a Power unit, the Battery unit is managed by a Battery Management System (BMS), the Power unit is used as a part of a Power Conversion System (PCS) and is controlled by a PCS controller, and the PCS controller acquires the SOC state and the SOH state of the Battery unit corresponding to each Power unit from the BMS at regular time;
s3: calculating chargeable energy and dischargeable energy of each submodule: according to the SOC and SOH of the sub-module batteries and the rated capacity information of the batteries obtained in the step S1, the chargeable energy and the dischargeable energy of each sub-module battery can be calculated, and then the maximum error absolute value of the dischargeable energy of all the sub-modules and the average value of the dischargeable energy of all the sub-modules is calculated;
s4: calculating chargeable energy, dischargeable energy and three-phase average dischargeable energy of each phase;
s5: calculating the error between each phase of dischargeable energy and the average dischargeable energy, and simultaneously obtaining the maximum absolute value of the error;
s6: and phase direct current distribution realizes three-phase balance: the direct current of each phase is distributed according to the principle that the direct current is in direct proportion to the phase dischargeable energy error, and the phase direct current cannot exceed the phase current rated value;
s7: and D, submodule direct-current voltage distribution to realize intra-phase submodule balance: each submodule in the phase distributes the submodule balanced voltage according to the principle that the submodule is in direct proportion to the dischargeable energy error, and each phase voltage is distributed to the submodule according to the principle of average distribution;
s8: controlling the phase current to generate an equalizing current: each phase current reaches the distributed direct current value through current closed-loop control;
s9: judging the end condition of the off-line equalization: and judging whether the off-line equalization is finished or not according to the ratio of the maximum absolute value of the sub-module dischargeable energy error to the sub-module average dischargeable energy, and when the ratio is smaller than a certain range, finishing the off-line equalization.
In one embodiment, in step S2, the PCS controller periodically obtains the SOC state and the SOH state of the battery unit corresponding to each power unit from the BMS, and the time interval is determined according to the state refresh rate of the battery energy storage system and is set to 0.1S-1 min. The acquisition mode is usually communication, and is specifically determined by interface specifications and protocols between the PCS and the BMS.
In one embodiment, in step S3, the chargeable and dischargeable energies of each sub-module are calculated by:
chargeable energy:
SOCE(x,n)＝[(SOCup-SOCx,n)×SOHx,n×CN]×VN
dischargeable energy:
SODE(x,n)＝[(SOCx,n-SOCdown)×SOHx,n×CN]×VN
in the formula, SOCupAnd SOCdownRespectively representing the upper and lower SOC boundaries of battery operation, 0 ≤ SOCdown≤SOCupLess than or equal to 1, x represents one of a, b and C phases, n represents the number of the sub-module in a certain phase, CNRated capacity of battery, VNIs the nominal voltage of the battery.
And calculating the average value of the dischargeable energy of the submodules, and then calculating the maximum absolute error value of the dischargeable energy of each submodule and the average value.
Average value of dischargeable energy of submodule:
Figure BDA0002811377730000051
maximum error absolute value of dischargeable energy of submodule:
ΔSODEsub_max＝max(|SODE(x，n)-SODEavg|)
in one embodiment, in step S4, the chargeable and dischargeable energies of each phase are calculated by:
calculating chargeable energy of each phase:
Figure BDA0002811377730000052
the dischargeable energy of each phase was calculated:
Figure BDA0002811377730000053
in the formula, a subscript x represents one of three phases a, b and c, N represents the nth submodule of the phase, and N is the number of submodules of each phase;
calculate the average dischargeable energy of the three phases:
Figure BDA0002811377730000054
in one embodiment, in step S5, the calculating the difference between the dischargeable energy and the average dischargeable energy of each phase and the calculating the absolute value of the maximum value of the difference specifically includes:
and (3) calculating errors of dischargeable electric quantity and average dischargeable energy of each phase:
ΔSODEa＝SODEa-SODE
ΔSODEb＝SODEb-SODE
ΔSODEc＝SODEv-SODE
in the formula,. DELTA.SODEa，ΔSODEb，ΔSODEcThe dischargeable energy errors of the three phases a, b and c are shown, respectively, and the subscripts a, b and c show the three phases abc.
