一种基于单片机的新型三相多费率电能表的设计

Design of a New Three-phase Multi-rate Watt-hour Meter Based on singlechipJishun JiangSchool of Electric and Electronic Engineering Shandong University of TechnologyZibo, 255091, Chinajandj8@Lanlan YuSchool of Electric and Electronic Engineering Shandong University of TechnologyZibo, 255091, Chinayulanlan124@Abstract—With the development of the society, the demand of electric power becomes bigger and bigger. The phenomenon of unbalanced electricity in different time is worse and worse. In order to adjust electric power burthen with reason and save energy, we put forward the design of a novel multi-rate three-phase watt-hour meter. The design principle of a novel multi-rate three-phase watt-hour meter based on AT89LV5 is proposed in this paper. The designs of hardware and software flow, as well as the analysis of experiment data are presented in detail. By trial manufacturing in Zibo Billion Electron Limited Company, it demonstrates that this multi-rate three-phase watt-hour meter has the characteristics which are walking precision, accurate measurement, automatic meter reading, flexible time period setting and low cost. Therefore, this novel multi-rate watt-hour meter has a broad application prospect.Keywords-multi-rate, three-phase watt-hour meter, AT89LV52I.I NTRODUCTIONThe development and application of computer technology push the construction of intellectualized section exteriorly. Because the phenomena of bigger demand of electric power and unbalanced electricity in different time is worse and worse, electric power company has encouraged people to use multi-rate watt-hour meter [1] in order to adjust electric power burthen with reason and save energy. The traditional multi-rate watt-hour meter always adopts mechanical tinplate to measure. There are some shortcomings that the measurement precision falls with machine abrasion, single time period setting and strong manpower [2]. In this paper, we propose a novel multi-rate three-phase watt-hour meter based on AT89LV52. This multi-rate three-phase watt-hour meter adopts AD7752 for measurement. It has the characteristics which are time-sharing measurement, accurate measurement, LCD display, automatic meter reading, flexible time period setting, timely emendation, low cost and novel design.II.STRUCTURE AND WORKING PRINCIPLE The novel multi-rate three-phase watt-hour meter proposed in this paper is based upon AT89LV52 singlechip [3]. AT89LV52 has the flash memorizer with 8k bytes, cryptographical program memorizer with third class, RAM with 256 bytes, 32 programmable I/O lines, three time/ counter with 16 bits and a two class halt with six vectors. The interface circuit adopts I2C bus unit which is a 8 bits singlechip with good performance and suitable price. The system structure diagram is shown in figure 1.Figure 1. System structure diagramThe principle of this multi-rate watt-hour meter is reading in the multi-rate time segments using RS485 bus and noting in X25045 then take over correctional clock with RS485 bus and write in clock CMOS chip S3530A. The three-phase AC voltage and electric current pass through potentiometer and mutual inductance instrument respectively so as to produce small signal which is sent to AD7752 to complete measurement. The clock CMOS chipS3530A gives clock information per second in the course of automatic move and analyze this clock belongs to which period of time according to advance periods of time set inX25045 then save the electrical energy in RAM memorizer according to corresponding period of time. We write it to corresponding address of X25045 when the electrical energy achieves one degree in order to make the multi-rate measurement come true. This watt-hour meter has functionsof clear LCD display, missing phase detection, burthen control, halt electricity check and storage, automatic meter reading and so on.III.T HE DESIGH OF HARDWARE CIRCUIT A．Electrical energy measurementThe three-phase electrical energy measurement is realized by the low consume CMOS chip AD7752 of ADIAT89LV52Electricalenergy measureAD7752Checking andrelay controlClock S3530ALCD displayHT1621MemorizerX25045Serialcommunication RS485978-1-4244-4507-3/09/$25.00 ©2009 IEEEcompany. The inside of AD7752 adopts digital circuit besides ADC, filter and multiplication circuit which can eliminate noises effectively. The sampling course of voltage and electric current in three-phase AC power supply loop is shown in figure 2 in which IA stands for voltage sampling of A phase. The sampling circuits of B phase and C phase are similar to A phase. The power after integral is transformed to electrical pulse for output. The pulse of fan-out CF enters into interregnum INT0 of AT89LV52 throughphotoelectricity insulation 4N25. CPU measures the electrical energy [4]. We adjust the pulse number of CF by combining the state of S1 and S2. The connection of electrical energy and pulse is M W =. In which, W is the electrical energy with the unit of kilowatt-hour, M is the total pulse number, C is the pulse number of ammeter. We choose C equals to 3000 that is to say every kilowatt-hour is3000 pulses.Figure 2.Circuit schematic diagramof watt-hour meterB ． LCD displayThe LCD display [6] adopts HT1621 CMOS chip of HOLTEK Company to achieve twelve bits digital display. HT1621 is the LCD drivers with 128 segments (432×) inner memorizer. The interior of HT1621 consists of control and time