CN103532194A - Self-balance control strategy for battery SOC (State-of-Charge) in chain type energy storage system powered by independent batteries - Google Patents

Abstract

A self-balance control strategy for the battery SOC (State-of-Charge) in a chain type energy storage system powered by independent batteries belongs to the field of power electronic technologies. The self-balance control strategy is characterized in that the SOC of a battery pack is detected in real time, a phase-shift PWM (Pulse Width Modulation) control mode is adopted when the SOC of the battery pack is in a normal work state, an SHE (Selective Harmonic Elimination)-PWM control mode is automatically converted when the SOC of the battery pack reaches a certain degree of unbalance, the balance of the SOC is regulated through the utilization of differential charging and discharging, the phase-shift PWM control mode is automatically converted after SOC values are regulated to close numbers, and the batteries in different stages carry out same depth balance charging and discharging. The control strategy provided by the invention can effectively balance the difference of all battery modules and can be used for various chain type energy storage systems powered by the independent batteries. The availability ratio of the battery modules and the energy storage system is improved, and the service life of the batteries is effectively prolonged.

Description

Battery SOC Self Equilibrium Control strategy in the chain type energy-storage system of independent battery power supply

Technical field

The invention belongs to electric and electronic technical field, relate in particular to battery SOC Self Equilibrium Control strategy.

Background technology

The renewable and clean energy resource such as wind energy and solar energy has randomness and fluctuation, and the stability of interconnected electric power system and controllability have been brought to great challenge, and battery energy storage and power back-off technology can well address these problems.Whether battery energy storage system is independent according to power supply, is divided into the chain type energy-storage system of independent battery power supply and the chain type energy-storage system based on common DC bus.System based on common DC bus, has solved the constraint of Access Network voltage to battery serial number, is easy to modularization, can expand flexibly, but along with the increase of parallel module number, and the increase of interconnection line distance, interconnection line signal is easily interfered; Between modules, influence each other, when straight-through fault occurs an inverter leg, the disturbance meeting of battery affects the normal operation of other inversion module, and intermodule exists circulation to disturb.If remove the interconnection line between inverter, form independent battery electric power system, can well make up above-mentioned defect, and do not need the control signal of intermodule, can realize the electrical isolation of each module controls system, make system installation and maintenance easier to be quick, parallel running is more reliable, therefore becomes gradually new study hotspot.

Yet in the chain type energy-storage system of independent battery power supply, each inversion unit of homophase flows through identical electric current, and each battery module must discharge and recharge simultaneously.Therefore, the difference of the state-of-charge that each battery pack causes due to reasons such as production technology and uses (State Of Charge, SOC refer to the ratio of the capacity of battery pack residual capacity charged state complete with it) constantly expands in charge and discharge process.The normal range of operation of supposing battery SOC is 30% to 100%, and so, in charging process, when there being the SOC of battery module to rise in advance 100%, or while having the SOC of battery module to be down to 30% in advance in discharge process, whole battery energy storage system is just by out of service.Visible, the battery module that finishes the earliest to discharge and recharge will become the bottleneck factor that determines whole energy storage system capacity and availability factor, and the difference of each battery module SOC will seriously reduce the utilance of battery energy storage system, shortens the useful life of battery.

Herein for the unbalanced problem of each battery pack SOC in the chain type energy-storage system of independent battery power supply, a kind of Novel Control is proposed, detect in real time battery pack SOC state, battery pack SOC adopts phase-shift PWM controlled mode when normal operating conditions, when battery pack SOC reaches scarcely the degree of balance, automatically switch to particular harmonic and eliminate PWM(Selective Harmonic Elimination PWM, SHE-PWM) control mode, utilize the otherness of each battery pack SOC to discharge and recharge to carry out equilibrium and regulate, after adjustment SOC value is convergent, automatically switch to again phase-shift PWM controlled mode, the balance that makes each battery module carry out same depth discharges and recharges, thereby greatly improve availability factor and the power system capacity of whole chain type energy-storage system, effectively extend the useful life of battery pack and even whole energy-storage system.

Summary of the invention

The object of the invention is provides a kind of battery SOC Self Equilibrium Control strategy for the chain type energy-storage system of independent battery power supply, regulating cell group SOC makes it convergent, improves the availability factor of battery module and energy-storage system, extends battery, and harmonic carcellation, improve the quality of power supply.The invention is characterized in, described control strategy comprises the following steps:

Step (1), after energy-storage system starts, adopts phase-shift PWM controlled mode;

Step (2), when each battery pack SOC being detected and reach scarcely the degree of balance, automatically switches to SHE-PWM control mode;

Step (3), when adjusting to battery pack SOC when convergent, automatically switches to phase-shift PWM controlled mode.