Calculating the maximum value of the absolute value of the dischargeable energy error of each phase:
ΔSODEmax＝max(|ΔSODEa|，|ΔSODEb|，|ΔSODEv|)
in one embodiment, in step S6, the phase-to-phase balancing is implemented by phase-to-phase direct current distribution, which specifically includes:
the direct current of each phase is distributed according to the principle that the direct current is proportional to the dischargeable energy error of the phase:
Figure BDA0002811377730000061
Figure BDA0002811377730000062
Figure BDA0002811377730000063
in the formula Ia，Ib，IcRespectively representing three-phase direct current commands of a, b and c, subscripts a, b and c represent three phases abc, INRepresenting the system phase current rating.
In one embodiment, in step S7, the dc voltage distribution of the submodules realizes intra-phase submodule equalization, and the specific method includes:
calculating phase reference voltage: in order to simultaneously complete the phase-to-phase balance and the sub-module balance, the phase voltage generated by each sub-module and the sub-module balance voltage are distributed according to the principle that the ratio of the maximum absolute value of the dischargeable energy error to the average value is in direct proportion.
Figure BDA0002811377730000064
Wherein, Up，baseIs a phase voltage reference value, Us，baseEqualizing the voltage reference value, Δ SODE, for the submodulesmaxIs the maximum absolute value of the phase dischargeable energy error, Δ SODEsub_maxFor the maximum absolute value of the error in the dischargeable energy of the submodule of the system, SODE is the mean value of the phase dischargeable energy, SODEavgIs the average value of the dischargeable energy of the submodules, KbaseTo equalize the voltage scaling factor.
In order to keep the voltage of each submodule below its nominal value, the sum of the phase voltage averaged over the submodule and the equalization voltage of the submodule is not greater than the nominal value of the submodule voltage. Thus, the phase voltage reference value and the sub-module equilibrium voltage reference value satisfy the following constraints.
Figure BDA0002811377730000065
Available phase reference voltage:
Figure BDA0002811377730000066
reference voltage for submodule equalization:
Figure BDA0002811377730000071
wherein, UNThe effective value of the rated line voltage of the system is obtained.
In a star topology, the abc three-phase direct-current voltages are required to be equal and equal to a phase voltage reference value:
Ua＝Up，base
Ub＝Up，base
Uc＝Up，base
in the formula of Ua，Ub，UcThe dc voltage commands for the three phases a, b, and c are shown, respectively, and the subscripts a, b, and c indicate the three phases abc.
And (3) calculating the error between the dischargeable energy of the submodules in each phase and the average value of the dischargeable energy:
Figure BDA0002811377730000072
Figure BDA0002811377730000073
Figure BDA0002811377730000074
calculating the maximum absolute value of the dischargeable energy error of each phase module:
ΔSODEa，max＝max(|ΔSODEa，n|)
ΔSODEb，max＝max(|ΔSODEb，n|)
ΔSODEc，max＝max(|ΔSODEc，n|)
each submodule in the phase distributes the submodule balance voltage according to the principle that the submodule is in direct proportion to the dischargeable energy error, and each phase voltage is distributed to the submodule according to the principle of average distribution:
Figure BDA0002811377730000075
Figure BDA0002811377730000076
Figure BDA0002811377730000077
wherein, Ua，n，Ub，n，Uc，nThe dc voltages of the nth sub-module of the three phases a, b and c are indicated, the subscripts a, b and c indicate the three phases abc, and n indicates the number of the sub-module.
In one embodiment, in step S8, the method for controlling the phase current to generate the equalizing current includes:
and through phase current closed-loop control, each phase current of the system with the short-circuited outlet is stabilized to a set value of phase current distribution so as to meet the requirement of off-line balance.
In one embodiment, in step S9, the method for determining the end condition of offline equalization includes:
calculating the ratio of the maximum value of the absolute value of the sub-module dischargeable energy error to the average dischargeable energy of the sub-module:
Figure BDA0002811377730000081
end conditions of offline equalization:
K＜Kover
if the end conditions are met, setting the direct-current voltage of each submodule to be 0, setting the balance current to be 0, and ending the off-line balance of the system; if the above condition is not satisfied, the process goes to step S3 to loop.
For better illustration and understanding of the above-mentioned technology, the following description is given in conjunction with specific application examples, but the present invention is not limited to the following specific application examples.
