CN112564219B - Offline equalization method for cascade battery energy storage system with short-circuit outlet and direct-current control - Google Patents
Offline equalization method for cascade battery energy storage system with short-circuit outlet and direct-current control Download PDFInfo
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Abstract
The invention provides an off-line equalization method of a cascade battery energy storage system with outlet short circuit and direct current control, which comprises the following steps: shorting each phase power outlet of the cascade battery energy storage system; obtaining battery voltage and SOC, SOH, SOF rated capacity information of each submodule of the cascade battery energy storage system; calculating chargeable energy and dischargeable energy of each sub-module; 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 sub-modules realizes the balance among the sub-modules in the phase; phase current control generates balanced current; and judging the end condition of the offline balancing. The invention can more conveniently and safely realize the offline equalization of the battery energy before the operation of the cascade battery energy storage system, and greatly reduce the workload of equalization maintenance before the operation of the battery energy storage system.
Description
Technical Field
The invention relates to the field of battery energy storage systems, in particular to an off-line equalization method of a cascade battery energy storage system with short outlet and direct current control.
Background
The cascade H-bridge battery energy storage system is suitable for being applied to high-voltage high-power energy storage occasions due to the characteristics of high equivalent switching frequency, good output voltage harmonic characteristic, easiness in expansion of modular design, convenience in fault redundancy control and the like. Before the cascade H-bridge battery energy storage system operates, the battery electric quantity of each submodule needs to be balanced so that the system operates normally, and the situation that the operation boundary of the system is reduced or even the starting fails due to the excessive uneven state of charge of the battery is avoided. At present, the battery equalization work before the operation of the battery energy storage system is mostly carried out by taking a single module as a unit, and the battery module of the system is equalized by carrying out manual charge and discharge.
Through searching, the prior art has a plurality of battery equalization technologies, such as application number: 201810264044.3, filing date: 2018-03-28, which discloses a battery pack equalization system taking battery life into consideration and a control method thereof, comprises a sampling module, an equalization module, a battery life prediction module and a control module, wherein the battery life prediction module receives battery information collected by the sampling module and predicts battery life; the control module is used for receiving battery pack information acquired by the sampling module and battery life information acquired by the battery life prediction module when the battery pack enters a charge-discharge 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 for balancing, and controlling the balancing module to execute. The battery life prediction module is used for providing battery life information to correct the voltage difference of adjacent single batteries, so that the condition that the open circuit voltage of the batteries is inconsistent due to different attenuation degrees of the service lives of the different single batteries is effectively considered, the energy waste caused by over-equalization can be avoided, the equalization efficiency is improved, the equalization time is reduced, and the service life of the batteries is effectively prolonged.
However, at present, research on automatic offline equalization technology of a cascade H-bridge battery energy storage system has not been reported yet.
Disclosure of Invention
Aiming at the blank existing in the prior art, the invention provides a method for realizing offline equalization of a cascade H-bridge battery energy storage system through direct current control by using outlet short circuit.
The invention provides an off-line equalization method of a cascade battery energy storage system with outlet short circuit and direct current control, which comprises the following steps:
s1: shorting the power outlets of each phase of the cascade H-bridge battery energy storage system;
s2: acquiring battery voltage, SOC, SOH, SOF and rated capacity information of each submodule of the cascade H-bridge battery energy storage system;
s3: according to the SOC, SOH and rated capacity information of each sub-module battery obtained in the step S2, chargeable energy and dischargeable energy of each sub-module battery are calculated, and then the maximum error absolute value of the dischargeable energy of all sub-modules and the average value thereof is calculated;
s4: summing the chargeable energy and the dischargeable energy of the submodule obtained in the step S3 to obtain chargeable energy, dischargeable energy and three-phase average dischargeable energy of each phase:
s5: the dischargeable energy of each phase obtained in the step S4 is differenced from the average dischargeable energy, so that dischargeable energy errors of each phase are obtained, and the maximum absolute value of the errors is obtained;
s6: on the result of S5, the direct current of each phase is distributed according to the principle of being in direct proportion to the dischargeable electric quantity error of the phase, the direct current of the phase cannot exceed the rated value of the current of the phase, and the distribution of the direct current of the phase realizes three-phase balance;
s7: on the basis of S6 phase direct current distribution, distributing the equalizing voltages of the sub-modules in the phase according to the principle of being in direct proportion to the dischargeable energy errors, distributing the voltages of the phases to the sub-modules according to the principle of average distribution, and realizing the equalizing of the sub-modules in the phase:
s8: on the basis of S7, controlling phase currents to generate balanced currents, and enabling the currents of all phases to reach distributed direct current values through current closed-loop control;
s9: judging whether the off-line equalization is finished or not through the ratio of the maximum absolute value of the dischargeable energy error of the sub-module to the average dischargeable energy of the sub-module, and considering that the off-line equalization is finished when the ratio is small to a set range.
