CN105676131A - Vanadium cell dynamic state of charge (SOC<d>)estimation method based on charging/discharging energy efficiency - Google Patents

Abstract

Based on the estimation method of dynamic SOC _d of vanadium battery based on charge and discharge energy efficiency, the battery work is divided into the charging process and the discharging process, and the battery energy is divided into the charging side energy and the discharging side energy accordingly; the charging and discharging efficiency of the battery under different currents will be The charge side energy is mapped to the discharge side energy to obtain the static SOC _s of the battery; the discharge capacity of the reference load is used as the reference energy, and the dynamic SOC _d of the battery under this load is estimated according to the static SOC _s and the discharge capacity of the battery under different loads. The specific steps It is: (1) use different currents to charge the battery separately, obtain the efficiency of the battery under different currents, and then obtain the static SOCs of the battery; (2) use different loads to discharge the battery, and obtain the function of the energy released by different loads relative to the reference load relationship, and then obtain the dynamic SOC _d of the battery.

Description

A dynamic battery state-of-charge estimation method for vanadium batteries based on charge-discharge energy efficiency

technical field

The invention relates to a method for estimating the SOC (battery state of charge) of an all-vanadium redox flow battery, which is mainly used in a DC micro-grid. The energy on the charging side of the battery is mapped to the discharging side through the efficiency relationship to obtain the static SOC _s of the battery. The discharge capacity is used as the reference energy, and the dynamic SOC _d of the battery under this load is estimated according to the static SOC _s and the discharge capacity of the battery under different loads.

Background technique

Energy and the environment are two major problems facing the world today, and the emergence of microgrids provides new ideas for solving these two problems. Microgrid is a small-capacity power supply system composed of distributed power generation equipment, energy storage equipment, loads and related control and protection equipment. As an important part of the microgrid, energy storage devices play an important role in smoothing the power and energy fluctuations of the microgrid system, improving the stability and dispatchability of the system, and improving the power quality. All-vanadium redox flow batteries have been used more and more because of their advantages such as environmental friendliness, long cycle life, safety and reliability, and large-scale energy storage.

SOC estimation is one of the core contents of the battery management system research, which directly affects the power control and energy management of the battery. SOC research needs to be able to reflect two aspects: ① determine whether the battery can continue to work, that is, the research of the static state of charge SOC _s ; ② reflect the time for the battery to maintain the current working state, that is, the research of the dynamic state of charge SOC _d .

The application of all-vanadium redox flow batteries in microgrids is mainly to stabilize the power and energy fluctuations of the system, improve the stability and dispatchability of the system, and absorb excess energy and power when the system energy and power are redundant. Fills the system's energy and power gaps when missing. Therefore, energy storage devices are always in a charging or discharging state, and its research can also be divided into two parts: charging and discharging. At present, the research on the discharge part mostly adopts constant current discharge; while charging, the constant current and constant voltage mode is mostly used, and the constant current mode is used to charge to a certain voltage, and then the constant current mode is used to charge until the current drops to a certain value. In the DC microgrid, the working conditions of the battery are more complicated, the current changes momentarily during charging, and DC/DC is often needed when discharging, and factors such as charge and discharge rate, temperature, cycle times, and SOH of the battery will also affect The accuracy of SOC estimation, so the method proposed by the present invention is more suitable for the operating conditions of the battery in the microgrid.

Invention content:

The object of the present invention is to propose a method suitable for SOC estimation of all-vanadium redox flow batteries according to the application conditions of vanadium batteries in DC microgrids.

The technical solution of the present invention is: based on the method for estimating the dynamic SOC _d of a vanadium battery based on charge and discharge energy efficiency, the battery work is divided into the charging process and the discharging process, and the battery energy is divided into the charging side energy and the discharging side energy accordingly; Under the charging and discharging efficiency of the battery, the charging side energy is mapped to the discharging side energy to obtain the static SOC _s of the battery; the discharge capacity of the reference load is used as the reference energy, and the battery under this load is estimated according to the static SOC _s and the discharge capacity of the battery under different loads The dynamic SOC _d of the specific steps are:

(1) Use different currents to charge the battery separately, obtain the efficiency of the battery under different currents, and then obtain the static SOCs of the battery;

1) Start the vanadium battery, use the charger to charge the vanadium battery in constant current and constant voltage mode until it is fully charged, and keep the vanadium battery in a rotating hot standby state; let it stand for 10 minutes, and then discharge it at 1C with the reference load until it reaches the discharge cut-off When the condition is met, the discharge is stopped, and the battery charge reference energy W _cn and discharge reference energy W _dn are obtained.