As shown in fig. 2, this embodiment is a 5MW battery energy storage system, the rated voltage is 10kV, the rated phase current is 288A, the nominal voltage of the battery cluster is 768V, each phase has 20 sub-modules, and the total system has 60 sub-modules. And the alternating current grid-connected reactor is 6 mH.
In this embodiment, the sub-module battery is an energy storage battery module with a nominal voltage of 51.2V, a maximum charge-discharge rate of 4C and a nominal capacity of 100Ah, which is formed by connecting 16 segments of 3.2V/100Ah lithium iron phosphate battery monomers in series, and each sub-module battery cluster is formed by connecting 15 battery modules in series. The upper operating limits of the battery SOC are set to 0.9, and the lower operating limits are set to 0.1.
Specifically, the implementation process of this embodiment refers to the process of fig. 1:
s1: each phase power outlet of the short-circuit cascade H-bridge type battery energy storage system;
s2: obtaining nominal voltage, SOC, SOH, SOF and rated capacity information of each sub-module battery cluster of the modular multi-level energy storage system;
the energy conversion system acquires the information of 60 sub-module battery clusters of three phases from the battery management system at regular time every 1s in a communication mode. The upper and lower SOC operating limits are set to 0.9 and 0.1, respectively. The information obtained is as follows:
information of phase A:
state of charge SOCa [0.51,0.46,0.53,0.50,0.47,0.51,0.52,0.52,0.50,0.45,0.48,0.46,0.47,0.50,0.49,0.54,0.44,0.46,0.52,0.55]
State of health SOHa [0.93,0.91,0.90,0.92,0.95,0.92,0.91,0.90,0.95,0.92,0.94,0.91,0.93,0.96,0.91,0.92,0.91,0.92,0.91,0.93]
The nominal voltage UN of the battery cluster is [768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768], in V;
nominal capacity CN of the battery cluster is [100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100], unit Ah;
dischargeable current Idchg ═ 400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400, in units a;
the chargeable current Ichg ═ 400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400, in units of a.
B phase information:
state of charge SOCb ═ 0.64,0.58,0.60,0.50,0.63,0.62,0.57,0.56,0.64,0.60,0.62,0.56,0.58,0.58,0.62,0.43,0.60,0.62,0.58,0.57 ];
state of health SOHb [0.94,0.97,0.92,0.90,0.90,0.94,0.93,0.94,0.90,0.95,0.97,0.94,0.90,0.95,0.90,0.95,0.94,0.92,0.95,0.90 ];
the nominal voltage UN of the battery cluster is [768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768], in V;
nominal capacity CN of the battery cluster is [100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100], unit Ah;
dischargeable current Idchg ═ 400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400, in units a;
the chargeable current Ichg ═ 400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400, in units of a.
C phase information:
state of charge SOCc [0.73,0.73,0.70,0.71,0.75,0.73,0.70,0.73,0.71,0.79,0.75,0.72,0.57,0.76,0.65,0.54,0.66,0.73,0.59,0.71 ];
state of health SOHc ═ 0.92,0.91,0.95,0.91,0.92,0.95,0.93,0.90,0.92,0.95,0.94,0.94,0.93,0.94,0.93,0.95,0.92,0.95,0.93,0.92 ];
the nominal voltage UN of the battery cluster is [768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768], in V;
nominal capacity CN of the battery cluster is [100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100], unit Ah;
dischargeable current Idchg ═ 400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400, in units a;
the chargeable current Ichg ═ 400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400, in units of a.
S3: calculating dischargeable energy of each sub-module;
the chargeable/dischargeable energy of each sub-module is calculated based on the information acquired at S2.
Phase A:
chargeable energy source ═ 27.86,30.75,25.57,28.26,31.37,27.56,26.56,26.27,29.18,31.80,30.32,30.75,30.71,29.49,28.65,25.44,32.15,31.09,26.56,25.00], in kWh;
dischargeable energy SODE ═ 29.28,25.16,29.72,28.26,27.00,28.97,29.35,29.03,29.18,24.73,27.43,25.16,26.43,29.49,27.26,31.09,23.76,25.44,29.35,32.14, in kWh.