In a second aspect of the present invention, a terminal is provided, including 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 the cascade battery energy storage system under the control of the outlet short circuit and the direct current when executing the program.
The invention aims to realize offline balancing of batteries in a cascade H-bridge battery energy storage system, and realizes balancing of battery modules with different initial electric quantity by using direct current control, and realizes the purpose of offline balancing of batteries in a convenient mode while considering the safe operation boundary of the system. According to the method, only the outlets of the cascade H-bridge battery energy storage system are short-circuited, the initial electric quantity of the battery energy storage system can be conveniently and rapidly balanced in an off-line mode through controlling the output voltage and the phase current of each module, and heavy workload in the traditional independent pre-charging and discharging process of the battery module is omitted.
Compared with the prior art, the embodiment of the invention has the following beneficial effects:
the invention provides a quick offline balancing method of a cascade H-bridge battery energy storage system, which adopts an outlet short circuit to realize the offline balancing of the battery energy storage system through direct current control and provides a quick method for the offline balancing maintenance of the battery energy storage system. Meanwhile, the method considers the safe operation boundary of the system, and ensures that the balanced voltage and current of the system are below the rated value. Finally, the purpose of rapidly and safely realizing offline equalization in the cascade H-bridge battery energy storage system is achieved.
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Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
FIG. 1 is a flow chart of a method for offline balancing of a cascade battery energy storage system with outlet shorting and DC control in accordance with a preferred embodiment of the present invention;
fig. 2 is an off-line equalization schematic diagram of a cascade battery energy storage system with outlet shorting and dc control in accordance with a preferred embodiment of the invention.
Detailed Description
The following describes embodiments of the present invention in detail: the embodiment is implemented on the premise of the technical scheme of the invention, and detailed implementation modes and specific operation processes are given. It should be noted that variations and modifications can be made by those skilled in the art without departing from the spirit of the invention, which falls within the scope of the invention.
Fig. 1 is a flow chart of a method for offline balancing of a cascade battery energy storage system with outlet shorting and dc control in accordance with a preferred embodiment of the present invention. Referring to fig. 1, the method for implementing offline equalization of the cascade H-bridge battery energy storage system by adopting the outlet short circuit in the embodiment includes the following steps:
s1: shorting the power outlets of each phase of the cascade H-bridge battery energy storage system;
s2: acquiring battery voltage, state of charge (SOC), state of health (SOH), SOF (state of function, functional state of battery) and rated capacity information of each submodule of the cascade H-bridge battery energy storage system; in the cascade H-bridge type battery energy storage system, each sub-module comprises a battery unit and a power unit, the battery units are managed by a battery management system (Battery Management System, BMS), the power units are used as a part of a power conversion system (Power Conversion System, PCS) and controlled by a PCS controller, and the PCS controller periodically acquires the SOC state and the SOH state of the battery units corresponding to each power unit from the BMS;
s3: calculating chargeable energy and dischargeable energy of each sub-module: according to the sub-module battery SOC, SOH and battery rated capacity information obtained in the step S1, chargeable energy and dischargeable energy of each sub-module battery can be calculated, and then the maximum error absolute value of the dischargeable energy of all sub-modules and the average value thereof is calculated;
s4: calculating chargeable energy, dischargeable energy and three-phase average dischargeable energy of each phase;
s5: calculating errors of dischargeable energy and average dischargeable energy of each phase, and meanwhile obtaining the maximum absolute value of the errors;
s6: phase direct current distribution realizes three-phase balance: the direct current of each phase is distributed according to the principle of being in direct proportion to the dischargeable energy error of the phase, and the direct current of the phase cannot exceed the rated value of the phase current;
s7: the submodule direct-current voltage distribution realizes the equalization of the intra-phase submodule: each sub-module in the phase distributes sub-module equalizing voltage according to the principle of being in direct proportion to dischargeable energy error, and distributes each phase voltage to the sub-module according to the principle of average distribution;
s8: the control phase current produces an equilibrium current: the current of each phase reaches the distributed direct current value through current closed-loop control;
s9: judging the end condition of offline equalization: judging whether the off-line equalization is finished or not through the ratio of the maximum absolute value of the dischargeable energy error of the sub-module to the average dischargeable energy of the sub-module, and if the ratio is small to a certain range, considering that the off-line equalization is finished.