Described battery SOC Self Equilibrium Control strategy, it is characterized in that: in described step (1), described system is that the power supply of independent battery group, isolated form half-bridge DC/DC converter and the combination of tandem type H bridge DC/AC converter form, AC directly accesses network system, by high-frequency PWM control mode, triggers H bridge.

Described battery SOC Self Equilibrium Control strategy, is characterized in that: in described step (2), and below meeting during two conditions simultaneously, the firing control of the tandem type H bridge IGBT of automatic switchover DC/AC converter:

Condition 1: the active power of output of energy-storage system meets controlled range

Under phase-shift PWM controlled mode, the total active power controlled range of default is [P _n, P _n], under SHE-PWM control mode, the total active power controlled range of system is

when energy-storage system adopts SHE-PWM control mode to carry out internal cell SOC Self Equilibrium Control, the active power of output of whole energy-storage system can be than reducing to some extent under normal operating mode;

Condition 2: battery pack SOC degree of unbalance meets adjustable extent

The actual degree of unbalance ε of battery pack SOC is:

$\mathrm{\ϵ}=\sqrt{{({\mathrm{SOC}}_1-\stackrel{\‾}{\mathrm{SOC}})}^2+{({\mathrm{SOC}}_2-\stackrel{\‾}{\mathrm{SOC}})}^2+\·\·\·+{({\mathrm{SOC}}_n-\stackrel{\‾}{\mathrm{SOC}})}^2}=\sqrt{\underset{k=1}{\overset{n}{\mathrm{\Σ}}}{({\mathrm{SOC}}_k-\stackrel{\‾}{\mathrm{SOC}})}^2}$

Wherein $\stackrel{\&OverBar;}{\mathrm{SOC}}=\frac{{\mathrm{<figure-callout\; id="1"\; label="SOC"\; filenames="HDA0000397758700000012.png,HDA0000397758700000042.png"\; state="\{\{state\}\}">SOC</figure-callout>}}_1+{\mathrm{SOC}}_2+\&CenterDot;\&CenterDot;\&CenterDot;+{\mathrm{SOC}}_n}{n}=\frac{\underset{k=1}{\overset{n}{\mathrm{\&Sigma;}}}{\mathrm{SOC}}_k}{n},$ System cascade number is n, SOC _kthe SOC value that represents k level battery;

In meeting the total active power controlled range of system, when degree of unbalance ε>=ε of battery pack SOC being detected _maxtime, by high frequency phase-shift PWM controlled mode, automatically switch to SHE-PWM control mode and carry out the balanced adjusting of SOC; Wherein: ε _maxfor default battery pack SOC degree of unbalance threshold value, its large I is got different numerical value according to the performance of different batteries and parameter.

Described battery SOC Self Equilibrium Control strategy, it is characterized in that: in described step (2), SHE-PWM control mode adopts the odd function pulse of 1/2 periodic symmetry, and operating frequency is 50Hz, by Newton iteration method solution SHE-PWM harmonic carcellation Nonlinear System of Equations, by gained switch angle [alpha] _kadopt piecewise function α=f (M with which amplitude modulation degree Ma _a) linear fit; By in real time dynamic Ma value, obtain Real-Time Switch angle, then according to battery pack SOC value dynamic assignment, arrive H bridge switch pipe impulse generators at different levels, produce required triggering signal.

Described battery SOC Self Equilibrium Control strategy, is characterized in that: in described step (3), and when battery pack SOC being detected when convergent, i.e. battery pack SOC degree of unbalance ε≤ε _min, by SHE-PWM control mode, automatically switch to high frequency phase-shift PWM controlled mode, finish unbalanced control mode; Wherein: ε _minfor default battery pack SOC degree of balance threshold value, its large I is got different numerical value according to the performance of different batteries and parameter.

Tool of the present invention has the following advantages:

1) SHE-PWM control mode adopts power frequency 50Hz, and switching loss is little, has eliminated the harmonic wave of specific times, has improved the quality of power supply of energy-storage system; The method of employing matched curve realizes the real-time online of SHE-PWM and controls, and has solved traditional SHE-PWM off-line look-up method and has taken up room greatly, the problem that computing time is long.