Phase B:
chargeable energy SOCE ═ 18.77,23.35,21.20,22.81,18.66,20.21,23.57,24.55,18.17,21.89,20.43,24.55,22.12,22.12,19.35,19.28,21.66,19.78,23.35,22.81,% kWh;
the dischargeable energy SODE ═ 38.98,35.76,35.33,27.65,36.63,37.54,33.57,33.21,37.32,36.48,38.74,33.21,33.18,35.02,35.94,24.08,36.10,36.74,35.02,32.49, in kWh.
And C phase:
chargeable energy source ═ 12.01,11.88,14.59,13.28,10.60,12.40,14.28,11.75,13.42,8.03,10.83,12.99,23.57,10.11,17.86,26.27,16.96,12.40,22.14,13.42], in kWh;
the dischargeable energy SODE ═ 44.51,44.03,43.78,42.63,45.93,45.96,42.85,43.55,43.10,50.34,46.92,44.76,33.57,47.65,39.28,32.10,39.57,45.96,35.00,43.10, in kWh.
And further calculating the average value of the dischargeable energy of the submodules and the maximum absolute value of the error between the dischargeable energy of each submodule and the average value.
The submodule dischargeable energy average value SODEavg is 35.10 kWh;
the maximum value Δ SODEsubmax of the absolute value of the dischargeable energy error of the submodule is 15.25 kWh.
S4: calculating dischargeable electric quantity of each phase and average dischargeable electric quantity of three phases;
summing according to the charge-discharge energy of each submodule to obtain:
total chargeable energy of phase a SOCE 575.33 kWh;
the total dischargeable energy of phase a, SODE, 558.24 kWh;
total chargeable energy source of phase B is 692.98 kWh;
total dischargeable energy of phase B, SODE, 708.63 kWh;
total chargeable energy of C phase SOCE 288.801 kWh;
total dischargeable energy of phase C, SODE 854.60 kWh;
the three-phase average dischargeable energy SODE is 701.94 kWh.
S5: calculating the error between each phase of dischargeable electric quantity and the average dischargeable electric quantity;
from the results of S4, it was found that:
the dischargeable energy error Δ SODE of phase a is-143.70 kWh;
dischargeable energy error Δ SODE ═ 8.96kWh for phase B;
the dischargeable energy error Δ SODE of the C phase is 152.66 kWh.
The maximum absolute value of the error thus obtained is 152.66 kWh.
S6: phase direct current distribution realizes three-phase balance;
the proportion of the absolute value of the discharge energy error and the maximum error of the photograph is distributed to the direct current of each phase as follows:
phase a direct current:
Figure BDA0002811377730000111
b-phase direct current:
Figure BDA0002811377730000112
c-phase direct current:
Figure BDA0002811377730000113
s7: the direct current voltage distribution of the submodules realizes the equalization of the submodules in the phase;
calculating an equilibrium voltage proportionality coefficient: kbase 50.07%
Calculating a phase voltage reference value: up, base 2724.11V
Calculating a sub-module balance voltage reference value: us, base 5440.86V
And (3) calculating the error of the dischargeable energy of each phase module from the average value thereof:
phase a submodule dischargeable energy error from average: Δ SODE ═ 1.37, -2.75,1.81,0.35, -0.92,1.06,1.44,1.12,1.27, -3.18, -0.48, -2.75, -1.48,1.58, -0.66,3.18, -4.15, -2.48,1.44,4.23], in kWh;
error of dischargeable energy of B phase module from average: Δ SODE ═ 4.33,1.11,0.68, -7.00,1.98,2.89, -1.08, -1.44,2.68,1.83,4.09, -1.44, -1.47,0.37,1.29, -10.57,1.45,2.09,0.37, -2.16], in kWh;
error of dischargeable energy of phase C sub-module from average: Δ SODE ═ 1.78,1.30,1.05, -0.10,3.20,3.23,0.12,0.82,0.37,7.61,4.19,2.03, -9.16,4.92, -3.45, -10.63, -3.16,3.23, -7.73,0.37], in kWh;
so as to obtain the maximum absolute value of the error between the dischargeable energy of each phase submodule and the phase average value:
ΔSODEa,max＝4.23kWh；
ΔSODEb,max＝10.57kWh；
ΔSODEc,max＝10.63kWh；
according to the submodule direct voltage distribution principle, the direct voltage of each phase submodule can be obtained as follows:
phase A:
submodule voltage Uan ═ 224.47, -40.83,252.63,158.76,77.24,204.21,228.91,208.16,218.04, -68.50,105.40, -40.83,40.68,237.80,94.04,340.56, -130.75, -23.05,228.91,408.25], in V;
phase B:
submodule voltage Ubn ═ 247.74,164.74,153.67, -43.94,187.27,210.59,108.42,99.13,205.06,183.32,241.42,99.13,98.34,145.77,169.48, -135.84,173.44,190.04,145.77,80.56, in V;
and C phase:
the submodule voltage Ucn ═ 181.85,169.47,162.98,133.69,218.03,219.01,139.39,157.08,145.68,331.07,243.58,188.14, -98.29,262.06,47.98, -135.84,55.25,219.01, -61.72,145.68], in V;
s8: controlling the phase current to generate balanced current;
the current direction of the current closed-loop control system is the calculated value of S5 flowing out from each phase grid-connected inductor, so that the phase current is stabilized to a set value, and the balance requirement is met.
