Design of energy management instrument with pulse metering based on IC 71M6533

Keywords pulse metering energy management instrument 71M6533 rail mounting

With the advancement of China's urbanization process and economic development, the total energy consumption has continued to increase, so energy management is imperative. Energy management of industrial and mining enterprises and buildings depends on data collection and analysis of energy information.

In addition to electrical energy, other types of energy consumption also need to be collected, such as water and gas. At present, most of the water meters and gas meters have a pulse output, which is not suitable for the direct collection needs of energy management systems. Therefore, it is difficult to integrate non-electric energy consumption information into the energy management system. The existing pulse collector is a product developed for the old mechanical watt-hour meter. It completes the digital conversion of electrical energy pulses to electrical degrees, but it cannot convert water, gas, etc. into corresponding digital equivalents.

In view of the above situation, this article introduces an energy management instrument with pulse metering.

The instrument has the functions of three-phase multi-function electric energy meter and pulse collector. In addition to measuring common power parameters and realizing energy measurement, it also has three external input pulse measurement functions, which can perform signal acquisition, calculation processing, and storage on the meter based on pulse circuit technology, and pass it together with the electrical parameters measured by the meter itself The RS485 bus is uploaded to the energy management platform, and its schematic diagram is shown in Figure 1.

Figure 1 Schematic diagram of instrument functions

Instrument design is mainly based on the following standards:

(1) GB / T 20866-2007 data collector based on user pulse meter;

(2) IEC 61557-8: 2007 Test, measurement or monitoring equipment for electrical safety protection measures of low-voltage power distribution systems with AC 1000V and DC 1500V or less;

3.1 Overall block diagram

Based on product function considerations, combined with factors such as appearance structure, convenient production, debugging and maintenance operations, the hardware is divided into processors, voltage and current signal acquisition, memory, display LCD, key input, energy pulse input, energy pulse output, communication, etc. section. Among them, the signal acquisition part sets the grid voltage and current signals to the range allowed by the 71M6533 input. The memory uses non-volatile ferroelectric memory FM25CL04, and its principle block diagram is shown in Figure 2.

Figure 2 Functional block diagram of the instrument hardware

3.2 Main chip selection

The instrument selects the SOC, TERIDIAN Energy Meter IC 71M6533, which is dedicated to the three-phase multi-function meter solution (see Figure 3). This chip integrates energy measurement and management. It is equipped with a high-precision 22-bit delta-sigma ADC, 7 analog inputs, digital temperature compensation, precision reference voltage, and an independent 32-bit calculation engine. It exceeds 2000: 1 Measurement accuracy is better than 0.1%.

Moreover, the SOC chip requires only a few low-cost external components, which greatly simplifies the hardware and software design, so that the development design can be completed efficiently and quickly.

Figure 3 IC 71M6533 functional block diagram

3.3 Signal acquisition

(1) Three-phase AC voltage and current signal acquisition:

Based on the comprehensive consideration of cost, internal space and 0.5-level precision design, the voltage signal sampling is selected by the resistance network voltage division method, the current signal sampling is selected by the current transformer plus resistance sampling method, and the diode BAV199 is used for clamping protection. As shown in Figure 4.

Voltage signal sampling circuit

Current signal sampling circuit

Figure 4

(2) External input pulse signal acquisition:

Refer to GB / T 20866-2007 "Data Collector Based on User Pulse Meter" to count three external input pulse signals with a pulse width of 80ms ± 20ms Filter out). Then according to the pulse transformation ratio set by the user, it is converted into the corresponding water and gas equivalent. The principle is shown in Figure 5.

Figure 5 Pulse input circuit

3.4 Human-machine interface

The instrument is rich in functions and provides more parameter information to users. It uses 122 * 32 dot-matrix LCD with backlight as the display unit and uses membrane keys to facilitate parameter viewing and setting (such as voltage, current, power, Power factor, electrical energy, etc.).

The green LED lights EX1, EX2, and EX3 respectively indicate three external input energy pulses, and the red LED light EP is used to indicate the instrument's active energy pulse output.

