CN103715733A

CN103715733A - Triangle connection cascade energy storage system two stage equalization control method

Info

Publication number: CN103715733A
Application number: CN201310462155.2A
Authority: CN
Inventors: 凌志斌; 郭海峰; 张百华; 陈满; 李勇琦; 李永兴; 杨宗强
Original assignee: Peak and Frequency Regulation Power Generation Co of China Southern Power Grid Co Ltd; Shanghai Jiao Tong University
Current assignee: Peak and Frequency Regulation Power Generation Co of China Southern Power Grid Co Ltd; Shanghai Jiao Tong University
Priority date: 2013-09-30
Filing date: 2013-09-30
Publication date: 2014-04-09
Anticipated expiration: 2033-09-30
Also published as: CN103715733B

Abstract

The invention provides a two-level balance control method for a delta-connected cascaded energy storage system. The method includes the following steps: the first step: obtaining the SOC and SOH information of each chain link of the chain energy storage system; the second step: calculating respectively Calculate the rechargeable power and dischargeable power of each chain link; the third step: calculate the total rechargeable power and dischargeable power of each line and the whole system; the fourth step: the distribution and control of the power of each line; the fifth step: in the On the basis of determining the power of each line, the voltage of each chain link is allocated according to the ratio of the charging/discharging power of each chain link, so that the proportional power distribution can be realized. The present invention aims at maximizing the capacity utilization rate of the energy storage system, that is, the batteries of all chain links are fully charged and fully discharged at the same time, and at the same time, considering the safe operation boundary, it can more reasonably reflect the energy storage system in different operating conditions and The demand for equalization capability in the SOC state optimizes the equalization performance within the achievable range.

Description

A kind of triangle connects cascade energy-storage system two-stage balance control method

Technical field

What the present invention relates to is energy-storage system balance control method, and a kind of two-stage SOC equalization methods that is applied to triangle cascade energy-storage system specifically, for high capacity cell energy storage occasion.Belong to battery energy storage field.

Background technology

Cascade energy-storage system is with its modular construction, and under Same Efficieney, the feature that voltage is high, electric current is little, current harmonics is little and efficiency is high, receives publicity day by day.The mutual decoupling zero of control of cascade energy-storage system three lines that triangle connects, its control method is simple compared with the control method of Y-connection, and this topological structure has the two-stage equalization function to battery equally.

The equilibrium of cascade energy-storage system is controlled to research both at home and abroad at present few.2008, Japanese scholars Akagi etc. are at < < A transformerless battery energy storage system based on a multilevel cascade PWM converter[C] .Power Electronics Specialists Conference, IEEE, in 2008:4798-4804 > >, propose the cascade energy storage PCS for battery energy storage, and power control and battery pack SOC balance control method are studied.In literary composition, energy-storage system mutually in balanced control to adopt inject deviation voltage signal, make mutually in the power of each chain link and the deviation of power average be proportional to the SOC of chain link and the deviation of this phase SOC average; Alternate balanced control of energy-storage system adopts injection residual voltage method, makes respectively the upper secondary power producing mutually be proportional to the SOC of each phase and the deviation of three-phase SOC average.Domestic Liu's Wenhuas etc. are controlled [J] at < < large capacity chain type battery energy storage system and charge and discharge balancing thereof. power system automation apparatus, 2011,31 (3): in 6-11 > >, adopted the method for direct control zero-sequence current to realize alternate SOC equilibrium.In above-mentioned equalization methods, controlling target is all that equal power is directly proportional to the deviate of SOC.This take eliminate the simple and easy to understand of control strategy that SOC deviation is direct target, but also have the following disadvantages: the static equilibrium that 1) is applicable to energy-storage system, for the energy-storage system in dynamic operation, this control strategy does not consider that the ability of equalization and integral body discharge and recharge contacting of time.For the energy-storage system in actual motion, ability of equalization reasonable value is not only relevant to the deviation of SOC, also relevant to the absolute value of SOC.2) the SOC secure border while not considering actual motion.In order to guarantee the safe operation of battery, based on SOC estimation error often large (nearly 10%) and battery charging and discharging both end voltage variation reason greatly, the range of operation of restriction SOC in service is no more than 10%-90%.SOC value is apart from SOC upper lower limit value during apart from difference, and its demand to the ability of equalization is different.Currently only consider that the control method of SOC deviation size cannot reflect the difference of controlling in above-mentioned situation.3) do not consider the factor of the capacity volume variance of battery in same energy-storage system.Along with the aging of energy-storage system battery in service and after damaging, change, the SOH of battery is in different states, and the battery of same SOC is but being stored the electric weight of different sizes, is storing the battery of same charge in different SOC states.The simple control of carrying out with SOC and SOC deviation may cause in unidirectional charging or discharge process of energy-storage system, and forward and reverse balanced situation repeatedly appears in the battery that capacity is less, has increased the weight of balanced burden, has reduced efficiency.4) more important point is, the cascade energy-storage system connecting for triangle, and due to " phase " that do not exist physically, residual voltage injection method can not be applicable to the equilibrium of energy-storage system and control.