S9: judging the end condition of off-line equalization;
in this embodiment, a criterion parameter K for ending off-line equalization is set in consideration of the system capacity and the sub-module SOC control accuracyover＝5％。
Calculating the ratio of the maximum value of the absolute value of the error of the dischargeable quantity to the average dischargeable quantity: k is 43.44%;
end condition K < K not satisfying off-line balanceoverThen, the process goes to step S3, and the off-line equalization is performed in a loop until the off-line equalization end condition is satisfied, and the off-line equalization is ended.
The embodiment shows that the off-line balancing of the battery energy before the operation of the cascaded H-bridge battery energy storage system can be realized more conveniently and safely by taking the off-line balancing of the cascaded H-bridge battery energy storage system adopting the outlet short circuit and the direct current control as the target, and simultaneously considering the operation boundary of the system compared with the traditional balancing maintenance work of a single battery module, and the workload of the battery balancing maintenance of the battery energy storage system before the operation is greatly reduced.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. The features of the preferred embodiments of the present invention described above may be used in any combination without conflict.

Claims (10)

1. An outlet short circuit and direct current controlled cascade battery energy storage system offline equalization method is characterized by comprising the following steps:
s1: each phase power outlet of the short-circuit cascade H-bridge type battery energy storage system;
s2: obtaining battery voltage, SOC, SOH, SOF and rated capacity information of each submodule of the cascade H-bridge type battery energy storage system after the connection of S1;
s3: according to the SOC and SOH of each submodule battery and the rated capacity information of the battery obtained in the S2, the chargeable energy and the dischargeable energy of each submodule battery are calculated, and then the maximum error absolute value of the dischargeable energy of all submodules and the average value of the dischargeable energy is calculated;
s4: summing the chargeable energy and the dischargeable energy of the sub-modules obtained in the step S3 to obtain chargeable energy, dischargeable energy and three-phase average dischargeable energy of each phase:
s5: the dischargeable energy and the average dischargeable energy of each phase obtained in the step S4 are subjected to subtraction to obtain a dischargeable energy error of each phase, and the maximum absolute value of the error is obtained;
s6: on the result of S5, the direct current of each phase is distributed according to the principle that the direct current is in direct proportion to the error of the dischargeable electric quantity of the phase, the direct current of the phase does not exceed the rated value of the phase current, and the direct current distribution of the phase realizes the balance among three phases;
s7: on the basis of S6 phase direct current distribution, distributing sub-module balancing voltage to each sub-module in the phase according to the principle that the sub-module is in direct proportion to the dischargeable energy error, and distributing each phase voltage to the sub-modules according to the average distribution principle to realize the intra-phase sub-module balancing:
s8: on the basis of S7, controlling the phase current to generate balanced current, and enabling each phase current to reach the distributed direct current value through current closed-loop control;
s9: and judging whether the off-line equalization is finished or not according to the ratio of the maximum absolute value of the sub-module dischargeable energy error to the sub-module average dischargeable energy, and when the ratio is smaller than a set range, considering that the off-line equalization is finished.