In one embodiment, in step S2, the PCS controller periodically obtains the SOC state and 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 takes 0.1S-1min. The acquisition mode is generally communication, and is specifically determined by the interface specification and protocol between the PCS and BMS.
In one embodiment, in step S3, the chargeable energy and dischargeable energy of each sub-module are calculated, and the specific method is as follows:
chargeable energy:
SOCE (x,n) ＝[(SOC up -SOC x,n )×SOH x,n ×C N ]×V N
dischargeable energy:
SODE (x,n) ＝[(SOC x,n -SOC down )×SOH x,n ×C N ]×V N
in SOC up And SOC (System on chip) down Representing the upper and lower boundaries of SOC of battery operation, SOC being 0-0 down ≤SOC up Less than or equal to 1, x represents one of three phases a, b and C, n represents the number of a submodule in a certain phase, and C N For the rated capacity of the battery, V N Is the nominal voltage of the battery.
And calculating the average value of the dischargeable energy of the sub-modules, and then calculating the maximum error absolute value of the dischargeable energy of each sub-module and the average value.
Average value of the sub-module dischargeable energy:
maximum absolute value of the dischargeable energy of the sub-module:
ΔSODE sub_max ＝max(|SODE (x，n) -SODE avg |)
in one embodiment, in step S4, chargeable energy and dischargeable energy of each phase are calculated, which specifically includes:
the chargeable energy of each phase was calculated:
calculate the dischargeable energy of each phase:
wherein, the 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;
calculating the average dischargeable energy of the three phases:
in one embodiment, in step S5, the error between the dischargeable energy of each phase and the average dischargeable energy is calculated and the absolute value of the maximum error is calculated, which specifically includes:
calculating errors of dischargeable electric quantity and average dischargeable energy of each phase:
ΔSODE a ＝SODE a -SODE
ΔSODE b ＝SODE b -SODE
ΔSODE c ＝SODE v -SODE
in the formula delta SODE a ，ΔSODE b ，ΔSODE c The dischargeable energy errors of the three phases a, b, c are shown, respectively, and the subscripts a, b, c represent the three phases abc.
Calculating the maximum value of the absolute value of the dischargeable energy error of each phase:
ΔSODE max ＝max(|ΔSODE a |，|ΔSODE b |，|ΔSODE v |)
in one embodiment, in step S6, phase-to-phase equalization is implemented by phase-to-direct current distribution, which specifically includes:
the direct current of each phase is distributed according to the principle of being proportional to the phase dischargeable energy error:
wherein I is a ，I b ，I c Respectively representing a, b and c three-phase direct current instruction, subscripts a, b and c represent abc three phases, I N Representing the system phase current rating.
In one embodiment, in step S7, the submodule dc voltage distribution realizes phase internal submodule equalization, and the specific method is as follows:
calculating phase reference voltage: in order to enable phase-to-phase equalization and sub-module equalization to be completed simultaneously, the phase voltages generated by each sub-module and sub-module equalization voltages are distributed according to the principle of being proportional to the ratio of the maximum absolute value of the dischargeable energy error to the average value.
Wherein U is p，base U is the reference value of phase voltage s，base For equalizing voltage reference value of submodule, delta SODE max As the maximum absolute value of the phase dischargeable energy error, ΔSODE sub_max For the maximum absolute value of dischargeable energy error of the system submodule, SODE is the average value of the phase dischargeable energy avg As average value of dischargeable energy of sub-module, K base Is the proportional coefficient of the equalizing voltage.
In order for the voltage of each sub-module to be no greater than its nominal value, the sum of the phase voltage averaged over the sub-module and the sub-module balancing voltage needs to be no greater than the nominal value of the sub-module voltage. Thus, the phase voltage reference value and the sub-module balance voltage reference value satisfy the following constraint.
Phase reference voltage can be obtained:
sub-module balanced reference voltage:
wherein U is N Is an effective value of the rated line voltage of the system.