2) Stand still for 10 minutes, and then charge with 5-8 charging currents (such as 30A, 40A, 50A, 60A, 70A, 80A) at different currents of 0.1-1C. When the voltage reaches the upper limit, the current starts to decrease Stop charging to obtain the charging energy W _c of the battery under different currents; stand still for 10 minutes, then discharge at 1C with a reference load, stop discharging until the discharge cut-off condition is reached, and obtain the discharging energy W _d of the battery under different currents;

3) Use formula (1) to obtain the efficiency of the battery under different currents of the battery:

$\mathrm{<span\; class="notranslate">\; \&eta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}\mathrm{<span\; class="notranslate">\; \%</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Fit the battery efficiency η(i) under different currents to obtain the function of battery efficiency under different currents:

η=f(i(t))(2)

4) Calculate the charging energy of the battery per unit time as:

W _c (t)=u(t)i(t)Δt(3)

Mapped to the discharge side as:

W _d (t) = f(i(t)) u(t)i(t)Δt(4)

The energy mapped to the discharge side during the charging process of the battery for a period of time is obtained as:

${\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

The static SOCs of the battery at this time can be calculated as:

${\mathrm{<span\; class="notranslate">\; SOC</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}\mathrm{<span\; class="notranslate">\; \%</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

(2) Using different loads to discharge the battery, obtain the functional relationship of the energy released by different loads relative to the reference load, and then obtain the dynamic SOC _d of the battery;

1) Start the vanadium battery, use the charger to charge the vanadium battery in the constant current and constant voltage mode until it is fully charged, and keep the vanadium battery in a rotating hot standby state;

2) Stand still for 10 minutes, and then discharge with 5-8 discharge currents (0.6kW, 1.2kW, 1.8kW, 2.4kW, 3.0kW) at 0.1-1C under different loads until the discharge cut-off condition is reached Stop discharging, and obtain the discharge energy W _dR of different loads; perform data fitting on the discharge energy under different loads, and obtain the function expression f(R) of the battery discharge energy under different loads;

a) The remaining energy of the battery at the end of the battery discharge with the load R can be calculated by formula (7):

W _R ＝W _dn -f(R)(7)

Calculate the energy stored in the battery at the current moment according to the static SOC _s of the battery:

W _r =W _dn SOC _s (8)

Then, the energy released at the moment of discharging with a certain load R in the current state of the battery can be obtained:

ΔW＝W _r -W _R (9)

It can be obtained that the dynamic SOC _d of the battery when it is discharged with the load R at this time is:

${\mathrm{<span\; class="notranslate">\; SOC</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; W</span>}}{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; R</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

Beneficial effects of the present invention: the present invention is applicable to the SOC estimation method of all-vanadium redox flow batteries in DC microgrids, which divides battery work into charging process and discharging process, and correspondingly divides battery energy into charging side energy and discharging side energy. The charge-side energy is mapped to the discharge-side energy through the charge-discharge efficiency of the battery under different currents, and the static SOC _s of the battery is obtained; the discharge capacity of the reference load is used as the reference energy, and the battery is estimated according to the static SOC _s and the discharge capacity of the battery under different loads. Dynamic SOC _d at this load.

Description of drawings:

Figure 1 All vanadium redox flow battery test platform;

Figure 2 Static SOC _s estimation results;

Figure 3 Dynamic SOC _d estimation results.

detailed description:

The all-vanadium redox flow battery test platform is shown in Figure 1. The battery adopts a 3kW/3kWh all-vanadium redox flow battery developed in cooperation with Shanghai Shenli Technology Co., Ltd. The working voltage range is 39-52V, and the discharge cut-off voltage is 39V. The upper computer detection and data acquisition system can realize real-time acquisition of voltage and current, and the acquisition accuracy is 0.1V and 0.1A respectively. The DC/DC converter adopts Shanghai Wenkai Power Equipment Co., Ltd. WYJ-3000W48V converter, and the output voltage is 0-48V. The load is a 48V light board, including 60 light bulbs with a specification of 48V/60W, which are directly connected in parallel through a switch.

1. Charge the battery with different currents to obtain the efficiency of the battery at different currents, and then obtain the static SOCs of the battery.

1) Start the vanadium battery, use the charger to charge the vanadium battery in constant current and constant voltage mode until it is fully charged, and keep the vanadium battery in a rotating hot standby state; let it stand for 10 minutes, and then discharge it with a reference load of 0.6kW until it reaches the discharge Discharging is stopped when the cut-off condition is reached, and the battery charging reference energy W _cn and discharging reference energy W _dn are obtained.

2) Stand still for 10 minutes, then charge with different currents (30A, 40A, 50A, 60A, 70A, 80A), stop charging when the voltage reaches the upper limit and the current starts to decrease, and get the charging energy of the battery under different currents W _c ; stand still for 10 minutes, then discharge at 0.6kW, stop discharging until reaching the discharge cut-off condition, and obtain the discharge energy W _d of the battery under different currents.

3) Equation (1) can be used to obtain the efficiency of the battery under different currents of the battery:

$\mathrm{<span\; class="notranslate">\; \&eta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}\mathrm{<span\; class="notranslate">\; \%</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Fit the battery efficiency η(i) under different currents to obtain the function of battery efficiency under different currents:

η=f(i(t))(2)

4) Calculate the charging energy of the battery per unit time as:

W _c (t)=u(t)i(t)Δt(3)

Mapped to the discharge side as:

W _d (t) = f(i(t)) u(t)i(t)Δt(4)

The energy mapped to the discharge side during the charging process of the battery over a period of time can be obtained as:

${\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

The static SOCs of the battery at this time can be calculated as:

${\mathrm{<span\; class="notranslate">\; SOC</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}\mathrm{<span\; class="notranslate">\; \%</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Figure 2 shows the estimation results of the static SOC _s of the all-vanadium redox flow battery.