2. The method for offline equalization of an outlet short-circuit and dc-controlled cascaded battery energy storage system according to claim 1, wherein in S2, in the cascaded H-bridge battery energy storage system, each submodule includes a battery unit and a power unit, the battery unit is managed by a battery management system, the power unit is controlled by a PCS controller as part of a power conversion system, and the PCS controller periodically obtains SOC state and SOH state of the battery unit corresponding to each power unit from the BMS; the PCS controller acquires the SOC state and the SOH state of the battery unit corresponding to each power unit from the BMS at regular time, the time interval is determined according to the state refresh rate of the battery energy storage system, and the time interval is 0.1s-1 min.
3. The outlet short circuit and direct current controlled cascade battery energy storage system offline equalization method of claim 1, wherein in S3, chargeable energy and dischargeable energy of each submodule are calculated, and the specific method is as follows:
rechargeable energy SOCE of each submodule(x，n)：
SOCE(x，n)＝[(SOCup-SOCx，n)×SOHx，n×CN]×VN
Dischargeable energy SODE of individual submodules(x，n)：
SODE(x，n)＝[(SOCx，n-SOCdown)×SOHx，n×CN]×VN
In the formula, SOCupAnd SOCdownRespectively representing the upper and lower SOC boundaries of battery operation, 0 ≤ SOCdown≤SOCupLess than or equal to 1, x represents one of a, b and C phases, n represents the number of the sub-module in a certain phase, CNRated capacity of battery, VNIs the nominal voltage of the battery; SOCx，n、SOHx，nRespectively representing the charge state and the health state of each nth submodule battery of the x phase;
calculating the average value of dischargeable energy of the submodules, and then calculating the maximum error absolute value of the dischargeable energy of each submodule and the average value;
mean value SODE of dischargeable energy of submoduleavg：
Figure FDA0002811377720000021
In the above formula, N is the number of submodules of each phase;
maximum error absolute value Delta SODE of dischargeable energy of submodulesub_max：
ΔSODEsub_max＝max(|SODE(x，n)-SODEavg|)。
4. The method for off-line equalization of the outlet short-circuit and direct-current controlled cascaded battery energy storage system according to claim 1, wherein in step S4, chargeable energy, dischargeable energy and three-phase average dischargeable energy of each phase are calculated by:
calculating chargeable energy SOCE of each phasex：
Figure FDA0002811377720000022
Calculating the dischargeable energy SODE of each phasex：
Figure FDA0002811377720000023
In the formula, a subscript x represents one of three phases a, b and c, N represents the nth submodule of the phase, and N is the number of submodules of each phase; SOCE(x，n)Chargeable energy for each submodule; SODE(x，n)Is the dischargeable energy of each sub-module;
calculating three-phase average dischargeable electric quantity:
Figure FDA0002811377720000031
in the formula, SODEa、SODEb、SODEcThe three phases are respectively a, b and c which can discharge electricity.
5. The outlet short circuit and direct current controlled offline equalization method for the cascaded battery energy storage system according to claim 1, wherein in S5, the method specifically comprises:
and calculating the dischargeable energy of each phase and the error of the average dischargeable energy:
ΔSODEa＝SODEa-SODE
ΔSODEb＝SODEb-SODE
ΔSODEc＝SODEc-SODE
in the formula,. DELTA.SODEa，ΔSODEb，ΔSODEcRespectively representing dischargeable energy errors of a, b and c three phases, and subscripts a, b and c represent abc three phases; SODEa、SODEb、SODEcThe three-phase dischargeable electric quantity is respectively a, b and c, and the SODE is the average dischargeable electric quantity of the three phases;
calculating the maximum value Delta SODE of the absolute value of the dischargeable energy error of each phasemax：
ΔSODEmax＝max(|ΔSODEa|，|ΔSODEb|，|ΔSODEc|)。
6. The outlet short circuit and direct current controlled offline equalization method for the cascaded battery energy storage system according to claim 1, wherein in S6, the method specifically comprises:
the direct current of each phase is distributed according to the principle that the direct current is proportional to the dischargeable energy error of the phase:
Figure FDA0002811377720000032
Figure FDA0002811377720000033
Figure FDA0002811377720000034
in the formula Ia，Ib，IcRespectively representing three-phase direct current commands of a, b and c, subscripts a, b and c represent three phases abc, INIndicating system phase current rating, Δ SODEmaxFor maximum absolute value of dischargeable energy error of each phase, SODEa、SODEb、SODEcThe three phases are respectively a, b and c which can discharge electricity.
