Working principle and application of three-phase electric energy meter with MC68HC908LJ12 chip installed on rail

Model ADL-300EF Guide Rail Type Installation Three-Phase kWh Meter Design and Application
Abstract: This paper introduces a three-phase electric energy meter with MC68HC908LJ12 as the main control chip, explains its working principle, software and hardware design methods and product structure characteristics, and gives an application example in low-voltage power distribution terminals. The electric energy meter has a miniaturized volume, modular structure, and flexible wiring methods with optional primary and secondary access. It can be used in conjunction with a miniature circuit breaker and directly installed in a distribution box. It is used for low-voltage power distribution terminal electric energy metering, realizing the automation of electricity metering management.
Keywords: guide rail type installation; three-phase kWh meter; low-voltage power distribution terminal
JIN Anguo1, QIAN Xusheng2, TU Shiliang3
(1 Shanghai Ankerui Electric Co., Ltd., Shanghai 201801;
2 Nanjing Power Supply Company, Nanjing 210008, Jiangsu;
3 School of Computer Science and Technology, Fudan University, Shanghai 200433)
Abstract: Introduction was made to a guide rail installation three-phase kwh meter taking MC68H908LJ12 as main control chip. Discription was made to its working principle, software and hardware design method and product's structural features, applied example at the terminal of low-voltage power distribution given out. The meter is with miniaturized size, A/D converting structure, selectable fl exible wiring means from primary connection to secondary connection, matching with miniaturized circuit breakers, directly installed in power distribution box, used for power energy measurement, to have realized automation of power energy masurement management.
Key words: guide rail type installation; three-phase kWh meter; low-voltage power distribution terminal JIN An-guo1, QIAN Xu-sheng2, TU Shi-liang3
（1 Shanghai Ankerui Electrical Co., Ltd, Shanghai 201801, China;
2 Nanjing Power Supply Company, Nanjing 210008, China;
3 School of Computer Science, Fudan University, Shanghai 200433, China）
0 Introduction
With the rapid development of economy, the demand for electricity in all walks of life is increasing, and the shortage of power resources and the imbalance of power consumption are very serious. In order to alleviate the contradiction between power supply and demand, advocating conservation and rational use of electric energy and improving the national power efficiency has become one of the basic national policies of the country to promote the construction of a conservation-oriented society.
A large amount of electric energy consumption is concentrated in low-voltage power distribution terminals. In order to strengthen the assessment and management of terminal electric energy metering, guide users to use electric energy effectively, reasonably and balanced, and facilitate users' on-site use and the upgrading and transformation of power distribution facilities, a miniaturized rail-mounted electric energy meter is designed to address the inconvenience of on-site installation and wiring of traditional wall-mounted or electrical cabinet electric energy meters. It has the advantages of high measurement accuracy, strong overload capacity, wide operating voltage range, stable and reliable performance, and low power consumption. In addition, it is small in size, simple in appearance, and modular in structure. It can be used in conjunction with a miniature circuit breaker and installed in a distribution box to achieve integrated design and management of low-voltage power distribution terminal electric energy metering.

1 Design method
1.1 Hardware design
The hardware design mainly consists of power supply circuit, metering circuit, communication circuit and main MCU control part. The system principle block diagram is shown in Figure 1. ADL-300EF type rail-mounted three-phase energy meter design and application The real-time voltage and current signals in the power grid are sent to the power metering chip ATT7030A for calculation and processing through the sampling circuit, and the power pulse is output. The MC68HC908LJ12 chip accumulates, stores, displays and manages the pulses to realize the entire meter function [1].

1.1.1 Main controller
The main controller is the MC68HC908LJ12 chip, which integrates two 16-bit timers TIM1 and TIM2, 6-channel 10-bit ADC, serial communication interface SCI and serial peripheral expansion interface SPI, and has 12 KB of high-speed flash FLASH and 512 B of RAM memory. It has a built-in phase-locked loop, and can obtain a 32 MHz clock with a low-frequency 32.768 kHz crystal oscillator, which greatly improves the system's anti-interference ability. It has functions such as low voltage reset, illegal operation code reset, and illegal address reset, which greatly enhances the chip's reliability and stability, and has its own LCD driver, which simplifies the circuit structure. The MC68HC908LJ12 chip not only has powerful functions, but also has a high cost-effectiveness. It can easily realize various measurement and control functions and has a very wide range of applications in electric meters.

The main control part is based on the MC68HC908LJ12 chip, which connects, controls and manages other modules. The principle of the main control part is shown in Figure 2. The working principle of the main control MCU is to collect and accumulate power pulse signals in real time, switch rates according to the real-time clock, save time-sharing power, freeze monthly power, and cyclically display power in each period.

4 Conclusion
With the advancement of technology, electric power instruments with easy installation, simple meter reading, low cost, high performance and intelligence are becoming more and more popular in the measurement and management of low-voltage terminal distribution. The miniaturized structure, novel installation method and intelligent functions of the ADL-300EF rail-mounted three-phase energy meter are very suitable for the time-sharing multi-rate measurement of modern low-voltage distribution terminal electricity and the integrated design of low-voltage distribution projects. At the same time, it also saves the cost of low-voltage distribution construction, making its application more realistic and economically valuable.