Summary of the invention

The present invention is directed to the deficiency that prior art exists, propose to be connected cascade energy-storage system two-stage balance control method based on chargeable capacity with triangle that can discharge capacity.The method turns to target with energy storage system capacity utilance maximum, the battery of all chain links is full of electricity simultaneously and is discharged simultaneously, consider safe operation border simultaneously, can more reasonably embody energy-storage system demand to the ability of equalization under different operating conditions and SOC state, optimization equalization performance in attainable scope.

For achieving the above object, the invention provides a kind of triangle and connect cascade energy-storage system two-stage balance control method, described method comprises the steps:

The first step: SOC, the SOH information of obtaining each chain link of chain type energy-storage system

In chain type energy-storage system, each chain link is comprised of battery unit and power cell, battery unit is by battery management system (BMS) management, and power cell is controlled by PCS controller as the part of power conversion system (Power Conversion System, PCS).PCS controller regularly obtains SOC state and the SOH state of the battery unit that each power cell is corresponding from BMS, the time interval is from 0.1s-10min.Obtain manner can be communication modes, can be also analog quantity mode, specifically by the interface between PCS and BMS, is determined.

Second step: calculate each chain link chargeable electric weight and can discharge electricity amount

The rated capacity of the SOC obtaining according to the first step, SOH information and battery unit, calculate respectively each chain link chargeable electric weight and can discharge electricity amount.

Can discharge electricity amount:

Q _f(x,n)--(SOC _x,n-SOC _down)XSOH _x,nxC _N

Chargeable electric weight:

Q _c(x,n)＝(SOC _up-SOC _x,n)XSOH _x,nXC _N

In formula, soc _upand SOC _downrepresent respectively the SOC up-and-down boundary of battery operation, o≤SOC _down<SOC _up≤ 1.Subscript f represents electric discharge, and c represents charging, and x represents one of ab, bc, ca tri-lines, and n represents the chain link numbering in a certain line.C _nfor battery rated capacity.

The 3rd step: calculate the total chargeable electric weight of each line and whole system and can discharge electricity amount

That calculates ab, bc and ca tri-lines can discharge electricity amount:

Q_{f, ab} = \frac{1}{N} Σ_{n = 1}^{N} Q_{f (ab, n)}

Q_{f, bc} = \frac{1}{N} Σ_{n = 1}^{N} Q_{f (bc, n)}

Q_{f, ca} = \frac{1}{N} Σ_{n = 1}^{N} Q_{f (ca, n)}

In formula, subscript f represents electric discharge, and n represents n chain link in this line.N is the chain number of every line.

Calculate three lines total can discharge electricity amount:

Q _f,sum＝Q _f,ab+Q _f,bc+Q _f,ca

Calculate ab, bc and ca tri-lines charge capacity separately:

Q_{c, ab} = \frac{1}{N} Σ_{n = 1}^{N} Q_{c (ab, n)}

Q_{c, bc} = \frac{1}{N} Σ_{n = 1}^{1} Q_{c (bc, n)}

Q_{c, ca} = \frac{1}{N} Σ_{n = 1}^{N} Q_{c (ca, n)}

In formula, subscript c represents charging, and n represents n chain link in this line.N is the chain number of every line.