In star topology, abc three-phase direct voltages are required to be equal and equal to the phase voltage reference value:
U a ＝U p，base
U b ＝U p，base
U c ＝U p，base
in U a ，U b ，U c The direct-current voltage commands of the three phases a, b and c are respectively shown, and subscripts a, b and c represent abc three phases.
Calculating the error between the dischargeable energy of each phase Xiang Nazi module and the average value thereof:
calculating the maximum absolute value of the dischargeable energy errors of each phase of sub-module:
ΔSODE a，max ＝max(|ΔSODE a，n |)
ΔSODE b，max ＝max(|ΔSODE b，n |)
ΔSODE c，max ＝max(|ΔSODE c，n |)
each sub-module in the phase distributes sub-module equalizing voltage according to the principle of being in direct proportion to dischargeable energy error, and distributes each phase voltage to the sub-module according to the principle of average distribution:
wherein U is a，n ，U b，n ，U c，n The direct current voltage of the nth sub-module of the three phases a, b and c is represented, the subscripts a, b and c represent the three phases abc, and n represents the numbers of the sub-modules.
In one embodiment, in step S8, the phase current is controlled to generate an equalizing current by:
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 that the requirement of off-line equalization is met.
In one embodiment, in step S9, the end condition of the offline balancing is determined, and the specific method is as follows:
calculating the ratio of the maximum value of the absolute value of the dischargeable energy error of the submodule to the average dischargeable energy of the submodule:
end condition of offline equalization:
K＜K over
if the ending condition is met, setting the direct voltage of each submodule to be 0, setting the equalizing current to be 0, and ending the offline equalization of the system; if the above condition is not satisfied, the process goes to step S3 to cycle.
For a better description and understanding of the above-described techniques, the following description is made in connection with specific application examples, but the present invention is not limited to the following specific application examples.
As shown in fig. 2, the present 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 n=20 sub-modules, and the total system has 60 sub-modules. The AC grid-connected reactance is 6mH.
In this embodiment, the sub-module battery is an energy storage battery module with a nominal voltage of 51.2V, a maximum charge-discharge multiplying power of 4C and a nominal capacity of 100Ah, which is formed by connecting 16 3.2V/100Ah lithium iron phosphate battery cells in series, and each sub-module battery cluster is formed by connecting 15 battery modules in series. The upper operation limit of the battery SOC was set to 0.9, and the lower operation limit was set to 0.1.
Specifically, the implementation procedure of this embodiment refers to the procedure of fig. 1:
s1: shorting the power outlets of each phase of the cascade H-bridge battery energy storage system;
s2: obtaining nominal voltage, SOC, SOH, SOF and rated capacity information of each sub-module battery cluster of the modularized multi-level energy storage system;
the energy conversion system acquires information of 60 sub-module battery clusters in three phases from the battery management system at regular time every 1s in a communication mode. The upper and lower operating limits of SOC are set to 0.9 and 0.1, respectively. The information obtained is as follows:
a phase information:
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]
Cluster nominal voltage un= [768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768], unit V;
the nominal capacity cn= [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], unit a;
chargeable current ichg= [400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400], unit 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 somb= [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];
cluster nominal voltage un= [768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768], unit V;
the nominal capacity cn= [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], unit a;
chargeable current ichg= [400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400], unit a.
And 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];
cluster nominal voltage un= [768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768,768], unit V;
the nominal capacity cn= [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], unit a;
chargeable current ichg= [400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400,400], unit a.
S3: calculating the dischargeable energy of each sub-module;
and (3) respectively calculating the chargeable/dischargeable energy of each sub-module according to the information acquired in the step (S2).
Phase A:
chargeable energy space= [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], unit kWh;
the 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], unit kWh.
And B phase:
chargeable energy space= [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], unit 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], unit kWh.
And C phase:
chargeable energy space= [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], unit 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], unit kWh.
And further calculating the average value of the dischargeable energy of the sub-modules and the maximum error absolute value of the dischargeable energy of each sub-module and the average value.
The sub-module may discharge an average of energy, sodeavg= 35.10kWh;
the sub-module may discharge a maximum value of the absolute value of the energy error Δsodesubmax=15.25 kWh.
