Design of energy consumption collection device for data center

1 Introduction
With the rapid development of data centers, the energy consumption problem of data centers has become more and more prominent. The energy management and power supply and distribution design of data centers have become hot issues. An efficient and reliable data center power distribution system solution is an effective way to improve the power efficiency of data centers and reduce equipment energy consumption. To achieve energy saving in data centers, it is necessary to first accurately monitor each power load. However, there are many load circuits in data centers. Traditional measuring instruments cannot meet the requirements of cost, volume, installation, construction and other aspects. Therefore, it is necessary to adopt a multi-circuit monitoring device suitable for the centralized monitoring requirements of data centers. This article introduces a design method for a measuring device suitable for the use of precision power distribution cabinets in data centers. The device is suitable for single-channel input, single-stage output, single-point detection; dual-channel input, single-stage output, single-point detection; dual-channel input, single-stage output, dual-point detection system power input mode. It can accurately measure various parameters of the power distribution system, including the bus voltage and frequency of the three-phase incoming line and the current, phase splitting and total active power, reactive power, power factor, active energy and reactive energy of the two three-phase incoming lines. And accurately measure the current, active power, reactive power, power factor, active energy, reactive energy, on/off status of branches and other electrical parameters of 36 outgoing (single-phase) branches, and realize centralized monitoring of computer room data through remote communication.
2 Design ideas
To achieve the integrated measurement of 14 three-phase multi-function power meters using a single device, unconventional hardware design ideas are required. We know that the most common implementation methods of three-phase multi-function power meters are generally three-phase power chip + CPU, high-precision ADC chip + CPU, three-phase SOC chip and single chip (CPU with ADC inside). For a single device to realize the functions of 14 three-phase multi-function meters, it is not very suitable to use multiple combinations of any of the above methods. Considering the cost of hardware and the difficulty of software implementation, we choose to use the design method of multiple electronic switches + single chip (CPU with ADC inside).
3 Overall hardware
The system design takes into account that the device is used in a precision power distribution cabinet in a data center, and needs to measure various electrical parameters of 2 three-phase incoming lines and 36 outgoing lines. Since the current of the incoming line circuit is generally large, it can reach several hundred amperes, and the current of the outgoing line circuit is relatively small, generally below 63 amperes. Therefore, the incoming line current of the device uses 5A current input, built-in small 5A current transformer, and the outgoing line current uses 20mA current input, external 100A/20mA transformer. Since the device is installed inside the cabinet, the device itself does not have a display. If a display is required, a touch screen is used, and the data is transmitted to the touch screen for display through the RS485 communication connection. The overall hardware system is shown in Figure 1. It is mainly divided into signal processing part, power supply part, communication part, setting part, data storage part and CPU part. Figure 1 3.1 Signal processing Signal processing part The most critical part is the signal processing of AC sampling and the switching of electronic switches. Since this design adopts the AC sampling method, the ADC can only sample positive signals, and the AC signal is a sine wave signal with both positive and negative signals. Therefore, the signal needs to be raised to ensure that the lowest point of the signal can also be sampled by the ADC. Here, TL431 is used to raise the signal. The current signal collected can also be sampled by the ADC by raising it to the lowest point. As shown in Figure 2. There are 42 current signals in total. In this design, they are divided into 7 groups, each with 6 current signals. Each group of current signals is selected by an electronic switch CD4051, Figure 3. The electronic switch is controlled by the CPU to conduct in time. At the same time, 7 current signals flow into the CPU's ADC for AD conversion. Figure 2 Figure 3 3.2 Power supply device Use a switching power supply module. The input voltage of the power supply module is AC85V~265V, the input frequency is 45Hz~60Hz, and it has multiple isolated voltage outputs to meet the requirements of different power supply voltages for various functions. The output voltage is stable, the failure rate is small, the output ripple is <1%, and the conversion efficiency is ≥75%. It has overvoltage and overcurrent protection. The module has been used in the actual field and has high stability, reliability and anti-interference ability. The device can be equipped with dual power supply mode, dual AC, dual DC or one AC + one DC power supply mode, so that the device can still work normally when the precision distribution cabinet is cut or repaired. 3.3 Communication The communication interface module adopts the universal RS-485 and Modbus RTU communication protocols, which can realize telemetry, remote control, remote signaling and other functions. In this design, since the device has no display, after being installed in the cabinet, the local display needs to transmit data to the touch screen through communication, which requires a communication port. Therefore, the device is designed as a dual communication mode, which can communicate with 2 systems. 