3.5 output interface

The pulse output interface is an optocoupler isolation type, the pulse waveform is a standard square wave, and the pulse width is 80ms ± 20ms. The hardware principle is shown in Figure 6.

Figure 6 Pulse output circuit

3.6 Communication circuit

The instrument has a RS485 communication interface, using Modbus-RTU protocol, all measured data and pulse energy can be remotely transmitted through this port. The hardware design uses high-speed optocoupler 6N137 and 485 chip SN75LBC184, and its circuit is shown in Figure 7.

Figure 7 Communication circuit

With the help of the software development environment of keil μvison3, the front and back-end design and modular programming are adopted to achieve the requirements of high reliability. The process is shown in Figure 8.

Figure 8 Flow chart of instrument software

(1) The experiment of meter measuring electricity and measuring energy accuracy

Input the signal with rated value of AC220V and 5A to the instrument. The experimental data of voltage and current are as follows (the experimental instrument is the calibration device of Nanjing Dandick DK-34B1 AC sampling transmitter):

The electric energy experiment data are as follows (the experimental instrument is PTC three-phase portable electric energy meter inspection device, HC-3100 three-phase standard electric energy meter):

The experimental results show that the meter's measurement of electricity and the accuracy of measurement of electricity meet the requirements of 0.5.

(2) Whether the meter's collection of external input pulses meets the accuracy requirements experiment.

A pulse receiving comparison test was carried out on the instrument: the signal generator was connected to the counter and the instrument respectively to make the signal generator output a square wave pulse with a voltage amplitude of 4V and a duty cycle of 60% at frequencies of 3Hz, 8Hz and 1Hz Under the conditions of the test, test the pulse collection of the instrument, and the results are as follows.

The experimental results show that the accuracy of the external pulse input collected by this instrument meets the requirements of 0.5 level.

(1) Nominal voltage value: AC100V, 220V, 380V

(2) Current nominal value: AC1A, 5A

(3) Pulse: passive signal, pulse width 80ms ± 20ms, the instrument provides a bias voltage of + 5V

(4) Frequency range: 45 ~ 65Hz

(5) Overload: 1.2 times can continue to work normally, 2 times for 1 second

(6) Power consumption: the power consumption of each voltage and current input loop is less than 0.5VA

(7) Accuracy class: electrical measurement signal 0.5, cumulative error of pulse counting ≤1 ‰

(8) Working power supply: voltage range AC85 ~ 265V or DC100 ~ 350V, power consumption ≤3W

(9) Insulation resistance: ≥100MΩ

(10) Power frequency withstand voltage: 2kV / 1min between the communication terminal group and the signal input and output terminal groups

(11) Average trouble-free working time: ≥50000h

(12) Temperature: working temperature -10 ℃ ~ + 50 ℃, storage temperature -20 ℃ ~ + 70 ℃

(13) Humidity: ≤93% RH, no condensation, no corrosive gas

(14) Altitude: ≤2500m

This paper presents for the first time a novel energy management instrument with pulse metering. Using TERIDIAN Energy Meter IC 71M6533, using its on-chip high-precision 22-bit delta-sigma ADC and independent 32-bit calculation engine, using a series of development tools, combined with rich experience in meter design, completed the instrument development. Compared with traditional data collectors, it has the advantages of low cost, high precision, intuitive and easy to read, simple installation and convenient networking. At present, the instrument has been successfully used in multiple engineering projects.

The article comes from: "Electronic Technology", Issue 11, 2012.

references

[1] Zhong Zhong et al. Model selection and solutions of smart grid user-side power monitoring and energy management system products [J]. Machinery Industry Press, 2011-10.

[2] TERIDIAN SEMICONDUCTOR CORP. 71M6533 / H and 71M6534 / H Energy Meter IC DATA SHEET November 2009.

About the Author:

Yu Jing, female, undergraduate, engineer of Wuhan Ankerui Electric Co., Ltd., the main research direction is intelligent power monitoring and power management system