A remote DC power monitoring system design

Guide: This system is designed to realize remote control of DC power supply, remote adjustment output and remote signal and telemetry input.

1 Introduction

In the mid-1960s, American scientist Mass made a large number of experimental studies on the charging process of open batteries, and proposed an acceptable charging curve for batteries with the minimum outgas rate, as shown in Figure 1. Experiments have shown that if the charging current changes according to this curve, the charging time can be greatly shortened and the battery capacity and life are not affected. In principle, this curve is called the optimal charging curve. After the battery is discharged, it is returned to the working capacity by direct current through the battery in the opposite direction to the discharge current. This process is called battery charging. When the battery is charged, the positive pole of the battery is connected with the positive pole of the power supply, the negative pole of the battery is connected with the negative pole of the power supply, and the voltage of the charging power supply must be higher than the total electromotive force of the battery. There are two types of charging methods: constant current charging and constant voltage charging.

Substations, power plants, and communication equipment rooms need a stable and reliable DC power supply system to charge the battery and supply power to the control loop and the closing loop. The DC power supply manages battery charge and discharge, monitors switch status, and DC system operation to ensure safe and efficient operation of power supplies and equipment during operation. The power monitoring system has evolved from a simple monitoring function to a system with three remote and alarm functions, and a relatively complete management and remote monitoring function. The power monitoring system is based on the power monitoring and management scheme of the rail-mounted power monitoring instrument. The program is mainly composed of a touch screen, single-phase or three-phase AC signal acquisition unit and a transformer, which can collect and display voltage, current, active power, reactive power, power factor, harmonics and electric energy in real time for the data center power supply. “Energy saving and emission reduction” has become an important indicator to measure the sustainable development of enterprises in the future. With the expansion of telecommunications, banking, and large-scale enterprise services, the management and maintenance costs and rising electricity bills brought by the huge data centers have become a major problem for business executives.

2 system hardware design

2.1 hardware circuit design

The DC power system needs to collect multiple analog and digital quantities and requires multi-path nodes and adjustable voltage output of 0 V~4 V, which is the “four remote” function. The monitoring unit has two serial ports, one for connecting to the smart device and the other for communicating with the TC35i. The monitoring unit also requires a keyboard and LCD display. According to the above requirements, the system needs to add more peripherals based on the minimum system of the microcontroller. Using a single-chip microcomputer with a dual serial port to reduce the number of peripherals increases system cost and limits the versatility of the microcontroller itself. Its hardware schematic is shown in Figure 1.

2.1.1 MCU

The single-chip microcomputer adopts the general SST89E516, which is based on the 8051 core with 64 KB flash MCU, three 16-bit timer/counters, one UART, 36 GPIOs, and supports ISP; watchdog circuit, clock circuit and power-down save circuit The FM3104.FM3104 is a cost-effective integrated device from RAMTRON that integrates a watchdog, low-voltage detection, timer, clock circuit and ferroelectric memory. I2C communication is used. The clock circuit and the ferroelectric memory are respectively two addresses, wherein the ferroelectric memory is used to store system parameters such as an alarm number, a telemetry alarm limit value, and the like.

2.1.2 TC35i interface circuit

Siemens' TC35i is an industrial-grade GSM module that supports Chinese short messages. The frequency band is dual-band GSM 900 MHz and GSM1 800 MHz, supporting data, voice, short message and fax. The system uses the 16C550 to expand a serial port and communicate with the TC35i in a TTL-level serial port.

2.1.3 display, keyboard circuit

The display circuit uses 128 x 64 liquid crystal. The interface chip selection of the liquid crystal is determined by GAL16V8. In order to simplify the system design, the keyboard adopts the integrated circuit ZLG7290, and the communication between the single chip and the ZLG7290 adopts the I2C communication mode.

2.1.4 analog signal acquisition circuit

The analog signal acquisition circuit consists of three parts: tuning, isolation and conversion. Different analog signal tuning circuits are different. For example, the DC voltage is set to 0 V~4 V using a precision resistor divider method, and the AC voltage is set to 0 V~4 V using a voltage transformer. The circuit uses a linear optocoupler.

The set analog signal is subjected to voltage limiting processing and is input to the multiplex switch. Then, after the voltage conversion (V/F), it is input to the CPU for processing. V/F conversion using integrated circuit AD654.AD654 is a low-cost, 8-pin package voltage-frequency (V/F) converter from Analog Devices, Inc., with a single supply voltage of 4.5 V~36 V; dual supply voltage It is 5 V~18 V; the output frequency range is 0 kHz~500 kHz; the linearity error is 0.06% (at 250 kHz); the input impedance is 250 MΩ; and the input voltage range is 0 V~Vs-4 V for a single power supply. The dual power supply is -Vs~Vs-4 V.