Calculate ab, bc and the total chargeable electric weight of ca tri-lines:

Q _c,sum＝Q _c,ab+Q _c,bc+Q _c,ca

The 4th step: the distribution of each linear heat generation rate and control

According to the ratio of the put/charge capacity of each line, according to gross power instruction Psum, distribute power as follows:

During electric discharge, the discharge power instruction of ab, bc and ca tri-lines is respectively:

P_{ab} = \frac{Q_{f, ab}}{Q_{f, ab} + Q_{f, bc} + Q_{f, ca}} \times P_{sum}

P_{bc} = \frac{Q_{f, bc}}{Q_{f, ab} + Q_{f, bc} + Q_{f, ca}} \times P_{sum}

P_{ca} = \frac{Q_{f, ca}}{Q_{f, ab} + Q_{f, bc} + Q_{f, ca}} \times P_{sum}

During charging, the charge power instruction of ab, bc and ca tri-lines is respectively:

P_{ab} = \frac{Q_{c, ab}}{Q_{c, ab} + Q_{c, bc} + Q_{c, ca}} \times P_{sum}

P_{bc} = \frac{Q_{c, bc}}{Q_{c, ab} + Q_{c, bc} + Q_{c, ca}} \times P_{sum}

P_{ca} = \frac{Q_{c, ca}}{Q_{c, ab} + Q_{c, bc} + Q_{c, ca}} \times P_{sum}

Ab, bc and ca tri-line current sizes:

| I_{ab} | = \frac{P_{ab}}{U_{sab}}

| I_{bc} | = \frac{P_{bc}}{U_{sbc}}

| I_{ca} | = \frac{P_{ca}}{U_{sca}}

Ab, bc are identical with three line voltage-phases separately with ca tri-line current phase places.

Control three line current differences and can realize the power proportions between three lines, realize the equilibrium between three lines.

The terminal voltage Uab of three lines, Ubc and Uca are respectively:

{\overset{\cdot}{U}}_{ab} = {\overset{\cdot}{U}}_{sab} + {\overset{\cdot}{U}}_{Lab}

{\overset{\cdot}{U}}_{bc} = {\overset{\cdot}{U}}_{sbc} + {\overset{\cdot}{U}}_{Lbc}

{\overset{\cdot}{U}}_{ca} = {\overset{\cdot}{U}}_{sca} + {\overset{\cdot}{U}}_{Lca}

The 5th step: the distribution of chain link power and control

On the definite basis of each linear heat generation rate, according to each chain link can charge/discharge electric weight the voltage of each chain link of pro rate, can realize power division proportionally.

During charging, ab, bc and ca tri-linear chain economize on electricitys are pressed according to Q _{c (ab, n)}, Q _{c (bc, n)}, Q _{c (ca, n)}pro rate is as follows:

U_{ab, n} = \frac{Q_{c (ab, n)}}{N \times Q_{c, ab}} \times U_{ab}

U_{bc, n} = \frac{Q_{c (bc, n)}}{N \times Q_{c, bc}} \times U_{bc}

U_{ca, n} = \frac{Q_{c (ca, n)}}{N \times Q_{c, ca}} \times U_{ca}

During electric discharge, ab, bc and ca tri-linear chain economize on electricitys are pressed according to Q _{f (ab, n)}, Q _{f (bc, n)}, Q _{f (ca, n)}pro rate is as follows:

U_{ab, n} = \frac{Q_{f (ab, n)}}{N \times Q_{f, ab}} \times U_{ab}

U_{bc, n} = \frac{Q_{f (c, n)}}{N \times Q_{f, bc}} \times U_{bc}

U_{ca, n} = \frac{Q_{f (ca, n)}}{N \times Q_{f, ca}} \times U_{ca}

In formula, U _{ab, n}, U _{bc, n}, U _{ca, n}the AC voltage that represents respectively n chain link of ab, bc, ca tri-lines.Subscript ab, bc, ca represent ab, bc and ca tri-lines, and n represents the numbering of chain link in this line, and N represents the chain number of every line.

The voltage of controlling each chain link controlled the power proportions of each chain link, realized the equilibrium of chain internode.