3.4 Settings Since the device does not have a display, it is not very convenient to set some parameters. Here, a dip switch is used to set parameters such as communication address and baud rate. 3.5 Data storage This design uses FM31256 ferroelectric memory with clock. On the basis of realizing data storage, a real-time clock is integrated to record various faults or states. 3.6 CPU Combining the hardware and software processing methods of this design, the CPU in this design uses ST's 32-bit processor STM32F103VBT6 based on the latest ARM Cortex-M3 core architecture. The clock frequency can reach up to 72MHz, with built-in 128K Flash, 20K RAM, 12-bit AD, 4 16-bit timers, 3 USART communication ports and other resources. It has a very high cost performance and can meet the application of this design. [page] 4 Software Design The program design process is shown in Figure 4. The design focus of this software is on signal sampling. Since multiple signals are switched through electronic switches, each current signal must be sampled once in each sampling cycle, so the AD sampling rate must be increased. For example: the cycle of each signal is 20ms, 32 points are collected in each cycle, and all current loops are divided into 7 groups, each with 6 points. That is, at the same time, the CPU will sample 7 of them. And the CPU needs to switch 6 times to achieve the sampling of all 42 currents. Therefore, the AD sampling frequency of the CPU must be increased by 6 times on the basis of 32 points in each cycle to ensure that all 42 current signals are collected in one cycle. In addition, the CPU must also control the timing of the electronic switch switching, otherwise it is easy for the signal in the electronic switch to remain, resulting in the CPU collecting the signal of the previous channel when collecting the signal of this channel. Figure 4 Another focus of the software is the operation of the signal. Since the amount of data operation is very large, it is equivalent to completing the operation of the current, active power, reactive power, power factor, active energy, reactive energy of 42 single-phase circuits within 20ms, and also handling various other events at any time, such as communication. Therefore, the software algorithm and the CPU operation rate are very important. In this design, the CPU clock frequency uses 72MHz to ensure data processing within each signal cycle. After testing, the time used for the entire measurement cycle is about 13ms, which fully meets the completion of all operation tasks within 20ms. 5 Measurement accuracy According to 5.6.2 of YD/T-2011 "Technical Requirements and Inspection Methods for Network Cabinets for Data Equipment", the measurement accuracy of the detection device configured in the cabinet is required to be level 2 or higher (i.e. the error is within ±2%). The measurement accuracy of the device designed according to this scheme was tested, and the results are shown in Tables 1 to 7. It can be seen from the data in the table below that its measurement accuracy far exceeds the level 2 requirements and fully meets the requirements of the standard. It is a multi-circuit acquisition device with high accuracy. The design measurement accuracy of this device is 1% for voltage and current; 1% for electric energy.




















6 Application of the device
The AMC16MA series multi-circuit monitoring device for data centers designed in the above manner has been widely used in precision power distribution cabinets in data centers. Combined with the configured touch screen, a complete precision power distribution cabinet monitoring system is realized to achieve refined management of server terminal equipment. The monitoring system can achieve the following functions, and the display interface is shown in Figure 5: Figure 5 5.1 Incoming line monitoring: 1) Three-phase voltage, three-phase current, system frequency; 2) Active power, reactive power, apparent power, power factor of each phase and total; 3) Active power and reactive power of each phase and total; 4) Voltage imbalance, current imbalance; 5) Incoming line switch monitoring. 6) Optional monitoring of harmonic current; 5.2 Outgoing line monitoring: 1) Rated current setting, current value of each phase; 2) Load percentage; 3) Switching quantity status monitoring; 4) Active power, reactive power, apparent power, power factor of each phase; 5) Active electric energy and reactive electric energy of each phase; 6) The phase of each loop of the outgoing line can be configured arbitrarily. 5.3 Alarm function: 1) Incoming line overcurrent 2-stage threshold over-limit alarm, the alarm value can be set arbitrarily; 2) Incoming line undercurrent 2-stage threshold over-limit alarm, the alarm value can be set arbitrarily; 3) Incoming line overvoltage, undervoltage, phase loss, overfrequency, underfrequency over-limit alarm; 4) Sound and light alarm function. 5.4 Communication: 1) The collected data can be uploaded through the touch screen; 5.5 Event record: 1) Various electrical parameter over-limit alarm records (current alarm and alarm record 128 each) 2) Switching quantity action event record 128. 6 Conclusion The multi-circuit monitoring device designed according to the ideas of this article is a product dedicated to the precision power distribution cabinet of the data center. The product can meet the requirements of the precision power cabinet for multi-circuit power distribution. The product hardware design is simple, and it has achieved a high cost-effectiveness in terms of performance and cost. It is an ideal monitoring device for power management in the data center.