circuits, RAM, LCD drive and watch timer. It has the merits of small volume and low cost so that it is suit to watt-hour meter. We use serial interface which only has four lines between HT1621 and AT89LV52. The detailed connection is shown in figure 3. P20, P21, P22 and P23 of AT89LV52 connect to CS, RD, WR and DATA respectively with the use to refurbish the display of RAM. HT1621 drive CMOS chip has 48 nodes in which COM0, COM1, COM2, COM3 connect to the communal end and drive output of LCD and SG0, SG1, SG2, SG3 connect to drive output of every segment respectively. In addition, an adjustable resistance of 20k Ω is put between VDD and VLCD to adjust the display contrast of LCD. Experiment shows that the contrast is better with VDD=5V and VLCD=4V.C ． Serialmemorizer Serial memorizer adopts low power consumption chip X25045 of XICOR company .It has three functions which are watchdog timer WTD, voltage supervision and serial memorizer E2PROM with 512 bytes. WTD can be set 200ms, 600ms and 1400ms time intervals. The softwareprogram is read into X25045. During the normal running of program, WTD receives the trigger signal in time intervals in order to ensure the normal running of program. X25045 will output a high potential through RESET line if WTD does not receive trigger signal in time intervals. The trigger watt-hour meter reset in order to prevent program flying away. As the serial memorizer chip, 512 bytes of X25045 are used to storage the watt-hour meter code, multi-rate periods of time, the apex electricity, smooth electricity, vale electricity and total electricity of last month and this month. Storage can be divided into two same areas. One is used as data storage. The other is used for backup. The number of storage can be revised 100,000 times. Data can be stored for 100 years. It is connected with AT89LV52 by SPI agreement bus. The connection is shown in figure 3.D ． Clockcircuit The clock circuit is completed by S3530A chip. It is a low power consumption clock chip that supports I2C Bus. It sets the clock and calendar according to the data received by CUP communicating with RS485. At the same time, it continues to walk time by its own oscillation. The crystal oscillator of 32.768 kHz is put between Xin and Xout of S3530A which is connected with CPU through latching. SDA foot and SCL foot connect to P1.6 and P1.7 of AT89LV52 respectively. There are two interrupt alarming foots can be set as second output or minute output synchronizing pulse which supply interrupt signal to AT89LV52 with one second period. Single-chip system willreadout the current time through I2C communication interface according to this signal and calculate the period of time that this moment belongs to so as to realize the electrical energy measurement in different periods of time [5]. This clock circuit has spare lithium battery. The power supply VCC supply power in normal wiring and electrified for lithium battery of 3.6V. When there is power off, the system will automatically convert lithium battery to clock circuit for power supply. The clock will still running accurately even the power is off.Figure 3.Partial circuit figure of watt-hour meterE ． RS485 CommunicationMAX485 chip can implement RS485 communication control of multi-rate watt-hour meter. MAX485 chip has RS485 communication protocol. It can take 128 hypogenous computers. Its transmission distance is greater than 1km and its transfer rate is up to 250kb per second. The watt-hour meter connects with the unit controller through the RS485 bus. Each unit has a cell controller can manage 128 multi-rate watt-hour meter. The cell controller connects to power management computer. Each watt-hour meter has one and only meter number with eight bits of hex. The electrician should write the user’s information and meter number and then import to the power management computer for initial installation so ad to complete the connection of user and management computer. Management computer sends setting of period of time and clock information with the manner of broadcast communication without address information. PC uploads information by the way of calling address.F ． Lack Phase detection and relay controlIt can achieve relay control [7] with P27 of AT89LV52. P27 can control relays using 4N25 photoelectricity isolator so as to complete power supply and power control. Lack Phase detection gets the signal from fan-out of the relay and connects to 1 foot of photoelectricity isolator after passing a 75K resistance, the diode half-wave rectifier and capacitive filtering respectively. We detect the 4 foot of isolator to determine whether there is the lack of phase. If there is lack of phase, we detect again after 2 seconds overtime. We break off the power immediately if there is lack of power after the twice confirmation. In power protection circuit, it uses the INT1 interrupt foot of AT89LV52 to detect signal. When there is a sudden power off, INT1 jumps into a low voltage and the INT1 interrupt enters to the power protectionprogram relying on the energy storage capacitor to save data. In the system, pulse output of AD7752, relay control port and the inputs of lack phase detection all use photoelectric isolator 4N25. It sends electrical signal by light coupling which can enhance the ability of anti-jamming.IV. T HE DESIGN OF SOFTWAREA ． The distribution of resourceThe software program includes main program, X25045 