Schneider UPS Energy Saving Method

1. Flexible planning for on-demand expansion

Generally, the construction of data centers is not in one step, and the expansion of the next few years will be considered, and the UPS capacity is generally considered to be larger in the design, and several sets of high-power UPS are installed at one time, and the initial load is only 10%-20% of the planned capacity, so that the utilization rate of UPS is very low, forming a waste of electric energy. How to avoid this situation, from the perspective of UPS power supply system, should include:

Schneider UPS Energy Saving Method

(1) Power supply plan design

At present, there are two main types of UPS power supply plans: scattered power supply and converged power supply. Scattered power supply is when a UPS supplies power to one or more devices. The advantage of sloppy power supply is the danger of sloppy, and most of the equipment will not be cut off due to the abnormality of a UPS; The disadvantage is that the UPS is sloppy and inconvenient, and the wiring is not easy to plan. The other is to choose converged power supply, which is directly supplied by a set of high-power UPS to all loads in the data center. The advantages of convergent power supply are that it is convenient for planning, handling and protection; The defect is that if the UPS system is abnormal, it is easy to cause a large-scale power outage in the data center, and this defect can be avoided by selecting a parallel architecture. As a result, the above two plans have their own advantages and disadvantages, and today's data centers generally choose the converged power supply plan. Due to the limitation of the number of UPS parallel machines, and when the number of UPS system parallel machines exceeds 4, its reliability is not much higher than that of a single power supply system. When the total installed capacity of UPS in the computer room exceeds the certain limit, it is advocated that the computer room be divided into several areas for power supply according to several phases of planning. When planning, you can refer to: the capacity of a single machine should not exceed 400kVA, and the number of parallel machines should not exceed 3.

(2) Schneider UPS online parallel expansion function

The planning of UPS capacity of the data center can choose the gradual expansion plan according to the load capacity requirements of different periods, so that the investment plan is more economical, and the UPS operation can also be at a better power point. At present, the UPS in the medium and high power sections have the function of redundancy and parallelism, which not only improves the reliability of the system, but also provides conditions for the expansion of the computer room. As long as a sufficient amount of air switches are reserved in the distribution box before and after the UPS during planning, and the corresponding space is planned in the computer room, the UPS parallel expansion function can be completed. The key is the process of parallelism, a variety of brands of UPS parallel machine need to correct the UPS settings, at this moment requires UPS to have the necessary operation in the repair of the bypass situation, UPS is directly carried by the mains, if the mains shakes at the moment or even power failure, will form a large-scale paralysis of the system. Therefore, it is necessary to have the function of online parallel expansion, that is, when UPS is connected to expand capacity, it is only necessary to correct the new UPS software to be common with the original UPS system, and directly merge the new UPS into the original system without closing the original UPS system.

(3) Choose modular UPS to complete gradual expansion

Now, modular UPS has begun to be applied in China, and the characteristics of modular UPS mainly include: expandable, short mean fault correction time (MTTR), and economical completion of "N+X" redundant parallel.

2. Improve the energy efficiency of the UPS itself and optimize the load power curve

At present, UPS is an online double-change architecture, and there is power loss in both rectifier and inverter during operation. Taking a UPS with a capacity of 400kVA as an example, each kilowatt-hour is calculated at 0.95 yuan, and for every 1% improvement in UPS power, the annual electricity cost saved is 400×0.8×0.01×24×365×0.95=26630.4 yuan. It can be seen that the operating power of the improved UPS can save a lot of electricity costs for the data center, and it can be seen that the improved UPS power is a direct way to reduce the energy consumption of the entire computer room. Therefore, the acquisition of UPS, as far as possible to acquire higher power UPS.

Of course, the high power of UPS is not only high power at full load, but also necessary to have a higher power curve, especially in the "1 + 1" parallel system, according to the system planning, the capacity of each UPS shall not be greater than 50%, if the power is only below 90%, even if the full load power reaches more than 95%, it is meaningless, so it is necessary to adopt a method to optimize the power curve, so that the UPS power can also reach higher power at a lower load.

Graph of the relationship between UPS power and output power

In addition to improving the power of the UPS itself, some functions on the UPS can also be used. Let's say something like ECO in the form of an economic run. Its principle is to activate this function in a better mains environment, so that the UPS is directly supplied by the static bypass, at the moment the inverter is in standby condition, normal operation, but no output energy, once the mains is abnormal, UPS immediately switches to the inverter power supply status, the switching time is generally within 1ms, as shown in Figure 2 for details, blue is the input waveform, yellow is the output voltage waveform. Because the inverter is in standby mode at this moment, the loss itself is very small, and the power of the whole UPS can reach more than 97% at this moment, saving more than 3% of the power compared with the normal form.

Waveform diagram of ECO form to normal power supply form

In order to use the ECO form, it is necessary to have the following conditions:

(1) It is necessary to choose two sets of high-reliability thyristors for static bypass, and the combination of contactor and thyristor shall not be selected. Thyristors, on the other hand, do not have this problem, and together they can shorten the switching time.

(2) It is advocated to be used in a better power environment, such as a first-class power supply unit.

