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Talking about the Application of Electricity Sensor in Uninterrupted Power Supply of Data Center

Mar 16, 2021

Talking about the Application of Electricity Sensor in Uninterrupted Power Supply of Data Center

With the rapid development of Internet technology and applications, cloud computing, cloud storage, big data and other related new Internet services are increasing day by day, and data centers have entered the stage of large-scale construction. The huge-scale construction and application of data centers have led to rapid growth in data center power demand. According to the forecast of ICT Research, China's data center power consumption in 2016 has exceeded 100 billion kWh, which is equivalent to the total annual power generation of the Three Gorges Hydropower Station. At the same time, global data center power consumption has exceeded 1,000 billion kilowatt-hours. According to US media surveys, the power consumption of data centers on major websites around the world is equivalent to the power of 30 nuclear power plants. The huge power consumption capacity brings new challenges to the construction and operation of data centers.

At present, during the operation of the data center, data center power safety accidents due to power failures, equipment failures, lightning incidents, etc. occur from time to time. In fact, the loss caused by the power failure of the data center is not only a direct economic loss of tens of millions of dollars. For many internationally renowned brands and listed companies, the negative impact of invisible values such as brand and stock price is incalculable.

With the development of new power semiconductor devices, the invention and application of new power electronic power change topologies, as well as the development of modern control theory and digital control technology, the uninterrupted power supply technology of data centers has been significantly improved, which improves the reliability of the power supply system. Cost and skills, configuration flexibility and scalability provide effective technical support.

Any failure of the power supply of a large data center may cause major economic losses or catastrophic consequences to owners and customers. Therefore, one of the keys to the reliable operation of a data center is the uninterrupted power supply of IT equipment. On the premise of ensuring uninterrupted power supply, continuously improving the reliability of the uninterrupted power supply architecture has always been the core demand of data center users.

Generally, the uninterrupted power supply system of the data center generally includes high-voltage power distribution system, transformer, diesel generator set, low-voltage power distribution system, lightning protection device, UPS, battery pack, front cabinet, rack distribution unit (PDU), connector, etc. Link. Among them, UPS, as the core component of the uninterrupted power supply system, plays a pivotal role. In order to keep the uninterrupted power supply system always operating efficiently, it may be more appropriate to choose the double-conversion online mode under certain circumstances. Especially in geographic areas where AC power is highly distorted and/or has great voltage changes, double-conversion on-line UPSs do not need to frequently switch to battery power to maintain normal output. Lower battery usage can save battery capacity to cope with long-term power outages and extend battery life. In addition, reducing battery replacement costs can offset the advantages of the online interactive UPS's low initial cost and low operating cost. In some special cases, it may be necessary to use double-conversion online UPS. For example, for some medical equipment or instruments, power factor correction (PFC), smaller physical size, or frequency conversion are required. The efficiency mentioned above includes:

2 High conversion efficiency (Po/Pin>96%)

2 The sine wave distortion rate of the input current waveform is small (<5%)

2 Excellent dynamic load following response

2 N+X redundant working mode

In order to make the UPS work in the above-mentioned high-efficiency mode, it is inseparable from the measurement of the voltage and current information of some key positions by the power sensor.

As its name suggests, a double-conversion online UPS will perform two power conversions. First, convert the AC input (including all voltage spikes, distortion, and other anomalies) to DC. Then, under the precise regulation of UPS, DC is converted to AC again. This AC output can even have a different frequency from the AC input. When there is an AC input, all power supplied to the load equipment goes through this double conversion process. When the AC input exceeds the specified range, the UPS will obtain power from the battery so that the UPS output will not be affected. In most double-conversion online design schemes, this conversion between the AC input and the battery inside the UPS takes several milliseconds. Similarly, in these conversion processes, the stored energy is provided to the inverter by the capacitor in the "DC link" (please refer to the figure above). Therefore, even if the power entering the "DC link" is temporarily interrupted, the UPS output voltage will not be affected and the power supply can be continued.

In the above-mentioned electric energy conversion process, many links such as AC input, DC link and final AC output will require a power sensor to monitor the input and output voltage or current. The main factors are as follows:

1. According to the monitored voltage value or current value to judge the current grid or load status and then decide which mode the UPS needs to work

2. Perform precise closed-loop control according to the monitored voltage value or current value to meet the demanding load requirements.

In addition, it is important to pay special attention to the selection of current sensors on the UPS AC input and AC output terminals according to different application characteristics.

The current sensor used at the UPS AC input terminal is mainly considered based on the primary current as a sine wave, and then the maximum measurable peak range of the current sensor can be determined according to the designed overload factor and ripple factor.

When selecting the current sensor used in the AC output of the UPS, it is necessary to pay attention to another key indicator of the UPS with non-linear load—harmonic factor (CF=Crest Factor). Generally, the selection of the CF value range of the UPS depends on the selection of different loads. Different, usually set between 2.1-3.0, so you need to pay special attention to this point when selecting the measurable range of the current sensor, otherwise it will cause a blind zone in the control due to insufficient sampling range and make the final UPS AC output The voltage is distorted.

One more thing to note is: usually UPS equipment that is used as a voltage source output will have the ability to resist instantaneous output short-circuits, which requires the UPS control unit to respond quickly to the detection of output current, so as the current sensor of the detection link, The parameter requirements for response time should also be considered, otherwise it may cause delay and imbalance of the protection.

Therefore, choosing a suitable power sensor is crucial to the overall performance improvement of the uninterruptible power supply in the data center, so as to ensure the efficient operation of the equipment.