S4: calculating the dischargeable electric quantity of each phase and the average dischargeable electric quantity of the three phases;
according to the charge and discharge energy of each sub-module, summing to obtain:
total chargeable energy of phase a, space= 575.33kWh;
total dischargeable energy of phase a sode= 558.24kWh;
total chargeable energy of phase B, space= 692.98kWh;
phase B total dischargeable energy sode= 708.63kWh;
total chargeable energy of phase C, space= 288.801kWh;
total dischargeable energy of phase C sode= 854.60kWh;
three-phase average dischargeable energy sode= 701.94kWh.
S5: calculating the error between the dischargeable electric quantity of each phase and the average dischargeable electric quantity;
from the results of S4, it is possible to:
dischargeable energy error Δsode= -143.70kWh for phase a;
dischargeable energy error Δsode= -8.96kWh for phase B;
dischargeable energy error Δsode= 152.66kWh for phase C.
The maximum absolute value of the error thus obtainable is Δsodemax= 152.66kWh.
S6: phase direct current distribution realizes three-phase balance;
the direct current of each phase is distributed according to the proportion of the photo-dischargeable energy error and the absolute value of the maximum error as follows:
a phase A direct current:
phase B dc current:
c phase direct current:
s7: the direct-current voltage distribution of the submodules realizes the balance of the submodules in the phase;
calculating the proportional coefficient of the balanced voltage: kbase=50.07%
Calculating a phase voltage reference value: up, base= 2724.11V
Calculating a sub-module equalizing voltage reference value: us, base= 5440.86V
Calculating the error between the dischargeable energy of each phase sub-module and the average value of the dischargeable energy:
the phase a sub-module may discharge the error of energy and average: Δsode= [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], units kWh;
the B phase sub-module may discharge the error of energy and average: Δsode= [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], units kWh;
the C-phase sub-module may discharge the error of energy and average: Δsode= [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], units kWh;
thus, the maximum absolute value of the error between the dischargeable energy of each phase sub-module and the average value of the phases can be obtained:
ΔSODEa,max＝4.23kWh；
ΔSODEb,max＝10.57kWh；
ΔSODEc,max＝10.63kWh；
according to the submodule direct-current voltage distribution principle, the submodule direct-current voltages of each phase can be obtained as follows:
phase A:
submodule voltages 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], units V;
and B phase:
submodule voltages 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], units V;
and C phase:
sub-module 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], unit 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 flowing out of each phase of parallel network inductance and the current is S5, so that the phase current is stabilized to a set value, and the balance requirement is met.
S9: judging the end condition of offline equalization;
in the present embodiment, the criterion parameter K for the end of offline equalization is set in consideration of the system capacity and the sub-module SOC control accuracy over ＝5％。
Calculating the ratio of the maximum value of the absolute value of the dischargeable quantity error to the average dischargeable quantity: k=43.44%;
end condition K of not satisfying offline equalization is less than K over And jumping to the step S3, and circularly performing off-line equalization until the off-line equalization ending condition is met, and ending the off-line equalization.
According to the embodiment, the invention aims to realize offline balancing of the cascade H-bridge battery energy storage system adopting outlet short circuit and direct current control, and meanwhile, compared with the traditional balancing maintenance work of a single battery module, the offline balancing of the battery energy before the operation of the cascade H-bridge battery energy storage system can be realized more conveniently and safely by considering the operation boundary of the system, and the workload of the balancing maintenance of the battery before the operation of the battery energy storage system is greatly reduced.
While the present invention has been described in detail through the foregoing description of the preferred embodiment, it should be understood that the foregoing description is not to be considered as limiting the invention. Many modifications and substitutions of the present invention will become apparent to those of ordinary skill in the art upon reading the foregoing. The features of the above-described preferred embodiments of the present invention may be used in any combination without collision with each other.