read and write program, RS485 serial communication program, interrupt serve program, timer handling program, HT1621 display control program, electrical energy measurement in different period of time and power down protection program, and system self-checking and anti-interference handling program. Interrupt resource distribution of system is: INT0 interrupt is used as AD7752 pulse measurement, INT1 as synchronization detecting, timer T0 as 100 ms timing, T1 as 1ms timing, and T2 as baud rate generator for serial communication program. RS485 asynchronous communication is set to receive interrupt and check information for sending.B ． Moduledesigh The flow chart of main program is shown in figure 4. The watt-hour meter should be able to initialize at each power up time. The initializing program includes setting working mode of timers, serial stomata and interrupts for AT89LV52, writing control word into X25045, S3530A and HT1621. This system sets three periods of time. The singlechip reads clock value from S3530A per second then analyze this clock belongs to which period of time according to advance periods of time set in X25045 then save the electrical energy in RAM memorizer according to corresponding period of time. We write it to corresponding address of X25045 when the electrical energy achieves onedegree. The LCD display with 16 bits shows period of time TABLE I.COMPARE OF NORMAL METER AND TESTING METERand electrical energy information in turn.Normal Tested ErrorItem meter meter (%)The testing result indicates that the error of this multi-rate watt-hour meter is less than 1%, belongs to 1.0grade. The return reading of electrical energy is precisionand the emendation of time is timely and right. By testing, the method of decreasing errors for electricity metering can be obtained. Firstly, adjust the sampling resistance of AD7752 to accurate value. Secondly, the value of thisresistance is needed less varying with temperature. Thirdly, during electricity metering progress, when mantissa portion of electricity is less than 0.01, the remaining pulse should be accessed together, thus cumulative error caused by lack of 0.01degree energy loss could be avoided.VI. C ONCLUSION AND E XPECTATIONThe multi-rate watt-hour meter achieves electrical energy computation in different time according to different time setting. It adopts RS485 for serial communication and realizes automatic meter reading and real-time emendation.The results of production in Billion Electron Company show that the multi-rate three-phase watt-hour meter proposed inthis paper has the characteristics of novel design technique,accurate measurement, and flexible time period setting.Various technical indexes achieve the technique standard for Figure 4.Flow chart of main programnational intelligent card watt-hour meter. Therefore, it has wide application.V. T ESTING RESULTREFERENCESError measurement and running test have been made in Zibo Billion Electron Co., Ltd. The epigenous computer [1] Bu Zhengliang, Yin Xianggen, Tu Guangyu. “Development of HVWatt-hour meter.” Automation of Electric Power Systems, 2006, completes the setting of time management. There are 30(19): 89-93.three-rate period of time. The first period of time is vale [2] Kosukegawa M., Sakumoto Y. “Traceability system of electric energyelectricity from 00 point 00 minute to 06 point 30 minutes. standard and tendency in static watthour meter development in Japan.” The second period of time is apex electricity from 06 point Sixth International Conference on Metering Apparatus and Tariffs for 30 minutes to 22 point 30 minutes. The third period of time Electricity Supply, 1990,4: 259-263.[3] Xuehai Li. Applied tutorial of singlechip. Electronic industryis smooth electricity from 22 point 30 minutes to 24 point 00 publishing company, 2003.minute. The setting of rate period of time is sent to computer [4] Al-Khateeb Tarik, Blundel Martin. “An electronic meter for measuringmanagement system by electric power company according the saving in electrical power.” The Ninth Arab International to national policy and saved in X25045. The apex electricity, Conference on Solar Energy (AICSE-9), Kingdom of Bahrain, 2007,4 smooth electricity, vale electricity and total electricity per (209):328-333.month read saved in electrical energy meter and sent to [5] Liu Ying, Liu Qingyu. “Development of a self-calibration precisionelectrical measuring meter.” Proceedings of the 1998 Conference epigenous computer through cell controller. The Precision Electromagnetic Measurements, 1998,7:276.communication baud rate is 9600 bits per second. The [6] Gao Yun-Peng, Teng Zhao-Sheng, Liu Peng. “Design of three-phasecheckout platform of 0.1 grade standard electronic power multi-functional harmonic energy meter.” Journal of Hunan University meter is used as standard meter and the multi-rate watt-hour Natural Sciences, 2008, 35(9): 53-57.meter is the tested meter. Billion Electron Company has [7] Qu Qingchang. “Key technology to three-phase electric meter and highvoltage electric power measurement.” Acta Metrologica Sinica, 2007, carried out testing according to different load running. The vol28: 25-30.measured data is shown in table 1 with the burthen of 30kW.Apex electricity 3.000 2.996 0.13% Calm electricity 3.000 2.995 0.17% Vale electricity 3.000 2.997 0.10% Total electricity9.0008.9880.13%06.09.10:306.09.10:300.00.00.0Time0:01 0:01 0.00。