2.1.5 digital signal acquisition circuit

The digital signal means that the magnitude of the amplitude is discrete and the amplitude representation is limited to a limited number of values. A binary code is a digital signal. The binary code is less affected by noise and is easy to be processed by digital circuits, so it has been widely used. The digital signal is isolated by TLP521 and sent to the bus driver 74HC244.GAL16V8 to generate 74HC244 chip selection. The MCU queries the digital signal every 10 ms and adds debounce processing.

2.1.6 empty contact output circuit

The empty contacts are used to control the on/off of the DC module and other devices. A 5 V relay is used to output an empty contact signal. The 5 V relay control is also controlled by the bus. The data port is driven by the 74HC273 and MC1413 to control the relay. The GAL16V8 produces a 74HC273 chip select that expands multiple empty contacts.

2.1.7 Analog voltage reference

The analog signal is given by the digital DS1845 potentiometer divider. The digital potentiometer divides the 2.5 V reference voltage and superimposes the total current-limit voltage signal. The amplified output is used as the reference for the DC module to adjust the voltage.

2.2 circuit reliability design

2.2.1 Shielding, isolation and absorption

The communication lines designed by this system use shielded twisted pair wires to shield external interference and perform photoelectric isolation. The analog input signals in each range are uniformly converted into voltage signals of 0 V~4 V and sent to the A/D converter. In order to improve the anti-interference ability of the system, a differential amplifier and an isolation amplifier are used.

2.2.2 Grounding

Signal grounding ensures that the signal logic of the same logic system is accurate, eliminating the interference caused by the unequal potential of the same logic system, and the protection grounding ensures the safe operation of all parts of the system. The digital signal ground and the analog signal are connected at a single point. The signal ground and the earth are connected by a 3KV102 capacitor.

3 system software design

3.1 software design ideas

Using a real-time operating system, timer T0 generates a 10 ms interrupt and uses a 10 ms interrupt count to generate 200 ms, 500 ms, and 1 s tasks, respectively. The block diagram of the system software module is shown in Figure 2.

3.2 short message module wireless transmission

The short message module wireless transmission is divided into active uploading of alarm information and passive calling. The alarm information is active upload, while remote control, telemetry and remote adjustment are realized by short message summoning or control. The alarm information processing flow is shown in Figure 3.

The alarms are classified into remote signaling alarms and telemetry alarms. The method for realizing the remote alarm is to define a number of bits as an alarm bit, and the remote signal that needs to generate an alarm is connected to the position, and once the remote signal is triggered, the alarm information is generated.

The alarm information of the short message module must be sent in Chinese characters. Each Chinese character uses UNICODE encoding, which occupies two bytes, such as "Electric 0x7535 sub 0x5b50". Converting Chinese characters into UNICODE encoding is difficult to program under the MCU. Because the alarm information of DC power monitoring is limited, and Microsoft's operating system provides such functions, it is necessary to write all the used Chinese characters into the code space in the form of a table. The UNICODE code of the alarm information is directly checked according to different alarm codes of the DC system. The remote remote control information processing flow is shown in Figure 4.

Remote control and query measurement information are sent in TEXT mode. When the short message module receives the short message in the following format, and the password is correct, the DC power message is summoned to return a short message according to the received number or a remote command is issued, and the control result is returned.

SMS content format: "; password; function code (; content 1) (; content 2) (; ...)". Among them, the password is 6 characters / number; the function code contains 2 characters, as listed in Table 1; The length of the content is not fixed. Such as: query system measurement information SMS content format: "; 1234156; 01"; remote control device switch format: "; 123456; 02".

4 Conclusion

The system expands the short message module for the characteristics of less DC power transmission information, and designs a wireless transmission scheme for DC power supply monitoring. The power monitoring system based on short message transmission does not need to build an additional wireless communication network, but performs dedicated wireless data transmission through an existing wide-area, stable network.

0 times
Window._bd_share_config = { "common": { "bdSnsKey": {}, "bdText": "", "bdMini": "2", "bdMiniList": false, "bdPic": "", "bdStyle": " 0", "bdSize": "24" }, "share": {}, "image": { "viewList": ["qzone", "tsina", "tqq", "renren", "weixin"], "viewText": "Share to:", "viewSize": "16" }, "selectShare": { "bdContainerClass": null, "bdSelectMiniList": ["qzone", "tsina", "tqq", "renren" , "weixin"] } }; with (document) 0[(getElementsByTagName('head')[0] || body).appendChild(createElement('script')).src = 'http://bdimg.share. Baidu.com/static/api/js/share.js?v=89860593.js?cdnversion=' + ~(-new Date() / 36e5)];