7. The outlet short circuit and direct current controlled offline equalization method for the cascaded battery energy storage system according to claim 1, wherein in S7, the method specifically comprises:
calculating a phase voltage reference voltage: in order to simultaneously complete the phase-to-phase balance and the sub-module balance, the phase voltage and the sub-module balance voltage generated by each sub-module are distributed according to the principle that the ratio of the maximum absolute value of the dischargeable energy error to the average value is in direct proportion:
Figure FDA0002811377720000041
wherein, Up，baseIs a phase voltage reference value, Us，baseEqualizing the voltage reference value, Δ SODE, for the submodulesmaxIs the maximum absolute value of the phase dischargeable energy error, Δ SODEsub_maxFor the maximum absolute value of the error in the dischargeable energy of the submodule of the system, SODE is the mean value of the phase dischargeable energy, SODEavgThe average value of the dischargeable energy of the submodule;
in order to make the voltage of each submodule not greater than the rated value, the sum of the inter-phase balance voltage averaged over the submodule and the submodule balance voltage is not greater than the rated value of the submodule voltage, so that the phase voltage reference value and the submodule balance voltage reference value satisfy the following constraint:
Figure FDA0002811377720000042
reference voltage U for obtaining phase voltagep，base：
Figure FDA0002811377720000043
Submodule balanced reference voltage Us，base：
Figure FDA0002811377720000044
Wherein, UNThe effective value of the rated line voltage of the system is;
in a star topology, the abc three-phase direct-current voltages are required to be equal and equal to a phase voltage reference value:
Ua＝Up，base
Ub＝Up，base
Uc＝Up，base
in the formula of Ua，Ub，UcRespectively representing three-phase direct-current voltage commands of a, b and c, and subscripts a, b and c represent three phases abc;
and (3) calculating the error between the dischargeable energy of the submodules in each phase and the average value of the dischargeable energy:
Figure FDA0002811377720000051
Figure FDA0002811377720000052
Figure FDA0002811377720000053
calculating the maximum absolute value of the dischargeable energy error of each phase module:
ΔSODEa，max＝max(|ΔSODEa，n|)
ΔSODEb，max＝max(|ΔSODEb，n|)
ΔSODEc，max＝max(|ΔSODEc，n|)
each submodule in the phase distributes the submodule balance voltage according to the principle that the submodule is in direct proportion to the dischargeable energy error, and each phase voltage is distributed to the submodule according to the principle of average distribution:
Figure FDA0002811377720000054
Figure FDA0002811377720000055
Figure FDA0002811377720000056
wherein, Ua，n，Ub，n，Uc，nThe dc voltages of the nth sub-module of the three phases a, b and c are indicated, the subscripts a, b and c indicate the three phases abc, and n indicates the number of the sub-module.
8. The outlet short circuit and direct current controlled offline equalization method for the cascaded battery energy storage system according to claim 1, wherein in S8, the phase current control generates equalization current, and the specific method is as follows:
and through phase current closed-loop control, stabilizing the phase current of the system with the short-circuited outlet to the direct current set value of each phase calculated in the step S5 so as to meet the requirement of off-line balance.
9. The outlet short circuit and direct current controlled offline equalization method for the cascaded battery energy storage system according to claim 1, wherein in S9, the method specifically comprises:
calculating the ratio K of the maximum value of the absolute value of the sub-module dischargeable energy error to the average dischargeable energy of the sub-module:
Figure FDA0002811377720000057
in the formula,. DELTA.SODEsub_maxFor maximum absolute value of dischargeable energy error, SODE, of a sub-module of the systemavgThe average value of the dischargeable energy of the submodule;
end conditions of offline equalization:
K＜Kover
in the formula, KoverA criterion parameter for off-line equalization ending;
if the end conditions are met, setting the direct-current voltage of each submodule to be 0, setting the balance current to be 0, and ending the off-line balance of the system; if the above condition is not satisfied, the process goes to step S2 to loop.
10. A terminal comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor is configured to execute the method for offline equalization of a cascaded battery energy storage system according to any one of claims 1 to 9.
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