Compare with existing method for balancing powers, the invention has the beneficial effects as follows:

The present invention has considered the SOC border of battery operation, is beneficial to the protection to battery; Consider the SOH of battery, embodied the impact of cell degradation, balanced control is more reasonable.Balanced control be take all batteries and is full of simultaneously, discharges simultaneously as target, and target is distincter, reasonable.The power control ability that can bring into play to greatest extent PCS, improves balanced effect.Finally reach the object that improves battery capacity utilance and extending battery life.

Accompanying drawing explanation

By reading the detailed description of non-limiting example being done with reference to the following drawings, it is more obvious that other features, objects and advantages of the present invention will become:

Fig. 1 is that the triangle of one embodiment of the invention connects cascade energy-storage system structured flowchart.

Embodiment

Below in conjunction with specific embodiment, the present invention is described in detail.Following examples will contribute to those skilled in the art further to understand the present invention, but not limit in any form the present invention.It should be pointed out that to those skilled in the art, without departing from the inventive concept of the premise, can also make some distortion and improvement.These all belong to protection scope of the present invention.

Embodiment

The present embodiment is 2MW battery energy storage system, rated voltage 10kV, and triangle connects, and every line N=20 chain link connects reactance 20mH.

In the present embodiment, in the operation of battery SOC, be limited to 0.9, under operation, be limited to 0.1.The SOH of battery is 0.9, rated capacity 400Ah.

In the present embodiment, will be by the monomer series-connected rated voltage 960V that forms of 300 joint 3.2V/400Ah ferric phosphate lithium cell, the batteries of rated capacity 400Ah.

The process of the present embodiment is as follows:

PCS obtains the three lines SOC information of totally 60 chain links by the every 3s of communication modes from BMS, and the SOH of chain batteries is 0.9, SOC operation bound and is respectively 0.9 and 0.1, and rated capacity is 400AH.Three line SOC information are as follows: SOC _ab=[0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31,0.31]

SOC _bc=[0.26,0.3,0.32,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3]

SOC _ca=[0.3,0.28,0.3,0.36,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3,0.3]

The rated capacity of the SOC obtaining according to step 1, SOH information and battery unit, calculate respectively each chain link chargeable electric weight and can discharge electricity amount.

Calculating each chain link of three lines can discharge electricity amount:

Q _f,ab=[75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6,75.6]AH

Q _f,bc=[57.6,72,79.2,72,72,72,72,72,72,72,72,72,72,72,72,72,72,72,72,72]AH

Q _f,ca=[72,64.8,72,93.6,72,72,72,72,72,72,72,72,72,72,72,72,72,72,72,72]AH

Calculate the chargeable electric weight of each chain link of three lines:

Q _c,ab=[212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4,212.4]AH

Q _c,bc=[230.4,216,208.8,216,216,216,216,216,216,216,216,216,216,216,216,216,216,216,216,216]AH

Q _c,ca=[216,223.2,216,194.4,216,216,216,216,216,216,216,216,216,216,216,216,216,216,216,216]AH

The 3rd step: calculate the total chargeable electric weight of three lines and whole system and can discharge electricity amount

Calculate the chargeable electric weight of every line:

Q _c,ab=212.4AH

Q _c,bc=216.36AH

Q _c,ca=215.28AH

Calculate total chargeable electric weight:

Q _c=212.4AH+216.36AH+215.28AH=644.04AH

That calculates every line can discharge electricity amount:

Q _f,ab=75.6AH

Q _f,bc=71.64AH

Q _f,ca=72.72AH

Calculate total can discharge electricity amount:

Q _f=75.6AH+71.64AH+72.72AH=219.96AH

The 4th step: the distribution of each linear heat generation rate and control

When the power instruction that PCS receives is 900kW charging, three line current phase places are identical with three line voltages.According to the chargeable electric weight of three lines, distribute power as follows:

Pab=212.4/644.04*900kW=296.8kW

Pbc=216.36/644.04*900kW=302.4kW

Pca=215.28/644.04*900kW=300.8kW

Three line current sizes:

Iab=29.68A

Ibc=30.24A

Ica=30.08A

Ab, bc and the pressure drop of tri-grid-connected reactance power frequencies of ca are respectively 186.4V, 189.9V and 188.9V, the phase place corresponding line voltage 90 degree electrical degrees that lag behind.