Claims (9)
1. An off-line equalization method of a cascade battery energy storage system with outlet short circuit and direct current control is characterized by comprising the following steps:
s1: shorting the power outlets of each phase of the cascade H-bridge battery energy storage system;
s2: acquiring battery voltage, SOC, SOH, SOF and rated capacity information of each submodule of the cascade H-bridge battery energy storage system after the connection of the S1;
s3: according to the SOC, SOH and rated capacity information of each sub-module battery obtained in the step S2, chargeable energy and dischargeable energy of each sub-module battery are calculated, and then the maximum error absolute value of the dischargeable energy of all sub-modules and the average value thereof is calculated;
s4: summing the chargeable energy and the dischargeable energy of the submodule obtained in the step S3 to obtain chargeable energy, dischargeable energy and three-phase average dischargeable energy of each phase;
s5: the dischargeable energy of each phase obtained in the step S4 is differenced from the average dischargeable energy, so that dischargeable energy errors of each phase are obtained, and the maximum absolute value of the errors is obtained;
s6: on the result of S5, the direct current of each phase is distributed according to the principle of being in direct proportion to the dischargeable energy error of the phase, the direct current of the phase cannot exceed the rated value of the current of the phase, and the distribution of the direct current of the phase realizes three-phase balance;
s7: on the basis of S6 phase direct current distribution, distributing the equalizing voltages of the sub-modules in the phase according to the principle of being in direct proportion to the dischargeable energy errors, distributing the voltages of the phases to the sub-modules according to the principle of average distribution, and realizing the equalizing of the sub-modules in the phase:
s8: on the basis of S7, controlling phase currents to generate balanced currents, and enabling the currents of all phases to reach distributed direct current values through current closed-loop control;
s9: judging whether the off-line equalization is finished or not through the ratio of the maximum absolute value of the dischargeable energy error of the sub-module to the average dischargeable energy of the sub-module, and considering that the off-line equalization is finished when the ratio is small to a set range;
s4, calculating chargeable energy, dischargeable energy and three-phase average dischargeable energy of each phase, wherein the specific method comprises the following steps of:
calculating the chargeable energy SOCE of each phase x ：
Calculating dischargeable energy SODE of each phase x ：
Wherein, the 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 sub-module; SODE (x,n) Dischargeable energy for each sub-module;
calculating three-phase average dischargeable energy:
in SODE a 、SODE b 、SODE c Three phases of the energy which can be discharged are a, b and c respectively.
2. The method for offline equalization of an outlet short circuit and direct current controlled cascade battery energy storage system of claim 1, wherein in S2, each sub-module in the cascade H-bridge battery energy storage system comprises 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 a part of a power conversion system, and the PCS controller periodically acquires the SOC state and SOH state of the battery unit corresponding to each power unit from the battery management system; the PCS controller obtains the SOC state and the SOH state of the battery unit corresponding to each power unit from the battery management system at regular time, the time interval is determined according to the state refresh rate of the battery energy storage system, and 0.1s-1min is taken.
3. The method for offline balancing of the cascade battery energy storage system with outlet short circuit and direct current control according to claim 1, wherein in S3, chargeable energy and dischargeable energy of each sub-module are calculated, and the specific method is as follows:
rechargeable energy SOCE of each sub-module (x,n) ：
SOCE (x,n) ＝[(SOC up -SOC x,n )×SOH x,n ×C N ]×V N
Dischargeable energy SODE of individual submodules (x,n) ：
SODE (x,n) ＝[(SOC x,n -SOC down )×SOH x,n ×C N ]×V N
In SOC up And SOC (System on chip) down Representing the upper and lower boundaries of SOC of battery operation, SOC being 0-0 down ≤SOC up Less than or equal to 1, x represents one of three phases a, b and C, n represents the number of a submodule in a certain phase, and C N For the rated capacity of the battery, V N Is the nominal voltage of the battery; SOC (State of Charge) x,n 、SOH x,n Respectively representing the charge state and the health state of the nth sub-module battery of the x phase;
calculating the average value of the dischargeable energy of the sub-modules, and then calculating the maximum error absolute value of the dischargeable energy of each sub-module and the average value;
average value SODE of sub-module dischargeable energy avg ：
In the above formula, N is the number of sub-modules of each phase;
maximum error absolute delta SODE of dischargeable energy of sub-module sub_max ：
ΔSODE sub_max ＝max(|SODE (x,n) -SODE avg |)。
4. The method for offline balancing of the cascade battery energy storage system with outlet short circuit and direct current control according to claim 1, wherein in S5, specifically comprises:
calculating errors of dischargeable energy and average dischargeable energy of each phase:
ΔSODE a ＝SOOD a -SODE
ΔSODE b ＝SOOD b -SOOD
ΔSODE c ＝SODE c -SODE
in the formula delta SODE a ，ΔSODE b ，ΔSODE c The dischargeable energy errors of the three phases a, b and c are respectively represented, and subscripts a, b and c represent abc three phases; SODE a 、SODE b 、SODE c Three phases of dischargeable energy are a, b and c respectively, and SODE is the calculated three-phase average dischargeable energy;
calculating the maximum value delta SODE of the absolute value of the dischargeable energy errors of each phase max ：
ΔSODE max ＝max(|ΔSODE a |,|ΔSODE b |,|ΔSODE c |)。
5. The method for offline balancing of the cascade battery energy storage system with outlet shorting and direct current control according to claim 4, wherein in S6, specifically comprises:
the direct current of each phase is distributed according to the principle of being proportional to the phase dischargeable energy error:
wherein I is a ，I b ，I c Respectively representing a, b and c three-phase direct current instruction, subscripts a, b and c represent abc three phases, I N Indicating the current rating of the system phase, ΔSODE max The maximum value of the absolute value of the dischargeable energy error for each phase.