2. Use different loads to discharge the battery, obtain the functional relationship of the energy released by different loads relative to the reference load, and then obtain the dynamic SOC _d of the battery.

a) Start the vanadium battery, use the charger to charge the vanadium battery in a constant current and constant voltage mode until it is fully charged, and keep the vanadium battery in a rotating hot standby state;

b) Stand still for 10 minutes, then discharge with different loads (0.6kW, 1.2kW, 1.8kW, 2.4kW, 3.0kW) respectively, and stop discharging when the discharge cut-off condition is reached, and obtain the discharge energy W _dR of different loads; Perform data fitting on the discharge energy under different loads to obtain the function expression f(R) of the battery discharge energy under different loads;

c) The remaining energy of the battery at the end of the battery discharge with the load R can be calculated by formula (7):

W _R ＝W _dn -f(R)(7)

Calculate the energy stored in the battery at the current moment according to the static SOC _s of the battery:

W _r =W _dn SOC _s (8)

Then, the energy released at the moment of discharging with a certain load R in the current state of the battery can be obtained:

ΔW＝W _r -W _R (9)

It can be obtained that the dynamic SOC _d of the battery when it is discharged with the load R at this time is:

${\mathrm{<span\; class="notranslate">\; SOC</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; W</span>}}{{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; R</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

Figure 3 shows the estimation results of the dynamic SOC _d of the vanadium redox flow battery.

The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and can also be made without departing from the gist of the present invention within the scope of knowledge possessed by those of ordinary skill in the art. Variations.

Claims (1)

1. based on the dynamic SOC of the vanadium cell of charge-discharge energy efficiency_dEvaluation method, is characterized in that being divided into charging process and discharge process by battery operated, the energy content of battery is divided into charged side energy and discharge side energy accordingly; By the efficiency for charge-discharge of battery under different electric currents, charged side energy is mapped as discharge side energy, it is thus achieved that battery static state SOC_s; Using baseline load discharge capacity as reference energy, according to static SOC_sWith the dynamic SOC under this load of the discharge capacity estimation battery of battery under different loads_d, concretely comprise the following steps:

(1) adopt different electric current respectively battery to be charged, it is thus achieved that the efficiency of battery under different electric currents, and then obtain battery static state SOCs;

1) starting vanadium cell, use charger to adopt constant current constant voltage pattern that vanadium cell is charged, until being full of, making vanadium cell keep rotating hot stand-by duty; Stand 10 minutes, then carry out 1C electric discharge with reference load, until it reaches stop electric discharge during electric discharge cut-off condition, obtain battery charge reference energy W_cnWith electric discharge reference energy W_dn。

2) stand 10 minutes, then it is charged with different electric current 0.1-1C 5-8 charging current (30A, 40A, 50A, 60A, 70A, 80A) altogether respectively, when voltage reaches the moment stopping charging that upper limit current starts to reduce, obtain the rechargeable energy W under battery difference electric current_c; Stand 10 minutes, then carry out 1C electric discharge with reference load, until it reaches electric discharge cut-off condition stops electric discharge, obtains the discharge energy W under the different electric currents of battery_d;

3) efficiency of battery under battery difference electric current is tried to achieve by formula (1):

By battery efficiency η (i) matching under different electric currents, obtain the function of battery efficiency under different electric current:

η=f (i (t)) (2)

4) calculate and obtain battery charging power in the unit interval and be:

(3)

W_c(t)=u (t) i (t) Δ t

Being mapped to discharge side is:

(4)

W_d(t)=f (i (t)) u (t) i (t) Δ t

Integration obtains the energy being mapped to discharge side in a period of time in battery charging process:

Can be calculated battery static SOCs now is:

(2) adopt different loads that battery is discharged, it is thus achieved that the functional relationship of different loads releasable energy relative reference load, and then obtain the dynamic SOC of battery_d;

1) starting vanadium cell, use charger to adopt constant current constant voltage pattern that vanadium cell is charged, until being full of, making vanadium cell keep rotating hot stand-by duty;

2) stand 10 minutes, then discharge with different load 0.1-1C 5-8 discharge current (0.6kW, 1.2kW, 1.8kW, 2.4kW, 3.0kW) altogether respectively, until stopping electric discharge when reaching electric discharge cut-off condition, it is thus achieved that unequally loaded discharge energy W_dR; Discharge energy under different loads is carried out data fitting, obtains the function expression f (R) of battery discharging energy under different loads;

3) dump energy of battery when obtaining battery with load R electric discharge end can be calculated by through type (7):

W_R=W_dn-f(R)(7)

According to battery static state SOC_sCalculate and obtain the energy that battery current time stores:

W_r=W_dn·SOC_s(8)

It is then possible to adopt the energy that a certain load R discharging time is released when obtaining battery the present situation:

Δ W=W_r-W_R(9)

Dynamic SOC when battery now discharges can be obtained with load R_dFor:

。