Tri-end output voltages of Uab, Ubc and Uca are respectively:

Uab=Usab+U _Lab=10000V-j186.4V=10001.74∠-1.07

Ubc=Usbc+U _Lac=10000V-j189.9V=10001.8∠-1.09

Uca=Usca+U _Laa=10000V-j188.9V=10001.78∠-1.08

Wherein angle is with respect to corresponding line voltage phase angle.

When the power instruction that PCS receives is 600kW electric discharge, three line current phase places are contrary with three line voltages.According to the chargeable electric weight of three lines, distribute power as follows:

Pab=75.6/219.96*600kW=206.2kW

Pbc=71.64/219.96*600kW=195.4kW

Pca=72.72/219.96*600kW=198.4kW

Three line current sizes:

Iab=20.62A

Ibc=19.54A

Ica=19.84A

Ab, bc and the pressure drop of tri-grid-connected reactance power frequencies of ca are respectively 129.5V, 122.7V and 124.6V.The leading corresponding line voltage 90 degree electrical degrees of phase place.

Tri-end output voltages of Uab, Ubc and Uca are respectively:

Uab=Usab+U _Lab=10000V+j129.5V=10000.8∠0.74

Ubc=Usbc+U _Lac=10000V+j122.7V=10000.75∠0.70

Uca=Usca+U _Laa=10000V+j124.6V=10000.78∠0.71

Wherein angle is with respect to corresponding line voltage phase angle.

The 5th step: the distribution of chain link power and control

The power that distributes each chain link on the definite basis of each linear heat generation rate, according to each chain link can charge/discharge electric weight Q _{c (a, n)}/ Q _{f (a, n)}, Q _{c (b, n)}/ Q _{f (b, n)}, Q _{c (c, n)}/ Q _{f (c, n)}ratio, distribute power as follows:

Each chain link charge power when PCS gross power is 900kW charging:

P _c,ab=[14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84,14.84]kW

P _c,bc=[16.10,15.09,14.59,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09]kW

P _c,ca=[15.09,15.59,15.09,13.58,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09,15.09]kW

Each chain link voltage:

U _c,ab=[500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09,500.09]V

U _c,bc=[532.45,499.17,482.53,499.17,499.17,499.17,499.17,499.17,499.17,499.17,499.17,499.17,499.17,499.17,499.17,499.17,499.17,499.17,499.17,499.17]V

U _c,ca=[501.67,518.39,501.67,451.51,501.67,501.67,501.67,501.67,501.67,501.67,501.67,501.67,501.67,501.67,501.67,501.67,501.67,501.67,501.67,501.67]V

Each chain link discharge power when PCS gross power is 600kW electric discharge:

P _f,ab=[10.31,10.31,10.31,10.31,10.31,10.31,10.31,10.31,10.31,10.31,10.31,10.31,10.31,10.3110.31,10.31,10.31,10.31,10.31,10.31]kW

P _f,bc=[7.86,9.82,10.80,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82]kW

P _f,ca=[9.82,8.84,9.82,12.77,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82,9.82]kW

Each chain link voltage:

U _f,ab=[500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04,500.04]V

U _f,bc=[402.01,502.51,552.76,502.51,502.51,502.51,502.51,502.51,502.51,502.51,502.51,502.51,502.51,502.51,502.51,502.51,502.51,502.51,502.51,502.51]V

U _f,ca=[495.05,445.54,495.05,643.56,495.05,495.05,495.05,495.05,495.05,495.05,495.05,495.05,495.05,495.05,495.05,495.05,495.05,495.05,495.05,495.05]V

The voltage of controlling each chain link controlled the power that discharges and recharges of each chain link.

Above specific embodiments of the invention are described.It will be appreciated that, the present invention is not limited to above-mentioned specific implementations, and those skilled in the art can make various distortion or modification within the scope of the claims, and this does not affect flesh and blood of the present invention.