2) utilize two kinds of control methods of phase-shift PWM and SHE-PWM, according to battery pack different operating state, realize automatic switching mode, improved the availability factor of battery and energy-storage system, solve the unbalanced problem to capacity limits of battery SOC, and effectively extended the life-span of battery module.

Accompanying drawing explanation

Fig. 1 is battery SOC Self Equilibrium Control strategic process figure of the present invention.

Fig. 2 is independent battery chain type (n=3) inversion system A phase structure figure.

Fig. 3 is SHE-PWM1/2 periodic symmetry pulse schematic diagram.

Fig. 4 is phase-shift PWM output voltage waveform.

Fig. 5 is SHE-PWM output voltage waveform.

Fig. 6 is phase-shift PWM harmonic wave of output voltage fft analysis figure.

Fig. 7 is SHE-PWM harmonic wave of output voltage fft analysis figure.

Fig. 8 is that the electric discharge of battery SOC forward is from equilibrium figures.

Fig. 9 is that battery SOC reverse charging is from equilibrium figures.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in more detail.

As shown in Figure 2, independent battery chain type (n=3) energy-storage system of take is example, the validity of the battery SOC Self Equilibrium Control strategy that checking the present invention proposes.This system DC side adopts lithium battery, and (battery rated voltage is Un=60V, rated capacity is 10Ah), DC/DC inverter adopts isolated form half-bridge structure, and DC/AC inverter adopts full bridge structure, and in figure, Li is power filter inductance, switching device S1-S8, dividing potential drop capacitor C 2-C5, DC bus capacitor C1, energy storage inductor Ls, filter inductance Lo1 and Lo2, output voltage is Uo.The given power instruction P of system _ref=3Kw=0.5P _n, after whole device starts, DC/DC side adopts duty ratio and phase shifting angle to control, and DC/AC side adopts phase-shift PWM triggering mode, and frequency is 2000Hz, and the staircase voltage waveform of generation is as shown in Figure 4.

By SOC curve (being the front operating state of 1s) the known phase-shift PWM method that is parallel to each other, make each battery with identical speed electric discharge, the SOC that three batteries detected when 1s is respectively SOC ₁=0.725, SOC ₂=0.72, SOC ₃=0.713.

Calculate the now mean value of three SOC

$\stackrel{\&OverBar;}{\mathrm{SOC}}=\frac{{\mathrm{<figure-callout\; id="1"\; label="SOC"\; filenames="HDA0000397758700000012.png,HDA0000397758700000042.png"\; state="\{\{state\}\}">SOC</figure-callout>}}_1+{\mathrm{SOC}}_2+{\mathrm{SOC}}_3}{3}=0.7193$

Battery pack SOC degree of unbalance is

$\mathrm{\&epsiv;}=\sqrt{{({\mathrm{SOC}}_1-\stackrel{\&OverBar;}{\mathrm{SOC}})}^2+{({\mathrm{SOC}}_2-\stackrel{\&OverBar;}{\mathrm{SOC}})}^2+{({\mathrm{SOC}}_3-\stackrel{\&OverBar;}{\mathrm{SOC}})}^2}=0.853$

Now system active power meets adjustable extent

battery pack SOC degree of unbalance ε>=ε _max, be switched to SHE-PWM control mode and carry out regulating from balanced.

SHE-PWM control mode adopts the odd function pulse of 1/2 periodic symmetry, and operating frequency is 50Hz, switching tube within each cycle a switch once, the concrete mode principle of switching tube trigger impulse as shown in Figure 3, α wherein _kbe k level H bridge switch angle, A mutually k level H bridge output voltage is:

Due to the hree-phase symmetry of network system own and inverter Y-connection mode, can eliminate 3 times and 3 multiple subharmonic, by formula (3), can be found out that 1/2 cyclic symmetry of SHE-PWM modulator approach eliminated even-order harmonic, therefore only need to eliminate 5,7 subharmonic, and reach ac output voltage amplitude V _om, obtain the Nonlinear System of Equations that 3 grades of H bridge switch angles solve and be:

$\left\{\begin{array}{c}\cos a_1+\cos a_2+\cos a_3=M_a\\ \cos {5a}_1+\cos {5a}_2+\cos {5a}_3=0\\ \cos {7a}_1+\cos {7a}_2+\cos {7a}_3=0\end{array}\right.$

Wherein: which amplitude modulation degree

By Newton iteration method, solve above-mentioned equation group, then carry out piecewise function matching, result is:

