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# Introduction to Calculation Method of UPS Reserve Battery Capacity

The battery is an important part of the UPS system. Its advantages and disadvantages are directly related to the reliability of the entire UPS system, and its capacity is also critical to the normal operation of the UPS system. The battery capacity has caused waste of investment. The capacity is small and does not meet the UPS backup time, causing safety incidents, which will also seriously affect battery performance and life due to the battery discharge ratio.

Therefore, several commonly used battery capacity calculation methods are introduced for reference.

First, constant power method (check form method)

The method is an embodiment of energy conservation law, and the power supplied by the battery is equal to the latter slightly greater than the load consumption power.

W load≤W battery, p load≤P battery, p load = {P, (va)×PF} /ηP battery = constant power data for battery actual test; P load is the total power provided by the battery pack; p (va) is UPS nominal capacity (VA); PF is the UPS power factor;ηFor the inverter conversion efficiency; PNC is the power provided by each Cell; n is the number of batteries configured in the machine; n is the number of cell cells Cell; VMIN is terminated by the battery cell. The specific calculation steps are as follows:

P load = {p (va)×PF} /η

PNC = p load / (n×you)

In the constant power discharge parameter table under the VMIN provided by the manufacturer, find the type battery corresponding to the P battery equal to or slightly larger than the power value of the PNC. If the power value p battery listed in the table is less than the PNC. The requirements can be achieved in parallel in parallel batteries. Constant power method (check form method) is the most common method of UPS battery capacity calculation. The determination of battery capacity and model is based on the actual test data of the corresponding model, and the battery discharge power data is limited, and the battery at all discharge time cannot be met. Capacity calculation. Different voltage grade batteries and the same voltage level Different capacity batteries have no linear relationship with battery capacity values, so different voltage grades and capacity are not simple to configure, and need to be configured in strict accordance with the constant power provided. Different brand battery products have different performance, and the discharge parameters are different, and different brands of batteries that consider their capacity can not be interchangeable.

Battery constant power data comes from new battery test data, and the constant power method (check form method) does not consider the depreciation of the battery and the temperature change, and take care of the UPS battery operating environment stable, and the UPS load is 80 for a long time By the following runtime is running.

Second, the estimation method

This method is to reflect the concept of power formulas and battery capacity. Definition according to YD / T799-2002, battery capacity (AH) refers to a constant current (0.1c10) A, which is available at a given time pointing voltage (1.80 V), and the battery can be provided at a given time pointing voltage (1.80 V). Products with continuous discharge time (10h) H (i×T).

The power conventional calculation formula is W = UIT, P = UI.

According to the determined UPS brand and model, the lowest voltage of the battery pack is known.

I battery = W battery / (U battery×T) = p battery / U battery

C10 = i battery / KCHC10 battery 10 hour capacity

KCH capacity converting coefficient (1 / h) - DCF126 series of battery different discharge time different discharge termination voltage, battery capacity conversion table (25 ° C).

In the UPS system, most of the case load capacity remains unchanged, and the battery pack gradually decreases as the discharge time is gradually increased, according to P = UI, the battery pack discharge current is gradually increased. For the convenience of calculation, the maximum operating current of the battery pack is the calculation data.

The specific calculation is as follows:

The IMAX battery pack provides maximum current

UMIN battery pack bottom working voltage value

IMAX = {P (VA)×PF} /η×Umin)

C10 = I / KC

According to the calculation formula, since the lowest operating voltage value of the battery pack is employed, it will result in a substantial capacity of the requirements of the battery pack. This is because the discharge current required when the battery is just discharged is significantly less than IMAX. According to current experience, the C10 value can be calculated based on the C10 value is multiplied by 0.75 correction factor.

Third, power method

This method is more comprehensively considering the battery state during the entire use of the estimation method, and the battery capacity can be accurately calculated when the battery is changed in the battery. The specific calculation method is as follows:

I = (p (va)×PF) / U

Qi≥Kit / H (1 + A (T-25))

I battery set current q battery pack capacity (AH)

K battery insurance factor, take 1.25T battery discharge time

H battery discharge coefficient, U battery discharge time inverting

Output voltage (V) (V) (when the cell voltage is 1.85V) A battery temperature coefficient (1 / ° C) When discharge hour ratio≥10 o'clock, take 0.006, when 1≤Discharge rate<10时，取0.008，当放电率<1时，取0.01。

T active battery is the lowest ambient temperature value, where there is a heating device, press 15 ° C, when there is no heating equipment, press 5 ° C. This method is compared to considering environmental factors and battery capacity attenuation, and the UPS full-load usage is large when the use of this method is used to calculate the battery capacity. 80kVAUPS for 30 min in rear preparation time as an example, use a brand DCF126-12 series battery for calculation.

80kvaups DC termination voltage is 300V and u critical = 300V, DC voltage is 348V battery pack to use 29 12V batteries, so n = 29, n = 6, U terminal pressure = 1.75VUPS power factor PF = 0.8, inverter conversion effectivenessη= 0.95.

(1) Constant power method

P (w) = {p (va)×PF} /η= {80×1000×0.8} /0.95=67368.4 (w)

PNC = p (w) / (n×n) = 67368.4 / (29×6) = 387.2 (W)

Check DCF126-12 Series Battery Constant Power Table (Table 1) It is understood that the DCF126-12 / 120 battery termination voltage is 1.75V provides a power of 217W.

Number of battery packs = 387.2 / 217 = 1.78

That is: 2 groups of 120ah, 58 sections 120ah batteries.

(2) Estimation method

IMAX = {P (VA)×PF} /η×Umin) = (80×1000×0.8) / (0.95×300) = 224.6 (a)

When the DCF126 series battery different discharge time is different discharge termination voltage, the capacity conversion table (25 ° C) of the battery (Table 2) can be known to KCH = 0.98.

C10 = I / KCH = 224.6A / 0.98 = 229 (AH)

According to the experience, the calculation can be corrected on the basis of the calculation. Therefore, the number of battery needs is required

229×0.75 = 172 (AH). That is: Optional 1 group 172h battery can meet the use of the load, according to the design specifications of the brand 12V series battery capacity, 1 set of 12v200ah batteries or 2 groups of 12V100AH ​​batteries, typographic 200ah batteries, or 58-section 100ah batteries.

(3) Power method

IMAX = {P (VA)×PF} /η×U critical) = (80×1000×0.8) / (0.95×300) = 224.6 (a)

Qi≥Kit / {hηK (1 + A (T-25))}

≥1.25×224.6×0.5 / {0.4×0.8 (1 + A (T-25))}

≥438ah

The capacity converter of the 30min battery is 0.4, (reference the brand DCF126 battery Different discharge time limit, the battery capacity conversion table), the temperature is 25 ° C.

Due to the actual discharge process, the discharge current is obviously less than IMAX, according to the experience, and can be corrected in the calculation based on the use of experience. Therefore, the number of batteries is required to be 438×0.75 = 328.5 (AH) That is to: select 3 groups of 120ah, 87 sections 120ah batteries.  Recommend: LiFePO4 Battery Manufacturer Energy storage battery Manufacturer Integrated machine energy storage battery series Manufacturer Lead lithium battery Manufacturer Outdoor Backup Battery Manufacturer Portable outdoor power supply Manufacturer Power battery Manufacturer Powerwall LiFePO4 Battery Manufacturer Battery rack Manufacturers Telecom LiFePO4 Battery Manufacturer Wall mounted battery storage Manufacturer China Lifepo4 Battery
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