Claims

1. A two-level balance control method for a delta-connected cascaded energy storage system, characterized in that the method comprises the steps of:

Step 1: Obtain the SOC and SOH information of each chain link of the chain energy storage system;

Step 2: According to the SOC, SOH information obtained in the first step and the rated capacity of the battery unit, calculate the rechargeable power and discharge power of each chain link; among them:

The dischargeable power is obtained by the following formula:

Q _t(x,n) ＝(SOC _x,n -SOC _down )XSOH _x,n xC _N

The rechargeable power is obtained by the following formula:

Q _c(x,n) ＝(SOC _up -SOC _x,n )XSOH _x,n XC _N

In the formula, soc _up and SOC _down represent the upper and lower boundaries of the SOC of the battery operation, o≤SOC _down <SOC _up ≤1, the subscript f represents discharge, c represents charge, x represents one of the three lines ab, bc, and ca, and n represents Chain link number in a line, C _N is the rated capacity of the battery;

Step 3: According to the rechargeable power and dischargeable power of each chain link obtained in the second step, calculate the total rechargeable power and dischargeable power of each line and the entire system;

Calculate the dischargeable electricity of the three wires ab, bc and ca:

{Q Q}_{f f,, ab ab} = = \frac{11}{N N} {Σ Σ}_{n no = = 11}^{N N} {Q Q}_{f f ((ab ab,, n no))}

{Q Q}_{f f,, bc bc} = = \frac{11}{N N} {Σ Σ}_{n no = = 11}^{N N} {Q Q}_{f f ((bc bc,, n no))}

{Q Q}_{f f,, ca ca} = = \frac{11}{N N} {Σ Σ}_{n no = = 11}^{N N} {Q Q}_{f f ((ca ca,, n no))}

In the formula, the subscript f represents discharge, n represents the nth link in the line, and N is the number of links in each line;

Calculate the total dischargeable power of the three wires:

Q _f,sum = Q _f,ab +Q _f,be +Q _f,ca

Calculate the charging power of the three lines ab, bc and ca:

{Q Q}_{c c,, ab ab} = = \frac{11}{N N} {Σ Σ}_{n no = = 11}^{N N} {Q Q}_{c c ((ab ab,, n no))}

{Q Q}_{c c,, bc bc} = = \frac{11}{N N} {Σ Σ}_{n no = = 11}^{N N} {Q Q}_{c c ((bc bc,, n no))}

{Q Q}_{c c,, ca ca} = = \frac{11}{N N} {Σ Σ}_{n no = = 11}^{N N} {Q Q}_{c c ((ca ca,, n no))}

In the formula, the subscript c means charging, n means the nth link in the line, and N is the number of links in each line; calculate the total rechargeable power of the three lines ab, bc and ca:

Q _c,sum =Q _c,ab +Q _c,bc +Q _c,ca ;

Step 4: According to the results obtained in the above steps, distribute and control the charging and discharging power of each line: according to the ratio of the dischargeable/charging power of each line, and according to the total power command P _sum , the power distribution is as follows: when discharging, ab, The discharge power commands of the three wires bc and ca are:

{P P}_{ab ab} = = \frac{{Q Q}_{f f,, ab ab}}{{Q Q}_{f f,, ab ab} + + {Q Q}_{f f,, bc bc} + + {Q Q}_{f f,, ca ca}} \times \times {P P}_{sum sum}

{P P}_{bc bc} = = \frac{{Q Q}_{f f,, bc bc}}{{Q Q}_{f f,, ab ab} + + {Q Q}_{f f,, bc bc} + + {Q Q}_{f f,, ca ca}} \times \times {P P}_{sum sum}

{P P}_{ca ca} = = \frac{{Q Q}_{f f,, ca ca}}{{Q Q}_{f f,, ab ab} + + {Q Q}_{f f,, bc bc} + + {Q Q}_{f f,, ca ca}} \times \times {P P}_{sum sum}

When charging, the charging power commands of ab, bc and ca three lines are respectively:

{P P}_{ab ab} = = \frac{{Q Q}_{c c,, ab ab}}{{Q Q}_{c c,, ab ab} + + {Q Q}_{c c,, bc bc} + + {Q Q}_{c c,, ca ca}} \times \times {P P}_{sum sum}

{P P}_{bc bc} = = \frac{{Q Q}_{c c,, bc bc}}{{Q Q}_{c c,, ab ab} + + {Q Q}_{c c,, bc bc} + + {Q Q}_{c c,, ca ca}} \times \times {P P}_{sum sum}