(1) first order H bridge angle

${\mathrm{\&alpha;}}_1\left\{\begin{array}{cc}-111.4\&times;{\mathrm{Ma}}^3+487.8\&times;{\mathrm{Ma}}^2-692.9\&times;{\mathrm{<figure-callout\; id="1"\; label="Ma"\; filenames="HDA0000397758700000012.png,HDA0000397758700000042.png"\; state="\{\{state\}\}">Ma</figure-callout>}}^1+367..3& (1.2\&le;\mathrm{Ma}<1.8)\\ 37.03\&times;{\mathrm{Ma}}^3-182.9\&times;{\mathrm{Ma}}^2+237.2\&times;{\mathrm{Ma}}^1-16.19& (1.8\&le;\mathrm{Ma}-2.5)\end{array}\right.$

(2) second level H bridge angle

${\mathrm{\&alpha;}}_2=\left\{\begin{array}{cc}72.53\&times;{\mathrm{Ma}}^3-284.9\&times;{\mathrm{Ma}}^2+341.6\&times;{\mathrm{Ma}}^1-59.91& (1.2\&le;\mathrm{Ma}<1.7)\\ 6.555\&times;{\mathrm{<figure-callout\; id="1"\; label="Ma"\; filenames="HDA0000397758700000012.png,HDA0000397758700000042.png"\; state="\{\{state\}\}">Ma</figure-callout>}}^1+42.84& (1.7\&le;\mathrm{Ma}<1.9)\\ -23.12\&times;{\mathrm{Ma}}^3+143.3\&times;{\mathrm{Ma}}^2-346\&times;{\mathrm{<figure-callout\; id="1"\; label="Ma"\; filenames="HDA0000397758700000012.png,HDA0000397758700000042.png"\; state="\{\{state\}\}">Ma</figure-callout>}}^1+353& (1.9\&le;\mathrm{Ma}\&le;2.5)\end{array}\right.$

(3) third level H bridge angle

$a_3=\left\{\begin{array}{c}-2.93\&times;{\mathrm{Ma}}^3-11.95\&times;{\mathrm{Ma}}^2+18.94\&times;{\mathrm{<figure-callout\; id="1"\; label="Ma"\; filenames="HDA0000397758700000012.png,HDA0000397758700000042.png"\; state="\{\{state\}\}">Ma</figure-callout>}}^1+88.45(1.2\&le;\mathrm{Ma}<1.9)\\ 8.332\&times;{\mathrm{Ma}}^3-101.2\&times;{\mathrm{Ma}}^2+304.8\&times;{\mathrm{Ma}}^1-206.7(1.9\&le;\mathrm{Ma}\&le;2.5)\end{array}\right.$

While stablizing, M _ain=2.17 substitution fitting functions, can obtain every grade of H bridge trigger angle:

α ₁=15.791°，α ₂=40.56°，α ₃=63.381°

The switching tube trigger impulse that produces corresponding A phase according to the trigger angle obtaining, moves 120 ° and 240 ° by A phase trigger impulse popin, obtains the trigger impulse of B phase, C phase H bridge switch pipe.A exports staircase voltage as shown in Figure 5 mutually, and the output voltage under two kinds of triggering modes is carried out to Fourier decomposition, analyzes its harmonic content, as shown in Figure 6 and Figure 7.

The power that the H bridge of the different angles of flow transmits is different:

Under forward discharge condition, according to the difference of each battery module of homophase SOC size, select the angle of flow of its corresponding H bridge, the selection first order H bridge of battery SOC maximum, the velocity of discharge is the fastest, SOC is declined the fastest; The selection third level H bridge of battery SOC minimum, the velocity of discharge is the slowest, SOC is declined the slowest; Carry out this otherness electric discharge, make the initial SOC of all differences in time t, drop to same value, realized regulating from balanced of each battery module SOC; When degree of unbalance ε≤ε being detected _min, complete Self Equilibrium Control, automatically switch to phase-shift PWM controlled mode, all batteries discharge with degree, and simulation result is as shown in Figure 8.

SOC ₁-ΔSOC ₁t=SOC ₂-ΔSOC ₂t=SOC ₃-ΔSOC ₃t=SOC

In like manner, can realize battery pack reverse charging Self Equilibrium Control, result as shown in Figure 9.