3. Descend the harmonics of the input current and improve the power factor

The fundamental reason for the occurrence of harmonics is that the power line presents a certain impedance, which is equivalent to a passive network composed of resistance, inductance and capacitance, and the non-sinusoidal current due to the nonlinear load occurs to form the current and voltage distortion in the circuit, which is called harmonics. The hazards of harmonics include: causing additional losses and heat generation of electrical components (such as capacitors, transformers, motors, etc.); The temperature of electrical components increases, the power is low, the insulation aging is accelerated, and the service life is reduced; * The equipment is operating normally; The increase of reactive power and the decrease of the active capacity of power equipment (such as transformers, cables, and distribution equipment); Low power supply; Exhibits resonance, especially when diesel generators generate electricity; The empty opening trips, the fuse blows, and the equipment is damaged for no reason. UPS is a non-linear load for the power grid, and a large number of harmonics will occur during operation. Taking the UPS equipped with a 6-pulse rectifier as an example, its input power factor is generally about 0.75, and the harmonic is greater than 30%. The primary ways to reduce the harmonics of UPS operations are:

(1) 12-pulse rectifier is selected. The principle is to add a phase-shifting transformer and a 6-pulse rectifier on the input side on the basis of the original 6-pulse rectifier. With this skill plan, you can reduce the harmonics to about 10%. The advantage is that it is relatively simple, and the harmonic improvement is obvious; The drawback is that the power factor improvement is limited and the price is slightly higher.

(2) Use a passive filter. According to the principle of LC filter circuit, the harmonics generated by UPS are filtered out, and the power factor is compensated. The advantage is that the skills are simple and the cost is low; The defect is that it can only compensate for the harmonics of the characteristic order, which is greatly affected by the load impedance and cannot be applied to the full power range.

(3) Select an active filter. The principle is to use controllable power semiconductor equipment to inject a current equal to the amplitude of the harmonic source current and opposite the phase to the power grid, so that the total harmonic current of the power supply is zero, and the intention of real-time compensation of harmonic current is reached. The advantage is that it can compensate for harmonics of multiple orders and is not affected by the size of the load impedance; The disadvantage is that the acquisition cost is higher.

(4) The rectifier is designed by using high-frequency IGBT rectification and PFC power factor correction circuit. The principle is to use high-frequency PWM to control IGBT conduction, segment the input voltage waveform, make the input current waveform as close to the sine wave as possible, and compensate for the phase difference between the input voltage and the current. The advantages are light size, cheap price and good function; The defect is that the skill structure is complex, not easy to protect, and the capacity is limited due to the influence of power equipment.

4. Battery management and power distribution management skills

UPS is equipped with battery packs, and the user's investment in the battery pack often accounts for a large part of the investment of the entire UPS power supply system, and even exceeds the contribution of UPS itself, and the service life of the battery is significantly lower than that of UPS equipment. Since the primary material of the battery is heavy metal lead, sulfuric acid and plastic that is not easy to decompose, it will form a serious pollution to the environment. Therefore, reducing the number of batteries used and extending the cycle life of batteries not only saves direct and indirect battery investment, but also reduces the overall environmental pollution. Therefore, UPS can complete the energy saving of batteries through the following skills.

(1) Parallel machine sharing battery pack function. The principle of sharing the battery pack is to make the rectification synchronization and bus current sharing of two or more UPSs in the parallel system through special rectifier control and fault isolation skills, so that the UPS bus in the system is directly connected in parallel, and then the batteries that meet the requirements of the backup time of the system are connected to the parallel bus system after parallel connection, so as to complete the sharing of batteries and reduce the battery investment. Taking "1+1" as an example, the traditional UPS plan, the system is backed up for one hour, and when considering one of the UPS's faults, the battery of UPS2 cannot be used for UPS1, so it is necessary for UPS1 and UPS2 to be equipped with a set of one-hour battery packs each, so that the talent guarantee system can be backed up for one hour after the power is off. After choosing the shared battery pack plan, the battery in the system can still supply energy to UPS2 after the UPS1 problem, so the whole system only needs to be equipped with one set of 1-hour batteries. It not only saves the direct investment of the battery, but also saves the investment of the computer room in terms of space, load-bearing and air conditioning, and also reduces the pollution to the environment. Or equip a little battery and add a generator set.

(2) Intelligent battery management skills. There are many factors that affect battery life, including temperature, charging, discharging, number of cycles, etc. If the above elements can be comprehensively treated, the service life of the battery can be greatly extended, the battery replacement cycle can be extended, and the battery investment can be saved. UPS's intelligent battery management skills mainly include: battery floating charge management (average float charge control), charging temperature compensation, intelligent discharge termination voltage control, in addition to battery timing automatic detection and battery leakage detection functions. In addition, it is possible to select a UPS with a wide input voltage range to reduce the number of battery discharges. After the above skills, the battery life can be extended by 2-3 years.

(3) Intelligent UPS power distribution management skills. The principle is to detect the UPS battery voltage or handle the power supply time of the equipment, complete the multiple power-off protection function of different levels of load in the computer room, reduce the battery investment, and improve the battery utilization rate. There are two main plans for intelligent UPS power distribution management skills: software completion methods and hardware completion methods.

5. Choose a new energy-saving UPS power supply: UPS using fuel cells.

Schneider UPS Energy Saving Method

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