6. The method for offline balancing of the cascade battery energy storage system with outlet shorting and direct current control according to claim 1, wherein in S7, specifically comprises:
calculating a phase voltage reference voltage: in order to enable phase-to-phase equalization and sub-module equalization to be completed simultaneously, the phase voltages generated by each sub-module and sub-module equalization voltages are distributed according to the principle of being proportional to the ratio of the maximum absolute value of the dischargeable energy error to the average value:
wherein U is p,base U is the reference value of phase voltage s,base For equalizing voltage reference value of submodule, delta SODE max As the maximum absolute value of the phase dischargeable energy error, ΔSODE sub_max For the maximum absolute value of dischargeable energy error of the system submodule, SODE is the average value of the phase dischargeable energy avg An average value of dischargeable energy of the sub-module;
in order for the voltages of the sub-modules not to be greater than their nominal values, it is necessary that the sum of the inter-phase equilibrium voltage and the sub-module equilibrium voltage averaged over the sub-modules is not greater than the nominal value of the sub-module voltage, so that the phase voltage reference value and the sub-module equilibrium voltage reference value satisfy the following constraint:
reference voltage U for obtaining phase voltage p,base ：
Sub-module balanced reference voltage U s,base ：
Wherein U is N An effective value of the rated line voltage of the system;
in star topology, abc three-phase direct voltages are required to be equal and equal to the phase voltage reference value:
U a ＝U p,base
U b ＝U p,base
U c ＝U p,base
in U a ，U b ，U c The three phases a, b and c direct-current voltage instructions are respectively represented, and subscripts a, b and c represent abc three phases;
calculating the error between the dischargeable energy of each phase Xiang Nazi module and the average value thereof:
calculating the maximum absolute value of the dischargeable energy errors of each phase of sub-module:
ΔSODE a,max ＝max(|ΔSODE a,n |)
ΔSODE b,max ＝max(|ΔSODE b,n |)
ΔSODE c,max ＝max(|ΔSODE c,n |)
each sub-module in the phase distributes sub-module equalizing voltage according to the principle of being in direct proportion to dischargeable energy error, and distributes each phase voltage to the sub-module according to the principle of average distribution:
wherein U is a,n ,U b,n ,U c,n The direct current voltage of the nth sub-module of the three phases a, b and c is represented, the subscripts a, b and c represent the three phases abc, and n represents the numbers of the sub-modules.
7. The method for offline balancing of the cascade battery energy storage system with outlet short circuit and direct current control according to claim 1, wherein in S8, the phase current control generates balanced current, and the specific method is as follows:
and stabilizing the current of each phase of the system with the short-circuited outlet to the direct current set value of each phase obtained by S5 through phase current closed-loop control, so as to meet the requirement of off-line equalization.
8. The method for offline balancing of the cascade battery energy storage system with outlet shorting and direct current control according to claim 1, wherein in S9, specifically comprises:
calculating the ratio K of the maximum value of the absolute value of the dischargeable energy error of the submodule to the average dischargeable energy of the submodule:
in the formula delta SODE sub_max SODE is the maximum absolute value of dischargeable energy error for a system sub-module avg An average value of dischargeable energy of the sub-module;
end condition of offline equalization:
K<K over
wherein K is over The criterion parameters are the criterion parameters for finishing off-line equalization;
if the ending condition is met, setting the direct voltage of each submodule to be 0, setting the equalizing current to be 0, and ending the offline equalization of the system; if the above condition is not satisfied, the process goes to step S2 to loop.
9. 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 perform the method of off-line equalization of the outlet shorting and dc controlled cascade battery energy storage system of any one of claims 1-8 when the program is executed by the processor.
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