The present invention, at the battery SOC Self Equilibrium Control strategy of chain type (3 grades) energy-storage system that is applied to for example independent battery power supply described in specification and claims, should be understood that, the invention is not restricted to above embodiment, can also have a lot of distortion.All distortion that those of ordinary skill in the art can directly derive or associate from content disclosed by the invention, all should think protection scope of the present invention.

Claims (5)

1. battery SOC Self Equilibrium Control strategy in the chain type energy-storage system of independent battery power supply, is characterized in that, said method comprising the steps of:

Step (1), after energy-storage system starts, adopts phase-shift PWM controlled mode;

Step (2), when battery pack SOC being detected and reach scarcely the degree of balance, automatically switches to SHE-PWM control mode;

Step (3), when adjusting to battery pack SOC when convergent, automatically switches to phase-shift PWM controlled mode.

2. battery SOC Self Equilibrium Control strategy according to claim 1, it is characterized in that: in described step (1), described system is that the power supply of independent battery group, isolated form half-bridge DC/DC converter and the combination of tandem type H bridge DC/AC converter form, AC directly accesses network system, by high-frequency PWM control mode, triggers H bridge.

3. battery SOC Self Equilibrium Control strategy according to claim 1, is characterized in that: in described step (2), and below meeting during two conditions simultaneously, automatic switchover control mode:

Condition 1: the active power of output of energy-storage system meets controlled range

Under phase-shift PWM controlled mode, the total active power controlled range of default is [P _n, P _n], under SHE-PWM control mode, the total active power controlled range of system is

when energy-storage system adopts SHE-PWM control strategy to carry out inner SOC Self Equilibrium Control, total active power of system can be than reducing to some extent under normal operating mode;

Condition 2: battery pack SOC degree of unbalance meets adjustable extent

The actual degree of unbalance ε of battery pack SOC is:

$\mathrm{\&epsiv;}=\sqrt{{({\mathrm{SOC}}_1-\stackrel{\&OverBar;}{\mathrm{SOC}})}^2+{({\mathrm{SOC}}_2-\stackrel{\&OverBar;}{\mathrm{SOC}})}^2+\&CenterDot;\&CenterDot;\&CenterDot;+{({\mathrm{SOC}}_n-\stackrel{\&OverBar;}{\mathrm{SOC}})}^2}=\sqrt{\underset{k=1}{\overset{n}{\mathrm{\&Sigma;}}}{({\mathrm{SOC}}_k-\stackrel{\&OverBar;}{\mathrm{SOC}})}^2}$

Wherein $\stackrel{\&OverBar;}{\mathrm{SOC}}=\frac{{\mathrm{SOC}}_1+{\mathrm{SOC}}_2+\&CenterDot;\&CenterDot;\&CenterDot;+{\mathrm{SOC}}_n}{n}=\frac{\underset{k=1}{\overset{n}{\mathrm{\&Sigma;}}}{\mathrm{SOC}}_k}{n},$ System cascade number is n, SOC _kthe state-of-charge (SOC:State Of Charge refers to the ratio of the capacity of battery pack residual capacity charged state complete with it) that represents k level battery;

In meeting the total active power controlled range of system, when degree of unbalance ε>=ε of battery pack SOC being detected _maxtime, by high frequency phase-shift PWM controlled mode, automatically switch to SHE-PWM control mode and carry out the balanced adjusting of SOC; Wherein: ε _maxfor default battery pack SOC degree of unbalance threshold value, its large I is got different numerical value according to the performance of different batteries and parameter.

4. battery SOC Self Equilibrium Control strategy according to claim 1, it is characterized in that: in described step (2), SHE-PWM control mode adopts the odd function pulse of 1/2 periodic symmetry, operating frequency is 50Hz, by Newton iteration method solution SHE-PWM harmonic carcellation Nonlinear System of Equations, by gained switch angle [alpha] _kadopt piecewise function α=f (M with which amplitude modulation degree Ma _a) linear fit; By dynamic Ma value, obtain Real-Time Switch angle, then according to battery pack SOC value dynamic assignment, arrive H bridge switch pipe impulse generators at different levels, produce required triggering signal.

5. battery SOC Self Equilibrium Control strategy according to claim 1, is characterized in that: in described step (3), and when battery pack SOC being detected when convergent, i.e. battery pack SOC degree of unbalance ε≤ε _min, by SHE-PWM control mode, automatically switch to high frequency phase-shift PWM controlled mode, finish unbalanced control mode; Wherein: ε _minfor default battery pack SOC degree of balance threshold value, its large I is got different numerical value according to the performance of different batteries and parameter.

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