{P P}_{ca ca} = = \frac{{Q Q}_{c c,, ca ca}}{{Q Q}_{c c,, ab ab} + + {Q Q}_{c c,, bc bc} + + {Q Q}_{c c,, ca ca}} \times \times {P P}_{sum sum}

ab, bc and ca three-wire current magnitude:

| | {I I}_{ab ab} | | = = \frac{{P P}_{ab ab}}{{U u}_{sab sab}}

| | {I I}_{bc bc} | | = = \frac{{P P}_{bc bc}}{{U u}_{sbc sbc}}

| | {I I}_{ca ca} | | = = \frac{{P P}_{ca ca}}{{U u}_{sca sca}}

The ab, bc and ca three-wire current phases are the same as their respective three-wire voltage phases;

The power ratio between the three wires can be realized by controlling the different currents of the three wires, and the balance between the three wires can be realized;

Three-wire terminal voltage

and

They are:

{\overset{\cdot \cdot}{U u}}_{ab ab} = = {\overset{\cdot \cdot}{U u}}_{sab sab} + + {\overset{\cdot \cdot}{U u}}_{Lab lab}

{\overset{\cdot &Center Dot;}{U u}}_{bc bc} = = {\overset{\cdot \cdot}{U u}}_{sbc sbc} + + {\overset{\cdot \cdot}{U u}}_{Lbc Lbc}

{\overset{\cdot \cdot}{U u}}_{ca ca} = = {\overset{\cdot \cdot}{U u}}_{sca sca} + + {\overset{\cdot \cdot}{U u}}_{Lca Lca};;

Step 5: Distribution and control of link power

On the basis of determining the power of each line, the voltage of each chain link is distributed according to the ratio of the charging/discharging power of each chain link, that is, the power distribution according to the ratio is realized.

2. The two-stage equalization control method for a delta-connected cascaded energy storage system according to claim 1, wherein in the first step: in the chain energy storage system, each chain link is composed of a battery unit and a power unit , the battery unit is managed by the battery management system, and the power unit is controlled by the power conversion system controller as a part of the power conversion system, and the power conversion system controller regularly obtains the SOC state and SOH state of the battery unit corresponding to each power unit from the battery management system, The time interval is from 0.1s-10min.

3. The two-stage equalization control method for a delta-connected cascaded energy storage system according to claim 1, characterized in that, in the fifth step, specifically:

When charging, the voltages of ab, bc and ca three-wire links are distributed according to the ratio of Q _c(ab,n) , Q _{c(bc,n) and} Q _c(ca,n) as follows:

{U u}_{ab ab,, n no} = = \frac{{Q Q}_{c c ((ab ab,, n no))}}{N N \times \times {Q Q}_{c c,, ab ab}} \times \times {U u}_{ab ab}

{U u}_{bc bc,, n no} = = \frac{{Q Q}_{c c ((bc bc,, n no))}}{N N \times \times {Q Q}_{c c,, bc bc}} \times \times {U u}_{bc bc}

{U u}_{ca ca,, n no} = = \frac{{Q Q}_{c c ((ca ca,, n no))}}{N N \times \times {Q Q}_{c c,, ca ca}} \times \times {U u}_{ca ca}

During discharge, the voltages of ab, bc and ca three-wire links are distributed according to the ratio of Q _f(ab,n) , Q _{f(bc,n) and} Q _f(ca,n) as follows:

{U u}_{ab ab,, n no} = = \frac{{Q Q}_{f f ((ab ab,, n no))}}{N N \times \times {Q Q}_{f f,, ab ab}} \times \times {U u}_{ab ab}

{U u}_{bc bc,, n no} = = \frac{{Q Q}_{f f ((c c,, n no))}}{N N \times \times {Q Q}_{f f,, bc bc}} \times \times {U u}_{bc bc}

{U u}_{ca ca,, n no} = = \frac{{Q Q}_{f f ((ca ca,, n no))}}{N N \times \times {Q Q}_{f f,, ca ca}} \times \times {U u}_{ca ca}

In the formula, U _ab,n , U _bc,n , U _ca,n represent the AC side voltage of the nth chain link of the three wires ab, bc, ca respectively; the subscripts ab, bc, ca represent the three wires ab, bc, and ca , n represents the number of chain links in the line, and N represents the number of chain links in each line;

Controlling the voltage of each chain link controls the power ratio of each chain link and realizes the balance between chain links.